Altener Workshop“Biomass gasification (10 MWth) and co-firing with coal

in Zeltweg power plant (137 MWel) in Austria ”Grenoble/France, 14. – 15. September 2000

THERMIE SF/010/96

BIOCOCOMB –

GASIFICATION OF BIOMASS AND CO-COMBUSTION OF THE GAS IN A PF BOILER IN ZELTWEG

POWER PLANT

Dr. Andreas MORY, DI Josef TAUSCHITZVerbund - Austrian Hydro Power AG

Geschäftsstelle Klagenfurt, Kohldorfer Strasse 98A-9020 KLAGENFURT, AUSTRIA

ABSTRACT

Verbund – Austria´s largest electricity supplier – has carried out one of the successful European projects for co-firing of biomass together with coal. The so called “BioCoComb” project for biomass gasification and co-firing of the product gas in a pf-fired boiler of the 137 MWel power plant of Zeltweg was a co-operation of five European utilities and an Austrian plant supplier, Austrian Energy and Environment. The project was funded by the European Commission within the Thermie B programme.

After start-up of the installation in late 1997, tests and standard operation until now have shown, that this technology offers a cheap and reliable possibility for biomass conversion in a large scale. Operating experiences are very good, all major technical problems are solved, the technology is developed far enough for replication and market penetration.

So what are the reasons why until now no further installation of this type has followed-up the successful demonstration unit? It seems, that mainly non-technical barriers hinder further market development:

- Liberalisation and competitive market- Pressure on prices and costs- Less investment activities under uncertain frame conditions- Not settled legal and political background for renewable energies- No reliable future scenarios for development of renewable energy market- Changing legislation for waste treatment and landfill

In the actual market situation of dropping electricity prices and cheap fossil fuels, clean biomass is not always an economical very attractive alternative. So it is understandable that many projects have to shift also to other fractions of biomass (waste and demolition wood etc.) or to mixtures of biomass with other supplementary fuels, to reach economical viability. Besides the high pressure in the European electricity market the uncertain future developments lead to a strategy “to act as late as possible”.

But nevertheless further support for electricity production from renewable energies is necessary and should be agreed internationally. Different systems and mechanisms of supporting in the different European countries show, how difficult it is, to establish a satisfying and properly working market and how different regional circumstances and frame conditions are and how different they effect the development of a market. So a comparison between some European countries within the Thermie B project “Technical constraints and non-technical barriers for replication of successful co-firing demonstration projects” show different reasons that hinder a better market penetration for co-firing of biomass and waste.

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1 INTRODUCTIONThe world wide greenhouse discussion, limited resources of fossil fuels, international environmental activities (like the meetings of Toronto, Kyoto and Buenos Aires) and legal definitions force an increased use of renewable energy resources for electricity production. Forestal and agricultural biomass has a considerable potential for future energy supply, offering substantial advantages for environmental protection and CO2-reduction compared to fossil fuels /1/.Compared to world-market prices of coal, the energetic use of agricultural and forestal biomass, including residuals from saw mills and wood industries, is still not economically competitive. Only the price of the cheapest biomass fraction "bark" is near the price of coal. But during the last years it was always expected that changed frame conditions will offer future options for the use of biomass.Within these circumstances Verbund – who produces more than 50 % of the public electricity demand in Austria in 71 hydro and 5 thermal power plants – started with research activities in the field of biomass electrification. The very long experience in conventional combustion technologies helped during the development of new innovative concepts for the utilisation of biomass.

2 SUITABLE CONVERSION TECHNOLOGIES FOR BIOMASSDue to the low specific volumetric energy density and the resulting high transport volume, biomass is not suitable as single main fuel in large biomass fired power plants. But in smaller quantities – fitting to the local available amount – biofuels are a good alternative. So decentralised small biomass power plants of known conventional combustion and conversion technology were investigated first. But due to the higher specific investment and staff costs and the lower efficiency compared to a large power plant, small units showed poor economical prospects.Respecting these facts further investigations were concentrated on different options and technologies for co-firing of biomass in large coal-fired power plants. These large units are flexible (within relatively wide limits) to operate with different shares of a co-fuel. So the capacity of the co-firing installations can be ideally adapted to the local availability of biomass, which is mainly limited by a cost optimal transport distance. The most significant economical advantages of the co-firing conception – depending on the type of project – are:

1) When a co-firing system is added to an existing plant, many parts of the existing plant infra-structure can be used and this keeps the investment costs low.

2) At a new plant installation, the specific investment costs of a larger plant are lower (economy of scale), so all the shared costs of the installations related to biomass combustion are specific lower, too.

Regarding these advantages Verbund decided to continue its engagement in biomass utilisation by realising co-firing projects.

2.1 Co-firing concepts for biomass

Most coal-fired power stations burn pulverised coal. The direct use of biomass without pre-treatment, just by adding biomass directly to the coal flow, is not possible in such firing systems, because coal mills are not suitable to grind coarse biomass pieces, like bark, forest residues or chopped wood to the required fineness. New solutions had to be found and Verbund´s research activities compared four different concepts of co-firing (fig. 1):

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a) Grinding of biomass in special mills and combustion of pulverised biomass as additional fuel in the coal boiler.

b) Co-combustion on a grate for biomass integrated at the bottom end of the boiler hopper.c) Combustion of biomass in a separate unit and injection of the created fluegas in the boiler. d) Partial Gasification of biomass in a separate unit and combustion of the product gas as

additional fuel in the coal boiler. Option a) has meanwhile been investigated in several EU-projects. Main disadvantages are the high specific energy consumption for milling and high operating and maintenance costs. Technically solved, this is a solution for special applications, where economical frame conditions justify the higher costs.Option b) is the most elegant solution for co-firing of coarse biomass particles. The flue gases from the biomass combustion rise directly into the furnace, no heat losses occur, no complicated duct systems are necessary. But unfortunately the installation of such a grate requires sufficient space below the boiler, what makes in many cases a retrofit complicated or impossible.Option c) and d) are similar, but combustion units require larger volumes and cross sections and are therefore more expensive than gasification plants. Due to smaller dimensions gasification units have a – as an important advantage – higher flexibility in arranging and integrating the main components into existing plants.

According to modernisation strategies in Verbund and the applicability of the above described concepts finally b) and d) were realised in large scale. Draukraft, a Verbund subsidy, has realised an integrated Biomass combustion grate at the 124 MW e

power plant of St. Andrä and it is working properly since 1994. The operation experience indicates many positive features of the system, but the disadvantage of the space requirement in or under the boiler limits a wider dissemination.The second demonstration project is at Zeltweg 137 MWe power plant, where biomass is gasified in a separate gasification reactor, working on the principle of a circulating fluidised bed. The product gas is led at high temperatures to the coal boiler, where it is burned together with the coal (see following description).

2.2 Characteristic behaviour of biomass when co-firing

Independent from the technical concept of co-firing, some characteristics of biomass behaviour at combined combustion with coal have to be regarded and specific solutions have to be found:

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biom asscom bustion cham ber(external)

biom ass

biom ass g rate

biom ass

biom ass

biom ass

gasifier

ho tgas withwood c har dust

biom ass dust

grate com bustion

m ill

fluegas1000 °C

biom ass g ratebelow thecom bustioncham ber

biom ass g asifier

biom ass m ill

bo iler

bo ilerbo iler

boiler

a.)

c.)

b.)

d.)

Fig. 1: Biomass co-firing concepts

Residence time of the fuel in the combustion chamber: In large pf-units any fuel has to be prepared for a quick combustion (2 - 3 sec) with a minimum of emissions. Biomass in pieces and chips has a much longer combustion time and is not homogenous enough for a continuous smooth combustion.

Sla gging of biomass ashes: Temperatures in the furnace of conventional coal boilers range between 1.000 °C and 1.250 °C. But the softening or melting points of many biomass types are significant lower. That causes slagging on heat exchanger surfaces.

Hi gh temperature corrosion from biomass types with high chlorine content: straw in large shares might cause corrosion on heat exchangers with surface temperatures >400 °C.

Damage or deactivation of catalysts for flue gas denitrification by alkaline substances, which are created during biomass combustion.

Ash qualit y: Ashes from hard coal fired power plants – removed with modern precipitators – are often used in the cement industry. The effects of components of biomass ash in traces on the usability of the coal ash has to be checked for each application.

Changes of the boiler behaviour caused by the higher specific gas flow which results mainly from the higher water content of biomass compared to coal. Boilers are designed for a certain fuel quality and quantity and consequently for a certain flue gas flow. Changes in the gas flow, which exceed certain tolerable limits, will require adaptations of heat exchangers, recuperators, ducts or fans.

These are the main technical constrains for the layout and design of any co-firing installation and they have to be regarded and solved to get a satisfying and properly working plant.

3 BIOCOCOMB: EU-PROJECT FOR BIOMASS GASIFICATION AT ZELTWEG POWER PLANT

Zeltweg power plant (fig. 2), with an installed capacity of 137 MWel was set into operation in 1962. Twenty years later the firing system was changed from lignite to hard coal (tangential fired) /2, 3/.

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Fig. 2: Aerial view of Zeltweg power plant with biomass gasification plant

Main steam data (HP/ reheat) are 185 bar/44 bar at 535 °C (plant data see tab. 3). The flue gas cleaning systems for dust, NOx and SO2 were renewed and represent the state of the art. NOx-removal is achieved by an SNCR-system with ammonia injection /4/. For SO2-removal a CFB-reactor is installed. The plant is situated in a rural region in Styria/Austria with a lot of forest industry (saw mills) in the vicinity, which predestinates this location for a biomass project.

3.1 BioCoComb - an innovative technical concept at Zeltweg

At Zeltweg power plant a biomass co-firing system with an integrated combustion grate like the one at the Verbund power plant St. Andrä was not possible, simply because of lack of space. So a new approach for biomass conversion by partial gasification in a separate, external CFB-reactor and co-firing of the particle loaded “biogas” in the combustion chamber was developed /5, 7/.

BIOCOCOMB is an innovative process for co-firing of biomass with fossil fuels. Innovative is the way, how the Circulating Fluidized Bed (CFB) is operated and how the CFB is combined with a coal fired boiler (fig. 3).

The abbreviation BIOCOCOMB is an acronym of “Biofuel preparation for Co-Combustion” where preparation means reaching the minimum requirements for co-combustion with pulverised coal. So the gasifier is not more than a thermo-mechanical mill for fuel preparation. The energy of biomass is transported from the gasifier into the coal boiler in three different forms: sensible heat, low calorific value (LCV) gas and fine combustible char particles. Besides the CO2-reduction by coal substitution as the main environmental benefit, this concept offers the additional option of NOx-reduction by using the LCV-gas as a reburning fuel /6/, what again is an interesting fact regarding environmental protection.

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boiler

boiler-house

10,0 0

19,0 0 gasifier

control-rooms

Fig. 3: The Zeltweg Gasifier and its connection to the boiler

The concept of the process is based on a CFB-reactor, where gasification of biomass and mechanical attrition of the created char takes place. The wood char is ground to a fine powder, which guarantees a complete combustion in the furnace of the power plant. For co-combustion a low gas quality is absolutely sufficient and therefore no predrying or milling of the biomass and no hot gas (850°C) cleaning or gas cooling is necessary (fig. 4). This reduces the costs dramatically compared to all other concepts for the use in gas engines or -turbines, which need a clean, dust- and tar-free high quality gas. When partial gasification is sufficient, the residence time of the fuel in the CFB is shorter, what yields to a much smaller and therefore cheaper gasifier.

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boiler

predrying

no predrying

biom ass

Use of the product gas directly in a gas turbine / gas enginerequirem ents for a gas turb ine / gas eng ine: gas w ith h igh quality

requierm ents for co-firing in a boiler: a low gas quality is sufficientUse of the product gas as additional fuel in a boiler

biom ass

hot gascleaning

no hot gas c lean ing

gasi

fier (

pres

sure

gasi

ficat

ion)

smal

l ga

sifie

r

gas turbineorgas engine

Fig. 4: Main technical components at different gasification concepts

Overview of innovative features

Using a CFB for preparation of biomass to reach minimum requirements for co-firing in a coal-fired boiler. A CFB is very flexible to a wide range of fuel types.

No milling, no predrying of the biomass, because a low gas quality is sufficient for co-firing in a stable coal flame.

Partial gasification of biomass is aimed with maximum transport of residual fine char particles in the gas.

Partial gasification requires a shorter residence time, what leads to a smaller, cheaper gasifier design.

The gas is led at high temperatures from the CFB to the furnace (no gas cooling). Therefore no condensation of hydrocarbons is possible.

No hot gas dust removal equipment for the LCV-gas is required, the char dust particles, leaving the CFB, are small enough for complete combustion.

The possible use of the generated LCV-gas for reburning was never before applied at such a scale.

The efficiency of the biomass conversion to electricity is as high as of the coal fired unit.

3.2 The BIOCOCOMB project:partners, financing and timetable

In 1993 the innovative conception of partial gasification and attrition of biomass in a CFB and combustion of the produced gas in a power plant was completed and Verbund was searching for partners and financing concepts for the erection of the first demonstration plant. Together with Austrian Energy as main supplier and 4 partners from 4 other European countries and in co-operation with Universities and local authorities an EU-Thermie proposal was submitted, which led to an EU-contract (SF 010/96 AT/IT/DE) for a 28 % support, that closed the missing gap of 1,34 Mio Euro of the total project budget of approx. 4,83 Mio Euro.

Fig. 5: Technical concept, partners and tasks of the Zeltweg biomass project

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Each of the six partners – ELECTRABEL from Belgium, ENEL from Italy, ESB from Ireland, EVS from Germany, Austrian Energy and VERBUND from Austria – contributes a clearly defined task to this international demonstration project, as shown in fig. 5. The scientific advise is given by the Technical University of Graz.With great ambition the detail planing phase for a 10 MWth gasifier started in September 1996 and only eight months later the erection works began in May 1997, hot commissioning took place in November. First gasification was reached on 10th of December 1997 and a complex measurement and testing programme was carried out in January 1998 with special participation of ENEL and Austrian Energy. In June the plant was set officially in operation by the Austrian Minister for economy and trade. Extensive tests, measurements and monitoring phases were carried out in the following years.In the operating period 1998/99 other fractions of biomass and mixtures of biomass with supplementary fuels (waste wood, demolition wood, plastics, sewage sludge etc.) were tested. After proving, that all plant emissions are still below the legal limits, the plant got a permanent permission for using specified waste fractions as additional fuels in combination with biomass for standard operation. Parallel to BioCoComb another EU-project (“Biogames”, Joule 3) for “Computer Modelling of biomass gasification in a CFB” was started and had measurement campaigns for investigating the chemical and physical behaviour of the gasifier.In August 1999 the EU project BioCoComb was finished and the plant continued with commercial operation /8/.

3.3 Process scheme and technical details

Fuel support: Bark is intended as main fuel, but the gasifier with all auxiliary components must cope with a wide range of different types of biomass like old wood, waste and demolition wood, saw dust or wood chips, to guarantee flexibility to the market conditions.

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C YC LO N E

G A S IF IE R

O ILBU R N E R

TO B O ILE R

P R O D UC T-G AS D U C T

C O M P R ES S E DAIR

S T O K E RFE E D E R

M E TA L S E PA R ATO R

IN TE R - M E D IAT E FU E L SILO

S C R E W C O N V E Y O R

W EIG H IN G B E LT C O N VE Y O R

FU

C LA SS IF IE R

AIR FR O M E XT E RN A L AIR PR E H E ATE R

C O O LIN G W AT ER

A S H C O O LIN G S C R E W

AS H R O TA R Y F E ED E R

W AT E R C O O LIN G

IG N IT IO N G A S

FU E L C H U TE

TR A ILO R

LIG H T O IL

SA N DSILO

BU

CK

ET

ELE

VATO

R

Because the CFB is working with a FD-fan, the gasifier is set at a slight overpressure, requiring gas tight components. A duplex rotary feeder with a purging mechanism prevents gas escape at the fuel entrance. This feeder limits the particle size to 30 x 30 x 100 mm. A special separator picks out coarse, oversized particles, which are almost unavoidable, and a shredder chops them to suitable size before they are returned to the conveying path.Gasifier: The CFB-gasifier (fig. 7) is a simple steel construction with a brick and concrete refractory inside. The gasification chamber is a vertical tube without internal mechanical components or heat exchangers. At the bottom is the open grid of air nozzles, where all the fluidising and combustion/gasification air is pressed into the system. The air is taken from the power plant´s recuperator at 270°C. Fine sand of a defined particle fraction is used as bed material.Biomass will partly combust, creating the necessary temperature of 850°C, and partly gasify because of lack of oxygen in the upper part of the gasifier. Reaction temperature and bed behaviour are the main parameters to be controlled by varying the air flow. Large biomass particles will remain in the fluidised bed until they are, due to gasification and attrition, small enough to pass the gas cyclone. All fine particles, mainly wood char dust and ash, leave the gasifier with the gas through the hot gas duct to the boiler. Larger particles recirculate and enter the gasification reactor near the nozzle grid, where an oxygen surplus is available for combustion.

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Fig. 7: The BIOCOCOMB gasifier

Fig. 6: Scheme of the Zeltweg process

Sand discharger: At the bottom end of the gasifier a water-cooled screw conveyor allows dischargement of bed sand and incombustible (mineral and metal) parts. Ash is not expected in this bottom sand, because ash is very fine and light and will leave the gasifier with the gas.Control and instrumentation: The C&I concept and all protection circuits were developed by the Irish partner ESB in co-operation with Verbund and AE. The sophisticated system allows manual or automatic operation and manages the complicated switch from combustion to gasification mode (or reverse). The problem during this switching period is the enormous change of the specific air demand. So both, biomass and air flow have to be changed to keep the bed behaviour in stable conditions. Further on the control logic is reverse in the two operation modes and has to be changed from air flow to fuel flow control.Gasburner: The hot gas enters the boiler via a specially designed burner nozzle, that guarantees rapid ignition, stable flame, deep penetration into the coal flame and good mixing. The combustion behaviour was modelled by ENEL with a CFD-programme. Regarding this calculations ENEL defined the optimum point of injection of the product gas into the boiler.Reburning: The product gas is used as a reburning fuel in the coal boiler, to decrease the NOx-emissions by converting NOx to nitrogen. Ongoing measurements will bring experience and know-how to increase the biofuel share to 15 - 20 % of total fuel input and to predict the consequences for the reburning behaviour.

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3.4 Operation experience

More than 5.000 tons of biomass and supplementary fuels have been gasified since start up. Main base fuel was spruce bark with a water content of approx. 55 % (composition at 60 % see tab. 1), but also chopped wood and saw dust from larch trees were used either solely or in combination with the supplementary fuels.Operation experiences are very positive and promising: Ignition and gasification behaviour in the gasifier is very good, the combustion of the gas in the boiler is good, too. The critical change-over from gasification to combustion and reverse is smooth with a slight and acceptable temperature increase. The power range of the gasifier was varied between 5 and 20 MW th, the maximum load is depending mainly on the humidity of the fuel. The quality of the product gas is similar to the pre-calculated values (see tab. 2). The burn out of carbon is excellent, so almost no carbon was found in the discharged bed material. Heating up and cooling down the installation is kind to the refractory.The reburning effects in the boiler have an astonishing good performance, where a decrease of 10-15 % of the ammonia water consumption is gained with 3 % of the total thermal input of the power plant coming from biofuels. Initial problems with the fuel conveying system during the first operating period, like bridges in the dosing silo, slipping of frozen biomass on inclined belts or blocking on the rotating disc separator, are all solved.

4 OTHER FUELS THAN BIOMASSIn the early beginning of the BioCoComb project the situation of the biofuel market was promising for a good future development compared to fossil fuels. Meanwhile dropping fossil fuel prices and the competitive electricity market have dramatically increased the economical pressure an projects for electricity production from biomass. So it is understandable, that many projects have shifted from pure biomass to a much wider range of biomass based fuels and in some cases also to specified fractions from waste (incl. waste wood, demolition wood, sewage sludge, plastics etc.).All these fuels have different elementary compositions, causing different effects on emissions or corrosion. The basic idea of the BioCoComb process is to keep the system as simple as possible, so there is no product gas cleaning or cooling. But then one has to accept some restrictions for the fuel selection in terms of contaminations (fluoride, chlorine, heavy metals, alkalines etc.). As long as contaminations in the fuel and/or the ratio between the co-firing fuel and coal are low enough, no problems occur: the gaseous emission, liquid and solid residues of the power plant after co-firing remain still in the allowed emission limits.If one wants to use other fuels with higher contaminations or in a higher ratio, the gas has either to be cleaned before entering the boiler or the flue gas cleaning system of the power plant has to be adjusted. But all these measures increase the costs and have to be regarded in the economical evaluation of the total project. The Zeltweg idea is to stay at a simple and cheap stage of technical equipment for a specific range of selected fuels from biomass and waste, that are available in this region.

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Fig. 8: Gasification plant with fuel conveying and preparation system

So what are the fuels for the Zeltweg gasification plant? Regarding concentration and emission limits it is now allowed to co-fire not only clean biomass, but also mixtures of biomass with so called supplementary fuels as fractions from waste - and demolition wood, railway sleepers, plastics (PVC-free), sewage sludge and residues from electronic industry (casings, plastics etc.) up to a maximum annual amount. Biomass remains the main fuel, but the supplementary fuels are very important to improve not only the heating value, but also the price of the fuel mixture.

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5 DISSEMINATION BARRIERS AND ACTIVITIESThe European scene of Biomass projects has proven technical availability for different co-firing technologies. But still market penetration is very slow and replication projects after successful demonstration projects are not found very often. It seems, that mainly non-technical barriers hinder further market development. The main topics in this context are:

- Liberalisation and competitive market with high pressure on prices and costs- Less investment activities under uncertain frame conditions- Not settled legal and political background for renewable energies- No reliable future scenarios for development of renewable energy market- Changing legislation for waste treatment and landfill with a strong influence on future

development of amounts

In the actual market situation of dropping electricity prices and cheap fossil fuels, biomass is not a very attractive alternative. Besides the high pressure in the European electricity market the uncertain future developments lead to a strategy “to act as late as possible” to prevent bad investments.

Further support for electricity production from renewable energies is necessary and should be co-ordinated internationally. Not only financial support is necessary, but also the legal and political background has to be prepared. Different systems and mechanisms of supporting in the different European countries show, how difficult it is, to establish a satisfying and properly working market and how different regional circumstances and frame conditions are and how different they effect the development of a market. A comparison between some European countries within the Thermie B project “Technical constraints and non-technical barriers for replication of successful co-firing demonstration projects” showed many different reasons that hinder a better market penetration for co-firing of biomass and waste.

The activities of Verbund for broad dissemination of the results of the EU-Thermie project BioCoComb were integrated part of the complete project and were carried out with strong effort:

- Participation in European dissemination projects: In the Thermie B project “Constraints of co-firing” Verbund was one of the project partners. In the Altener Project “Co-firing” both Biomass installation of Verbund were reported and a presentation of the BioCoComb project was given at a Altener workshop.

- More than 40 presentations of the project in Conferences, meetings, exhibitions or workshops in Europe and USA.

- Numerous publications in different international journals - Winner of the PowerGen Europe ´98 innovation award and of the Austrian Solar Prize.- Plant presentations at Zeltweg for interested visitors and groups.- Project description on a Verbund video- Ongoing participation in EU- research projects (“Biogames”, Joule 3, 2 proposals in 5th frame

programme) for further development of the technology and know-how transfer

All these activities on the national and international floor also can be seen as part of lobbying for biomass utilisation in Austria.

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6 CONCLUSION Research activities of Verbund resulted in 2 demonstration projects to promote technologies for biomass co-firing in the thermal power plants of Zeltweg (137 MWe) and St. Andrä (124 MWe). In St. Andrä power station combustion grates were installed in the boiler hopper. Operation started in December 1994 and works properly without problems. At Zeltweg power station a CFB-gasifier started operation in December 1997. There the product gas is led through a hot gas pipe to the coal boiler without cleaning or drying. In both installations a thermal capacity of 10 MW of biomass replaces 3 % of the total input of hard coal. Operation experience in both plants is very promising.The positive results of operating such biomass units encourage Verbund to go on with developments of innovative conversion technologies for renewable biomass. Biomass prices are still too high to compete fossil fuels now, but under changing frame conditions (as results from Toronto, Kyoto or Buenos Aires conferences) and legal regulations for an increased use of renewables (White Book of the European Commission) the role of biomass will consequently become more important and –proper working supporting mechanisms provided – economical more viable. In its dissemination activities Verbund has actively promoted the idea of biomass co-firing as a proven technology for electricity production from biomass and is still participating in the promotion process.

7 LITERATURE

[1] Schröfelbauer H., Kopetz H., Höwener H., Tauschitz J., Zefferer H., Maier H., Mory A.: “Stromerzeugung aus Biomasse”; Fachsymposium Biomasse 1997 in Zeltweg; Verbund

[2] Schröfelbauer H., Draxler A., Tauschitz J.: “Modernisierung der Dampfkraftwerke St. Andrä und Zeltweg”; VGB Kraftwerkstechnik 76 (1996), Heft 6

[3] Schröfelbauer H., Kakl J., Tauschitz J., Knyrim W.: “Umbau der Kesselfeuerung von Braunkohle auf Steinkohle im Dampfkraftwerk Zeltweg”; VGB Kraftwerkstechnik 66, Heft 5, S. 462 - 472

[4] Zellinger G., Tauschitz J.: “Betriebserfahrungen mit der nichtkatalytischen Stickoxidreduktion in den Dampfkraftwerken der Österreichischen Draukraftwerke AG”; VGB Kraftwerk und Umwelt 1989

[5] Mory A., Tauschitz J.: “Mitverbrennung von Biomasse in Kohlekraftwerken”; VGB-Fachtagung "Feuerungen 1997"; Oktober 1997 Essen/Deutschland

[6] Staudinger G., Raupenstrauch H.: “Verfahren zum Zerstören von Stickoxiden in Rauchgasen von Feuerungsanlagen”, Österreichisches Patent 399.297, 1995

[7] Mory A., Tauschitz J.: “Co-Combustion of Biomass in Coal-Fired Power Plants in Austria”; VGB-PowerTech 1/99, Volume 79/1999, ISSN 1435-3199

[8] Mory A., Tauschitz J., Moritz G., Kesselring G.: “BioCoComb: Errichtung und Betrieb einer Biomassevergasungsanlage im Dampfkraftwerk Zeltweg”; Schriftenreihe der Forschung im Verbund, Band 55, Wien September 1999

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8 TABLESFuel Composition: spruce wood

Total Carbon (C) 19,65 %wtTotal Hydrogen (H) 2,40 %wtTotal Oxygen (O) 16,55 %wtTotal Nitrogen (N) 0,20 %wtTotal Sulphur (S) 0,00 %wt

Ash content 1,20 %wtMoisture (H2O) 60,00 %wt

total: 100,00 %wt

Lower heating value 6066,00 kJ/kg wetHigher heating value 8054,00 kJ/kg wetCarbon Conversion 0,90 %

Tab. 1: Fuel composition

Coal Biofuel

Thermal input: 330 MWth 10 MWth

(97 %) (3 %)Origin: polish coal wood chips

bark, sawdustsuppl. fuels

Electrical output: 137 MWel

Fuel consumption: 47 t/h 3 % heat inputresp. 2 – 4 t/h

Heating value of coal: 27 MJ/kg

Heating value of gas: 2 – 5 MJ/Nm3

Internal consumption: 7 kW/MWth 14 kW/MWth

Unconverted carbon to boiler: 10 Mol% Particle size of char dust to boiler: 200 µm

Air (270°C) consumption: 3.700 Nm³/h

Tab. 3: Main plant data

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Gas CompositionCalculated Measured

O2 0,00 0,00 % mole N2 38,12 43,62 % mole CO 2,76 2,73 % mole CO2 12,45 13,20 % mole CH4 0,00 1,11 % mole

others 0,00 1,04 % moleH2 9,03 3,32 % mole

H2O 37,64 35,00 % mole

total: 100,00 100,00 % mole

LHV 1732 kJ/kg wtHHV 1965 kJ/kg wt

Tab. 2: Gas composition at 60 % fuel humidity