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Abstract This work presents a simultaneous mixed-integer nonlinear programming (MINLP) optimisation model and an efficient iterative solution strategy that can be successfully applied to various heat-integrated water networks (HIWNs), including large-scale problems with a large number of water streams. These problems are highly nonlinear, non-convex and combinatorial. To circumvent such difficulties, including network complexity as well as identifying the roles of water streams in the heat exchanger network (HEN) whether they are hot or cold, a modified convex hull formulation proposed by Ahmetovic and Kravanja [1] is applied. The overall model combines the water network (WN), wastewater treatment network (WTN), heat integration (HI), and heat exchanger network synthesis (HENS) models. This model is iteratively solved in three steps including targeting and design steps. The proposed model and solution strategy are tested on large-scale problems. To the best of our knowledge, the results obtained for all the problems in this paper are better than those reported in the current literature.

Abstract Chemists, biologists, ecologists, and engineers have been developing a data-base to identify and evaluate risks to humans and the environment and strategies to minimize potential risks from large-scale coal liquefaction. Coal-liquids produced by various processes and under various stages of design and operating conditions have been screened for potential health and environmental effects. Toxicologically active materials have been fractionated and chemical constituents of biologically active fractions have been identified, and the environmental fate of problematic agents is being determined. Results indicate that coal-derived liquids are generally more toxicologically active than shale oil and petroleum crudes. Bioactive agents include primary aromatic amines (PAA), polynuclear aromatic hydrocarbons (PAH), phenolics, and others. Some components of coal-derived materials are taken up by biota and metabolized. Hydrotreating reduces PAA, PAH, and phenol content, as well as toxicological response to coal-liquids. Selective distillation restricts PAA and PAH content, and mutagenicity and carcinogenicity to high-boiling-range materials. Other process conditions and environmental factors also influence chemical characteristics and toxicological activity of coal-derived liquids. Recent findings indicate that biological responses to a given coal-derived liquid component vary, depending on whether that material is presented to the organism or environment as a pure compound or in a complex mixture. The data-base described provides input for assessment and has been used by developers when selecting process modifications and product slates that minimize risk to humans and the environment. These data have also been used in developing occupational health and industrial hygiene practices and may aid in selection of control technologies, mitigative strategies, special handling and accident prevention procedures, or spill-clean-up options to enhance the environmental acceptability of a coal liquefaction industry.

Abstract Operational optimization is the key to maximize the heat extraction efficiency of Enhanced Geothermal Systems (EGS). Injection/production flowrate is one of the operational parameters that can be easily manipulated to produce desired amount of energy. In this study, the effect of different flow schemes on the rate of heat production is analyzed over a period of 30 years. Seven flow schemes (four continuous functions namely constant flow, linear flow, exponential flow, mirror exponential flow, and three step functions with step sizes of six months, three years and ten years) developed on the basis of mathematical functions were examined. A doublet EGS model with a single fracture was simulated using a commercial thermal reservoir simulator. The reservoir and well data were obtained from the FORGE (Frontier Observatory for Research in Geothermal Energy) site at Milford Utah. The results were analyzed on the basis of their temperature decline curves for the produced water and the total amount of heat extracted over the entire period. The exponential flow scheme is the optimum case considering the rise in energy demand over the next 30 years. The amount of heat extracted per unit volume of water decreases with increase in total water volume circulated.

Abstract In this study, laboratory tests using six-cycles of nitrogen (N2) injection were carried out to investigate nitrogen flushing effect on coal seam gas recovery. In each test, N2 was injected for 200 min into a coal sample saturated with carbon dioxide (CO2), in a triaxial-loaded cell. Nitrogen injection was paused for about 20 h to allow gas desorption from the coal sample before commencing the next cycle. It was observed that CO2 levels of the outlet flow recovered from 3%-7% to 20%–40%, with no significant change in gas flow rate. The displaced CO2 in each cycle accounts for 4–7% of the initial total gas volume. Analysis of the test results indicated that at least 22 injection cycles were required to drop the residual gas content below the threshold limit value (TLV). The test results also confirmed that N2 injection can promote gas desorption from coal matrix and reduce un-desorbable residual gas content. In comparison with the continuous injection method, the flushing efficiency was lower for the cyclic injection method (5.6 days vs 21.5 days). However N2 consumption was about 60% less, and its utilization ratio was higher for cyclic injection method. Additionally, a post-injection effect of seam gas desorption was observed following each injection cycle. This study demonstrated that cyclic N2 injection method has several potential advantages for different field applications. This injection method can improve coal seam gas recovery with much reduced N2 consumption, and in particular, reduce the cost for separating gas mixture product in nitrogen enhanced coalbed methane recovery (N2-ECBM) project.

Diminishing fuel resources and stringent emission mandates have demanded cleaner combustion and increased fuel efficiency. Three water addition rates, i.e., 2, 4, and 6 wt% in biodiesel-diesel blend (B5) was investigated herein. Combustion characteristics of the emulsified fuel blends were compared in a naturally-aspirated diesel engine at full load and different engine speeds. More specifically, biodiesel was produced from waste cooking oil (WCO) and to further increase waste utilization, recycled biodiesel wastewater was used as additive in B5. The result obtained showed that low-level water addition (i.e., 2 and 4 wt%) in B5 led to different results from those obtained using higher water addition rates (i.e., >5 wt%) reported by the previous studies. In more details, the findings of the present study revealed that low level water addition in B5 could considerably reduce CO, HC, CO2, and NOx emissions. Among water-containing B5 fuel emulsions, the optimal water addition level in terms of engine performance parameters and emissions was found at 4 wt%. In particular, the emitted CO2, HC, and NOx were decreased by over 8.5%, 28%, and 24%, respectively, at maximum speed of 2500 rpm.

Abstract The world has witnessed a paradigm shift in the last decade in the way countries engage with each other. A cooperation based international paradigm is being challenged by countries engaging in rivalry with each other, motivated by their national interests. The developmental pathway the world charts in the future is going to be path defining for global energy and emissions use. India, expected to play a critical role in the global energy and emissions debate, would continue to impact and be impacted by these pathways. In India specific literature, however, little attention has been paid to development pathways related uncertainties and their impact on India’s energy and resource futures. We seek to address this gap by modelling India’s electricity futures and associated water demands under different development pathways. Our analysis shows that alternative development pathways would have significantly different implications for the energy access and equity, electricity generation mix, associated water withdrawals, and carbon dioxide emissions in India. We conclude by arguing that energy, emissions and water policies should be conceived with an explicit understanding of uncertainties related to potential development pathways that the world and India can chart.

Abstract Although CO2 storage in deep saline aquifers is now accepted as a potential option for atmospheric CO2 mitigation, the chemico-mineralogical property alterations in the aquifer formation associated with CO2/brine/rock mineral interactions, the corresponding influence on formation hydro-mechanical properties and the effect of rock mineral structure, are not yet fully understood. This study was therefore conducted to obtain a comprehensive understanding of the effect of long-term CO2 exposure on the chemico-mineralogical structure and corresponding strength characteristics of saline aquifer rock formations using silicate cement (SS) and carbonate cement (CS) Hawkesbury sandstone samples collected from the Sydney basin. Sandstone samples were first reacted with brine+CO2 under different injection pressures (both sub-critical (4, 6 MPa) and super-critical (8, 10 MPa)) under a constant temperature of 35 °C. A comprehensive chemico-mineralogical analysis (ICP-AES and XRD) was first conducted on both the rock mass pore fluid and the rock matrix over the saturation period of one year, giving special attention to the alteration of dominant rock minerals (quartz, calcite and kaolinite). The overall influence after 12 months of saturation with brine and CO2 on the strength characteristics of the two types of sandstones (SS and CS) was then investigated and correlated with the chemico-mineralogical reaction, in order to understand the coupled process. According to the test results, compared to the silicate cement-dominant mineral structure (SS), the presence of a carbonate cement-dominant mineral structure (CS) in the aquifer rock formation creates more significant alterations in the formation's chemico-mineralogical structure upon CO2 injection. This is because calcite mineral reactions occur at much greater rates compared to quartz mineral reactions in CO2-exposed environments. In addition, although some minor precipitation of kaolinite minerals may also occur upon CO2 injection, the effect may not be significant. Overall, rock mineral changes in deep saline aquifers upon CO2 injection have a significant influence on the strength characteristics of the reservoir rock mass, depending on the aquifer mineral structure, and CS formations are subject to much greater strength property changes upon exposure to CO2 than SS formations. Interestingly, CO2 injection causes a strength gain in SS sandstone and a strength reduction in CS sandstone. These mechanical property alterations in aquifer rock formations are also dependent on the CO2 injection pressure and phase, and increasing the injecting CO2 pressure significantly enhances the changes, due to the highly acidic environment created by the enhanced CO2 solubility process. Changing the CO2 phase from sub- to super-critical condition also accelerates the reaction mechanisms, due to the greater chemical potential of super-critical CO2. However, overall SS sandstone exhibits more stable chemical-mineralogical and mechanical characteristics upon CO2 injection than CS sandstone, and exhibits more suitable characteristics for CO2 sequestration.

Algae cofiring scenarios in a 360 MW coal power plant were studied utilizing an ecologically based hybrid life cycle assessment methodology. The impacts on the ecological system were calculated in terms of cumulative mass, energy, industrial exergy, and ecological exergy. The environmental performance metrics, including efficiency, loading, and renewability ratios were also quantified to assess the sustainability of cofiring scenarios from a holistic perspective. The analysis results revealed that cumulative mass and ecological exergy consumption were higher for algae cofiring compared to single coal firing due to high material and energy inputs for the algae cultivation. On the contrary, total energy and industrial exergy utilization were reduced with an increasing share of algae cofiring where algae is dried with solar energy. Additionally, natural gas dried algae cofiring scenarios had a lower renewability ratio in comparison with single coal firing. The results of this study are vital for the policy makers to decide on more environmentally friendly algae cofiring options by considering the potential impacts on ecological system.

Abstract Despite the great potential of camelina ( Camelina sativa L. Crantz) as a promising biofuel feedstock, in-farm energy flow of the crop and its associated environmental impacts has not received sufficient attention from researchers. In order to assess net energy gain and to identify energy saving and environmental friendly production operations, a two year study was conducted at central Montana. We investigated the effects of tillage method (CT (conventional tillage) vs. NT (no-tillage)) and N (nitrogen) fertilizer rate (0, 45, 90 kg N ha −1 ) on energy balance and GHG (greenhouse gas emission) of dryland camelina production. Results indicated that energy input and GHG emission were 5 and 8% lower in NT than in CT. Application of 45 and 90 kg N ha −1 increased camelina energy input by 186 and 365%, while increased energy output by only 21 and 64%, respectively. There was no significant difference in net energy gain in response to N fertilization, but lower energy efficiency in response to higher N inputs. Averaged across tillage systems, the GHG emission was 32.0 kg C eq ha −1 with 0 N applied, and the GHG emission increased by 206 and 389% when 45 and 90 kg N ha −1 was applied. Overall, N fertilizer had the biggest share in total energy input. Averaged over all experimental treatments, 14,945 MJ ha −1 net energy was obtained from camelina crop in this study which shows the potential of this crop as a bioenergy feedstock. Our result showed that implementation of NT is strongly recommendable for camelina production in this region. Moreover, improvement of N use efficiency has the highest priority to improve energy performance and reduce GHG emissions in camelina production.