Coal short-contact-time

Figure 1. Fraction SESC 4 Monterey coal, short-contact-time SRC...

A New Outlook on Coal Liquefaction Through Short-Contact-Time Thermal Reactions Factors Leading to High Reactivity... 

These observations suggest that new coal liquefaction technology may be possible based on short contact time reactions. The purpose of this and the related papers in this volume by R.H. Heck and W.C. Rovesti is to show some potential advantages for optimized or integrated short contact time liquefaction processes over conventional technology. 

Advantages for Short Contact Time Coal Liquefaction... 

The significance of these calculations is that lower rank coals will require 5% lower conversion than higher rank coals for a given end product. Also, the more severe a coal is to be upgraded, the lower its conversion has to be in the initial phases of liquefaction. One very pertinent question to be addressed is whether or not coals can be converted to the levels shown in Figure 5 in a short contact time process. This paper will deal with that question as well as what compositional features of the coal and the solvent influence short contact time conversions. 

The Effect of Coal Composition on Short Contact Time Conversion... 

The classic work of Storch and co-workers showed that essentially all coals below 89% C f can be converted in high yields to acetone soluble materials on extended reaction (12). We have investigated the behavior of coals of varying rank toward short contact time liquefaction. In one series of experiments, coals were admixed with about 5 volumes of a solvent of limited H-donor content (8.5% Tetralin) and heated to 425°C for either 3 or 90 minutes. The solvent also contained 18% p-cresol, 2% y-picolene, and 71.5% 2-methylnaphthalene and represented a synthetic SRC recycle solvent. The conversions of a variety of coals with this... 

Another parameter is the intrinsic extractability of the parent coals by pyridine. As can be seen in Figure 12, the shape of the curve of pyridine extract yield from the various coals vs. their carbon content follows the same trend as the short contact time conversions of these coals. 

Similarly, a subbituminous coal (Wyodak-Anderson) which gave only 60% conversion at 427°C in 2 minutes could be converted to >70% at 460°C with no ill effects (see Figure 17). At 470°C there was an indication that conversion had begun to decline at 2 minutes however, this data is extremely limited. The implications of these results with a western subbituminous coal is that a low sulfur boiler fuel may potentially be produced in a single-stage short contact time process. 

We have observed that at short contact times the conversion of bituminous coals is also responsive to the level of H-donor in the solvent. Table IV shows the conversions of an Illinois 6... 

Hydrogen donors are, however, not the only important components of solvents in short contact time reactions. We have shown (4,7,16) that condensed aromatic hydrocarbons also promote coal conversion. Figure 18 shows the results of a series of conversions of West Kentucky 9,14 coal in a variety of process-derived solvents, all of which contained only small amounts of hydroaromatic hydrocarbons. The concentration of di- and polyaromatic ring structures were obtained by a liquid chromatographic technique (4c). It is interesting to note that a number of these process-derived solvents were as effective or were more effective than a synthetic solvent which contained 40% tetralin. The balance between the concentration of H-donors and condensed aromatic hydrocarbons may be an important criterion in adjusting solvent effectiveness at short times. 

To summarize, we have identified a number of features unique to short contact time coal liquefaction. The important factors... 

Upgrading of Short-Contact-Time Solvent-Refined Coal... 

In the solvent-refined coal pilot plant at Wilsonville, Alabama, the coal slurry is heated to reaction temperature in 3-4 minutes residence time in the preheater. The slurry is then held in the dissolver for an additional 40 minutes before it is filtered to obtain specification solvent-refined coal. By bypassing the dissolver and going directly to the filters, samples of short-contact time (SCT) SRC were produced from Illinois 6 (Monterey) and West Kentucky coals. 

Although the comparisons are by no means exact, a process based on short-contact time dissolution and catalytic upgrading would appear to have potential for significantly higher yields of high quality liquids from coal. 

Continuous Bench-Scale Experimentation With encouraging results obtained from microautoclave tests, experimentation emphasis moved to the bench-scale unit Here the concept of adding Light SRC to the recycle solvent on a continuous basis was tested Earlier work (j>) performed on short contact time coal liquefaction showed Indiana V coal to be out-of-solvent balance Also the operability of the continuous bench-scale SRT unit was highly dependent upon the quality of the solvent ... 

Although Neavel obtained high yields of pyridine-solubles with naphthalene at short contact times for some US bituminous coals (201. conversions were much lower after longer extraction times. This trend is not evident for Linby coal... 

A feasible procedure for the recovery of oil from the residual solids in the first stage of coal hydrogenation consists in treating the heavy oil slurry from the hot catchpot with superheated steam (25). At short contact times of a spray of heavy oil slurry with superheated steam, a high recovery of oil, with little or no coking or secondary asphaltene production, was achieved. 

Short-contact time liquefaction products from bituminous coal... 

One of the objectives of this work was to determine the effect of higher reactor pressure and space velocity on conversion and product quality. Heretofore, only temperature had been used to adjust or maintain conversion and product quality. Two different coal extract types were used in this study - namely, whole filter feeds obtained from Wilsonville short contact time coal extract (SCT) operations (Wilsonville run numbers 145 and 146 with 287 and 580 pounds of Indiana V coal feed per hour, respectively), and a conventional solvent refined coal (SRC-I)/ Koppers heavy residue creosote oil (KC-Oil) feed blend. The SRC-I was obtained from the Fort Lewis, Washington SRC-I facility... 

A short contact time SCT) coal extract, as prepared at Wilsonville, is obtained by feeding the coal slurry through only the slurry preheater and transfer lines. The conventional solvent refined coal has a residence time in the slurry preheater, transfer lines, and dissolver. The SCT coal extract is, consequently, reacted at higher temperatures to produce similar yields of SRC-type product at very high flow rates. The SCT coal extract used for the studies reported herein was received as non-deashed material which would have been used as a feedstock for the U.S. Filter or Kerr-McGee Critical Solvent Deashing at Wilsonville. 

Short contact time coal extracts show a greater percentage denitrogenation in the total liquid product than SRC-I coal extract when processed by LC-Fining. Also, short contact time coal extracts show a lower C1-C4 gas yield. 

Non-deashed short contact time coal extracts show a higher 500°F+ and 650°F+ conversion than SRC-I coal extracts at a given 850°F+ conversion in the LC-Finer. Deashed short contact... 

This study describes the results of processing both conventional solvent refined coal extract (SRC-I) and short contact time coal extract. Both coal extracts have been run at several space velocities, temperatures, and total reactor pressures for comparative purposes. The effect of catalyst deactivation has also been considered. The short residence time coal extract was run in both a deashed and non-deashed mode of operation. 

Product characterization from liquefaction has not been extensive. Phi 1p and Russell (95) have examined products by Py-GCMS from metal halide catalyzed hydrogenation of a vitrinite, alginite, and inertinite, each from a different source. They were able to correlate Py-GCMS results with reaction temperature. King, et al. (96) examined the short contact time liquefaction of macerals separated by DGC from a single hvB bituminous coal. They found correlations between density and reactivity and composition of the products. 

The yields of the reaction of maceral concentrates with pyridine and iodine show some interesting trends and are given in Table V. Unlike the results from the thermal reactions such as vacuum pyrolysis (Table IV) or short contact time liquefaction (29), the vitrinites are more reactive than the spori-nites. The inertinites are less reactive but the magnitude of the difference in the comparison with the other maceral groups from the Indiana and Kentucky coals is much less than what has been found for the yields from the thermal reactions. 

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