Sources and Properties of Raw Material Feedstock - Article Example

Sources and properties of raw material feedstocks of hydrogen manufacture by steam methane reforming process Introduction About 95% of the hydrogen produced today in the United States is made via steam methane reforming, a process in which high-temperature steam (700 - 1000°C) is used to produce hydrogen from a methane source, such as natural gas. In steam methane reforming, methane reacts with steam under 3-25 bar pressure (1 bar = 14.5psi) in the presence of a catalyst to produce hydrogen, carbon monoxide, and a relatively small amount of carbon dioxide. Steam reforming is endothermic - that is, heat must be supplied to the process for the reaction to proceed. Subsequently, in what is called the "water-gas shift reaction," the carbon monoxide and steam are reacted using a catalyst to produce carbon dioxide and more hydrogen. In a final process step called "pressure-swing adsorption," carbon dioxide and other impurities are removed from the gas stream, leaving essentially pure hydrogen. Steam reforming can also be used to produce hydrogen from other fuels, such as ethanol, propane, or even gasoline1. Steam Reforming Reactions Methane: CH4 + H2O (+heat) → CO + 3H2 Propane: C3H8 + 3H2O (+heat) → 3CO + 7H2 Ethanol: C2H5OH + H2O (+heat) → 2CO + 4H2 Sources and Properties of Raw Material Feed Stocks The major raw material feedstock used in Hydrogen production is Methane. The major source of methane is extraction from geological deposits known as natural gas fields. It is associated with other hydrocarbon fuels and sometimes accompanied by helium and nitrogen. Apart from gas fields, an alternative method of obtaining methane is via biogas generated by the fermentation of 1. http://www.eere.energy.gov organic matter including manure, wastewater sludge, municipal solid waste (including landfills), or any other biodegradable feedstock, under anaerobic conditions Source: Megan Strait, Glenda Allum, Nisha Gidwani, Synthesis Gas Reformers: www.owlnet.rice.edu The Physical and Chemical Properties of Methane2,3 Molecular formula : CH3OH Molar mass : 32.04 g/mol Appearance colourless liquid Density : 0.7918 g/cm³, liquid Melting point : –97 °C (176 K) Boiling point : 64.7 °C (337.8 K) Solubility in water : Fully miscible Acidity (pKa) ~ 15.5 Viscosity : 0.59 mPa·s at 20 °C Dipole moment : 1.69 D (gas) Toxic (T) : NFPA 704 Hazards MSDS External MSDS EU classification : Flammable (F) 2. http ://en.wikipedia.org 3. United States Geological Survey publication Apart from the feedstock, a catalyst, a metallic catalyst like nickel is required in the process in order to stabilize the reaction. Requirements 1.Feedstock: Hydrocarbons such as a. Methane b. refinery feedstock or c. olefins or d. Light parafins 2.catalyst: Metal -based catalyst (nickel) or Mg+ or Ca+ 3.Water 4. Ceramic Absorbent 5. Additionally, oxygen can be used to oxidize the carbon (CO), liberating the hydrogen formerly bound to the carbon and oxygen Estimates of Typical Raw Materials Cost Approximate price ranges were obtained from M.W. Kellogg for the primary and secondary reformers and catalyst. These prices reflect the differences in construction materials used for each reactor. Due to the high pressures and temperatures in the primary reformer tubes, a 25% chromium-20% nickel alloy is the preferred tube material. The secondary reformer, with its simpler design, can be priced as a large, refractory-lined vessel containing a fixed-bed nickel catalyst. Primary reformers cost on the order of $5 million, secondary reformers on the order of $1 million, and primary reformer catalyst approximately $200/ft3. Therefore catalyst cost for the primary reformer is $138,000, less than three percent of the total primary reformer installed cost. Since the primary reformer is such a major component of the process cost, the process was optimized so as to minimize the size of the primary reformer. Less attention is given to the amount of catalyst supplied to the primary reformer since it becomes almost negligible when compared to the cost of the reactor itself 4,5. 4. Gerhartz, W. et. al. Ullmann's Encyclopedia of Industrial Chemistry. 5th Edition. VCH, Federal Republic of Germany, 1985 5. http://www.owlnet.rice.edu Methane is the most common form of available natural gas and hence the global estimate of natural gas (availability) will be a close estimate of methane availability. Current estimates indicate that using natural gas to produce hydrogen during the transition period to a hydrogen economy would increase overall U.S. natural gas consumption by less than five percent. Although the technology for distributed natural gas reforming is advancing rapidly, several challenges remain. Capital equipment costs, as well as operation and maintenance costs, must be reduced and process energy efficiency must be improved in order to meet hydrogen cost targets. In order for hydrogen to be successful in the market place, it must be cost competitive with the available alternatives. In the light-duty vehicle transportation market, this means that hydrogen needs to be available at $2-$3/gge (untaxed). This would result in hydrogen fuel cell vehicles having the same cost to the consumer on a cost per mile driven basis as a comparable conventional internal combustion engine or hybrid vehicle. 6 About 4,900 trillion cubic feet of natural gas at the end of 1995, is enough for about 60 years supply at current world gas production rates. However, much of the world's known natural gas reserves are inconveniently located in remote and thinly populated areas, such as Western Siberia and the Persian Gulf. The United States and Canada have been girdled with large gas pipelines that transport gas from the producing fields of Texas, Louisiana, Oklahoma, and Alberta to consuming markets in California, New England, and elsewhere. At present, however, pipeline transport is generally not an economically feasible option for transporting natural gas across oceans. Moving natural gas between continents requires an innovative approach. 7 6. US Department of Energy, Energy efficacy and Renewable Energy: http://www1.eere.energy.gov 7. Worldwide Natural Gas Supply and Demand and the outlook for Global LNG Trade: http://tonto.eia.doe.gov The natural gas movement estimates in the above table is much higher than the amount of natural gas consumed in 1997, estimated at 23 trillion cubic feet (or 435 million tons), due to transshipments among pipeline companies. Each time a shipment changes physical possession it is counted as a separate shipment in the EIA records. However, the ton-mile estimates appropriately include only the distance traveled at each stage of shipment as identified in the above table. Presently Pipeline is the only mode of natural gas transportation, and therefore accounts for 100 percent of all movements. Interstate movements as well as imports/exports of natural gas shipments are expected to be transported long-distances to various locations in the United States. Based on average distance between state centroids an average length of inter-state movement of 240 miles is used and an average trip length of 100 miles and 30 miles, for the non-local and local natural gas movements, respectively are used. Regional Distribution of Global Gas Reserves Eastern Europe & Former Soviet Union 40.5% Middle East 32.7% Africa 6.7% Far East & Oceania 6.5% North America 6.1% Central & South America 4.2% Western Europe 3.3% Source: Oil and Gas Journal (December 30, 1996). As of January 1, 1997, the world’s proved world natural gas reserves were estimated to be 4,945 trillion cubic feet, 11.6 trillion cubic feet more than the estimate for 1996. Whereas natural gas reserves have declined slightly in the industrialized countries during the past decade, they have increased fairly dramatically in the EE/FSU and in the developing countries. Between 1995 and 1996, gas reserves in the Middle East grew by 20 trillion cubic feet, whereas the combined reserves of Africa, Western Europe, and Asia declined by about 19 trillion cubic feet. About 73 percent of the worlds proved gas reserves are located in the FSU and the countries of the Middle East. Reserves in the industrialized countries of the world have remained fairly stable over the past 20 years, although they have fallen continuously since 1993. On the other hand, reserves in the EE/FSU and developing countries have more than doubled. Natural gas reserves are less geographically concentrated than oil reserves worldwide. Further, despite high rates of increase in gas consumption, especially over the past decade, regional reserves-to-production ratios tend to be high, indicating excess capacity and the potential for greater exploitation of this resource. For example, Central and South America have a reserves-to-production (R/P) ratio of 73.9 years, the EE/FSU 80.4 years, and the Middle East more than 100 years. In contrast, the United States and Canada had R/P ratios for 1995 of 9.2 and 12.8, respectively. Additionally, in many areas, deposits of gas are known to exist but are not counted as reserves because the infrastructure needed to gather and distribute the gas is not available. Lack of infrastructure is the major barrier to increased liquids and non hydrocarbon gases. Thus, gross production must exceed the volume of gas delivered to the liquefaction plant by the amount of shrinkage. 10,11 ----------------------------------------------------------------------------------------------------------------- 10. British Petroleum Company, BP Statistical Review of World Energy 1996 (London, UK, June 1996). 11. U.S. number is from the Energy Information Administration, U.S. Crude Oil, Natural Gas, and Natural Gas Liquids Reserves, Annual Report 1995 (DOE/EIA-0216(95) (Washington, DC, November 1996; the Canadian number is from the Canadian Association of Petroleum Producers. Read More