Luminant Carbon Management Program

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1 Aqueous Piperazine as a New Standard for Amine Scrubbing Technology Gary Rochelle, Eric Chen, Stephanie Freeman, Thu Nguyen, David Van Wagner, Qing Xu, Alex Voice Post-Combustion CO 2 Capture Workshop July 12, 2010 eric.chen@mail.utexas.edu Outline Amine Scrubbing Technology Irreversibility Maximizing Temperature Swing Reagent Robustness Degradation Volatility Reclaiming Conclusions 2

2 Background The MEA 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) NETL detailed evaluations Most comparisons made to 30 wt% MEA Proprietary solvents make it difficult to compare improvements and new developments 3 Background Concentrated Piperazine (8 m, 40 wt%) Second generation amine technology Extensive performance data available Proprietary 2G solvent technology data unavailable for comparison High-temperature 2-stage flash process for piperazine Propose concentrated piperazine as new standard for technology comparisons and evaluations 4

3 Background 8 m Concentrated Piperazine 7 m MEA 8 m PZ CO 2 Abs Rate (mol/s-pa-m- 2 ) 4.3x10 7 2X Working Capacity (mol/eq) X Volatility Lean (ppm) 30 7 Thermal Stability ( C) Oxidative Degradation 18%/wk Neglig. Reclaiming Boil Pt ( C) Energy Use (kwh/tonne) % < Background Piperazine Species 5 Piperazine (PZ) H N N H Protonated PZ Carbamate H H N + O N O - PZ Carbamate Protonated PZ PZ Dicarbamate H N N O O - H H N + N H O O - N N O O - 6

4 T(C) Solubility Envelope for Piperazine Permits Concentrated Solvent PZ 6H 2 O (s) Aqueous PZ Solution 8 m PZ 10 m PZ Background H + PZCOO - H 2 O (s) Expected loading range CO 2 Loading (mol/mol alkalinity) 7 Irreversibility Maximizing Temperature Swing ENERGY ANALYSIS 8

5 PZ High Temperature 2-Stage Flash Process Flowsheet Absorber 40 C Scrubbed Flue Gas Ldg = 0.31 High Temperature 2-Stage Flash Steam Intercooling Cross-Exchanger T Approach = 5 C Flash Tank 17 bar 150 C Flash Tank 11 bar 150 C Flue Gas Concentrated Piperazine Solvent Ldg = Irreversibilities of Two Stage Flash 22 kwh/tonne CO 2 ABSORBER 40 C 34 kwh/tonne 14 kwh/ tonne 25 kwh/ tonne 9 kwh/tonne 150 C 150 C W IDEAL = 104 kwh/tonne, W REAL = 219 kwh/tonne 10

6 ABSORBER IRREVERSIBILITY 11 Absorber Driving Force CO 2 Mass Transfer at 40 C (Wetted Wall Column) Normalized Flux k g (10-7 mol/s Pa m 2 ) m MEA 8 m PZ % P CO2 40 C (Pa) 5 % 12

7 Absorber Exergy Loss 14 kwh/tonne Estimated Packing Area from k g Ln mean k g P = 2.4e-3 gmol/s-m 2 Lean: k g (P out -P lean *)= 2.2e-6 *( )*10 5 Rich: k g (P in -P rich *) = 5e-7*( )*10 5 Absorber packing volume 1.9e3 m 3 for 800 MW, 250 m 2 /m tonne CO 2 removed/mw-hr 25 x 25 x 13.5 m 1.5 m/s gas velocity Exergy lost/mole CO 2 RTln(P g /P * bulk liq) =RTln(0.12/0.05)= 14 kwh/tonne CO 2 13 CROSS-EXCHANGER IRREVERSIBILITY 14

8 CO 2 Solubility in 8 m PZ (40 C) P CO2 (Pa) CO 2 Capacity 0.88 mol/kg 8mPZ 0.48 MEA Loading (mol CO 2 /mol alk.) Cross-Exchanger Exergy Loss 25 kwh/tonne Steam Makeup for Unrecovered Sensible Heat Loss 15 Q C p T / capacity ( 3.5 J/mole K)*5K /(0.88 mole/kg) 20 kj/mole CO2 Steam at 155 C W loss T 0.75Q stm T T stm sink * 20* kwh/tonne CO 2 1e6 44*

9 TWO-STAGE FLASH IRREVERSIBILITY Amine Loss, k (%/wk) Thermal Stability Permits 150 C Stripping m MEA = m PZ T ( C) 18

10 8 m PZ Provides High P at 150 C P CO2 (bar) ºC H abs Habs (kj/mol CO2) CO 2 Loading (moles/equiv PZ) Two-Stage Flash Regeneration Exergy Losses - 43 kwh/tonne Flash losses 9 kwh/tonne Pressure loss of finite flash stages - 4 kwh/tonne W loss = 0.25RTln(29/17) RTln(17/11) Temperature driving force 5 kwh/tonne W loss = 0.75Q flash T/T = 0.75*95*5/423 Condenser loss 34 kwh/tonne moles H 2 O/mole CO 2 Condense at 125 C W loss = 0.625*40*(125-40)/( )

11 Total Equivalent Work Single Stage Flash Calculate total equivalent work for generic single stage flash H CO2 for 60, 70, 80 kj/mol T = 90 to 150 C H 1 T Correlate to H [ ] W W total equiv W CO2 equiv 0.75Q flash H2O W T comp flash W pump 5 T T 5 flash kj gmol K sink Maximizing Temp Swing Reduces Total Equiv Work 21 Wtotal(kWh/tonne CO 2 ) H CO2 =60 kj/mole 90 C Single stage flash at C Compression to 150 bar Lean P CO2 = 0.5 kpa at 40 C Greater T strip & H CO2 reduce W total W total = W equiv +W comp +W pump 70 Piperazine 150 C MEA 120 C (H CO2 -H H20 )(1/T) (kj/gmol-k) 80 22

12 Reboiler Duty of Amine Scrubbing Heat Duty (MJ/tonne CO 2 ) MEA KS-1 PZ Minimum with 105 C Steam Year W (kwh/tonne CO 2 ) Estimated Total Equivalent Work 12% CO 2, 90% Removal, 150 bar, 40 C W equiv T 0.75Q MEA Minimum Work = 109 kwh/tonne CO 2 Separation = 46 kwh/tonne Compression = 63 kwh/tonne stm T T stm Year sink W comp W PZ pump 24

13 Thermal Degradation Oxidative Degradation Amine Volatility Corrosion Result Solvent Reclaiming ROBUST SOLVENT MANAGEMENT Solvent Robustness Thermal Degradation at 135 C Amine Structure k (%/wk) PZ 0.07 AMP 1.2 DGA 2.1 HEP 2.8 MEA 8.1 EDA

14 Amine Remaining (%) Oxidative Degradation 0.4 mm Fe 2+, 0.1 mm Cr 3+, 0.05 mm Ni 2+ (55 C) 7 m MEA =0.4 8 m PZ =0.3 Solvent Robustness 98% O 2, 2% CO RPM Time (hours) 27 P Amine /[Amine] (Pa/m) 1.0 Amine Volatility at 40 C 7 ppm Solvent Robustness 7 m MEA 30 ppm 8 m PZ CO 2 Loading (mol/mol alkalinity) 28

15 Concentation (mm) Thermal Degradation Experiment Solvent Robustness Trace Fe 2+ in SS316 Cylinders 7 m MEA, 135 C, 0.4 ldg (6.7% loss amine/wk) 8 m PZ, 150 C, 0.3 ldg (0.4% loss/wk) Time (weeks) Reclaiming Concepts Traditional Thermal or distillation Reclaiming Atm or vacuum Boiling Point ( C): PZ=146, MEA=170 PZ thermally stable Ion Exchange or electrodialysis as with MEA K 2 SO 4 crystallization with addition of KOH 0.17 m sulfate solubility Solvent Robustness 29 30

Conclusions for Concentrated PZ A published amine system that requires only 2.6 MJ t or 220 kwh e per tonne CO 2 ( = 50%) 10-20% less energy than 30 wt% MEA Double the CO 2 mass transfer rate 1.

16 Conclusions for Concentrated PZ A published amine system that requires only 2.6 MJ t or 220 kwh e per tonne CO 2 ( = 50%) 10-20% less energy than 30 wt% MEA Double the CO 2 mass transfer rate 1.8 x capacity High P (17 11 bar) stripping at 150 C Easier solvent management than MEA Thermally stable Oxidatively stable Less volatile than 7 m MEA Good opportunities for reclaiming 31 Questions?

CO 2 Capture by Amine Scrubbing

CO 2 Capture by Amine Scrubbing By Gary T. Rochelle Luminant Carbon Management Program Department of Chemical Engineering The University of Texas at Austin US UK workshop May 9, 2010 Roadmap Research on