Assessment of the Turkish utility sector through energy and exergy analyses

The present study deals with evaluating the utility sector in terms of energetic and exergetic aspects. In this regard, energy and exergy utilization efficiencies in the Turkish utility sector over a wide range of period from 1990 to 2004 are assessed in this study. Energy and exergy analyses are performed for eight power plant modes, while they are based on the actual data over the period studied. Sectoral energy and exergy analyses are conducted to study the variations of energy and exergy efficiencies for each power plants throughout the years, and overall energy and exergy efficiencies are compared for these power plants. The energy utilization efficiencies for the overall Turkish utility sector range from 32.64% to 45.69%, while the exergy utilization efficiencies vary from 32.20% to 46.81% in the analyzed years. Exergetic improvement potential for this sector are also determined to be 332 PJ in 2004. It may be concluded that the methodology used in this study is practical and useful for analyzing sectoral and subsectoral energy and exergy utilization to determine how efficient energy and exergy are used in the sector studied. It is also expected that the results of this study will be helpful in developing highly applicable and productive planning for energy policies.     

Dynamic energy and exergy analyses of an industrial cogeneration system

The study deals with the energetic and exergetic analyses of a cogeneration (combined heat and power, CHP) system installed in a ceramic factory, located in Izmir, Turkey. This system has three gas turbines with a total capacity of 13 MW, six spray dryers and two heat exchangers. In the analysis, actual operational data over one‐month period are utilized. The so‐called CogeNNexT code is written in C++ and developed to analyze energetic and exergetic data from a database. This code is also used to analyze turbines, spray dryers and heat exchangers in this factory. Specifications of some parts of system components have been collected from the factory. Based on the 720 h data pattern (including 43 200 data), the mean energetic and exergetic efficiency values of the cogeneration system are found to be 82.3 and 34.7%, respectively. Copyright © 2009 John Wiley & Sons, Ltd.     

Energy and exergy analyses of an ice-on-coil thermal energy storage system

In this study, energy and exergy analyses are carried out for the charging period of an ice-on-coil thermal energy storage system. The present model is developed using a thermal resistance network technique. First, the time-dependent variations of the predicted total stored energy, mass of ice, and outlet temperature of the heat transfer fluid from a storage tank are compared with the experimental data. Afterward, performance of an ice-on-coil type latent heat thermal energy storage system is investigated for several working and design parameters. The results of a comparative study are presented in terms of the variations of the heat transfer rate, total stored energy, dimensionless energetic/exergetic effectiveness and energy/exergy efficiency. The results indicate that working and design parameters of the ice-on-coil thermal storage tank should be determined by considering both energetic and exergetic behavior of the system. For the current parameters, storage capacity and energy efficiency of the system increases with decreasing the inlet temperature of the heat transfer fluid and increasing the length of the tube. Besides, the exergy efficiency increases with increasing the inlet temperature of the heat transfer fluid and increasing the length of the tube.     

Energy sector reform,energy transitions and the poor in Africa

There is little systematic information about the impact of energy sector reform on all sources and methods of energy utilised or potentially utilised by the poor. It is not sufficiently known what fuels the poor use, if a larger range of fuels becomes available and affordable and if barriers to access and consumption are reduced. A detailed assessment is presented for four countries, three in Africa (Botswana, Ghana and Senegal) and for comparison one in Latin America (Honduras), of steps taken to reform the energy sector and their effect on various groups of poor households. The paper analyses the pattern of energy supply to, and use by, poor households and explores the link—or its absence—to energy policy. We investigate what works for the poor and which type of reforms and implementation are effective and lead to a transition to more efficient and clean fuels from which the poor benefit.     

Disaggregate energy consumption and industrial production in South Africa

This paper tries to assess the relationship between disaggregate energy consumption and industrial output in South Africa by undertaking a cointegration analysis using annual data from 1980 to 2005. We also investigate the causal relationships between the various disaggregate forms of energy consumption and industrial production. Our results imply that industrial production and employment are long-run forcing variables for electricity consumption. Applying the [Toda, H.Y., Yamamoto, T., 1995. Statistical inference in vector autoregressions with possibly integrated processes. Journal of Econometrics 66, 225–250] technique to Granger-causality, we find bi-directional causality between oil consumption and industrial production. For the other forms of energy consumption, there is evidence in support of the energy neutrality hypothesis. There is also evidence of causality between employment and electricity consumption as well as coal consumption causing employment.     

A review and assessment of the energy utilization efficiency in the Turkish industrial sector using energy and exergy analysis method

Exergy has been seen a key component for a sustainable society, and in the recent years exergy analysis has been widely used in the design, simulation and performance evaluation of thermal and thermo chemical systems. A particular thermo dynamical system is the society of a country, while the energy utilization of a country can be assessed using exergy analysis to gain insights into its efficiency and potential for improvements.Energy and exergy utilization efficiencies in the Turkish industrial sector (TIS) over the period from 1990 to 2003 are reviewed and evaluated in this study. Energy and exergy analyses are performed for eight industrial modes, namely iron–steel, chemical–petrochemical, petrochemical–feedstock, cement, fertilizer, sugar, non-metal industry, other industry, while in the analysis the actual data are used. Sectoral energy and exergy analyses are conducted to study the variations of energy and exergy efficiencies for each subsector throughout the years studied, and these heating and overall energy and exergy efficiencies are compared for the eight subsectors. The chemical and petrochemical subsector, and the iron and steel subsector appear to be the most energy and exergy efficient sectors, respectively. The energy utilization efficiencies for the Turkish overall industrial sector range from 63.45% to 70.11%, while the exergy utilization efficiencies vary from 29.72% to 33.23% in the analyzed years. Exergetic improvement potential for this sector is also determined to be 681 PJ in 2003, with an average increase rate of 9.5% annually for the analyzed years. It may be concluded that the methodology used in this study is practical and useful for analyzing sectoral and subsectoral energy and exergy utilization to determine how efficient energy and exergy are used in the sector studied. It is also expected that this study will be helpful in developing highly applicable and productive planning for energy policies.     

Energy analysis and exergy utilization in the transportation sector of Jordan

The transport sector is responsible for about 37% of total final energy demand in Jordan, and thus it is considered an important driver for determining future national energy needs. This paper presents energy analysis and exergy utilization in the transportation sector of Jordan by considering the sectoral energy and exergy flows for the last two decades. The transportation sector, in Jordan, is a two-mode system, namely, road, which covers almost all domestic passenger and freight transport and airways. The latter is mainly used for international flights. The average estimated overall energy and exergy efficiencies were found as 23.2% and 22.8%, respectively. This simply indicates that there is large potential for improvement and efficiency enhancement. It is believed that the present technique is practical and useful for analyzing sectoral energy and exergy utilization to determine how efficiently energy and exergy are used in the transportation sector. It is also helpful to establish standards, based on exergy, to facilitate applications in different planning processes such as energy planning. A comparison with other countries showed that energy and exergy efficiencies of the Jordanian transport sector are slightly lower than that of Turkey, and higher than those incurred in Malaysia, Saudi Arabia and Norway. Such difference is inevitable due to dissimilar structure of the transport sector in these countries.     

Energy and exergy analyses of sugar production stages

This paper presents the energy and exergy analyses of sugar production stages by using the operational data from Bor Sugar Plant, Turkey. For these purposes, all stages of sugar production, considered as a steady-state open thermodynamic system, were analysed by employing the first and second law of thermodynamics. In this regard, the first and second law efficiencies, the magnitude and place of exergy losses in these production stages were estimated and discussed in detail. It was concluded that the exergy loses took place mostly during the sherbet production process (η_I,sp=96.8% η_II,sp=49.3%) because of the irreversibility in the sub-operation stages, which are vapour production, circulation sherbet mixing and bagasse compression. Therefore, it is generally suggested that the irreversibility, mostly stem from the finite temperature differences at the production stages, should be reduced to conduct more productively the sugar production process. Copyright © 2003 John Wiley & Sons, Ltd.     

Energy and exergy analyses of a gasoline engine

This study presents comparative energy and exergy analyses of a four-cylinder, four-stroke spark-ignition engine using gasoline fuels of three different research octane numbers (RONs), namely 91, 93 and 95.3. Each fuel test was performed by varying the engine speed between 1200 and 2400 rpm while keeping the engine torque at 20 and 40 Nm. Then, using the steady-state data along with energy and exergy rate balance equations, various performance parameters of the engine were evaluated for each fuel case. It was found that the gasoline of 91-RON, the design octane rating of the test engine, yielded better energetic and exergetic performance, while the exergetic performance parameters were slightly lower than the corresponding energetic ones. Furthermore, this study revealed that the combustion was the most important contributor to the system inefficiency, and almost all performance parameters increased with increasing engine speed. Copyright © 2006 John Wiley & Sons, Ltd.     

Energy and exergy utilization in agricultural sector of Saudi Arabia

This paper presents an analysis of energy and exergy utilization in the agricultural sector of Saudi Arabia by considering the sectoral energy and exergy flows for a period of 12 years between 1990 and 2001. Energy and exergy analyses are conducted for its two essential devices, namely tractors and pumps, and hence the sectoral energy and exergy efficiencies are obtained for comparison for a period of 12 years. Two main energy sources are diesel for tractors and electricity for pumps in the sector. It is found that the overall exergy efficiencies in this sector are slightly less than the corresponding energy efficiencies, e.g. 74.19–69.20% for exergy efficiency and 74.94–74.60% for energy efficiency from 1990 to 2001. The present technique is proposed as a useful tool in sectoral analysis of energy and exergy utilization, developing energy policies and providing energy conservation measures.     

Air quality and climate change co-benefits for the industrial sector in Durban,South Africa

Industries in Durban, South Africa, are a major source of air pollutant emissions and large users of fossil fuel based energy. Durban’s energy strategy prioritises energy efficiency at industries as a key action, whilst industries are also the focus of the city’s air quality management plan (AQMP). In this paper, measures that have been introduced in industries in Durban to effect air quality improvements and reduce energy consumption are examined in terms of their respective impacts on greenhouse gas (GHG) and air pollutant emissions. It was found that co-benefits for GHG mitigation were achieved when petroleum refineries switched from using heavy fuel oil to refinery gas and methane rich gas. Within other industries, co-benefits for air quality stemmed from reducing fossil fuel energy consumption and the improved efficiency of combustion systems. Air quality and energy policies in the city are being executed independently, without consideration of the trade-offs or synergies of the interventions being implemented. Recommendations are made for authorities and industries to consider the co-benefits for GHG mitigation in their AQMPs and where these are not possible to consider offsetting the increased GHG emissions through improved alignment with energy strategies.     

Energy and exergy analyses of space heating in buildings

In the present study, energy and exergy analyses are presented for the whole process of space heating in buildings. This study is based on a pre-design analysis tool, which has been produced during ongoing work for the International Energy Agency (IEA) formed within the Energy Conservation in Buildings and Community Systems Programme (ECBCSP) Annex 37. Throughout this paper, in all of the calculations such as heat losses and gains were taken according to Turkish Standards Institution TSE, which is in accordance with the European Standard TS EN ISO 13789. In the analysis, heating load is taken account but cooling load is neglected and the calculations presented here are done using steady state conditions. The analysis is applied to an office in Izmir with a volume of 720 m³ and a net floor area of 240 m² as an example of application. Indoor and exterior air temperatures are 20 °C and 0 °C, respectively. It is assumed that the office is heated by a liquid natural gas (LNG) fired conventional boiler, an LNG condensing boiler and an external air–air heat pump. With this study, energy and exergy flows are investigated. Energy and exergy losses in the whole system are quantified and illustrated. The highest efficiency values in terms of energy and exergy were found to be 80.9% for external air–air heat pump and 8.69% for LNG condensing boiler, respectively.     

Energy and exergy analyses of direct ironsmelting processes

The paper discusses the concept of exergy, the energy and exergy balances of blast furnace ironmaking and DIOS-type direct ironsmelting processes, and exergy losses in these processes. The overall fuel efficiency of direct ironsmelting strongly depends on the utilisation of off-gas. It is shown that if off-gas is not utilised efficiently, the fuel efficiency of the direct ironsmelting process is enhanced strongly by increasing heat transfer efficiency and post-combustion ratio. Otherwise, when the off-gas is utilised efficiently, post-combustion ratio and heat transfer efficiency are less significant for the overall fuel efficiency.     

Energy,exergy, and sensitivity analyses of underwater compressed air energy storage in an island energy system

An underwater compressed air energy storage (UWCAES) system is integrated into an island energy system. Both energy and exergy analyses are conducted to scrutinize the performance of the UWCAES system. The analyses reveal that a round‐trip efficiency of 58.9% can be achieved. However, these two analyses identify different directions for further improvement. The heat exchangers, expanders, compressors, electric motors, and generators account for the most exergy destruction. A sensitivity analysis is also conducted to investigate the importance of different input parameters on the round‐trip exergy efficiency of the UWCAES system. The results of both local and global analyses show that the round‐trip exergy efficiency is most sensitive to the isentropic efficiency of the expanders and compressors, and the efficiencies of the electric motors and generators. The impacts of the heat exchangers, the self‐discharge rate of the air accumulator, the inner diameter of the pneumatic pipelines, and the insulation thickness of the hot‐oil tank on the round‐trip exergy efficiency are shown to be highly nonlinear.     

Energy and exergy analyses of OMW solar drying process

The energy and exergy analyses of the drying process of olive mill wastewater (OMW) using an indirect type natural convection solar dryer are presented. Olive mill wastewater gets sufficiently dried at temperatures between 34 °C and 52 °C. During the experimental process, air relative humidity did not exceed 58%, and solar radiation ranged from 227 W/m² to 825 W/m². Drying air mass flow was maintained within the interval 0.036–0.042 kg/s. Under these experimental conditions, 2 days were needed to reduce the moisture content to approximately one-third of the original value, in particular from 3.153 g_water/g_{dry matter} down to 1.000 g_water/g_{dry matter}.Using the first law of thermodynamics, energy analysis was carried out to estimate the amounts of energy gained from solar air heater and the ratio of energy utilization of the drying chamber. Also, applying the second law, exergy analysis was developed to determine the type and magnitude of exergy losses during the solar drying process. It was found that exergy losses took place mainly during the second day, when the available energy was less used. The exergy losses varied from 0 kJ/kg to 0.125 kJ/kg for the first day, and between 0 kJ/kg and 0.168 kJ/kg for the second. The exergetic efficiencies of the drying chamber decreased as inlet temperature was increased, provided that exergy losses became more significant. In particular, they ranged from 53.24% to 100% during the first day, and from 34.40% to 100% during the second.     

Assessment of the energy and exergy utilization efficiencies in the Turkish agricultural sector

This study deals with evaluating the energy and exergy utilization efficiencies in the Turkish agricultural sector over a 12‐year period from 1990 to 2001. In the energy and exergy analyses, two main energy sources, namely fuels and electricity, are taken into consideration, while the sectoral energy and exergy efficiencies are compared for this period. These main energy sources include diesel for tractors and other vehicles, and electricity for pumps. Overall energy utilization efficiencies are obtained to vary between 29.1 and 41.1%, while overall exergy utilization efficiencies are found to range from 27.9 to 37.4% in the analysed years, respectively. It may be concluded that the present technique proposed here may be used as a useful tool in analysing and evaluating the energy and exergy utilization efficiencies, identifying energy efficiency and/or energy conservation opportunities and dictating the energy strategies of countries. Copyright © 2005 John Wiley & Sons, Ltd.     

Energy and exergy analyses of cold thermal storage systems

This study deals with the assessment of the thermodynamic performance of cold thermal storage systems using exergy and energy analyses. Several cases are considered, including some storages which are homogeneous, and others which undergo phase changes. In some cases the storages are stratified. A full cycle of charging, storing and discharging is considered for each case. Four cold thermal storage cases are presented in an illustrative example. The results demonstrate that exergy analysis provides more realistic and accurate assessments of the efficiency and performance of cold thermal storage systems than those given by the more conventional energy analysis. In addition, exergy analysis is conceptually more direct since it treats cold as a valuable commodity. It is concluded that the potential usefulness of exergy analysis in addressing and solving cold thermal storage problems is substantial. Copyright © 1999 John Wiley & Sons, Ltd.     

Energy and exergy analyses of the oxidation and gasification of carbon

Exergy losses in gasification and combustion of solid carbon are compared by conceptually dividing the processes into several subprocesses: instantaneous chemical reaction, heat transfer from reaction products to reactants (internal thermal energy exchange) and product mixing. Gasification is more efficient than combustion because exergy losses due to internal thermal energy exchange are reduced from 14–16 to 5–7% of expended exergy, while the chemical reactions are relatively efficient for both processes. The losses due to internal thermal energy exchange may be reduced by replacing air with oxygen, although this introduces additional process losses for separation of oxygen from air, or alternatively, preheating of air by heat exchange with product gas. For oxygen-blown gasification of fuels with high calorific value, such as solid carbon, it is advisable to moderate the temperature by introduction of steam. At optimum gasification temperatures in the ranges of 1100–1200 K (for atmospheric pressure) and 1200–1300 K (for 10 bar pressure), up to 75% of the chemical exergy contained in solid carbon can be preserved in the chemical exergy of carbon monoxide and hydrogen.     

Energy,exergy and economic analysis of industrial boilers

In this paper, the useful concept of energy and exergy utilization is analyzed, and applied to the boiler system. Energy and exergy flows in a boiler have been shown in this paper. The energy and exergy efficiencies have been determined as well. In a boiler, the energy and exergy efficiencies are found to be 72.46% and 24.89%, respectively. A boiler energy and exergy efficiencies are compared with others work as well. It has been found that the combustion chamber is the major contributor for exergy destruction followed by heat exchanger of a boiler system. Furthermore, several energy saving measures such as use of variable speed drive in boiler's fan energy savings and heat recovery from flue gas are applied in reducing a boiler energy use. It has been found that the payback period is about 1 yr for heat recovery from a boiler flue gas. The payback period for using VSD with 19 kW motor found to be economically viable for energy savings in a boiler fan.     

Energy and exergy analyses of hydrogen production via solar-boosted ocean thermal energy conversion and PEM electrolysis

Energy and exergy analyses are reported of hydrogen production via an ocean thermal energy conversion (OTEC) system coupled with a solar-enhanced proton exchange membrane (PEM) electrolyzer. This system is composed of a turbine, an evaporator, a condenser, a pump, a solar collector and a PEM electrolyzer. Electricity is generated in the turbine, which is used by the PEM electrolyzer to produce hydrogen. A simulation program using Matlab software is developed to model the PEM electrolyzer and OTEC system. The simulation model for the PEM electrolyzer used in this study is validated with experimental data from the literature. The amount of hydrogen produced, the exergy destruction of each component and the overall system, and the exergy efficiency of the system are calculated. To better understand the effect of various parameters on system performance, a parametric analysis is carried out. The energy and exergy efficiencies of the integrated OTEC system are 3.6% and 22.7% respectively, and the exergy efficiency of the PEM electrolyzer is about 56.5% while the amount of hydrogen produced by it is 1.2 kg/h.