Pretreated coals

Carbon analyses were performed on each pretreated coal sample using a Carlo-Erba model 1106 CHN analyzer to measure the extent of alkylation as computed from the following formula ... 

If reactions of the above type occur during extraction, one would expect that gradually less hydrogen exchange takes place as the extraction proceeds because the number of reactive groups decreases. This assumption was tested in the last experiment shown in Table V. The coal was heated for 6 hours at 340°C. with nontritiated phenanthrene prior to extraction with tritiated phenanthrene. When this pretreated coal was extracted, the tritium content of the product was only 15.6% as compared with 21.4%, in the nonpretreated product. This decreased tritium content supports the above assumption and agrees with the proposed reaction mechanism. 

For the alkali-treated coal washed subsequently with HC1, levels of Mn, Pb, Rb, Sr, and Zn were reduced by 75% or more, while levels of Ba, Cd, Cr, Ni, and Se, were reduced by 30-60%. The coal that had been pretreated showed reductions of 75% or more for Mn, Pb, and Zn, while Cd and Ni were reduced by 60% or more. It is interesting to note that every alkali and alkaline earth metal determined was enriched in the pretreated coal relative to the coal that was leached with no pretreatment. Some of these, such as Ba and Ca, were more concentrated in the pretreated coal than in the raw coal. The high Cu concentration in the coal which was pretreated is a result of contamination from the stirrer used in the autoclave. The relatively high Cu levels in this sample caused an interference in the Zn determination. A different autoclave and stirrer was used for the non-oxidative treatments. 

Another method of calcium carbonate control is the use of pretreatment of coal with S0 to render the calcium innocuous as calcium sulfate. This technique was discovered in Exxon funded research and was subsequently made available to the project. The SC>2 reacts with the calcium in the coal and is then hydrolyzed to form the sulfate which does not form reactor deposits under EDS conditions. Inspections of reactors used to process SO2 pretreated coal have indicated the presence of only insignificant amounts of the calcium carbonate. 

At present, this conceptual coal conversion process is limited in its application to western coals because of their noncaking character and lower sulfur content compared with eastern bituminous coals. It is of interest to note, however, that certain chemical pretreatment processes (10,11) have been shown to eliminate the caking tendency of the coal and reduce its sulfur content. Recent experiments at ORNL (12) have confirmed the suitability of several chemically treated coals to mild hydrocarbonization. In fact, there is evidence to suggest that some of these pretreated coals are actually more reactive under hydrocarbonization conditions than untreated coal, thereby enhancing the yield of oil or gas. 

In a previous paper (21) we characterized aromatic acids trapped in lignite coal, and have found that these acids are quite similar qualitatively to those obtained from the present oxidation of the same pretreated coal. This indicated that the trapped acids were derived mainly from the hydrolytic degradation of lignin-like polymers. We also have observed that no trapped organic acid is isolated from the anthracite coal that no longer contains lignin-like polymers. 

A 10-in. diameter continuous fluidized-bed reactor system is being operated to produce nonagglomerating coal from high volatile bituminous coal by mild surface oxidation. Minimum pretreatment is defined by acceptability of the coal as a feed to the hydro gasifier. This corresponds to 24-26% volatile matter in the pretreated coal. The following operating variables, in the order of importance, contribute to satisfactory pretreatment—reaction temperature of 725°-750°F., oxygen reacted coal feed ratio of 1.0 1.5 std. cu. ft./lb.9 and a coal residence time of 1-2 hours. 

First-stage hydrogasification, at 1200° to 1300°F., with pretreated coal as the feed. 

We mounted samples of feed coal in epoxy resin under hydraulic pressure as described by Cole and Berry (2). An apparatus and procedure for vacuum-mounting the fragile chars was developed ana is described elsewhere (8). Samples of pretreated coal and hydrogasification residue were sieved, and tests were made on the sieve fractions to avoid error from size segregation. 

Particles from both first- and second-stage runs showed a great variation in both reflectance and structure. Some particles appear unchanged in structure from the pretreated coal. In others, additional... 

Particles from a run in which untreated coal was fed were also examined. This coal was from Pittsburgh No. 8 seam but from a different mine—Consolidation Coal Co/s Montour 4 mine. The hydrogasification reaction was conducted entirely in 18 feet of free fall. The run could not be completed because of gradual caking of coal in the feed tube and in the reactor. However, the structure of the residue that was obtained is of interest (Figure 4). It is much more uniform in appearance and reflectance than residues from runs with pretreated coal. Almost all of the particles have a degenerate foam structure—i.e., they are filled with... 

The free-fall residue also differs from the pretreated coal residue in that it has a grainy or mottled texture (Figure 5) in contrast to the smooth, unmottled appearance (except for small voids) of most particles... 

Figure 6. Texture of residue from pretreated coal...

Table III. Reflectance of Pretreated Coal and Char Heated in Hydrogen at 1850°F.

The pretreated coal is quite reactive. For example, at 25-30% carbon gasification with steam-hydrogen mixtures, the rate constant is more than twice that reported by Feldkirchner and Linden (6) in reactions of low temperature bituminous char with hydrogen. The greater reactivity is most likely attributable to the higher volatile content of our pretreated coal (25-26% ) than that of their char (17% ). 

Table I. Analyses of Pretreated Coals Used in the Gasifier...

Table II. Conditions of Operation and Results of Tests Using Pretreated Coals in the Fluid Bed Gasifier at 2.5 atm.

At temperatures greater than 1700°F the transient reactivity for rapid rate methane formation exists only briefly. For coals or coal chars prepared in inert atmospheres this period is seconds or less (6). IGT s studies suggest that for air-pretreated coal chars, this period is more extended although the total amounts of carbon which can be gasified by... 

Coal Used. The coal charged in all the tests discussed here was a single batch of high-volatile bituminous coal (Bruceton, Pa.) that had been pretreated at 450°C with a steam-air mixture to destroy its caking quality. The pretreated coal was crushed and sieved to a particle size of 20 to 60 mesh. Proximate and ultimate analyses of the pretreated coal are shown in Table I, in weight percent. 

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