Some Technical Aspects of High-Pressure Boiler Design

Abstract

In introducing the subject the authors suggest a classification of boilers on a pressure basis. Alternative methods of drum construction are reviewed, leading to an investigation of the effects of higher saturated steam temperatures on the physical characteristics of the metal and the factor of safety. Attention is paid to the analysis of stresses induced in the drums of large high-pressure installations, with comments on the limitations of standard design rules and formulae. Similar treatment of the subject of boiler tubes follows, attention being directed particularly to the combined effects of temperature and stress. The importance of accurate estimation of furnace exit temperature, especially in relation to superheat, and the effects of modern designs of water-cooled furnaces are then discussed. The influence of radiant heat emission from non-luminous gases in the convection passes is emphasized. A simple graphical method for determining the rate of natural circulation is outlined and the retarding influence of high pressure is discussed. Orthodox designs of high-pressure boilers, the relative merits of which are compared, present no serious difficulty in operation, providing adequate attention is paid to feed water treatment, some aspects of which are discussed. Further developments are contingent upon the economic extension of the range of commercial heat-resisting metals; the adoption of more logical and adequate rules and regulations governing design; and closer investigation into the behaviour of tubes, etc., under high pressures and temperatures and subject to the conditions prevailing in a boiler when in service.