Lithium Bromide Refrigeration Unit Control System Design

LiBr absorbed type refrigeration is an economy refrigeration equipment that makes cold water or cold and hot water by steam, hot water, fuel oil, gas and many waste heat. It has many good features such as lower power consumption, lower noise, stable running, wide energy adjustment, high automatic control, easy to fix, maintain and operate etc. And it has notable advantages on using low potential heat energy and waste heat. In addition, the system is also used widely because of no air pollution and no damage to ozone layer.The LiBr refrigeration station of Shandong Aluminium Co, Ltd was built in 1995, designed and manufactured by their own company. At that time, its control system was simple, less stable, more control parts used. So many failures were happened caused because of aging after more than 10 years' running. Therefore the company decided to rebuild abnormal unit.This paper introduces the redesign of control system for the refrigeration system. The Programmable Logic Controller (PLC) has high reliability, special application of technique to industry, which will be used in this control system. The system can be touch controlled on the big size liquid crystal screen. It has dynamic flow chart display, working condition display, failure alarms display ,etc. So the PLC can reduce the number of separate part used and trouble rate. In order to improve the reliability of the system, double PLC that is called double redundancy control will be used in the system. Once one PLC makes fault, the other can ensure normal control of the unit in time so it avoids damaging the unit because of stop working suddenly.The design of the control system mainly includes five parts: safety protection system, energy adjustment system, motor speed regulation system of frequency modulation, start and stop control system, manul control system. The safety protection system is to protect and monitor the whole set; The energy adjustment system is to match the refrigeration energy with the environment heat and completes the energy adjustment of the set; motor speed regulation system of frequency modulation completes the adjustment of cycling flow of lithium bromide; start and stop control system completes the normal or abnormal stop and start of the unit; manul control system completes the operation and control of the set by manual means.This control system is provided with high automatic level. It can control start or stop using one key, automatic control energy, liquid level automatic adjustment, automatic deal with light fault, important fault which must be given alarm and diluted to stop the unit. The design of the program emphasizes to improve adjustable quality of the energy and liquid level and increase the economy and stability, thus it is able to make all the system running safely and efficiently.