Technical and economic analysis of ethylene production process with considering energy and water minimization through pinch technique

The current research aims at finding a new appropriate way to optimize and reduce water consumption by using various forms of pinch technology in petrochemical complexes due to high rate of water consumption. For this purpose, precise studies were conducted on ethylene plant. In this research, cracked gas compressor (CGC) system was considered to analyze energy and minimize water consumption of heat exchanger network (HEN). Initially, process of the CGC system has been simulated with Aspen HYSYS. Next, Aspen Energy Analyzer software was used to identify cooling water (CW) heat exchangers and economic analysis of HEN. Consequently, composite curves and grand composite curves and other results of HEN simulation were examined. The results of HEN simulation indicate that 91% of cooling loads provided by CW utility is the most widely used fresh water. Despite water circulation system of cooling tower (CT), the rate of water loss is high in this utility. As the design temperature is 40 degrees C and the minimum approach temperature (Delta Tmin) is 10 degrees C, the new utility pinch point has been estimated 50 degrees C. In proposed modified case, air coolers were considered before the CW heat exchangers of the CGC system. In this way, air-cooled (AC) utility covers up cooling loads up to 50 degrees C in the modified unit. Then, the modified unit was compared with main unit. In the modified unit, 78% of cooling loads of the HEN have been covered by AC utility in which this action leads to 86% reduction in energy and water consumption of CW heat exchangers and CT. By reducing the rate of water loss in CT circulation systems, cost of supplying fresh water reduced to the lowest possible which leads to 34% optimization in HEN operating cost in the modified unit. Also in the CGC system, steam turbine is used for supplying power consumption of compressor used to CW steam turbine condenser. This condenser is the most commonly used equipment in terms of water consumption, so that there is 32% more than the total water consumption of the HEN. In the last part of this study, AC steam turbine condenser replaced the CW steam turbine condenser in the modified case. So in this case, the use of AC steam turbine condenser with power consumption (980 kw) leads to 98% reduction in water consumption of the steam turbine condenser.

Automated summary

The research aims to find a new way to optimize and reduce water consumption in petrochemical complexes. The cracked gas compressor (CGC) system was analyzed to minimize water consumption of the heat exchanger network (HEN). By using air coolers and replacing the CW steam turbine condenser, significant reductions in water consumption were achieved. The results show a potential for 34% optimization in operating costs and a 98% reduction in water consumption of the steam turbine condenser.