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ISSN 1018-5593

Commission of the European Communities

energy

Calcination of limestone in a circulating fluidized bed with coal

residues as fuel

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Commission of the European Communities

energy Calcination of limestone in a

circulating fluidized bed with coal residues as fuel

(This project was originally supported under the Demonstration programme. This programme ended in 1989 but all existing projects continue to be promoted

under the new Thermie initiative which commenced in 1990)

Kaldin BV SaeffelderstraaHO

6104 RA Koningsbosch The Netherlands

Contract No CS 008/89 NL

Final report

Directorate-General * Energy

1993 PARI EUROF. BlWWk N Q EUR 14828 EI

it IM . / / / i ? /?y r f I f M

Published by the COMMISSION OF THE EUROPEAN COMMUNITIES

Directorate-General XIII Telecommunications, Information Market and Exploitation of Research

L-2920 Luxembourg

LEGAL NOTICE Neither the Commission of the European Communities nor any person acting

on behalf of the Commission is responsible for the use which might be made of the following information

Cataloguing data can be found at the end of this publication

Luxembourg: Office for Official Publications of the European Communities, 1993

ISBN 92-826-6304-3

© ECSC-EEC-EAEC, Brussels • Luxembourg, 1993

Printed in Belgium

CONTENTS

CONTENTS Ill SUMMARY V-IX LIST OF TABLES AND FIGURES XI PROJECT DETAILS 1 1. INTRODUCTION 3 2. DESCRIPTION OF THE PLANT 5

2.1 General 5 2.2 Conditions for the design 5

2.2.1 General 5 2.2.2 Calcining humid limestone with fine­

grained coal as a fuel 6 2.2.3 Calcining humid limestone with coal

residues as fuel 6 2.2.4 Process-conditions of the drying unit. . 6 2.2.5 Emissions 7 2.2.6 Mass- and energy balance 7

2.3 Description of the design 8 2.3.1 General 8 2.3.2 Storage and dosage of raw materials and

fuel 9 2.3.3 The circulating fluidized bed (CFB) . . . 10 2.3.4 The pre-heating system. 12 2.3.5 The fluidized bed cooler. , . 12 2.3.6 The sifter-milling section 12 2.3.7 The product storage 13 2.3.8 The flue gas treatment unit 13 2.3.9 The measuring and controlling system . . 14 2.3.10 The drying unit 14

3. CALCINING LIMESTONE WITH COAL AS FUEL 16 3.1 Global description of the progress 16 3.2 Process-parameters 16 3.3 Disturbances and modifications 17 3.4 The warranty test 17 3.5 Emissions 19 3.6 Raw materials 19

3.6.1 Limestone 19 3.6.2 Fine-grained coal 20

3.7 Product-quality 20 3.8 Application of the product in sand-lime bricks . 22

3.8.1 General 22 3.8.2 Description of the sand-lime brick

production process of factory De Hazelaar 23 3.8.3 Composition of the mixture 23 3.8.4 Properties of sand-lime mortar and

-bricks 23 3.9 Mass- and energy-balance 25

4. CALCINING LIMESTONE WITH COAL RESIDUES 26 4.1 Introduction 26 4.2 Operation time 27 4.3 Global description of the progress 27 4.4 Process parameters 2 9

4.4.1 General 29 4.4.2 The CFB temperature 29 4.4.3 Sifter/milling section 29 4.4.4 The drying unit 3 0

4.5 Process - experiences, disturbances and modifications 30

4.6 Emissions 31 4.6.1 NO x-emission 31 4.6.2 Noise emission 32

4.7 Raw materials 33 4.7.1 Limestone 33 4.7.2 fine-grained coal 33 4.7.3 Coal residues 33 4.7.4 Other raw materials 34

4.8 Products-quality 34 4.8.1 General 34 4.8.2 Flyash-lime 35 4.8.3 Kaldin lime and Filter lime 3 6

4.9 Application of the product in sand-lime bricks. 38 4.9.1 Introduction 3 8 4.9.2 Use of lime at De Hazelaar 38 4.9.3 Composition of the sand-lime mortar. . . 38 4.9.4 Laboratory tests 39 4.9.5 Experiences in practice 40

4.10 Mass- and energy-balance 41 5. OTHER APPLICATIONS 43

5.1 Introduction 43 5.2 Slaking of the lime 43 5.3 Asphalt filler 43 5.4 Sewage skudge stabilization 43 5.5 Masonery mortars 44

6. ECONOMICAL ASPECTS 45 6.1 General 45 6.2 Raw materials 45 6.3 The product 45 6.4 Outlook 46

7 . PUBLICITY AND COMMERCIALIZATION 48 8. CONCLUSIONS 49 REFERENCES 51

IV

SUMMARY

Introduction In a cooperation between NOVEM and Kaldin BV, in Koningsbosch (in the province of Limburg, The Netherlands), a plant has been erected in which a fine-grained limestone is calcined in a fluidized bed with coal residues as fuel. It is expected that in this unit 14 tons of limestone can be calcined together with 12.5 tons of coal residues. The starting up of the plant and the introduction of the product on the market have been supervised in a measuring and monitoring program (no. 2534). All the activities which Kaldin has developed within this program are described in the following report. Description of the plant The calcination unit as designed by Lurgi is composed of the following parts: 1. Storage of raw materials and fuel, such as limestone,

coal, coal residues and oil. 2. The circulating fluidized bed (CFB) where the transition

of limestone into lime and carbondioxyde takes place. 3. Parts where drying and pre-heating of the limestone take

place with the use of hot flue-gasses leaving the CFB. Two cyclones take care of the feed-back of the material to the CFB.

4. The circulating fluidized bed cooler, in which the product leaving the CFB is cooled in a direct (air) and indirect (water) way.

5. The sifter and milling section, in which the product is classified and milled to the desired fineness.

6. Product storage. 7. Flue gas treatment, where the flue gasses are successively

cooled, undusted and emitted. The non-contaminated gasses can be used as drying-air in the drying-unit.

8. The measuring and controlling system with which the process can be controlled and directed.

Burning lime with fine-grained coal

Progress In April 1989 the plant has been started up followed by a period of about 9 months in which limestone has been calcined with only fine-grained coal as fuel. This phase is considered as phase 2 of the project. Especially during the first few months after starting up the plant disturbances occurred

mainly as a result of the generated amount of dust and the "sticky" character of this material. Some components of the unit blocked up regularly. After modifications have been made to several of these components, this kind of disturbances was partly reduced. The use of only coal as a fuel is disadvantagous, because of the occurence of caking in several components of the plant, thus reducing the total yearly production hours. In a warranty test it has been shown that the unit can operate without any disturbances while producing a product which can be used as a raw material for the production of sand-lime bricks. During this test, the NOx-emission has been measured by Kaldin at 940 mg/Nm3, which is above the limit mentioned in the nuisance act. After modifications have been made to the CFB, after the end of the measuring and monitoring program, the NO,,-emission has been reduced. The product The product which is produced in phase 2 is a mixture of mainly free CaO (about 62 % ) , Si02 and CaC03. Application in sand-lime bricks The main part of the product has been used as a raw material for the production of sand-lime bricks in the sand-lime brick factory De Hazelaar which is situated beside the Kaldin plant. In practice, an increase of product-loss has been found due to the relatively large variation in free CaO content of the Kaldin product during a large part of the program. Mass- and energy-balance During the warranty test an average energy efficiency for the calcination of CaC03 of about 48 % (related to the theoretically needed calcination energy) has been realized. During the entire phase 2 this was about 44 %.

The burning of lime with coal residues Progress On 30 January 1990, the first coal residues have been processed in the plant. This marked the beginning of phase 3 of the measuring and monitoring program. The original set-up of the program included a gradual increase of the coal residues input up to 12.5 tons per hour. In practice the coal residues input has been increased from about 2 tons in February to about 6 tons during the months July through September. Due to problems with the quality of the sand-lime bricks, the coal residues input has again been decreased to about 2 to 4 tons per hour until the end of phase 3. After the end of phase 3 the measuring and monitoring program has been

VI

concluded, which implies that no experience has been gained concerning the maximum anticipated input of coal residues. Only during short periods more than 6 tons of coal residues have been used (8 tons of coal residues and 16 tons of limestone per hour during a test). The average coal residues input has been 2.5 tons per hour at a limestone input of about 15 tons per hour. Besides coal residues also 1.2 tons of several types of coal per production hour have been used as fuel . Process-technological experiences and disturbances As a result of the use of coal residues as fuel some disturbances which occurred during phase 2 of the program did occur less during phase 3. These disturbances are mainly: - Caking in various components of the plant. The use of coal residues has an abrasive effect on the cakes.

- The incomplete fluidization of limestone due to the relatively coarse grains in the limestone. The input of coal residues reduces the average grain size of the bed-material which makes it easier to fluidize the bed.

Beside the reduction of several disturbances due to the use of coal residues, some other disturbances appeared as a result of the use of coal residues. These are the following: - as a result of afterburning, mainly of FBC coal residues, in the product-cooler sometimes sintering of the product does occur and in the flue gas pipes the temperature increased.

Emissions During the period when coal residues were used, the N0X-emission was higher than during the time when only coal was used. It exceeded the limit which is mentioned in the nuisance act (500 mg/Nm3). The NOx-emission varied between about 900 and 2100 mg/Nm3. No clear relation is visible between the NOx-emission and the type and quantity of coal residues which have been used. Modifications to the CFB have been made after the conclusion of the measuring and monitoring program and these have lead to a decrease of the NOx-emission. Tests have shown that when additional measures are taken, the N0X emission can be kept below 500 mg/Nm3, when using more than 2 tons of coal residues per hour. However, a reduction of the NOx-emission below the limit mentioned in the nuisance act often implies a decrease of product quality concerning the outburn of coal particles and the calcination ratio. The emission of noise of Kaldin lies above the maximum level which is mentioned in the private nuisance act. Modifications have and will be made to the main sources of noise, which lead to a decrease of the noise emission. However, at the end of the program, the maximum level was still exeeded.

VII

Coal residues The aim of the project has always been the use of Dutch coal residues as a raw material and fuel in the calcination of limestone. The Dutch types of coal residues, which have been supplied by Vliegasunie, AKZO and by DSM, have a relatively low heat of combustion compared to the used types of German coal residues which arise at fluidized bed combustion (in average 2.2 vs. 7.7 MJ/kg). Also the negative prices of the Dutch coal residues are lower than the negative prices of German coal residues. In view of the economic viability of the plant, it has therefor been decided to use German coal residues beside the Dutch coal residues. The product During the first part of phase 3 only one product, the so-called flyash-lime, has been produced. Depending on the coal residues input, the free CaO content of this product varies from 35 to 60 %. Since the end of September 1990 the dust from the cloth filter and the heat-exchanger are lead to a product-silo, this dust is considered as a separate product, the so-called "Filter lime". This product makes up about 25 % of the total product. The other 75 % of the product is since then called "Kaldin lime". Beside a relatively low free CaO content (about 34 % ) , the Filter lime consists mainly of CaC03 (about 25 %) and silicates (about 40 % ) . Kaldin lime mainly consists of free CaO (about 64 %) and of silicates (about 33 % ) . The variations in the Kaldin lime are smaller than the variations in the previously produced flyash-lime and the Filter lime. Application in sand-lime bricks During the measuring and monitoring program the application of fly-ash lime, Filter lime or Kaldin lime has almost completely been realized as a binding agent for the production of sand-lime bricks. Almost the entire product has been sold to sand-lime brick factory De Hazelaar. The assumed advantage of the use of coal residues in sand-lime brick production concerning a higher green strength of the product, could not be demonstrated in practice. Based on experiences in practice concerning the quality of the sand-lime bricks and elements, the quantity of free CaO which is dosed in a sand-lime mortar has not been decreased, which means that, compared to the previously used type of lime, much more Kaldin product had to be used in order to reach a similar quality of the sand-lime bricks and elements. Mass- and energy-balance During phase 3 in average 13.0 tons of CaC03 have been processed per production hour. The total quantity of used

- VIII

fossil energy amounts to 49.7 GJ/hr. This results in an energy efficiency during phase 3 of 46 %. About 40 % of the energy leaves the plant with the heated flue gasses. The average quantity of fossil energy which is needed for the production of 1 ton of free CaO is 8.3 GJ. During periods when the Kaldin plant has been operated at optimum conditions, this use of fossil energy is reduced to about 7.5 GJ per ton free CaO. The use of electric energy during an average period in which the plant is operated without interruptions, without the use of the drying-unit, is about 1100 kWh per hour (157 kWh per ton of free CaO, at 7 tons of free CaO per hour). Other applications Beside the application in C.S. bricks, other applications for the product have been studied, but have so far only reached an experimental stage. The most promising applications are the following: - as a filler in asphalt - in masonry mortars - in sludge stabilization Economical aspects The economic viability of the plant depends largely on 2 factors: 1. The price of the product, which is mainly influenced by

the free CaO content. 2. The price and carbon content of the coal residues. The use of coal residues with a high carbon content (and a high negative price) results in a good profitability of the plant. The sale of the Kaldin product has mainly been limited to sand-lime brick factory De Hazelaar. As a result of this restricted sale, together with the occurrence of disturbances in the plant, the production level (about 30,000 tons/yr in stead of the anticipated 90,000 tons/yr), and therefor also the proceeds, of the Kaldin plant reached a far lower level than which was anticipated.

IX

LIST OF TABLES AND FIGURES

TABLES

Table 1 -

Table 2 -

Table 3 -Table 4 -

Table 5 -

Table 6 -Table 7 -

Table 8 -Table 9 -Table 10 -Table 11 -Table 12 -

Start-case calculations concerning mass- and energy-balance for the calcination of limestone with coal and with coal residues, 8 Average raw material input and product output during phase 2, compared to the data of the warranty-test, 17 Specifications of raw material input and product during the warranty test ( 4 - 7 December 1989), 18 Chemical composition (main components) of the fine­grained limestone which is processed during phase 2, 20 Average properties of the product which is produced during phase 2, compared to the properties of the product which is produced during the warranty test, 21 Calculated average mineralogical composition of the product of phase 2 and the warranty period, 22 Properties of sand-lime mortar and -brick with different types of lime and 6.5 % water during phase 2 (at laboratory scale), 24 Use of raw materials and production per production hour during phase 3, 28 Average properties of flyash-lime (February -September 1990), 35 Average global mineralogical composition (in %) of Kaldin and Filter lime, 37 Average properties of Kaldin lime and Filter lime (October 1990 - April 1991), 37 Properties of sand-lime mortars with Dornap lime and with flyash-lime, based on laboratory tests, 40

FIGURES

Figure 1 - Schematic flow sheet of the calcination unit, 9 Figure 2 - Main properties of the product generated during

phase 2, 21 Figure 3 - Average raw material input and production per hour

per month during phase 3, 28 Figure 4 - Average properties of flyash-lime and a combination

of Kaldin lime and Filter lime per month, 36

XI -

PROJECT DETAILS

CALCINATION OF LIMESTONE IN A CIRCULATING FLUIDIZED BED

WITH COAL RESIDUES AS FUEL

Project number

Contractor

Contactpersons

Co-contractor

CS 008/89 NL

KALDIN B.V. SaeffeIderstraat 10 6104 RA Koningsbosch The Nederlands

Mr. M.P.G. Stassen Mr. R.H.W.W.M. Hermans (Phone no. 04743 - 2341)

LURGI NEDERLAND B.V. Backershagen 97 1082 GT AMSTERDAM

Author : Drs. H.M.L. Schuur Projectbureau voor Industrie en Milieu B.V.

Koningsbosch, March 1992

1 -

Kaldin calcination plant in Koningsbosch, The Netherlands

1. INTRODUCTION

Since about 1980 the energy policy of the Dutch government has for an important part been focused at the re-introduction of coal as a fuel. The activities which have been carried out in this policy, are placed in the National Clean Coal Program, N.O.K.). Because of the fact that with the burning of coal also residues arise, the attention of the N.O.K. has also been put to a useful re-use of these residues, in order to minimize their effect on the environment. In the same period the Holding De Hazelaar was investigating the technical possibilities to calcine a fine-grained limestone into lime and to use this lime as a raw material for the production of sand-lime bricks. In a cooperation between the Netherlands Agency for Energy and the Environment (NOVEM) and the Holding De Hazelaar the possibilities have been studied to calcine the fine-grained limestone with the energy which can be derived from coal residues with a high coal content (> 5 % ) . However, conventional technologies which are used to calcine limestone such as shaft and rotary kilns are not suitable for the processing of fine-grained materials. After the execution of desk-studies and pilot-plant tests it has been decided to calcine the fine-grained material with a circulating fluidized bed system which was developed by Lurgi GmbH in Frankfurt. Based on the results of these studies and tests, Kaldin b.v. has been founded. Thereupon, on the site of sand-lime brick company De Hazelaar in Koningsbosch, a demonstration plant has been built, which is in operation since april 1989. The construction of the plant and the introduction of the product on the market is covered by a measuring and monitoring program (no. 2534) which is financed by the NOVEM and the European Community. For the course of this program a monitoring panel has been installed. This panel was given all the information concerning the progress and acquired knowledge within the program and had the possibility to make changes in the program if necessary. The members of the panel are representatives of NOVEM, Kaldin, Lurgi and the Vliegasunie. The aim of the measuring and monitoring program project is to produce a type of lime in a technical and economic justifiable way based on: 1. Limestone which comes available as a side-product in

limestone quarries and 2. Coal residues with a relatively high coal content, with a minimum effect on the environment.

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The product, a fly ash-lime mixture, has to be at least applicable as a raw material in the sand-lime brick industry. This re-use of coal residues corresponds with the Dutch policy concerning energy and environment and will lead to a reduction of other sources of energy in the production process of Kaldin. In addition it contributes to a solution for the coal residue problem. Data have been collected concerning the technical, economical and environmental aspects of the process, about the quantity and quality of the product and about the application of this product as a raw material in sand-lime brick production. These data have to be collected in phases 2 and 3 of the following described phases of the project: Phase 1: Design and erection of the plant (Until April

1989) . Phase 2: Starting up the plant, test runs and warranty test

based on limestone and coal (period until July 1989) .

Phase 3: Demonstration of the use of coal residues in different mixtures up till 6.25 tons per hour (period until April 1991)

Phase 4: Continuation of the demonstration up till a maximum of 12.5 tons coal residues per hour (period until April 1992).

Phase 5: Optimizing the process and the production based on the information which is gained during the preceding phases (period until October 1992).

During the course of the project the deadlines for some phases have been changed. Phase 2 for example covers a longer period than which has been anticipated and only at the end of January 1990 the first amount of coal residues has been processed. An intervention in the pursued length of time of the program took place at the end of April 1991 when the entire program was brought to an end. Because of not anticipated costs, the realized project costs at the beginning of 1991 reached a level which had been planned for the end of the measuring and monitoring program (October 1992).

2. DESCRIPTION OF THE PLANT

2.1. General.

Calcining limestone is based on the following equation: CaC03 + energy > CaO + C02 limestone lime carbondioxyde

Depending on the calcination process, this reaction takes place at temperatures between 800 to 900 °C. The optimum temperature for the reaction to take place in a circulating fluidized bed lies between 900 and 1050 °C. The energy which is needed for this reaction, is provided by coal residues (with a carbon content higher than 5 %) by fine-grained coal and by oil. Beside a substantial saving in energy costs, the use of coal residues as a fuel leads to a product which contains burned-out coal residues. This treated coal residues can, in some applications, have a positive effect on the properties of the endproduct. Because of the use of fine-grained materials, the conventional lime production technologies, such as shaft and rotary kilns, can not be applied. In cooperation with NOVEM, pilot-plant tests have been carried out by Lurgi which indicated that the circulating fluidized bed technology was the best way to treat the fine-grained raw materials. Based on the results of these tests, Kaldin b.v. was founded and a plant has been developed and constructed. In the following paragraphs successively the conditions on which the design has been based and the final design of the plant will be described.

2.2. Conditions for the design. 2.2.1. General The unit has been developed to operate with the use of two different combinations of raw materials: 1. Calcining humid limestone with fine-grained, dry coal as a

fuel. 2. Calcining humid limestone with dry coal residues. Lurgi has warranted the operation of the unit for the first combination of raw materials. Although the unit has been designed for an operation with the use of coal residues, a warranty for this way of operation has not been given. This is the reason that for the use of coal residues as a fuel for the calcination of limestone a measuring and monitoring program has been started.

2.2.2. Calcining humid limestone with fine-grained coal as a fuel.

The conditions for the design are based on a limestone with d50 = 500 jum and pre-dried fine-grained coal with less than 8 % water and which can be transported pneumatically. The limestone input can be 21 tons per hour. Based on these parameters Lurgi has given the following warranties:

product output : > 10.4 tons/hour degree of calcination : > 97 %

- carbon outburn : > 98 % product fineness : d97 < 90 /xm

Beside these warranties, Lurgi has guaranteed that the unit will meet all the governmental requirements which are applicable for the operation of the plant. This means for example that the emission of different components and the production of noise has to meet the limits which are mentioned in Kaldin's private nuisance act (see section 2.2.4.). 2.2.3. Calcining humid limestone with coal residues as

fuel. The conditions for this design are also based on a limestone with dso = 500 jim but with dry coal residues as fuel. The lime­stone input can be 14 and the coal residues input 12.5 tons per hour. Although in the design of the calcination plant the use of coal residues, has been taken into account, Lurgi has not given any warranties concerning the product output or the quality of the product when using coal residues as a fuel. 2.2.4. Process-conditions of the drying unit. In order to re-use the flue-gasses from the calcination unit a drying unit has been designed. This unit has initially been designed for the drying of very fine-grained limestone which originates from chemical processes and has an average water content of about 25 % (m/m). Lurgi has warranted the water content of the endproduct at a maximum of 3 %. Other process-parameters on which the drying unit has been designed are the following (when operating the calcination unit with coal residues as fuel): input wet limestone : > 25.0 tons per hour product output : > 19.1 tons per hour.

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2.2.5. Emissions. Requirements for the environmental aspects of the Kaldin plant which are described in Kaldin's private nuisance act concern mainly the compartments air and noise. Concerning the compartment air, it is expected that the emissions of N0X and dust will probably be the most critical emissions. It is expected that requirements for other components which are mentioned in this nuisance act do not exceed the requirements. The requirements for all the different emissions are mentioned below.

Dust NO, S02 HF Pb Zn Cd Hg As Sb

< < < < < < < < < <

50 mg/Nm3 500 mg/Nm3 700 mg/Nm3

1 mg/Nm3 1 mg/Nm3 1 mg/Nm3 0,1 mg/Nm3 0,1 mg/Nm3 0,1 mg/Nm3 0,1 mg/Nm3

The noise rate level contour at the limit of the parcel as required in the nuisance act is 50 dB(a) during day time and 40 dB(a) when the unit is operated during the night. 2.2.6. Mass- and energy balance. Lurgi has carried out start-case calculations concerning the operation of the plant with fine-grained coal and with coal residues as fuel.

These calculations are based on a limestone with a CaC03 content between 85 and 92 % and a water content between 4 and 8 %. The heat of combustion of the coal is set at 26 MJ/kg and the coal content of the coal residues is 15 %. The output of free CaO has in both scenario's been set at 7.0 tons per hour. It is furthermore assumed that the production takes place continuously, except during weekends and holiday periods. The possible amount of production hours is therefore: 24 (hours) x 5 (days) x 48 (weeks) = 5780. Assuming that 80 % of these hours will be realized, the total amount of production hours per year will be 4608.

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Table 1 - Start-case calculations concerning mass- and energy- balance for the calcination of limestone with coal and with coal residues

Scenario 1 2 Coal coal residues

15.75 0 0 12.50 55.0 19.2

88,470 7.0

32,260 36.5

Limestone Coal

coal residues

Product

Free CaO Free CaO in product

t/h t/h GJ/h t/h GJ/h t/h t/j t/h t/j

%

42, 32,

15.75 1.694 44.1 0 0 9.2

r390 7.0

r260 76.3

2.3. Description of the design,

2.3.1. General. The calcination unit as designed by Lurgi is composed of the following parts: 1. Storage of raw materials and fuel, such as limestone, coal,

coal residues and oil. These parts take care of the storage, buffering of these materials and of the dosage to the furnace.

2. The circulating fluidized bed (CFB) where the transition of limestone into lime and carbondioxyde takes place.

3. Parts where drying and pre-heating of the limestone take place.

4. The circulating fluidized bed cooler, in which the product leaving the furnace is cooled in a direct (air) and indirect (water) way.

5. The sifter and milling section, in which the product is classified and milled to the desired fineness.

6. Product storage. 7. Flue gas treatment, where the flue gasses are successively

cooled undusted and emitted. The non-contaminated gasses can be used as drying air in the drying unit.

8. The measuring and controlling system with which the process can be controlled and directed.

Based on this division of the calcination unit in the following sections a description of every part will be given.

A schematic flow sheet of the calcination unit is given in figure 1.

Storage and dosage of raw materials and fuel. The main raw material which is used in the calcination unit is limestone, coal residues are used both as a raw material and as a fuel and fine-grained coal and oil are two types of fuel that are used. Air is needed as a source for the combustion of the fuels and as a transport medium. Limestone The storage of limestone takes place in open air on the terrain close to the plant. From this outdoor storage the limestone is tipped into a bunker by means of a shovel. The dosage of the limestone is performed by means of a centrex, a rotating arm which scrapes the bottom of the bunker and which moves the limestone to a central opening on the lower side of the bunker. By controlling the amount of revolutions per minute, the amount of limestone, which falls on a conveyor-belt can be dosed. From this conveyor-belt the limestone arrives at the transportation screw of the venturi dryer.

Figure 1 - Schematic flow sheet of the calcination unit

Coal The storage of fine-grained coal takes place in an explosion safe silo with a content of 120 m3, which has a de-aeration system and a cloth filter. The level to which the silo is filled can be monitored by a feeling weight. The dosage of the coal to the CFB is controlled by means of a rotary valve. By changing the amount of revolutions per minute, more or less material can be dosed. The amount of coal which is dosed depends also on the bulk density and on the fossil energy content of the fine-grained coal. coal residues 1 The coal residues 1 silo is suited for the storage of dry coal residues, which can be dosed to the fluidized bed without any pre-treatment. The silo has a content of 120 m3, and has a de-aeration system and a dust filter. The level to which the silo is filled can, like with the coal silo, be monitored by a feeling weight. The dosage and transport of the coal residues to the CFB is performed by means of a rotary valve and a pump. coal residues 2 The storage and dosing system of the coal residues 2 silo is identical to that of the coal residues 1 silo. To the coal residues 2 silo provisions have been made which make it possible to store materials that have been dried in the drying unit. This means that not only coal residues can be stored in this silo, but also for example dried sewage sludge or fine­grained limestone. Heavy oil The storage of heavy oil takes place in a tank with a content of 50 m3, which is provided with a level detection. Air Air is needed as an oxygen supplier for the combustion of the different kinds of fossil fuel. Beside this function, air is needed for the pneumatic transport of several materials. The two main current which lead to the CFB, the primary and the secondary air, are pre-heated by the fluidized bed cooler, before they are injected into the CFB. Both the primary and the secondary air supply are generated by two blowers with a pressure of 500 mBar at a flow rate of maximum 9000 Nm3 per hour. 2.3.3. The circulating fluidized bed (CFB) The circulating fluidized bed is the heart of the plant. This is where the actual calcination of limestone takes place at an optimum residence time and steady and even temperatures, within a range of 875 to 1050 "c. Both the residence time and the temperatures can be separately varied, which is an

10

important condition to reach the desired quality of the product. The CFB has been designed for the treatment of solid raw materials with an input capacity of about 25 tons per hour. When the calcination of limestone is carried out only with the use of coal, then about 21 tons of limestone and about 2.0 tons of coal can be processed. When only coal residues are used as a fuel, according to the engineering of the plant, 12.5 tons of coal residues can be used with an input of 14 tons of limestone. The circulating fluidized bed system is composed of different components which all contribute to an optimum process. These are: - The circulating fluidized bed

The recycling cyclone The syphon

The circulating fluidized bed The circulating fluidized bed (the furnace) is in theory a cylinder which consists of a refractory masonry, surrounded by an insulating layer with a steel lining on the outside. The circulation of the bed is obtained by the injection of air. The primary air is pre-heated in the fluidized bed cooler and then blown into the fluidized bed at the lower end of the furnace via multiple injection points. The secondary air is also pre-heated in the fluidized bed cooler, but is injected at a higher level of the CFB. The combustion in the CFB takes place in two phases. As a result of a oxygen-deficit, the combustion in the lower part of the CFB is under-stoichiometric. From the input of secondary air a surplus of oxygen does exist which leads to a complete combustion of the fuels, combined with an optimum calcination of the limestone. In the lower part of the CFB a high concentration of solid material does exist, which stimulates the combustion of the fuel. The residence time on the CFB can be controlled using the differential pressure over the CFB in combination with the amount of input and output of the materials. The recycling cyclone and syphon The recycling cyclone is attached to the CFB and is also covered with a fire-proof lining. The cyclone separates the major part of the product from the flue-gasses. After separation this material arrives in the syphon which is connected at the lower side of the cyclone. When the syphon is sufficiently filled with solid material, a part of the material is recirculated back to the CFB and at the same time another part is tapped from the syphon into the fluidized bed cooler.

11

2.3.4. The pre-heating system In the pre-heating system the hot flue gasses from the CFB are brought in contact with the cold humid limestone. As a result of water evaporation and pre-heating of the limestone, temperatures in this part of the system reach values between 500 and 700 *C. Thereafter the gasses are separated from the solid material in the first and second cyclone and the solid material is transported back to the CFB. The pre-heating system consists of 3 main parts:

a venturi; the primary cyclone; the secondary cyclone.

The venturi The aim of the venturi is to bring the humid limestone in contact with the hot flue gasses from the CFB. The venturi consists of a especially constructed narrowing in which the loss of pressure is limited together with an optimal mixing of the solid material with the flue gasses. The flue gasses are thereafter dedusted in the two cyclones which are placed after the venturi. Primary and secondary cyclone The primary and secondary cyclones are two identical cyclones which are connected in series and are meant to dedust the flue gasses. The solid material is thereafter transported back to the CFB. The flue gasses follow their way to the heat-exchanger and cloth filter where they are further cooled and dedusted. 2.3.5. The fluidized bed cooler The fluidized bed cooler has a double purpose; partly it will cool the calcined product from the CFB and partly the needed primary and secondary air supplies are pre-heated. In this way an optimum energy transmission takes place. The product which arises from the CFB is cooled from a temperature of 900 - 1000 °C down to less than 100 'c. From this cooler the product is transported to the intermediate bunker of the sifter-milling section. The cooling is performed with air (direct and indirect) and with water. The cooler is based on the principle of fluidized bed cooling and consists of 6 chambers. The transport of the product from one chamber to another is performed by air which is injected into the bottom part of each chamber. 2.3.6. The sifter-milling section The sifter-milling section can be considered a system in a system. In this section the product which arises from the

12

fluidized bed cooler is milled to a specific fineness (97 % smaller than 90 microns). To reach this fineness a closed milling section has been chosen. This means that the material is recycled until the desired fineness is obtained. The wind sifter and ball mill are the two main components of this section. From an intermediate bunker which provides a constant product input, the product is lead to the wind sifter via an elevator and a conveyor screw. The wind sifter separates the product into a fine-grained and a coarse-grained part. The fine-grained part is transported from the wind sifter to one of the productsilo's. The coarse-grained part is dosed to the ball mill. In the ball mill this coarse-grained material is milled to the desired fineness. The milled product is transported back to the wind sifter together with new material from the intermediate bunker. 2.3.7. The product storage For the storage of the endproduct two identical silo's have been constructed. Each silo has a content of 400 m3. On each silo a cloth filter has been installed in order to separate the solid particles from the pneumatic transport air. The possibility has been created to transport the dust from the heat exchanger and cloth filter directly to one of the silo's. The transport to the clients is carried out by silo-wagons. 2.3.8. The flue gas treatment unit The flue gas treatment unit has a double purpose. On the one side the flue gasses are dedusted before they can be emitted, on the other hand on economical basis, the energy which is present in the flue gasses has to be re-used as much as possible. The flue gas treatment unit is composed of the following components:

The heat exchanger - The cloth filter - The flue gas fan and chimney. The heat exchanger The heat exchanger is composed of two chambers which each have a vertically positioned bundle of pipes. In this process an indirect heat transfer to the open air takes place. This cooling air is heated and can be used as a drying-air in the drying unit. On the tube-side of the heat-exchanger a cleaning system is installed in order to remove the cakes of dust from the inside of the pipes. The dust which is removed from the inside of these pipes can be transported to the CFB or to one productsilo via two rotary valves, a conveyor screw and a pneumatic pump.

13

The cloth filter In the cloth filter the flue gasses are furthermore separated from the dust. The amount of dust in the flue gasses will finally reach a quantity smaller than 50 mg per Nm3 which means that it meets the requirements of Kaldin's private nuisance act. The cloth filter is composed of a cloth with an active specific surface of about 1000 m2. The amount of dust which has to be separated from the flue gasses is estimated at about 5 % (m/m) of the raw material input into the CFB. Just like the dust which is separated from the flue gasses in the heat-exchanger, this dust can be transported to one of the productsilo's or to the CFB. The flue gas fan and chimney The flue gas fan and the chimney are the last two parts of the plant which the flue gasses have to pass before they are emitted. The flue gas fan is provided with a regulator with which the amount of flue gasses per time period can be controlled and which as such can compensate a loss of pressure in the system which can be caused in the heat exchanger, the conduit-pipes, the cloth filter or the chimney. The chimney has a height of 41 m and provides as such in an effective dispersion of the flue gasses. 2.3.9. The measuring and controlling system Beside the already mentioned measuring and controlling equipment for the dosage of different materials, measuring and controlling points have been placed on several locations in the plant. Pressure and temperature sensors have been placed on critical locations and several flow rate sensors for nitrogen and oxygen have been placed in the flue gas channels of the plant. In the control centre all the signals can be monitored, controlled and saved. 2.3.10 The drying unit The drying unit has been designed to re-use the energy which is present in the flue gasses in an economically useful way. As described in section 2.3.8., via an indirect way the open air is heated to a temperature of maximum 250 *C. This air is free of contaminations and can therefore be used for the direct drying of several types of materials, without the possibility that they might become contaminated. Initially the unit was designed for the drying of a fine-grained limestone which arises from a chemical process with a water content of about 25 % (m/m). The drying unit bears a resemblance to the venturi pre-heating system of the calcination unit. The drying unit is composed of:

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a bunker a transport system, divided in a conveyor belt, an elevator and an input unit a venturi dryer a cyclone a cloth filter and

- a productsilo The storage of the materials which have to be dried takes place in open air on the terrain close to the plant. From this outdoor storage the material is dumped into a bunker by means of a shovel. The dosage of the material to the drying unit is performed by means of a centrex, which is comparable to the limestone dosage to the CFB. From the centrex this material is transported to the venturi-dryer via conveyor belts and an elevator. As a result of the intensive contact between the warm gasses and the humid material, the water will evaporate rapidly. In a cyclone and a cloth filter which are placed behind this venturi dryer, the gasses are separated from the solid material (mainly dust). The gasses are thereafter emitted via the central chimney. Depending on its application, the dried material can be stored in a productsilo with a content of 120 m3 or in the coal residues 2 silo of the calcination unit.

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3. CALCINING LIMESTONE WITH COAL AS FUEL

3.1. Global description of the progress

After the calcination unit had been built, according to the planning, in april 1989 it was started up with the use of coal as a fuel to calcine the limestone. This took place during a period of about 9 months. This period corresponds with phase no. 2 of the measuring and monitoring program. In the original project-planning the concluding date for phase no. 2 was 1 July 1989, but unlike this planned concluding date, only on 30 January 1990 the first coal residues has been processed and phase no. 3 was started. The reason for this delay can be found in a number of unforeseen disturbances which prevented a good progress of the operation. During the first 4 months after starting up the unit relatively short periods of production were alternated with long periods in which actions had to be taken to deal with the disturbances. In total during this phase of the project about 1600 production hours were realized. This involves an effectiveness of the available operation hours of 46 %. In September 1989 the first long run with fine-grained coal as fuel took place, and during the first week of December, in stead of in July, Lurgi has carried out a warranty test for the plant. On 30 January 1990 the first coal residues has been used and phase 3 of the measuring and monitoring program was started.

3.2. Process-parameters

The first detailed process data were registered during the warranty test which was carried out by Lurgi during a period of 72 hours, between 4 and 7 December 1989 (see § 3.5). These data can be considered as representative for periods of phase 2 in which a relative high production level has been obtained. During the entire phase 2, the plant has been mainly operated at a part of the maximum attainable production capacity. This explains the difference between the average production figures of the entire phase 2 and of the period during which the warranty test took place (table 2). The raw material input during the warranty test can be considered as an ideal situation, which can be attained when the plant is operated at (almost) its maximum capacity with no

16 -

disturbances in the process and only small variations in the composition of raw materials.

Table 2 - Average raw material input and product output during phase 2, compared to the data of the warranty test

Phase 2 total per hr

Warranty-period per hr

Limestone (tons) CaC03 (%) water (%) CaC03 (tons)

Coal (tons) Product (tons)

free CaO (%) free CaO (tons)

24,000

19,160 2,400

13,200 8,140

14.8 85.7 6.9

11.8 1.4 8.1

61.7 5.0

3.3. Disturbances and modifications Beside some small disturbances which were relatively easy to manage, during the first months after starting up the plant, main disturbances took place. The disturbances resulted often in adjustments of parts of the plant and adjustments in the way the plant was processed. From the time that the plant was started up, problems occurred as a result of an overdoses of dust and the nature of this material. This often resulted in obstructions and caking in several parts of the plant. In order to solve this problem adjustments have been made to several parts of the plant. This resulted in a decrease of the problems which occurred due to the generation of dust and the character of this material. The presence of coarse grains lead to an accumulation of coarse material on the bottom of the CFB. As a result thereof, the CFB had to be tapped off more often. After the installation of a sieve, the problem with accumulations of coarse material at the bottom of the CFB have been decreased.

3.4. The warranty test

During a period from 4 until 7 December 1989 Lurgi has carried out a warranty test in order to demonstrate that the plant can be operated under the given conditions and with the given

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product specifications. The warranted specifications (table 3) are all given for the calcination of limestone with only coal as fuel and not with the use of coal residues. During the warranty period no complications occurred and this period may therefore be considered as representative for a period during which the plant is operated almost at the maximum capacity with coal as a fuel and without any appearing disturbances. The specifications of the production process and of the product are given in tables 2 and 3. From these data can be concluded that the warranted specifications concerning product quantity, carbon outburn and the amount of product passing a sieve of 90 microns have been met.

Table 3 - Specifications of raw material input and product during the warranty test (4-7 December 1989)

Warranty Realized 19 ,

1, 1 1 . 99 , 95 ,

2,

.7

. 8 4

.7

. 2

.6

. 5

limestone (tons/hr) coal (tons/hr) product (tons/hr) carbon outburn (%) calcination ratio (%) > 90 /xm (%)

10.4 > 98.0

97.0 < 3.0

Concerning the calcination ratio it has to be stated that more than one definition can be applied. In this case the calcination ratio is defined as 100 x (CaC03 input - CaC03 output)/CaC03 input. When the calcination ratio is considered a measure for the efficiency of the plant to turn CaC03 into free (or active) CaO, the following equation can be applied:

Calcination ratio = free CaO in product total CaO in product

x 100 (%)

Independant of the way the calcination ratio is defined, the product which was generated during the warranty test did not meet the warranted calcination ratio. Because of the more constant process-conditions during the warranty test compared to those of the entire phase 2, the quality of the product which is generated during the warranty test is more constant than the average quality of the product which is generated during phase 2. The product generated during the warranty test has also a higher CaO content (both free and total).

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3.5. Emissions During the warranty test in December 1989 detailed measurements of flue gas components or of noise rate level have not been carried out. Only the regular 02 and NO,, measurements have been carried out with the standard equipment of Kaldin. In a mutual agreement between Lurgi and Kaldin additional emission measurements have been carried out in a later stage. The NOx-emission which was measured by Kaldin during the Warranty test is about 940 mg/Nm3 at 7 % 02, which is higher than the requirements which are mentioned in Kaldin's nuisance act (500 mg/Nm3). After gaining more experiences concerning the use of coal residues, and the corresponding level of the NOx-emission, effective modifications to the CFB have been made in order to decrease the NOx-emission. After the end of the program, with the use of only coal as a fuel the NOx-emission could be decreased to a level below 500 mg/Nm3, when using a limited quantity of combustion air. In this case the quality of the product, concerning the carbon outburn, could not always be guaranteed. Other randomly measured components such as C02, CO and S02 and components measured at dust samples such as the quantity of dust, Cd, Pb, Zn, Sb, Hg and fluorides, stay far below the requirements mentioned in the private nuisance act [1].

3.6. Raw materials

3.6.1. Limestone During the entire phase 2 a fine-grained limestone has been processed. This limestone arises as a side-product after crushing and sieving of limestone, which is used for lime production in conventional lime calcining kilns. The composition of the fine-grained limestone is shown in table 4. Most of the data have been provided by the supplier, only the CaC03 and water content are averages from the analyses which have been carried out by the Kaldin laboratory. The grain size of the limestone is between 0 and 3 mm, and in average (d50) 0.7 to 0.8 mm. The limestone is not a pure limestone but consists partly of sand and clay (about 10 to 15 % m/m). The presence of these components has a positive effect on the transportability of the limestone in the plant. On the other hand, the free CaO

19

content of the product is lower than it would be with the use of a pure limestone. During phase 2 in total about 24,000 tons of limestone have been processed.

Table 4 - Chemical composition (main components) of the fine-grained limestone which is processed during phase 2

Component

CaCO-j water Si02 A1203 Fe203 MgO

Average

85.7 6.9 9.3 1.0 1.0 0.3

Standard deviation 3.2 0.9 3.6 0.5 0.5 0.4

3.6.2. Fine-grained coal During phase 2 a total amount of 2400 tons of high quality fine-grained coal has been used. This fine-grained coal has such a quality that an almost complete combustion of the coal was attained and no process-technological problems of the plant can be attributed to the use of this coal.

3.7. Product-quality

The product which is generated with only coal as fuel is mainly a mixture of free lime (CaO) and silicates (mainly Si02/ coming from the limestone). Subsidiary components are CaC03/ Ca(0H)2, CaS04 and coal residues (coming from the coal). The colour of the product is off-white. During phase 2 about 14,000 tons of product have been generated. The average composition and properties of this product are shown in table 5. As a reference, the properties of the product which is produced during the warranty test are also shown. During the first months after the plant was started up large fluctuations occurred in the properties of the product (figure 2). This is caused by the regular interruptions in the production process (disturbances and modifications). After the plant started to generate the product in higher quantities and in a more regular way, the quality of the product improved and became more constant.

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Table Average properties of the product which is produced during phase 2, compared to the properties of the product which is produced during the warranty test

Phase 2 Warranty test Property Unit Avg. Avg. t80* Total CaO Free CaO fr CaO/tot CaO

rain % % %

4.2 68.9 61.7 89.6

4.8 74.2 65.8 88.7

the reactivity of the lime

apr may jun Jul aug sep oct nov dec jan _^_ CaO tot _^_ CaO free _^_ CaOtfCaOtot

Figure 2 - Main p r o p e r t i e s of t h e p r o d u c t g e n e r a t e d d u r i n g phase 2

21 -

The standard deviation of the free CaO content of the product which is generated during the warranty test corresponds to the standard deviation of types of lime which are sold by other lime-producing companies (about 1 % ) . This implies that a product which is produced in a continuous process, at almost the maximum capacity of the plant and with coal as fuel, has a composition which is sufficiently constant. The reactivity of the product was generally too high to be used as a raw material for the production of sand-lime bricks in the factory of De Hazelaar. This is mainly the result of the relatively low temperature (960 "C) at which the CFB was processed. Therefore in the milling section of the Kaldin plant a retarder has been added to the lime. Based on data such as the chemical properties of the product, the content of silicates of the limestone and the ash content of the coal, a global mineralogical composition of the product can be calculated. The results of these calculations are shown in table 6. The difference between the mineralogical composition of the two products is a lower free CaO content and a higher content of silicates of the average product which is generated during the entire phase 2 compared to the product generated during the warranty test.

Table Calculated average mineralogical composition of the product of phase 2 and the warranty period

Component (%) Phase 2 Warranty t e s t

CaO MgO Ca(0H)2 CaC03 Coal ash org. carbon silicates

57.8 0.5 4.5 8.0 1.3 0.1

27.8

6 2 . 5 0 . 5 3 . 7 7 .0 1 .1 0 . 1

2 5 . 1

3.8. Application of the product in sand-lime bricks

3.8.1. General About 86 % of the product of phase 2 (11,400 tons in total) has been used as a raw material for the production of sand-lime bricks in sand-lime brick factory De Hazelaar. Beside this application smaller amounts of this product have been

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sold to another sand-lime brick factory and have been used as a raw material in cement-production. 3.8.2. Description of the sand-lime brick production

process of factory De Hazelaar The production of sand-lime bricks is performed with a fine­grained sand which is extracted from the quarry situated near the factory. This sand is mixed with lime and water and thereafter stored in a reactor, in order to allow the lime to slake. Then the sand-lime mixture is remixed and pressed into moulds of specific sizes. The moulded products are steam-cured during 12 to 16 hours at about 200 "c and 16 Bar steam-pressure. Under these conditions the Si02 of the sand goes into solution and reacts with the free CaO to form calcium-silicates, which will harden the sand-lime bricks. 3.8.3. Composition of the mixture The composition of the sand-lime mixture is calculated based on the minimum amount of free lime which has to be available in this mixture. This implies that in a sand-lime mixture with Kaldin lime (which has a lower free CaO content than the type of lime which has formerly been used by De Hazelaar: Dornap lime) more Kaldin lime has to be dosed. This means that a higher amount of fine-grained particles is dosed to the mixture as was the case before Kaldin lime was used. The possible positive effect of the addition of this extra amount of fine-grained particles to the properties of the sand-lime bricks has not been taken into account in this calculation. 3.8.4. Properties of sand-lime mortar and -bricks Laboratory experiments On laboratory scale several experiments have been carried out with Kaldin lime compared to Dornap lime. In table 7 the results of a test with mixtures of Dornap lime and with the product which has been generated during the warranty test are shown. The increase of the free CaO content leads with all samples to an increase of both the apparent density, the green strength and the compressive strength. In order to realize a certain percentage of free lime in the mortar, more Kaldin lime had to be added than when Dornap lime is used, which makes it difficult to compare the two mixtures. The increase in fine­grained particles in the mixture can have a slightly positive effect on the green strength and on the compressive strength. However, it has to be stated that in practice no relation could be found between the measured green strength and a decrease of product-quality caused by fracturing. As a result thereof the data in table 7 are not easily to interpret.

23

At the end of phase 3 of the measuring and monitoring program the method for the determination of the green strength has been changed in such a way that a relation between the above mentioned parameters could be distinguished.

Table 7 - Properties of sand-lime mortar and -brick with different types of lime and 6.5 % water during phase 2 (at laboratory scale)

Type of lime Green Apparent Compressive and free lime strength density strength (* d.m.) (kPa) (kg/m3) (MPa)

Dornap 5.5 6.5 7.5

Kaldin 5.5 6.5 7.5

lime

lime

3.2 4.2 5.6

3.0 4.6 6.3

1780 1800 1820

1770 1790 1800

25.1 30.5 36.2

28.2 31.7 38.4

Experiences in practice Only after August 1989 when the production of the Kaldin plant reached a satisfactory level, the quality of the Kaldin lime became sufficiently constant to justify a 100 % replacement of Dornap lime by Kaldin lime. However, the variations in the quality of the limestone and of process-conditions of the Kaldin plant, still lead to variations in the reactivity and in the free CaO content of the Kaldin lime. In the sand-lime brick factory this caused difficulties with the production of sand-lime bricks and elements. As a result of the variations in the free CaO content of the Kaldin lime compared to the Dornap lime, mixtures of sand with Kaldin lime showed a variable need for water. As a result thereof several charges of sand-lime mortar were too dry or too wet. This has lead to a higher product-loss, because of fracturing and pressure-cracks.

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3.9'. Mass- and energy-balance

During the warranty period, when the plant has been processed at optimum conditions (no stops, no disturbances, almost maximum capacity) a total of 59 GJ of fossil energy (fine­grained coal) had to be used to calcine 16.0 tons of CaC03 per hour. This implies that an energy-efficiency of the Kaldin plant of about 48 % can be realized (related to the theoretically needed energy). During the warranty test the amount of fossil energy which is needed per ton of free CaO is 7.6 GJ. Considering the fact that Kaldin generates a product with a certain positive value of the inert fraction, the amount of energy needed for the production of 1 ton of product (5.0 GJ) has also to be taken into consideration. At a constant production, without any stops or disturbances and without the use of the drying unit, the electricity use is about 1100 kWh ( = 4.0 GJ) per production hour.

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4. CALCINING LIMESTONE WITH COAL RESIDUES

4.1. Introduction

On a laboratory scale, several investigators (Wittneben [2] and Bloem [3]) have found indications that the use of coal residues as a raw material in sand-lime bricks can have a positive effect on the green strength of the moulded product and on the compressive strength of the cured product (taking into account the only limited amount of parameters studied). The greatest disadvantage of the use of coal residues in this application is the discolouration of the sand-lime bricks. In stead of white this becomes grey, depending on the carbon content and the amount of coal residues which is used. In tests on a pilot-plant scale performed by Lurgi in 1985, it has been shown that the carbon in coal residues could be sufficiently burned out in a fluidized bed. After burning out the carbon, the coal residues could be used as a raw material for the production of sand-lime bricks, because the discolouration of the product is acceptable. A study carried out by Ingenieursbureau Dekker in 1985 [4] showed that the product (a coal residues-lime mixture) is suitable for the use in sand-lime brick production and it can result in a higher green strength of the moulded product, a higher compressive strength of the cured product and a saving of the amount of free lime which has to be dosed. During phase no. 3 of the measuring and monitoring program the above mentioned conclusions have been checked for the product which was generated by Kaldin and for the sand-lime bricks which have been produced by De Hazelaar with the use of Kaldin lime. In practice it appeared that several technological disturbances occurred during phase 2 which resulted in a delay of the time that the first coal residues could be processed. In stead of 1 July 1989, only on 30 January 1990 the first coal residues could be used. The measuring and monitoring program has been prematurely concluded after the end of phase 3. As a result thereof no experiences have been gained with the production of lime with a maximum coal residues input of 12.5 tons per hour. However during some short periods, for example during a test which was monitored by TNO in January 1991, the input of coal residues has been increased to a reach level which was as high as possible for that time.

26 -

4.2. Operation time

During phase 3, except for some periods, a continuous production has not been realized. In total, during phase 3 3960 hours production has been realized. This implies an efficiency of the use of the available operation time of 60 %, Compared to phase 2 this is an improvement of 12 %. During almost the entire phase 3 the plant has been operated in a continuous shift system (3 shifts, 5 days a week).

4.3. Global description of the progress

Originally the aim of the measuring and monitoring program was to increase the coal residues input gradually from 0 to 12.5 tons per hour. During this increase the effect on the process-conditions, the quality of the product and the quality of the sand-lime bricks have been monitored. During the first two months of phase 3 (February and March 1990) an input of about 2 tons coal residues per hour has been realized during the periods in which the coal residues has actually been processed. The limestone input during this period varied between 13 and 17 tons per hour. No disturbances were directly a result of the use of coal residues. In April 1990 the coal residues input has been increased to 3 - 4 tons per hour, interchanged with periods during which this input was less. Also with the use of this quantity of coal residues no disturbances occurred which could be related to use of coal residues. During large parts of the months July, August and September 1990 the coal residues input has been increased to about 6 tons per hour. Due to problems with the quality of the sand-lime bricks, at the end of September it has been decided to decrease the coal residues input back to 3 - 4 tons per hour. During the last couple of months in 1990 this has been reduced to about 3 tons per hour. During the entire phase 3 an average of 2.53 tons of coal residues per production hour has been processed.

During a short period in January 1991 (several hours), under the supervision of TNO [5], a test has been carried out with an input of 8 tons of coal residues per hour and 16 tons of limestone per hour. This resulted in a product output of 15 to 16 tons per hour, depending on the carbon content of the coal residues). During this test, stable process-conditions have been realized. From this test can be concluded that a further increase of the coal residues input was technologically

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possible. Also the quality of sand-lime elements with the product which was generated during this test was satisfactory. In a few tests, beside coal and coal residues, also heavy oil has been used as a fuel.

feb mar apr may jun Jul aug sep oct nov dec jan feb mar apr

. Limestone . Coal ± PFA . Product

Figure 3 - Average raw material input and production per hour per month during phase 3

Table 8 - Use of raw materials and production per production hour during phase 3

limestone coal residues coal heavy oil product (CaOf = 54.7 %) CaOf

total input and production (tons) 59,200 10,000 4,640

92 43,500 23,800

input and production per production hour (tons/hr) 15.0 2.53 1.17 0.02 11.0 6.0

28 -

The limestone input per hour varied generally between 13 and 16 tons per production hour. The average limestone input during phase 3 was 15.0 tons per hour. Because of the use of coal residues the use of coal has been decreased compared to phase 2. Moreover, the limestone which is used in phase 3 has in average a higher CaC03 content than in phase 2. This implies that even more energy was needed to calcine the total amount of available CaC03. During phase 3 beside coal residues several other industrial side-products have been processed in the Kaldin plant. These were mainly limestone granules and smaller quantities of petrocokes, SKW and marble powder. Some of those products have been processed successfully, others were not. These products are all discussed in section 4.7. Until the end of September 1990 the dust which accumulates in the cloth filter and the heat-exchanger has been transported to the intermediate bunker, after which it passes the sifter. Since then this dust has been transported to a productsilo and it is considered as a separate product, named "Filter lime". This product implies 25 % of the total production. The other 75 % of the total production is the main product of the Kaldin plant and is named "Kaldin lime".

4.4. Process parameters

4.4.1. General The process parameters during phase 3 do not deviate much from those during phase 2. Small differences are mainly present in the temperature of the CFB and the temperature of the primary and secondary air.

4.4.2. The CFB temperature - top CFB = 960 - 1010 "C - bottom CFB = 950 - 1000 °C The temperature of the CFB has mostly varied in the above mentioned ranges. Until September 1990 the temperatures corresponded mainly to the lowest figures. After September the temperature of the CFB has been increased in order to produce a less reactive lime. 4.4.3. Sifter/milling section Since September the dust from the heat-exchanger and the cloth filter has not any more been transported to the intermediate

- 29 -

bunker (as mentioned in § 4.3), but to a separate productsilo. As a result thereof, the ball mill and elevator have been partly unloaded. Hence, the sifter/milling section can now be used periodically in a cycle of for example 3 hours on and 2 hours off, in stead of being used continuously. 4.4.4. The drying unit During phase 3 in the drying unit a total of 1056 tons of wet material has been dried. This quantity is mainly composed of SKW and coal residues. The drying of relatively coarse-grained materials such as sand and limestone was realized without any difficulty. The drying of the fine-grained materials such as SKW and coal residues caused some problems relating to the transportability of the products, which have limited the drying of these materials during the course of the project. The water content of the dried material was always smaller than 1 %. This corresponds to the warranted limit which was given by Lurgi.

4.5. Process-experiences, disturbances and modifications

Many problems which occurred during the time that limestone has been calcined with only coal also occurred during the time that coal residues was used. However some differences in the behaviour of the disturbances can be noticed. Problems which mainly occurred when only coal was used as a fuel and which decreased when also coal residues was processed are the following: - Caking in several components of the plant, especially in

the recycling cyclone, venturi, first cyclone and the product cooler has been decreased. The use of coal residues has an abrasive effect on the cakes.

- As a result of the use of coal residues the average grain size of the bed material decreased, which made it possible to fluidize a slightly coarser limestone.

Beside the decrease of some disturbances, others did appear as a result of the use of coal residues: - As a result of after-burning of the coal residues, the

product temperature of the fluidized bed cooler increased which resulted sometimes in sintering and obstructions in the cooler chambers.

30 -

The increase of the flue gas temperature, also as a result of after-burning of the coal residues, lead to a deformation of the valves in the return pipe between the first cyclone and the CFB.

Other problems cannot directly be related to the use of only coal or coal + coal residues as fuel. These problems are mostly a result of the generation of a large volume of dust and the nature of this material. Depending on the type of coal residues, mostly a small amount of coal is allways needed in order to keep the the process conditions at a constant level.

4.6. Emissions

4.6.1. NO^-emission The components which are continuously analyzed in the flue gasses of Kaldin are N0X and 02. The N0X content is measured before the chimney at the same spot as the 02 measurement is performed. From these data (in ppm) the NOx-emission can be calculated in mg/Nm3, according to the unit in which this parameter is defined in the private nuisance act, with the aid of the following formulae:

N0X (mg/Nm3) = N0X (ppm) x 2.05 x 20.94 - 7 % 02 20.94 - % O,

When coal residues are used, a higher N0X content of the flue gasses is measured than with the use of only fine-grained coal. The NO^-emissions with coal residues varied between 900 and 2100 mg/Nm3, compared to 940 mg/Nm3 which was measured during the warranty test with only coal (see § 3.5). During a test period in phase 3, continuous measurements have been made by DHV of the following components: C02, CO, 02, N0X and S02 [l]. Samples of the dust have been taken every hour. These samples have been analyzed on the following components: Cd, Pb, Zn, Hg, Sb and fluorides. Also the analyses of DHV show a higher NO*-emission (1000 -1300 mg/Nm3 as an average per hour) than which is allowed according to the private nuisance act. Of the 3 samples of dust which have been measured, the amount of dust of one sample exceeds the limit mentioned in the

31

nuisance act. This is mainly caused by a damage of the cloth filter at the time the dust samples have been taken. In a later stage, the bags of the cloth filter have been replaced. The S02-emission stays largely below the limit of 700 mg/Nm3. Also the above mentioned components which have been measured on the dust samples stay largely below the limits mentioned in the nuisance act. After the end of phase 3, several tests have been carried out regarding possible measures which could be taken to reduce the N0X emission. From these test results it became clear that the NO* level depended largely on both the total amount of nitrogen present in the fuel and on the amount of air which is used for the combustion of the fuel. Following these results, modifications have been made to the CFB, which have resulted in a decrease of the NOx-emission. With the use of only coal as a fuel the NOx-emission can be decreased to a level below the limit mentioned in the private nuisance act (N0X < 500 mg/Nm3), when using a limited quantity of combustion air and a reduction of the quality of the product. When more than about 2 tons of coal residues are processed, additional measures have to be taken to further reduce the N0X emission to a level below 500 mg/Nm3. Tests have shown that this can be achieved up till a coal residue input of at least 8 tons per hour. The quality of the product concerning the carbon outburn and calcination ratio can however not be guaranteed.

4.6.2. Noise emission In April 1990 acoustic measurements have been carried out by Cauberg-Huygen concerning the noise emission of Kaldin and of De Hazelaar and the nuisance that this noise caused to the near environment of these factories [6]. When these results are compared with the limits mentioned in the private nuisance act, it appears that on some locations the noise level exceeds the limit which is set for the nighttime (40 dB(A) between 11.00 pm and 7.00 am). Based on these results, at the end of phase 3 modifications have been made to some components of the installation and vehicles which have led to a reduction of the noise level, although new acoustic measurements have not yet been carried out in order to quantify this reduction of noise rate level.

32

4.7. Raw materials

4.7.1. Limestone During phase 3 a total of about 59,200 tons of limestone has been calcined. The limestone is supplied in a fine-grained fraction (0/2 or 0/3). This material arises as a side-product from the crushing process in limestone quarries. Before September 1990 mainly limestone with a CaC03 content of about 86 % and a water content of 6.5 % has been processed. After September 1990 mainly a limestone with a CaC03 content of about 96 % and a water content of 3 % has been processed. The advantage of the use of this latter limestone is a higher free CaO content of the Kaldin product. Beside the fine-grained limestone from Belgian quarries, about 1600 tons of drinking water granules have been processed. These granules have a CaC03 content of about 95 %. During the time the drinking water granules could be supplied, they have been processed with a ratio of 1 part of granules to 5 parts of other types of limestone. A good fluidization of the bed was always maintained. 4.7.2. Fine-grained coal During phase 3 a total of 4640 tons of fine-grained coal have been used as a fuel. This coal has been furnished by different suppliers. The grain size of the coal was between 0 and 1 mm.

4.7.3. Coal residues The basic idea behind the Kaldin process has been the calcination of limestone with Dutch coal residues. Especially coal residues with a high carbon content (> 5 %) will be suitable. Therefor contracts with 3 Dutch companies (AKZO, DSM and Vliegasunie) have been signed concerning a regular supply of coal residues which arises from coal combustion processes at these companies. During the first part of phase 3 of the measuring and monitoring program the highest quantity of Dutch coal residues has been processed, but gradually these types of coal residues have been substituted by German FBC coal residues. At the end of phase 3 about 7,745 tons of German coal residues and only 2,309 tons of Dutch coal residues has been processed. The decision for this substitution is based on two reasons:

1. Better prices can be obtained for the German coal residues

33

2. The average net heat value of the German coal residues is higher (7.7 MJ/kg) than of the Dutch coal residues (2.2 MJ/kg).

The average net heat value of all the coal residues which was used during phase 3 is 6.4 MJ/kg and the average loss on ignition (which is a measure for the organic carbon content) is 21.3 %. The German FBC coal residues all originate from small static fluidized beds which are used for city-heating and for the generation of electricity. 4.7.4. Other raw materials Petrocokes During the months September and October 1990 a total of 88 tons of petrocokes has been used as fuel. This is a side-product of oil refinery. It has a fairly sticky nature and does consist mainly of cokes and for a smaller part of oil. The cokes has a higher temperature of ignition than the fine­grained coal. The residence time in the CFB is too short to obtain a complete combustion and therefor the not completely combusted material becomes a part of the product or leads to afterburning which causes a sintering in the fluidized bed cooler as mentioned in section 4.5.4. SKW SKW is a fine-grained calcium-carbonate which arises as a side-product with the production of fertilizers. This material consists mainly of CaC03, about 7 % of organic carbon and about 25 % water. The fossil energy content, represented as the heat of combustion, is 1.8 MJ/kg. Before being introduced into the CFB the SKW has to be dried in the drying unit.

4.8. Product-quality

4.8.1. General The product which is generated as a result of the calcination of limestone with coal residues is a mixture of free CaO, burned out coal residues and the inert fraction of limestone. The free CaO is a raw material for the production of several building materials such as sand-lime bricks. The burned out coal residues can serve as a filler or as a pozzolanic binder. During the first part of phase 3 (until the end of September 1990) one product was generated (the so-called "flyash-lime"). This product left the plant completely via the sifter-milling section. After September 1990, the dust which collected in the

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cloth filter and the heat-exchanger has been separately transported to one productsilo. This is a very fine-grained and relatively CaO-poor lime. It is since then called "Filter lime". The relatively coarse-grained and CaO-rich lime which still leaves the sifter-milling section is then called the "Kaldin lime" (see § 4.3). 4.8.2. Flyash-lime The flyash-lime has been produced during a period of 8 months since the beginning of phase 3. The increase of the coal residues input from 0 to 6 tons per hour has lead to a decrease of the free CaO content in this product from about 60 to 35 % (figure 4). The rest of the product consists mainly of burned out coal residues and of the inert part of the lime­stone. The average free CaO content during this part of phase 3 is 52.7 %. In table 9 the average properties of this product are given.

Due to the relatively large variations in the coal residues input and the variations in the composition of the coal residues, the quality of the flyash-lime also shows large variations. The reactivity of the flyash-lime (tso) has mostly been 3 to 4 minutes. In September 1990 it has been decided to increase the temperature of the CFB in order to produce a lime with a lower reactivity. As a result thereof in the sand-lime brick factory less retarder had to be dosed.

Table 9 - Average properties of flyash-lime (February - September 1990)

unit average Total CaO % 62.0 Free CaO % 52.7 tao min 4.3

- 35 -

feb mrt apr may jun jul aug sep okt nov dec jan feb mrt apr _*_ free CaO ___ tot CaO _^_ ealc. ratio

F i g u r e 4 - Average p r o p e r t i e s of f l y a s h - l i m e and a combinat ion o f Kald in l ime and F i l t e r l ime per month

The average f l y a s h - l i m e c o n s i s t s of t h e fo l lowing mineralo-g i c a l components:

Free CaO Ca(0H)2 CaC03 S i l i c a t e s , e t c .

50, 2, 7,

38. 4.8.3. Kaldin lime and Filter lime As mentioned in § 4.8.1, since the beginning of September 1990 the product has been separated into Kaldin lime and Filter lime. The largest volume of this product is Kaldin lime (about 75 % of the total product). This product reaches the productsilo via the sifter-milling section. The smaller product volume (25 %) is Filter lime which originates from the cloth filter and the heat-exchanger. Together with the separation of the product into Kaldin lime and Filter lime, another type of limestone (with a higher CaC03 content) started to be used. This resulted in an increase of both the free and total CaO content of the product. An

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overview of the properties of Kaldin lime and Filter lime are given in table 11. Kaldin lime Especially because of smaller variations in the coal residues input during the time that the endproduct has been generated in two separate volumes, the quality of the Kaldin lime is more constant than the quality of the flyash-lime. During periods, in which the coal residues input has been relatively constant, the standard deviation in the CaO content reached a level (1 - 2 %) comparable to other types of lime which are currently sold on the market. The average grain size (dso) of this product is about 27 ;im and the specific surface is about 1900 cm2/g (measured with Silas method). This is comparable to other types of lime which are currently on the market.

Table 10 - Average global mineralogical composition (in %) of Kaldin and Filter lime

Free CaO CaC03 Ca(0H)2 CaS04 Org. Carbon Silicates, etc.*

Kaldin lime 60.1 2.0 4.1 1.2 0.0

32.6

Filter lime 32.2 25.0 2.8 0.4 0.6

39.0 Including the components MgO, NaO, Ka0, A1203 and Fe203

Table 11 - Average properties of Kaldin lime and Filter lime (October 1990 - April 1991)

unit Kaldin Filter lime lime

Total CaO % 71.8 60.3 Free CaO % 63.2 34.3 t80 min 6.6 47

Filter lime The average free CaO content of Filter lime is far less than the free CaO content of Kaldin lime (34.3 % versus 63.2 % ) , while the difference in the average total CaO content is much smaller (see table 11). This is mainly caused by the higher amount of CaC03 (25 %) in the Filter lime and partly by the

37

higher amount of silicates (see table 10). The average grain size (d50) is about 5 /iin and the specific surface area is about 6700 cm2/g^ This is far less than the average grain size of types of lime which are currently on the market.

4.9. Application of the product in sand-lime bricks

4.9.1. Introduction As indicated in the introduction of chapter 4, the use of coal residues can have a positive effect on the quality of sand-lime bricks. The quality of sand-lime bricks with flyash-lime or a combination of Kaldin lime and Filter lime has been studied both in the laboratory and at production scale. 4.9.2. Use of lime at De Hazelaar During the time that the flyash-lime was produced almost the total quantity of this product has been sold to De Hazelaar. After the product was separated into Kaldin lime and Filter lime, especially a part of the Filter lime has been supplied to other sand-lime brick factories, but even during this period the main part of the product has been supplied to De Hazelaar. During phase 3 of the project, in total 41,500 tons of the Kaldin product has been processed at De Hazelaar and 1900 tons of (mainly) Filter lime has been sold to third parties. 4.9.3. Composition of the sand-lime mortar In order to obtain a sufficient green strength of the moulded product and compressive strength of the cured product, a minimum amount of CaO is necessary. This amount of CaO has always been the base for the calculation of the composition of the sand-lime mortar. The expectation was that, with the use of the Kaldin product in about the same quantity as the previously used Dornap lime, a comparable green strength and compressive strength could be obtained (with the use of less free CaO). The burned-out coal residues particles which replace a part of the fine-grained sand could help to keep the green strength at a sufficiently high level. In the beginning the Kaldin product (flyash-lime by that time) has been used in quantities which were based on an equal free CaO content in the sand-lime mortar as before. Due to the lower CaO content of the flyash-lime a larger amount of fine­grained particles was dosed to the sand-lime mortar. Based on the experiences in practice concerning the quality of the sand-lime brick elements, in a later stage the free CaO content in the sand-lime mortar has not been decreased. This

38

means that the fine-grained particles have always acted mainly as a filler in addition to the fine-grained sand particles. In practice during a longer period of time a mixture of Dornap lime and flyash-lime has been used for the production of sand-lime bricks and elements. 4.9.4. Laboratory tests With the flyash-lime several laboratory experiments have been carried out in which the properties of the sand-lime mortars and sand-lime bricks have been compared with the mortars and bricks which were produced using Dornap lime [8]. Following, the most important results will be discussed. For more detail the reader is referred to [8]. The samples have been produced by mixing the raw materials in a laboratory mixer and moulding the mortar into cylinder-shaped samples. Thereafter they are steam-cured in the plant. The green strength is determined after the moulding of the samples and the compressive strength after steam-curing. In table 12 the results of a comparative study between sand-lime bricks with a flyash-lime (free CaO = 37 %) and with Dornap lime are shown. From these results it can be concluded that a larger amount of fine-grained particles (the samples with fly-ash lime) result in an increase of the apparent density of the product, together with an increase of green strength and compressive strength. The water absorption and expansion of these samples are lower. In order to reach a similar free CaO content in the mortar, compared to Dornap lime, more than twice the amount of flyash-lime has to be dosed. It has however to be noted that question marks have to be placed with these tests. The apparent density of the samples is about 150 kg/m3 higher than the apparent density of the products which are produced in practice by De Hazelaar. As a result thereof all the data mentioned in table 12 deviate from the data of products generated in practice. This applies mainly to the green strength. In practice hardly ever can be seen that the green strength of a moulded sand-flyash-lime mortar is higher than of a moulded sand-Dornap lime mortar (based on an equal free CaO content). Therefor, at the end of phase 3 the moulding pressure for the preparation of the samples has been decreased. The result thereof was, in contradistinction with former times, that a clearer relation could be seen between the green strength and the product-loss as a result of fracturing (see section 4.9.5).

39

Table 12 - Properties of sand-lime mortars with Dornap lime and with flyash-lime, based on laboratory tests

Dornap lime (free CaO = 85 %)

Free CaO % 5.5 Green strength kPa 1.0 Compr. strength MPa 25.3 App. density kg/m3 1825 Water absorption % 13.2 Expansion mm/m 0.7

Flyash-lime (free CaO = 37 %)

Free CaO % Green strength kPa Compr. strength MPa App. density kg/m3

Water absorption % Expansion mm/m

5.5 1.7

31.9 1870 12.8 0.3

6.5 1.8

33.5 1825 13.1 0.7

6.5 2.2

35.8 1880 12.3 0.6

7.5 2.3

37.3 1840 13.0 0.9

7.5 3.9

42.3 1900 12.3 0.4

8.5 3.7

1860 13.2 1.4

8.5 5.0

43.6 1930 11.6 0.8

9.5 4.9

43.6 1860 13.7 1.4

9.5 6.8

46.7 1925 11.9 0.4

4.9.5. Experiences in practice

During the main part of phase 3 the product-loss of both bricks and elements was about the same as during phase 2. A good quality of sand-lime bricks and elements has been obtained with the use of a flyash-lime or a combination of Kaldin lime and Filter lime.

However, during some periods with a higher coal residues input in the Kaldin plant, an increase of product-loss has occurred, mainly in production of the large elements. Especially the larger elements are very sensitive for fracturing just after the moulding of the element and for pressure cracks during steam-curing. It has to be noted that the increase of product-loss is probably not only caused by the increase of the coal residues input in the Kaldin plant. In a latter stage, after the end of the measuring and monitoring program, with an input of more than 4 tons of coal residues per hour also a good quality of the sand-lime elements could be obtained. The above mentioned increase of the product-loss will therefor, beside the coal residues content in the product, have been generated by a complex of causes, such as the quality of the sand and variations in the quality of the lime and their interactions [9]. Moreover the personnel of the sand-lime brick plant gained more experience in the production of bricks and elements with the use of Kaldin lime and Filter lime. It can therefor be expected that the product-loss can be further decreased in the near future, also with a relatively high input of coal residues.

40 -

During phase 3, the supposed advantage of the use of coal residues in sand-lime bricks concerning a better green strength of the moulded product could not been proven. In practice, a mortar with a combination of Kaldin lime and Filter lime sometimes showed a slight increase, but sometimes also a slight decrease of the green strength compared to a mortar with Dornap lime (with an equal free CaO content of the mortar). The decrease of the green strength can probably be attributed to a higher need of water because of the higher content of fine-grained particles in the mortar.

4.10. Mass- and energy-balance

In average during phase 3 13.0 tons of CaC03 per hour have been processed in the CFB. This means that 13.0 times the theoretically needed energy for the calcination of 1 ton of CaC03 (= 1.77 MJ/kg) =23.0 GJ/hr is needed for the calcination of all the CaC03. The real amount of energy which is needed is naturally higher because of energy needed for the warming up of all the components, heat transmission to the walls, to the flue gasses, etc. By addition of all the sources of energy of the used types of fuel, and comparing this total amount with the theoretically needed amount of energy, the efficiency of energy for the calcination of CaC03 can be calculated. During the calcination of CaC03 with coal residues as fuel also fine-grained coal has been used. The average coal residues input during phase 3 (2.53 tons per hour) has replaced 600 kg of coal per hour (of an average composition). The total amount of processed fossil energy during phase 3 (mainly provided by coal and by coal residues) mounts up to about 50 GJ/hr. The efficiency of the fossil energy for the calcination of CaC03 during phase 3 therefor reaches 46 %. Compared to phase 2 this implies an improvement with 2 %. A direct relation between the efficiency and the coal residues input is not clear. About 40 % of the used energy is leaving the process with the flue gasses. When this energy is used in the drying unit, the overall energy efficiency of the plant is higher. The total amount of fossil energy which is needed for the production of 1 ton of free CaO is 8.3 GJ. This is high compared to energy which his needed for the production of 1 ton of free CaO in shaft kilns and rotary kilns. In shaft kilns this amount of energy is about 5 GJ and in rotary kilns about 6 GJ. During periods that the plant is operated under optimum conditions, and in a continuous shift system, the fossil energy use can be reduced to figures between 7.5 and 8.0 GJ per ton CaO.

41

Because in the Kaldin plant a product is generated which can, beside the value of the free CaO, also have a certain value as a (reactive) filler, the needed amount of fossil energy for the production of 1 ton of product has also to be taken into account. During phase 3 this is in average 4.5 GJ. During an average period in which the plant has been operated continuously and the drying unit has not been switched on, an average of 1100 kWh (=4.0 GJ) of electric energy per hour is used. This is higher than which was originally expected (800 kWh = 2.9 GJ/hr).

42

5. OTHER APPLICATIONS

5.1. Introduction As mentioned in section 4.9. almost the total amount of the product has been applied as a binding agent in calcium-silica­te production. In this application it was however not possible to notice an advantage of the use of this lime over the use of another type of lime. Beside the application in C.S. production, different applica­tions of the product have been studied. The most promising applications are the following:

a filler in asphalt sludge stabilization masonry mortars

5.2. Slaking of the lime Before the calcinated product can be used in some of the above mentioned appications, the free CaO of the product has to be slaked into Ca(0H)2. Because the slaking process of the product can sometimes be rather long and irregular (especially concer­ning the filter lime), tests have been carried out with a three-stage slaking installation. Both Kaldin lime and filter lime which were slaked with this installation are completely expansion-free with a water content < 1 %. With the slaked product generated in these tests, the possibilities of application in asphalt and masonry mortar have been studied.

5.3. Asphalt filler Fly-ashes, pulverized limestone and hydrated lime are materi­als which are often used as a filler in asphalt. In contradis­tinction to normal asphalt, in very open asphalt a filler with a Ca(0H)2 content of about 50 % is applied. Laboratory tests have indicated that the slaked product of the calcination process, especially the slaked filter lime is a good filler in very open asphalt. The potential market is estimated at 100.000 - 120.000 tons of Kaldin lime per year [7].

5.4. Sewage sludge stabilization The degree of stabilization of sewage sludges depends on the amount of waterreduction and on the hardening of the sludge which can be achieved. These properties are influenced by the amount of free CaO which can be dosed to the sludge and by the

43

amount of inert fine-grained particles which are used for the stabilization. Because of its higher free CaO content, Kaldin lime is more suitable for sludge stabilization and because of the higher quantity of fines the filter lime can be suitable. Tests on laboratory scale and in practice which were carried out after the end of phase 3 of the program, have shown promissing results. The potential market is estimated at 10.000 - 15.000 tons of lime per year.

5.5. Masonry mortars By using lime in a masonry mortar the workability and the waterretention of the mortar are positively influenced. It also decreases the elasticity modul of the hardened mortar, Laboratory tests have shown that both products, Kaldin lime and filter lime can replace a lime which is normally used in this application, especially in dry prefab masonry mortars. The potential market is estimated at 10.000 - 12.000 tons per year [7],

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ECONOMICAL ASPECTS

6.1. General In 1991 an interim evaluation of the economic aspects of the Kaldin plant has been carried out by DHV. The aim of this study was to determine the value of the project for the National Coal Investigation Program (NOK). The bureau A+ calculated the economic viability of the Kaldin plant when products with a different free CaO content are produced. The main conclusions of these studies, together with an exploitation overview will be discussed in the following sections. For more detail the reader is referred to [7] and [10]. 6.2. Raw materials The economic viability depends for a large part on the input of coal residues with a high carbon content. The coal residues which come available at electric power stations mainly have a relatively low carbon content. Moreover, these types of coal residue are currently used in other applications. The coal residues which come available with fluidized bed combustion have a much higher carbon con­tent. Although this type of coal residue arises at a smaller scale, in Germany a sufficiently high supply of these ashes is available at higher negative prices. Economically this type of coal residue is therefor more attractive than the Dutch types of coal residue arising from coal-fired electric power stati­ons. Mainly due to transportation costs, the limestone price in The Netherlands is relatively high compared to the effective cost of limestone at the quarry. The ideal situation is when a calcination plant is situated close to a limestone quarry, or when industrial side-product, such as drinking water granules can be used. 6.3. The product As indicated in section 4.6., the product consists partly of free CaO and partly of an inert fraction. To both parts a certain value can be attributed, but the price of the product depends mainly on the free CaO level in the product. An indication of the price of the product can be obtained by a calculation based on a price for the binder (free CaO) and a price for the filler (the inert fraction) with the following formulae, which is based on the current price level: price of the product = f 140,- x free CaO + f 40,- x inert.

45

One ton of a product with a free CaO content of 55 % (average of phase 3) would therefor achieve a price of f 95,- (without transportation costs). However, the value of the filler (in combination with free CaO) has so far not been demonstrated in C.S. brick production, but can become relevant in applications such as a filler in asphalt. It has been calculated [7] that the plant has the highest economical efficiency when a product with a free CaO content between 50 and 60 % is produced, although this optimum depends also on the possible applications of the product. Another aspect is that currently the main part of the Kaldin product is sold to sand-lime brick factory De Hazelaar. Other possible applications such as in masonry mortars, sludge stabilization, or as a filler in asphalt have only reached an experimental stage, but seem promising (chapter 5). Therefor, during the measuring and monitoring program less product could be produced than which was originally anticipated (about 32.000 in stead of 90.000 tons/yr). The proceeds of the Kaldin plant have therefore been lower than expected.

6.4. Outlook There are two ways in which the plant can be operated: 1. Burning limestone with coal 2. Burning limestone with coal residues and small amounts of

coal. For the process with limestone and coal it must be mentioned that due to problems with caking in several components of the plant, a production time of 8000 hours per year cannot be expected. Together with the high investment of the plant, this leads to a high cost price of the product. On the other hand the product will have a low price because of the low CaC03 content of the limestone, resulting in a low CaO content of the product. The use of a limestone with a high CaC03 content in this plant is only possible in combination with coal residues. These considerations lead to the conclusion that the production of lime with only limestone and coal will not result in an positive economic viability of the plant. When using coal residues a higher amount of production hours can be achieved, because the internal part of the components are "cleaned" by the coal residues. This will lead to lower costs of the product. Although Kaldin is still in the middle

- 46

of product development, new products can be produced with the use of a high coal residue input, which could have advantages over some traditionally used products. This means that, although at this moment a production at full capacity is not possible due to the limited market, in the future, some larger new markets could be opened with new products (see chapter 5).

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7. PUBLICITY AND COMMERCIALIZATION At the official opening of the Kaldin plant, in cooperation with NOVEM, a week of different activities was organised. These activities involve an opening ceremony and a number of lectures which have been given on the treatment of waste materials. The opening of the plant has been broadcasted on some television stations and several articles have been published in local and national papers. During the course of the measuring and monitoring program, representatives of companies from all over the world and representatives of the EC have visited the plant. On a request of the board of the province of Limburg, a paper was presented for the EUREKA representatives in Maastricht. A lecture on the Kaldin project has also been given on a symposium organized by "Haus der Technik" in 1991.

48

8. CONCLUSIONS During the measuring and monitoring program of the Kaldin plant it has been shown that it is possible to calcine limestone in a circulating fluidized bed with coal residues as a fuel. After modifications have been made to components of the plant no major technological disturbances occurred and the plant could be operated without interruptions. The use of only coal as a fuel is disadvantagous, because of the occurence of caking in several components of the plant, thus reducing the total yearly production hours. As a result of the use of coal residues some disturbances which can be related to caking decreased, because of the abrasive effect of the coal residues. Also the bed could better be kept in a fluidized state. A disadvantage of the use of coal residues is the chance of afterburning of the coal residues in some parts of the plant. The maximum coal residue input which could be realized is about 8 tons of coal residues (from Dutch + German origin) per hour with a limestone input of about 16 tons per hour. With this input, depending on the organic carbon content of the coal residues and the CaC03 content of the limestone, 15 - 16 tons of product per hour could be generated. The emissions of flue gas components were all, except for dust and N0X, below the requirements stated in Kaldin's private nuisance act. The dust emission was however the result of a defect on the cloth filter. After modifications to the CFB have been made (after the conclusion of the measuring and monitoring program) a clear decrease of the NOx-emission can be seen. When using only coal as a fuel, the NOx-emission is below the level mentioned in the private nuisance act (N0X < 500 mg/Nm3), when using a limited amount of air and with a reduction of the product quality. When more than about 2 tons of coal residues are processed additonal measures have to be taken to further reduce the NOx-emission below 500 mg/Nm3. However, a reduction of the NOx-emission below the limit mentioned in the nuisance act implies a reduction of the product quality concerning the outburn of coal particles and calcination ratio. The original aim of the Kaldin project was to use Dutch coal residues as a fuel. This coal residues has generally a relatively low heat of combustion and is sold for relatively low negative prices. In view of the economic viability of the plant, it has therefor been decided to use German FBC coal residues (with a higher heat of combustion and negative prices) beside the Dutch coal residues.

49

Depending on the coal residues input, the free CaO content of the product varies from 35 to 60 %. It can well be used as raw material for the production of sand-lime bricks. However, the assumed advantage of the use of coal residues in sand-lime brick production concerning a higher green strength of the product, could not be demonstrated in practice. Beside the application in C.S. bricks, other applications for the product have been studied, but have so far only reached an experimental stage. The most promising applications are:

as a filler in asphalt in masonry mortars in sludge stabilization

During the measuring and monitoring program, the sale of the Kaldin product has mainly been limited to sand-lime brick factory De Hazelaar, whereby the production level stayed far below the anticipated level (about 32,000 in stead of about 90,000 tons/yr). As a result of this restricted sale, the proceeds of the Kaldin plant reached a lower level than which was anticipated. Although at this moment a production at full capacity is not possible due to the limited market, in the future, some larger new markets could be opened with new products.

50 -

REFERENCES

[1] Anonymus (1991); Emissiemetingen aan de afgassen van de calcineringsinstallatie op 5 en 7 maart 1991, DHV afdeling Milieu en Infrastructuur, dossier E-2414-84-001

[2] Wittneben U. (1988); Moeglichkeiten zur Reducierung der Kalk- und Energiebedarfs bei der Kalksandsteinherstellung durch den Zusatz von Flugashe, Forschungsbericht no. 68, Forschungsvereinigung des Bundesverbandes Kalksandsteinindustrie eV Hannover

[3] Bloem P.J.C. & Sciarone B.J.G. (1989); Application of pulverized fly-ash and spray-dry absorbtion products in sand/lime-brick production, Kema Scientific & Technical Reports 7 (1), pp 35-45.

[4] Dekker W. (1985); Onderzoek van kalk- en calciumsulfaathoudende materialen die met kolenrijke vliegassen in een pilot-plant van een circulerend wervelbed zijn gebrand, om als grondstof in de kalkzandsteenindustrie te worden toegepast, Ingenieursbureau Dekker, rapport no. 32-511

[5] Rappoldt L.M. (1991); Technische evaluatie Kaldin, TNO rapport no. 91-043.

[6] Vossen J.M.M. (1990); Akoestisch onderzoek inzake de aanvraag van een nieuwe Hinderwetvergunning kalkzandsteenfabriek De Hazelaar b.v. Koningsbosch, Cauberg Huygen rapport no. 900207-2.

[7] Lahaye P.P.J. (1991); De analyse van de mogelijkheden tot het afsplitsen van productiestromen in het calcineerproces, A+, architectuur en bouwontwikkeling, rapport no. R.91.086.

[8] Dekker W. (1990); Het bepalen van eigenschappen van Kaldin kalk en Kaldin-vliegaskalk in kalkzandsteen, Ingenieursbureau Dekker, rapport no. 81-9003.

[9] Saraber A.J. en Schuur H.M.L. (1991); De begeleiding van de inzet van Kaldin kalk in de kalkzandsteenindustrie, PBI-rapport no. R91.013.

[10] Ellerbroek G. (1991); Tussentijdse evaluatie Kaldin-project, DHV Milieu & Infrastructuur, dossier no. E 3108-22-001

51

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European Communities — Commission

EUR 14828 — Calcination of limestone in a circulating fluidized bed with coal residues as fuel

Luxembourg: Office for Official Publications of the European Communities

1993 - XI, 51 pp., num. tab., fig. - 21.0 x 29.7 cm

Energy series / / ^-- / ? y

ISBN 92-826-6304-3

Price (excluding VAT) in Luxembourg: ECU 8.50

In a cooperation between NOVEM and Kaldin BV, in Koningsbosch (in the province of Limburg, The Netherlands), a plant has been erected in which a fine-grained limestone is calcined in a fluidized bed with coal residues as fuel. The product can be used as a raw material for the production of sand-lime bricks. The starting up of the plant and the introduction of the product on the market has been supervised in a monitoring programme, subsidized by NOVEM and the EC.

In April 1989 the plant was started up followed by a period in which lime­stone was calcined with only fine-grained coal as fuel. After nine months the first coal residues were processed in the plant. The average coal residues input was 2.5 tonnes per hour at a limestone input of about 15 tonnes per hour. During short periods more than 6 to 8 tonnes of coal residues were used with success.

As a result of the use of coal residues as fuel some disturbances which oc­curred when using only coal (caking, incomplete fluidization) reduced, oth­ers (afterburning with the use of FCB ashes) appeared.

During the period when coal residues were used, the NOx emission was higher than during the time when only coal was used. In both situations it exceeded the limit which is mentioned in the nuisance act (500 mg/Nm3). A reduction of the NOx emission below the limit mentioned in the nuisance act is feasible, but implies a decrease of product quality. Also, the emission of noise lies at around the limits mentioned in the private nuisance act.

The product (free CaO content 35 to 60%) has been used as a binding agent in the production of sand-lime bricks. The quality of the sand-lime bricks and elements has been satisfactory.

The sale of the Kaldin product has mainly been limited to the sand-lime brick factory De Hazelaar. As a result of this restricted sale, together with the oc­currence of disturbances in the plant and the relatively low production level (about 30 000 tonnes per year instead of the anticipated 90 000 tonnes per year), the proceeds of the Kaldin plant reached a lower level than had been anticipated, thus reducing the economic viability of the plant.

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