Rapid pyrolysis, increased volatiles

Figure 1 applies to pyrolysis in which the wood temperature is raised from 100 C in about 10 h to various final temperatures. The weight losses, depicted as volatiles, and solid residues have been determined after the trials, and originate mainly from Klason, v. Heidenstam, and Norlin (4), under consideration of data published by Goos (18) and Stamm (19). Measurements on small samples by Beall and Eickner (20), LeVan and Schaffer (21), and Elder (22) have been compared. Up to about 275 or 300 C — the temperature range in which cellulose rapidly disintegrates — increased final trial temperatures cause increased increments of volatiles beyond 300 C the increments steadily diminish. 

Table II. Increased Volatiles from Rapid Pyrolysis...

The yield of volatile matter in this process is a function of the coal type and ranges from approximately 20% w/w of the coal for a low-volatile bituminous coal to somewhat more than 55% w/w of the coal for a high-volatile C bituminous coal subbituminous coals may not show a volatile matter peak with increasing temperature. In addition to tarry products, the rapid pyrolysis of coal produces gases such as hydrogen, methane, and carbon monoxide as well as lesser amounts of hydrocarbons. Pyrolysis of coal is generally defined as the thermal decomposition of coal in the absence of air or other added substances. 

Rapid pyrolysis has been briefly mentioned, but in view of the increased importance in this method of the thermal decomposition of coal, more detailed considerations are warranted (Takeuchi and Berkowitz, 1989). The rapid pyrolysis (also often called flash pyrolysis) concept is based on the observation that most coals will release gases, liquids, and tarry materials when heated at certain temperatures, but when the heating is extremely rapid (102°C/s to 106°C/s) even higher proportions of volatile matter can be released (Weller et al., 1950 Kimber and Gray, 1967 Gibbins and Kandiyoti, 1989 Gibbins et al., 1991). 

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%. 

Pyrolysis liquids cannot be completely vaporised once they have been recovered from the vapour phase. If the liquid is heated to 100°C or more to try to remove water or distil off lighter fractions, it rapidly reacts and eventually produces a solid residue of around 50wt% of the original liquid and some distillate containing volatile organic compounds and water. The liquid is, therefore, chemically unstable, and the instability increases with heating, so it is preferable to store the liquid at room temperature. These... 

The purpose of this step is to volatilize inorganic and organic matrix components selectively from the sample, leaving the analyte element in a less complex matrix for analysis as a result, the duration of this step is a function of the complexity of the sample and can vary between 10 and 30 s. During it, the temperature is increased as rapidly as possible to volatilize matrix components but is kept below the level at which analyte losses might occur. The temperature to be used in the pyrolysis step will depend on the particular analyte and matrix. Recommended temperatures are usually provided in the... 

Wall and Straus (10) found the rate of volatilization of polypropylene at 375 °C to increase rapidly to a maximum at 40% conversion and then decrease rapidly with further heating. Similar behaviors were observed also for polyethylene (10). However, branches longer than a methyl group were found to eliminate the maxima in the rate curves even when present in quite low concentration (II). On the other hand, Ma-dorsky and Straus (12) and this work found the kinetics of pyrolysis to be first order. 

The present study was done to investigate rapid coal pyrolysis brought about through rapid mixing of finely ground coal with hot combustion gases. We were particularly interested in evaluating the potential of this procedure for increased yields of volatile matter and for the production of unsaturated hydrocarbons as constituents of the volatiles. 

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