The Engineering of Reliability into Waste Heat Boiler Systems

Abstract

Waste heat boiler systems are often a weak link in process plants and some failures have caused severe losses. The author considers that this situation can be avoided in future plants by following the guidelines laid down in the paper. The paper begins with a general description of a waste heat boiler system which is applicable to all processes. The evolution of the flowsheet for a typical plant is described and it is shown how the early involvement of engineering specialists can influence the choice of steam conditions and the positioning of items of equipment in the flowstreams, so as to ensure that reliable equipment can be designed and purchased. The early development of a computer model of the system is recommended since it frequently demonstrates how the duties of individual items deviate markedly from normal, under start-up, part-load and trip conditions. The various items of plant are described, potential problems are mentioned and methods of avoiding them given. In the case of boilers heated by process gas, reference is made to some of the special designs that have been developed for specific processes. The need to acquaint the equipment supplier of the special problems of a particular process is stressed, as is the importance of close attention to detailed design, fabrication and quality control. The main pre-commissioning steps are described. In operation, water quality is vital and continuous analysers are advocated in specified locations, with some linked to automatic trips which prevent contaminated condensate or feedwater from entering the treated water storage tank or deaerator.