Low temperature process cooling is an energy demanding part in many chemical production processes. Cooling systems operating at very low temperatures consume a large amount of high quality energy such as electricity or high pressure steam, used to drive refrigeration compressor units. Hence decreasing refrigeration load can make a major improvement on the process energy balance. In industrial process clusters with several processes operating at low temperatures, it is important to investigate opportunities for exchange of low-temperature energy between processes. This paper presents an investigation for a chemical cluster located in Stenungsund on the West Coast of Sweden. One chemical plant within the cluster operates two compression refrigeration systems at its steam cracker plant. One system is a propylene-based system with three temperature levels between 9 °C and -40 °C, driven by high pressure steam turbine drivers with a capacity of ca. 22 MW. The other is an ethylene refrigeration system with three temperature levels between -62 °C and -100 °C, electrically driven with a capacity of ca. 4.5 MW.
A previous Total Site Analysis (TSA) study of the cluster focused on integration opportunities within the cluster above ambient temperature, thereby decreasing the overall hot utility and cooling water and air demand. Utility savings below ambient temperature were not investigated in detail. This paper demonstrates how Heat Integration (HI) tools such as TSA and exergy analysis can be applied to target for shaft work and hot utility savings for processes and utility systems operating below ambient temperature. In total a savings potential corresponding to 15 % of the total shaft work consumption of the refrigeration systems was identified. In addition ca. 3.3 MW of utility steam which is currently used for sub-ambient process heating can be saved in addition to shaft work savings.