| Possessing the advantages of both shovel-truck and continuous mining technology, the semi-continuous mining technology containing shovel-truck-crusher station finds wider and wider application in Chinese and foreign open cast mines. The researches aiming at improving the efficiency of the semi-continuous mining systems are being attached great importance. Great progress has been made in the system analysis methods, modeling and application. However, the blocking property of the crusher station makes the mathematical modeling and analysis of this kind of mining system become a challenging problem to be solved. This paper carries out theoretical and applied research of the above-mentioned key problem in the semi-continuous surface mining systemsAnalyzing on the basis of queueing theory, the shovel-truck-crusher station system can be modeled as a mixed queueing network consisting of two kinds of customers---trucks and material units measured by the loading volume of the trucks. Because of the definite crusher bin volume, the trucks at the dumping mouth of the crusher station cannot dump when the bin is full. This phenomenon is called blocking. The material flow depends upon the truck flow, for the material is carried by the trucks. On the other hand, the material flow restricts the truck flow. When the bin is full, the material unit and the truck carrying it are both blocked. So the blocking property must be taken into account in order to model and analyze the property of the shovel-truck-crusher station systems.A queueing network model with blocking has been set up for the crusher station using the queueing network theory. That is an open tandem queueing network model with blocking, which consists of a M/M/2/∞queue modeling the dumping service and a M/D/1/N queue modeling the crushing process. Due to the finite bin volume, blocking appears with the bin of the M/D/1/N queue being full; it stops the departure of the customer having finished service at the first service station. The first service station is thus blocked. The arrival process of the second service station is not Poisson process any more. The existence of blocking makes the two queueing systems be related to each other, destroys the theoretical basis of queueing theory—the memorylessness. It is impossible to obtain the exact solution of the above open tandem queueing network model with blocking, so an approximate solution is unavoidable. By computer simulation the properties, mean number of trucks in system and in queue, blocking time, idle time and actual crusher output of the crusher station with different technical parameters (average arrival rate, designed output of the crusher and the bin volume) can be obtained. With the property of the crusher station having been obtained, the crusher station can be treated as a special node in the shovel-truck-crusher station system.The shovel-truck-crusher station system can be modeled as a mixed queueing network consisting of two kinds of customers---trucks and material units. A decomposion-synthesis method has been proposed to construct and analyze the queueing network model of the shovel-truck-crusher station mining system. The whole queueing network can be decomposed into two sub-networks according to the kind of customers:the closed queueing network of truck flow and the open queueing network of material flow. The two sub-networks can be analyzed independently, but their analysis results must be synthesized to generate the analysis result of the whole queueing network model of the shovel-truck-crusher station mining system.The queueing network of material flow consists of the following service stations: loading---loaded trucks traveling---dumping---crusher with bin. At the first two service stations, the material flow depends on the truck flow. Only the sub-system containing the last two service stations, dumping---crusher with bin, exerts influence on the truck flow. This sub-system is exactly the crusher station's queueing network model with blocking, the interaction between the material and truck flow can be defined by the crusher station's properties.In steady states, the average arrival rates and mean number of customers in the queueing system at the dumping mouth of the truck-flow sub-network are equal to those of the material-flow sub-network. It can be concluded that in steady state the average arrival rates and mean number of customers in the queueing system at the dumping mouth of the truck-flow sub-network depend on the corresponding parameters of the material-flow sub-network. By changing the curve expressing the relationship between the mean number of trucks in system and the average arrival rate into arrays containing average arrival rate---mean number in system, the abovementioned relationship curve can be used in the analysis of the truck flow sub-system.The extended summation algorithm (ESUM) was introduced to analyze the truck flow sub-network. The closed queueing network model of a practical shovel-truck system was constructed and analyzed by both ESUM and computer simulation. By means of contrast of the two results obtained by the two above-mentioned methods, it is proved that ESUM can be used effectively to analyze non-exponential queueing network models of shovel-truck systems with good accuracy.The queueing network of truck flow consists of the following service stations: loading---loaded trucks traveling---dumping---empty trucks traveling---loading. Two facts are very useful in analyzing the truck flow:In steady state, the throughput of the tandem closed queueing network is equal to the average arrival rate of the individual service station in the network.In steady state, the sum of the mean number in system at every service station of a closed queueing network is equal to the total number of trucks put into the network.According to the two facts and utilizing the arrays of average arrival rate---mean number in system obtained in the queueing network model of crusher station, the three mean numbers of trucks in system at the other three service stations corresponding to the array can be calculated by ESUM. If in steady state the sum of the four mean numbers in system of the four service stations is the same as the total number of trucks put into the queueing network model, the throughput of the network at such a situation is the steady state throughput of the whole queueing network model of the shovel-truck-crusher station mining system. Applying this throughput to the ESUM formula and the curves describing the properties of the crusher station, the property indices of the mining system can be obtained.In steady states, the average arrival rates and mean number of customers in the queueing system at the dumping mouth of the truck-flow sub-network are the same as those of the material-flow sub-network. This is the synthesizing basis of the two sub-networks. The two sub-networks can be analyzed separately in various steady states. The steady state, in which the common average arrival rate and the common mean number of customers in the queueing system appear at the dumping mouths in both sub-networks, is the steady state of the whole queueing network. On the basis of this the analysis of the whole network can be realized.According to the measured data and production statistics, two examples of the shovel-truck-crusher station mining system in Yuan Bao Shan Open Pit Coal Mine have been analyzed by the abovementioned analytic algorithm to solve the following problems:The influence of changing the type of trucks on the efficiency and output of the shovel-truck-crusher station system; The determination of the rational truck to shovel ratio of the shovel-truck-crusher station system. The results obtained proves that the model and analysis method proposed in this paper can be used effectively to evaluate the changing of truck type, the expansion of the crusher bin, and to determine the rational truck to shovel ratio. The results, conforming to the reality of the mine, are important to optimize the configuration of the haulage system and enhance the haulage efficiency. |
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