Coal Conversion Products Research Articles

EXERGY ANALYSIS OF COAL THERMAL CONVERSION PROCESSES

To develop energy-saving technologies and facilities that use coal, it is essential to evaluate the energy potential of the resulting products. Additionally, it is necessary to determine their suitability for specific technologies, processes, and installations. Alongside the energy method, it is proposed to use the exergy method, which allows for the assessment of not only the quantitative but also the qualitative aspects of thermal conversion processes. Thermal conversion methods such as combustion and gasification are of interest for both energy and industrial applications. The study includes calculations of the exergy efficiency of coal thermal conversion products, based on which material and exergy balances were compiled for the gasification process under air and oxygen blast conditions, as well as for the combustion process. An analysis was conducted to evaluate the impact of process temperatures on the characteristics of coal thermal conversion products (composition, output, exergy). Additionally, the exergy efficiency coefficients (overall, chemical and physical exergy) for these thermal conversion methods were calculated. Based on the analysis, optimal operating modes for coal thermal conversion processes were determined, depending on the final goals of the obtained products. The advantages of high-temperature oxygen and air gasification were identified, characterized by low exergy losses (24.9–28.9 %) and high chemical potential (12–13.46 MJ/kg of coal). The exergy efficiency of the oxygen gasification process is 68.3–71.2 %, while for air gasification, it is 70.2– 76.3 %. It was also established that, to achieve the highest fuel utilization efficiency, it is advisable to utilize the heat of the produced syngas. The utilization of 1 MJ/kg of coal from the physical exergy of the gas increases the overall exergy efficiency of air gasification by 3.5 % and that of oxygen gasification by approximately 0.7 %. A comparison of the exergy efficiency of the processes was conducted, revealing that coal gasification is a more rational method of thermal conversion compared to traditional combustion. This is because the highest losses are observed during the combustion process, with an exergy efficiency of 64.8 %. During coal combustion, irreversible losses account for 35 % of its initial exergy.

Hydrogen peroxide oxidation degradation of a low-rank Naomaohu coal

A mild controllable oxidation method was developed to depolymerize the macromolecular aromatic clusters of NMH coal into water-soluble products (WSPs) without ring-open reaction. Hydrogen peroxide (H2O2) was employed to oxidize coal sample at 60 °C, and the effect of reaction time on coal conversion and oxidation products was studied. The results showed that H2O2 is able to break bridge bonds and side chains connected to aromatic clusters, while Car-Car bonds of arene keep unchanged at same conditions. After 10 h oxidation, the coal conversion is 83.4 wt% and the aromaticity of oxidation residue is 7.43%, indicating most of aromatics have transferred to WSPs. The aromatic ring distribution in WSP can reflect that of NMH coal to some extent, where 1-ring, 2-ring and 3-ring compounds account for 58.4 mol%, 19.9 mol% and 21.7 mol%, respectively. Moreover, the pyrolysis of NMH coal and oxidation residue was conducted on an online pyrolysis-vacuum ultraviolet photoionization mass spectrometry, and the oxidation of several typical model compounds was also carried out to understand the oxidation mechanism. The results showed that the PhO-RPh bonds between aromatic clusters are most easily destroyed by H2O2. H2O2 oxidation degradation of coal are accompanied by generation of alkenes and decarboxylic reaction.

Method for separation of coal conversion products from oxygen carriers

Complete fuel conversion represents an important, but unresolved, aspect in Chemical Looping Combustion (CLC). Different system design approaches are currently being investigated to maximize carbon conversion in the fuel reactor. To achieve greater than ninety percent conversion of the fuel in “fluid-bed” type reducers will require that CLC systems be equipped with additional process equipment to ensure that unburnt fuel leaving the reducer is minimized. This paper presents results obtained from a laboratory test system simulating a char stripper design comprising two components; one for separating large char particles, based on material density differentials, and another for removing small char particles from the oxygen carrier (OC) leaving the reducer, based on elutriation. A test unit was designed, built and operated to identify optimum conditions for separating OC material from unburnt solid fuel – char. The results obtained are necessary for designing a high temperature unit operated at temperatures expected within a CLC system.

Sequential mineral transformation during underground coal gasification with the presence of coal partings

Underground coal gasification (UCG) can be adopted to convert unminable coal resources into synthesis gas for use in the production of electricity, fuels, and chemicals. UCG is a promising technology with many health, safety, and environmental advantages over conventional mining techniques. It is of great scientific significance to study the mineral transformation and identify the typical minerals in certain process conditions, because it may help to ensure the stable operation of the gasification processes and improve the utilization efficiency of coal seams. The presence of coal partings has an important impact on mineral transformation. In this paper, the UCG process has been subdivided into pyrolysis, reduction, and oxidation stages, and the progressive coal conversion products were prepared. Ulanqab lignite was used as the test coal. The minerals in the coal transformation products were identified by X-ray diffraction (XRD) and scanning electron microscopy coupled with an energy-dispersive spectrometer (SEM-EDS). The thermodynamic equilibrium simulation software, FactSage 7.2, was used to calculate the relevant phase diagram to assist in understanding the mineral transformations. The experimental results indicate that the different iron-bearing minerals occur in raw coal and non-coal partings which are nontronite (Na0.3Fe2Si4O10(OH)2.4H2O) and glauconite (K (Fe, Al)2(Si, Al)4O10(OH)2) respectively. Pyrrhotite is the main iron-bearing mineral in the pyrolysis products. In the reduction stage, the relative content of Al2O3 is increased due to the presence of non-coal partings, which reacts with FeO to produce hercynite (FeAl2O4) at a temperature above 1100 °C. When the temperature increases to 1300 °C, hercynite is converted to the thermodynamically-stable cordierite (Fe2Al4Si5O18). In the oxidation stage, mullite (Al6Si2O13) is produced when the oxidation temperature reaching 1300 °C, which could be used to reflect the underground reaction conditions in the coal seam. The phase diagram of (SiO2)6.2Al2O3-CaO-Fe2O3 proves that mullite and anorthite (CaAl2Si2O8) are the dominant minerals when the mole fraction of (SiO2)6.2Al2O3 is above 0.7. In addition, the ash melting point rises with an increase of Si and Al content in the presence of non-coal partings.

Evaluation of coal-related model compounds using tandem mass spectrometry.

Gas chromatography/mass spectrometry (GC/MS) is a routine and basic instrumental method for the analysis of complex coal conversion products in the chemical industry. To further enhance the practical potential of GC/MS in chemical industry, a tandem MS method for the selection of ion pairs applied in monitoring coal conversions was established using GC/quadrupole time-of-flight MS (GC/Q-TOF MS). The corresponding fragmentation pathways were explored and suitable ion pairs were screened. Fourteen coal-related model compounds (CRMCs) were analyzed using GC/Q-TOF MS with different collision-induced dissociation (CID) energies (5-20eV). The fragmentation pathways can offer a better understanding of chemical bond breaking, hydrogen transfer, rearrangement reactions and elimination of neutral fragments for CRMCs during the CID process. The precursor ions of aromatic hydrocarbons without alkyl chains were difficult to fragment with a CID energy of 20eV. But aromatic hydrocarbons with branched chains were prone to fragment via the loss of alkyl chains and further fragmented through ring-opening reactions. Compared with the Calk Car bond, the Car Car bond was difficult to fragment due to its high bond dissociation energy. The existence of heteroatoms facilitated fragmentation that was conducive to the screening of ion pairs. The CID technique of GC/Q-TOF MS will contribute to studies on the organic composition of coals and to building monitoring methods for coal conversions via fragmentation and ion pair selection.

Sequential Transformation Behavior of Iron-Bearing Minerals during Underground Coal Gasification

Detailed mineralogical information from underground coal gasification (UCG) is essential to better understand the chemical reactions far below the surface. It is of great scientific significance to study the mineral transformation and identify the typical minerals in certain process conditions, because it may help to ensure the stable operation of gasification processes and improve the utilization efficiency of coal seams. The transformation of iron-bearing minerals has the typical characteristics during the UCG process and is expected to indicate the process parameters. In this paper, UCG progress was subdivided into pyrolysis, reduction and oxidation stages, and the progressive coal conversion products were prepared. Two types of lignite with different iron contents, Ulankarma and Ulanqab coals, were used in this study. The minerals in the coal transformation products were identified by X-ray diffraction (XRD) and a scanning electron microscope coupled with an energy-dispersive spectrometer (SEM-EDS). The thermodynamic calculation performed using the phase diagram of FactSage 7.1 was used to help to understand the transformation of minerals. The results indicate that the transformation behavior of iron-bearing minerals in the two lignites are similar during the pyrolysis process, in which pyrite (FeS2) in the raw coal is gradually converted into pyrrhotite (Fe1−xS). In the reduction stage, pyrrhotite is transformed into magnetite (Fe3O4) and then changes to FeO. The reaction of FeO and Al2O3 in the low iron coal produces hercynite above 1000 °C because of the difference in the contents of Si and Al, while in the high iron coal, FeO reacts with SiO2 to generate augite (Fe2Si2O6). When the temperature increases to 1400 °C, both hercynite and augite are converted to the thermodynamically-stable sekaninaite.

Adsorption properties of coal from the Ishideiskoe deposit, semicokes, and ash and slag wastes from the combustion of coals from Siberia and Sakhalin

The results of studying the adsorption properties of black coal, semicoke, and waste coals from a number of coal deposits in Irkutsk oblast and Sakhalin and the Irsha-Borodino deposit are reported. The results of a comparative study of the adsorption capacity of adsorbents for organic compounds and metals (Mn, Cr, Fe, Cu, Zn, and Ni) from sulfuric acid and hydrochloric acid solutions are given. It was established that the adsorption of heavy metals on semicokes and ash residues in a sulfuric acid solution occurred somewhat better than in a hydrochloric acid solution. The test samples of coal and coal conversion products are good adsorbents.

Electrochemical properties of polymetacyclophaneoctols and metal-polymer nanocomposites on their basis

Crosslinked polymers based on macrocyclic polyphenols, in particular, metacyclophaneoctols, can serve as the matrices of proton-conducting membranes and electrode materials for a new generation of chemical current sources. Coking coal conversion products are the main source of raw materials for the production of metacyclophaneoctols. Here, a conductometric and potentiometric study of the properties of polymetacyclophaneoctols and metal-polymer nanocomposites on their basis was performed. It was found that the electrical conduction of the H form of polysulfonatotetraphenylmetacyclophaneoctol (0.2 S/cm) corresponds to the performance characteristics of the best proton-exchange membranes of hydrogen fuel cells. The nanocomposite on a polysulfonatotet-rametacyclophaneoctol matrix containing 5% palladium metal nanoparticles was proposed as a material for the negative electrode of a hydrogen fuel cell. Polysulfonatotetraphenylmetacyclophaneoctol containing 2% palladium nanoparticles and 10% silver was chosen as a material for the positive electrode, at which oxygen is reduced.

Bioassays for risk assessment of coal conversion products.

Traditional as well as biotechnological processing of coal leads to complex mixtures of products. Besides chemical and physical characterization, which provides the information for product application, there is a need for bioassays to monitor properties that are probably toxic, mutagenic or cancerogenic. Investigations carried out focused on the selection, adaptation and validation of bioassays for the sensitive estimation of toxic effects. Organisms like bacteria, Daphnia magna and Scenedesmus subspicatus, representing different complexities in the biosphere, were selected as test systems for ecotoxicological and mutagenicity studies. The results obtained indicate that bioassays are, in principle, suitable tools for characterization and evaluation of coal-derived substances and bioconversion products. Using coal products, coal-relevant model compounds and bioconversion products, data for risk assessment are presented.

98/00692 Bioassays for risk assessment of coal conversion products

In this paper, a new method of realizing process control by means of UCSD APPLE PASCAL advanced computer language is established by discussing the following problems which are often met in process control: 1.(1) Input data and signal on-line.2.(2) Output data and signal on-line.3.(3) Speed.4.(4) Interrupt technique.5.(5) Timer function and series of square wave pulses with changeable frequency.The idea of the method means using advanced computer language in place of traditional assembly language to program control softwares. The assembly language is only used in the small parts of control software, such as inputting/outputting data or signal, interrupt processing, etc., which require high running speed. The others are all programmed with advanced computer language. The software programmed with two kinds of computer languages is linked to form the CODE File of entire program which owns the characteristics of high running speed, stronger capability of processing data, more easily understood by control engineers, more simple programming, high precision, and high flexibility. The main contents in the paper are verified by experiments in laboratory.

97/02516 Investigation of coals and coal conversion products by FTIR methods

The influence of different coal lithotypes on grindability has been investigated using lignite from two of the most important Upper Miocene lignite basins in Serbia (Kolubara and Kostolac). Yellow xylite-rich types demonstrated the most negative impact on Hardgrove Grindability Index (HGI). All different types of xylite-rich coal, as well as total xylite-rich coal from the Kolubara basin have a negative influence on the grindability properties, while only the yellow type of xylite-rich coal from the Kostolac showed a negative impact on HGI. Matrix coal does not show a clear effect on HGI.A negative correlation between textinite content and HGI is observed in both basins, whereas contents of other macerals do not show influence on grindability properties.Content of total organic carbon demonstrated the negative impact on HGI. Correlation analysis indicates that the negative impact of the yellow type of xylite-rich coal and the sum of total xylite-rich coal on the grindability properties partly can be related to content of total organic carbon and high amount of soluble organic matter. Matrix lithotype does not show any significant correlation with bulk geochemical parameters in both basins.The peat-forming vegetation of all samples from both basins were dominated by decay-resistant gymnosperm (coniferous) plants, belonging to one or several of the families Taxodiaceae, Podocarpaceae, Cupressaceae, Araucariaceae, Phyllocladaceae and Pinaceae. Lignite from the Kolubara basin is characterized by a higher contribution of angiosperm vegetation than coal from the Kostolac basin. Peatification of the Kolubara coal occurred under more oxic conditions than the Kostolac one.Analysis of biomarkers indicated that the negative impact of all types of xylite-rich coal from the Kolubara on HGI can be related to the higher proportion of angiosperms, abundance of mid-chain n-alkanes and sesquiterpenoids, aromatization of non-hopanoid triterpenoids and hopanoids, and intense degradation of wood tissues in a more oxic environment. The positive impact of matrix coal on HGI in the Kolubara samples can be attributed to elevated content of non-aromatic hopanoids and low amounts of aromatic non-hopanoid triterpenoids and sesquiterpenoids, which seems to hinder the grindability properties.

Coke forms in nature and in power utilities: interpretation with SEM

Scanning electron microscopy (SEM) has grown to be a mature analytical technique. However, its use in coal science and technology can be more widely expanded. This paper is a summary showing how SEM-EDX was applied in such diverse fields as geology and the power industry. As reflected light microscopy, SEM is suited to the identification of textural changes in coal conversion products. However, in contrast with reflected light microscopy, SEM does not require sample polishing. An advantage for many applications is that X-ray micro-analysis gives information on the temperature history of heated coal. These features make SEM with energy dispersive X-ray analysis (EDX) a valuable tool in studies of industrial and geological samples. The paper gives examples where SEM has been successfully applied. Natural coke samples were fractured to study heating effects on coal and mineral matter. Pyrite was used as a geological thermometer, showing that 750 °C was the maximum temperature reached near the magmatic intrusion. High temperature combustion chars were analysed as-received, without polishing. Whole particles as seen by SEM gave more information about the combustion process than the polished blocks used in optical microscopy. This is because the effects of burn-off are more visible from the outer surface than from the internal structure.

Relation between release of conversion products in coal liquefaction and cross-linking

A study was made of the relation between the release of coal conversion products and cross-linking, using catalytic solvent-free hydrogenation in order to avoid problems in data interpretation caused by the presence of solvent. Twenty-five subbituminous and bituminous coals were hydrogenated in the absence of solvent at 5 and 10 MPa H 2 (cold), temperatures of 300, 350 and 400 °C and reaction time 30 min, with molybdenum sulfide as catalyst supported on the coal. The low-rank coals selected were more reactive than the bituminous ones. The subbituminous coals gave a maximum liquids production at 350 °C. At 400 °C the liquids yield decreased but the oil yield increased. Liquids from the hydrogenation of subbituminous coals were less asphaltenic than those from the bituminous ones. The residual chars were characterized by the extent of swelling in pyridine. For the subbituminous coals the swelling decreased with increasing conversion, reaching maximum cross-linking at the most severe conditions in most instances. The bituminous coals showed a different behaviour at low conversion, but at higher conversion the relation between conversion and swelling appeared to be similar to that for the subbituminous coals.

Comparison of hydrogen transfer from cyclic olefins and hydroaromatic donors under thermal and catalytic liquefaction conditions

A new class of compounds is being investigated for their ability to donate hydrogen during coal liquefaction. The compounds, known as cyclic olefins, are hydroaromatic species without an aromatic ring. These compounds are extremely reactive at coal liquefaction conditions, readily forming other partially saturated compounds and aromatics. This investigation demonstrates the effectiveness of these compounds for coal conversion and liquefaction products. 1,4,5,8-Tetrahydronaphthalene, also known as isotetralin, and 1,4,5,8,9,10-hexahydroanthracene are the two cyclic olefins employed in this study. Their hydrogen-donating ability, as reflected by the amount of coal converted to tetrahydrofuran solubles, is compared to that of their conventional hydroaromatic analogues, tetralin, dihydroanthracene, and octahydroanthracene, at equivalent donable hydrogen levels

Identification of coal pyrolysis products by scanning electron microscopy

Scanning electron microscopy (SEM) is a useful method for studying coal pyrolysis products. Using SEM, coked macerals were recognized by flow patterns originating from the plastic stage. Reduced coking properties could be observed on oxidized coals. Particular attention was given to coal conversion products obtained under the heating conditions of fluidized bed combustion, because coke formation has an adverse effect on the process. SEM-results were in general agreement with optical data.

Determination of polyaromatic hydrocarbons in high-boiling fractions of bituminous coal tar

A procedure is proposed that allows determination of the content of polyaromatic hydrocarbons in coal conversion products. It involves dialysis, extraction and g.c.-m.s. and SEC-g.p.c.-m.s. analysis. The contents of aromatics with a wide range of molecular weights can be determined. The procedure is suitable for high-boiling coal conversion products.

Dialytic removal of particulate matter from coal conversion products

A dialytic procedure which is effective for the removal of microparticulate and colloidal-sized suspended matter from coal-derived liquids is described. The method involves passing the sample, dissolved in methylene chloride, through a latex rubber membrane. The dialytic procedure appears promising as a convenient method for production of large, particulate-free samples of coal conversion products. Application of the technique is illustrated by separation of a high particulate (≈30wt% insoluble materials) stripper bottom sample from the SRC-II process and subsequent analysis of the organic composition and metals content of the dialysate. The material which traverses the membrane, the dialysate, is shown to be a representative sample of the soluble organic portion of the material being dialysed and found to be essentially free of metals. The true solubility of the dialysate renders it easier to characterize via instrumental methods than the original sample containing large amounts of insoluble materials.

Conversion and uses of liquid fuels from coal

This general paper surveys recent developments in converting coal, mainly into hydrocarbons for use in the transport and chemical industries. Primary conversions by direct, i.e. solvent extraction, and indirect methods are described, together with some of the subsequent refining procedures required to make acceptable products. Though it is unlikely that there will be an overnight world shortage of crude petroleum, political instabilities do not rule this out and ‘local’ shortages might be very acute. Most probably there will be a transitional period in which coal and oil contribute in complementary ways. As oil supplies diminish, coal will be needed increasingly for making essential transport distillates and chemical intermediates. Most conversion processes under development aim to make product oils which can be readily fitted into existing markets. However, coals differ considerably from crude oils in chemical composition and complexity. Thus, in making motor spirit, relatively few technical problems are expected, but in other areas, e.g. in diesel fuels and some ‘petrochemical’ intermediates, coal-conversion products are much less suited to current uses without further (usually expensive) processing. The relative merits of various processing methods are discussed. The paper also considers replacement sources for ‘petrochemicals’ and discusses the wider implications of making olefins. The scope for making intermediate chemicals by coal gasification and subsequent synthesis is outlined. Some areas of future difficulty including technical, economic and environmental matters, are discussed.

DUVAS: a real-time aromatic vapor monitor for coal conversion facilities.

A real-time field-portable derivative UV-absorption spectrometer (DUVAS) has been designed, built, and evaluated as an aromatic vapor monitor for use at coal conversion facilities. The instrument is microcomputer controlled, providing a variety of operating modes. Both laboratory and field measurements have been made. Among the aromatic vapors detected in headspace above various coal conversion products are benzene, toluene, phenol, cresols, and naphthalenes. The instrument should prove useful as an industrial hygiene tool both for area monitoring and for leak detection.

Thin Layer Chromatographic Screening of Coal Liquids

Abstract Procedures are described for the thin layer chromatographic (TLC) analysis of coal-derived liquids. After solvent selection using Selectosol (1) radial TLC, a series of compounds typically found in coal liquids was used to demonstrate their elution behavior on silica gel. It was determined that unactivated (Brockman 4) silica plates series developed with isooctane/tetrahydrofuran (THF) (80:20, v/v) provided the best separation. The order of elution was saturate >hydroaromatic >polynuclear aromatic (PNA)>phenols ≥ nitrogen bases. The use of two-dimensional TLC with reverse phase and silica contiguous on the same plate (Whatman Multi-K) is discussed for the rapid separation and identification of coal liquid components. Trimethylsilyl ether derivatives were prepared of phenols and alcohols present in coal conversion products. This technique proved most useful in that the TMS-derivatives behaved similarly to their parent PNA, in order of elution, on silica plates using a moderately active mobile phase (isooctane: THF,80:20, v/v). TLC and the reactions described provide a semi-quantitative measure of the degree of hydrogenation of coal-derived liquids.