Energy Requirement for Solvent Regeneration in CO 2

Transcription

1 Energy Requirement for Solvent Regeneration in CO 2 Capture Plants Amy Veawab Andy Aroonwilas Faculty of Engineering, University of Regina Regina, Saskatchewan, Canada S4S A2 Presented at the 9 th International CO 2 Capture Network, Copenhagen. June 16, 26

2 Outline Introduction/ motivation Research Objective Methodology Results & Discussion Conclusions Acknowledgement

3 Amine Treating Plant for CO 2 Capture Treated gas CO 2 Absorber Regenerator Reboiler CO CO 2 capture 2 capture unit unit Plant feature: Absorption process Chemical reaction Monoethanolamine (MEA) Flue gas treatment Coal Flue gas Electricity Steam Coal-fired Coal-fired power power plant plant HO-CH 2 -CH 2 -NH 2 Energy input for solvent regeneration Air

4 Utility & Energy Consumption Cooling water Treated gas CO 2 Steam consumption: Absorber Regenerator Steam 4,-5, kj/kg CO 2 Steam cost: Reboiler 7-8% of operating cost Electricity CO 2 + 2RR NH RR NH RR NCOO -

5 Solvent Regeneration CO 2 + Water vapor Energy utilization: (Steam) Liquid with high CO 2 content Heat of reaction (CO 2 Amine) Heat capacity (increase in Temp.) Heat of water vaporization Stripped CO 2 Liquid with low CO 2 content Water vapor Cost reduction: Energy-efficient solvents Process modifications

6 Research Objectives To evaluate reboiler heat duty of different solvent types under different operating conditions To correlate relationships between process parameters and reboiler heat-duty To establish a strategy for process cost reduction

7 Experiments (Flow-Through( Gas Stripping System)

8 Experiments Single Alkanolamine Blended Alkanolamine MEA (Monoethanolmine) DEA (Diethanolamine) MDEA (Methyldiethanolamine) MEA-MDEA DEA-MDEA Mixing Ratio (mol : mol) Rich CO 2 Loading Solvent Concentration 1 : 2 1 : 1 2 : 1.3 mol/mol.5 mol/mol 4. kmol/m 3 5. kmol/m 3 7. kmol/m 3

9 Experimental Validation lean CO 2 loading (mol/mol) Reboiler heat-duty (kj/kg CO 2 ) 3,8 4,8 5,4 literature a (1-4 tonnes/day units) this study.3 (at 3,767 kj/kg CO 2 ).25 (at 4,849 kj/kg CO 2 ).23 (at 5,23 kj/kg CO 2 ) a Estimated values from the work by Wilson et al. (24)

10 Methodology (Energy model simulation) Process flow model Design & property sub-models Input Information Steam Property Sub-Model Enthalpy, entropy, Others Property Sub-Model (Gas + Liquid) Viscosity, density Vapor pressure Others Process Flow Model & Simulator (Different Process Flow scheme) Rate Based Sub-Model Absorber design Regenerator design CO 2 -Amine reaction Result Representation Thermodynamic Sub-Model Vapor-liquid equilibrium Speciation Equipment Design Sub- Model Pump, blower Cooler, heat-exchanger Condenser, reboiler

11 Mechanistic Model (Mass-transfer & Hydrodynamics) Input InputInformation: Information: Packing Packinggeometry geometry Operating Operatingconditions conditions Liquid Liquid Distribution Distribution Model: Model: Liquid Liquiddistribution distributionpattern pattern Maldistribution Maldistribution Thermodynamic Thermodynamic Model: Model: Vapor-liquid Vapor-liquidequilibrium equilibrium(vle) (VLE) Speciation (from Speciation (fromnrtl NRTLmodel) model) Mass-transfer Mass-transferdriving driving force force Interfacial InterfacialArea Area Model: Model: Dimensions Dimensionsofofliquid liquidrivulet rivulet Gas/liquid Gas/liquidinterfacial interfacialarea area(local (localregion) region) Mass-Transfer Mass-Transfer Model: Model: Two-film Two-filmtheory theory Mass-transfer Mass-transfercoefficient coefficient(k(kgg and and kkll)) Enhancement Enhancementfactor factor Results: CO2 Absorption (Results): Column Column Design Design Procedure: Procedure: Adiabatic Adiabaticabsorption absorption Performance Performanceofoffull-length full-lengthcolumn column CO concentration profile CO22 concentration profile Temperature Temperatureprofile profile Mass Mass balance balance Energybalance balance Energy e-8 1.e-7 1.5e-7 2.e L = 3.8 m 3 /m 2 -h e-8 1.e-7 1.5e-7 L = 7.6 m 3 /m 2 - h 2.e-7 2.5e-7 3.e-7 2.5e-7 3.e-7 3.5e-7 3.5e section at various liquid loads. 2 1e-7 2e-7 3e-7 4e-7 5e L = 12.2 m 3 /m 2 -h 12 14

12 Effect of Lean-CO 2 Loading.5 Lean CO2 loading (mol/mol) Favorable Region Unfavorable Region Reboiler heat duty (kj/kg CO 2 ) Rich Loading:.5 mol CO 2 / mol DEA, Concentration: 4 kmol/m 3

13 Effect of Lean-CO 2 Loading (con( con t) Unfavorable Region Favorable Region 2 2 C O 2 p artial p ressu re (kpa) Operating line (lean CO2 loading =.8 mol/mol) Operating line (lean CO2 loading =.7 mol/mol) Equilibrium line 4 kpa 1 kpa C O 2 p artial p ressu re (kpa) Operating line (lean CO2 loading =.2 mol/mol) Operating line (lean CO2 loading =.15 mol/mol) Equilibrium line CO 2 loading of liquid (mol/mol) CO 2 loading of liquid (mol/mol)

14 Simulation Results.6.5 Lean loading (mol/mol) Simulation Experiment Experiment Experiment (1) Series3.1 Min. heat duty Heat duty (kj/kg CO2)

15 Simulation Results (Effect of Reboiler Temp.).6.5 Lean loading (mol/mol) C 11 C 12 C Heat duty (kj/kg CO2)

16 Simulation Results (Effect of Regen Feed Temp.).6.5 Reboiler Temp. = 12 o C Lean loading (mol/mol) C 1C 11C Heat duty (kj/kg CO2)

17 Effect of Rich-CO 2 Loading.5 Lean CO2 loading (mol/mol) Rich CO2 loading =.5 mol/mol Rich CO2 loading =.3 mol/mol Reboiler heat duty (kj/kg CO 2 ).3 mol/mol Rich CO 2 Loading >.5 mol/mol Rich CO 2 Loading Solution: MEA, Concentration: 5 kmol/m 3

18 Effect of Rich-CO 2 Loading (con( con t) Rich Loading :.3 mol/mol 1 Rich Loading :.5 mol/mol 1 CO 2 partial pressure (kpa) Equilibrium line (rich-co2 loading =.3 mol/mol) Operating line 4 kpa CO 2 partial pressure (kpa) Equilibrium line (rich- CO2 loading =.5 mol/mol) Operating line CO 2 loading of liquid (mol/mol) CO 2 loading of liquid (mol/mol)

19 Effect of Solvent Concentration.5 Lean CO2 loading (mol/mol) MEA concentration 4 kmol/m3 5 kmol/m3 7 kmol/m Reboiler heat duty (kj/kg CO 2 ) Solution: MEA, Rich Loading:.5 mol CO 2 / mol solution

20 Effect of Solvent Concentration (con( con t) 1.5 Relative CO2 stripping rate (-) MEA concentration 4 kmol/m3 5 kmol/m3 7 kmol/m Reboiler heat duty (kj/kg CO 2 ) 4 kmol / m 3 > 5 kmol / m 3 > 7 kmol / m 3 Solution: MEA, Rich Loading:.5 mol CO 2 / mol solution

21 Effect of Single Alkanolamine.5 Lean CO2 loading (mol/mol) Monoethanolamine (MEA) Diethanolamine (DEA) Methyldiethanolamine (MDEA) MEA DEA. MDEA Reboiler heat duty (kj/kg CO 2 ) MEA > DEA > MDEA Rich Loading:.5 mol CO 2 / mol solution, Concentration: 4 kmol/m 3

22 Effect of Blended Alkanolamine Lean CO2 loading (mol/mol) Monoethanolamine (MEA) MEA-MDEA (2:1 molar ratio) MEA-MDEA (1:1 molar ratio) MEA-MDEA (1:2 molar ratio) Methyldiethanolamine (MDEA) MEA. MDEA Reboiler heat duty (kj/kg CO 2 ) MEA > MEA-MDEA (2:1) > MEA-MDEA (1:1) > MEA-MDEA(1:2) > MDEA Rich Loading:.5 mol CO 2 / mol solution, Concentration: 4 kmol/m 3

23 Effect of Blended Alkanolamines (con( con t) MEA concentration (kmol/m 3 ) Average heat of reaction or Reboiler heat duty (kj/kg CO2) Without Synergy Effect Heat of reaction (MEA-MDEA) Reboiler heat duty of MEA-MDEA blend (at lean CO 2 loading =.13 mol/mol) MDEA concentration (kmol/m 3 )

24 Effect of Blended Alkanolamines (con( con t) Lean CO2 loading (mol/mol) Diethanolamine (DEA) DEA-MDEA (2:1 molar ratio) DEA-MDEA (1:1 molar ratio) DEA-MDEA (1:2 molar ratio) Methyldiethanolamine (MDEA) DEA. MDEA Reboiler heat duty (kj/kg CO 2 ) DEA > DEA-MDEA (2:1) > DEA-MDEA (1:1) > DEA-MDEA (1:2) > MDEA Rich Loading:.5 mol CO 2 / mol solution, Concentration: 4 kmol/m 3

25 Effect of Blended Alkanolamines (con( con t) DEA concentration (kmol/m 3 ) Average heat of reaction or Reboiler heat duty (kj/kg CO2) Reboiler heat duty of DEA-MDEA blend (at lean CO 2 loading =.6 mol/mol) Heat of reaction (DEA-MDEA) MDEA concentration (kmol/m 3 )

26 Conclusions Reduction in reboiler heat-duty can be achieved by operating the plants at: High rich-co 2 loading Favorable range of lean-co 2 loading Low reboiler temperature High lean-regen. feed temperature Blended MDEA-based solvents Reduce excess water vapor at the regenerator top Approach heat of reaction

27 Split-Flow Configuration Scheme feature: Division of rich-solution from the absorber into two streams. Reduce the associated latent heat required during solvent regeneration. CO2 TREATED GAS CONDENSER LEAN COOLER High CO 2 absorption efficiency SEMI-LEAN COOLER RICH-LEAN EXCHANGER-I REFLUX PUMP Moderate regeneration efficiency Reduce waste vapor Moderate CO 2 absorption efficiency STRIPPER ABSORBER REBOILER High regeneration efficiency Extremely low CO 2 content BLOWER RICH-LEAN EXCHANGER-II

28 McCabe-Thiele Diagram (Typical Process) - - RICH LEAN EXCHANGER CO2 CONDENSER REFLUX PUMP STRIPPER REBOILER CO2 partial pressure (kpa) Column bottom Typical Amine Process Equilibrium line Operating line CO 2 loading (mol/mol) Large driving force Small NTU Short column Column top 25 % CO 2 High water vapor RICH-LEAN EXCHANGER -I RICH-LEAN EXCHANGE R -II CO2 CONDENSER REFLUX PUMP STRIPPER REBOILER CO2 partial pressure (kpa) Split-flow Process Equilibrium line Operating line Column top High % CO 2 Very low water vapor Mid-point CO 2 loading (mol/mol)

29 Simulation conditions: Column Process capacity Process Simulation CO 2 capture efficiency 95% Packed type 1, tonne CO 2 /day Absorption solvent Aqueous MEA solution Solvent concentration 5. kmol/m 3 CO 2 content before regen. CO 2 content after regen. Reboiler temperature.5 mol CO 2 /mol MEA mol CO 2 /mol MEA up to 12 o C

30 Process Simulation Results (Case I) Result representation: Dimension of absorption column Height of regeneration column Reboiler heat duty (energy input) Case I: Reboiler temp. = 11 o C, CO 2 content after regen. =.17 mol/mol Typical amine process Specific absorber size 1. Specific NTU Regen 1. Reboiler heat duty (Btu/lb mol CO 2 ) 144, (7,6 kj/kg) Split-flow (Operation I-CI) , (2,9 kj/kg) Split-flow (Operation II-CI) Split-flow (Operation III-CI) Split-flow: , (3,1 kj/kg) , (3,5 kj/kg) % energy saving

31 Simulation Results (Cases II & III) Case II: Reboiler temp. = 11 o C, CO 2 content after regen. =.22 mol/mol Process Specific absorber size Specific NTU Regen Reboiler heat duty (Btu/lb mol CO 2 ) Typical amine process , (4,4 kj/kg) Split-flow (Operation I-CII) , (3,6kJ/kg) Split-flow (Operation II-CII) , (3,6 kj/kg) Process Case III: Reboiler temp. = 12 o C, CO 2 content after regen. =.17 mol/mol Typical amine process Split-flow (Operation I-CIII) Specific absorber size Specific NTU Regen Reboiler heat duty (Btu/lb mol CO 2 ) 78, (4,1 kj/kg) 64, (3,4 kj/kg) Split-flow: 18 % energy saving

32 Acknowledgement Natural Sciences and Engineering Research Council of Canada (NSERC) Roongrat Sakwattanapong