Experiences of biomass co-firing in Finland

Experiences 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 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 boilers

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


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 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 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 byFortum 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.

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


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

Receivingstation

Magnetic-roll

Crusher forbiomass

RI-JET

RI-JET

RI-BIO

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.


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 softeningtendency, chlorine content, calorific value, required residence time in thefurnace, ...)adequate availability of the biofuel(s) at a reasonable, cost-effectivedistanceeffect on slagging, fouling, life-timeeffect on deposit formation tendency on heat transfer surfaceseffect on air and flue gas flow rates that may increaseeffect on emissions and efficiencycofiring probably decreases maximum boiler outputmilling and air/fuel feeding capacities may limit biofuel fraction in cofiringoptimum design for any certain power plant is generally site-specific andmay require a lot of engineering and designoverall technical performance

Cofiring examples from Finland


Naantali 315 MWth boiler in Finland:– co-firing of sawdust and coal in one of the three PF-boilers– The power plant produces 19 bar and 5 bar steam to steam consumers and DH for the city

of Turku– Cofiring boiler is tangentially fired, Sulzer once-through boiler– Modern low-NOx burners (IVO RI-JET)– coal and sawdust are mixed by a bulldozer in the coal yard and the mixture is fed into the

boiler through the roller coal mills (Loesche)– Also refinery gas is used, oil in start-up and as supporting fuel– sawdust’s moisture, up to 65 %, do not cause any problems, as the wood fraction in fuel

blend won’t exceed 4 % on energy basis– milling capacity limits wood fraction in fuel blend

Blending of coal andsawdust in the coal yard ofNaantali power plant.


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

Saw dust + coal into same mill


Oy Alholmens Kraft Ab, Pietarsaari,Finland

Energy Globe 2002 Stig Nickull

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


Alholmens Kraft: CFB Technology

Alholmens Kraft,Pietarsaari, Finland

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

Fuels Wood, peat, coalStart-up 2001

• The design of the plant allows great fuelflexibility, the boiler is able to burn all mixturesof wood and coal from 100 % wood to 100 %coal.• Consumes a truck load of peat in 7 minutes


Utilisation of Fuels

Boiler

Annual consumption of fuels 3,5 TWhBiomass

45 %

Peat45 %

Heavy fuel oiland coal10 %

Production 560 GWh Heat1300 GWh Electricity

CFB Technology


Alholmens 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 points

Energy Globe 2002 Stig Nickull


The power plant generates electrical power, process steam for a paper mill and districtheat 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 ofbiomass fuels was started.

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

Wood fuel feeding system was modified in 2001.

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

Rauhalahti power plant in Jyväskylä


The plant generates electricalpower (20 MW) and districtheat (50 MW).

The main boiler is 72 MWth

BFB.

The main fuels are currentlypeat, forest residues, by-products from forest industryand reed canary grass.

Nowadays there is a separatefeeding system for reed canarygrass.


Vaskiluodon Voima Oy, Seinäjoki power plant

The plant generates electricalpower (125 MW) and district heat(100 MW).

The main boiler is 300 MWth CFB.

The main fuels are currently peat,forest residues and reed canarygrass.

There is no need for separatesulphur and NOx removal (when peatis used).


Kymijärvi power plant in Lahti

Kymijärvi power plant hasoperated successfully biomassand waste derived fuel firedgasifier from the beginning of1998.

The PC boiler is a Benson-type once-through boiler andthe plant produces electricpower (167 MW) and districtheat (240 MW) to the Lahticity.

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

Bottomash

Gasifier

Coal

540 °C/170 bar

Processing

Biomas

Fly ash

Pulverized coal flames

Gas flame

Natural Gas

50 MW

300 GWh/a -15 % fuel input

1850 GWh/a -80 %

350 MW

100 GWh/a -5 %

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

CO 2 Reduction -10 %


Additional 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)

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

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

Commissioning in the end of 1997

Investment 11.4 M€ (EU Thermie 3 M€)

Documents

Experiences of biomass co-firing in Finland