Process simulation of high pH reverse osmosis systems to facilitate reuse of coal seam gas associated water

Abstract

• First simulation of HERO process for CSG associated water treatment. • AqMB software comprehensively evaluated water treatment process options. • Identified major costs as acid consumption and power for air stripper. • Substantially improved economics by softening with sodium exchanged resin. This study has revealed the potential for a high pH reverse osmosis system to desalinate coal seam gas (CSG) (or coal bed methane (CBM)) associated water to facilitate beneficial reuse. To promote technology uptake in the CSG industry greater insight was required to understand the optimal water treatment plant design, the influence of solution composition, and process economics. Therefore, AqMB software was used to simulate the treatment of three CSG water compositions. Unit operations included: Filtration; Softening; Air Stripping; pH raising; and Reverse Osmosis. In all cases, the product water met reuse guidelines. However, process economics were less favourable as solution concentration increased. Hydrochloric acid regenerant for the cation resin was prohibitively expensive (up to A$17,554,687 per annum) and its use required air stripping to remove carbon dioxide formed in acidic conditions (power consumption 70 % of total process demand). Acid solutions also required large amounts of sodium hydroxide (up to A$4,546,682 per annum) to reach pH 10 wherein silica species were soluble. Use of a sodium chloride regenerated resin plus removal of the air stripping stage substantially improved economics to the point that the operational expenditure was predicted to be A$417 per ML of water treated; a value comparable to conventional reverse osmosis desalination units. AqMB software was advantageous in that it; simulated the entire water treatment process, not just reverse osmosis; generated robust predictions; and estimated operational costs. As an outcome, rapid interrogation of water treatment process designs was now possible.