Membrane Distillation Crystallization Hybrid Process for Zero Liquid Discharge in QAFCO Plant

Abstract

Qatar fertilizer company (QAFCO) is one of the world’s largest single site producer of ammonia and urea with production capacity of 12,900 metric tons per day. Currently, QAFCO faces major challenges in terms of water streams management that is generated from many processes such as wastewater from Harbor-Bosch process and brine solution from multi-stage flash (MSF) desalination process. To protect the environment; QAFCO has been making an effort to minimize the disposal of all types of water disposed into the sea. Here, this project proposes to develop a viable and economically effective process that can reach zero-liquid discharge (ZLD) of all processed water or wastewater from QAFCO facilities. The best method for ZLD is membrane distillation crystallization (MDC) hybrid process that concentrates and minimizes the volume of wastewater/brine streams to form solid through crystallizer. Membrane distillation (MD) is a thermally driven membrane process. It applies low-grade energy to create a thermal gradient across a microporous hydrophobic to vaporize water in the feed stream and condense the permeated vapor in the cold side. This research work aims to evaluate the performance of MDC for ZLD using commercial/fabricated electrospun nanofiber membrane (ENM) PVDF –base membranes at different type water streams. A general observation, higher water vapor flux and water recovery were exhibited at higher feed conductivity at 70°C. Moreover, the fabricated hydrophobic PVDF ENMs results confirmed the formation of nanofiber at the membrane surface using scanning electron microscopy (SEM). In addition, the water contact angle values of PVDF ENMs were greater than 100° and have stable mechanical and chemical properties. The ongoing research work will conduct a comparison between the optimum PVDF ENMs and the commercial MD membranes in terms of water recovery, salt rejection%, fouling/scaling, amount of collected solid and energy consumption at optimum operating conditions in MDC. In addition, it will perform a techno- economic feasibility assessment of the MDC hybrid process.