Release Of Volatile Matter Research Articles

탈휘발화 과정에서 혼탄의 반응률과 열적 거동에 관한 연구

본 연구 목적은 탈휘발화 과정에서의 역청탄과 아역청탄의 혼탄 열중량 곡선을 예측 하는 것이다. TSL (Thermal Shock Large) TGA를 통하여 실험을 수행 하였으며, 반응속도상수 분석은 Coats-redfern 방법을 이용하였다. 도출된 반응속도상수를 기반으로 단일탄의 Sum Method에 대한 일차적 검증을 하였으며, 혼탄시의 TG curve를 WSM(Weight Sum Method)와 저자가 제시한 MWSM (Modified Weight Sum Method)를 사용하여 예측 및 비교하였다. WSM 및 MWSM를 통한 예측결과와 TG curve 실험결과의 정량적인 비교를 위해 Linear least square method를 사용하였다. TG curve 상에서 서로 다른 기울기를 가지는 경우와 많은 휘발분의 방출로 인한 급격한 질량감소가 나타나는 구간의 경우 MWSM이 WSM 보다 실험결과에 더 정확한 결과를 예측함을 확인하였다. 탈휘발 과정에서의 혼탄의 열적 거동은 단일탄의 특성에서부터 예측할 수 있음을 확인할 수 있었다. The objective of this research is to predict the TG curve of blends of bituminous coal and sub-bituminous coal during devolatilization. TSL (Thermal Shock Large) TGA was used for Experiments, and Coats-redfern method was used for reaction order calculation. Based on reaction order, sum method was verified to be suitable for a single coal, then, prediction and comparison of TG curve of coal blends was conducted using both of WSM (Weight Sum Method) and MWSM (Modified Weight Sum Method), where the latter was developed in this research. The presented experiment results and WSM & MWSM were showed to be reasonable using linear least square method. MWSM performed more accurately than WSM for the case that TG curve had different slopes and the case that sharp weight loss happened due to release of volatile matter. The results showed that it's possible to predict the thermal behavior of coal blends during devolatilization based on the thermal behavior of single coals.

Surface physical properties and its effects on the wetting behaviors of respirable coal mine dust

In the present research work, coal dust physical properties as well as its wetting behaviors were analyzed systemically. The influences of different surfactants on coal dust's wetting behaviors were also investigated and compared with deionized water . Research results show that the finer the coal particle sizes, the more complex the coal particle micro structures are, which may cause the poor wetting abilities. Among the three different coal dust samples, the wetting performance is poor for the coal with higher volatile content due to the easier release of volatile matter and the easier formation of gas film around the particle. The fractal dimension and contact angles are presenting perfect correlations. With the increase of the fractal dimension, the contact angle would increase correspondingly, which indicates a poor wetting performance. The wetting behaviors of coal dust could be greatly improved by adding surfactant in the deionized water. However, the species of surfactant and its contents in the solvent are the two important factors for dust wetting abilities enhancement. For the two selected surfactants, sodium dodecyl sulfate (SDS) may be a better choice and 0.2% concentrations are recommended during coal dust suppression applications. Based on the experimental results, a wetting dynamic model was built to simulate coal dust wetting process. The calculated values agreed well with the experimental results. In the present paper, coal dust physical properties and its wetting behaviors were analyzed. The influences of different surfactants on coal dust’s wetting behaviors were investigated and compared with deionized water. The fractal dimension and contact angles were correlated with each other. Based on the experimental results, a wetting dynamic model was built to simulate coal dusts’ wetting process. ► Particle size and its micro structure have great effects on dust's wettability. ► Volatile content of coal is another important factor on its wetting behavior. ► The fractal dimension and contact angles are presenting perfect correlations. ► Using surfactants reasonably is important for dust wettability enhancement.

Effect of volatile matter release on optical properties of macerals from different rank coals

Ever since the recognition that macerals behave differently during the coking process, their thermal behaviour and its relationship with coke properties have become research topics of widespread interest. The present study is focused on the characterization of six bituminous coals of different rank from Upper Silesia (Poland) and their carbonized products obtained in a relatively high-capacity thermogravimeter under inert atmosphere and well-controlled heating conditions. A combined maceral–reflectance analysis was performed on samples carbonized at temperatures of 400, 450, 550, 750 and 1000°C. Under such conditions, only coals with a reflectance of over 1.0% passed through a fluid stage as a result of which the coal particles lost their integrity. The reflectance of all the macerals was observed to increase with the pyrolysis temperature, temperature being the most relevant factor in determining the reflectance of inertinite macerals. The amount of unreactive inertinite exhibited a wide range of variation, with the lowest rank coals showing the smallest proportion of unreactive inertinite. The reflectance cut-off values separating reactive and unreactive inertinite decreased with coal rank to a stable value of ca. 1.5% for the highest rank coal. A 67–75% volatile matter release was required to cause a significant increase in the reflectance of the components.

Gasification of biomass micron fuel with oxygen-enriched air: Thermogravimetric analysis and gasification in a cyclone furnace

The oxygen-enriched gasification of biomass micron fuel (BMF) was studied. Thermogravimetric analyses under different oxygen concentrations were performed to investigate the gasification behavior. The results showed that the increasing oxygen concentration enhanced the release of volatile matter and the combustion of fixed-carbon. The autothermal gasification of BMF using the oxygen-enriched air agent in a cyclone furnace was also studied. When the oxygen concentration increased from 21% to 31.4%, the gas yield increased from 72.14% to 81.41% and the lower heating value (LHV) of the produced gas increased to 6200 kJ/Nm3.

Emissions and performance from a biomass boiler for different solid biomass fuels

During biomass combustion, a number of physical and chemical processes occur in time and space during the combustion. The processes include: drying and preheating of the fuel, pyrolytic release of volatile matter, glowing combustion char, etc. In general the combustion of biomass produces, next to energy, ash, carbon dioxide and monoxide, unburnt hydrocarbons, oxides of nitrogen, particulate matter. This paper investigates characteristics of different biomass samples, such as the moisture, ash and fixed carbon content and the volatile matter. The paper tries to find a correlation for fuels from the North-West European region with their higher heating values. These correlations are compared to previous publications. Furthermore, the paper presents a performance and emissions evaluation for 40 kW biomass boiler. The results show that biomass is a valuable option for energy generation and the reduction of GHG gases.

Gasification reactivity of char with CO2 at elevated temperatures: the effect of heating rate during pyrolysis

ABSTRACTIntegrated coal gasification combined cycle (IGCC) technology is being promoted to make better use of energy resources, and an entrained‐flow gasifier is a key item of equipment in the process due to its high gasification efficiency, smooth discharge of molten ash, etc. The temperature and heating rate under entrained‐flow gasification conditions are very high, and these two parameters can influence the gasification reactivity of a char with CO2. Therefore, the clarification of characteristics and mechanisms of char gasification under conditions close to entrained‐flow gasification is very important. To obtain a valid kinetics of char gasification, it is necessary to clarify the effect of heating rate during pyrolysis on char reactivity. The effect of heating rate during pyrolysis on the gasification reactivity of three types of chars in CO2 was investigated experimentally at elevated temperatures in a novel fluidized bed. It was shown that even at elevated temperatures, the heating rate has significant influence on the char reactivity during gasification. A higher heating rate during pyrolysis leads to higher char reactivity of gasification, however it has only limited effect on the activation energy of char gasification with CO2. The char reactivity is closely related to its specific surface area and pore volume. The high reactivity of a char derived from pyrolysis at a high heating rate is most likely due to its enhanced porous structure as a result of the rapid release of volatile matter at a high heating rate. The effect of heating rate during pyrolysis on char reactivity is pronounced at low temperatures, and is very different for various coal types, i.e. very pronounced for a low‐rank coal. The gasification reactivity of a char is related to both the char pore structure and temperature, which suggests that even at elevated temperatures the gasification of a char with CO2 is controlled by both chemical reaction and diffusion inside the particles. Our results demonstrate that it is necessary to derive the gasification kinetics of a char at a high heating rate to obtain valid kinetic equations for an entrained‐flow gasifier. Copyright © 2010 Curtin University of Technology and John Wiley & Sons, Ltd.

A Numerical Modeling Study of Ignition of Single Coal Particles Under Microgravity Conditions

The ignition characteristics of single coal particles under microgravity conditions were investigated by means of numerical modeling, considering the effects of particle size, ambient temperature, and oxygen concentration as well as intraparticle thermal conduction. The predicted particle surface temperature and flame displacement agreed well with the experimental data observed under microgravity. It was revealed that when the coal particle size was greater than 100 µm, the intraparticle temperature distribution becomes significant. The primary ignition mechanism was heterogeneous for smaller particles but homogeneous for larger particles. The transition diameter for the ignition mechanism to switch from heterogeneous to homogeneous was found to depend on the ambient temperature, O2 concentration, and whether the intraparticle thermal conduction was considered or not. At a relatively low ambient temperature of 1123 K in air, the predicted transition diameter changed from 800 µm to 600 µm when intraparticle thermal conduction was considered. However, at 1500 K, the intraparticle thermal conduction had little effect on the ignition temperature and the transition diameter predicted was about 700 µm. It was shown that homogeneous ignition occurred when O2 concentration was low while heterogeneous ignition occurred when O2 concentration was high. It was also shown that the homogeneous ignition temperature was slightly lower than the heterogeneous ignition temperature. At high O2 concentrations, the predicted ignition temperature and ignition delay decreased with increasing O2 concentration, consistent with the literature findings, including those from the authors own previous studies. However, at low O2 concentrations, the predicted ignition temperature and ignition delay were less variant. The discrepancies of the predicted transition diameters for the isothermal particles and those with intraparticle thermal conduction considered were attributed to the heating rate and the influence of volatile matter release.

Characterization of the devolatilization rate of solid fuels in fluidized beds by time‐resolved pressure measurements

AbstractThe characterization of volatile matter (VM) release from solid fuel particles during fluidized‐bed combustion/gasification is relevant to the assessment of the reactor performance, as devolatilization rate affects in‐bed axial fuel segregation and VM distribution across the reactor. An experimental technique for the characterization of the devolatilization rate of solid fuels in fluidized beds is proposed. It is based on the analysis of the time series of pressure measured in a bench‐scale fluidized‐bed reactor as VM is released from a batch of fuel particles. A remarkable feature of the technique is the possibility to follow fast devolatilization with excellent time‐resolution. A mathematical model of the experiment has been developed to determine the time‐resolved devolatilization rate, the devolatilization time and the volume‐based mean molecular weight of the emitted volatile compounds. Devolatilization kinetics has been characterized for different solid fuels over a broad range of particle sizes. © 2011 American Institute of Chemical Engineers AIChE J, 2012

Study of the co-pyrolysis behavior of sewage-sludge/rice-straw and the kinetics

In order to study the co-pyrolysis characterisitics of sewage-sludge/rice-straw, pyrolysis experiments were carried out through a thermal analyzer. The pyrolysis processes were analyzed through the curves of TG and DTG. The results show that the co-pyrolosis behavior is not a simple summation calculation, but has obviouse synergistic effects. Rice straw significantly affects the release of volatile matter in the co-pyrolysis. It inhibits in the begining period, and promotes in the middle and later periods. With the increase of rice straw’s amount, the temperature range of the volatile matter’ release reduces, volatile matter release acceleratedly, both the speed and rate of weight loss increase. Kinetic analysis demonstrates that parameters in the stage of volatile matter liberation, which can be well linear fitted, have kinetic compensation effect in the process of co-pyrolysis.

Experimental Study on the Ignition Process of Single Coal Particles at Microgravity

In this paper, the first Chinese microgravity (μ-g) experimental study on coal combustion was introduced. An experimental system used to study the ignition process of single coal particles was built up, complying with the requirements of the 3.5 s drop tower in the National Microgravity Laboratory of China (NMLC). High volatile bituminous and lignite coal particles with diameter of 1.5 and 2.0 mm were tested. The ignition and combustion process was recorded by a color CCD and the particle surface temperature before and at the ignition was determined by the RGB colorimetric method. Comparative experiments were conducted at normal gravity (1-g). The experiments revealed that at different gravity levels, the ignition of all tested coal particles commenced in homogeneous phase, while the shape, structure, brightness and development of the flames, as well as the volatile matter release during the ignition process are different. At μ-g, the part of volatile was released as a jet, while such a phenomenon was barely observed at 1-g. Also, after ignition, flames were more spherical, thicker, laminated and dimmer at μ-g. It was confirmed that ignition temperature decreased as the particle size or volatile content increased. However, contradicted to existing experimental results, provided other experimental conditions except gravity level were the same, ignition temperature of coal particles was about 50–80 K lower at μ-g than that at 1-g.

Study on drying and combustion process in grate-CFB incinerator

The drying and combustion process in the combined grate and circulating fluidized bed (grate-CFB) municipal solid waste (MSW) incinerator was investigated experimentally and mathematically. The drying grate bed was simulated by a muffle furnace, which could be controlled at a constant temperature level. The kind of wastes, thickness of waste layer fed and temperature were chosen as the adjustable parameters to study their effect on the drying process. The experimental results indicated that the hydrophilic wastes were more difficult to be dried than the hydrophobic wastes. The higher the temperature is the easier the waste is to be dried. The thinner waste layer is favorable to drying the waste. The pyrolysis experiment in the furnace showed that the higher temperature level could reduce the conversion rate of carbon to carbon monoxide. The semi-empirical mathematical model that included the bed material distribution submodel, volatile matter release submodel, carbon particle combustion submodel and so on was proposed. A 260 t/d grate-CFB incinerator was modeled and the model predicted bulk density agreed with the measured value from industrial field test. The predicted flue gas (e.g. CO2, CO) concentration deviated slightly from the industrial test data. The parameters and variables used in the model were determined by the experiments or practical field test. This model can be used to design the grate-CFB incinerator and guide its operation.

CFD simulation and experimental validation of co-combustion of chicken litter and MBM with pulverized coal in a flow reactor

The influence of co-combustion of solid biomass fuels with pulverized coal on burnout and CO emissions was studied using a flow reactor. The thermal input on a fuel feeding basis of the test rig was approximately 7 kW. Accompanied with the measurements, a reactor model using the CFD code AIOLOS was set up and first applied for two pure coal flames (with and without air staging). Reasonable agreement between measurements and simulations was found. An exception was the prediction of the CO concentration under sub-stoichiometric conditions (primary zone). As model input for the volatile matter release, the HTVM (high temperature volatile matter as defined by IFRF [IFRF, www.handbook.ifrf.net/handbook/glossary.html. [1]]) was used. Furthermore, a relatively slow CO oxidation rate obtained from the literature and the ERE (Extended Resistance Equation) model for char combustion were selected. Furthermore, the model was used for simulating co-firing of coal with chicken litter (CL) and meat and bone meal (MBM). The conditions applied are relevant for future co-firing practice with high thermal shares of secondary fuels (larger than 20%). The major flue gas concentrations were quite well described, however, CO emission predictions were only qualitatively following the measured trends when O 2 is available and severely under-predicted under substoichiometric conditions. However, on an engineering level of accuracy, and concerning burnout, this work shows that co-combustion of the fuels can reasonably well be described with coal combustion sub-models.

Non-isothermal DSC and TG/DTG analysis of the combustion of Si̇lopi̇ asphaltites

In this research, non-isothermal combustion and kinetics of Silopi (Turkey) asphaltite samples were investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG/DTG). A sample size of 10 mg, heating rates of 5, 10, 15 and 20°C min−1 were used in the temperature range of 20–600°C, under air atmosphere. Two reaction regions were observed in DSC curves. The first region is due to the evaporation of moisture in asphaltite sample whereas, release of volatile matter and burning of carbon is called the second region.

Development of high temperature air combustion technology in pulverized fossil fuel fired boilers

High temperature air combustion (HTAC) is a promising technology for energy saving, flame stability enhancement and NO x emission reduction. In a conventional HTAC system, the combustion air is highly preheated by using the recuperative or regenerative heat exchangers. However, such a preheating process is difficult to implement for pulverized fossil fuel fired boilers. In this paper, an alternative approach is proposed. In the proposed HTAC system, a special burner, named PRP burner is introduced to fulfill the preheating process. The PRP burner has a preheating chamber with one end connected with the primary air and the other end opened to the furnace. Inside the chamber, gas recirculation is effectively established such that hot flue gases in the furnace can be introduced. Combustible mixture instead of combustion air is highly preheated by the PRP burner. A series of experiments have been conducted in an industrial scale test facility, burning low volatile petroleum coke and an anthracite coal. Stable combustion was established for burning pure petroleum coke and anthracite coal, respectively. Inside the preheating chamber, the combustible mixture was rapidly heated up to a high temperature level close to that of the hot secondary air used in the conventional HTAC system. The rapid heating of the combustible mixture in the chamber facilitates pyrolysis, volatile matter release processes for the fuel particles, suppressing ignition delay and enhancing combustion stability. Moreover, compared with the results measured in the same facility but with a conventional low NO x burner, NO x concentration at the furnace exit was at the same level when petroleum coke was burnt and 50% less when anthracite was burnt. Practicability of the HTAC technology using the proposed approach was confirmed for efficiently and cleanly burning fossil fuels.

Modeling the development of char structure during the rapid heating of pulverized coal

A mathematical model for the swelling of a coal and the formation of a char structure during devolatilization is developed, based on a simplified multibubble mechanism. The formation of a char has been considered as having two successive steps: a multibubble stage, followed by a single-bubble stage. During the multibubble stage, the rupture of bubbles is governed by a force balance and the release of volatile matter is determined by the rate at which bubbles rupture. When a cenospheric structure has formed, the single-bubble model applies. During this stage, the rupture of a bubble is determined by its wall stress, and volatile species are released through both bubbles rupturing and direct diffusion of volatile species to the particle's surface. A sensitivity study has been carried out, based on which parameters have been determined for the present modeling work. The model predicts experimental trends for the swelling of a coal and the structural characteristics of chars under different heating conditions. The model is the first to provide a complete quantitative description of the evolution of a char's structure for a pulverized coal during rapid heating. Using standard properties of density fractions of a coal, the model predicts the heterogeneity of a char's structure and quantifies the distribution of different structures. The results predicted by the model agree with experimental measurements.

Combustion characteristics of lignite and oil shale samples by thermal analysis techniques

Abstract In this research thermal analysis and kinetics of ten lignite's and two oil shale samples of different origin were performed using a TA 2960 thermal analysis system with thermogravimetry (TG/DTG) and differential al analysis (DTA) modules. Experiments were performed with a sample size of ~10 mg, heating rate of 10C min-1. Flow rate was kept constant (10 L h-1) in the temperature range of 20-900C. Mainly three different reaction regions were observed in most of the samples studied. The first region was due to the evaporation of moisture in the sample. The second region was due to the release of volatile matter and burning of carbon and called as primary reaction region. Third region was due to the decomposition of mineral matter in samples studied. In kinetic calculations, oxidation of lignite and oil shale is described by first-order kinetics. Depending on the characteristics of the samples, the activation energy values are varied and the results are discussed.

Influence of laminar flow on preorientation of coal tar pitch structural units: Raman microspectroscopic study

In order to estimate the role of laminar flow of viscous, aromatic matter of carbonaceous precursor on microtextural preorientation in pregraphitization stage, we performed experiments with coal tar pitch (CTP). The principal hypothesis of preorientation of basic structural units (BSUs) in the case of laminar flow (pressure impregnation of CTP into porous matrix) and secondary release of volatiles during carbonization were studied. Glass microplates, planar porous medium with average distance between single microplates 5 μm were used as suitable porous matrix. Samples of CTP were carbonized up to 2500 °C. Optical microscopy reveals large flow domains in the sample of cokes carbonized between glass microplates. Raman microspectroscopy and high resolution transmission electron microscopy (HRTEM) show that at nanometric scale, the samples do not support the proposed hypotheses. With increasing temperature of pyrolysis, the graphitization of CTP impregnated into porous matrix proceeds to lower degree of structural ordering in comparison with single pyrolyzed CTP. This is explained by the release of volatile matter during carbonization in geometrically restricted spaces. More evident structural changes were discovered with the sample of single coke, where parts of fine grain mosaics, relicts of ‘so called QI parts’, reveal higher structural organization, in comparison with large and prolonged flow domains, similar to flow domains of cokes from microplates.

Effect of Hydrogen Sulfide on Organic Sulfur Behavior in Coal and Char during Heat Treatments

The effect of hydrogen sulfide on organic sulfur behavior has been investigated for subbituminous and bituminous coals during heat treatments in free-fall and fixed-bed reactors. The organic sulfur content in the solid phase was observed to increase, even with the rapid release of volatiles. The change in the amount of sulfur and its rate of increase were found to be approximately inversely related to the carbon content of the raw coal and volatile matter release rates. Increases in sulfide and thiophene forms were identified by sulfur K-edge X-ray absorption near-edge structure analysis for the hydrogen sulfide-adsorbed chars. Langmuir's adsorption isotherm was found to characterize the effects of hydrogen sulfide concentration on the uptake behavior of sulfur by rapid pyrolysis chars in nitrogen streams containing hydrogen sulfide at 1073 K in a fixed bed. Gasification of the hydrogen sulfide-adsorbed char showed a lower conversion of sulfur from the solid phase to the gaseous products compared to the loss of carbonaceous substances from the gasified chars.

Characterization of adsorbent prepared from oil-palm shell by CO 2 activation for removal of gaseous pollutants

Characterization of activated carbon prepared from oil-palm shell, an abundant agricultural solid waste from palm-oil processing mills in some tropical countries, by carbon dioxide (CO 2) activation was carried out in this paper. The effects of activation temperature on the textural and chemical properties of the activated carbon were studied. It was found that significant weight losses occurred during the activation process due to continual release of volatile matter and carbon burn-off through weak carbon–CO 2 oxidation, resulting in an increase of solid density and a decrease of apparent density. Hence, the activated carbons prepared from oil-palm shells possessed well-developed porosities and predominant microporosities, which were verified by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM), respectively. The development of microporosity for the oil-palm-shell activated carbon would lead to potential applications in gas-phase adsorption for the removal of air pollutants. Adsorption test results showed a linear relationship between the BET surface area and the adsorptive capacity for both nitrogen dioxide (NO 2) and ammonia (NH 3) gases. This could be elucidated by the neutral surface functional groups of the oil-palm-shell activated carbon, as detected by Fourier Transform Infrared Spectroscopy (FTIR).

Devolatilization rate of biomasses and coal–biomass blends: an experimental investigation

Devolatilization behavior of different coals and biomasses under heating conditions typical of conventional pyrolysis processes was investigated. Thermogravimetric analyses were performed on coals (with high and low volatile matter), biomasses (pine sawdust and dried sewage sludge) and coal–biomass blends with different weight ratios. The different behavior of coals and biomass fuels in the devolatilization process (different amount and nature of volatile species released, different rate of devolatilization and different reactivity of produced chars) was analyzed for abstracting kinetic data. In addition, analyses of coal–biomass blends revealed that in the operative conditions used (i.e. low heating rate 20 °C/min and high nitrogen flowrate), primary reactions of the thermal decomposition of biomass fuels are not significantly affected by the presence of coal, and also coal does not seem to be influenced by the release of volatile matter from biomass. This led to the first conclusion that the weight loss of a blend can be obtained from the weighted sum of reference materials. Further, a kinetic analysis was performed in order to fit the experimental results and verify simple sub-models (namely, distribution activation energy model and lumped model) to be used in comprehensive combustion codes (computational fluid dynamic) assuring a major accuracy compared with SFOR model, but maintaining both simplicity and computational velocity. A quite good fitting was obtained for all materials and blends studied.