Recycle Ratio Research Articles

Optimization of nano-emulsion production in ultrasonic microreactors: The effects of pre-homogenization, circulating ratio and hybrid frequency application

The study first investigated the effects of individual ultrasound and high-speed shearing on emulsification, both obtaining emulsions with average sizes of approximately 1 μm. Subsequently, a combined strategy to utilize shearing instrument producing coarse emulsion for ultrasonic microreactor was proposed. Immiscible liquids were drawn into the stirring chamber by rotating paddles, where they underwent strong shearing and thorough mixing. The pre-mixed liquids were introduced into microchannel and subjected to further processing by oscillating cavitation bubbles. Through optimization of experimental parameters such as residence time and recycle ratio, the average emulsion size was significantly reduced to 522 nm. Finally, a dual-frequency strategy using ultrasound frequencies of 20 and 40 kHz consecutively further reduced the emulsion size to 307 nm. In comparison with conventional sonoreactors and high-pressure homogenizers, this dual-frequency approach demonstrated superior emulsification performance with less surfactant addition and energy input, indicating its high applicability on continuous emulsification process with proper design and optimization.

Comprehensive comparison of integrated fixed-film activated sludge (IFAS) and AAO activated sludge methods: Influence of different operational parameters

Due to limited land availability in municipal wastewater treatment plants, integrated fixed-film activated sludge (IFAS) technology offers significant advantages in improving nitrogen removal performance and treatment capacity. In this study, two systems, IFAS and Anaerobic-Anoxic-Oxic Activated sludge process (AAO), were compared by adjusting parameters such as hydraulic retention time (HRT), nitrifying solution recycle ratio, sludge recycle ratio, and dissolved oxygen (DO). The objective was to investigate pollutant removal capacity and differences in microbial community composition between the two systems. The study showed that, at an HRT of 12 h, the IFAS system exhibited an average increase of 5.76%, 8.85%, and 12.79% in COD, NH4+-N, and TN removal efficiency respectively, compared to the AAO system at an HRT of 16 h. The TP concentration in the IFAS system reached 0.82 mg/L without the use of additives. The IFAS system demonstrated superior effluent results under lower operating conditions of HRT, nitrification solution recycle ratio, and DO. The 16S rDNA analysis revealed higher abundance of denitrification-related associated flora, including Proteobacteria, Bacteroidetes, and Planctomycetota, in the IFAS system compared to the AAO system. Similarities were observed between microorganisms attached to the media and activated sludge in the anaerobic, anoxic, and oxic tanks. q-PCR analysis indicated that the incorporation of filler material in the IFAS system resulted in similar abundance of nitrifying bacteria genes on the biofilm as in the oxic tank. Additionally, denitrifying genes showed higher levels due to aeration scouring and the presence of alternating aerobic-anaerobic environments on the biofilm surface, enhancing nitrogen removal efficiency.

A dynamic model of growth phase of bio-conversion of methane to polyhydroxybutyrate using dynamic flux balance analysis.

Biological conversion of waste methane to biodegradable plastics is a way of reducing their production cost. This study addresses the computational modeling of the growth phase reactor of the process of polyhydroxybutyrate production. The model was used for investigating the effect of gas recycling and inlet gas retention time on the reactor performance. The model was run by the use of a genome-scale metabolic network of Methylocystis hirsuta in a dynamic flux balance analysis framework. The reactor has been modeled for two separate feeding scenarios: a pure methane feed and a biogas feed. The mass transfer coefficient parameter was predicted as a function of superficial gas velocities by the regression of data from published experiments. The results show an increase of removal efficiency by 38% and biomass concentration by 2.8g/L with the increase of gas recycle ratio from 0 to 30 at the empty bed residence time of 60 .

Effect of syngas recirculation in the pyrolysis zone on the rice husk gasification process using the downdraft reactor

As one of the world's largest rice producers, Indonesia has an abundance of rice husk as a byproduct of rice milling. Rice husks were utilized to examine downdraft gasification with syngas recirculation system. This study attempts to produce better syngas than conventional downdraft gasifier. With an equivalency ratio of 0.20, syngas was recirculated into the reactor in the pyrolysis zone with valve openings at 25%, 50%, and 75%. This study determined the syngas recycling ratio that maximizes H2 and CO gas and decreases tar. Increasing the syngas recirculation valve (25%, 50%, and 75%) accelerates flame propagation and pyrolysis zone temperature. Syngas study showed no recirculation condition produces the maximum CO2 and CH4. Different recirculation valve openings little affect CO and CH4 gas composition. The H2 gas composition demonstrates that valve openings significantly change H2 gas generation and that the peak was at 50% syngas recirculation. Tar content decreased to 30% and 35% at 50% and 75% valve openings. Based on H2/CO comparison and tar concentration, 50% opening syngas recirculation became the optimum case.

Experimental study on the triaxial compression mechanical performance of basalt fiber-reinforced recycled aggregate concrete after exposure to high temperature

The use of basalt fiber-reinforced recycled aggregate concrete (BFRRC) can effectively treat waste concrete and reduce the consumption of natural resources. BFRRC is often in complex triaxial compression in engineering applications and may exposure to high temperature conditions. To evaluate the conventional triaxial compression mechanical performance of BFRRC after exposure to high temperature, 324 cylindrical specimens were produced. The specimens were designed and fabricated by varying several experimental parameters: the recycled coarse aggregate replacement ratio, basalt fiber dosage, temperature, and lateral confining pressure. The specimens previously exposed to high temperature were subjected to conventional triaxial compression tests and the effects of various experimental parameters on the mechanical performance indexes of BFRRC were analyzed. The results show that the peak stress and elastic modulus of BFRRC all raise with greater fiber dosage and confining pressure but decrease with higher replacement ratio and temperature. The maximum increase of the peak stress and elastic modulus is 352.45% and 224.59%, respectively. The peak strain of BFRRC has two variation trends of gradual increase and gradual decrease with the replacement ratio rising. And the peak strain gradually grows with the temperature and confining pressure increasing. The fiber dosage, however, does not exert the considerable impact on the peak strain. The maximum increase of the peak strain is 132.22%. The research provides a scientific basis for the triaxial mechanical performance, fire resistance design, and post-disaster assessment of BFRRC, and promotes the popularization and application of BFRRC in building structures.

Effect of internal and external recycle ratios on the nutrient removal efficiency of anaerobic/anoxic/oxic (VIP) wastewater treatment plant

Abstract Due to the disposal of different wastewater into the water bodies, the rate of surface water pollution is increasing. The virginia initiative plant (VIP), one of the most efficient and economical wastewater treatment systems, was assessed. The experiments were carried out by a laboratory-scale VIP system used for this study, with a flow rate of 100 L/day and a solid retention time rate estimated at 10 days. The system works on three different ratios for internal rotation (100, 150, and 200%) and three for external rotation (80, 90, and 100%), and the effective volumes were 20, 40, and 60 L for anaerobic, anoxic, and oxic reactors, respectively. The results showed that the VIP system achieved the best removal efficiency of organic matter represented by COD, phosphorous, and ammonia (86, 94, and 93%, respectively). The impact of internal and external rotation ratios was tested by removing COD, phosphorous, and ammonia. The percentages of internal rotation significantly affect the biological removal of nitrates. The relationship between them is inverse, while the percentages of external rotation significantly impact the biological removal process of phosphorus. The relationship between them is positive, whereas the internal and external rotation percentages did not considerably affect the efficiency of removing both ammonia and COD. According to the research results, internal and external rotation ratios enhanced the removal efficiency of phosphorus and nitrates. The VIP system proved to be an effective method for domestic wastewater treatment with a flow conforming to Iraqi standards for draining wastewater with all organic matter, phosphorous, and nitrogenous compounds to rivers.

Freeze-thaw, chloride penetration and carbonation resistance of natural and recycled aggregate concrete containing rice husk ash as replacement of cement

This study investigated the effect of using rice husk ash (RHA) as replacement of cement (i.e., replacement ratios of 0%, 10%, 20% and 30%) on the durability of natural aggregate concrete (NAC) and recycled aggregate concrete (RAC). We examined the freeze-thaw resistance, chloride penetration resistance, and carbonation resistance of NAC and RAC (with 50% recycled coarse aggregate replacement ratio). It was found that during the freeze-thaw process, both NAC and RAC showed an overall weight increase, which was further enhanced by the addition of RHA. Meanwhile, the compressive strength of NAC was reduced more obviously than that of RAC after 100 freeze-thaw cycles. A replacement of 10% cement with RHA resulted in larger reduction in strength loss for NAC (by 36%) compared to RAC (by 4%). As the RHA replacement ratio increased, the chloride penetration resistance of RACs was improved more rapidly than that of NACs, and the difference in the total charge passed between NACs and RACs also decreased considerably. In addition, an increase in the RHA replacement ratio led to an increase in the carbonation coefficient of NAC. Conversely, in the case of RAC, the carbonation coefficient displayed an initial decrease at a 10% RHA replacement ratio, followed by a subsequent upward trend, indicating a positive impact of RHA on preventing carbonation for RAC.

Mechanical properties of recycled brick powder engineering cementitious composites under freeze-thaw cycling environment

With the continuous advancement of urbanization construction, the number of discarded red bricks caused by construction demolition is impressive because of the characteristics of construction materials in the early stage of our country. This study used the recycled brick powder produced in crushing red waste bricks to partially or wholly replace quartz sand, combined with different doses of PVA fiber to prepare green recycled brick powder engineering cementitious composites (ECC). First, the strain hardening and multiple cracking behaviors of recycled brick powder ECC with different fitting ratios were verified using four-point bending tests. Then, a rapid freeze-thaw experiment was conducted to study the effects of different fitting ratios on the quality failure rate, phase dynamic elastic modulus, and compressive flexural resistance of recycled brick powder ECC. Based on the evaluation parameters of compressive strength loss rate and frost resistance, the ECC freeze-thaw prediction model of recycled brick powder was established by the Monte Carlo method to expand the number of samples. The research results show the best frost resistance of recycled brick powder ECC with a 25% recycled brick powder ratio and 1% PVA fiber. Scanning electron microscopy was used to observe raw materials and cement-based materials, and the reasons of macroscopic phenomena were explained from a microscopic perspective.

Axial compressive behavior of steel reinforced GGBS-RFBP-FA ternary composite geopolymer recycled fireclay brick aggregates concrete columns

In this study, the axial compressive behaviors of steel reinforced ternary composite geopolymer recycled fireclay brick aggregates concrete columns were investigated. The ternary binder material used in this study was produced by the combination of industrial by-products (i.e., granulated blast furnace slag (GGBS), recycled fireclay brick powder (RFBP), and fly ash (FA)) and alkali-activated solution. A total of 60 square steel reinforced composite columns (with a 200-mm side length and 600-mm height) were tested under axial compression. The tested variables included the mix proportion of ternary composite geopolymer concrete with recycled aggregates containing recycled fireclay brick aggregates (GRA-RFBAC), the recycled coarse aggregate replacement ratios (0%, 30%, 50%, 70%, 100%), the longitudinal reinforcement ratios (1.13%, 2.01%), and the hoop stirrup reinforcement ratios (0.81%, 1.62%). Each group contained three identical samples. The ductility, failure mode, and axial load-bearing capacity of the columns were recorded and analyzed. The experimental results revealed that the damage progression and patterns of steel reinforced GRA-RFBAC columns were similar to those of ordinary Portland cement based recycled concrete columns. The ultimate bearing capacity of steel reinforced GRA-RFBAC columns decreased with an increasing replacement ratio of recycled coarse aggregate and increased with an increasing reinforcement ratio of longitudinal and hoop stirrups. Meanwhile, the stress-strain model of steel reinforced GRA-RFBAC columns under axial compression was proposed based on the experimental results. The present study suggests an efficient and environmental-friendly compression member.

Circular recycled aggregate concrete-filled stainless steel tube stub columns after exposure to fire: Experiments, simulations, and design

This paper presents experimental and numerical investigations into the post-fire cross-section compressive behaviour and resistances of circular recycled aggregate concrete-filled stainless steel tube (RACFSST) stub columns. Twelve stub column specimens, fabricated from concretes with three recycled coarse aggregate replacement ratios (0%, 35% and 70%), were tested after exposure to the ISO-834 standard fire for 0 min (i.e. at ambient temperature), 15 min, 30 min and 45 min. The experimental investigation included heating and cooling of specimens, cylinder tests and post-fire tensile coupon tests and stub column tests. The test results, including load–end shortening curves, failure loads and failure modes, were fully reported and the initial compressive stiffnesses and confinement effect were discussed. The numerical investigation was subsequently conducted, where thermal and mechanical finite element models were developed and validated against the test results and then used to perform parametric studies to generate further numerical data. Given the absence of design codes for stainless steel–recycled aggregate concrete composite structures after exposure to fire, the relevant design rules for circular natural aggregate concrete-filled carbon steel tube stub columns at ambient temperature, as set out in the European code, Australia/New Zealand standard and American specification, were assessed, using post-fire material properties, for their applicability to circular RACFSST stub columns after exposure to fire, based on the test and numerical data. The assessment results generally revealed that the European code and the Australian/New Zealand standard led to an acceptable level of design accuracy and consistency, while the American specification resulted in rather conservative and scattered post-fire cross-section compression resistance predictions.

Post-fire behaviour and resistances of square recycled aggregate concrete-filled stainless steel tube stub columns

Experimental and numerical studies on the cross-section compressive behaviour and residual resistances of square recycled aggregate concrete-filled stainless steel tube (RACFSST) stub columns after exposure to fire are reported in this paper. An experimental programme was firstly carried out on twelve stub column specimens with three recycled coarse aggregate replacement ratios (0%, 35% and 70%) after exposure to the ISO-834 standard fire for 0 min (i.e. at ambient temperature), 15 min, 30 min and 45 min. The test results, including load–end shortening curves, failure loads and failure modes, were presented, with the initial compressive stiffness and confinement effect analysed. The experimental programme was followed by a numerical modelling programme, where thermal and mechanical finite element models were developed and validated against the test results and afterwards used to conduct parametric studies to generate additional numerical data over a wide range of cross-section dimensions. Based on the test and numerical data, the relevant design rules for square natural aggregate concrete-filled carbon steel tube stub columns at ambient temperature, as specified in the European code, Australia/New Zealand standard and American specification, were evaluated, using post-fire material properties, for their applicability to square RACFSST stub columns after exposure to fire. The evaluation results generally revealed that the European code and Australian/New Zealand standard led to a good level of design accuracy, while the American specification resulted in slightly conservative post-fire cross-section compression resistance predictions.

Moisture Recycling in the Colombian Andes

AbstractThe Colombian Andes (CA) are located over the northwestern corner of tropical South America (NW‐TropSA), where land and atmosphere interchange moisture and energy in a complex way owing to the orographic influence on the recycling of moisture over land. We aim to understand where and when water vapor evaporated from land turns into rainfall through moisture recycling, using the Water Accounting Model‐2layers (WAM‐2), an offline model to track atmospheric moisture forced with data from ERA‐5 at its native 0.25° resolution during 1980–2020. We define the spatiotemporal distribution of sources (high evaporation recycle ratios, ϵC) and receptors (high precipitation recycle ratios, ρC) of continental moisture at diverse timescales, including monthly, seasonal, annual and interannual (ENSO). Referring to the regional runs of WAM‐2 over NW‐TropSA (4°S–12°N/80°W–66°W), at elevations above 1,000 m.a.s.l., the CA has a mean annual ρC of 11% (ranging 6%–16%) and a mean annual ϵC of 35% (ranging 27%–40%). Moisture recycling in the CA exhibits a strong annual cycle over the region. The seasonal dynamic of moisture recycling shows two clear‐cut sources of moisture: the eastern foothills of the Eastern and Central ranges of the CA. Both foothills are also regions of high rainfall, although moisture recycling mechanisms differ. Sources of continental moisture grow spatially during September‐October‐November and March‐April‐May. The seasonal availability of moisture recycled coincides with regions where orography interacts with low level jets sourcing humidity. At interannual timescales, sources and receptors of continental moisture in the CA are modulated by the extreme phases of ENSO.

Conceptualization and process simulation of a CO2 based methanol production plant

The present study conceptualizes and simulates a methanol production process through the direct hydrogenation of captured CO2. CuO/ZnO/ZrO2 was employed as the catalyst and Aspen HYSYS was used for the process simulation. Configurational optimization of the process flowsheet was carried out using a step-by-step hierarchical approach. Many alternate flowsheets were resulted, and their capital investment, product cost, and profitability measures were calculated. The discrimination among the competing flowsheets was carried out on the basis of net profit and percent return on investment. The retained flowsheet was further analyzed for optimizing the recycle ratio and evaluating the effect of the price of captured CO2, green H2, natural gas (fuel), and catalyst on the economic performance of the plant. The optimum value of the recycle ratio was computed to be 4.23. Additionally, it was found that the price of H2 is the most important parameter in defining the feasibility and profitability of the process. Mathematical correlations were also developed that relate profitability and price of the above-mentioned feed materials.

Enhancing performance and sustainability: CRB600H high-strength reinforcement in recycled concrete

This paper addresses the urgent need for high-performance, eco-friendly construction materials due to increasing urbanization. It introduces CRB600H high-strength reinforcement to enhance recycled aggregate concrete (RAC) beam performance. Comparative analysis with conventional concrete (CC) beams demonstrates RAC's inferior shear performance, which CRB600H reinforcement effectively improves. A novel optimization method for high-strength reinforcement is established based on equal strength principles, demonstrating cost-efficiency. Economic analysis reveals that despite rising production costs with increased recycled aggregate replacement ratios, CRB600H reinforcement substantially reduces expenses, even when more expensive than HRB400 reinforcement. The environmental analysis reveals that the CRB600H reinforcement significantly influences the environmental performance of reinforced concrete beams. Utilizing 100% RAC beam with CRB600H as an illustrative example, the contribution rates of steel bars to Global Warming Potential (GWP), Acidification Potential (AP), Eutrophication Potential (EP), and Cumulative Energy Demand (CED) are determined as 39.30%, 56.85%, 51.87%, and 55.76%, respectively. In comparison to CC beam with HRB400, the 100% RAC beam with CRB600H exhibit reductions of 10.27%, 18.59%, 19.03%, and 16.93% in terms of GWP, AP, EP, and CED, respectively. In conclusion, CRB600H reinforcement offers cost-effective, eco-friendly solutions, promising significant advancements in RAC applications.

A review of high-performance carbon nanotube-based carbon fibers

With the growing importance of high-performance carbon fibers (CFs), researches have been conducted in many applications such as aerospace, automobile and battery. Since conventional CFs which were made from polyacrylonitrile, pitch and cellulose display either high tensile strength or high modulus properties due to structural limitations, it has been a challenge to develop CFs with both tensile strength and modulus with high conductivity. Therefore, various studies have been conducted to obtain high-performance multifunctional CFs. Among them, 1-dimensional carbon nanotubes (CNTs) have been used commonly to make CFs because of high mechanical and conducting properties. In this review, the recent development of CFs was introduced briefly, and CNT-based composite CFs were introduced. Many efforts are being made to create high-performance CFs by combining various carbon nanomaterials and polymers, which can have potential to be utilized in aerospace, defense and other industries. The those fibers may be nextgeneration high-performance fibers due to both high strength and high modulus as well as high conducting properties. The challenges and outlook for commercialization of CNT-based CFs are addressed in terms of aspect ratio of CNTs, solvent recycling, and mass-production.

Amplification Ratio of a Recycled Plastics-Compliant Mechanism Flexure Hinge

This research focuses on the fabrication of plastic flexure hinges from diverse plastics such as ABS, PP, HDPE, and LDPE. To enhance hinge efficiency, the recycling ratios are also investigated. The amplification ratio of different recycle ratios and plastic types are measured. The results show that the input and output displacements of all PP, ABS, and HDPE hinges are linear. The presence of recycled plastics has no impact on this basis. The pure PP, ABS, and HDPE flexure hinges achieve the highest amplification ratios of 5.728, 8.249, and 5.668. The addition of recycled plastics reduces the amplification ratio. This decrease in the amplification ratio, however, is small. At a 25% recycle ratio, the PP, ABS, and HDPE flexure hinges have 12%, 13.3%, and 21.7% lower amplification ratios than the pure plastic hinges. Furthermore, the utilization of recycled plastics may lessen the need for new plastic made from raw materials. With the PP flexure hinge, a maximum input value of 157 µm could result in an output value of 886 µm. At a maximum input value of 115 µm, the ABS flexure hinge could achieve an output value of 833 µm. Finally, a maximum input value of 175 µm might result in an output value of 857 µm when using the HDPE flexure hinge. The average amplification ratio values for all recycling ratios for PP, ABS, and HDPE flexure hinges are, respectively, 5.35, 7.60, and 5.02. The ABS flexure hinge frequently outperforms the PP and HDPE flexure hinge in terms of amplification ratios. Among these plastics, HDPE flexure hinges have the lowest amplification ratio. In general, increasing the thermoplastic polyurethane (TPU) content of the LDPE/TPU blend increases the amplification ratio. The cause could be the TPU’s high compatibility with the LDPE polymer. The LDPE/TPU blend hinge offers a broader range of the amplification ratio of 2.85–10.504 than the PP, ABS, and HDPE flexure hinges. It is interesting that changing the blend percentage has a much greater impact on the amplification ratio than changing the recycling ratio. The findings broaden the range of applications for plastic flexure hinges by identifying optimal plastic types. The impact of the hinge shape on the performance of the injected plastic flexure hinge might be studied in further research.

Comprehensive energy, exergy, and economic analyses of a geothermal and flue gas-based dual-source power, hydrogen, and freshwater trigeneration system

Designing a ploy-generation system to produce various products is an effective method to improve the common power plant’s performance. Hence, the current investigation proposes a green poly-generation system driven by geothermal and flue gas. The proposed scheme consists of an organic Rankine cycle, proton exchange membrane electrolyzer, saline water desalination unit, and Allam cycle to produce power, hydrogen, and freshwater. The produced oxygen in the electrolyzer feeds the Allam cycle to perform an oxyfuel process to achieve zero CO2 emission. Per the 4E analysis, the system produces 27,720 kW net power, 931 kmol/h hydrogen, and 616.7 kmol/h freshwater. In this way, the energy and exergy efficiencies are obtained at about 16.87% and 51.65%. The total exergy destruction rate is estimated at about 78,926 kW, in which the organic Rankine cycle and its vapor generator have the highest portions among the different parts and equipment by about 69% and 18.87%. The sensitivity analysis indicates that by the CO2 recycle ratio of 60%, the highest energy and exergy efficiencies reach 19.3% and 54.33%. Furthermore, the unit cost of hydrogen and electricity productions are 0.07$/kWh and 7.24 $/GJ, which is a considerable reduction compared to similar methods.

The Significance of the Factors Increasing the Asphalt Pavement Recycling Rate in the Country, Determined Using Multiple-Criteria Decision-Making Methods

Asphalt pavement, a component of transport infrastructure, deteriorates under the influence of destructive factors. The damages which have occurred during its period of use are repaired and the asphalt pavement is recycled when its further rehabilitation is economically and technically irrational. The material from the asphalt pavement layer that has reached its limit state is milled out or broken and crushed and then is repeatedly used in the production of hot-mix asphalt (HMA) or warm-mix asphalt (WMA) mixtures. In this paper, the dynamics of the percentage recycling ratio (RR) of old asphalt pavement material was investigated. RR represents the quantity of reclaimed asphalt pavement (RAP) used in the production of HMA and WMA mixtures in Europe and the USA, divided by the total amount of RAP prepared in the country. Factors and goals affecting it are analyzed. An original system of 10 criteria that increase the RR country has been created. Decision makers do not know which factors have the maximum influence in increasing the use of RAP and this should go in connection with environmental pollution reduction and achieving economic utility. By applying different multiple-criteria decision-making (MCDM) methods and using the importance given to these criteria by 14 experts, the normalized subjective weights of the criteria were determined. Analytic hierarchy process (AHP), rank correlation, average rank transformation into weight—linear (ARTIW-L) and non-linear (ARTIW-N), and direct percentage weight (DPW) methods were used in the study. The results show that the RAP recycle rate is close to 100% in countries with a sustainable economic background. In the Baltic countries, it is mostly increased by the adequacy of regulatory documents, the strategy promoting asphalt recycling in the country, and the homogeneity and classifying of RAP. The number and capacity of RAP stocks, the number and productivity of asphalt milling equipment and the wear and tear of the asphalt pavement have the least influence on the increase in RR. The opinions of experts in assessing the significance of all criteria are consistent. The averages of the weights of criteria determined by four MCDM methods (AHP, ARTIW-L, ARTIW-N, DPW) made it possible to obtain more reliable results. These results can be used to make strategic decisions and to create a plan of practical actions to increase the RAP recycling rate in the developing countries.

1D modeling of methanation reactor with circulation (MeRCi) for assessment of reaction characteristics

For a power-to-gas (PtG) system, methanation has attracted attention to synthesize methane from carbon dioxide and hydrogen. There is a problem that heat generated by the reaction causes thermal degradation of the catalyst. Then, we have proposed a methanation reactor with circulation (MeRCi), where the temperature of the catalyst bed is controlled by recycling a part of the product gas. In this study, a one-dimensional model of the MeRCi was developed, and the methanation process was numerically simulated for assessment of reaction characteristics. The catalyst amount, the recycle ratio, and the catalyst bed length were changed. For comparison, the simulation of a straight-tube fixed-bed reactor was also simulated. Based on the gas temperature distribution of the straight-tube reactor, the simulation results show a good agreement with the experimental data, and the validity of our numerical model was confirmed. Even for the higher recycle ratio, the methane conversion rate at the reactor outlet does not change much, showing the high conversion rate within the simulation conditions. The increase of the catalyst packing density as well as the catalyst bed length enlarges the methane conversion rate. By considering the fact that the methane conversion rate is sufficiently high when the catalyst packing density is over 500 kg/m3, the reaction rate must be kept at certain level to keep the high methane conversion rate. As for the catalyst bed length, there is a minimum value at which the methane conversion rate is unexpectedly dropped where unreacted hydrogen and carbon dioxide are retained in the products.

Multiphase Multicomponent Transport Modeling of Cyclic Solvent Injection in Shale Reservoirs

Summary A thorough understanding of fluid transport in ultratight shale reservoirs is crucial for designing and optimizing cyclic solvent injection processes, known as huff ’n’ puff (HnP). We develop a two-phase multicomponent numerical model to investigate hydrocarbon and solvent transport and species mixing during HnP. Unlike the conventional modeling approaches that rely on bulk fluid (advective) transport frameworks, the proposed model considers species transport within nanopores. The chemical potential gradient is considered the driving force for the movement of nonideal fluid mixtures. A binary friction concept is adopted that considers friction between different fluid molecules and between fluid molecules and pore walls. After validating the developed model against analytical solutions and experimental data, the model examines solvent HnP enhanced oil recovery (EOR) mechanisms by considering four-component oil and Eagle Ford crude oil systems. The impacts of injection pressure, primary production duration, soaking time, and solvent type on the oil recovery are examined. The results reveal that the formation of a solvent-oil mixing zone during the huff period and oil swelling and vaporization of oil components during the puff period are key mechanisms for enhancing oil recovery. Furthermore, the incremental recovery factor (RF) increases with injection pressure, even when the injection pressure exceeds the minimum miscibility pressure (MMP), implying that MMP may not play a critical role in the design of HnP in ultratight reservoirs. The results suggest that injecting solvents after a sufficient primary production period is more effective, allowing reservoir pressure depletion. Injecting the solvent without enough primary production may result in significant production of the injected solvent. The results show that the solvent-oil mixing zone expands, and the solvent recycling ratio decreases as soaking time increases. However, short soaking periods with higher HnP cycles are recommended for improving oil recovery at a given time frame. Finally, CO2 HnP outperforms CH4 or N2 HnP due to the higher ability of CO2 to extract a larger amount of intermediate and heavy components into the vapor phase, which has higher transmissibilities as compared with the liquid phase.