Natural Gas Desulfurization for Fuel Cell Applications by Adsorption

Transcription

1 Natural Gas Desulfurization for Fuel Cell Applications by Adsorption Gökhan O. Alptekin, Ambal Jayaraman, Margarita Dubovik, Mathew Schaefer, Robert Amalfitano, Mike Ware and Kristin Bradley 28 AIChE Spring National Meeting AIChE/ACS Jointly Co-sponsored Session April 6 th -1 th, 28 New Orleans, LA TDA Research Inc. Wheat Ridge, CO 833

2 Introduction Advances in fuel cell technologies have the potential to revolutionize the way power is generated and distributed Fuel cells require an ample supply of high quality fuel Pipeline natural gas is the fuel of choice because of its abundance and well-developed supply infrastructure LPG is also a fuel option for remote locations In addition to naturally ocurring 2 S chemical odorants made with sulfur-containing compounds are added to natural gas for leak detection Common odorants include mercaptans, sulfides and TT The total sulfur content of the pipeline gas averages about 4 ppmv but can be as high as 1-12 ppmv Most fuel cell developers prefer a passive sorbent that can remove sulfur at ambient temperature instead of the complex two-step hydrodesulfurization and subsequent 2 S removal with a metal oxide sorbent 2 TDA

3 Sulfur Poisoning Sulfur compounds contaminate the catalysts used in fuel cell systems and degrade power generation performance Sulfur also poisons the catalysts used in the refomers, WGS reactors and NOx traps Source: De Wild, The removal of sulfur-containing odorants from natural gas for PEMFC, Proceedings of Fuel Cell Seminar, p227, 22 Source: Israelson, Results of Testing Various Natural Gas Desulfurization Sorbents, J. of Materials Engineering and Performance, Vol. 13 (3), June 24 Traditionally sulfur removal is carried out with a two-step process: DS of the organic sulfur compounds and subsequent 2 S removal It is not practical for small-scale residential units or for transportation systems 3 TDA

4 Project Objective TDA Research, Inc. is developing a passive adsorbent for ambient temperature natural gas desulfurization Water Air Air Steam EX Fuel Desulfurizer Prereformer Steam Reformer WGS PROX PEMFC Steam EX Water Burner Fuel Desulfurizer Prereformer SOFC Fuel Cell Off Gas PEM System SOFC System Requirements of the sorbent igh sulfur capacity (minimum replacement frequency, small size) Low cost Reducing total sulfur concentration to sub-ppm levels Inertness (no side reactions or chemisorption of hydrocarbons) Tolerance to possible natural gas contaminants (hydrocarbons, CO 2, 2 O) Ease of disposal (no toxicity, flammability, pyrophorocity) 4 TDA

5 Introduction Outline Outline Natural Gas Desulfurization Sorbent Performance Effect of Moisture Sorbent Regeneration COS Removal LPG Desulfurization Sorbent Performance Desulfurization of Natural Gas Liquids (NGLs) Sorbent Performance Effect of Aromatics Field Demonstrations Conclusions 5 TDA

6 SulfaTrap TM Series Sorbents igh selectivity to all sulfur species igh capacity Over 3% wt. breakthrough capacity (lb of sulfur per lb sorbent) Over 5% wt. saturation capacity igh sulfur removal efficiency Reduce sulfur levels to less than 5 ppbv Regenerable operation Demonstrated stable capacity for over 1 cycles Oxidizing (e.g. air), reducing (e.g., 2 or natural gas) or inert gases (e.g., N 2 ) can be used for regeneration Low cost Tolerance to natural gas contaminants Moisture, heavy hydrocarbons, CO 2 Easy disposal No flammability, toxicity or pyrophorocity 6 TDA

7 C S Dimethyl Sulfide C C S Tetrahydrothiophene C C S C C C C C Tert-butyl Mercaptan Natural Gas Desulfurization Typical Organic Sulfur Compounds in Nat. Gas DMS TT TBM Among the organic sulfur species DMS was found to be the most difficult to remove In the presence of mass transfer limitations (i.e. short gas-solid contact times) TBM and DMS breakthrough the same time Concentration (ppmv) T= 2 o C, P= 2 psig, DMS = 12.3 ppmv, TBM = 9 ppmv, TT= 9 ppmv , h -1 12, h Time (min) DMS DMS TT TT TBM TT Typical Natural Gas Composition Component Volume % Volume % Sample Jan. 24 Sample June 24 Methane Ethane Propane Butane Isobutane Pentane.1.11 Isopentane.1.1 Neopentane.1.1 exane 25 ppm 28 ppm Carbon Dioxide.7.81 Nitrogen TDA

8 Performance Comparison T= 2 o C, P= 3 psig, DMS = 12.3 ppmv, TBM = 9 ppmv, TT= 9 ppmv in Nat. Gas GSV= 6, h -1 DMS Concentration (ppmv) Norit Norit RGM3, RGM3 Activated Activated Carbon Carbon Grace Grace X Zeolite X Siemens Siemens Sample Sample 4 4 Sample TDA s SulfaTrap TM Siemens Sample 5 Siemens Sample 4 Grace X Zeolite Norit RGM3 Activated Carbon Siemens Siemens TDA's SulfaTrap- TDA Sample Sample 5 5 BR3 SulfaTrap TM -R3 Pre-Breakthrough Capacity (% wt.) 3.12% 1.96%.85%.36%.18% Time (min) TDA s sorbent showed the highest sulfur adsorption capacity 6% higher sulfur capacity than Siemens Sample #5 8 TDA

9 Concentration (ppmv) EM IPM PM Mercaptan Removal Breakthrough Profile SulfaTrap-R3 5 ppmv 2 O in natural gas, Total Sulfur Content= 81 ppmv, GSV= 6, h -1 6, h-1 GSV equal concentration of each odorant Ethyl Mercaptan (EM) i-propyl Mercaptan (IPM) Propyl Mercaptan (PM) 2 1 3% total capacity 3% total capacity Time (min) SulfaTrap TM -R3 sorbent could remove mercaptans with high capacity (higher capacities are achieved for larger mercaptan species) Earlier tests already showed its effectiveness for TBM 9 TDA

10 ydrocarbon Adsorption T= 2 o C, P= 17 psia, DMS = 17. ppmv, TBM= 7 ppmv, TT= 5 ppmv, GSV= 6, h Relative Intensity Feed Analysis GC Test Time (min) Breakthrough DMS B-Merc Test Start Test Time Concentration, % vol Ethane---> <---Propane <---C4s&C5s <---exane Run Time, min Ethane Concentration, % vol. Propane Iso Butane N-butane Iso-Pentane Neo-Pentane Pentane exane Ethane The sorbent does not adsorb any hydrocarbon species from the natural gas Even the heavy hydrocarbons such as hexane were not removed 1 TDA

11 2 Effect of Moisture T= 2 o C, P= 5 psig, DMS = 46 ppmv in Nat. Gas GSV= 6, h ppm DMS 5 ppm 2O 44 ppm DMS 35 ppm 2O 44 ppm DMS 146 ppm 2O 6, h -1 GSV 1.74 % BT Loading 1.64 % BT Loading 1.27 % BT Loading Breakthrough Concentration (ppmv) Run Time (min) Most competing sorbents fail in the presence of high levels of moisture Pipeline spec for moisture is 7 lb/mmscf (corresponds to 154 ppmv 2 O in the gas) SulfaTrap TM -R3 sorbent maintains a stable sulfur capacity at high moisture levels, but capacity decreases if the water content goes above 1, ppmv 11 TDA

12 SulfaTrap TM -R2 Fluctuations in moisture level could some times reach above 2, ppmv 2 O. Fuel cell manufacturers prefer a sorbent which is more robust and does not have appreciable changes in sulfur capacity with mositure levels ence the commercial sulfur sorbent needs to be able to handle any level of moisture in the natural gas We developed a moisture tolerant variation of our sorbent SulfaTrap TM -R2 DMS Concn. (ppmv) T= 2 o C, P= 3 psig, DMS = 25 ppmv, EM = 25 ppmv, 2 O = 4, ppmv in Nat. Gas GSV= 6, h -1 DMS EM Time (min) SulfaTrap TM R2 has high sulfur capacity in the presence of very high moisture levels 12 TDA

13 Temperature Programmed Desorption Profile for SulfaTrap TM -R TT 35 1 Temperature 3 Concentration (ppm) DMS TMB Temperature (C) Time (min) If non-oxidizing gases are used, the sulfur species are simply released from the sorbent without any transformations Sulfur balance between the adsorption and regeneration indicates full regeneration The sorbent-dms interaction is the weakest as evident by low desorption temperature SulfaTrap TM -R2 is fully regenerated by heating to 3 o C in N 2 13 TDA

14 DMS Concentration (ppmv) Regeneration Capability of SulfaTrap TM -R2 P= 3 psig, DMS = 7 ppmv, TBM= 7 ppmv, TT= 15 ppmv, GSV= 75, h -1 T Adsorption= 2 o C T Regeneration = 3 o C DMS Breakthrough Profiles in the 1-Cycle Test Total Sulfur Capacity Cycle 1, ydrogen Regeneration Cycle 2, Natural Gas Regeneration Cycle 3, Natural Gas Regeneration Cycle 4, Natural Gas Regeneration Cycle 5, Natural Gas Regeneration Cycle 6, Natural Gas Regeneration Cycle 7, Natural Gas Regeneration Cycle 8, Natural Gas Regeneration Cycle 9, ydrogen Regeneration Cycle 1, ydrogen Regeneration Time (min) SulfaTrap TM -R2 maintains its capacity for 1 adsorption/regeneration cycles SulfaTrap TM -R2 regenerates using inert gases (such as nitrogen), hydrogen or natural gas by applying temperature swing Although sulfur-free natural gas is preferred, sulfur-laden gas can also be used provided that it is at temperature Breakthrough Capacity 2.5% 2.% 1.5% 1.%.5%.% ydrogen Regeneration Natural Gas Regeneration Cycle 14 TDA

15 COS Removal Sulfur compounds that are naturally present in the natural gas are mostly 2 S or COS Majority of this sulfur is removed at the well-head or at the distribution facilities, but a few ppm of 2 S and COS still remains in the gas COS is harder to remove than 2 S due to its neutrality and similarity to CO 2. Also 2 S reacts with CO 2 present in the natural gas to produce COS and water All this makes it more difficult to remove COS at low temperatures (in the range of ambient to 2 o C) 15 TDA

16 SulfaTrap TM -R5 for COS Removal T= 22 o C, P= 1 psig, COS Inlet= 1 ppmv, 2 O Inlet= 6 ppmv, CO 2 Inlet=.7% vol., in natural gas, GSV= 2, h -1, Sample size= 1 cc 4 COS Breakthrough (ppmv) Alco a S elexso 6% lo a d in g SulfaTrap TM -R3 % loading.3% wt. capacity SulfaTrap TM -R3 (modified).2% wt. capacity loading (in itial R5) 2, h-1 GSV 1 p p m v C O S in let 5 ppmv water Balance Natural Gas 1 SulfaTrap TM -R5.74% wt. capacity loading (curr ent R5) Run T ime (min) SulfaTrap TM -R5 sorbent achieves acceptable COS capacity 16 TDA

17 igh COS removal Efficiency with R5M T= 22 o C, P= 1 psig, COS Inlet=.1 ppmv, 12 2 O Inlet= 6 ppmv, CO 2 Inlet=.7% vol., in natural gas, GSV= 2, h -1, Sample size= 1 cc 1 SulfaTrap-R2 Modified SulfaTrap-R5 COS Concentration, ppbv Proprietary Carbon B Modified SulfaTrap-R5B Time, min. We have further improved the SulfaTrap TM -R5M sorbent to achieve better COS removal efficiency Modified SulfaTrap TM -R5M sorbent reduces the COS content to less than 5 ppbv 17 TDA

18 Desulfurization of LPG Liquified petroleum gas (LPG) has higher power density than natural gas on volume basis LPG-fed systems are suitable fuel for portable systems and applications in remote locations Mercaptans (mostly ethyl, n-propyl and isopropyl mercaptans) are the primary sulfur species in LPG Methane Methane Ethane Ethane Propane/Propylene Butylene Butylene AAA Propane Industrial AAA Propane Grade Propane Industrial Grade Propane GC Time, 24 sec GC Time, sec Iso-Butane Iso-Butane n-butane n-butane The presence of unsaturated hydrocarbons affects the performance of the desulfurization sorbents 18 TDA

19 Sorbent Performance in LPG T=2 C, P=5 psig, GSV= 5,-3, h -1, Ethyl Mercaptan Inlet = 13 ppmv 25 ppmv Ethyl Disulfide (Relative Intensity) GSV = 3, h ppmv EM GSV = 5, h ppmv EM C 2 5 S C 4 1 S 2 Ethyl Mercaptan Diethyl disulfide Time (min) TDA s SulfaTrap TM -R6 sorbent achieved sulfur capacity of.63% and 2.35% wt. at GSV of 3,h -1 and 5,h -1, respectively (based on diethyl disulfide breakthrough) 19 TDA

20 SulfaTrap TM -R8 for Disulfide Removal T=2 C, P=5 psig, GSV= 3, h -1, Inlet EM = 1 ppmv, EDS = 1 ppmv Disulfide Concentration (ppmv) Diethyl disulfide (EDS) Inlet 1 ppm EM, 1 ppm EDS Time (min) Disulfides when present in natural gas are more difficult to remove Disulfides are also formed during desulfurization of some streams (e.g. LPG desulfurization) TDA s SulfaTrap TM -R8 sorbent achieved sulfur capacity of 2.5% (based on diethyl disulfide breakthrough) 2.5% wt Sulfur 2.71% wt Sulfur 2 TDA

21 Desulfurization of Natural Gas Liquids Conventionally caustic wash or solvent treatment is used to remove the sulfur species (mercaptans and DMS) from NGLs, which is not selective to DMS The amount of DMS present in the NGLs could sometimes be as high as 5-1 ppm In order for the NGLs to be a viable byproduct, the sulfur present in the form of DMS needs to be removed to much lower levels. Adsorption is a viable technique for DMS removal from NGLs. Simulated NGL Mixture BP - NGL Mix % mol. Propane 32.73% Butane 29.11% Pentane 15.% exane 7.5% eptane 12.1% Toluene 3.5% Dimethyl Sulfide (DMS) +.685% Propyl Mercaptan (PM) +.48% 3.5% aromatics + DMS 664 ppmw PM 57 ppmw But the NGLs also contain aromatic species like benzene, toluene, ethyl benzene and xylenes (as high as 9% on molar basis) Sorbent needs to retain its selectivity for organic sulfur species in the presence of aromatics compounds. 21 TDA

22 Desulfurization of Natural Gas Liquids DMS concn. (ppmw) T=4 o C, P= 15 psia, LSV=4h -1 BP - NGL Mix Desulfurization 3.5% aromatics UOP-13X SulfaTrap-R2A ml Fuel Desulfurized/g of Sorbent SulfaTrap TM -R2A has more than twice the adsorption capacity of UOP- 13X at 5 ppmw DMS breakthrough in the presence of aromatics SulfaTrap TM -R2A sorbent can achieve ~1.5% wt. sulfur capacity vs..7% wt. of UOP-13X 22 TDA

23 Effect of Aromatics T=4 o C, DMS Conc.= 75 ppmw S, NPM=1,2 ppmw S, P= 2 psig, LSV=4h Normalized ydrocarbon peak Area from GC-MS UOP-13X Benzene Toluene Ethyl Benzene Xylene Total Sulfur Concn. (ppmw S) SulfaTrap-R2A Benzene Toluene Ethyl Benzene Xylene ml Fuel Desulfurized/g sorbent UOP-13X Sorbent ml Fuel Desulfurized/g sorbent TDA SulfaTrap TM -R2A Sorbent The adsorption of aromatic hydrocarbons was evident with the UOP-13X sorbent competitive adsorption between aromatics and sulfur No hydrocarbon adsorption was observed with the SulfaTrap TM -R2A ighly selective sulfur adsorption 23 TDA

24 Field Demonstrations Natural gas Demonstration Partners Siemens Delphi FuelCell Energy Fuel Cell Technology Logan Energy GTT Gaz de France 5kW e desulfurizer at Siemens s R&D center in Pittsburgh, PA 2.2 L sorbent bed (oversized) provided 1 year continuous operation 5 kw e desulfurizer at FCTC in Johnstown, PA (then delivered to Fort Meade Army base, MD) 2. L sorbent No voltage drop over 12,2 hr testing 24 TDA

25 Large Scale Demonstrations Several demonstrations were carried out with Siemens at large scale (1 and 125 kw e CP SOFC systems) Two large-scale demonstrations were carried out in Europe in Italy and Germany European gas contains high concentrations of COS TDA s 1 kwe Desulfurizer at GTT, Milano, Italy In 27, TDA produced and delivered 1,5 lb of SulfaTrap TM -R series sorbents in-house In 28, we already had a 78 lb order; this is expected to grow up to 2, lb 25 TDA

26 Field Demonstrations LPG 18 cc sorbent can treat a 2 lb commercial LPG tank.5 cc sorbent treat 2 lb Coleman tank SulfaTrap TM -P -R6 Sorbent LPG Fuel Tanks 75 W MesoGen SOFC Battery Charger Field testing with Mesoscopic Devices 75-1 W e portable SOFC as field battery chargers 2 cc sorbent provided 1 day continuous operation Other partners: FuelCell Energy Adaptive Materials Protogenics 26 TDA

27 Conclusions TDA s sorbent SulfaTrap TM -R3 can be effectively and economically used for natural gas desulfurization TDA s SulfaTrapTM-R2 sorbent works under any levels of moisture for desulfurization of natural gas TDA s SulfaTrap TM -R5 sorbent has very good COS removal capacity TDA s SulfaTrap TM -R6 sorbent can achieve 2.35% wt. capacity for desulfurization of LPG TDA s SulfaTrapTM-R8 sorbent can remove disulfides with a capacity greater than 2.5% wt. TDA s SulfaTrapTM-R2A sorbent has 1.5% sulfur capacity for desulfurization of NGLs SulfaTrap TM Series sorbents could be used either individually or in combinations depending on the gas composition 27 TDA