No abstract

The advantages of gas turbine power plants in general and closed cycle systems under gas pressure in particular for waste heat recovery are well known. A satisfactory efficiency for electric power generation and good conditions to obtain a significant amount of hot water above 100°C lead to a high fuel utilization. However, as in most of projects, it is not much possible to produce high temperature steam or water without significantly decreasing the electricity production. A new method for an additional generation of high quality process or domestic heat is proposed. The basic feature of this method lies in arranging one or two steam generators or preheaters in parallel with the low pressure side of the recuperator. The high total efficiency and the noteworthy flexibility of this system are emphasized. This arrangement is suitable for any kind of heat source, but the applications presented in this paper are related to helium direct cycle nuclear power plants the main features of which are a single 600 MW(e) turbomachine, a turbine inlet temperature of 775°C, no or one intermediate cooling and a primary circuit fully integrated in a pre-stressed concrete reactor vessel.

Considering the concern about a more efficient, rational use of heat sources, and a greater location flexibility of power plants owing to cooling capability, closed gas cycles can offer new solutions for fossil or nuclear energy. An efficient heat conversion into power is obtained by the combination of a main non-intercooled helium cycle with a flexible, superheated, low-pressure bottoming steam cycle. Emphasis is placed on the matching of the two cycles and, for that, a recuperator bypass arrangement is used. The operation of the main gas turbocompressor does not depend upon the operation of the small steam cycle. Results are presented for a conservative turbine inlet temperature of 750 C. Applications are made for a coal-fired power plant and for a nuclear GT-HTGR. Overall net plant efficiencies of 39 and 46 percent, respectively, are projected.

A now unavoidable concern is the best possible use of a given energy source in order to meet the demand of power and heat. The most efficient, rational, thermodynamically satisfactory way of producing heat is to cogenerate it with power and to handle it as a by-product. Another basic condition is to supply heat without disturbing the operation of main turbogenerators. Closed helium cycle, non-intercooled, gas turbine coal-fired and nuclear power plants which meet these requirements are presented in this paper. Low-pressure steam and hot water are recovered from the precooler; medium, high pressure steam and steam superheating are generated by means of a bypass arrangement of the recuperator. The concept offers attractive overall energy conversion coefficients, very flexible heat production conditions and significant potentialities of reducing oil consumption. Results are given for the conservative 750 C gas turbine inlet temperature.

The present European ARIANE space program will expand into the large ARIANE 5 launch vehicle from 1995. It is assumed that important associated missions would require the generation of 200 kWe or more in space during several years at the very beginning of the next century. For this reason, in 1983, the French C.N.E.S. (Centre National d’Etudes Spatiales) and C.E.A. (Commissariat a` l’Energie Atomique) have initiated preliminary studies of a space nuclear power system. The currently selected conversion system is a closed Brayton cycle. Reasons for this choice are given: high efficiency of a dynamic system; monophasic, inert working fluid; extensive turbomachinery experience, etc. A key aspect of the project is the adaptation to heat rejection conditions, namely to the radiator geometry which depends upon the dimensions of the ARIANE 5 spacecraft. In addition to usual concepts already studied for space applications, another cycle arrangement is being investigated which could offer satisfactory compromises among many considerations, increase the efficiency of the system, and make it more attractive as far as the specific mass (kg/kWe), the specific radiator area (m2/kWe), and various technological aspects are concerned. Comparative details are presented.