Pyrolysis coal, rapid

Flash Pyrolysis Coal is rapidly heated to elevated temperatures for a brief period of time to produce oil, gas, and char. The increase in hydrogen content in the gases and hquids is the result of removing carbon from the process as a char containing a significantly reduced amount of hydrogen. Several processes have been tested on a rela-... 

N. Nskala, P. L. Walker (Jr), R. H. Essenhigh, Characteristics of Chars Produced by Pyrolysis Following Rapid Heating of Pulverised Coal, 1977, US. Dept, of Chem. Nat. Tech. Inform. Service, FI-2030-Tr-2. 

Process development on fluidized-bed pyrolysis was also carried out by the ConsoHdation Coal Co., culminating in operation of a 32 t/d pilot plant (35). The CONSOL pyrolysis process incorporated a novel stirred carbonizer as the pyrolysis reactor, which made operation of the system feasible even using strongly agglomerating eastern U.S. biturninous coals. This allowed the process to bypass the normal pre-oxidation step that is often used with caking coals, and resulted in a nearly 50% increase in tar yield. Use of a sweep gas to rapidly remove volatiles from the pyrolysis reactor gave overall tar yields of nearly 25% for a coal that had Eischer assay tar yields of only 15%. 

H. R. Linden High temperature pyrolysis of coal with high energy sources seems to follow readily predictable paths similar to hydrocarbon pyrolysis. The effects of pressure, gas atmosphere, reaction time, and the volatile matter" content of the coal bear the same relationship to yields of methane, ethane, ethylene, acetylene, and hydrogen as for simple hydrocarbons. Effective reaction temperature, although not directly measurable, could be estimated by means of a suitable chemical thermometer, such as the C-. H-. -C. H4-H. system which approaches equilibrium very rapidly. As Dr. Given also noted, equating the volatile matter" to the reactive portion of the coal is an oversimplification but adequate for empirical purposes the C H ratio of the coal would probably be more suitable. 

Another rapid technique for characterizing non-volatile materials which has been applied to coal macerals is pyrolysis mass spectrometry (Py-MS) (82-84). The evaluation of the complex data produced by this technique has been aided by the use of statistical analysis. Homologous series of molecules can be identified and variation between the various maceral groups is quite evident. 

Coal gasification can be considered to occur in two stages rapid pyrolysis followed by relatively slower heterogeneous reactions between the gaseous reactants and the remaining char. 

P.J.J. Tromp and J.A. Moulijn, Slow and Rapid pyrolysis of Coal, in Y. Juriim (Editor), New Trends in Coal Sciences, Kluwer Acad. Publ., Dordrecht, 1988, pp. 305-309. 

A schematic diagram of the entrained flow reactor is shown in Figure 1. At the top of the reactor, a screw feeder and semi-venturi system is used to entrain the ground coal particles in the cold primary gas stream. The coal is then injected into the reactor where it is entrained in, and heated by, the preheated secondary gas. The pyrolyzing coal particles fall in a thin stream through the reactor and are collected by a movable water-cooled collector probe. The time which the particles spend in the reactor is controlled by moving the collector probe up and down the reactor axis. The pyrolysis reactions are rapidly quenched in the collector probe, and the particles are separated from the gas stream by a cyclone in the collection system. 

Free-fall reactors (FFR) are a good choice for rapid or flash pyrolysis. They have been widely harnessed to pyrolyze coal and, more recently, biological mass. A pioneering group at Ankara University was the first to attempt pyrolysis of waste plastics in a FFR. Then-results are very promising indeed compared with other alternatives in the literature. 

Until fairly recently, no significant publications were produced on rapid or flash pyrolysis of waste plastics harnessing a FFR. A review of FFR developments is therefore given below regarding coal or biomass applications. 

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