Papers by Mikhail Granovskiy
Journal of Fuel Cell Science and Technology, 2008
ABSTRACT The combination of fuel cells with conventional mechanical power generation technologies... more ABSTRACT The combination of fuel cells with conventional mechanical power generation technologies (heat engines). promotes effective transformation of the chemical energy of fuels into electrical work. The implementation of solid oxide fuel cells (SOFCs) within gas turbine systems powered by natural gas (methane) requires an intermediate step of methane conversion to a mixture of hydrogen and carbon monoxide. State-of-the-art Ni-YSZ (yttria-stabilized zirconia) anodes permit methane conversion directly on anode surfaces, and contemporary designs of SOFC stacks allow this reaction to occur at elevated pressures. An exergy analysis of a gas turbine cycle integrated with SOFCs with internal reforming is conducted. As the efficiency of a gas turbine cycle is mainly defined by the maximum temperature at the turbine inlet, this temperature is fixed at 1573 K for the analysis. In the cycle considered, the high-temperature gaseous flow from the turbine heats the input flows if natural gas and air, and is used to generate pressurized steam, which is mixed with natural gas at the SOFC stack inlet to facilitate its conversion. This technological design permits avoidance of the generally accepted recirculation of the reaction products around the anodes of SOFCs, which reduces the capacity of the SOFC stack and the entire combined power generation system correspondingly. At the same time, the thermal efficiency of the combined cycle is shown to remain high and reach 65-85% depending on the SOFC stack efficiency. The thermodynamic efficiency of the SOFC stack is defined as the ratio of electrical work generated to the methane oxidized (through the intermediate conversion). For a given design and operating condition of the SOFC stack, an increase in the thermodynamic efficiency of a SOFC is attained by increasing the fuel cell active area. Achieving the highest thermodynamic efficiency of the SOFC stack leads to a significant and nonproportional increase in the stack size and cost. For the proposed steam generating scheme, increasing the load of the SOFC stack is accompanied by a decrease in steam generation, a reduction in the steam to methane ratio at the anode inlet, and an increased possibility of catalyst coking. Accounting for these factors, the range of appropriate operating conditions of the SOFC stack in combination with steam generation within a gas turbine cycle is presented.
International Journal of Hydrogen Energy, 2007
This study addresses economic aspects of introducing renewable technologies in place of fossil fu... more This study addresses economic aspects of introducing renewable technologies in place of fossil fuel ones to mitigate greenhouse gas emissions. Unlike for traditional fossil fuel technologies, greenhouse gas emissions from renewable technologies are associated mainly with plant construction and the magnitudes are significantly lower. The prospects are shown to be good for producing the environmentally clean fuel hydrogen via water electrolysis driven by renewable energy sources. Nonetheless, the cost of wind-and solar-based electricity is still higher than that of electricity generated in a natural gas power plant. With present costs of wind and solar electricity, it is shown that, when electricity from renewable sources replaces electricity from natural gas, the cost of greenhouse gas emissions abatement is about four times less than if hydrogen from renewable sources replaces hydrogen produced from natural gas. When renewable-based hydrogen is used in a fuel cell vehicle instead of gasoline in a IC engine vehicle, the cost of greenhouse gas emissions reduction approaches the same value as for renewable-based electricity only if the fuel cell vehicle efficiency exceeds significantly (i.e., by about two times) that of an internal combustion vehicle. It is also shown that when 6000 wind turbines (Kenetech KVS-33) with a capacity of 350 kW and a capacity factor of 24% replace a 500-MW gas-fired power plant with an efficiency of 40%, annual greenhouse gas emissions are reduced by 2.3 megatons. The incremental additional annual cost is about $280 million (US). The results provide a useful approach to an optimal strategy for greenhouse gas emissions mitigation. Crown
Energy Conversion and Management, 2008
In this paper, a high-temperature chemical heat pump, which employs the reversible catalytic meth... more In this paper, a high-temperature chemical heat pump, which employs the reversible catalytic methane conversion reaction, is proposed. The reaction shift from exothermic to endothermic and back is achieved by changing the steam concentration in the reaction mixture. This heat pump, coupled with the second steam cycle of a supercritical water (SCW) nuclear power plant on one side and a thermochemical water-splitting cycle on the other, permits the transmission of some part of the heat generated in the first steam cycle to a higher temperature level in order to transfer it into the water-splitting cycle.
Journal of Power Sources, 2007
A necessary step in the use of natural gas (methane) in solid oxide fuel cells (SOFCs) is its pre... more A necessary step in the use of natural gas (methane) in solid oxide fuel cells (SOFCs) is its preliminary conversion to hydrogen and carbon monoxide. To perform methane conversion within fuel cells and avoid catalyst carbonization the molar ratio between methane and steam (or steam with carbon dioxide) should be 1:2 or higher at the SOFC inlet. In this article two possible technological approaches to provide this desirable ratio in a combined SOFC-gas turbine system are compared. The first approach involves generation of the required steam in the coupled gas turbine cycle. The second (which is more traditional) involves recycling some part of the exhaust gases around the anodes of the SOFC stack.
Journal of Power Sources, 2006
Published data from various sources are used to perform economic and environmental comparisons of... more Published data from various sources are used to perform economic and environmental comparisons of four types of vehicles: conventional, hybrid, electric and hydrogen fuel cell. The production and utilization stages of the vehicles are taken into consideration. The comparison is based on a mathematical procedure, which includes normalization of economic indicators (prices of vehicles and fuels during the vehicle life and driving range) and environmental indicators (greenhouse gas and air pollution emissions), and evaluation of an optimal relationship between the types of vehicles in the fleet. According to the comparison, hybrid and electric cars exhibit advantages over the other types. The economic efficiency and environmental impact of electric car use depends substantially on the source of the electricity. If the electricity comes from renewable energy sources, the electric car is advantageous compared to the hybrid. If electricity comes from fossil fuels, the electric car remains competitive only if the electricity is generated on board. It is shown that, if electricity is generated with an efficiency of about 50-60% by a gas turbine engine connected to a high-capacity battery and an electric motor, the electric car becomes advantageous. Implementation of fuel cells stacks and ion conductive membranes into gas turbine cycles permits electricity generation to increase to the above-mentioned level and air pollution emissions to decrease. It is concluded that the electric car with on-board electricity generation represents a significant and flexible advance in the development of efficient and ecologically benign vehicles.
International Journal of Hydrogen Energy, 2006
A life cycle assessment of hydrogen and gasoline vehicles, including fuel production and utilizat... more A life cycle assessment of hydrogen and gasoline vehicles, including fuel production and utilization in vehicles powered by fuel cells and internal combustion engines, is conducted to evaluate and compare their efficiencies and environmental impacts. Fossil fuel and renewable ...
International Journal of Exergy, 2008
Exergy analysis can help integrate separate technologies following the principles of industrial e... more Exergy analysis can help integrate separate technologies following the principles of industrial ecology. An application of exergy analysis to calculate depletion numbers, which relate exergy destruction and total exergy use, is demonstrated for a gas turbine cycle combined with a hydrogen generation unit. The design includes a Solid Oxide Fuel Cell (SOFC) with internal natural gas reforming and a Membrane Reactor (MR) in place of a combustion chamber. The depletion number for the separate technologies is found to be more than two times greater than for the combined system, implying the latter is more environmentally benign and like an ecosystem.
International Journal of Exergy, 2008
Exergy analysis can help integrate separate technologies following the principles of industrial e... more Exergy analysis can help integrate separate technologies following the principles of industrial ecology. An application of exergy analysis to calculate depletion numbers, which relate exergy destruction and total exergy use, is demonstrated for a gas turbine cycle combined with a hydrogen generation unit. The design includes a Solid Oxide Fuel Cell (SOFC) with internal natural gas reforming and a Membrane Reactor (MR) in place of a combustion chamber. The depletion number for the separate technologies is found to be more than two times greater than for the combined system, implying the latter is more environmentally benign and like an ecosystem.
Journal of Power and Energy Systems, 2008
ABSTRACT Increases in the power generation efficiency of nuclear power plants (NPPs) are mainly l... more ABSTRACT Increases in the power generation efficiency of nuclear power plants (NPPs) are mainly limited by the permissible temperatures in nuclear reactors and the corresponding temperatures and pressures of the coolants in reactors. Coolant parameters are limited by the corrosion rates of materials and nuclear-reactor safety constraints. The advanced construction materials for the next generation of CANDU reactors, which employ supercritical water (SCW) as a coolant and heat carrier, permit improved ``steam'' parameters (outlet temperatures up to 625°C and pressures of about 25 MPa). An increase in the temperature of steam allows it to be utilized in thermochemical water splitting cycles to produce hydrogen. These methods are considered by many to be among the most efficient ways to produce hydrogen from water and to have advantages over traditional low-temperature water electrolysis. However, even lower temperature water splitting cycles (Cu-Cl, UT-3, etc.) require an intensive heat supply at temperatures higher than 550-600°C. A sufficient increase in the heat transfer from the nuclear reactor to a thermochemical water splitting cycle, without jeopardizing nuclear reactor safety, might be effectively achieved by application of a heat pump, which increases the temperature of the heat supplied by virtue of a cyclic process driven by mechanical or electrical work. Here, a high-temperature chemical heat pump, which employs the reversible catalytic methane conversion reaction, is proposed. The reaction shift from exothermic to endothermic and back is achieved by a change of the steam concentration in the reaction mixture. This heat pump, coupled with the second steam cycle of a SCW nuclear power generation plant on one side and a thermochemical water splitting cycle on the other, increases the temperature of the ``nuclear'' heat and, consequently, the intensity of heat transfer into the water splitting cycle. A comparative preliminary thermodynamic analysis is conducted of the combined system comprising a SCW nuclear power generation plant and a chemical heat pump, which provides high-temperature heat to a thermochemical water splitting cycle for hydrogen production. It is concluded that the proposed chemical heat pump permits the utilization efficiency of nuclear energy to be improved by at least 2% without jeopardizing nuclear reactor safety. Based on this analysis, further research appears to be merited on the proposed advanced design of a nuclear power generation plant combined with a chemical heat pump, and implementation in appropriate applications seems worthwhile.
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Papers by Mikhail Granovskiy