Simulation and optimization for compressor unit of cracked gas in ethylene plant

Abstract

This work is aimed at studying factors involved in polymer fouling for a cracked gas compressor in an ethylene plant by developing a HYSYS model and simulation. Wash oil and water have usually been decided to disperse or dissolve some polymers generated inside the compressor and to reduce the discharge temperature of the compressor respectively. They have also been used for an olefins plant’s gas feed type in order to decrease high polymer fouling with various amount of feed rate subjecting to operating condition design. However, in practice, wash oil has less impact on compressor discharge temperature, the main factor to consider high potential polymer fouling in the cracked gas compressor, and therefore has usually been hard to determine the feed rate. On the other hand, wash water has been employed to handle the variation of the temperature. Then, the flow rate of wash water needed to handle the temperature has been calculated by the HYSYS program. To simulate the process by HYSYS, information regarding the cracked gas operating condition has been gathered to formulate the HYSYS model and then has been used to validate the model. With the accurate model, the optimal wash water flow rate is obtained with respect to its constraint of 1,200 l/hr to 100 l/hr to achieve the discharge temperature of the compressor at 90 ℃. Optimization results have shown that the optimal wash water flow rates of the 1st, 2nd and 3rd stage compressors are at 465 l/hr, 380 l/hr and 505 l/hr, respectively.