A Heat-Recovery System for Process Steam Industries

Abstract

A new cost-effective method for integrating heat recovery into a process steam system has been conceived which conserves boiler fuel and capital—the cost of the recovery components is less than the cost of additional boiler capacity. The essential element is the use of the process equipment not only as the condenser of a boiler loop but also as the condenser of a refrigeration cycle. This method can be incorporated into any process steam system where sizable effluent losses are available from the processes being served. This article presents a case study of an application to paper making. The company, which cogenerates process steam and electricity, was planning to add an additional paper machine. Although there was some spare boiler capacity, the new machine would have required investment in an additional boiler. Inasmuch as some of the existing capacity was gas-fired, the tentative plan was to add a sizable coal-fired boiler. A study was made of a design incorporating the new heat recovery method, as an alternative to the coal-fired boiler. Actually, several versions of the new method were analyzed—for both technical and economic feasibility. Virtually every version saved capital and saved fuel, although electric power production was reduced. The economic analysis—taking into account interest, depreciation, and taxes—showed that most versions were preferable to the planned new boiler.