Experiences in Europe and List of Biomass Co-firing Plants

 

Netherlands:

In the Netherlands, the capacity of coal-fired installations amounts to 4,000 MWe, divided over 8 units (generating capacity under the power sector is 17,700 MWe). The first co-firing trials have been executed in 1993 with 5 to 10 wt % demolition wood, sewage sludge and pet cokes. In the 1 MWth coal-fired KEMA test boiler positive results from these tests in terms of combustion performance, ash quality and emissions behaviour have led to successful introduction of co-firing in all Dutch coal-fired power plants. Four electricity generation companies (EPON, EPZ, EZH and UNA) have all developed plans to modify their conventional coal fired installations to accommodate woody biomass as a co-fuel. Fly ash implications for co-combustion: A Key issue is the validation of the quality of the ashes produced during these trials.

Power Station Type of Combustion
1 Gelderland 13

Direct co-combustion with separate milling, injection of pulverised wood in the pf-lines and

simultaneous combustion

2 Amer 8  Direct co-combustion: separate dedicated milling and combustion in dedicated biomass burners
3 Amer 9 Direct co-firing: biomass is milled separately in dedicated mills and combusted in separate burners
4 Amer 9

Indirect co-firing : gasification in an atmospheric circulating bed gasifier and co-firing of the fuel gas in the

coal-fired boiler

5 Borssele 12

Practice 1: direct co-firing by separate milling and combustion  Practice 2: direct cofiring

by mixing with the raw coal before the mills

6 Maasvlakte 1 & 2

Practice 1: direct co-firing of biomass, pulverised in a separate hammer mill, injection into

the pf-lines and simultaneous combustion Practice 2: liquid organics fired in separate oil burners

7 Willem Alexander Direct co-gasification
8 Maasbracht Direct co-firing of palm-oil in dedicated burners

 

From the results of these unique co-firing trials it was concluded that co-firing of waste wood up to about 25%, chicken manure up to a few percent and RDF (refused derived fuel) up to about 15% (on an energy basis) is possible without for instance significant influence on the properties of the fly ash. Therefore the ash can be sold to cement industries.

Co-firing units in the Netherlands range from 420 to 650 MWe capacity. Co-firing fuel experience 1996-2000 include: Pet cokes (dried),sewage sludge, paper sludge, (waste) wood, hydrocarbon gas, biomass pellets, citrus pellets, municipal waste, coffee grounds, cacao shells, animal fat, meat and bone meal.

Gelderland power station (see below)
In the Gelerland power station waste and demolition wood is collected in the Netherlands in 3 locations. It is chipped and metal, plastics or textiles are removed manually. Small pieces of plastic are removed by wind sifting and stone, sand and glass particles are sieved out. Wood chips are then transported in containers to the power plant.  The chips are then unloaded to a reception area at the plant onto a hopper and conveyed to the grinder area.  After further cleaning from magnets, wind-sifting the rest of the dirt is removed. The material is then delivered to the hammer mill (15ton/hr) which beats it up into particles of no more than 4mm. This stream material is sieved and divided further before being transported to the dust collector. The static classifier removes about 10% of the material <800um.  Drying using pre-heated air is used to dry the material in the mill stage.

RTEmagicC gelderland NL - Coal  oil pulversied wood  demolition wood.jpg

Each mill operates at about 1.8 tonnes per hour, with a final product density of 200 to 240 kg/m3.  A metering system fed the powder into four separate burner injection lines, each capable of conveying 1.1 to 3.5 tonnes per hour.  Four special wood burners with a capacity of 20MWth each were mounted in the side of the boiler (two on each side) below the lowest rows of the existing 36 coal burners.  At present Electrabel is feeding the pulverized wood directly into the pulversied coal transport lines.  There is a reduction of fly ash as wood produces a lot less than coal.

There is some mixed biomass pellets used in co-firing for the Maasvlakte plant (see below).  The pellets are made from sewage sludge, waste wood and paper sludge available in the vicinity of the plant.  The pellets are blended with raw coal on the conveyor belts.  BioMass Nederland started in the beginning of 1998 with the production of pellets consisting of biomass (pruning), sewage sludge and paper sludge. The yearly production is estimated to be 150,000 tonnes of material with a higher heating value of about 16 MJ/kg. This amount of fuel will replace 30,000 tonnes of coal and thereby leading to an equivalent reduction in CO2 emissions.

RTEmagicC maasvlakte NL -pellets  paper orsewage sludge.jpg

Denmark:

Denmark is also progressive in co-combustion experiences and operation.  Straw is a popular feedstock due to the high yields and high cereal.  Feeding of animals was optimised through nutrition and researched a decrease in cattle has meant a reduction in the demand for straw.  Co-combustion represents a means to use this plentiful by-product.  In contemporary times the burning of straw in hot water boilers for farm heating became very popular and it is still done today.  The problems for implementing straw for electricity production included the relatively low density of straw, the requirement for handling and processing and the high salaries in Denmark.  The typical farmer has 50ha of straw producing crops, where each hectare yields 4 tonnes of straw.

Power Station Type of Combustion
 1 Heat power plant Studstrup  Direct co-combustion: separate feeding and combustion in combined coal/straw burners
 2 Heat Power Plant Ensted  indirect co-combustion: separate combustion with steam-side integration
 3 Heat power plant Avedore  Direct combustion in the same furnace
 4 CHP plant Grenaa  Fluid-bed. Mixed fuel.
 5 CHP plant Herning  Grate firing of biomass. Gas burner above.

 

Straw moisture must not exceed 30% and should be relatively evenly distributed as loads of very wet straw cause problems in handling equipement. Suppliers of straw are rewarded for dryer straw, therefore it is in their interest to store the straw for longer periods before the plant can receive it. Spring is the time for purchasing and contracting straw for the coming season and the average price is 3.4 €/GJ. In seasons with rainfall in the harvesting season, the rain leaches potassium and chlorine from the straw which is advantageous for burner operation.

Since there is no pulp production industry in Denmark, there is substantial potential for forestry residues.  Some higher quality products are already being supplied to power stations. There are some lower quality residues being used to make pallets and chipboards.  After a slow start, the collection of residues from Danish forests is now taking off at a considerable rate and in 2004, 50% of extracted forest products were used as biofuels. The Baltic countries were the first to export products such as wood chips, logwood and whole stems, at a reasonable price favourable enough to cover transportation costs.  Imports of chips from hardwood species from America is also see in Denmark.

The Avedore CHP co-firing plant (see below) in Copenhagen, Denmark, supplies a great deal of heat for the district heating network. The plant is based on the Parellel co-firing technique whereby the biomass, in this case straw and wood is combusted in a separate combustion chamber but the steam and heat produced is linked to the coal fired system.

RTEmagicC Avedor DK - natgas  coal  niomass  oil 02.jpg

Maintenance

Planned outages have been mainly due to maintenance of hammer mills and debalers. Both components are subject to severe wear and make change of wear parts or repair necessary. The wear parts in the debalers, i.e. fixed and rotating cutters are expensive and time-consuming to re-place. Therefore repair is performed on site by adding wear-resistant weld material to critical parts for every 2000 hours of operation. Down time is typically one working day. The frequency of change of hammers in the hammer mills is based on the amount of straw processed, typically once a week. The replacement is performed within 30 minutes. Co-firing of straw does not have any impact on the maintenance of the boiler and auxiliary systems.

Experience in Denmark: Studstrup Power Station (see below), unit 1 was converted to use straw in 1995 as part of a 2 year demonstration programme (now demolished).   The facility saw a fully commercial straw pre-processing plant which handled 20tonnes/hr and corresponded to 20% total energy input.  The burner system was modified.  Performance of the boiler was very positive for further co-firing, however, in 1998 fly ash from co-firing was not allowed to be used in the cement or concrete production so co-firing was stopped from this point.  Some years later the requirements for fly ash use for cement was revised and the 350 MWe Studstrup Power Station Unit 4 was converted to co-firing of straw on a 10% energy basis in the first quarter of 2002.  The coal is mainly imported from South Africa and Colombia.  Most of the straw comes from wheat but also barley, oats, hay and rape straw.

RTEmagicC Studstrup DK - coal  oil  biomass.jpg

Changes to the burner system were slight, they included: oil lance and flame scanner were relocated in order to clear the core of the burner for pneumatic straw feeding.  Straw-to-air ratio and straw-size distribution have been optimised to the opposed wall-firing giving a loss of ignition (LOI) in the bottom ash at almost the same level as when firing coal alone.  There are no problems regarding bottom ash, which is sold for brick production.  Measurements of LOI in fly ash show that co-firing of straw generally improves the carbon burn out.  In some cases char particulates from straw can be observed visually in the fly ahs. But this does not contribute significantly to the LOI.  The char particulates are broken down in the ash handling equipment and are not observed in the delivered fly ash.  NOx emissions at 10% co-firing was seen as the same or slightly reduced as coal alone firing.  The nitrogen content in straw varies depending on the fertiliser used and the climatic conditions.  Considering the introduction of potassium and chlorine into the combustion system for, the possibilities of corrosion, slagging or fouling are increased.  However, potassium chloride reacts with coal ash and sulphur to create potassium alumina-silcate, potassium sulphide and chlorine (released as a gas, therefore almost no chlorine is found in deposits).  And in general straw at 10% has a negligible impact on corrosion rates.  However, between 1996 and 1998 deposits were investigated on Strudstup 1 but this was handled by increased soot blowing.  At a straw share of 20%, some slagging problems occurred.  In Studstup Unit 4, deposit formation has not been studied yet but during the first 3 years of operation no fouling problems have been observed and increased soot blowing has not been necessary.

A lower content of sulphur than coal and a higher level of chlorine in straw means that flue gas chemistry is also changed.  These changes can be handled with problem in the flue gas desulphurisation plant.  High dust SCR catalyst deactivation is another possible issue for biomass co-firing.  However tests revealed there is no distinguishable difference for deactivation of HD catalyst exposure to flue gas from coal or from straw co-firing.  Observed deactivation is caused by ash poisoning and formation of ash surface layers.  Increased deactivation is related to the formation of sub-micron particles from potassium, therefore it is largest for coal with low ash or high sulphur content and high for straw with high potassium content.

The sale and use of fly ash is required for the successful implementation of co-firing.  Limits on the alkali content in fly ash had before restricted co-firing.  However, the revised European standard EN450-1 and a compliance programme in connection with the Danish concrete industry has meant straw/coal fly ash is now allowed.

In Studstrup Unit 1 tests were performed co-combusting miscanthus and triticale.  Tests showed that the straw processing plant and the boiler was capable of handling the fuels.  Some losses were observed, Loss of ignition in bottom ash and a higher energy consumption for pre-treatment of miscanthus.

More country based reports to follow.

Finland

 

Power Station Type of Combustion
1 Alholmens Kraft Oy, Pietarsaari Direct, CFB boiler
2 Etelä -Savon Energia Oy, Mikkeli Direct, CFB boiler
3 Forssa Energia Oy , Forssa Direct, BFB boiler
4 IPO WOOD Oy, Kiuruvesi Direct, grate-fired boiler
5 Joensuun Energia, Joensuu Direct, BFB boiler
6 Lahti Energia Oy, Kymijärvi Power Plant In-direct (gasification of biomass, product gas burned with fossil fuel in Benson type once through boiler)
7 Savon Voima Lämpö Oy, Iisalmi power plant Direct, BFB boiler
8 Järvi-Suomen Voima Oy, Savonlinna Direct, BFB boiler
9 Kokkolan Voima Oy, Kokkola Direct, BFB boiler
10 Jyväskylän energiantuotanto, Rauhalahti power plant, Jyväskylä Direct, BFB boiler
11 Fortum Power and Heat Oy, Kuusamo Direct, BFB boiler
12 Oriketo dh-plant, Turku Energia Oy, Turku Direct, BFB boiler
13 Jämsänkosken Voima Oy, Jämsänkoski Direct, BFB boiler
14 Vapo Oy , Kevätniemi sawmill, Lieksa Direct, BFB boiler

 

 Belgium

 

Power Station Type of Combustion
1 Ruien power plant units 3 & 4 Direct co-combustion + co-milling (olive cake)
2 Ruien power plant unit 5 Direct co-combustion + co-milling (olive cake) : wood dust + olive cake Indirect co-combustion: gasified wood chips
3 Langerlo power plant units 1 & 2 Direct co-combustion with co-milling
4 Rodenhuize power plant unit 4 Direct co-combustion with co-milling (olive cake) or separate milling (wood pellets)
5 Mol power plant Direct co-combustion + co-milling

 

Austria

 

Power Station Type of Combustion
1 Ebensee direct co-combustion in pulverised coal boiler
2 Frantschach direct co-combustion in CFB boiler
3 Lenzing direct co-combustion in CFB boiler
4 St. Andra power plant direct co-combustion in CFB boiler
5 Zeltweg power plant indirect co-combustion with pre-gasification

 

Sweden

 

Power Station Type of Combustion
1 Stora Enso Fors Mill Direct, CFB
2 Helsingborg ÖRESUNDSKRAFT AB Direct, PF
3 Linköping TEKNISKA VERKEN I LINKÖPING AB Direct, grate
4 Norrköping (Händelö) SYDKRAFT ÖST VÄRME AB Direct, CFB
5 Skellefteå SKELLEFTEÅ KRAFT AB Direct, BFB
6 Uppsala VATTENFALL AB Direct, PF
7 Örebro SYDKRAFT MÄLAR VÄRME AB Direct, CFB
8 Västerås MÄLARENERGI AB n.a.
9 Värtaverken Stockholm (FORTUM) Direct

 

Hungary

 

Power Station Type of Combustion
1 Bakonyi Power Plant Fluidised bed combustion, 2 boilers for co-firing
2 AES Borsod Power Plant pulverised combustion
3 AES Tiszapalkonya Power Plant n.a.
4 Vértesi  Power Plant  n.a.
5 Mátrai Power Plant n.a.

 

United Kingdom

 

Power Station Type of Combustion
1 Caledonian Paper (owner), Scotland direct, CFB
2 Slough Heat and Power direct, CFB
3 Kingsnorth direct, PF

4 Longannet

direct, PF
5 Drax direct, PF
6 Eggborough direct, PF
7 Ferrybridge direct, PF
8 Fiddlers Ferry direct, PF
9 Ratcliffe direct, PF
10 Rugeley direct, PF
11 Aberthaw (owner Innogy) direct, PF
12 Cockenzie direct, PF
13 Cottam direct, PF
14 Didcot (owner Innogy) direct, PF
15 Ironbridge direct, PF
16 Tilbury (owner Innogy) direct, PF

 

Germany

 

Power Station

Type of Combustion Using Sewage Sludge

1 Berrenrath Rheinbraun

fluidized bed

2 Boxberg III VEAG

dry-bottom

3 Braunsbedra EWAG

stoker

4 Buschhaus BKB

dry-bottom

5 Duisburg H. Stadtwerke

wet-bottom

6 Farge Bremen Preussen Elektra

dry-bottom

7 Franken II Bayernwerke

wet-bottom

8 Heilbronn EnBW

dry-bottom

9 Lausward Stadtw. Düsseld.

wet-bottom

10 Lünen Innovatherm

fluidized bed

11 Mumsdorf Mibrag

dry-bottom

12 Karlsruhe RDK EnBW

dry-bottom

13 Voerde STEAG

wet-bottom

14 Wahlheim Neckarwerke

wet-bottom

15 Weiher II SaarEnergie

wet-bottom

16 Weisweiler RWE

dry-bottom

 Using Biomass and Waste Wood

1 Afferde El.Werke Wesertal

fluidized bed

2 Berrenrath Rheinbraun

fluidized bed

3 Heilbronn EnBW

dry-bottom

4 Jänschwalde VEAG

dry-bottom

5 Lübbenau VEAG

dry-bottom

6 Moabit BEWAG

fluidized bed

7 Pforzheim Stadtwerke

fluidized bed

8 Schwandorf - Bayernwerke

dry-bottom

Using Waste Materials

1 Bremen Entsorg.-betrieb

 

2 Jänschwalde VEAG

dry-bottom

3 Leverkusen HKW Bayer AG

fluidized bed

4 Schwarze Pumpe VEAG

dry-bottom

5 Wolfsburg VW

wet-bottom

6 Berrenrath Rheinbraun

 

7 Hamm VEW Energie

wet-bottom

 

Italy

 

Power Station

Type of Combustion

1 Waste to Energy Brescia

Direct co-combustion (mass burn combustion)

2 Power Plant Sulcis #2 (in operation since 2006)

Direct co-combustion (CFB) 

3 Power Plant Fusina #4

Direct co-combustion: tangentially-fired, pulverised coal boiler

 

Spain

 

Power Station

Type of Combustion

1 Heat power plant La Pereda

Direct co-combustion: CFB