Wet compression

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Wet Compression is a process for increasing the performance of stationary (power plant) gas turbines .

procedure

Before entering the compressor, water is fed into the intake air flow through nozzles , usually in the order of 1 to 2% of the intake mass flow. In order to avoid droplet wall / blade interaction and to reduce erosion on the compressor blades, the smallest possible droplet size is important. Downstream behind the injection of the water droplets (in the area of ​​the strongly accelerated flow in the area of ​​the compressor inlet), the relative humidity exceeds the saturation limit of 100%. Due to the short exposure of the two-phase flow to these conditions, the effects of homogeneous nucleation can be neglected. The occurrence of heterogeneous nucleation depends strongly on the quality of the air entering.

In the case of water droplets entering the compressor, the terms wet compression or overspray fogging are used. If the phase change only takes place within the intake tract, the term inlet fogging has become established.

Basics

Two main mechanisms are the basis for increasing performance:

  1. Intercooling effect: within the normally multistage turbo compressor , the air flow is cooled by evaporation of the water droplets; the work process moves from adiabatic to isothermal compression. This reduces the specific power consumption of the compressor and the output mechanical (net) power of the gas turbine increases (as does its efficiency).
  2. Increase in the mass flow: the power turbine relaxes a higher volume flow, for which a considerably lower compression work in the gas turbine compressor has to be expended than for the combustion air. A relevant point here is the incompressibility of the water present in the compressed gas flow. With the increasing mass flow, the useful work output increases.

Side effects

With the method, performance increases of over 10% of the gas turbine output can be achieved. It is an open process; the water used is released into the atmosphere with the flue gas and is lost to the process. Technical side effects such as reaching the mechanical limit performance, reduced distance between the operating point and the surge limit of the compressor, mechanical erosion of the compressor blades by drops, changes in the step loads within the compressor and turbine, blade vibrations and reduced gaps must be controlled by suitable technical measures.

Web links

References to technical implementations can be found at: