• Energy Research
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Industrial producers face the task of optimizing production process in an attempt to achieve the desired quality such as mechanical properties with the lowest energy consumption. In industrial carbon fiber production, the fibers are processed in bundles containing (batches) several thousand filaments and consequently the energy optimization will be a stochastic process as it involves uncertainty, imprecision or randomness. This paper presents a stochastic optimization model to reduce energy consumption a given range of desired mechanical properties. Several processing condition sets are developed and for each set of conditions, 50 samples of fiber are analyzed for their tensile strength and modulus. The energy consumption during production of the samples is carefully monitored on the processing equipment. Then, five standard distribution functions are examined to determine those which can best describe the distribution of mechanical properties of filaments. To verify the distribution goodness of fit and correlation statistics, the Kolmogorov-Smirnov test is used. In order to estimate the selected distribution (Weibull) parameters, the maximum likelihood, least square and genetic algorithm methods are compared. An array of factors including the sample size, the confidence level, and relative error of estimated parameters are used for evaluating the tensile strength and modulus properties. The energy consumption and N2 gas cost are modeled by Convex Hull method. Finally, in order to optimize the carbon fiber production quality and its energy consumption and total cost, mixed integer linear programming is utilized. The results show that using the stochastic optimization models, we are able to predict the production quality in a given range and minimize the energy consumption of its industrial process.

Abstract Nowadays, natural gas is viewed as the solution to the problem of energy supply for Latin America, Europe and North America for the next few decades; Brazil is increasingly becoming dependent upon the Bolivian natural-gas supply — many industries and some entrepreneurs are deciding to construct industrial cogeneration systems and new thermal power-stations burning natural gas because of its low environmental impact and attractive price. However, natural gas is a finite resource: this will cause, in the future, an increase of its unit price. This paper details questions involved in the energy generation and presents solid-waste burning as a possible alternative fuel for the future, especially in the context of cogeneration practice in which the thermal and electric energy are used primarily for the industries located in an industrial district. Two cogeneration schemes are proposed for the burning of municipal solid wastes, associated or not with natural gas, and their technical and economic feasibilities are examined.

Abstract A unique large scale pilot plant of the CellFlux thermal energy storage concept is experimentally investigated. This storage concept consists of a regenerator type thermal energy storage volume, which is coupled to a finned tube heat exchanger by a circulating intermediate working fluid. The system investigated in this work operates at a temperature of 390 °C and uses air as intermediate working fluid which is conveyed by a centrifugal fan. The storage volume has a bed length of over ten meters and is of a novel design, where the air flows in horizontal direction. Since this approach could cause a flow maldistribution, a thorough analysis is of major interest for the accuracy of subsequent numerical simulations. The experiments reveal that the mass flow along the centerline can be up to 20% higher than the mean bulk flow. A significant maldistribution between top and bottom area, however, is not observed. As an alternative to the typically used rock filling, the storage volume is equipped with standard hollow bricks. These bricks are cost effective but do not have a well-defined shape. Thus, the predictability of the pressure drop by correlations found in the literature is unclear. It turns out that the measured pressure drop is evenly distributed in axial flow direction but generally higher than expected from the assumption of pure channel flow. Further experiments are conducted to validate the heat capacity of the bricks and to derive a correlation for the inner heat transfer between bricks and storage walls. Eventually, the aim of the experimental investigation is a general proof of concept as basis for the numerical investigation. Thus, all specifications of the plant and the storage material are provided. The plant is analyzed towards plausibility of heat losses, showing that heat losses can be predicted well within the given uncertainties.

Abstract Integration of microbial electrosynthesis (MES) with renewable energy supply has been proposed as a novel approach for energy storage and CO2 transformation into fuels and chemicals. However, the efficiency of renewable energy conversion into biochemicals is yet to be improved in MES. In this study, molybdenum-doped bismuth vanadate was deposited on fluorine-doped tin oxide glass (FTO/BiVO4/Mo) to serve as MES photoanode for efficient solar energy harvesting and reduction of overpotential for oxygen evolution reaction (OER). By applying a fixed bias of 3 V to MES systems under 0.5 sun illumination, a more negative cathode potential (–0.72 ± 0.03 V vs. SHE versus –0.38 ± 0.03 V vs. SHE in the dark) was achieved owing to the reduced OER overpotential at FTO/BiVO4/Mo photoanode, which led to a 25% increase in current density and 46-fold increase in acetate production rate. Higher electron recovery (~62%) and excellent stability (7 days) were also observed in MES reactors with sun illumination on FTO/BiVO4/Mo photoanode. Based on acetate production and energy input from simulated sunlight, 0.97 ± 0.19% solar energy was theoretically converted into acetate, which is one of the highest conversion efficiencies ever reported in hybrid MES systems. These results demonstrate that integrating FTO/BiVO4/Mo photoanode with MES systems could significantly enhance the solar-to-biochemical conversion efficiency by lowering the energy requirement for initiating the anodic OER and maintaining the negative cathode potential, which enables MES technology to be economically more viable for renewable energy storage and CO2 valorization.

Abstract Power-to-gas (PtG), as a promising technology proposed to store surplus renewable energy (RE), can hardly be commercialized for its low profitability. In this paper, three approaches are proposed in this paper to enhance the profitability of the PtG. Firstly, a cooperative union containing PtG is proposed and its sustainability analysis is undertaken based on Shapley Value method. Secondly, the PtG reaction heat, as an essential by-product of PtG which is valuable and therefore requires further study, is fully exploited for district heating in the operation of regional integrated energy system, which is solved by an improved SOCP method. Thirdly, a symbiosis cooperation mode is designed for wind power and PtG to enhance the benefit of PtG through optimization-based trading strategy, which is a MINLP model and solved by Big-M method. The results show that the daily profit of PtG is significantly increased with the cooperative union as the symbiosis cooperation mode can produce a 15.1% profit lift, meanwhile, exploitation of reaction heat can produce an 8.6% profit lift. Finally, our study reveals the conflict of interest between wind power and the cogeneration. A sensitivity study on the proportion of reaction heat used for district heating is performed to verify the mutually beneficial relation between PtG and the cogeneration. The findings of this paper can guide the commercialization of PtG.

Abstract Low efficiency of heat conduction and absorption is a key problem to restrict the application of phase change materials (PCMs). Foam metals, which work as random heat transfer networks, are often used to improve the thermal conductivity of PCMs. But further improvements are still required in engineering. Interestingly, random micro-channels also widely exist in natural heat and mass transfer systems (e.g., minor veins of leaves and blood capillaries) that always appear with ordered branching networks of macro-channels. But the ordered branching networks, which perform as efficient transfer networks, are rare in metal-foam-enhanced PCMs. Therefore, this work enhances the PCMs’ heat-absorption efficiency by constructing heat transfer networks mimicking leaf veins. Given the gap that there lack trusted design criteria to design the heat transfer networks, we propose an innovative optimization criterion mimicking the generating process of leaf veins. Combine the criterion with an original flexibility-oriented optimization framework, a generating design method is established. The optimization performance is discussed in point-area PCM structures. Compared with the metal-foam-enhanced PCM plate, the heat-absorption efficiency of the generating-based PCM plate is increased to 196.67% in concentrating heat from the PCMs, and the heat-absorption efficiency is also enhanced for more than 3.79 times in dispersing heat to the PCMs. With these improvements, the proposed method is applied in cooling high-power electronic devices which solves the overheating problem and prolongs the working time to 400.00%. Further applications can be expended to PCM-cooling systems, heat pump, collection and output of solar energy and waste heat, etc.

Buildings account for over one-third of global emissions and energy use. Meeting climate pledges will require achieving high operational energy efficiency with low embodied impacts in new construction. Yet, a systematic identification of the relative influence of building design parameters on both operational and embodied efficiencies has rarely been attempted. In this paper we explore for the first time the sensitivity of a wide range of design and operation parameters in terms of embodied carbon, construction cost, as well as heating and cooling loads for multi-storey buildings. We devised a model to estimate the relative importance of a large set of input variables, describing a building’s shape, size, layout, structure, ventilation, windows, insulation, air, and use for residential and office multi-storey buildings, across different climates. We found that increasing building compactness, using steel or timber instead of concrete frames, lowering window-to-wall ratio, choosing the most suitable glazing, and employing mechanical ventilation with heat recovery are the most important measures to decrease embodied emissions and operational energy. The most significant trade-offs with construction cost were found for the choice of frame material and in the decision whether to install mechanical ventilation. We estimate that 28–44% of yearly heating and cooling energy and 6 Gt cumulative embodied CO2e until 2050 could be saved in multi-storey buildings, without employing new technologies.

Abstract The goal for performing heat exchanger network (HEN) retrofit is not only to reduce utility consumption but to ensure that the retrofit is economically viable. The problem of using heat transfer enhancement for retrofit lies with the uncertainty of the best location in which to apply enhancement, the augmentation level and dealing with downstream effects after enhancement is conducted. To solve these problems, a systematic methodology is proposed. The first step in this methodology is the identification of candidate heat exchangers. In the second step, two methods, sensitivity analysis and an area ratio approach are compared for the identification of the best candidate heat exchangers to enhance. Heat transfer enhancement is then performed on the best candidate heat exchanger and, a non-linear optimisation based model is used to deal with the downstream effects after enhancement, subject to meeting set constraints on the HEN, such as the stream target temperatures and heat transfer area. Following this approach, the problems posed by the use of enhancement for retrofit can be addressed in a simple and computationally inexpensive manner. Heat transfer enhancement is an attractive option for HEN retrofit as it can provide energy saving without the need for topology modifications and additional heat transfer area with an added benefit of reduced implementation time, as modifications can be carried out during normal shutdown periods.

Abstract The pyrolysis char derived from solid waste peat was used in the removal of biomass tar. A laboratory dual-stage reactor was designed to obtain a cost-effective and eco-friendly tar removal approach using peat pyrolysis char-based catalyst. Rich pore structure of pyrolysis char can enhance the adsorption and removal performance of tar, the KOH and CO2 activation method were used to increase the pore structure of pyrolysis char. Toluene was chosen as the model compound of biomass tar for basic research. The effects of pyrolysis char and transition metal Fe on toluene removal were studied. The investigated reforming parameters were reaction temperature (700–900 °C), residence time (0.3–0.8 s) and steam-to-carbon ratio (1.5:1–4:1). The results indicated that the peat pyrolysis char-based Fe catalysts showed excellent catalytic performance (toluene conversion >89%) and gas selectivity, especially the catalyst that activated by CO2 had the best selectivity for syngas (88.1 mol%), and the waste peat catalyst was compared with other waste pyrolysis char-based catalysts. Textural characterization showed that the excellent catalytic activity and stability of the catalysts are due to the presence of FeC and FeSiO3 structures. Such the peat pyrolysis char can as a carrier be used to remove tar and produce high content syngas in pyrolysis process.