Using column generation to solve an industrial mixing problem

The problem considered in this paper is a real world problem. It concerns the management of the deliveries of coal to the several plants of a coke industry firm in order to meet the demand of several clients at minimal purchasing, transportation and production cost. The problem is solved using a column generation technique. At the lower level, a mix of one ton satisfying all the client quality requirements is determined for each plant at each period. At the upper level, the deliveries of coal and the level of use of the mixes are determined in order to meet the demands of the clients.