ASU and CO 2 Processing Units for Oxyfuel CO 2 Capture Plants Vince White, Air Products, UK

Transcription

1 ASU and CO 2 Processing Units for Oxyfuel CO 2 Capture Plants Vince White, Air Products, UK whitev@airproducts.com Capricorn Hotel, Yeppoon, Queensland, Australia 12th September 2011

2 Oxyfuel Combustion Requires Air Separation Units Steam Boiler &Turbine CO 2 Purification & Compression CO 2 Transport & Sequestration O 2 Supply Steam Boiler & Turbines MW e CO 2 Transport & Sequestration CO 2 Purification & Compression Oxygen Coal Flue Gas Recycle

3 Oxyfuel CO 2 Purification 3 Oxyfuel combustion of coal produces a flue gas containing: CO 2 + H 2 O Any inerts from air in leakage or oxygen impurities Oxidation products and impurities from the fuel (SOx, NOx, HCl, Hg, etc.) O 2 Supply Oxygen Coal Steam Boiler & Turbines Flue Gas Recycle Purification requires: Cooling to remove water Compression to 30 bar: integrated SOx/NOx/Hg removal Low Temperature Purification Low purity, bulk inerts removal High purity, Oxygen removal Compression to pipeline pressure MW e CO 2 Purification & Compression CO 2 Transport & Sequestration

4 CO 2 Purity Issues H 2 O CO 2 SO 2 NO O 2 Ar + N 2 + O 2 Basic Design Case < 500 ppm > 90% mol From H&MB From H&MB < 4% mol < 4% mol EOR Case < 50 ppm > 90% mol < 50 ppm From H&MB 100 ppm < 4% mol 4 Regulations regarding onshore and offshore disposal are being drafted world wide Co disposal of other wastes (NOx, SO 2, Hg) is a sensitive issue Important that the CO 2 can be purified for disposal or EOR

5 Air Products Oxy-Fuel CO 2 Capture and Purification with Air Products PRISM Membrane Boiler Steam Cycle Heat Recovery Needs Engineering Data Mature Tech, Needs Data Commercial Product CO 2 CO 2 Compression Raw Flue Gas Sour Compression & AP Acid Gas Column TSA Unit Mercury Removal Auto Refrigerated N 2, Ar, O 2 Removal Process Condensate Collection Process Condensate Major Utilities Cooling Water Electric Power Offgas [To Atmosphere] O 2 and CO 2 Rich [To Boiler] Expander Optional APCI PRISM Membrane 5

6 Air Products CO 2 Purification and Compression Technology for Oxyfuel Sour Compression SOx, NOx, Hg Removal Auto Refrigerated Inerts Removal Ar, N 2, O 2 Air Products PRISM Membrane For Enhanced CO 2 + O 2 Recovery 6 SOx/NOx removed in compression system NO is oxidised to NO 2 which oxidises SO 2 to SO 3 The Lead Chamber Process FGD and DeNOx systems Optimization Elimination Low NOx burners are not required for oxyfuel combustion Hg will also be removed, reacting with the nitric acid that is formed Removal minimises compression and transportation costs. Optional O 2 removal for EOR grade CO 2 CO 2 capture rate of 90% with CO 2 purity >95% CO 2 capture rate depends on raw CO 2 purity which depends on air ingress Inerts vent stream is clean, at pressure and rich in CO 2 (~25%) and O 2 (~20%) Polymeric membrane unit selective for CO 2 and O 2 in vent stream will recycle CO 2 and O 2 rich permeate stream to the boiler. CO 2 capture rate increases to >97% and ASU size/power reduced by ~5% Needs Engineering Data Mature Tech, Needs Data Commercial

7 NOx SO 2 Reactions in the CO 2 Compression System We realised that SO 2,NOx and Hg can be removed in the CO 2 compression process, in the presence of water and oxygen. SO 2 is converted to Sulfuric Acid, NO 2 converted to Nitric Acid: NO + ½O 2 NO 2 (1) Slow 2 NO 2 N 2 O 4 (2) Fast 2 NO 2 + H 2 O HNO 2 + HNO 3 (3) Slow 3 HNO 2 HNO NO + H 2 O (4) Fast NO 2 + SO 2 NO + SO 3 (5) Fast SO 3 + H 2 O H 2 SO 4 (6) Fast Rate increases with Pressure to the 3 rd power only feasible at elevated pressure Little Nitric Acid is formed until all the SO 2 is converted Pressure, reactor design and residence times, are important. 7

8 Air Products CO 2 Compression and Purification System: Removal of SO 2, NO x and Hg 1.02 bar 30 C 67% CO 2 8% H 2 O 25% Inerts SOx NOx BFW Condensate cw bar 30 bar cw Water Dilute HNO 3 30 bar to Driers Saturated 30 C 76% CO 2 24% Inerts cw 8 Dilute H 2 SO 4 HNO 3 Hg

9 Compression Options to 30 bar Axial Compressor (plus inline radial) Higher compression ratios Higher outlet temperature So better integration options Simpler configuration No intercoolers But higher power consumption Offset with integration opportunities Can be single train to ~8 900MWe Integrally geared compressor Lower power consumption Less opportunity for integration Might need multiple trains for >500 MWe plants 9

10 CO 2 Compression and Purification System Inerts removal and compression Flue Gas Vent 1.1 bar ~25% CO 2 ~75% inerts Flue Gas Expander Flue Gas Heater Aluminium plate/fin exchanger -55 C Driers bar Raw CO 2 Saturated 30 C 75 85% CO 2 CO 2 product ~96% CO 2 ~4% Inerts 60 C dp

11 CO 2 Purity and Recovery 55 C is as cold as we can make the phase separation CO 2 purity depends on pressure With 75% CO 2 in the feed, at 30 bar and 55 C, CO 2 purity is 95% Higher pressure gives lower purity CO 2 CO 2 recovery depends on pressure Lower pressure gives lower CO 2 recovery At 15 bar and 55 C, CO 2 recovery is 75% At 30 bar and 55 C, CO 2 recovery is 90% CO 2 recovery depends on feed composition Increases from zero at 25mol% to 90% at 75mol% Reducing air ingress increases CO 2 capture rate 11

12 Optimising Heat Exchange in a CPU Aim: minimise area under curve between hot and cold streams Use two pressure levels to minimise area/improve efficiency Impure CO 2 boils as a curve minimising area/improving efficiency Pure CO 2 boils at a constant temperature flat line in cooling curve 12

13 Cooling Curve Low Purity Mode Process refrigeration is provided by vaporising product CO 2 at two pressures bar Duty 20 bar Lines are curved since evaporating CO 2 is not pure, only around 95% 13

14 Cooling Curve Pure CO Process refrigeration is provided by vaporising product CO 2 at three pressures, the highest being the column reboiler bar 18 bar Lines are straight since evaporating CO 2 is pure 28 bar Duty

15 Compression Options from 30 bar to Pipeline Pressure Integrally geared compressor only feasible option Expander wheels can be integrated onto compressor bull wheel 10 stage Integrally Geared Compressor 15

16 Can we improve on ~90% CO 2 Capture? Vent stream is at pressure and is CO 2 (and O 2 ) rich Flue Gas Vent 1.1 bar ~25% CO 2 ~25% O 2 ~50% N 2 Flue Gas Expander Flue Gas Heater Aluminium plate/fin exchanger -55 C Driers bar Raw CO 2 Saturated 30 C 75 85% CO 2 CO 2 product ~96% CO 2 ~4% Inerts 60 C dp

17 Air Products Oxy-Fuel CO 2 Capture and Purification with Air Products PRISM Membrane Flue Gas Expander Flue Gas Heater To Boiler Membrane Aluminium plate/fin exchanger 55 C Driers bar Raw CO 2 Saturated 30 C 75 85% CO 2 CO 2 product ~96% CO 2 ~4% Inerts 60 C dp

18 Advantages of Air Products CO 2 Purification Technology for Oxyfuel Vent stream is clean, at pressure and rich in CO 2 (~25%) and O 2 (~20%) Polymeric membrane unit selective for CO 2 and O 2 in vent stream will recycle CO 2 and O 2 rich permeate stream to boiler. CO 2 Capture increase to >97% ASU size/power reduced ~5% Membrane skid at the Air Products Vattenfall Oxyfuel Pilot Plant 18

19 Path to Large-Scale Demonstration Cylinder fed bench rig Photo courtesy of Imperial College London 160 kw th oxy-coal rig Photo courtesy of Doosan Babcock Batch 15 MW th oxy-coal combustion unit Renfrew, Scotland Photo courtesy of Alstom Power 6 kw th slip stream 30 MW th oxy-coal pilot plant DOE Project Host: Alstom,Windsor, CT Photo courtesy of Vattenfall Schwarze Pumpe, Germany 0.3 MW th slip stream Large-Scale (~300 MW) Demo 1 MW th slip stream

20 The effect of Pressure on SO 2 and NO Conversion (1 sl/min, 7 and 14 barg) Inlet 14 bar g After Compressor & Receiver Conversion Inlet 7 bar g After Compressor & Receiver Conversion (Point A) (Point C) (Point A) (Point C) ppm SO % % ppm NOx % % 20

21 Key Learnings from Imperial College Work NO oxidation rate confirmed to increase rapidly with increased pressure At low temperature (~ C), SO 2 oxidation to SO 3 / H 2 SO 4 only occurs at an appreciable rate in presence of NO 2 and a condensed phase Significant conversion can occur even with very small liquid phase volumes (i.e., very low L/G ratios) Speculation that condensation creates a fine mist with large interfacial surface area, and that reaction is occurring at the interface Speculation that reactions are accelerated at low ph Recognized need to develop internal capability to explore broader range of parameters and to increase rate of data generation 21

22 DOE Project: Air Products Sour Compression PDU Side View of PDU Acid Reactor (C102) 1 st campaign Jan nd campaign April May

23 DOE Project: Air Products Sour Compression PDU Key Results Oxyfuel 22 January For the overall process, total SO 2 removal was % (based on gas compositions). For the overall process, total NOx removal was % (based on gas compositions). ppmv Reactor Outlet Reactor Outlet 20:38:24 20:52:48 21:07:12 21:21:36 21:36:00 21:50:24 22:04:48 22:19:12 22:33:36 The effects of variations in the SO 2 /NOx feed ratio, column pressure, gas flowrate and liquid recirculation on the reactor performance were explored. Process performance was most sensitive to SO 2 /NOx feed ratio, over the range of parameter values investigated. SO 2 was removed from the flue gas through both sulfite and sulfate mechanisms. Time Reactor Outlet Reactor Inlet Reactor Inlet Reactor Inlet Reactor Inlet Condition D SOx Conversion >99% NOx conversion >90% (NOx zero +/ 20 ppmv) [FLUGAS]NO.SCALED [FLUGAS]SO2.SCALED

24 Lab-Scale Reactor System Commissioned Sept to further our understanding of SO x /NO x reaction chemistry during compression Wide range of conditions possible: CO 2 O 2 N 2 SO 2 / N 2 NO / N 2 MFC MFC MFC MFC MFC MFC Gas Humidifier To Analysis Backpressure Regulator To Vent Absorber Column Process Flow Water Flow High P Water Pump Recirc Pump Control Valve Up to 3000 ppm SO 2 24 Up to 1000 ppm NO x Temperature range from ambient to 400 C Pressure range from atmospheric to 30 atm 3 modes of operation: Dry gas Humidified gas Gas liquid

25 Sour Compression Modelling Concurrent with the technology demonstration projects, lab experiments and ASPEN modelling were carried out to develop a robust reaction model Goals of modelling: Single reaction model to describe reactions in compression train and in column Use literature reactions and kinetics wherever possible Same model can be used to describe lab data and to describe pilot data from multiple configurations / scales (Renfrew, Windsor, Schwarze Pumpe) Modelling timeline: 2005: 1st reaction model developed from literature references (no data available at this time) October 2009: research program with Imperial College initiated September 2010: startup of Air Products lab reactor system July 2011: Final version of reaction model developed from lab data 25

26 Lab unit results Sour Compression Model compared to experimental data 100% 90% 80% 70% 60% 50% 40% 30% 20% 100% 10% 90% 0% 80% 0% 20% 40% 60% 80% 70% 100% Model prediction 60% Lab unit results Column Configuration 50% 40% 30% 20% 10% 0% Compression Train Configuration SO2 removal NO conversion N removal N2O yield 45 line 0% 20% 40% 60% 80% 100% Model Prediction 26

27 27 The Vattenfall Air Products Oxyfuel CPU Pilot Plant

28 Air Products CO 2 Purification Unit (CPU) Pilot Plant at Vattenfall s Schwarze Pumpe CO 2 Returned To OxPP Raw Flue Gas Sour Compression TSA Unit Mercury Removal Auto Refrigerated Inerts +O 2 Removal Process Condensate Collection Process Condensate O 2 and CO 2 Rich [To OxPP] Inerts Vent [To OxPP] Air Products PRISM Membrane 28

29 29 50/50 Flue Gas Mix From Before and After OxPP FGD

30 50/50 Flue Gas Mix From Before and After OxPP FGD 400 Inlet K432 Inlet Column Exit Column NO NO x NO and NO 2 (ppm, Dry) NO Time (minutes)

31 Conclusions Purification of the CO 2 from oxyfuel fired coal power plants is a technology ready for commercialisation Several advances in CPU technology have been described which will improve the performance of the CPU and the power plant Air Products is developing commercial offerings for CPU plants on demonstration plants 31

32 Air Separation Processes Adsorption Pressure swing (PSA) and Vacuum swing (VSA) Small scale, up to ~200 tonnes/day O 2 single train Limited purity O 2 (~93%) Cryogenic distillation Most flexible higher purity, liquids Large scale, up to ~5000 tonnes/day O 2 Other Ion Transport Membrane in development at ~100 tonnes/day O 2 32

33 Overview Of The Process Main and Boost Air Compression Air Cooling and Pretreatment Cryogenic Separation Storage Oxygen Air Heat Heat 33

34 Cryogenic Heat Exchange Brazed aluminium plate fin exchangers Cools air streams against product streams to recover refrigeration Ambient to cryogenic temperatures Boost Air Nitrogen Main Air Gaseous Oxygen Main Heat Exchanger 34 Liquid Oxygen Condensed Boost Air Nitrogen Main Air

35 35 Aluminium Plate-Fin Heat Exchanger Completed Core

36 Distillation Technology Structured Packing Lower pressure drop saves up to 10% of air compressor power Better turndown Higher plant capacity Sieve trays Shorter columns 36

37 37 Structured packing

38 Reboiler-Condenser High pressure nitrogen condenses and boils low pressure oxygen Aluminium plate fin heat exchanger Can be thermosyphon or downflow (falling film) type THERMOSYPHON TRAYS OR PACKING DOWN FLOW TRAYS OR PACKING SPLASH BAFFLE VAPOR LIQUID LIQUID LIQUID LEVEL LIQUID LEVEL CORE CORE VAPOR LIQUID LIN LIQUID LEVEL SPLASH BAFFLE LIN GAN GAN 38

39 Introduction to ASU cycles Low pressure gaseous oxygen (LPGOX) cycle Liquid oxygen boiling (LOXBOIL) cycle Pumped liquid oxygen (PLOX) cycle 39

40 LPGOX (GOX compression) cycle Gaseous oxygen is taken from the low pressure column and compressed in an oxygen compressor MAC Air Pretreatment Columns Waste GOX Oxygen compressor Waste LIN Main Exchanger Expander Subcooler 40

41 LOXBOIL cycle Liquid oxygen is taken from LP column increased in pressure by static head and boiled by condensing air from the main air compressor (MAC) Air Pretreatment AIR GOX LPGAN Waste Low Pressure Column Main Exchanger Subcooler High Pressure Column LOX Boil Exchanger 41

42 Pumped LOX cycle Liquid oxygen is taken from the LP column, pumped to pressure and boiled against condensing high pressure air from the booster air compressor (BAC) MAC Air Pretreatment Columns GOX Booster Compressor Waste Main Exchanger Expander LOX Pump Subcooler 42

43 Oxygen Requirements for Oxycoal CO 2 Capture Oxygen pressure is low Boiler runs close to atmospheric pressure Oxygen purity is low (<97%) Air leaks into boiler, impurities must be removed from CO 2 Easier to remove argon from CO 2 than from O 2 Oxygen demand is large 500MWe power plant needs ~10,000 tonnes/day O 2 No use for co products High efficiency and low capital desirable New opportunities to optimise the ASU 43

44 Low Purity, Low Pressure Dual HP Column Cycle for Oxyfuel

45 Oxycoal Reference ASU Cycle Integration is not always required or desirable With no integration, three column cycle is best Minimum power input, high O 2 recovery But three column cycle still ideal for integration Adiabatic compression with heat recovery Optional N 2 at 2.5 bar(a) if it can be used So Reference ASU based on three column cycle 45

46 ASU Machinery and Drives Significant part of ASU cost (capital and power) Critical to optimise efficiency vs. capital cost Likely to reach referenced machinery limits Can use multiple trains for a single cold box Centrifugal or axial air compressors Centrifugal up to ~5000 tonnes/day O2 Axial up to ~8000 tonnes/day O2 GT derived units will be even larger Electric Motor or Steam Turbine drive (GT unsuitable) Motors simplify operation but may have starting issues Steam turbines more efficient for power generation than mechanical drives balances extra electrical losses 46

47 Oxycoal Reference ASU Designs developed for a scalable reference plant Column diameters within manufacturing capabilities (referenced to 7000 te/d) 47 Size te/d O 2 Machinery options Power MW 3,000 4,000 Centrifugal 1 or 2 train or axial 1 train ,000 5,500 Centrifugal 1 or 2 train or axial 1 train ,500 7,000 Centrifugal 2 train or axial 1 train ,000-10,000 Centrifugal or axial 2 train 53-82

48 Oxycoal ASU Flexibility Turndown limited by compressors not cold box Normally % Can increase range with efficiency penalty More compression trains or multiple plants give wider, more continuous range Rapid ramping possible Dynamic modelling: 5% / minute within ±2% purity Model predictive control (MPC) will be used Instantaneous back up system For plant trip and peak shaving ASU make liquid for tank refill 48

49 Oxygen Supply Concepts Sale of equipment consumer purchases ASU ASU vendor scope of supply may vary Lump sum turnkey Reimbursable turnkey Proprietary Kit Vendor could have operating contract Sale of gas supplier owns & operates ASU Long term contracts (15 20 years) Fixed and variable cost elements Co product credits may be available Integration possible but more complicated 49

50 Conclusions Air Products Oxycoal ASU has low specific power with or without power cycle integration Integration needed to get lower specific power boiler modification & novel expanders Single cold box to 10,000 te/d O 2 modest scale up Single train machinery up to about 8,000 te/d O 2 Rapid load change possible Heat integration beneficial depends on specifics 50

51 Thank you