Experience with co-combustion of biomass and waste in coal-fired power plants

Transcription

1 Experience with co-combustion of biomass and waste in coal-fired power plants Topsøe Catalysis Forum August 2009 Bo Sander, DONG Energy Power, Denmark

2 GENERATION - HCASA DONG Energy Power in Europe Power production capacity EDF E.ON Enel RWE Vattenfall Endesa Electrabel Iberdrola EnBW PPC CEZ British Energy Statkraft Fortum EDP Scottish&Southern Edision Axpo Verbund SE Union Fenosa Scottish Power DONG Energy Essent Nuon Drax GW EDP Iberdrola 23 Scottish Power 6 Scottish&Southern 10 Drax 4 British Energy 12 Endesa Union Fenosa 32 7 EDF 114 Nuon 4 Essent 5 Electrabel 28 Statkraft 11 Axpo 9 DONG Energy 6 EnBW 14 RWE 44 Enel 45 E.ON 45 Verbund 8 Vattenfall 33 CEZ 12 SE 7 Edision 10 Fortum 11 PPC

3 Production of renewable energy in Denmark PJ Renewable share of total energy consumption: 17 % Renewable share of power production: 29 % 1980 '85 '90 '95 '00 '05 '07 Wind Straw Wood Biogas Waste Heat Pumps 3

4 Biomass - background CO 2 -reduction in Denmark by replacing coal based power production by wind power, biomass and natural gas Political agreement in 1993 to obligate power plants to apply 1.4 mio. tonnes of biomass (mainly straw) for power production in 2000 Limited national and international experience with straw combustion in1993 Large development program for development and demonstration of straw combustion technology initiated Obligation to be fulfilled in

5 Danish biomass resources: Wood, straw and animal manure 2007 supply of biomass for energy Straw: 18 PJ Wood: 60 PJ (import 19 PJ) Animal manure: 4 PJ (potential 20 PJ) 9% of Danish energy consumption Use of straw 18 PJ tonnes 5

6 Handling of straw 4 tonnes straw per hectare 500 kg big bales 24 bales on each truck 6

7 Biomass as fuel for power production Technical challenges: low energi density large volumes difficult handling properties working environment dust and fungal spores potassium and chlorine slagging, fouling and corrosion flue gas cleaning utilisation of residues 7

8 Technologies applied for straw and wood at DONG Energy power plants Grate firing of straw and wood chips 12 plants 4 central, 8 local Co-firing of straw in coal-fired power plant 2 central plants Co-firing of wood pellets, gas and oil 1 central plant CFB combustion of straw and coal 1 local plant CFB combustion of straw and coal not further applied due to no possibilities for use of residual products 8

9 Grate firing of straw Fouling: Superheater design for thick deposits Straw feeding Combustion Slagging Chloride corrosion: superheater steam temperature 540 C Typical emissions (10% O 2, dry): CO 200 mg/nm 3 SO mg /Nm 3 HCl 50 mg/nm 3 NO x 200 mg/nm 3 Dust 10 mg/nm 3 Residues: Bottom ash is spread on farmland as fertiliser Fly ash is converted to liquid fertiliser product Watercooled vibrating grate 9

10 Coal fired power plant 10

11 Co-firing of straw in coal-fired power plants Low investment costs, low emissions and high electrical efficiency Focus areas: combustion straw handling superheater corrosion fly ash utilisation SCR catalyst deactivation Combined coal/straw burner Straw handling plant 11

12 Co-firing at Studstrup power plant unit 3&4 2 x 350 MWe 12

13 Co-firing of straw super heater corrosion 10 Corrosion rate in mm/1000h 1 0,1 0,01 0,001 Straw-firing 20% straw-firing 10% straw-firing 0, Metal temperature in C 13

14 Ash chemistry by co-firing of straw No increase of LOI/unburned carbon in fly ash by 10% straw co-firing Content of K 2 O, CaO, P 2 O 5, SO 3 and Cl may increase by cofiring dependent on coal and straw composition, combustion conditions and straw share Low capture of Cl in ash 5-10% of potassium from straw is found as water soluble potassium in fly ash (potassium sulphate) Potassium from straw is captured as potassium-aluminasilicates by reaction with coal ash No increase in formation of submicron particles Higher content of potassium in submicron particles KOH/KCl/K gas Coal ash K-Al-silicate ash 80-85% 75% 90% K in straw SO 2 K 2 SO 4 gas 5-10% 15% 10% Straw ash particles - Quarts - Ca-silicate K 2 SO 4 heterogeneous condensation 14

15 Co-firing of straw Fly ash utilisation and SCR catalyst deactivation Fly ash utilisation: For cement (low alkali coal must be applied) For concrete (EN450 max. 20 weight-% straw eq. to 13% on energy basis) No poisoning of SCR catalysts by potassium observed during 5000 hours test: 1,1 1 0,9 0,8 0,7 0,6 0, Exposure time (hours) Coal reference Straw co-firing hours exposure test finalised results soon available 15

16 Full scale SCR Commisioning of full scale SCR plant at Studstrup power plant in 2007 Severe plugging of catalyst after a few weeks of operation Plugging caused by straw char particles Ash screens installed for protection of catalyst Plugging tests in slip stream reactor: plugging by reduced flue gas flow Washing of catalysts removed half of plugging New catalyst layers have been installed Ash and straw char particles from screen in slip stream reactor 16

17 Wood pellets The Avedøre power plant unit 2 17

18 Development of biomass capacity in power plants 18

19 New biomass initiatives Demand for further reduction of CO 2 -emissions from energy production Main measures increase wind power capacity increase biomass use in large power plants carbon capture & storage Potential biomass resources: imported wood animal manure energy crops Technical development conversion of coal-fired plants to 100 % wood pellets thermal pretreatment of difficult biomass to increase co-firing potential 19

20 Low-Temperature CFB gasifier for thermal pretreatment of animal manure fibres and other difficult biomasses Pyrol. gas Char gas 500 kw test plant at DTU 2005 Stable operation, no agglomeration 6 MW demonstration plant 2010 at DONG Energy power plant CFB Pyrolysis Chamber ~ 650 C Fuel Control gas Pyrol. gas Char gas Ash Char Inerts Char gas Ash Inerts 1. cyclone Char ~730 C Inerts cyclone Ash BFB Char Reaction Chamber Air Steam 20

21 Co-combustion of waste in coal fired power plants vs. dedicated waste incinerators Higher electrical efficiency Lower investment costs No landfilling of fly ash Low formation of PCDD/DF (dioxine) SRF (Solid Recovered Fuel) for co-firing: SRF main components Paper and carboard Wood Polymers SRF compared to coal: High content of chlorine High content of heavy metals Similar content of ash and moisture Lower calorific value 21

22 Full scale SRF co-firing tests at Esbjerg power plant 2 month test from december 2008 to january tonnes of SRF co-fired Capacity up to 20 tonnes/hour (10 % on energy basis) 11 measurement campaigns performed (emissions, residues, waste water, corrosion, fouling, flue gas cleaning etc.) 22

23 Results from SRF co-firing tests Efficient combustion: TOC-emission < 2 mg C/Nm3 LOI in fly ash < 5 % Low emission of PCDD/DF ng/nm 3 No negative impact on performance of flue gas desulphurisation plant Increased amount of waste water due to high chlorine level Increased emission of HCl and heavy metals Fly ash: No increase in LOI Low content of chloride Increased content of CaO and heavy metals Tests of application in concrete on-going Increased content of unburnt material in bottom ash No indications of increased super heater corrosion Protection of high dust SCR catalyst by ash screen is required Commercial SRF co-firing plant in planning 23

24 Conclusion cofiring of biomass and waste in coal fired power plants Co-firing of straw in coal-fired plants implemented in commercial scale focus on reliable handling system for straw slagging, fouling and corrosion catalyst performance risc of plugging utililsation of fly ash for cement and concrete alkali chemistry Increased use of biomass in large power plants in planning conversion of coal fired power plants to 100 % wood pellets SCR catalyst deactivation rate to be investigated alkali resistant catalyst - R&D on-going thermal pretreatment of difficult biomass to increase co-firing potential 6 MWth LT-CFB gasifier demo-plant in planning Co-firing of SRF in coal-fired plant tested in full scale Commercial plant in planning 24