Utility Exchanger Network Design for Non-Isothermal Utility Considering Process Control

Abstract

This paper investigates a preliminary control strategy based on bypass control loop of Utility Exchangers Network (UEN) for non-isothermal utilities in a Total Site Heat Integration (TSHI) system. Few details on the design and control of non-isothermal utility systems, e.g. hot water loops, that includes Total Site heat recovery are presented in the literature. Heat Exchanger Networks (HEN) can be considered as a combined Heat Recovery Network (HRN) and UEN for each individual processes within the Total Site. Control strategy presented in the current paper are based on the control of utility side in a process – utility heat exchanger match to control process stream target temperature and analyse Total Site (TS) utility system in a Process Integration point of view. Bypass control has been used in the research. A Hot Water loop as representative of a large industrial plant utility system is studied as a case study. The process stream segment target temperature to be achieved and process stream segment supply temperature and flow rate may vary up to ±15 %. The HW utility temperature in the loop is controlled by using indirect heat transfer from higher and lower level utility and by using HW loop bypass. A 24 h period has been considered for the study. Results show that the HW utility loop has a 2.4 MW heat deficit in time-average condition. By controlling the HW utility loop using the proposed heuristics, utility heating requirement may vary between 0.7 to 3.5 MW, which is supplied by the Low Pressure steam main.