Physical sustainability assessment for the China society: Exergy-based systems account for resources use and environmental emissions

As a physical assessment of the sustainability of the China society, presented in this paper is an exergy-based systems account for resources use and environmental emissions of the China society in 2006 as the most recent year with statistics availability. Exergy analysis is applied to elucidate the resources flows from the natural environment into the society, between other countries or regions and the society, between the sectors of the society, and the emissions outflows into the natural environment from different sectors. For the China society broken down into seven sectors (i.e., extraction, conversion, agriculture, industry, transportation, tertiary and households) as one of the most complicated cases, systems account of environmental emissions as greenhouse gases and “three wastes” is carried out for the first time, combined with an updated resources account. The total societal exergy consumption amounts to 101.1 EJ, of which 93.6% is due to resources use accounted as 94.6 EJ, of which 23.2% is by the industry sector, 22.8% by conversion, 20.4% by households, 12.3% by agriculture, 9.0% by tertiary, 6.9% by extraction and 5.4% by transport, and 6.4% due to environmental emissions accounted as 6481.6 PJ, including greenhouse gas emissions of 5706.1 PJ, with the highly remarkable fraction of 49.05% from CH₄ of the same importance as 50.91% from CO₂ and only 0.04% from N₂O, and “three wastes” emissions of only 775.5 PJ. The extraction sector is shown as the leading emitter with 32.6% of the total emissions, followed by the industry with 20.0%, agriculture with 17.3%, and conversion sector with 16.8%. To characterize the network performance in context of environmental resources from a systems ecological perspective, exergy-based ecological efficiency and resources conversion coefficient are found as 88.8% and 91.3% for the extraction sector, 29.0% and 30.0% for the conversion sector, 31.5% and 33.5% for the agriculture sector, 34.8% and 36.1% for the industry sector, 16.3% and 17.3% for the transportation sector, 38.4% and 38.5% for the tertiary sector, and only 1.3% and 1.3% for the households sector, respectively. Comparisons with other societies and with China society in previous years are made to further illustrate the physical sustainability of the societal system on the international and development horizons.     

Modelling the energy and exergy utilisation of the Mexican non-domestic sector: A study by climatic regions

This paper presents the development of a bottom-up stock model to perform a holistic energy study of the Mexican non-domestic sector. The current energy and exergy flows are shown based on a categorisation by climatic regions with the aim of understanding the impact of local characteristics on regional efficiencies. Due to the limited data currently available, the study is supported by the development of a detailed archetype-based stock model using EnergyPlus as a first law analysis tool combined with an existing exergy analysis method. Twenty-one reference models were created to estimate the electric and gas use in the sector. The results indicate that sectoral energy and exergy annual input are 95.37 PJ and 94.28 PJ, respectively. Regional exergy efficiencies were found to be 17.8%, 16.6% and 23.2% for the hot-dry, hot-humid and temperate climates, respectively. The study concludes that significant potential for improvements still exists, especially in the cases of space conditioning, lighting, refrigeration, and cooking where most exergy destructions occur. Additionally, this work highlights that the method described may be further used to study the impact of large-scale refurbishments and promote national regulations and standards for sustainable buildings that takes into consideration energy and exergy indicators.     

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.     

Exergetic and thermoeconomic analyses of diesel engine powered cogeneration: Part 2 – Application

This paper is Part 2 of the study on the exergetic and thermoeconomic analysis of diesel engine powered cogeneration (DEPC) systems. In Part 1, formulations and procedure for such a comprehensive analysis are provided while this paper provides an application of the developed formulation that considers an actual DEPC plant installed in Gaziantep, Turkey. The plant has a total installed electricity and steam generation capacities of 25.3 MW and 8.1 tons/h at 170 °C, respectively. Exergy destructions, exergy efficiencies, exergetic cost allocations, and various exergoeconomic performance parameters are determined for the entire plant and its components. The exergy efficiency of the plant is determined to be 40.6%. The exergoeconomic analysis is based on specific cost method (SPECO) and it is determined that the specific unit exergetic cost of the power produced by the plant is 10.3 $/GJ.     

Performance of the Dutch Energy Sector based on energy, exergy and Extended Exergy Accounting

The performance of the Dutch Energy Sector is analyzed using the Standard Exergy Analysis as well as Extended Exergy Accounting (EEA) method. Performance indicators based on energy, exergy and cumulative exergy consumption (CExC) are evaluated for three subsectors: exploitation, transformation, and distribution of energy. It is shown that performance indicators based on CExC are much lower than those based on energy and exergy concepts. The EEA method is applied for analysis of four branches: cokeries and refineries, refineries, central electricity production, and distribution and decentral electricity production. The EEA method originally proposed by Sciubba is modified by evaluating the cost-to-exergy conversion factor from the monetary value and CExC of the feedstock. It was found that the monetary equivalent of extended exergy is higher than the respective product sales. Finally, it is shown that performance indicators of selected energy branches based on extended exergy are much lower than those based on the CExC.     

The potential biomass for energy production in the Czech Republic

Biomass production is a promising alternative for the Czech Republic's (CZ) agricultural sector. Biomass could cover the domestic bio-energy demand of 250 PJ a⁻¹ (predicted for 2030), and could be exported as bio-fuels to other EU countries. This study assesses the CZ's biomass production potential on a regional level and provides cost–supply curves for biomass from energy crops and agricultural and forestry residues. Agricultural productivity and the amount of land available for energy crop production are key variables in determining biomass potentials. Six scenarios for 2030 with different crop-yield levels, feed conversion efficiencies and land allocation procedures were built. The demand for food and fodder production was derived from FAO predictions for 2030. Biomass potential in the CZ is mainly determined by the development of food and fodder crop yields because the amount of land available for energy crop production increases with increasing productivity of food and fodder crops. In most scenarios the NUTS-3 regions CZ020, 31 and 32 provided the most land for energy-crop production and the highest biomass potentials. About 110 PJ a⁻¹, mostly from agricultural and forestry residues, can be provided from biomass when the present Czech agricultural productivity is maintained. About 195 PJ a⁻¹ (105 PJ from energy crops) can be provided when production systems are optimised with regard to fertilizer regimes and 365 PJ a⁻¹ (290 PJ from energy crops) when the yield level of Dutch agriculture is reached. Costs for woody biomass decrease with increasing plantation yield and range between 2.58 and 4.76 € GJ⁻¹. It was concluded that Czech agriculture could provide enough biomass for domestic demand and for export if agricultural productivity is increased.     

Energy balance in Iran's agronomy (1990–2006)

In this study data from 17 years (1990–2006) were collected to determine energy intensive areas and evaluate energy parameters of Iran's agronomy sector. All the direct and indirect inputs of energy for the production of 19 agricultural commodities were evaluated. The inputs and outputs were calculated by multiplying the amounts of inputs and outputs by their energy equivalents. The results indicated that total energy input increased from 32.40 GJ ha^?1 in 1990 to 37.20 GJ ha^?1 in 2006. At the same period, total output energy increased from 30.85 to 43.68 GJ ha^?1. The results show that irrigation with 40.0% and fertilizer (28.4%) had the highest share in energy consumption. The average net energy gain was a positive value; however, about 87% of the input energy emanates from non-renewable sources of energy. The mean energy ratio was estimated to be 1.07 and showed an increasing trend during the period rising from 0.95 in 1990 to 1.17 in 2006. This indicates that increased use of inputs ha^?1 in production was accompanied by a larger increase in the output levels. It can be inferred from the results that improvements in irrigation and fertilizer application can significantly affect the energy efficiency of Iranian agriculture.     

Thermal modeling of a packed bed thermal energy storage system during charging

The process of charging of an encapsulated ice thermal energy storage device (ITES) is thermally modeled here through heat transfer and thermodynamic analyses. In heat transfer analysis, two different temperature profile cases, with negligible radial and/or stream-wise conduction are investigated for comparison, and the temperature profiles for each case are analyzed in an illustrative example. After obtaining temperature profiles through heat transfer analysis, a comprehensive thermodynamic study of the system is conducted. In this regard, energy, thermal exergy and flow exergy efficiencies, internal and external irreversibilities corresponding to flow exergy, as well as charging times are investigated. The energy efficiencies are found to be more than 99%, whereas the thermal exergy efficiencies are found to vary between 40% and 93% for viable charging times. The flow exergy efficiency varies between 48% and 88% for the flows and inlet temperatures selected. For a flow rate of 0.00164 m³/s, the maximum flow exergy efficiency occurs with an inlet temperature of 269.7 K, corresponding to an efficiency of 84.3%. For the case where the flow rate is 0.0033 m³/s, the maximum flow exergy efficiency becomes 87.9% at an inlet temperature of 270.7 K. The results confirm the fact that energy analyses, and even thermal exergy analyses, may lead to some unrealistic efficiency values. This could prove troublesome for designers wishing to optimize performance. For this reason, the flow exergy model provides the most useful information for those wishing to improve performance and reduce losses in such ITES systems.     

Performance and thermo-economic assessments of geothermal district heating system: A case study in Afyon,Turkey

In this study energy, exergy and exergoeconomic analysis of the Afyon geothermal district heating system (AGDHS) in Afyon, Turkey is performed through thermodynamic performances and thermo-economic assessments. In the analysis, actual system data are used to assess the district heating system performance, energy and exergy efficiencies, exergy losses and loss cost rates. Energy and exergy losses throughout the AGDHS are quantified and illustrated in the flow diagram. The energy and exergy efficiencies of the overall system are found to be 37.59% and 47.54%, respectively. The largest exergy loss occurs in the heat exchangers with 14.59% and then in the reinjection wells with 14.09%. Besides, thermo-economic evaluations of the AGDHS are given in table. Energy and exergy loss rates for the AGDHS are estimated to be 5.36 kW/$ and 0.2  kW/$, respectively.     

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.     

Developments in international solid biofuel trade—An analysis of volumes,policies, and market factors

This paper presents and analyses international solid biofuel trade and concludes upon interactions with bioenergy policies and market factors. It shows that trade has grown from about 56 to 300 PJ between 2000 and 2010. Wood pellets grew strongest, i.e. from 8.5 to 120 PJ. Other relevant streams by 2010 included wood waste (77 PJ), fuelwood (76 PJ), wood chips (17 PJ), residues (9 PJ), and roundwood (2.4 PJ). Intra-EU trade covered two thirds of global trade by 2010. Underlying markets are highly heterogeneous; generally though trade evolved whenever supply side market factors coincided with existing/emerging demand patterns. Market factors and policies both defined trade volumes; though policy changes did not have as prominent effects on trade developments as in the liquid biofuel sector. Economic viability is the key limiting factor. Main exporting countries have low feedstock costs and already existing wood processing industries. Trade-relevant aspects are the commodity's monetary value; determined by its homogeneity, heating value, and bulk density. Consumer markets are diverse: in residential heating, demand/trade patterns have been influenced by local biofuel availability and short-term price signals, i.e. mainly price competitiveness and investment support for boilers/stoves. Commodities are mainly sourced regionally, but price differences have triggered a growing trade. The industrial segment is greatly influenced by policy frameworks but more mature (e.g. established routes). Trade is strictly linked to margins (defined mainly by policies) and combustion technologies. Uncertainties in the analysis are due to data gaps across and within databases regarding import/export declarations. To estimate bioenergy related trade, anecdotal data was indispensable. We believe datasets should be streamlined across international institutions to eventually enable reporting of global trade beyond digit-6-level. Research is needed to provide further insights into informal markets. Interrelations between trade factors are particularly relevant when mapping future trade streams under different policy/trade regime scenarios.     

Effects of meteorological variables on exergetic efficiency of wind turbine power plants

This present paper deals with exergy efficiency results of the Wind Turbine Power Plants (WTPPs). Effects of meteorological variables such as air density, pressure difference between state points, humidity, and ambient temperature on exergy efficiency are discussed in a satisfactory way. Some key parameters are given monthly for the three turbines. Exergy efficiency differs from 0.23 to 0.27 while temperature is changing from 268.15 K to 308.15 K with air density 1.368–1.146 (kg/m³). While pressure difference (ΔP) between inlet and outlet of the turbine differs from 100 to 1100 (Pa), exergy efficiency decreases fairly for different wind speeds. While specific humidity is changing from 0.001 to 0.015 (kg_water/kg_{dry air}), exergy efficiency decreases gently. Generally these meteorological variables are neglected while planning WTPPs, but this neglect can cause important errors in calculations and energy plans. Obtained results indicate that while planning WTPPs meteorological variables must be taken into account.     

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.     

EUBIONET III—Solutions to biomass trade and market barriers

The EUBIONET III project has boosted (i) sustainable, transparent international biomass fuel trade, (ii) investments in best practice technologies and (iii) new services on biomass heat sector. Furthermore, it identified cost-efficient and value-adding use of biomass for energy and industry. The aims of this article are to provide a synthesis of the key results of this project. Estimated annual solid biomass potential in the EU-27 is almost 6600 PJ (157 Mtoe), of which 48% is currently utilised. The greatest potential for increased use lies in forest residues and herbaceous biomass. Trade barriers have been evaluated and some solutions suggested such as CN codes for wood pellets and price indexes for industrial wood pellets and wood chips. The analysis of wood pellet and wood chip prices revealed large difference amongst EU countries, but also that on the short term prices of woody and fossil fuels are barely correlated. Sustainable production and use of solid biomass are also deemed important by most European stakeholders, and many support the introduction of harmonised sustainability criteria, albeit under a number of preconditions. The study identified also that a number of woody and agro-industrial residue streams remain un- or underutilised. The estimated European total potential of agro-industrial sources is more than 250 PJ (7.2 Mtoe), the amount of unutilised woody biomass (the annual increment of growing stock) even amounts to 3150 PJ (75 Mtoe). Finally 35 case studies of biomass heating substituting fossil fuels were carried out, showing that the potential to reduce GHG emissions ranges between 90 and 98%, while costs are very similar to fossil fuel heating systems. Overall, we conclude that solid biomass is growing strongly, and is likely to heavily contribute to the EU renewable energy targets in the coming decade.     

Energy and exergy efficiencies in the Chinese transportation sector, 1980-2009

This paper aims at analyzing energy and exergy efficiencies in the Chinese transportation sector. Historical data is used to investigate the development of efficiencies from 1980 to 2009. Firstly, we calculate energy consumption values in PJ (petajoule) for nine transportation modes of five transportation sub-sectors. Then, the weighted energy and exergy efficiencies for each transportation mode, calculated by multiplying weighting factors with efficiency values of that mode, are summed up to calculate the weighted mean overall efficiencies for a particular year. We find that: (1) In 2009, the energy consumed in transportation sector was 12179.80 PJ, whereas that was 589.25 PJ in 1980. (2) Highways transport was the biggest energy consumer, which consumed 82.0% of total transport energy consumption in 2009. (3) Up to 2009, the oil consumed by transportation accounted for 75.1% of that in the whole country, which is more than the net oil import. (4) The average overall energy and exergy efficiencies are found to be 21.22% and 19.95%, respectively. (5) A comparison with other countries showed that energy and exergy efficiencies of the Chinese transportation sector are slightly lower than those of Jordan, Malaysian, Saudi Arabian and Norwegian, and higher than that incurred in Turkish.     

Energy metrics of photovoltaic/thermal and earth air heat exchanger integrated greenhouse for different climatic conditions of India

In this paper, a study is carried out to evaluate the annual thermal and exergy performance of a photovoltaic/thermal (PV/T) and earth air heat exchanger (EAHE) system, integrated with a greenhouse, located at IIT Delhi, India, for different climatic conditions of Srinagar, Mumbai, Jodhpur, New Delhi and Bangalore. A comparison is made of various energy metrics, such as energy payback time (EPBT), electricity production factor (EPF) and life cycle conversion efficiency (LCCE) of the system by considering four weather conditions (a–d type) for five climatic zones. The embodied energy and annual energy outputs have been used for evaluation of the energy metrics. The annual overall thermal energy, annual electrical energy savings and annual exergy was found to be best for the climatic condition of Jodhpur at 29,156.8 kWh, 1185 kWh and 1366.4 kWh, respectively when compared with other weather stations covered in the study, due to higher solar intensity I and sunshine hours, and is lowest for Srinagar station. The results also showed that energy payback time for Jodhpur station is lowest at 16.7 years and highest for Srinagar station at 21.6 years. Electricity production factor (EPF) is highest for Jodhpur, i.e. 2.04 and Life cycle conversion efficiency (LCCE) is highest for Srinagar station. It is also observed that LCCE increases with increase in life cycle.     

A novel polygeneration system integrating the acetylene production process and fuel cell

This paper presents a novel polygeneration system that integrates the acetylene process and the use of fuel cells. The system produces acetylene and power by a process of the partial oxidation/combustion (POC) of natural gas process, a water–gas shift reactor, a fuel cell and a waste heat boiler auxiliary system to recover the exhaust heat and gas from the fuel cell. Based on 584.3 kg/h of natural gas feedstock, a POC reactor temperature of 1773 K, an absorber pressure of 1.013 MPa and a degasser pressure of 0.103 MPa, the simulation results show that the new system achieved acetylene production of 1.9 MW, net electricity production of 1.7 MW, power generation efficiency of 26.8% and exergy efficiency of 43.4%, which was 20.2% higher than the traditional acetylene production process. The new system's exergy analysis and the flow rate of the products were investigated, and the results revealed that the energy conversion and systematic integration mechanism demonstrated the improvement of natural gas energy conversion efficiency.     

Energy use and carbon dioxide emissions from steel production in China

In 1996, China manufactured just over 100 Mt of steel and became the world's largest steel producer. Official Chinese energy consumption statistics for the steel industry include activities not directly associated with the production of steel, ‘double-count’ some coal-based energy consumption, and do not cover the entire Chinese steelmaking industry. In this paper, we make adjustements to the reported statistical data in order to provide energy use values for steel production in China that are comparable to statistics used internationally. We find that for 1996, official statistics need to be reduced by 1365 PJ to account for non-steel production activities and double-counting. Official statistics also need to be increased by 415 PJ in order to include steelmaking energy use of small plants not included in official statistics. This leads to an overall reduction of 950 PJ for steelmaking in China in 1996. Thus, the official final energy use value of 4018 PJ drops to 3067 PJ. In primary energy terms, the official primary energy use value of 4555 PJ is reduced to 3582 PJ when these adjustments are made.     

Exergy analysis of cogeneration power plants in sugar industries

In this paper, exergy analysis of a heat-matched bagasse-based cogeneration plant of a typical 2500 tcd sugar factory, using backpressure and extraction condensing steam turbine is presented. In the analysis, exergy methods in addition to the more conventional energy analyses, are employed to evaluate overall and component efficiencies and to identify and assess the thermodynamic losses. The analysis is carried out for a wide range of steam inlet conditions selected around the sugar industry’s export cogeneration plant. The results show that, at optimal steam inlet conditions of 61 bar and 475 °C, the backpressure steam turbine cogeneration plant perform with energy and exergy efficiency of 0.863 and 0.307 and condensing steam turbine plant perform with energy and exergy efficiency of 0.682 and 0.260, respectively. Boiler is the least efficient component and turbine is the most efficient component of the plant.     

Performance investigation of thermal energy storage system with Phase Change Material (PCM) for solar water heating application

In order to harvest solar energy, thermal energy storage (TES) system with Phase Change Material (PCM) has been receiving greater attention because of its large energy storage capacity and isothermal behavior during charging and discharging processes. In the present experimental study, shell and tube TES system using paraffin wax was used in a water heating system to analyze its performance for solar water heating application. Energy and exergy including their cost analyses for the TES system were performed. Accordingly, total life cycle cost was calculated for different flow rates of the Heat Transfer Fluid (HTF). With 0.033 kg/min and 0.167 kg/min flow rates of water as HTF, energy efficiencies experienced were 63.88% and 77.41%, respectively, but in exergy analysis, efficiencies were observed to be about 9.58% and 6.02%, respectively. Besides, the total life cycle cost was predicted to be $ 654.61 for 0.033 kg/min flow rate, which could be reduced to $ 609.22 by increasing the flow rate to 0.167 kg/min. Therefore it can be summarized that total life cycle cost decreases with the increase of flow rate.