Economic application of heat pumps in integrated distillation systems

Abstract

The influence of relevant parameters on the economics of distillation plants involving distinct heat pump cycles is scrutinised and the results are compared to conventional and integrated schemes. On the basis of the COP, energy costs and efficiencies, simple expressions are proposed for preliminary economic analysis and design of heat pump assisted distillation. The influence of heat pump type, purity requirement, column pressure drop, feed rate, energy cost, relative volatility etc. on the energetic aspects and economic range of application is presented. Heat pumps can be economical substitutes for conventional distillation process design whenever direct refrigeration or chilled water are required for condensation and for separating close boiling mixtures in columns of small pressure drop. A design strategy for selecting the most economical distillation system, considering different types of heat pump structures (vapour recompression, bottom flash, closed cycle, absorption cycle), is proposed, based on pinch technology, primary energy rate, energy cost factor and estimated payback time of excess capital. The strategy is demonstrated by industrial case studies.