Performance and System Optimisation of Flue Gas Desulphurisation for Oxy-coal Combustion

Transcription

1 Performance and System Optimisation of Flue Gas Desulphurisation for Oxy-coal Combustion Jinying Yan*, Rainer Giering, Richard Faber and Uwe Burchhardt Vattenfall R&D Projects Michaela Zennegg and Thomas Schmidt Babcock Noell GmbH The 3rd Oxyfuel Combustion Conference, Ponferrada, Spain, September 9-13, FGD for oxyfuel combustion J. Yan et al.,

2 Agenda Long-term performance (2008 to 2012) FGD system for oxyfuel combustion CO 2 capture pilot plant at Schwarze Pumpe - Sulphur removal efficiency - Achievable clean flue gas - Slurry chemistry and impacts on performance - Impacts of external oxidation - Emission characteristics (to air, liquid and solid streams) System Optimisation for Oxy-coal combustion (reported by Babcock Noell GmbH) - Conducted tests - Results Conclusions 2 FGD for oxyfuel combustion J. Yan et al.,

3 FGD System (1) - Operation hours from 2008 to 2012 From September 2008 to December 2012 the OxPP was operated with air firing: ~ h oxyfuel combustion: ~ h 3 FGD for oxyfuel combustion J. Yan et al.,

4 FGD System (2) General Information Characteristics: Flue gas: Process: approx Nm³/hr wet lime stone process (wet) approx. 155 kg limestone/h SO 2 -removal: > 99 % Variations: up to 3 trays up to 4 spray levels Gypsum: CaSO 4 approx. 100 kg/hr (used as construction material) Contractor: (Bilfinger) Babcock Noell GmbH 4 FGD for oxyfuel combustion J. Yan et al.,

5 FGD System (3) Flow Chart Main difference to normal FGD is the separate oxidation in the reaction tank to avoid air ingress during oxyfuel operation 5 FGD for oxyfuel combustion J. Yan et al.,

6 FGD Performance (1) for Normal Lignite ( ) Under design conditions: SO 2 removal efficiency can easily be achieved over 99% (e.g %), SO 2 concentration is in clean flue gas in a range of mg/nm 3 as the inlet SO 2 concentration is in a range of mg/nm 3 FGD Performance (oxyfuel combustion) Outlet SO2 (mg/nm3, dry) , ,8 99, , ,2 99, , ,6 98, , ,0 97, , ,4 Outlet SO2 SO2 removal 97,2 0 97, SO2 removal (%) Inlet SO2 (mg/nm3, dry) 6 FGD for oxyfuel combustion J. Yan et al.,

7 FGD Performance (2) for Lignite with Higher Sulphur Content For high sulphur lignite: SO 2 concentration up to mg/nm³ dry Suluhr removal efficiency > 99 % 7 FGD for oxyfuel combustion J. Yan et al.,

8 Slurry Chemistry (1) ph and Impact on performance Impacts of slurry ph on SO 2 removal and concentration in clean flue gas Trend graphs show the impact in oxyfuel operation mode in general (Red lines mark the SO 2 -removal efficiency and the SO 2 - value in the flue gas regarding the unit design) 8 FGD for oxyfuel combustion J. Yan et al.,

9 Slurry Chemistry (2) Impact of Oxidation Process Oxidation combined degas reduces the effects of CO 2 partial pressure on slurry chemistry; Impacts of slurry ph on residual limestone contents are similar between oxyfuel and airfiring after the oxidation process; Slight lower residual limestone could be expected in the slurry for oxyfuel combustion under the same slurry ph 9 FGD for oxyfuel combustion J. Yan et al.,

10 Emission Characteristics (1) to Air Emissions to air Emissions to liquid and solids Emission characteristics have been changed with significant reduction of the emissions to air Depending oxidation air flow H 2 O: vol%, CO 2 :18 21 vol%, O 2 : vol%, SO 2 : near 0, NO: near 0, NO 2 : near 0 CO 2 loss: ~ 0.9 % M in/out xx-measurement points and data (mass balance) 10 FGD for oxyfuel combustion J. Yan et al.,

11 Emission Characteristics (2) to Solids (gypsum) No significant changes in heavy metals contained in the FGD by-products (gypsum) in comparison with the FGD by-products from conventional combustion flue gas treatment VGB Investigation* OxPP measurements Nature gypsum Hard coal plants Lignite plant Air-firing Oxyfuel As mg/kg 0,22-3,79 0,21-2,7 2,04-2,6 0,65 0,45 Be mg/kg <0,1-0,71 <0,05-0,65 0,1-0,42 <0,6 <0,6 Pd mg/kg <2,5-21,41 0,27-22 <3-11,1 <0,6 <0,6 Cd mg/kg <0,02-0,52 <0,02-0,29 <0,02-0,15 <0,4 <0,4 Co mg/kg 0,01-4,39 0,06-2,2 0,49-0,53 <0,6 <0,6 Cr mg/kg 0,65-24,9 1,02-9,72 2,75-4,8 2,6 3,2 Cu mg/kg 0, ,2-8,56 1,1-4,65 <0,6 <0,6 Mn mg/kg 4, , ,7-64,9 16,8 13,7 Ni mg/kg 0,3-13,4 0,3-12,9 1,63-3,2 1,3 1,7 Hg mg/kg <0,006-0,09 0,1-1,32 0,66-0,9 0,82 0,85 Te mg/kg <0,1 - <0,2 <0,1- <0,3 <1,3 <1,3 Tl mg/kg <0,05-0,2 <0,05-0,42 <1,0 <1,0 V mg/kg 0,93-26,4 1,22-7,7 3,55-5,4 1,5 1,5 Zn mg/kg <3-41 1,7-53,2 24,3-43 8,3 8,3 * Based on the VGB report, comparison of nature gypsum and FGD gypsum, VGB-TW 707, VGB, FGD for oxyfuel combustion J. Yan et al.,

12 Emission Characteristics (3) to Liquid (FGD blow-down) Generally similar wastewater characteristics (FGD blow-down) are expected for the FGD operated for oxyfuel combustion in comparison with air-firing due to similar salt balance required for flue gas cleaning. There may be little differences in specific components between oxyfuel and air-firing in case if there may be small changes in some component distributions in gas phase. Limits Air-firing Oxyfuel Suspended solids mg/l 30 COD mg/l 80/ Nitrogen compounds mg/l - 24,6 3,69 Sulphate mg/l Sulphite mg/l 20 <0,1 <0,1 Sulphide mg/l 0,2 Cd mg/l 0,05 0,036 0,037 Cr mg/l 0,5 <0,01 <0,01 Cu mg/l 0,5 <0,01 <0,01 Hg mg/l 0,03 0,0089 0,0015 Ni mg/l 0,5 0,325 0,432 Pb mg/l 0,1 <0,01 <0,01 Zn mg/l 1 0,537 0, FGD for oxyfuel combustion J. Yan et al.,

13 Conducted Tests Optimising Variables - Variation of number of spraying levels and recirculation flow - Variation of number of Trays objective: optimisation of energy consumption - Variation of material of Trays objective: advantages and disadvantages of different materials, e.g. corrosion, pressure loss, temperature resistance, accessability etc. Tray in FGD of Oxyfuel Pilot plant Operation without Tray Operation with Tray 13 FGD for oxyfuel combustion J. Yan et al.,

14 Results: Impacts L/G and SO 2 -Load SO 2 -concentration in clean gas vs. SO 2 -load SO 2 -concentration in clean gas [mg/nm³ dry] limit value standard plant with lignite limit value Oxyfuel Reduction of recirculation flow resp. L/G Standard operation 60% of recirculation flow 85 % of recirc. flow 70% of recirc. flow 100 % of recirc. flow, std. operation SO 2 -load [kg/h] 14 FGD for oxyfuel combustion J. Yan et al.,

15 Results: Impacts of L/G and Trays SO 2 -removal efficiency vs. L/G ratio SO 2 -removal efficiency [%] 50 % operation with 1 Tray operation with 2 Trays L/G [Bm³/h] 100 % 15 FGD for oxyfuel combustion J. Yan et al.,

16 Results: Variation of Materials of Trays Comparison of a synthetic material Tray and a stainless Steel Tray: Tray material characteristics synthetic material stainless steel corrosion resistance temperature restistance accessability SO2 removal efficiency pressure loss expenses FGD for oxyfuel combustion J. Yan et al.,

17 Conclusions for FGD performance High SO 2 removal efficiency (over 99%) is easily achieved and operation is stable; SO 2 concentration in clean gas highly depends on the mass transfer and absorption equilibrium, which affected by slurry chemistry (ph) and inlet flue gas concentration. Similar behaviour is expected for oxyfuel combustion in comparison with air-firing; Impacts of CO 2 partial pressure on slurry chemistry seems to be minimised by the degassing process in the external reaction tank, which makes a similar slurry chemistry between oxyfuel combustion and airfiring; In oxyfuel combustion, emissions to air have significantly been reduced in terms of common combustion pollutants. Similar contaminations are expected in FGD wastewater and by-products compared with that from air-firing; The long-term performance could be kept in system scale-up due to the similarities in slurry chemistry and absorption mechanisms between oxyfuel and air-firing flue gas treatments 17 FGD for oxyfuel combustion J. Yan et al.,

18 Conclusions for System Optimisation Possibility to achieve SO 2 -removal efficiency > 99 % by operation with 1 up to 3 Trays, number of Trays depends on pressure reserve of booster fan and on the maximum recirculation flow possibility to find the optimum balance between SO 2 -removal efficiency and energy consumption Verification tests shown that up to doubled SO 2 -concentrations can be removed reliably further test with higher Sulphur content will be conducted Tray materials used in small scale facilities show influences on SO 2 - removal efficieny and pressure loss further tests will be conducted to learn about the dependencies between different materials 18 FGD for oxyfuel combustion J. Yan et al.,

19 Thank you for your attention!