Integration of low-grade heat from exhaust gases into energy system of the enterprise

Abstract

In the paper is presented the way of Process Integration application for waste heat utilisation from exhaust gases streams with partial condensation. It is based on the construction of Hot Composite Curve representing the gaseous mixture cooling with accounting for the gas-liquid equilibrium of condensable vapour part. With Cold Composite Curve for streams requiring heating, the Pinch Point is determined. Then the structure of Heat Exchanger Network (HEN) for utilised Heat Integration into the energy system of the factory is developed accounting for the possible splitting of two-phase flow on gas and liquid streams and selection of plate heat exchanger (PHE) types for specific positions in HEN. The method is illustrated by a case study of heat utilisation from exhaust gases after superheated steam tobacco drying and flue gases from natural gas-fired boiler. The heat transfer areas of PHEs in HEN are optimised with the total annualised cost as an objective function. The payback period of the received solution is less than four months with a substantial saving of energy, reduction of greenhouse gases and other harmful emissions of combustion processes.

Review of Developments in Plate Heat Exchanger Heat Transfer Enhancement for Single-Phase Applications in Process Industries

“…Process integration with the use of efficient PHEs for a carbon dioxide post-combustion capture unit HEN [145] enabled a decrease in energy consumption by 24% compared to the decrease of 11% that could be obtained with the use of shell-and-tube heat exchangers, with over 10% lower investment costs. Process integration with the use of PHEs for waste heat recovery from exhaust gas streams at tobacco factories [146] resulted in a decrease in carbon dioxide emissions by 600 t/y, with a payback period of about four months. The importance of using PHEs in the development and retrofitting of HENs for different industries was emphasised by Li et al [147] and shown through practical examples of HEN retrofitting with a detailed PHE design in [13].…”