Operating at a Temperature between

A solid oxide fuel cell (SOFC) consists of two electrodes anode and cathode, with a ceramic electrolyte between that transfers oxygen ions. A SOFC typically operates at a temperature between 700 and 1000 °C. at which temperature the ceramic electrolyte begins to exhibit sufficient ionic conductivity. This high operating temperature also accelerates electrochemical reactions therefore, a SOFC does not require precious metal catalysts to promote the reactions. More abundant materials such as nickel have sufficient catalytic activity to be used as SOFC electrodes. In addition, the SOFC is more fuel-flexible than other types of fuel cells, and reforming of hydrocarbon fuels can be performed inside the cell. This allows use of conventional hydrocarbon fuels in a SOFC without an external reformer. 

The first MCFC was demonstrated by Broers in 1950 [336], and the first MCFC at high pressure was built by Reiser and Schroll [337] in 1980. As shown in Figure 32, at present the MCFC it is the most efficient fuel cell, and this will be discussed in the following. The MCFC, operating at a temperature between 600 and 650°C, is generally considered a second-generation fuel cell [316,338,339], It can be used with coal gas and even more so with natural gas as a fuel. 

In the sidewalls separating the furnaces, there are flues for boilers which operate at a temperature between 2,200°F and 2,700°F. They burn a mixture of rich gas from the ovens and poor gas from gas generators. Each oven is fed with about 15 tons of pulverized coal by an automatic coal-car. The doors are hermetically sealed and distillation begins. 

The common gases used for CVD synthesis of SiO are silane and oxygen, dichlo-rosilane (SiCl H ) and nitrous oxide (N O), or tetraethylorthosilicate (SiCOCjHj) ). SijN has high electrical resistance and dielectric strength and is suitable as a passivating layer and storage capacitor in dynamic random access memory. The Si source for SijN can be SiH, SiCl or SiCl H, the nitride source being NHj or N +Hj. The common precursor for the CVD of SijN in the semiconductor industry is SiCljHj -i-NHj and the deposition is operated at a temperature between 750 and 900 °C and a pressure of 25-115 Pa [5]. 

The three chemical reactions in the toluene—benzoic acid process are oxidation of toluene to form benzoic acid, oxidation of benzoic acid to form phenyl benzoate, and hydrolysis of phenyl benzoate to form phenol. A typical process consists of two continuous steps (13,14). In the first step, the oxidation of toluene to benzoic acid is achieved with air and cobalt salt catalyst at a temperature between 121 and 177°C. The reactor is operated at 206 kPa gauge (2.1 kg/cm g uge) and the catalyst concentration is between 0.1 and 0.3%. The reactor effluent is distilled and the purified benzoic acid is collected. The overall yield of this process is beheved to be about 68 mol % of toluene. 

Figure 16 shows an effectiveness factor diagram for a first order, irreversible reaction which has been calculated from eq 95 for various values of the modified Prater number / . From this figure, it can be seen that for exothermal reactions (/ > 0) effectiveness factors above unity may be observed when the catalyst operates at a temperature substantially above the bulk fluid phase temperature. This is caused by the limited heat transfer between the pellet and the surrounding fluid. The crucial parameters controlling occurrence and size of this effect are again the modified Prater number and the Arrhenius number. 

The dehydrogenation catalyst must be sufhciently active to allow for very short contact times and the use of low temperatures, to minimize thermal cracking reactions. Carbon deposits are eliminated by heatihg in the presence of a gas containing oxygen. -This means that the catalyst must be thermally stable to avoid being deactivated during the oxidation of the deposits. The best catalysts contain alamina and chromium oxide, but these cannot be employed in the presence of steam. Operations are conducted at a temperature between 550 and 700 C, and low pressure, less than 0.1.10 Pa absolute. 

Description of the process. The process involves the utilization of two separate CFBs, both operated at ambient pressure (Figure 16.11). The first is a flash pyrolysis reactor in which waste is converted with the addition of steam, at a temperature between 700 and 900°C, into product gas and tar. The reducing atmosphere avoids the dioxins formation. The prodnct stream, made of fuel gas and HCl in a composition strongly dependent on feed/steam ratio, is quenched to recover HCl, which is then further purified. The second CFB is a combustor that provides heat for flash pyrolysis by burning the residnal tar the... 

An extra feature of the equipment shown in Figure 21.3 is the design of the condensation train. It is known that under certain conditions, the pyrolytic products when condensed, form a mist or aerosol, similar to the smoke produced by cigarettes or a barbecue. These aerosols, may accumulate as a wax on the walls of condensers, but often they do not settle inside collection vessels. This problem was solved by making the gases flow upwards through a vertical condenser, effectively creating a reflux-like effect, similar to a distillation column. Furthermore, this condenser was operated at a temperature that cooled the products to a point at which they condensed, but did not solidify, and allowed the liquid droplets to coalesce and hence be collected. The optimal operation of the condenser was with water at temperatures between 50 and 60°C [86]. 

It can be shown experimentally that this reaction is favored by development in the liquid phase, at a temperature between 220 and 250°C. The reaction rate is too low below 180°C, while the excessive formation of by-products occurs above 260 C The pressure must also be kept above 30.10° Pa absolute. The presence of water (>30 per cent volume) and the use of catalysts help to reduce the severity of the operating conditions, particularly the pressure, which is reduced to about 3 to 7. 106 Pa absolute in the latest systems, while the temperature ranges from 150 to 200°C. 

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