• Energy Research
• 7. Clean energy close
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Abstract Work exchanger network (WEN) integration is crucial way to conserve energy for gas networks. Refinery hydrogen allocation network (HAN) determines its work sources and sinks of hydrogen streams and even WEN. Hydrogen gas streams are always non-ideal and there is also energy loss in their pressurization and depressurization processes through direct work exchangers. Based on thermodynamic principles for gas property and work exchange through compressors, expanders and direct work exchangers, this paper proposes a novel methodology for cost-effective refinery hydrogen networks. A stage-wise superstructure consisting of hydrogen allocation network (HAN) and work exchanger network (WEN) is built as problem illustration and the corresponding mixed integer nonlinear programming (MINLP) models for HAN and WEN are formulated to successively perform mass and work networks integration for total annualized cost (TAC) minimization. A refinery case is studied and results show that WEN can conserve 27.4% power utility consumption and reduce 50.9% investment cost. Case study results comparison demonstrates that the consideration of thermodynamic principles is of great significance to real-world energy conservation and investment cost reduction of WEN.

Diesel engines have proved its utility in transport, agriculture and power sector. Environmental norms and scared fossil fuel have attracted the attention to switch the energy demand to alternative energy source. Oil derived from Jatropha curcas plant has been considered as a sustainable substitute to diesel fuel. However, use of straight vegetable oil has encountered problem due to its high viscosity. The aim of present work is to reduce the viscosity of oil by heating from exhaust gases before fed to the engine, the study of effects of FIT (fuel inlet temperature) on engine performance and emissions using a dual fuel engine test rig with an appropriately designed shell and tube heat exchanger (with exhaust bypass arrangement). Heat exchanger was operated in such a way that it could give desired FIT. Results show that BTE (brake thermal efficiency) of engine was lower and BSEC (brake specific energy consumption) was higher when the engine was fueled with Jatropha oil as compared to diesel fuel. Increase in fuel inlet temperature resulted in increase of BTE and reduction in BSEC. Emissions of NO from Jatropha oil during the experimental range were lower than diesel fuel and it increases with increase in FIT. CO (carbon monoxide), HC (hydrocarbon), CO(2) (carbon dioxide) emissions from Jatropha oil were found higher than diesel fuel. However, with increase in FIT, a downward trend was observed. Thus, by using heat exchanger preheated Jatropha oil can be a good substitute fuel for diesel engine in the near future. Optimal fuel inlet temperature was found to be 80 degrees C considering the BTE, BSEC and gaseous emissions. (C) 2010 Elsevier Ltd. All rights reserved.

Abstract This study examined an innovative self-heat-recuperation technology that circulates latent and sensible heat in the thermal process and applied it to the NGL (natural gas liquid) recovery process. A CGCC (column grand composite curve) was used to assess the thermodynamic feasibility of implementing the heat pump system and self-heat-recuperation technology into a conventional distillation column. The proposed distillation based on self-heat recuperation reduced the energy consumption dramatically by compressing the effluent stream, whose temperature was increased to provide the minimum temperature difference for the heat exchanger, and circulating the stream heat in the process. According to a simulation of the proposed sequence, up to 73.43 and 83.48% of the condenser and reboiler energy, respectively, were saved compared to a conventional column. This study also proposes heat integration to improve the performance of self-heat recuperation. The results showed that the modified sequence saves up 64.35, 100.00 and 31.60% of the condenser energy requirements, reboiler energy requirements and OP (operating cost), respectively, compared to a classical heat pump system, and 90.24, 100.00, and 67.19%, respectively, compared to a conventional column. The use of these sequences to retrofit a distillation column to save energy was also considered.

Abstract This paper presents a modified Jaya algorithm (MJaya) for optimizing the material costs and electric-thermal performance of an Underground Power Cable System (UPCS). Three power cables arranged in flat formation are considered. Three XLPE high voltage cables are situated in the thermal backfill layer for ensuring the optimal thermal performance of the cable system. The cable backfill dimensions, cable backfill material, and cable conductor area are selected as design variables in the optimization problem. In the study, the Finite Element Method model is validated experimentally. The Particle Swarm Optimization (PSO), Jaya, and MJaya algorithms are used for multiobjective optimization in order to design a cable system in such a way to minimize the cable backfill costs and maximize the allowable electric current flowing through the cables. For the case study, calculations performed using the Jaya algorithm indicated 1.7 mln Euro cable system costs while cable ampacity is equal to I = 1460 A. The calculations are performed for the objective function values equal to w1 = 0.5 and w2 = 0.5. Such an optimization parameters set allow obtaining low costs of UPCS alongside with reasonable cable line ampacity. What is more, the results of the optimization obtained by Jaya, MJaya, and PSO algorithms are compared. Therefore, Coverage and Hypervolume metrics are incorporated. It is concluded that both the Jaya and MJaya algorithms performed better when compared to the PSO algorithm.

Abstract Nanoscale measurements using atomic force microscopy are performed in order to scrutinize the friction phenomena observed in microscale ball-on-disc tribological tests under (boundary lubrication) BL regime. Two reference biodiesels, one derived from a vegetable source (soybean) and the other from animal fat, are compared. A linear dependence of the friction coefficient ( μ ) with the Stribeck parameter ( S = viscosity × velocity/load) is observed: μ = 0.11 − 26.54 × S for the animal fat and μ = 0.12 − 51.56 × S for the soybean biodiesel. The nanotribological tests allowed highlighting the cohesion component of friction force in the BL regime that is associated to the intrinsic characteristics of the biodiesels, the respective friction coefficients being μ = 0.0206 for the animal fat and μ = 0.0233 for the soybean biodiesel. The better lubricity of the animal fat biodiesel compared to the soybean observed in microscale is attributed to the presence of sulfur and to the higher amount of mono- and di-glycerides contaminants in it. The polarity and/or chemical affinity of the respective sulfur and OH groups facilitate them to reacting with the steel surfaces during the rubbing action. At nanoscale level, the same ranking in friction is observed among the biodiesels, being that here the friction phenomena are attributed to the cohesive forces other than those related to viscosity.

This study investigates the thermoeconomic performance of a new integrated system including a regenerative two stage organic Rankine cycle which is coupled with a parabolic trough collector via a thermal storage tank. The cold energy of liquefied natural gas (LNG) is used to absorb the heat duty of condenser. The LNG subsystem not only allows the ORC cycle to produce more power by reducing its condensate pressure, but also provides the system with extra power via the LNG expander and chilled water. The system is capable of producing power with solar fraction of a hundred percent during the day. The thermoeconomic analysis is performed to optimize the system for design point conditions. The analysis also reveals the exergoeconomic criteria on system components. Results show that solar collector has the most value of Z˙+C˙D which is due to both high exergy destruction and high investment costs of solar collector. Also, storage tank and condenser are the second and third important components with respect to exergoeconomic criterion. Parametric analysis is performed on the system to show the effects of eleven key thermodynamic parameters on system performance. In order for optimization, the product cost rate and exergy efficiency are chosen as the objectives. Eleven decision variables including inlet temperature and pressure of the turbines, heat exchanger minimum temperature differences along with the mass flow rate of storage tank, condensate pressure and LNG pressure were chosen according to parametric analysis. With the aid of TOPSIS decision making technique, the optimal point was selected among the Pareto frontier of the genetic algorithm. Results show that system can reach the efficiency of 19.59% and product cost rate of 3.88 million dollars per year.

Abstract This paper focused on the intake and exhaust structure optimization of a single-screw expander (SSE) by using numerical method. The effects of internal volume ratio, the shape and clearance height of the intake port and exhaust area were numerically analyzed (R123 and HFO-1336mzz(Z) were selected as working fluids) to reduce the energy losses (more than 30%) caused by pressure loss and leakage in intake process and exhaust pressure loss. The suggestions of reducing the internal volume ratio and clearance height at intake port and removing the closed helix line were given based on the simulation results. Then, the optimized SSE was developed and experimentally tested in ORC system with R123 as working fluid. Results showed that the filling factor of the prototype was reduced from 125% to nearly 100% and the highest shaft efficiency was increased from 56% to 67.7% at 3000 rpm. The enhanced performance of the new prototype proves the correctness of the numerical optimization and this is expected to provide guidance for the design of SSE.

Abstract In this paper, a novel design of counter flow curved double-pass solar air heater (DPSAH) is proposed, and its performance characteristics are numerically investigated and compared with various parallel designs under different flow and geometric conditions. The developed model is first experimentally validated. The hydraulic and thermal performance of various DPSAH designs (smooth curved single pass, smooth parallel curved double-pass, smooth counter curved double-pass, roughened parallel curved double-pass, and roughened counter curved double-pass) show that counter flow curved DPSAH with asymmetrically placed turbulators is thermally better compared to other designs. A maximum of 23% augmentation in thermal performance was observed. To predict the performance of the best design, new correlations for Nusselt number (Nu) and friction factor (f) are developed in terms of Reynolds number (Re) and relative roughness height (d/H). The data estimated from these correlations are in good agreement with the values of f and Nu predicted from the model.

Abstract In this paper, the integration of a biomass-based diesel–wind system is investigated. The system consists of a pitch controlled wind turbine, which is equipped with an induction generator. The induction generator is connected to an ac bus-bar in parallel with a diesel-generator set consisting of a diesel engine driving a synchronous generator. A power plant can generate electric power using biomass from the olive tree in Spain. A gasifier is capable of converting tons of wood chips per day into a gaseous fuel that is fed into a diesel engine. While there are significant systems whose models may be exactly obtained from physical laws and whose states are measured, it is much less realistic to assume that all the parameters, such as the higher heating value of the biogas or wind speed, are exactly known. It is then natural to investigate what happens to control systems involving unknown, or not precisely known, parameters. In this paper, the derived model of biomass-based wind–diesel systems is quite valid for robust control studies.