Air Separation Device Purification Systems, Energy-saving Control System

Air separation plant is an important part of petrochemical industry production equipment, is one of the important objectives of Chinese energy conservation and emission reduction. In this paper, the molecular sieve purification system of the air separation plant is researched, the distributed control system is designed to transform the research object and then conserve energy and reduce emission.In selecting the control scheme, the original molecular sieve purification system is an open-loop control system that switching at regularly intervals, and the moisture and impurities are absorbed alternatively by two molecular sieve absorbers of this system, and a lot of waste nitrogen is used, and the life of molecular sieve is reduced. While the closed loop control system designed in this paper has the ability of anti-interference and self-adjust, besides it can decide whether to switch molecular sieve according to the feedback value (the carbon dioxide content at the outlet) and stander value of the system, the amount of waste nitrogen can be reduced and the life of molecular sieve can be extended.In transforming the equipment, the Programmable Logic Controller with strong anti-interference ability and communication function is chosen. The carbon dioxide content at the outlet of molecular sieve is detected on-line by infrared gas analyzer, and molecular sieve is switched automatically according to the carbon dioxide content, so that the automatic control of molecular sieve purification system of air separation device can be implemented.In updating control strategy, due to the close affinity among different processes, a small amount of irrelevant variables is analyzed using partial least-squares regression, in order to control the whole system. The maximum cycle time of alumina and molecular sieve according to the total air pressure, air temperature and relative humidity, besides the thickness of alumina and molecular sieve is computed, the statistic information is extracted from the history data of molecular sieve purification system, and the statistic model of molecular sieve purification system is built using partial least-squares regression, so that the carbon dioxide content at the outlet of molecular sieve purification system can be predicted, and then the switching time of molecular sieve purification system can be controlled.The experiments and result of field operation shows, the automatic control of molecular sieve is realized by the purification system of air separation designed in this paper, the energy consumption is efficiently reduced, the demand for energy control is met, and the object of energy conservation and emission reduction of molecular sieve purification system is realized.