In this study, a coal washing plant in Zonguldak was optimized using equalization of incremental product quality approach which maximizes plant yield for a given ash constraint based on float-sink data. By maximization of yield using Solver which is an optimization routine available in Excel for the identical elementary ash content and the specified ash level of 9.50%, the optimum cut points were determined for washing of coarser size fraction (100-18 mm) and finer size fraction (18-0.5 mm) by Drewboy Heavy Medium (HM) Bath and HM Cyclone, respectively. The results were compared with the plant operations in terms of product yield and ash content. Calculated yield % and ash % values with experimental yield % and ash % values from float-sink data of the used coal were also compared and they were in good agreement (R-2 > 0.99). By equalization of the incremental ash in order to get composite ash of 9.5%, the composite yield was maximized to 30.71% while the plant's yield was about 24.00%. This approach identified the optimum operating conditions for individual cleaning circuits as 1.693 and 1.682 for Drewboy HM Bath and HM Cyclone, respectively. It is worth pointing out that, this increase (6.71%) in the yield would be remarkable when considering the whole life of the washery and the annual production of the plant (about 700000 tons). In addition, the yield was maximized to 33.41% for the target ash of 11.61% by similar optimization studies. The optimum operating cut points for HM Drewboy Bath and HM Cyclone was determined as 1.900 and 1.888, respectively. Yield optimization was also performed by taking a equals to 80, which can be assumed ideal for HM separators. The results obtained by the two different calculations were very close to each other. (C) 2013 Elsevier B.V. All rights reserved.