Natural gas fuel cell

Another interesting development in natural gas fueled fuel cell area is the Direct Fuel Cell developed by Energy Research Corporation (ERC Danbury, CT). This is a carbonate fuel cell which could use directly either natural gas or coal gas without the necessity of external supply (usually by steam reforming of hydrocarbon fuel) of hydrogen. Since the galvanic combustion of methane is essentially a zero entropy process, the maximum theoretical efficiency could be 100%. A carbonate fuel cell was chosen because  

The operating temperature of about 650°C is high enough to be able to operate the process on nonnoble metal electrodes. 

A significant amount of reforming could take place at this temperature. 

Since steam is generated at the negative electrode and fuel also is consumed there, the electricity generation process ensure the complete conversion of fuel into reactive species within fuel cells (based on favorable mass transfer and nonequilibrium reaction conditions arising from current production). 

Nickel catalysts are used for the catalytic coating on the electrodes. However, the overall conversion efficiency (based on lower heating value of the fuel) was about 60% in a 2-megawatt plant without employing the bottoming 

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This natural gas fuel cell power system is based on a pressurized TSOFC combined with a combustion turbine developed by Siemens Westinghouse (52). Most TSOFC power plant concepts developed to date have been based on atmospheric operation. However, as shown in... 

A natural gas fuel cell vehicle running on hydrogen produced from natural gas may have little or no net C02 benefits compared to hybrid vehicles. Natural gas does have major benefits when used to replace coal plants. Coal plants have much lower efficiencies at around 30% compared to natural gas plants at 55%. Compared with natural gas, coal has nearly twice the C02 emissions, while gasoline has about one third more C02 emissions than natural gas. 

BARP, B., DIETHELM, R., Natural Gas Fuel cells for Residential Applications, European Fuel Cell News 3 (1996) March 17-18. 

Numerous natural gas fuel cell/fuel processor systems are under development for residential applications. Because off-heat could well be used for heating purposes and hot water generation in residential applications, the overall system efficiency is usually high for such systems. 

Various Technical Reports Posted on the Strategic Center for Natural Gas Fuel Cell Reference Shelf Available online at http //www.netl.doe.gov/scng/enduse/fc refshlfhtml... 

In order to determine the performance potential of fuel cells powered by bio-fuels, the resultsobtained were compared with two reference fuels hydrogen and natural gas. Fuel cell characteristics for two reference fuels hydrogen and methane were calculated for a comparative baseline. The type of fuel supplied is not the only... 

In early 2000, FCE s Direct Fuel Cell (DFC) went into a joint public/private development with NETL. This system uses internal conversion of the natural-gas fuel to hydrogen, as opposed to an external unit. This reduces costs and creates efficient use of excess heat. The DFC system has already passed 8600 hours and a one-year milestone at FCE s headquarters. 

Because of the modular nature of fuel cells, they are attractive for use in small portable units, ranging in size from 5 W or smaller to 100 W power levels. Examples of uses include the Ballard fuel cell, demonstrating 20 hour operation of a portable power unit (32), and an IFC military backpack. There has also been technology transfer from fuel cell system components. The best example is a joint IFC and Praxair, Inc., venture to develop a unit that converts natural gas to 99.999% pure hydrogen based on using fuel cell reformer technology and pressure swing adsorption process. 

B. Baker, S. Gionfriddo, A. Leonida, H. Maru, P. Patel, "Internal Reforming Natural Gas Fueled Carbonate Fuel Cell Stack," Final Report prepared by Energy Research Corporation for the Gas Research Institute, Chicago, IL, under Contract No. 5081-244-0545, March, 1984. M. Farooque, Data from ERC testing, 1992. 

In a natural gas fueled PAFC, water is condensed out of the fuel stream going to the fuel cell to increase the partial pressure of hydrogen. In a coal gasification MCFC, water often is added to the fuel stream prior to the fuel cell to prevent soot formation. The addition of excess steam not only prevents the soot formation, but also causes a voltage drop of approximately 2 mV per each percentage point increase in steam content (45). The use of zinc ferrite hot gas cleanup can aggravate the soot formation problem because of the catalytic effect of the sorbent on carbon formation, and requires even higher moisture levels (46). 

A flow diagram for a natural gas fueled, 4 MW class, solid state fuel cell power cycle is presented in Figure 9-11. A brief process description is given below, followed by a performance summary. Selected state point values are presented in Table 9-16. 

Table 9-16 Stream Properties for the Natural Gas Fueled Solid State Fuel Cell...

Siemens-Westinghouse Power Corporation, Pittsburgh, PA, and Solar Turbines developed a conceptual design of an economically and technically feasible 20-MW, 70-% efficient natural gas-fueled power system that employs solid oxide fuel cells operating at elevated pressure in conjunction with an Advanced Turbine System gas turbine. The fuel cell, operated at 9 atm pressure, generated 11 MW of power. Two Solar Mercury 50 gas turbines were used to generate 9 MW of power. The results of the study indicated a system efficiency near 60 %. A low COE relative to conventional power generation is predicted. 

The process simulation code Aspen-HYSYS 3.2 has been used for residential PEM fuel cell system calculations. Natural gas has been simulated as three different sources for hydrogen production. The chemical compositions of the natural gas fuel are summarized in Table 1. The average molecular weight of natural gas is around 16.6 kg/kmol. All simulation studies are performed based on this composition. 

Molten carbonate fuel cell (MCFC)—Carbonate electrolyte with conventional metal catalyst. It can use coal gas and natural gas fuel, and is suited for 10 kW to 2 mW power plants. 

Autothermal reformers and CPO are being developed by a number of groups, mostly for fuel processors of gasoline, diesel, and JP-8 fuels and for natural gas-fueled proton exchange membrane fuel cell (PEMFC) cogeneration systems. A few examples are the following ... 

Use Manufacture of formaldehyde, acetic acid, and dimethyl terephthalate chemical synthesis (methyl amines, methyl chloride, methyl methacrylate) antifreeze solvent for nitrocellulose, ethylcellulose, polyvinyl butyral, shellac, rosin, manila resin, dyes denaturant for ethanol dehydrator for natural gas fuel for utility plants (methyl fuel) feedstock for manufacture of synthetic proteins by continuous fermentation source of hydrogen for fuel cells home-heating-oil extender. 

Natural-gas fueled fuel cells are more efficient than the conventional hydro-gen-oxygen (air) fuel cells since they reduce capital costs and simplify the process by eliminating the external source of hydrogen supply. Acceptable efficiencies also have been found for these processes. With the developing technology, new electrode materials and catalytic materials could be used to further improve this technique of alternate electricity generation from natural gas [28]. 

Design, integrate and demonstrate a natural gas fueled T-kW gt el cell power plant. 

Phase II Demonstration and delivery of a high efficiency reformate tolerant 7-kWf,gt fuel cell stack and power plant utilizing molded bipolar plates and natural gas fuel processor to Argonne National Laboratory for independent testing and verification. 

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