Gas Conversion Rate Research Articles

Effective removal of nitrate by palygorskite-supported nanoscale zero-valent iron from aqueous solution

Nitrate nitrogen (NO3--N) has become an important pollutant in industrial and agricultural production processes in China. In this study, Palygorskite-supported nanoscale zero-valent iron (nZVI/PG) adsorbent was prepared using the liquid-phase reduction method for the removal of NO3--N from water. Benefiting from the good dispersion uniformity of nZVI on the Palygorskite carrier, the prepared nZVI/PG exhibited a significantly increased specific surface area compared to nZVI, with a noticeable reduction in nZVI aggregation. The Fe/PG mass ratio of 2:1 was found to be the optimal loading ratio for the removal of NO3--N by nZVI/PG, with a removal capacity of 24.36 mg/g and a removal efficiency of 81.23 %, with a nitrogen gas conversion rate of 40.92 %. The removal process of NO3--N by nZVI/PG followed a pseudo-second-order kinetic model, with the removal rate inversely proportional to the initial concentration of NO3--N and directly proportional to the dosage. nZVI/PG exhibited high removal efficiency for NO3--N within the pH range of 2 to 9, with the highest selectivity for NO3--N conversion to N2 observed at pH 5. The main mechanism for the removal of NO3--N by nZVI/PG was found to be adsorption and reduction, with the main products being NH4+-N, NO2--N, and N2.

Microwave plasma-assisted hydrogen production via conversion of CO2–CH4 mixture

A method concerning re-use of the main greenhouse gases: CO2 and CH4 at the same time producing value-added chemicals (H2 + CO) is presented in this paper. The method involves the methane dry reforming using an atmospheric pressure operated 915 MHz microwave plasma source with a swirl gas flow. The effect of the CO2 to CH4 flow rates ratio, the total gas flow rate and the absorbed microwave power on the volume concentration of the gaseous plasma component in the outlet gas (%), CO2 and CH4 conversion rate (%), hydrogen production rate (g h−1) and energy yield of hydrogen production (g kWh−1) was investigated experimentally. The recorded results of the CO2 and CH4 conversion rate were about 82% and 88%, respectively. The best results in terms of the hydrogen production rate and energy yield of hydrogen production were equal to 156 g h−1 and 24 g kWh−1, respectively.

Rapid nucleation and growth of tetrafluoroethane hydrate enhanced by bubble and gas cycling

The application of hydrate technology is predominantly limited by the rapid nucleation and stable formation of hydrates, which could be promoted by the disturbance of bubbles. In this study, the effect of bubble generation and different bubble sizes on the nucleation and growth characteristics of R134a hydrates were investigated. The impact of three methods (depressurization-induced R134a vaporization, depressurization combined with stirring and gas cycling bubbling) of bubble effect and size on the nucleation, growth characteristics, and stability of R134a hydrate formation were explored. The research results indicate that utilizing only the depressurization method to induce R134a vaporization and bubble formation leads to a gas consumption rate of 19.6 mmol/min, which is 868 times higher than that in a pure water system. Furthermore, refining bubble size through stirring under depressurization conditions further augments the gas conversion rate by 8.6 %, and the optimal temperature for R134a hydrate formation is identified to be as low as 4 °C. Importantly, utilizing gas cycling as a means to generate bubbles enables uniform and rapid nucleation and growth of hydrates. Within a short 10 min, R134a hydrates was rapidly and stably formed, achieving a formation rate 35 times faster compared to the boiling-condensation method. In comparison to stirring-depressurization, the gas cycling method further increases the gas consumption rate by 10 %. The drawback of slow nucleation and growth rates in hydrates, as well as the need to enhance their stability, is addressed by the gas cycling method.

Study on formation of methane hydrate in rotating packed bed

Offshore oilfield development process often carries a large amount of associated gas, most of it needs to be emptied or burned, resulting in a large amount of waste and environmental pollution. Hydrate storage and transportation technology has the advantages of simple process treatment, good offshore adaptability, good safety and relatively low investment. It is one of the important recovery technologies for associated gas in offshore oil fields. However, the long induction period of hydrate formation, the difficulty of gas dissolution, and the difficulty of continuous formation hinder the improvement of hydrate formation rate and gas storage density, and hinder the development of hydrate storage and transportation technology. High-gravity technology may be one of the development directions of new hydrate rapid formation reactors due to its small size and high mass transfer capacity. In this paper, a small-scale RPB was designed independently, and the effects of high-gravity factor, initial pressure, and packing type on hydrate formation were assessed by calculating the gas consumption, gas consumption rate, gas storage density, and gas conversion rate of hydrate formation under each experimental condition. The results show that in the range of high-gravity factor and pressure tested in the experiment, the increase of high-gravity factor and pressure can significantly accelerate the hydrate formation rate, which can be increased by up to 177 %, and the maximum gas storage density can reach 148.88 V/V. The type of packing has a strong influence on the rate of hydrate formation, and the principle of packing selection changes when dealing with solid-containing systems, and the rate of hydrate formation can be increased by 20 % with the proper selection of packing type. This study can provide a basis for subsequent high-gravity hydrate experiments and industrial applications.

Optimal parameter adjustment of catalytic combustion heaters for oil shale in-situ conversion of low calorific value gases

Oil shale resources are huge, and in order to develop and utilize them rationally, it is crucial to research heaters suitable for downhole in-situ conversion mining. Compared with the problems of short life and multi-stage energy utilization of downhole electric heaters, combustion heaters have advantages such as high thermal efficiency and low cost. The heater uses low calorific value industrial waste gas as the fuel for gas injection, which reduces carbon emissions and environmental pollution and saves gas injection costs. In this paper, we propose to apply catalytic combustion of low calorific value industrial waste gas to generate high temperature exhaust gas suitable for mining, and establish the relationship between gas injection flow rate, combustion chamber parameters and gas injection duration by mathematical methods. The effect of the downhole high-pressure environment on the catalytic combustion characteristics of low calorific gas was simulated and the formula for calculating the content of low calorific gas in the exhaust gas was modified. The results show that the determination of the relational equation solves the problem of excessive axial volume in the design process of downhole heaters. Under high pressure conditions downhole, the exhaust gas temperature and low calorific gas conversion rate are significantly improved. The catalyst ignition temperature ranged from 973 K to 1073 K. Increasing the downhole pressure to 5 MPa increased the conversion of low calorific value gas from 74.56% to 88.22%. The gas injection rate and calorific value range can be calculated by correcting the equation for the content of low calorific gas in the exhaust gas. The conclusion of the study provides a reference basis for the selection of catalytic combustion process parameters for low calorific industrial waste gas, and also provides an important theoretical basis for the construction of the downhole test prototype.

Modeling and analysis of the multiphysics transport parameters of a kilowatt-class multistack module of reversible solid oxide cells

Degradation and reliability-related issues are major obstacles in the large-scale commercialization of multistack modules of reversible solid oxide cells. Understanding various transport processes, the distributions of multiphysics parameters, and chemical/electrochemical reactions is critical for improving the performance and reliability of modules. In the present study, a simplified method based on the distributed resistance analogy approach was developed for constructing a three-dimensional model of a kilowatt-class multistack module comprising reversible solid oxide cells. The uniformity of the parameter distribution and the fuel gas conversion rate were predicted, and the effects of the number of stacks, number of cells, cascade configuration, and module scale were investigated under dual-mode operation. The uniformity factor of the gas flow ranges from 0.152 to 0.817 in modules of different sizes and configurations; this range is considerably greater than the uniformity factors of the other transport parameters under dual-mode operation. The uniformity factors of flow, temperature, and current density are 17.7%–78.1% lower under parallel stack configurations than under series stack configurations. Doubling the number of cells resulted in the flow uniformity factor increasing by 108%–212%, and doubling the active area of the cells resulted in the uniformity factors of the temperature and current density increasing by 107%–135%. High reactant conversion rates and low nonuniformity factors are achieved for parallel multistack modules with a power of 8–32 kW, which is appropriate for large-scale applications.

Numerical simulation of flow channel geometries optimization for the planar solid oxide electrolysis cell

In a solid oxide electrolysis cell (SOEC), the flow channel design influences the gas distribution, mass transfer, temperature distribution, and electrochemical properties significantly. This study evaluates the overall performance of SOECs with rectangular, triangular, trapezoidal, and semicircular flow channels and examines the effect of the geometry of the flow channel cross-section on the electrolysis process, gas flow, and material distribution. The trapezoidal flow channel shows the best electrochemical performance, but requires a high power and high pressure drop; the triangular flow channel has the most uniform gas velocity and distribution; and the semicircular flow channel shows the maximum gas velocity. The trapezoidal shape is found to be the optimal shape. Sensitivity analysis of the SOEC with the trapezoidal flow channel indicates that increasing the operating temperature improves the electrochemical performance, and reducing the inlet gas's steam volume fraction increases the gas conversion rate and decreases the electrolysis voltage.

Experimental Investigation Into Effects of Thermodynamic Hydrate Inhibitors on Natural Gas Hydrate Synthesis in 1D Reactor

Thermodynamic hydrate inhibitors (THIs) are often used in marine gas field operations to prevent the formation of natural gas hydrate (NGH), and it is important to study the effect of THIs on hydrate synthesis characteristics. Herein, the effects of water (H2O), sodium chloride (NaCl), and ethylene glycol (EG) on NGH synthesis characteristics under different initial pressure conditions are tested using the self‐developed 1D NGH production simulation test system. The effects of each THI on the maximum synthesis rate and maximum synthesis amount of NGH are investigated using two physical quantities, peak of temperature increment and maximum gas conversion rate. The results show that the 2.65 wt% salt solution has the minimum inhibition effect on the maximum synthesis rate of NGH, and the solution with a 3:1 mixture of H2O and EG has the maximal inhibition effect on the maximum synthesis rate of NGH. When only H2O and EG or H2O and NaCl are present in the reactor, the higher the concentration of EG or NaCl, the more significant is the inhibition effect on the maximum synthesis amount of NGH.

Analysis of cocoa particle roasting process in a μ-reactor

Thermal energy changes the chemical composition of cocoa, which is related to its quality, during roasting. The effect of the heating rate on the physicochemical changes of cocoa, and the dynamics of generation and degradation of volatile compounds during heating are still unknown. Therefore, the weight loss of cocoa and the chemical composition of the released gases released at temperatures from 40 to 350 °C were identified in using a μ-reactor (PTV-GC-MS) with heating rates of 2 (β 1 ), 4 (β 2 ), and 8 °C sec −1 (β 3 ). The thermal process was divided into three stages (raw ‒ dry, dry – roasted, and roasted – over-roasted). Higher heating rates cause lower volatilization at the same temperature due to shorter residence times. Likewise, more compounds were identified in the gas-fraction at β 1 than at β 2 and β 3 with the same temperatures. Also, a 2D phenomenological model coupled to kinetics was made to predict phenomena such as thermal differentials, water and gas content, solid fractions, conversion, pressure, and gas outlet rate. • Cocoa quality begins in the tree and develops in the processing. • Small-scale studies and modelling are valuable tools to understand cocoa roasting. • A 2D model coupled to kinetics was able to show experimentally invisible phenomena.

Development of CO gas conversion system using high CO tolerance biocatalyst

Acetogenic bacteria (acetogens) are microorganisms with high potential as biocatalysts that can convert C1 gas, such as carbon dioxide (CO2) or carbon monoxide (CO), into biomass or biochemicals; however, high CO concentrations cause growth retardation in these microorganisms. In this study, we performed adaptive evolution of Eubacterium limosum, an acetogen, for approximately 400 generations under high CO synthetic gas (syngas) conditions to obtain E. limosum ECO2, which can rapidly proliferate even under high CO conditions. A mutation was revealed in H636R in the Acetyl-CoA synthase (ACS) protein of the ECO2 strain through whole-genome re-sequencing, and the mutation increased the CO gas conversion rate. By analyzing the transcript profiling of the ECO2 strain under high CO syngas conditions, the transcript levels of the methyl branch in the Wood–Ljungdahl pathway and the energy conservation system increased at high CO concentration conditions. Finally, to convert CO into value-added biochemicals, 2,3-BDO (2,3-butanediol) biosynthesis pathways were constructed and transformed into the E. limosum ECO2 strain. This strain showed capability to produce 2.60 mg L-1h−1 of 2,3-BDO through CO 66% syngas fed-batch fermentation. This was 6.5-fold higher than that of the wild type. We developed a microorganism with high CO tolerance, and this strain showed high application potential as a biocatalyst that can efficiently convert CO gas into value-added chemicals.

Characterization of Bacillus subtilis Ab03 for efficient ammonia nitrogen removal

An efficient ammonia nitrogen degrading bacterial strain was isolated from a fish and shrimp pond and identified as Bacillus subtilis (Ab03). Firstly, the strain was continuously domesticated in ammonium solution to improve its nitrogen removal capacity. The performance of the strain in terms of nitrogen removal efficiency under different culture conditions was then examined. Finally, the nitrogen removal process and related strain mechanisms were analyzed by nitrogen balance. The results showed the strain Ab03 could remove 91.67% of NH4+-N at 300 mg/L under the conditions of glucose as the single carbon source, C/N of 15, pH of 7.5, the temperature of 35 ℃ and dissolved oxygen of 7–8 mg/L. It was also found that under conditions where ammonia nitrogen was the only nitrogen source, strain Ab03 could also undergo aerobic denitrification for simultaneous conversion, with a final gas conversion rate of 74.81%.

Numerical investigation of the influence of particle shape, pretreatment temperature, and coal blending on biochar combustion in a blast furnace

Using carbon-neutral from biomass is a promising solution to achieve carbon neutrality in pulverized coal injection (PCI) technology in an ironmaking blast furnace (BF). In this paper, a 3D CFD model, including the whole region of lance-blowpipe-tuyere-raceway surrounding coke bed, is improved to describe the in-furnace phenomena related to biochar injection under industrial-scale BF conditions. The factors such as particle shape, carbonization temperature, and coal blending are considered to determine the influence on flow and thermochemical behaviors of biochar particles. The results show that, in comparison to spherical particles, the cylindrical particles show a slower gas conversion rate and smaller burnout as a result of the shorter traveling time in the raceway; High carbonization temperature decreases the burnout of biochar in the raceway. From the perspective of the economy, BC-773 has an appropriate ratio of volatile matter (VM) to fixed carbon, which burns more fully and releases a large amount of heat in a limited time, and has the potential to better replace PCI coals in BF practice. The overall gas temperature and burnout of the biochar/coal blend show a non-additivity, indicating there is a synergistic effect during the co-combustion process. This model provides an effective way for understanding and optimizing biomass injection technology in BF practice.

Synthesis gas conversion over Cu and Ca modified model Mo6S8 catalysts: A systematic theoretical investigation

We present a combined density functional theory (DFT) and microkinetic modeling study of synthesis gas conversion on Cu and Ca modified Mo6S8 catalysts to value-added products. Our results show that CO∗ + H∗ → HCO∗ + (H) → H2CO∗ + (H) → H3CO∗ + (H) → CH3OH∗ → CH3OH (g) is an optimal pathway on the Ca–Mo6S8 surface. With the combination of Energetic span model (ESM) and binding energy analysis, we conclude that Ca–Mo6S8 is a promising catalyst for formaldehyde and methanol from synthesis gas conversion. Meanwhile, the most energetically favorable outcome on the Cu–Mo6S8 surface is the production of ethanol. Microkinetics simulations are carried out on the basis of the first-principles data, which predict the synthesis gas conversion rate and the product distribution. This study demonstrates that introducing metal Cu or Ca into Mo6S8 will design high-performance catalysts with synergistic interactions for tuning selectivity.

Regulation of influent sulfide concentration on anaerobic denitrifying sulfide removal

ABSTRACTThe objective of this study is to find a comprehensive regulation for sulfide removal and elemental sulfur transformation based on the denitrifying sulfide removal process. The experiment was performed based on several influent sulfide concentrations (150–600 mg/L) and nitrate-to-sulfur (N/S) molar ratios (0.5–2.0) at reaction times of 24 and 48 h. Sulfide and nitrate removals were mainly dependent on the influent sulfide concentration at sulfide concentrations of 150–200 and 400–600 mg/L, but on the N/S ratio at sulfide concentrations of 250–350 mg/L. Up to 99.7% and 93.8% of sulfide and nitrate were removed, respectively, with 26.5% of elemental sulfur formed at sulfide concentrations of 250–350 mg/L (N/S of 1.0). Only 4–9.4% of elemental sulfur was formed, with sulfide and nitrate removals of 99.9% and 98.7%, respectively, at sulfide concentrations of 150–200 mg/L. Meanwhile, 46.9–94.7% of sulfate was formed with a nitrogen gas conversion rate of 18.2–57.1%. Fewer microorganisms were detected by fluorescence in situ hybridization (FISH) at high sulfide concentrations of 400–600 mg/L, suggesting that the processes of anaerobic denitrification and desulfurization were inhibited.

Pilot Test of a Fermentation Tank for Producing Coal Methane through Anaerobic Fermentation

The development and utilization of clean energy has long been a focus of research. In the coal bed methane field, most coal bed biogenic methane experiments are small static sample tests in which the initial conditions are set and the process cannot be batch-fed elements and microbial strains, and the gas cannot be collected in batches. Although significant results have been achieved in the coal-to-biogenic methane conversion in China, findings are restricted to the laboratory scale. No successful commercialization of coal bed biogenic methane production has been achieved yet. This study used a large-capacity fermentation tank (5 L) to conduct biogenic methane experiments. Results were compared to those from the traditional laboratory test. The gas production rate and gas concentration were higher when the 250 mL methane test volume was increased to a 5 L fermentation volume, increasing by 20.9% and 2.3%, respectively. The inhibition effect of the liquid phase products was reduced in the large fermentation tank, and the microbial activity was extended by batch feeding trace elements (iron and nickel) and methane strains and by semi-continuous collection of the gas. However, the gas conversion rate can be increased by retaining the H2 and CO2 in the intermediate gas products in the fermentation tank. The gas production rate was increased from 17.9 to 24.6 mL/g, increasing by 37.4%. The simulation pilot test can lay a foundation for the transition from a coal bed biogenic methane laboratory static small sample test to a dynamic pilot test, optimizing the process parameters to improve the reaction efficiency and move forward to commercialization test.

Characterization and Kinetics for Co-Pyrolysis of Zhundong Lignite and Pine Sawdust in a Micro Fluidized Bed

Co-pyrolysis behaviors of Zhundong lignite and pine sawdust under isothermal conditions were investigated with a focus on the gas releasing characteristics using a micro fluidized bed reactor. The kinetic parameters were deduced by measuring time-dependent changes in the composition of evolved gases from the pyrolysis reactions, employing the universal integral method. The gas release intensity and conversion rate of pine sawdust were quite different from those of Zhundong lignite because of the difference in chemical structure and element content. The effect of blending ratio on the degree of conversion varied significantly for different gas components; H2, CO, and CH4 conversion became quicker with an increasing biomass ratio, while the variation of CO2 was not obvious. The generally used mechanistic models for gas–solid reactions were examined as ways to interpret the experimental data, and reaction kinetics was deduced with respect to the formation of an individual gas component. The obtained activati...

3D numerical study of the performance of different burner concepts for the high-pressure non-catalytic natural gas reforming based on the Freiberg semi-industrial test facility HP POX

In this work, new test burner concepts for the non-catalytic partial oxidation of natural gas are evaluated using numerical modeling. The 3D CFD model for reactive flow calculations incorporates a detailed reaction mechanism containing 28 species and 112 reactions, and is extensively validated against data obtained in the semi-industrial test facility HP POX in Freiberg. The validation cases operate at 61bar(a) and outlet temperatures of approximately 1688K. The CFD models demonstrate that the optimized burner concepts result in a significantly higher natural gas conversion rate, which allows for a more compact reactor design or, alternatively, for a higher throughput in existing industrial facilities. In addition, the final burner concepts are tested experimentally. Optical measurements demonstrate that the CFD model is capable of reproducing the complex 3D flame structures and reliably predicting the overall performance of the reactor.

Influence of Sodium Halides on the Kinetics of CO2 Hydrate Formation

The mechanism of gas hydrate formation in the presence of kinetic influencing additives has attracted much interest due to the importance of optimizing hydrate formation in areas such as energy supply and the environment. This paper presents experimental studies into hydrate formation of CO2 gas in the presence of sodium halide salts. Pressure and temperature changes versus time during the hydrate formation process were measured under the isochoric conditions. The effect of anion type and concentration on gas maximum uptake, conversion, storage capacity, induction time, and hydrate growth rate has been examined. Surface potential measurements of the hydrates provided further understanding of how halide anions affect CO2 hydrate formation kinetics. It is shown that sodium halides at an approximately 50 mM (mmol/L) concentration can increase gas consumption and conversion to hydrates, and sodium iodide and sodium bromide in a range of concentrations between 50 and 250 mM can significantly increase the hydra...

Chemical-looping combustion of solid fuels in a 10 kW reactor system using natural minerals as oxygen carrier

Chemical-looping combustion (CLC) is an unmixed combustion concept where fuel and combustion air are kept separate by means of an oxygen carrier, and the CO2 capture is inherently achieved. This work presents findings from a continuously operated 10kW pilot for solid fuels. Using petcoke as fuel, the following oxygen carriers are compared: (a) ilmenite, (b) ilmenite + lime, (c) manganese ore, and (d) manganese ore + lime. Compared to ilmenite, the use of manganese ore as oxygen carrier greatly enhanced the rate of gasification. By adding lime particles to the Mn ore, performance improved further. The addition of lime to ilmenite had a small beneficial effect on gas conversion and char gasification rate.

Decomposition of 1-Decanol Emulsion by Water Thermal Plasma Jet

Water-insoluble organic compound of 1-decanol was decomposed by a water plasma system operated at atmospheric pressure. It was dispersed in water by a surfactant generating an oil-in-water emulsion, and then, the emulsion was used as the feeding liquid and plasma-forming gas of the water plasma jet. The input power supplied to the dc water plasma system was less than 1 kW. High decomposition rate over 99.9999% was achieved with the conversion of 1-decanol emulsion into H2, CO, CO2, CH4, condensed liquid, and solid-state carbon. The gas conversion rate of carbon in 1-decanol and the removal rate of total organic carbon concentration were increased by increasing the arc current due to enhanced O radicals in the high temperature of the water plasma jet. Different from the decomposition of water-soluble 1-butanol, noticeable changes in the decomposition rate and pH level were not founded in the treatment of 1-decanol emulsion according to carbon concentration in the feeding liquid. The main organic substance in the treated liquid of 1-decanol emulsion was methanediol which was produced by the hydration of formaldehyde.