Padmakar Vishnubhatt

Perchloroethylene 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

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.

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 isother...

Effect of pyritic sulfur and mineral matter 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.

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 co...

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 proce...

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.

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.

Removal of Residual Chlorine in Coal by Steam Stripping

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.

KINETIC MODELING OF PERCHLOROETHYLENE EXTRACTION DESULFURIZATION OF COALS

ABSTRACT The kinetic modeling of the perchloroethylene reaction-extraction process has been carried out on the basis of batch extraction data. In this paper, modeling results of both second order as well as the pseudo-first order model has been presented. Multiple parameter estimates have been found which minimize the model-data discrepancies. Novel methods have been devised to illustrate multiple estimates of the kinetic parameters. Ill-posedness of the kinetic modeling problem bas been analyzed using the expression for extractability and the Hessian matrix of the model-data discrepancy function. Root Mean Square Errors (RMSE) for various types of coals have been evaluated to represent the model-data discrepancy function It was found that the RMSE was between 2-8% of the estimated initial concentration of ex tract able organic sulfur, depending upon the type of coal. A novel method, called “RMSE Contours” has also been developed to present the sensitivity of parameters to the kinetic models. The second o...