Evidence of coal and tire interactions in coal–tire coprocessing for short residence times

In this paper, the factors controlling the hydrocoprocessing of coal and waste tires in tubing bomb reactors are studied. The fixed experimental conditions were 400°C and 10 MPa of H₂ pressure. Five different coprocessing times (60, 30, 10, 5 and 3 min) and two coal–tire ratios (80% coal–20% tire and 20% coal–80% tire) were the studied variables. Results are compared with those obtained when coal and tire were processed by isolate. At these conditions, it was observed that reaction time has no effect on tire conversion in obtaining the possible maximum value. However, with coal, reaction time is a fundamental variable because total conversion depends on it. In tire, reaction time has no effect on total conversion, but it affects product distribution in obtaining lower oils yields at longer reaction times due to hydrocracking reactions. In hydrocoprocessing of both materials, a synergism in asphaltenes formation is observed at short reaction times. This synergism has been explained by the inter-reactions between coal and tire radicals. Besides, tire addition to coal hydrogenation processes improves the quality of the oils.     

Emission control in the combustion of coal–water and organic coal–water fuels

Promising methods for decreasing anthropogenic emissions due to the combustion of coals of different ranks and coal–water fuel (CWF) and organic coal–water fuel (OCWF) slurries on their basis are considered. The maximum concentrations of the main anthropogenic emissions of sulfur, nitrogen, and carbon oxides (SO _x , NO _x , and CO _x ) formed upon the combustion of solid fuels in a powdered state and as the components of CWF and OCWF slurries were determined. The concentrations of the most hazardous oxides formed upon the combustion of coals of different ranks (brown and black coals) and CWF and OCWF slurries were compared. The experimental results substantiated the use of CWF and OCWF slurries for emission control in coal-burning power engineering. The addition of a combustible liquid component to a CWF slurry (the production of an OCWF slurry) makes it possible to ensure acceptable environmental and energy characteristics.     

Burn-out of pulverised coal and biomass chars☆

The burn-out of carbon in pulverised fired power stations is commercially important. Interest in the burn-out of biomass chars is growing because biomass is increasingly being co-fired with coal to reduce the carbon dioxide emissions. The significance of carbon burn-out is that it is linked with the efficiency of the plant and the suitability of the coal ash for construction purposes. Residual carbon in ash has generally increased in recent years because of the influence of the lower temperatures and slower mixing resulting from the use of low NO_x burners. The amount of unburned carbon is thus a function of the plant design and operating conditions but it is also linked to the ease of combustion of the coal and the char formed. These latter factors are related to the properties of the coal and this paper attempts to quantify the impact of certain coal and char properties on carbon-out. An approach for assessing biomass combustion performance is also discussed.     

Effect of coal particle size distribution,volume fraction and rank on the rheology of coal–water slurries

The aim of this study was to understanding of the effect of coal particle size distributions on rheology of coal–water slurries (CWS). Experiments have been carried out on the coal samples that were different in rank. Besides two different Turkish lignites (Soma and Istanbul–Agacli), a bituminous coal from Siberia (Russia) has been used. In addition to the determination of the chemical and physical properties of the coal samples, their zeta potentials were also measured. The pulps of different solids percentage composed of coal particles with d₅₀ sizes of 19, 35 and 50 μm were used to determine the effect of volume fraction on the viscosity of the slurry.     

Ignition temperature of coal. 1. Influence of the coal’s composition,structure, and properties

The reactions of coal with the materials used in determining the ignition temperature of unoxidized coal according to Ukrainian State Standard DSTU 7611:2014 are analyzed. First, the ignition temperature of various types of coal from Ukraine, Russia, Canada, Australia, the Czech Republic, Poland, and Indonesia is determined. The influence of the composition, structure, and properties of the coal on its ignition temperature is assessed. The ignition temperature of the unoxidized coal is found to be closely related to the content of organic carbon C^daf and aromatic carbon C_ar, the structural parameter δ characterizing the degree of saturation of the coal’s organic mass, and also the vitrinite reflection coefficient R_o and the yield of volatiles V^daf.     

Flocculation of heterodisperse suspensions of fine coal (−0.5 mm)

Coal particles (−0.5 mm) were flocculated with fine magnetite by polyacrylamide-based polymers. The magnetic flocs obtained were retained in a magnetic field and their stability studied under different flow rates of water. Flocs formed by coarser particles were more easily broken. It is postulated that this is due to breakage of polymer bridges between particles.     

The effect of toluene-insoluble fraction of coal on catalytic activities of a Ni-Mo-γ-Al2O3 catalyst in the hydrotreating of coal liquids

Feedstocks prepared with 723 K⁺ distillation residues obtained from the Australian brown coalderived oil and hydrogenated creosote oil were hydrotreated to elucidate the effects of toluene-insoluble fractions of coal on the catalytic activities of a Ni-Mo-γ-Al₂O₃ catalyst. The toluene-insoluble fractions exerted harmful effects on the catalyst by deactivation due to carbonaceous deposits formed on the catalyst surfaces. The deactivation of the catalyst was more significant in hydroconverting of 623 K⁺ residues to 623 K⁻ oil fractions and hydrodenitrogenation reactions than in hydrodesulfurization reaction.The analyses of carbonaceous deposits on the spent catalyst surfaces by using an EPMA and a CP/MAS ¹³C-NMR indicated that the toluene-insoluble fractions were too refractory to be hydrogenated on the catalyst surfaces and hindered the reactant molecules from accessing to the active sites compared to asphaltenes.     

Influence of the preparation of organic coal–water fuel on its ignition

The integral ignition characteristics of a single droplet (initial radius 0.3–1.0 mm) of various organic coal–water fuels (prepared by means of a homogenizer or a ball mill) in an oxidant flux at 800–1100 K are compared. The fuel samples are based on spent motor, turbine, and transformer oils, filter cake from K coal, water, and plasticizer. The influence of the drop radius, the fuel composition, and the method and duration of sample preparation on the properties of the fuel (in particular, its structural stability and viscosity in the initial state) and on its ignition characteristics (the ignition delay, the time for total combustion, and the duration of the initiation stage) is determined. The limiting duration of structural stability is compared for samples of organic coal–water fuel prepared by means of a homogenizer and by means of a ball mill.     

Extraction of Taiheiyo coal with supercritical water–phenol mixtures

Taiheiyo Japanese sub-bituminous coal was extracted with supercritical water (SCW) and phenol mixtures at 673 K and at over fluid densities ranging from 0 to 0.5 g/cm³. The extraction yield with SCW was 0.55–0.60, but increased with increasing the ratio of phenol to water, showing a maximum of 0.7 at water–phenol ratio of 4.5:0.5 and then decreased to 0.50–0.55 for pure phenol.The main products for the SCW–phenol extraction were bisphenol alkyl compounds, while these compounds could not be detected when SCW was used as the solvent. For elucidating the mechanism of SCW–phenol extractions, reactions between phenol and model compounds of hydrolysis products (formaldehyde, acetone, propionic acid, and 2-propanol) were conducted. In SCW, formaldehyde reacted with phenol to produce polymers, while neither acetone nor propionic acid reacted with phenol. The 2-propanol dehydrated to form propene, which reacted with phenol to form 2-isopropylphenol. The reaction rate increased with increasing water density. In SCW–phenol extraction of coal, phenol seems to inhibit reactions that lead to hydrolysis products or those that might cross-link to form the macromolecules. Phenol can be used with SCW to reduce retrograde reactions in residual coals.     

Characteristics of the ignition of organic coal–water fuels for boiler installations

The ignition processes of organic coal–water fuels (OCWFs) in the flow of a heated oxidant (temperature, 700–1000 K; velocity, 0.5–5 m/s) were studied. The experiments were carried out with the small single drops of OCWFs (radii, 0.2–0.5 mm), which correspond to the injection devices of typical boiler installations. The component base of the test composition fuels included B2 brown coal, typical waste coals (the filter cakes of G and D coals), spent motor and transformer oils, and petroleum residue. The influence of the component composition (the properties and concentrations of solid and liquid combustible components) on the characteristics of the initiation of the combustion of single OCWF drops was found. The dependences of the delay times of ignition and complete combustion on the temperature of an oxidant and on the drop sizes of OCWFs were determined. It was established that, at maximum oxidant temperatures (above 900 K) and minimum drop sizes (smaller than 300 μm), difference between the integral characteristics of ignition was sufficiently small (smaller than 10%) for the fuels prepared from components with substantially different properties.     

Possibility of obtaining hydrogen from coal/waste–tyre mixture

Technically applicable gas with a high hydrogen content (ca 78%) was obtained through a two-stage pyrolysis of the mixture of Lazy bituminous coal with 15% waste tyre-rubber. The experiments were carried out in a laboratory pyrolysis unit with a 100 g charge. The incorporation of a thermal-degradation module in the stream of steam–gas mixture at the output of the pyrolysis reactor induced the decomposition of volatile products and significantly increased the yield of hydrogen. The influence of temperature of the cracking module (in the range between 900 and 1200 °C) on the amount of hydrogen in the pyrolysis gas was monitored. The solid by-product (carbonaceous residue) may be used as smokeless fuel or a sorbent precursor.     

The biodesulphurization of a semianthracite coal in a packed-bed system☆

The purpose of this study was to improve the desulphurization yield of a high sulphur-content semianthracite from northern Spain adapted to the process conditions of a packed-bed reactor, for which three 5-kg packed columns of coal were set up with the pH stabilized at 1.5. The process was begun by inoculating the first column with a culture obtained from micro-organisms native to the coal itself, mainly Thiobacillus ferrooxidans and Leptospirillum ferrooxidans, grown in a stirred reactor. The percolate of this column was then used to seed the second column, the percolate of which was then inoculated into the last one. The purpose was to obtain from the last column a better adapted and more active biomass which would give a better desulphurization yield for coal. Results show an increased yield from the first column to the last over the first 20 days of treatment, but the total desulphurization in the third column was less than expected, owing to a high precipitation of jarosite.     

Integration of coal pyrolysis process with iron ore reduction:Reduction behaviors of iron ore with benzene-containing coal pyrolysis gas as a reducing agent☆

An integrated coal pyrolysis process with iron ore reduction is proposed in this article. As the first step, iron oxide reduction is studied in a fixed bed reactor using simulated coal pyrolysis gas with benzene as a model tar compound. Variables such as reduction temperature, reduction time and benzene concentration are studied. The carbon deposition of benzene results in the retarded iron reduction at low temperatures. At high temperatures over800 °C, the presence of benzene in the gas can promote iron reduction. The metallization can reach up to 99% in20 min at 900 °C in the presence of benzene. Significant increases of hydrogen and CO/CO2 ratio are observed in the gas. It is indicated that iron reduction is accompanied by the reforming and decomposition of benzene. The degree of metallization and reduction increases with the increasing benzene concentration. Iron oxide can nearly completely be converted into cementite with benzene present in the gas under the experimental conditions. No sintering is found in the reduced sample with benzene in the gas.     

Mössbauer study of iron exchanged into Victorian brown coal

Mössbauer spectroscopy was used to characterize iron species introduced by an ion exchange method into Victorian brown coal to promote its hydroliquefaction. The iron speciation does not depend on the nature of the treatment solution (iron(II) sulphate, chloride or acetate). The two principal phases identified are divalent iron bound to dissolved humic material and a precipitate of microparticulate ferric oxyhydroxide; lesser amounts of both are also present before exchange. There is no evidence of association between iron and tin when introduced simultaneously into the coal.     

Large-eddy simulation of coal combustion in 15 MW pilot-scale boiler-simulation facility

High-fidelity modeling provides a useful approach to investigate the multiscale multiphysics mechanism in the pulverized coal combustion. This research focuses on understanding the pulverized coal combustion in a pilot-up facility: General electric (GE) 15 MW pilot-scale boiler simulation facility (BSF). The heat flux to the boiler water wall, O₂ concentration, and gas temperature are the quality of interest (QoI's) for this research, as they are the most important parameters for designing a full-scale pulverized coal boiler. Even the heat flux in boiler is largely determined by the heat transfer mechanism, and other detailed multiphysics mechanisms, including multiphase turbulent flow, radiation heat transfer, ash deposition, coal devolatilization, and oxidation, also need to be accounted. This work applies large-eddy simulation (LES) code on high-performance computing facility to simulate pulverized coal combustion in BSF. The physics-based submodel that contains the significant sensitivity for QoI's has been identified using the detailed impact factor analysis on this high-fidelity modeling. Results indicate that the most sensitive submodel on QoI's is the wall-heat-transfer coupling with the ash-deposition model, which allows us to prioritize to improve this submodel in the LES simulation. Thus, ash deposition and wall-heat-transfer processes have been modeled and integrated into coal combustion numerical simulation. The simulation results show quantitative agreement between the simulation with experimental data regarding gas temperature, O₂ concentration, and heat-flux profile across the exposed boiler walls. Another implication of this research is to demonstrate a positive societal impact of extreme computing and accelerate the development of new combustion technology using a capable exascale computing technique.     

Ignition of droplets of coal–water–oil mixtures based on coke and semicoke

To permit expansion of the resource base and utilize industrial waste, coal–water–oil fuels may be prepared on the basis of coke and semicoke, as well as common petroleum derivatives (fuel oil and spent compressor, turbine, and transformer oils). The minimal oxidant temperature corresponding to stable ignition of coal–water–oil slurries is established. Typical variation in fuel temperature in the course of reaction is determined, as well as the delay time of ignition and the total combustion time for individual droplets of such fuel suspensions. For droplets of initial size 0.5–1.5 mm, the influence of the various factors (droplet size, oxidant temperature, and concentration of the components) on the threshold (minimum) temperature and inertia of ignition is studied. It is shown that stable ignition of coke and semicoke in such fuel is possible at moderate oxidant temperatures: 700–1000 K.     

Influence of petrographic and mineral matter composition of coal particles on their combustion reactivity☆

Combustion at programmed temperature in a thermobalance is a rapid technique, which monitors coal burning characteristics and has shown its utility to classify coals according to their combustion performance. However, combustion profiles are affected by different coal properties and characteristics such as particle size, rank, maceral composition and mineral matter content, whose separate effects are difficult to determine. The objective of this work was to ascertain the influence of coaly and mineral matter composition and distribution on burning profiles as determined by thermogravimetric analysis, by using coals of different rank, and fractions of these coals obtained by density separation. Five coals ranging in rank from lignite to anthracite and with variable mineral matter content and composition were used in this study. Density fractions were separated from each coal to obtain samples with different organic/mineral matter proportions. Some of the factors influencing coal combustion profiles are widely recognised as the negative effect of increasing both rank and inertinite content on the reactivity. The favorable effect of mineral matter content on the reactivity has shown to be related to the maceral size within the density fractions and the intimate association organic/mineral matter that favors the diffusion of the reacting gas. Catalytic effects of the mineral matter could not be demonstrated.     

Influence of activation on the pore structure of adsorbents obtained from coal–alkali mixtures

The activation of carbon sorbents in CO₂ is investigated. The sorbents are produced by the thermolysis of naturally oxidized SS coal steeped in potassium hydroxide, with an alkali/coal ratio R _KOH = 0.01 and 0.05 g/g. The influence of CO₂ activation on the texture of the sorbents obtained is established. After 10-min activation, the increase in specific surface area of the sorbents is a maximum (about 100%). Longer activation increases the loss of material. The pore volume formed on activation is proportional to the proportion of carbon-bearing material removed. The volume of adsorbing pores formed in the sorbents is greatest when the loss of material is 25–35%.     

Mössbauer study of iron catalysis in Victorian brown coal liquefaction

Mössbauer spectroscopy was used to investigate the means by which iron promotes the hydroliquefaction of Victorian brown coal. Microparticulate ferric oxyhydroxide incorporated in the initial coal is reduced during hydrogenation through magnetite and troilite to α-iron, which transforms to cementite at 380 °C. It is proposed that a transient divalent iron species slows the initial thermal degradation of coal and that α-Fe is responsible for enhancing the ultimate liquefaction yield.