In recent years, the subway system has experienced rapid development all over the world. However, the air quality in the station has attracted more public attention. This paper concentrates on the variation of the PM2.5 and PM10 concentrations on platformsin the entire operation periods of the train. The train frequency and piston wind are considered to investigate the influence of passing trains number, the train arrival and departure on the PM2.5 and PM10 concentrations on the platforms. The results show that the diurnal average concentrations of PM2.5 and PM10 on platforms are 81 and 147 μg/m3 , respectively. The maximum concentrations of PM2.5 and PM10 (104 and 173 μg/m3 , respectively) occur in the morning rush hours, when the number of passing trains is the largest. The piston wind can push the polluted air in the tunnel into the platform and increase the PM concentrations on platforms. Moreover, passengers walking can also cause the suddenly sharp increase of PM2.5 and PM10 concentrations when the train stops at the station. It can be deduced thatreasonable ventilation strategy and efficient air filtration system are necessary to be studied in the further research for the improvement of air quality and energy saving of the ventilation and air-conditioning system in subway stations.
Geothermal resources for global new energy development because of its wide distribution, huge reserves and environment-friendly. The enhanced geothermal system (EGS) is one of the key technologies for the extraction and utilization of geothermal energy in high-temperature rock masses in deep formations. The use of supercritical carbon dioxide (S-CO2) as a working medium in EGS has many advantages for heat exploitation. But the change of thermal properties of supercritical carbon dioxide is very rapidly during EGS production, which affects the transport of fluids and rock-fluid heat exchange. To investigate the effect of S-CO2 in EGS, in the present work, we develop the heat and mass transfer models for S-CO2 in EGS based on the Embedded Discrete Fracture Model (EDFM). The simulation results show that the complex fracture network has significant effects on the heat and mass transfer of supercritical carbon dioxide in the reservoir. In addition, S-CO2 not only has higher heating efficiency than water, but also captures and stores carbon dioxide.
The operational flexibility of coal-fired power plants during peak shaving processes becomes an urgent problem with the penetration of intermittent renewable power in the power grid. However, the original control systems for the power units have some deficiency during rapid peak shaving processes. In this paper, a revised control system by regulating high-pressure extraction steam was added to improve the operational flexibility during load change processes. Based on the transient models of a 660 MW supercritical coal-fired power unit, comparison on the original and revised control systems for the main parameters were proposed. It turns out that when compared with the original control system, the revised control system exhibits a better control performance during peak shaving processes, especially for the loading down process. The differences of the output power, live steam pressure, live steam pressure and reheat steam temperature between the original and revised control systems during load down process are −1006.41 MW·s, 21.26 MPa·s, 256.17 °C·s, and 680.17 °C·s, respectively. The study can provide a guidance for the control optimization and flexibility improvement of coal-fired power plants during peak shaving processes.
Pyrolysis is an effective way to convert aquatic plants into high-value products. The pyrolysis oil has high energy density but is difficult to utilize. In order to clean and economically convert the acids in pyrolysis oil into high grade esters, improving the quality of pyrolysis oil, this study chose seawater and freshwater reeds as raw materials, upgrading reed pyrolysis oil through catalytic esterification by reed biochar-based solid acid catalyst and comparing the catalytic effect of reed biochar-based solid acid catalysts with commercial 732 and NKC-9 solid acid catalysts. After analyzing the pyrolysis products of two kinds of reeds, seawater reed pyrolysis oil generated from 600°C (has the highest acid content) was chosen as raw oil to upgrade its quality, and biochar generated from 600°C and 700°C was chosen to produce catalysts. The acid content in upgraded oil was significantly reduced, and ester became the main component of upgraded oil. Among the six catalysts, 732-catalyzed upgraded oil had the highest ester content (21.97%). The 700°C freshwater reed biochar-based catalyst has comparable catalytic effect to that of NKC-9, the ester contents of their upgraded oil were 18.71% and 19.98%, respectively. Catalytic effects were proportional to surface sulfonic acid contents of the catalysts. Compared with raw pyrolysis oil, heat value of upgraded oil increased by 15.16%-76.54%, and viscosity decreased from 11.47Pa·s to about 3Pa·s. The commercial catalysts decreased the pH of upgraded oil to a lower value, but the reed biochar-based solid acid catalyst increased the pH value of upgraded oil to about 5, this was attributed to the fact that reed biochar-based solid acid catalyst has a superior thermal stability than that of the commercial catalysts, so that sulfonic acid group was not easily peeled off after being heated. The obtained results could provide a guidance for the relationship between biomass feedstocks, pyrolysis conditions, catalytic activity of biochar-based solid acid catalyst and upgrading effect of pyrolysis oil.
Full-spectrum solar energy utilization has drawn widespread attention for cascading solar energy utilization. A spectral splitting approach is described and a prototype is originally presented. Innovatively, the fullspectrum solar energy is first split and then concentrated onto photovoltaics and solar thermochemical reactor. In this case, the irreversible loss would be expected to be reduced. Here, thermodynamic evaluation of prototype is conducted. The monocrystalline silicon photovoltaics and methanol decomposing are adopted. The results show that the solar-to-electricity efficiency would be 37% in the hybrid system, 19% higher than individual concentrating solar photovoltaics and 9% higher than individual solar thermochemical system. An optimal working spectral range is about 280-1100nm for the silicon photovoltaics. The proposal of hybrid approach of solar photovoltaics and endothermal reaction leads to a feasible strategy for cascading solar energy utilization.
Natural gas hydrates (NGHs) are considered as an alternative and potential energy. Three classes of NGHs deposits are classified according to the layers present around. Studies on appropriate method for different classes of NGHs deposit was extremely important. Considering the huge seawater source, and its higher temperature than the hydrate deposit, the combination mode of seawater flow erosion and thermal simulation was investigated in this study. The results indicated that the combination mode will provide great driving force for methane hydrate (MH) decomposition with the higher temperature and higher seawater flow velocity. Via the combination mode, there are three obvious stages for hydrate decomposition: a) water saturation; b) residual gas displacement and sudden hydrate formation/ decomposition; c) continuous hydrate decomposition. What’s more, the seawater flow process has more obvious promotion effect for hydrate decomposition than temperature increase, due to the plenty heat-loss. In short, the huge seawater source has already decided the great potential of this combination method for actual hydrate production.
Coal plays an indispensable role in the chemical industry, in which methanol from coal is a largely crucial part. In the process of coal-to-methanol chain, a large amount of CO2 is emitted into the atmosphere, which should be captured and utilized. In this paper, firstly Aspen Plus software is used to simulate the whole process of coal-to-methanol production chain. The simulation results indicate that the carbon footprint of a certain amount of coal-to-methanol process is 3.01t CO2/t methanol, and then we compare the carbon footprint of methanol production processes with two cases which are CCS (Carbon Capture and Storage) and CCU (Carbon Capture and Utilization) with P2G (Powerto-Gas) to reduce carbon emissions. It shows that CO2 emission of methanol production after CCS is 0.64 t CO2/t methanol with reducing by 78.7% and that after CCU with P2G is 1.42 t CO2/t methanol, with reducing by 52.82%, and simultaneously increases methanol production doubly to 1378.31kt/y. The results show that CCS and CCU are effective ways to alleviate global warming.
In response to some serious issues like the energy crisis and environmental problems associated with the conventional compression refrigeration system, thermal air-conditioning systems were therefore developed to overcome the mentioned problems. A completely novel integrated adsorption and absorption (AD-AB) refrigeration system driven by low-grade temperature heat sources is proposed in this investigation. This novel cycle focuses on the inherent characteristics of the adsorption and absorption phenomena. The innovation here is that the generator of the absorption cycle becomes the evaporator of the adsorption cycle. Therefore, the generation and evaporating pressure are associated with the heat source temperature. Moreover, the adsorber in the adsorption system replaces the condenser in the standard absorption system. Thus, the generation pressure is associated with the heat source temperature and can be adjusted according to the solution concentration and generation temperature.
The increasing scarce of conventional energy resource and deteriorating environmental problem push the world toward more and more sustainable way in energy conversion and utilization. Close Brayton cycle using super-critical CO2as working fluid is a promising technology for coal-fired, renewable energy-driven, waste energy-driven power production. Heat integration inside the CO2power cycle or with external resources are effective way in improving the super-critical CO2power cycle (SCO2) performance. In the present study, an integration system of solar thermal collector, SCO2, and organic Ranking cycle(ORC)is proposed. An equation of state-based model is developed for the simulation and simultaneous optimization of the proposed integration system. A case study is elaborated to test the superiority of three integration systems with different SCO2structure and validate the effectiveness of the proposed optimization model. The working fluid of ORC are screened and sensitivity analysis of key parameters on the integration system performance are conducted.
Competitiveness change after the establishment of carbon emissions trading mechanism is explored on the basis of Beijing industry energy consumption and carbon emissions price data. It is demonstrated that additional costs incurred by carbon trading mechanism have less effect on the industrial competitiveness. Scenario analysis is also conducted to discuss changes under different price.