Modelling, Integration and Optimisation for Recirculating Cooling Water System Operation

Abstract

Recirculating cooling water systems are extensively used for heat removal from processes in the process industry. Two aspects are focused on to improve the economic performance of cooling water systems and processes with cooling demand: the integration of key components in cooling water systems, including cooling towers, cooler networks and piping networks, and the integration of cooling water systems and processes with cooling demand. For the internal integration of cooling water systems, integration models were established for the operation of cooling water systems in the literature [1]; [2]; [3]. There are some limitations in the literature: they were limited to one cooling tower and cooler networks in parallel configurations; detailed heat transfer in coolers is not considered in the literature [1]; the pressure drop in coolers is ignored in the literature [2] and [3]. To overcome those limitations in the literature, in this thesis, a nonlinear integration model of cooling water systems is developed for multiple cooling towers and cooler networks in both parallel and complex configuration. The model includes cooling tower modelling, cooler network modelling and hydraulic modelling. In cooling tower modelling, correlation expressions of tower characteristics, air inlet conditions and water inlet conditions are developed to predict temperature of water leaving towers and humidity of air leaving towers respectively. In cooler network modelling, detailed heat transfer in individual coolers is considered. In hydraulic modelling, pressure drop in both coolers and pipes are taken into account. The nonlinear model is solved by the solver CONOPT in GAMS to determine the optimal water distribution and air flowrate. For the integration of cooling water systems and processes with cooling demand, a new equation-based simultaneous optimisation method is proposed, in which an integration model of cooling water systems and processes is developed. Condensing turbines are taken as an example to illustrate the method. Case studies prove that the models are effective to solve the problems. The standalone optimisation of cooling water systems reduces the operating cost by 5.6%, compared with the base case. The simultaneous optimisation increases the total profit by 337 k£/yr, compared with focusing only on maximising the power generation of condensing turbines.

Date of Award	24 May 2017
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Robin Smith (Co Supervisor) & Nan Zhang (Main Supervisor)