Combustion open circuit plants

Usually, a gas turbine plant operates on open circuit , with internal combustion (Fig. 1.3). Air and fuel pass across the single control surface into the compressor and combustion chamber, respectively, and the combustion products leave the control surface after expansion through the turbine. The open circuit plant cannot be said to operate on a thermodynamic cycle however, its performance is often assessed by treating it as equivalent to a closed cyclic power plant, but care must be taken in such an approach. 

The Hawthorne and Davis analysis is first generalised for the [CBT]i open circuit plant, with fuel addition for combustion,/ per unit air flow, changing the working fluid from air in the compressor to gas products in the turbine, as indicated in Fig. 3.11. Real gas effects are present in this open gas turbine plant specific heats and their ratio are functions off and T, and allowance is also made for pressure losses. 

Complete combustion in a conventional open circuit plant... 

In practical open circuit gas turbine plants with combustion, real gas effects are present (in particular the changes in specific heats, and their ratio, with temperature), together with combustion and duct pressure losses. We now develop some modifications of the a/s analyses and their graphical presentations for such open gas turbine plants, with and without heat exchangers, as an introduction to more complex computational approaches. 

Fig. 9.2 shows how a simple open circuit gas turbine can be used as a cogeneration plant (a) with a waste heat recuperator (WHR) and (b) with a waste heat boiler (WHB). Since the products from combustion have excess air, supplementary fuel may be burnt downstream of the turbine in the second case. In these illustrations, the overall efficiency of the gas turbine is taken to be quite low ((tjo)cg = ccJf ca 0.25), where the subscript CG indicates that the gas turbine is used as a recuperative cogeneration plant. 

Extended periods at open circuit and idle conditions should be avoided to improve catalyst layer stability, hi a fuel-ceU hybrid vehicle, this can be accomphshed by utilizing the energy-storage system (e.g., batteries or capacitors) in a manner analogous to that employed in hybrids that use internal combustion engines. Owing to parasitic power requirements, fuel-cell power plants are inefficient at extremely low power therefore, the time spent at these conditions should be minimized to maximize efficiency and life. 

Fig. 1.2 shows a gas turbine power plant operating on a closed circuit. The dotted chain control surface (F) surrounds a cyclic gas turbine power plant (or cyclic heat engine) through which air or gas circulates, and the combustion chamber is located within the second open control surface (Z). Heat (2b is transferred from Z to Y, and heat (2a is rejected from Y. The two control volumes form a complete power plant. 

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