Designing compact heat recovery systems to increase energy efficiency

Abstract

Heat recovery in industry is limited by thermodynamic and economic factors. Increased heat recovery in an existing heat exchanger calls for higher costs in terms of capital and pumping due to increased exchanger size and pressure drop. One design option to offset the rapid growth of surface area to meet the upgraded heat load is to seek strategies to increase the heat recovery by increasing the heat transfer coefficient with a moderate increase on pressure drop. Compabloc heat exchangers have the construction features that make them suitable for such purposes. This paper presents a new design methodology for this type of exchanger and discusses its application in retrofit projects. The approach exploits the use of utility paths as the simplest and more practical way of identifying energy savings projects. The importance of analysing and quantifying temperature disturbance propagations is discussed. Applications to two case studies demonstrate the economic viability of using compabloc exchangers to achieve large energy recovery and savings. It is demonstrated that with an additional pumping cost of $66,776.12 USD/year, a total surface area of 1140.8 m2 and capital investment of $1062,272.0 USD, 24.8 MW of additional energy can be recovered, saving $5339,675.52 USD/year, giving a payback of 2.8 months.