Design and Construction of Power Station Feed Heaters

Abstract

The paper presents a survey of a number of aspects of the design and construction of feed heaters for present-day steam-turbine cycles. Many papers have been published in recent years which cover a variety of the detail factors which can enter into the design of a feed heater (for example, the design of tube plates). No attempt has been made to add to such information. The aim of the paper is to present the overall picture and to confine detail description to those items where existing literature is scanty or where the author feels that information of interest can be presented. Firstly, a methed is discussed whereby the optimum economic size of the individual feed heater can be investigated. This is followed by consideration of the thermal design of the heater nest, and of the pattern of temperature difference introduced by the advent of heaters containing desuperheating and drain-cooling sections. Several methods are shown by which such sections may be arranged in a feed-heater nest. The remainder of the paper deals with particular aspects of detail construction. The choice of tube materials and their safe working stresses is discussed. The problem of the production of a satisfactory roller expanded tube to tube-plate joint is examined in some detail, together with methods for the consistent production of this joint. An account is given of development work on means for evaluating the soundness of expanded joints by both non-destructive methods and by tube pull-out tests. A description is given of the investigational work which has taken place and has led to the introduction of welded tube to tube-plate joints with both ferrous and non-ferrous tubes. Information is presented regarding the amount of torque necessary to achieve desired loadings in heavy bolted constructions and the problem of achieving uniform bolt loading is discussed. A method of investigation is described which enables the resilience of compressed asbestos jointing to be examined when subjected to a cycle of loading, including heating which simulates working conditions as closely as possible. The main problems occurring in the design of tube plates and heater headers are examined in a brief discussion.