In power plants operating with overheated steam it is often necessary to control pressure or temperature of the fundamental energy medium. The pressure of the steam can be directly and almost immediately controlled by a feeding pump upstream a steam generator, e.g. a boiler. However, it is much more complicated concerning the steam temperature. For this reason, there are mostly used steam coolers controlling its temperature by injecting cooling water directly into the steam flow.
In general, the steam cooler has a shape of a tube with a nozzle at its end. The coolers are inserted directly in the steam pipeline to which these are mounted by demountable flanged joints. If it is needed, this design enables easy dismantling of the device during the shutdown of the energy unit. Steam coolers are based on the principle of heat exchangers. The principle of cooling water spraying may vary. However, in general the cooling water supplied through the pipeline into the nozzle shall have the same or slightly higher pressure than the pressure in the steam pipeline. This water is supplied into the cooler’s nozzle from which it is sprayed into droplets dispersed as finely as possible. Thanks to that the evaporation surface increases many times and water droplets are mixed with the steam flow much better. As soon as the water dispersion is in the steam pipeline, due to the high temperature it is being evaporated, which is a process during which the evaporation heat is supplied to the evaporated water. Therefore, the flowing steam is deprived of this part of energy and its temperature drops. Design of the steam coolers is strengthened by one or more factors influencing the cooling process. It is the cooling water flow entering the steam cooler, pressure drop during expansion of water during spraying from the nozzle, velocity of the sprayed water, size of the water dispersion droplets, velocity of the steam and water flow as well as turbulences generated during mixing of steam with water.
In case of installations under very high temperatures of superheated steam, e.g. in power plant steam systems, the inner part of the steam pipeline is often equipped with shields from sheet metal rings at the point of spraying, that is to prevent eventual contact of water dispersion droplets and the wall of the pipe that has substantially higher temperature than water. Water contacting the wall of the pipe, in case of abrupt cooling at the contact point would cause additional stress, that would have a negative impact on the service life of the steam pipeline.
One of the biggest advantages of steam coolers is, that these do not contain any moving parts. They are able to control the temperature within a wide range of steam flow. And they can have dimensions for steam flows ranging from tenths of kg/hour up to hundreds of tons/hour.
Steam coolers may be made of carbon, stainless steel, refractory alloyed steel and nickel alloys.