Techno-economic analysis of cleaner alternatives for recovering ammonium chloride from wastewater generated by polyvinyl chloride thermal stabilizer plants

Abstract

The current conventional process for recovering NH4Cl from wastewater generated by organotin mercaptide-based polyvinyl chloride thermal stabilizer plants through evaporative crystallization is energy intensive and has not yet been discussed. Three energy-saving process variants, namely mechanical vapor recompression (MVR), double-effect evaporation (DEE), and thermal vapor recompression (TVR) processes, have been proposed and evaluated in terms of both technical and economic feasibility, treating the case as a cost-cutting project aimed to avoid off-site wastewater treatment costs. Comparative evaluation has also been carried out with the conventional (CON) process used as a reference. Under the studied conditions, the MVR, DEE, and TVR processes provided energy savings in the ranges of 60%–76%, 35%–43%, and 26%–37%, respectively, confirming that applying the three alternative processes for recovering NH4Cl results in a significantly cleaner and more sustainable recovery process. Under typical conditions and with a plant capacity of 5000 kg/h, the MVR, DEE, and TVR processes required an additional investment of 2.3, 1.0, and 0.2 million USD, respectively, compared to the CON process. The revenue was primarily driven by cost savings due to the elimination of off-site wastewater treatment, which accounted for 86.9% of the total revenue. Sensitivity analysis showed that the off-site wastewater treatment cost was found to be the most influential factor on economic feasibility. When economic targets can be traded off, MVR process is highly recommended as an alternative to the conventional energy-intensive process. If economic feasibility comparable to the conventional process is still targeted, DEE and TVR are recommended. The results of this study dismiss concerns that cleaner processes would have a negative economic impact.

Keywords

• Ammonium chloride
• Energy saving
• Evaporative crystallization
• Polyvinyl chloride
• Thermal stabilizer
• Wastewater