Models of optimum current planning of separate extraction of different grades of a mineral in joint occurrence

Abstract

Efficient mining of mineral reserves of a complex composition (copper and iron ore or coal) is secured by separate processing of different classes or grades of ores and coals occurring at the same location and extracted in a stable volume flow. An example is the Neryungrin coking coal deposit. During the first years of operation, coking coal will be extracted in an area where transitional and unoxidized zones are contiguous. The contact has a sinuous shape, with a frequent interpenetration of the areas of coking and steam coal. It would be impossible to separate excavation stopes to work exclusively the zones of either steam or coking coal. Figure i, based on actual data, shows that each stope contains a succession of areas of coals of the two classes.The reserves planned for mining within a calendar quarter are selected so as to ensure the required outputs of each of the two coal grades. This does not guarantee the proper ratio of the two grades within shorter periods of time because of the variability of coal classes in a stope and the type of excavators used. This poses the planning problem of optimizing the operation of the excavation work systems (EWS) assuming separate working of the two types of coal. The goal is to obtain a time-stabilized flow of coking coal. Models describing the EWS behavior under these conditions belong to the class of dynamic models with discrete time. In contrast to static models, they account for coal variability within a stope as well as the composition of the loading plant during the plan interval. The strategy involves breaking the plan interval (0, T) into a set of unit periods (j = i, 2, .... J) whose length is determined by the possibility of describing the system's behavior in the unit period j by a static model.The conditions introducing the dynamic properties into this system are the periodic maintenance stoppages of the excavators and the switching of excavators to the working of new mlnlng-englneerlng blocks (k, i) according to prescribed sequences. The situation change step is the length of the most frequent type of preventive maintenance inspection (MI), which, for example for the exacvators EKG-12.5 and EKG-81, is taken at 3 days. This interval on average is equal to the working time of a mlning-engineering block. Two alternative models are used which differ in the degree to which they incorporate the relations between the system operation during different unit periods of a plan interval. The models of a dynamic system, including that of EWS, which consider only how the system operates in a given period j as affected by the result of its operation in the preceding periods and the system state within time j, or systems with direct dynamic relations, are referred to as conditionally dynamic models (CDMs). The models that, in addition to direct dynamic relations, incorporate also so-called reverse dynamic relations, which reflect the impact of the future conditions of system operation and incorporate their operation in the current period, are called full dynamic models (...