Oxyfuel Combustion - Experience of FGD and FGC at 30 MW th

Transcription

1 Flue-gas Cleaning Processes for CO 2 Capture from Oxyfuel Combustion - Experience of FGD and FGC at 30 MW th Oxyfuel Combustion Pilot 1 st IEA Oxyfuel Combustion Conference Cottbus, Germany, September 8-11, 2009 Dr. Jinying Yan, Dr. Richard Faber*, Dr. Jürgen Jacoby, Dr. Marie Anheden, Rainer Giering Vattenfall Research and Development AB Thomas Schmidt, Gerhard Ross, Felix Stark Babcock Noell GmbH Daniel Kosel Vattenfall Europe Generation AG & Co. KG

2 Outlines Background Description of the FGD and FGC systems Main performance under oxyfuel conditions Understanding oxyfuel related issues Ongoing work Conclusions 2

3 Background (1) Purposes of the test program: Investigation of the performance of WFGD system under oxyfuel combustion conditions for CO 2 capture by Vattenfall. Adjustment of the common FGD-design by Babcock Noell to cope with: - The strict requirements for the operation with very high removal efficiency and prevention of air in-leakage into the flue gas system. - The unknown impacts of high CO 2 partial pressure of the flue gas. Testing of the removal efficiencies of FGD and FGC systems. 3

4 Background (2) The evaluation of FGD and FGC mainly includes: Flue gas Characterisation Achievable removal efficiencies for most important acidic gas components Major mass and energy balance of the system including emission characteristics Slurry chemistry and dby-product (gypsum) properties (FGD) Composition and chemistry of condensate (FGC) 4

5 FGD System (1) Flow Diagram 5

6 FGD System (2) Main Design Parameters Boiler capacity MW th 30 Fuel Lignite/hard coal Flue gas flow rate Nm 3 /h wet 12,000 Inlet SO 2 mg/nm 3,dry 11,500 Required SO 2 removal % 99 Absorber diameter m 1.5 Absorber height m 16.5 Total slurry volume m

7 Main Performance of FGD (1) Typical Operation Conditions and Performance Main Performance of FGD (1) Acid Gas Removal Operation Mode: Oxyfuel Range Average Removal Efficiency [%]: 99,62 99,88 99,83 SO 2 Inlet [mg/nm³,dry] : SO 2 Outlet [mg/nm³,dry] Flue Gas Inlet [Nm³/h,wet]:

8 Main Performance of FGD (2) Acid Gas Removal Achievable removal efficiencies for SOx, NOx, HCl and HF under Oxyfuel combustion conditions Rem moval efficiency (%) SO2 HCl HF NO2 Acidic gas components expected removal efficiency; not measurable due to low clean gas concentration and uncertainty of measurement for this range * Inlet concentrations of HCl, HF, and NO 2 in flue gas are relatively much lower than SO 2 8

9 Main Performance of FGD (3) Slurry Chemistry The gypsum quality is acceptable and should be carefully controlled when slurry ph is maintained in higher levels. The concentration of HCO 3- in liquid phase may be varied with slurry ph in a relatively large range compared with other components. Gypsum content % > 98 CaCO3 CO3 (TGA) % < 0.6 SO 4 2- mg/l HCO - 3 mg/l NO - 3 mg/l Cl - mg/l

10 Understanding FGD Process under Oxyfuel Conditions (1) Comparison of flue gas properties p under both air-firing and oxyfuel combustion conditions an example Oxyfuel Air-firing SO 2 mg/nm 3, dry CO 2 vol%, dry H 2 O vol% 27 7 Density ( kg/m

11 Understanding FGD Process under Oxyfuel Conditions (2) Evaluation of impacts on slurry process by using flue gas titration experiments under both air-firing and Oxyfuel combustion conditions Slurry ph SO 2 in clean gas Using flue gas to titrate the slurry buffer system under oxyfuel condition 11

12 Understanding FGD Process under Oxyfuel Conditions (3) Comparison of slurry buffer systems and ph dependence SO2 concentration in clean gas under both air-firing and oxyfuel combustion conditions Comparison of slurry ph buffer systems Impacts of slurry ph on SO 2 in clean gas 12

13 FGC System (1) -Purpose and Main Design Parameters Further reduction of the flue-gas temperature before compression part. Reduction of water content in the flue-gas. Reduction of particles in the flue-gas. Further reduction of sour gas components (SO 2, SO 3 ). Design data: Flue gas flow rate Nm 3 /h dry 8200 Inlet SO 2 mg/nm 3,dry 200 Inlet SO 3 mg/nm 3,dry 20 SO2 removal efficiency % 99,5 Inlet temperature C 75 Outlet temperature C 29 13

14 FGC System (2) Flow Diagram 14

15 Performance Data FGC (1) SO 2 removal efficiency % (inlet concentration approx 135 mg/nm³)* Average SO 2 outlet concentration mg/nm³ 9,5 SO 3 removal efficiency % (inlet concentration approx 12 mg/nm³) * Average SO 3 outlet concentration mg/nm³ 48 4,8 Condensate discharge m³/h 1,6 Average ph in 1 st stage - 2,4 Average outlet temperature C 30 * SO 2 removal efficiency of FGD reduced during FGC tests 15

16 Performance data FGC (2) Condensate Chemistry Strong increase in CO 2 solubility above ph 5, HCO O3 [mg/l] SO4 [mg/l] [ph] HCO3 Sulfate (2nd stage) Sulfate (1st stage) 0 16

17 Performance data FGC (3) SO 2 Removal Efficiency 99% [Removal efficie ency SO2 [%] 98% 97% 96% 95% 94% 93% 92% 91% 90% [ph] SO2 removal efficiency Lower SO 2 removal efficiency due to low inlet concentrations. 2 y 17

18 Performance data FGC (4) NOx Removal Efficiency No significant NOx removal from flue-gas NO2 [mg/nm³] NO [mg/nm³] [mg/nm³] Inlet Outlet But accumulation of Nitrite and Nitrate in the washing water (due to long residence time) Nitrite [mg/l] Nitrate [mg/l] [mg/l] 2nd stage 11,56 48,

19 Ongoing g work For FGD: Mass balance evaluation for important flue gas components such as CO 2, emission regulated components and air in-leakage, Optimisation of the FGD system to reduce the mass transfer work required by the high removal efficiency, Technology transfer to demonstration applications, For FGC: Continued investigation on influence of operating conditions on removal efficiency and cooling performance, Long-term monitoring i of corrosion (especially in heat exchanger), Optimisation of FGC system to improve cooling duty and removal efficiency. 19

20 Conclusions - Known flue gas cleaning techniques work also for oxyfuel, - High removal efficiencies of most acid gases are achievable with very low residual concentrations (over 99% for SO 2 ) in clean flue gas with good byproduct quality, - External oxidation process works well to prevent air-inleakage into the flue gas system, - High CO 2 partial pressure in flue gas has significant impacts on the slurry buffer system increasing in ph buffer capacity and changing the ph buffer profiles, - Strong increase of CO 2 solubility at ph above ph 5,5 in FGC, - Importance to monitor corrosion in FGC due to low ph of condensate, - Further development may focus on optimisation of the absorption process to enhance the mass transfer in order to reduce energy consumption. 20

21 Thank you!

22 Understanding FGD Process under Oxyfuel Conditions (4) FGD should be transferred from air-firing conditions to oxyfuel combustion conditions during the start-up procedure. Slurry is the slowest process during the transition period. However, it does not very significantly affect the SO 2 removal. CO 2 H 2 O Slurry T O 2 Transition profiles of FGD from air-firing to oxyfuel combustion 22

23 Performance data FGC- Fluegas temperatures Tem peratures U 0 H U B10 C T 0010 [ C ] U 0 H U B10 C T 0020 [ C ] U 0 H U B20 C T 0010 [ C ] U 0 H U B20 C T 0020 [ C ] 23

24 FGC - Experiences from the commissioning and first test results Other performance data Particle removal during 1st commissioning test unsuccessful Inlet concentration 1,24 mg/nm³ Outlet concentration 8,84 mg/nm³ Droplets and metal particles detected after FGC probably measurement problem 24

25 Experiences from the commissioning and first test results Accumulation in liquid phase Reduction of ph value in 1st stage Only condensate as washing water Accumulation of certain components 1 st stage Cond. [μs/cm] ph Cl - Fl - SO 3 2- SO 4 2- NO 2 - NO < < <0.1 <0.2 < < nd stage Cond. [μs/cm] ph Cl - Fl - SO 2-3 SO 2-4 NO - 2 NO < <0.1 < All concentrations in [mg/l] 25