An adaptive neuro–fuzzy inference model for prediction of coal char conversion in CO2 gasification

Today, in industry, the gasification of coal as an important energy source is an interesting perspective. In this study, the application of adaptive neuro–fuzzy inference system (ANFIS) technique for estimation of char conversion in CO₂ gasification is investigated. The main variables affecting char conversion are particle size, reaction time, and reaction temperature, which are chosen as input variables of the proposed model. Experimental data which are gathered from the literature are applied for training, testing, and validation of developed ANFIS model. The results reveal the exact estimation of char conversions with the corresponding experimental values with the regression coefficients (R²) greater than 0.99.     

Kinetics of woodchips char gasification with steam and carbon dioxide

Kinetics of woodchips char gasification has been examined. Steam and CO₂ were used as the gasifying agents. Differences and similarities between kinetics of steam gasification and CO₂ gasification have been discussed. Comparison was conducted in terms of gasification duration, evolution of reaction rate with time and/or conversion, and effect of partial pressure on reaction rate. Reactor temperature was maintained at 900 °C. Partial pressure of gasifying agents varied from 1.5 bars to 0.6 bars in intervals of 0.3 bars. Steam and CO₂ flow rates were chosen so that both gasifying agents had equal amount of oxygen content. CO₂ gasification lasted for about 60 min while steam gasification lasted for about 22 min. The average reaction rate for steam gasification was almost twice that of CO₂. Both reaction rate curves showed a peak value at certain degree of conversion. For steam gasification, the reaction rate peak was found to be at a degree of conversion of about 0.3. However, for CO₂ gasification the reaction rate peak was found to be at a conversion degree of about 0.1. Reaction rates have been fitted using the random pore model (RPM). Average structural parameter, ψ for steam gasification and CO₂ gasification was determined to be 9 and 2.1, respectively. Average rate constant at 900 °C was 0.065 min⁻¹ for steam gasification and 0.031 min⁻¹ for CO₂ gasification. Change in partial pressure of gasifying agents did not affect the reaction rate for both steam and CO₂ gasification.     

Process optimization and robustness analysis of municipal solid waste gasification using air‐carbon dioxide mixtures as gasifying agent

In this work, a computational fluid dynamics (CFD) model was coupled with an advanced statistical strategy combining design of experiments (DoE) and the Monte Carlo method to comparatively optimize and test the robustness of two municipal solid waste (MSW) gasification processes one using air‐carbon dioxide (CO₂) mixtures as a gasifying agent and the other using air alone. A 3^k full factorial design of 18 computer simulations was performed using as input factors for air‐CO₂ mixtures the equivalence ratio and CO₂‐to‐MSW ratio, while MSW feeding rate and air flow rate were used for air gasification. The selected responses were CO₂, H₂, CO, and C_nH_m generation, CH₄/H₂ and H₂/CO ratios, carbon conversion, and cold gas efficiency (CGE). Findings were that DoE allowed determining the best‐operating conditions to achieve optimal syngas quality. Monte Carlo identified the best‐operating conditions reaching a more stable high‐quality syngas. Air‐CO₂ mixture gasification showed enhanced responses with major improvements in CO₂ conversion and CGE, both up to a 13% increase. The optimal operating conditions that set the optimized responses showed to not always imply the most stable set of values to operate the system. Finally, this combined optimization process performance revealed to grant professionals the ability to make smarter decisions in an industrial environment.     

Performance analysis of hybrid catalytic conversion of CO2 to DiMethyl ether

The performance of the single-step and sequential-steps catalytic CO₂-hydrogenation to DiMethyl Ether (DME) was systematically analyzed. CuO–ZnO model-catalysts for CO₂-hydrogenation to methanol were synthesized via different methods namely co-precipitation, sequential precipitation and precipitation-impregnation of the precursors. Moreover, co-precipitation and co-impregnation methods were applied to establish bifunctional catalytic structures composed of CuO–ZnO over HZSM-5 for direct CO₂-hydrogenation to DME in a single-step.In addition, the performance of the catalytic bed made of sequential layered-arrangements of the CuO–ZnO and ZSM-5 catalysts as well as random mixture of these catalysts were also analyzed both experimentally as well as through the performed model-based study. It was observed that a faster conversion of the generated methanol to DME, secured by establishing a closer distance between the catalytic materials responsible for CO₂-hydrogenation to methanol and methanol-dehydration to DME, will improve the overall selective CO₂-conversion. This was demonstrated by obtaining the highest combined yield of methanol and DME products at the reactor outlet in those cases. Similarly, a bifunctional catalyst, for instance synthesized by co-impregnation method (made of 1:2 CuO–ZnO:ZSM-5), showed one of the most promising DME selectivity of 65% and DME yield of 12.5% under the highest reaction temperature of 260 °C, lowest tested GHSV of 200 h^?1, and maximum operating pressure 20 bar for the lowest H₂/CO₂ ratio of 3.     

Influence of impregnated copper and zinc on the pyrolysis of rice husk in a micro-fluidized bed reactor: Characterization and kinetics

Catalytic performance of Cu and Zn catalysts was investigated during rice husk (RH) high-temperature pyrolysis under isothermal conditions in a micro-fluidized bed reactor. The results showed that the presence of Cu and Zn evidently influenced the release characteristics and conversion of the gas components. The impregnated Cu promoted the conversion of H₂, CH₄, CO and CO₂, while Zn showed positive catalytic effect on the conversion of H₂, CH₄ and CO₂ and negative effect on the conversion of CO. The X-ray diffraction patterns of the residue chars revealed that metallic copper nanoparticles (Cu⁰) were formed during Cu impregnated biomass pyrolysis. Textural characterization and SEM images showed that the impregnation of Cu and Zn, particularly Zn, promoted the generation of micropores and mesopores, with the pore sizes predominantly at around 1.3 nm and 3.9 nm. Reaction kinetics for generating these gases was studied based on model fitting method, and the most probable reaction mechanism was obtained based on the relative error between experimental and calculated conversion data. The resulting apparent activation energies were 85.08, 12.56, 49.72 and 38.37 kJ/mol for the formation of H₂, CO, CH₄ and CO₂ from pure RH pyrolysis. The presence of Cu decreased the forming activation energies of the four gases, and Zn decrease the forming activation energies of H₂, CH₄ and CO₂ while increased the value for the formation of CO.     

Cooperative effect of Pt and Cu on CeO2 for the CO-PROX reaction under CO2–H2O feed stream

Catalyst improvement for the preferential oxidation of CO (CO-PROX) is essential in developing efficient fuel cell technologies. Here, we investigate the promotion of the Cu/CeO₂ system with Pt, prepared by impregnation and alcohol-reduction methods, in the CO-PROX reaction under ideal and realistic feed compositions. The high Pt dispersion in PtCu/CeO₂ prepared by impregnation led to a CO conversion of 62% and CO₂ selectivity of 83% at 50 °C under a feed stream composed of H₂/CO/O₂, while monometallic Cu/CeO₂ and Pt/CeO₂ showed negligible activity at these conditions. By adding CO₂–H₂O to the feed stream, PtCu/CeO₂ catalysts prepared by both methods presented similar activity. The maximum CO conversion temperature was shifted to 100 °C. Under these conditions, Cu/CeO₂ was inactive, and Pt/CeO₂ showed identical conversion but lower CO₂ selectivity. In-situ XANES revealed that fast oxidation of Cu species at low temperatures is responsible for Cu/CeO₂ deactivation, while preferential adsorption of CO on Pt⁰ sites in PtCu/CeO₂ avoided deactivation. The use of deactivation-resistant Pt sites as complimentary sites for CO activation associated with improved oxygen mobility over Cu–CeO₂ surface proved to be an effective strategy for CO-PROX under H₂O/CO₂ feed stream at low temperatures.     

Steam methane reforming on LaNiO3 perovskite-type oxide for syngas production,activity tests,and kinetic modeling

The kinetic experiments at various working conditions (ie, temperature: 500°C-900°C, pressure: 1-15 bar, H₂O/CH₄ ratio [S/C ratio] of 1-2.5, and gas hourly space velocity of 900-1700 1/h) in the presence of LaNiO₃ perovskite-type oxide were done to consider and assess the outcome of steam methane reforming (SMR) and to build up its kinetic models depending on Langmuir-Hinshelwood method in a fixed bed reactor. The outcomes demonstrate, the methane conversion, H₂ and CO yields and formed CO₂ are affected by the working parameters. Elevated temperature is profitable for more methane conversion, H₂ and CO yield. While high temperature has a negative effect on mol% of CO₂ in outlet products. The high working pressure will not profit SMR respect to CH₄ conversion and products distribution. The efficacy of S/C ratio on the CH₄ conversion and CO yield depended on temperature range. H₂ yield considerably diminishes with an increment in S/C ratio, while the trend was reverse for CO₂ value in outlet gas. The accuracy of suggested kinetic model was evaluated by correlation and statistical tests. Outcomes exhibited that the obtained data were well anticipated through the suggested model, owning to presumption of nonideal gas phase and by utilizing reasonable equation of state of PPR78.     

Forest biomass waste combustion in a pilot-scale bubbling fluidised bed combustor

Combustion experiments of forest biomass waste in a pilot-scale bubbling fluidised bed combustor were performed under the following conditions: i) bed temperature in the range 750-800 °C, ii) excess air in the range 10-100%, and iii) air staging (80% primary air and 20% secondary air). Longitudinal pressure, temperature and gas composition profiles along the reactor were obtained.The combustion progress along the reactor, here defined as the biomass carbon conversion to CO₂, was calculated based on the measured CO₂ concentration at several locations. It was found that 75-80% of the biomass carbon was converted to CO₂ in the region located below the freeboard first centimetres, that is, the region that includes the bed and the splash zone.Based on the CO₂ and NO concentrations in the exit flue gas, it was found that the overall biomass carbon conversion to CO₂ was in the range 97.2-99.3%, indicating high combustion efficiency, whereas the biomass nitrogen conversion to NO was lower than 8%.Concerning the Portuguese regulation about gaseous emissions from industrial biomass combustion, namely, the accomplishment of CO, NO and volatile organic compounds (VOC) (expressed as carbon) emission limits, the set of adequate operating conditions includes bed temperatures in the range 750°C-800 °C, excess air levels in the range 20%-60%, and air staging with secondary air accounting for 20% of total combustion air.     

Development of hybrid models for prediction of gas permeation through FS/POSS/PDMS nanocomposite membranes

The present paper aims to use intelligent methods for prediction of gas permeation in binary-filler nanocomposite membranes containing fumed silica (FS) and octatrimethylsiloxy polyhedral oligomeric silsesquioxane (POSS) nanoparticles incorporated within a polymer matrix of polydimethylsiloxane (PDMS). Two reliable and rigorous hybrid models, i.e., differential evolution-adaptive neuro-fuzzy inference system (DE-ANFIS) and coupled simulated annealing-least square support vector machine (CSA-LSSVM) were developed in order to predict pure gas permeability of including H₂, CH₄, CO_2, and C₃H₈ through the nanocomposite membranes. The coupled simulated annealing (CSA) optimization algorithm was also used for tuning of the model parameters. The impacts of several key parameters such as pressure, FS nanoparticles loading as well as the kinetic diameter of gases on permeation were investigated. The experimental data were randomly divided into two main groups, namely training (70%) and testing (30%) sets. The results of the study suggested that DE-ANFIS model is a more robust and accurate model than the CSA-LSSVM with the R² values of 0.9981 and 0.9689, respectively.     

La1−x(Ce,Sr)xNiO3 perovskite-type oxides as catalyst precursors to syngas production through tri-reforming of methane

LaNiO₃ (LN), La_0.95Ce_0.05NiO₃ (LCN) and La_0.95Sr_0.05NiO₃ (LSN) perovskites were synthesized by the polymeric precursor method to act as catalyst precursors for the Tri-reforming of methane (TRM). The majority phase determined for the LCN perovskite was LaNiO₃, whereas, for LN and LSN, it was La₂NiO₄. It was not possible to determine segregated strontium phases for LSN, but LCN presented a small amount of CeO₂. All the catalysts presented similar methane conversions (around 75%), however differed in CO₂ conversion. LCN was the sample with the highest CO₂ conversion (32%), while the values recorded for the LN and LSN samples were 21.9 and 17.1%, respectively. The partial substitution of La³⁺ by Ce⁴⁺ leads to a higher CO₂ conversion due to the redox properties of cerium, which promotes CO₂ disproportion at the oxygen vacancies generated by cerium, providing more oxygen species that oxidize the coke at the surface. The most active sample for CO₂ conversion (LCN) was also the least selective for hydrogen, generating a synthesis gas with an H₂/CO ratio of 1.2, while the less active LN and LSN samples were more selective for hydrogen (H₂/CO = 1.5–1.6). Thus, it is possible to generate synthesis gas suitable for different applications depending on the metal incorporated into the LaNiO₃ perovskite.     

Carbon stock estimates for forests in the Castilla y León region, Spain. A GIS based method for evaluating spatial distribution of residual biomass for bio-energy

Analysis of aboveground biomass and carbon stocks (as equivalent CO₂) was performed in the Castilla y León region, Spain. Data from the second and third Spanish Forest Inventories (1996 and 2006) were used. Total aboveground biomass was calculated using allometric biomass equations and biomass expansion factors (BEF), the first method giving higher values. Forests of Castilla y León stored 77,051,308 Mg of biomass, with a mean of 8.18 Mg ha⁻¹, in 1996 and 135,531,737 Mg of biomass, with a mean of 14.4 Mg ha⁻¹, in 2006. The total equivalent CO₂ in this region’s forests increased 9,608,824 Mg year⁻¹ between 1996 and 2006. In relation to the Kyoto Protocol, the Castilla y León forests have sequestered 3 million tons of CO₂ per year, which represents 6.4% of the total regional emission of CO₂. A Geographic Information System (GIS) based method was also used to assess the geographic distribution of residual forest biomass for bio-energy in the region. The forest statistics data on area of each species were used. The fraction of vegetation cover, land slope and protected areas were also considered. The residual forest biomass in Castilla y León was 1,464,991 Mg year⁻¹, or 1.90% of the total aboveground biomass in 1996. The residual forest biomass was concentrated in specific zones of the Castilla y León region, suitable for the location of industries that utilize biomass as energy source. The energy potential of the residual forest biomass in the Castilla y León region is 7350 million MJ per year.     

Single‐chamber microbial electrochemical cell for CH4 production from CO2 utilizing a microbial consortium

We report the first single‐chamber microbial electrochemical cell for conversion of CO₂ to CH₄, with an average CH₄ production rate of 0.47 ± 0.05 mL day^?1 cm^?2 at an applied potential of 600 mV, utilizing a methanogenic microbial community collected from the formation water in the San Juan coal basin (Colorado, USA). CH₄ production was only observed at the graphite rod cathode after an electrochemical pre‐treatment that facilitates biofilm formation. The carbon contained within the CH₄ arose predominantly from the CO₂ source, as verified by experiments during which the CO₂ source was repeatedly turned off and on. Modest quantities of acetic acid and ethanol were also produced. DNA extraction and sequencing from the microbial community showed that from the Archaea kingdom, only 2 species survived prolonged exposure to CO₂ and CH₄ production, methanobacterium sp. (81.4%), and methanoculleus sp. (18.6%), while in the bacterial kingdom, anaerobaculum thermoterrnum (67.1%) was the predominant surviving species.     

Methanation of CO2 on bulk Co–Fe catalysts

The efficiency of CO₂ methanation was estimated through gas chromatography in the presence of Co–Fe catalysts. Scanning electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, and Mössbauer spectroscopy were applied for ex-situ analysis of the catalysts after their test in the methanation reaction. Thermal programmed desorption mass spectroscopy experiments were performed to identify gaseous species adsorbed at the catalyst surface. Based on the experimental results, surface reaction model of CO₂ methanation on Co–Fe catalysts was proposed to specify active ensemble of metallic atoms at the catalyst surface, orientation of adsorbed CO₂ molecule on the ensemble and detailed reaction mechanism of CO₂→CH₄ conversion. The reaction step when OH group in the FeOOH complex recombined with the H atom adsorbed at the active ensemble to form H₂O molecule was considered as the rate-limiting step.     

Biomass-derived CO2 rich syngas conversion to higher hydrocarbon via Fischer-Tropsch process over Fe–Co bimetallic catalyst

Biomass-derived syngas (CO₂ + CO + H₂) has emerged as a potential non-fossil fuel source to yield transportation fuel via Fischer Tropsch Synthesis (FTS) reaction. Thus, the present study demonstrates the conversion of CO₂ containing syngas into fuel range hydrocarbon via Fischer Tropsch Synthesis over Fe–Co bimetallic catalyst. The experimental tests were carried out in a fixed bed continuous reactor to investigate the effect of CO₂ on CO/CO₂ conversion. Accordingly, obtained data were validated by FTS kinetic model for a plug flow reactor. It was found that the unique combination of Fe and Co bimetallic catalyst facilitates both FTS and water gas shift (WGS) reaction simultaneously that helps to convert CO₂ along with CO. It was also observed that the presence of iron in the catalyst helps in conversion of CO₂ into hydrocarbons, only when a particular concentration of CO₂ in syngas is reached, i.e., critical ratio R_C (CO₂/CO + CO₂) due to the occurrence of reverse water gas reaction (RWGS) which varies with the temperature and the feed gas composition (H₂/CO/CO₂ molar ratio). At 240 °C and hydrogen deficient condition, the critical ratio was measured to be 0.74 whereas for hydrogen balanced condition, it was measured 0.6. The kinetic model developed in the present study predicted trends for % CO conversion, % carbon conversion, and % CO₂ conversion which is applicable for a wide range of critical ratio R_C (CO₂/(CO + CO₂) = 0 to 1). The model also predicted that a positive conversion of CO₂ could be achieved at lower CO₂ concentration by increasing the reaction temperature. At 260 °C and 280 °C, the value of Rc were 0.31 and 0.18 were measured.     

Experiments on supercritical CO2 adsorption in briquettes

CO₂ storage in deep coal seams is one of the safe methods to mitigate the effects of greenhouse. In the present work, experiments of supercritical CO₂ adsorption were performed at 35℃, 45℃, and 55℃ on briquettes, the porosity of which can be controlled. Curves of CO₂ adsorption increased at three rates at pressures ranging from 8 to 13 MPa, and the adsorption decreased linearly with the increase of temperatures from 35℃ to 55℃. The adsorption of supercritical CO₂ was fitted best with Brunauer, Emmett, and Teller model compared with the Langmuir model and Dubinin? Radushkevich model.     

Partial oxidation of ethanol in a membrane reactor for high purity hydrogen production

Partial oxidation of ethanol was performed in a dense Pd–Ag membrane reactor over Rh/Al₂O₃ catalyst in order to produce a pure or, at least, CO_x-free hydrogen stream for supplying a PEM fuel cell. The membrane reactor performances have been evaluated in terms of ethanol conversion, hydrogen yield, CO_x-free hydrogen recovery and gas selectivity working at 450 °C, GHSV ∼ 1300 h⁻¹, O₂:C₂H₅OH feed molar ratio varying between 0.33:1 and 0.62:1 and in a reaction pressure range from 1.0 to 3.0 bar. As a result, complete ethanol conversion was achieved in all the experimental tests. A small amount of C₂H₄ and C₂H₄O formation was observed during reaction. At low pressure and feed molar ratio, H₂ and CO are mainly produced, while at stronger operating conditions CH₄, CO₂ and H₂O are prevalent compounds. However, in all the experimental tests no carbon formation was detected. As best results of this work, complete ethanol conversion and more than 40.0% CO_x-free hydrogen recovery were achieved.     

Study on the limestone sulfation behavior under oxy-fuel circulating fluidized bed combustion condition

In order to investigate the behavior of limestone sulfation under oxy-fuel circulating fluidized bed (CFB) combustion condition, experiments were conducted in a 50 kW oxy-fuel CFB system under the O₂/CO₂ and air combustion conditions. A small cage, containing limestone particles, was dipped into the dense zone of the CFB combustor during the experiments. The calcination of limestone, pore structure of the product layer, and calcium conversion were studied. It was found that the increasing of temperature would promote the calcination of limestone and the high concentration of CO₂ would inhibit calcination of limestone. The formation process of the product layer was completely different between the direct and indirect sulfation, while it was almost the same during the indirect sulfation under the oxy-fuel and air combustion. However, both the temperature and gas compositions played important roles in determining the pore structures of the product layer during the limestone indirect sulfation process. Under the O₂/CO₂ combustion condition, the calcium conversion of indirect sulfation was always higher than that of direct sulfation. The highest final calcium conversion after 60 min was found at 900 °C under the O₂/CO₂ combustion condition.     

Utilization of CO2 for syngas production by CH4 partial oxidation using a catalytic membrane reactor

In this research, a synthetic flue gas mixture with added methane was used as the feed gas in the process of dry reforming with partial oxidation of methane using a laboratory scale catalytic membrane reactor to produce hydrogen and carbon monoxide that can present the starting point for methanol or ammonia synthesis and Fischer-Tropsch reactions. 0.5% wt% Rh catalyst was deposited on a γ-alumina support using rhodium (III) chloride precursor and incorporated into a shell and tube membrane reactor to measure the yield of synthesis gas (CO and H₂) and conversion of CH₄, O₂ and CO₂ respectively. These measurements were used to determine the reaction order and rate of CO₂. The conversion of CO₂ and CH₄ were determined at different gas hourly space velocities. The reaction order was determined to be a first-order with respect to CO₂. The rate of reaction for CO₂ was found to follow an Arrhenius equation having an activation energy of 49.88 × 10⁻¹ kJ mol⁻¹. Experiments were conducted at 2.5, 5 and 8 ml h⁻¹ g⁻¹ gas hourly space velocities and it was observed that increasing the hourly gas velocities resulted in a higher CO₂ and CH₄ conversions while O₂ conversion remained fairly constant. CO₂ had a high conversion rate of 96% at 8 ml h⁻¹ g⁻¹. The synthesized catalytic membrane was characterized by Scanning Electron Microscopy (SEM) and the Energy Dispersive X-ray Analysis (EDXA) respectively. The micrographs showed the Rh particles deposited on the alumina support. Single gas permeation of CH₄, CO₂ and H₂ through the alumina support showed that the permeance of H₂ increased as the pressure was increased to 1 × 10⁵ Pa. The order of gas permeance was H₂ (2.00 g/mol) > CH₄ (16.04 g/mol) > N₂ (28.01 g/mol) > O₂ (32 g/mol) > CO₂ (44.00 g/mol) which is indicative of Knudsen flow mechanism. The novelty of the work lies in the combination of exothermic partial oxidation and endothermic CO₂ and steam reforming in a single step in the membrane reactor to achieve near thermoneutrality while simultaneously consuming almost all the greenhouse gases in the feed gas stream.