Institutional Repository of GuangZhou Institute of Energy Conversion, CAS
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Effect of particle size, water saturation, inorganic salt and methane on the phase equilibrium of CO2 hydrates in sediments
No full textUnderstanding the thermal stability of gas hydrate in complex marine geological environment is of importance to hydrate-based carbon sequestration. In this work, the factors affecting the equilibrium of CO2 hydrate in ocean sediments, including quartz sands, inorganic salts and gas impurities were quantitatively measured in a temperature range from 273 to 283 K and a phase equilibrium model of hydrate was established. To reveal the distribution in pore structure, the micro-morphologies of hydrate-bearing sediments were measured by cryo-SEM. Results showed that reduction of initial water saturation, addition of NaCl and CH4 were found to have inhibitory effect on CO2 hydrate equilibrium. Initial water saturation reduced the equilibrium temperature by the capillary pressure, but only 0.3-0.7 K temperature depression was observed as the water saturation reduced to 5 %. About 5.7 K in the average temperature depression was found by the addition of 10 wt% NaCl and 24 mol% CH4. NaCl and CH4 influenced the hydrate equilibrium by changing the water activity and chemical potential of hydrate water lattice. SEM images showed that the hydrate formed in pores of quartz sand had porous surface and coated the sand particles like a layer of cells which are 5-20 mu m in diameter, suggesting the hydrate layer exists between the liquid and gas phase. Based on the van der Waals-Platteeuw model, a hydrate equilibrium model was developed. The model provided a good prediction of the hydrate equilibrium in the presence of quartz sand, NaCl and CH4 with an averaged deviation of +/- 4.2 %, which had the potential to be applicated in more complexed ocean sedimentary environment
National Key Research and Development Program of Intergovernmental International cooper-ation Projects[2022YFE0198800]
No full textProduction of carbon nanotubes via catalytic pyrolysis of polyethylene over Ni/ZSM-5 prepared by ethylene glycol assisted impregnation
No full textThe design of efficient catalysts is important for the recycling of plastic wastes. In this study, a series of high -dispersion nickel based catalysts were developed by ethylene glycol (EG) assisted impregnation method and applied for the carbon nanotubes (CNTs) production from pyrolytic catalysis of polyethylene. The effect of the addition amount of EG on the catalyst performance was investigated. Results indicated that the catalysts pre -pared by ethylene glycol assisted impregnation show a good catalytic performance, comparing with conventional impregnation, and the Ni/ZSM-5-EG(3) catalyst displayed a higher yield of carbon deposits (32.37 wt%), including 289 mg/gPE high-value CNTs. To understand the relationship between the catalyst structure and performance, the physicochemical properties of the catalyst were characterized through various technical means. The results indicated that the addition of EG during the catalyst preparation process effectively promoted the dispersion of nickel metal, resulting in formation of smaller NiO particle size. High dispersion and smaller Ni species could enhance the conversion of polyethylene into carbon nanomaterials. This study provides promising directions for the preparation of high-performance catalysts for the preparation of high-value chemicals from plastics waste
Operational characteristics of the super-long gravity heat pipe for geothermal energy exploitation
No full textAs a novel geothermal heat transfer technology, the super-long gravity heat pipe (SLGHP) demonstrates great potential for the efficient exploitation of deep geothermal energy. Despite the rapid advances made to the SLGHP technology, its operational characteristics remain to be fully investigated. In this study, the underlying phenomenological mechanisms of the SLGHP are compared with those of normal-size gravity heat pipes (NSGHPs), and the operational characteristics of the SLGHP are analyzed in view of its distinctive geometric features. It is noted that the thermal resistance caused by the vapor flow is negligible in the NSGHPs, while it dominates the overall thermal resistance of the SLGHP. The dominance of the vapor flow thermal resistance allows making the one-dimensional simplification (along the pipe length direction) in the mathematical model of the SLGHP geothermal energy extraction system. Under these circumstances, the temperature gradient along the SLGHP length can be theoretically deduced based on the pressure drop of vapor flow. Close observation of the temperature gradient expression indicates that the desirable SLGHP working fluid should have the following properties: i) large latent heat of vaporization, and ii) a strong dependence of the saturated vapor pressure on the temperature. In cases where the saturated vapor pressure of the working fluid is highly dependent on the temperature, as in the case of ammonia, the working temperature profile of the SLGHP can be formulated as a linear function of the depth. This unique working temperature characteristic offers valuable guidance to determine the length of the SLGHP adiabatic section in practical geothermal applications. The on-site observed operational characteristics provide the necessary theoretical foundation for modeling the multiphase heat transfer process in SLGHP, which will lead to a valuable engineering analysis and design tool supporting the application and commercialization of the SLGHP technology
Study of efficient catalytic electrode for hydrogen evolution reaction from seawater based on low tortuosity corn straw cellulose biochar/Mo2C with porous channels
No full textPorosity and channel structure has important effects on the performance of hydrogen evolution reaction (HER) of nanostructured electrocatalysts in acid solution and seawater. Mesopore usually helps to enhance the reaction kinetics and mass transfer, while the macroporous channel structure also affects the electrocatalyst. Traditional graphene materials do not have such structure. Therefore, this paper designs a method to synthesize Mo2C composite nanomaterial in situ on corn straw biochar, inspires by the natural channel structure of conducting water, salt and organic matter in plants. Characteristic characterization shows that the material also has a large number of mesoporous and vertical distribution of large porous channel structure, through the decrease of tortuosity and porosity, ensure the catalyst surface electrolyte transport and hydrogen timely escape, alleviate the process of metal ion precipitation blocking pore channel, so as to improve the rate of hydrogen evolution reaction. The results shows that the overpotential of the catalyst was 48 mV and 251 mV under 10 mA cm-2 acidic electrolyte and simulated seawater electrolyte, respectively. This method provides new ideas for the design of efficient electrocatalysts for seawater decomposition, then the HER performance in alkaline and neutral environments needs to be further explored
Prediction of CO/NOx emissions and the smoldering characteristic of sewage sludge based on back propagation neural network
No full textSmoldering can achieve effective disposal of sewage sludge (SS) with high moisture content at low energy input, providing social and economic benefits. However, smoldering is accompanied by the emission of high concentrations of CO/NOx, and thus, it requires sufficient attention. This study comprehensively investigates the effects of SS characteristics and experimental parameters on CO/NOx emissions and smoldering characteristics. Results showed that when the moisture content of SS increases from 35% to 50%, CO concentration increases while NOx formation is simultaneously inhibited. After airflow rate exceeds 5 cm/s, the concentrations of CO and NOx begin to decrease. When SS concentration is increased to 20%, the emission concentration of gas pollutants is directly increased. However, high temperatures inhibit the formation of NOx. When the particle size range is 180-270 mu m, the formation of CO/NOx is promoted. Finally, a back propagation (BP) neural network model is constructed with SS characteristics and experimental parameters as input conditions, and CO/NOx emission concentration, smoldering velocity, and smoldering temperature as output parameters. The BP neural network model can effectively predict the emission concentration of CO/NOx and smoldering characteristics, providing support for intelligent control scenarios related to SS smoldering, it will help to further explore the great potential of smoldering treatment
Technological Project of Heilongjiang Province the open competition mechanism to select the best candidates[2022ZXJ05C01]
No full textCharacteristics of photothermal transfer and biochemical reaction in up-flow direct absorption hydrogen reactor with embedded ribs
No full textThe anaerobic fermentation process of microbial community is a promising method to treat wastewater with high ammonia nitrogen, but it needs to provide suitable temperature. An innovative direct absorption anaerobic reactor was established to reduce the temperature fluctuation of biogas slurry by adding ribs to ensure the high efficiency and stability of anaerobic fermentation process. The effects of flow rate and number of ribs on gas production in the process of photothermal conversion and anaerobic fermentation were analyzed by numerical simulation. The results show that the addition of ribs can effectively reduce temperature fluctuation and increase gas production. Compared with 2269.7 mL/L gas production and temperature fluctuation of up to 8 K without ribs, the gas production increased by 863.1 mL/L and decreased to 0.1624 K when the number of ribs was 9, respectively. Simultaneously, a curve was fitted according to gas production to predict the best working conditions.(c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved
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