IMPREGNATION AND RECOVERABILITY OF ELEMENTAL SULFUR IN COAL USING THE PERCHLOROETHYLENE DESULFURIZATION PROCESS

During the perchloroethylene extraction process, C-S bond cleavage reactions occur, which liberate labile sulfur from the organic matrix of coal into the solvent medium i.e., perchloroethylene, where it is dissolved and extracted. In this paper, the effect of impregnation of elemental sulfur in raw coal on its forms of sulfur analyses has been investigated. The effect of the same sulfur-impregnated coal on its organosulfur extractability has also been explored. Studies were conducted to observe whether the impregnated elemental sulfur was fully recoverable by the perchloroethylene extraction process. It was observed that sulfur can be very easily impregnated into the microstructure of coal. On the basis of tests on raw and impregnated coals, based on ASTM D-2492 standard, the impregnated sulfur reflects mostly in the form of organic sulfur. The impregnated sulfur which appears in the form of organic sulfur is fully recoverable via the perchloroethylene extraction     

PERCHLOROETHYLENE EXTRACTION DESULFURIZATION OF LOW SULFATE COALS

ABSTRACT

The perchloroethylene coal refining process utilizes perchloroethylene (PCE) as its solvent in all phases of the precombustion desulfurization process, including wet grinding, organic sulfur removal, gravitational separation of pyrites and mineral matter, and recovery of elemental sulfur (S₈). The Process is capable of producing compliance coal which emits less than 1.2?lb SO_X/MBTU when burnt, starting from 5 mass percent sulfur Midwestern and Eastern U.S. coals. However, the process efficiency was found to be very strongly dependent upon the degree of weathering or the level of coal oxidation. In this paper, perchloroethylene extraction data of fresh, low-sulfate coals are summarized and critically assessed. The extraction efficiency of the organic sulfur removal ranged from 5 to 30 percent for fresh coals, while that for weathered coals ranged from 30 to 60 percent. This study provides a valuable insight into the chemical reaction mechanism of perchloroethylene desulfurization process.     

ENVIRONMENTAL AND ECONOMIC ISSUES IN THE USE OF PERCHLOROETHYLENE AS THE SOLVENT IN PERCHLOROETHYLENE COAL CLEANING PROCESS

ABSTRACT

The Perchloroethylene coal cleaning process effectively removes both organic and inorganic forms of sulfur in coal. Complete recyclability of the solvent is the key to both economic and environmental issues concerning the use of perchloroethylene in this process. Recyclability of the solvent has been fully established by repeated batch operation as well as FTIR structural investigations of solvent molecules. In the current investigation, the solvent has been subjected to various analyses after each stage in the operation i.e., before extraction, after extraction and after distillation. The organic desulfurization is based on an extraction-reaction mechanism and is catalyzed by the mineral matter inherently and naturally present in coal. This paper also aims at studying the role played by the solvent (perchloroethylene) in the extraction process as well as in the catalytic reaction occurring in the system. This paper also presents data on the effect of re-using ‘sulfur-rich mother liquor’, rich in extracted sulfur, on the organosulfur extraction efficiency. These data are very important from the point of view of process engineering and economics.     

PERCHL0R0ETHYLENE EXTRACTION DESULFURIZATION OF WEATHERED COALS

Abstract

The perchloroethylene extraction process has proven to be an effective pre- combustion coal desulfurization process which offers a complete process package including wet grinding, organic sulfur removal, pyrite and mineral matter separation, solvent recovery, and byproducts and sulfur recovery. In this paper, coal weatherability was investigated for various Midwestern and Eastern U.S. coals, and its effect on organosulfur extractability by the perchloroethylene process was identified. Both “natural” and “artificial” weathering of these coals were experimentally investigated. A statistically significant difference in the extraction efficiency between fresh and weathered coals vas observed. A strong relation between the extractability and degree of weathering of the coal was established. The results provide a valuable insight into the process engineering of this process.     

PERCHLOROETHYLENE EXTRACTION DESULFURIZATION OF LOW SULFATE COALS

The perchloroethylene coal refining process utilizes perchloroethylene (PCE) as its solvent in all phases of the precombustion desulfurization process, including wet grinding, organic sulfur removal, gravitational separation of pyrites and mineral matter, and recovery of elemental sulfur (S₈). The Process is capable of producing compliance coal which emits less than 1.2 lb SO_X/MBTU when burnt, starting from 5 mass percent sulfur Midwestern and Eastern U.S. coals. However, the process efficiency was found to be very strongly dependent upon the degree of weathering or the level of coal oxidation. In this paper, perchloroethylene extraction data of fresh, low-sulfate coals are summarized and critically assessed. The extraction efficiency of the organic sulfur removal ranged from 5 to 30 percent for fresh coals, while that for weathered coals ranged from 30 to 60 percent. This study provides a valuable insight into the chemical reaction mechanism of perchloroethylene desulfurization process.     

LIGAND ASSISTED DESULFURIZATION OF LIGNITE USING THE PERCHLOROETHYLENE COAL REFINING PROCESS

ABSTRACT

The perchloroethylene coal refining process was used on North Dakota lignite coal. Effects of extraction time, perchloroethylenexoal ratio and artificial weathering were studied to determine their effects on the removal of organic sulfur. The artificial weathering conditions used were found to be too harsh and caused a decrease in the amount of organic sulfur removed, unlike normal weathering conditions. Additional studies were done involving various ligands, and showed that the addition of certain ligands during the process aided in the extraction of organic sulfur from the coal.     

EFFECT OF FILTRATION TEMPERATURE ON ORGANIC SULFUR REMOVAL FROM COAL BY PERCHLOROETHYLENE COAL CLEANING PROCESS

Abstract

The perchloroethylene extraction desulfurization process removes the organic sulfur in coal via a hybrid mechanism of solvent extraction and chemical reaction. The nature and extent of the reaction is controlled by the extraction time and temperature of operation. Although the extraction temperature is kept identical for all types of coals (120°C), the organosulfur extraction time still depends upon the type of coal. If the reaction mixture is left too long in the extraction environment, the intermediate labile sulfur released by the reaction forms cross-links with the organic matter in the macromolecule of coal. This is detrimental to the process efficiency. Constant temperature has to be maintained throughout the extraction, till coal is separated from the solvent. If not, the extracted labile sulfur re-enters the coal macromolecule to form inter-penetrating polymer networks with the organic matter in coal. In this paper, it has been established that the time required for separation and isothermality of the process are crucial to maintain the reaction progressing toward sulfur and organic sulfur liberation from the macromolecule. The data presented in this paper are important from the viewpoint of process development, because the process mandates the separation of coal and solvent at the operating temperature.     

STATISTICAL ANALYSIS OF ORGANOSULFUR EXTRACTION DATA OF OHIO 5/6 COAL USING THE PERCHLOROETHYLENE COAL CLEANING PROCESS

ABSTRACT

The perchloroethylene coal cleaning process removes both organic and pyritic forms of sulfur using perchloroethylene as the solvent medium. The effect of process variables including temperature, extraction time, solvent to coal ratio and particle size of coal has been studied by a systematic 2⁴ full factorial experimental design with a single replicate. The process was found to be strongly dependent on the type of coal. Hence, this variable was controlled by choosing one single type of coal, i.e., Ohio 5/6 (1:1 mixture of Ohio 5 and Ohio 6 coals) throughout this entire investigation. The significant effects and interactions have been quantified by F-tests. The estimates of significant effects have been obtained by Yates algorithm. Residual probability and normal probability plots have been obtained to test model adequacy. Finally, a computational model has been developed to predict the organosulfur extraction efficiency of this coal at various values of process variables. The parity plots conclude that the model has a good interpolational predictive capability.     

EFFECT OF PYRITIC SULFUR AND MINERAL HATTER ON ORGANIC SULFUR REMOVAL FROM COAL

Abstract

The perchloroethylene coal cleaning process uses perchloroethylene as the solvent to remove both organic and inorganic forms of sulfur without any significant loss to its calorific value. The process removes these forms of sulfur in two sequential unit steps. The objective of this investigation was to determine the exact sequence of operations in the Process. Hence, organosulfur was removed before and after depyriting and demineralizing the coal. The extent of total sulfur as well as organic sulfur removal were compared in both cases. It was found that the desulfurization is more efficient when organosulfur is extracted before pyritic sulfur and not vice versa, in the sequential removal of organic and inorganic forms of sulfur. The data presented in this paper reestablishes a fact that the mineral matter content in coal is quintessential to its organosulfur extractability.     

EFFECT OF MOISTURE IN COAL ON ITS ORGANIC SULFUR EXTRACTABILITY

Abstract

The extent of organic sulfur removed by the perchloroethylene desulfurization process depends upon several factors including the type of coal, the amount of catalyst present in it, and the temperature of organosulfiir extraction. Moisture in coal also plays a very important role in this extraction process. In this paper, the role played by moisture and its subsequent effect on the process efficiency has been investigated. It has been found that the moisture in coal affects the extraction process in two ways. Firstly, in presence of water, the temperature of the operation is reduced. This affects the organosulfiir extraction efficiency adversely. Secondly, the naturally available catalytic ingredients in coal, essential for the organosulfiir extraction, are soluble in water. Therefore, in presence of water, the catalytic potency of these catalytic species is lost, and thus reducing the organosulfiir extractability. The data presented in this paper are also important from the point of view of process development, because it has been experimentally established that the moisture content in coal has to be sufficiently reduced in order to improve the overall process efficiency.     

KINETICS OF PERCHLOROETHYLENE EXTRACTION DESULFURIZATION OF COALS

ABSTRACT

The perchloroethylene coal cleaning process selectively removes the organic sulfur from coal via a hybrid mechanism of chemical reaction and physical solvation It was found that the chemical reaction was catalyzed by the inorganic species present in the coal. In this paper, a kinetic study was experimentally carried out to determine rate constants of the reaction. It was confirmed that the extent of organosulfur extraction depended strongly on the type of coal, and also that there is a critical extraction time which is required as the minimum time for each type of coal. Isothermal batch kinetic studies were done for various types of coal. A relation was established between the type of coal and its kinetics and hence the minimumtime for extraction.     

COBENEFICIATION OF COALS IN PERCHLOROCTHYLENE EXTRACTION DESULFURIZATION

ABSTRACT

The perchloroethylene (PCE) coal refining process has been investigated for its process feasibility, operational reproducibility, organic sulfur selectivity, process efficiency, minimization of residual chlorine by steam stripping and process optimization. It was found that some coals result in a better organosulfur extraction than others. It was also confirmed that the PCE extraction process was a hybrid system of chemical reaction and physical solvation. It was further established that the coals giving a higher organosulfur extraction contain some naturally available ingredients, which promote the extraction process. Coals giving a much lower organosulfur extraction lack these species. This paper focuses on demonstration of the process feasibility of cobeneficiating both types of coals, together. In this novel process, both types of coal are blended together in fixed proportions and subjected to the PCE process. This process of cobeneficiating coals is industrially significant because of its cost effectiveness. It not only removes the organosulfur from one type of coal, but also significantly improves the organosulfur extraction from the other.     

ENVIRONMENTAL AND ECONOMIC ISSUES IN THE USE OF PERCHLOROETHYLENE AS THE SOLVENT IN PERCHLOROETHYLENE COAL CLEANING PROCESS

The Perchloroethylene coal cleaning process effectively removes both organic and inorganic forms of sulfur in coal. Complete recyclability of the solvent is the key to both economic and environmental issues concerning the use of perchloroethylene in this process. Recyclability of the solvent has been fully established by repeated batch operation as well as FTIR structural investigations of solvent molecules. In the current investigation, the solvent has been subjected to various analyses after each stage in the operation i.e., before extraction, after extraction and after distillation. The organic desulfurization is based on an extraction-reaction mechanism and is catalyzed by the mineral matter inherently and naturally present in coal. This paper also aims at studying the role played by the solvent (perchloroethylene) in the extraction process as well as in the catalytic reaction occurring in the system. This paper also presents data on the effect of re-using 'sulfur-rich mother liquor', rich in extracted sulfur, on the organosulfur extraction efficiency. These data are very important from the point of view of process engineering and economics.     

PROCESS ENGINEERING STUDIES OF THE PERCHLOROETHYLENE COAL CLEANING PROCESS

ABSTRACT

The perchloroethylene coal cleaning process has proven to be very effective in removing both organic and pyritic sulfur from high-sulfur coals. The process removes 30%- 70% of the organic sulfur and 90%- 99% of the pyritic sulfur with very little loss (<1.0 wt%) of hydrocarbons and their heating value. The process has been investigated on a bench- scale and a fully continuous, mini-pilot scale (5 kg/hr). This paper discusses scientific and technological issues related to the process engineering and the reaction chemistry of the process. The objective of this paper is to report the status of the process development and to address the important issues of the process commercializability.     

PERCHL0R0ETHYLENE EXTRACTION DESULFURIZATION OF WEATHERED COALS

The perchloroethylene extraction process has proven to be an effective pre- combustion coal desulfurization process which offers a complete process package including wet grinding, organic sulfur removal, pyrite and mineral matter separation, solvent recovery, and byproducts and sulfur recovery. In this paper, coal weatherability was investigated for various Midwestern and Eastern U.S. coals, and its effect on organosulfur extractability by the perchloroethylene process was identified. Both “natural” and “artificial” weathering of these coals were experimentally investigated. A statistically significant difference in the extraction efficiency between fresh and weathered coals vas observed. A strong relation between the extractability and degree of weathering of the coal was established. The results provide a valuable insight into the process engineering of this process.     

REMOVAL OF RESIDUAL CHLORINE FROM INDIANA 5 COAL BY SUPERCRITICAL CARBON DIOXIDE EXTRACTION

ABSTRACT

The perchloroethylene coal desulfurization process has unique advantages as a precombustion coal cleaning process, that include high cleaning efficiencies, mild process conditions, minimal output of undesirable byproducts, and cost effectiveness. However, the use of perchloroethylene in the process renders an important process engineering problem of complete recovery and reuse of perchloroethylene. thus requiring a “zero discharge” condition of the solvent. Therefore, the treated coal must be stripped of any residual perchloroethylene. Carbon dioxide (CO₂) in its supercritical state has been investigated for its ability to remove chlorine from Indiana 5 coal, that has been desulfurized by the perchloroethylene (PCE) process. The reduction of CI contenttffrom a PCE treated and filtered coal has been as high as 78% The exprements have been carried out. following a statistical experimental design and the discerning characteristics of the process been identified. The solvent density and extraction conditions can be tailored in such a way as to optimally remove CI from the coal without any detrimental effects on the coal matrix. The supercritical CO₂ extraction process can be successfully implemented to the PCE coal cleaning process by replacing energy intensive steps of steam stripping and vacuum dying     

WASHABILITY CURVES FOR PYRITE REMOVAL IN COAL USING PERCHLOROETHYLENE AS HEAVY MEDIUM

Abstract

Pyritic sulfur is removed from raw, high sulfur coal by gravitational separation using a suitable solvent, or heavy medium. This is possible due to the inherent difference in the specific gravity of clean coal and the mineral matter in it. The effectiveness of perchloroethylene (PCE) as a heavy medium was experimentally evaluated. The most important factors governing the efficiency of this process are the quantity of clean coal yield and depyriting efficiency. It was found that the pyritic sulfur removal efficiency as well as the clean coal yield depended strongly on its particle size distribution and mineral matter content. This paper presents valuable data on the effect of particle size of coal on clean coal yield as well as pyritic sulfur removal efficiency. A “master” curve is obtained to determine a workable size range which gives the most optimal yield of clean and depyrited coal.     

EFFECT OF FILTRATION TEMPERATURE ON ORGANIC SULFUR REMOVAL FROM COAL BY PERCHLOROETHYLENE COAL CLEANING PROCESS

The perchloroethylene extraction desulfurization process removes the organic sulfur in coal via a hybrid mechanism of solvent extraction and chemical reaction. The nature and extent of the reaction is controlled by the extraction time and temperature of operation. Although the extraction temperature is kept identical for all types of coals (120°C), the organosulfur extraction time still depends upon the type of coal. If the reaction mixture is left too long in the extraction environment, the intermediate labile sulfur released by the reaction forms cross-links with the organic matter in the macromolecule of coal. This is detrimental to the process efficiency. Constant temperature has to be maintained throughout the extraction, till coal is separated from the solvent. If not, the extracted labile sulfur re-enters the coal macromolecule to form inter-penetrating polymer networks with the organic matter in coal. In this paper, it has been established that the time required for separation and isothermality of the process are crucial to maintain the reaction progressing toward sulfur and organic sulfur liberation from the macromolecule. The data presented in this paper are important from the viewpoint of process development, because the process mandates the separation of coal and solvent at the operating temperature.     

LIGAND ASSISTED DESULFURIZATION OF LIGNITE USING THE PERCHLOROETHYLENE COAL REFINING PROCESS

The perchloroethylene coal refining process was used on North Dakota lignite coal. Effects of extraction time, perchloroethylenexoal ratio and artificial weathering were studied to determine their effects on the removal of organic sulfur. The artificial weathering conditions used were found to be too harsh and caused a decrease in the amount of organic sulfur removed, unlike normal weathering conditions. Additional studies were done involving various ligands, and showed that the addition of certain ligands during the process aided in the extraction of organic sulfur from the coal.     

FRICTION AND WEAR TESTING FOR COAL SLURRY FUEL DEVELOPMENT

ABSTRACT

Friction and wear characteristics of coal slurries in transportation and atomization/firing systems are areas of concern in considering their use as substitutes for neat liquid fuels. The main wear phenomena encountered in slurry fuel usage are erosive and sliding wear of metal surfaces in contact with the coal slurry. Laboratory experiments have been devised and carried out to characterize and better understand these slurry wear mechanisms. The dependence of wear on the characteristics of the coal slurry and the properties of the wear surfaces have been studied. Coal slurries prepared from an Ohio coal desulfurized using a novel perchloroethylene extraction process have been studied. A Cameron-Flint reciprocating slider tribometer has been used to study sliding wear phenomena. Erosive wear has been investigated using an impingement type wear tester. The importance of impingement angle of coal slurry on platelet formation during erosion has been determined. Results of This angle corresponding to peak erosion is lover than for the softer 1020 steel, and can be attributed to the hardness of the steels.

Wear tests on 1020 steel were carried out using coal slurries formulated from run-of-mine coal and coal freed of mineral matter and organic sulfur by the perchloroethylene coal cleaning process (Lee et al., 1989). It was observed that run-of-mine coal created two kinds of indentations on the 1020 steel - larger indentations attributable to large mineral matter particles, and smaller indents. Only smaller indents were present in the wear tests with a slurry prepared with cleaned coal, which was largely freed of mineral matter.