Analysis of typical chloride solution treatment by osmotically assisted reverse osmosis for evaluating application potential in geothermal reinjection well protection

Abstract

Ions in geothermal water is one of the main inducements causing well corrosion and fouling problems, which sequentially increases maintenance cost and shortens facility lifespan. This work proposed to use split co-current osmotically assisted reverse osmosis to pre-treat geothermal water into diluted and concentrated solutions after heat utilization, for achieving internal dilution and ion enrichment purposes simultaneously. By establishing the mathematical model and calculation procedure under full water permeation, the discharge properties and energy consumption performance of single and multi-stage configurations to treat 4 typical chloride solutions (NaCl, KCl, CaCl2 and MgCl2) in geothermal water are mathematically analyzed. Beneficial from the inlet split of solute amount and water permeation ability under any appliable hydraulic pressure difference, the system is capable to treat salt water into diluted and concentrated solutions effectively. It is estimated that concentrated side achieves more significant concentration variance than diluted side, for it experiences steeper variance rate with the decreasing of solution volume. Upgrading single stage to multi-stage configuration, the treatment degree can be further enhanced especially as the concentration of inlet solution is high, but this will induce the continuous accumulation of energy consumption generated by the water permeation at each stage as expense.