Removal of Hydrocarbons from Drill Cuttings Using Flotation Enhanced Stirred Tank (FEST)

Abstract

Treatment of drill cuttings (DC) by washing processes consumes a considerable volume of solvents, resulting in high chemical wastes and operating cost. To minimize the chemical use, this work aims to develop an integrated process of dissolved air flotation (DAF) and mechanical stirring, called Flotation Enhanced Stirred Tank (FEST), as a pretreatment process for DC washing, in which total petroleum hydrocarbon (TPH) was a major pollutant of concern. The performance of an individual DC treatment process (stirring and DAF) was firstly investigated to determine the optimal experimental range. Then, response surface methodology with central composite design was applied to optimize three operational factors (saturated pressure (P_s), mixing speed (V_m), and treatment time (t)) for the integrated process, having TPH removal efficiency as the response output. Effects of hydrodynamic condition in terms of a/G ratio on the TPH removal performance were also analyzed. The experimental results revealed that mixing speed and saturated pressure were the significant factors affecting the TPH removal efficiency. FEST could yield the maximum TPH removal of 47% under the P_s of 4 bars, V_m of 400 rpm, and t of 70 min, showing its better performance than a single process from which less than 40% TPH removal was achieved. Combining DAF with stirring resulted in more turbulence in the system and thus improving the contact between hydrocarbon and bubbles. Therefore, better TPH removal could be obtained from FEST at lower a/G ratios compared to DAF. Furthermore, using saline water as a treatment medium was also possible. Overall, FEST exhibited its potential as an environmentally friendly process for the pretreatment of DC.