Postcombustion Capture Amine Scrubbing By Gary T. Rochelle Department of Chemical Engineering The University of Texas at Austin July 7, 2014
Some Message The Problem : CO 2 from Existing Coal Power The Solution: Amine Scrubbing deployed by 2020 Advances in Solvents and Processes Reduce Energy from 400% to 200% of Minimum W Provide Stable, Benign Amine Systems As Limestone Slurry Rules FGD after 30 yrs; Amine Scrubbing will dominate CO 2 capture
2. Absorption/stripping = The technology Near Commercial Tail End Technology for Existing Plants Oxycombustion and gasification are not. Expensive in $$ and energy
CO 2 Capture & Storage Disposal Well Net Power 3-6 atm stm 150 atm CO 2 Coal Turbines Boiler -NO x ESP CaCO 3 FGD Abs/Str NH 3 Flyash CaSO 4
Amine Scrubbing (Bottoms, 1930) 30 wt% MEA CO 2 Packed Absorber 1 bar DT=5C Stripper 2 bar Packing or Trays 12% CO 2 5% O 2 0 ppm SO 2 40 o C 115C Reboiler 45 psig stm
Other process components Additional gas pre-cleaning to remove SO 2 -- neutralizes amine SO 3 causes amine aerosols NO 2 results in carcinogenic nitrosamine Chloride -- causes corrosion Particulate-- fouls equipment, causes amine aerosols Gypsum -- fouls solvent Gas precooling to 40 o C to min energy use H 2 O wash to remove volatile & aerosol amine CO 2 compression to 150 bar for storage
Gas Turbine/ Combined Cycle Modern CH 4 power, sometimes base-loaded Compress 300% excess air Inject and burn CH 4 to get 2000+F Expand to atm pressure (1000F) Extract heat in steam boiler to 300F 3-5% CO 2 without recycle, 15% O 2 Does not require direct contact cooler 6-7% CO 2 with recycle, 5-10% O 2 Get energy from low P steam
Tail End Technology Development Characteristic of Absorption/Stripping Low risk, low cost, less calendar time Resolve problems in small pilot plants Using real flue gas Demo Full-scale absorbers with 100 MW gas
Other Solutions for Existing Coal Plants Combustion with O 2 producing mostly CO 2 O 2 plant gives equivalent energy consumption Gas recycle, boiler modification for high CO 2 Gas cleanup, compression including air leaks Coal Gasification Remove CO 2 and burn H 2 in new combined cycle O 2 plant, complex gasifier, cleanup, CO 2 removal Neither is Tail end Both require high development cost & time
Practical Problems = 40-70 $/MWh Energy = 20-25% of power plant output Issues of absorption/stripping 10-15%, Low P steam (25-35% of steam flow) 5-10%, CO 2 Compression 3%, Fans and pumps $15/ton CO 2 (0.25 MWh/ton CO 2 x $60/MWhr) Capital Cost $1000-1500/kw (e.g., $800 million-$1.2 billion for a 800MW plant) Absorbers same diameter as FGD, 50 ft packing Strippers somewhat smaller + heat exchangers Compressors $20-50/ton CO 2 for capital charges & maintenance Amine degradation/environ. impact ($1-5/ton CO 2 ) 10
T H E U N I V E R S I T Y O F T E X A S A T A U S T I N Texas Carbon Management Program Why amine scrubbing is here to stay 1. It was first: history repeats 2. It is remarkably energy efficient 3. Capital cost will come down 4. Problems are manageable 11
T H E U N I V E R S I T Y O F T E X A S A T A U S T I N Texas Carbon Management Program 1. History Repeats in the Power Industry CaCO 3 Slurry:::Amine Scrubbing CaCO 3 Event Amine 1948 1 st commercial plant 1980 1970 Too commercial for Gov. support But too costly, too dirty to use 1970-82 Government funds advanced alts In hope of game changer 1990 1995-1975-85 Govern. & EPRI fund test facilities 2010-1977 Power Industry deploys 250+ MW 2017? 2014 First choice dominates 2030?
T H E U N I V E R S I T Y O F T E X A S A T A U S T I N Texas Carbon Management Program Background 1. It was first: The MEA 1G Standard Amine scrubbing with absorption/stripping Post-combustion technology 80 years experience in acid gas treating Amine capture processes (Econamine & KS-1) 30 wt % (7 m) MEA benchmark (1 st generation) Reasonably fast, high DH abs, low m, low cost Not thermally or oxidatively stable 13
Aqueous Abs/Str: Near commercial 100 s of plants for treating H 2 & natural gas MEA and other amine solvents No oxygen 10 s of plants with gas combustion Variable oxygen, little SO 2 Fluor, 30% MEA, 1000 tpd (80 MW gas), 15% O 2 MHI, KS-1, 283 tpd (30 MW), <2% O 2 A few plants with coal combustion Abb-Lummus, 20% MEA, 6,8,33 MW Fluor, 30% MEA, 0.1,0.2,0.2,(6) MW pilots CASTOR, 30% MEA, 1 MW MHI, KS-1, 1, 25 (7) MW Cansolv, 125 MW
T H E U N I V E R S I T Y O F T E X A S A T A U S T I N Texas Carbon Management Program Background 2. 2G is Remarkably Energy Efficient. e.g. Piperazine [PZ] (5-8 m, 30-40 wt%) 2G/3G amine technology Fastest rate of CO 2 absorption Resistant to oxidation & thermal degradation High-T/P advanced flash process Twice the capacity of 7 m MEA Sufficiently high DH abs = 65-70 kj/mol Higher chemical cost, greater viscosity, constrained by solid precipitation 15
2. Advanced Flash Stripper is remarkably efficient 5% H 2 O 20K LMTD 25% H 2 O Cold Rich BPS 5% Warm Rich BPS 14% 121 o C Rich Solvent 0.40 Ldg Steam heater Lean Solvent 0.30 Ldg. 5K Avg. LMTD 150 o C Flash 16
W EQ (kj / mol CO 2 ) Alternative stripper configurations 8 m PZ, 150 o C 37 36 35 34 33 10% Interheated stripper Advanced flash stripper Simple stripper Flash stripper+cold rich BPS 32 0.26 0.28 0.30 0.32 0.34 Lean loading (mol CO 2 / mol alkalinity) 17
W (kwh/tonne CO 2 ) T H E U N I V E R S I T Y O F T E X A S A T A U S T I N Texas Carbon Management Program 500 400 300 200 Estimated Total Equivalent Work 12% CO 2, 90% Removal, 150 bar, 40 C 1.08 GJ/t 0.72 GJ/t W equiv 0.75 Q T MEA Energy Analysis stm T stm T sink W comp W PZ pump 100 Minimum Work = 109 kwh/tonne = 0.39 GJ/t CO 2 Separation = 46 kwh/tonne = 0.17 GJ/t Compression = 63 kwh/tonne = 0.23 GJ/t 0 2000 2004 2008 Year 18
Thermodynamic Efficiency of Common Separation Processes Process Efficiency (%) W minimum / W actual CO 2 Capture by Amine Scrubbing 54 Cryogenic Air Separation 25 Common Distillation 15-35 Water Desalination by Reverse Osmosis 21 Therefore it is improbable that we will be better than 200 kwh/ton CO 2, with any technology.
3. Capital Costs will Decrease. Annualized Equipment Cost for Amine Scrubbing, $/tonne CO 2 MEA-SS PZ-SS PZ-AFS CAPEX 22.2 22.1 19.4 Absorber 5.2 4.7 4.7 Amine/Amine Exchangers 1.8 4.8 5.2 Reboiler/Steam Heater 4.3 5.7 2.3 Compressor 5.6 3.6 3.5 All Other Units 5.3 3.3 3.7 20
3. Opportunities to decrease CAPEX Absorber Merge SO 2 polish, DCC, CO 2 absorption, water wash Single vessel, concrete, intercooling Cross Exchanger, Steam heater Greated DP, Less expensive plate and frame Larger single unit Compressor Greater stripper P Larger single unit Intercooled, supersonic 21
4. Amine Problems will be solved As with CaCO 3 scrubbing Problem Resolution Corrosion Oxidation Thermal Degradation Nitrosamine Amine Aerosol Use Stainless Inhibitors Control Chemistry Stable Amine (PZ) Inhibitors Stable Amine (PZ) Lower Stripper T Thermal decomposition Reduce NO x Advanced water wash?
Aqueous Solvent Alternatives MEA is hard to beat Stripper Energy Requirement Mass Transfer Rates Makeup and Corrosion
Carbonate & Tertiary/Hindered Amines CO 3= + CO 2 + H 2 O 2 HCO - 3 20 kj/gmol Carbonate Bicarbonate very slow HO-CH 2 -CH 2 -N-CH 2 -CH 2 -OH MDEAH + + HCO - 3 CH 3 60 kj/gmol, slow Methyldiethanolamine (MDEA) CH 3 HO-CH 2 -CH 2- NH 2 + CO 2 AMPH + + HCO - 3 CH 3 60 kj/gmol, slow 2-Aminomethylpropanolamine (AMP, KS-1(?))
Primary and Secondary Amines 60-85 kj/gmol, fast 2 HO-CH 2 -CH 2 -NH 2 + CO 2 HO-CH 2 -CH 2 -NH-COO - + MEAH + Monoethanolamine (MEA) MEA Carbamate (MEACOO - ) 2 NH 3 + CO 2 NH 2 -COO- + NH 4 + Ammonia HN CH 2 -CH 2 NH + CO 2 + HPZ-COO - CH 2 -CH 2 Piperazine (PZ)
Fast Solvents Amine (m) Capacity - H abs @P CO2 =1.5kPa k g, avg x1e-7 @40 C Deg rate @135 o C mol/kg solv kj/mol mol/s Pa m 2 1e-9 s -1 PZ 8 0.79 70 8.5 1.2 1-MPZ 8 0.83 67 8.4 7 MDEA/PZ 5/5 0.99 70 8.3 45 2-MPZ/PZ 4/4 0.84 70 7.1 3 MDEA/PZ 7/2 0.80 68 6.9 45 2-MPZ 8 0.93 72 5.9 5 HEP 7.7 0.68 69 5.3 35 MEA 7 0.47 82 4.3 134
T H E U N I V E R S I T Y O F T E X A S A T A U S T I N Texas Carbon Management Program Why Advanced Capture Processes flounder 1. Separation driven by mechanical compression is not energetically competitive with thermal swing. 2. Anhydrous solvents, slurries, and solids are not more reversible than amine solutions. 3. Solids and slurries have poor equipment alternatives for heat exchange & contacting 4. More expensive solvents & polymers will not compete in the dirty coal environment 27
T H E U N I V E R S I T Y O F T E X A S A T A U S T I N Texas Carbon Management Program Why amine scrubbing is here to stay 1. It was first: history repeats 2. It is remarkably energy efficient 3. Capital cost will come down 4. Problems are manageable 28