Emissions from wood-fuelled equipment Senior research scientist Heikki Oravainen Technical Research Centre of Finland
VTT IN BRIEF 2007 9 Key Customer Sectors: Biotechnology, pharmaceutical and food industries Electronics Energy ICT Real estate and construction Machines and vehicles Transport and logistics Forest industry Process industry and environment Focus areas of research: Bio and chemistry processes ICT Technology in the community Microtechnologies and electronics Applied materials Industrial systems management Energy 2
VTT STAFF AND LOCATIONS STAFF Espoo 1 891 Oulu 383 Tampere 301 Jyväskylä 129 Turku 36 Lappeenranta 14 Other locations 26 Total 2 780 31.12.2006 Sweden Tampere Turku Oulu Raahe Kajaani Nurmijärvi Helsinki Espoo Estonia Kuopio Jyväskylä 3 Lappeenranta Russia
Carbon content of different fuels 100 90 80 C + O2 CO2 + energy % of dry matter 70 60 50 40 30 20 10 0 Anthracite Coal Brown coal Peat Wood Straw 4
Hydrogen content of different fuels 7 6 H 2 + ½O 2 H 2 O + energy % of dry matter 5 4 3 2 1 0 Anthracite Polish bituminous coal Hungarian brown coal Peat Wood Wheat straw 5
2,5 Nitrogen content of different fuels 2 N + O NO x % of dry matter 1,5 1 0,5 0 Anthracite Polish bituminous coal Hungarian brown coal Peat Wood Wheat straw 6
3,5 Sulphur content of different fuels 3 S + O 2 SO 2 % of dry matter 2,5 2 1,5 1 0,5 0 Anthracite Polish bituminous coal Hungarian brown coal Peat Wood Wheat straw 7
35 30 Ash content of different fuels % of dry matter 25 20 15 10 5 0 Anthracite Polish bituminous coal Hungarian brown coal Peat Wood Wheat straw 8
CO 2 emission factors of different fuels 450 400 350 Zero emission kgco2/mwh 300 250 200 150 100 50 0 Coke Peat Coal Heavy fuel oil Light fuel oil Natural gas Biomass fuels 9
Carbon balance over a country Atmosphere Forest grow Decomposition Combustion Decomposition Export Forests Cuttings Country border Woody products and their use including combustion Import 10
WOOD Ash Ash 0.4 1.2% Proximate analysis Moisture Moisture 8 65 % 8 65 % Carbon residue 11 16% Volatiles 84 88 % Carbon (C) 48-52% Ash Oxygen 2(O) 38-42% Hydrogen (H) Nitrogen (N) 2 Ultimate analysis Calorific value of dry matter ~ 19 MJ/kg 11 10/2003
Different woods Basically all wood species have quite similar combustion properties Moisture content of wood is the most important factor Moisture content can vary from 8% of pellets to 65% of wet bark Combustion techniques are different depending on moisture content, but woods with all moistures can be burned with low emissions and efficiently Combustion of very moist wood is more demanding and investment costs for appliances higher Other important parameter is particle size of wood and it s distribution Wood pellets having even quality are easy to burn, forest chips are more difficult Alkaline metals (especially potassium (K) can cause slagging and fouling problems in power plant boilers, but co-firing with sulphur containing fuel lowers problems 12
Modern wood burning technology Very low CO and hydrocarbon emissions CO 2 -neutral Very low sulphur dioxide (SO 2 ) emissions NO x -emission limits in some countries mean that something has to be done to lower NO x -emissions. NH 3 -injection etc. Particulate emissions are reduced by Cyclone separators (-- 5 MW) Fabric filters (in some countries) Electrostatic precipitators (5 MW - ) 13
Modern wood burning technology Even fuel feeding and automatic combustion control are key factors Combustion is usually optimised based on O 2 -measurement in flue gases Wet wood needs adiabatic combustion, which means that combustion is done in a well insulated combustion chamber before flue gas cooling NO x -emissions can be lowered by staged combustion and secondary measures like NH 3 -injection etc. Particulate emissions are reduced by Cyclone separators (-- 5 MW) Fabric filters (in some countries) Electrostatic precipitators (5 MW - ) In Scandinavia plants run normally unmanned and they can be remote controlled over internet 14
Flue gas condensation option If wet wood fuels (sawdust, bark, forest chips, ) are burned, flue gases contain a lot of water vapour Many plants have flue gas condensation units which have several advantages: By condensing water vapour of flue gases, the energy of water vaporisation is gained back efficiency can be over 100% From the same amount of fuel more heat output is gained Reduction in SO 2, NO x and particulate emissions 15
Emission standards Emission standards and other requirements vary from country to country CO, NO x, SO 2 and particulates are normally controlled Requirements for efficiency are set Limits can be also for noise and for visual water vapour as in Austria near ski resorts Smaller units are tested in laboratory (< 300 kw) using European standards It is now custom that efficiency requirement is 90% to get subsidies for investment Particulate emission limits will be lower in the future (fear of fine particles) Large plants have set requirements which have to be proved by official, standardised measurements before start-up the plant 16
Wood pellet heating station in Finland Fuel silo for wood pellets Ash container 17
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