Simultaneous synthesis of non-isothermal water networks integrated with process streams

Abstract

This paper is an extension of our previous study [1] and addresses simultaneous synthesis of non-isothermal water networks heat-integrated with hot and cold process streams. Hence, the scope of heat integration is expanded by enabling heat integration of process streams such as waste gas streams and reactor feed and effluent streams simultaneously with the water network's hot and cold streams. A recently proposed superstructure [2] for the synthesis of non-isothermal water networks is extended in order to enable additional heat integration options with process streams. The model and solution strategy are modified in order to enable achieving the solution of the problem within the reasonable computational time. Pseudo heat exchanger cost was introduced in order to find heat exchange matches. They are used as constraints within the mixed-integer nonlinear programming (MINLP) model that simultaneously addresses the synthesis problem. The objective function of the proposed model accounts for operating costs, including fresh water, utilities and treatment operating cost, and investment costs of heat exchangers and treatment units. The results indicate that by solving a unified network, rather than stand-alone non-isothermal water network and separate process heat exchange network, additional savings in utilities consumption and total annualised cost can be achieved.