Coal conversion mechanisms

A new countercurrent continuous centrifugal extractor developed in the former USSR (214) has the feature that mechanical seals are replaced by Hquid seals with the result that operation and maintenance are simplified the mechanical seals are an operating weak point in most centrifugal extractors. The operating units range between 400 and 1200 mm in diameter, and a capacity of 70 m /h has been reported in service. The extractors have been appHed in coke-oven refining (see Coal conversion processes), erythromycin production, lube oil refining, etc. 

J. "The Nature and Origins of Asphaltenes in Processed Coals Chemistry and Mechanisms of Coal Conversion to Clean Fuel", Annual Rept. for 1978 from Mobil Res. Dev. Corpn. to Electric Power Research Institute, AF-1298, Vol. 2. 

We propose, therefore, that the operative mechanisms of coal conversion in both Tetralin-like media and our strongly basic systems may be the same, involving hydride donation by the H-donor... 

Dreibelbis, W.G, Ealy, J.A. Porter, W.E. (1982) Industrial hygiene monitoring for evaluation of employee exposure and control measures in coal conversion program at Oak Ridge National Laboratory. In Cooke, M. Dennis, A.J., eds, Polycyclic Aromatic Hydrocarbons Mechanisms, Methods and Metabolism, Proceedings of the Eight International Symposium, Columbus, OH, Battelle Press, pp. 351-361... 

Thus the question of the nature of critical link scission in conventional conversions must be reconsidered. Brower has recently questioned the conventional scheme (11 a,b), and it is clear that the detailed mechanism of coal conversion is yet to be developed. 

At the present time, few, if any, details of chemical reaction mechanisms in coal conversion are known with certainty. This situation is particularly distressing in the areas of coal liquefaction and pyrolysis where chemical kinetics may strongly influence process efficiency and product quality. To improve this situation, in recent years a number of research groups have been performing chemical studies of coal and "model" compound reactions. 

This work presents the first systematic application of these methods to coal chemistry. This analysis is intended not only to suggest likely reaction mechanisms, but also to demonstrate the unique power of thermochemical kinetics methods for semi-quantitative analysis of the complex chemistry of coal conversion. 

A number of coal-derived liquids were examined by cyclic-voltammetry and other electrochemical techniques and found to show some activity. At anodic potentials films form on glassy carbon electrodes. It is suggested that this film formation is caused by oxidative coupling of radical cationic species with neutral ring structures through a mechanism similar to that which causes charring and coking in coal conversion processes. 

We have developed several new measurement techniques ideally suited to such conditions. The first of these techniques is a High Pressure Sampling Mass Spectrometric method for the spatial and temporal analysis of flames containing inorganic additives (6, 7). The second method, known as Transpiration Mass Spectrometry (TMS) (8), allows for the analysis of bulk heterogeneous systems over a wide range of temperature, pressure and controlled gas composition. In addition, the now classical technique of Knudsen Effusion Mass Spectrometry (KMS) has been modified to allow external control of ambient gases in the reaction cell (9). Supplementary to these methods are the application, in our laboratory, of classical and novel optical spectroscopic methods for in situ measurement of temperature, flow and certain simple species concentration profiles (7). In combination, these measurement tools allow for a detailed fundamental examination of the vaporization and transport mechanisms of coal mineral components in a coal conversion or combustion environment. 

The mechanical behaviour is improved by reduction of A1 content, alloying with further elements and thermomechanical treatments, which leads to alloys for eventual applications in conventional power plants - in particular in steam turbines - or in coal conversion plants. Exhaust units in cars and electric heating elements are near application. 

A lOkWfl, prototype has been constructed and tested from IFP-Lyon [53]. Three interconnected fluidized bed reactors are considered (Figure 5.11) one reactor is operated as fuel reactor and two reactors are used as air reactors. The reactors are bubbUng bed reactors. The control system is based on the use of pneumatic non-mechanical valves that allow the solid circulation to be independent of the gas flow rate in the reactors. In 2011, the same facility has been modified to be operated with coal by the addition of a carbon stripper. New analyses have been carried out in order to test the OC activity, the effect of the temperature in the coal conversion and the gasification reaction [54] that occurs in the fuel reactor. 

A comprehensive analysis dealing with the various asymptotic cases of gas-liquid mass transfer in series with various particle conversion mechanisms in the bulk has been presented recently by Doraiswamy and Sharma [l] Such a model has been successfully applied to oxydesulfurization of coal [l5l]. As far as we know, no analysis has been presented as yet for the case where the particles are small with respect to the gas-liquid film for mass transfer, and consequently may enhance the gas-liquid mass transfer process. According to our experience it plays a role in a new process that we recently developed for the concentration of hydrogen from lean gas mixtures with a slurry containing finely hydridable metal part-Icles [16,139,152-154], (Fig. 23). 

Further details and specialized information on the mechanisms, product qualities, and proce.sses applied to the heating of coal in solvents can be found in the abundant literature [20]. What follows are some of the results of research conducted at West Virginia University, where investigations of the conversion of coal into pitches suitable for graphite production have been carried out... 

Neavel, R.C., MCoal Plasticity Mechanism Inferences from Liquefaction Studies , Proceedings of the Coal Agglomeration and Conversion Symposium, Morgantown, W.Va., May 1975 (.published April 1976). 

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