Gasification Experiments Research Articles

Gasification characteristics of a simulated waste under separate and mixed atmospheres of steam and CO2

Downdraft gasifier is attractive for small-scale solid waste treatment, but the gasification characteristics are worthy of deep research. In this study, a two-stage continuous feeding apparatus was developed to examine the effect of moisture content of the mixed feedstock on co-gasification. Furthermore, considering the effect of CO2 from flue gas, the gasification experiments were carried out when CO2 participated in the gasification alone or in a mixed atmosphere of CO2 and steam. The pyrolysis residue plays an essential role in the gasification with steam, which can improve the syngas yield, especially the H2 yield reaches 0.345 m3/kg when steam and feedstock mass ratio (S/F) is 0.8. CO2 is inferior to steam in promoting H2 formation. But when CO2 and feedstock mass ratio (C/F) rises from 0.74 to 1.48, the gas yield increases from 60.52% to 77.15%, and the yields of tar and residue cut down correspondingly. CO2 is still an alternative gasifying agent, which can partially substitute steam in the gasification process. However, when CO2 coexists with a small amount of steam (S/F = 0.4), introducing excessive CO2 (C/F = 1.48) will intensify the competition between steam and CO2.

Green ammonia production via microalgae steam catalytic gasification process over LaFeO3 perovskite

Ammonia (NH3) is a potential carbon-free energy carrier. This study proposed a green route for NH3 production via microalgae steam catalytic gasification process over LaFeO3 perovskite. The experiments of pyrolysis, catalytic pyrolysis, steam gasification, and steam catalytic gasification were compared in a fixed bed reactor. Compared with pyrolysis, steam is introduced as the gasifying agent for reforming volatile-N and gasifying char-N during steam gasification, thus promoting the fuel-nitrogen transfer into the gas phase. Synergistic effects of steam and LaFeO3 are able to promote the hydrogenation of char-N, the decomposition of proteins, and the deamination of amides, resulting in a remarkable release of NH3. More importantly, steam and LaFeO3 can significantly promote the conversion of HCN into NH3, which will enhance the selectivity of NH3. Proper steam concentration can provide considerable amounts of H radicals for enhanced NH3 production, whereas excessive steam is likely to facilitate the NH3 conversion to H2. Gasification temperature exerts positive effects on the NH3 yield at 700–800 °C, but further increase in temperature causes a reduction in NH3 production, as a result of its decomposition into N2. The highest conversion of nitrogen into NH3 (55.98 wt%) is obtained at 800 °C with a steam concentration of 54 vol% and the catalyst-to-feedstock ratio of 1. Moreover, the LaFeO3 perovskite also exhibits desirable stability during the long-term cycling both in the activity and structure aspect.

Catalytic biomass gasification of sawdust: integrated experiment investigation with process modeling and analysis

AbstractThis paper reports on the investigation of the gasification from biomass using a laboratory scale fluidized bed gasifier. Main influencing factors, such as the temperature, steam flow rate and CaO to biomass mass ratio were studied. A model was developed for hydrogen-rich gas production from biomass via using ASPEN PLUS software. Sawdust was used as raw material for this study. Different operating conditions were considered and the model was verified. The results showed that the production of H2 and CO2 increased while the production of CO and CH4 decreased with increasing temperature. When the steam was used as the gasifying agent at different temperatures, the production of H2 increased significantly and its growth rate was ~48%. The increase of CaO to biomass mass ratio from 0% to 50% resulted in hydrogen content increasing from 40% to 68%. Simulation results showed that the model was suitable for biomass gasification process, which could provide some reference value for further biomass gasification experiment.

To stimulate, and to inhibit: A theoretical understanding of the sodium-catalytic mechanism of coke gasification

For the ironmaking process, previous research on alkali-catalytic coke gasification has focused mainly on macroscopic kinetic behavior to stimulate CO production and has neglected microscopic reaction mechanisms, especially the inhibition of carbon matrix graphitization. Here, this work combined sodium-vapor-adsorption coke gasification experiments and corresponding theoretical calculations to investigate the microscopic mechanism of the sodium-catalytic coke gasification reaction. X-ray diffraction and Raman characterization showed coke gasification with graphitization of the carbon matrix and inhibition by sodium addition. Molecular dynamics simulations based on the reactive force field (ReaxFF) well reproduced the experimental results and confirmed the sodium-catalytic effect. Comprehensive reaction pathways in coke gasification with and without sodium have been summarized from ReaxFF simulation trajectories, where sodium-containing elementary reactions were verified by density functional theory. Calculations showed that the sodium atoms not only reduced the activation energy substantially in the initial carbon layer oxidation, but also adsorbed at carbon layer defects spontaneously and inhibited carbon matrix reconstruction. This behavior hindered carbon layer growth but facilitated carbon layer oxidation and accelerated CO molecule production. This mechanism, which was obtained from combined experimental and theoretical approaches, provides theoretical support for an in-depth understanding of the catalytic role of sodium in carbon material gasification.

Production forecast analysis of BP neural network based on Yimin lignite supercritical water gasification experiment results

In the future coal gasification industry, quick and accurate prediction of the gas products can guide industrial production and make production more efficient. This paper carried out the SCWG experiment of Yimin lignite and discussed the effects of temperature, concentration and residence time on gasification. After that, the experimental data were divided into a training set, validation set, and test set according to a ratio of 70%, 15%, and 15%. Then, the regression was performed in the BP neural network, and the number of hidden layers, linear fitting model, and MIV were discussed. The results show that the single-layer neural network has a better fitting effect than the two-layer neural network. The R2 of the ANN model for the products is 0.9921, the RMSE is 0.2952, the MeanRE is 0.0673, and the MaxRE is 0.1957, which is far better than the linear regression. In addition, the mean impact value of temperature, residence time, and concentration is 0.7493, 0.2188, and −0.1051, which shows temperature is the most critical variable.

Processing of household waste via hydrothermal gasification and hydrothermal liquefaction for bio-oil and bio-hydrogen production: Comparison with RSM studies

This study focuses on bio-hydrogen production from household mixed waste via hydrothermal gasification (HTG) and hydrothermal liquefaction (HTL) experiments. HTG and HTL studies were performed at temperature 280–420 °C and 280–360 °C, catalyst of 1–5 wt% and varying solvent proportion. Bentonite/Nb-TiO2 catalyst was synthesized via sol-gel method. Maximum hydrogen yield from HTL was 26 wt% (catalyst load: 3 wt%) and HTG was 39 wt% (catalyst load: 4 wt%) for solvent to waste ratio of 13.33 mL/g, ethanol to water ratio of 1:1 and time of 60 min. Enhanced hydrogen yield in the HTG process was via gas water shift, methanation and reforming reactions in the system due to ethanol as half-solvent and optimum solvent to biomass load. Second product from HTL process was bio-oil which resulted in yield of 33 wt% with O/C and H/C values of 0.1 and 0.95 with HHV of 34.74 MJ/kg. Mechanistic reactions like depolymerisation, hydration, reduction and hydrolysis reaction in the HTL system resulted in higher proportion of gaseous product. Optimization studies showed that temperature and solvent to waste ratio are the desired variables in the hydrogen production process. This study provides support for energy nexuses from household mixed waste.

Effects of the secondary air inlet position and gasifying agents on grape branch gasification in an improved downdraft gasifier

Gasification experiments on grape branches were carried out in a self-improved downdraft gasifier at 800 °C, under atmospheric pressure, using air, steam, and air–steam as gasifying agents.

Comparison of Tar Samples from Reaction Zone and Outlet in Ex-Situ Underground Coal Gasification Experiment

Tar remaining in the gasification cavity during underground coal gasification (UCG) is an important pollution source, while the reported studies only focus on the tar behavior at the outlet. The present work aims to compare the tar properties from the reaction zone and the outlet, analyze the tar evolution during gasification, and discuss possible measures to control tar pollution. Tar was sampled with a self-developed equipment from an ex-situ underground coal gasification experimental system and analyzed by GC-MS. The gas composition, temperature, and PM10 were also compared for the reaction zone and the outlet. Compared with the tar from reaction zone, the tar from outlet has a smaller percentage of high boiling point content, PAHs, C, O, N, S, Cl, Si, and a larger percentage of H. The PAHs percentage in tar at the outlet in this work is closer to the field data than the lab data from literature, indicating the experimental system gives a good simulation of tar behavior in underground coal gasification. Condensation due to a fast temperature drop is one of the main reasons for PAHs decreasing. Tar cracking and soot formation also cause the decrease of heavy tar, proven by the light gas and particulate matter results.

Two-stage gasification of dried sewage sludge: Effects of gasifying agent, bed material, gas cleaning system, and Ni-coated distributor on product gas quality

Dried sewage sludge gasification was conducted using a two–stage gasifier composed of a fluidized bed gasifier and tar–cracking reactor to produce a gas with low levels of tar, NH3, and H2S. In this work, the influence of the type of gasifying agent and bed material and the equivalence ratio on the product gas quality were investigated. Furthermore, the possibility of gasification without a hot filter and electrostatic precipitator, which are usually applied to remove impurities generated during gasification, was examined. Finally, the efficiency of a Ni–coated distributor for tar and NH3 removal was evaluated. Overall, steam/O2 gasification produced H2–rich (38–39 vol%) gases. Further, olivine reduced the tar and NH3 contents in the product gas obtained from steam/O2 gasification to 138 mg/Nm3 and 236 ppmv, respectively. A gas cleaning system without a hot filter and electrostatic precipitator produced a gas with only 8 mg/Nm3 of tar. Moreover, a Ni-coated distributor was found to be very effective in reducing the NH3 content to 60 ppmv. Dried sewage sludge gasification experiments in air were conducted four times for 4 h, producing gases with very low levels of tar (3–10 mg/Nm3) and NH3 (60–90 ppmv).

Evaluation of Pig Manure for Environmental or Agricultural Applications through Gasification and Soil Leaching Experiments

The current study aimed at evaluating an untreated pig manure, firstly for its suitability for soil amendment in combination with an agricultural/bio-solid biochar, and secondly for its potential to be used for adsorption of hazardous species, replacing expensive activated carbons. Column soil leaching experiments were designed to simulate field conditions, and physical, chemical and mineralogical analyses were performed for raw materials and/or leachates. For activated carbon production, the manure was gasified by steam or carbon dioxide at high temperatures. Biochars were analyzed for organic and mineral matter, structural characteristics and organic functional groups. Activation by steam or carbon dioxide greatly enhanced specific surface area, reaching values of 231.4 and 233.3 m2/g, respectively. Application of manure to the soil promoted leaching of nitrates and phosphates and raised COD values of water extracts. Biochar addition retained these ions and reduced COD values up to 10 times at the end of the three-month period. The concentrations of heavy metals in the leachates were low and, in the presence of biochar in soil blends, they were significantly reduced by 50–70%. The manure presents a significant potential for adsorption of various pollutants or improvement of soil amendment if carefully managed.

Migration of Co, Cd, Cu, Pb to the groundwater in the area of underground coal gasification experiment in a shallow coal seam in the experimental mine ‘Barbara’ in Poland

A numerical model of inorganic pollutants migration in the area of ​​ underground coal gasification (UCG) reactor in the post-operational phase was constructed in this study. Also the deceleration of migration and the shape of the contaminant plume in individual geological formations of the reactor surroundings, resulting from different values ​​of sorption affinity, were compared. The simulations were carried out for four selected metals (Co, Cd, Cu, Pb), which in relation to the raw coal and post-process char showed different sorption properties. The sorption parameters of the tested systems were determined experimentally on the basis of the Freundlich isotherm equation. The retardation coefficients were calculated and the degree of sorption intensity in hydrogeological media was classified from II (in the cobalt-char and metals-coal systems) to the IV class of sorption intensity (in the copper-char system).The modeling was carried out using the finite element method (FEM) in the COMSOL Multiphysics computing environment in a two-dimensional plane. The simulation of pollutant migration was carried out for the transient state, with the assumed time horizon up to 20 years after the termination of the UCG experiment. The bottom of the cavity formed due to the coal gasification in situ (10 m × 20 m ellipse) was assumed as the source of contamination and the spread of metals in a horizontal plane 200 m long and 200 m wide was analyzed.To compare the extent to which sorption phenomena affect the spread of pollutants, an additional model was constructed, taking into account only the advection–dispersion movement of the contaminant plume. The consequence of sorption interactions for the tested systems was the delay of the contaminant plume migration depending on time since the termination of the gasification process and depending on the distance from the source of pollution. Due to high sorption affinities, the post-process char acts as an effective buffer for inorganic pollutants and slows down the migration of analyzed metals even 20 years after UCG experiment. The greatest slowdown in migration in relation to the velocity of groundwater flow as a result of sorption occurred for copper transport in the char layer.

Synergistic effects, gas evolution and ash interaction during isothermal steam co-gasification of biomass with high-sulfur petroleum coke

This work investigated the co-gasification behavior of rice straw (RS) and a high-sulfur petroleum coke (PC). An isothermal gasification experiment under a steam atmosphere was conducted on a self-designed thermogravimetry (TG) coupled with mass spectrometry (MS). The results indicate that the high sulfur content in PC seem to have no significant effect on co-gasification. RS showed obvious catalytic effect only after it was completely gasified into ash. Affected by the high concentration of steam, the main components of synthesis gas are H2 and CO2. The RS ash presents a violent melting state, and the lower RS addition ratio only shows a strong catalytic effect in the initial stage of the reaction. The high addition ratio makes the ash particles in the liquid phase contact and react well with the PC particles, and will not inhibit the gasification of the PC particles before the PC particles are completely wrapped.

Study of Electrochemical Catalytic Coal Gasification: Gasification Characteristics and Char Structure Evolution.

Electrochemical catalytic coal gasification experiments with Fuxin (FX) coal under a CO2 atmosphere were conducted to evaluate the effects of power and temperature on coal gasification and char structure evolution during electrochemical catalytic gasification (ECG). When the power was 400 W, with temperature increasing from 800 to 1000 °C, the CO content in the gas products increased by 8.16%, the H2 content increased by 8.39%, and the CH4 concentration in the gas products initially increased and then decreased. When the temperature is 900 °C, with power increasing from 0 to 400 W, the CO content in the gas products increased by 58.27%, the H2 content increased by 81.33%, and the CH4 concentration in the gas products increased from 1.31 to 2.37%. The gasification reactivity and the concentration of combustible gas generated during ECG were higher than those during common coal gasification. Thermal electrons play important roles in ECG. These electrons could promote ring opening reactions and aromatic compound cracking and inhibit aromatization reactions while increasing the number of oxygen-containing functional groups in char, consequently enhancing the char gasification reactivity.

Experimental and Kinetic Studies on Steam Gasification of a Biomass Char

The maximum gasification rate of corn stalk char (CSC) appeared at high conversion range, and its quite different gasification behaviors from other carbonaceous materials are all derived from the catalytic effect of alkali and alkali earth metals (AAEMs), so it is necessary to study the effect of AAEMs and gasification kinetics of such biomass char. However, there are few systematic discussions about this effect and kinetic modeling. Thus, in this study, CSC samples were prepared in a fast pyrolysis fixed-bed reactor, and its gasification experiments were conducted on a pressurized magnetic suspension balance at various total pressures (0.1–0.7 MPa), steam concentrations (10–70 vol.%) and temperatures (725–900 °C). Moreover, a water-leached CSC (H2O-CSC) was also prepared to evaluate the impact of AAEMs on the gasification performance of CSC, and some well-known models were adopted to describe the gasification behaviors. On the basis of these results, the effect of primary AAEMs on the gasification behaviors of CSC and gasification kinetic modeling were obtained. Results showed total pressure had no obvious influence on the gasification rate of CSC, and the reaction order varied at 0.43–0.55 with respect to steam partial pressures. In addition, the modified random pore model (MRPM) and Langmuir–Hinshelwood (L-H) model were satisfactorily applied to predict the gasification behaviors of CSC. The catalytic effect of AAEMs on CSC gasification was weakened due to water-leaching treatment. A random pore model (RPM) could describe the gasification behavior of H2O-CSC well, followed by grain model (GM) and volumetric model (VM).

Experimental study on the influence of O2/CO2 ratios on NO conversion and emission during combustion and gasification of high-temperature coal char

NO is one of the major pollutants generated in the process of coal thermal conversion, and shall be controlled in order to fulfil the requirements of industrial production and environmental protection. The ratio of oxygen concentration to carbon dioxide concentration (O2/CO2 ratio) is one of the key factors that affect the thermal coal-N transformation and nitrogen oxide generation. However, there are few related research in this field at present and the conclusion needs to be refined. This study adopted the coal self-preheating combustion technology to obtain the high-temperature coal char on a bench-sale test rig, and combustion and gasification experiments of this modified fuel were carried out on TG-MS combined analyzer. The sum of the percentage content of O2 and CO2 was always 21% and Ar percentage content was 79% to simulate actual combustion. With the advanced equivalent characteristic spectrum analysis (ECSA) method, a quantitative analysis was conducted on the release rate and generative rules of gas products with temperature change during combustion and gasification of graphite and high-temperature coal char under different O2/CO2 ratios. As per the results, O2/CO2 ratio was the main factor affecting combustion characteristics of fuel and NO emission. In the atmosphere of 11% CO2 + 10% O2 + 79% Ar, NO emission reached the highest level. NO, HCN and N2 release time of the high-temperature char of Shenmu bituminous coal was earlier than that of the high-temperature coal char of Shenmu semi-coke, with wider temperature range corresponding to the period of evolved gas. Reaction (NO + CO → 1/2N2 + CO2) was the most cardinal reaction that affected the release of NO during coal thermal conversion progress.

Steam and supercritical water gasification of densified canola meal fuel pellets

In this research, canola meal was densified using bio-additives including alkali lignin, glycerol, and l-proline. The fuel pellet's formulation was optimized. The best fuel pellet demonstrated relaxed density and mechanical durability of 1015 kg/m3 and 99.0%, respectively. Synchrotron-based computer tomography technique indicated that lack of water in pellet formulation resulted in a twofold increase in pellet porosity. Thermogravimetric analysis showed that ignition temperature (240 °C) and burn-out temperature (640 °C) for fuel pellet were smaller than those for coal. Impacts of process parameters were evaluated on the quality of the gas product obtained from pellet's steam gasification and hydrothermal gasification. The gasification experiments showed production of untreated syngas with a suitable range of H2/CO molar ratio (1.3–1.6) using steam gasification. Hydro-thermal gasification produced a larger molar ratio of H2/CO (1.8–51.2) for the gas product. Modeling of pellet's steam gasification showed an excellent agreement with experimental results of steam gasification.

Screening of UCG chemical reactions and numerical simulation up-scaling of coal seam from laboratory models

Underground coal gasification (UCG) is a promising option for utilising deep-seated coal for the in-situ production of syngas. In this study, we modelled and screened the chemical reactions using the previous laboratory UCG experiments to investigate the complicated chemical reaction processes to apply them to field scale UCG operations. First, we constructed 1D and 3D numerical models by matching simulation with the laboratory coal combustion and gasification experiments involving a combustion tube test and then physically scaled the 3D experiments reported by Thorsness et al. and Stańczyk et al., respectively. We considered 5 chemical reactions from 12 chemical reactions by matching simulation to the experimental results. We adjusted the chemical reaction parameters used in our numerical simulations to match those of the experimental data. The numerical simulation results show that the proposed model can be applied in the laboratory as well as in the field-scale UCG operations to predict gasification behaviours, especially the temperature distribution, gas production rate, and gas composition.

Investigation of gasification kinetics of multi-component waste mixtures in a novel thermogravimetric flow reactor via gas analysis

A novel gasification fed-batch reactor enabling both thermogravimetric and gas analysis of large samples (up to tens of grams) was designed and tested. Air gasification experiments on food-court waste representative samples and its components were performed at 700 °C and 800 °C using ER = 0.3. At both temperatures, the lignocellulosics fraction produced highest H2 concentration (greater than 21% at 800 °C) while the plastic components generated less H2 regardless of process temperature (2.44%-7.08%). Synergistic effects of multiple components gasification with respect to H2 production was noticed through its non-linear evolution at 700 °C (ranging from 1.18% to 5.38%). A strong negative effect was observed at 800 °C; plastic addition reduced H2 production when combined with lignocellulosic and organic matter (1.02% to 9.73%). The same effects were observed for CH4 formation. This phenomenon was validated by kinetic analysis of decay curves of all components and their mixtures at the beginning of gasification in entire temperature region.

Gas production Characteristics during Electrochemical Catalytic Coal Gasification

To study the influences of temperature and power on coal gasification in the electrochemical catalytic gasification (ECG) process, gasification experiments of FX coal in CO2 atmosphere were performed in ECG system. The effects of temperature and power (thermal electrons) on gas production characteristics during ECG of coal have been studied in detail. Experimental results showed that the combustible components (CO, CH4 and H2) increased with temperature and power. The heat value, gas yield and cold gas efficiency increased with temperature and power. The heat value, gas yield and cold gas efficiency in ECG are higher than those in CCG at the same temperature. In addition, compared with temperature, power (thermal electrons) has a greater impact on gas production characteristics.

Effect of Lignite Properties on Its Suitability for the Implementation of Underground Coal Gasification (UCG) in Selected Deposits

Two experimental simulations of underground coal gasification (UCG) processes, using large bulk samples of lignites, were conducted in a surface laboratory setup. Two different lignite samples were used for the oxygen-blown experiments, i.e., “Velenje” meta-lignite (Slovenia) and “Oltenia” ortho-lignite (Romania). The average moisture content of the samples was 31.6wt.% and 45.6wt.% for the Velenje and Oltenia samples, respectively. The main aim of the study was to assess the suitability of the tested lignites for the underground coal gasification process. The gas composition and its production rates, as well as the temperatures in the artificial seams, were continuously monitored during the experiments. The average calorific value of gas produced during the Velenje lignite experiment (6.4 MJ/Nm3) was much higher compared to the result obtained for the experiment with Oltenia lignite (4.8 MJ/Nm3). The Velenje lignite test was also characterized by significantly higher energy efficiency, i.e., 44.6%, compared to the gasification of Oltenia lignite (33.4%). The gasification experiments carried out showed that the physicochemical properties of the lignite used considerably affect the in situ gasification process. Research also indicates that UCG can be considered as a viable option for the extraction of lignite deposits; however, lignites with a lower moisture content and higher energy density are preferred, due to their much higher process efficiency.