Combustion gas turbine arrangements

Figure 4.2. Combustion gas turbine arrangements and their thermodynamic diagrams, (a) Basic unit with PV and TS diagrams, (b) Unit with an air preheater and TS diagram.

For test purposes it is important that the combustion chamber is of a silo type arranged tangentially. A picture of the gas turbine is shown in Fig. 1. 

In a gasification-based power plant, the hot, high pressure coal gases from the gasifier turn a gas turbine. Hot exhaust from the gas turbine is then fed into a conventional steam turbine, producing a second source of power. This dual, or combined cycle arrangement of turbines is not possible with conventional coal combustion. It offers major improvements in power plant efficiencies. 

In AFBC applications, the convective heat transfer surface is arranged so that maximum steam generation is accomplished by coohng the product combustion gas down to the lowest permissible stack temperature. In PFBC operation, the product combustion gas is maintained at its highest permissible temperature, that of the fluidized bed combustor, so that maximum turbine power and efficiency can be obtained. PFBC operates at bed temperatures (815-870°C) much lower than conventional combustion turbine inlet temperatures (1150-1430°C), so the turbine performance in PFBC is relatively poor, but it still contributes significantly to the power plant generating output and efficiency. 

Apart from the hazard of an explosion within the acoustic chambers, there are other explosion hazards, characteristic of any gas-fired plant. In particular there is the possibility of the acciunulation of a flammable gas/air mixture within the turbine and associated inlet and exhaust systems, and its ignition by the combustion process itself, e.g., at startup. This hazard is relatively easier to mitigate, with adequate purging and reliable gas safety shutoff arrangements. 

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