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Modelling catalytic fixed bed reactors with a small tube-to-particle diameter ratio requires a detailed description of the interactions between fluid flow, intra-particle transport, and the chemical reaction( s) within the catalyst. Particle-resolved computational fluid dynamics (PRCFD) simulations are the most promising approach to predict the behaviour of these reactors accurately, since they take into account the local packed bed structure explicitly. In this work, a conjugated heat and mass transfer model for use in PRCFD simulations is presented in order to couple the fluid flow through the fixed bed with transport and reaction in the porous catalyst, while guaranteeing the no-slip boundary condition at the fluid-solid interface. For this purpose, the solutions of the solid and fluid domain are computed separately and are coupled by calculation and updating the boundary condition at the particle surface. Owing to the consideration of secondary gradients, the developed transfer model is also valid for unstructured calculation meshes containing non-orthogonal cells at the fluid-solid interface. Such meshes are often used to resolve complex geometries, such as a packed bed, in a computationally efficient manner. The coupling approach is validated using cases for which an analytical solution or literature correlations derived from experimental data are available. The simulation results of a short catalytic packed bed with rings catalysing the partial oxidation of n-butane to maleic anhydride exemplify the potential of PRCFD involving reactions to analyse the catalyst performance in great detail. [ABSTRACT FROM AUTHOR]

This study examined the desulfurization capacity of a high specific surface area activated carbon (AC) and its modifications for real diesel fuel of different sulfur concentrations. Adsorbent's evaluation strategy included desulfurization experiments under batch and continuous conditions. Batch experiments were conducted by a homogeneous stirring of adsorbent and diesel fuel, while for the continuous tests, a fixed bed reactor was used to generate breakthrough desulfurization curves. In the fixed bed reactor's tests, the sulfur removal – considering an initial concentration of about 6 parts per million weight (ppmw) – was substantial for the first 30 ml fuel per gram of adsorbent. For this specific quantity, the total sulfur content of the cumulatively processed fuel was less than 2 ppmw. The batch experimental results are elaborated using a mechanistic kinetic model for batch adsorption considering the total sulfur mass balance. Mass transfer coefficients are derived this way for all the conditions and adsorbents tested. The adsorption equilibrium data from batch experiments are utilized to model the fixed bed experimental results. In this way, mass transfer coefficients for the fixed bed are derived. In any case, the modeling results indicate that sulfur is not the only adsorbate of the process, but other adsorbates act competitively to sulfur, thereby complicating the process. [ABSTRACT FROM AUTHOR]

Coal is the most valuable gasification resource due to its abundance and low cost for commercial applications. But utilization of low-rank Indian coals for gasification is challenging due to difficulty in washing. For utilizing low-grade high ash raw coal, blending is one of the effective methods to control the gasification performances. So, the present study explores the gasification of such a low-rank raw coal blend and compares the results with washed coal blend. The blending effects on raw gas yield (kg/kg of coal) and heating value (Kcal/Nm3) were investigated for coal blends-WH (washed coal with high-rank coal) and RH (raw coal with high-rank coal). In WH, raw gas yield is 1.210 to 1.225 (kg/kg of coal), whereas, in RH is 1.189 to 1.213 (kg/kg of coal), though the fixed carbon content of WH (40.75–41.74%) is lower than RH (44.73–45.25%). In washed coal, raw gas yield is minimum (0.75 kg/kg of coal). The heating value is lower in WH (2730–2871 Kcal/Nm3) than in RH (2884–2978 Kcal/Nm3). Statistical correlation is developed between gaseous components of raw gas and heating value; H2/CO ratio is the most significant parameter. RH gasification is economically viable than WH. [ABSTRACT FROM AUTHOR]

Transformation of methyl lactate to acrylic acid was investigated over Ca3(PO4)2, Ca2(P2O7) and their mixture in the temperature range of 250-425 °C. The initial concentration of methyl lactate in water was varied from 2 wt% to neat methyl lactate. The results showed that these phosphate catalysts did not contain any measurable amounts of either acid sites or basic sites. The best catalyst was Ca3(PO4)2 giving 62% selectivity to acrylic acid at 75% conversion at 400 °C using GHSV of 95280 h−1 and 2 wt% methyl lactate in the initial feed. This catalyst exhibited larger surface area in comparison to Ca2(P2O7). Elemental analysis revealed that some Ca leaching occurred during reaction, while in case of Ca2(P2O7) the calcium leaching was 3.4 fold higher than observed for Ca3(PO4)2. Long-term results over Ca3(PO4)2 showed that extensive catalyst deactivation occurred during the first 11 h time-on-stream, after which the activity dropped only slightly. In addition to kinetic studies with different parameters, also, kinetic modeling was performed and the activation energies for formation of different products were determined over different catalysts. [ABSTRACT FROM AUTHOR]

Tetrahydrofuran (THF) manufacture is explored in this work using the route from 1, 4 butanediol (BD) in the fixed bed chromatographic reactor (FBCR). Major problem faced in this manufacture is the existence of THF-water minimum boiling azeotrope. Use of FBCR helps to circumvent the azeotrope, thereby offering a simplified process. Binary adsorption experiments, reaction in the FBCR environment and regeneration experiments are presented. Use of molecular sieves and rectification helps to obtain almost pure THF as the product and BD for recycle. A complete process to manufacture THF from BD is thus developed. [ABSTRACT FROM AUTHOR]

The utilization of corncob residues in pyrolysis offers a promising source for both renewable energy and chemical production. In this study, corncob was decomposed in the presence of aluminum oxide nanoparticles (Al2O3 NPs) catalyst using a fixed bed reactor under an inert atmosphere. Pyrolysis of corncob was carried out in the presence of Al2O3 NPs at different heating rates i.e. 5, 10, 15 and 20°C/min in an oxygen-free atmosphere using TGA technique. Kinetic and thermodynamic studies were performed using the best fit models including Ozawa–Flynn–Wall (OFW), Kissinger–Akahira– Sunose (KAS) and Friedman methods. The average activation energies for Friedman, OFW, KAS were 177.3, 162.9 and 167.8 kJ/mol, respectively for pure corncob and 111.0, 102.5 and 118.06 kJ/mol, respectively for Al2O3- corncob sample. Activation energy was found to be the lowest in the OFW model. Results showed that the presence of Al2O3 NPs catalyst not only reduced pyrolysis temperature and activation energy but also improved the quality of bio-oil. [ABSTRACT FROM AUTHOR]

Pyrolysis of Prunus dulcis was performed in the presence off our catalysts (ZnCl2, Fe2O3, Alumina, and ZSM-5) using a fixed bed tubular reactor. The factors affecting the product yield were premeditated. Prunus dulcisshowed a high heating value of 19.72 MJ/Kg which makes it very efficient for biofuel usage. Biochar obtained showed high carbon content and large heating values. Different pyrolytic product yields were obtained with different catalysts. Among all the catalysts, alumina and ZSM-5 showed a maximum yield of liquid product. FT-IR, GC-MS, and elemental analysis were performed to determine the product yield and bio oil compositions. [ABSTRACT FROM AUTHOR]

The present work reports the techno-economic analysis of hydrogen generation using Dimethyl Ether Steam Reforming (DMESR) and Methanol Steam Reforming (MSR) processes. For both processes, steady-state simulation models were developed using Aspen Plus. The two processes are analysed by taking into account the kinetics of the Cu/ZnO/Al2O3 catalyst for MSR and Cu–Ni/γ-Al2O3 catalyst for DMESR in an RPLUG model simulated as a Fixed Bed Reactor (FBR) at a temperature of 250°C and pressure 20 bar. The work dives into heat integration opportunities to reduce the operating cost of the two processes. The article also provides a gist of the approximate cost to produce hydrogen by the two processes by taking into consideration the cost of equipment and utilities involved. It is found that the TAC for DMESR is marginally higher than MSR mainly because of the higher cost of utilities involved. It was also found that NPV for MSR is comparatively higher than DMESR. The article also provides TAC for Selective Methanation of Carbon Monoxide (SMC) for both processes with the purpose of minimising CO. [ABSTRACT FROM AUTHOR]

The phenomenon of the secondary reactions of volatiles prevails during the pyrolysis process of scrap tires, but less is known about the influence of volatiles' residence time and temperature on the pyrolytic oil compositions. Experiments on the secondary reactions caused by residence time and temperature of volatiles were carried out on a lab-scale fixed bed reactor. The regularity of the secondary reactions was presented in detail according to the distribution of liquid and gaseous pyrolytic products. Considering the inadequacy of lab-to-industry research, experiments were further carried out on a pilot-scale auger reactor. The results of the pilot-scale system were corresponding well to the regularity obtained in lab-scale experiment, demonstrating the universality of the regularity in this work. At in situ pyrolysis condition without any secondary reactions, limonene content reached up to 46.24% while a high yield of BTEX (50.55%) was obtained at 700℃/60 s. A remarkable increase of methane and ethane was observed at 700℃/60 s, reaching 0.058 and 0.040 g·(g scrap tire)−1, respectively. This paper provided a novel strategy to selectively produce target products in a simple and economical method. The results were of great significance for guiding the optimisation of pyrolysis parameters in industrial equipment to obtain desired valuable products. [ABSTRACT FROM AUTHOR]

Carbon nanofibers are promising green materials for sustainable technology within a wide range of applications including environment, energy, health and high-technology. Accordingly, drug adsorption is an important subject in connection with its environmental and pharmaceutical applications. This study aims to investigate the adsorption performance of carbon nanofibers in batch and fixed bed column processes. Carbon nanofibers were used as adsorbent to remove triflupromazine hdyrochloride from aqueous solutions. Adsorption kinetics were studied using Lagergren first order and Pseudo second order models. Intraparticle diffusion graph was plotted using kinetic data and showed that intraparticle diffusion is the single step controlling the adsorption rate. Experimental equilibrium data was modeled by using Langmuir and Freundlich equations and has a better fit to the Langmuir model. Triflupromazine adsorption on carbon nanofibers was found to be H-type according to Giles classification. The effect of temperature and the effect of pH on adsorption were studied to determine optimum adsorption conditions. Adsorption capacity of carbon nanofibers was decreased with increasing temperature due to the exothermic and physical nature of the process. Thermodynamic parameters confirmed the exothermic nature of the adsorption. Results showed the effective adsorption of drug molecules by carbon nanofibers. Maximum adsorption capacity was calculated as 165.41 mg/g at pH 9 using Langmuir equation. Modeling of the fixed bed column data was done by using Thomas model and Yoon–Nelson model. Results showed the important effect of the operating conditions on the removal performance of carbon nanofibers. Removal capacity was increased with an increase in the flow rate and the increase in the fixed bed length. [ABSTRACT FROM AUTHOR]

In the current economic growth, the development of energy from sustainable resources plays a vital role in saving of fossil energy like hydrocarbons, methane extraction, crude oil and other natural resources. In this present work, a new method has been developed to prepare liquified fuels from waste LDPE with improved yield. Single screw conveying machine is attached with pyrolysis setup was designed and fabricated to mix plastic wastes with nano zeolite particle catalyst using various proportions such as 8, 10,12 and 14 wt.%. The distribution of nano zeolite particle with waste plastics was found to be uniform, which increases the heat transfer rate, pyrolysis temperature and lower the reaction rate with an improved pyrolytic oil yield of 7% compared with normal pyrolysis setup. The FT-IR results of prepared oil show clear peaks of carbon and oxidising agent chemical bonds in all liquid oil samples and also, alkanes present in the oil are confirmed with the GC-MS results. The liquid oil has a higher heating value range of 9830–9860 kCal/kg, which is close to conventional diesel heating value. [ABSTRACT FROM AUTHOR]

Heavy metals resistant and polyaromatic hydrocarbon (PAH)-degrading bacteria isolated from Marchica lagoon. Six isolates, Pseudomonas putida, Orchobactrum antropi, Staphylococus epidermidis, Brevundimonas diminuta, Serratia ficaria and Bacillus anthracis were characterized on the basis of biochemical and 16S rDNA. The strains that showed high resistance to heavy metals were also studied for their antibiotics resistance and growth kinetics. The minimal inhibitory concentrations (MIC) of metals at variant concentrations (10-38 mM) were determined in liquid and solid medium. Strains were showed an extreme resistance against metals with the MIC values of Cu (9 mM), Cd (6.25 mM), Cr (2.5 mM), Ag (0,625), and Hg (0,156). Furthermore, growth rates were decreased in the presence of metals (compared to the control). The anthracene elimination from synthetic wastewater was determined in a submerged aerobic fixed-film reactor. Optimal conditions for bacterium growth and biodegradation of anthracene are determined as: temperature of 37 °C, pH 7, and initial anthracene concentration of 20 mg/l. It emerged that at anthracene concentrations 5-40 mg/l, COD removal efficiency were 84.62%; 90.62%; 91.36% and 71.4% respectively. [ABSTRACT FROM AUTHOR]

This work focuses on the simulation of a fixed bed drying process for wheat grains. A rigorous model based on Fick's law was developed and validated against experimental results. The impact on outputs and computational burden was studied after imposing different simplifying hypotheses. Neglecting internal temperature gradients, the external mass transfer resistance, and the difference between grain and air temperatures saved 18% of execution time with respect to the more rigorous model. These simplifications are adequate for some practical applications. Nevertheless, simulations with a simpler model that only used an average moisture content for the grains yielded worse predicted drying rates. [ABSTRACT FROM AUTHOR]

Rates of mass and heat transfer (by analogy) at the surface of a helical coil imbedded in a fixed bed of inert cylindrical packing were measured under upward two-phase (gas-liquid) flow by the electrochemical technique. The effects of geometrical and hydrodynamic parameters were considered. The performance of cylindrical packing was compared with that of Raschig rings and spheres. The analogy between heat and mass transfer was discussed and the importance of the present study for the design and operation of heterogeneous reactors that need rapid cooling in case of highly exothermic reactions was highlighted. [ABSTRACT FROM AUTHOR]

The current study had focused on continuous production of biodiesel from Vernonia cinerea seeds using a fixed bed reactor loaded with green catalyst. The free fatty acid (FFA) of the underexploited Vernonia cinerea seeds is very high. Two-phase solvent extraction (TPSE) methodology was implied for the extraction of oil to reduce the FFA and eliminate two-step transesterification process. At the experimental conditions of 60:40 n-hexane-to-methanol ratio, 65ºC temperature, and 4 hours of extraction time, 40% of Vernonia cinerea oil was obtained with FFA of 1.8%. The FFA of the oil got reduced by 78.5% by the implication of TPSE method. The characterization of the bio-oil was performed using FT-IR and GC-MS analysis. Pyrgostylus striatulus shells were calcined and supported on activated carbon. This was utilized as the green catalyst for biodiesel production. A complete analysis of the shells before and after calcination and after loading on activated carbon was studied using Hammett indicator, XRD, SEM, EDX, and BET analyses. Fixed bed reactor loaded with the calcined catalyst was utilized for the conversion of Vernonia cinerea oil and methanol into biodiesel. A maximum conversion of 96% was observed at the process conditions of 65ºC, 25:1 methanol-to-oil-molar ratio, 350-mm catalyst bed height and residence time of 6 hours. FT-IR analysis and 1HNMR analysis were performed to check the conversion of oil to biodiesel. The physio-chemical properties of methyl esters from Vernonia cinerea oil were analyzed. Findings of this research support that the produced biodiesel meets the ASTM standards indicating the fuel to be commercialized. [ABSTRACT FROM AUTHOR]

Considering the physicochemical properties of residual rice husk, which is suitable for gasification and its vast availability in Colombia, an experimental analysis of the energy potential of rice husk for small-scale fixed bed gasification processes was conducted, thereby facilitating the implementation of the circular economy model in compact rice mills. Because of the impact of air flow on the process equivalence ratio (ER), gas calorific value, and gasifier thermal power, the optimum air superficial velocity (VSair) considering the end use of the producer gas for both internal combustion engines (ICEs) and atmospheric burners (AB), is examined. According to the results, biomass consumption rate, cold gas efficiency (CGE), and process temperature increased in the ranges 1–1.55 kg/h and 45–65% and 825–950°C, respectively, when ER goes from 0.23 to 0.3. To obtain the highest process performance, the process should be conducted at a VSair ~ 5.1 m/min and ER ~ 0.3. Under these parameters, a gas with thermal power and lower heating value (LHV) of 3.6 kWth and 4.78 MJ/Nm3, respectively, was obtained. These properties allow for an engine fuel quality (EFQ) of 1817 kJ/kg. For comparison, an ICE designed to be fueled with natural gas (EFQ of natural gas approx. 2650 kJ/kg) would have a ~ 30% drop in its maximum power when fed with the producer gas obtained through rice husk gasification. [ABSTRACT FROM AUTHOR]

Fixed bed reactor as a commonly used catalytic device and adsorption equipment in the chemical industry has attracted widespread attention. This paper presents a simple and feasible method which combines CFD with DEM to simulate the fixed bed reactor with the diameter ratio ranges in 2–8. The variation of the void ratio with different diameter ratios obtained from the model used in this paper was in comparison with the theoretical results derived by de Klerk and Dixon. The maximum error between the simulated results and the theoretical results was less than 10%, indicating that the model used in this study had a high degree of confidence. On this basis, the effects of the diameter ratio on the distribution of velocity and pressure were investigated. The distribution of velocity and pressure at different diameter ratios illustrated that when the diameter ratio was 5, the velocity distribution was uniform, and the pressure drop was relatively insignificant, which was beneficial to the reaction process. The model used in this paper could provide a new and concise method for the design and verification of fixed bed reactor. [ABSTRACT FROM AUTHOR]

Thermogravimetric analysis (TGA) and differential thermal gravimetric (DTG) were used to study the efficiency of slow pyrolysis of chicken skin waste (CSW) through determining the apparent activation energy. CSW was heated from 50°C to 900°C at 5°C/min, 10°C/min, 15°C/min, and 20°C/min. The CSW was further investigated in pyrolysis using a fixed bed reactor where the maximum production of bio-oil was achieved at 550°C. The crude bio-oil products demonstrated different classes of organic and complex mixture of hydrocarbons compound. The proposed decomposition pathway suggested that most CSW was cracked around 340–440°C even at a low heating rate to produce mostly long-chain hydrocarbons. [ABSTRACT FROM AUTHOR]

The analysis of this study focuses on the production of H2 based on the methanol steam reforming in an isothermal, steady state and one-dimensional model. Two reactors namely, fixed bed reactor (FBR) and H2 selective membrane reactor (MR) are being evaluated by simulation. FBR consists of a cylindrical column packed with Cu/ZnO/Al2O3 catalyst particle bed, whereas MR is a cylindrical reactor with one reaction tube consisting of an inert nature membrane (Pd/Ag) are considered. At the complete conversion of methanol, the yield of H2 is significantly affected by H2 selective membrane, temperature and pressure conditions. H2 yield of 2.72 has been achieved after the almost complete conversion of methanol at 593 K temperature, the pressure of 1 atm and steam/methanol ratio of 1.5 in FBR. H2 yield, molar flow rate of CO2 has also been increased, and CO concentration has been reduced by using MR. Similarly, H2 yield has increased to 2.76 with decreasing CO concentration using MR at the same operating conditions with an increase in pressure in the reaction zone to 2 atm. Hence, the results indicate that the H2 yield with a small amount of CO has been achieved in MR at optimum operating conditions. Abbreviations: FBR: Fixed Bed Reactor; MR: Membrane Reactor; SRM: Methanol Steam Reforming; MD: Methanol Decomposition; WGS: Water Gas Shift; PROX: Preferential Oxidation; S/M: Steam to Methanol Molar Ratio in Feed; O/C: Oxygen to Carbon Ratio; L/D: Length to Diameter Ratio; POX: Partial Oxidation; ATR: Auto-Thermal Reforming; SR: Sweep Ratio (sweep gas/methanol molar ratio) [ABSTRACT FROM AUTHOR]

Solid soda lime sorbents are promising materials for CO2 removal in closed-circuit breathing systems. In this study, the soda lime sorbent Drägersorb 800+ has been tested in a fixed bed reactor. The changes in composition, structure, and texture of the sorbent occurring in the process of CO2 sorption have been studied using thermogravimetry, X-ray diffraction analysis, nitrogen adsorption (BET), mercury porosimetry and scanning electron microscopy methods. A non-stationary model has been developed for simulating CO2 chemisorption in the fixed bed. The results of the simulation have been found to be in a good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

The present study evaluates the feasibility of using natural Lagerstroemia speciosa bark (NLSB) and chemically modified Lagerstroemia speciosa bark (CLSB) in removing Cr(VI) from aqueous solution in fixed bed column process. The effect of influent flow rate, bed depth and inlet Cr(VI) ion concentration on the Cr(VI) removal capacity of NLSB and CLSB was investigated. The column exhaustion time increased with increase in bed depth and reverse trend was obtained with increase in flow rate and influent Cr(VI) ion concentration. The Bohart–Adams, Thomas and Yoon–Nelson dynamic models were applied at various studied experimental conditions to predict the breakthrough curve behavior and to determine the characteristics fixed bed column parameters that are very crucial in scale up of the column process for its industrial scale application. Both Thomas and Yoon–Nelson models showed very good agreement with the column data and explained the mechanism of Cr(VI) adsorption by NLSB and CLSB in column process. The high Cr(VI) adsorption capacity and regeneration efficiency of NLSB and CLSB in column suggest its applicability in removal of Cr(VI) present in industrial effluents. [ABSTRACT FROM AUTHOR]

A chemical-looping combustion process based on a single fixed bed reactor for utilizing steelmaking converter off-gas, which is intermittently discharged and has a low and greatly fluctuating heat value, has been presented. Based on this process, the redox performances of CuO/Al2O3 synthesized by an incipient wetness impregnation method were investigated. The results showed that CuO/Al2O3 exhibited high reactivity, and for a complete CO conversion through the discharging period, the gas hourly space velocity (GHSV) of the reduction reaction could be raised up to 8000 h−1 by elevating the reaction temperature to 350 ℃. Furthermore, carbon deposition from CO and formation of CuAl2O4 did not occur because of the low operating temperature. The proposed process based on CuO/Al2O3 showed a good applicability, with which the safe and clean utilization for the converter off-gas could be realized. [ABSTRACT FROM AUTHOR]

In the present study, the treatability of olive mill wastewater (OMWW) using an anaerobic fixed bed biofilm reactor packed with granular activated carbon (GAC) and inoculated with non-acclimated biomass was performed in a semi-continuous mode under mesophilic conditions. Three organic loading rates (OLR) varied from 0.94 to 2.81 g COD/(L d) were applied. The results of batch adsorption tests on GAC and the experimental data from PBBR-GAC operation were used to set up a COD mass balance in order to investigate the effect of adsorption on the COD removal during the three anaerobic treatment steps. Despite the slight accumulation of volatile fatty acids (VFAs) during the second and the third steps, between 735 and 1135 mg COD/L (as acetic acid), a stable environment for methanogens was maintained for a period of 104 days. During the three steps, degradation levels were up to 80% of COD and 85% of phenolic compounds. An averaged specific biogas production of 1.77 LN/d and a methane (CH4) concentration of about 60%, corresponding to a CH4 yield of 0.31 L CH4produced/g CODdepleted, were reached at an OLR of 2.81 g COD/(L d). The results show that the COD mass balance was not closed during the first two steps, while in the third step, it could be around 96%. This finding suggests that the adsorption of organic substances on activated carbon occur just during the two first steps, while at 2.81 g COD/(L d) OLR no adsorption is occurring and the introduced COD becomes completely available for CH4 production. [ABSTRACT FROM AUTHOR]

In this study, an adsorption technique was explored for the removal of toluene present in the gas phase by taking granular activated carbon as an adsorbent in a fixed bed adsorption column. Breakthrough curves were experimentally found out at varying bed height (0.015–0.025 m) and inlet concentration (7000–11500 ppm). Modelling and simulation studies were subsequently carried out to enable the comparison between predicted and experimental breakthrough curves. Here orthogonal collocation technique was employed to solve the model equations by discretising non-linear coupled partial differential equations into set of ordinary differential equations which were solved by using ODE15s solver of Matlab. The discretisation procedure has been described in detail. Finally, the flow rate was found out to be the most sensitive parameter after carrying out sensitivity analysis. [ABSTRACT FROM AUTHOR]

The purpose of the present work is to treat saline Tuna fish wastewater, with the salt concentration of 43 g L−1 and total organic carbon (TOC) of 8.3 g L−1, using an anaerobic fixed bed reactor involving salt-tolerant bacteria from the natural hypersaline environment during 150 days. The highest volatile solids (VS) removal efficiency of 84.1% was recorded for the organic loading rate (OLR) of 1.04 g TOC L−1.d−1 and the lowest salinity of 14.6 g NaCl L−1. In addition, the maximum biogas production of 0.8 L−1.d−1 for a working volume of 4 L and an organic loading rate of 2.07 g TOC L−1.d−1 correlated with the decrease of Volatile fatty acids (VFA) content. The Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis (PCR-DGGE) and the phylogenetic analysis of the bacterial community showed the action of hydrolytic, acidogenic, halotolerant sulfate-reducing and halophilic fermentative bacterium during the processing time. A stable archaeal and methanogenic community's diversity including hydrogenotrophic methanogens was demonstrated with Quantitative-PCR (Q-PCR). The highest bacterial population abundance was detected for 1.45 g TOC L−1.d−1 and the important methanogenic community abundance for 2.07 g TOC L−1.d−1 may be related to the highest biogas production in this charge for an effluent salinity of 27.7 g NaCl L−1. [ABSTRACT FROM AUTHOR]

Low-temperature co-pyrolysis of lignite coal and biomass blends was studied at different ratios using a fixed bed reactor and a thermogravimetric analyzer (TGA). The results show that the addition of biomass during low-temperature pyrolysis was found to promote the collapse of macro-pores, leading to the formation of more fine meso-pores in chars. As a stabilizer the hydrogen atoms produced from the pyrolysis of biomass samples reacted with the radical fragments which inhibited the polymerization, and resulted in an increase in the tar and gases yields. The effect of hydrogen from co-pyrolysis on the chemical structure of char was obvious. The combustion reactivity of co-pyrolysis chars was lower than that of lignite char, indicating that the content of volatile is more important than the pore structure and oxygen-containing groups to combustion reactivity for biomass/lignite char obtained from low-temperature co-pyrolysis. [ABSTRACT FROM AUTHOR]

Recently, the advanced oxidation processes have been used to treat wastewater containing various dye pollutants via various methods of purification. In this work, the removal of the Carmoisine dye from contaminated waters by a photocatalytic method in a recirculating thin-film fixed bed reactor (TFFBR) was investigated and was compared with photolysis. By the surface response method via Minitab software, the experiments were designed in such a way that the effects of different parameters on the process were studied. The effect of various parameters, for instance, pH of solution, reaction time, initial dye concentration, flow rate, hydrogen peroxide concentration on the dye removal efficiency has been investigated. By the screening and optimization stages in the response surface method, the optimal conditions for performing the process were as follows: 45 min of time, pH 2, 13.33 mM of H2O2 concentration, the flow rate of 0.25 Lmin−1, and 10 mg/L of dye concentration. The proficiency of removing color by advanced oxidation is more than 97% under optimum conditions. [ABSTRACT FROM AUTHOR]

The present work focused on the application of response surface methodology (RSM), Box–Behnken design (BBD), for prediction of products distribution of Fischer-Tropsch synthesis (FTS) using a Co/ZrO2 catalyst in a fixed bed reactor. The effect of four independent operating variables such as reaction temperature, pressure, space velocity and H2/CO ratio on the responses (CH4 and C5+ selectivities) in FTS were investigated. The analysis of variance (ANOVA) results showed that the suggested quadratic models could well predict CH4 and C5+selectivities. The optimized operating condition was temperature 200.73 °C, pressure 20 bar, space velocity 1662.58 h−1 and H2/CO ratio 1.93. [ABSTRACT FROM AUTHOR]

This paper investigated the thermal fragmentation of three lignite samples with temperature of 100 °C–200 °C and drying time of 0–90 min using the fixed bed reactor. The effects of a variety of factors such as temperature and drying time on fragmentation ratio were studied. The results showed that fragmentation ratio was positively related to temperature and drying time, and the degree of fragmentation was different for different lignite samples. Additionally, it was demonstrated that the point load strength remarkably decreased with the increase of temperature and drying time. The fragmentation ratio as a function of point load strength represented that lignite with higher strength had a lower fragmentation ratio, and the possibility of secondary fragmentation of dried lignite decreased with the increase of point load strength. Fragmentation ratio decreased with the increase of lignite density. The mineral matters of lignite significantly had influence on fragmentation. The mass inhomogeneity degree was given to depict the mineral element compositions. A fragmentation prediction equation was established based on mass inhomogeneity degree, which was associated with moisture content and ash content. [ABSTRACT FROM AUTHOR]

CO2 adsorption on solid sorbents under dynamic conditions is driven by a number of factors, among them textural features (pore volumes, pore size distribution, surface area...), surface chemistry (polarity, presence of active site and/or unsaturated coordinative sites...) and the overall active sites accessibility. Depending on the strength of the interaction with CO2 (chemisorption or physisorption), solid sorbents are broadly divided in two groups, although a sharp distinction between the two phenomena (in many cases concurrent) is obviously not possible. CO2 adsorption data acquired in a lab-scale fixed bed reactor under dynamic conditions and in typical conditions of post-combustion CO2 capture on materials produced from the work-up of carbonized rice husk were here reported and compared with pertinent literature on commercial and ad-hoc synthetized sorbents. Some attempts to correlate adsorption capacities and materials' textural properties or other relevant adsorption parameters have been also proposed. [ABSTRACT FROM AUTHOR]

The use of biomass has been promoted to meet the need for sustainable production of ethylene, which is the most used petroleum-derived in the polymer industry. Ethanol is an alternative feedstock to yield the so-called bio-ethylene through catalytic dehydration in fixed-bed reactors. As the reaction system is strongly endothermic, it is very important to know accurately the reactor temperature to assure the process performance. However, in the industrial context, the process measurements are often uncertain and not all variables can be directly measured online. In this regard, this paper analyses the mathematical modelling and numerical simulation of the ethanol catalytic dehydration and contributes with a monitoring scheme using the Bayesian method known as particle filter. Numerical simulations helped understanding the process behaviour and locating the best position for the temperature sensor in the reactor. From temperature measurements, the proposed inferential tool estimates hidden state variables and unmeasured disturbances, using Sequential Importance Resampling algorithm for the particle filter. The proposal is investigated according to the number of particles and the criterion total error reduction. The results show that the monitoring scheme is able to estimate satisfactorily the process variable profiles, as the temperature and chemical conversion, along the reactor length. [ABSTRACT FROM AUTHOR]

In this research, the influence of effective parameters on ozone penetration in the soil contaminated with anthracin has been investigated. The soil was then contaminated with anthracin, a polycyclic aromatic hydrocarbon, after washing and moisture removal stored in a dark environment for one week in closed containers. The parameters studied are as follows: the soil height, the soil particle size, contaminant concentration, ozonation time, and moisture percent. The maximum removal efficiency was 92%. In this study, it was observed that by changing the size of the soil particles, there are significant changes in the penetration rate. Also, the pollutant concentration, the height of the soil column, and moisture affect penetration rate. It was also observed that the highest penetration rate occurred in the first 10 min of the ozonation process. In the next step, by obtaining the governing equations for the decomposition of ozone by contaminate, organic and inorganic materials, soil active sites and spontaneous ozone decomposition, a model for ozone penetration in the soil was presented, and by comparing experimental data and modeling results, the coefficients of reaction rate of ozone kinetic reactions with pollutant, organic matter and inorganic soil, soil active sites and spontaneous ozone decomposition were obtained approximately. [ABSTRACT FROM AUTHOR]

The dimerization of propene to 4-methyl-1-pentene (4MP1) was studied in a fixed-bed reactor at 150 °C temperature, 8 MPa pressure, and 1 h−1 liquid hourly space velocity (LHSV) in the presence of solid superbase with 20 wt% one-pass conversion to hexene and 88% selectivity toward 4MP1. Based on the reaction results, propene competes with 4MP1 for adsorption on the catalyst surface. A higher reaction pressure or a lower liquid rate of 4MP1, controlled by a suitable propene LHSV or reaction temperature, was beneficial to the adsorption of propene, which reduced the isomerization of 4MP1. Under optimized conditions, propene dimerization was stable for 200 h, and isomerization was limited to less than 5%, yielding products with about 19% one-pass conversion to hexene by weight and 87% selectivity toward 4MP1. [ABSTRACT FROM AUTHOR]

The production of fungal biocontrol agents by solid-state fermentation (SSF) processes in inert supports demands deeper studies in SSF-modelling and SSF-optimisation to cope with scale-up issues. Here, we report the systematic application of fractional factorial and central composite designs to optimise the conidia productivity and maximum specific growth rate of the biological control candidate Trichoderma asperellum strain Th204 using two inert supports: polyurethane foam (PUF) and rice husk (RH), in a pilot 16 L fixed bed fermenter. By using response surface methodology, 2D contour graphs and Spearman's correlation coefficients, axial temperature, conidia concentration, bed moisture and pressure drop gradients were modelled. C:N ratio and airflow rate were identified as significant factors. Optimal conditions using PUF a C:N ratio of 18.1 and airflow of 0.8 m3 h−1 were found, with the highest productivity of 3.09 × 107conidia g−1 initial dry matter h1. Polynomial models and response surfaces found in this study are advantageous to design strategies to scale-up the SSF process in fixed bed fermenters for fungal biological control candidates. [ABSTRACT FROM AUTHOR]

The main goal of this paper is to characterize the change of structural behavior (i.e. the appearance of the so-called 'strange terms') arising in the homogenization process when applied to distributed microscopic chemical reactions taking place on fixed-bed nanoreactors, at the microscopic level, on the boundary of the particles of critical size. The presence of non-homogeneous distributed functions of the reaction kinetics may be originated by many different reasons. The case of quick oscillation is often due to own structure of the fixed bed reactor since the flux of the fluid acts on each particle in a non-homogeneous way. In some other cases, the non-homogeneous distributed functions of the reaction kinetics is artificially provoked in order to control a certain desired global effect. Our main result gives a complete classification of the strange terms according the assumed periodicity on the distributed functions of the reaction kinetic. [ABSTRACT FROM AUTHOR]

A low tube-to-particle diameter ratio (dt/de,p) fixed bed, packed with spherical and nonspherical catalyst supports, was used to investigate pressure drop at varying temperature (298-673 K) and inlet pressure (245-294 kPa). The dt/de,p ranged from 3 to 6, namely, a large wall-effect fixed bed, with an average void fraction between 0.38 and 0.61. These conditions pertain to multitubular fixed-bed reactors used for exothermic reactions. The pressure drop was notably influenced by the particle size and morphology as well as temperature. The use of particles with dt/de,p < 5 and relatively large bed void fractions (>0.55) appeared suitable for pressure drop control. The fluid velocity profiles were calculated by applying the Navier-Stokes-Darcy-Forchheimer equation computing the respective permeability parameters with refitted state-of-the-art pressure drop correlations. The fluid flow exhibited different velocity zones across the fixed bed, the highest velocity zone being located near the reactor wall. The axial velocity component was influenced by the catalyst morphology, as well as temperature and inlet pressure. [ABSTRACT FROM AUTHOR]

In the present study arsenic contaminated simulated water and groundwater was treated by the combination of biological oxidation of tri-valent arsenite [As (III)] to penta-valent arsenate [As (V)] in presence of Acidothiobacillus ferrooxidans bacteria and its removal by adsorptive filtration in a bioreactor system. This method includes the immobilisation of A.ferrooxidans on Granulated Activated Carbon (GAC) capable of oxidising ferrous [Fe (II)] to ferric [Fe (III)]. The Fe (III) significantly converts the As (III) to As (V) and ultimately removed greater than 95% by the bed of GAC, limestone, and sand. The significant influence of Fe (II) concentration (0.1-1.5 gL−1), flowrate (0.06-0.18 Lh−1), and initial As (III) concentration (100-1000 µgL−1) on the arsenic removal efficiency was investigated. The simulated water sample containing the different concentration of As (III) and other ions was used in the study. The removal of other co-existing ions present in contaminated water was also investigated in column study. The concentration of arsenic was found to be <10 µgL−1 which is below Maximum Contaminant Level (MCL) as per WHO in treated water. The results confirmed that the present system including adsorptive-filtration was successfully used for the treatment of contaminated water containing As (III) ions. [ABSTRACT FROM AUTHOR]

Pyrolysis is a thermal process where organic materials such as biomass and oil are decomposed and lighter materials such as gas, vapor, liquid products, and char are produced. The aim of this study was to investigate the pyrolysis behavior of sewage sludge in different operating conditions. Using a fixed bed, the influence of some important parameters such as pyrolysis temperature, heating rate, particle size, and N2 flow rate on product yields was studied. Results showed that with increase in temperature from 400 to 700°C, the char yield decreased from 30.1 to 7.50%, while the gas yield increased from 35.8 to 52.4%. The gas yield also increased from 46.9 to 49.1% as the heating rate increased from 20 to 60°C/s, while the oil yield increased from 45.2 to 46.8% as heating rate increased to 40°C/s and then the increase leveled off. [ABSTRACT FROM AUTHOR]

The performance of catalytic tri-reforming under industrially relevant situations (e.g., pellet catalysts, pressurized reactor) was investigated using surrogate biogas as the feedstock. Tri-reforming using Ni/Mg/Ce0.6Zr0.4O2/Al2O3 pellet catalysts was studied in a bench scale fixed-bed reactor. The feed molar ratio for CH4:CO2:air was fixed as 1.0:0.70:0.95. The effects of temperature (800-860°C), pressure (1-6 bar), and H2O/CH4 molar feed ratio (0.23-0.65) were examined. Pressure has substantial impact on the reaction and transport rates and equilibrium conversions, making it a key variable. At 860°C, CO2 conversion increased from 4 to 61% and H2/CO molar ratio decreased from 2.0 to 1.1 as the pressure changed from 1 to 6 bar. CO2 conversion and H2/CO molar ratio were also influenced by the temperature and H2O/CH4 molar ratio. At 3 bar, CO2 conversion varied between 4 and 43% and the H2/CO molar ratio varied between 1.2 and 1.9 as the temperature changed from 800 to 860°C. At 3 bar and 860°C, CO2 conversion decreased from 35 to 8% and H2/CO molar ratio increased from 1.7 to 2.4 when the H2O/CH4 molar ratio was increased from 0.23 to 0.65. This work demonstrates that the tri-reforming technology is feasible for converting biogas under scaled-up conditions in a fixed-bed reactor. [ABSTRACT FROM AUTHOR]

Adsorption of La(III) and Ce(III) from aqueous solutions by novel chitosan modified with poly(vinyl alcohol) as a promoter of mechanical and chemical properties and 3-mercaptopropyltrimethoxysilane as a promoter of the functional group was investigated in batch and continuous modes. The FTIR analyses showed that mecapto groups have been successfully added to chitosan/poly(vinyl alcohol). The BET surface area, pore diameter, and pore volume of adsorbents were 1.68 m2 g−1, 2.516 nm, and 0.058 cm3 g−1, respectively. The effects of the operating parameters such as pH, contact time, initial metal ion concentration, adsorbent dosage, and temperature were studied in batch mode operation. Optimum pH was found to be 5. According to the Langmuir model, the maximum adsorption capacities for La(III) and Ce(III) ions were 263.16 and 251.41 mg g−1, respectively. The thermodynamic study showed that the adsorption process of both metal ions was endothermic and spontaneous favored at the higher temperature. In the column study, the effects of the flow rate and initial concentration were investigated. The maximum adsorption capacities based on the Thomas model for La(III) and Ce(III) ions were 460.94 and 374.83 mg g−1 at a flow rate of 4 mL min−1 and an initial metal concentration of 300 mg L−1, respectively. [ABSTRACT FROM AUTHOR]

Removal of Congo Red (CR) azo dye by adsorption process using Amberlite IRA-400 resin was evaluated in both batch and fixed bed system. From the batch adsorption results, maximum loading efficiency (99.99%) of CR dye was obtained at the conditions pH 4.5, temp. 303 K, contact time 180 min., Amberlite IRA-400 dose 0.5 g. The isotherm study ascertained on favorability of adsorption process as the value of separation factor (KL = 0.88) and Freundlich constant (1/n = 0.96 < 1.0) obtained from Langmuir and Freundlich equations are rational, though, overall adsorption process showed best fit with Langmuir (R2 = 0.99) than Freundlich model (R2 = 0.97). The kinetic data studied at three different CR dye concentration (50, 75, 100 mg) and results were fitted with both pseudo-first-order and second-order model equations. The values ofR2obtained are of 0.95 and 0.99 for former and later one, respectively, ensuring on best fitting of pseudo-second-order kinetics and also suggesting about the chemisorptions type of adsorption. The bed depth service model was applied for competitive analysis of the CR dye adsorption in column variables indicating mass transfer from aqueous solution to Amberlite IRA-400 phase. Fourier transform infrared analysis of CR-loaded resin Amberlite IRA-400 showed a band shifted from 1057 to 1130 cm−1confirming CR adsorption with Amberlite IRA-400. Scanning electron microscope analysis of resin before and after adsorption was well evident from the phase patterns. Selective separation of CR dye from waste effluent of a textile industry bearing CR dye along with other trace heavy metal was achieved. [ABSTRACT FROM PUBLISHER]

In this paper, at first by means of the differential quadrature element-incremental method as a computationally efficient and accurate numerical tool in conjunction with the Newton-Raphson method, the behaviour of the bicomponent fixed-bed adsorption is studied. The kinetics of the adsorption is formulated based on the linear driving force (LDF) approximation. Then, an inverse algorithm is employed to estimate the overall mass transfer coefficients of the adsorption column by using the measured time histories of the mole fractions of outlet multicomponent. The method allows one to obtain the values of the LDF mass transfer coefficients for the different adsorbents and adsorbates. The conjugate gradient method is adopted for the optimization procedure of the inverse algorithm. The robustness and applicability of the present inverse approach are demonstrated by solving different examples with the exact data of the known kinetics. [ABSTRACT FROM PUBLISHER]

This study evaluates the feasibility of commercial chitosan (CQ) and modified chitosan (MQ) by epichlorohydrin to be used as a solid phase to remove fluorescein (FSC) from aqueous solutions by two different approaches: in batch and on a fixed column bed. For the batch study, all parameters that influence sorption capacity were evaluated, such as: pH, mass, ionic strength, temperature and time of contact. In the optimized condition, 75% removal was obtained for FSC using CQ, while the modification allowed an increase up to 99%, as well as an increase in the stability of the polymer. In the fixed column bed study, the influence of all the parameters was evaluated through breakthrough curves, and the thermodynamics parameters of each approach were obtained. The results of these studies demonstrate that the modification with epichlorohydrin enhanced the sorptive properties (from 35% to 95% in fixed bed experiments) and the polymer stability (making it insoluble), making it suitable to be used in wastewater treatment. [ABSTRACT FROM AUTHOR]

Automobile emissions are composed of NOxand unburned hydrocarbon that contribute significantly to major environmental and health issues. In this study, encapsulatedMoringa oleiferabeads (EMBs) were synthesized usingMoringa oleiferapod powder that was cross-linked with calcium alginate and used as a biosorbent for reducing the emission gas concentrations from the single-cylinder diesel engine. The breakthrough curve was attained from single and double stage of fixed bed column by the influence of temperature ranging from (80°C–120°C) ± 5°C with a feed flow rate varying from 8 to 10 kg hr–1and bed height varying from 15 to 30 cm. Based on the experimental results, the maximum biosorption capacity (qo) was found to be 14.45 and 123.51 mg g–1for HC and NOx, respectively, and was obtained at 80°C–90°C with double stage of BH–30cm under flow rate of 8 kg hr–1. Further, breakthrough curves were investigated, and the experimental data were fitted using well-established models like Thomas, Yoon–Nelson, and Wang models. In addition, mass transfer models like Weber–Morris and Boyd were investigated to identify the rate-limiting step of the overall biosorption process. [ABSTRACT FROM PUBLISHER]

We apply the wet impregnation procedure to prepare the Fe–Co–Ce catalyst supported by silica. The effects of operational conditions such as temperature, pressure, and the feed ratios of reaction on the selectivity and yield were studied. The production of light olefins from syngas (CO and H2) over this catalyst in a fixed bed reactor via Fischer–Tropsch synthesis (FTS) was investigated. The reactor tests were determined through the design experiments.The optimum condition was determined in a way that the selectivity of methane was the least and other olefins have the maximum selectivity. The results indicated that the catalyst at 350°C, 3 bar, and syngas with H2/CO ratio 1/1 has shown the better catalytic performance for FTS. [ABSTRACT FROM AUTHOR]

Hydrogen production from the steam-reforming reaction of glycerol was studied over charcoal as catalyst in a tubular fixed-bed reactor. The results showed that charcoal was a novel kind of catalyst, which not only had an active effect on the reforming process, but can decrease the cost of production. The optimum conditions were obtained at 800°C, S/C of 4, WHSV of 1.5 h−1. Hydrogen yield and potential hydrogen yield were up to 75.12% and 84.31%, as well as the carbon conversion reached 89.08% at the optimum conditions. The results of SEM and TGA indicated that there was polymerization and polycondensation of glycerol still in steam-reforming process. [ABSTRACT FROM PUBLISHER]

Extraction of Crotalaria juncea (Sunn hemp) oil from its seeds is important to study because of its proven promising clean fuel characteristics. Soxhlet-based solvent extraction with some modification has been tried to extract the oil. In a fluid-solid mass transfer system, where, solids are present as packed bed, dynamic behavior of bed can be described in terms of concentration of solute in solids/solvent-time profile. Some of the well-known semi-empirical models of adsorption dynamics are modified and applied since leaching of oil is just the reverse of the phenomenon of adsorption in porous media. Modified Bohart-Adams model (non-linear), modified Bed Depth Service Time (BDST) (linear), and modified Thomas model (non-linear forms) are applied. It is found that these models fit to the experimental result reasonably well. Results suggest that higher bed height, with proper shape (annular) of the bed, having a higher solvent velocity will work best. Comparing the error values (SSE, SAE, and ARE) in the four cases, it is very clear that the modified BDST model is the most suitable. In the light of transient study it is established that the modified Soxhlet apparatus with cylindrical and annular beds, performs best while leaching Crotalaria juncea oil from their seeds. [ABSTRACT FROM AUTHOR]

Many polluted sites are simultaneously contaminated with polycyclic aromatic hydrocarbons and heavy metals. In the present study, batch and continuous column experiments were performed utilizing self-composition soil to describe the sorption behavior of two contaminants: lead (Pb2+) and pyrene (PYR). Operational conditions such as contact time, bed depth, and flow rate were optimized. The effect of soil organic matter content on the process of adsorption of both contaminants was investigated. The presence of PYR in solution at neutral pH (6.0–7.5) decreased Pb2+sorption. Similar behavior was observed for PYR in the presence of Pb2+in solution. At room temperature, batch experimental data conducted as a function of contact time were analyzed using the Langmuir and Freundlich isotherms. Results revealed that Pb2+sorption isotherms were fitted better by the Langmuir model and PYR sorption isotherms were fitted better by the Freundlich model. Column adsorption experiments were carried out at room temperature and under operating parameters (bed depth, flow rate, and initial contaminant concentration). Breakthrough curves were well fitted to the two-site first-order kinetic model with a sum of square errors less than 0.14. The Pb2+adsorption kinetic data were processed also for the Thomas model with a good accuracy. [ABSTRACT FROM PUBLISHER]

The Fischer–Tropsch (FT) synthesis is an important method for producing valuable key raw materials such as heavy and light hydrocarbons in various industries. The effects of process conditions (temperature of 503–543 K, pressure of 10–25 bar, and gas hourly space velocity (GHSV) of 1,800–3,600 Nml gcat−1h−1) on the FT product distribution using Co–SiO2/SiC catalyst in a fixed bed reactor were studied by the design of experimental procedure and the Taguchi method. The optimization of the reaction conditions for the production selectivity of C2–C4and heavy hydrocarbon (C5+) that has not been completely indicated elsewhere was investigated. The effect of operating conditions on the average carbon number distribution, dispersion, and skewness was also studied. Data analysis indicated the highest selectivity for the light hydrocarbons at a pressure of 20 atm, GHSV of 2,400 Nml gcat−1h−1, and temperature of 543 K resulting in a highest selectivity for heavier hydrocarbons (C5+) and the minimum amount of methane in the reaction products that is optimal at the pressure of 10 atm, GHSV of 1,800 Nml gcat−1h−1, and a temperature of 503 K. Furthermore, based on the surface plot, temperature has more significant effects than the other parameters. In addition, the obtained results indicated that the maximum average number of carbon was obtained in a pressure of 10 atm and a temperature of 503 K. [ABSTRACT FROM PUBLISHER]

Traveling grate boilers with high pollutant emissions are widely used in China. The main objective of this study is to investigate the characteristics of NO reduction by char layer. Experiments were carried out on a fixed-bed furnace with two different coal bed heights (6 and 12 cm). The concentrations of NO, O2, CO2, CO, and H2were measured and compared to reveal the effect of char layer. Results show that the trend of NO emission presents a double-peak distribution on the coal bed surface for different stoichiometries. The first peak is higher than the second one. The maximum yields of NO emission are 493.30 (6 cm) and 384.09 mg/m3(12 cm) for Huainan coal, and 560.19 mg/m3(6 cm) and 468.29 mg/m3(12 cm) for Mongolia coal. The thicker bed height condition forms more char. The char layer reduces NO generated from the flame front. The presence of CO strongly enhances NO–char reaction. [ABSTRACT FROM PUBLISHER]