Feed Distribution and Hunting in Marine Water-Tube Boilers

Abstract

Data and experience are given concerning the phenomenon of hunting in naval water-tube boilers and its elimination by arranging the internal feed water distributing piping to spray the water in the steam space of the boiler drum. Various internal feed-distributing arrangements are described, and calibration tests are given of various designs of feed-distributing piping. The paper discusses the factors causing circulation in a water-tube boiler, the conditions essential to give the equilibrium necessary for steady boiler operation, and the variations which occur in the steam volume below the water level in a boiler with changes in boiler load. The characteristics of boiler hunting are discussed and an analysis is given of the various factors in the hunting cycle. It is shown that hunting is due to the existence of a continuing time-lag between the rate of feed supply and the rate of steam generation, and that the time-lag and hunting are eliminated if the feed supply is heated to boiling point before it enters the circulation circuit. A review is made of feed-distributing arrangements in service, and various points are suggested to which consideration should be given to obtain a feed-distributing arrangement which will obviate hunting with highly rated water-tube boilers. Features concerning the water level control in naval boilers fitted with augmentors are discussed.