The operational economy of cofired biomass boilers in CHP plants

Transcription

1 The operational economy of cofired biomass boilers in CHP plants European Biomass CHP in Practice March 9th 10th 2006 Fernwärme Wien, Vienna Janne Kärki VTT Technical Research Centre of Finland P.O.Box 1603, FIN Jyväskylä FINLAND Tel , 1

2 Primary energy sources in electricity production in Finland 2004 Nuclear power 25.1% Indigenous energy sources Wind power 0.1% Waste 1.1 % Peat 7.5% Coal 18.3% Indigenous energy sources 37.2% Solid biofuels 11.6 % Hydro power 16.9% Oil 2.1% Natural gas 11.6% Net electricity import 5.7% Source: Energy Statistics 2004 In 2004 the total electricity production was 86.8 TWh 2

3 Use of forest chips in Finland Rovaniemi Oulu Use, m over Kokkola Pietarsaari Oulu NivalaKajaani Vaasa Joensuu Kaskinen Ilomantsi Joensuu Jyväskylä Tampere Mikkeli Turku Jyväskylä Jämsänkoski Kitee Jämsä Pori Mikkeli Tampere MäntyharjuRautjärvi Rauma Valkeakoski Kuusankoski Forssa Iitti Turku Riihimäki Anjalankoski Porvoo Tammisaari Source: Wood Energy Technology Programme 3

4 Traditional wood based fuels Recent new biomass fuels: stumps and agrobiomass New wood based fuels 4

5 Cofiring of different fuels in Finland: Cofiring of coal and peat with various types of biomass fuels is widely used in large-scale electricity and heat production in Finland The mixture of biomass and peat is very typical fuel in Finland Energy production based merely on biomass might be hampered by limitations in the supply and/or quality of the biomass. Biomass might not meet the total fuel demand in a cost-efficient way Fuel 2 Fuel 4 Fuel 1 Fuel 3 5

6 Cofiring of different fuels in Finland: Fluidised Bed Combustion (FBC) technology has become the dominant technology in larger CHP plants FBC technology has many advantages in combustion of wet and inhomogeneous biomass (e.g. high combustion efficiency) 550MW th 194kg/s, 165bar, 545 C World s largest biofuelled boiler applying CFB technology: Operates with anything from 100 % coal to 100 % biofuel Consumes a truck load of peat in 7 minutes 30,000 truck deliveries annually Furnace measures 8.5 m by 24 m and 40 m in height 6

7 New fuels increase the challenges in multifuel operation Cofiring biomass, waste wood and recycled fuels poses many challenges to power plant operators which might have a great influence on the total economy of the plant. Variable costs of a biofuel-fired boiler depend not only on the procurement costs of the fuels, but also on the the total operability of the boiler. It is not necessarily economical to use the cheapest fuel available, if the effects on the boiler operation are significant. Poor usability of the fuel mainly results from problems in the fuel feed, unstable combustion process or harmful behaviour of the ashes. 7

8 Fluidised bed boilers: problems in cofiring challenging fuels Deposit formation on heat transfer surfaces Bed material agglomeration High temperature corrosion Disturbances in combustion process Operation of the boiler auxiliary equipment (e.g. flue gas fans) Increase of operational and maintenance costs (shut-down, furnace cleanning) Reduction of boiler efficiency Negative influence on boiler lifetime 8

9 Fluidised bed boilers: problems in cofiring challenging fuels Main causes of unscheduled shut-downs are due to fuel related problems. Typical annual maintenance costs for a large (>100 MW th ) fluidised bed boiler are in the range of k /a and for smaller boilers (<100 MW th ) in the range of k /a. Maintenance costs include costs of overhaul, repairs and material. Unavailability factors from 7 different modernised fluidised bed boilers in the size range of MW th. Source: Muoniovaara, Kvaerner Power Oy,

10 Fuel and operation optimization a cost analysis The energy and emission markets have significant effect on power plant s economy. The CO 2 -emission trading has totally changed the cost effects of easily controllable peat and coal in Finland. In some cases it might be profitable not to produce anything, buy the substituting power from the markets and sell the emission allowances. Many plant owners have increased the share of biomass which means that the fuel prices have also increased. In optimising the overall economics of the boiler one has to take into account: output of the plant fuel costs including taxes and subsidies boiler operational costs costs from emissions 10

11 Case-study: 130 MW th multifuel-boiler Basic data BFB-boiler, MW 130 Fuel input, GWh/a 590 Heat output, GWh/a 375 Electricity output, GWh/a 117 Process efficiency, % 79 Boiler efficiency, % 90 CO 2 -emission limit (tn/year) Basic operation cost data Peat procurement cost, /MWh 8 Chips and sawdust (e2) procurement cost, /MWh 12 Bark (e2) procurement cost, /MWh 12 Logginng residue chips (e1) procurement cost, /MWh 12 CO 2 -emission allowance, /tn 25 Subsidy for biomass electricity, e1, /MWh 6,9 Subsidy for biomass electricity, e2, /MWh 4,2 Heat production tax for peat, /MWh 0,0 Extra operation cost factors refinement of the bed, renewal of the tubes, /m 200 cleaning of the superheaters, costs of one sootblowing cycle, 150 shut-down, summer /2 days shut-down, winter /2 days losses during operation, /MWh 25 11

12 14 Case-study: 130 MW th multifuel-boiler Scenario with annual average of 40 % peat and 60 % biomass Heat production tax Fuel Subsidy for biomass electricity Total costs ,9 8,9 9,1 10,1 11,5 11,9 12,0 11,8 11,6 11,3 10,6 10,0 10,1 11,0 Costs, /MWh Annual average Month ave + CO2 (25 /tn) 12

13 Case-study: 130 MW th multifuel-boiler Fuel costs Extra operation costs CO2 emission costs/income Total costs Annual total costs, % 20 % 40 % 60 % 100 % Case / Share of Peat vs. Biomass in the Fuel Blend 13

14 Case-study: 130 MW th multifuel-boiler The effect of CO 2 allowance price on total operation costs /tn 25 /tn 20 /tn 15 /tn 10 /tn Annual total costs, % 20 % 40 % 60 % 80 % 100 % Case / Share of Peat vs. Biomass in the Fuel Blend 14

15 Source: 15

16 Conclusions Cofiring common fossil fuels with solid biomass and recycled fuels poses challenges for CHP plant operators. The increase in operation and maintenance costs caused by e.g. deposit formation and beg agglomeration can increase the total energy production costs significantly. In optimising the overall economics of the boiler one has to take into account the boiler s fuel costs including taxes and subsidies, boiler operational costs and the costs from possible emissions. Nowadays CO 2 -emission trading has a major influence on selection of the optimal fuel blend. Increase of the share of biofuels in cofired boiler means usually significant annual savings although boiler efficiency is expected to decrease and operational problems increase simultaneously. 16