Performance Analysis of a Novel Compact Flotation Unit

Abstract

The oil and gas industry produces large quantities of water as a by-product of petroleum production. Discharge specification of produced water requires efficient management and sophisticated technology. Conventional technologies such as those based on gravity separation, cyclonic separation method, filtration techniques, flotation technique, and natural gas/air sparge tube systems are used for treating produced water. However, most, if not all, of these technologies require a large footprint. This problem has created a challenge for the produced water industry, as well as for operators managing the offshore production facilities. Responding to the challenge at hand, Siemens Water Technologies Corporation has developed a novel compact flotation unit (CFU) equipped with a dissolved gas flotation (DGF) pump for treating produced water. The CFU has a small foot print and shorter residence time. The DGF pump is equipped with a unique, dual-sided impeller, which pulls the blanket gas on one side and the produced water on the other. Under applied backpressure, the gas entering the DGF pump dissolves in a portion of a recycled, cleaned water stream. The dissolved gas generates bubbles due to the pressure drop when the mixture of produced water and gas passes through a special valve before entering the CFU. The ratio of the inlet produced water flow rate to the DGF pump output rate plays an important role in optimum separation of oil droplets from the produced water. Besides the above-mentioned ratio, generation of an adequate number and size of bubbles provides another critical key factor in efficient operation of the CFU system. To validate our theoretical approach regarding the controlled forced vortex of the multiphase flow, we performed various tests in the shop facility of Siemens Water Technologies Corporation, as well as on a platform facility offshore Louisiana. We used a response surface methodology technique to analyze the CFU performance data and to generate an optimum surface response for free oil and grease removal efficiency. For optimizing the size of the piping and CFU dimensions, we used the rigorous yet simple principles of the constrained similitude. The free oil removal efficiency results in the shop and field tests, for CFU without the use of packing material, were satisfactory. Additionally, we found that CFU system tests resulted in the removal efficiency of water soluble oil (WSO). We did not expect this additional outcome as the CFU system was not designed to affect the removal of WSO.