Study of Pyrolysis Characteristics and Kinetic Analysis of Shenmu Coal at a High Heating Rate Using TG-FTIR

Coal pyrolysis is a fundamental reaction in the thermal processing and utilization of coal.Investigating the behavior and kinetics of coal pyrolysis is crucial for optimizing,designing,and developing a composite riser for the staged pyrolysis gasification process of pulverized coal.In this study,the non-isothermal pyrolysis behavior and kinetics of coal were examined at different heating rates(30,50,100,300,500,700,and 900℃/min)using thermogravimetry(TG)coupled with Fourier-transform infrared spectroscopy.Analysis of the TG/derivative TG(TG/DTG)curves indicated that coal pyrolysis mainly occurred between 300℃ and 700℃.Higher heating rates led to more volatiles being released from the coal,and a higher temperature was required to achieve rapid pyrolysis.Kinetic analysis showed that both the model-free methods(Friedman,Flynn-Wall-Ozawa,and Kissinger-Akahira-Sunose)and the model-based method(Coats-Redfern)effectively describe the coal pyrolysis process.The change in the Ea values between the two kinetic models was consistent throughout the pyrolysis process,and the most probable mechanism was the F2 model(secondary chemical reaction).In addition,the heating rate did not change the overall reaction order of the pyrolysis process;however,a higher heating rate resulted in a decrease in the Ea value during the initial pyrolysis stage.

Effect of demineralization on pyrolysis characteristics of LPS coal based on its chemical structure

The critical issue in developing mature Oxy-Coal Combustion Steam System technology could be the reactivity of deminer-alized coal which,is closely related to its chemical structure.The chemical structures of Liupanshui raw coal(LPS-R)and Liupanshui demineralized coal(LPS-D)were analyzed by FTIR and solid-state 13C-NMR.The pyrolysis experiments were carried out by TG,and the pyrolysis kinetics was analyzed by three iso-conversional methods.FTIR and 13C-NMR results suggested that the carbon structure of LPS coal was not altered greatly,while demineralization promoted the maturity of coal and the condensation degree of the aromatic ring,making the chemical structure of coal more stable.The oxygen-containing functional groups with low bond energy were reduced,and the ratio of aromatic carbon with high bond energy was increased,decreasing the pyrolysis reactivity.DTG curve-fitting results revealed that the thermal weight loss of LPS coal mainly came from the cleavage of aliphatic covalent bonds.By pyrolysis kinetics analysis of LPS-R and LPS-D,the apparent activation energies were 76±4 to 463±5 kJ/mol and 84±2 to 758±12 kJ/mol,respectively,under different conversion rates.The reactivity of the demineralized coal was inhibited to some extent,as the apparent activation energy of pyrolysis for LPS-D increased by acid treatment.

Insight into the key kinetic steps in the pyrolysis of coking and non-coking coals,characterization of the pyrolysis products

The chemical composition,structural and plastometric properties of different-ranked coals from Mongolia deposits were studied.The non-isothermal iso-conversion Ozawa-Flynn-Wall and Friedman model-free methods were used to assess kinetic parameters and to differentiate decomposition steps.Key peculiarities of the pyrolysis kinetics of brown and bituminous coals were revealed and discussed in terms of the composition and plastometric properties.Brown coal was shown to undergo three decomposition steps with ever increasing activation energy as temperature increased because of the decomposition of thermally more and more stable molecular fragments.The pyrolysis of bituminous coals occurred in four steps,the activation energy having extreme mode of temperature dependence.An important new finding was that the temperature range of the second,major pyrolysis step well corresponded to that between the softening and re-solidification temperatures according to Gieseler plastometry.The yield and composition of the pyrolysis products obtained under isothermal conditions were also characterized depending on coal rank and temperature,and the ways for qualified utilizations were offered.

Co-pyrolysis characteristics and interaction route between low-rank coals and Shenhua coal direct liquefaction residue

To reasonably utilize the coal direct liquefaction residue(DLR), contrasting research on the co-pyrolysis between different low-rank coals and DLR was investigated using a TGA coupled with an FT-IR spectrophotometer and a fixed-bed reactor. GC–MS, FTIR, and XRD were used to explore the reaction mechanisms of the various co-pyrolysis processes. Based on the TGA results, it was confirmed that the tetrahydrofuran insoluble fraction of DLR helped to catalyze the conversion reaction of lignite. Also, the addition of DLR improved the yield of tar in the fixed-bed, with altering the composition of the tar. Moreover, a kinetic analysis during the co-pyrolysis was conducted using a distributed activation energy model. The co-pyrolysis reactions showed an approximate double-Gaussian distribution.

Synergistic effects of dodecane-castor oil acid mixture on the flotation responses of low-rank coal:A combined simulation and experimental study

The utilization of an appropriate collector or surfactant is crucial for the beneficiation of low-rank coal.However,in previous studies,the selection of surfactants was primarily based on flotation procedures,which hinders the understanding of the interaction mechanism between surfactant groups and oxygen-containing functional groups at the surface of low-rank coal.In this study,we investigate the flotation of low-rank coal in the presence of a composite collector by using a combined theoretical and experimental approach.The maximum flotation mass recovery achieved was 82.89%using a 3:1 mixture of dodecane and castor oil acid.Fourier-transform infrared and X-ray photoelectron spectroscopic analyses showed that castor oil acid was effectively adsorbed onto the surface of low-rank coal,enhancing the hydrophobicity of the coal.In addition,the diffusion coefficient of water molecules in the water-composite collector-coal system was greater than that in the dodecane system.Moreover,due to the presence of castor oil acid in the flotation process,the adsorption distance of dodecane and low-rank coal became shorter.Molecular dynamics simulations revealed that the diffusion and interaction of surfactant molecules at the interface of low-rank coal particles and water was enhanced because the adsorption of the dodecane-castor oil acid mixture is primarily controlled by hydrogen bonds and electrostatic attraction.Based on these results,a better surfactant for flotation of low-rank coal is also proposed.

Influences of Temperature and Coal Particle Size on the Flash Pyrolysis of Coal in a Fast-entrained Bed

The experiments on the flash pyrolysis of a lignite were carried out in a fast-entrained bed reactor as a basic study on a so-called ＇ coal topping process＇. The investigation focused on the effects of pyrolysis temperature and coal particle size on the product distribution and composition. The experimental results show that an increase in the pyrolysis temperature results in a higher yield of gaseous products while a larger particle size leads to a decrease of the liquid yield. An optimum temperature for the liquid yield was found to be 650℃. A certain amount of phenol groups was found in the liquid products, which may be used to produce high-valued fine chemicals. The FTIR analyses of the coal and chars show that aliphatic structures in the chars are gradually replaced by aromatic structures with the increasing of pyrolysis temperature and coal particle size. The results of this study provide fundamental data and optimal conditions to maximize light oils yields for the coal topping process.

Thermodynamical Study on Production of Acetylene from Coal Pyrolysis in Hydrogen Plasma

The chemical thermodynamic equilibrium of acetylene production by coal pyrolysis in hydrogen plasma was studied. The thermodynamic equilibrium is obtained by using the method of free energy. Calculated results show that the hydrogen concentration in the equilibrium system is very important for the acetylene production by coal conversion and the energy consumption for the production of acetylene per-kilogram strongly depends on the hydrogen concentration and the temperature.

A density functional theory study on the decomposition of aliphatic hydrocarbons and cycloalkanes during coal pyrolysis in hydrogen plasma

To get deep understanding of the reaction mechanism of coal pyrolysis in hydrogen plasma, the decomposition reaction pathways of aliphatic hydrocarbons and cycloalkanes, which are two main components in volatiles from coal, were investigated. Methane and cyclohexane were chosen as the model compounds. Density functional theory was employed, and many reaction pathways were involved. Calculations were carried out in Gaussian 09 at the B3LYP/6-31G（d,p） level of the theory. The results indicate that the main pyrolysis products of methane and cyclohexane in hydrogen plasma are both hydrogen and acetylene, and the participation of active hydrogen atoms makes dehydrogenation reactions more favorable. H2 mainly comes from dehydrogenation process, while many reaction pathways are responsible for acetylene formation. During coal pyrolysis in hydrogen plasma, three main components in volatiles like aliphatic hydrocarbons, cycloalkanes and aromatic hydrocarbons lead to the formation of hydrogen and acetylene, but their contributions to products distribution are different.

CFD Simulation of a Hydrogen/Argon Plasma Jet Reactor for Coal Pyrolysis

A Computational Fluid Dynamics(CFD) model was formulated for DC arc hydrogen/argon plasma jet reactors used in the process of the thermal H_2/Ar plasma pyrolysis of coal to acetylene. In this model, fluid flow, convective heat transfer and conjugate heat conductivity are considered simultaneously. The error caused by estimating the inner-wall temperature of a reactor is avoided. The thermodynamic and transport properties of the hydrogen/argon mixture plasma system, which are usually expressed by a set of discrete data, are fitted into expressions that can be easily implemented in the program. The effects of the turbulence are modeled by two standard k-εequations. The temperature field and velocity field in the plasma jet reactor were calculated by employing SIMPLEST algorithm. The knowledge and insight obtained are useful for the design improvement and scale-up of plasma reactors.

Influence of heating rate on reactivity and surface chemistry of chars derived from pyrolysis of two Chinese low rank coals

A series of char samples were derived from pyrolysis of two typical low-rank coals in China （Shengli lig- nite and Shenmu bituminous coal） at low, medium and fast heating rates, respectively, to the same pyrol- ysis temperature 750℃. Then these chars were characterized by means of thermogravimetric analysis and Fourier transform infrared spectrometer with the aim to investigate the influence of heating rate in pyrolysis process on gasification reactivity and surface chemistry of them. Besides, a homogeneous model was used to quantitatively analyze the activation energy of gasification reaction. The results reveal that Shengli lignite and its derived chars behave higher gasification reactivity and have less content of oxygen functional groups than Shenmu coal and chars. Meanwhile, chars derived from Shengli lignite at 50℃/min and Shenmu coal at 200℃/min have the greatest gasification reactivity, respectively. The oxygen functional groups in Shengli lignite are easily thermo-decomposed, and they are less affected by the heating rate, while that in Shenmu coal have a significant change with the variation of heating rate. In addition, there is no good correlation between the change of oxygen functional groups and that of the gasification reactivity of the derived chars from pyrolysis at different heating rates.

Effect of occurrence mode of heavy metal elements in a low rank coal on volatility during pyrolysis

The harmful trace elements will be released during coal utilization, which can cause environment pollution and further endangering human health, especially for heavy metal elements. Compared to combustion, the release of heavy metal elements during coal pyrolysis process, as a critical initial reaction stage of combustion, has not received sufficient attention. In the present paper, a low rank coal, from Xinjiang province in China, was pyrolyzed in a fixed bed reactor from room temperature, at atmospheric pressure, with the heating rate of 10 °C/min, and the final pyrolysis temperature was from 400 to 800℃ with the interval of 100℃. The volatility of heavy metal elements (including As, Hg, Cd and Pb) during pyrolysis process was investigated. The results showed the volatility of all heavy metal elements increased obviously with increasing temperature, and followed the sequence as Hg > Cd > As > Pb, which was mainly caused by their thermodynamic property and occurrence modes in coal. The occurrence modes of heavy metals were studied by sink-andfloat test and sequential chemical extraction procedure, and it can be found that the heavy metal elements were mainly in the organic and residual states (clay minerals) in the raw coal. And most of the organic heavy metals escaped during the pyrolysis process, the remaining elements were mainly in the residual state, and the elements in Fe-Mn state also tended to remain in the char.

A review on nitrogen transformation and conversion during coal pyrolysis and combustion based on quantum chemical calculation and experimental study

The emission of NOx during coal combustion contributes to the formation of acid rain and photochemical smog,which would seriously affect the quality of atmospheric environment.Therefore,the decrease of NOx is of great importance for improving the efficient utilization of coal.The present review comprehensively summarized the influence factors and mechanisms of migration and transformation of nitrogen during the coal pyrolysis and combustion based on experimental study and quantum chemical calculation.Firstly,in the process of pyrolysis:the occurrence state and transformation of nitrogen were concluded.The influence of temperature,atmosphere,heating rate and catalyst on formation of NOx precursor and nitrogen migration path at the molecular level were summarized;Secondly,during the process of combustion:the influence of temperature,ambient oxygen concentration,physical structure of coal char,catalyst on heterogeneous oxidation of char(N)were summarized;The effects of char surface properties,catalyst and ambient atmosphere on heterogeneous reduction of NOx were also concluded.Based on the quantum chemical calculation,the reaction path of heterogeneous oxidation of char-N and heterogeneous reduction of NOx were described in detail.Current studies focus more on the generation of HCN and NH3,but in order to reduce the pollution of NOx from the source,it is necessary to further improve the process conditions and the optimal formula of producing more N2 during pyrolysis,as well as clarify the path of the generation of N2.Experiments study and quantum chemistry calculation should be combined to complete the research of directional nitrogen reduction during pyrolysis and denitration during combustion.

Infrared Spectra and Pyrolysis of Selected Molecular Models of Coal: Insight from Density Functional Calculations

Equilibrium structures and infrared spectra of four typical molecular models of coal have been studied by density functional calculations. Combining theoretical calculations on the coal models with experimental FT-IR spectra of selected low rank perhydrous coals, a plausible molecular representation for this kind of coals was proposed, and its predicted IR spectra reasonably match the experimental observation. Calculations indicate that the cleavage of the C-C bridge bond for the coal structures considered here occurs at about 540 ℃ and the C-O ether bridge bond may break under temperature ranging from 500 to 600 ℃for the aryl-CH2-O-CH2-aryl ether bond or from 200 to 300 ℃ for the aryl-CH2-O-aryl ether bond, showing remarkable effect of the local structural environment. The coal model containing the carboxyl group may release CO2 at about 300 ℃ through the decarboxylation with a barrier of 69 kcal/mol.

Physicochemical,mineralogy,and thermo-kinetic characterisation of newly discovered Nigerian coals under pyrolysis and combustion conditions

In this study,the physicochemical,microstructural,mineralogical,thermal,and kinetic properties of three newly discovered coals from Akunza(AKZ),Ome(OME),and Shiga(SHG)in Nigeria were examined for potential energy recovery.Physicochemical analysis revealed high combustible but low levels of polluting elements.The higher heating values ranged from 18.65 MJ/kg(AKZ)to 26.59 MJ/kg(SHG).Microstructure and mineralogical analyses revealed particles with a rough texture,surface,and glassy lustre,which could be ascribed to metals,quartz,and kaolinite minerals.The major elements(C,O,Si,and Al),along with minor elements(Ca,Cu,Fe,K,Mg,S,and Ti)detected are associated with clays,salts,or the porphyrin constituents of coal.Thermal analysis showed mass loss(ML)ranges from 30.51%to 87.57%and residual mass(RM)from 12.44%to 69.49%under combustion(oxidative)and pyrolysis(non-oxidative)TGA conditions due to thermal degradation of organic matter and macerals(vitrinite,inertinite and liptinite).Kinetic analysis revealed the coals are highly reactive under the oxidative and non-oxidative conditions based on the Coats-Redfem Model.The activation energy(Ea)ranged from 23.81 to 89.56 kJ/mol,whereas the pre-exponential factor(kQ)was from 6.77×10^(-4)/min to 1.72×10^(3)/min under pyrolysis and combustion conditions.In conclusion,the coals are practical feedstocks for either energy recovery or industrial applications.

Characterization of Carbon Deposits Formed During Plasma Pyrolysis of Xinjiang Candle Coal

Carbon deposits were formed on the reactor wall during plasma pyrolysis of the Xinjiang candle coal in our V-style plasma pyrolysis pilot-plant. The carbon deposits were studied using a scanning electronic microscope （SEM） and the X-ray diffraction （XRD） method. It was found that carbon deposits located at different parts in the reactor exhibited different microscopic patterns. The formation mechanism of the carbon deposits was deduced. The downward increase in the graphitization degree of the carbon deposits was found and interpreted.

Effects of calcium on the evolution of nitrogen during pyrolysis of a typical low rank coal

This study aims to investigate the effects of calcium on the migration of nitrogen in coal(coal-N)to N-containing gas species,particularly,NH3 and HCN(volatile-N)in volatiles,as well as the chemical transformation of the N in char during coal pyrolysis under different temperatures.The pyrolysis experiments of Shengli brown coal and its derived coal samples loaded with different contents of calcium were conducted under 600–800°C in a novel fluidized bed reactor.The experimental results showed that during coal pyrolysis,the generation of NH3 is mainly derived from secondary reactions among volatiles,tar and char with the catalytic effect of mineral matter,especially calcium in coal.Increasing pyrolysis temperature from 600 to 800°C could enhance the release of N in coal to volatiles.Meanwhile,the increased pyrolysis temperature could also inhibit the generation of NH3 while facilitating the formation of HCN.The release of HCN is more sensitive to pyrolysis temperatures.Specifically,under higher pyrolysis temperatures,more N-containing structures in coal would become thermally unstable and crack into HCN;On the other hand,higher pyrolysis temperature could also enhance the decomposition of N in coal to N-containing species in tar or N2,thus reducing the release of HCN and NH3.Nitrogen in tar could either undergo secondary decomposition reactions,generating NH3,HCN,N2 and other N-containing species in gas phase,or experience condensation polymerization by forming macromolecular structure and be retained in char at high pyrolysis temperatures.Calcium could significantly restrain the release of N from coal,thus reducing the yields of NH3 and HCN.During coal pyrolysis,calcium catalytically enhances the fracture and combination of chemical bonds,generating abundant free radicals.These free radicals could continuously attack N-containing structures and consequently release the N-containing gaseous products,such as NH3,HCN,N2 etc.,resulting in the decrease of N in char.Calcium also plays important roles in nitrogen transformation in char during coal pyrolysis by catalytically intensifying the transformation of N in char from pyridinic nitrogen(N-6)and pyrrolic nitrogen(N-5)to quaternary type nitrogen(N-Q)during coal pyrolysis.

Preparation of CaO-containing carbon pellets from coking coal and calcium oxide:Effects of temperature,pore distribution and carbon structure on compressive strength in pyrolysis furnace

CaO-containing carbon pellets(CCCP)were successfully prepared from well-mixed coking coal(CC)and calcium oxide(CaO)and roasted at different pyrolysis temperatures.The effects of temperature,pore distribution,and carbon structure on the compressive strength of CCCP was investigated in a pyrolysis furnace(350-750℃).The results showed that as the roasting temperature increased,the compressive strength also increased and furthermore,structural defects and imperfections in the carbon crystallites were gradually eliminated to form more organized char structures,thus forming high-ordered CC.Notably,the CCCP preheated at 750℃exhibited the highest compressive strength.A positive relationship between the compressive strength and pore-size homogeneity was established.A linear relationship between the com-pressive strength of the CCCP and the average stack height of CC was observed.Additionally,a four-stage caking mechanism was developed.

Study on the influence of crown ether on arsenic behavior during coal pyrolysis

The influence of crown ether on behaviors of arsenic at different temperatures and residence time was investigated during the pyrolysis of Tuanbo （TB） coal. The modes of occurrence of arsenic were determined by sequential chemical extraction, density fractionation and demineralization. The results indicated that at the same temperature and residence time, the arsenic removal adding dibenzo-18-crown-6 was higher than that adding 18-crown-6, and were all higher than that of TB coal during pyrolysis. When temperature was 850 ℃ and residence time was 30 min, the arsenic removal of TB coal was 30.63%; at the same condition, the arsenic removal while adding 18-crown-6 was 33.21%, higher than that of TB coal; and the arsenic removal while adding dibenzo-18-crown-6 was 67.41%, significantly higher than that of TB coal. From the results, we can see that adding crown ether can improve the arsenic removal during coal pyrolysis, and especially be conducive to the arsenic which is mainly associated with sulfates ＆ monosulfides and that in stable forms.

Combustion characteristics of semicokes derived from pyrolysis of low rank bituminous coal

Various semicokes were obtained from medium-low temperature pyrolysis of Dongrong long flame coal.The proximate analysis,calorific value and Hardgrove grindability index(HGI) of semicokes were determined,and the ignition temperature,burnout temperature,ignition index,burnout index,burnout ratio,combustion characteristic index of semicokes were measured and analyzed using thermogravimetry analysis(TGA).The effects of pyrolysis temperature,heating rate,and pyrolysis time on yield,composition and calorific value of long flame coal derived semicokes were investigated,especially the influence of pyrolysis temperature on combustion characteristics and grindability of the semicokes was studied combined with X-ray diffraction(XRD) analysis of semicokes.The results show that the volatile content,ash content and calorific value of semicokes pyrolyzed at all process parameters studied meet the technical specifications of the pulverized coal-fired furnaces(PCFF) referring to China Standards GB/T 7562-1998.The pyrolysis temperature is the most influential factor among pyrolysis process parameters.As pyrolysis temperature increases,the yield,ignition index,combustion reactivity and burnout index of semicokes show a decreasing tend,but the ash content increases.In the range of 400 and 450 °C,the grindability of semicokes is rational,especially the grindability of semicokes pyrolyzed at 450 °C is suitable.Except for the decrease of volatile content and increase of ash content,the decrease of combustion performance of semicokes pyrolyzed at higher temperature should be attributed to the improvement of the degree of structural ordering and the increase of aromaticity and average crystallite size of char.It is concluded that the semicokes pyrolyzed at the temperature of 450 °C is the proper fuel for PCFF.

Influence of dispersants on coal-water slurry prepared from the solid residue of plasma pyrolysis of coal

This work presents the influence of dispersants on coal-water slurry(CWS),which was prepared from the solid residue of plasma pyrolysis of coal.The effects of dispersant type,solid concentration,dispersant content,and temperature on the rheological properties of CWS are examined.A suitable empirical model regarding the relation between viscosity and temperature is proposed.Through the sedimentation experiment of CWS,dispersants are found to significantly promote the stability of CWS.