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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.

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 The use of compressed air in industry is an important and yet overlooked energy carrier. Although there are different energy-saving measures discussed in the specialized literature, there is little discussion on the energy performance of the production and use of compressed air. This study developed a new approach to assess the energy performance of compressed air systems based on a six-step local energy benchmarking methodology. The methodology includes an energy management procedure to monitor and control the electricity consumption and sustain the energy performance of compressed air systems in time. The procedure monitors the production and use of compressed at plant and at manufacturing section levels based on the real-time monitoring of relevant variables to calculate energy performance indicators, energy baselines, and CUSUM charts. Monitoring the consumption of compressed air at the section level in a case study reduced the demand between 11 and 47%. While electricity consumption to produce compressed air at the plant level reduced by an estimated 23%. This approach permits the rapid detection of inefficiencies in the production and demand sides of the compressed air system, highlighting inefficiencies that are frequently hidden in the total electricity consumption of manufacturing plants.

Abstract The pervasive renewable vibration energy has been considered as a promising alternative to electrochemical energy of batteries for powering wireless sensors and wearable electronics, but its efficient harvesting is still an unsolved problem. To tackle this issue, this paper presents an innovative mechanical modulation mechanism, which we name ‘cantilever-driven rotor’, to convert vibrations to uni-directional rotation aiming to achieve improved energy harvesting performance. Compared with the conventional cantilever-based energy harvesters (CBEHs), the rotor-based energy harvester (RBEH) can provide both enhanced output power (1.8 mW versus 0.3 mW) and extended working bandwidth (4.5 Hz versus 1.9 Hz) under a harmonic vibration of 0.8 g (1 g = 9.8 m/s2). Moreover, electric outputs of the RBEH can persist for 27 s after the external excitation vanishes. With the electric energy generated by the RBEH from the harmonic vibration, a wireless acceleration sensor could be powered to perform with its full functionality. When attached to the human ankle, the RBEH can maintain the normal operation of a Timer under a walking speed of 6 km/h. This work provides a basically different vibration-to-rotation conversion mechanism with superior performance in vibration energy exploitation and potential applications in self-sustained wireless sensors and wearable electronics.

Abstract The NO reducibility of semi-coke has attracted ever-increasing attention. While little previous work focused on the difference between pyrolyzed and gasified semi-cokes on NO reduction. The co-reduction of pyrolyzed and gasified semi-cokes toward NO deserves specific research to optimize the use of the low-volatile carbon-based fuels. This study focused on NO reduction by the pyrolyzed semi-coke, gasified semi-coke and their respective ash free cokes through a laboratory-scale quartz reactor. Experimental results indicated that the yield of CO2 peaked between 800 °C and 850 °C. The high conversion of CO to CO2 represented strong reaction between NO and semi-coke in NO heterogeneous reduction. The comparison of ash free cokes and their original semi-cokes demonstrated that minerals of semi-coke mainly contributed to the NO reduction below 800 °C. The kinetic analysis revealed that the apparent activation energy of blended semi-cokes increased almost linearly with the decline of pyrolyzed semi-coke fraction. The larger specific surface area benefited the NO diffusion and the adsorption capacity, which lowered the apparent activation energy in the kinetic control zone. Besides, the mixture comprised of 75% pyrolyzed and 25% gasified semi-coke showed a superior NO reduction ratio compared with pyrolyzed semi-coke beyond 750 °C.

Abstract Recently China has brought out several incentive policies to break high-cost limitation and stimulate investment in photovoltaic industry. Under this favorable policy environment, PV power is undoubtedly facing enormous development opportunities. Firstly, after analyzing current policy environment and interactions between involved variables, a simulation model of China's PV power development was built using system dynamics methodology considering both economic and technical factors. Secondly, sensitivity analyses are made to analyze the sensitivities of key variables and the effectiveness of relevant policies. The simulated results of generation, investment and capacity during 2012–2032 indicate the future developing trend, and evaluate the rationality and effect of incentive policies. The model allows an understanding of PV power's long-term development pattern under China's latest incentive policies, thus helping to provide reference for policy-making institutions.