Abstract

The system with solar panels and a battery (PV/BESS system) gets residential attention as a measure against natural disasters and fluctuation of electricity costs. This paper aims to evaluate Japan’s comprehensive economic profits from the PV/BESS system. This paper uses the optimization model with battery degradation and the one that keeps the state-of-charge (SoC) high. The payback period is calculated from the reduction in electricity costs. The battery’s lifespan is also calculated by the operation decided by optimization. As a result, the optimization with degradation achieves the least gap between the payback period and the battery’s lifespan. Including the effect of outage mitigation decreases the
payback period. Considering the reduction in electricity costs and outage mitigation, introducing the PV/BESS system in a household can be economically viable.

Abstract

Ring-type DC microgrids (DCMGs) are attracting attention from the viewpoint of expanding the use of renewable energy and improving power resilience. In the short-circuit protection of ring-type DCMG, the direction of current flow is not determined in the ring wiring. Therefore, the method of setting the trip threshold of the circuit breaker that is included in the main line of the ring-type DCMG in steps, as used in the conventional radiation-type DCMG, does not realize protection coordination. Thus, the purpose of this study was to achieve protection coordination of multiple circuit breakers with the same trip threshold in a simpler way. The authors propose a method of enabling protection coordination by combining a semiconductor circuit breaker (SCCB) with a capacitor as an energy source, which is able to interrupt the circuit as soon as the current reaches a threshold. To verify the method, two SCCBs with a trip threshold set at 30 A were connected in series, and four patterns of capacitors (0, 50, 100, and 150 μF) were connected between the SCCBs. The experimental results showed that when the capacitance was 50 μF or less, the current flowing through the SCCB on the power supply side was higher than the trip threshold, and protection coordination could not be achieved in some cases. On the other hand, when the capacitance was 100 μF or more, the current flowing through the SCCB on the power supply side was smaller than the trip threshold, showing that the protection coordination was successful. The experiments demonstrated that short-circuit protection can be coordinated between SCCBs by connecting two SCCBs in series with the same trip threshold and connecting a capacitor of approximately 100 μF or more between the SCCBs.

Abstract

This study established a Class I gas hydrate reservoir model (namely, a double-layer reservoir consisting of an upper hydrate-bearing layer and its underlying free gas water mixing layer) based on the hydrate exploration data from the Site GMGS4-SC_W02 in Shenhu area of South China Sea. Then a numerical simulation of hydrate extraction using the TOUGH+HYDRATE simulator was carried out. The gas-liquid production characteristics during hydrate exploitation using horizontal wells under different production schemes were analyzed. The production potential and the risk of methane leakage were evaluated. The results showed that the depressurization method is the optimal way for the low permeability Class I reservoirs exploitation in the view of long-term production. In addition, depressurization combined with thermal stimulation (in-situ wellbore heating) production did not show significant synergistic effects on increasing production and efficiency for Class I reservoirs. Instead, the pure thermal stimulation method can make a large amount of methane leak from the reservoir to the overburden layer, with the underlying free gas being the main source of methane leakage.

Abstract

Compared with onshore oil fields, offshore oil fields have lower well pattern completeness, larger well spacing, and stronger heterogeneity, necessitating a profile control and flooding system as well as corresponding laboratory evaluation methods to achieve deep reservoir regulation and efficient development. This study compared the performance of different chemical agents, simulated the heterogeneous development process of offshore oil reservoirs in both vertical and planar planes, and conducted multi-point pressure measurements. By analyzing the profile control and flooding effects under different reservoir conditions and the differences in pressure gradient distribution during the displacement process, the regulation mechanisms under different reservoir conditions were revealed. The results showed that during the development of vertically heterogeneous reservoirs, the pressure gradient difference along the high-permeability layer was less than 0.01 MPa/m, indicating a relatively uniform distribution. This indicates that the selected chemical system can achieve deep regulation of the high-permeability layer, increasing the recovery factor by 50.4%. During the development of planar heterogeneous reservoirs, the pressure gradient in the near-well zone was significantly greater than that in the far-well zone, resulting in an increase in the pressure at the core boundary. This indicates that the selected chemical system can achieve the development effect of subsequent fluid bypassing and further expansion of the swept area, increasing the recovery factor by 31.1%. This study provides theoretical guidance and technical support for field implementation.

Abstract

Exhaust heat exchangers play a crucial role in the waste heat recovery from internal combustion engines, yet their performance is often compromised by soot particle deposition. In this paper, a new particle deposition prediction model based on the Lagrange method is proposed, which considers thermophoresis force, drag force, and wall shear removal. Based on this model, how different tube bundle arrangements and tube geometries affect soot deposition and the thermal hydraulic performance of heat exchanger tube bundles were studied. Results indicate that increasing the transverse spacing between tubes reduces the soot deposition while increasing the longitudinal spacing has the opposite effect. Additionally, increasing the ellipticity of the heat exchange tubes lowers the fouling thermal resistance but at the cost of reduced heat transfer efficiency. We identified that a staggered tube bundle with a tube ellipticity of 0.8 and a transverse spacing of 16mm provides optimal performance without sacrificing heat transfer capacity.

Abstract

The process of imbibition agents entering pore throats under capillary pressure, displacing and extracting crude oil through spontaneous imbibition, is an important mechanism for enhancing oil recovery in tight reservoirs. Current research primarily focuses on the mechanism of imbibition to improve oil recovery in tight reservoirs, with relatively few studies on the distance of imbibition. Utilizing nuclear magnetic resonance techniques, this study has established a quantitative characterization method for the imbibition distance of surfactants in tight cores based on nuclear magnetic resonance T2 spectrum and projection curve. Through one-dimensional core inlet imbibition experiments and multi-cycle two-dimensional imbibition experiments, the study analyzed the effects of imbibition pressure, core permeability, initial oil saturation, and other factors on the imbibition distance. The results showed that for a core with a permeability of 0.1mD, as the imbibition pressure increased, the imbibition distance increased from 42mm to 60mm, and the oil saturation at inlet decreased by 0.09. As permeability increased, the imbibition distance increased significantly. Under experimental conditions, core permeability had the greatest impact on imbibition distance, followed by imbibition pressure, and initial oil saturation had the smallest impact. In the case of multi-cycle two-dimensional imbibition, the ultimate imbibition distance increased from 60mm for one-dimensional cores to 85mm for multi-cycle two-dimensional cores, representing a 16.8% increase in sweep distance compared to single-cycle development. This study provides quantitative insights and experimental methods for understanding the reverse imbibition distance of surfactants in tight reservoirs, laying a theoretical foundation for the development of imbibition in tight reservoirs.

Abstract

The penetration rate of renewable energy sources (RES) in hydrogen production systems has continued to increase in recent years. However, the intermittent nature of these sources presents significant operational challenges, especially for the electrolyzers. One possible solution is using grid electricity to complement the RES power supply with the battery to smooth the fluctuations. In this paper, an optimal dispatching scheme is proposed for hydrogen production plants integrating the battery. With the proposed dispatching scheme, a hydrogen production plant can reduce the total cost through participation in the wholesale electricity market while satisfying the hydrogen demand. Simulation based on actual data from Kyushu is conducted to evaluate the performance of the proposed optimal dispatching scheme. Compared with the normal operation method, the proposed scheme reduces the total cost by 12.6% for hydrogen production plants.

Abstract

Ionic liquid compressor is a type of compressors applied in hydrogen refueling stations. It uses ionic liquid (IL) for piston sealing and is driven by a hydraulic system. Previous literature mainly focused on piston motion and pressure variation. However, few studies referred to the influence of IL supplement on energy consumption and capacity. In this study, a lumped parameter model (LPM) of ionic liquid compressors is established. Power proportions of all parts are presented. Moreover, specific power and capacity are obtained under different amounts of IL supplement. Results show that the gas indicated power accounts for the main portion of the shaft power. The powers used for IL flow and hydraulic transmission will increase as the IL supplement amount increases, resulting in a rise in the shaft power. Insufficient and excessive IL supplement can both decrease capacity of compressors. Decreasing IL supplement amount can decrease the shaft power but specific power will rise if there is too little supplement amount.

Abstract

With the depletion of non-renewable energy, renewable energy such as wind energy has received more and more attention. Wind speed prediction plays an important role in promoting the utilization of wind energy. This paper focuses on how to realize the wind speed ensemble prediction at multiple stations. First, convolutional neural networks are introduced to wind speed prediction because of its ability to mine input features. Then, the dropout mechanism is incorporated into the model so that multiple runs can obtain multiple predictions. Next, the kernel density estimation method is used to obtain the probability density function of wind speed prediction. At the same time, in order to complete the multi-station wind speed prediction at the same time, the four-dimensional input-output structure tensor is proposed for wind speed prediction. Finally, the model proposed in this study is verified on two datasets of Tibet, China. The experimental results show that: (1) The model proposed in this study can obtain high-accuracy deterministic prediction results and appropriate ensemble prediction intervals. (2) The appropriate dropout ratio is important to neither overfit nor reduce the prediction accuracy.

Abstract

Recently, Carnot batteries, as an emerging electrical energy storage technology, are expected to solve the renewable electrical energy storage challenges faced globally. The selection of the working fluid is crucial to improving the system performance; however, the selection of existing working fluids is limited to a predefined database, and this approach does not allow for the design and discovery of novel working fluids. Therefore, in this paper, a model-based group contribution method for cross-scale preferential selection of working fluids was proposed for Rankine-based Carnot batteries. The result shows that the absolute average relative deviation of power-to-power efficiency, coefficient of performance, and power generation efficiency are 8.5%, 5.9%, and 2.6%, respectively.