Biomass

Experiences of biomass co-firing in FinlandExperiences of biomass co firing in Finland

Heikki OravainenVTT Technical Research Centre of Finland

IEA Biomass Combustion and CofiringWorkshop on 21 October 2008 in The Netherlands

VTT TECHNICAL RESEARCH CENTRE OF FINLAND2

Cofiring of biofuel with coal

� The basic idea is the reduction of CO2 emissions

� The investments when introducing biofuel to existing coal boilersremain small compared to a new boiler using only biofuelsremain small compared to a new boiler using only biofuels

� The amount of available biomass is locally restricted and withseparate energy production from biomass, the efficiency for energyproduction is usually lower than with large coal boilersp y g

� There can be changes in the availability of biofuels and with cofiring itis possible to reduce the need for storage of biofuels

� In cofiring, the choice of fuel can be decided on the basis of theprevailing price level more flexibly than when using a single fuel

� The emissions of CO2, SO2 and NOx can be reduced� The emissions of CO2, SO2 and NOx can be reduced


Innovative concept for direct co-firing

� Co-firing biofuel in existing pulverised coal fired boilers by using burnertechnology sets high demands for biofuel grinding technology.

� The critical factor is the particle size to ensure proper combustion� The critical factor is the particle size to ensure proper combustionefficiency and stable flame. The maximum particle size depends on boilerconditions like particle residence time and furnace temperaturedistribution. There are several opinions on maximum particle size varyingfrom one to a few millimetersfrom one to a few millimeters.

� To grind biomass sufficiently not only simple crushing process but alsovery complex and expensive micro milling system is needed.

� In addition, micro milling leads to very strict safety precautions becauseof dust explosion risk and will further increase the costs.


Innovative concept for direct co-firing

� According to ÅF-ENPRIMA Engineering’s and Fortum’s experience fromfull-scale co-firing tests, the latter of the grinding stages is notneeded, if suitable burners like the one designed and patented byF t dFortum are used.

� In such case, particle size distribution of biomass can be as large as:100 % < 8 mm and 30-40 % < 1 mm.

� Investment costs of 50 MW biofuel pretreatment (milling), feeding andburning devices are in the range of 800 000 € to 1,6 milj. € dependingon the moisture content of the fuel.o o u o o u

� Investment costs are lowest for dry wood pellets having high energydensity. Costs are increasing when wet wood material; bark, saw dust,logging residue etc are utilised to substitute coallogging residue etc. are utilised to substitute coal.


ÅF-Enprima (former Fortum) Engineering’s co-firing concept for direct co-firing of biomass and coalconcept for direct co firing of biomass and coal

Savolainen, K., Nyberg, K. and Dernjatin, P., Co-firingbiomass in the pulverised fuel boiler. BIOENERGY2003,International Nordic Bioenergy Conference, Jyväskylä,Finland, From 2nd to 5th September 2003.

Receivingstation

Magnetic-rollroll

Crusher for biomass

RI-JET

RI JET

RI-BIO

RI-JET


Cofiring of biofuel with coal

Several details and factors should be considered before modifyingan existing boiler for cofiring:

characteristics of the biofuel (particle size ash melting and softening� characteristics of the biofuel (particle size, ash melting and softeningtendency, chlorine content, calorific value, required residence time in thefurnace, ...)

� adequate availability of the biofuel(s) at a reasonable, cost-effectivedistancedistance

� effect on slagging, fouling, life-time� effect on deposit formation tendency on heat transfer surfaces� effect on air and flue gas flow rates that may increase� effect on emissions and efficiency� effect on emissions and efficiency� cofiring probably decreases maximum boiler output� milling and air/fuel feeding capacities may limit biofuel fraction in cofiring� optimum design for any certain power plant is generally site-specific and

may require a lot of engineering and designmay require a lot of engineering and design� overall technical performance

Cofiring examples from Finland


� Naantali 315 MWth plant in in Finland:p– co-firing of sawdust and coal– coal and sawdust are blended in the coal yard and the mixture is fed into the

boiler through coal millssawdust’s moisture up to 65 % do not cause any problems as the wood fraction– sawdust s moisture, up to 65 %, do not cause any problems, as the wood fractionin fuel blend won’t exceed 4 % on energy basis

– milling capacity limits wood fraction in fuel blend

Blending of coal and sawdust in the coal yard of Naantali power plantNaantali power plant.


Cofiring of wood in existing pulverised coal boilers,Vaskiluoto Power Station, Vaasa

Saw dust + coal into same mill


O Alholmens Kraft Ab Pietarsaari

Fluidised Bed Combustion* BIOFUELS: Bark, wood chips, logging residue

Oy Alholmens Kraft Ab, Pietarsaari, Finland

p gg g* PEAT AND COAL

Energy Globe 2002 Stig Nickull


Alholmens Kraft: CFB Technology• The design of the plant allows great fuel flexibility, the boiler is able to burn all mixtures f d d l f 100 % d t 100 %

Alh l K ft

of wood and coal from 100 % wood to 100 % coal.• Consumes a truck load of peat in 7 minutes

Alholmens Kraft,Pietarsaari, Finland

Steam 550 MWth194/179 kg/s194/179 kg/s165/40 bar545/545 °C

Fuels Wood, peat, coalStart-up 2001Start up 2001


CFB Technology

Utilisation of Fuels

Annual consumption of fuels 3,5 TWhBiomass

Boiler

Biomass45 %

Peat45 %

Heavy fuel oiland coal10 %

Production 560 GWh HeatProduction 560 GWh Heat1300 GWh Electricity


Alholmens Kraft: Fuel FeedingAlholmens Kraft: Fuel Feeding

• Biofuel consumption 1000 m3/h

• Coal consumption 110 m3/h

• Four independent feeding lines

• Common feeding lines for both fuels

• 11 feeding pointsg p

Energy Globe 2002 Stig Nickull


Rauhalahti power plant in Jyväskylä� The power plant generates electrical power, process steam for a paper mill and district heat for the city of Jyväskylä.

� Rauhalahti power plant was originally designed for pulverised peat and coal.

� It was converted to bubbling fluidised bed boiler (295 MWth) in 1993 and the use of biomass fuels was started.

� The main fuels are currently peat, by-products from sawmills and forest residues (wood chips stumps) Also some coal and reed canary grass are usedchips, stumps). Also some coal and reed canary grass are used.

� Wood fuel feeding system was modified in 2001.

Æ The share of forest fuels, forest chips and stumps has been increasing significantly.


� The plant generates electrical power (20 MW) and district heat (50 MW)heat (50 MW).

� The main boiler is 72 MWth

BFB.

� The main fuels are currently peat, forest residues, by-products from forest industry

d dand reed canary grass.

� Nowadays there is a separate feeding system for reed canary grass.


Vaskiluodon Voima Oy, Seinäjoki power plant

� The plant generates electrical power (125 MW) and district heat (100 MW)(100 MW).

� The main boiler is 300 MWth CFB.

� The main fuels are currently peat, forest residues and reed canary grass.

� There is no need for separate sulphur and NOx removal (when peat is used).


Kymijärvi power plant in Lahti

� Kymijärvi power plant has operated successfully biomass and waste derived fuel fired

540 °C/170 bar350 MW

CO 2 Reduction -and waste derived fuel fired gasifier from the beginning of 1998.

� The PC boiler is a Benson-

Processing

Biomas

Pulverized coal flames50 MW

300 GWh/a -15 % fuel input

Power* 600 GWh/aDistrict Heat* 1000 GWh/a

210 %

� The PC boiler is a Bensontype once-through boiler and the plant produces electric power (167 MW) and district

Gasifier

Coal Fly ash

Gas flame

50 MW

1850 GWh/a -80 %power (167 MW) and district heat (240 MW) to the Lahti city.

� The boiler uses 1850 GWh/a

Bottomash

Coal y

Natural Gas1850 GWh/a -80 %

100 GWh/a -5 %

� The boiler uses 1850 GWh/a (270.000 tons/a) of coal and about 100 GWh/a natural gas.


Additional information about the Lahti gasifierAdditional information about the Lahti gasifier

Plant Kymijärvi CHP plant, Lahti, Finland

Gasifier manufacturer Foster Wheeler Energia Oy, Finland

Type of technology atmospheric pressure CFB gasifier, no gas clenaing, gas co-fired in PC boiler

Capacity of the gasifier 60 MWth ( 40-90 MWth depending on fuel)Capacity of the gasifier 60 MWth ( 40 90 MWth depending on fuel)

Annual availability of the gasifier 96.1...99.3 % (1998-2001)

Feedstocks Wood chips, wood waste, saw dust, shavings, demolition wood, SRF (Solid Recovered Fuel), plastic waste

Commissioning in the end of 1997g

Investment 11.4 M€ (EU Thermie 3 M€)

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Biomass