Reverse Osmosis at a Refinery

Chlorinated secondary effluent arrives at the pumping station, which is adjacent to the sewage treatment plant in Riyadh, through an open channel which flows to the pump station inlet basins. The 4.63 MGD of effluent is then pumped 19 kilometers to the refinery by either of two full capacity pumps which take suction from the inlet basins. The effluent is pumped through a 

Boiler Feed Wafer To Fire Wafer Storage 

24-inch diameter cement lined carbon steel pipeline. The pipeline is equipped with vacuum relief valves and air-release safety valves at the two highest points in the line plus air-release safety valves at the third highest point in the line. The pipeline is also equipped with pigging facilities (for pipeline cleaning) which consist of 2 pigs, a pig launcher and pig receiver. 

All surface waters and municipal effluents contain suspended solids as well as dissolved solids and the presence of suspended solids dictates the need for a pretreatment section. Experience has shown that effective removal of the suspended solids in pretreatment is a prerequisite to efficient reverse osmosis membrane performance. Suspended solids in secondary effluent are primarily organic in nature and, due to their small size, it is difficult to remove them by settling. Therefore, it is necessary to aggregate the smaller particles into larger particles which can more easily be removed by settling and filtration. 

The refinery clarification equipment has the capability of adding any of the chemicals mentioned above. However, lime clarification was chosen as the method to be used. The combined secondary effluent and the plant return streams (5.64 MGD) are pumped from the surge ponds to the rapid mix basin in the clarifier. The rapid mix basin has two compartments in series and each compartment has a high speed mixer. Lime and sodium hydroxide are added to the first compartment and these are vigorously mixed with the secondary effluent in both compartments. As a result, the pH of the effluent from the rapid mix basin is raised to between 10.8 to 11.0. At this pH, much of the bicarbonate in the water reacts with the lime and forms an insoluble calcium carbonate and the magnesium in the water reacts with hydroxyl ions to form insoluble magnesium hydroxide. 

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