Hybrid cycle

The pressurized hybrid cycle provides the basis for the high electric efficiency power system. Applying conventional gas turbine technology, power system efficiencies in the 55 to 60 percent range can be achieved. When the pressurized hybrid system is based on a more complex turbine cycle— such as one that is intercooled, reheated, and recuperated—electric efficiencies of 70 percent or higher are projected. 

Countries around the world are developing interest in the high-efficiency hybrid cycles. A 320 kW hybrid (SOFC and gas turbine) plant will entered service in Germany in 2001, operated by a consortium under the leadership of RWE Ener-gie AG. This will be followed in 2002 by the first 1 MW plant, which will be operated by Energie Baden-Wurttemberg AG (EnBW), Electricite de France (EDF), Gaz de France, and Austria s TIWAG. 

And not only the distance between the nearest similar atoms by bond length (d) is the basic dimensional characteristic, but also the distance to geometric center of cycle interacting atoms Of) as the geometric center of total electron density of all hybridized cycle atoms. 

Then the basic stabilization equation for each cycle atom will take into account the average energy of hybridized cycle atoms ... 

Advantages — High binding capacity multiple hybridization cycles possible. 

The reversible potential for the sulfur dioxide electrolysis is only 0.17 V, less than 10% that of water electrolysis (minimum of 1.23V at 298K and 1 bar) [65,69]. However corrosion problems in the electrolysis step are severe due to the presence of high concentration (about 50%) sulfuric acid. The overall thermal efficiency of the process, considering both thermal and electrical energy input derived from the same heat source, is estimated as 48.8% [116]. However, in terms of economics and process complexity the hybrid cycles face tough competition from advanced water electrolyzers. 

Struck BD, Schutz GH, Van Velzen D, (1990) Cathodic hydrogen evolution in thermochemical-electrochemical hybrid cycles. In electrochemical hydrogen technologies-Electrochemical production and combustion of hydrogen Wendt H (ed), Elsevier, New York, pp 213-259... 

Dokiya M, Kotera Y (1976) Hybrid cycle with electrolysis using Cu-Cl system. Int J Hydrogen Energy 1 117-121... 

Deneuve E, Roncato JP (1981) Thermochemical or hybrid cycles of hydrogen production- technolo-echonomical comparison with water electrolysis. Int J Hydrogen Energy 6 9-23... 

Table 2.4 Standard parameters for analysis of SOFC-heat engine hybrid cycles.

Fig. 2.16 The influence of the excess air X and the efficiency //ah of the heat transfer in the air heater on the system efficiency //sysi of the SOFC-heat engine hybrid cycle.

Stiller C., Thorud B., Scljcbo S., Mathisen 0., Karoliussen H., Bolland O. (2005) Finite-volume modeling and hybrid-cycle performance of planar and tubular solid oxide fuel cells. Journal of Power Sources 141, 227-240. 

The thermochemical cycles (S-I > 850°C) or hybrid cycles (S-electrolysis > 850°C) still feature many uncertainties in terms of feasibility and performances. Uncertainties still exist in parts of the flow sheet and technologies needed to provide high temperature heat whether from solar or nuclear nature. Potential assets of thermochemical cycles lie in a theoretical potential for a global efficiency above 35% and a scaling law of the hydrogen plant after the volume of reactants instead of the total surface of electrolytic cells. In return, their practical feasibility and economic viability have to be entirely demonstrated. Especially, a global efficiency above 30% is to be demonstrated to compete with alkaline electrolysis. Moreover, the safety of co-located nuclear and chemical plants has to be demonstrated. 

Borgard, J.M., D. Doizi (2009), Energy Analysis of the CuCl Hybrid Cycle , these proceedings. 

Dokiya, M, Y. Koter (1976), Hybrid Cycle with Electrolysis Using Cu-Cl System , Int. J. of Hydrogen Energy, Vol. 1, pp. 117-121. 

The hybrid copper-chloride thermochemical cycle is a hybrid cycle which requires both electricity and heat to split the water molecule. It was described first by Dokiya (1976) and then Carty (1981). 

Other processes considered worth of further investigation are the so-called Westinghouse process, a sulphuric acid hybrid (HyS) cycle where the low-temperature step mns in an electrolysis cell to produce the hydrogen, the CuCl cycle, a lower temperature (< 500°C) hybrid cycle investigated at ANL, or the so-called UT-3 process based on a four-step cycle with calcium and bromine. 

Due to high T and 2 law efficiencies of sulfuric acid based cycles, to date, more than 20 sulfuric acid and/or metal sulfate decomposition based TCWSCs have been reported. Despite difficulties that challenge efficient electrolytic oxidation of sulfur dioxide (SO2), the Westinghouse hybrid cycle still remains as one of the most studied TCWSCs. The Westinghouse cycle is as follows [14] ... 

Solar thermochemical S-NH3 water splitting cycle 3.1. S-NHs hybrid cycle... 

Also, CRIEPI has conducted to develop anode materials in the sulfur-based hybrid cycle (SHC)... 

H. Kawamura, et al., Electrical Conductive Ceramic Anodes in Sulfur-based Hybrid Cycle for Hydrogen Production , Proceedings International Hydrogen Energy Congress and Exhibition IHEC 2005. 

The results obtained today shows that we have to develop a parallel way on Westinghouse cycle (sulphur hybrid cycle). Some difficulties concerning the iodine loop justify that we engage works on this alternative process. 

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