• Energy Research

Abstract This study aimed to investigate the free gas accumulation behavior in a reservoir using a multiple-well system for methane hydrate production achieved by depressurization. Twenty-year simulations of gas production from a large-scale 3D methane hydrate reservoir model with different reservoir permeabilities were conducted, and the effects of different reservoir and operating conditions on the free gas accumulation behavior were fully examined. The simulation results indicated that the free gas accumulation behavior was affected by the reservoir permeability, and methane gas was inclined to accumulate within a certain permeability range, which was defined as the “free gas accumulation zone” for the first time. For an actual methane hydrate reservoir with a porosity of 0.31–0.51 and an initial hydrate saturation of 0.34–0.54, the free gas accumulation zone was estimated to be 37–145 mD at most. On the other hand, a low wellbore pressure could contribute to enhancing gas recovery by narrowing the free gas accumulation zone. In addition, the free gas accumulation zone was dramatically enlarged with the increase in well spacing, so a proper well spacing should be carefully designed to avoid the free gas accumulation zone. The prediction method proposed in this study could be applied to future commercial gas production from actual methane hydrate deposits achieved by depressurization using multiple-well systems.

Lithium-ion battery state of health (SOH) accurate prediction is of great significance to ensure the safe reliable operation of electric vehicles and energy storage systems. However, safety issues arising from the inaccurate estimation and prediction of battery SOH have caused widespread concern in academic and industrial communities. In this paper, a method is proposed to build an accurate SOH prediction model for battery packs based on multi-output Gaussian process regression (MOGPR) by employing the initial cycle data of the battery pack and the entire life cycling data of battery cells. Firstly, a battery aging experimental platform is constructed to collect battery aging data, and health indicators (HIs) that characterize battery aging are extracted. Then, the correlation between the HIs and the battery capacity is evaluated by the Pearson correlation analysis method, and the HIs that own a strong correlation to the battery capacity are screened. Finally, two MOGPR models are constructed to predict the HIs and SOH of the battery pack. Based on the first MOGPR model and the early HIs of the battery pack, the future cycle HIs can be predicted. In addition, the predicted HIs and the second MOGPR model are used to predict the SOH of the battery pack. The experimental results verify that the approach has a competitive performance; the mean and maximum values of the mean absolute error (MAE) and root mean square error (RMSE) are 1.07% and 1.42%, and 1.77% and 2.45%, respectively.

In this study, the main purpose is to develop low-cost catalysts with high activity and stability for high quality syngas production via steam reforming of biomass tar in biomass gasification process. The calcined waste scallop shell (CS) supported copper (Cu) catalysts are prepared for steam reforming of biomass tar. The prepared Cu supported on CS catalysts exhibit higher catalytic activity than those on commercial CaO and Al2O3. Characterization results indicate that Cu/CS has a strong interaction between Cu and CaO in CS support, resulting in the formation of calcium copper oxide phase which could stabilize Cu species and provide new active sites for the tar reforming. In addition, the strong basicity of CS support and other inorganic elements contained in CS support could enhance the activity of Cu/CS. The addition of a small amount of Co is found to be able to stabilize the catalytic activity of Cu/CS catalysts, making them reusable after regeneration without any loss of their activities.

In this study, steam gasifications of a kind of marine biomass, i.e., Zostera marina (eelgrass), and the biochars derived from pyrolysis of it were carried out for the biohydrogen production in a fixed-bed reactor. The effects of reaction temperature and water injection rate on the hydrogen production were investigated. In order to understand the effect of sea salts attached on the surface of eelgrass for the hydrogen production, the eelgrass washed by water (washed-eelgrass) was also used as the feedstock. It was observed that hydrogen productions from the gasification of washed-eelgrass as well as its biochar were higher than those of raw eelgrass and its biochar, indicating that the impurities of raw eelgrass had a negative effect on the hydrogen production. The biochar derived from the pyrolysis of washed eelgrass at 550 °C had the largest amount of hydrogen yield at the gasification temperature of 850 °C with a water injection rate of 0.15 g/min. It was found that both the hydrogen production and reaction rates were enhanced by mixing washed-eelgrass biochar obtained at 350 °C with the calcined seashells at a weight ratio of 1 to 2, especially at the gasification temperature of 650 °C. Meanwhile, in the presence of the calcined seashell, CO2 content decreased sharply whereas the hydrogen yield had no obvious increase.

This study investigated how biomass pyrolysis varies with the different fractions of magnesite mixing into biomass. The pyrolysis occurred with simultaneous decomposition of magnesite without use of any gasification reagent, and was analyzed in terms of producer gas yield and quality. As magnesite fraction increased from 0 to 30 %, the yield of producer gas and its calorific value increased from 48.6 % to 66.3 % and 8.29 to 8.93 MJ/Nm3, respectively. The carbon and hydrogen conversion increased from 44.1 % to 60.7 % and 43.1 % to 66.2 %, respectively. The characterization results revealed that magnesite particles facilitated the conversion of fixed carbon and the thermal/catalytic cracking of tar to produce H-rich gas. The in-situ generated CO2 from magnesite decomposition could be reduced to CO/CH4 in the reductive atmosphere of the pyrolysis products. This study proposes the concept of converting low-energy–density biomass into gas without oxygen and provides a novel approach for producing H-rich gas from biomass.

Abstract A downer reactor is ideal for fast pyrolysis during coal gasification as solids holdup distributions and residence time distribution in the reactor are fairly uniform and residence time is short. Because pyrolysis is a rapid reaction, in the downer solid–solid mixing is critical to promote pyrolysis reaction. Thus, solid–solid mixing in the downer was studied through numerical modeling in this study. An Eulerian–Lagrangian method was applied and implemented by combining Computational Fluid Dynamics and Discrete Element Method (CFD–DEM). The heat carrying media of silica sand was modeled to flow from the top of the downer while coal particles were introduced through two lateral nozzles in normal and tangential arrangements. Numerical results showed that tangential arrangement had lower solids holdups while higher particle velocities than normal arrangement. Mixing among binary solid particles was poor at the entrance of downer. The extent of mixing increased rapidly and approached an almost constant value in the downstream regions of the downer. High air velocity and small solid particle size could lead to better mixing for both normal and tangential arrangements. But tangential arrangement had better mixing of binary solid particles than normal arrangement, and when the particle sizes were reduced from 2 to 1 mm, the influence of nozzle arrangement was reduced.

AbstractTransition‐metal‐based layered double hydroxides (TM‐LDHs) nanosheets are promising electrocatalysts in the renewable electrochemical energy conversion system, which are regarded as alternatives to noble metal‐based materials. In this review, recent advances on effective and facile strategies to rationally design TM‐LDHs nanosheets as electrocatalysts, such as increasing the number of active sties, improving the utilization of active sites (atomic‐scale catalysts), modulating the electron configurations, and controlling the lattice facets, are summarized and compared. Then, the utilization of these fabricated TM‐LDHs nanosheets for oxygen evolution reaction, hydrogen evolution reaction, urea oxidation reaction, nitrogen reduction reaction, small molecule oxidations, and biomass derivatives upgrading is articulated through systematically discussing the corresponding fundamental design principles and reaction mechanism. Finally, the existing challenges in increasing the density of catalytically active sites and future prospects of TM‐LDHs nanosheets‐based electrocatalysts in each application are also commented.

Abstract This study aimed to give a better visualization of the hydrate dissociation and gas production behaviors during methane hydrate production under actual wellbore conditions via 3D images. A real 3D methane hydrate reservoir model was built in this study, and three different types of production methods using horizontal wells (depressurization or hot water injection) were designed. Meanwhile, the gas production and fluid flow behaviors under actual wellbore conditions were revealed through 3D visualization. The simulation results indicated that for the depressurization scenario, the pressure loss in the wellbore mainly affected gas production at the early stage of the depressurization process, while the effect on the long-term gas production behavior was not quite significant. However, for the hot water injection scenario, the heat and flow losses in the wellbore both had great influence on the gas production and fluid flow behaviors, which would cause the decrease in gas production and have a negative impact on the processes of heat transfer, hydrate dissociation, and gas-liquid two-phase flow in the reservoir. Especially, at the end of 1.5 yr, the decrease in total gas production caused by the flow loss (19.4%) was much larger than that caused by the heat loss (4.1%). Therefore, for the future field trials and further investigations on 3D visualization of the actual methane hydrate production process, such losses in the wellbore should be taken into account for the accurate prediction of the long-term gas production behavior.