SRC solvent

The SRC (solvent refined coal) process of Pittsburgh Midway Coal Mining Gulf Oil) is an advanced version of the Pott-Broche extraction process. The purpose of the SRC method is to desulfurize coal to yield a solid, low-sulfur fuel. 

Compound Type Mass Z-Series SRC Solvent No.l SRC Solvent No. 2 SRC Solvent No. 3 SRC Solvent No. 4 CO-Steam Product... 

Results of the GC-MS analysis indicated that the product distributions were related to the severity of the process. When the solvent stripping temperature was lowered in removing recycle solvent after reaction, the SRC solvent exhibits a much larger concentration of light components. 

A flow diagram of the solvent-refined coal or SRC process is shown ia Figure 12. Coal is pulverized and mixed with a solvent to form a slurry containing 25—35 wt % coal. The slurry is pressurized to ca 7 MPa (1000 psig), mixed with hydrogen, and heated to ca 425°C. The solution reactions are completed ia ca 20 min and the reaction product flashed to separate gases. The Hquid is filtered to remove the mineral residue (ash and undissolved coal) and fractionated to recover the solvent, which is recycled. 

In the SRC work, coal was slurried with a process-derived anthracene oil and heated to 400—455°C at 12.4—13.8 MPa (1800—2000 psi) of hydrogen for 0—1 h. A viscous Hquid was extracted. The product stream contains some hydrocarbon gases, and H2S. The residue is gasified to generate hydrogen for the process. The remaining filtrate is separated into solvent, which is recycled, and SRC, a low ash, tadike boiler fuel. 

Solvent Refined Coal Process. Work ia the mid-1960s by the Speacer Chemical Co. (9) and dating the 1970s by the Gulf Chemical Corp. led to two solvent refined coal (SRC) processiag schemes SRC-I for productioa of low ash soHd boiler fuels and SRC-II for distillates, eg, "syn-cmde."... 

Solvent-Refined Coal (SRC) This processing concept was initiated by the Pittsburgh Midway Coal Mining Co. in the early 1960s. The SRC-I process operating mode is designed to produce a solid fuel for utility applications. Typical operating conditions and product yields for SRC-I are shown in Table 27-14. 

In absolute terms, the quantities of reactor solids found in various processes do vary considerably. The rate of accumulation is related to several factors, such as coal characteristics, recycle solvent quality and reactor design. However, it can be stated in general terms that liquefaction of low rank coals (sub-bituminous C and lignites) does result in higher rates of accumulation of solids than do similar operations with bituminous coals. For example, during normal operations of the SRC-I pilot plant at Wilsonville, Ala., it has been found that the amount of solids retained varies from about 0.2-0.5 wt.% (moisture-free) for bituminous coals to 1.0-1.9 wt.% (moisture free) for a subbituminous C coal (Wyodak) (72). Exxon also reports much larger accumulations for lignites and subbituminous coals than those found for bituminous coals (73). 

This paper will concentrate on factors which lead to high conversion at short time. R.H. Heck, T.O. Mitchell, T.R. Stein and M.J. Dabkowski discuss the relative ease of conversion of short and long contact time SRCs to higher quality products. C.J. Kulik, W.C. Rovesti and H.E. Liebowitz discuss some new leads presently being explored at the Wilsonville PDU in which short contact time liquefaction is being coupled with rapid product isolation via the Kerr-McGee Critial Solvent Deashing Process. 

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... 

As discussed above, the composition of the solvent used in short contact time conversions can be important. The concentration of H-donors is one factor to be considered. It is known that in long contact time conversions, solvents having high H-donor contents have a better ability to prevent char formation as sulfur is removed from the SRC. Thus, higher yields of upgraded liquids are observed when solvents containing high concentrations of H-donors are used. 

Table III shows that hydrogenated and unhydrogenated SRC recycle solvents were equally effective for the conversion of a western subbituminous coal at low reaction severity. At higher severity but at times shorter than 10 minutes, significantly higher conversions were achieved only with the hydrogenated solvents which could donate more hydrogen.

Kleinpeter and Burke have recently reported (24) that solvents can also be over hydrogenated and thus become less effective in short time processes. Figure 19 shows some of their work in which a process-derived SRC recycle solvent was hydrogenated to various severities and used for the conversion of an Indian V bituminous coal. The results clearly show a maximum at intermediate hydrogenation severities. Our assessment of this observation is that the loss in conversion was due primarily to the loss in condensed aromatic nucleii rather than conversion of hydrogen donors to saturates. 

The product workup consisted of continuously extracting the filter cake with tetrahydrofuran (THF) and combining the THF and filtrate to make up a sample for distillation. In some experiments the THF extracted filter cake was extracted with pyridine and the pyridine extract was included in the liquid products. Extraction with pyridine increased coal conversion to soluble products by an average of 1.6 weight percent. The hot filtrate-THF-pyridine extract was distilled. Distillation cuts were made to give the following fractions, THF (b.p. <100 C), light oil (b.p. 100-232 C), solvent (b.p. 232-482), and SRC (distillation residue, b.p. >482 C). 

SRC pilot plant. An analysis and distillation data for the solvent are shown in Table 2. The solvent contained 5 percent of material boiling below 232 C, the cutoff point between light oil and solvent in the product distillation, and 4-5 percent of material boiling above 482 C, the cutoff point between solvent and SRC. 

SRC yields are greater than 100 percent due to the presence of solvent in the SRC. The average SRC prepared from West Kentucky 9/14 coal blends does not meet new source standards for SO2 emissions after the first step of the two-step process although all of the inorganic sulfur and an average 12 percent of the organic sulfur are removed. 

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