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  • 8/8/2019 Cost and Performance for a Fueling Hydrogen Station

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    Cost and Performance Comparison OfStationary Hydrogen Fueling Appliances

    Task 2 ReportApril 2002

    Prepared by:Duane B. Myers, Gregory D. Ariff, Brian D. James, John S. Lettow,

    C.E. (Sandy) Thomas, & Reed C. Kuhn

    One Virginia Square3601 Wilson Boulevard, Suite 650

    Arlington, Virginia 22201703/243-3383

    Prepared for:

    The Hydrogen Program OfficeOffice of Power Technologies

    U.S Department of EnergyWashington, D.C.

    UnderGrant No. DE-FG01-99EE35099

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    FORWARD

    This work was funded by the Hydrogen Program Office of the U.S. Department of Energy under Grant No. DE-FG01-99EE35099 and represents the second task of three to be completed under this contract. The first task presented a broad overview of the costs for creating infrastructures to

    supply direct hydrogen, methanol, and gasoline to support fuel cell vehicles (FCVs). Aconclusion of the report resulting from the first task was that the costs of maintaining theexisting gasoline infrastructure per vehicle supported are up to two times more expensive thanthe estimated costs of maintaining either a methanol or a hydrogen fuel infrastructure.

    The second task, as detailed in this report, was to provide a detailed analysis of the cost of providing small-scale stationary hydrogen fueling appliances (HFAs) for the on-site productionand storage of hydrogen from natural gas to fuel hydrogen FCVs. Four potential reformingsystems were studied: 10-atmosphere steam methane reforming (SMR) with pressure-swingadsorption (PSA) as gas cleanup, 20-atm SMR with metal membrane gas cleanup, 10-atmautothermal reforming (ATR) with PSA gas cleanup, and 20-atm ATR with metal membrane gas

    cleanup.We acknowledge the support of the Department of Energy, especially Sig Gronich, DOEHydrogen Team Leader. We thank Phoebe Smith for the many aesthetic and instructive imagesshe created for this report.

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    Table of Contents

    Page

    FORWARD.....................................................................................................................................i

    EXECUTIVE SUMMARY........................................................................................................... 1 1 INTRODUCTION..............................................................................................................5 2 DFMA METHODOLOGY................................................................................................6

    2.1 Cost Estimation Using DFMA...................................................................................... 62.2 Production Volume Considerations.............................................................................. 72.3 Markup Rate Assumptions............................................................................................ 72.4 Design Considerations .................................................................................................. 9 2.5 Sample DFMA Cost Analysis..................................................................................... 10

    3 REFUELING APPLIANCE HYDROGEN PRODUCTION RATE ANDMANUFACTURING QUANTITY................................................................................ 12

    4 STEAM METHANE REFORMING VS. AUTOTHERMAL REFORMING........... 13 4.1 Overview of SMR and ATR ....................................................................................... 13

    4.1.1 Natural Gas Compression.................................................................................... 144.1.2 Natural Gas Purification ...................................................................................... 154.1.3 Catalytic Steam Reforming ................................................................................. 164.1.4 Water-Gas Shift Reaction.................................................................................... 18

    4.2 SMR System Flowsheets, Cost and Performance....................................................... 184.2.1 Reactor and Vessel Sizing ................................................................................... 214.2.2 Heat Exchanger Sizing ........................................................................................ 234.2.3 Water Purification................................................................................................ 24 4.2.4 Other Equipment ................................................................................................. 24 4.2.5 Assembly ............................................................................................................. 26 4.2.6 SMR Reformer System Bill of Materials and Cost ............................................. 264.2.7 SMR Performance and Efficiency....................................................................... 26

    4.3 ATR System Flowsheets, Cost and Performance ....................................................... 334.3.1 Reactor and Vessel Sizing ................................................................................... 334.3.2 Heat Exchanger Sizing ........................................................................................ 354.3.3 Water Purification................................................................................................ 36 4.3.4 Other Equipment ................................................................................................. 36 4.3.5 Assembly ............................................................................................................. 37 4.3.6 Alternate ATR Designs ....................................................................................... 374.3.7 ATR Reformer System Bill of Materials and Cost.............................................. 374.3.8 ATR Performance and Efficiency ....................................................................... 42

    5 GAS CLEANUP TECHNOLOGIES..............................................................................42 5.1 Pressure Swing Adsorption (PSA).............................................................................. 42

    5.1.1 PSA Gas Separation ............................................................................................ 425.1.2 PSA Design ......................................................................................................... 44 5.1.3 PSA System Cost................................................................................................. 49

    5.2 Metal Membranes ....................................................................................................... 50

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    5.2.1 Metal Membrane Gas Separation ........................................................................ 505.2.2 Hydrogen Permeability in a Reformer System Membrane Assembly ................ 565.2.3 Membrane Material Cost ..................................................................................... 585.2.4 Membrane Durability .......................................................................................... 64 5.2.5 Membrane System Total Cost ............................................................................. 67

    5.3 Preferential Oxidation (PrOx)..................................................................................... 725.4 Gas Cleanup Summary Comparison........................................................................... 735.4.1 Effect on Hydrogen Compressor ......................................................................... 735.4.2 Gas Cleanup Selection and Cost Summary......................................................... 74

    6 HYDROGEN COMPRESSORS..................................................................................... 74 6.1 Existing Industrial Hydrogen Compressors................................................................ 756.2 Small-Scale Innovative Natural Gas and Hydrogen Compressors ............................. 786.3 Service Station Hydrogen Compressor Design........................................................... 786.4 Compressor System Assembly and Test..................................................................... 906.5 Hydrogen Compressor Cost Summary ....................................................................... 93

    7 STATIONARY STORAGE OF COMPRESSED HYDROGEN................................. 94 7.1 Compressed Hydrogen Storage Requirements ........................................................... 947.2 Types of Liners ........................................................................................................... 96

    7.2.1 Metal Liners......................................................................................................... 97 7.2.2 HDPE Polymer Liners......................................................................................... 97 7.2.3 Metallized Polymer Bladders .............................................................................. 98

    7.3 Types of Fiber ............................................................................................................. 997.4 Stress Rupture and Safety Factor.............................................................................. 1007.5 Current Pressure Vessel Pricing................................................................................ 1017.6 Projected Carbon Composite Pressure Vessel Pricing.............................................. 1027.7 Valving and Connection Hardware........................................................................... 1067.8 Storage System Cost Summary................................................................................. 107

    8 DISPENSERS ................................................................................................................. 108 9 TOTAL COST OF SMR- AND ATR-BASED STATIONARY FUELING

    APPLIANCES ............................................................................................................... 109 9.1 Capital Cost Summary.............................................................................................. 109

    9.1.1 Miscellaneous Capital Costs.............................................................................. 1099.1.2 Total Capital Cost.............................................................................................. 110

    9.2 Hydrogen Cost .......................................................................................................... 111 9.2.1 Method for Comparison of Cases...................................................................... 1119.2.2 Operating Cost Assumptions............................................................................. 1139.2.3 Results ............................................................................................................... 115

    10 CONCLUSIONS ............................................................................................................ 119 APPENDIX: Cost Estimate for Scale-up of Small-Scale HFA ............................................ 121

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    List of FiguresPage

    Figure 2-1. Approximate G&A, OH, and R&D Expenses of Prototypical HFA Company .......... 9Figure 2-2. HFA Manufacturer Markup Rates............................................................................... 9

    Figure 2-3. Detailed Cost Analysis of a Boiler Tube-Sheet......................................................... 10Figure 2-4. Sample Assembly Analysis for a Boiler.................................................................... 11Figure 2-5. Sample Bill of Materials for a Boiler ........................................................................ 11Figure 3-1. HFA Production Parameters...................................................................................... 12Figure 4-1. Natural Gas Composition .......................................................................................... 14Figure 4-2. Two-Bed HDS System with Natural Gas Preheater (not to scale) ............................15Figure 4-3. HDS Pipe Section(not to scale) ................................................................................16Figure 4-4. SMR Process Conditions........................................................................................... 18Figure 4-5. SMR Flowsheet ......................................................................................................... 20Figure 4-6. HDS Preheater, with Tube-in-Tube Design(not to scale) ........................................21Figure 4-7. SMR Reformer Vessel(not to scale) .........................................................................21

    Figure 4-8. Tubes and Tube-Sheets for Shell-and-Tube Vessel .................................................. 22Figure 4-9. Proposed Layout of 10 atm SMR Reformer System................................................. 25Figure 4-10. Bill of Materials for 10 atm SMR RS...................................................................... 27Figure 4-11. Bill of Materials for 20 atm SMR RS...................................................................... 30Figure 4-12. ATR Process Conditions ......................................................................................... 33Figure 4-13. ATR Flow Sheet...................................................................................................... 34Figure 4-14. ATR Vessel(not to scale) .......................................................................................35Figure 4-15. Bill of Materials for 10 atm ATR RS...................................................................... 38Figure 4-16. Bill of Materials for 20 atm ATR RS...................................................................... 40Figure 5-1. PSA Flow Diagram, Showing Valve Configuration ................................................. 45Figure 5-2. Batta Cycle Timing Chart.......................................................................................... 45

    Figure 5-3. Parameters Used to Calculate Manufacturing Cost of the PSA systems .................. 49Figure 5-4. Hydrogen Permeability of Selected Metals............................................................... 52Figure 5-5. Neat Hydrogen Permeation Through Palladium Alloys............................................ 54Figure 5-6. Hydrogen Permeation with Gas Mixtures, ................................................................ 55Figure 5-7. Geometry for a Flat Metal Membrane Permeating Hydrogen from a Mixed Gas

    Stream....................................................................................................................................56Figure 5-8. Historical Prices for Platinum and Palladium ........................................................... 58Figure 5-9. Estimated Material Costs of a 25-micron Palladium Membrane System to Cleanup

    the Reformer Gas for a Stationary Fuel Cell System ............................................................ 60Figure 5-10. Estimated Cost of a 12-micron Palladium Membrane ............................................ 61Figure 5-11. Approximate Market Prices for Various Hydrogen-Permeable Metals .................. 64

    Figure 5-12. Thermal expansion of Pd24Ag tubes with and without hydrogen .......................... 66Figure 5-13. Proposed Membrane Assembly............................................................................... 70Figure 5-14. Parameters Used to Calculate Manufacturing Cost of a Planar Membrane Gas

    Cleanup System ..................................................................................................................... 71Figure 5-15. Gas Cleanup Summary............................................................................................ 74Figure 6-1. Hydrogen Compressor Attributes.............................................................................. 75Figure 6-2. Typical Chemical Process Industry Compressor Application Ranges...................... 76Figure 6-3. Simplification of Typical Compressor Crankcase Elements..................................... 77Figure 6-4. Norwalk 150 H2 Compressor.....................................................................................77Figure 6-5. Notional Hydrogen Compressor................................................................................ 81

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    Figure 6-6. Bill of Materials - High Inlet Pressure Hydrogen Compressor................................. 82Figure 6-7. Bill of Materials - Low Inlet Pressure Hydrogen Compressor.................................. 84Figure 6-8. Plate Valve................................................................................................................. 87Figure 6-9. Cutaway of Damped Plate Valve .............................................................................. 88Figure 6-10. Compressor and Blowdown Vessel Assembly........................................................ 90

    Figure 6-11. Interstage Cooler Manufacture and Assembly ........................................................ 91Figure 6-12. Skid Assembly and Mounting ................................................................................. 92Figure 6-13. Compressor System Test ......................................................................................... 93Figure 6-14. Hydrogen Compressor Cost Summary (4.8 kg/h rated capacity)............................ 94Figure 7-1. Dispensable Hydrogen Storage Requirement Based on 69% Capacity Factor ......... 95Figure 7-2. NGV2 Mandated Safety Factors for Composite Wrapped Pressure Vessels.......... 101Figure 7-3. Summary of Pressure Vessel Price Quotes ............................................................. 102Figure 7-4. Tank Cost Estimate Details ..................................................................................... 103Figure 7-5. Connection Schematic for Large Steel Tanks ......................................................... 106Figure 7-6. Connection Schematic for ASME Tanks and Composite Tanks............................. 107Figure 7-7. Summary of Hydrogen Storage Systems................................................................. 108

    Figure 9-1. HFA Costs for a 115 kg H2/day System..................................................................110Figure 9-2. Discounted Cash Flow Calculation Assumptions ................................................... 111Figure 9-3. Natural Gas Cost to Commercial Customers, 1983-2001. ...................................... 114Figure 9-4. Cost of Hydrogen from Four HFA Options ............................................................ 116Figure 9-5. SMR-PSA Cost of Hydrogen .................................................................................. 116Figure 9-6. ATR-PSA Cost of Hydrogen................................................................................... 117Figure 9-7. SMR-Membrane Cost of Hydrogen ........................................................................ 117Figure 9-8. ATR-Membrane Cost of Hydrogen......................................................................... 118Figure A-1. Scaleup Factors Applied to SMR-PSA System for 8-Times Capacity................... 120Figure A-2. Estimated Cost of Hydrogen for 1464-Vehicle HFA ............................................. 121

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    EXECUTIVE SUMMARY

    Over several studies, Directed Technologies, Inc. has analyzed the costs of representativehydrogen fueling stations (HFAs) to supply the early-introduction hydrogen powered fuel cellvehicles (FCVs) and the cost of hydrogen produced by these HFAs. In previous studies we

    evaluated the impact of fuel choice on FCV, the cost of other sizes and quantities of HFAs, andthe infrastructure maintenance costs of various fuels. In this study we analyzed the costs for aninter mediate production rate (250/year) of HFAs sized to support communities of 183 vehicleseach1 (about one-eighth the size of the current average gasoline station). This small HFA ischosen to allow economical hydrogen production in the early years when there are low numbersof FCVs present in any geographical area. While the focus of this report is on the economics of hydrogen production at this small unit size, it is noted that significant hydrogen cost reductionscan be achieved by scaling the HFA unit to a larger size. The Appendix to this report containsdetails of an eight-fold capacity HFA that results in a 45% reduction in the cost of hydrogen.

    For the baseline HFA, we compare the costs and efficiencies of two hydrogen-generation

    technologies (steam methane reforming and autothermal reforming) and two hydrogen purification technologies (pressure swing adsorption and metal membrane). Based on this studywe conclude that the most cost-effective option as determined by the wholesale cost of

    hydrogen is steam methane reforming (SMR) with pressure swing adsorption (PSA) hydrogen purification. The initial capital cost to install the preferred SMR-PSA to support 183 vehicles is$253,014 per unit. The wholesale cost of hydrogen for this option including storage anddispensing but excluding sales taxes2 and retail markup is $3.38/kg, or $1.55 per gallon of gasoline equivalent.3 Autothermal reforming (ATR) of natural gas is a lower initial-cost option, but the resulting cost of hydrogen is higher ($3.59/kg) because the ATR is less efficient than theSMR. The capital costs for the four primary options studied, assuming a ten-year lifetime, arelisted in Figure 1. For reference, the maximum hydrogen production4 required to support 183

    vehicles is 115 kg/day, or 2,000 standard cubic feet per hour (scfh).The range of capital costs, $225,000 to $275,000 depending on the HFA option, corresponds to atotal annual investment of $56.25-$68.75 million per year to support the introduction of ~50,000new FCVs per year.

    This study indicates thatwith current technology, pressure swing adsorption (PSA) is more cost effective and reliable than metal membrane hydrogen purification. The higher costs of membrane units relative to PSAs are not justified by the potential for better hydrogen recoveryand smaller size.

    1 The HFA is sized to permit refueling of approximately 20 fuel cell vehicles each day. Because the vehicles dont need to refuel each day, eachHFA is able to support the entire hydrogen needs of a community of 183 vehicles.2 Sales taxes refer to federal and state highway taxes.3 The conversion to gasoline equivalent will depend on the efficiency benefit of FCVs over conventional internal combustion vehicles at the timeof introduction. The initial efficiency benefit of a FCV is estimated to be roughly 2.2 times better than an internal combustion engine vehicle ona lower heating value basis tank-to-wheels on a 1.25 accelerated combined EPA driving schedule, with the potential for realistic improvements inthe FCV design to increase the efficiency benefit to at least 2.67. The gasoline-equivalent cost represents the 2.2 efficiency benefit.4 The HFA is sized to produce 115kg/day if run at full power for the full day. However, a utilization factor of 69% is used to adjust for seasonal,and diurnal fluctuations in hydrogen demand. Thus the 183 vehicles supported by the station is a true measure of how many vehicles can be fullyaccommodated by the HFA.

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    A Design for Manufacturing and Assembly (DFMA) costing approach was used to obtain costestimates. This methodology is used extensively by industry for product cost estimation and tocompare the relative cost of competing manufacturing and assembly approaches. The DFMAmethodology is both a rigorous cost estimation technique and a method of product redesign toachieve lowest cost. The DFMA approach used for this analysis provides a solid framework for

    the cost study and is the only fair way to compare the cost of potential HFA configurations.A breakdown of factors making up the capital costs is provided in Figure 1. The combined costsfor hydrogen compression, storage, and dispensing are roughly equal to the cost for the reformer and purification system. Capital recovery (i.e., amortization of the initial investment over the lifeof the HFA) accounts for ~48% of the cost of hydrogen for SMR and ~40% of the cost of hydrogen for the ATR.

    $0

    $50,000

    $100,000

    $150,000

    $200,000

    $250,000

    $300,000

    SMR + PSA ATR + PSA SMR + Membrane ATR + Membrane

    C a p

    i t a l

    C o s t

    10% ContingencyMiscellaneousCompressor, Storage, DispenserReformer System

    $253,014

    $228,957

    $273,359

    $247,186

    Figure 1. Contribution of Subsystems to Capital Cost for 115 kg/day HFAs. The Miscellaneous categoryincludes on-site installation, freight, taxes & insurance, and initial spares. The Reformer System category

    includes the hydrogen production and gas cleanup subsystems.

    The other contributors to the cost of hydrogen are the cost of natural gas, the cost of electricity,

    operation and maintenance expenses (O&M), and taxes and insurance. The breakdown of thecost of hydrogen with the contributions from each is given in Figure 2.

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    Costs in $/kg H 2 SMR/PSA ATR/PSA SMR/Membrane ATR/MembraneHydrogen Cost 5 $3.38 $3.59 $3.74 $4.28Capital Recovery 1.66 1.50 1.78 1.62

    Natural Gas 0.95 1.17 1.01 1.44

    Electricity 0.23 0.41 0.37 0.68O&M 0.33 0.31 0.33 0.33Taxes & Insurance 0.23 0.20 0.24 0.22Gasoline equiv.

    ($/gal) $1.55 $1.65 $1.72 $1.96

    HFA is assumed to run an average of 69% of capacity with 98% availability.Capital Recovery assumes a 10% after-tax return on investment over its 10-year life. A 38% marginal tax rate (34%federal, 4% state and local) is included in the return on investment calculation. Natural gas price is based on the 19-year national average commercial rate of $5.34 per thousand scf.Electricity price is based on the 10-year national average commercial rates of 7.5 per kW-hr.The cost for water usage is negligible.O&M includes yearly hydrogen desulfurization bed replacement and reformer and shift catalyst replacement after

    five years. It also includes general maintenance for compressors, valves, etc.Tax and Insurance costs refer to annual property taxes at 1.5% of capital investment and annual insurance premiumsat 1% of capital investment. Highway/road sales taxes are not included.Gasoline equivalent price is based on an efficiency gain of 2.2 for hydrogen FCVs over current gasoline ICEVs.

    Figure 2. Cost of Hydrogen Produced from the 2,000 scfh HFA Options

    We conclude that the wholesale cost of hydrogen produced from early-year HFAs (i.e. 2000scfhHFAs produced in 250 per year quantities) will be nearly competitive with the retail price of gasoline on a per vehicle-mile basis, especially in regions with reformulated gasolinerequirements. We feel that this comparison of the untaxed cost of hydrogen with the taxed priceof gasoline is valid for the near to mid-term as hydrogen is unlikely to be taxed until it begins tosignificantly displace gasoline road-tax revenues. When there are sufficient FCVs to justify alarger number of higher-volume stations, the cost of hydrogen is expected to decreasesignificantly by taking advantage of economies of scale.

    An appendix to this report describes a brief scale-up analysis6, detailing the reduced hydrogencost that results by increasing the size of the HFA from 2,000 scfh to 16,000 scfh. An HFA of this size would support roughly 1464 vehicles, which is comparable to current gasoline stations.A breakdown of the estimated cost of hydrogen for this HFA is given in Figure 3. Using scale-up factors common to chemical processes, the capital cost of this 8x HFA was estimated to be$1.16 million, resulting in a hydrogen cost of $1.87-$2.48/kg (dependent on assumptions aboututility discounts, natural gas feedstock cost, and equipment life). Thus, the 1x HFA derivedhydrogen cost of $3.38/kg is appropriate when discussing the early introduction of fuel cellvehicles where many small stations need to be distributed over the country to support a sparseFCV population, and the significantly lower hydrogen cost of $1.87-$2.48/kg, resulting from an8x HFA, is appropriate for the latter years when the FCV population and population density ismuch higher.

    5 Subtotals may not add to exactly the listed total cost due to rounding.6 For this scale-up analysis, production volume was maintained at 250 HFA units/year. It should be noted that for larger production runs, costreductions beyond those indicated here would be likely.

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    Costs in $/kg H 2 16,000scfh SMR/PSA HFAHydrogen Cost 7 $1.87Capital Recovery $0.77

    Natural Gas $0.59Electricity $0.15

    O&M $0.24Taxes & Insurance $0.13

    Gasoline equiv. ($/gal) $0.85Estimates are based on a scaled-up version of a 2,000scfh HFA. Scale-up may not retain accuracy of original analysis.HFA is assumed to run an average of 69% of capacity with 98% availability.Capital Recovery assumes a 10% after-tax return on investment for a 15-year life. A 38% marginal tax rate(34% federal, 4% state and local) included in the return on investment calculation. Natural gas price is based on the 19-year national average industrial rate of $3.30 per thousand scf.Electricity price is based on the 10-year national averageindustrial rates of 4.65 per kW-hr.The cost for water usage is negligible.O&M includes yearly hydrogen desulfurization bed replacement and reformer and shift catalystreplacement every five years. It also includes general maintenance for compressors, valves, etc.Tax and Insurance costs refer to annual property taxes at 1.5% of capital investment and annual insurance premiums at 1% of capital investment. Highway/road sales taxes are not included.Gasoline equivalent price is based on an efficiency gain of 2.2 for hydrogen FCVs over current gasolineICEVs.

    Figure 3. Cost of Hydrogen from 16,000 scfh (8x) SMR/PSA HFA with Optimistic Assumptions

    7 Subtotals may not add to exactly the listed total cost due to rounding.

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    1 INTRODUCTION

    Over the next several decades, hydrogen fuel cell vehicles (FCVs) are expected to increasinglyreplace gasoline powered internal combustion engine vehicles (ICEVs) as the primaryautomotive platform. Whether this transition occurs rapidly or not will depend on many factors

    including FCV cost, performance, safety and perceived environmental impact. However, acritical factor in the successful transition is the reality and perception of hydrogen fuelavailability. Any successful transition pathway must achieve a cost effective route for the supplyof hydrogen fuel to FCVs during this transition period when there are few FCVs spread outover a large geographic area.

    The most promising hydr ogen supply pathway, more fully described in multiple past DirectedTechnologies Inc. reports8,9, consists of small scale natural gas reformation units producing purehydrogen gas which is then compressed to >5,000 psi for dispensing to FCVs. These HydrogenFueling Appliances, or HFAs, consist of

    a natural gas reformer unit,

    a gas cleanup unit to purify the reformer outlet to a pure 99.99+% hydrogen stream, hydrogen compressor (to allow onsite storage) onsite storage of the hydrogen (for reformer unit load leveling) and hydrogen dispenser to allow dispensing of the hydrogen into vehicular high pressure

    storage tanks at 5,000psi.

    The HFA units are designed for a deliberately low hydrogen production rate, approximately2,000 scfh (115 kg/day) of hydrogen, so as to support small communities of fuel cell vehicles.Each HFA can support approximately 183 FCVs which is approximately one sixth the vehiclefleet supported by a typical gasoline fueling station. This small size is chosen to alloweconomical hydrogen production in the early years when there are low numbers of FCVs present in any one geographical area. If there are more FCVs than one Hydrogen FuelingAppliance can handle, a second, third or fourth HFA unit can be placed next to the first so as toincrease capacity. Thus the hydrogen fueling appliances are modular to allow incrementalgrowth in demand. Similarly, single HFA hydrogen stations may be distributed across thecountry providing a network of hydrogen refueling opportunities.

    While the above described transition pathway is plausible, it will only be successful if thehydrogen produced from the HFAs is economical. Consequently, the focus of this report is onthe cost estimation of the HFA. Past studies examining the capital cost of HFAs have been for larger or small units or at either very low or very high annual unit production rates. While thoseestimates are useful, they do not answer the question of what the projected cost of HFAs would

    be if produced in moderate (250 units/year) quantities consistent with annual FCV productionrates of 50,000/year.

    8 Hydrogen Infrastructure Report, C.E. Thomas, Brian D. James, Ira F. Kuhn, Jr., Franklin D. Lomax, Jr.,.and George N. Baum, all of DirectedTechnologies Inc., prepared for the Ford Motor Company as part of Fords Direct-Hydrogen-Fueled Proton-Exchange-Membrane Fuel CellSystem for Transportation Applications contract (Contract No DE-AC02-94CE50389) to the U.S. Department of Energy, Office of Transportation Technologies, July 1997.9 Distributed Hydrogen Fueling Systems Analysis, C.E. Thomas, John P. Reardon, Franklin D. Lomax, Jr., Jennifer Pinyan, Ira F. Kuhn, Jr., prepared for The Hydrogen Program Office, Office of Power Technologies, U.S. Department of Energy, under Grant No. DE-FG01-99EE35099,October 2000.

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    Additionally, this report examines multiple natural gas reformation chemical pathways (SteamMethane Reforming (SMR), Autothermal Reforming (ATR)) and multiple gas cleanup methods(Pressure Swing Adsorption (PSA), membrane separation, Preferential Oxidation (PrOx)) todetermine the most cost effective approach. Each system requires a careful chemical and

    mechanical engineering analysis to capture the appropriate performance parameters and costfactors. Once moderately detailed mechanical designs and material and energy balances arecreated for all system components, a complete system Bill of Materials is generated. This Bill of Materials allows a line-by-line, element-by-element cost assessment to be conducted.

    A Design of Manufacturing and Assembly (DFMA) costing approach is used to obtain costestimates. This methodology, described more fully in the next section, is used extensively byindustry for product cost estimation and to compare the relative cost of competing manufacturingand assembly approaches. The DFMA methodology is both a rigorous cost estimation techniqueand a method of product redesign to achieve lowest cost. The DFMA approach used within thereport provides a solid framework for this cost study and is the only fair way to compare the cost

    of competing HFA approaches.2 DFMA METHODOLOGY

    2.1 Cost Estimation Using DFMA

    The cost estimation methodology employed in this report is based on the Design for Manufactureand Assembly (DFMA) techniques developed by Boothroyd and Dewhurst, described inProduct

    Design for Manufacture and Assembly, 2 nd edition .10 The DFMA process has been formallyadopted by the Ford Motor Company (among others) as a systematic means for the design andevaluation of cost-optimized components and systems. These techniques are powerful and are

    flexible enough to incorporate historical cost data and manufacturing acumen that have beenaccumulated by Ford since the earliest days of the company. Directed Technologies has adaptedand expanded the formal DFMA technique to include lessons from Ford and its own experienceto develop a system of tools and methods for cost estimation of engineering designs.

    The DFMA methodology was used to estimate costs for equipment for which high-volumemanufacturing methods may not currently exist. Detailed manufacturing and assembly methodswere designed to construct the equipment from the ground up as much as possible rather thanusing factored estimates that are common at this level of capital cost estimation. For off-the-shelf equipment such as valves and instruments, a catalog or quoted price with volume discountwas used.

    The cost of any component includes direct material cost, manufacturing cost, and assembly cost.Direct material costs are determined from the exact type and mass of material employed in thecomponent. This cost is usually based on either historical volume prices for the material or vendor price quotations. In the case of materials not widely used at present, the manufacturing process must be analyzed to determine the probable high-volume price for the material. The

    10 Boothroyd, Geoffrey, Peter Dewhurst, Winston Knight.Product Design for Manufacture and Assembly, Second Edition . Marcel Dekker, Inc., New York. 2002.

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    manufacturing cost is based on the required features of the part and the time required to generatethose features in a typical machine of the appropriate type. The cycle time can be combined withthe machine rate (the hourly cost of the machine based upon amortization of capital andoperating costs) and the number of parts produced per cycle to yield an accurate manufacturingcost. The assembly costs are based upon the amount of time to complete the given operation and

    the cost of either manual labor or of the automatic assembly process train. The piece costderived in this fashion is quite accurate as it is based upon an exact physical manifestation of the part and the technically feasible means of producing it as well as the historically proven cost of operating the appropriate equipment and amortizing its capital cost.

    2.2 Production Volume Considerations

    For each type of reforming system detailed in this report, a production volume of 250 identicalunits per year was assumed. This assumption impacts batch size and equipment considerations,as well as the amortization of equipment costs and the cost of purchased parts to the reformer manufacturer. In addition, a production life of two years (500 units) was generally assumed,

    where applicable, for life volume of equipment and tooling. After this time, equipment isassumed to require replacing due to either wear or design changes. Naturally, increasing production volume and/or life results in reduced costs. However, 250 units was assumed as anappropriate production volume for initial introduction of the product, as discussed in Section3.

    2.3 Markup Rate Assumptions

    Markup rate refers to the additional cost percentage to account for general and administrative(G&A) expenses, material scrap, spending on research and development (R&D), and profit. Insome instances, markup rate also includes allowances for manufacturing and office buildingexpenses, but thesefacilities expenses are usually tabulated separately in standard costestimation practice.11 The markup rate is applied as a percentage increase to the material,manufacturing and assembly cost. The value of markup rate varies depending on who is performing the work.

    In this analysis, two levels of markup may be applied to each component of the final system.The lower level represents the markup applied by a vendor who sells a manufactured componentto the appliance manufacturer (the final assembler). The higher level is the markup applied bythe appliance manufacturer. The final resulting cost is thus actually a projected price to theappliance purchaser (fueling station owner). In addition, the projected cost of hydrogen to theconsumer (potentially a FCV motorist) is provided in this report, with inclusion of operatingexpenses to the reformer purchaser.

    Because the production levels for the refueling appliance are low by mass-manufacturing benchmarks, only final assembly of the refueling appliance is assumed to take place within theHFA companys facility. Manufacture and assembly of all subcomponents occurs at a vendorsfacility where the machines used for those operations do not idle when not producing HFAcomponents but, rather, can be used to produce other non-HFA components. This method of

    11 Standard automotive cost estimation, as practiced by Ford Motor Company and with which the authors are most familiar, typically does notinclude facilities cost in the markup rates.

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    sub-contracting out the majority of the manufacturing work can be cost effective, particularly atlow production volumes, as it allows shopping around to find a vendor who has relatively highmachine utilization, and thus low price, but adequate excess capacity to undertake the HFA job.Because markup rate will vary from vendor to vendor depending on specific circumstances andmachine utilization, a standard markup rate of 30% is used for all vendor manufacturing and

    assembly operations as a reasonable upper limit. Typically automotive markup rates are 22% to25% for highly utilized machines operating at 2 shifts. If all operations were to be brought in-house but performed at very low production rates, required markup rates could easily soar to100% or more.

    Determining the appropriate markup rate for the HFA manufacturer is more difficult as itrequires amortizing the expenses of the business over a moderately low production rate.Consequently, a prototype HFA company was analyzed to gauge the approximate operatingexpenses. These expenses were then translated into markup rate percentages.Figure 2-1outlines the General and Administrative (G&A) and Overhead (OH) expenses of a prototypicalHFA company.

    Figure 2-2details the markup rates applied to reflect the HFA companys G&A, OH, R&D,scrap, and profit for system assembly work conducted on the reformer system (the SMR or ATR system including the PSA and abbreviated RS). A straight 31% markup rate is applied to boththe HFA company assembly work and to the components purchased by the HFA company fromthe various vendors that manufacture the subassemblies. However, the hydrogen compressor,storage, and dispenser subsystems are complete, largely off-the-shelf assemblies merelyassembled into the system. Thus a lower markup percentage of 15% is added to thosecomponents. This is reasonable as these components are quite expensive and the HFA companyis merely packing these components into the final assembly, but at the same time there are realcosts associated with inclusion in the system.

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    General & Administrative (G&A) Expenses $2,297,500

    Management Staff Direct Labor (11 staff) $945,000Fringe Benefits @ 50% Direct Labor $472,500Travel Budget $150,000Office Supplies Misc. $30,000Advertising Budget $500,000Legal Budget $200,000

    Overhead (OH) Expenses $1,908,000

    Engineering Staff OHDirect Labor(10 engineer @ $75k/yr) $750,000Fringe Benefits @ 50% Direct Labor $375,000

    Facilities OHManufacturing Facility(30,000 ft2 @ $12/ft2) $360,000

    Office Facility(15,000 ft2 @ $25/ft2) $375,000Office Utilities $48,000

    Research And Development (R&D) Budget $1,500,000 Figure 2-1. Approximate G&A, OH, and R&D Expenses of Prototypical HFA Company

    Category Markup up onManufactured/Assembled

    Components

    Markup on PassThrough

    ComponentsProfit 15% 5%OH 3% 3%G&A 7% 3%R&D 4% 2%Scrap 2% 2%Total 31% 15%

    Figure 2-2. HFA Manufacturer Markup Rates

    2.4 Design Considerations

    Before the cost analysis described above could be performed, a detailed design of each systemhad to be created. This analysis examined both reforming (SMR and ATR) options from atraditional process-engineering point of view. The unit operations that make up the reformer systems in this study are similar to the industrial reforming operations used to produce hydrogenat large scale (~ 450 kg/hr). Recent patents for small-scale reformer units were consulted for background information and to find any process improvements that may be used in first-generation hydrogen fueling stations.12,13

    12 U.S. Patent 6,296,81413 U.S. Patent 6,316,134

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    Once the necessary vessel volumes and conditions (pressure, temperature, gas composition, etc.)were determined, the vessels and other components were designed. In this design process, aneffort was made to not only follow good DFMA practice by designing for ease of manufactureand assembly, but also to ensure long life and good performance and to acknowledge existing

    codes (i.e. ASME, TEMA) for pressure vessels and shell-and-tube heat exchangers. These codesspecify design criteria for diameters and thicknesses for various components. While the codeswere not strictly adhered to, they were generally taken as good practice for design. Tube andshell thicknesses and tube-sheet thicknesses were calculated using the ASME standards as aminimum, with thickness added to compensate for corrosion where appropriate. Thesecalculations take into consideration the properties of the material to be used, operating pressuresand temperatures, and the geometry of the design. The target life for the design of allcomponents (with the exception of some catalysts and adsorbents, as discussed in Section 4) wasa minimum of ten years. Materials were chosen based on cost as well as strength, corrosionresistance, and machinability.

    2.5 Sample DFMA Cost AnalysisWhile it is not feasible to demonstrate all levels of detailed cost analysis for all components inthis report, it is instructive to give samples of the various analyses performed.Figure 2-3throughFigure 2-5detail the cost estimation for the inlet tube-sheet in the boiler of the 10-atmosphere autothermal reforming (ATR) system, the assembly for the boiler, and a final bill of materials for the boiler. Production of the boiler subcomponents (including the tube-sheet) andassembly of the boiler are assumed to be performed by a vendor, and these activities incur thevendors markup rate. In the bill of materials, an additional markup rate is applied by the systemmanufacturer. This level of analysis is common to all components for which an off-the-shelf analogy or price-quote is not available.

    Tube-Sheet Material SS 316Material cost/kg $/kg $8.82Material density g/cm^3 8Tube-Sheet Volume cm^3 411.851839Tube-sheet Mass kg 3.294814712Material cost $ $29.06

    SETUPBatch size 63Setup rate $/min $3.00Setup time minutes 92Setup cost $ $276.00Setup cost/unit $/unit $4.38

    MACHINING tool change tool position machine time process time tool wearOperation repeat s s/operation s/operation s rate, $/min $/operation Cost, $/unitcenterdrill 7 0 10.1 6.2 114.1 $3.00 0 $5.71drill 7 12 10.1 10.06 153.12 $3.00 0 $7.66countersink 7 12 10.1 4.884 116.888 $3.00 0 $5.84end mill (periph.) - rough 1 12 20 225 257 $3.00 0 $12.85remove piece 1 69.4 69.4 $1.00 $1.16Total per header 710.508 $33.21

    Machining Markup FactorsVendor Manufactures 30.00%

    Cost SummaryMaterial Cost $29.06Machining Cost $37.59Markup Cost $20.00

    Total Cost pre-markup $ $66.65Total Cost post-markup $ $86.65

    Figure 2-3. Detailed Cost Analysis of a Boiler Tube-Sheet

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    Labor Rate $/min $1.75 additional 75cent/minute to account for assistantMachine Rate $/min $0.50

    Units/yr 250

    Operation # repeats time, sec Machine Op.? Cost/Op.

    Place Outlet Header 1 35.9 $1.05Insert Tubes 7 44.1 $1.29Weld tubes to header 7 1260 1 $47.25Place Baffles 2 35.4 $1.03Place Inlet Header 1 35.9 $1.05Weld tubes to header 7 1260 1 $47.25Ultrasound weld inspection 14 840 1 $31.50Place Outlet end-dome 1 40.9 $1.19Weld end-dome to header 1 1930 1 $72.38Apply inner insulation 1 31 $0.90Apply adhesive tape 1 40.6 $1.18Place Shell 1 55.3 $1.61Weld shell to outlet header 1 1930 1 $72.38Inlet end-dome 1 40.9 $1.19Weld end-dome to header 1 1930 1 $72.38Ultrasound weld inspection 2 600 1 $22.50Turn assembly on side 1 120 $3.50Insert reformate ports 2 10.8 $0.32Weld reformate ports 2 1930 1

    $72.38Apply outer insulation 1 31 $0.90Apply adhesive tape 1 40.6 $1.18Remove finished part 1 6 $0.18Total 12248.4 $454.58

    3.4 hrs0.5 shifts

    122 shifts/yr

    Markup Rate 30.00%

    Total Cost pre-Markup $454.58Total Cost post-Markup $590.95

    Figure 2-4. Sample Assembly Analysis for a Boiler

    Component Name Part Name Quantity Unit Cost Cost Mfg Markup Cost w/ MarkupBoiler Inlet Header End-dome 1 $82.47 $82.47 31% $108.04

    Tube-Sheet 1 $86.65 $86.65 31% $113.51Boiler Outlet Header End-dome 1 $158.88 $158.88 31% $208.13

    Tube-Sheet 1 $472.65 $472.65 31% $619.17Boiler Core Boiler Shell 1 $2,156.78 $2,156.78 31% $2,825.38

    Baffles 2 $30.17 $60.34 31% $79.05Tubes 7 $63.37 $443.58 31% $581.09Boiler Insulation 1 $27.03 $27.03 31% $35.41Reformate inlet and outlet 2 $26.34 $52.68 31% $69.02

    Boiler Assembly 1 $590.95 $590.95 31% $774.15

    Total $4,132.02 $5,412.95 Figure 2-5. Sample Bill of Materials for a Boiler

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    3 REFUELING APPLIANCE HYDROGEN PRODUCTION RATE ANDMANUFACTURING QUANTITY

    Figure 3-1summarizes the hydrogen production rate parameters for the HFA and the parametersfor a single HFA service station and a larger station with six HFA units ganged together. EachHFA produces a maximum of 115 kg H2 per day, sufficient to support 183 fuel cell vehicles if each vehicle achieves 80 mpge and travels 12,000 miles per year. Thus is it appropriate for amoderate to large fleet or a small public service station. This relatively small hydrogen refueling plant is well-sized for the early days of fuel cell vehicle production when high geographicconcentrations of fuel vehicles are not expected.

    Single HFA ServiceStation

    Six HFA ServiceStation

    Number of HVAs 1 6Peak Design H2 Production Rate 115 kg/day

    2,000 scfh690 kg/day12,000 scfh

    Fuel Cell Vehicles refueled each day(Based on 80% tank refills)

    20 120

    Fuel Cell Vehicles supported by station 183 1,098Fuel Cell Vehicles supported by 250HFAs

    45,750

    Assumptions/BasisStation Capacity Factor 14 69% Station Availability Factor 98%15 Fuel Cell Vehicle fuel economy16 80 mpge17 Fuel Cell Vehicle mileage per year 12,000 miles/year Fuel Cell Vehicle range 380 milesHydrogen stored onboard vehicle 4.76 kg H2

    Figure 3-1. HFA Production Parameters

    The parameters for a 6-HFA service station are also contained inFigure 3-1. The station is sizedto match the 125 vehicle refuelings conducted in the average US gasoline service station. Thestation gangs together 6 hydrogen fueling appliances and can refuel 120 FCVs per day andsupport a community of 1,098 fuel cell vehicles.

    An annual HFA production rate of 250 is assumed for the cost analysis. This level of HFA production is sufficient to supply hydrogen for new FCVs produced at a rate of 45,750 vehicles per year. There are approximately 130 million automobiles in the United States withapproximately 7 million new gasoline automobiles sold in North America each year. Sales of thetop-selling single model automobile are about 250,000 each year. Thus this selection of HFA

    14 H2 production de-rating factor to account for daily and seasonal fluctuations in demand.15 Based on 22 days per year with one 8-hour shift of scheduled station down time.16 Mileage based on the 1.25 accelerated combined federal drive schedule.17 mpge = miles per gallon equivalent = FCV fuel economy with hydrogen consumptions translated into an equivalent amount of gasoline energy(based on lower heating value of both hydrogen and gasoline).

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    manufacturing rate assumes only a modest annual production run of FCVs and is consistent withthe hydrogen FCV startup scenario. Additionally, at this production rate, HFA hydrogen production facilities sufficient for 457,000 FCVs (approximately 8% of new vehicle sales) will be in place at the end of a 10-year period (the estimated life of the HFA).

    4 STEAM METHANE REFORMING VS. AUTOTHERMAL REFORMING4.1 Overview of SMR and ATR

    Both steam reforming and autothermal reforming are used industrially for convertinghydrocarbons to hydrogen. Methane-rich natural gas, propane, methanol, ethanol, naphtha(gasoline), and biomass are all possible sources of hydrogen by reforming. Natural gas andgasoline are widely available and would require minimal changes in distribution infrastructure tosupply the proposed hydrogen generating stations with fuel. However, natural gas is used as thefeedstock for this analysis because of its advantages over gasoline as a reforming fuel:

    1. Methane has the highest possible ratio of hydrogen-to-carbon and results in the lowestcarbon dioxide emissions per kg of hydrogen generated.2. Natural gas contains lower levels of sulfur and other impurities than does gasoline (~10

    ppm vs. ~300 ppm). Sulfur can poison catalysts in the reforming process, so removingsulfur from gasoline would be significantly more costly than from natural gas.

    3. Natural gas reforming requires no on-site liquid storage tanks since the reforming processis fed continuously from the natural gas pipeline.

    4. Natural gas is produced from predominantly domestic supplies and would reduce theneed for imported crude oil.

    Some localities may have an oversupply (i.e., a very inexpensive supply) of one of the other

    fuels or lack a natural gas infrastructure, which could outweigh the inherent advantages of natural gas reforming. However, for the vast majority of locations, natural gas will be the preferred feedstock to the HFA.

    The natural gas composition used for this study is shown inFigure 4-1. This is a normalizedversion of the gas composition used in the 1997 DOE Hydrogen Infrastructure Report18 with1% oxygen added. The composition is representative of an average U.S. city, but deviationsfrom the average are common.

    Thermal efficiency is a measure of the performance of a reforming process and is defined as

    LHV gas Natural LHV H iciencyThermalEff ,,

    2= (Equation 4-1 )

    18 Thomas, C.E., et al., Section 1, Hydrogen Infrastructure Report, 1997.

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    Component Volume %

    Methane 90.7Ethane 3.6Propane 1.9

    Carbon dioxide 1.0 Nitrogen 1.8Oxygen 1.0Water 0.01Sulfur 10 ppm

    Figure 4-1. Natural Gas Composition

    The lower heating value (LHV) is the amount of heat evolved by full combustion of the fuel withall combustion products remaining in the vapor phase. The natural gas rate counts all natural gasfed to the system, including feed to the reformer and to any combustion devices used to generateheat. Compressors and other motor-driven equipment were assumed to use electrical drives

    rather than natural gas drives, so the motor power is not accounted for in the thermal efficiencycalculation. Calculating the thermal efficiency using the higher heating value (HHV) of hydrogen and natural gas results in an efficiency about 5% higher than that defined in Equation4-1.

    Autothermal reforming (ATR) is generally considered the lower initial-cost option for hydrogengeneration because of a simpler reactor design, and steam methane reforming (SMR) is generallythe higher-efficiency option because of more complete methane conversion. The processingoptions chosen for this comparison emphasize the relative strengths of each process, with theresult that there are many other potential variations that involve tradeoffs between capital costand efficiency. A few of these options are discussed in Sections 4.2 and 4.3, but the choicescovered in this analysis are not exhaustive.

    The basic processing steps are common to both SMR and ATR:

    1. Natural gas compression2. Natural gas purification (i.e., sulfur removal)3. Catalytic steam reforming of methane to hydrogen and carbon monoxide (CO)4. Water-gas shift to convert carbon monoxide (CO) to carbon dioxide (CO2) and additional

    hydrogen

    Mass and energy balances andchemical equilibrium compositions were calculated in aHYSYS process simulation.19

    4.1.1 Natural Gas Compression

    Natural gas is distributed by the utility at just slightly above atmospheric pressure and must becompressed to achieve a more favorable combination of equilibrium, reaction rates, and

    19 HYSYS is a chemical engineering simulation environment and is a product of AEA Technology

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    equipment sizing. The natural gas compressor design is identical for all of the considered processing options, although the motor size is larger for higher discharge pressures.

    4.1.2 Natural Gas Purification

    The most common impurities in city natural gas are sulfur compounds, particularly mercaptancompounds used as odorants. Sulfur poisons the reforming catalyst by forming nickel-sulfide, sothe natural gas sulfur level must be reduced to less than 1 ppm. The total sulfur content of thenatural gas was assumed to be 10 ppm. Typically there are several ppm of H2S naturallyoccurring in and several ppm of mercaptan odorant added to distributed natural gas. Mercaptansare converted irreversibly to hydrogen sulfide by the hydrodesulfurization (HDS) reaction over acobalt-molybdenum or nickel-molybdenum catalyst

    S H H R H SH R 22 +=+ (Equation 4-2)

    A small fraction of the product H2 from the reforming process is recycled to the HDS reactor to

    facilitate this reaction. The reaction stoichiometry is one H2 per mercaptan molecule, but anexcess of H2 is added to ensure complete conversion of mercaptans to H2S.

    The H2S is removed from natural gas by absorption in a bed of zinc oxide (ZnO). The H2S reactswith ZnO in a 1:1 mole ratio to form zinc sulfide (ZnS) and water. In both the SMR and ATR cases, the ZnO bed volume was sized to handle 10 ppm average sulfur content and 75%conversion of ZnO to ZnS. The HDS catalyst and ZnO absorbent are contained ina singlevessel, which is an arrangement used for relatively low sulfur content gas streams.20 The proposed parallel two-bed design is illustrated inFigure 4-2. One bed is sized to last 6 months,and the valves are arranged so that the flow path can be switched without interrupting gas flow.The vessel is constructed from standard flanged pipe sections to minimize material and assemblycosts, as shown inFigure 4-3.

    Hot Reformate

    Hot Reformate

    NG

    NG

    HDS SectionManualShut-off

    Valve

    HDS Preheater

    Figure 4-2. Two-Bed HDS System with Natural Gas Preheater (not to scale)

    20 Elvers, Barbara, et al., ed.Ullmanns Encyclopedia of Industrial Chemistry , Volume A12, page 192, 1989.

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    steam than is available from other parts of the process. The S/C ratio chosen for any particular reformer will depend on site-specific economic factors, especially on the price of natural gas.Locations with higher natural gas price will realize a greater reduction in hydrogen cost byincreasing thermal efficiency than will locations with low natural gas price. We have chosen aS/C ratio of 3 for this analysis (see Section 4.2 for details). The S/C ratio for ATR is typically

    ~1. The tradeoffs for higher S/C ratios in ATR are discussed in more detail in Section4.3.6. Traditional industrial reforming uses catalysts containing 10-20 weight percent nickel (Ni) as theactive ingredient. The nickel is dispersed on a high temperature-stable support, often the high-temperature phase of aluminum oxide containing Group IIA elements (e.g., Mg) as stability andanti-coking additives. The platinum group metals, particularly ruthenium (Ru) and rhodium(Rh), are highly active catalysts for steam reforming21 but have not been in widespread industrialuse because of the added cost over nickel. Ruthenium is approximately 4 times as active asnickel at 800C.22 The platinum group metals by themselves are not active for the water-gas shiftreaction, and loss of the shift reaction in the reformer would significantly increase the size of thedownstream water-gas shift reactor.

    We propose to achieve the benefits of both metals by using a traditional Ni-based reformingcatalyst loaded with 0.5-1.0 weight percent ruthenium. The benefits of the proposed catalyst arethat platinum-group metals tend to avoid coking caused by methane decomposition to carbon,that ruthenium is the most active platinum group metal catalyst, and that the price of rutheniumover the past 10 years has averaged only 5-10% of the cost of rhodium.23 Ruthenium is morestable than nickel at high temperatures and should remain better dispersed over several years of catalyst use. Some platinum-group metal reforming catalysts are available commercially.Haldor-Topse sells a reforming catalyst that contains a platinum-group metal and generallycosts about 50% more than the traditional nickel catalyst.24 Toyo Engineering (Japan) andSynetix both advertise the availability of precious-metal steam reforming catalysts on their websites.25,26

    We used a reactor model taking into account intrinsic reaction kinetics and mass transfer limitations to calculate the reformer reactor sizes. Kinetic expressions for the reforming reactionwere taken from the open literature27,28 and confirmed by comparisons to rule-of-thumb factorsfor industrial reforming reactors.29 In general, the ATR requires more reforming catalyst thanthe SMR. The higher rate of reaction at ATR temperatures is more than offset by the dilutioneffect of inert nitrogen reducing the partial pressure of the reactants.

    21 Rostrup-Nielsen, J.R. and J-H. Bak Hansen, CO2-Reforming of Methane over Transition Metals. J. Catalysis , 144, p 38-49 (1993).22 Rostrup-Nielsen and Bak Hansen, ibid.23 Johnson-Matthey Platinum Historical Price Report, http://www.platinum.matthey.com, 2002.24 Personal communication with David Kelling, Haldor-Topse, January 2002.25 Toyo Engineering website, http://www.toyo-eng.co.jp/Technology26 Synetix website, http:/ /www.synetix.com27 Rostrup-Nielsen and Bak-Hansen, ibid.28 Rostrup-Nielsen, Jen R.Catalytic Steam Reforming . Springer-Verlag, Berlin, 1984.29 Ridler, D.E., and M.V. Twigg, Steam Reforming inCatalyst Handbook , Martyn V. Twigg, ed. Manson Publishing, London, 1996.

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    4.1.4 Water-Gas Shift Reaction

    Additional hydrogen is produced by exothermic reaction of carbon monoxide with water by thewater-gas shift (WGS) reaction

    222 H COO H CO +=+ Hrxn = -90 kJ/gmole (Equation 4-6)

    In the presence of excess water some WGS reaction takes place in the reforming reactor,however the equilibrium to hydrogen is much more favorable at temperatures below 450C. Thewater-gas shift catalyst is chromium-promoted iron oxide, which is the traditional catalyst for thehigh-temperature water gas shift process. The shift reactor was sized to provide an average of three seconds of contact time between the flowing gas and the catalyst, which is in the mid-rangeof size used in industrial systems.30

    The proposed process does not include a separate low temperature water gas shift reactor since atthis relatively small scale the cost of hydrogen would increase by about 1/kg to pay for the cost

    of an additional reactor (~$10,000-12,000), not including the increased cost for assembly,foundation size, and building size. While 1-2/kg may seem a small effect, the point is thatinclusion of a low temperature water gas shift reactor increases the cost of hydrogen rather thandriving it down, thus the reactor is not cost effective.

    4.2 SMR System Flowsheets, Cost and Performance

    Steam reforming systems were designed for nominal 10 atm operation with pressure swingadsorption (PSA) H2 purification and 20 atm operation with membrane H2 purification. Thehydrogen purification processes are described in detail in Section5. The SMR processingconditions are listed inFigure 4-4and the flow sheet is shown inFigure 4-5.

    Pressure10 atm SMR 1000 kPa (nominal)20 atm SMR 2000 kPa (nominal)

    TemperaturesHDS/ZnO 400CReformer Inlet 430CReformer Outlet 800CShift Inlet 450CShift Outlet 250CCondenser Outlet 55C

    MiscellaneousS/C 3Figure 4-4. SMR Process Conditions

    The steam-to-carbon (S/C) ratio of 3 was chosen to trade off the methane conversion andlikelihood of catalyst coking with the amount of heat available by burning the waste gas from the

    30 Satterfield, Charles N., Heterogeneous Catalysis in Industrial Practice, 2 nd ed . McGraw-Hill, New York, 1991.

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    hydrogen purification step. Slightly higher thermal efficiencies could have been achieved byreducing the S/C ratio to less than 3, but the risk of catalyst coking would increase.

    The proposed designs do not integrate heat transfer as much as theoretically possible so that the process conditions are not over constrained. For example, if air used to cool the condenser is

    used to cool the shift reactor, only one of the temperatures (condenser or shift reactor) may be setindependently without adding extra control valves and instrumentation. Additionally, if the air pressure drop is relatively high due to a flow path through multiple units, the blower or fan costincreases significantly. In the proposed design, a portion of the air used to cool the condenser isrouted to the burner to sustain the combustion. For optimum temperature control, independent blowers or fans are used to provide the other cooling-air needs.

    The steam boiler, reformer, reformate cooler, and shift reactor are all based on shell-and-tubeheat exchanger designs. A consistent manufacturing and assembly approach was used for all of the shell-and-tube units.

    A possible variation of the SMR is to operate at atmospheric pressure. The choice of materialsthat are acceptable to use at reformer temperatures is dramatically increased at low pressure. For example, the steam boiler design described in Section4.2.2 has Incoloy 800H tubes with a wallthickness of 0.90 mm to operate at 10 atm. If instead the pressure were 1 atm, the tubes could beconstructed of 316SS with a wall thickness of 0.25 mm or less. The potential cost savings atlower pressure for units like the boiler, however, may be offset by larger reactor sizes for thereformer and shift reactor. Both steam reforming and water gas shift reaction rates decrease withdecreasing pressure, leading to larger catalyst beds to achieve equivalent conversion.

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    ReliefValve

    P

    Temp

    Temp

    F

    P

    Temp

    BoilerSMR

    Condenser

    WaterKnockout

    HydrogenPurificationHydrogen

    Compressor

    Natural GasCompressor

    HDSPreheater

    HDS/ZnO

    WaterDI Bed

    HydrogenStorage

    Natural GasMain Shutoff Valve Filter

    Relief Valve

    Natural GasFlow Control Valve

    Relief Valve

    CItyWater

    VentB

    Co

    ReliefValve

    Pressure-ReducingValve

    Natural Gas to Burner

    Natural Gas to Reforming

    Reformate (800C)

    Reformate (760C)

    Nat. Gas (400C)

    D I W a t e r

    ( 2 5 C )

    Steam (450C)

    Nat. Gas (400C)

    R ef or m

    a t e ( 8 0 0 C )

    Burner Exhaust (506C)

    Burner Exhaust (160C)

    Raffinate (55C)

    Dry Gas (55C)

    Water (55C)

    Hydrogen

    Raffinate

    RaffinateSurge Tank

    Figure 4-5. SMR Flowsheet

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    4.2.1 Reactor and Vessel Sizing

    Natural Gas Pretreatment

    The natural gas feed is heated to 400C for operation of the HDS catalyst and ZnO absorption

    bed. The proposed design uses the hot reformate stream to preheat the natural gas in a double- pipe heat exchanger with a finned inner pipe, as shown inFigure 4-6. The reformate is inside theinner pipe so that only the tube is designed for this high temperature stream, and the natural gasis in the annular space. There is the potential for a small fraction of the natural gas to decomposeto carbon by thermal cracking on the hot surface of the inner tube, and the thermal cracking ismore likely to occur in natural gas with a high fraction of higher hydrocarbons. The preheater could be moved downstream of the reformate cooler if coking is a problem without significantlychanging the total cost.

    Figure 4-6. HDS Preheater, with Tube-in-Tube Design (not to scale)

    The hydrodesulfurization (HDS) catalyst and zinc oxide (ZnO) absorbent are combined into asingle vessel, shown previously inFigure 4-3. The operating temperature of the HDS/ZnO bedis 400C. The HDS catalyst volume is sized to provide a gaseous hourly space velocity (GHSV)of 3000 hr -1, and the ZnO volume is designed to last 6 months. The vessels to hold the catalystand the absorbent are made from sections of 4-inch diameter stainless steel pipe with flangedends and screens to contain the catalyst and absorbent. Two such vessels are used in each

    reforming system, so that one bed may be used in the process while the other is changed out,giving the pair a one-year life.

    Steam Reformer

    The proposed reactor design is a shell-and-tube heat exchanger with the reforming catalyst in thetubes and the burner exhaust in the shell (seeFigure 4-7and Figure 4-8). The natural gas andsteam mixture flows countercurrent to the combustion gas from the burner.

    BurnerOuter Insulation

    Inner Insulation

    Flue Gas

    NG & Steam Reformate

    BaffleReactor Tube Tube Sheet

    Shell

    End-dome

    Figure 4-7. SMR Reformer Vessel (not to scale)

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    Figure 4-8. Tubes and Tube-Sheets for Shell-and-Tube Vessel(Such a configuration is used, with varying numbers of tubes, for the SMR vessel, the HTS,

    and most heat exchangers.)

    Tubes are (1.27 cm) outside diameter. Using fewer larger diameter tubes would simplify thetube sheet construction, but heat transfer to the center of larger tubes would be insufficient tomake up for the endothermic reaction.

    One of the biggest challenges to designing a steam reformer at this scale is the materialsselection for the reformer tubes. The tube metal is exposed to ~1000C combustion exhaust(oxidizing atmosphere) on the outside and 800C reformate (reducing atmosphere) on the inside.The alloy chosen for the tubes, the tube sheets, and the outlet end dome is Haynes 556. Other possible alloys for the reformer tubes are other Haynes alloys such as 230 and Inconel alloyssuch as 617 and 625. All of the potential high-temperature resistant alloys are a factor of five tonine times more expensive than the common stainless steels and are difficult to work with. The

    bulk cost of Haynes 556 was estimated at $60/kg, and DFMA techniques were used to estimatethe cost for tube forming. The cost for construction and assembly of the entire reformer was alsoestimated using DFMA. Orbital welding was used to weld the individual tubes to the tubesheets.

    The tube sheets to which the tubes are welded at both ends of the reactor are significantcontributors to the reformer cost. As a result, the number of tubes in the reformer is one of themost important factors in determining the overall cost. We have chosen a number of tubes thatresult in a reasonable length (100 cm) to avoid excessive pressure drop and stress on theunsupported tube metal. There are 180 tubes for the 10 atm SMR and 134 tubes for the 20 atmSMR.

    The 10-atmosphere steam-reforming reactor requires 16.7 L of catalyst to approach theequilibrium conversion of methane at 800C (from the kinetic model). The amount of catalystneeded to reach equilibrium methane conversion is 10.9 L for the 20 atm system due to faster reaction rate at higher pressure. However, the equilibrium conversion of methane is only 73% at20 atm compared to 84% at 10 atm.

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    The shell is constructed of Incoloy 800H. The shell is lined with 1 (2.54 cm) of insulation toreduce heat loss to the surroundings while at the same time reducing the shell metal temperature.Lowering the shell metal temperature allows the shell wall to be thinner than if the insulationwas only on the outside of the shell. An additional 5.1 cm (2 inches) is added to the shelldiameter to account for the insulation thickness. The outside of the shell is wrapped with of

    insulation. Incoloy 800H has excellent oxidation resistance at the temperatures to which it isexposed through the insulation in the reformer shell (~500-600C). With an adequate insulationliner, the reformer shell may be constructed of a more conventional stainless steel. For a safetymargin and to guard against oxidation at higher temperatures due to leaks in the insulation,however, we chose the more resistant Incoloy 800H.

    The burner is sized to provide enough heat for the reforming reaction and to generate thesuperheated steam for the reformer (see Section4.2.2). A nominal 150 kW (500,000 Btu/hr) burner including flame detector and affiliated equipment is $700 (quote from Martin Controls).

    Shift Reactor

    The shift reactor is a shell-and-tube design similar in concept to the reforming reactor. The shiftcatalyst is contained in the tubes, and the cooling air is in the shell. The process stream is cooledfrom 450C at the reactor inlet to 250C at the reactor outlet. The rate of the shift reaction slowsconsiderably with the temperature drop, but the equilibrium shifts to 95% conversion of CO at250C from 61% at 450C.

    The 10-atmosphere shift reactor contains 130 kg of catalyst to approach the equilibriumconversion of CO at 250C. The 20-atmosphere shift reactor contains 83 kg since the shiftreaction proceeds more quickly at higher pressure. The pressure does not affect the equilibriumconversion of CO, since the water gas shift reaction has the same number of moles of products asof reactants.

    4.2.2 Heat Exchanger Sizing

    Reformate Cooler

    The reformate stream is cooled to 450C for the water-gas shift reaction. A variable speed blower supplies the cooling air to the reformate cooler. The reformate cooler is a shell and tubeheat exchanger with the reformate inside finned tubes (Haynes 556 tubes with 316SS fins). Theouter shell is a thin metal jacket (316 SS) to contain the cooling air at essentially atmospheric pressure.

    Boiler

    Deionized water is evaporated and superheated to 450C by heat transfer with the burner gasesleaving the reformer. The boiler is a shell and tube-type heat exchanger, although the shell is not pressure rated because it contains atmospheric pressure burner exhaust. The steam is generatedand superheated inside finned tubes constructed of Incoloy 800H with 316SS fins.

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    Condenser

    The condenser is a bank of stainless steel finned tubes with cross-flow of air as the cooling fluid.The condenser design is similar to a commercially available room heater that uses condensingsteam to provide heat. The heat exchanger plus fan assembly can be purchased for about $1200

    plus the cost of motor, speed controller, and motor starter (all off-the-shelf items). The heatexchanger and fan assembly for the 20 atm system is about double (~$2500) the cost for the 10atm system because of the higher pressure rating.

    Water Knockout Vessel

    A vessel is needed to separate condensed water before sending the reformate gas to the gascleanup system. The knockout vessel is designed to reduce the vapor velocity to 1 m/s or less sothat the water is removed by gravity separation. A one-stage separator provides a cleanseparation since no other compounds are present in significant quantities in the liquid water phase. The proposed design is a section of 4 steel pipe with welded end caps and welded inlet

    tap. The knockout vessel is elevated so that water is returned to the deionization tank (Section4.2.3) by gravity feed.

    4.2.3 Water Purification

    The water requirement for steam fed to the SMR systems is approximately 1-1.5 liters/minute.Ions such as calcium and chloride common in city water can cause serious fouling and corrosion problems at the high temperatures in the reforming system and can poison reforming and shiftcatalysts. The water used to generate steam must be deionized before it is fed to the reformer system. The proposed water purification system is a carbon filter followed by a deionization(DI) tank. The deionization tank is a low-pressure rated vessel filled with deionization resin thatis changed on a regular schedule. US Filter provides a service that includes setup of the carbonfilter and deionization tank for ap proximately $1500 initially and resin replacement cost of approximately $1500 per year.31 The deionization resin life is dependent on source water quality, so the replacement cost listed here could vary in any specific situation.

    The volume of water recovered from the condenser after the high-temperature shift reactor isapproximately 35% of the volume fed to the reformer. This water may contain trace levels of metals picked up from the catalysts and may not be suitable for direct discharge to municipalsewer. The proposed design mixes the condensate with fresh city water to make up thenecessary water rate.

    4.2.4 Other Equipment

    Fans and Blowers

    Costs for cooling fans and blowers were estimated from catalog prices for standard items. Thefans with associated equipment (motors and motor starters) are included in the bills of materialsfor the heat exchangers.

    31 Personal communication with Randy Pittman, US Filter Corporation, February 2002.

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    Instruments

    The instruments included in the design are only those necessary to assure proper operation for awell-established process, such as thermocouples and pressure transducers to provide signals to

    automatic control valves (seeFigure 4-5). The first several installations will have a higher levelof instrumentation to verify the design conditions and to collect data for process improvements.Instrument lists for the 10 atm and 20 atm systems are identical and are included with the system bills of materials.

    Pallet

    Figure 4-9shows a proposed layout of a 10-atmosphere SMR reformer system (RS) containingthe major components at their approximate relative sizes. The reforming components would fiton an eight-by-thirteen foot pallet, with the hydrogen compressor, storage system, and dispenser housed separately. This size of footprint offers generous room for the necessary vessels and to

    allow easy access for servicing the components. The SMR and HTS reactors, and the HDSsystem are placed near the edges of the footprint, making them especially easy to service andremove for catalyst replacement. The 20-atmosphere SMR system would have a similar floorplan, but would not require the bulky PSA system and 250-gallon raffinate surge tank,reducing the necessary footprint to an eight-by-ten foot area. In both cases, all of the reformer components would be secured to an appropriately sized, skid-mounted pallet for transportationand installation purposes. This pallet would be placed directly onto a concrete slab at theinstallation site.

    13'

    8'

    PSA

    RaffinateSurgeTank

    NGCompressor

    Reformate Cooler

    HTS

    Condenser

    Water KO

    SMRHDS

    Boiler

    Figure 4-9. Proposed Layout of 10 atm SMR Reformer System(Cylindrical vessels are secured in racks (not shown), and all components are attached

    to a skid-mounted pallet.)

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    4.2.5 Assembly

    The cost to assemble the reformer system (RS) was calculated from the time to required to setthe vessels on the pallet, the materials and labor to install the necessary length of piping betweenvessels, the material and labor to insulate the piping, and the labor to pressure test the completed

    assembly. Eight man-days were allotted for this process. (With a team of two workers, each unittakes four workdays, meaning that five such teams would be required to produce 250 units in one220-day workyear.)

    4.2.6 SMR Reformer System Bill of Materials and Cost

    The overall SMR RS bill of materials is shown for a 10 atm system inFigure 4-10and for a 20atm system inFigure 4-11. The cost for each reforming system (RS) includes the gas cleanupsystem, which is described in detail in Section5. The initial capital cost for the 10atm SMR-PSA RS is $123,545, while that for the 20atm SMR-membrane RS is $137,036.

    4.2.7 SMR Performance and EfficiencyThe thermal efficiency of the 10 atm SMR is 70% (LHV basis), corresponding to a hydrogen production of 0.30 kg per kg of natural gas fed (including fuel to the burner). The thermalefficiency of the 20 atm reformer is 66%, with a hydrogen production of 0.26 kg per kg of natural gas fed (including fuel).

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    Controls System Thermocouples 5 $40.00 $200.00 $10,750 31.00% $

    Mass Flow Meter 1 $2,000.00 $2,000.00 31.00% $2,620

    Pressure Transducers 3 $400.00 $1,200.00 31.00% $1,572.0

    Computer 1 $800.00 $800.00 31.00% $1,04

    I-P Converters 5 $300.00 $1,500.00 31.00% $1,965

    PLC 1 $1,000.00 $1,000.00 31.00% $1,31

    I/O Cards 2 $600.00 $1,200.00 31.00% $1,57

    Pneumatic Control Valves 3 $400.00 $1,200.00 31.00% $1,572.

    Instrument Air System 1 $300.00 $300.00 31.00% $393

    Pressure Relief Valve 3 $50.00 $150.00 31.00% $196.

    Controls Software 1 $600.00 $600.00 31.00% $786

    Control Cabinet 1 $600.00 $600.00 31.00% $786

    Structural Supports Skid-mounted floor 1 $3,000.00 $3,000.00 $4,400 31.00% $3,930.

    Vessel stands/frames 7 $200.00 $1,400.00 31.00% $1,834.

    Total Sub System Cost

    Sub-system Name Component Name Part Name Material Basic dimensions Quantity Unit Cost Cost w/o Mfg Markup Mfg Markup Cost w/ Markup w/ Mfg Marku

    $5,670Assembly 1 $4,360.00 $4,360.00 31.00% $Piping (incl. insulation) 1 $1,310.00 $1,310.00 31.00% $

    10atm SMR RS Total

    Figure 4-10. Bill of Materials for 10 atm SMR RS (3 of 3)

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    Computer 1 $800.00 $800.00 31.00% $1,048.00

    I-P Converters 5 $300.00 $1,500.00 31.00% $1,965.00

    PLC 1 $1,000.00 $1,000.00 31.00% $1,310.00

    I/O Cards 2 $600.00 $1,200.00 31.00% $1,572.00

    Pneumatic Control Valves 3 $400.00 $1,200.00 31.00% $1,572.00

    Instrument Air System 1 $300.00 $300.00 31.00% $ 393.00

    Pressure Relief Valve 3 $50.00 $150.00 31.00% $196.50

    Controls Software 1 $600.00 $600.00 31.00% $786.00

    Control Cabinet 1 $600.00 $600.00 31.00% $786.00

    $6,325 Assembly 1 $4,360.00 $4,360.00 31.00% $5,71


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