ABSTRACT As a part of process engineering study of the perchloroethylene (PCE) coal desulfurization process, the minimization of residual chlorine content after the desulfurization process has been studied in detail. The residual chlorine in the coal is removed by a novel process, which involves the use of steam as the displacing agent. Steam, when passed through a bed of the PCE treated coal, washes away the residual solvent in coal. Two designs, viz. fluidized bed and packed bed steam strippers are discussed in detail. This paper presents the results of the design implementations and discusses the advantages and disadvantages of each design. It was found that the chlorine content of the coal treated in the packed bed steam stripper was not only decreased to a level lower than before steam stripping, but to a level lower than that of the raw samples before the PCE extraction.
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.
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.
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.
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.
ABSTRACT A novel reaction-extraction model for removal of organosulfur compounds from coal by the Perchloroethylene Organodesulfunzation Process has been proposed. The model treats the coal as a reactant to observe the effect of slurry composition on the rate of “lock-up” reaction where the liberated organosulfur species from coal re-enters the coal organic matrix. A series of batch organodesulfunzation extractions were conducted to observe the effect of solvent-to-coal ratio on the extent of organosulfur removal. Based on this data, kinetic parameters for the organosulfur “liberation” and “lock-up” reactions were simulated using the model. The ratio of first-order rate constant of “lock-up” reaction to that of the “liberation” reaction was found to be 4.03. Optimal design parameters and operating conditions have been obtained for a wide range of PCE-to-coal ratio for Indiana 5 coal. Mathematical models representing the optimal slurry composition as a function of the ratio of rate constants, extraction capacity, and the corresponding extraction performance have been developed. This study is very significant from the point of view of reaction and process engineering, which in turn assist in achieving an optimal and economical equipment design.
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.
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.
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 SOX/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.
In the Perchloroethylene (PCE) Organodesulfurization Process, the liberation reaction of sulfur from organic coal compound is known to be reversible. Since the rate of backward reaction is determined by the concentrations of both coal and sulfur in the slurry mixture, the organosulfur extractability substantially depends on the PCE-to-coal ratio. A simplified kinetic model is introduced that can describe the organodesulfurization reaction in a quantitative manner. The model assumes that there exist two different species of organic materials in coal. In PCE solution, both species accept sulfur to form organic sulfur compounds, but only one species release sulfur. Batch extraction data of Ohio 5/6 and Indiana 5 coal samples are used to calculate the equilibrium constant, K{sub eq}. K{sub eq} is 8.2 for Ohio 5/6 coal, but K{sub eq} cannot be exactly determined for Indiana 5 coal. Instead, the feasible range of K{sub eq} is graphically represented. It is demonstrated that the indeterminacy of K{sub eq} for Indiana 5 coal is inherent. This study contains a few very significant results: the proposed kinetic model correctly describes the PCE coal cleaning process for wide range of PCE-to-coal ratio. Also it is fully discussed that there exists an inherent restriction in identifying themore » kinetics of the process.« less
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