Fuel heat exchange

Figure 33.36 is an example of a 300 kW aircraft SOFC APU design [70]. In this system design, the power generation subsystem consists of twin 150 kW hybrid SOFCs and the fuel processing subsystem consists of an ATR FR and a DS. A fuel heat exchanger (HEX) is used to cool the reformate gas stream. A portion of exhaust gases from the SOFC are recycled via the CGR and AGR blowers. 

Stress corrosion cracking of a U-bend waste fuel heat exchanger tube. 

The reference MSFR is a 3-GWth reactor with a total fuel salt volume of 18 operated at a maximum fuel salt temperature of 750°C (Mathieu et al., 2009 Merle-Lucotte et al., 2012). The system includes three circuits the fuel circuit, the intermediate circuit, and the power conversion circuit. The fuel circuit, defined as the circuit containing the fuel salt during power generation, includes the core cavity, the inlet and outlet pipes, a gas injection system, salt-bubble separators, pumps, and fuel heat exchangers. 

Helping to propel capacities upward has been the advent of greatly improved preheaters, which partially calcine the stone and significantly improve thermal efficiency. Modem preheaters improve capacity by 15—20% and decrease fuel consumption a similar percentage. Other kiln appurtenances and accessories that enhance efficiency and lime quahty are the contact coolers, and such kiln internals as metal refractory trefoil systems that act as heat exchangers, dams, and lifters. 

To recover the sensible heat content of water-saturated exit kiln air, heat exchangers are being employed to contact the exit air with incoming fresh air. Fuel savings of about 30% are being achieved. 

Fossil Fuel-Fired Plants. In modem, fossil fuel-fired power plants, the Rankine cycle typically operates as a closed loop. In describing the steam—water cycle of a modem Rankine cycle plant, it is easiest to start with the condensate system (see Fig. 1). Condensate is the water that remains after the steam employed by the plant s steam turbines exhausts into the plant s condenser, where it is collected for reuse in the cycle. Many modem power plants employ a series of heat exchangers to boost efficiency. As a first step, the condensate is heated in a series of heat exchangers, usually sheU-and-tube heat exchangers, by steam extracted from strategic locations on the plant s steam turbines (see HeaT-EXCHANGETECHNOLOGy). 

The simplest unit employing vacuum fractionation is that designed by Canadian Badger for Dominion Tar and Chemical Company (now Rttgers VFT Inc.) at Hamilton, Ontario (13). In this plant, the tar is dehydrated in the usual manner by heat exchange and injection into a dehydrator. The dry tar is then heated under pressure in an oil-fired hehcal-tube heater and injected directly into the vacuum fractionating column from which a benzole fraction, overhead fraction, various oil fractions as side streams, and a pitch base product are taken. Some alterations were made to the plant in 1991, which allows some pitch properties to be controlled because pitch is the only product the distillate oils are used as fuel. 

It is possible to deactivate a metal ioa by adding a compouad such as disahcyhdeae alkyl diamiae, which readily forms a chelate with most metal atoms to reader them iaeffective. Metal deactivator has beea showa to reduce oxidatioa deposits dramatically ia the JFTOT test and ia single tube heat exchanger rigs. The role of metal deactivator ia improving fuel stabiUty is complex, siace quantities beyond those needed to chelate metal atoms act as passivators of metal surfaces and as antioxidants (13). 

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