•The pyrolysis kinetics of superfine pulverized coal are obtained.•Different models of Coat-Redfern, Starink, and simplified DAEM are successfully employed.•A novel application of piecewise Coat-Redfern based on the tangent-bisecting method is developed.•The kinetic compensation effect is established, and its mechanistic implications are discussed.Coal pyrolysis is a complex process with multiple characterized kinetics that play a crucial role in understanding the devolatilization mechanisms, predicting the products distribution, and designing the reactors, etc. However, there is little knowledge about the pyrolysis kinetics of superfine pulverized coal. In this paper, typical thermogravimetric experiments at low heating rates are performed, which can identify individual species and provide reliable kinetic data. Then, three classical kinetic models are combined to analyze the superfine coal pyrolysis process, including Coats-Redfern (model-fitting type), Starink (model-free group) and distributed activation energy model (DAEM, continuous distribution category). Firstly, a five-reaction decomposition regime is identified through a tangent-bisecting method. Then, a novel application of piecewise Coats-Redfern model based on the tangent-bisecting method is developed, which shows that the coal particle size has a notable impact on the pyrolysis kinetics. Superfine pulverized coal can promote the primary pyrolysis process while inhibit the secondary reactions. Secondly, the Starink model is employed, and the arithmetic mean activation energy increases initially with increasing the particle size, and then declines, attributing to the contradictory effect of particle size. Finally, The distribution function f(E) is deduced based on the Miura-Maki DAEM, which spreads broadly with a single sharp peak. Additionally, the kinetic compensation effect (KCE) of k0 and E is observed for the Miura-Maki DAEM, which can be utilized to establish certain mechanistic implications. The findings from this work give a better interpretation on the kinetic parameters, and provide us a new perspective to understand the effect of particle size on the coal pyrolysis kinetics.

•A combination of XPS and NMR is adopted for analyzing char chemical structures during superfine pulverized coal pyrolysis.•The chemisorbed NO can be transformed into pyridine N with the favor of adjacent oxygenated groups in chars.•Particle size has significant influence on oxygen-containing configurations in chars.The properties of the coal-derived char play crucial roles in coal conversion reactions and the formation of air pollutants. The nascent char is highly reactive due to the existence of numerous free radicals, active sites, and organic functional groups on its surface. Here, we showed that a combination of nuclear magnetic resonance spectroscopy (NMR) and X-ray photoelectron spectroscopy (XPS) techniques is an effective and precise way to characterize the occurrence, distribution, and evolution of organic functionalities in coal chars. Using these methods, we explored detailed information about chemical features of superfine pulverized coal chars in different atmospheres, and we also discussed the influence of particle size on the evolutionary behavior of functionalities. Results indicate that, in both N2 and CO2 atmospheres, the content of CO species increases with the reduction in char particle sizes. This increment facilitates the heterogeneous reduction of NOx on char surfaces. The chemisorbed NO is susceptible to being incorporated into chars, and being transformed into pyridine-type nitrogen with the favor of adjacent oxygen-containing groups. Moreover, the significant increment in oxygen-containing groups with the reduction of particle size is further confirmed through 13C NMR analysis. It was shown that there is an excellent correlation between estimates derived from XPS and NMR for oxygen configuration. The findings from this work provide some new insights into NOx reduction mechanisms and shed light on the practical application of superfine pulverized coal in the future.

The novel superfine pulverized coal combustion technology shows plenty of advantages, and a complementary description of the representative molecular structures plays a paramount role in better understanding its utilization processes. In this work, the carbon skeletal features of superfine pulverized coal were elucidated through 13C NMR analysis. The changes of the coal chemical properties after the demineralization treatment were characterized. Furthermore, the influence of particle size on coal molecular structures was focused on, and the detailed evolution mechanisms were discussed based on the structural and lattice parameters. The final results indicate that decreasing particle size engenders the local coal maturation due to the thermal and mechanical strain effects. The oxygen-substituted aromatic carbon increases in smaller coal fractions at the expense of oxygenated aliphatic carbon. Additionally, the oxidation effect of atmospheric oxygen during the superfine comminution is confirmed. Furthermore, the acid treatment promotes the cleavage of certain chemical bonds, which imposes a significant influence on the attachments and oxygen-containing groups in coal. In all, this research provides some new insights into the role of mechanochemical effect during the coal comminution and is helpful for better understanding the coal chemical structures at a molecular level. The data obtained here will promote the development of the representative molecular models of superfine pulverized coal, and improve the prediction of its behavior during practical application.

The coal fragmentation and resulting particle size distribution (PSD) have significant influences on the physical and chemical properties, which play a crucial role in coal conversion and utilization processes. In this paper, a comprehensive comminution theory of superfine pulverized coal was proposed, in combination of particle fracture mechanisms, fractal dimension analysis, and energy laws of comminution. The subtle crystalline changes of aggregate structures as a result of the coal comminution were validated through synchrotron-based high-resolution X-ray diffraction, and the distribution patterns of sub-micrometer aggregate clusters were identified according to the fractal fragmentation theory. Finally, a novel energy dissipation assumption is proposed on the basis of the molecular sliding mechanism, which is suitable for the evaluation of energy consumption of the comminution-induced sub-micrometer particles. The results here can improve the interpretation and modeling of coal macromolecular networks and offer a new way for predicting the PSD of grinding products. The findings from this work provide some new insights into the phenomenon of limit fineness of mechanical comminution from a molecular level perspective, which is helpful for the development of fragmentation methodology and equipment in the field of ultrafine grinding.

•Six constitutional isomers of Huadian oil shale kerogen molecular model were constructed.•One model was found to have good agreement between the calculated and experimental spectra.•Geometry optimization and molecular dynamics calculation were performed on 3D structural models.•Several 3D structures were generated, including the energy-minimum 3D structure.•Van der Waals interactions have a greatest effect on the physical density of this kerogen.Based on chemical structure analysis, supplemented with fast pyrolysis results, six constitutional isomers of two-dimensional (2D) molecular models of the Huadian oil shale (HDOS) kerogen were constructed. One model yielded good agreement between simulated and experimental 13C NMR spectra. Geometry optimization and molecular dynamics calculation were performed on three-dimensional (3D) structural models translated from the optimized 2D model. Several 3D structures were generated, including an energy-minimum 3D structure. The simulated results show that van der Waals (vdW) interactions have a greatest effect on the physical density of the HDOS kerogen. In addition, the nonbonding interactions, especially vdW interactions arisen from various flexible chains, play important role in the stabilization of the energy-minimum 3D structure.

•To study temperature effect on product yield and properties of shale oil and gas.•Higher temperature raised both oil and gases yields but reduced oil/gas yield ratio.•To compare shale oil’s element and distilled fraction distribution to crude oils’s.•490 °C is a transition temperature for the content of chemical class fractions.•Improving temperature raised C1–C4 contents and alkene/alkane gas ratios.Oil shale samples from Huadian were retorted in a stainless-steel cylindrical retort under argon atmosphere to determine retorting temperature effect on the product yield and characteristics of shale oil and non-condensable gases produced. Increasing temperature from 430 °C to 520 °C improved both oil and gas yields, but reduced the oil/gas yield ratio. Raising temperature increased nitrogen content in the derived shale oil and decreased the atomic H/C ratio and oxygen content, but had no significant effect on the sulfur content. It was also noticed that the boiling point of shale oil generated at 490 °C was lowest, and the shale oils obtained at 430 °C and 460 °C showed similar boiling point distributions. The produced shale oils had similar atomic H/C ratio as well as higher light oil content compared to crude oils produced in China, and could be classified as sweet and high-nitrogen oil in terms of the classification method of crude oil. The oil derived at 490 °C contained the lowest amount of saturates and the highest amount of aromatics, asphaltenes and non-hydrocarbons. C1–C4 hydrocarbon gas contents rose with increasing temperature. Higher ethene/ethane, propene/propane, butene/butane and alkene/alkane ratios obtained at higher temperature were linked to secondary cracking reactions.

•Contents of aliphatics and oxygenated compounds are affected by H/C and O/C.•Aliphatic carbon chains are transferred into aromatic rings in the deeper ore bed.•From 485 to 590 °C, ester and ketone contents decrease while alcohol increases.•Long chain hydrocarbons (> C20) take the largest proportions in the alkanes.Curie-point pyrolysis-GC/MS experiments were conducted on three oil shales derived from different mines in Huadian Basin to characterize the fast pyrolysis features and the oil product distribution regularities. Pyrolysis experiments at two different Curie temperatures of 485 °C and 590 °C were carried out on all the three oil shales respectively to study the influence of temperature on the pyrolysis shale oils. The results showed that in the sedimentation process of kerogen, part of the aliphatic chains are transferred into aromatic rings leading to the decrease of aliphatics and increase of aromatics. Also, part of the oxygen-containing functional groups are removed leading to the decrease of oxygen-containing organic compound proportion in the shale oil. With the increase of temperature from 485 °C to 590 °C, large amounts of n-alkanes were transferred into cycloalkanes and alkenes due to the secondary cracking reactions. Oxygen-containing organic compounds including phenols, alcohols, esters, and ketones existed in the pyrolysis oil products of all samples. Contents of alcohols increased with temperature while that of esters and ketones decreased obviously.

New insights into the heterogeneous reduction reaction between NO and char-bound nitrogen [char(N)] were obtained by a combination of density functional theory (DFT) and conventional transition state theory (TST). A detailed description of the nature of NO chemisorption is reported based on the HOMO and LUMO, Mulliken atomic charges, and spin densities. It is suggested that, during chemisorption, char(N) contributes electrons to NO. The seven most stable structures (I–VII) resulting from NO chemisorption were identified, and the exothermicity was found to increase in the order III < V < IV < VI < VII< II < I. This finding is reasonable considering the fact that the HOMO of char(N) is predominantly reflected in the active C(2) atom and the LUMO of NO is mainly concentrated on the N(8) atom. Three stepwise reactions leading to N2 formation have been characterized with low energetic penalty acceptable for occurring at the practical heterogeneous combustion temperature. The highest energy penalty was calculated to be 270.794 kJ/mol. A kinetic similarity over the temperature range of 850–1000 K between the rate-limiting step and char gasification was found (10–3–100 compared to 10–4–10–1 s–1, respectively). By comparison with previous experiments, the calculated results were validated, and on the basis of these results, the reburning of superfine bituminous coal is recommended.

The CO2 control technologies have been studied extensively in recent years, among which the oxy-fuel combustion shows a vast number of advantages to be explored commercially in the near future. However, unexpected problems, such as bad combustion characteristics and serious slagging and depositing issues, show up with the replacement of N2 by CO2. These inherent disadvantages in normal O2/CO2 combustion can be restrained via combining the superfine pulverized coal and oxy-fuel combustion technology. The axial NO emission characteristics of this new technology were focused here. The effects of the oxidizer staging were also studied in detail. Results indicate that the axial NO emissions of the unstaged O2/CO2 combustion basically showed “M” type of distributions along the furnace. The “M” type can be divided into the main homogeneous and heterogeneous reaction zones. The oxidizer-staged O2/CO2 combustion can mitigate NO emissions effectively. Coals with smaller particle sizes and higher volatiles are more advantageous for eliminating NO in the staged O2/CO2 combustion technology. The superfine pulverized coal used with certain low NO combustion technologies shows significant superiority in both combustion performance and NO abatement.

•Mechanochemistry is of great importance in the superfine coal fragmenting process.•Common char with carbonyl oxygen bonded is modeled to represent the superfine char.•The surface oxygen is responsible for high reactivity of CO desorption.•A certain amount of NO is trapped in the carbonaceous matrix in the form of char(N).Mechanochemistry plays a crucial role in characterizing the superfine char surface chemistry properties. Conventional char with carbonyl oxygen(> CO) bonded to its surface is applied to represent the superfine char model for the first time. Comparisons of two char models are performed and the results reveal that surface oxygen is responsible for high reactivity of CO desorption. Comprehensive density functional theory (DFT) calculations at B3LYP/6–31 G(d) level are performed to determine the NO consumption mechanism in the presence of oxygen. The results show that a certain amount of NO is trapped in the carbonaceous matrix in the form of char(N), leading to a satisfactory agreement with previous experimental observations.CO desorption, NO fixation, CO vertical chemisorption, oxygen migration and CO2 desorption take place to yield char(N). The order of the calculated energetic penalty is NO fixation (7.23 kJ/mol) < CO2 desorption (68.26 kJ/mol) < oxygen migration (96.62 kJ/mol) < CO desorption (361.01 kJ/mol), indicating that CO desorption is the rate limiting step. Char(N) formation is kinetically feasible because (1) the overall process is observed exothermic by 224.07 kJ/mol and (2) the temperature required for rate limiting step (600 °C) is much lower than the practical heterogeneous combustion temperature.Mechanochemistry is of great importance in the fragmenting process of superfine pulverized coal. Carbonyl oxygen on char surface increases with the decrease of coal particle size. The role played by carbonyl oxygen is studied by density functional theory, being aimed to get insights into the favorable role of oxygen and to clarify the NO consumption mechanism.

The nitrogen-containing compounds in Huadian shale oil (HDSO) produced by pyrolysis of Huadian oil shale at the final temperature of 520 °C in a fixed bed reactor were characterized in detail by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). We find that HDSO contains six basic nitrogen classes, but the other basic N2O1, N2O2, N3 and N3O1 classes determined in US Western shale oil (USSO) and Russian Slanet shale oil (RSSO) are not found in HDSO; while the neutral nitrogen classes are almost the same as those in USSO and RSSO. The basic Nx classes predominate in all basic classes in HDSO, and the relative abundance of the basic N1 class is much higher than that in USSO and RSSO. In HDSO most basic N1 and N1O1 class species consist of the nitrogen-polycyclic aromatic compounds with 1–7 aromatic rings and 0–42 carbon atoms of the alkyl side chains; while the major neutral N1 and N1O1 compounds identified contain 1–5 aromatic rings and 0–35 carbon atoms of the alkyl side chains. Furthermore, pyridines and tetrahydroquinolines which contain 15–28 and 11–24 carbon atoms of the alkyl side chains respectively are dominant in all basic nitrogen species; indoles and carbazoles are the most abundant in all neutral N1 species. The N1O1 species containing 1–4 aromatic rings and 1–24 carbon atoms of the alkyl side chains are relatively abundant. Most likely a substantial amount of the N2 class species identified in HDSO are azaindoles and azaquinlines series.Highlights► Nitrogen compounds in Huadian shale oil (HDSO) was characterized by ESI FT-ICR MS. ► The N1 and N1O1 are the most abundant in all nitrogen-containing classes in HDSO. ► The basic Nx class species predominate in all basic nitrogen species of HDSO. ► Most N1 and N1O1 class species in HDSO contain 1–7 aromatic rings. ► The alkyl pyridines with 20–33 carbon atoms are rather rich in HDSO.

Superfine pulverized coal combustion is a new pulverized coal combustion technology that has better combustion stability, higher combustion efficiency, and comprehensive cost-effective operation. The novelty of this present paper is that fundamental experiments on an electrically heated drop-tube furnace were carried out to understand the NOx emissions of air-staging combustion for two superfine pulverized bituminous coals used in China for the first time. The results indicate that high-volatile-containing Neimenggu (NMG) coal possesses better effectiveness of NOx abatement than low-volatile-containing Shenhua (SH) coal. Interesting saddle-point effects of the highest NOx emissions have been found for both coals around the average particle size of 17.44 μm for SH coal and ∼30 μm for NMG coal. For different stoichiometric ratios and positions of over fire air (OFA) ports, NMG coal provides a higher ability of deNOx efficiency than SH coal. The superfine pulverized coal combustion of the NMG_25.86 μm particle can even reach the highest deNOx efficiency up to 70%. The findings of this paper will provide guidance for further studies on the NOx emission characteristics of superfine pulverized coal combustion.

A sample of kerogen isolated from Huadian oil shale was studied using a combination of solid-state 13C NMR, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR), and X-ray diffraction (XRD) techniques to evaluate its structural characteristics. 13C NMR results indicate that the carbon skeletal structure of this kerogen is mainly composed of a fairly high fraction of aliphatic carbon (86.1%), with a very low aromaticity (fa) of 9.7%; methylene (CH2) carbons dominate in all types of aliphatic carbons and the majority of them exist as many long straight chains but not saturated alicyclics. The average methylene carbon chain length (Cn) is between 12 and 24. There are only one fused aromatic ring (e.g., naphthalene) or two single aromatic rings (one benzene ring and one penta-heterocycle) per 100 carbon atoms. However, aromatic rings in this kerogen have a very high value of substitutive degree (δ = 0.42–0.75). Furthermore, XRD analysis suggests that most methylene straight chains and aromatic carbons can not form crystalline but amorphous structure and are linked to each other by various bridge bonds and methylene (CH2) chains. FT-IR, XPS, and 13C NMR results show that organic oxygen in the kerogen exists as mainly three types of oxygen functional groups. Both XPS and 13C NMR results agree on the same ordering of their respective contents: C–O and C–OH groups are dominant, followed by O═C–O, and C═O or O–C–O groups. The 13C NMR results further suggest that more oxygen of C–O and C–OH groups is bound to aromatic carbons. XPS shows that over half the total amount of organic nitrogen in Huadian kerogen exists as aromatic heterocycles, which concludes pyrrolic nitrogen richest in total organic nitrogen, pyridinic, and protonated-pyridinic forms. A relatively high content of amino nitrogen over 30 mol % also is present in this kerogen, which is much higher than that of other same type kerogens. Organic sulfur is distributed in this kerogen as aromatic and aliphatic sulfur, sulfone, and sulfoxide in the order of the relative mole fraction.

Surface nitrogen complex formation upon reaction of coal char with NO at 600°C was studied by X-ray photoelectron spectroscopy. Particle size had a noticeable effect on the magnitude of changes, which was observed on the surface of the coal char in the nitrogen functional group. The surface increased its -NO, pyridine-N-oxide, and -NO2 functional group contents with a decrease in particle size. The chemisorption processes of NO molecules on the char were simulated using the ab initio Hartree-Fock method and density functional theory. Molecular modeling was applied to determine the thermodynamics of the reactions. Mechanisms were proposed to explain the formation of the -NO, pyridine-N-oxide, and -NO2 functional groups at 600°C.

The effects of particle size, stoichiometric ratio (λ), atmosphere, temperature, and recycled NO on the emissions of three fractional nitrogens, [N]N2O, [N]NO, and [N]NO2, during the combustion of superfine pulverized coal in O2/CO2 atmosphere were investigated in the present study. NO2 has shown little contribution to NOx compared with N2O and NO in all the cases. As the stoichiometric ratio increases, the trend is much similar in CO2/O2 and N2/O2. However, the conversion ratio from fuel-N to NOx in CO2/O2 atmosphere is less than that in N2/O2 atmosphere especially at λ > 1.2. [N]NO makes up the largest portion of [N]NOx at λ > 1, and [N]N2O dominates at λ < 1 resulting from the presence of hydrocarbons and CO at low stoichiometric ratio. For the three coals, [N]N2O increases as the mean particle size increases while [N]NO shows the opposite trend because the evolution of volatile nitrogen was delayed and the reburning-like scheme happened. There exists a minimum for the conversion ratio from fuel-N to NOx at the particle size range of 15−25 μm under the combined effects of [N]N2O and [N]NO. As temperature goes up, [N]NO and the conversion ratio from fuel-N to NOx increase while the [N]N2O decreases obviously. The conversion ratio from fuel-N to NOx decreases while the reduction rate increases as recycled NO increases. Recycled NO is destroyed in the flame through its reactions with hydrocarbon radicals in the form of CHi, and reduction reactions occur between recycled NOx and fuel-N. The increase in NO concentration accelerates the formation reactions of N2O and also promotes the conversion of char-N to N2O.

The anisotropy of mass transfer for oxygen in the ash layer of Dachengzi shale char particles has been studied by burning the cubic shale char particles with different open surfaces in a TG209F1 thermogravimetric analyzer according to the modified one-dimensional combustion model. The combustions of the cubic shale char particles undergo three stages, and the mass-transfer resistance gradually increases. The burn-out of the cubic char particle at 900 °C needs less time than that at 750 °C for the same mass-transfer direction. In addition, the burn-out time of the cubic char particle for the combustion along the direction perpendicular to the bedding planes is much more than that along the direction parallel to the bedding planes under the same burning temperature. The impact of the mass-transfer direction on the combustion rate is much greater than that of the burning temperature, and increasing the air flow rate is considered to be an effective way to accelerate the combustion rate of the whole char particle. The average ash layer effective diffusivity of shale char is 0.80 × 10−5 m2 s−1 (900 °C) and 0.43 × 10−5 m2 s−1 (750 °C), respectively, along the direction perpendicular to the bedding planes, while it is 6.55 × 10−5 m2 s−1 (900 °C) and 5.90 × 10−5 m2 s−1 (750 °C), respectively, along the direction parallel to the bedding planes. The severe anisotropy of mass transfer for oxygen in the ash layer of the shale char particle is confirmed through the analysis of the experimental results.

The pyrolysis experiments of the mixture fuels of Huadian oil shale and its shale char prepared at a retorting temperature of 520 °C were conducted using a Q5000IR thermogravimetric analyzer, and the characteristics of the copyrolysis at different mixing ratios were obtained. The release of organic matter tended to decrease while the decomposition of inorganic constituents tended to increase slightly with increasing shale char fraction. The interaction during the copyrolysis was investigated by comparing the experimental result with the theoretical one and only some little interaction was observed. The reactivity between 250 and 600 °C followed a decreasing trend with the increase of shale char fraction due to the lower volatile content and carbon condensation structures in shale char, and for each sample, the reactivity increased first and then decreased as the temperature increased because of the rearrangement of internal structure of sample particles. According to the kinetic analysis, increasing the shale char fraction in the mixtures would result in a decreasing apparent activation energy at temperatures ranging from 250 to 600 °C since the pyrolysis of shale char in this temperature range did not undergo the process of the decomposition of bitumen which existed in the pyrolysis of oil shale and needed much energy.

The fuel characteristics of two typical seaweeds (Enteromorpha clathrata and Sargassum natans) were studied. It was found that both the contents of volatile and ash are high, and the ash melting characteristics were different. High contents of alkali metals especially K and Na were also found in seaweed ash. The ignitions of seaweed particles were observed using a thermal microscope, which demonstrated that particle ignition proceeded in the homogeneous mode. Combustion experiments of seaweed have been conducted using a DTA-60H thermal analyzer, and the combustion processes were studied. Furthermore, the thermogravimetric mass spectrum (TG-MS) analysis was used for the gaseous products analysis during the combustion. It provided the fundamental data for the development and utilization of seaweed biomass.

It is an important problem for a new comprehensive utilization technology of oil shale how to obtain both shale oil with a high yield and shale char with good combustion properties referring to ignition mechanism, pyrolysis, and pore structure. In this present work, pyrolysis experiments of 14 shale chars obtained by retorting oil shale under different conditions were performed in a thermogravimetric analyzer; organic matter within these shale chars was extracted by an acetone/hexane mixture solvent and identified using a gas chromatography/mass spectrometry method, and then the effects of four retorting factors (retort temperature, residence time, particle size, and heating rate) were discussed on the pyrolysis characteristics of shale chars. The pyrolysis history of shale chars formed by retorting different oil shales at a retort temperature of 520 °C is very similar below the pyrolysis temperature of 660 °C, and above 660 °C there exist different mass losses attributed to large decomposition of carbonates and organic matter containing amide groups. Either increasing retort temperature from 430 to 460 °C or prolonging residence time at a retort temperature of 430 °C can obviously decrease mass loss of shale char in the low-temperature stage of pyrolysis and, however, have little influence on the pyrolysis history of all the samples including oil shale in the high-temperature stage. In this study particle size and heating rate show little effect on the pyrolysis of shale char. As a result, for achieving high shale oil yield, good combustion characteristics of shale char, and minimum energy loss during retorting, it is more important to optimize both retort temperature and residence time.

In this paper, a model on attrition of quartzite particles as an inert bed material in fluidized beds has been established on the particle–particle collision. For the convenience of describing the attrition of quartzite particles in fluidized beds, we chose the attrition rate constant (kARC) as one main characteristic parameter to develop the model.In order to verify the validity of the developed model, an attrition experiment of quartzite particles has been carried out in a lab-scale circulating fluidized bed. The predicted results from the population model were close to the experimental data as far as the engineering use is concerned. Finally, a sensitivity analysis was performed by using the developed model to examine effects of initial particle diameter, attrition time, and fluidization number on kARC.Graphical abstractGenerally, particle attrition takes place through surface abrasion, i.e., very fine particles break away from surface of original particle. In fluidized beds, movements of particles are very vigorous, which might lead to a significant amount of particle collisions so as to give birth to attrition. Based on the particle–particle collision, a model on attrition of particles has been established.

The ash fusing characteristics on three sorts of seaweed (a kind of marine biomass) were studied by using thermal microscope, X-ray diffractometer (XRD), ash composition analysis, and simultaneous thermogravimetry/differential thermal analysis. It was presented that there were lots of alkali metals especially K and Na in all seaweed ash samples. XRD analysis shows that the crystalline phase intensities of alkali chlorides reduce with increasing the ashing temperature, due to the evaporization of alkali chlorides. Therefore, the evaporization of alkali chlorides in seaweed biomass should be considered during the thermal conversion. The low ash fusion temperatures of seaweed make the ashing temperatures recommended by both GB and ASTM norms to exceed the limit of temperature to prepare seaweed ash. At a high ashing temperature, Gracilaria cacalia and Sargassum natans will generate some high-melting matters which influence the identification of the ash fusion points. So, it is more exact and referenced that the seaweed biomasses were ashed at a lower temperature (such as 530 °C). Besides, the slagging characteristics and fusing characteristics of each sample are quite different. Gracilaria cacalia is the easiest to slag, followed by Sargassum natans. Enteromorpha clathrata is the hardest to slag among them. Gracilaria cacalia and Sargassum natans show a great range from the ash deformation temperature to hemispherical temperature, and Enteromorpha clathrata reveals a small temperature difference between deformation temperature and hemispherical temperature.

The effects of oxygen concentration, particle size, and heating rate on the coal combustion characteristics under an O2/CO2 atmosphere were investigated. The results indicated that the oxygen concentration played the most important role. As the oxygen concentration increases, the ignition and burnout temperatures decrease and the comprehensive combustion property index S increases. Moreover, the improvement of the oxygen concentration intensified the effects of the other factors. The ignition mechanism changes from hetero-homogeneous type to homogeneous type as the oxygen concentration increases. The ignition and burnout temperatures decrease slightly as the mean particle size decreases, and the index S increases measurably as the mean particle size decreases. The heating rate has different effects on the ignition temperature, burnout temperature, and index S at different oxygen concentrations.

At present, there is a growing tendency to use low cost, commercially available oil-shale ash as a building material, a chemical filling material, an adsorbent, and so forth. To obtain oil-shale ash with higher porosity, the pore structure of oil-shale ash samples obtained from different combustion modes of oil shale was measured by using a N2 isothermal adsorption/desorption method. The surface morphology of sample particles was photographed by field emission scanning electron microscopy, and their surface fractal dimensions were computed by a simple N2 adsorption isotherm method as well. As a result of a comparison between pore structures of oil-shale ash samples, the oil-shale ash, formed at a fast combustion mode without ash agglomeration occurring, has a larger pore volume and specific surface area because it has more pores and a rougher surface.

Pyrolysis experiments of Enteromorpha clathrata (ENT) (a species of seaweed) have been conducted using a DTG-60H thermal analyzer, and the pyrolysis characteristics obtained at different heating rates (20, 30, 40, and 50 °C min−1) are analyzed. The results indicate that the nonisothermal mass loss process of samples is composed of dehydration, rapid mass loss, slow mass loss, and solid residue decomposition. The devolatilization stage of ENT starts earlier than that of woody biomass because the basic components in seaweed are preferable for pyrolysis compared to lignocellulosic materials. The FTIR analysis is employed to investigate the changes in the main components of sample, while the TG-MS analysis is used for the gaseous products analysis during the pyrolysis. And because of the difference between the compositions of seaweed and woody biomass, gas formation here is not the same as the one from woody biomass. The characteristic parameters of pyrolysis at different heating rates show that the maximum rate of pyrolysis mass loss, the peak temperature, the initial and final temperature for devolatilization, and the heat release will increase with increasing heating rate. The kinetic parameters are calculated by using the Coats–Redfern method, which indicates that the kinetic function of pyrolysis mechanism is different from the woody biomass. The kinetic compensation effect exists between the activation energy and the frequency factor.

In this paper, an industrial cold experiment was conducted for studying regulating characteristics of a loop seal in a 65 t/h oil shale-fired circulating fluidized bed (CFB) boiler. The starting characteristic of the loop seal, and the effect of the supplying air and the fluidizing air in the loop seal were investigated. Compared with other regulating modes, the combined regulating mode of keeping the fluidizing air rate constant and regulating the supplying air rate can make the loop seal obtain better regulating quality, and offer more reliable guarantee for steady operation of the CFB boiler as well. In order to prevent circulating material depositing and slagging at the bottom of the loop seal, it was suggested that the fluidizing air rate and the supplying air rate is 2–3 and 1.2–1.5 times of the minimum fluidizing velocity of circulating material, respectively. These experimental results may be used as a reference for regulating the loop seal of the 65 t/h CFB boiler in hot condition and designing a new loop seal.Regulating characteristics of an industrial loop seal were investigated in a 65t/h oil shale-fired circulating fluidized bed boiler. Compared with different regulating modes, the combined regulating mode of keeping the fluidizing air rate constant and regulating the supplying air rate was proposed.