Optimization of combined Reverse Osmosis: thermal Zero Liquid Discharge system parameters for an Ammonia and Urea production complex

Abstract

Zero liquid discharge (ZLD) has shown to be a promising technology to recycle water with good quality. The ZLD objective is to purify the water from all the liquid waste. The ZLD approach is concentrated on reducing wastewater for possible reuse. In conventional ZLD systems, thermal processes are fundamental. The biggest challenge to implement thermal ZLD systems widely is its intensive energy consumption. As a solution, thermal ZLD systems are integrated with membrane-based reverse osmosis (RO) technology to reduce both capital and operational costs. This study, therefore, focuses on the optimizing a RO/thermal ZLD system based on one of the most important parameters of design—the salinity of the reject brine of evaporator. To give more practical aspect to the results, solution is based realistic design data of a petrochemical complex as the producer of ammonia (2050 ton day−1) and urea (3250 ton day−1). Results show that increasing the salinity of brine stream in evaporator reduces the total required heating surface area of the ZLD plant as well as its required power. This decrease is evident at lower amounts of Xb, but the rate is lowered with increasing of this parameter. So, further increase in Xb does not have much effect on reducing the total heating surface area and power consumption. It means that there is an optimum amount of Xb which can be selected for different applications.