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Abstract In this study, we develop indices for the overall technical efficiency (OTE) and energy-saving target ratio (ESTR) using data envelopment analysis (DEA) to calculate the relative efficiency and energy-saving potential of 30 provinces in China from 1997 to 2014. The results are as follows: (1) the OTE of China is 79.187%, indicating that there is 20.813% potential for improvement. The OTE exhibits decreasing efficiency values from the coastal areas to the inland areas and has clear geographical relationships. The average values of OTE in the east, midland and west are 0.932, 0.694 and 0.703. Theoretically, the total energy savings of CE, HE, ME and BE are 11080.60PJ, 5124.71PJ, 4729.24PJ and 6797.39PJ. (2) Regarding CE, HE, ME and BE, the provinces with the highest comprehensive ranks are Henan, Shanxi, Shaanxi, and Gansu, which simultaneously have the greatest energy-saving potentials and energy-saving targets. (3) The HE has the largest average ESTR of 38.357% and the values for BE, CE, and ME are 25.759%, 23.874%, and 22.143%, respectively. The CE category is the greatest in total energy savings (40.171%), which is followed by BE (24.150%), HE (18.384%), and ME (17.293%).

Abstract For a fixed bed gasifier, coal gas is mainly derived from dry distillation zone and gasification zone. The upstream gas from gasification zone will inevitably affect the composition and production of dry distillation gas. Therefore, the composition of upstream gas and the reaction conditions of dry distillation zone were simulated to perform experiments of Yining coal pyrolysis under a series of atmospheres. Some new discoveries are obtained. H2O and the hydrogen-containing gas have a significant impact on the release of dry distillation gas. H2O inhibits the release of CO, CO2 and CH4, but promotes the release of H2 which is not from char−H2O gasification. When the hydrogen-containing gas passes through dry distillation zone, the path of stabilizing radicals is completely changed, resulting in that coal pyrolysis changes from a process of generating H2 under inert atmosphere to a process of consuming a large amount of H2. In addition, water gas shift reaction is the only homogeneous reaction observed obviously in dry distillation zone, which can promote the production increase of CO2, but can not prevent the production decrease of H2 in coal gas.

Abstract For biomass/waste fueled power plants, stricter regulations require a further reduction of the negative impacts on the environment caused by the release of pollutants and withdrawal of fresh water externally. Flue gas quench (FGQ) is playing an important role in biomass or waste fueled combined heat and power (CHP) plants, as it can link the flue gas (FG) cleaning, energy recovery and wastewater treatment. Enhancing water evaporation can benefit the concentrating of pollutant in the quench water; however, when FG condenser (FGC) is not in use, it results in a large consumption of fresh water. In order to deeply understand the operation of FGQ, a mathematic model was developed and validated against the measurements. Based on simulation results key parameters affecting FGQ have been identified, such as the flow rate and temperature of recycling water and the moisture content of FG. A guideline about how to reduce the discharge of wastewater to the external and the withdrawal of external water can be proposed. The mathematic model was also implemented into an ASPEN Plus model about a CHP plant to assess the impacts of FGQ on CHP. Results show that when the FGC was running, increasing the flow rate and decreasing the temperature of recycling water can result in a lower total energy efficiency.

Abstract Intensive energy consumption and high pollutant emission have always been the obstacles for achieving the sustainable development of the iron and steel (I&S) industry. The complex material flows, energy flows and emission flow of I&S industry require better assessment to implement comprehensive governance and impact analysis. The 48-month data of a typical I&S enterprise is used for evaluating intensities and analyzing influencing factors from the perspective of material, exergy and emission networks. The results show that the exergy intensity and carbon emission intensity of the whole site including main processes and auxiliary processes are 23.804 GJ/t-CS and 1642.7 kg/t-CS, respectively. In particular, auxiliary process plays a critical role, whose exergy loss accounts for about 28.85% of the total. The terms of energy structure, technology capacity, product structure and environmental conditions are considered to analyze on the influencing factors of the case, and then providing relevant suggestions. On the whole, integration assessment of material-exergy-emission networks of I&S industry is necessary and helpful to find their changes and migration, and to further implement energy management and emission reduction.

Abstract Fe3+-mediated coal-assisted water electrolysis (CAWE) for hydrogen production is an effective way to utilize coal resources. Low-rank coal, which has a high abundance, is rich in mineral matter and oxygen-containing functional groups (OGs). To promote the development of Fe3+-mediated CAWE of low-rank coal, the roles of mineral matter and OGs in Fe3+-mediated CAWE are investigated in this study. Besides, to understand the reaction mechanism of coal electrolysis and provide guidance for the effective use of electrolyzed coal, the microstructural, surface structure, and microcrystalline changes of the coal are analyzed via Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction, respectively. The results show that minerals and OGs have a positive and negative influence on the Fe3+-mediated CAWE, respectively. The hydrogen yields of demineralized coal and oxidized coal are 33.15% and 68.47% lower than that of raw coal owing to the influence of minerals and OGs, respectively. After electrolysis, the degree of aromatic ring condensation increases whereas coal rank decreases; the content of –OH on the coal surface increases and the composition of organic sulfur on the coal surface is altered; and the crystallite diameter of the coal changes.

Abstract Thermal desalination technologies play a dominant role in seawater desalination, especially in GCC countries. However, the energy-intensive nature of these technologies limits their applications to relatively affluent regions. Therefore, it is of great significance to introduce new heat sources, e.g. renewable energy and industry waste heat, for thermal desalination. The spray-assisted low-temperature desalination (SLTD) is a novel technology that utilizes low-grade heat sources effectively. This paper specially adopts the SLTD technology to sensible heat sources. The performance of a conventional steam-driven SLTD system employing sensible heat sources is firstly investigated. Analytical results reveal that the conventional configuration is unable to make full use of the sensible heat sources. In order to improve energy utilization, the configuration is modified to enable internal heat recovery. The proposed configuration is able to boost the freshwater production by as much as 79%, while the desalination cost is reduced by 11%.

Abstract Trading energy efficiency (TEE) is adopted by more and more countries to cope with global climate change. This article studies the effects of TEE by investigating an optimization model, and several interesting conclusions are obtained. Firstly, it is observed in the model that TEE stimulates energy efficiency innovation, that is, promotes the firms to increase innovation investments. Secondly, it is proved that TEE reduces the marginal emission and total emission of the firms, while outputs are promoted by TEE. Meanwhile, TEE does not reduce energy inputs. Finally, TEE under carbon tax performs better than that without carbon tax. Based on these results, to improve the energy efficiency and reduce the emission of greenhouse gases, it is suggested for the governments to adopt TEE with carbon tax.

Abstract Global environmental change is driven by food production. Biogas from food waste is a better source of clean energy. Ghana’s energy strategy targets a 10% increase in renewable energy and modern biomass in the national electricity generation mix. Studies on the assessment of electricity generation potential and economic feasibility of biogas to electricity projects in Ghana’s major cities are scarcely available. This study assesses the electricity generation potential of biogas from food waste through anaerobic digestion technology. The municipal solid waste generation potential of Accra and Kumasi was estimated from 2020 to 2039. The potential theoretical methane yield from food waste was calculated using Buswell’s equation. The study analyzed anaerobic digestion projects’ economic feasibility using the total life cycle cost, net present value, investment payback period, levelized cost of energy, and internal rate of return methods. A sensitivity analysis based on two scenarios (optimistic and pessimistic) was performed to analyze the influence of changes in the composition of food waste, per capita waste generation rate, population growth rate, per capita GDP growth rate, discount rate, capacity factor, electricity generation efficiency, waste collection efficiency, and methane production potential on the economic feasibility of the projects. The main findings indicate that the amount of waste generation in Accra during the project life cycle is 899,000 t/y to 3,359,000 t/y, while that of Kumasi is 915,000 t/y to 3,159,000 t/y. The power generation potential of the project in Accra ranges from 80.43 to 300.49 GWh/y, and in Kumasi ranges from 60.63 to 209.31 GWh/y. Economically, the project is feasible in Accra and Kumasi. The net present value of the project in Accra and Kumasi is $217,800,000 and $156,100,000. The sensitivity analysis shows that the project is infeasible in all the cities with a discount rate exceeding 20%. When the discount rate exceeds 20%, the project becomes highly infeasible in Accra compared to Kumasi. This study will offer itself as scientific guidance for investment in biogas to electricity projects in Ghana’s cities.

Abstract To understand the relationship between green building energy performance and regional commercial estates, this study analysed Australia’s Commercial Building Disclosure (CBD) program database. This database discloses the annual energy use intensity (EUI) and the corresponding energy rating (1–6 stars) of 2460 National Australian Built Environment Rating System (NABERS) certified office buildings. The study selected for analysis Australia’s six largest cities and then used panel data regression, where commercial estate factors (total stock of office buildings, vacancy rate, average gross face rent, and government incentives such as financial support) served as independent variables and the EUI was the dependent variable. The p-values of all the models are below 0.05, indicating that the results are statistically significant. Results showed the commercial real estate factors were significantly related to the EUI for buildings with a rating of 1 star and above. The correlation between EUI and commercial real estate factors became less strong with the rating level increasing. The effect of ‘green building’ branding makes the office buildings more attractive with regard to tenancy and their energy performance more reflective of the variation in the commercial real estate market. This study is a frontrunner in contextualising green building energy performance and ratings in the context of regional commercial estate, and the regression models employed in the study could be used to define regional baselines for energy ratings in future studies.