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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.

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Presentation on theme: "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."— Presentation transcript:

1 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 (2)AQSim, Inc., Glen Ridge, NJ OLI’s 24 th User Conference Hyatt Hotel, Morristown, NJ October 23 – 24, 2007

2 2 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

3 33 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.

4 4 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

5 5 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 MEA HEX MEA makeup Some CO 2 remains in the regenerated MEA  Additional drawback of MEA technology:  Low CO 2 loading, i.e., grams of CO 2 absorbed per gram of absorbent.  For a 500 MW th coal-fired plant, MEA makeup ~ 22.7 tons/hr  MEA recirculated ~ 6,599 tons/hr

6 6 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  Compress the CO 2 off-gas to 100 bar  2 stages at 0.18 MBtu/ton CO 2 each Source: J. L. Anthoney, Dept. of Chem. Eng, Kansas State U.

7 7 Conventional MEA scrubbing for CO 2 removal Proposed process for CO 2 removal by scrubbing with using Ca(OH) 2 slurry MEA cost, $/ton: 1,293Limestone cost, $/ton: Corrosion inhibitor cost, $/ton: (20% of MEA cost) Lime, $/ton: Activated carbon (AC) for MEA cleaning, $/ton: 1,322 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 Caustic (NaOH), $/ton: (needed for MEA reclaiming) Costs are based on 2005 dollars (as provided by the IECM program) Cost of Raw Materials  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

8 88 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

9 99 Research Approach 1. Use OLI’s Environmental Simulation Program (ESP, v ) 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 Three-Fold Approach:

10 10 Research Approach 1. Use the OLI’s Environmental Simulation Program (ESP, v ) 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. Three-Fold Approach (cont’d):

11 11 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 Three-Fold Approach (cont’d):

12 12 Importance of the Proposed Integrated Technology  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 The proposed integrated technology for simultaneous removal of CO 2 and SO 2 could be of interest to many industrial facilities including:

13 13 CO 2 Gas Absorption Reaction (carbonation reaction): CO 2 (g) + Ca(OH) 2  CaCO 3 + H 2 O  H o 298 K  -113 kJ/mole Calcination Reaction: CaCO 3  CaO + CO 2 (g)  H o 298 K  178 kJ/mole Lime Slaking Reaction: CaO + H 2 O  Ca(OH) 2  H o 298 K  -65 kJ/mole Chemical Reactions for CO 2 Removal Lime Slaker CalcinerCarbonator CO 2 H2OH2O CO 2 in flue gas CaCO 3 CaOCa(OH) 2

14 14

15 15 Carbonator: Exothermic Reaction  G, kJ/mole  G R ad  H R are calculated by HSC software CO 2 (g) + Ca(OH) 2  CaCO 3 + H 2 O  G R at 298 o K = kJ/mole  H R, kJ/mole  H R at 298 o K = kJ/mole

16 16  G, kJ/mole CaCO 3 (s)  CaO (s) + CO 2 (g) Calciner: Endothermic Reaction  G R at 1198 o K = kJ/mole  G R at 1273 o K = kJ/mole  H R, kJ/mole  H R at 1198 o K = kJ/mole  H R at 1273 o K = kJ/mole Typical Calciner Temperature Range 1220 o K – 1420 o K  G R ad  H R are calculated by HSC software

17 17  G, kJ/mole CaO (s) + H 2 O  Ca(OH) 2 Lime Slaker: Exothermic Reaction  G R at 298 o K = kJ/mole  H R, kJ/mole  H R at 298 o K = kJ/mole  G R ad  H R are calculated by HSC software

18 18 SO 2 Gas Absorption Reaction: SO 2 (g) + Ca(OH) 2  CaSO 3 (s) + H 2 O  H o 298 K  -163 kJ/mole Forced Oxidation of CaSO 3 to CaSO 4 : CaSO 3 (s) + 1/2O 2 (g)  CaSO4 (s)  H o 298 K  -556 kJ/mole Chemical Reactions for SO 2 Removal 18 Lime Slaker CalcinerCarbonator CO 2 H2OH2O CO 2 in flue gas CaCO 3 CaOCa(OH) 2 Lime Slaker SO 2 in flue gas Ca(OH) 2 CaSO 3 or CaSO 4 Makeup CaO to compensate for Ca lost in CaSO 3 or CaSO 4

19 19 SO 2 Absorption: Exothermic Reaction  G, kJ/mole  G R at 298 o K = kJ/mole  G R ad  H R are calculated by HSC software  H R, kJ/mole  H R at 298 o K = kJ/mole

20 20 Forced Oxidation of CaSO 3 : Exothermic Reaction  G, kJ/mole  G R at 298 o K = kJ/mole  H R, kJ/mole  H R at 298 o K = kJ/mole  G R ad  H R are calculated by HSC software

21 21 Co-Production of Lime and Syngas: CaCO 3 + CH 4 (g)  CaO + 2CO (g) + 2H 2 (g)  H o 298 K  426 kJ/mole Chemical Reactions for Co-Production of SynGas  Typical Calciner Temperature Range 1220 o K – 1420 o K  Hence, co-production of Syngas can take place within the calciner temperature range

22 22 SynGas Production: Endothermic Reaction  G, kJ/mole  H R, kJ/mole  G R ad  H R are calculated by HSC software

23 23 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.

24 24 Process Flow Diagram (PFD) as Simulated in ESP 24

25 25 User defined  H R = kJ/mole CO 2  H R (30 wt% MEA in water) = kJ/mole CO 2 & Mass of MEA (30 wt%) to absorb 1 kg CO 2 = 17 kg MEA solution Simulation of CO 2 Removal Using DOE/IECM

26 26 Simulation of SO 2 Removal Using DOE/IECM User defined

27 27 Simulation Results of MEA-Based Technology for CO 2 Removal Using the Integrated Environmental Control Module (IECM)

28 28 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 CO 2

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31 31 CO 2 removal = (2.667E6 tons/yr) / 6575 hrs/yr ~ 406 tons/hr for a 500 MW th coal-fired plant

32 32 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%

33 33 MEA scrubber plant cost about $281M / $700M ~ 37% of the 500 MW th plant cost

34 34

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36 36 Simulation Results of Wet-FGD Technology for SO 2 Removal Using the Integrated Environmental Control Module (IECM)

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42 42 Air Preheater

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45 45 ESP Simulation Results

46 46 ESP Simulation Results Flue Gas Stream 46

47 47 ESP Simulation Results Flue Gas Stream 47

48 48 ESP Simulation Results Flue Gas Stream 48

49 49 ESP Simulation Results Utility Water 49

50 50 ESP Simulation Results Flue Gas Stream 50

51 51 ESP Simulation Results Flue Gas Stream 51

52 52 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

53 53 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


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