Advanced AQCS for Oxy-fuel Combustion System; Controlling Mercury & SO3

Transcription

1 Special Workshop on SO2, SO3, Hg and Boiler Corrosion Issue Under Oxyfuel Combustion Condition Advanced AQCS for Oxy-fuel Combustion System; Controlling Mercury & SO3 Babcock-Hitachi K.K. Hirofumi Kikkawa Noriyuki Imada Takayuki Saito January 26, 2011 Contents 1. Introduction 2. Mercury & SO3 Behavior in Coal-Fired Power Plant 3. Pilot Plant Test Facility 4. High Mercury Oxidation & Low SO2 Conversion Catalyst TRAC TM 5. SO3 Behavior in AQCS 6. Mercury Behavior in AQCS 7. Conclusion Babcock Hitachi k.k All rights reserved.

2 Hitachi s Approach of Low CO2 Emission Technology Current Thermal Power Plant High Efficiency Step-1 - High Temperature Gas Turbine deg-c Class A-USC CO2 Emission Current Technology High Efficiency Step-2 CO2 Capturing A-USC: Advanced Ultra Super Critical Direct CO2 Capturing - Oxy-fuel Combustion - Chemical Scrubbing - IGCC-CO IGCC: Integrated Coal Gasification Combined Cycle 1

3 Development Subjects in Oxy-fuel Combustion Boiler Boiler High radiation intensity: CO2,H2O -same heat absorption as air combustion -reduce oxygen consumption ASU O2 Mill ASU -reduce initial cost -reduce power consumption compact & low power ASU: Air Separation Unit SCR AH GC Mill outlet pipe -keep gas temp dig-c Re-circulation line -reduce corrosive gas: SO3 AQCS -keep SCR,DESP,FGD performance -installation of gas cooler DESP FGD CPU Fan AQCS: Air Quality Control System GC: Gas Cooler Liq.CO2 stack CPU -reduce corrosion potential (Hg,SOx,NOx,Cl etc) -reduce power consumption compact & low power CPU: CO2 Compression and Purification Unit 2

4 Development Process for Oxy-fuel Combustion Fundamental study - Laboratory test - Basic combustion test (0.4MWth test facility) Burner Furnace 0.4MWth test facility Verification study - Large scale combustion test (4MWth test facility) - Total system test (1.5MWth test facility) Burner Furnace 4MWth test facility AQCS Furnace Feasibility study - Trial design of actual plant (500MW class) - Cost evaluation 1) Trial design - System flow (Process analysis) - Equipments design (Numerical analysis) - Control system (Dynamic analysis) 2) Cost evaluation - Initial cost (Construction, Equipment) - Running cost (Utility check) 1.5MWth test facility 3

5 Mercury & SO3 Behavior in Coal-Fired Power Plant 4

6 Behavior of Mercury & SO3 in Power Plant Oxidation Metal Hg Hard to remove from flue gas HgCl2 Absorption into FGD slurry Adsorption on ash particle Easier to remove from flue gas SO3 gas mist Oxidation of SO2 Condensation on ash particle Collision with Electrostatic spray droplets collection Boiler SCR Hg in Coal A/H DESP Hg,SO2 Hg2+,SO3 HCl,NH3,H2O SO2 WESP Gas Cooler Hg2+ SCR Catalyst SO3 Ash Particulate (S.A., Gas Temp.) FGD Spray Nozzle Stack Re-emission Absorption (HgCl2,SO2) 5

7 Comparison of Flue Gas Compositions Typical Flue Gas Compositions in Conventional System (High Sulfur Coal) Condition N2[%] CO2 [%] H2O [%] SO2 [ppm] SO3 [ppm] Hg [ g/m3n] Air Combustion > , Oxy-Combustion < , Gas re-circulation ratio:75% Boiler SCR 2 Hg + 4 HCl + O2 = 2 HgCl2 + 2 H2O 4 NO + 4 NH3 + O2 = 4 N2 + 6 H2O DESP W-FGD CPU ASU Gas Re-circulation Line ASU : Air Separation Unit CPU : CO2 Purification Unit 50 70deg-C Hg Capture Tower Increase in SO3 & Hg concentrations due to flue gas re-circulation Increase in corrosion potential by SO3 & Hg 6

8 Mechanism of SO3 Removal across Gas Cooler Boiler ASU SCR Cooler FGD ESP CPU Gas re-circulation Picture of finned tubes 160 deg-c Ash SO3 (Gas) Finned tube 90 deg-c (< acid dew point) Adsorbed SO3 mist SO3 Concentration [-] Location of cooler without Cooler(160 deg-c) with Cooler(90 deg-c) SCR Outlet ESP Inlet ESP Outlet FGD Outlet - Below acid dew point, gaseous SO3 changes the form into mist - Mist attached to ash and neutralized by alkali in ash is removed across ESP with ash 7

9 Pilot Plant Test Facility 8

10 Pilot Plant Test Facility Flue gas treatment facility FF Combustion facility GC SCR DESP Oxygen Supply Unit FGD Control room 9

11 Schematic Diagram of the Pilot Test Plant Coal O2 Item Coal Feed Rate Gas Flow Rate DeNOx Efficiency Burner Heat Exchanger E Condition 110~200 kg/h 1100~1300 m3/h approximately 90 % Gas Reheater A D Gas Cooler B DryDESP C SCR reactor BUF Pump IDF WFGD GRF A E:Hg Sampling Points SCR : Selective Catalytic Reduction DESP : Dry Electrostatic Precipitator WFGD : Wet Flue Gas Desulfurization GRF: Gas Re-circulation Fan 10

12 Structure of Gas Cooler Flue Gas 覗き窓 Cooling medium Cooling medium Nozzle Compressor Air Soot Blower Structure of Gas Cooler Finned tube 11

13 Properties of Test Coals Coal Name A B C D kj/kg 28,870 25,970 27,880 15,660 % Moisture % Volatile Matter %, dry Fixed Carbon %, dry Ash %, dry C %, dry H %, dry O %, dry N %, dry S %, dry Cl mg/kg Hg μg/kg Higher Calorific Value Total Moisture Proximate Analysis Ultimate Analysis 12

14 High Mercury Oxidation & Low SO2 Conversion Catalyst TRACTM TRACTM:Triple Action Catalyst 13

15 Properties of SCR Catalyst New Catalyst with Higher Hg Oxidation & Lower SO2 Conversion at Lower Cl Conc. & Higher Temp. High New Catalyst Amount of Active Components Increase Conventional Technology Decrease Low Low High SO2 to SO3 Conversion Activity Hg Oxidation Activity Hg Oxidation Activity Lower SO2 conversion is required to improve corrosion problem Temperature Low High High Low Low High Cl Concentration 14

16 Comparison of Hg Oxidation & SO2 Conversion Rate SO2 Conversion Activity ratio (-) Hg Oxidation Rate (%) 100 New Catalyst Conventional Catalyst Conventional Catalyst New Catalyst Temperature (oc) Hg oxidation - Hg oxidation activity* :1.4~1.7 times higher - SO2 conversion activity : Approximately half Temperature (oc) SO2 conversion Higher Hg removal Less SO3 formation *Hg oxidation activity = k Log(1(1- Hg oxidation rate(%)/100)) 15

17 SO3 Behavior in AQCS 16

18 Flue Gas Composition at SCR inlet (Coal : A & D) Air combustion Oxy-fuel combustion SO2 (ppm,dry) H2O (%) HCl (ppm,dry) SO2 (ppm,dry) H2O (%) HCl (ppm,dry) Component Flue gas rate (m3n/h) CO2 (%,dry) O2 (%,dry) High Sulfur Coal : SO2 & HCl conc. increased by a factor of 4 due to the recirculation of flue gas (re-circulation ratio = 4). Low Sulfur Coal : SO2 or HCl conc. did not increase so much as recirculation ratio because part of SO2 or HCl reacted with alkali in ash. 17

19 SO3 Removal across DESP in Oxy-fuel Combustion Flue gas Soot Blower Test condition Measurement point - Coal : High surfer coal (S=2.9%) - Moisture content in flue gas :30-40% DESP Cooler Re-circulation line SO3 at DESP outlet [ppm] Finned tubes 0.2ppm Without Cooler (160 deg-c) With Cooler (90 deg-c) SO3 was reduced under 1ppm with 90 deg-c cooler system. Carbon steel can be used for re-circulation line. 18

20 Before S/B coefficient (-) 伝熱係数α Relative overall heat 2transfer (kcal/ min m ) Cleaning of Finned Tube by S/B After S/B Soot Blowing Time Q1 A T gin TWin T gout TWout T gin TWin ln T gout TWout Q1 : Amount of Heat Transfer A : Surface area of heat exchanger : Overall heat transfer coefficient Tgin : Gas temperature of GC inlet T gout : Gas temperature of GC outlet TWin : Heat medium temperature of GC inlet TWout : Heat medium temperature of GC outlet 19

21 Relative 伝熱係数α overall heat transfer coefficient (-)2 ) Effect of Lime Injection on Ash Deposition SO3:90ppm Soot Blowing Lime Injection SO3 90ppm+Lime Time SO3 90ppm - S/B removed ash from finned tube even when SO3 conc. and gas temperature were 90 ppm and 90 deg-c respectively. - Injection of lime decreased ash deposition and interval of S/B operations. 20

22 Mercury Behavior in AQCS 21

23 Effect of DESP temperature on Hg removal Hg Removal (%) 100 ( ):LOI(%) 80 ( ) ( ) 60 ( ) ( ) Air comb. Coal A (S: 0.5%) Coal B (S: 0.3%) Coal C (S: 3.2%) Coal D (S: 1.5%) Oxy comb. Coal A (S: 0.5%) Coal B (S: 0.3%) Coal C (S: 3.2%) Coal D (S: 1.5%) S : Sulfur (dry ash free) ( ) 40 (1.4) (2-2.1) ( ) 200 DESP Temperature (oc) - Mercury removal across DESP increased with decrease of DESP temperature in both oxy-fuel and air combustion system. - Higher mercury removal across DESP was observed at lower sulfur content in coal. 22

24 Effect of Sulfur Content in Coal on Hg removal 100 Hg removal (%) DESP:90oC Air, 90 oc Air 160 oc Oxy, 90 oc Oxy,160 oc Air Comb. 40 DESP:160oC 20 Oxy Comb S (%,d.a.f.) - DESP 90oC : Little difference in mercury removal was observed between air and oxy-fuel combustion system. Mercury removal decreased little with increase of sulfur content. - DESP 160oC : Mercury removal decreased drastically with increase of sulfur content, especially in oxy-fuel combustion system. 23

25 Hg(P) 6 Hg++ 4 η=90% η=97% Hg0 2 η=63% 0 Hg concentration (μg/m3n) Hg concentration (μg/m3n) Hg Behavior in Oxy-fuel Combustion (DESP=90 160C) 12 Hg(P) 10 η=75% 8 Hg++ η=94% 6 Hg0 4 η=77% 2 0 SCR inlet SCR DESP DESP outlet inlet outlet DESP Temp. : 90 oc FGD outlet SCR inlet SCR DESP DESP FGD outlet inlet outlet outlet DESP Temp. : 160 oc Mercury removal at FGD outlet (at stack) increased from 94% to 97% (outlet conc. decreased to 1/3 )by decreasing DESP temperature from 160 to 90 oc. 24

26 Summary (1) Mercury oxidation activity of the new catalyst was 1.4~1.7 times higher than that of the conventional catalyst and the SO2 to SO3 conversion rate was about half of the conventional catalyst. (2) As SO3 was reduced under 1ppm with 90 deg-c cooler system, carbon steel can be used for re-circulation line. (3) S/B removed ash from finned tube in GC even when SO3 conc. and gas temperature were 90 ppm and 90 deg-c respectively. Injection of lime into flue gas decreased ash deposition and interval of S/B operations. (4) Mercury removal across DESP increases with decreased of DESP temperature and sulfur content in coal. Adsorption of Hg on ash particles was inhibited under high SOx condition. (5) Mercury removal at stack increased from 94% to 97% (outlet conc. decreased to 1/3 )by decreasing DESP temperature from 160 to 90 deg-c. 25

27 Acknowledgements This study was partly carried out under contract with New Energy and Industrial Technology Development Organization (NEDO) in the fiscal year

28 27

29 SO2 Removal : Transition from Air to Oxy-fuel (Coal:C) Oxy comb. SO2 Conc. at SCR inlet (ppm) FGD outlet FGD inlet FGD (%) SO2 Removal across 1000 SO2 conc. at FGD outlet (ppm) Air comb :38 8:38 Time 14:38 By shifting from air firing to oxy-fuel combustion, SO2 conc. at FGD outlet decreased rapidly due to less flue gas volume. 28