Evaporator without separate condensate pre-heater

Evaporator without separate condensate pre-heater

Evaporator without separate condensate pre-heater

In this configuration all of the flue gases from the waste heat boiler are utilized for heating the condensate. The primary heat source for the deaerator is the evaporator which produces a water/steam mixture. Stork often accommodates connections for such flows in the deaerator and so this can be used as a heating medium.

The pressure/temperature in the deaerator evaporator is sliding and depends on:

  • the operation of the gas turbine
  • the percentage of supplementary firing (if installed)
  • supply temperature of the condensate.

The deaerator operation reaches a maximum during:

  • low gas turbine load
  • No supplementary firing
  • High ambient temperature (reduction of exhaust gas flow from GT)

In particular, the degree of supplementary firing and reduction of the condensate temperature lead to a drop in the deaerator pressure. The lower flue gas temperature at the inlet of the deaerator- evaporator results from supplementary firing, while the supply of condensate increases. These effects together result in a lower pressure in the deaerator- evaporator.

However, a minimum deaerator pressure level must be maintained in connection with the required water/steam velocity in the evaporator and the circulation requirements. The minimum values need to be specified by the boiler manufacturer/system designer.

Apart from a minimum pressure in the deaerator, the rate of pressure drop must also be limited. An excessively steep pressure drop gradient can result in cavitation in the boiler feed water pump. Stork is able to take account of the provisions necessary in the deaerator in order to achieve a minimum pressure and maximum pressure drop rate. The boiler manufacturer/system designer is responsible for setting both the minimum operating pressure and the permissible pressure drop gradient.