Simultaneous Removal of SO 2 and CO 2 From Flue Gases at Large Coal-Fired Stationary Sources Y. F. Khalil (1) and AJ Gerbino (2) (1) Chemical Engineering Department, Yale University, New Haven, CT 06520 (2) AQSim, Inc., Glen Ridge, NJ 07028 OLI s 24 th User Conference Hyatt Hotel, Morristown, NJ October 23 24, 2007 1
Presentation Outline Motivation for developing alternative technologies for CO 2 capture: - U.S. GCCI - Integrated control technologies (ICTs) - Technical and economic barriers of CO 2 capture using MEA Research objectives Research apporach for modeling CO 2 and SO 2 capture using: - OLIs ESP - ICEM (DOE model) Results and discussion: IECM and ESP Summary Roadmap for future work 2
Motivation #1: The U.S. Global Climate Change Initiative (GCCI) GCCI is one of the primary drivers for CO 2 emission reduction. Between 2002 and 2012, this initiative targets 18% reduction in the greenhouse gases (GHGs) intensity. A second goal of this initiative is to provide a portfolio of commercially-ready CO 2 removal technologies for 2012 assessment. 3
Motivation #2: Integrated Control Technologies (ICTs) More cost effective compared to single-effect technologies Less footprint and, hence, easier to retrofit Possibility of sharing some unit operations Possibility of shared raw materials Example: simultaneous removal of CO 2 and SO 2 4
Motivation #3: Monoethanolamine (MEA) Scrubber for CO 2 Capture MEA scrubbing is the conventional technology for CO 2 capture from flue gases Unfortunately this technology is energy-intensive -- a significant amount of energy is required for recovering the MEA solvent: 67% of the MEA plant operating cost is attributed to steam requirements for solvent regeneration and 15% of the cost is for MEA makeup. MEA is corrosive and requires adding corrosion inhibitors Some CO 2 remains in the regenerated MEA MEA makeup For a 500 MW th coal-fired plant, MEA makeup ~ 22.7 tons/hr MEA recirculated ~ 6,599 tons/hr MEA HEX Additional drawback of MEA technology: Low CO 2 loading, i.e., grams of CO 2 absorbed per gram of absorbent. 5
Total Energy Usage for Recovery & Compression: MEA System 3.4 million BTU/ton CO2 5.2% 5.2% 4.5% Absorption Feed Compr 1st stage - 1-10 atm 2nd stage - 10-100 atm 85.1% Total Energy: 3.41 MBtu/ton CO 2 Slightly compress the feed gas to 1.2 bar 0.15 MBtu/ton CO 2 Desorb CO 2 in the stripper 2.9 MBtu/ton CO 2 Source: J. L. Anthoney, Dept. of Chem. Eng, Kansas State U. Compress the CO 2 off-gas to 100 bar 2 stages at 0.18 MBtu/ton CO 2 each 6
Cost of Raw Materials Costs are based on 2005 dollars (as provided by the IECM program) Conventional MEA scrubbing for CO 2 removal MEA cost, $/ton: 1,293 Corrosion inhibitor cost, $/ton: 258.6 (20% of MEA cost) Activated carbon (AC) for MEA cleaning, $/ton: 1,322 Caustic (NaOH), $/ton: 624.7 (needed for MEA reclaiming) Proposed process for CO 2 removal by scrubbing with using Ca(OH) 2 slurry Limestone cost, $/ton: 19.64 Lime, $/ton: 72.01 Note: In the proposed process, CaO will be produced in-situ. Make-up could be in the form of CaCO 3 or CaO to compensate for Ca loss as CaSO 3 or CaSO 4 5.1 kg MEA (pure solvent) per 1 kg CO 2 removed From reaction stoicheometry: ~ 1.16 kg Ca(OH) 2 per 1 kg SO 2 removed ~ 1.68 kg Ca(OH) 2 per 1 kg CO 2 removed 7
Research Objectives Model the simultaneous removal of SO 2 and CO 2 gases by chemi-sorption in a slurry of hydrated lime [Ca(OH) 2 ]. Benchmark the performance/effectiveness of this proposed technology with: - MEA scrubbing approach for CO 2 removal - Wet flue gas desulfurization (FGD) for SO 2 removal - These separate-effect technologies (MEA and FGD) are typically connected in series in a fossil-fired power plant 8
Research Approach Three-Fold Approach: 1. Use OLI s Environmental Simulation Program (ESP, v-7.0-55) to model the simultaneous removal of SO 2 and CO 2 gases by scrubbing into a slurry of hydrated lime [Ca(OH) 2 ]. Three hypothetical flue gas compositions are to be evaluated : CO 2 concentrations of 3%, 14%, and 25%; representative of exhaust streams of a NG-fired power plant, coal-fired power plant, and a cement production plant, respectively. - Only the coal-fired plant (11 15% CO 2 ) is discussed in this presentation Concentration of SO 2 in the flue gas is assumed to be 2000 ppm 9
Research Approach Three-Fold Approach (cont d): 1. Use the OLI s Environmental Simulation Program (ESP, v-7.0-55) to model the simultaneous removal of SO 2 and CO 2 gases by scrubbing into a slurry of hydrated lime [Ca(OH) 2 ]. Flue gas flow rate was kept constant at ~ 1.6x10 6 acfm (~ 2.7x10 6 m 3 /hr); such flow rate is typical of a 500 MW th coal fired power plant. The proposed process includes a SO 2 scrubber, a CO 2 scrubber, a calciner, a lime slaking reactor, and a few auxiliary unit operations such as heat exchangers, filters and dryers. 10
Three-Fold Approach (cont d): Research Approach 2. Use the Integrated Environmental Control Model (IECM) software to predict the performance of a coal-fired plant that uses MEA scrubbing for CO2 capture and wet FGD unit for SO 2 removal IECM software has been developed by the Center for Energy and Environmental Studies, Carnegie Mellon University for DOE in 2007 (Current Version: 5.21; February 2, 2007) 3. Compare ESP predictions with IECM predictions for CO 2 and SO 2 removal 11
Importance of the Proposed Integrated Technology The proposed integrated technology for simultaneous removal of CO 2 and SO 2 could be of interest to many industrial facilities including: Fossil-fuel-based power generation stations; which contribute about 30% of the World s CO 2 emissions Coal-fired gasification combined cycle (IGCC) turbines Cement production plants Petrochemical plants 12
Chemical Reactions for CO 2 Removal CO 2 Gas Absorption Reaction (carbonation reaction): CO 2 (g) + Ca(OH) 2 CaCO 3 + H 2 O ΔH o 298 K -113 kj/mole Calcination Reaction: CaCO 3 CaO + CO 2 (g) ΔH o 298 K 178 kj/mole Lime Slaking Reaction: CaO + H 2 O Ca(OH) 2 H 2 O ΔH o 298 K -65 kj/mole Ca(OH) 2 Lime Slaker CaO CO 2 in flue gas Carbonator Calciner CO 2 CaCO 3 13
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Carbonator: Exothermic Reaction CO 2 (g) + Ca(OH) 2 CaCO 3 + H 2 O ΔG, kj/mole ΔG R at 298 o K = -72.643 kj/mole ΔH R, kj/mole ΔH R at 298 o K = -113.03 kj/mole ΔG R ad ΔH R are calculated by HSC software 15
Calciner: Endothermic Reaction CaCO 3 (s) CaO (s) + CO 2 (g) ΔG R at 1198 o K = -5.528 kj/mole ΔG R at 1273 o K = -16.169 kj/mole ΔG, kj/mole Typical Calciner Temperature Range 1220 o K 1420 o K ΔH R at 1198 o K = 164.949 kj/mole ΔH R at 1273 o K = 163.207 kj/mole ΔH R, kj/mole ΔG R ad ΔH R are calculated by HSC software 16
Lime Slaker: Exothermic Reaction CaO (s) + H 2 O Ca(OH) 2 ΔG R at 298 o K = -57.804 kj/mole ΔG, kj/mole ΔH R at 298 o K = -65.145 kj/mole ΔH R, kj/mole ΔG R ad ΔH R are calculated by HSC software 17
Chemical Reactions for SO 2 Removal SO 2 Gas Absorption Reaction: SO 2 (g) + Ca(OH) 2 CaSO 3 (s) + H 2 O ΔH o 298 K -163 kj/mole Forced Oxidation of CaSO 3 to CaSO 4 : CaSO 3 (s) + 1/2O 2 (g) CaSO4 (s) ΔH o 298 K -556 kj/mole CaSO 3 or CaSO 4 SO 2 in flue gas Lime Slaker Ca(OH) 2 H 2 O Makeup CaO to compensate for Ca lost in CaSO 3 or CaSO 4 Ca(OH) 2 Lime Slaker CaO CO 2 in flue gas Carbonator Calciner CO 2 CaCO 3 18
SO 2 Absorption: Exothermic Reaction ΔG, kj/mole ΔH R, kj/mole ΔG R at 298 o K = -114.736 kj/mole ΔH R at 298 o K = -162.509 kj/mole ΔG R ad ΔH R are calculated by HSC software 19
Forced Oxidation of CaSO 3 : Exothermic Reaction ΔG, kj/mole ΔH R, kj/mole ΔG R at 298 o K = -498.504 kj/mole ΔH R at 298 o K = -556.469 kj/mole ΔG R ad ΔH R are calculated by HSC software 20
Chemical Reactions for Co-Production of SynGas Co-Production of Lime and Syngas: CaCO 3 + CH 4 (g) CaO + 2CO (g) + 2H 2 (g) ΔH o 298 K 426 kj/mole Typical Calciner Temperature Range 1220 o K 1420 o K Hence, co-production of Syngas can take place within the calciner temperature range 21
SynGas Production: Endothermic Reaction ΔG, kj/mole ΔH R, kj/mole ΔG R ad ΔH R are calculated by HSC software 22
Mitigation of Operating Risks of the Calciner Lime Sintering (decrease in surface area and pore size of CaO) Reducing the operating temperature of the calciner results in less sintering of the produced calcium oxide and, hence, more reactive lime (CaO) in the lime slaker. Cost of CaO Makeup Due to Loss of Reactivity Because calcium is used continuously in a cyclical manner, sintering and corresponding reduction in reactivity is a cumulative process that may require periodic makeup of calcium oxide. If calcium can be recycled say 500 times, then it may easily be considered to be cost effective. 23
Process Flow Diagram (PFD) as Simulated in ESP Slaked Lime Lime Split 2 Lime Split 1 V-1 H2O/CaOH2 Feed SO2 Scrubber Vent Vent Gas C Quench Water Flue Gas Quench Quenched flue Gas SO2 Scrubber CO2 Scrubber CaCO3 Filtrate Blowdown Slaker CaO C Quench Liquid Out SO2 Scrubber Bottom CO2 Scrubber Bottoms CaCO3 Filter CaSO3 Filtrate CaCO3 Cake CO2 CaSO3 Filter Dryer Dry Cake Calciner CaSO3 Blowdown CaSO3 Blowdown 24
Simulation of CO 2 Removal Using DOE/IECM User defined ΔH R = -84.6 kj/mole CO 2 ΔH R (30 wt% MEA in water) = -84.6 kj/mole CO 2 MEA solution & Mass of MEA (30 wt%) to absorb 1 kg CO 2 = 17 kg 25
Simulation of SO 2 Removal Using DOE/IECM User defined 26
Simulation Results of MEA-Based Technology for CO 2 Removal Using the Integrated Environmental Control Module (IECM) 27
CO 2 Coal-Fired Boiler Absorber Remove heat of chemisorption Cool lean regenerated MEA solvent by removing sensible heat Stripper Heat the rich MEA solvent by extracting sensible heat from the lean MEA solvent Supply heat of desorption using steam in the reboiler Possible Power Plant Capture Add-ons Cool flue gas to absorber conditions (25 o C) Compress flue gas to overcome pressure drop in Absorber Post compression of CO 2 to desired product pressure 28
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CO 2 removal = (2.667E6 tons/yr) / 6575 hrs/yr ~ 406 tons/hr for a 500 MW th coal-fired plant 31
CO 2 (mole%) in input flue gas = 2.048E4 lb-mole/hr / 1.706E5 lb-mole/hr ~ 12% CO 2 removal efficiency = 90% (user defined) and CO 2 escape with flue gas = 10% 32
MEA scrubber plant cost about $281M / $700M ~ 37% of the 500 MW th plant cost 33
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Simulation Results of Wet-FGD Technology for SO 2 Removal Using the Integrated Environmental Control Module (IECM) 36
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Air Preheater 42
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ESP Simulation Results 45
ESP Simulation Results Flue Gas Stream 46
ESP Simulation Results Flue Gas Stream 47
ESP Simulation Results Flue Gas Stream 48
ESP Simulation Results Utility Water 49
ESP Simulation Results Flue Gas Stream 50
ESP Simulation Results Flue Gas Stream 51
Summary OLI s ESP was a useful simulation tool for modeling CO 2 and SO 2 capture using Ca(OH) 2 slurry Other insights and opportunities for improving the ESP simulation capabilities 52
Roadmap for Future Work Simulate CO 2 capture using the monoethanolamine technology Compare performance/co 2 capture efficiency and raw materials requirements versus CO 2 capture using Ca(OH) 2 slurry Calculate the energy requirements for the Ca(OH) 2 technology and compare to MEA energy requirements Demonstrate improved Ca utilization in the proposed technology (i.e., Ca consumed to remove S and C) Estimate calcium make-up requirements (tons/hr) for the simultaneous removal of CO 2 and SO 2 53