New fouling prevention method using a plasma gliding arc for produced water treatment

The objectives of the present study were to test a new plasma-based method for bicarbonate removal in water produced from hydraulic fracturing for shale gas and to verify bicarbonate removal as a mechanism for mineral fouling prevention. The study employed dual hypotheses: (1) gliding arc plasma can reduce bicarbonate concentration of produced water to negligible levels, and (2) water without bicarbonate content is unable to cause mineral fouling in the form of calcium carbonate scale even in the presence of extremely high concentrations of calcium ions as is often found in produced water. The plasma treatment of produced water reduced the concentration of bicarbonate ions from a range of 684–778 ppm to zero. Subsequently, heat transfer fouling tests were conducted with water samples, where the concentration of bicarbonate ions varied from 0 to 500 ppm with a fixed concentration of calcium ions of 5000 ppm. The weight of mineral scale that accumulated on a heating element over time was determined. The present test results showed that no fouling was formed over 30 h on the heating element in the water without bicarbonate ions. This proof-of-concept study demonstrated that plasma treatment is capable of reducing the concentration of bicarbonate ions in produced water to a level where CaCO3 fouling can be prevented on a heat transfer surface. The plasma gliding arc may represent a new non-chemical fouling prevention method for the treatment of produced water. © 2014 Elsevier B.V. All rights reserved.

The present study investigated the feasibility of using a plasma gliding arc discharge (GAD) to prevent CaCO3 fouling in produced water. A two-part mechanistic approach was employed to demonstrate the GAD plasma treatment method. The study demonstrated that the GAD could effectively reduce the bicarbonate ions to zero in produced water. Subsequently, the effect of bicarbonate modulation was verified as a mechanism for CaCO3 fouling prevention. Additional research is necessary to investigate reasons behind the differences in required plasma treatment time to achieve complete bicarbonate removal. Future studies should also include the following two topics: (1) a comprehensive experimental fouling study of scale thickness versus time for given heat flux and initial water conditions; and (2) investigations of methods for increasing the energy efficiency of plasma treatment such as plasma discharges with operating parameters conducive to lowering bicarbonate concentration in produced water as a way of potentially allowing for thermal treatment of sea water and wastewaters with a high mineral content. Acknowledgment