Minimum Unit Cost Research Articles

Determining the Normal Degree of Capacity Utilisation: Insights from the History of Economic Thought

ABSTRACT Several issues related to the normal degree of capacity utilisation have become crucial in the recent debate within demand-led growth theories. By going back over the history of economic thought, the paper aims to highlight the main findings that may nourish the current debate. Our reconstruction identifies the main factors affecting the firm's choice as to the size and degree of utilisation of productive capacity and draws attention to three points that appear to require particular attention in the debate on demand-led growth: firstly, the degree of utilisation corresponding to the maximum profit does not necessarily correspond to the minimum unit cost associated with the plant; secondly, the size of productive capacity depends on the variability of the output produced by the firm; finally, and in connection with the two previous points, the determination of normal utilisation requires defining the market structure in which the firm is supposed to operate and is therefore affected by the notion of competition adopted.

Design and optimization of a combined supercritical CO2 recompression Brayton/Kalina cycle by using solar energy and LNG cold energy

Solar energy and LNG cold energy have broad application scenarios as two renewable sources, but their complementary potential has not been fully explored. To fill this gap, this paper constructs a novel combined cycle that utilizes solar energy and recovers LNG cold energy to generate power. This combined cycle consists of a supercritical carbon dioxide recompression Brayton cycle, an ammonia-water mixture Kalina cycle, and an LNG cryogenic power system. A systematic evaluation was conducted on the thermodynamics and exergoeconomic of the model, and the simulation results under basic operating conditions show that the first law efficiency, second law efficiency, net power output and total unit cost reach 55.73 %, 47.72 %, 13.709 MW and 27.44 $·GJ−1 respectively. The genetic algorithm and elitist non-dominated sorting genetic algorithm are used to optimize the system performance. By using the parallel direct search method, the maximum first law efficiency, as well as second law efficiency and a minimum total unit cost of 59.45 %, 52.23 % and 24.81 $·GJ−1 are obtained respectively. The optimal first law efficiency, second law efficiency, and total unit cost of the system, which are 53.52 %, 50.33 % and 26.44 $·GJ−1 respectively, are searched simultaneously from the multi-objective optimization results by LINMAP decision-making method. Furthermore, this paper analyzes the exergy flow rate of the system and heat transfer processes of the heat exchangers under optimal operating condition. A total of 23,059.35 kW of LNG cold energy is fully utilized by the system in the LNG gasification process. The exergy loss ratio and cost ratio of each equipment analysis demonstrates that the heat exchangers (HX) have the largest percentage both exergy loss ratio and cost ratio, especially the HX4.

Optimal Management in the Operation of Complex Technical Systems

Developing a cost management system for a complex technical system (CTS) at the stages of its life cycle is a modern trend aimed at creating sustainable cooperation ties based on requirements, including those of manufacturers and consumers. The article explores the concept of a complex technical system. The principles and properties of a complex technical system were described. A model of a procedure for checking the operability of a complex technical system with an arbitrary distribution of the time of independent manifestation of a failure was proposed for the example of compressor station equipment. Models of operation of complex technical systems based on information about their state were considered. It was also shown how to optimize maintenance decisions for these systems in terms of the minimum average unit cost and how reliable this ensures. Additionally, proof of the existence of an optimal verification strategy was given. An algorithm for determining the moments of verification was developed to ensure the minimum cost. The methods of collecting, processing, and effectively using information for making decisions about the technical condition of complex products and the possibility of further exploitation were improved based on selecting informative diagnostic features and constructing models that comprehensively consider the maximum and current level of their parameters. This allowed for the quality of the final products to be ensured. The practical use of the proposed methods of diagnosis and forecasting made it possible to increase the actual CTS resource by 1.5–2.0 times. This also increased the productivity of the technological process by 1.6 times due to the reduction of the number of stops for maintenance for replacement, adjustments, and sub-adjustments. As a result, the value of the lack of basic production was reduced from 1.2 % to 0.8 %, and the cost of manufacturing products was decreased by 1.2–2.0 times.

Determination of the optimal period for computations control in complexes of automated control systems programs

The purpose of the study is to determine the optimal period for monitoring calculations in complex software complexes of automated control systems. To achieve this goal, it is necessary to solve such problems as the analysis of periodic control systems, which boils down to determining the performance costs of computing systems for control, as well as ensuring a minimum of these costs. Theoretical foundations and descriptions of the process of evaluating the effectiveness of the automated control systems functioning are given. A rationale for the method of determining the optimal period for monitoring calculations in software complexes of the automated control systems is provided in the paper. An analytical study of control systems is carried out. The difference between the considered problem setting and the existing ones lies in the fact that the accuracy of error detection by the periodic control system is taken into account, while it is taken into account that for real control systems the probability of error detection is quite high. Thus, the results of studying the operational periodic control systems have shown that the main parameters that affect the optimal period of control are the mean time between failures. The dependence of the optimal control period on the probability of recovery is shown for different values of the duration of recovery by a reliable method. As the probability decreases, the optimal control period also decreases, which is associated with the need to spend a large proportion of the time on restoration using a reliable method; the corresponding increase in average unit costs can be compensated by an increase in the frequency of control procedures, i. e. a decrease in the control period. The dependence of the minimum average unit cost of control and the optimal period of its implementation on the average time between the errors appearance is given. With constant durations of control and recovery procedures and constant error detection probability, the optimal control period decreases, and the minimum average unit cost increases somewhat with a decrease in the average time between failures. This can be explained as follows: the more often an error can occur, the more often you need to control in order to reduce the losses due to working with the error.

Principles of transport means maintenance optimization: equipment cost calculation

Purpose. Justification of principles and methodology for effective calculation of the equipment costs and optimization of transport means maintenance. Methodology. The results of the presented scientific research were obtained using general and special methods of cognition: abstract and logical analysis, systematization and combination, method of theoretical generalization, method of dialectical cognition, deduction and induction, and statistical analysis. This paper analyzes the relationship between the probability of failure prevention by the maintenance system and the associated costs. The research investigates how the variation in the technical condition change rate influences the length of the operation cycle and the rate of its decline. The study’s outcomes are analyzed, including the formation of points of minimum unit costs, the effect of spare parts’ cost, and the practical importance of the conclusions drawn. Findings. This paper outlines the economic methodology for determining the specific expenses of maintaining means of transport. The methodology considers the distribution of expenses for spare parts, labor, and other components. Using this methodology, it is possible to estimate the total costs of maintenance and make informed decisions about the efficient use of resources. It has been determined that the cost of spare parts impacts the efficiency of the maintenance system. Therefore, it is imperative to balance the cost for spare parts and safety, while considering the probability of failure. The method outlined in this work is versatile, which allows its adaptation and application to the specialized road transport. Originality. The paper further develops the methodological approach to calculating equipment costs for transport maintenance, which is used to improve service efficiency and reduce expenses. The approach enables a comprehensive evaluation of the outcomes of enhancing failure prevention probability through the maintenance system. It also aids in managing unused parts’ resources, particularly during short operating cycles. Practical value. The study’s findings can optimize the maintenance system, increase operational efficiency, and enhance the safety and reliability of means of transport, while reducing the costs associated with spare parts, labor, and other maintenance components. This approach aids in conserving resources, reducing operating costs, and is crucial for the financial stability and profitability of management companies.

Fleet Ownership Model for Mineral Export Products Concerning Indonesia’s Downstream Mineral Policy: A Case Study of Copper Ore Exports

Indonesia’s copper ore has a contribution of 3% in the world’s copper ore needs and has rank of the 5th largest export of mining materials after briquette, kerosene, coal, and crude oil. According to Mineral and Coal Mining Law Number 4 of 2009 that raw materials of mining products have been prohibited to be exported including copper ore due to increasing the value of mineral export products. Thus, it would affect to the current copper ore shipment, which should firstly be processed by smelter to be work-in-process products, namely cathodes. In order to comply with the downstream policy, this study aimed to select the optimum vessel used for delivering copper ores to smelter as well as to define the minimum unit cost for transporting cathodes from smelter to importing countries. The method of non-linear programming was used to produce the minimum unit cost of transport for these three scenarios of fleet ownership model: (1) charter vessel, (2) new shipbuilding vessel, (3) second-hand vessel. The results obtained that the selected domestic ship was a new shipbuilding scenario with the type of bulk carrier, transporting copper ores from site to smelter. Meanwhile, the selected export ship was a voyage charter scenario with the type of general cargo vessel, delivering cathodes from smelter to importing countries.

On the best coefficient of performance and specific heating or cooling power combination for adsorption refrigerators and heat pumps

The performance parameters of adsorption refrigerators or heat pumps are the coefficient of performance (COP) and the specific cooling power (SCP) or specific heating power (SHP), respectively. Higher COPs are associated with the longer cycle times required for more complete desorption and adsorption processes, resulting in a lower number of cycles per unit time and consequently in lower SCP or SHP, unless large masses of adsorbent material are used. The inverse situation occurs for shorter cycle times, associated with smaller COPs and higher SCP or SHP. This behavior leads to a relevant question: what is the combination of COP and SCP or SHP corresponding to the optimal performance of adsorption refrigerators or heat pumps? Although this question is recurrent in literature, its objective answer is still lacking. This work proposes an objective criterion to answer this question, setting the best balance between the COP and the SCP or SHP of adsorption refrigerators or heat pumps, as corresponding to the minimum unit cost of the obtained useful effect. The proposed criterion allows obtaining the cycle time that corresponds to the searched optimal performance. The dependence of the COP and the SCP or SHP on the cycle time can be obtained from numerical simulations for an adsorption system. Once these dependencies are known, it can be identified the cycle time leading to the minimum unit cost of the obtained useful effect, which corresponds the best balance between the COP and the SCP or SHP.

A novel solar desalination system based on an evacuated tube collective condenser heat pipe solar collector: A thermo-economic and environmental analysis

Solar desalination has captivated consideration to overcome the problem of the scarcity of freshwater, with simple-design, economic, and environment-friendly solutions. This study navigates a novel solar-evacuated glass tube collector integrated with a collective condenser heat pipe system for solar desalination. A newly designed heat pipe array was represented in this work by affixing all the evaporator tube units of the heat pipes to a single condenser unit and was attached to the evacuated tube solar collector. The innovative assembly of the heat pipe provided uniform heating of water and rapid steam generation. The present system acts as a solar collector and as a stand-alone basin for freshwater formation. The performance assessment of the neoteric system was conducted based on half-filled and three-fourth-filled conditions of the water flow pipe kept within the collective condenser heat pipe. The maximum heat pipe temperature recorded during the half-filled state was 156.9°C and 151.48°C in the three-fourth-filled state. The half-filled state of the water flow pipe delivered a total distilled water content of 8,050 ml/day, whereas the three-fourth-filled state delivered 5,925 ml/day of distilled water. The maximum energy and exergy efficiency of the presented system was 19.27% and 3.92%, respectively. The economic minimum unit cost of freshwater by the present system is 4.27 INR, and the payback period is 2.9 years. The present eco-friendly energy system saves 4.25 kWh of electricity and 4.16 × 10−3 tons of CO2 equivalent per year.

Integration of Supercritical CO2 Recompression Brayton Cycle with Organic Rankine/Flash and Kalina Cycles: Thermoeconomic Comparison

The use of the organic Rankine cycle (ORC), organic flash cycle (OFC) and Kalina cycle (KC) is proposed to enhance the electricity generated by a supercritical CO2 recompression Brayton (SCRB) cycle. Novel comparisons of the SCRB/ORC, SCRB/OFC and SCRB/KC integrated plants from thermodynamic, exergoeconomic and sustainability perspectives are performed to choose the most appropriate bottoming cycle for waste heat recovery for the SCRB cycle. For comprehensiveness, the performance of the SCRB/OFC and SCRB/ORC layouts are examined using ten working fluids. The influence of design parameters such as pressure ratio in the supercritical CO2 (S-CO2) cycle, pinch point temperature difference in heater and pre-cooler 1, turbine inlet temperature and pressure ratio for the ORC/OFC/Kalina cycles are examined for the main system indicators including the net output power, energy and exergy efficiencies, and unit cost of power production. The order of the exergy efficiencies for the proposed systems from highest to lowest is: SCRB/ORC, SCRB/OFC and SCRB/KC. The minimum unit cost of power production for the SCRB/ORC system is lower than that for the SCRB/KC and SCRB/OFC systems, by 1.97% and 0.75%, respectively. Additionally, the highest exergy efficiencies for the SCRB/OFC and SCRB/ORC systems are achieved when n-nonane and R134a are employed as working fluids for the OFC and ORC, respectively. According to thermodynamic optimization design, the SCRB/ORC, SCRB/OFC and SCRB/KC systems exhibit sustainability indexes of 3.55, 3.47 and 3.39, respectively.

A novel combination of absorption heat transformer and refrigeration for cogenerating cooling and distilled water: Thermoeconomic optimization

A novel cogeneration system consisting of an absorption heat transformer and refrigeration system integrated with a water desalination system is proposed, analyzed, and optimized. The cogeneration and desalination systems interacted thermally. The proposed system is flexible in producing cooling and distilled water with variable fractions. Influences on system performance are investigated of the decision parameters. A maximum value of 39 °C is achieved for gross temperature lift. Also, it is observed that the condenser temperature, which is influenced by climate conditions, affects system performance. The system performance is optimized considering such criteria as exergy efficiency, the rate of distilled water production, and total product unit cost. Depending on the criteria used for optimization, the results indicate a minimum total product unit cost of 42.6$/GJ, a maximum exergy efficiency of 27.9%, and a maximum distilled water mass flow rate of 0.53 kg/s. The minimum total capital cost rate and exergy destruction cost rate are found to be 11 $/h and 3.89 $/h, respectively. Under optimized conditions, the generator is seen to contribute the most to the total exergy destruction rate. The values of levelized cost of energy and water and payback period are 0.013 $/kWh, 9 $/m3 and 1.8 year, respectively.

Determination of optimal oil pumping plans

This paper presents the results of determining the optimal plans for pumping oil through the main oil pipelines of Kazakhstan. The calculation methodology is based on determining the minimum unit cost of pumping depending on oil flow rate. Oil pumping energy-saving modes are determined under optimal operating conditions of pumping units and heating furnaces at stations. Determination of the optimal pumping plan is implemented as a separate module of the SmartTranPro software. Pumped oil volumes on the oil pipeline sections were determined on the basis of the automated system of control and metering of electrical energy data of KazTransOil JSC. Optimal pumping plans for monthly oil volumes in the Kalamkas – Karazhanbas and Dzhumagaliev – Atasu pipeline sections for cold and warm periods were calculated on the basis of the found dependence of the pumping unit cost. For each range of oil mass flow rate, specific costs for oil pumping and a list of operating pumps at oil pumping stations located along the pipeline section are indicated.

Mathematical model of optimization of repair activities of power equipment

The tasks related to the efficient operation and maintenance of the power equipment in a working condition are considered. In the work, a model is built and a method is proposed for optimizing the intensity of performance indicators, which does not take into account the structure and with instant indexing of failure. At this stage, a lower estimate is obtained for the minimum average unit costs, taking into account the residual resource of the elements of such a system. This makes it possible to provide the required level of emergency repair frequency. The collection and accumulation of such information is in demand when planning subsequent preventive restorations of elements and equipment of electric power enterprises.

Multi-objective optimization of a cold-climate two-stage economized heat pump for residential heating applications

Energy consumption and environmental concerns are the two main drivers optimize heat pump systems. However, under extreme weather conditions especially in heating mode, conventional heat pumping systems face challenges when operating in cold-climates such as in Minneapolis, MN, USA. In the current work, a two-stage vapor injected heat pump system was optimized for residential applications at low ambient operating conditions using R-32, R-290, R-410A, R-454A and R–452B as working fluids. The system model was simulated using nondominated sorting genetic algorithm II (NSGA-II) method to obtain the Pareto-Frontier curves. The final solution for decision-making was selected based on a technique for order performance by similarity to ideal solution (TOPSIS) method. The system with R-32 and R-290 had a minimum unit cost of heat (UCH) of 0.19 $ kWh−1 and a maximum heating coefficient of performance (COP) of and 5.2, respectively. From the specific exergy costing (SPECO) analysis of the system, the results showed that the highest and lowest total investment cost were contributed with R-290 by 1.35 $ hr−1 and R-32 by 0.09 $ hr−1, respectively. Whereas, the maximum and minimum total cost rate of destruction were associated with R-290 by 1.73 $ hr−1 and R–452B by 1.33 $ hr−1, respectively.

Exergoeconomic analysis and optimization of a combined cooling, heating and power system based on organic Rankine and Kalina cycles using liquified natural gas cold energy

With the increase of liquified natural gas trade, more and more attention has been paid to the liquified natural gas cold energy utilization. In order to better recover and utilize liquified natural gas cold energy, a novel combined cooling, heating and power system based on liquified natural gas cold energy utilization and exhaust gas waste heat recovery is proposed in this paper. The system consists of a three-stage organic Rankine cycle, a Kalina cycle and liquified natural gas direct expansion. To evaluate the performance of the combined cooling, heating and power system, a mathematical model was established, and through the thermodynamic analysis the net output power, thermal efficiency, and exergy efficiency of the system were 1257.708 kW, 43.43%, and 70.4%, respectively. The effects of the pump and compressor outlet pressure, n-hexane mass flow rate in the first Rankine cycle, turbine inlet temperature, and isentropic efficiency of the turbines on the system performance were analyzed. Moreover, exergoeconomic analysis is used to calculate the total product unit cost of the combined cooling, heating and power system, which was found to be 51.1 $/GJ. In addition, single- and multi-objective optimizations of the system were performed. The multi-objective optimization results show that the maximum exergy efficiency and minimum total product unit cost of this novel combined cooling, heating and power system were 80.49% and 48.04 $/GJ, respectively. This work shows a great potential in utilizing the liquified natural gas cold energy and waste heat of exhaust gas by a combined cooling, heating and power system.

Comprehensive analysis of a novel power and cooling cogeneration system based on organic Rankine cycle and ejector refrigeration cycle

A novel combined power and cooling system based on the organic Rankine cycle and the ejector refrigeration cycle for highly efficient utilization of low-grade heat is presented, in which the endothermic process adopts a dual-pressure evaporation approach and the two vapor generators are connected in series. A mathematical model is developed to evaluate the system thermodynamic and exergoeconomic characteristics. The effects of key parameters on system performance are evaluated. Results show that a higher low-pressure evaporation temperature and a higher vapor fraction at the low-pressure vapor generator are conducive to increasing the system cooling output. An optimal high-pressure evaporation temperature exists that gives the maximum exergy efficiency and the minimum sum unit cost of product. Compared with the net power output of the system, the cooling output is more sensitive to the variation of condensation temperature. Among the system components, the ejector has the highest exergy destruction rate and the lowest exergy efficiency. Furthermore, optimization of the system’s performance and working fluid selection for fixed cooling outputs was conducted. The results show that reducing the exergy destruction in the endothermic process is the key to improving system performance, while perfluoropropane was found to be the most suitable working fluid for the proposed system. In the cooling output range of 300–700 kW, a minimum sum unit cost of product of 45.79–58.87 $/MWh can be achieved, and corresponding ranges of net power output, energy efficiency and exergy efficiency are 614.93–430.58 kW, 14.32–19.25%, and 32.3–22.62%, respectively. Finally, the performance of the proposed system is compared with two typical systems for a cooling output range of 300–700 kW. The results show that the sum unit cost of product is reduced by 7.9–11.1%, and the net power output increased by 23.6–40.6% compared with the system with parallel vapor generators. Compared to the system with the ejector installed after the turbine, the sum unit cost of product is increased by 9.16–13.28%, and the net power output is increased by 129.73–118.38%.

The logistics system planning for red onion: case study of Sulawesi and Maluku Islands

Red onion is a horticultural product produced in several regions of Java Island. This commodity only grows in certain seasons where the production time of one region to other regions is different. The lack of logistics design makes traders from producing regions unable to deliver it to demanded areas due to inappropriate selection of transportation combination and its schedule. This increases its distribution cost in Sulawesi Island and Maluku regions. This research aims to plan a red onion logistics system distribution for West Sulawesi, Southeast Sulawesi, Central Sulawesi, Gorontalo, North Sulawesi, Maluku and North Maluku, by taking into account the production location based on the onion harvest time, combination of shipping method, ship type, scheduling and quality so it will arrive on time with maintained quality. The logistic system is designed by using an optimization method to obtain optimal transportation modes and minimum unit costs. The optimization results show that the most suitable shipment is to use container ship owned by private shipping company, either in full container load (FCL) or in less container load (LCL). The average logistics costs to Sulawesi Island and Maluku Region are IDR 3,037/kg (USD 0.21/kg) and IDR 2,296/kg (USD 0.16/kg), respectively. These are 31% and 27% lower than the previous values, while the average damage rates are 4% and 5%, 6% and 5% lower than before.

Logistics System of Exported Fishery Product : a Case Study of Fisheries Centre in Natuna

As one of potential fishery areas in Natuna, the Integrated Marine and Fisheries Center (SKPT) has been producing the fishery commodities of 350,000 kg per month. Currently, SKPT Natuna is cooperating with Japan to export one of fishery products, which is frozen octopus. However, the existing export logistics system is considered ineffective and inefficient due to the higher logistics cost and higher lead time. This study aims to develop logistics system model with respect to obtain the optimum travel duration and the schedule of ship arrival at each transit point by considering minimum unit cost. The method used is the Shortest Path Problem [1] to optimize 24 cargo delivery schedules for one year so that the optimum routes defined are different for each delivery schedule depending on the availability of ship. The result shows the total duration of the delivery required is 32 days and the total shipping cost is Rp. 31,3 million/TEU. Thus, the optimum route obtained is able to reduce the shipping cost of frozen octopus by 45% and shorten the lead time by 15% compared to the current logistics system.

Exergoeconomic Evaluation and Optimization of Dual Pressure Organic Rankine Cycle (ORC) for Geothermal Heat Source Utilization

In the present study, a dual-pressure organic Rankine cycle (DORC) driven by geothermal hot water for electricity production is developed, investigated and optimized from the energy, exergy and exergoeconomic viewpoint. A parametric study is conducted to determine the effect of high-stage pressure and low-stage pressure variation on the system thermodynamic and exergoeconomic performance. The DORC is further optimized to obtain maximum exergy efficiency optimized design (EEOD case) and minimum product cost optimized design (PCOD case). The exergy efficiency and unit cost of power produced for the optimization of EEOD case and PCOD case are 33.03% and 3.059 cent/kWh, which are 0.3% and 17.4% improvement over base case, respectively. The PCOD case proved to be the best, with respect to minimum unit cost of power produced and net power output over the base case and EEOD case.

Parametric analysis of combined power and freshwater producing system for natural gas engine heat recovery

The present paper focuses on exergoeconomic optimization of a proposed system with the goal of cogenerating freshwater and power, simultaneously. The cogeneration system includes Internal Combustion Engine, Organic Rankine Cycle, and Reverse Osmosis desalination unit. The thermodynamic model of the cogeneration system is investigated from energy, exergy, and exergoeconomic viewpoint. In addition, the variation of some key parameters including the engine speed, turbine inlet pressure, the number of the active vessels, freshwater mass flow rate, and the unit cost of freshwater to obtain optimum working condition is analyzed. The results show that the optimum value of the unit cost of power generation and freshwater occurs when the engine speed is 4000 rpm. Based on the optimization, the optimal condition does not occurred at the speed that exergy destruction becomes minimum. Furthermore the optimum value of the turbine inlet pressure was obtained respect to the maximum exergy efficiency and minimum unit cost of fresh water. The result showed that the optimum value of the turbine inlet pressure is 2690 kPa. There is an optimum value for the number of the active vessels that is achieved when 3 pressure vessels exist in the stage. In addition, the multi-objective optimization of the system based on the Pareto method revealed that at the optimum working condition, the exergy efficiency and freshwater mass flow rate are 30.7% and 2.926 kg/s, respectively. As a final result, it can be stated that the optimal values are not achieved in the minimum exergy destruction.

Algorithm for optimizing the parameters of the maintenance process according to the state with a constant periodicity of control over the criterion of minimum unit cost of operation

Algorithm for optimizing the parameters of the maintenance process according to the state with a constant periodicity of control over the criterion of minimum unit cost of operation