Flue-Gas Treatment by Methane Tri-Reforming Combined with Lime Carbonation and Syngas Production

Transcription

1 High Temperature Solid Looping Cycles Network, Oviedo, Spain, Sept Flue-Gas Treatment by Methane Tri-Reforming Combined with Lime Carbonation and Syngas Production M. Halmann 1 and A. Steinfeld 2 1 Weizmann Institute of Science, Dept. Environmental Sciences and Energy Research, Rehovot, Israel 2 ETH Zurich Swiss Federal Institute of Technology, Dept. Mechanical and Process Engineering, and Paul Scherrer Institute, Villigen, Switzerland

2 2 Tel-Aviv,

3 Composition of Flue Gases Chunshan Song, Chemical Innovation, 31, 21, 2001 CO 2 H 2 O O 2 N 2 Coal-Fired Boilers 12-14% 8-10% 3-5% 72-77% Gas-Fired Boilers 8-10% 18-20% 2-3% 67-72% 3

4 How to Capture CO 2 from Power Station Flue Gases? 1. By Pressure Swing Absorption into Organic Amines. 2. By Carbonation of Alkaline Metal or Alkaline Earth Oxides, Hydroxides, or Silicates. 3. By Methane CO 2 /Steam Reforming, or by Coal Gasification. 4 We propose to combine methods 2 and 3

5 Lime Carbonation vs. Limestone Calcination The exothermic lime carbonation is the reverse of the endothermic limestone calcination CaO + CO 2 = CaCO 3 ΔH o 298K = -178 kj/mol This carbonation of lime, while initially rapid, virtually ceased in the range of 70-72% conversion of CaO, probably because of blocking of the pores between the product CaCO 3 particles. 5 Bhatia & Perlmutter, AIChE J., 29, 79, 1983

6 Methane Tri -Reforming to Syngas Combining Endothermic and Exothermic Reactions by By simultaneous catalytic reforming of CH 4 with steam and with CO 2, which are both strongly endothermic reactions, 6 CH 4 + H 2 O = CO + 3H 2 ΔH = 206 kj/mol (1) CH 4 +CO 2 = 2CO + 2H 2 ΔH = 247 kj/mol (2) and also with oxygen by an exothermic reaction, CH 4 + 1/2O 2 = CO + 2H 2 ΔH = -38 kj/mol (3) an overall thermo-neutral (autothermal) process of tri-reforming was achieved. Ashcroft et al, Nature, 352, 225,1991

7 Tri -reforming of power station flue gases Tri-reforming had been proposed for the utilization of the power station flue gases for syngas production. Using specific catalysts, the high-temperature reaction of the flue gases with natural gas results in the combined steam/co 2 reforming and partial oxidation of methane. 7 Song and Pan, Catal. Today, 98, 463, 2004

8 Combining Flue Gas Tri-Reforming with Lime Carbonation Taking flue gases released from a coal fired power station with an average molar composition of 13CO 2-9H 2 O - 4O 2-74N 2 and adding to it steam, air, natural gas and lime in the ratio 31 : 24 : 20 : 35 results in an initial reaction composition of 13CO H 2 O + 9O CH CaO + 93N 2 8 Halmann & Steinfeld, Internat. J. Hydrogen Energy, online 31 Aug. 2009

9 Equilibrium Distribution vs. Temperature for the System at 1 bar of 13CO H 2 O + 9O N CH CaO 0.35 Mole Fractions CaCO H O H 2 CO CaO CO Temperature, K H2(g) CH4(g) CO(g) CO2(g) H2O(g) CaCO3(s) CaO(s)

10 The Equilibrium Reaction at 1000 o K can be represented by the Equation 13CO H 2 O + 9O CH CaO + 93N 2 = 49.4H CO CO CaCO CaO H 2 O + 93N 2 Most of the carbon will appear as syngas At 1000 o K the reaction is weakly endothermic: ΔH = +237 kj/mol CO 2 in the original flue gas 10

11 Scheme of Gasifier and Calciner Reactors for CO 2 Capture and Syngas Production Adapted from Weimer et al, Fuel, 87, 1687, 2008 Numbers are relative moles 20CH 4 Gasifier Syngas+N 2 +H 2 O Calciner 15CO 2 Flue Gas + Steam + Air ~1000 K 35CaO 9.7CaCO CaO K 5.3CaO To Cement Plant 5.3CaCO 3 Makeup 11

12 From the Flue Gas Reaction with Methane, Lime and Air at 1000 K: Proposed Syngas Conversion to Methanol From 500 MWe coal-fired power station, assuming 90% yield in syngas conversion, Predicted annual production: 3.4x10 6 metric ton methanol CO 2 emissions: a) from the flue gas treatment, b) from fossil-fuel fired calcination of CaCO 3. c) from fuel burned for process heat. 12

13 Solar Energy Driven Carbonation Calcination Cycles The CaO + CO 2 = CaCO 3 reaction cycles had been tested in a laboratory reactor of fluidized CaO/SiO 2 particles irradiated with concentrated solar energy. In carbonation steps at o C, CO 2 was removed from ambient air. In calcination steps at o C, CO 2 was released. 13 Nikulshina, Gebald & Steinfeld, Chem Eng. J., 146, 244, 2009

14 CO 2 Emission Avoidance Relative to Conventional CH 3 OH Production by Methane Tri-Reforming Negative value means excess vs. conventional methanol synthesis Flue Gas Treatment Solar Calcination Fossil Fuel Calcination Methane-Steam Reforming 13% -33% 14

15 Fuel Savings Relative to Conventional CH 3 OH Production by Methane Steam- Reforming Flue Gas Treatment Solar Calcination Fossil Fuel Calcination Methane 21% 9% Tri-Reforming 15

16 Conclusions on Flue Gas Treatment by Methane Tri-Reforming and CaO Carbonation 1. May be applied to CaO, syngas and methanol production. 2. May result in overall CO 2 emission avoidance and fuel savings. 3. Recycling of CaO by CaCO 3 calcination would yield pure CO But: From the flue gas of just one 500 MWe coal-fired burner, methanol production would supply 7.6% of the 2008 world production capacity of methanol. CaO production would supply 0.06% of the 2008 world clinker production capacity Additional gains may be achieved by solar-driven calcination of CaCO But: Solar reactors of the required size still require development. 16

17 Another High Temperature Solid Looping Cycle: Ammonia Production by a Cyclic Process via Alumina and Aluminum Nitride The production of NH 3 by a two-step cyclic process was tested as an alternative to its current industrial production by the Haber- Bosch process. The first, endothermic step, is the production of AlN by the reduction of Al 2 O 3 with carbon in a N 2 atmosphere above 1300 C: Al 2 O 3 + 3C + N 2 = 2AlN + 3CO The CO may be water-gas shifted to syngas. The second, exothermic step, is the steam-hydrolysis of AlN to produce NH 3 and reproduce Al 2 O 3 below 375 C; Al 2 O 3 is recycled to the first step: 2AlN + 3H 2 O = Al 2 O 3 + 2NH 3 17 Gálvez, Halmann, Steinfeld, Ind. Eng. Chem. Res. 46, 2042, 2007 Gálvez et al, Ind. Eng. Chem. Res. 47, 2231,2008

18 Advantages of Ammonia Production by the Cyclic Process via Alumina and Aluminum Nitride over Haber-Bosch Process Advantages: 1) No need for high pressure; 2) No need for expensive catalysts; 3) Petcoke or charcoal as feedstock instead of natural gas; 4) Process heat may be supplied by concentrated solar energy. 5) Considerable CO 2 emission avoidance and fuel savings. 6) Anhydrous ammonia could be the stored hydrogen and transportation fuel of the future. But: Pure N 2 required as feedstock. 18

19 19 View of the Weizmann Institute Solar Energy Research Facility

20 20 Thanks!