Development of flotation enhanced stirred tank (FEST) process for petroleum hydrocarbons removal from drill cuttings

Abstract

This work aims to develop the treatment process for the removal of total petroleum hydrocarbons (TPH) from DC by using the combination of air floatation and stirring processes, called Flotation Enhanced Stirred Tank (FEST). Initially, stirring, induced air flotation (IAF), and dissolved air flotation (DAF) are individually investigated over DC washing. Afterward, the combination process between “stirring-DAF” and “stirring-IAF-DAF” are continuously observed for finding the better conditions of TPH removal efficiency. To optimize the operational terms of the treatment process, the Design of Experiment (DOE) is applied to design the experimental conditions within the central composite design-response surface methodology (CCD-RSM). Consequently, the result of the stirring process showed that the higher rotational speed represented a better result of removal efficiency, i.e., 200, 400, and 600 rpm could remove TPH around 20%, 25%, and 30%, respectively, for 1h of treatment time. In IAF treatment, the results indicated that the lowest airflow rate (1 LPM) gave the least treatment performance compared to the higher airflow rate (2-3 LPM). After 60 min of treatment time, the washing performance using 2 and 3 LPM was about 28% and 30% of the removal percentage, respectively, while it showed roughly 22% of TPH that eradicated by 1 LPM. Moreover, it was signified that almost 40% of that was removed by microbubbles generated by a saturated pressure 4 bars at the same time in the DAF unit. Hence, to obtain the improved TPH removal percentage, the studied DOE of the combination process between “stirring-DAF” and “stirring-IAF-DAF” were examined. The results demonstrated that the optimum removal percentage would achieve approximately 50% of TPH from DC when Ps was 4 bars, Vm was 400 rpm, and t was 70 min with a correlation R2 = 0.8691. Then, in the three combination units that contained four variables (Qg, Ps, Vm, and t) were analyzed by varying their studied levels in DOE as well. Similarly, the optimum elimination of TPH would receive approximately 60% with the conditions of Qg was 2 LPM, Ps was 2 bars, Vm was 800 rpm, and the time t was 60 min.