Microwave Treatment of Oil-Contaminated Drill Cuttings at Pilot Scale

This paper details a new technology for the continuous treatment of contaminated drill cuttings at a throughput of 500 kg/hr, and can be scaled-up for use in offshore locations. The change in legislation for oily cuttings discharges in the North Sea at the beginning of the century resulted in the introduction of a 1% residual oil limit for discharged cuttings. At the time, because nothing was capable of achieving a 1% level offshore, only two options existed to deal with oily cuttings: containment for onshore processing (skip and ship), and injection (CRI). With time, a thermomechanical cuttings cleaning process has produced cuttings with oil <1%, although with a significant deck space impact and restricted throughput. Previous studies have shown that microwave treatment is able to reduce oil levels to well below 1% in a laboratory environment, and this work has studied the scale-up of the system to a 500 kg/hr continuous process. The manufacture of a pilot-scale cuttings treatment system involved the collaboration between microwave and electromagnetic engineering specialists, bulk solids handling, and process engineering disciplines. The feed cuttings are conditioned in a solids mixer, before being fed by way of a conveyor to a specifically designed microwave cavity. The oil is removed and recovered using an extraction and condensation system, with the product oil being very similar in composition to the base oil in the drilling mud. Residual oil levels of <0.1% are obtainable, and cuttings throughputs of 500 kg/hr are possible using a 30-kW microwave source. The microwave process typically consumes 60 kWh of electrical energy per tonne of cuttings, and the trade-off between microwave power, residual oil content, cuttings throughput, and overall energy requirements are discussed in this paper. This is the first step in the development of a modular system, with low-deck impact, flexible processing rates, and reduced environmental signature.