Process Waste Heat Recovery with a Supercritical Carnot Engine

Abstract

We describe the optimization of a supercritical CO2 Carnot engine aimed at utilizing waste heat from industrial processes. The approach is illustrated using data from a flow sheet for a toluene production chemical process [1], [2]. First, the maximum power that can be drawn from a stream carrying waste heat in the process is calculated. This heat is coupled with a supercritical working fluid Carnot engine and calculations are carried out to optimize the size and frequency of the engine. The impact of compression ratio, upper isotherm temperature, and engine pressure are considered. It is found that with a relatively small engine and frequency, on the order of 1.5 L and 50 Hz, having a moderate upper isotherm temperature and a compression ratio of 2, almost 1 million kWh of energy is recovered from a single waste stream, thereby reducing cooler loads, energy costs, and environmental emissions. The approach provides a novel computational adjunct for calculating the efficient potential recovery of waste heat in chemical process design.