Linc Energy knows that one of the challenges involved with the processing of UCG syngas is dealing with wastewater. The water produced from a UCG operation is not comparable to water produced by the coal seam gas (CSG) industry. CSG water is derived from dewatering of the coal seam. Consequently this produces vast quantities of saline water (this may be several hundred mega litres (ML) per year) which consequently must be stored in dams or treated for other uses.
Conversely, water produced by the UCG process is not from dewatering, but from the gasification process itself, and is therefore of only minor quantities. When syngas is produced, it is ‘wet’ and contains products which require separation before the gas can be processed by the Gas to Liquids (GTL) plant. The wastewater is organic, and is primarily sent to lined on-site dams for storage. Organic water is not difficult to treat, and there are a variety of tried and tested treatment processes, many of which are biological, which can be applied.
In 2009 Linc Energy commissioned Veolia Water Solutions & Technologies to custom design and build an advanced wastewater treatment system. The system comprises a series of operations including a three stage aerobic Moving Bed Biofilm Reactor (MBBR®), a two stage de-nitrification system, clarifier, sand filter and a granular activated carbon filter. The unit can handle a throughput of 24,000 litres per day. Diagram 1 provides an illustration of the current MBBR process employed at Chinchilla.
The MBBR technology is an advanced and efficient biological wastewater treatment process. It is based on specially designed plastic biofilm carriers or biocarriers that are suspended and in continuous movement within the tanks. The biofilm grows protected within the engineered plastic carriers, which are carefully designed to have a high internal surface area. With this technology it is possible to handle extremely high (organic) loading conditions without any problems of clogging, and enables Linc Energy to treat its wastewater on a relatively small footprint.
Currently, the water quality output from this process is very good, with most of the organic content being removed. Further final water quality improvements are proposed by the addition of advanced water treatment unit operations, such as ultrafiltration and reverse osmosis, which in turn will provide greater opportunities for reuse options. These include primarily re-injection into the coal seam in order to maintain the hydrostatic pressures required for the gasification process.