There are applications for steam coolers in very complex situations. One common example is if a cooler is not working continuously and only has to function occasionally. This can occur for example during start up and shut down or in case of an emergency to protect the main steam lines. In this instance the nozzle section will become very hot. The moment the cooler is required to start, thermal shock will occur and the cooler will be permanently damaged. In practice a very limited number of cycles can be expected before the cooler is damaged.
After years of investigation, Avs and Hora developed a solution for this particular problem, the “cooled desuperheater”.
To avoid thermal stress in the cooler valvebody, the temperature differential between the cooling water and the superheated steam temperature should be significantly reduced. A temperature reduction of the valvebody to the saturated steam temperature, instead of superheated, will bring the temperature differential down to figures which will not lead to thermal shock. The cooler is now suitable for numerous starts and stops.
Life expectancy of > 25 years. Number of possible cycles > 100.000
A limited amount of saturated steam is bypassing the superheater and is brought into a “cooling jacket”. This saturated steam is cooling the valvebody, keeping it on saturated temperature. The saturated steam leaves the jacket and will mix up with the super heated steam. The saturated steam flow to the cooler is controlled by a small control valve and a manual stop check valve.
The first four coolers have been installed at a large English powerplant recently. The results are as expected: excellent!