FULL-SCALE INVESTIGATIONS ON CO- FIRING OF STRAW

Transcription

1 FULL-SCALE INVESTIGATIONS ON CO- FIRING OF STRAW Bo Sander, Elsam Engineering A/S, Denmark IEA Workshop, May 2004, Rome

2 Outline of presentation Background The Studstrup straw co-firing concept Experiences from straw co-firing at Studstrup Fly ash properties Deposit formation and corrosion SCR catalyst deactivation Conclusions and further work Side 2 Elsam Engineering

3 Background Straw is the main biomass ressource for CHP in Denmark High investment costs for grate-fired stand alone boilers Co-firing is an interesting option due to low investment costs, high efficiency and low emissions : Successful demonstration of straw co-firing at the 150 MWe coal-fired Studstrup unit 1 (20% on energy basis) : No commercial use of co-firing technology due to problems with industrial use of fly ash 2001: Revised requirements for fly ash in cement production 2002: Start up of commercial operation of straw co-firing at the 350 MWe coal-fired Studstrup Unit 4 (10% on energy basis) Side 3 Elsam Engineering

4 Plant description Co-firing of straw at Studstrup unit 4 Year of commissioning 1985 Type Opposed wall fired Benson boiler Unit & electric capacity 824 MW / 350 MW Coal burners 24 (in 4 rows of 6 pcs.) Modified coal and straw burners 4 in top row HP Steam data 286 kg/s, 240 bar, 540 C RH Steam data 256 kg/s, 45 bar, 540 C Straw input 20 t/h (10% straw share at full load) Straw consumption >100,000 t/year Desulphurisation Semi-dry FGD plant Side 4 Elsam Engineering

5 Straw shredder Side 5 Elsam Engineering

6 Straw hammer mill Side 6 Elsam Engineering

7 Main fuels South African coal (low alkali) 1,6 1,4 Colombian coal Danish straw % dry basis - 1,2 1 0,8 0,6 0,4 0,2 0 Potassium Chlorine 2002 harvest 2003 harvest Side 7 Elsam Engineering

8 LOI in fly ash 4 3,5 3 LOI (%) 2,5 2 1,5 1 0, % load % load % load % load Coal alone Straw co-firing Side 8 Elsam Engineering

9 Water soluble potassium and chlorine in fly ash 0,05 0,045 0, % of potassium from straw as K 2 SO 4 in fly ash 0,035 Weight-% 0,03 0,025 0,02 0,015 0,01 0,005 0 Watersoluble potassium Watersoluble chloride Coal 7% straw co-firing 9% straw co-firing Side 9 Elsam Engineering

10 Impactor measurements of submicron particle size distribution mg/nm Coal Straw co-firing ,021 0,042 0,087 0,18 0,35 0,71 Particle size (micro meters) Side 10 Elsam Engineering

11 Impactor measurements chemical composition Potassium measured by EDX % ,01 0, Particle size (micro meters) Coal 1 Coal 2 Coal 3 Co-firing 1 Co-firing 2 Co-firing 3 Side 11 Elsam Engineering

12 Potassium chemistry at co-combustion of straw in coal-fired PF boiler 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 Side 12 Elsam Engineering

13 Utilisation of fly ash from straw co-firing Coal fly ash is mainly used for cement and concrete in Denmark Fly ash from co-firing of straw at Studstrup unit 4 is presently used for cement production low alkali coal is required Use of fly ash from co-firing in concrete is not allowed by EN450 A revised EN450 will allow co-firing of 20% straw (dry mass basis) if quality requirements can be met A compliance test programme initiated in cooperation with Danish concrete industry By amendment of national rules use of co-firing fly ash in concrete in Denmark is expected by the end of 2004 Side 13 Elsam Engineering

14 Deposit formation and corrosion Deposit formation: No slagging/fouling problems at Studstrup unit 4 No need for increased soot blowing Corrosion: Results from Studstrup unit : No chloride corrosion No chloride detected in corrosion samples At 10% straw corrosion rates are similar to coal alone At 20% straw increased corrosion rates (factor 2-3) due to potassium sulphate Studstrup unit 4: Long term corrosion tests initiated in September 2002 Side 14 Elsam Engineering

15 Trends for corrosion rates for austenitic TP347HFG 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 Side 15 Elsam Engineering

16 High dust SCR catalyst deactivation Slip stream reactors for exposure of high dust SCR catalysts at Studstrup unit 4 (straw co-firing) and Studstrup unit 3 (coal) 3x3 elements 150x150x500 mm elements Flue gas downstream ECO Flue gas temperature C Design flow 4,6 m/s Soot blowing by air November 2002 July hours of exposure 7% straw on energy basis Side 16 Elsam Engineering

17 High dust SCR test plant Side 17 Elsam Engineering

18 Pressure loss for the coal/straw high dust SCR reactor 1,8 1,6 1,4 1,2 1 0,8 0,6 0,4 0,2 0 ' :40:00.000' ' :15:00.000' ' :00:00.000' ' :00:00.000' ' :00:00.000' ' :00:00.000' ' :09:00.000' ' :09:00.000' ' :09:00.000' ' :09:00.000' ' :09:00.000' ' :09:00.000' ' :09:00.000' ' :46:00.000' ' :56:00.000' Side 18 Elsam Engineering mbar

19 High dust SCR catalyst deactivation Results for Topsoe catalyst Relative catalyst activity vs. exposure time 1,1 1 0,9 0,8 0,7 0,6 0, Exposure time (hours) Coal reference Straw co-firing No distiguishable difference in deactivation rate Similar results for two other catalyst types Side 19 Elsam Engineering

20 Conclusions from two years operation of 10% straw co-firing at Studstrup unit 4 Acceptable availability of the straw pre-processing unit has been achieved LOI in fly ash is reduced by co-firing NO x emissions by co-firing are maintained at the same level as coal firing alone or marginally reduced No increase in boiler deposit formation Fly ash can be used for cement production and in near future presumably also for concrete No increase in deactivation of high dust SCR catalyst by 7% cofiring Side 20 Elsam Engineering

21 Further work on straw co-firing IN PROGRESS: Long term corrosion tests Studies on alkali-chlorine-sulphur chemistry CFD based model for co-firing plant optimisation IN PLANNING: Long term high dust SCR catalyst deactivation tests Side 21 Elsam Engineering