• Energy Research
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Abstract Propane (C3H8) is being considered as an alternative refrigerant, besides being used as an alternative fuel, because of its low Global Warming Potential and zero Ozone Depletion Potential. Using blends of C3H8 with CO2 as refrigerants, diminishes the fire safety concerns in case of accidental leak of this flammable substance in refrigeration applications. This paper reports on the effects of CO2 on laminar burning speed and flame instability of C3H8/air blends at elevated temperatures and pressures. The flame structures were investigated in a Schlieren system. The laminar burning speeds of C3H8/CO2/air mixtures were measured in a spherical chamber and were fitted by a power-law mathematical correlation. The one-dimensional flame code from Cantera with kinetic model was also used to predict laminar burning speed. The high-speed photography showed that CO2 inhibits the flame instability because of its hydrodynamic and diffusional-thermal effects. Results showed that the laminar burning speed decreased with increasing CO2 mole fraction in the mixtures and that CO2 promotes the flame stability. The high temperature C3H8 oxidation was governed by the reaction of H + O 2 = O + OH . The effects of CO2 on laminar burning speed were mainly determined by the reaction of CO 2 + H = CO + OH and the high energy capacity (specific heat) of CO2.

Abstract This paper uses quantile regression to demonstrate how electricity price distributions are linked to fundamental supply and demand variables. It investigates the California electricity market (zone SP15) for selected trading hours using data from January 8, 2013 to September 24, 2016. The approach quantifies a non-linear relationship between the fundamentals and electricity prices, just as predicted by the merit order curve. Natural gas, greenhouse gas allowance prices and load all have a positive effect on electricity prices, with the effect increasing with the quantiles. In contrast, solar production and wind production both have a negative effect on electricity prices. The effect of solar production increases with quantiles, whereas the effect of wind production decreases with quantiles. This paper also includes a stress testing case study in which a producer faces the risk of high solar and wind production, and investigates the effect on the lower tail of the price distribution. Overall, the results demonstrate how the proposed approach can be a helpful risk management tool for participants in the electricity market.

Abstract This paper investigates the thermochemical and physical conversion processes of coal gasification numerically with particular interest on calcination in a bubbling fluidized bed furnace. A comprehensive Eulerian-Eulerian three-dimensional model is developed for studying the gasification process. Three calcination cases are carried out under different operating conditions while one inert case is conducted to evaluate the effect of calcination. The presented numerical results aim at determining the mechanism of coal gasification in an air-steam environment with different flowrates. Evidence of particle segregation is found in the bed of coal and limestone due to density reduction and diameter shrinkage. Char conversion is investigated for different air-coal and steam-coal ratios, also the effect of bed temperature, fluid flowrate and fuel feeding rate on the carbon conversion is studied comprehensively. The highest char conversion rate is observed in the airflow rate of 17.0 kg/h where the bed temperature is found to be maximum. A noticeable impact of calcination is found in the gaseous emission while increasing CO2 concentration. Time averaged solid and gas temperature and species concentration profiles indicate the steady-state condition of numerical simulation.

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 In order to assess the feasibility of utilizing renewable hydrogen as transport fuel for fuel cell vehicles, four possible low-carbon hydrogen supply routes for a hydrogen refueling station located in Shanghai are studied. Route Ⅰ and II are onsite hydrogen supply routes powered by a stand-alone or grid-connected photovoltaic (PV)-wind generation system separately. Route Ⅲ and IV are offsite hydrogen supply routes, in which hydrogen is produced by a stand-alone or grid-connected PV-wind generation system located in Qinghai Province respectively and delivered via liquid hydrogen truck to Shanghai. The microgrid system for hydrogen production is designed and optimized with the aid of HOMER Pro® software. The results show that in hydrogen production stage, Route Ⅳ shows the best economic performance, both in the total net present cost (NPC) cost and levelized cost of energy (LCOE) cost. As for the whole hydrogen supply chain, Route IV is also the most economic hydrogen supply way, the levelized cost of hydrogen (LCOH) of which is slightly lower than that of Route II. The sensitivity results show that the total LCOH cost of Route Ⅳ is feasible based on the current shorter electrolyzer's lifetime. Therefore, it indicates that nowadays, producing hydrogen from a grid connected PV-wind hybrid power system in renewable energy rich area (Qinghai Province) and delivering it via liquid hydrogen truck to a refueling station in east coast area (Shanghai) of China may be a feasible solution.

International audience

Nowadays, climate change is a major global societal challenge that significantly increases environmental stress. Most international organizations and policies have promoted initiatives to minimize emissions, reduce fossil fuel dependence and increase renewable energy resource integration into different sectors. An energy transformation toward more renewable systems is thus a priority. Under this scenario, the present paper describes and evaluates an alternative energy conversion matrix–based model to combine sector electrification, power generation units from renewables, and new clean technologies. The proposed green matrix-based model allows analysing future scenarios, including electricity participation in end–use consumption and electric power generated by renewables —potentially integrated into different sectors—. The proposed model is evaluated in the state of Maine (United States). This case study is focused on decarbonizing both residential heating and transport sector through the integration of large offshore wind power plant. Results and discussion is also included in the paper, providing expected energy demand reductions and decreasing emissions through the integration of renewables. This energy transition integration case study is proposed in three road-maps with different penetration rates and time scales. The proposed green matrix–based model can be also applied to other areas and energy resources, as an alternative way to analyse and estimate renewable integration into different sectors. 2023-24

Abstract A robust computational framework was developed and implemented to numerically resolve the radiation view factor, F i j , within three-dimensional geometries, and, in particular, thermoelectric generators (TEGs). The proposed numerical methodology utilizes a graphics processing unit-accelerated ray-tracing algorithm to capitalize on the parallel nature of the view factor formulation. The shadow effect, resulting from interference with the TEGs conductive interconnectors and thermoelectric legs, was accounted for via the Moller-Trumbore ray-triangle intersection algorithm with back-face culling enabled. The effect of interconnector thickness, thermoelectric leg height-to-width ratios, TEG packing density, and the number of junctions on F i j is explored for various TEG configurations. Validation is performed against analytical values for planar and non-planar geometries, in addition to a point-in-polygon intersection algorithm for single-junction TEGs. Results indicate that for a constant packing density, F i j asymptotically decreases with increasing distance across the TEG’s hot- and cold-sides. For an increasing packing density and constant distance across the TEG’s junction, F i j decreases. In a multi-junction device, F i j was found to asymptotically increase with junction number, implying that for large multi-junction TEG designs, a simpler model may serve to accurately predict the view factor. The code developed herein is open-source and can be found at https://github.com/AasherH/GPU-Accelerated-View-Factor-Calculator .

Abstract Pyrolysis characteristics of Beizao oil shale in nitrogen were investigated by thermogravimetric analysis coupled with deconvolution procedure. A new method was proposed to separate multistep thermal decomposition process. Kissinger-Kai method was employed to determine the peak positions of main components involved in the complex reaction, and the overlapping peaks were separated by bi-Gaussian function according to the thermal knowledge of sub-reaction. The results showed that four parallel reactions were observed in the whole process, including the decomposition of kerogen, pyrite, carbonate, as well as removal of crystal water from clay minerals. Furthermore, the kinetic parameters of the separated reactions were estimated by traditional model-free and model-fitting methods on the basis of deconvolution analysis, wherein the optimal reaction models were modified with the accommodation function. Eventually, these parameters were optimized to predict the pyrolysis behavior. It was found that the obtained kinetic parameters and four-component reaction models can well characterize the entire pyrolysis process of Beizao oil shale.