Volatile Matter Content Of Coal Research Articles

Pyrolysis kinetic analysis and model constructions of different ranks of coal and validation by GA–BP neural networks

In the current steel industry, environmental pressures are mounting. If the reducing gases generated from coal pyrolysis can be utilized for reducing iron ore, the goal of low-carbon production with controllable costs can be achieved. However, the release of volatile content in coal has a significant impact on the pyrolysis process and final products. Therefore, in this study, the pyrolysis characteristics and gaseous products of four types of coal with different volatile matter content was investigated by thermogravimetry-mass spectrometry (TG-MS) technology. The results showed that coals with higher volatile matter content demonstrated stronger reactivity during pyrolysis. As the volatile matter content in coal increased, the starting temperature for releasing the reducing gases decreased, leading to a significant increase in the released gas volume. In addition, the three kinetic factors were calculated by isoconversional method, distribution of the activation energy model (DAEM) and Coats-Redfern (CR) method respectively, and the pyrolysis reaction mechanism function suitable for all coal types was reconstructed based on common solid reaction models. Finally, a predictive model based on a GA-improved back-propagation neural network (BPNN) was developed, which useing 21 input parameters to predict the TG curves, activation energy (E), lnA and mechanism function (fα) and achieving R2 values above 0.95. This study contributes to a comprehensive understanding of the pyrolysis mechanism of coals with different volatile matter content, providing scientific guidance for effective utilization.

Impact of Organic Sulfur on Coal Graphitization

AbstractThe utilization of high‐sulfur coal, especially high‐organic coal, has always been a difficult hot spot in the energy field. To study the influence of sulfur in coal on coal‐based graphite products, a series of coal samples with different sulfur content and different degrees of coalification were collected for proximate analysis, ultimate analysis, and sulfur species analysis. The structural characteristics of coal‐based graphite products were analyzed by X‐ray diffraction (XRD). The relationships between the sulfur in coal and the yield (Y), graphitization degree (G), cell diameter (La), and stacking height (Lc) of coal‐based graphite products were explored. The yield of coal‐based graphite ranges from 8.92 % to 64.45 %, and it was found that the yield of coal‐based graphite is not only affected by the degree of coalification, fixed carbon content, and volatile matter content of coal but also significantly inhibited by organic sulfur in coal when the reflectance is less than 2.00 %. The graphitization degree (G) of coal‐based graphite is distributed between 76.02 % and 91.02 %, and positively related to the degree of coalification, and negatively related to the content of volatile matter. Organic sulfur in coal is an unfavorable factor for the graphitization degree (G) of coal‐based graphite. Both the cell diameter (La) and stacking height (Lc) of coal‐based graphite are positively correlated with the degree of coalification and negatively correlated with the volatile matter content in coal. Organic sulfur in coal plays an important inhibitory role on the cell diameter (La) of coal‐based graphite. Still, it has almost no effect on the stacking height (Lc) of coal‐based graphite, resulting in a low ratio of horizontal‐to‐vertical (La/Lc), which is not conducive to the horizontal development of coal‐based graphite cells.

Combustion behavior of granulated and pulverized coal in a PCI rig: combustibility and pressure variation analysis

The effect of the coal volatile matter content and particle size has been investigated in a new lab-scale pulverized coal injection rig (PCI rig) in terms of combustion efficiency and pressure variation. Two coals typically used for blast furnace injection (a high and a low volatile bituminous coal) and their blends experienced combustion under pressurized conditions and extremely high heating rates and short residence times such as those experienced by coal particles in industrial process. Combustion tests were conducted for a low volatile coal prepared in the particle size ranges of 25–75 µm, 105–250 µm and 250–500 µm. Burnouts were lower for the larger particle size sample, but the intermediate particle size sample (105–250 µm) yielded similar conversion to that of the finer sample. The burnouts of the high and low volatile coal, as well as those of their blends were proportional to the volatile matter content of samples in the test conditions. The measurement of pressure variation in the reactor chamber indicated a displacement in the beginning of reactions to longer times as larger was the particle size of coal. The high volatile coal reached the maximum pressure variation earlier than the low volatile one and the combustion of this coal in the blends may have anticipated the reaction of the low volatile coal portion in the blends.

The Relationship between Unburned Carbon Levels in Coal Combustion Ash and Volatile Matter Content in Coal

ABSTRACT In this study, considering a specific coal fired power plant, fly ash samples were analyzed in terms of unburned carbon (UBC) and amount of UBC in these samples were compared to coal volatile matter content. UBC which can be used as an expression to tell efficiency of power plants is basically reasoned by either coal properties or by the conditions of combustion environment in boiler. Coal combustion boilers are utilized in terms of their design conditions and they are really hard to utilize them out of these ranged conditions. That is why in order to investigate the effect of these abovementioned parameters, either laboratory scale or pilot scale combustion tests should be conducted. Briefly in this study, a period of same conditions of same boiler utilization of different types of coals considered, and different amounts of UBC in fly ashes were correlated with high or low amount of volatile matter content in coal. Obtained correlation between coal volatile matter and UBC in ash showed that volatile matter content of coal is dominantly affecting the coal burnout.

Characterising pulverised fuel ignition in a visual drop tube furnace by use of a high-speed imaging technique

This study investigates the ignition characteristics of pulverised coal, biomass and co-firing by use of a visual drop tube furnace (VDTF) and a high speed imaging technique. Three coals (anthracite, a bituminous coal and a lignite), four biomasses (Pine, Eucalyptus, Olive Residue and Miscanthus) and various biomass-coal mixtures were tested. With each coal, biomass or their mixture, a distinct flame was established within the VDTF through the continuous feeding of the fuel under the environment of air and at a furnace temperature of 800°C. To observe the ignition point, a Phantom v12.1 high-speed camera was used to capture the videos of fuel combustion at 500 frames per second (FPS). A technique was developed using MATLAB's image analysis tool to automate the ignition point detection. The results of the image processing were used to statistically analyse and determine the changes to the ignition behaviour with different fuels and co-firing ratios.The results obtained with the tested coals have shown that the distance to ignition increases as the coal volatile matter content decreases, whereas the opposite trend was found for the biomass fuels. Further, the addition of biomass to the anthracite significantly reduces the distance to ignition but a much less pronounced effect on the ignition was found when biomass was co-fired with the bituminous coal or lignite. The synergistic effect on the ignition of biomass-anthracite mixture is mainly attributed to the high volatile content and the potential effects of catalysis from the alkali metals present in the biomass. The results of this study have shown that the VDTF testing coupled with the image analysis technique allows for an effective and simple method of characterising ignition behaviours of pulverised coal, biomass and their mixtures.

Influences of coal size, volatile matter content, and additive on primary particulate matter emissions from household stove combustion

Aiming to reduce primary particulate matter (PM) emission from household coal combustion, we conducted experimental investigations on several coal properties that affect PM emission factors (EFs). Fourteen coal chunk samples with various volatile matter contents on dry and ash-free basis (Vdaf, 2.84–48.7%) were tested to examine the effect of coal volatile matter content. Eight coal briquette samples with various mineral additives were tested to examine the effect of coal additive. Two coal chunk samples with Vdaf of 32.9% and 9.3%, respectively, were made into three different sizes to examine the effect of coal size. Due to low combustion temperature and low burning efficiency of the volatile matter in household stoves, PMs emitted from household coal combustion often have a high fraction of carbonaceous compositions. Both PM2.5 EF and the fraction of its carbonaceous constituents increase with an increase in the coal volatile matter content till about Vdaf=35% and then stay roughly flat. Addition of extraneous minerals results in a significant reduction of PM emissions. Increasing the coal size from ∼1cm to ∼10cm leads to a reduction of PM EFs by ∼80%. The coal volatile matter content determines the total amount of organic compounds to be devolatilized during coal pyrolysis stage. The coal size and ash content affect the escape of these organic compounds from burning coal chunks or briquettes. Together, they all affect the burning completeness of these organic compounds in household stoves and subsequently the total amount of organic precursors to form carbonaceous constituents in PMs.

Coal combustion under Calcium Looping Process conditions

Coal of three kinds was burned in an oxygen-enriched atmosphere using a twin-fluidized bed solid circulation system under conditions of the Calcium Looping Process. This twin-fluidized bed system comprised a fast bed regenerator (calciner), into which fuel and oxygen-enriched gas were fed, and a bubbling bed absorber (carbonator), into which air was fed. Inert quartz sand was used as the bed material to evaluate the coal combustion behavior, including char transportation from regenerator to absorber and formation of CO and CO2 there. First, the circulation rate and the residence time of solids in the regenerator (calciner) were measured to determine the suitable operation conditions. The effect of gas feed staging to the regenerator on the solid residence time was evaluated. By reducing the ratio of the primary gas feed rate to total gas feed rate to 0.5, average solid residence time of about 40s was attained. Under this gas-feed condition, coal combustion experiments were conducted. Effects of volatile matter content of coal on CO and CO2 formation in the absorber and NOx emissions from the regenerator were investigated. High-volatile matter coal was found to be favorable to reduce CO and CO2 formation in the absorber, but conversion of the fuel-N to NOx of high-volatile matter coal was higher than that from low-volatile coal.

Application of LIBS for direct determination of volatile matter content in coal

Volatile matter content is an important index of coal quality characteristics. Laser-induced breakdown spectroscopy (LIBS) is a promising analytical spectroscopy technique. In this paper, a broad set of coal samples with different amounts of volatile matter content were tested by LIBS. Analytical methods with partial correlation and principal component regression were used to extract related LIBS spectral information based on coal structure, which indicates a strong correlation with the content of volatile matter to establish the calibration model. The experimental results derived from the correlation are consistent with those from standard analysis procedures (thermo-gravimetric analysis, TGA). This demonstrates that LIBS is a viable approach to directly determine the volatile content rather than indirect ultimate analysis.

Emission factors and particulate matter size distribution of polycyclic aromatic hydrocarbons from residential coal combustions in rural Northern China

Coal consumption is one important contributor to energy production, and is regarded as one of the most important sources of air pollutants that have considerable impacts on human health and climate change. Emissions of polycyclic aromatic hydrocarbons (PAHs) from coal combustion were studied in a typical stove. Emission factors (EFs) of 16 EPA priority PAHs from tested coals ranged from 6.25 ± 1.16 mg kg −1 (anthracite) to 253 ± 170 mg kg −1 (bituminous), with NAP and PHE dominated in gaseous and particulate phases, respectively. Size distributions of particulate phase PAHs from tested coals showed that they were mostly associated with particulate matter (PM) with size either between 0.7 and 2.1 μm or less than 0.4 μm (PM 0.4). In the latter category, not only were more PAHs present in PM 0.4, but also contained higher fractions of high molecular weight PAHs. Generally, there were more than 89% of total particulate phase PAHs associated with PM 2.5. Gas-particle partitioning of freshly emitted PAHs from residential coal combustions were thought to be mainly controlled by absorption rather than adsorption, which is similar to those from other sources. Besides, the influence of fuel properties and combustion conditions was further investigated by using stepwise regression analysis, which indicated that almost 57 ± 10% of total variations in PAH EFs can be accounted for by moisture and volatile matter content of coal in residential combustion.

Simulation of the Influence of the Coal Volatile Matter Content on Fuel NO Emissions in a Drop-Tube Furnace

The influence of the volatile matter content on fuel NO emissions from a coal-burning drop-tube furnace (DTF) was analyzed by means of a numerical model for 25 different coals utilized by Korean power plants. The numerical results were fully validated against experimental results obtained using an actual DTF. The results show that the numerical model incorporating the chemical percolation devolatilization submodel is more accurate than that incorporating the two-competing-rates submodel to predict combustion and emission, particularly the devolatilization process and NO. Furthermore, the conversion ratio of fuel N to NO decreases with increasing volatile matter content because the volatile matter releases HCN, which furthers NO reduction. The destruction ratio increases with the amount of HCN produced during the devolatilization process. This paper indicates that HCN is the predominant intermediate species and the volatile matter content has a significant impact on NO emissions from the combustion of coal.

Three-dimensional simulation of the pulverized coal combustion inside blast furnace tuyere

A three-dimensional multi-phase model using Eulerian approach has been developed to simulate the coal heat transfer, devolatilization and combustion process inside a blast furnace tuyere. The information including velocity field, temperature distribution and combustion characteristics has been obtained in details and the effect of coal particle diameter, coal type and coal injection angle on the pulverized coal combustion process has been presented. The predicted results show that the coal combustion process inside tuyere are affected by coal particle size, coal type and coal injection angle. For the smaller coal particle diameter, the volatile matter released from the coal more rapidly, this results in a higher coal burnout at the exit of the tuyere. The coal burnout is depended on the coal volatile matter content; a higher coal burnout will be obtained for the coal with a higher volatile matter content. The coal injection angle affects the flow patter inside the tuyere, which results in a different mixing and burning process of the pulverized coal. When the coal diameter changes from 30 μm to 90 μm, the coal burnout decreases from 51.03% to 44.21%; when the coal volatile matter is reduced from 34.32% to 19.95%, the coal burnout decreases from 46.04% to 35.02% and for the coal injection with an angle, the coal burnout is 46.04%, a little bit higher than that of 44.51% without injection angle.

NOx emissions of an opposed wall‐fired pulverized coal utility boiler

AbstractThe present paper was addressed to the effects of operational variables and coal properties on NOx emission level of a 600‐MW opposed wall‐fired pulverized coal utility boiler. The in situ experiments were performed to study the effects of operational variables on boiler performance by changing individual variables while the other variables were held nearly constant on the basis of the nominal load operation. It was found that the oxygen level was a significant parameter to affect the NOx emission. The impacts of coal properties on NOx emission indicated that NOx emission level decreased with the increase of the ratio of the nitrogen content to low heating value because the volatile matter content in coal significantly influenced the in‐flame NOx formation. Coal volatile content was the dominant parameter to affect fuel NOx formation through affecting the reducing condition in the inner near‐burner zone when the low NOx burners were applied in the boiler. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd.

Gasification Reactivity and Kinetics of Typical Chinese Anthracite Chars with Steam and CO2

The gasification reactivities of six typical Chinese anthracite chars with steam and CO2 at 0.02−0.1 MPa and 920−1050 °C were investigated by using thermogravimetric analysis (TGA). The reactivities of anthracite chars during steam gasification were found to have a good correlation to the coal volatile matter contents. The higher the coal volatile matter content, the higher the reactivity. The difference in reactivities of anthracite chars during CO2 gasification seems to be more dependent on the catalytic effect of inherent minerals in anthracite. The results show that the greater the alkali index, the higher the reactivity. The reactivities of demineralized anthracite chars vary very little compared with those the undemineralized chars at higher temperatures, whereas the reactivities of demineralized chars from Jincheng and Rujigou are lower than those of undemineralized ones and the reactivities of demineralized chars from Yangquan, Hunan, Guangdong, and Longyan are higher than those of undemineralized...

Prediction of grindability with multivariable regression and neural network in Chinese coal

Grindability index of coal is usually determined by Hardgrove Grindability Index (HGI). The correlation between the proximate analysis of Chinese coal and HGI was studied. It was found from statistical analysis that, the higher the moisture and the volatile matter content in coal, the less the HGI will be. On the contrary, the higher the ash and the fixed carbon content in coal, the higher the HGI will be. But the correlation between proximate analysis and HGI in coals is nonlinear. The prediction equation of HGI reported in literature, which is based on proximate analysis of coal and linear regression method, is not correct for coals in China. In this paper, the generalized regression neural network (GRNN) method was used to predict the HGI. A higher precision in the prediction result was obtained through such new method. By this method, the HGI can be estimated indirectly from the proximate analysis of coal when the HGI measurement equipment is not available.

Estimating the Combustibility of Various Coals by TG-DTA

To estimate the combustibility of 12 different coals involving anthracite, bituminous, and lignite, experiments of the coal combustion were carried out by using thermogravimetry (TG) and differential thermal analysis (DTA). High-reactivity combustibles region and low-reactivity combustibles region were observed during coal char combustion process. Also, two reaction rate constants (k 1 and k 2 ) for these two combustibles were determined. The value of the reaction rate constant of the low-reactivity combustibles (k 2 ) is much smaller than that of the high-reactivity combustibles (k 1 ) in each coal and also k 2 shows lower temperature dependence. These are reasons why 5-10% unburned carbon remains in the ash discharged from moat of the coal-fired power plants. The ignition temperature increases with decreasing volatile matter content of coal. Three ranks of coals as anthracite, bituminous, and lignite show the different ignition ways

The effect of pulverized coal injection and volatile matter content of coal on combustion characteristics around the raceway zone in the blast furnace

A two-dimensional mathematical model is developed to describe transport phenomena in a packed bedof coke in front of a blast furnace tuyere with and without pulverized coal injection (PCI). The model consists of two submodels: one is a pulverized coal (PC) combustion model in the blowpipe and the other is a combustion model in the packed bed of coke where the thermal radiation is considered. In this model, coke particles in the raceway are treated as a continuous phase, and both phases of gas and coke particles are calculated by using the Eulerian approach. This model is applied to practical operating conditions in the blast furnace. As the residence time of PCparticles in the blowpipe is quite short, its burn-off in the blowpipe is very small, and the PC particles mainly burn in the raceway cavity. While the burn-off of PC particle increases with the volatile matter content, some particles reach the inner wall of tuyere when high-volatile coal is used. When PC is injected into tuyere, more oxygen is consumed, and a higher temperature rise appears at the region closer to the tuyere tip in the raceway than those of all coke operation. The temperature profiles in the raceway with PCI and without PCI are different from each other due to the difference of flow regime.

Ignition temperature of pulverized coal particles: Experimental techniques and coal-related influences

Laboratory measurements of the visual and combustion sequences during the ignition of pulverized coals, chars, and petroleum coke are reported. Two experimental techniques—the first using a pulse of coal and the second, a continuous flow of coal and air in near stoichiometric proportions—are shown to give similar gas temperatures for the onset of flashing. The first flash temperature, commonly referred to as the minimum gas temperature for ignition, is shown to decrease with an increase in the volatile matter content of coal, particle size, and ambient oxygen concentration. However, little oxygen is consumed during this initial visual event. At a gas temperature, about 100°–200°C higher than the first flash temperature, the oxygen consumption is seen to increase rapidly and this is accompanied by the rapid generation of NO x . This characteristic temperature decreases with an increase in the ambient oxygen concentration but appears to be independent of particle size. It is found to be very close to the flame formation temperature. These two temperatures appear to be better indicators of the ignitability of pulverized coals in combustors than the first flash temperature.

Wastswater characteristics of LTC process of coal

Abstract Low temperature carbonization (LTC) is a process in which coal is heated (500–800°C), in absence of oxygen, yielding products like coke, tar, oil, liquor and gases. The liquor contains several pollutants like phenols, ammonia, cyanide, thiocyanate. Therefore, the characteristic of the liquor are of significant importance, with reference to environmental pollution. The quality and quantity of liquor is dependent on the nature of the coal and process of carbonization. In the present study, the strength of the liquor has been correlated with the temperature of carbonization and the volatile matter content of coal, using Gray‐King Assay apparatus for the carbonization. Present study indicates that the pollution load of liquor is directly proportional to the volatile matter content of coal. The temperature of carbonization also influences the concentration of the pollutants in the waste liquor.

Thermal analyses of Ohio bituminous coals

A suite of twenty-one bituminous coal samples from Ohio were analyzed by differential scanning calorimetry (DSC) and non-isothermal thermogravimetry (TG) techniques. Three regions of endothermic activity may be distinguished in the DSC scans in an inert atmosphere. The first peak (25–150°C) corresponds to loss of moisture from the coal, a second, very broad endotherm peaking in the range 400–500°C corresponds to devolatilization of the organic matter and a partially resolved endotherm at temperatures above 550°C probably corresponds to cracking and coking processes subsequent to the pyrolysis step. Evidence obtained from experiments with sealed pans suggest an autocatalytic effect exerted by the pyrolysis products. The use of the DSC technique to quantify the volatile matter content of coal seems less reliable than the proximate analyses obtained from non-isothermal TG in inert and O 2 atmospheres. Good agreement with ASTM values is observed by the latter method for a range of volatile matter and ash content.