Keywords
Records with Keyword: Energy
Chemical Analysis of Different Parts of Date Palm (Phoenix dactylifera L.) Using Ultimate, Proximate and Thermo-Gravimetric Techniques for Energy Production
Ramadan A. Nasser, Mohamed Z. M. Salem, Salim Hiziroglu, Hamad A. Al-Mefarrej, Ahmed S. Mohareb, Manawwer Alam, Ibrahim M. Aref
November 27, 2018 (v1)
Subject: Materials
Keywords: date palm, Energy, proximate analysis, thermo-gravimatric analysis, ultamiate analysis
The objective of the study was to analyze chemical structure of date palm (Phoenix dactylifera L.) by employing ultimate, proximate and thermo-gravimetric techniques. Samples from different anatomical parts of date palm, namely trunk, frond base, frond midrib, leaflets, coir, fruit stem, date stone, and fruit empty bunches were considered for the experiments. Based on the findings in this work palm leaflet samples gave the highest amount of extractives content (32.9%), followed by date palm stone specimens with 31.5%. Cellulose content values of 32.8% and 47.5% were obtained for date palm stone and palm coir samples, respectively. Overall the hemicellulose contents of all samples were relatively similar to those of typical wood or non-wood lignocellulosic materials with the two exceptions of palm coir and palm leaflets. Both palm coir and palm leaflet specimens had 12.6% and 16.1% hemicellulose content. Volatile matter values of 74.3% and 87.5% were determined for leaflets and fruit em... [more]
How Much Detail Should We Use to Compute Societal Aggregated Exergy Efficiencies?
Miguel Palma, Tânia Sousa, Zeus Guevara
November 27, 2018 (v1)
Subject: Energy Policy
Keywords: efficiency, Energy, energy carriers, energy use, Exergy, useful exergy
The current method used for calculating societal aggregated exergy efficiencies is reviewed. Cooling is introduced as an end-use category; conversion efficiencies for heating processes are obtained for each energy carrier; and electricity shares per end-use are retrieved for each sector, improving the accuracy of the estimated values of aggregated exergy efficiencies. We show that: (1) cooling uses are a relevant end-use in Portugal and that their introduction decreased overall efficiency by 3.4% in 2009; and (2) disaggregating the heating second law efficiencies for each energy carrier has a significant effect on the aggregated efficiencies of the country, decreasing aggregated efficiency by 1.3% in 2009. We studied two other factors that showed no significant impact on aggregated exergy efficiency: a technological lag of 10 years in the efficiency of stationary mechanical drive devices and the use of a year-specific ambient temperature to compute exergy efficiencies of heating proces... [more]
Generation of Hydrogen, Lignin and Sodium Hydroxide from Pulping Black Liquor by Electrolysis
Guangzai Nong, Zongwen Zhou, Shuangfei Wang
October 22, 2018 (v1)
Keywords: black liquor, electrolysis, Energy, Hydrogen, lignin
Black liquor is generated in Kraft pulping of wood or non-wood raw material in pulp mills, and regarded as a renewable resource. The objective of this paper was to develop an effective means to remove the water pollutants by recovery of both lignin and sodium hydroxide from black liquor, based on electrolysis. The treatment of a 1000 mL of black liquor (122 g/L solid contents) consumed 345.6 kJ of electric energy, and led to the generation of 30.7 g of sodium hydroxide, 0.82 g of hydrogen gas and 52.1 g of biomass solids. Therefore, the recovery ratios of elemental sodium and biomass solids are 80.4% and 76%, respectively. Treating black liquor by electrolysis is an environmentally friendly technology that can, in particular, be an alternative process in addressing the environmental issues of pulping waste liquor to the small-scale mills without black liquor recovery.
Biofuel Impacts on World Food Supply: Use of Fossil Fuel, Land and Water Resources
David Pimentel, Alison Marklein, Megan A. Toth, Marissa Karpoff, Gillian S. Paul, Robert McCormack, Joanna Kyriazis, Tim Krueger
October 15, 2018 (v1)
Subject: Energy Policy
Keywords: agriculture, Biofuels, Energy, food security, fossil fuels, natural resources, Renewable and Sustainable Energy
The rapidly growing world population and rising consumption of biofuels are increasing demand for both food and biofuels. This exaggerates both food and fuel shortages. Using food crops such as corn grain to produce ethanol raises major nutritional and ethical concerns. Nearly 60% of humans in the world are currently malnourished, so the need for grains and other basic foods is critical. Growing crops for fuel squanders land, water and energy resources vital for the production of food for human consumption. Using corn for ethanol increases the price of U.S. beef, chicken, pork, eggs, breads, cereals, and milk more than 10% to 30%.
Energy and Exergy Analyses of Tube Banks in Waste Heat Recovery Applications
Mustafa Erguvan, David W. MacPhee
September 21, 2018 (v1)
Keywords: Computational Fluid Dynamics, efficiency, Energy, entropy, Exergy, HRSG, tube banks
In this study, energy and exergy analyses have been investigated numerically for unsteady cross-flow over heated circular cylinders. Numerous simulations were conducted varying the number of inline tubes, inlet velocity, dimensionless pitch ratios and Reynolds number. Heat leakage into the domain is modeled as a source term. Numerical results compare favorably to published data in terms of Nusselt number and pressure drop. It was found that the energy efficiency varies between 72% and 98% for all cases, and viscous dissipation has a very low effect on the energy efficiency for low Reynolds number cases. The exergy efficiency ranges from 40⁻64%, and the entropy generation due to heat transfer was found to have a significant effect on exergy efficiency. The results suggest that exergy efficiency can be maximized by choosing specific pitch ratios for various Reynolds numbers. The results could be useful in designing more efficient heat recovery systems, especially for low temperature appl... [more]
Simultaneous Energy and Water Optimisation in Shale Exploration
Doris Oke, Thokozani Majozi, Rajib Mukherjee, Debalina Sengupta, Mahmoud M. El-Halwagi
July 31, 2018 (v1)
Subject: Optimization
Keywords: Energy, hydraulic fracturing, membrane distillation, optimisation, Water
This work presents a mathematical model for the simultaneous optimisation of water and energy usage in hydraulic fracturing using a continuous time scheduling formulation. The recycling/reuse of fracturing water is achieved through the purification of flowback wastewater using thermally driven membrane distillation (MD). A detailed design model for this technology is incorporated within the water network superstructure in order to allow for the simultaneous optimisation of water, operation, capital cost, and energy used. The study also examines the feasibility of utilising the co-produced gas that is traditionally flared as a potential source of energy for MD. The application of the model results in a 22.42% reduction in freshwater consumption and 23.24% savings in the total cost of freshwater. The membrane thermal energy consumption is in the order of 244 × 10³ kJ/m³ of water, which is found to be less than the range of thermal consumption values reported for membrane distillation in... [more]
Minimizing the Effect of Substantial Perturbations in Military Water Systems for Increased Resilience and Efficiency
Corey M. James, Michael E. Webber, Thomas F. Edgar
July 31, 2018 (v1)
Keywords: control, Energy, military, Water
A model predictive control (MPC) framework, exploiting both feedforward and feedback control loops, is employed to minimize large disturbances that occur in military water networks. Military installations’ need for resilient and efficient water supplies is often challenged by large disturbances like fires, terrorist activity, troop training rotations, and large scale leaks. This work applies the effectiveness of MPC to provide predictive capability and compensate for vast geographical differences and varying phenomena time scales using computational software and actual system dimensions and parameters. The results show that large disturbances are rapidly minimized while maintaining chlorine concentration within legal limits at the point of demand and overall water usage is minimized. The control framework also ensures pumping is minimized during peak electricity hours, so costs are kept lower than simple proportional control. Thecontrol structure implemented in this work is able to sup... [more]
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