Geometrical analysis of thermo-compressors in multiple-effects distillation units based on the second law of thermodynamics

Abstract

Thermo-compressors are used instead of mechanical compression devices in many industries and play a main role in the process. Through the process of designing desalination systems, amount of exergy dissipation is a very important economical factor. Most of the exergy losses in multi-effect distillation systems with thermal vapor compression (multiple-effect desalination–TVC) occur in the thermo-compressor. The aim of this article is to investigate geometrical effects in thermo-compressors by numerical methods based on the second law of thermodynamics to obtain lower exergy loss and consequently, higher entrainment ratio. A lot of geometrical parameters such as converging and diverging angles in mixing section, diffuser, nozzle location and also its throat area ratio affect thermo-compressors’ performance. The modifications in the above-mentioned parameters were applied to a thermo-compressor established in a desalination unit in Kavian petrochemical company which is working with 15 barg of motive pressure. Numerical simulation of the base model has an accurate agreement with experimental data with about 1.3% discrepancy in maximum discharge pressure and just 6.7% in entrainment ratio. Results of the analysis indicate that thermo-compressor’s performance is sensitive to the mixing area converging angle. The other parameter which mostly affects the performance is the location of nozzle in thermo-compressor’s body.

Keywords:

• Thermo-compressor
• Geometrical analysis
• Exergy analysis
• Multiple-effect distillation