Char Particle Size Research Articles

Investigation on the interaction of NH3&CH4 co-activated char under reburning conditions

In the current global context, there is a pressing need to curtail greenhouse gas emissions, making the utilization of a coal and zero-carbon energy blend an imperative strategy for reducing carbon emissions from coal-fired power generation. The planar flame burner serves as a tool to simulate the temperature and atmospheric conditions within the reburning zone, facilitating extensive examination of the physical and chemical structural alterations, as well as the nitrogen oxide reduction potential, during NH3/CH4 activation for reburning pulverized coal. Experimental results underscore that blending high-activity fuels optimizes the combustion performance of coal char. Through the addition of NH3 and CH4, the NO reduction capability of coal char is bolstered by approximately 0.67 times compared to sole reliance on recirculating flue gas transport. Furthermore, NH3 introduction facilitates the conversion of C]O double bonds into C–O single bonds, rendering them more amenable to reduction by NO. While the joint influence of NH3 and CH4 does not significantly impact char particle size, it does foster the evolution of N-Q to N-5 and N-6 on the char surface. Furthermore, there was a significant increase in the BET-specific surface area, which rose by 50%. Additionally, the total pore volume increased by approximately 21.43%. The comprehensive understanding of NH3 and CH4 modified pulverized coal reburning technology holds significant promise for optimizing power plant operations and mitigating carbon dioxide and nitrogen oxide emissions.

Novel coal char-based cement grout: An experimental study on geotechnical and rheological properties

Coal char, a light and porous coal byproduct, is conventionally used for combustion and gasification, which leads to high carbon dioxide and other air pollutants emissions. In this study, the feasibility of using coal char in cement grout is evaluated. The coal char pyrolyzed at 850 °C is produced from Powder River Basin coal in Wyoming. Effects of char contents (up to 50%) and particle sizes (<300 μm and 300–850 μm) on geotechnical and rheological properties of char-cement grouts are comprehensively investigated. Compared to cement grout, the compressive strength of char-cement grout is 16% higher, and the final setting time is 55% shorter. The addition of coal char effectively reduces the bleeding in grouts without leading to a significant increase in Marsh viscosity. In general, coal char can provide many advantages towards improving engineering performance and broadening application of conventional cement grout.

A percolation model of fly ash formation during the combustion of non-uniform porous char

An improved percolation model has been introduced to predict the particle size distributions (PSDs) of produced residue during pulverized coal char combustion. A three-dimensional cluster of interconnected sites representing a single char particle is constructed at a given size. These sites are classified into surrounding gas, macropores, carbon, or ash. Non-uniform porous char structures and the melting performances of the ash particle have been considered to approach the most realistic scenario. The char fragmentation and ash coalescence process is simulated by checking the connectivity and proximity of occupied sites. The effects of char particle sizes are addressed by using char PSD data as the input to the model. The numerical results were compared with the measured PSDs of fly ash and show a good agreement. The effects of porous char structure and included minerals on the sizes of produced particles during combustion are further investigated. The simulation results indicate that the mean sizes of produced particles initially decrease (N<0.7) and then increase with char consumption. The char fragmentation behavior dominates in the preliminary and middle stages of char burning, while the ash coalescence is the primary behavior in the char burnout stage. The mean sizes of produced particles increase with the lower char porosity and the higher extent of pore aggregation. The size difference between PM20 and PM20+ increases when the macropores are repositioned to be aggregated. The mean sizes are positively related to the ash content and ash coalescence parameter in the middle and late stages of char burning.

The competition/inhibition effect of H2O/CO2-char gasification in typical in situ gasification-chemical looping combustion (iG-CLC) conditions via particle-resolved simulation

In the fuel reactor of in-situ gasification chemical looping combustion (iG-CLC), the solid fuel (e.g., coal, biomass) goes through two typical processes: devolatilization and char gasification. Then the pyrolysis and gasification products react with oxygen carrier to produce CO2 and H2O ideally. The slow char gasification rate during iG-CLC is responsible for combustion efficiency. Therefore, a deeper understanding of char conversion characteristics is required to optimize iG-CLC conditions. In this paper, a particle-resolved simulation with detailed heterogeneous reactions is conducted, in which the effects of char particle size and reaction temperature on char conversion characteristics are carefully studied. To understand the competition between CO2 gasification and H2O gasification, single-particle simulations are carried out under mixed and separate atmospheres. The char gasification rate in CO2/H2O mixtures (rmix) is lower than the sum of the char-H2O gasification rate (rH2O) and the char-CO2 gasification rate (rCO2). We find that the competition for active sites between char-H2O gasification and char-CO2 gasification is not significant, while the inhibition of gasification products play an important role in char-CO2 gasification, particularly the inhibition of CO (from char-H2O or char-CO2 gasification), due to the accumulation of H2 and CO inside the char particle. The inhibition effect is quantified via particle-resolved simulations and then a quantitative formula is attained to describe the complex relationship between H2O gasification and CO2 gasification. Then the point-source model for H2O/CO2-char gasification is developed for computational fluid dynamics simulations. Straightforward cloud diagrams are presented to explore the relationship between conversion rate characteristics and physicochemical properties of char, providing useful information for the optimization of iG-CLC conditions.

Comparison of oxy-fuel preheated combustion characteristics of high- and low- volatility carbon-based fuels

A comparative evaluation and analysis study of combustion characteristics, main pollutant emission behaviors, and fuel-N conversion paths of high- and low- volatility carbon-based fuels are conducted under O2/CO2 atmospheres in a preheating combustion reactor, i.e., CFB. Compared with conventional air combustion, the oxy combustion with high oxygen concentrations from 21% to 27.3% is studied. The studies show that the net calorific value of the preheated coal gas of semi-coke in O2/CO2 is up to 2 times that in air, and the net calorific value of the preheated coal gas of bituminous coal in O2/CO2 is up to 1.3 times that in air. During the preheating process of semi-coke, CH4 and HCN occupy a discreet proportions of preheating coal gas. Fuel characteristics and preheating atmosphere have no effect on the particle size of preheated coal char. Under an O2/CO2 atmosphere, the highest BET surface area of preheated coal char of bituminous coal is up to 30 times that of raw coal and that of semi-coke is up to 40 times that of raw coal. The carbon structure modification ratio of preheated coal char during the preheating process of bituminous coal is larger than that during the preheating process of semi-coke. With the increase in the concentration of oxygen in the primary stream, the NO emission decreased during the bituminous coal combustion process but increased during the semi-coke combustion process. In addition, the main generation path of NO in the reduction zone in O2/CO2 is NH3-NH2-NH-HNO-NO. In O2/CO2, the total promotion effect of reactions on NO formation in the combustion process of semi-coke preheated fuel is larger than that of bituminous coal.

Experimental study on effects of multistage reactant and air jet velocities on self-preheating characteristics and NOx emission of burning pulverized coal

To explore the NOx control strategies deeply, this study investigated the effects of multistage reactant and air jet velocities, including preheated fuel jet velocity (vpf), ratio of internal secondary air jet velocity to external secondary air jet velocity (R12) and ratio of first-staged tertiary air jet velocity to second-staged tertiary air jet velocity (M12), on combustion characteristics and NOx emission of pulverized coal on a 30 kW self-preheating combustion test rig. During preheating, as vpf increased, the temperature at different locations increased. And the concentrations of the main combustible gases (CO and H2) in the coal gas and the conversion rate of each component in the pulverized coal increased first and then decreased at the outlet. Moreover, vpf also influenced the particle characteristics greatly. The particle size of preheated coal char decreased first and then increased, while its specific surface area and reacting activity increased first and then decreased. The good self-preheating characteristics had a positive impact on the subsequent combustion and NOx emission. During combustion, vpf, R12 and M12 had different effects on the temperature distribution in the down-fired combustor (DFC). Under different vpf, the temperature distribution was relatively complex, and it was mainly regulated by the self-preheating characteristics, combustion share and jet velocity of the preheated fuel. As R12 increased, the temperature increased gradually in the upper part of the DFC, meaning the upper combustion was promoted. M12 mainly affected the position of the main combustion region, which shifted down as M12 increased. Moreover, increasing M12 could also reinforce the combustion in the main combustion region. vpf, R12 and M12 also influenced combustion efficiency and NOx emission obviously with certain change regularities. As vpf and R12 increased, the combustion efficiency increased first and then decreased, while NOx emission decreased first and then increased. As M12 increased, the combustion efficiency decreased first and then increased, while NOx emission increased first and then decreased. Moreover, compared to lower M12, it was more favorable to improve the combustion when M12 was higher.

Porous Carbons Derived from Desiliconized Rice Husk Char and Their Applications as an Adsorbent in Multivalent Ions Recycling for Spent Battery

Recycling of spent lithium-ion batteries (LIBs) has attracted increasing attentions recently on account of continuous growth demand for corresponding critical metals/materials and environmental requirement of solid waste disposal. In this work, rice husk as one of the most abundant renewable fuel materials in the world was used to prepare rice husk char (RC) and applied to recycle multivalent ions in waste water from hydrometallurgical technology dispose of spent LIBs. Rice husk char with specific surface area and abundant pores was obtained via pickling and desilication process (DPRC). The structural characterization of the obtained rice husk char and its adsorption capacity for multivalent ions in recycled batteries were studied. XRD, TEM, SEM, Raman, and BET were used for the characterization of the raw and the modified samples. The results show rice husk chars after desilication has more flourishing pore structure and larger pore size about 50–60 nm. Meanwhile, after desilication, the particle size of rice husk char decreased to 31.392 μm, and the specific surface area is about 402.10 m2/g. Its nitrogen adsorption desorption curve (BET) conforms to the type IV adsorption isotherm with H3 hysteresis ring, indicating that the prepared rice husk char is a mesoporous material. And the adsorption capacity of optimized DPRC for Ni, Co, and Mn ions is 7.00 mg/g, 4.84 mg/g, and 2.67 mg/g, respectively. It also demonstrated a good fit in the Freundlich model for DPRC-600°C, and a possible adsorption mechanism is proposed. The study indicates biochar materials have great potential as an adsorbent to recover multivalent ions from spent batteries.

Experimental and modeling investigation on char combustion and char-nitrogen evolution characteristics under different conditions

The proper description of char combustion and char-nitrogen (char-N) evolution characteristics are imperative to analyze the operating performance of decoupling combustion systems. The char-O2 combustion and char-CO2 gasification reactivity of three typical coal chars, including lignite, bituminous, and anthracite, was tested in a lab-scale fixed-bed reactor in the temperature range of 1023 K–1223 K. The relevant chemical kinetic parameters were determined by applying a one-dimensional packed-bed reactor model embedded with a lumped particle model. Meanwhile, a 1-dimensional spherical particle model is necessary for describing the char-N conversion behaviors. Experimental results show that the conversion rate of char-N in the entire bed to NO (XNO, bed) gradually decreases with increasing temperature, and the decrease of coal rank leads to a decline in the NOx emission. Further simulation results indicate that for a single char particle in the initial combustion stage, if the char particle size increases (0–1000 μm), the external gas mass transfer coefficient decreases (0–5 m·s−1), or the oxygen content decreases (0–20%), the char-N conversion to NO (XNO, p) will gradually decrease. However, due to the complicated effects of temperature on multiple factors, involving reactivity, CO/CO2 ratio in products, and dual nature of CO influence on char-NO reaction, the relationship between char-N conversion and temperature for a single particle is not fixed. When the oxygen concentration is low, the XNO, p increases as temperature rising; while, an opposite trend may be formed under high oxygen conditions.

Whey as a sustainable binder for the production of extruded activated carbon

Whey, the main by-product of the dairy industry, is proposed as a sustainable binder for the production of extruded activated carbon. Coconut shell char was mixed with controlled quantities of either rehydrated whey powders or partially dehydrated liquid whey. After extrusion, extrudates were dried, and carbonised or activated under N2 or CO2 atmosphere, respectively. A comprehensive study of the effect of different parameters including binder proportion, coconut shell char particle size and carbonisation temperature was carried out. The composition of whey prompted Maillard reactions boosted with temperature that conferred a resin-like behaviour to the binder. Quality parameters of the resulting extrudates were their ball-mill hardness, real and bulk densities. All whey-bound pellets retained their original shape after the high temperature treatment. The hardness of those whey extrudates was particularly remarkable considering the biomass origin of this binder. The carbonisation temperature had little effect in the hardness or densities of the carbon pellets. The best pellet formulation comprised the use of coconut shell char powders with particle sizes < 212 µm, in mixtures having a 7/3 char/dry whey mass ratio. The properties of the pellets obtained after the activation of such pellets were comparable to those of commercial activated carbon extrudates. The use of partially dehydrated liquid whey rather than re-hydrated dry whey rendered very similar results. The alkalinity of the binder made the resulting activated carbons adequate for H2S removal at room temperature. An economic estimation of the process placed whey in a practical position within the binder market.

Numerical simulation of gasification of a shrinking char particle in supercritical water

The technology of supercritical water gasification provides a promising way for clean and efficient utilization of coal for hydrogen production. Char conversion is the rate-determining step of the gasification process, and the development of char particle size and shape directly affects the drag force, heat transfer and particle conversion characteristics in a supercritical water gasifier. Thus, a 2D transient CFD-based model was developed in this work to describe the conversion of a shrinking char particle in supercritical water, and the dynamic mesh method was used for particle surface tracking. 0.1 and 1 mm sized char particles were gasified at 873 to 1023 K, and the char conversion was obviously restrained by heat and mass transfer with the increase of particle size and temperature. The effect of convection was then studied with Reynolds number varying from 0 to 200. Convection effectively promoted the char conversion by enhancing the heat and mass transfer, and meanwhile, irregular development of particle shape was caused by the uneven temperature and supercritical water distribution on the particle surface. Owing to the special high concentration of supercritical water which ensured relative uniform distribution of supercritical water all the time, the irregular shape development was not obvious even at high Reynolds number. Moreover, the wake vortex formed at high Reynolds number promoted the fluid mixing, and an inflection point with the minimum carbon consumption rate appeared on the downstream side.

Gasification Kinetics of Victorian Brown Coal-Derived Char in Fluidized Bed Reactor

Abstract In a chemical looping combustion (CLC) system, gasification kinetics of char holds immense importance being the rate-limiting reaction in the fuel reactor. This paper studied the gasification kinetics of char derived from Victorian brown coal (VBC) in a fluidized bed reactor which mimics the fuel reactor conditions of a chemical looping combustion process. Mass of char, char particle size, and gas flow conditions were optimized to ensure the gasification reaction free from mass transfer limitations. Effect of oxygen carrier (OC), hematite, being the bed material was also studied. The experiments were conducted in the temperature range of 800 °C–950 °C, which is a typical range for fuel reactor. The experimental results were modeled with the help of grain model (GM) and random pore model (RPM) to analyze the kinetic parameters. Activation energy was found to be around 177 kJ/mol in sand bed and 175.5 kJ/mol in the hematite bed. Reaction in hematite bed was found to be 42% faster on average compared with the reaction in a sand bed. Fastest total conversion of char took as low as 4.1 min in hematite bed at 950 °C. While catalytic effect of hematite was ruled out due to insignificant change in activation energy, it was concluded that increase in CO2 partial pressure at the vicinity of char particle enhanced the reaction rate in the case of hematite bed. This study has generated relevant information for the CLC of Victorian brown coal with hematite as the oxygen carrier.

Modeling and experimental approaches for determining fluoride diffusion kinetics in bone char sorbent and prediction of packed-bed groundwater defluoridator performance

Fluoride (F) in groundwater (GW) in excess of 1.5 mg/L is a globally distributed problem impacting the health of hundreds of millions of people, many of whom cannot access centralized treatment infrastructure. Animal (e.g., cow) bone char has received emerging interest as a low-cost F sorbent for use in decentralized household and community water treatment. Pilot column tests using full-sized granular bone char particles can be used to assess treatment performance of fixed-bed contactors, but are costly, time consuming, and require large amounts of test water. Rapid small-scale column tests (RSSCTs) can be used to simulate F uptake in bone char contactors if the relationship between F intraparticle diffusion kinetics and bone char particle size is known. Two common approaches to the RSSCT assume either constant (CD) or linear proportional (PD) sorbate diffusivity as a function of sorbent particle size. This study used experimentally determined pseudo-equilibrium and kinetic F sorption data in model groundwater as inputs to the homogeneous surface diffusion model (HSDM) to determine F intraparticle diffusion coefficients for different-sized bone char particles, and to fit RSSCT and pilot column breakthrough data to evaluate CD and PD approaches. Results of this study, corroborated by incorporation of additional literature data, indicate approximately linearly proportional diffusivity of F as a function of bone char particle size. Congruently, the PD-RSSCT approach provided a superior simulation of pilot column F breakthrough compared to the CD-RSSCT. PD-RSSCT breakthrough data closely matched pilot breakthrough on a scaled service time basis up to around 500 bed volumes, corresponding to a relative F breakthrough of about 40%, and provided a slightly conservative indicator of F removal thereafter. The PD-RSSCT was compared with a hybrid modeling and empirical workflow using the HSDM with experimentally determined pseudo-equilibrium and kinetic parameter inputs as time-and-cost-saving approaches to evaluating full-sized groundwater treatment system performance. This comparison and a sensitivity analysis of HSDM input parameters used in the hybrid workflow indicated that greater precision can be obtained using the PD-RSSCT.

Reaction kinetics of coal char in oxy-fuel combustion environment and characterization of reacted char

ABSTRACT The work primarily focuses on combustion kinetics of devolatilized coal char fines (75–120 µm), including the estimation of kinetic parameters and char morphological transformation in oxy-fuel environment (O2-CO2 and O2-N2). Experimental work has been carried out to study the effect of higher CO2 concentration and elevated O2 concentrations on the ignition, burnout behavior of pulverized coal char both non-isothermally and isothermally. The coal chars obtained from pyrolyzing three different types of coal are used in experiments; a high ash (HA) coal, a medium ash (MA) coal, and a low ash (LA) coal. Three different kinetic models, namely VM, GM and RPM, have been employed to determine the kinetic parameters. The kinetic parameters are observed to be a strong function of oxygen concentration for all the three models. The estimated activation energy employing non-isothermal analysis for LA coal char using VM lies in the range of 203–212 kJ/mol. In comparison, the activation energy predicted by GM for HA coal char lies in the range 137–144 kJ/mol. Moreover, the activation energy estimated for MA coal char by RPM varies in the range of 134–142 kJ/mol. It is also explored during the non-isothermal analysis that an increase in char particle size from 75–120 µm to 250–300 µm shows a small increase in the values of apparent activation energy and pre-exponential factor. The activation energy values calculated employing the isothermal method are 106–126 kJ mol−1 (using RPM) for coal char MA and 96–135 kJ mol−1 (using GM) for coal char HA. Both the isothermal and non-isothermal kinetic analysis reveals that the combustion of coal char LA follows VM while coal char MA and HA follows RPM and GM in order. SEM images and BET surface area analysis for partially converted coal chars are further analyzed to justify the suitability of different reaction mechanism followed by various coal chars.

Pore structure of wastewater sludge chars and their water retention impacts in different soils

Feasibility of pyrolysing wastewater sludge for char and energy production is dependent on the usability of the produced sludge char. This study aimed to produce mechanistic information of char impacts on amended porous media by determining (1) pore structure of sludge chars with 3D image analyses and (2) their influence on water retention and shrinkage properties of three contrasting soils. The pore structure of the chars consisted of crevices and large spheres. Their water retention impacts were minor, even though the low-porous char slightly increased porosity in the amended materials in various pore-size ranges. The dominating, though small, impacts were the increase in easily drainable interpores and decrease in smallest pore sizes relevant for plant available water. The char impacts were more visible in fine-than coarse-textured soils. The chars also significantly reduced shrinkage in clay soils. The results were insensitive to sludge feedstock or char particle size. • 3D imaging showed how sludge char pore space consisted of crevices and large spheres. • Dominating pore sizes were ≤50 μm, but their water retention impacts were minor. • Mechanistic analysis showed how interpore impacts on porosity dominated. • The char water retention impacts were clearer in fine-than coarse-textured media. • Variability in production process and particle size had a low impact on the results.

Experimental study on gasification of oil sludge with steam and its char characteristic

Hydrogen can be prepared by oil sludge (OS) gasification with steam, which is of great significance for industrial hazardous waste treatment and resource conservation. The gasification performance was studied by a tube furnace reactor. The OS gasification was carried out at different temperatures (600, 700, 800 and 900 °C) and with different steam to OS ratio (SOS) (0.1:1, 0.3:1, 0.5:1). During the gasification process, hydrogen production first increased and then decreased, and hydrogen production was faster in 5–15 min. The yield of hydrogen of OS gasification reached the maximum when the SOS was 0.3:1 at 800 °C. The highest hydrogen yield per unit mass OS was 48.50 mL min−1 g−1. After gasification, the char yield was high, generally more than 50%. It was necessary to treat the char and incineration was an effective solution for low carbon fuels. Thus particle size distribution, incineration thermogravimetric analysis and heavy metal leaching concentrations analysis were carried out. The results showed that the average particle size of char ranged from 85 to 120 µm. The char incineration process could be divided into three stages: water evaporation, the precipitation and combustion of volatiles, and the combustion of fixed carbon and heavy components. After OS gasification at 800 °C, the leaching concentrations of typical heavy metals (As, Cr, Cu, Ni, Pb and Zn) were all up to the standard. Therefore, OS gasification combined with char incineration was an effective approach for the utilization of solid waste, which can recover hydrogen energy and reduce environmental risks.

Gasification kinetic modelling of Victorian brown coal chars and validity for entrained flow gasification in CO2

The gasification kinetic modelling of two Victorian brown coal (Yallourn and Maddingley) chars and the validity for entrained flow gasification were investigated in this study. The study was conducted in a thermogravimetric analyzer (TGA) at 750–1100 ℃, 30%–90% CO2 concentration using different char particle sizes within 20–106 µm. It was found that random pore model and modified volumetric model are applicable for TGA results, but volumetric model and grain model are not. The effect of particle size under 106 µm on gasification rate is very limited. Activation energies of Maddingley char and Yallourn char in CO2 gasification are 219–220 and 197–208 kJ/mol, respectively. The pre-exponential factors are in the same order of magnitude, and they increased as particle size decreased. A mathematical model was developed to predict carbon conversion over time for entrained flow gasification of Victorian brown coal chars at 1000–1400 ℃.

Identifying the contribution of rich-CO2/H2O gasification on the char conversion in typical atmospheres of chemical looping with oxygen uncoupling via single particle simulation

Char conversion is an important but also complicated step during the combustion of solid fuels (i.e. coal and biomass) in chemical looping with oxygen uncoupling (CLOU). Potentially, both the lean-O2 oxidation and rich-CO2/H2O gasification reactions of char contribute to the char conversion. However, the contribution degree of char gasification reaction has rarely been quantified in typical CLOU atmosphere. In this work, the single particle simulation is conducted to theoretically understand the effects of different operation conditions on the char conversion, and to identify the contribution degree of rich-CO2/H2O gasification in CLOU. A 10-step heterogeneous reaction mechanism is used for the gas-char reactions, and the random pore model is adopted to account for the evolution of porous char structure as well as its impact on reaction rates. The detailed conversion processes of chars with different sizes are simulated in various concentrations of gasification/oxidation agents and at different temperatures. The amounts of char consumed by lean-O2 combustion, rich-CO2 gasification, and rich-H2O gasification are assumed to be proportional to the amounts of surface adsorbed species generated by char reacting with O2, CO2, and H2O, and a formula to quantitatively calculate the relative contributions of the gasification reactions (both with CO2 and steam) is finally proposed. The results indicate that the gasification reactions (occurring in the inner core of the char particle) hardly influence the oxidation reaction (dominating the heterogeneous reaction in the external layer of the char particle) under CLOU conditions. The CO2-char gasification contributes less than 3% on the char conversion, while the contribution of H2O-char gasification can even reach 2–18%. The char-H2O gasification contributes more significantly (18% for 0.5 vol.% O2, and 2% for 4 vol.% O2) under the O2-deficient conditions. Generally, the overall contribution of gasification reactions on the char conversion is between 1 and 20% in CLOU, which depends on the reaction temperature, gas composition, and char particle size.

Numerical modeling of a batch fluidized-bed gasifier: Interaction of chemical reaction, particle morphology development and hydrodynamics

The present study aims to analyze the interaction of chemical reactions, particle morphology change and hydrodynamics in fluidized-bed gasifiers. The char gasification in a batch fluidized-bed gasifier was modeled. The two-fluid model approach was coupled with an extended version of the uniform conversion model accounting for inert ash fraction. Model assumptions were confirmed via measurement of char density, porosity and particle size distribution at different stages of conversion in a lab-scale fluidized-bed gasifier. The CFD model correctly predicts the effects of particle structure change on chemical reactions, approved by a first of its kind comprehensive validation against unsteady experiments. Based on the validated CFD model, the interaction of hydrodynamics and local particle density variations due to chemical reactions is analyzed, and the effect of the initial bed height is studied.

Catalytic coal gasification for methane production: A review

Catalytic coal gasification for methane production is a promising technology in the clean coal utilization field. In this review, the technologies for coal-derived natural gas production, the catalytic coal gasification processes and the used reactors were compared. The compared catalysts mainly included single-component, composite, and disposable catalysts. The effects of catalyst properties included composition, preparation method, supporter and loading amount were further illustrated. The influences of coal properties included char preparation method, particle size, and ash content on catalytic performance were investigated. The effects of temperatures and pressures on gasification performance were discussed in details. The evaporation, melting, decomposition, and inactivation of catalyst under various temperatures and pressures were also analyzed. It is expected to provide comprehensive information on the researches of catalytic coal gasification for methane production.

Characteristics of Preheating Combustion of Power Coal with High Coking Properties

Yankuang coal with the high coking property is difficult to use through direct combustion. The main purpose of this paper is to study the combustion characteristics and NOx emissions of this type of coal using preheating combustion technology. The experimental results show that after the pulverized coal is preheated, the char residue characteristic is significantly reduced from 5 to 1. During the preheating process, the preheating temperature is stable at about 910°C, and the particle size of char after preheating is reduced, and the pore structure and specific surface areas are increased. The combustion temperature of preheated fuel is stable at around 1100°C, and the combustion efficiency can reach more than 99% under different conditions. Changing the structure of the secondary air nozzles during the preheating combustion process can influence the characteristics of emissions. The NOx emission of the central nozzle is about 112 mg/Nm3 lower than that of the annular nozzle. Changing the tertiary air distribution modes can reduce the final NOx emissions to 215 mg/Nm3 (@6%O2), and the corresponding conversion ratio of fuel N to the final NOx is 4.2%. The results of this experiment prove that the Yankuang coal can achieve stable combustion by preheating combustion technology, and this proposed a new way for the utilization of Yankuang coal.