15th North American Waste to Energy Conference May May 21-23, 2007, Miami, Florida USA

NAWTEC15-3202

DRY ASH COLLECTION AT COAL FIRED POWER PLANTS AND

POTENTIAL FOR WTE FACILITIES

Lead Author: Vincenzo Cianci Research and Development Dep.

Magaldi Ricerche e Brevetti s.r.i., Salerno -ITALY Via Irno 219 85134 Salerno - Italy

Co-author: Daniele Coppola Magaldi Power s.p.a., Salerno -ITALY

Via Irno 219 85134 Salerno- Italy

Co-author: Werner Sunk Earth Engineering Center,

Columbia University, New York, NY 10027

Summary

Remarkable environmental and economical benefits derive from an innovative technology for dry bottom ash removal from coal-fired power plants that may be applied at WTE facilities combusting unprocessed MSW or RDF. This paper describes the MAC system technology that offers a very reliable and broadly proved solution for dry bottom ash collection and handling. Up to now the MAC system has been installed widely and successfully at coal-fired power stations. However, because of the flexibility of the MAC dry ash collector and the wide experience of MAGALDI GROUP in conveying solid bulk materials, this system is ready to be tested for the collection of bottom ash from WTE boilers. The MAC system concepts are discussed in detail as follows:

• Description of various system configurations; • Main differences with traditional wet systems and principal advantages, emphasizing

environmental and economical aspects; • Evaluation of the main criteria for developing a new MAC system that can be applied in WTE

facilities.

In addition, an overview on the MAC reference facilities is presented with a closer examination of the Fusina RDF cofired power plant (Venice, Italy).

1. Introduction

In Waste-To-Energy (WTE) power plant, the bottom ash is typically discharged into a water quenching tank. The water level provides a seal and prevents ambient air from entering the combustion chamber. Also quenching the bottom ash with water stops combustion immediately and prevents fugitive emissions. However, one of the disadvantages of quenching are the high concentration of water in the ash (up to 30-40% [3]) leading to unnecessary costs of transporting and landfilling water. Furthermore, the wet ash tends to bind like cement and form accretions

41

that adhere on metals [4] thus lowering the value of WTE metals and resulting in the loss of small ferrous and non-ferrous metal pieces. Other significant drawbacks of the wet systems consist of lower boiler thermal efficiency due to the high unburned carbon content (UBC) in the bottom ash. Dry ash extraction and processing is state of the art technology at coal-fired power plants. The main equipment is a totally enclosed reinforced stainless steel belt conveyor that conveys the discharged dry ash to the ash processing equipment. Due to the processing of the ash in dry state, the system allows for a more efficient

Copyright © 2007 by ASME

screening of the ash [13] and separation of the fine fraction « 1 mm) that is relatively high in salts and other contaminants [4], thus increasing the value of bottom ash for beneficial use outside landfills. Nevertheless, although these systems work in many coalfired power plants all over the globe, the feasibility of using such equipment at WTE facilities needs to be tested. While power plants use very homogeneous fuels, the MSW fuel in WTE plants contains, if not processed in a RDF plant, different materials in all particle sizes (e.? root stocks, bicycles, etc.). As some of these blg chunks and materials do not burn completely or are not combustible, they need to be processed by the dry extraction system. Therefore, th� steel belt conveyor must be designed so as to reslst the impact of these big and heavy remaining chunks and also to avoid failures due to jamming of metallic objects between moving and fixed parts (e.g. steel wires, etc.).

. The first occurrence has already been taken 1Oto consideration in the dry system design by means of the lateral off-set construction of the hoppers in relation to the MAC systems that minimize the free fall distance of the ash and prevent direct impacts on the belt conveyor. The flexibility of the design of the dry ash collecting systems can ensure that the conveyor can withstand such impacts. As the steel belt is enclosed within a sealed casing that it is maintained at a negative press�re with relation to the throat of the combustIOn chamber, dust and emissions are drafted into the boiler without the help of a fan. In addition, the ambient air that is sucked into the enclosure acts both as a cooling mediurn and as tertiary air for the oxidation of unburned carbon in the ash. At this time, there is no major reason that will inhibit the use of this system in the WTE industry. With minor changes in design, the MAC system and the downstream equipments could be adapted to handle WTE bottom ash for better contaminants reduction, material recovery and beneficial use of the remaining bottom ash.

2. Description Extraction Power Plant

of the System

Dry Bottom at Coal-Fired

42

2.1. Extraction Belt

The MAGALDI Superbelt is the centerpiece of the MAC extractor. It is a metal conveyer belt made up of a stainless steel wire mesh belt covered by overlapping stainless steel plates that are arranged to form a continuous pan (Figure 1). The belt is designed to withstand the arduous operative conditions of dry bottom ash conveying and the overload conditions �at can occur during the operations, such as the lmpacts of big ash lumps that are occasionally dislodged from the walls of the combustion chamber. The belt is driven by a drive pulley that transfers the force by friction (Figure 2). The return d� at the tail section is equipped with an automatic tensioning device to compensate for changes in the length of the belt due to temperature

PAN

MESH -

"­'ROLLER

variations during operation.

Figure 2 - Section of Magaldi Superbelt

Figure I - Magaldi Superbelt

Copyright © 2007 by ASME

The intennediate belt sections are equipped with support and return idlers. The belt runs continuously underneath the boiler's throat, receiving ash from the furnace, at a speed that can be adjusted from few millimetres per second up to 10 centimetres per second. The speed is set up in order to keep the ash bed height at 1 cm at the conveyer start and up to 10 cm at its end. Furthennore, the speed of the belt conveyor ensures a retention time for the ash of 8-10 minutes, to guarantee adequate cooling. As noted earlier, the infiltration of ambient air is controlled to a minimum by enclosing the belt in a sealed housing. A transition hopper is installed between the belt and the boiler throat. The bottom of the transition hopper is equipped with doors that allow the MAC system to run also in discontinuous mode and allow for minor maintenance operations without the necessity to shut down the boiler. Figure 3 shows the typical cross sections of the MAC extraction belt. The bottom of the MAC extractor is equipped with a scraper chain conveyor (Figure 5) for removing

Figure 3 - MAC extractor: cross section (left); side view (right)

43

•

Figure 4 - Air inlets control scheme

the fine ash accretions from the belt to the bottom of the casing.

2.2. Operation

During nonnal operation, the MAC system does not require any personnel supervision. The belt runs at a speed of few cmls when the bottom doors are open.

Figure 5 - Spill chain view

Copyright © 2007 by ASME

During conveying, the bottom ash is progressively cooled and the UBC content is reduced [7]. The cooling and post-combustion effects are achieved by the countercurrent flow of air that is drawn into the MAC system using only the negative draft of the boiler (Figure 4). The mass flow ratio between cooling air and ash rate ranges from 2. 5 to 3. 5, depending on the actual needs. The amount of ambient air through the MAC system at coal-fired power stations is less than 1. 5% of the total amount of combustion air. This quantity is controlled by pneumatically actuated dumpers. Experimental tests verified that in a plant where the MAC system is installed (Unit #4, Italy; plant owners: ENEL-Interpower) the air flow through the MAC system did not disturb the combustion process and nor affected the rate of formation of NO x [1].

2.3. System Downstream Configuration

As the ash is removed in a dry state, a variety of conveying system arrangements are possible, depending on the actual needs of the particular facility:

1. Ash can be directly discharged from the MAC extractor into a removable storage container through a double gate valve (this method is recommended only for boilers with limited ash production or when final ash destination is uncertain).

2. A single crushing stage can be provided at the extractor discharge to reduce the ash grain size distribution. After sizing, the ash can be dumped onto a mechanical conveyor heading for a storage silo (Figure 6).

3. After the sizing by a primary crushing stage, the bottom ash can be transported to a storage silo by means of a pneumatic vacuum system (this configuration is adopted in few cases [ 2]).

4.

Figure 6 - Configuration with single crushing stage

[II Boiler rn Bottol"l

valves

[]] Me-chanicat SE>cd

m MAC extroctor

(1] Pre-crusher 1]J secondo.ry necho.nica\ conv(>yor

rn PriMary crusher III Final silo.

to pulverize the bottom ash before it is sent to a silo. To accomplish this, a primary crusher is used to initially size the material as it falls off the extractor belt, then a secondary crusher further reduces the particle size of the bottom ash to meet the requirements of the pneumatic handling system. Therefore, the ash can be conveyed by means of a pneumatic conveying system to the final silo (Figure 7). A trial operation showed that mixed fly and bottom ash from a coal fued power plant can be reused as raw material for cement production [6]. By mixing the ash its disposal is simplified as the combined ash is sent to the same final destination (the cement industry). This configuration has now been adopted by Magaldi clients as the standard arrangement for all future bottom ash system retrofits.

3. MAC System Experience at the Fusina RDF Co-Fired Plant

The latest improvements on the MAC systems led to the possibility of operating the bottom ash extractor at RDF co-fired boilers [11]. ENEL, the owner and operator of the Fusina power station (Venice, ITALY), has been operating the boilers of the units #3 and #4 in co-combustion mode with a coal-RDF fuel mixture since 1998. The amount of RDF that is co-fued represents about 2. 5% ( 3. 5 t/h) of the total heat input of the boiler. The operating conditions of the MAC system at the belt level are not severe: the cooling air temperature ranges from 200- 300°C while the ash temperature, where it is in contact with the belt, is a little higher. Combustion of unbumed particles in the bottom ash takes place in the zone close to the boiler throat where the

conditions are much more favourable for combustion reactions.

UJ Boiler

ill BetteM valves

44

Figure 7 - Configuration with two crushing stages and possibility of mixing fly and bottom ash

(1] Mechanical []] Pre-crusher I1J Interl'\edJo.te I]] Secondary 5E'al tank crusher

[!] MAC rn Prll'1ory £II Secondary GIl rina! Silo. E')(tractor crusher l"IE"cho.nlcol

conveyor

Copyright © 2007 by ASME

100

90

80

70

60

50

40

30

20

10

,

Figure 8 - Laboratory tests on the UBC reduction

Unbumt reduction vs residence time at dilrerent bed temperature

1

/ /

/ /

V ---�

/ -..--. .L.----io""""

10 15 20 Rnid,nc:, tim' In .v,n (min)

L,....--

2'5 30 35

I_Sed temperature" 300 'C _Bed temporature" 400 'C 8ed temperature" 500 'C ' "

Figure 9 - RDF post-combustion in the MAC

extractor at the Fusina PP

The post-combustion at the Fusina power plant (Figure 9) can be called "uncontrolled" since the MAC system has been installed. In order to move from the Magaldi Ash Cooler to the Magaldi Ash Post-Combustor, two significant constraints have to be taken into consideration:

1) Residence time; 2) Heat generation.

The presence of relatively large grains of unburned material imposes a longer residence time for a complete combustion of these particles. Laboratory tests performed on bottom ash derived from the Fusina co-combustion power plant have demonstrated the relation between residence time and unburned conversion at different temperatures (figure 8). The laboratory tests showed that the minimal bed temperature to activate the post-combustion of RDF on the extractor is 400°C. With a bed temperature of 400°C the reaction is mainly controlled by diffusive phenomena.

Following these studies, in order to control the post-combustion temperature, inlet valves are provided on both sides of the conveyor casing (Figure 10) allowing the adjustment of the amount of ambient air that enters the system. The Fusina experience with RDF-fuel has been satisfactory for the MAC system, in terms of increased boiler efficiency and reliability of the system [11]. Observations of the operating MAC system have shown that only a thin layer of molten RDF (mostly plastic particles) appears on the belt which does not affect the performance of the system (Figure 11). Unexpected post­combustion of RDF on the MAC conveyor belt has not led to uncontrolled phenomena or operating problems. Furthermore, it has been observed that the molten RDF particles do not

Figure 10 - Post-combustion air to improve post-combustion on the belt

Post·combustion Air

Cooling -Air

45 Copyright © 2007 by ASME

clog the primary crusher rotor due to the "cleaning action" of falling bottom ash.

4. Benefits of improving MAC Systems at MSW-fired facilities

It is believed that dry bottom ash extraction and processing at WTE facilities may result in several environmental and economic benefits as discussed below. However, it is not possible to generalize the quantitative analysis of benefits resulting from the implementation of a dry system. Depending on the actual situation of a specific WTE facility some benefits can be more significant than others.

4.1 Elimination of Water

We have observed at WTE facilities a make up water consumption in the plunger ash extractor with a water to ash mass ratio ranging from 0.5 and 0.7. Part of this water is drawn into the boiler due to evaporation and part of it is lost due to the leakages of the water system. Also, a significant amount of water is lost because the water content (20-40%w) of the wet ash is discharged by the plunger ash extractor The elimination of water would yield to the following direct benefits:

• Water savings: for each ton of ash that is handled by the extraction system we can assume an average of 0.6 tons of water that is now consumed by the wet system. A dry ash system would save this amount of water and could lower the costs of the WTE facility's water consumption.

• Cleaner working environment around the ash system: eliminating water leakages along the extraction line would prevent the formation of puddles and dirty locations. A cleaner working environment is also a safer working environment.

Figure 11 - Molten RDF on the Belt

46

Other significant indirect benefits achieved by the elimination of water from the ash extraction and processing system are taken into consideration in the following paragraphs.

4.2. Ash Disposal and Reuse

Landfilling unit costs are proportional to the total weight of water and ash sent to disposal. Eliminating an average content of 30% of water in the ash allows lowering the disposal costs by 30%. Furthermore, collecting bottom ash in a dry state will result in higher quality of ash and the recovered metals [13]. The absence of water leads to a more efficient metal recovery process from the ash by the downstream equipments and allows the separation of the minus I mm fraction of bottom ash which has higher content of salts and other contaminants [5]. In addition, the post­combustion on the belt in coal-fired power plants reduces the UBC content of bottom ash from approx. 7 % by weight on average to less then 1 %w [7]. The dry system valorises the bottom ash and makes it a more attractive material for different industries with lower concentrations of UBC, contaminants and metal residues. Thus, ash disposal costs can be saved and could be turned into benefits for the WTE facilities.

Figure 12 - Unburned carbon in bottom ash; tests at Monfalcone PP, ENEL-Italy

UnbumMi C%

American colli DrySysiam

AI/at.

4.3. Energy Savings Aspects

The adoption of a MAC dry ash handling system on coal-fired boilers has led to increasing the boiler efficiency by recovering most of the heat crossing the bottom opening of the boiler. This heat is the sum of radiant flux from the furnace, sensible heat, and the chemical energy content of ash that are lost in wet ash collection systems.

Copyright © 2007 by ASME

Ta ble I - Then nal losses of wet a nd dry systems.

Overall data about Sines Power Station

Coal feed rate It/h) 115 13%

.�--.-''::''----.---.-. Ash content in coal

..... ... ...... _, .. _ ....... . _ ...... _ ..... .

Bottom ash 1 Fly ash split Bottom ash feed rate Global unit efficiency

Thennal power losses [kW]

Radiation at boiler's throat - -.---.-------.--.� ... --.. -.--. Ash sensible heat Radiation from external

�rfC!�es ". =-:::--Ash chemical energy (UBC

content)* Total Savings with MAC system per unit [kW]

10% 190% ......... _ .... __ ._ ..... __ .... _-

_ .. ___ ._ . ... !.5 t/h __

38% Wet Dry

system system 691 0

----_. __ .-

229 21 0 106

596 73 1516 200

1316

Figure 13 - Then nal losses of wet a nd dry systems

1600

1400

[ 1200

. 1000 � . £

j 600

8. 600

I 400 �

200

CAsh ehemlc.lenergy (UBC contllnt)

DRad!.Uon from extemlliaurfacea

CAsh .. nalb .. h .. t

523

Difference

In tests performed at the Monfalcone facility, one unit was equipped with a dry system and the second with a wet system [12]. Samples from both units were taken to make a comparison between the UBC content in the discharged bottom ash. Figure 12 shows the results of tests conduced with two different types of coal, South African coal which is difficult to burn and easy to burn American coal: a reduction of 7 5% of UBC was detected in both cases. The third series

47

of data shown in Fig. 1 2 relate to the average value of UBC determined for all different coal samples available for both wet and dry systems and represents the typical performances of dry and wet systems ( 5.7% UBC is determined for the wet system, while only 0.8 % UBC remain in the ash by operating a dry system).

Apart from the possibility of post-combustion of the UBC content in ash, the dry system allows to recover the heat in form of radiant flux since the metal conveyor almost thoroughly reflects the radiation back into the combustion chamber. Furthermore, most of the ash enthalpy in the form of sensible heat is recovered by the counter current stream of cooling air and is drawn back into the combustion chamber through the throat of the boiler. At the Sines coal-ftred power plant (Portugal, 4 coal ftred units, 314 MW electric output each), where wet and dry systems coexist, energy losses of both systems have been evaluated by experimental and numerical tests. Table 1 and Figure 13 summarize the results of this study.

The thermal power savings of 1316 kW improved the Sines PP's boiler efftciency by 0. 20% on average.

At this time, there is no operating wet ash system that has been replaced by a dry system at a WTE facility but, on the basis of the Magaldi experience and the WTERT information, a hypothetical case is presented in Table 2 and Figure 14 for a WTE unit combusting 35 tons per hour.

Figure 14 - Expected thenna l losses for a WTE fa cility

12000

10000

i o!!. 8000 .. .. .. .. £ 6000 li J 0 ... ;;; 4000 E .. � 2000

8021

CAsh ett.micalenergy (USC content)

• R_d"tion from •• ternal aurt.cea

DAsh sensible; heat

8815

Copyright © 2007 by ASME

Table 2 -Expected thermal power losses at a WTE unit

Overall data about a WTE unit

Fuel type MSW

T.����.�.I ... p?'.�.(;lr.:.P�.� ... �!1.i.! . . [�yytl ... _ +____ __ �� ....... _ _ _ __ _ ..

Operating hours per year __ ��� _ ____ . __

LHV [kJ/kgj 9000 ... ��yy���(;l!!���E��JtJ.�L . 35 Ash content in MSW-fuel 30% BC?t!C?.� ... �.�!.1.L . . �.IX ... ��.� .. �plit

................... . __ _ _ �Qr.�_�_Oo/c_o _._

Bottom ash feed rate 10 tlh

Thennal power losses [kYij Wet

system Dry

system Radiation at boiler's bottom C?PEll1iI19 _ . Ash sensible heat Radiation from external surfaces

180 0

1875 125 o

Ash chemical energy (UBC 6417 . <:.911!Ell1tr�____. .. ................................. _ _ __ ... _

Total 8472 Savings with MAC system [kYij per unit

6407

106

1833 1958

** Estzmated UBC content: 7% for wet ash and 2% for dry ash.

The thennal power savings of 6407 kW would increase the boiler efficiency of the hypothetical WTE unit by 7. 3 %. Assuming a fixed MSW feed rate to the boiler and an effective operating time of 8400 hours per year, this improvement would increase the generation of electricity by 14. 7 GWh per unit and year on average or 44.1 GWh per year for the whole plant ( 3 units).

From the above preliminary estimate, appears that a significant improvement may be achieved

48

when burning a low quality solid fuel (e.g. MSW) than burning a better solid fuel (e.g. bituminous coal) [9]. This is due to the fact that heat recovery from the bottom ash of a WTE has a much higher impact on thennal efficiency than for a coal fired boiler.

4.4. Maintenance, Reliability and Safety Aspects

Further benefits can be achieved by the use of a dry ash handling system in terms of lower maintenance requirements. The absence of water eliminates the erosion/corrosion problems associated with the water handling circuit (pumps and piping), the plunger ash extractor and the bottom ash pit. The MAC system has demonstrated very high reliability. With more than 300,000 hours of MAC systems operation, there has not been loss of energy production in boilers equipped with the MAC systems due to system failure or malfunctions. As stated earlier, maintenance activities can be perfonned with the system in operation, without needing to shut down or reduce the load of the boiler. Since the system operates in a fully automatic mode, the risk of hazards for personnel is negligible [8].

5. Reference Facilities

The MAC system has been installed over 70 times at coal-fired power plants worldwide. Table 3 lists the most recent applications since 1999.

Copyright © 2007 by ASME

Table 3 - MAC reference list since 1999

Plant - #Units Country Owner Size Type Start-up

Baoshan #2 People's Rep. Baoshan Iron & Steel Co. 350MW Retrofit 2006 of China Ltd ••• M_O'_'

.. H •••• • •••••••• _HH. -.. - ._---_ .... ---

Y onghung #3 #4 South Korea Korea Eastern Power Co. 2 x 87 0 New 2006 Ltd. MW ·.M .. ···· ·

... " .... _-_ ......... _

......

_ .. - ............ _ ..

- . - "."H_

I········ · Hadong #7 #8

•••••• • ••• M_ ••• _

Durgapur ...........

-.. ..... _ ..

South Korea

India --

_ ..... _ .

.............

!s<?g()1j2 .... .... ................ -.

JaEan

Baoshan #3 People's Rep. of China

• M ••••• • _. ..

...

.......

_ ......

Torrevaldaliga Nord Italy #2 #3 #4 Abofio #2

__ .�Eain

Baoshan #1 People's Rep. of China

Sines #2 Portugal

Tean #7 #8 South Korea

Mindanao PhiliEEines -

Kashima Japan ---------

Sines #4 Portugal ._._

..... _-_ ...

,_._--_ .. _-

Calli de # 1 #2 Australia -------

Jia Wang #3 #4 People's Rep. of China

--_ ..... _------

Datong #6 People's Rep. of China

... _--_ .. _._---_ ............. .

Memuro Japan

Mount Piper # 1 #2 Australia ._-_ .............. _ ......

Wallerawang #7 #8 Australia _._--

Changchun # 1 #2 People's Rep. of China

_._. __ ._-_ .. _---_ ......

Fiumesanto #3 #4 Italy

Jia Wang #1 #2 People's Rep. of China

._-_ ...

................. __ .

. _.

Genova #9 • • H • •• H •••••

Los Barrios ...... .

Genova #5 #6 #7 #8

Tuopai #1 #2

Iskenderun # 1 #2

Kobe #2 �ydgos2:cz #K 3 #.!<:� . ..

Tomatoh-Atsuma #4 • M •••

Kobe #1

Italy SE!I:�� ... -.

Italy People's Rep.

of China __ HH •• _ •• ___ •• _ ••• __ • __ ••••• H ••

Turkey

Jap�� ._ Poland

Japan ... ------........

Japan

Korea Eastern Power Co. Ltd.

The West Bengal Power DeveloEment Co. Ltd.

J Power Baoshan Iron & Steel Co.

Ltd

ENEL

HidroCantabrico Baoshan Iron & Steel Co.

Ltd CPPE

Korea Western Power Co. Ltd.

Steag State Power Inc. Sumitomo Metal Industries Ltd.

CPPE

CS Energy Ltd.

Jiangsu Provincial Electric Power ComEany

SP Power Development Co. Ltd.

Nippon Beet Sugar Mfg Co.

Delta Electricity

Delta Electricity

Changchun Second Heat & Power Co. Ltd.

Endesa Italia

Jiangsu Provincial Electric Power ComEany

Enel Endesa

Enel Sichuan Tuopai Heat &

Power Ltd.

Iskenderun Enerji Uretim

Kobe Steel ZesEol Elektro Bydgoszcz Hokkaido Electric Power

Corp . Kobe Steel

49

2 x 500 New 2005 MW -................. _. __ .........

300MW New 2005 .- _ .. _--

600MW New 2005 ..... __ . __ .... __ . __ ... __ ._-_

.- .,,_ .. -

. ......... .. ... ........... _ _ ...... .

350MW

3 x 660 MW

. ..... _

---

556 MW .. _--"._-----_ ...

350MW

314 MW 2 x 500

MW

.•.

... _._------

105 MW

507 MW

314 MW 2 x 350

MW 2 x 135

MW

200MW ... .

......... --_ .

15MW

2 x 660 MW

2 x 500 MW

... _ .. _ .. -

2 x 200 MW

-_ .... _ ... __ .

2 x 320 MW

Retrofit 2005

New 2005

Retrofit 2005

Retrofit 2005

Retrofit 2005

New 2004

New 2004

New 2004

Retrofit 2004

Retrofit 2004

New 2003

Retrofit 2003

New 2003 _. __ .... __ ..... _ .............. .

Retrofit 2003

Retrofit 2003

Retrofit 2003

Retrofit 2003 --------.-.. -------.-

..... -........ -.---... -.�.

2 x 135 New 2002 MW _.H ••••••

160MW Retrofit 2002 _H ____ •••• HH • •• H ••••••••••••••• H._�._ •• _ ••

_ ••• _ ••••

550MW Retrofit 2002 4 x 35 MW Retrofit 2001

.... _ ...... _ ......... __ ... __ ._ .. _

...... _--

2 x 7 5 MW New 2001

2 x 605 New 2001 MW _ .. _._--_ ._. __

.. _ .. ........•.. _ .. __ .

7 00MW New 2000 65MW Retrofit 2000

. __ ._--_ .. _--_ .. _ .. __ ._- ....

- ....... _ .... _ ••••• HH�_ ••••••••• _ . __ ••

7 00MW New 1999

7 00MW New 1999

Copyright © 2007 by ASME

6. Key-Criteria for Implementing the MAC System in the WTE Industry

As the MAC dry ash handling system has been widely installed on coal fired boilers but has just one reference at a RDF co-fired power plant, its design development at WTE facilities has to be carried on carefully in order to achieve the expected dry system benefits rather than unexpected problems by operating and manage this system. In order to ensure the project enhancement up to its successfully industrial implementation at WTE facilities, we recognize some key-criteria in the dry ash handling system design as follows:

• Cooling air feed rate: Because of the large quantities of ash that need to be processed by the dry extraction system and in order to ensure the post-combustion of the UBC content as well as the desired cooling effect, a dry system at WTE facilities needs a relevant amount of cooling air. Assuming that for a single ton of processed ash the dry system needs 2. 5 -7- 3. 5 tons of cooling air, the cooling air needs for a typical WTE unit (35 tIh MSW, bottom ash 10 tIh on average) would range between 25 to 35 tlh. Such an air inlet from the bottom opening of a boiler must be carefully evaluated in order to ensure best possible conditions for combustion in the boiler. It will be considered to control the amount of air drawn into the boiler through the MAC system by the combustion air control system (SYNCOM) of the boiler.

• Dusting: Large amounts of airborn particles must be considered during discharging and processing dry ash. A dusty environment leads to higher costs in terms of cleaning operations (a wet bottom ash processing area is far from being a clean location) and a higher health risk for employees as well as people in the close neighbourhood must be taken into consideration. The fine fraction of ash from the combustion of MSW is indeed higher in content of heavy metal salts and other contaminants. Therefore, it is essential to provide solutions against dust diffusion. In order to prevent dusting many solutions could be installed such as dust aspirators in the unloading areas, spraying nozzles for low and controlled wetting of the ash, closed casings for the ash processing equipment, etc;

50

• Engineers: The dry ash system is readily adaptable to RDF facilities and WTE that pre-shred MSW and recover bulky metallic objects before the feed enters the furnace, such as the SEMASS process [16, 17].

7. Conclusion

At this time there is no major reason that indicates that dry ash processing systems are not feasible for the WTE industry. As dry ash systems have been widely adopted at coal-fired power plants, they could be adapted with minor changes in design to handle WTE bottom ash and fit with the downstream equipments for contaminants reduction, material recovery and beneficial use of the remaining bottom ash. The presence of large objects in the bottom ash of mass-burn plants (e.g. bicycles, unburned root stocks, washing machines, etc.) will require some innovative thinking and collaboration between Magaldi and WTE engineers. The dry ash system is readily adaptable to RDF facilities and WTE that pre-shred MSW and recover bulky metallic objects before the feed enters the furnace, such as the SEMASS process.

Copyright © 2007 by ASME

8. References

[I] E. Carrea, S. Orsino, J. Barsin, "Full Scale Trias and Numerical Modelling of a Dry Bottom Ash Extraction System from a 330 MW Coal Fired Boiler", Proceedings of 2000 International Joint Power Generation Conference, Miami Beach, Florida, July 23- 26, 2000;

[ 2] W. P. Reilly, J. Tomaszek, "New Design Bottom Ash System at Cristal River Unit no. 2", Edison Electric Institute Prime Movers Committee Meeting Boiler Subcommittee, Washington, D.C., October 24, 1994;

[3] W. Sunk, "Increasing the Quantity and Quality of Metals Recovered at Waste-to Energy Facilities", NA WTEC 14, Tampa, FL, May 2006;

[4] "Trockenaustrag von KVA", Institut fur Umwelt- und Verfahrenstechnik, Jan 2006;

[ 5] R. Bunge, "The Incinerator of the Future: an Omnivore for Municipal Waste", ISWA, March 24th 2006 /NRI;

[6] R. Sorrenti, V. Quattrucci, M. Voltan, "Dry Extraction and Recycling of Bottom and Fly Ash, Costs Reduction and Better Valorization of By Products", 2001;

[7] E. Carrea, M. Graziadio, "Bottom Ash Carbon Content Reduction by Means of MAC Dry Extraction System, a Therrnie Project", Power Engineering International, 1996;

[8] V. Cianci, "Risk evaluation on the tail section of MAC", May Ith 2006;

[9] S. Vlachos, A. Carrea, "Dry Ash System Retrofit Improves Efficiency of Unit at Ptolemais Power Station", Power Engineering International, May/June 1996;

[10] R. Tarli, M. Voltan, "Dry System Improves ENEL Bottom Ash Handling", Power Engineenring International, Nov 1993;

[II] B. Brozzi, R. Busatto, S. Malloggi, M. Urbani, E. Dell' Andrea, G. Teardo, M. Scala, "Centrale di Fusina: Esperienza di Funzionamento in CoFiring CDR­Carbone sulle Unita 3 e 4", Termie Project, 2006;

[12] V. Quattrucci, "The MAC System -Dry Bottom Ash Extraction ", Bulk Solids

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Handling, Vol 17, Number 1, January/March 1997;

[13] A. Selinger, V. Schmidt, "The ABB Dry Ash Concept: INREC™'', Waste Materials in Construction: Putting Theory into Practice, 1997 Elsevier Science B.V. All rights reserved;

[14] United Authors, "Boiler Cleaning and Ash Handling Systems", Steam: its generation and use - Edition: 41, pp. 24.1 - 24. 21, 2005;

[1 5] United Authors, "Waste-To-Energy Installations", Steam: its generation and use-Edition: 41, pp. 29.1- 29. 23, 2005;

[16] P. Estevez, "Management of Municipal Solid Waste in Santiago, Chile: Assessing Waste-to-Energy Possibilities", An industrial Ecology Study, Dec 9th 2003;

[17] Energy Answers Co., "Technology Description and Performance History", SEMASS Resource Recovery Facility, http://www.energyanswers.com/pdf/semas s_tech_desc_and_perf_history.pdf.

9. Contacts

• Vincenzo Cianci, R&D Dept. - Magaldi Ricerche e Brevetti s.r.l.

Via Irno 219,84135 Salerno-Italy, Phone: Phone: + 39 089 688223, vincenzo.cianci@magaldi.com;

• Daniele Coppola, Sales Dept. - Magaldi Power s.p.a.

Via lrno 219, 84135 Salerno-Italy, Phone: Phone: +39 089 489248, daniele.coppola@magaldi.com;

• Werner Sunk, Industrial Environmental Engineering, Columbia University 500 West 120th St., #926 Mudd Bldg, New York, N.Y. 10027 Phone: +1 ( 21 2) 854-9136; Fax: +1 ( 212) 854-7 081; ws 217 2@colurnbia.edu;

• Mario Magaldi, Chairman - Magaldi Group,

• Via Imo 219, 84135 Salerno-Italy, Phone: Phone: +39 089 688268, mario.magaldi@magaldi.com.

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