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Hydrogen energy technology—Update 1976
International Journal of HydrogenEnergy, Vol. 1, pp. 331-340. Pergamon Press, 1976. Printed in Northern Ireland
HYDROGEN ENERGY TECHNOLOGYmUPDATE
19761"
J. B. PA~OSORN and D. P. GREGORY Energy Systems Research, Institute of Gas Technology, Chicago, IL 60616, U.S.A. AIMraet--Hydrogen, a chemical commodity and fuel now produced from natural gas, could, in the future, become a widely used fuel produced from water and diverse energy sources. Since the initial flurry of interest in "hydrogen economy" concepts, serious feasibility studies, technology assessments, and experimental studies have identified economic and technological problem areas. Production now appears to be the focus of most hydrogen research and development efforts as shown by a review of the teelmical papers presented at the First World Hydrogen Energy Conference. Specific industrial uses, electric power storage, and perhaps additions of hydrogen to supplement the natural gas supply appear to be near-term prospects for hydrogen utilization. INTRODUCTION WITH the recognition that our conventional fossil energy and fossil fuel supplies are limited, not only in amount but by economics of production, environmental impact, and political decisions-both national and international--serious efforts are being made to technically and economically assess unconventional or alternative energy sources. These sources include geothermal heat, nuclear energy (fission and fusion), waste materials, solar energy (direct heating and photovoltaic conversions), and the indirect forms of solar energy--wind power, tides and waves, agricultural fuel crops, and ocean thermal gradients. In most cases, conversion to electricity as the deliverable energy form was contemplated or developed first. However, it is also technically feasible to produce a chemical fuel--hydrogen--from these same energy sources, as was recognized and advocated in recent years [1-3]. Hydrogen would have more desirable attributes than electricity in terms of ease of storage, efficiency and economics of long-distance transmission, and local distribution in established delivery systems; also hydrogen could be blended wit5 conventional fuel gases and combusted in existing equipment. The concept of hydrogen as a "universal fuel" was propelled by enthusiasts to the status of "Hydrogen Economy." In this concept of a future energy system, hydrogen would be produced from water using a nonfossil energy source. Then it would be stored and transported to various markets as are today's chemical fuels, or it might be liquefied and delivered for special applications as a cryogenic fuel. Hydrogen would serve residential and commercial markets as a heating and cooking fuel, the industrial market as a chemical commodity and as a fuel to generate process heat and steam, ~ e transportation market as an automotive and aircraft fuel, and the electricity generation market as a fuel for fuel cells and turbines and as an energy storage intermediate. Unfortunately, some of hydrogen's proponents have tended to ignore economics and other alternative fuels, and have unrealistically shortened the time frame for the use of hydrogen in.some applications. We believ~ that the euphoria over hydrogen's prospects probably reached a peak around 1974. In March of 1974, The Hydrogen Economy Miami Energy (THEME) Conference was held during which many conceptual energy systems, hydrogen production schemes and hydrogen applications were proposed [4]. Since that time, feasibility studies, technology assessments, economic studies and laboratory experimentation have injected considerable realism into the prospects for hydrogen as a fuel and commodity. Areas for research and development have been identified and will have to be fully exploited before hydrogen can enter the general fuel market. Considering the U.S. energy supply and demand situation, much of the identified research must be continued or started immediately if hydrogen is contemplated to be an alternative and supplemental fuel for the era beginning around 2000. During the first week of March 1976, another major conference in hydrogen was held, again in Miami: the First World Hydrogen Energy Conference, sponsored by E R D A and the University of Miami [5]. This conference featured about 140 technical papers and had over 700 participants t Paper Presented at the 3rd Energy Technology Conference, Washington, D.C. 29-31 March 1976. 331
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from 30 different countries. We highlight below some of the important findings presented at this conference together with certain other recent studies having major impact on the prospects for hydrogen as a medium for energy delivery. HYDROGEN PRODUCTION In the United States today, most of our hydrogen is made by catalytic steam-reforming of natural gas. Some is also made by partial oxidation of petroleum hydrocarbons. A very minor amount is produced from water by electrolysis. The cost of the hydrogen produced varies with the cost of natural gas, but production costs of about $1.40 to $1.50/million Btu of hydrogen are typical for input natural gas at $0.60 to $0.65/1000 SCF. Until the price of natural gas escalates significantly, because of increased costs of production, deregulation, or other factors, none of the alternatives for hydrogen production appears to have an economic advantage. Because of the limited supply, however, natural gas is not a suitable long-term source for hydrogen fuel. Hence, research on hydrogen sources and production methods is a valid major concern at this point, and this is reflected by the fact that, of the 140 papers published at the First World Hydrogen Energy Conference, about 70 were concerned with hydrogen production.
Thermochemica[hydrogenproduction One area receiving considerable attention is thermochemical hydrogen production, primarily but not exclusively envisioning nuclear (process) heat as the energy input for water-splitting via a sequence of chemical reactions. Thirty presentations were made that included descriptions of thermochemieal hydrogen production in a truly worldwide effort. In Japan, an experimental system is under development to combine solar photovoltaic, photochemical, and/or thermochemical reaction steps into water-splitting cycles. Much of the reported work is taking place at the Yokohama National University [6], where the chemistry is based on iron sulfates and hydrogen iodide. Other thermochemical work is proceeding at the National Chemical Laboratory for Industry in Tokyo on calcium iodate-hydrogen iodide cycles [7]. The chemistry and some operating data for reactions have been reported by these researchers in which they have estimated energy efliciencies of about 35% for the hybrid photochemical cycles and 22% to 34% for the calcium iodate procedures when some of the heat input is supplied at 550* to 800.C. In Germany, development work on the high-temperature, helium-cooled nuclear reactor is continuing at the Nuclear Research Center, Jiilich [8]. Process heat applications including thermochemical hydrogen production are being considered, and laboratory work on metal sulfate cycles is continuing. At Jiilich, the implications of an intermediate cooling circuit (for safety reasons) are now being considered. Also in Germany, at Aachen, laboratory and analytical work are continuing on iron chloride cycles. The reverse Deacon reaction, direct thermal reduction of ferric chloride, and hydrolysis of ferrous chloride to produce hydrogen and iron oxide, are being studied experimentally. The goal of this research is a demonstrated cycle (closed loop operation). At the EURATOM Laboratories in Ispra, Italy, researchers are also working on iron chloride cycles similar to those under investigation at Aachen. The latest published cycle, Mark-15, is shown below [9]: 3FeC12 + 4H20--~ Fe304 + 6HCI + H2 Fe304 + 8HCI---~FeCI2 + 2FeC13 + 4H20 2FeC13 ~ 2FeC12 + 0 2 Cl2 + H20--'- 2HCl + ½02
(1) (2) (3) (4)
The problem step is acknowledged to be the ferric chloride decomposition. In the United States, experimental research on thermochemical hydrogen was reported for Los Alamos Scientific Laboratory, Westinghouse Research Laboratories, Institute of Gas Technology, General Atomic Co., and Rohm and Haas Co. The LASL research team [10] has investigated several generic types of cycles in the laboratory, including those based on sulfuric acid decomposition and on metal oxide-metal sulfate cycles. In
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terms of reaction workability in the laboratory, no entirely satisfactory cycle has been identified at LASL although several cycles have been operated with recycled materials. The Westinghouse research [11] is concentrating on the development of a hybrid thermoelectrochemical cycle based on the decomposition of sulfuric acid: 2H20 + SO2--, H2SO4 + H2 H2SO4 ~ H20 + SO3 SO3--~ SO2 + ~O2
Electrochemical Thermochemical Thermochemical
(5) (6) (7)
Process efficiencies over 40% are predicted to be attainable. The Institute of Gas Technology [12] is concentrating experimental efforts on iron chloride cycles, and a laboratory-demonstrated cycle circumventing direct reduction of ferric chloride was presented. Laboratory data on a high-temperature solar hybrid cycle was also presented. Cd + 2H20--, Cd(OH)2 + H2
Electrochemical
Cd(OH)2--~ CdO + n 2 0
Thermochemical
(9)
Thermochemical
(10)
CdO--* Cd + ~O2
(8)
General Atomic Co. [13] presented its candidate thermochemical cycle for development: 2H20 + SO2 + xI2~ H2SO,, + 2HI,,
(11)
H2S.O,c-~H20 + SO3
(12)
SO3---, SO2 + ~)2 2HI~--* xI2 + H2
(13) (14)
Depending upon operating procedures and process assumptions, efficiencies of 30% to 50% -have been calculated for the cycle. Researchers at Rohm and Haas Co. [14] presented a low-temperature thermochemical cycle based on aqueous phase chemistry of iodine and iodic acid. Efficiency was not considered as important as economics and the advantage of utilizing low temperature (350°C) heat. In summary, considerable information on preferred thermocbemical cycles is now available. It is evident that proof of concept for thermochemical hydrogen production has been achieved in the laboratory. For efficient operation, though, high temperature nuclear heat will be required from an HTGR-type reactor; otherwise solar heat or nuclear fusion heat will be necessary. The relationship between economics and efficiency for thermochemical hydrogen is not definitive. Convincing arguments have been presented that a thermal efficiency over 40% is attainable for some cycles operated with heat inputs above 800°C.
Hydrogen from coal and water Hydrogen can be produced from coal by the reaction of coal with steam and the subsequent purification of the resulting gas mixtures. This production route is important because it offers a way to produce hydrogen at a cost less than that from production routes using nuclear or solar energy, but hydrogen made from coal cannot compete economically with hydrogen made from gas or oil at today's feedstock prices. Hydrogen made from coal is a key intermediate in many coal gasification and synthetic off production processes, as well as being a possible contender as a feedstock for ammonia or methanol, in steelmaking, and in oil refining; it also may possibly be used as a special purpose fuel. At the conference, an IGT study [15] compared the overall efliciencies of three pure hydrogenfrom-coal processes and compared them with a methane-from-coal process. The commercially available Koppers-Totzek process, and two processes under IGT development, U-GASTm and Steam-Iron, have reported overall efficiencies of 57%, 66% and 63%, compared to 74% for HYGAS ® (methane-from-coal). The paper concluded also that coal-to-methane is less expensive than coal-to-hydrogen. A General Atomic study [16] considered the use of nuclear process heat to drive a hydrogenfrom-coal process. It concluded that the methane-reforming step should be the heart of the
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overall process, which can utilize nuclear heat at 870°C, above which temperature there will be significant materials problems. In their overall process, part of the hydrogen produced by the steam-reforming of methane would be recycled into a hydrogasifier that produces a methane-rich gas stream from coal. This stream feeds the reformer.
Water electrolysis The efforts reported on the electrolysis of water at the First World Hydrogen Energy Conference were considerably less extensive than those for thermochemical hydrogen; twelve papers were published. In the United States, major development efforts are under way at Brookhaven National Laboratory under E R D A sponsorship. General Electric Co. is also doing research on electrolysis, partially sponsored by ERDA. Other companies or programs represented at the conference included those of Teledyne Energy Systems, Oklahoma State University, Billings Energy Research Corp., Stanford University and Energy Research Corp. At Electricit6 de France [17], bubble formation on electrodes is being studied under elevated pressure conditions at a temperature of 140°C in potassium hydroxide electrolytes. Also under study is the corrosion of asbestos separators in potassium hydroxide electrolyzers operating from 1000 to 140°C. Apparently, researchers at Electricit6 de France are investigating the materials aspects of conventional electrolyzers (those constructed without exotic materials or noble metal catalysts) under operating conditions that would enhance performance and efficiency. As a means of energy storage for off-peak electric power, researchers at Brookhaven [18] are experimenting on the system of water electrolysis followed by metal hydride formation, hydride decomposition (to release hydrogen), and then fuel cell operation or combustion of the hydrogen to regenerate electricity. Advantages over pumped hydraulic storage are possible. The Brookhaverr workers are attempting to increase the performance of conventional alkaline electrolyzers by operating at higher temperatures (120 ° to 1500C). Separator materials and corrosion effects are being investigated. According to a Brookhaven paper, the Teledyne Alkaline Electrolysis Cell and the General Electric Solid Polymer Electrolyzer, both operating from 120 ° to 1500C, are reported to look most promising for achieving the goals of high efficiency and low capital cost
[18]. Researchers and potential manufacturers in the electrolyzer field continue to be very optimistic about the technological advances they hope to make. Two main approaches are being taken. One is to increase the temperature of operation, and thus the performance of conventional alkaline electrolyte cells; this requires replacing asbestos and possibly some other typical materials of construction. The other appro/mh is to use inherently expensive electrodes and electrolytes in an acid system, relying on the far superior performance levels to counteract the high capital cost. Neither approach appears to have unique merit over the other.
Other.hydrogen production techniques The First World Hydrogen Energy Conference attracted about 10 papers which together describe a variety of new or unusual procedures for producing hydrogen from water. Most of these papers contain some experimental results, although the data are incomplete and the conclusions nondefinitive. Laboratory results of photosynthetic hydrogen production from algae (Anabaena cylindrica) under fluorescent-lamp irradiation in an argon atmosphere were reported by researchers at Flinders University of South Australia [19]. Stabilization of the system and protection of the hydrogen-producing enzyme were considered to be problems for research and development. A similar approach to hydrogen production is being investigated at the University of Miami [20]. At the Hydrogen Conference, prospects for microbial production of hydrogen were also described with a brief review of the action of photosynthetic bacteria to produce hydrogen under special conditions [21]. The production of hydrogen in a photochemical cell was proposed by Japanese investigators in 1972 [22]. An attempt to analytically characterize the photocurrents of p-type and n-type semiconductors was presented at the 1976 Hydrogen Conference [23]. In the attendant scheme for water-splitting, light energy (photons) is absorbed at a semiconductor electrode that produces a photocurrent (electrical potential) for an electrochemical cell. Hydrogen is collected at the
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cathode (for example, platinum), and oxygen is evolved at the semiconductor-anode (for example, titanium dioxide) [24]. HYDROGEN STORAGE, TRANSMISSION, DISTRIBUTION AND MATERIALS EFFECTS Since the THEME Conference in 1974, few significant advances have occurred in assessing or developing delivery components in a hydrogen energy system.
Storage Brooldaaven National Laboratory has continued to make progress in the area of electric power storage using hydrogen, and iron-titanium hydride has been chosen as a preferred storage medium. Four papers were published on iron-titanium hydride at the First World Hydrogen Energy Conference. With iron-titanium hydride, hydrogen can be stored (hydrided, exothermic reaction) at moderate pressures and at normal process coolant stream temperatures (25* to 400C); then the hydrogen can be evolved (hydride decomposed, endothermic reaction) with "waste" or low-temperature heat (100" to 150"C). Use of manganese to form a ternary alloy for hydriding, TiFexMny can further improve the temperature-pressure matching of hydride storage to fuel cell system waste heat and cooling water [25]. Storage of wind energy using hydrogen (via water electrolysis) is under system study and component development at Oklahoma State University [26]. In a feasibility study performed at IGT for ERDA on small-scale storage and delivery of wind power as hydrogen and electricity for farms, most of the long-term storage or large volume hydrogen applications were found to be uneconomical [27]. Satisfactory automotive storage (onboard tankage) of hydrogen is one of several major problems that will have to be solved before hydrogen could become generally used as an automotive fuel. Five papers were presented on automotive storage of hydrogen during the First World Hydrogen Energy Conference, but no new technologies for vehicular storage of hydrogen were disclosed. The four known methods were reviewed: cryogenic liquid hydrogen storage, compressed hydrogen gas tankage, metal hydride storage and storage as a reactant chemical and water or as a decomposable chemical. Chemical reaction systems (for storage) to generate hydrogen from water could include a reactive agent such as an alkali metal hydride. One area of hydrogen storage that has received considerable study is liquefaction. A process analysis with energy inputs and pertinent thermodynamic analyses has been performed by Linde Division of Union Carbide Corp. for NASA-Langley Research Center. This was part of the NASA effort to assess hydrogen's technical and economic prospects as an alternative aircraft fuel. The Linde work revealed that the practical power requirement for hydrogen liquefaction is about 5.7 kWhr/lb of hydrogen as compared with a theoretical work of liquefaction of 1.34 kWhr/lb [28]. Storage of hydrogen in underground aquifers and depleted petroleum reservoirs or gas fields has been assessed at Southern California Gas Co. [29]. No insurmountable technical or environmental problems are anticipated with this potentially large-scale and very economical means of hydrogen storage. Areas identified for investigation are the compatibility of hydrogen with residual reservoir hydrocarbons and the materials compatibility of piping and compressor units at underground natural gas storage facilities.
Transmission In the area of hydrogen transmission, little new technology was disclosed at the First World Hydrogen Energy Conference. Except for a brief cost analysis of underwater pipeline transmission of hydrogen (from an ocean thermal energy conversion platform), nothing new on pipeline operating conditions or costs has been developed since the THEME Conference and the recent publications by KONOPKA[30], Sn,naT [31] and LEErn [32]. Upon analysis of these and other assessments, our opinion is that hydrogen fuel would be best transported in large quantities over long distances (more than 100 miles) as a gas at 1000 to 1500 psi in large-diameter pipelines. Costs would be 2 to 3 times that of natural gas on an energy basis if hydrogen were used to fuel the compressor stations. Transmission eflieieneies would be approximately 99.5% per 100 miles.
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Distribution The U.S. gas distribution system typically consists of one or more networks of low-pressure piping that carry the fuel gas to the ultimate consumers from the various sources of supply: city-gate stations, gas-storage facilities and gas-manufacturing plants. At the Hydrogen Conference, one paper extensively considered the distribution of hydrogen fuel gas in a conventional distribution network [33]. This study concluded that the diversity of equipment, operating conditions and materials of construction require that the compatibility of the distribution system with hydrogen be verified by demonstration. The flow rates and pressures of a gas distribution system using hydrogen probably will be different from those for natural gas. Increased operating pressures are predicted for hydrogen flow conditions of equivalent (to natural gas) energy delivery. Procedures will have to accommodate various safety aspects, but leakage is not considered an especially severe problem with hydrogen.
Materials effects In high-pressure storage and transmission systems, materials compatibility with hydrogen is known to be an important aspect for investigation. Hydrogen degradation of metals is recognized in the failure of certain structures, and the mechanisms by which this occurs are under study. Three categories of hydrogen degradation have been proposed: a. Hydrogen-reaction embrittlement b. Internal hydrogen embrittlement c. Hydrogen-environment embrittlement. Hydrogen-reaction embrittlement i~ the result of chemical reaction between hydrogen and a metal or an alloy. Some examples are the formation of irreversible hydrides of titanium, zirconium and tantalum. The decarburization of steels and the formation of high-pressure water bubbles and methane in metal voids are other examples of hydrogen-reaction embrittlement. Both internal and environmental hydrogen embrittlement are caused by hydrogen atoms dissolving in the metal. Internal hydrogen embrittlement can be produced by hydrogencontaining chemical solutions. This problem is often encountered in metal- or petrochemicalprocessing faeilities. Hydrogen-environment embrittlement is the degradation of mechanical properties due to the adsorption of hydrogen at the surface of a metal. This type of embrittlement occurs when cracks form in the metal in the presence of hydrogen. Rate of strain is an important parameter in the degree of embrittlement exhibited. Low strain rates promote maximum embrittlement, allowing hydrogen transport near the cracks. Metals conditioned to high-strength levels are often more susceptible to embrittlement than their lower strength counterparts. With ERDA sponsorship, researchers at Sandia Laboratories (Livermore) are experimentally studying the hydrogen compatibility of pipeline steels and materials for containment of irontitanium hydride. In a paper presented at the First World Hydrogen Energy Conference, they have qualitatively listed steels and metal alloys in order of their susceptibility to hydrogen embrittlement by the three categories described above [34]. HYDROGEN UTILIZATION Most hydrogen-energy research has been carried out as a long-term concept with the objective of using hydrogen as a "universal" fuel for many different applications at some fairly distant point in the future. However, some shorter term prospects for using hydrogen (within a decade) have been proposed. These include use as an automobile fuel, as an aircraft fuel, and in special industrial applications.
Automotive applications Independent studies by Exxon [35] and IGT [36] evaluating alternative automobile fuels (from U.S. domestic energy sources) for the future were completed and published during 1974. The results were almost identical in showing that, in the near-term, coal and oil shale should be used as raw materials, and used most advantageously by conversion to a gasoline-like or diesel-like
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fuel. Methanol made from coal has merit in the near- and mid-term future. Hydrogen only has merit when nuclear or solar energy is used as the prime energy input, but this is not likely to become important until around the year 2000. Major problems in using hydrogen for ground vehicles concern not only supply, but on-board storage of hydrogen and provisions for distribution and refueling with hydrogen. Thirteen papers on hydrogen-automobiles were present,d at .the Hydrogen Energy Conference, six of which dealt with engines, three with fuel storage, four with overall vehicle designs, and none with supply, distribution, or fuel handling and vehicle refueling. One of the most significant development/demonstration programs reported was the Billings Energy Research Hydrogen Bus [37-42]. This project included (a) engine testing to show that water-injection eliminates backflash (preignition in the intake manifold) and decreases nitrogen oxides production without degrading engine performance; (b) development of a dynamic vehicletesting procedure and application of this to a 21-passenger transit bus, showing that the 4000-1b hydride fuel tank penalty was more than offset by the increase in fuel efficiency of the engine; (c) pilot operation of a 6-passenger automobile fitted with a hydride storage tank to demonstrate reliable and satisfactory operation; (d) a design study for a hydride tank that could be regenerated by exhaust heat; (e) an engineering study of a hydride-powered transit bus; and (f) the design and modification of a 21-passenger Winnebago minibus to operate on hydrogen. The prototype hydrogen bus went into operation on a 13-mile trip between the cities of Provo and Orem, Utah, in February 1976.
Aircraft applications Six papers were presented on the topic of hydrogen as an aircraft fuel. As.a result of a series of NASA studies on hydrogen production, airport ground handling, liquefaction and aircraft designs, NASA [43] has concluded that, if coal is to be used as a raw energy source, the cost and efficiency of supplying a kerosene-like fuel from coal are similar to those bf supplying liquid hydrogen. Problems in handling liquid hydrogen in the refueling operations must still be solved, and existing facilities are certainly more compatible with coal-derived liquid hydrocarbons. Because of this, hydrogen as an aircraft fuel will only be justified, on the standpoint of overall consumption of coal, for aircraft larger than the Boeing 747. However, the use of other (nuclear or solar) energy sources or of improved hydrogen production technologies would justify the use of hydrogen as a preferred aircraft fuel. Another NASA paper [44] concludes with the significant statement that "sooner or later a national policy decision will have to be made to off-load the growing demand for .... natural or synthetic petroleum. If this decision singles out air transportation as the industry to initiate the introduction of LH2, it won't find the aerospace industry unprepared." Another NASA study [45] indicates that significant improvements in efficiency of aircraft piston engines can be expected if some hydrogen is generated from a portion of the aircraft fuel and supplied (with regular fuel) to the engine.
Industrial applications In the near-term U.S. industrial hydrogen market (including captive uses), a recent study for NASA estimated that the market size was on the order of 3 x 1012 SCF/year, increasing at about 5% per year [46]. Much of this hydrogen is now produced from natural gas or oil. An IGT study [47] indicated that large-scale operations, such as ammonia and methanol plants and oil refineries, can produce bulk on-site hydrogen from natural gas at such low prices today that in the near-term future, the only competitive source is likely to be coal gasification. However, smaller users, such as plants for producing fats and soaps and some specialized metallurgical processes, normally pay higher prices for merchant hydrogen. These prices are comparable to costs of electrolytic hydrogen produced with off-peak power. CONCLUSIONS From the studies that we have surveyed since the 1974 THEME Conference on hydrogen and particularly from the 1976 First World Hydrogen Energy Conference, we have made the following observations. 1. An economical alternative to the conventional production of hydrogen from petroleum and natural gas is needed to expand hydrogen supply prospects, and increased sources of supply will
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be required before hydrogen can be considered as an alternative or supplemental fuel. Coal gasification offers the best near-term prospect for hydrogen, but other fuels more compatible with existing systems, such as SNG, liquid hydrocarbons, or methanol, could preferably be produced from coal. For specific industrial uses, such as ammonia synthesis, hydrogen-from-coal could become competitive during the next decade. Water electrolysis for fuel or commodity hydrogen would be practical only with cheap hydropower or off-peak electric power. 2. Significant exploratory research on the production of hydrogen from water and nonfossil energy sources is under way through work on thermochemical, photochemical, biochemical and combination processes. Thermocbemical production is laboratory-proved .in stepwise (noncontinuous) procedures, but most of these procedures would require high-temperature, gas-cooled reactors if nuclear heat were the energy source. High-temperature heat is acknowledged as a requirement for efficient operation of thermochemieal processes. 3. Hydrogen constitutes a viable storage medium for electric power, and research to improve electrolyzer efficiency from 70% to 90% is encouraging. Metal hydride storage is technically feasible and fuel cell reconversion of hydrogen to electricity appears practical 4. Exploratory and advanced research are required for hydrogen production and delivery concepts. Energy sources other than coal and nuclear (fission) process heat should receive greater emphasis. Hydrogen from any source could supplement the natural gas supply by addition of hydrogen to pipeline gas. Experimental tests of model pipeline transmission loops, underground storage of gaseous hydrogen and model distribution systems are imperative. These tests will indicate feasibility and problem areas for hydrogen in using the existing systems that now handle 27% of our total energy supply. 5. Hydrogen has been demonstrated to be a superior fuel for operation of many types of internal combustion engines, including turbine engines; it would provide excellent performance as an aircraft fuel, and it produces high efficiencies when used as the fuel in a fuel cell. Delivery systems, fuel tankage, safe and practical handling and of course, economical supply are the problem areas needing more attention. A moderate-scale demonstration of hydrogen usage for some residential or commercial purpose, perhaps for a form of mass transport, would foster further interest in these problem areas. REFERENCES 1. H. R. L:NDEr~,IS our environment really doomed? New technology says no! A.G.A. Mon. 53, 14-17 (1971). 2. D. P. GREGORY,The gas industry's role in the nuclear age, A S H R A E J. 13, 38--40 (1971). 3. G. DEBEN!& C. MARCHETTI,Hydrogen, key to the energy market, Eurospectra 9, 46 (1970). 4. T. N. VEZIROOLU,Ed., Hydrogen Energy, THEME Proceedings, New York: Plenum, 1975. 5. T. N. VEZmOOLU, Ed., Proceedings of the 1st Worm Hydrogen Energy Conference, Vols. 1-3. Coral Gables, Florida: University of Miami, 1976. 6. T. OttTA, et al., Water-splitting-system synthesized by photochemical and thermoelectric utilizations of solar energy. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 7. K. FuJn, et al., The calcium-iodine cycle for the thermochemical decomposition of water. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida~ March 1-3, 1976. 8. R. SCHULTEN,et al, The concept of "nuclear hydrogen production" and progress of work in the Nuclear Research Center Juelich. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 9. A. BROGGI., G. DEBENI & D. VAN VELZEN, Definition and analysis of th'ermochemical processes for hydrogen production based on iron-chlorine reactions. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 10. M. G. BOWMAN, Progress in the Los Alamos Scientific Laboratory program to develop thermochemical processes for hydrogen production. Paper presented at the 1st World Hydrogen Conference, Miami Beach, Florida, March 1-3, 1976. 11. L. E. BRECHER, S. SPEWOCK ~: C. J. WARDE, The Westinghouse sulfur cycle for the thermochemical decomposition of water. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 12. J. PANOBORN,Laboratory investigations on thermochemical hydrogen production. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 13. J. L. RUSSELL,et al., Water-splitting---A progress report. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976.
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14. P. A. Kn'n~, D. F. MA~ONEY& J. E. SOKa~R, A low-temperature, three-step water-splitting process. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 15. C. L. TSAROS,J. L. ARORA& K. B. BURNHAM,The manufacture of hydrogen from coal. Paper presented at the 1st World Hydrogen Conference, Miami Beach, Florida, March 1-3, 1976. 16. R. N. OUAD~, Hydrogen production from coal using a nuclear heat source. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 17. P. GoDm, et al., Optical study of the release of hydrogen and of oxygen in a micro-electrolysis cell in function of pressure, temperature, current density and surface condition of the electrodes. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976, (Abstract only in printed form). 18. S. SmmvAsAu & F. J. SALZANO, Prospects for hydrogen production by water electrolysis to be competitive with conventional methods. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 19. G. NEro, et al., The photosynthetic production of hydrogen. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 20. A. Mrrsul, Bioconversion of solar energy in salt water photosynthetic hydrogen production systems. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 21. J. E. ZA~Ic & J. BROSSEAU,Microbial hydrogen production. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 22. A. Fu~smuA & K. HONDA, Electrochemical photolysis of water at a semiconductor electrode, Nature 238, 37-38 (1972). 23. J. O'M. Bocrdus & K. UosArd, The theory of hydrogen production in a photochemical cell. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 24. A. J. NoZlg, Hydrogen generation by photoelectrolysis of water. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 25. J. J. REILLY & J. R. JomqsoN, Titanium alloy hydrides; their properties and applications. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 26. H. J. ALLISON,A wind energy system utilizing high pressure electrolysis as a storage medium. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March I-3, 1976. 27. R. R. TIsoN & N. P. BmDEmaAS, A farm energy system employing hydrogen storage. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 28. C. R. BAKER& R. L. SHAm~R,A.smdy of the efficiency of hydrogen liquefaction. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 29. A. B. WAL~gS, Technical and environmental aspects of underground hydrogen storage. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 30. A. J. KONOPKA& J. Wum~t, Transmission of gaseous hydrogen. Paper presented at the 9th Intersociety Energy Conversion Engineering Conference, San Francisco, August 26-30, 1974. 31. C. F. Smuyr, Transmission of hydrogen, in J. Hord, Ed., Selected Topics on Hydrogen Fuel, NBS Spe~al Publication 419, 6.1-6.11. ~oulder, Colorado: National Bureau of Standards, 1975. 32. G. LEETH, Nuclear heat transmission considerations. Paper presented at the First National Topical Meeting on Nuclear Process Heat Applications, Los Alamos, New Mexico, October 1-3, 1974. 33. J. P~,qOBORN & J. SHARER, Technical prospects for commercial and residential distribution and utilization of hydrogen. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 34. J. H. SWISHER,A. J. WEST & S. L. ROBINSON,Status of ERDA program on hydrogen compatibility of structural materials for pressure vessels and pipelines. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 35. F. H. KANT,et aL, Feasibility study of alternative fuels for automotive transportation, U.S. Environmental Protection Agency Report No. EPA-460/3-74-O09. Linden, New Jersey: Exxon Research and Engineering Co., June 1974. 36. J. PANOBOmq & J. GR~LIS,Alternative fuels for automotive transportation--A feasibility study, U.S. Environmental Protection Agency Report No. EPA-460/3-74-012. Chicago: Institute of Gas Technology, July 1974. 37. R. L. WOOLI~y & D. L. I-IEmtms~, Water induction in hydrogen-powdered IC engines. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 38. R. L. Woota.Ey & G. J. GERMANE,Dynamic tests of hydrogen-powered IC engines. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1974. 39. D. L. H.emugse~, D. B. MACKAY& V. R. ANm~SON, Prototype hydrogen automobile using a metal hydride. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976.
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40. D. B. MACKAY,Automotive hydride tank design. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 41. T. WALL, et al., Engineering study of hydrogen-fueled bus operation. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 42. R. E. BILLINGS,A hydrogen-powered mass transit system. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 43. R. D. Wrrco~rd, The thermal efficiency and cost of producing hydrogen and other synthetic aircraft fuels from coal. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 44. P. F. KORYClNSr~,Some early perspectives on ground requirements of liquid hydrogen air transports. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 45. W. A. MENASD,P. I. MOVmnAN & J. H. RurE, New potentials for conventional aircraft when powered by hydrogen-enriched gasoline. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 46. J. C. GILLIS, D. P. GREC,ORV & J. B. PANGBORN, Survey of hydrogen production and utilization methods, Project 8962 Final Report. Chicago: Institute of Gas Technology, August 1975. 47. K. DARROW, N. BmDEm~IAN& A. KONOPKA,Commodity hydrogen from off-peak electricity. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976.
HYDROGEN ENERGY TECHNOLOGYmUPDATE
19761"
J. B. PA~OSORN and D. P. GREGORY Energy Systems Research, Institute of Gas Technology, Chicago, IL 60616, U.S.A. AIMraet--Hydrogen, a chemical commodity and fuel now produced from natural gas, could, in the future, become a widely used fuel produced from water and diverse energy sources. Since the initial flurry of interest in "hydrogen economy" concepts, serious feasibility studies, technology assessments, and experimental studies have identified economic and technological problem areas. Production now appears to be the focus of most hydrogen research and development efforts as shown by a review of the teelmical papers presented at the First World Hydrogen Energy Conference. Specific industrial uses, electric power storage, and perhaps additions of hydrogen to supplement the natural gas supply appear to be near-term prospects for hydrogen utilization. INTRODUCTION WITH the recognition that our conventional fossil energy and fossil fuel supplies are limited, not only in amount but by economics of production, environmental impact, and political decisions-both national and international--serious efforts are being made to technically and economically assess unconventional or alternative energy sources. These sources include geothermal heat, nuclear energy (fission and fusion), waste materials, solar energy (direct heating and photovoltaic conversions), and the indirect forms of solar energy--wind power, tides and waves, agricultural fuel crops, and ocean thermal gradients. In most cases, conversion to electricity as the deliverable energy form was contemplated or developed first. However, it is also technically feasible to produce a chemical fuel--hydrogen--from these same energy sources, as was recognized and advocated in recent years [1-3]. Hydrogen would have more desirable attributes than electricity in terms of ease of storage, efficiency and economics of long-distance transmission, and local distribution in established delivery systems; also hydrogen could be blended wit5 conventional fuel gases and combusted in existing equipment. The concept of hydrogen as a "universal fuel" was propelled by enthusiasts to the status of "Hydrogen Economy." In this concept of a future energy system, hydrogen would be produced from water using a nonfossil energy source. Then it would be stored and transported to various markets as are today's chemical fuels, or it might be liquefied and delivered for special applications as a cryogenic fuel. Hydrogen would serve residential and commercial markets as a heating and cooking fuel, the industrial market as a chemical commodity and as a fuel to generate process heat and steam, ~ e transportation market as an automotive and aircraft fuel, and the electricity generation market as a fuel for fuel cells and turbines and as an energy storage intermediate. Unfortunately, some of hydrogen's proponents have tended to ignore economics and other alternative fuels, and have unrealistically shortened the time frame for the use of hydrogen in.some applications. We believ~ that the euphoria over hydrogen's prospects probably reached a peak around 1974. In March of 1974, The Hydrogen Economy Miami Energy (THEME) Conference was held during which many conceptual energy systems, hydrogen production schemes and hydrogen applications were proposed [4]. Since that time, feasibility studies, technology assessments, economic studies and laboratory experimentation have injected considerable realism into the prospects for hydrogen as a fuel and commodity. Areas for research and development have been identified and will have to be fully exploited before hydrogen can enter the general fuel market. Considering the U.S. energy supply and demand situation, much of the identified research must be continued or started immediately if hydrogen is contemplated to be an alternative and supplemental fuel for the era beginning around 2000. During the first week of March 1976, another major conference in hydrogen was held, again in Miami: the First World Hydrogen Energy Conference, sponsored by E R D A and the University of Miami [5]. This conference featured about 140 technical papers and had over 700 participants t Paper Presented at the 3rd Energy Technology Conference, Washington, D.C. 29-31 March 1976. 331
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HYDROGEN ENERGY TECHNOLOGY--UPDATE 1976
from 30 different countries. We highlight below some of the important findings presented at this conference together with certain other recent studies having major impact on the prospects for hydrogen as a medium for energy delivery. HYDROGEN PRODUCTION In the United States today, most of our hydrogen is made by catalytic steam-reforming of natural gas. Some is also made by partial oxidation of petroleum hydrocarbons. A very minor amount is produced from water by electrolysis. The cost of the hydrogen produced varies with the cost of natural gas, but production costs of about $1.40 to $1.50/million Btu of hydrogen are typical for input natural gas at $0.60 to $0.65/1000 SCF. Until the price of natural gas escalates significantly, because of increased costs of production, deregulation, or other factors, none of the alternatives for hydrogen production appears to have an economic advantage. Because of the limited supply, however, natural gas is not a suitable long-term source for hydrogen fuel. Hence, research on hydrogen sources and production methods is a valid major concern at this point, and this is reflected by the fact that, of the 140 papers published at the First World Hydrogen Energy Conference, about 70 were concerned with hydrogen production.
Thermochemica[hydrogenproduction One area receiving considerable attention is thermochemical hydrogen production, primarily but not exclusively envisioning nuclear (process) heat as the energy input for water-splitting via a sequence of chemical reactions. Thirty presentations were made that included descriptions of thermochemieal hydrogen production in a truly worldwide effort. In Japan, an experimental system is under development to combine solar photovoltaic, photochemical, and/or thermochemical reaction steps into water-splitting cycles. Much of the reported work is taking place at the Yokohama National University [6], where the chemistry is based on iron sulfates and hydrogen iodide. Other thermochemical work is proceeding at the National Chemical Laboratory for Industry in Tokyo on calcium iodate-hydrogen iodide cycles [7]. The chemistry and some operating data for reactions have been reported by these researchers in which they have estimated energy efliciencies of about 35% for the hybrid photochemical cycles and 22% to 34% for the calcium iodate procedures when some of the heat input is supplied at 550* to 800.C. In Germany, development work on the high-temperature, helium-cooled nuclear reactor is continuing at the Nuclear Research Center, Jiilich [8]. Process heat applications including thermochemical hydrogen production are being considered, and laboratory work on metal sulfate cycles is continuing. At Jiilich, the implications of an intermediate cooling circuit (for safety reasons) are now being considered. Also in Germany, at Aachen, laboratory and analytical work are continuing on iron chloride cycles. The reverse Deacon reaction, direct thermal reduction of ferric chloride, and hydrolysis of ferrous chloride to produce hydrogen and iron oxide, are being studied experimentally. The goal of this research is a demonstrated cycle (closed loop operation). At the EURATOM Laboratories in Ispra, Italy, researchers are also working on iron chloride cycles similar to those under investigation at Aachen. The latest published cycle, Mark-15, is shown below [9]: 3FeC12 + 4H20--~ Fe304 + 6HCI + H2 Fe304 + 8HCI---~FeCI2 + 2FeC13 + 4H20 2FeC13 ~ 2FeC12 + 0 2 Cl2 + H20--'- 2HCl + ½02
(1) (2) (3) (4)
The problem step is acknowledged to be the ferric chloride decomposition. In the United States, experimental research on thermochemical hydrogen was reported for Los Alamos Scientific Laboratory, Westinghouse Research Laboratories, Institute of Gas Technology, General Atomic Co., and Rohm and Haas Co. The LASL research team [10] has investigated several generic types of cycles in the laboratory, including those based on sulfuric acid decomposition and on metal oxide-metal sulfate cycles. In
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terms of reaction workability in the laboratory, no entirely satisfactory cycle has been identified at LASL although several cycles have been operated with recycled materials. The Westinghouse research [11] is concentrating on the development of a hybrid thermoelectrochemical cycle based on the decomposition of sulfuric acid: 2H20 + SO2--, H2SO4 + H2 H2SO4 ~ H20 + SO3 SO3--~ SO2 + ~O2
Electrochemical Thermochemical Thermochemical
(5) (6) (7)
Process efficiencies over 40% are predicted to be attainable. The Institute of Gas Technology [12] is concentrating experimental efforts on iron chloride cycles, and a laboratory-demonstrated cycle circumventing direct reduction of ferric chloride was presented. Laboratory data on a high-temperature solar hybrid cycle was also presented. Cd + 2H20--, Cd(OH)2 + H2
Electrochemical
Cd(OH)2--~ CdO + n 2 0
Thermochemical
(9)
Thermochemical
(10)
CdO--* Cd + ~O2
(8)
General Atomic Co. [13] presented its candidate thermochemical cycle for development: 2H20 + SO2 + xI2~ H2SO,, + 2HI,,
(11)
H2S.O,c-~H20 + SO3
(12)
SO3---, SO2 + ~)2 2HI~--* xI2 + H2
(13) (14)
Depending upon operating procedures and process assumptions, efficiencies of 30% to 50% -have been calculated for the cycle. Researchers at Rohm and Haas Co. [14] presented a low-temperature thermochemical cycle based on aqueous phase chemistry of iodine and iodic acid. Efficiency was not considered as important as economics and the advantage of utilizing low temperature (350°C) heat. In summary, considerable information on preferred thermocbemical cycles is now available. It is evident that proof of concept for thermochemical hydrogen production has been achieved in the laboratory. For efficient operation, though, high temperature nuclear heat will be required from an HTGR-type reactor; otherwise solar heat or nuclear fusion heat will be necessary. The relationship between economics and efficiency for thermochemical hydrogen is not definitive. Convincing arguments have been presented that a thermal efficiency over 40% is attainable for some cycles operated with heat inputs above 800°C.
Hydrogen from coal and water Hydrogen can be produced from coal by the reaction of coal with steam and the subsequent purification of the resulting gas mixtures. This production route is important because it offers a way to produce hydrogen at a cost less than that from production routes using nuclear or solar energy, but hydrogen made from coal cannot compete economically with hydrogen made from gas or oil at today's feedstock prices. Hydrogen made from coal is a key intermediate in many coal gasification and synthetic off production processes, as well as being a possible contender as a feedstock for ammonia or methanol, in steelmaking, and in oil refining; it also may possibly be used as a special purpose fuel. At the conference, an IGT study [15] compared the overall efliciencies of three pure hydrogenfrom-coal processes and compared them with a methane-from-coal process. The commercially available Koppers-Totzek process, and two processes under IGT development, U-GASTm and Steam-Iron, have reported overall efficiencies of 57%, 66% and 63%, compared to 74% for HYGAS ® (methane-from-coal). The paper concluded also that coal-to-methane is less expensive than coal-to-hydrogen. A General Atomic study [16] considered the use of nuclear process heat to drive a hydrogenfrom-coal process. It concluded that the methane-reforming step should be the heart of the
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overall process, which can utilize nuclear heat at 870°C, above which temperature there will be significant materials problems. In their overall process, part of the hydrogen produced by the steam-reforming of methane would be recycled into a hydrogasifier that produces a methane-rich gas stream from coal. This stream feeds the reformer.
Water electrolysis The efforts reported on the electrolysis of water at the First World Hydrogen Energy Conference were considerably less extensive than those for thermochemical hydrogen; twelve papers were published. In the United States, major development efforts are under way at Brookhaven National Laboratory under E R D A sponsorship. General Electric Co. is also doing research on electrolysis, partially sponsored by ERDA. Other companies or programs represented at the conference included those of Teledyne Energy Systems, Oklahoma State University, Billings Energy Research Corp., Stanford University and Energy Research Corp. At Electricit6 de France [17], bubble formation on electrodes is being studied under elevated pressure conditions at a temperature of 140°C in potassium hydroxide electrolytes. Also under study is the corrosion of asbestos separators in potassium hydroxide electrolyzers operating from 1000 to 140°C. Apparently, researchers at Electricit6 de France are investigating the materials aspects of conventional electrolyzers (those constructed without exotic materials or noble metal catalysts) under operating conditions that would enhance performance and efficiency. As a means of energy storage for off-peak electric power, researchers at Brookhaven [18] are experimenting on the system of water electrolysis followed by metal hydride formation, hydride decomposition (to release hydrogen), and then fuel cell operation or combustion of the hydrogen to regenerate electricity. Advantages over pumped hydraulic storage are possible. The Brookhaverr workers are attempting to increase the performance of conventional alkaline electrolyzers by operating at higher temperatures (120 ° to 1500C). Separator materials and corrosion effects are being investigated. According to a Brookhaven paper, the Teledyne Alkaline Electrolysis Cell and the General Electric Solid Polymer Electrolyzer, both operating from 120 ° to 1500C, are reported to look most promising for achieving the goals of high efficiency and low capital cost
[18]. Researchers and potential manufacturers in the electrolyzer field continue to be very optimistic about the technological advances they hope to make. Two main approaches are being taken. One is to increase the temperature of operation, and thus the performance of conventional alkaline electrolyte cells; this requires replacing asbestos and possibly some other typical materials of construction. The other appro/mh is to use inherently expensive electrodes and electrolytes in an acid system, relying on the far superior performance levels to counteract the high capital cost. Neither approach appears to have unique merit over the other.
Other.hydrogen production techniques The First World Hydrogen Energy Conference attracted about 10 papers which together describe a variety of new or unusual procedures for producing hydrogen from water. Most of these papers contain some experimental results, although the data are incomplete and the conclusions nondefinitive. Laboratory results of photosynthetic hydrogen production from algae (Anabaena cylindrica) under fluorescent-lamp irradiation in an argon atmosphere were reported by researchers at Flinders University of South Australia [19]. Stabilization of the system and protection of the hydrogen-producing enzyme were considered to be problems for research and development. A similar approach to hydrogen production is being investigated at the University of Miami [20]. At the Hydrogen Conference, prospects for microbial production of hydrogen were also described with a brief review of the action of photosynthetic bacteria to produce hydrogen under special conditions [21]. The production of hydrogen in a photochemical cell was proposed by Japanese investigators in 1972 [22]. An attempt to analytically characterize the photocurrents of p-type and n-type semiconductors was presented at the 1976 Hydrogen Conference [23]. In the attendant scheme for water-splitting, light energy (photons) is absorbed at a semiconductor electrode that produces a photocurrent (electrical potential) for an electrochemical cell. Hydrogen is collected at the
J. B. PANGBORN AND D. P. GREGORY
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cathode (for example, platinum), and oxygen is evolved at the semiconductor-anode (for example, titanium dioxide) [24]. HYDROGEN STORAGE, TRANSMISSION, DISTRIBUTION AND MATERIALS EFFECTS Since the THEME Conference in 1974, few significant advances have occurred in assessing or developing delivery components in a hydrogen energy system.
Storage Brooldaaven National Laboratory has continued to make progress in the area of electric power storage using hydrogen, and iron-titanium hydride has been chosen as a preferred storage medium. Four papers were published on iron-titanium hydride at the First World Hydrogen Energy Conference. With iron-titanium hydride, hydrogen can be stored (hydrided, exothermic reaction) at moderate pressures and at normal process coolant stream temperatures (25* to 400C); then the hydrogen can be evolved (hydride decomposed, endothermic reaction) with "waste" or low-temperature heat (100" to 150"C). Use of manganese to form a ternary alloy for hydriding, TiFexMny can further improve the temperature-pressure matching of hydride storage to fuel cell system waste heat and cooling water [25]. Storage of wind energy using hydrogen (via water electrolysis) is under system study and component development at Oklahoma State University [26]. In a feasibility study performed at IGT for ERDA on small-scale storage and delivery of wind power as hydrogen and electricity for farms, most of the long-term storage or large volume hydrogen applications were found to be uneconomical [27]. Satisfactory automotive storage (onboard tankage) of hydrogen is one of several major problems that will have to be solved before hydrogen could become generally used as an automotive fuel. Five papers were presented on automotive storage of hydrogen during the First World Hydrogen Energy Conference, but no new technologies for vehicular storage of hydrogen were disclosed. The four known methods were reviewed: cryogenic liquid hydrogen storage, compressed hydrogen gas tankage, metal hydride storage and storage as a reactant chemical and water or as a decomposable chemical. Chemical reaction systems (for storage) to generate hydrogen from water could include a reactive agent such as an alkali metal hydride. One area of hydrogen storage that has received considerable study is liquefaction. A process analysis with energy inputs and pertinent thermodynamic analyses has been performed by Linde Division of Union Carbide Corp. for NASA-Langley Research Center. This was part of the NASA effort to assess hydrogen's technical and economic prospects as an alternative aircraft fuel. The Linde work revealed that the practical power requirement for hydrogen liquefaction is about 5.7 kWhr/lb of hydrogen as compared with a theoretical work of liquefaction of 1.34 kWhr/lb [28]. Storage of hydrogen in underground aquifers and depleted petroleum reservoirs or gas fields has been assessed at Southern California Gas Co. [29]. No insurmountable technical or environmental problems are anticipated with this potentially large-scale and very economical means of hydrogen storage. Areas identified for investigation are the compatibility of hydrogen with residual reservoir hydrocarbons and the materials compatibility of piping and compressor units at underground natural gas storage facilities.
Transmission In the area of hydrogen transmission, little new technology was disclosed at the First World Hydrogen Energy Conference. Except for a brief cost analysis of underwater pipeline transmission of hydrogen (from an ocean thermal energy conversion platform), nothing new on pipeline operating conditions or costs has been developed since the THEME Conference and the recent publications by KONOPKA[30], Sn,naT [31] and LEErn [32]. Upon analysis of these and other assessments, our opinion is that hydrogen fuel would be best transported in large quantities over long distances (more than 100 miles) as a gas at 1000 to 1500 psi in large-diameter pipelines. Costs would be 2 to 3 times that of natural gas on an energy basis if hydrogen were used to fuel the compressor stations. Transmission eflieieneies would be approximately 99.5% per 100 miles.
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Distribution The U.S. gas distribution system typically consists of one or more networks of low-pressure piping that carry the fuel gas to the ultimate consumers from the various sources of supply: city-gate stations, gas-storage facilities and gas-manufacturing plants. At the Hydrogen Conference, one paper extensively considered the distribution of hydrogen fuel gas in a conventional distribution network [33]. This study concluded that the diversity of equipment, operating conditions and materials of construction require that the compatibility of the distribution system with hydrogen be verified by demonstration. The flow rates and pressures of a gas distribution system using hydrogen probably will be different from those for natural gas. Increased operating pressures are predicted for hydrogen flow conditions of equivalent (to natural gas) energy delivery. Procedures will have to accommodate various safety aspects, but leakage is not considered an especially severe problem with hydrogen.
Materials effects In high-pressure storage and transmission systems, materials compatibility with hydrogen is known to be an important aspect for investigation. Hydrogen degradation of metals is recognized in the failure of certain structures, and the mechanisms by which this occurs are under study. Three categories of hydrogen degradation have been proposed: a. Hydrogen-reaction embrittlement b. Internal hydrogen embrittlement c. Hydrogen-environment embrittlement. Hydrogen-reaction embrittlement i~ the result of chemical reaction between hydrogen and a metal or an alloy. Some examples are the formation of irreversible hydrides of titanium, zirconium and tantalum. The decarburization of steels and the formation of high-pressure water bubbles and methane in metal voids are other examples of hydrogen-reaction embrittlement. Both internal and environmental hydrogen embrittlement are caused by hydrogen atoms dissolving in the metal. Internal hydrogen embrittlement can be produced by hydrogencontaining chemical solutions. This problem is often encountered in metal- or petrochemicalprocessing faeilities. Hydrogen-environment embrittlement is the degradation of mechanical properties due to the adsorption of hydrogen at the surface of a metal. This type of embrittlement occurs when cracks form in the metal in the presence of hydrogen. Rate of strain is an important parameter in the degree of embrittlement exhibited. Low strain rates promote maximum embrittlement, allowing hydrogen transport near the cracks. Metals conditioned to high-strength levels are often more susceptible to embrittlement than their lower strength counterparts. With ERDA sponsorship, researchers at Sandia Laboratories (Livermore) are experimentally studying the hydrogen compatibility of pipeline steels and materials for containment of irontitanium hydride. In a paper presented at the First World Hydrogen Energy Conference, they have qualitatively listed steels and metal alloys in order of their susceptibility to hydrogen embrittlement by the three categories described above [34]. HYDROGEN UTILIZATION Most hydrogen-energy research has been carried out as a long-term concept with the objective of using hydrogen as a "universal" fuel for many different applications at some fairly distant point in the future. However, some shorter term prospects for using hydrogen (within a decade) have been proposed. These include use as an automobile fuel, as an aircraft fuel, and in special industrial applications.
Automotive applications Independent studies by Exxon [35] and IGT [36] evaluating alternative automobile fuels (from U.S. domestic energy sources) for the future were completed and published during 1974. The results were almost identical in showing that, in the near-term, coal and oil shale should be used as raw materials, and used most advantageously by conversion to a gasoline-like or diesel-like
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fuel. Methanol made from coal has merit in the near- and mid-term future. Hydrogen only has merit when nuclear or solar energy is used as the prime energy input, but this is not likely to become important until around the year 2000. Major problems in using hydrogen for ground vehicles concern not only supply, but on-board storage of hydrogen and provisions for distribution and refueling with hydrogen. Thirteen papers on hydrogen-automobiles were present,d at .the Hydrogen Energy Conference, six of which dealt with engines, three with fuel storage, four with overall vehicle designs, and none with supply, distribution, or fuel handling and vehicle refueling. One of the most significant development/demonstration programs reported was the Billings Energy Research Hydrogen Bus [37-42]. This project included (a) engine testing to show that water-injection eliminates backflash (preignition in the intake manifold) and decreases nitrogen oxides production without degrading engine performance; (b) development of a dynamic vehicletesting procedure and application of this to a 21-passenger transit bus, showing that the 4000-1b hydride fuel tank penalty was more than offset by the increase in fuel efficiency of the engine; (c) pilot operation of a 6-passenger automobile fitted with a hydride storage tank to demonstrate reliable and satisfactory operation; (d) a design study for a hydride tank that could be regenerated by exhaust heat; (e) an engineering study of a hydride-powered transit bus; and (f) the design and modification of a 21-passenger Winnebago minibus to operate on hydrogen. The prototype hydrogen bus went into operation on a 13-mile trip between the cities of Provo and Orem, Utah, in February 1976.
Aircraft applications Six papers were presented on the topic of hydrogen as an aircraft fuel. As.a result of a series of NASA studies on hydrogen production, airport ground handling, liquefaction and aircraft designs, NASA [43] has concluded that, if coal is to be used as a raw energy source, the cost and efficiency of supplying a kerosene-like fuel from coal are similar to those bf supplying liquid hydrogen. Problems in handling liquid hydrogen in the refueling operations must still be solved, and existing facilities are certainly more compatible with coal-derived liquid hydrocarbons. Because of this, hydrogen as an aircraft fuel will only be justified, on the standpoint of overall consumption of coal, for aircraft larger than the Boeing 747. However, the use of other (nuclear or solar) energy sources or of improved hydrogen production technologies would justify the use of hydrogen as a preferred aircraft fuel. Another NASA paper [44] concludes with the significant statement that "sooner or later a national policy decision will have to be made to off-load the growing demand for .... natural or synthetic petroleum. If this decision singles out air transportation as the industry to initiate the introduction of LH2, it won't find the aerospace industry unprepared." Another NASA study [45] indicates that significant improvements in efficiency of aircraft piston engines can be expected if some hydrogen is generated from a portion of the aircraft fuel and supplied (with regular fuel) to the engine.
Industrial applications In the near-term U.S. industrial hydrogen market (including captive uses), a recent study for NASA estimated that the market size was on the order of 3 x 1012 SCF/year, increasing at about 5% per year [46]. Much of this hydrogen is now produced from natural gas or oil. An IGT study [47] indicated that large-scale operations, such as ammonia and methanol plants and oil refineries, can produce bulk on-site hydrogen from natural gas at such low prices today that in the near-term future, the only competitive source is likely to be coal gasification. However, smaller users, such as plants for producing fats and soaps and some specialized metallurgical processes, normally pay higher prices for merchant hydrogen. These prices are comparable to costs of electrolytic hydrogen produced with off-peak power. CONCLUSIONS From the studies that we have surveyed since the 1974 THEME Conference on hydrogen and particularly from the 1976 First World Hydrogen Energy Conference, we have made the following observations. 1. An economical alternative to the conventional production of hydrogen from petroleum and natural gas is needed to expand hydrogen supply prospects, and increased sources of supply will
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be required before hydrogen can be considered as an alternative or supplemental fuel. Coal gasification offers the best near-term prospect for hydrogen, but other fuels more compatible with existing systems, such as SNG, liquid hydrocarbons, or methanol, could preferably be produced from coal. For specific industrial uses, such as ammonia synthesis, hydrogen-from-coal could become competitive during the next decade. Water electrolysis for fuel or commodity hydrogen would be practical only with cheap hydropower or off-peak electric power. 2. Significant exploratory research on the production of hydrogen from water and nonfossil energy sources is under way through work on thermochemical, photochemical, biochemical and combination processes. Thermocbemical production is laboratory-proved .in stepwise (noncontinuous) procedures, but most of these procedures would require high-temperature, gas-cooled reactors if nuclear heat were the energy source. High-temperature heat is acknowledged as a requirement for efficient operation of thermochemieal processes. 3. Hydrogen constitutes a viable storage medium for electric power, and research to improve electrolyzer efficiency from 70% to 90% is encouraging. Metal hydride storage is technically feasible and fuel cell reconversion of hydrogen to electricity appears practical 4. Exploratory and advanced research are required for hydrogen production and delivery concepts. Energy sources other than coal and nuclear (fission) process heat should receive greater emphasis. Hydrogen from any source could supplement the natural gas supply by addition of hydrogen to pipeline gas. Experimental tests of model pipeline transmission loops, underground storage of gaseous hydrogen and model distribution systems are imperative. These tests will indicate feasibility and problem areas for hydrogen in using the existing systems that now handle 27% of our total energy supply. 5. Hydrogen has been demonstrated to be a superior fuel for operation of many types of internal combustion engines, including turbine engines; it would provide excellent performance as an aircraft fuel, and it produces high efficiencies when used as the fuel in a fuel cell. Delivery systems, fuel tankage, safe and practical handling and of course, economical supply are the problem areas needing more attention. A moderate-scale demonstration of hydrogen usage for some residential or commercial purpose, perhaps for a form of mass transport, would foster further interest in these problem areas. REFERENCES 1. H. R. L:NDEr~,IS our environment really doomed? New technology says no! A.G.A. Mon. 53, 14-17 (1971). 2. D. P. GREGORY,The gas industry's role in the nuclear age, A S H R A E J. 13, 38--40 (1971). 3. G. DEBEN!& C. MARCHETTI,Hydrogen, key to the energy market, Eurospectra 9, 46 (1970). 4. T. N. VEZIROOLU,Ed., Hydrogen Energy, THEME Proceedings, New York: Plenum, 1975. 5. T. N. VEZmOOLU, Ed., Proceedings of the 1st Worm Hydrogen Energy Conference, Vols. 1-3. Coral Gables, Florida: University of Miami, 1976. 6. T. OttTA, et al., Water-splitting-system synthesized by photochemical and thermoelectric utilizations of solar energy. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 7. K. FuJn, et al., The calcium-iodine cycle for the thermochemical decomposition of water. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida~ March 1-3, 1976. 8. R. SCHULTEN,et al, The concept of "nuclear hydrogen production" and progress of work in the Nuclear Research Center Juelich. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 9. A. BROGGI., G. DEBENI & D. VAN VELZEN, Definition and analysis of th'ermochemical processes for hydrogen production based on iron-chlorine reactions. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 10. M. G. BOWMAN, Progress in the Los Alamos Scientific Laboratory program to develop thermochemical processes for hydrogen production. Paper presented at the 1st World Hydrogen Conference, Miami Beach, Florida, March 1-3, 1976. 11. L. E. BRECHER, S. SPEWOCK ~: C. J. WARDE, The Westinghouse sulfur cycle for the thermochemical decomposition of water. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 12. J. PANOBORN,Laboratory investigations on thermochemical hydrogen production. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 13. J. L. RUSSELL,et al., Water-splitting---A progress report. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976.
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14. P. A. Kn'n~, D. F. MA~ONEY& J. E. SOKa~R, A low-temperature, three-step water-splitting process. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 15. C. L. TSAROS,J. L. ARORA& K. B. BURNHAM,The manufacture of hydrogen from coal. Paper presented at the 1st World Hydrogen Conference, Miami Beach, Florida, March 1-3, 1976. 16. R. N. OUAD~, Hydrogen production from coal using a nuclear heat source. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 17. P. GoDm, et al., Optical study of the release of hydrogen and of oxygen in a micro-electrolysis cell in function of pressure, temperature, current density and surface condition of the electrodes. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976, (Abstract only in printed form). 18. S. SmmvAsAu & F. J. SALZANO, Prospects for hydrogen production by water electrolysis to be competitive with conventional methods. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 19. G. NEro, et al., The photosynthetic production of hydrogen. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 20. A. Mrrsul, Bioconversion of solar energy in salt water photosynthetic hydrogen production systems. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 21. J. E. ZA~Ic & J. BROSSEAU,Microbial hydrogen production. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 22. A. Fu~smuA & K. HONDA, Electrochemical photolysis of water at a semiconductor electrode, Nature 238, 37-38 (1972). 23. J. O'M. Bocrdus & K. UosArd, The theory of hydrogen production in a photochemical cell. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 24. A. J. NoZlg, Hydrogen generation by photoelectrolysis of water. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 25. J. J. REILLY & J. R. JomqsoN, Titanium alloy hydrides; their properties and applications. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 26. H. J. ALLISON,A wind energy system utilizing high pressure electrolysis as a storage medium. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March I-3, 1976. 27. R. R. TIsoN & N. P. BmDEmaAS, A farm energy system employing hydrogen storage. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 28. C. R. BAKER& R. L. SHAm~R,A.smdy of the efficiency of hydrogen liquefaction. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 29. A. B. WAL~gS, Technical and environmental aspects of underground hydrogen storage. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 30. A. J. KONOPKA& J. Wum~t, Transmission of gaseous hydrogen. Paper presented at the 9th Intersociety Energy Conversion Engineering Conference, San Francisco, August 26-30, 1974. 31. C. F. Smuyr, Transmission of hydrogen, in J. Hord, Ed., Selected Topics on Hydrogen Fuel, NBS Spe~al Publication 419, 6.1-6.11. ~oulder, Colorado: National Bureau of Standards, 1975. 32. G. LEETH, Nuclear heat transmission considerations. Paper presented at the First National Topical Meeting on Nuclear Process Heat Applications, Los Alamos, New Mexico, October 1-3, 1974. 33. J. P~,qOBORN & J. SHARER, Technical prospects for commercial and residential distribution and utilization of hydrogen. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 34. J. H. SWISHER,A. J. WEST & S. L. ROBINSON,Status of ERDA program on hydrogen compatibility of structural materials for pressure vessels and pipelines. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 35. F. H. KANT,et aL, Feasibility study of alternative fuels for automotive transportation, U.S. Environmental Protection Agency Report No. EPA-460/3-74-O09. Linden, New Jersey: Exxon Research and Engineering Co., June 1974. 36. J. PANOBOmq & J. GR~LIS,Alternative fuels for automotive transportation--A feasibility study, U.S. Environmental Protection Agency Report No. EPA-460/3-74-012. Chicago: Institute of Gas Technology, July 1974. 37. R. L. WOOLI~y & D. L. I-IEmtms~, Water induction in hydrogen-powdered IC engines. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 38. R. L. Woota.Ey & G. J. GERMANE,Dynamic tests of hydrogen-powered IC engines. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1974. 39. D. L. H.emugse~, D. B. MACKAY& V. R. ANm~SON, Prototype hydrogen automobile using a metal hydride. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976.
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40. D. B. MACKAY,Automotive hydride tank design. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 41. T. WALL, et al., Engineering study of hydrogen-fueled bus operation. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 42. R. E. BILLINGS,A hydrogen-powered mass transit system. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 43. R. D. Wrrco~rd, The thermal efficiency and cost of producing hydrogen and other synthetic aircraft fuels from coal. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 44. P. F. KORYClNSr~,Some early perspectives on ground requirements of liquid hydrogen air transports. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 45. W. A. MENASD,P. I. MOVmnAN & J. H. RurE, New potentials for conventional aircraft when powered by hydrogen-enriched gasoline. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976. 46. J. C. GILLIS, D. P. GREC,ORV & J. B. PANGBORN, Survey of hydrogen production and utilization methods, Project 8962 Final Report. Chicago: Institute of Gas Technology, August 1975. 47. K. DARROW, N. BmDEm~IAN& A. KONOPKA,Commodity hydrogen from off-peak electricity. Paper presented at the 1st World Hydrogen Energy Conference, Miami Beach, Florida, March 1-3, 1976.