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Lecture 14. Hydrogen Production

Lecture 14. Hydrogen Production . Fuel cell system Fueling fuel cells Why hydrogen ? Hydrogen from fossil fuels. Fuel Cell System. Fuel Processing Subsystem. Fuels for Fuel Cells. Why Hydrogen ?.

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Lecture 14. Hydrogen Production

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  1. Lecture 14. Hydrogen Production • Fuel cell system • Fueling fuel cells • Why hydrogen ? • Hydrogen from fossil fuels

  2. Fuel Cell System

  3. Fuel Processing Subsystem

  4. Fuels for Fuel Cells

  5. Why Hydrogen ? 1. Hydrogen is the lightest element in the Periodic Table of Elements; its ordinal number is 1.2. Pure hydrogen is very seldom on Earth; predominantly, it is found in chemical compounds such as water H2O, hydrogen sulfur H2S, ammonia NH3, hydrocarbons CnHm, ...3. Hydrogen is nothing really new. It was discovered by Henry Cavendish (1731-1810) and almost at the same time by Antoine Lavoisier (1743-1794). Industrial hydrogen chemistry began 150 years ago. Prior to the usage of natural gas, so called town gas was used in order to heat homes, cook meals or light streets; it contained up to 70% hydrogen.4. Hydrogen is not an energy. Hydrogen is an energy carrier, a secondary energy carrier, to be precise (like water steam or electricity,... ); for its production, energy is needed.

  6. Why Hydrogen ? 5. Presently, hydrogen is produced almost exclusively from fossil fuels, through steam reforming of natural gas or partial oxidation of hydrocarbons. Only a few percent come from electrolysis of water. Low temperature electrolysers are state-of-the-art, high temperature/high efficiency electrolysers are still subject of research and development.6. 600 billion norm cubic meters of hydrogen are traded annually worldwide. That seems much; it represents energetically, however, only about half of the end energy demand of Germany alone. From an energy economy standpoint, hydrogen energy is at its very beginning!7. So far, there is only one industrial branch using hydrogen energetically, the space industry, and furthermore, it is dependent on it, because, although hydrogen needs three times more volume per unit of energy, it has, however, only one third of the weight, compared with hydrocarbons in use like gasoline, Diesel or the like. - Non-energetically, hydrogen is used for fat hardening, cooling of electrical generators, in methanol synthesis, in electronics production, ...

  7. Why Hydrogen ? 8. On principle, there is no absolute technological safety; that is true for energy technology safety, too. Each energy carrier has its specific safety risks dependent on its physical/chemical nature. Hydrogen has a high affinity to air or oxygen (O2); the ignition range of a hydrogen/air (oxygen) mixture is wide, the ignition energy is very small. The diffusivity of hydrogen in air, however, is very high, so that hydrogen leakage or hydrogen flames diffuse quickly vertically up into the air. The energy carrier hydrogen has two inherent safety advantages relative to all other energy carriers:* per se, long time follow up casualties of unknown extent are impossible, because, on principle, (radio-)toxicities and radioactivities are inexistent and* hydrogen does not contribute to the Greenhouse Effect

  8. Why Hydrogen ? 9. Never in the history of the energy supply of mankind was only one energy form in use, never did an additional energy form replace fully its predecessors; the energy demand of a growing human population needed them all:* Up until far into the 18th century exclusively renewable energies were in use* The 19th century was the century of coal, with complementary mineral oil at its end* The 20th century saw the emergence of natural gas and nuclear fission* Many plausible arguments indicate that the 21th century is going to become the century of energy sustainability, energy efficiency, conservation of energy, all sorts of renewable energy again, and the secondary energy carrier hydrogen.

  9. Why Hydrogen ? 10. The history of energy of the last two centuries, the 19th and 20th, were clearly dominated by the primary energy raw materials coal, oil, natural gas, and uranium: The energy supply system was - and is as before - energy raw material-oriented. The 21th century, on the other hand, is expected to be different: It will be technology-oriented, because energy efficiency and conservative energy usage limit the amount of primary energy necessary; they help to provide more energy services with fewer energy raw materials. For renewable energies, operational primary energy raw material is inexistent, and the secondary energy carrier hydrogen is the lightest element.

  10. Why Hydrogen ? 11. Energy supply means the simultaneous run through the energy conversion chains and the chains of energy material: From primary energy to secondary energy to end energy to useful energy, and finally to energy services; their supply to cost and in time is the only reason for the run through the chains; all preceding chain links have no meanings in themselves, they are means to an end. - In parallel, the energy materials chain is run through: it begins with the primary energy raw materials taken out of Earth’s crust and ends - after many physical and chemical conversions - with the residues and their transfer into the geosphere. It is not really the energy conversion which is of environmental relevance; it is the material conversion chain with its numerous open ends to the environment, which causes conflicts with it. The renewable energy and solar hydrogen energy conversion chains have no material conversion chains at all to be run through simultaneously; consequently, all potential operational material influences on the environment must be inexistant!

  11. Why Hydrogen ? 12. Coal, mineral oil, and natural gas are hydrocarbons whose atomic hydrogen/carbon-ratio H/C is Coal : Oil : Natural Gas = <1 : 2 : 4. For a prospective hydrogen energy economy it tends to become infinite.13. In the last 120 years the carbon tonnage relative to the unity of energy in the energy supply of mankind decreased by 35%; the decrease continues. Thus, a decarbonisation is under way, along with hydrogenation, and - since the atomic weights of carbon and hydrogen are 12 and 1, respectively, a dematerialisation. With the transition from coal to oil to natural gas and - in a prospective hydrogen energy economy - further to hydrogen, energy becomes lighter and lighter.14. Gaseous or liquefied hydrogen transport over pipelines, in tanker ships, in railcars or on tanker trucks is state-of-the-art; likewise hydrogen storage in high pressure flasks or in containers, in metal hydride or liquefied hydrogen storage; the same applies for filling or emptying devices. Recently, a robot LH2 filling station was put into operation in Munich, Germany, and a GH2 filling station is operable in Hamburg, Germany.

  12. Why Hydrogen ? 15. Hydrogen liquefaction follows the traditional Claude process. Magnetic-caloric liquefaction offers higher efficiencies; it needs, however, still much more R+D.16. Catalytic burners are well understood and can be purchased on the market.17. The H2/O2 steam generator for spinning reserve applications in the 100 MWe range is readily developed, and so is the H2/air internal injection engine for stationary applications or on-board usage.18. The utilization of hydrogen and air or hydrogen and oxygen in aircraft engines or engines of space launchers is well understood. Legendary are the numerous space launchers using hydrogen; in the 1980s a TUPULEW 155 was operated successfully with one hydrogen engine at the rear.

  13. Why Hydrogen ? 19. The great challenge of today is the fuel cell which was published for the first time by William Grove (1811-1896). It is a chemo-electrical energy converter not dependent on the restrictions of the Carnot process (Sadi Carnot 1796-1832), which for higher thermal efficiencies needs higher temperatures and, thus, better and more expensive materials. - The fuel cell operates w/o noise, is compact and - without moving parts - free of vibrations. It utilizes - with or without a reformer - a multiplicity of chemical energy carriers such as natural gas, coal gas, methanol, biogas, even gasoline, or hydrogen. The fuel cell is highly efficient with a total energy utilization of 90% and more, with a comparatively high electricity yield. Its emissions are almost zero, with literally no pollutants when operated on hydrogen and oxygen; then, only warm air and water vapor are exhausted. Fields of application are* Heat-power-blocks in the range of a few kilowatts to a few megawatts* as the chemical-electrical energy converter on board electric busses and automobiles, and* as topping cycles of gas turbine/steam turbine combined cycles with expected overall electrical efficiencies of 70%

  14. Why Hydrogen ? 20. The hydrogen energy conversion chain is environmentally clean over its entire length as long as the primary energies used are clean. An exemplary chain is the solar hydrogen chain with electricity production in hydropower plants, solar power or wind power plants or biomass converters with follow-up electrolysis of water, transport and storage and, finally recombination of hydrogen and oxygen or air for the production of heat and electricity. The two projects HYSOLAR and Solar-Wasserstoff-Bayern have experimentally exemplified the direct coupling of solar-voltaic electricity and electrolysis with a unit capacity of up to 350 kilowatt. Clean hydrogen energy chains are also possible when hydrogen is produced from fossil fuels, under the condition that the unavoidably co-produced carbon dioxide is sequestered and stored without influencing the Greenhouse. A typical process is under experiment in Norway: Natural gas from underneath the sea is on the spot steam reformed, and the carbon dioxide is immediately re-injected into the underground into the emptied natural gas field. So far, 1 million cubic meters of carbon dioxide have been reinjected.

  15. Why Hydrogen ? 21. The solar-hydrogen residential home in Freiburg/Germany is an - almost - Zero-Energy-Home (zero= no commercial energy from the market over its entire life) which converts solar summer electricity into hydrogen and oxygen and recombines them in winter for the production of electricity and heat. With that experience, even a "Negative"-Energy-Home seems not too far fetched, one which takes more energy from the sun than is needed for its own supply.

  16. Why Hydrogen ? 22. Hydrogen technology on the market:-Steam reforming of natural gas-Partial oxidation of hydrocarbons-Water electrolysis-Alkaline fuel cell-Phosphoric acid fuel cell-Hydrogen engines in space launchers-Hydrogen compressers and pumps-all sorts of storage-all sorts of transportation means-hydrogen catalysis-hydrogen sensories

  17. Why Hydrogen ? Hydrogen technologies on the verge of the market-Low temperature/high efficiency electrolysers-Hydrogen internal injection engines with external and internal mixture formation for stationary and on board applications-Robot filling stations-Proton exchange membrane fuel cells for busses and automobiles-Solid oxide fuel cells for residential applications-H2/O2-spinning reserve

  18. Why Hydrogen ? Pre-market demonstration necessary:-No-emission city bus fleets-Fuel cell supported district heating systems-Molton carbonate fuel cells for industrial application-Hydrogen production from fossil fuels and supply options-Transatlantic pilot transport of hydrogen from renewables-Hydrogen pilot airline and on-ground hydrogen infrastructure

  19. Why Hydrogen ? Research and Development-High temperature electrolysers/fuel cells-The fuel cell as topping cycle of combined systems-Photochemical hydrogen production-Material research on membranes-Reaction kinetics on surfaces-Low-NOX combustion chambers-Mecano-catalytic water splitting

  20. H2 Production for Fuel Cells

  21. Hydrogen Production ThermochemicalA steam reforming process is currently used to produce hydrogen from such fuels as natural gas, coal, methanol, or even gasoline. To draw on renewable energy sources, the gasification or pyrolysis of biomass—organic material—can be used to generate a fuel gas that can be reformed into hydrogen. ElectrochemicalThe electrolysis of water produces hydrogen by passing an electrical current through it. PhotoelectrochemicalThe photoelectrochemical (PEC) process produces hydrogen in one step, splitting water by illuminating a water-immersed semiconductor with sunlight. PhotobiologicalPhotobiological systems generally use the natural photosynthetic activity of bacteria and green algae to produce hydrogen.

  22. Current Price of Hydrogen 1 Gigajule: 25.5 m3 CH4 277 kWh electricity

  23. Current Price of Hydrogen

  24. Hydrogen from Fossil Fuels • Fossil Fuels • Petroleum (separate into different boiling fractions) • Mixture of gaseous, liquid and solid hydrocarbons • Coal & Coal Gases (Coal gasification) • Most abundant & complex chemicals. • Natural gas (C1-C4 hydrocarbons) • Low boning point hydrocarbons, mainly methane  

  25. Hydrogen from Fossil Fuels • Fuel cell requirements for the principal types of FC

  26. Hydrogen from Fossil Fuels • Desulphurization Technology • Hydrodesulphurization (HDS) (C2H5)2S +H2 2C2H6 +H2S • H2S is removed by ZnO H2S + ZnO ZnSO4 • Researches at NMSU to look for better desulphurization adsorbents • Steaming Reforming • CH4 + H2O  CO + 3H2 [H=206 kJ/mol, >700 C] • CO + H2O  CO2 + H2 [H=-41 kJ/mol, 200-500 C]

  27. Hydrogen from Fossil Fuels • CH3OH + H2O  CO2 + 3H2 [H=49.7 kJ/mol] • Dry/CO2 Reforming • CH4 + CO2 2CO + 2H2 [H=247 kJ/mol] • This may occur in internal reforming fuel cells • Internal Reforming (High T fuel cells, MCFC, SOFC) • To utilize the waste heat from FC for reforming reactions • H2 is produced in an internal reformer attached to FC

  28. Hydrogen from Fossil Fuels • Internal Reforming (High T fuel cells, MCFC, SOFC) • Indirect or integrated internal reforming (separate reformer) • Direct internal reforming (reforming occurs at anode) • Direct Methanol FC, SOFC • Direct hydrocarbon oxidation (No H2 produced) within FC • This may holds the key for high T PEMFC.

  29. Hydrogen from Fossil Fuels • Other ways of producing H2 from fossil fuels • Partial oxidation: CH4 + 0.5O2 CO + 2H2 [H=-247 kJ/mol] • At high T with or without catalyst • Autothermal Reforming • Combination of both steaming reforming and partial oxidation • Pyrolysis or thermal cracking • Heat hydrocarbon in the absence of air to produce H2 and carbon.

  30. Hydrogen from Fossil Fuels • Further fuel processing – CO removal • 1). CO + H2O CO2 + H2 [H=-41 kJ/mol, 200- 500 C] • Two stage shift reaction to remove CO to below 5000 ppm • 2). CO + O2 CO2 • Selective oxidation of CO can remove CO to below 100 ppm, but could • produce explosive gas mixtures. • 3). CO + H2 CH4+H2O • Methanation can remove CO and avoid producing explosive gases. • 4). Palladium/platinum membranes for H2 purification • 5). Pressure Swing Adsorption (PSA) for H2 separation and purification

  31. Practical Fuel Processors Flow Diagram of Ballard 250-kW PEMFC Plant

  32. Practical Fuel Processors Heat-Exchanger Reformer

  33. Practical Fuel Processors Plate Reformer

  34. Practical Fuel Processors Membrane Reactor Reformer

  35. Practical Fuel Processors Membrane Reactor Reformer

  36. Fuel Reforming Calculations • Example 1. For an idealized reformer conmsuming methane (CH4) fuel and operating with combined SR and WGS reactions, (1) what is the maximum H2 concentration in the product? (2) What is the stream-to-carbon ratio for the combined reactions? (3) In a real fuel reformer, why might you want to operate the reactor with a higher steam-to-carbon ratio? (4) What quantity of heat is consumed by the reaction, assuming, for simplicity, that the reactants and products enter and leave the reactor at STP? (5) The HHV for methane and hydrogen are 880 MJ/mol and 284 MJ/mol, respectively. Determine the reforming efficiency.

  37. Fuel Reforming Calculations • What is the maximum H2 concentration? • CH4 + H2O(g) CO + 3H2 [SR of CH4] • CO + H2O(g) CO2 + H2 [WGS] • CH4 + 2H2O(g)CO2 + 4H2 • yH2 = 4 (moles) H2/[4 (moles) H2+ 1 (mole) CO2] • = 80%

  38. Fuel Reforming Calculations • (2) What is the stream-to-carbon ratio for the combined reactions? • Steam-to-carbon ratio = S/C = nH2O/nC = 2 • (3) In a real fuel reformer, why might you want to operate the reactor with a higher steam-to-carbon ratio? • A higher steam-to-carbon ratio allow us to reduce carbon deposition, to increase H2 yield. Typically S/C ratio is between 3.5 and 4 to prevent carbon deposition.

  39. Fuel Reforming Calculations • (4) What quantity of heat is consumed by the reaction, assuming, for simplicity, that the reactants and products enter and leave the reactor at STP? 206.4 – 41.2 = 165.2 (kJ/mol) for the combined SR and WGS. If water enters Liquid, additional 2*44.1=88.2 (kJ/mol) of heat is required. Total of 253.4 (kJ/mol) is required at STP.

  40. Fuel Reforming Calculations • (5) The HHV for methane and hydrogen are 880 MJ/mol and 284 MJ/mol, respectively. Determine the reforming efficiency. • Reforming efficiency = HHV_H2/HHV_fuel • = 4*284 /880=129%

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