Gasification Reaction Rate Research Articles

Reactivity for pyrolysis and co2 gasification of alkali metal loaded waste wood char

In this study, different carbonization processes were performed for thinning wood waste as organic industrial waste and forestry waste biomass to produce waste wood char, which is used as solid and gaseous fuel. Waste biomass samples were added to Na + (NaOH) using thermogravimetry with a differential thermal analyser (TG/DTA), where the behaviour of thermal decomposition and the effect of additive amount of alkali metal were investigated. Waste wood char yields were increased at the peak temperature and weight loss was decreased with the increment of Na + (NaOH) loaded value. The fi xed carbon amount of waste wood char was also increased with the maximum Na + (NaOH) loaded value at 100:1, and then it was decreased. Furthermore, in order to evaluate the effect of Na + (NaOH) loaded value on char reactivity, an isothermal CO 2 gasifi cation experiment was performed at temperatures between 700°C and 900°C for chars obtained by pyrolysis at 900°C. It was shown that the reaction rate was increased with increasing temperature and the reaction rate of raw char was markedly slower than Na + (NaOH) loaded char. The activation energies of char were in decreasing trend with increasing Na loaded value. However, the activation energies of CO 2 gasifi cation of char samples were conversely increased when Na + loaded on char sample was more than 50:1. If too large amounts of Na + (NaOH) were loaded on char sample, the rate of gasifi cation reaction and the activation energy will be decreased as Na + reacts with the char surface covering the gasifying agent.

Absorption-enhanced steam gasification of biomass for hydrogen production: Effect of calcium oxide addition on steam gasification of pyrolytic volatiles

The effect mechanism of calcium oxide (CaO) addition on gasification of pyrolytic volatiles as a key sub-process in the absorption-enhanced steam gasification of biomass (AESGB) for H2 production at different conditions was investigated using a two-stage fixed-bed pyrolysis–gasification system. The results indicate that CaO functions as a CO2 absorbent and a catalyst in the volatiles gasification process. CaO triggers the chemical equilibrium shift to produce more H2 and accelerates volatile cracking and gasification reactions to obtain high volatile conversion rates. Increasing the gasification temperature could improve the reaction rate of cracking and gasification of volatiles as well as the catalytic effect of CaO, which continuously increase H2 yield. When the gasification temperature exceeds 700 °C, the sharp decrease in CO2 absorption capability of CaO drastically increases the CO2 concentration and yield, which significantly decrease H2 concentration. The appropriate temperature for the absorption-enhanced gasification process should be selected between 600 °C and 700 °C in atmospheric pressure. Increasing the water injection rate (represented as the mass ratio of steam to biomass) could also improve H2 yield. The type of biomasses is closely associated with H2 yield, which is closely related to the volatile content of biomass materials.

Reaction and diffusion of chlorine dioxide gas under dark and light conditions at different temperatures

Chlorine dioxide (ClO2) gas is a powerful oxidizing agent in many industrial applications for food processing, drinking water and cleaning treatments. It is considered for use in an increasing number of fresh food applications over a wide range of temperature and pH conditions due to its sanitizing capability. During the disinfectant treatment in a closed chamber or packaging system, ClO2 gas is typically exposed to environmental factors such as light, temperature, and humidity which influence its disinfectant efficiency. Determining ClO2 gas reaction rates and mass transfer properties are extremely important for the design of proper sanitization treatments. The aim of this work was to determine the diffusion coefficient for ClO2 gas in air and reaction rates under dark, UV-A and fluorescent lamp exposure. The effect of temperature on the diffusion of ClO2 was also assessed. A system was designed to measure these properties. The diffusion coefficient was found to be 0.129, 0.145, 0.173cm2s−1 at 5, 23, and 40°C, respectively. Degradation of ClO2 gas under dark, UV-A and fluorescent lamp exposure was found to follow a first-order reaction. Degradation using a 40W UV-A lamp was approximately four orders of magnitude larger than with a 34W fluorescent lamp. A methodology is proposed for quantifying the amount of ClO2 gas needed in a package and/or treatment chamber.

Study on the analysis of gaseous products from lignite steam gasification with waste catalysts

We performed the steam gasification of lignite char physically mixed with three kinds of waste catalysts obtained from the hydrotreating process of petroleum plants. Steam gasification of lignite char with waste catalysts and K2CO3 was investigated on a fixed bed reactor with gas chromatography and a gas analyzer at the temperature range of 800–900 °C. The gasification reaction rate, carbon conversion and the maximum release rate of major gases increased with increasing gasification temperature. The carbon conversions of the lignite char with waste catalysts were more than 90% and similar to K2CO3. The higher reaction index of lignite char and the largest H2 gross production, 203.3 mmol/gc, was observed with the waste catalyst III. Waste catalysts could be alternatives of K2CO3 for the H2 production from steam lignite gasification.

Municipal solid waste conversion to transportation fuels: a life-cycle estimation of global warming potential and energy consumption

This paper utilizes life cycle assessment (LCA) methodology to evaluate the conversion of U.S. municipal solid waste (MSW) to liquid transportation fuels via gasification and Fischer-Tropsch (FT). The model estimates the cumulative energy demand and global warming potential (GWP) associated with the conversion of 1 Mg (1 Mg = 1000 kg) of MSW delivered to the front gate of a refuse-derived fuel (RDF) facility into liquid transportation fuels. In addition, net energy production is reported to quantify system performance. The system is expanded to include substituted electricity and fuel. Under a set of default assumptions, the model estimates that 1 Mg of MSW entering the RDF facility yields 123 L of gasoline, 57 L of diesel, 79 kg of other FT products, and 193 kWh of gross electricity production. For each Mg of MSW, the conversion process consumes 4.4 GJ of primary energy while creating fuels and electricity with a cumulative energy content of 10.8 GJ. Across a range of waste compositions, the liquid fuels produced by gasification and FT processing resulted in a net GWP ranging from −267 to −144 kg CO2e per Mg MSW, including offsets for conventional electricity and fuel production. The energy requirement associated with syngas compression for FT processing was significant and resulted in high levels of process-related GWP. The model demonstrates that an increased biogenic MSW fraction, assumed to be carbon neutral, reduced the GWP. However, a greater GWP reduction could be obtained through reduced FT pressure requirements, increased gas reaction rates, or a less carbon intensive power mix.

Coal Char Gasification in the Mixture of H2O, CO2, H2, and CO under Pressured Conditions

The kinetic study of coal char gasification at elevated pressure is very limited and much less than that at atmospheric pressure, especially in the mixture of H2O, CO2, H2, and CO. The inhibition effect of H2 and CO and a suitable reaction model are both needed to be studied under pressured conditions. A Langmuir–Hinshelwood (L-H) type model has been widely adopted to describe coal char gasification at atmospheric pressure. But its applicability to pressured conditions is questionable. In this paper, the experiments of coal char gasification in the mixture of H2O, CO2, H2 and CO were carried out using a modified pressured thermogravimetric analyzer (PTGA) system at 0.5 MPa and within 1148–1198 K. Experimental results indicate that the gasification reaction rates of H2O and CO2 under pressured conditions are much higher than those at atmospheric pressure, and the inhibition effects of H2 and CO are also stronger. The kinetic parameters in L-H model were determined from pressured pure H2O and CO2 gasification (N2 as diluent). And the applicability of L-H model to pressured conditions was verified. It is shown that the L-H models based on common or separate active sites assumptions could not give satisfactory predictions to experimental data. Finally, we proposed a modified L-H model. This model only needs several extra experiments to calculate the modification factor, and can describe char gasification in the mixture of H2O, CO2, H2 and CO under pressured conditions very well.

Coal Chemical Looping Gasification for Syngas Generation Using an Iron-Based Oxygen Carrier

The chemical-looping gasification (CLG) of coal is a clean and effective technology for syngas generation. Sharing principles with chemical-looping combustion (CLC), CLG also uses oxygen carriers to transfer lattice oxygen to the fuel. Investigations into CLG with different O/C ratios are carried out in a fluidized bed reactor with steam used as the gasification–fluidization medium. The effect of the active component content of the oxygen carrier on the gas selectivity is performed, and reaction mechanisms between the Fe2O3 oxygen carrier and coal with steam as the gasification agent are discussed. Moreover, we also assessed the reactivity of the CaO-decorated iron-based oxygen carrier particles in multicycle reactions. The carbon conversion efficiency is increased from 55.74 to 81% with increasing O/C ratio, whereas the content of H2 first decreases and then increases. The addition of CaO can increase the carbon conversion efficiency and the gasification rate substantially and reduce the generation rate of H2S from 1.89 × 10–3 to 0.156 × 10–3 min–1. Furthermore, X-ray diffraction (XRD) images indicate that the CaO-decorated iron-based oxygen carrier particles were completely regenerated after six redox cycles. Finally, the peak fitting of gasification reaction rate curves is used to explore the reaction mechanism between coal char and the CaO-decorated iron-based oxygen carrier, indicating that the reactions in the CLG include three stages: the complex reactions involved an oxygen carrier, coal char, and steam; the gasification of coal char; and the reduction of Fe3O4 to FeO. The two-segment modified random pore model (MRPM) fits the experiment data well.

The Effects of Slag Compositions on the Coal Gasification Reaction in Molten Blast Furnace Slag

The char-CO2 gasification reactions in molten blast furnace slag were studied kinetically by the isothermal thermogravimetry using STA409PC thermal analyzer. The effects of slag compositions (SiO2, MgO, CaO, and Al2O3) on gasification reaction were investigated. The results showed that CaO has certain catalytic effects on gasification reaction; however, when the gasification reaction temperature reached a certain value, the catalytic effect of CaO on gasification could be neglected. MgO also played a catalytic role in the gasification reaction. In this experiment, the gasification reaction rate increased with increasing the MgO content from 8 to 10 mass%, whereas it decreased with increasing the MgO content from 10 to 12 mass%. SiO2 had no catalytic effect on gasification reaction.

Effect of supercritical water on the stability and activity of alkaline carbonate catalysts in coal gasification

The stability and activity of alkaline carbonate catalysts in supercritical water coal gasification has been investigated using density functional theory method. Our calculations present that the adsorption of Na2CO3 on coal are more stable than that of K2CO3, but the stability of Na2CO3 is strongly reduced as the cluster gets larger. In supercritical water system, the dispersion and stability of Na2CO3 catalyst on coal support is strongly improved. During coal gasification process, Na2CO3 transforms with supercritical water into NaOH and NaHCO3, which is beneficial for hydrogen production. The transformation process has been studied via thermodynamics and kinetics ways. The selectively catalytic mechanism of NaOH and the intermediate form of sodium-based catalyst in water-gas shift reaction for higher hydrogen production has also been investigated. Furthermore, NaOH can transform back to Na2CO3 after catalyzing the water-gas shift reaction. Thus, the cooperative effects between supercritical water and Na2CO3 catalyst form a benignant circle which greatly enhances the reaction rate of coal gasification and promotes the production of hydrogen.

The effect of supercritical water on coal pyrolysis and hydrogen production: A combined ReaxFF and DFT study

The reaction mechanism of coal pyrolysis and hydrogen production in supercritical water (SCW) was investigated using the molecular dynamic simulations via the reactive force field (ReaxFF) method combined with the density functional theory (DFT) method. Our calculations present that the water clusters in SCW weaken the C–C bonds in aromatic rings, thus the C(ring)–C(ring) bond cracking energy decreases as much as 287.3kJ/mol and 94.6kJ/mol compared with that in pure coal pyrolysis and in coal pyrolysis in vapor state, respectively. After the aromatic rings break into small cyclic structures, such as quaternary rings and ternary rings, the water clusters in SCW further weaken their C–C ring bonds to induce the small cyclic rings to open. During this process, the water clusters (without any radicals) in SCW turn into H radical-rich water clusters after providing OH radicals to the cyclic rings. This is the main source for the production of hydrogen molecules in SCW–coal system. The combination of H radicals produced by coal with water clusters in SCW is another pathway which forms H radical-rich water clusters. Under the catalysis of water molecules or clusters, H radical-rich water clusters decompose into H2 and OH radicals. These OH radicals further bind with coal intermediates and result in the breaking of coal intermediates into smaller products. Therefore, the cooperative effects between SCW and coal form a virtuous circle, which greatly enhances the reaction rate of coal gasification, promotes the production of small molecules, and increases the yield of hydrogen.

Development of a Kinetic Model for Industrial Entrained Flow Coal Gasifiers

The characteristics of the industrial Texaco entrained flow coal gasifier are numerically studied in this paper. A kinetic model is proposed by dividing the gasifier into two zones to obtain the temperature and product concentration distribution along the reactor. These two zones are the pyrolysis–combustion zone and the reduction zone. The pyrolysis–combustion zone is modeled using the stoichiometry method. A detailed investigation was carried out on the gasification reaction rates in the reduction zone. The particle swarm optimization technique is introduced in this paper to address the lack of heterogeneous reaction kinetic parameters based on the random pore model for the specific feed Shenfu coal, and the huge deviation of the industrial product gas composition from the theoretical composition at equilibrium state. With the evaluated optimum kinetic parameters, robust agreement is achieved between the model outputs and the industrial data. Moreover, a sensitivity analysis related to the O2-to-coal ratio and coal slurry concentration was carried out in light of the proposed model.

Reduction Behavior of Panzhihua Titanomagnetite Concentrates with Coal

The reduction behavior of the Panzhihua titanomagnetite concentrates (PTC) briquette with coal was investigated by temperature-programmed heating under argon atmosphere in a vertical tube electric furnace. The mass loss behavior of the PTC-coal mixture was checked by thermogravimetric analysis method in argon with a heating rate of 5 K (5 °C)/ min. It was found that there are five stages during the carbothermic reduction process of the PTC. The devolatilization of coal occurred in the first stage, and reductions of iron oxides mainly occurred in the second and third stages. The reduction rate of iron oxide in the third stage was much higher than that in the second stage because of the significant rate of carbon gasification reaction. The iron in the ilmenite was reduced in the fourth stage. In the final stage, the rutile was partially reduced to lower valence oxides. The phase transformation of the briquette reduced at different temperatures was investigated by X-ray diffraction (XRD). The main phases of sample reduced at 1173 K (900 °C) are metallic iron, ilmenite (FeTiO3), and titanomagnetite (Fe3–x Ti x O4). The traces of rutile (TiO2) were observed at 1273 K (1000 °C). The iron carbide (Fe3C) and ferrous-pseudobrookite (FeTi2O5) appeared at 1473 K (1200 °C). The titanium carbide was found in the sample reduced at 1623 K (1350 °C). The shrinkages of reduced briquettes, which increased with increase in the temperature, were found to depend greatly on the temperature. With increasing the reduction temperature to 1573 K (1300 °C), the iron nuggets were observed outside of the samples reduced. The nugget formation can indicate a new process of ironmaking with titanomagnetite similar to ITmk3 (Ironmaking Technology Mark 3).

Experiment Research on Gasification Character of Pulve-rized Coal at Medium Temperature

In this paper, effect of gasification temperature and residence time on gasification characteristics of typical pulverized coals under atmosphere pressure were studied on a one-dimensional electric heating drop tube furnace system to evaluate gasification characteristics of pulverized coal at medium temperature. The results show that the gasification rate increases with the raising of the gasification temperature under the temperature among 1150℃and1450℃, and as the temperature is above1350℃, the increasing rate become slower. Cold gas efficiency and carbon conversion meet the maximum value when the temperature approaches the ash fusion point of coal. With the further rise of the temperature, ash on the surface of the char starts to be melted, the gasification reaction rate decreases, due to the hindrance of the effective contact between coal char and gasification agent. The gasification efficiency would become steady when the residence time exceeds 8s.

저급 석탄과 혼합한 폐촉매의 수증기 가스화 반응에 미치는 영향

We have investigated the kinetics and activity of waste catalysts for steam-lignite gasification. Waste catalysts I, II, III and reference <TEX>$K_2CO_3$</TEX> were used and physical mixed with a coal. The gasification experiments were carried out with the low rank coal loaded with 1 wt% and 5 wt% catalyst at the temperature range from 700 to <TEX>$900^{\circ}C$</TEX> using thermobalance reactor. It was observed that the carbon conversion reached almost 100% regardless of the kinds of catalysts at <TEX>$900^{\circ}C$</TEX>. The shortest time to reach the designated conversion was obtained for 1 wt% waste catalyst II and 5 wt% <TEX>$K_2CO_3$</TEX> at <TEX>$900^{\circ}C$</TEX>. The gasification reaction rate constant increased with increasing the temperature. Highest rate constant was obtained with <TEX>$K_2CO_3$</TEX> at <TEX>$900^{\circ}C$</TEX>. The lowest activation energy was 69.42 kJ/mol for 5 wt% waste catalyst II. The waste catalyst had an influence on the reduction of activation energy.

Steady-state nonequilibrium temperature gradients in hydrogen gas–metal systems: challenging the second law of thermodynamics

Differences in gas reaction rates between disparate surfaces have been proposed as a means to achieve steady-state pressure and temperature gradients within a single blackbody cavity, thereby challenging the second law of thermodynamics (Sheehan 1998 Phys. Rev. E 57 6660; Sheehan 2001 Phys. Lett. A 280 185; Capek and Sheehan 2005 Challenges to the Second Law of Thermodynamics (Theory and Experiment) (Fundamental Theories of Physics Series vol 146) (Dordrecht: Springer)). This paper reports on laboratory tests of this hypothesis; specifically, molecular hydrogen is found to dissociate preferentially on rhenium surfaces versus tungsten at identical elevated temperatures and reduced pressures (T ⩽ 2100 K; ). Steady-state nonequilibrium H/H2 ratios over the surfaces suggest that temperature gradients could be maintained under blackbody cavity conditions. Preliminary results from bimetallic blackbody cavity experiments are discussed.

Carbon conversion predictor for fluidized bed gasification of biomass fuels—from TGA measurements to char gasification particle model

When a solid fuel particle is injected into a hot fluidized bed, the reactivity of fuel char in gasification reactions (between char carbon and steam and CO2) plays a significant role for reaching a good carbon conversion. In this paper, the gasification reactivity data of some solid waste recovered fuels (SRF) obtained from thermogravimetric analysis (TGA) experiments is presented. Gas mixtures (H2O, H2, CO2, CO), were used in the experiments to find the inhibitive effects of CO and H2. Average char gasification reactivity values are determined from the TGA results. Kinetic parameters for char carbon gasification reactivity correlations are determined from this data. The Uniform Conversion model is used to account for the change of gasification reaction rate as function of carbon conversion. Some discrepancies, due to complicated ash–carbon interactions, are subjects of further research. In the carbon conversion predictor, laboratory measured reactivity numbers are converted into carbon conversion numbers in a real-scale fluidized bed gasifier. The predictor is a relatively simple and transparent tool for the comparison of the gasification reactivity of different fuels in fluidized bed gasification. The residence times for solid fuels in fluidized bed gasifiers are simulated. Simulations against some pilot-scale results show reasonable agreement.

Prompt considerations on the design of Chemical-Looping Combustion of coal from experimental tests

The Chemical-Looping Combustion of coal in the reactor system has been proposed as an interesting option to process a solid fuel in a CLC system. In this process, a solid fuel is directly fed to the fuel reactor in a CLC system. Solid fuel pyrolysis, char gasification and oxidation of gaseous products by reaction with the oxygen-carrier are the main chemical processes happening in the fuel reactor. The aim of this study is to analyze the performance of ilmenite as oxygen-carrier for CLC of coal regarding to the conversion of gaseous products from char gasification. Successive reduction–oxidation cycles were carried out in a fluidized bed using bituminous coal char as reducing agent. The changes on chemical and physical properties of ilmenite particles were determined. An activation process of ilmenite through the redox cycles was evidenced which was justified by an increase of porosity. The results showed that the activation for ilmenite reduction reaction was completed after seven redox cycles. However, the oxidation reaction rate was increasing still after 16 redox cycles because the porosity was not fully developed. The gasification reaction rate and the ilmenite reactivity were analyzed. The effect of ilmenite itself and the influence of the gasification agent, i.e. H2O, CO2 or H2O/CO2 mixtures, and temperature on the gasification rate were evaluated. Limited use of CO2 in the fluidizing gas was identified in order to maintain high gasification rates. Higher temperature improved the char gasification rate, mainly using steam as gasification agent, and the combustion efficiency of the gasification products. Nevertheless, the effect of temperature on the combustion efficiency was of lower relevance than that on the gasification rate. Finally, a theoretical approach was developed to easily evaluate the conversion of char in the fuel-reactor by gasification.

Beneficiation of High Phosphorus Limonite Ore by Sodium-carbonate-added Carbothermic Reduction

The characteristics of Huimin high phosphorus limonite ore and the beneficiation of this iron ore by sodium-carbonate-added carbothermic reduction, ultrafine grinding and magnetic separation were investigated. Iron particle size in reduced ore without Na2CO3 additive is tiny and the fayalite is abundant. It is indicated that the formation of fayalite is the main hindrance to accelerate the reduction of limonite. With a mass ratio of Na2O3 to ore of 10% additive, the reduction of limonite can be reinforced. The reinforcing affect may be caused by the increase of the reducing reaction activity of FeO and the acceleration of the carbon gasification reaction rate. Fluorapatite were not reduced in the low temperature reduction process and entered to gangue phases, after ultrafine grinding-magnetic separation process, a qualified iron concentrate with 76.47% Fe, a recovery of 73.20% is obtained with simultaneous decrease in the phosphorus content down to 0.25%.

Modeling of coal char gasification in coexistence of CO2 and H2O considering sharing of active sites

In a coal gasifier, CO2 gasification and H2O gasification occur at the same time. Many researchers have constructed CO2 gasification model and H2O gasification model separately. Only a few models explain the competition between CO2 gasification and H2O gasification. These models are divided into two types according to the properties of the active sites. Some models assume that CO2 gasification and H2O gasification occur at separate active sites, whereas others assume that all of the active sites are shared and are common to both CO2 and H2O gasification. There are some coals whose gasification reaction rates, with CO2 and H2O in coexistence, cannot be described by the conventional models. In this study, a Langmuir–Hinshelwood type gasification model was modified to explain the char gasification by CO2 and H2O. In the proposed model, CO2 gasification and H2O gasification partially share active sites. Coal chars, which were prepared through pyrolysis using a drop tube furnace at ambient pressure and 1673K, were gasified with CO2 and H2O using a pressurized drop tube furnace (PDTF) and a thermogravimetric analyzer (TGA) at various temperatures. The proposed model was found to describe the gasification reaction rates of the experiments more accurately than the conventional models.

Adaptability of Coal Gasification in Molten Blast Furnace Slag on Coal Samples and Granularities

In this work, coal gasification in molten blast furnace (BF) slag was performed at atmospheric pressure in a molten bath reactor in the temperature range from 1573 to 1773 K. The effects of coal samples and coal granularities on the gasification reaction rate, carbon conversion, and gas composition were studied, and the kinetic mechanism function was calculated. The results show that the method using coal gasification to recover sensible heat of molten BF slag is possible and effective. The coal gasification using molten BF slag as a carrier has wide adaptability on coal granularities and coal samples. It is effective to gasify lean coal. In this study, the gasification reaction rate of Shennan (SN) coal that represents lean coals is high and almost equal to that of Datong (DT) and Fuxin (FX) coals. The carbon conversion of all types of coal can become 0.99. Under the action of molten slag, the tar and hydrocarbon decompose fully; the content of other hydrocarbons in synthesis gas is almost zero. The reaction rates using different coal granularities increase in the order of 0.177 < 0.125 < 0.147 mm, but the difference is little. The calorific capacity of synthesis gas under different conditions is almost equal and can become 10 000 kJ/m3. The mechanism functions are different before and after the carbon conversion rate of 0.5. The mechanism function is shown as follows:f(a)={3(1−a)[−ln(1−a)]2/3a≤0.52(1−a)[−ln(1−a)]1/2a>0.5