A Novel Approach to the Management of RO Concentrate Derived from Coal Seam Gas Water Treatment

The extraction of coal seam gas (CSG) produces significant quantities of brackish water. After separation, the brackish water is typically treated by RO plants to enable beneficial use of up to 90% of the water, with the remaining RO concentrate (or brine) stored until its final management is determined. Reducing brine volume through further treatment can significantly reduce the cost and legacy risks associated with long term brine storage. Traditionally the preferred brine concentrating methods has been through the use of capital and mechanical vapor re-compression type brine concentrators (BCs). BCs are not only expensive to construct, but require significant energy to operate (25 kWh/m3 of product water), which reduces the amount of gas that can be sold on the market. The undesirability of the high capital cost and energy demand plus the extraordinary scale of the CSG brine management problem have presented the opportunity to use more energy efficient methods. Working with one of the major CSG producers in Australia, CH2M HILL developed an innovative approach to RO brine concentration by combining a series of established treatment technologies in a unique manner. The process, referred to as MAX-RO, referring to maximum attainable recovery using ultra-high pressure RO. RO treatment is limited to 90% recovery by the level of silica in the associated water. At this recovery, silica in the RO brine reaches 200 mg/L, the safe level given the use of modern antiscalants. Where associated water salinity is 2,200 mg/L, the maximum attainable brine concentration is thus limited to 25,000 mg/L TDS. To overcome this limitation, RO brine is first treated chemically to remove silica and then filtered using a high-flux ceramic ultrafilter. The chemically stabilized water can then processed by ultra-high pressure RO (up to 1,800 psi) enabling a maximum brine strength nearing 160 g/L TDS. This represents a significant brine volume reduction while avoiding the heavy energy use associated with evaporative methods (75% less power input is required as compared to MVR) while employing readily available water treatment process equipment.

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