The Modified Configuration of Wet Wash System in the Gulf of Thailand

"Wet Wash" is a concept whereby cuttings are fluidized then sent to centrifuges to seperate the fluids from the cuttings. A modified configuration of this Wet Wash system improves fluids performance while minimizing environmental impact and optimizing operating costs. The original Wet Wash system, introduced in 2006, started at the shale shakers where big cuttings were removed by the scalping deck and diverted overboard. Only the small cuttings from the primary deck were fluidized and transported to a big bowl centrifuge. For the original system, the % Synthetic on Cuttings (SOC) for this process was always over 8.0%. The system was unable to lower the SOC due to concerns for the capability of the big bowl centrifuge to handle big cuttings. With a modified centrifuge unit, a more robust unit with a design change in feed nozzles being able to handle more torque, all cuttings from both scalping deck and primary deck are fluidized and transported to a big bowl centrifuge with no big cuttings diverted overboard. Utilizing the previous configuration of Wet Wash whereby cuttings from the scalper deck were diverted overboard, the % SOC was always over 8.0%. It was efficient in the removal of solids, but it was still yielding high SOC. In 2012 the use of Cuttings Dryers was introduced to further reduce % SOC. On Jack-up rigs, the Cuttings Dryer can operate in a normal manner, but on Tender Assisted rigs, where the cuttings are fluidized and pumped to the Dryer, there is a trade-off. High content of Low Gravity Solids (LGS) from the continual grinding of the solids to ultrafine particles that could not be removed by centrifuges had become an issue. High dilution rates were required to keep mud system under control due to excessive ultrafine solids. The Wet Wash system was re-visited for Tender Assisted rigs. With the modified configuration of Wet Wash system where no cuttings were diverted overboard, fluids performance was improved from reduction of ultrafine solids contamination in the mud system, resulting in less dilution rate and mud chemicals treatment. The % SOC was also lower than 8.0%. With proper Preventative Maintenance (PM) program in place, there was neither down time of the centrifuge nor report of excessive wear of equipment from handling big cuttings. The novelty of the modified Wet Wash configuration is in the ability to improve fluids performance and reduce environmental impact with the optimum operating cost.

Screen Bowl Centrifuge Dewatering Process: A Parameteric Study

Screen bowl centrifugation process is widely used for fine coal dewatering due to its relatively low cost, high capacity of providing low-moisture content product as well as relative ease of operation and maintenance. However, screen bowl centrifuge tends to lose a significant amount of ultrafine clean coal to the main effluent and screen-drain streams. This study aims at obtaining a better understanding of the parameter main effects and interaction effects with an ultimate goal of improving the dewatering performance of a screen bowl centrifuge. A three-level factorial experimental design has been utilized to conduct a test program using a continuously operated screen bowl centrifuge having a bowl diameter of 0.5 meter. The results of this study indicate that moisture content of the clean coal product is affected by both feed solid content and the pool depth maintained in the centrifuge. On the other hand, clean coal recovery to the product launder was found to be a function of feed solid content and volumetric feed flow rate but independent of the pool depth. The interaction effect of feed flow rate and feed solid content also appeared to have a significant effect on the clean coal recovery.