1 Introduction 2 Some parameters of the negative impact of the number of conveyors in the system Uvod Neki parametri negativnog utjecaja broja transportera u sustavu The prevailing method of conveyance in coal mines, both in underground and open-cast mining, is belt conveyor system. In addition to an indisputably large number of advantages, belt conveyors have also some shortcomings, which are reflected, among others, in the existence of a large number of units in the system. Lengths of belt conveyors in coal mines range from few tens to few thousand meters. At points where conveyors are connected into the system, a number of problems occur – such as the necessity for an automated loading/unloading, successive start-up operation, maintenance of power stations and negative environmental impact. Many researchers proved that the reliability of a multi-conveyor system is lower compared to the reliability when this number is minimal. The aim of this paper is to analyse the possibilities for reducing the number of conveyors in a system, through maximum increase of the conveyor length, depending on the characteristics of a belt as a bearing and haulage apparatus. The aim is also to discuss possibilities for reducing the number of units by applying horizontal bend conveyors. The results of these researches arose from the team work of relevant departments of BERG Faculty, Technical University Košice (Slovakia) and the Faculty of Mining and Geology, University of Belgrade (Serbia). Continuous transportation systems are composed of numerous elements and their reliability depends upon the number of these elements and also on the reliability of each 453 M. Grujić, D. Malindžak, D. Marasova ISSN 1330-3651 UDC/UDK 621.867.23:658.5 POSSIBILITIES FOR REDUCING THE NEGATIVE IMPACT OF THE NUMBER OF CONVEYORS IN A COAL TRANSPORTATION SYSTEM Miloš Grujić, Dušan Malindžak, Daniela Marasova Belt conveyors are usually applied in coal conveyance, whether the reference is made to conveyance in mines themselves or from mines to the nearest consumers. These conveyance systems have often a large number of transporting units, which may have a negative impact on the system reliability and the environment. This paper deals with the possibilities for reducing the number of conveyors in a coal conveyance system by maximizing the conveyor length and the possibility of applying horizontal bend conveyors. Key words: negative impact, number of conveyors, reducing, transportation system Subject review Trakasti transporteri primjenjuju u transportu ugljena, bilo da se koristi u rudnicima ili od rudnika do najbližeg potroša . Ovi sustavi imaju veliki broj transportnih jedinica, što može imati negativan utjecaj na pouzdanost sustava i okoliš. U ovom radu za smanjenje broja transportera u sustavu transporta ugljena, du ine transportera i uz primjene horizontalnih lukova transportera. se obično ča transporta često se razmatraju mogućnosti povećavanjem lj mogućnost Ključne riječi: broj transportera, negativni utjecaj, smanjenje, transportni sustav Pregledni članak Mogućnosti za smanjenje negativnog utjecaja broja transportera u sustavu transporta ugljena Mogućnosti za smanjenje negativnog utjecaja broja transportera u sustavu transporta ugljena Technical Gazette 18, (2011), 3 453-458 particular element. Coal transportation systems may, in some cases, comprise more than 10 elements and their overall reliability is less than 50 % of the minimum reliabillity of each particular conveyor. The large number of conveyors within the coal transportation system also has a significantly unfavorable bearing on the environment. It is recorded that considerable air pollution, soil degradation etc. occurs at transfer points. This problem is particularly pronounced during the transportation of coal fines from the mine to the coal-fired power plants. The transportation of coal from the mine toward primary consumers (coal-fired power plants, separation plants etc.) is usually developed through transportation systems that consist of several belt conveyors. If one of the reliability parameters of the -th element of the system is indicated as , then the reliability of the system will be as follows: i r i . 1 Õ = = m i i r r (1) Here represents the number of conveyors in the system. The coefficient of time efficiency and the coefficient of readiness may be considered as the most comprehensive indicators of reliability during coal transportation by belt conveyors. If one transportation system is composed of conveyors of equal or approximately equal reliability (ideal case), then the overall reliability of the system will be: m m . m i r r = (2) The diagram (Fig. 1) shows how the reliability of the transportation system changes with the increase in the number of conveyors and spare elements within the system The parameters of reliability also affect the efficiency of transmission within the transportation system. Receiving ability of the transportation system, with directly connected conveyors, depends upon the minimum capacity of a conveyor within the system and the parameter : . Q k min br