Operational optimization of low-temperature energy systems

Abstract

Low-temperature energy systems provide cooling at below-ambient temperatures, i.e. using refrigeration systems. The costs associated with refrigeration systems tend to be very large, essentially due to the high capital cost of the compression trains and the operating cost of the shaftwork required to drive them. Recent research has been focused on the synthesis of refrigeration systems. However, the optimisation of the operating conditions of existing refrigeration systems is an important challenge and little research has addressed it. This work addresses operational optimisation of refrigerated processes, taking into account an existing centrifugal compressor of an operational refrigeration system. Previous work on synthesis of refrigeration cycles is used as a basis and extended to address multistage centrifugal compressors with a common shaft and multilevel refrigeration cycles. For the optimisation of multilevel cycles, the refrigeration temperature levels and duties of each level are optimised to find a set of operating conditions that minimize the shaftwork demand of the compressors for a given process cooling duty while taking into account equipment constraints, which include the same rotational speed for different stages, minimum and maximum allowable inlet flow rates, etc.