Westinghouse cycle

The Westinghouse cycle is a variant of sulfur—iodine and is a hybrid concept that requires both thermal and electrical energy. When the product of reaction (4.31) is cooled, sulfurous acid is formed and this is electrolyzed at around 80 °C to produce hydrogen and sulfuric acid for recycling, i.e., 

The decomposition of sulfuric acid at 850 900 °C [reaction (4.31)], a component of all the sulfur cycles, places severe specifications on the materials of plant construction due to the extremely corrosive nature of the species at high temperatures. This is one of the major issues that is being addressed by the European HYdrogen THErmochemical Cycles (HYTHEC) programme. The 

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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] ... 

The Westinghouse cycle has many advantages widely reported and discussed in the literature. However, it is known that the Westinghouse cycle is hampered by the low water solubility of SO2 and challenges presented by the acidity of the SO2 electrolytic oxidation process [15]. To date, many efforts have been made to improve the efficiency of the electrolytic process for oxidation of SO2. Prior work has involved the use of a depolarized electrolyzer as well as addition of a third process step - examples include S-I, S-Br and S-Fe cycles given below ... 

Hydrogen production by the Westinghouse cycle modelling and optimization of the two-phase electrolysis cell... 

Material properties are assumed to be constant in the CFD simulation. Data representative of the operating conditions frequently described in the literature [9,11] are used the cell is operated under atmospheric pressure conditions with sulphuric acid solutions at 30 wt% in the cathode compartment and 50 wt% in the anode compartment, as recommended by the Westinghouse cycle efficiency evaluations. The desired specific flow-rate is imposed at the fluid inlet, where the temperature is maintained at 323 K. Adiabatic conditions prevail at the domain boundaries. 

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. 

The fuel coal, represented by C , is oxidized with chemically bound oxygen. The heated combustion gases are routed to a gas turbine to run the electrolysis step. The SO2 and H2O are applied in a Westinghouse cycle. An optimum efficiency is seen at 57 % [15]. 

The HyS cycle, or Westinghouse cycle, is a combination of electrochemical and thermochemical processes (Elder and Allen, 2009). Compared to the S—I cycle, this cycle is advantageous in that it only consists of two main stages. The first stage involves the electrolysis of water and SO2 as follows ... 

The referenced Siemens Westinghouse pnblication presented the cycle concept and overall performance valnes. Neither specific stream information nor assnmptions were presented. The stream data and assumptions presented here were developed by Parsons. The stream data were developed using an ASPEN simulation which yielded performance numbers in general agreement with the publication. 

Section 8, the cell voltage increases with cell pressure. Thus, operating with an elevated pressure will yield increased power and efficiency for a given cycle. In addition, the use of a pressurized SOFC will also allow integration with a combustion turbine. The combustion turbine selected for integration by Siemens Westinghouse is the unique 1.4 MW Heron reheat combustion turbine, a proposed product of Heron (53). 

The cycle discussed here is based on a Siemens Westinghouse publication for a 4.5 MWe plant. Recent information from Siemens Westinghouse, plans for commercialization of a scaled down 1 MWe version of this dual pressure TSOFC/Heron cycle. A 1 MW cycle was not available in the literature. 

Siemens-Westinghouse Power Corporation of Pittsburgh, PA developed and fabricated the first advanced power plant to combine a solid oxide fuel cell and a gas turbine. The microturbine generator was manufactured by Northern Research and Engineering Corporation of Woburn, Mass. The factory acceptance test was completed in April 2000. Southern California Edison will operate the new hybrid plant at The National Fuel Cell Research Center at the University of California-Irvine. A year of testing in a commercial setting will be performed at this site. The system cycle is expected to generate electric power at 55 % efficiency. 

Carty R, Cox K, Punk J, Soliman M, Conger W (1977) Process sensitivity studies of the Westinghouse sulfur cycle... 

The overall cell reaction is exactly similar to the zinc-silver oxide cell, with the final discharge products being silver and Fe(OH>2. The emf of the cell is only 1.34 V, but the cell has a superior cycle life and better reliability. Batteries up to 10 kWh have been built by Westinghouse for telecommunications and submersible vehicles. 

Iron-air cells have been developed by Matsushita Battery Industrial Co. and by the Swedish National Development Co., which have given an energy density of 80 Wh/kg at C/5 and a cycle life of 200 cycles to 60% depth of discharge. The latter company have produced 15-30 kWh batteries for EV testing. One limitation of the iron-air system for this application is the low power density achieved - a maximum value of 30-40 W/kg is reported. Similar cells are also being developed by Westinghouse (USA) and Siemens (Germany). 

Westinghouse Electric Corporation (1980), A Study on the Electrolysis of Sulfur Dioxide and Water for the Sulfur Cycle Hydrogen Production Process, AESD-TME-3043, July. 

Brecher, L.E., S. Spewock, C.J. Warde (1977), The Westinghouse Sulfur Cycle for the Thermochemical Decomposition of Water , International Journal of Hydrogen Energy, Vol. 2, pp. 7-15, Pergamon Press. 

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. 

The Westinghouse sulphur cycle, also known as the HyS cycle, was developed in the United States by Westinghouse during the oil crises of the 1970s (Brecher, 1976). In the HyS process, unlike the electrolysis of water, hydrogen is actually produced at the electrolyser cathode (Brecher, 1976). Similarly, sulphuric acid is produced at the electrolyser anode (Brecher, 1976). The HyS cycle consists of a decomposition step and an electrolysis step expressed as the following equations. 

A simplified transient analysis model of the sulphur iodine and Westinghouse hybrid sulphur cycle was presented by Brown, et al. (2009). This model is utilised in this paper via coupling to a PBMR-268 model and a simple point kinetics model. Some of the key tenants of the analysis model are summarised however interested readers are referred to the original paper for greater detail. The S-I and HyS analysis model is a control-volume model which treats the chemical plant as a closed system. 

Unlike molten carbonates, solid oxides use a hard ceramic electrolyte instead of a liquid. That means the fuel cell can be cast into a variety of useful shapes, such as tubes. With higher temperatures, sofcs may be able to cogenerate steam at temperatures as high as i,ooo°f. The Siemens Westinghouse Power Corporation has built the first advanced hybrid system, which combines a gas turbine with a tubular sofc. As of 2003, the 220 kW hybrid system has operated in California for more than 2,000 hours with a respectable 53 percent efficiency, comparable to current combined cycle gas turbines. The ultimate goal is an efficiency of 70 percent or more. 

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