Planning BOF repair system in conditions of quasi-periodic operation of units

Using the example of the steelmaking production of JSC EVRAZ United West Siberian Metallurgical Plant, the paper considers the task of synchronous calendar planning in the interval of several planned periods of operation of basic oxygen furnace (BOF), BOF shops, production as a whole, as well as ongoing repairs of BOF for steelmaking production (two BOF shops with two and three BOFs). Scheduled stops of the BOF for repair depend on the actual achieved duration of the lining campaign and production schedules of the units and are performed when the current duration of the BOF campaign reaches a given standard value. Thus, the current duration of the BOF campaign is described by a discrete, nonlinear quasi-periodic function that does not have a fixed period, but has some regularity. Technological limitations were forma­lized, determining the minimum and maximum values of the number of melts per day that each of the workshops can produce with one or two BOFs operating simultaneously. The authors formulated the conditions to avoid performing two “cold” repairs in one shop in one planned period and ensuring daily processing by BOF shops of all cast iron coming from the blast furnace shop. In the proposed mathematical formulation of the problem, it is required to find such schedules of BOF repairs and such calendar plans of their work that satisfy the formulated constraints and optimize the non-linear criterion. The proposed criterion is aimed at ensuring the constant readiness of the shops for implementation of the production program and design productivity. The task is formulated for the conditions of trouble-free operation and stable provision of the shops with liquid cast iron as the main component of the metal charge of BOF smelting.