machine design, Vol.5(2013) No.2, ISSN pp

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1 machine design, Vol.5(2013) No.2, ISSN pp OPTIMIZATION OF WORKING LIFE OF TRANSPORTATION SYSTEMS Ferid OSMANOVIĆ 1, * - Alan TOPČIĆ 2 1 Federal Administration for Inspection Affairs, Sarajevo, Bosnia and Herzegovina 2 University of Tuzla, Faculty of Mechanical Engineering, Tuzla, Bosnia and Herzegovina Research paper Received ( ); Revised ( ); Accepted ( ) Abstract: For every production system the flow of materials and its associated transportation system presents integrating factors which in accordance with the technical and technological requirements of the production process have a major impact to the overall efficiency and production cost. Keeping that in mind, special attention should be paid to the analysis of the transportation system as a whole, and all of its components, to ensure maximum efficiency and cost minimization. Since the operational costs increases over time, it is crucial to find a way to determine the optimal moment of time for replacing the existing transportation system with the new one. This paper has the purpose to present a methodology for determining of the optimal replacement timing for the existing transportation system with new one in accordance with its minimal maintenance and operating costs. Key words: transportation system, working life, optimization, costs reduction 1. INTRODUCTION The flow of material through a production system presents the basis for successful realisation of set production goals, and this is being accomplished within the internal transport subsystems. Certainly, the flow of material within the production system is in compliance with the existing technological applications, thereby integrating the production system in one unit. The immediate implementation of transportation tasks within the production system needs to be accomplished in such a way that the flow of materials provides the conditions that will ensure the right material (qualitatively and quantitatively), at the right time, at the right place, with the minimal total transportation cost. For the realization of established transportation tasks within the production system the appropriate transportation equipment and devices is used. These transportation devices and equipment depending on the transportation timing integrity can be continuous or cyclic type (Figure 1). In the function of concrete working conditions choice of transportation devices of one or another type or even theirs combination within transportation system, all with the aim to ensure the above mentioned setting, will depend. Regardless of the type of installed transportation devices and equipment, transportation tasks within production systems require the integration and coordination of transportation facilities into a singular transportation system, with precisely defined tasks and limitations. Underground coal mining, in terms of transportation issues (export of mineral raw materials) is a delicate task, not only because of the extremely difficult working conditions that transportation facilities are exposed to (transport of different rock materials, transportation equipment installed in the vicinity of underground openings excavated pit and old works with prominent pit pressures and installed on a clay surface - the effect of swelling / proliferation rooms,...), but also because of the constant need for lowering the total costs of operation to maximize production efficiency. Given that transport material take a significant part of the total costs of underground coal mining, it is obvious that a slightly cost reductions in material flow adds value to increasing of overall production profit. During its exploitation lifetime transportation devices and equipment are "outwear" (depreciation), the needs for maintenance in increasing, availability and time frame between failures is shortened, fail time is increased and the reliability and effectiveness of transportation devices and equipment is decreased. Over certain time period, this will lead to a need to substitute the existing transportation system in a whole or some of its components with the new one. Fig.1. Transportation devices and equipment depending on the transportation timing integrity Ability to determine the optimal moment of replacement is a delicate task. This optimal replacement moment must be given special attention, which means analysis of all aspects of the existing transportation assets. We also have *Correspondence Author s Address: Braće Kršo br. 49, Vogošća, Bosnia and Herzegovina, fosmanovic@yahoo.com

2 to consider all available alternatives in the line with set transportation tasks that would ensure efficient flow of materials within the production systems. The above task is further complicated when considering transportation systems - the sets of interconnected transportation equipment and devices that implement the flow of materials within the production system, and whose work is significantly characterized by stochastic processes. 2. THEORETICAL CONSIDERATIONS Long-term observation of parameters that illustrate operating of transportation systems in exploitation conditions, have significant impact to their effectiveness, could lead to changes in the incomes and costs of production systems within transportation systems operate, it is possible trough comprehensive analysis of acquired data to develop a model for determining the optimal lifetime of transportation system, i.e. determining the timing of replacement of the existing transportation systems (or its components) with new one. In developing this model the costs of operation and maintenance of the existing transportation system take into account. Analyzing the cost of any transportation system in a given time interval, then the total cost of operation, maintenance and utilization (C t ) are the sum of variable costs (C v ) and constant cost (C k ): C t = C v + C k (1) Variable costs are calculated using the formula: C v = C pe + C pm + C tp + C od + C z (2), where are: C pe driving energy costs, C pm the cost of supporting material, C tp the cost of technical inspection and cleaning, C od maintenance costs, C z costs of downtime. Cost of driving energy (C pe ) are changeable during operation, and depend on the concept of the drive unit, the conception and construction of the transportation system, its efficiency, working conditions, time of use, energy price, way of maintenance, etc. Costs of supporting materials (C pm ) depend on the same factors as the cost of driving energy, but intensity of influence of these factors is different. These costs are significantly influenced by the costs of various types of industrial oils, fats and liquids. Costs of technical inspection, cleaning and corrosion protection (C tp ), are not great, but can significantly contribute to prolonging the exploitation. Depend on the concept of building of transportation system, the construction characteristics of transportation systems, their effectiveness, working conditions, time of use, cost of services, cost of materials, etc. Maintenance costs (C od ) represent a very significant factor in the variable costs. Those costs are result of the failure or cancellation, as well as wear of transportation system or its elements. Depend on the concept of the drive unit, the concept of building transportation systems, their effectiveness, working conditions, time of use, the cost of services, the cost of materials and parts, etc. 88 Costs of downtime (C z ) if they are frequent and longterm, these costs will reach a large amount. Factors that influence on these costs are: the effectiveness of transportation system, the conditions of exploitation, during use, the loss per unit of outages, etc. Constant costs (C k ) are unchanged during a specified period of exploitation. As a example of those costs can used the cost of registration and insurance which stay unchanged in the total annual amount, regardless of the effective time of operation. Those costs depend on the cost of transportation system, time of depreciation, cost of registration and insurance, etc. Based on the cost of operation and maintenance, revenue is realized by transportation system operation and the actual value of the transportation system in the i-th year(s) of operation (i = 1, 2, 3,..., n) can be established in relations presented below. Income of existing transportation system D(t) during operation is a function of P(t) and the cost of G(t), i.e.: D (t) = P (t) G (t) (3) and for a i-th year of operation is calculated according to the formula: D i =P i G i, where are: P i the turnover in the i-th year of exploitation, G i the total cost of the i-th year exploitation. Costs of operation and maintenance of the transportation system, i.e. the total cost (C t ) at a given time interval of monitoring of operational parameters of the transportation system are a function of its age and can be presented by functional dependencies C t (t) =G(t). Incomes of the new transportation system Q(t) in the i-th year of old transportation systems, taking into account the cost of replacing old with new one transportation system Z(t) is calculated according to the formula: Q(t)=D 1 Z(t) (4) and for a i-th year of operation is calculated according to the formula: Q i =D 1 Z i, where are: D 1 incomes of a new transportation system in the first year of operation, Z i the cost of replacing of transportation system in the i-th year of operation. Income of a new transportation system in the first year of operation is calculated using the formula: D 1 = P 1 G 1 (5) where are: P 1 income in the first year of operation, G 1 the total cost in the first year of operation. The function of the cost of replacing of existing transportation system with new one according to the operation period can be calculated using the formula: Z(t)=C a(t) (6) where are: Z(t) a function of the cost of replacing of transportation systems, depending on the period of operation, C the price of new transportation system, a (t) decline function of purchase price of transportation system.

3 Looking at the annual earned incomes of transportation system (D i ) for a certain period of operation (i = 1, 2, 3,.., n), then the at the beginning of each year, based on the available data on the transportation system and the state of its environment, a enactment of decision is characterized by two possible alternatives: 1. Keep the old transportation system that will accomplish annual income: D i =P i G i ; 2. Replace the old transportation system with new one that will annually bring income: Q i =D 1 -Z i. For calculation of optimal operation time of transportation systems, as a planed period of operational time bookkeeping operational period is taken, and in first year of that period of time the new transportation system is introduced. Based on the previous equations, in order to achieve maximum income potential with transportation system, the greater the value obtained from the two (Q i or D i ) is considered as the optimal. Subsequently, it is adequately labelled with the result; "Keep the old Transport System" - mark: KOTS or "Introduce the New Transport System " - mark: INTS. The process of determining of optimal time for replacing of existing transportation system is realised through search and analysis of set of generated results in the observation period of time. tested transportation systems installed in pit "Stranjani" and pit "Haljinići". a) b) 3. EXPERIMENTAL RESEARCH The application of the presented theoretical model to determine the optimal time for replacing the existing transportation system with new one was tested in three different transportation systems used in underground mining of coal: Coal Mines of Central Bosnia (transportation system combined type pit "Grahovčići", Cola mine "Abid Lolić" Bila-Travnik; transportation system continuous type pit "Stranjani" - Cola mine "Zenica" Zenica; transportation system combined type pit "Haljinići" - Cola mine "Kakanj" Kakanj), Figure 2 and Table 1. This research is based on the monitoring the operating parameters, costs of operating, as well as the maintenance of the existing transmission system. Presented the research carried out in accordance with the action plan illustrated by the Figure 3. The data gathered that summarizes effectiveness of work, maintenance, service conditions, income and expenses of the studied transportation system was carried out in the period of 10 years, i.e. from the time of installation of the existing transportation system until its total depreciation that is calculated at 10% annually. The data that related to the operation of the new transportation system are derived based on the theoretical indicators that deterministically describe behaviour of the transportation system, and are not influenced by stochastic parameters that interact on the operation of the transportation system. In-situ data collected on the existing transportation system were statistically analyzed and presented in the table. This data is run through a theoretical model developed to determine the optimal timing of replacement of the existing transportation system (Table 2 - Data for the transportation system of the pit "Grahovčići"). This approach to cost analysis of the existing and new transportation systems is fully applied to the other two c) Fig.2. Transportation system combined type pit "Haljinići, Cola mine "Kakanj" Kakanj: a) pit transport by scraper conveyor, b) transport of coal to the surface - belt conveyor, c) transport to the separation - cyclic type of transportation device trucks Fig.3. Plan of activities for realisation of presented researches 89

4 Table 1. Transportation devices and equipment installed in observed transportation systems of coal mines 90 Pit Type Transportation devices type TS-74 (Chamber machine), type TS-74, (III concentrator), type TS-74, (II concentrator), type TS-74, (I concentrator), Belt Conveyor (TT 10), Belt Conveyor (TT 9), Belt Conveyor (TT 8), Belt Conveyor (TT 7), Belt Conveyor (TT 6), Belt Conveyor (TT 5), Belt Conveyor (TT 4), Belt Conveyor (TT 3), Belt Conveyor (TT 2), Belt Conveyor (TT 1), External transport (Truck, type: Magirus) External transport (Truck, type: FAP). One chained scraper conveyor, type TOT-732, (Leading scraper conveyor), type Samsun, (drive off), Belt Conveyor (TT 8), Belt Conveyor (TT 7), Belt Conveyor (TT 6), Belt Conveyor (TT 5), Belt Conveyor (TT 4), Belt Conveyor (TT 3), Belt Conveyor (TT 2), Receiving bunker Belt Conveyor (TT 1), External transport (Truck K-1) External transport (Truck K-2) External transport (Truck K-3) External transport (Truck K-4) type TS-74, (II Chamber machine), type TS-74, (I Chamber machine), type DGT-440b, (II concentrator), type DGT-440b, (I concentrator), Belt Conveyor (TT 7), Belt Conveyor (TT 6), Belt Conveyor (TT 5), Belt Conveyor (TT 4), Belt Conveyor (TT 3), type LOT 2 Belt Conveyor (TT 2), Belt Conveyor (TT 1). Grahovčići - Cola mine "Abid Lolić" Bila-Travnik Haljinići- Cola mine "Kakanj" Kakanj Stranjani- Cola mine "Zenica" Zenica Combined transportation system Combined transportation system Continuous transportation system In compliance with the data presented in the table obtained functional dependence of incomes realized by the existing transportation system D(t) and a new transportation system Q(t) during the observation period of 10 years for all three analyzed transportation system is presented on Figure 4. a) b) c) Fig.4. The functional dependence of income which realizes the existing transportation system D (i) and a new transport system Q (i) during the observation period of 10 years for: a) pit "Grahovčići", b) pit "Stranjani", c) pit "Haljinići" the value of the income earned by the existing transmission system - in situ data theoretical change in the value of income of the new transport system D(t) - empirical equations change in income over time for the existing transportation system Q(t) - theoretical equations change in income over time for the new transportation system For each of the considered cases in accordance with the presented data, regression analysis was performed with

5 the aim of establishing a one-dimensional regression models using the least squares method, and the calculated value of the coefficient of determination (R 2 ) for each of the resulting empirical equation. By solving the obtained theoretical empirical functions that describes variations of income of existing D(t) and the new one Q(t) transportation system at time t, the optimal point of time for replacing the existing transportation system with new one is determined, Table 3. Table 2. Tabular overview of incomes and costs for the transportation system of the pit "Grahovčići Expenses and Revenues The Transportation System Operation Time [ Year ] Effective time T ef [h] Actual production t.k.u ,5 166,1 117,9 143, ,5 125, ,3 91,4 3 Achieved performance [t/h] 28,48 32,39 23,32 26,85 22,47 25,97 23,42 24,48 13,13 18,22 4 The price of a ton [BAM] Revenue (1 3 4), [BAM] , ,1 7176, ,1 6293,5 6701,2 3416,3 4569,1 6 Preventive maintenance [h] Subsequent maintenance [h] Total hours of maintenance [h] Price of workshop hours[bam] Cost of workshop hours (8 9), [BAM] ,9 26,0 25,5 27,0 29,8 30,7 30,6 29,4 30,1 33,7 11 Cost of spare parts [BAM] ,2 172,0 146,9 125,9 197,9 189,7 208,4 188,0 189,7 235,7 12 Ratio of costs for shop hours and spare parts costs 0,259 0,151 0,173 0,215 0,151 0,162 0,147 0,156 0,159 0, Maintenance costs (10+11), [BAM] ,1 198,0 172,4 152,9 227,7 220,4 238,9 217,3 219,8 269,4 14 Price [KWh/BAM] 0,09 15 Installed power, P in [kw] Electricity costs ( ), [BAM] ,9 218,8 215,6 228,1 216,5 229,6 239,9 259,1 246,4 237,4 17 Mileage trucks [km] 28700, , , , , , , ,2 18 Fuel costs [BAM] ,1 49,8 35,4 43,1 34,2 40,1 37,8 40,2 20,5 27,4 19 Cost of oil and lubricants [BAM] ,9 4,5 3,2 3,9 3,1 3,6 3,4 3,6 1,8 2,5 20 Cost of tires [BAM] ,8 21 Cost of downtime (3 4 7), [BAM] ,6 1036,4 700,9 946,4 1000,9 1235,9 1109,0 1054,1 5980,5 1047,7 22 Costs of insurance [BAM] ,6 23 Depreciation [BAM] ,6 225,6 225,6 225,6 225,6 232,6 232,6 240,1 240,1 240,1 24 Gross Income operator [BAM] Utility bills [BAM] Operation costs (18 25), [BAM] ,5 2519,5 2165,1 2431,3 2464,7 2774,2 2655,1 2677,5 2187,2 2635,5 27 Total costs (13+26), [BAM] ,7 2717,6 2337,5 2584,2 2692,3 2994,6 2894,1 2894,8 2407,1 2904,9 28 Income of transport. system (5-27), [BAM] ,5 5588,4 3556,6 4591,8 3007,7 3682,4 3399,4 3806,3 1009,2 1664,1 29 Coefficient and amortization a i 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0, Price of a new transportation system [BAM] The cost of replacing the transport. system [BAM] ,4 1804,8 1579,2 1353, ,4 697,8 480,2 240, Income of the new transport. system (28-31), Q i [BAM] ,1 2965,7 3191,3 3416,9 3642,5 3840,1 4072,7 4290,3 4530,4 4770,5 33 The maximum earned income is D max [BAM] ,5 5588,4 3556,6 4591,8 3007,7 3682,4 3399,4 3806,3 1009,2 1664,1 34 Optimal replacement time KOTS KOTS KOTS KOTS KOTS INTS INTS INTS INTS INTS 4. CONCLUSION The results of the analysis of the working costs and reached incomes of the existing transportation system (based on In-situ data) and the new transportation system (based on a theoretical analysis of the incomes/costs of a new transportation system during the exploitation and the costs of replacement of the old transportation system with new one in the i-th year) based on the application of one dimensional regression models for determination of the optimal timing of replacement of transportation system has resulted in determining the different time intervals of the replacement of existing by new transportation system, which it is possible to explain by different working conditions in which analysed transportation systems operate. It is important to note that under the term replacement of the existing transportation system with new one did not suggest only complete replacement of entire system, it is possible to replace only some components i.e. transportation devices and equipment integrated within existing transportation system. Clearly, identification of individual components of a transportation system must be based on a thorough analysis of all the parameters that determine system performance (degree of utilization, availability, efficiency, etc). As it previously mentioned, the observation time used for the analysis is the accounting annual depreciation rate of 10%. Keeping this in mind, with evident tendency of increased operational and maintenance costs of the existing transportation systems has led to the fact that optimal moment of time for replacement of existing transportation systems is shorter than previously 91

6 estimated bookkeeping lifetime of transportation systems. Changes in the annual rate of depreciation will lead to changes in timing of replacement of existing transportation system with new one; however there is still an opportunity of application of the presented model for determination of optimal replacement time. Table 3. Determination of the optimal timing for replacement of old transportation system (or its components) with new one The transportation system of pit: Grahovčići Stranjani Haljinići Changes of theoretical empirical function of revenue for existing D (t) and the new Q (t) transportation system D(t) = t t Q(t) = t D (t) = t t Q(t) = t D (t) = t t Q(t) = t Optimal time for replacement [years] 5,4 6,2 6,7 Considering the fact that the exploitation of coal mines primarily prioritizes the planned volume of production, often it is the case that not enough attention is paid to the analysis of work of installed transportation systems. As a result of this situation there is a real risk for failure of transportation system, and the inability to transport materials which can lead to stopping of production equipment activities. This definitely represents the least favourable situation, and significantly raises the cost of coal mining. That's why proper determination of the optimal timing of replacement of the existing transportation system with new one, with the presented model, is great foundation for the development of quarterly and annual production plans. In addition, it creates preconditions for timely action of replacing the old equipment with new, and eliminates possibility of transportation system failure or longer transport delays. 5. REFERENCES [1] Šelo R. & Tufekčić Dž. (2002). Flexible Transport, Faculty of Mechanical Engineering in Tuzla, ISBN: , Tuzla, Bosnia and Herzegovina [2] Osmanović F. (2007). Application of a mathematical model of optimization on the life of transportation systems in underground mines (master thesis), Faculty of Mechanical Engineering in Tuzla, COBISS.BH-ID , Tuzla, Bosnia and Herzegovina [3] Osmanović F. & Pirić E. (2009). Defining the parameters of the reliability of transportation systems using Weibul's model, Proceedings of the 2009 DEMI - 9 th international conference on accomplishments in electrical and mechanical engineering and information technology, University of Banja Luka, Faculty of Mechanical Engineering in Banja Luka, ISBN , Živko Babić (Ed.), pp , Banja Luka, Bosnia and Herzegovina; [4] Topčić A., Šelo R. & Cerjaković E. (2010). Optimisation of reloading segments of internal transportation systems, Technics, Technologies, Education, Menagement TTEM, Vol. 5, No. 2 (June 2010), ( ), ISSN ; [5] Topčić A., Cerjaković E. & Herić M. (2013). Simulation of Reloading Segments of Internal Transportation Systems by Artificial Neural Networks, Journal of Production Engineering, Vol.16, No.1, (February 2013), (51-54), ISSN ; [6] McNearny R. L. & Nie Z. (2000). Simulation of a conveyor belt network at an underground coal mine, Mineral Resources Engineering, Vol.09, (2000), ISSN: [7] Cerjaković E., Tufekčić Dž., Topčić A., Šelo R. & Ćelović Š. (2010). Stabilisation of production lines by using of simulation study methodology, International Virtual Jurnal for scinece, technics and innovations for industry Machines Technologies Materials MTM, Year IV, Issue 1-2/2010, (May 2010), (24-27), ISSN [8] Garrido R.A. & Allendes F. (2002). Modeling the Internal Transport System in a Containerport, Transportation Research Record: Journal of the Transportation Research Board, Volume 1782/2002, (84-91), ISSN: