Co-firing of biomass. Lecture on 10 th October Matti Nieminen VTT Technical research centre of Finland Ltd

Transcription

1 Co-firing of biomass Lecture on 10 th October 2017 Matti Nieminen VTT Technical research centre of Finland Ltd

2 2 Content Why biomass co-firing? What is co-firing? Co-firing Biomass fuel characteristics Co-firing concepts PC boiler Direct co-firing in Finland Co-firing experiences outside Finland Indirect co-firing Separate boilers with common steam turbine Indirect co-firing based on gasification Indirect co-firing based on pyrolysis oil Summary

3 3 Why biomass co-firing? Reduction of fossil CO 2 emissions Low cost biomass available Biomass side-product (bark, wood waste, etc.) Biomass derived waste has to be incinerated Industrial sludges Difficulties to combust biomass as a single fuel Money.. (tax reductions, investment subsidies, etc.)

4 4 Possibilities to reduce CO 2 emissions in energy production

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8 8 CO-FIRING

9 9 What is co-firing? Combustion of two or more fuels together in a boiler Co-firing of biomass with fossil fuel (usually coal or peat) Co-firing of biomass with other biofuels or waste fractions In Finland very common practice Fluidised bed boiler enables co-firing very easily Co-firing more challenging to arrange in pulverised coal fired boilers Direct co-firing, indirect co-firing Indirect co-firing of biomass with oil or natural gas

10 10 Co-firing of biomass with coal Energy density of biomass low compared to coal Moisture content of biomass typically high Biomass will produce more flue gases (per produced energy) In practice, capacity of the boiler will be reduced when biomass cofiring is started Corrosion issues Ash quality will change

11 11 Towards lower CO 2 emissions and higher efficiencies with co-firing technology Fossil + bio co-firing High plant efficiency Fossil CO 2 emissions 0 1 %-pts eff. penalty Up to 50% CO 2 reduction Good plant efficiency Zero (=biogenic) CO 2 emissions Lowest OPEX* and CAPEX Higher OPEX* and CAPEX than without co-firing Highest OPEX* and CAPEX * operating costs without CO 2 allowances Boiler figures:

12 12 Direct co-firing of biomass in coal power plants Biomass co-firing in modern power plants with efficiencies up to 45 % is the most cost-effective biomass use for power generation. In the case of co-combustion of up to 5 % energy of biomass only minor changes in the fuel handling equipment are needed and the boiler output is not noticeably derated. For biomass exceeding ~10% share changes in mills, burners and dryers are needed. If not carefully designed, firing biomass fuels in an existing coal fired power plant involves risks of increased plant outages and possible interference in plant operation due to the differences in combustion characteristics of coal and biomass These are all manageable but that they require careful consideration of fuels, boiler operating conditions, and boiler design.

13 13 Biomass fuels - properties heating value: usually low compared to fossil fuels chemical composition: complex, several organic substances and compounds moisture content: high, can be more than 60 w-% density, particle size, and other characteristics affecting handling: low bulk density, large particle size, often difficult to remove from silos ash content, ash fusion properties, and chemical composition: low ash content, but ashes have low melting points due to different salts harmful components: large quantities of alkaline metals, chlorine, sometimes also heavy metals Torrefied biomass: a tailored biomass fuel for co-firing in PC boiler

14 14 Torrefaction The main idea is to modify biomass so that it becomes brittle and can be milled easily by coal mills.

15 15 A selection of torrefaction technologies

16 16 Chraracteristics of fuels from boiler design point of view

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19 19 Characteristics of agricultural residues Deposits in the furnace and on the superheater due to straw-coal co-firing in a PC-boiler

20 20 Different co-firing concepts

21 21 Co-firing concepts Pulverised fuel fired boiler Direct co-firing Biomass is combusted together with the main fuel (coal) Small percentage (few percent) can be mixed with coal, milled together and injected to the furnace with coal Larger share: Milled separately Milled biomass injected to coal powder pipelines after mills Large share of biomass usually: Milled separately Separate biomass burners

22 22 Direct co-firing of biomass with coal Pulverised fuel boiler Biomass Milling Biomass burner < 5 % Furnace Coal Milling Coal Burner

23 23 Co-firing of biomass with coal Fluidised bed boiler - Fuels can be mixed and fed to the furnace as a mix or using separate feeding lines - Robust technology enables efficient biomass co-firing

24 24 Direct biomass co-firing in Finland Practically all fluidised bed boilers use a fuel mixture instead of single fuel Some larger fluidised bed boilers use coal and biomass as a varying mixture Biomass typically forest residue, energy wood (small wood), bark, etc. One or several feeding systems depending on physical characteristics of the biomass

25 25 UPM Kaipola An industrial power plant with combined heat and power fluidized-pulverized boiler 104 MWth / 26 MWe A variety of different fuels can be used independently, these include sludge, bark and peat, as well as pulverized coal in the coal burners. Kaipola s plant generates the steam needed for paper drying and also supplies about 10% of the mill s annual electricity requirement. Boiler output 104 MW (80% by fluidized bed), supplier Kvaerner Pulping Electricity output 26 MW, Turbine supplier ABB Stal, Sweden Main fuels Other fuels sludge, bark and peat coal ( max 50% ) can be burned in burner or crushed in fluidized bed Support fuel heavy oil

26 26 Rauhalahti CHP plant in Jyväskylä Was originally designed for pulverised peat and coal. Fluidised bed boiler (295 MW th ) was installed 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 is used is used through dedicated burners. Wood fuel feeding system was modified in The share of forest fuels, forest chips and stumps has been increasing significantly.

27 27 Possibility to utilise 100% biomass in co-fired CFB Alholmens Kraft, Pietarsaari, Finland CFB technology: 550MW th 194kg/s, 165bar, 545 C Uses 40 % peat, 20 % coal, 30 % of biomass (forest residues, industrial wood and bark etc.) and 10 % SRF. The design of the plant allows great fuel flexibility, the boiler is able to combust all mixtures from 100 % biomass to 100 % coal.

28 28 Jyväskylän Energia, Keljonlahti CFB (CHP) Steam 458 MW th 164/43 bar 560/560 C Output 200 MW e / 240 MW DH Fuels Peat Wood Some coal Start-up 10/2010

29 29 PC boiler co-firing example: Helen, Finland Hanasaari CHP-plant: coal fired plant producing electric power (220 MW) and district heat (445 MW) to the city of Helsinki co-firing experiments with wood pellets (5 to 10 % share) during started using pellets constantly from late 2014 with 5-7 % share (first at their other plant, Salmisaari and then at Hanasaari after permits) also R&D work conducted on the possible utilisation of torrefied biomass biomass share reaching possibly up to 40 % in the future

30 30 PC boiler co-firing example with sawdust Naantali 315 MW th CHP-plant: co-firing of sawdust and coal from early 2000 s coal and sawdust are blended in the coal yard and the mixture is fed into the boiler through coal mills sawdust s moisture (up to 65 %), do not cause any problems, as the wood fraction in fuel blend won t exceed 5 % on energy basis milling capacity limits wood fraction in fuel blend also some experiments with straw co-firing (see figure below)

31 31 Co-firing experiences outside Finland

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37 37 Co-firing example from Denmark There is a long experience of co-firing at 350 MW e Studstrup Power Station Unit 4: The use of a separate straw feeding system is essential to warrant successful straw-coal co-firing. After the straw bales are processed the pulverized straw is fed pneumatically onward and fired through the centre-pipe of the coal burners. The maximum straw capacity at full boiler load is 20 ton/h which corresponds to a straw share of 10% on energy basis Pneumatic feeding system of straw at Studstrup power plant, courtesy of Dong Energy 37

38 38 Source: The handbook of biomass combustion and co-firing

39 39 Co-firing of wheat straw in Shandong, China Straw is crushed and milled Pneumatic feeding Separate burners for wheat straw Share of wheat straw: 0 20 % (of energy) Unloading and crushing Pneumatic feeding

40 40 The World s largest CFB in operation ŁAGISZA Południowy Koncern Energetyczny SA (PKE) Poland Steam Power 930 MW th 370/307 kg/s 275/55 bar 565/580 C 460 MW e Fuels Coal from 10 different mines Slurry (washery reject) Wet 0 30% Dried 0 50% Biomass 0 10% Start-up 2008 Source: Pasi Vainikka/VTT

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42 42 Biomass co-firing experiencies in USA

43 43 INDIRECT CO-FIRING BASED ON SEPARATE BOILERS WITH ONE STEAM TURBINE

44 44 AVEDØRE PLANT Two boilers and two gas turbines with one steam turbine plant The European Bioenergy Networks (EUBIONET)

45 45 Source: The handbook of biomass combustion and co-firing

46 46 INDIRECT CO-FIRING BASED ON GASIFICATION

47 47 C A R B O N Oil Coal Biomass Waste/SRF Gasification - combustible product gas G A S C L E A N I N G Syngas Energy (Fuel gas) Chemical industry IGCC co-firing gas fired boilers O 2 A i r S t e a m kilns

48 48 Clean biomass Indirect co-firing with coal NO GAS CLEANING NEEDED (CLEAN BIOMASS) Gasifier Fuel Bed material CFB or BFB Coal-fired boiler Condensing power plant / CHP plant Air Bottom ash Example Lahti I gasifier and Vaskiluoto

49 49 CFB BIOMASS GASIFIER 50 MW FUEL,

50 10/10/ Proven reference: Lahti Energia (Kymijärvi power plant), Finland -in operation since no commissioning problems -gasifier availability > 95 % -boiler emissions decreased Main boiler, 360 MW th Gasifier feed preparation CFB gasifier of 60MW

51 51 Gasification + Gas cleaning + Gas fired boiler + Flue gas cleaning Gas boiler Flue gas cleaning Gasifier Gas cooling Gas cleaning Bag house, Ca(OH) 2 + activated carbon Steam turbine SRF High pressure steam Natural gas/ oil Electricity, process steam

52 52 Kymijärvi WtE power plant, KYVO II, Lahti Energia Oy, Finland Fuel: SRF, t/a Two circulating fluidised bed gasifiers (2 x 80 MWth), both equipped with gas cooling and gas filtration Gas is combusted in a 160 MW th gas fired boiler as a single fuel (540 o C/120 bar; 50 MW e and 90 MW dh ) Source: Lahti Energia Oy Commissioned in 2012 Gasifier and boiler supplier Valmet (former Metso Power), Finland video

53 53 In-direct co-firing of biomass in a PC boiler Example: Vaskiluodon Voima power plant in Vaasa, Finland Largest biomass fired gasifier in the world with fuel input of 140 MW Biomass is mainly forest residues but there is a possibilty to utilise also some agrobiomass The plant produces electric power (230 MW) and district heat (175 MW) to the Vaasa city Possibility to replace % of the coal previously used at the plant (coal consumption t/a) Operation started 2013

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55 55 Vaskiluodon Voima, Vaasa

56 56 Co-firing of biomass (and waste) based on gasification - in operation since no commissioning problems - high fuel operating flexibilityhours - gasifier availability > 95 % - boiler emissions decreased - payback time ca. 8 years Main boiler 360 MW th Gasifier feed preparation CFB gasifier of 60MW CFB gasification plants one gasifier (60 MW, no gas cleaning) in Lahti followed by direct gas co-firing in PC boiler two new gasifiers (2x80 MW) at Lahti waste-to-energy plant (supplier: Metso) one large gasifier (140 MW) in Vaasa (supplier: Metso) lime kiln gasifier (48 MW) at Joutseno (supplier Andritz) lime kiln gasifier (12 MW) at Varkaus was returned to air-blown operation mode after succesfull O 2 -blown test campaigns for Neste Oil and Stora Enso (Foster Wheeler) one lime kiln gasifier (87 MW) in Äänekoski at Metsä Fibre site

57 57 Biomass rich in harmful impurities/waste derived fuels (SRF, high quality RDF) Wheat straw: rich in potassium & chlorine Demolition wood waste: heavy metals SRF/RDF : heavy metals, chlorine Plastic waste with some PVC: chlorine Sewage sludge: heavy metals Emissions Boiler corrosion Fouling Gasification + Gas Cleaning + Co-firing

58 58 High efficiency WtE technology based on gasification DRY CLEANING AND CHLORINE REMOVAL Filter -Coal/oil-fired boiler Fuel Bed material CFB or BFB 450 C Ash treatment -Condensing power plant / CHP plant -Ovens/kilns -HRSG of gas-fired combined cycle plant Air Bottom ash Ca(OH) 2 Fly ash

59 59 Gasification & gas cleaning example: Fuel Contaminants CFB gasification (70 % RDF/30% wood) Ca Hg Sn Sb As Cd Pb V Mn Co Ni Cu Zn Mo Cr Si Mg ppm-wt (d.b.) < Cl 4700 SRF+wood waste Air blown CFB gasification & dry gas cleaning at 395 o C Vapour phase Na, ppm(m) 0,0 Cleaned gas K, ppm(m) 0,0 Cl, ppm(m) 109,0 Al, ppm(m) 0,0 Ca, ppm (m) 0,0 Hg, ppm(m) 0,025 Sn, ppm(m) 0,0 Sb, ppm(m) 0,0 As, ppm(m) 0,0 Cd, ppm(m) 0,0 Pb, ppm(m) 0,024 V, ppm(m) 0,0 Mn, ppm(m) 0,0 Co, ppm(m) 0,0 Ni, ppm(m) 0,0 Cu, ppm(m) 0,11 Zn, ppm(m) 0,51 Mo, ppm(m) 0,0 Cr, ppm(m) 0,0 Si, ppm(m) 0,0 Mg, ppm(m) 0,0

60 60 Gasification and gas cleaning enables high efficiency utilisation of biomass rich in alkalimetals and/or chlorine - Harmful impurities are removed in gas cleaning section - Cleaned gas does not contain ash - Most of the chlorine removed => Minimized risk of corrosion or fouling CHP plant: SRF/RDF to power % Condensing power plant: SRF to power %

61 61 Gas cleaning: gas cooling followed by filtration developed at VTT since late 1990 s Bed material/ Ca-based additive Gas cooler Coal burners Fuel feeding Sorbent Filter Gas burner Clean gas combustion - no corrosion - low emissions - no dioxins

62 62 Essent Energie, the Netherlands Amer powerplant MWe MWth (district heating) Input coal 1,5 Mt/y Electricity efficiency 41,5% Overall efficiency 60% Low-NO x -burners Electrostatic fly ash catchers Wet desulphurization of flue gases Re-use of side-products 100% Emissionrequirements (at 6% O 2 ): BEES NO x 400 mg/nm 3 SO mg/nm 3 Dust 20 mg/nm 3

63 63 Wood gasifier 1 wood discharge building 5 silo fly gas elevator woodtransport silo wood storage silo bottom ash gasifier building woodgas blow off pipe Amer powerplant 9

64 64 Source: The handbook of biomass combustion and co-firing

65 65 Source: The handbook of biomass combustion and co-firing

66 66 I INDIRECT CO-FIRING BASED ON USE OF PYROLYSIS OIL

67 67 Liquid Bioenergy Carrier via Fast Pyrolysis Fast pyrolysis is a rapid (1-2 s) thermal (about 500 C) process done under inert conditions to convert solid biomass into liquid, gas and char fractions The produced liquid ( pyrolysis oil or bio-oil ) is a complex mixture of numerous different compounds. It also has low ph and it contains water. The heating value of pyrolysis oil is about half of conventional fuel oils The produced oil can be used as a substitute for fussil oils like HFO in many industrial processess VTT has developed world-class expertise in the production and analytics of biomass based pyrolysis oils

68 68 Integrated Pyrolysis VTT s Patented Technology Fluid bed boiler Heat and Power Flue gases Fast pyrolysis Boiler fuel Sand + char Pyrolysis fuel Bio oil Hot sand

69 69 Fortum Joensuu: an Integrated Bio-Oil Demonstration Plant Bio-oil capacity 30 MW Annual production t, 210 GWh Start-up 2013 Feedstock Forest residues, sawdust Reactor and pyrolysis oil recovery inside the boiler building Fuel receiving, drying and crushing Bio-oil tanks Source:

70 70 Summary CO2 emissions can be reduced efficiently by biomass co-firing Co-firing enables high efficiency energy production from biomass Challenges related to combustion of biomass are usually milder in co-firing (compared to 100% biomass firing) Co-firing can be retrofitted to existing coal fired power plant High share of biomass co-firing may cause fouling and/or corrosion In large scale logistics may cause challenges Co-firing may have negative impact on ash quality

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72 72 Thank you for your attention!