Present-Day Feed-Water Treatment for High-Pressure Boilers

Abstract

The paper is concerned with industrial boiler plant generating steam for power and process at pressures of 1000–2000 lb/in2 and having a high make-up of treated feed water. The capital and running costs of the water treatment plant and process are therefore much more important than in power station boilers where make-up is small. A few figures are given to illustrate this point and a plea is made that water treatment should be studied carefully at an early stage in any project for new boilers. The quality of feed and boiler waters now in use, or recommended, is shown in two tables and it is clear that above about 1500 lb/in2 the trend is toward ‘pure’ feed water, though this may not be essential. The next section discusses the control of steam purity to prevent corrosion and deposits, by elimination of carbon dioxide and oxygen, addition of volatile amines, control of the concentration of salts and silica in the boiler water, and the possibility of steam washing. A short description is given of the circumstances which, it is believed, have caused numerous cases of corrosion in high-pressure boilers, and countermeasures are suggested. These comprise strict deaeration of the feed water, addition of alkalis to the boiler feed water, to prevent corrosion in the pre-boiler equipment and in the boiler, and the avoidance of hot spots or sluggish flow by boiler design and operation. The paper concludes with a reference to the prevention of corrosion in boilers which are standing during erection or normal operation, and to acid cleaning.