Fischer assay

Table 10. Average Yields and Range of Yields of Fischer Assay of Various Coals ...

Properties. A high volatile western Kentucky bituminous coal, the tar yield of which by Fischer assay was ca 16%, gave a tar yield of ca 26% at a pyrolysis temperature of 537°C (146—148). Tar yield peaked at ca 35% at 577°C and dropped off to 22% at 617°C. The char heating value is essentially equal to that of the starting coal, and the tar has a lower hydrogen content than other pyrolysis tars. The product char is not suitable for direct combustion because of its 2.6% sulfur content. 

Properties. Results for the operation using subbituminous coal from the Wyodad mine near Gillette, Wyoming, are shown in Table 13. Char yields decreased with increasing temperature, and oil yields increased. The Fischer assay laboratory method closely approximated the yields and product assays that were obtained with the TOSCOAL process. 

Value assumed from Fischer assay and moisture content. The addition of steam to the process prevented accurate measurement of water produced in retorting. 

Sample preparation for the modified Fischer assay technique, a standard method to determine the Hquid yields from pyrolysis of oil shale, is necessary to achieve reproducible results. A 100-g sample of >230 fim (65 mesh) of oil shale is heated in a Fischer assay retort through a prescribed temperature range, eg, ca 25.5—500°C, for 50 min and then soaked for 20 min. The organic Hquid which is collected is the Fischer assay yield (7). The Fischer assay is not an absolute method, but a quaHtative assessment of the oil that may be produced from a given sample of oil shale (8). Retorting yields of greater than 100% of Fischer assay are possible. 

A total material balance assay is a Fischer assay in which the retort gases are collected. A complete material balance closure and yields in excess of those expected from Fischer assay results are achieved. More complete descriptions of both the Fischer assay and the Tosco material balance assay methods have been reported (9). 

The Fischer assay is an arbitrary but precise analytical tool for determining the yield of produces from low-temperature carbonization. A known weight of coal is heated at a controlled rate in the absence of air to 773 K (932°F), and the produces are collecled and weighed. Table 27-3 gives the approximate yields of products for various ranks of coal. 

TABLE 27-3 Fischer-Assay Yields from Various Ranks of Coal (As-Received Basis)... 

The procedure is designed to maintain the proper amount of water in the crystallization mixture so that the monohydrate 1 is obtained. It has the highest melting point and is the least hydroscopic. Other hydrated forms, such as the dihydrate (m.p. 35-60°) and mixed hydrates, may be isolated. A Karl Fischer assay of the water content is not necessary if the obtained material melts within the range given. 

All of the tests conducted in the pilot plant were with a single batch of Colorado oil shale from the U.S. Bureau of Mines mine at Rifle, Colo. Mine run material was crushed to 1/4-in. size at the mine and sieved elsewhere into various fractions. We selected a —6+10 U.S. Standard sieve size material for most of these tests because it was the largest size which we could successfully feed with our existing equipment. This material had a Fischer assay oil yield in the 20-25 gal/ton range. 

Procedure. The site was developed on a five-spot pattern about 25 ft square, as shown in Figure 2. The wells were rotary drilled with water and completed with 50 ft of 7-in. casing and cemented to the surface. A 6%-in. hole was drilled below the casing to a total depth of 100 ft in the oil shale. Two additional wells were drilled off pattern as observation wells. A Fischer assay determined the oil yield of the section as 19.0-26.5 gal/ton. Two sand-propped hydraulic fracture treatments were applied for emplacing NG1 in the formation. 

Procedure. Green River site 1 was located 5 mi west of the Rock Springs sites 4 and 5. The oil shale zone of interest, at approximately 346-385 ft, was selected after studying the analysis of cores cut from an earlier well. As determined by Fischer assay, oil yield of the cored section averaged about 21.0 gal/ton. 

Shale oil and a fuel gas have been produced by microwaveheating oil shale in a standard microwave oven in conjunction with experimentation to develop an in situ microwave retorting process. Various grades of oil shale have been subjected to high microwave fields. The derived oil has been submitted to various physical and chemical testing methods, and the chemical composition of the evolved gas has been evaluated. The specific gravity pour point yields of oil, water, gas, and losses and spent shale are compared with parallel data obtained with the Fischer assay procedure. Important differences in oil flow properties and gas composition are discussed in view of microwave interactive theory. 

A modified Fischer assay apparatus was obtained from the Colorado School of Mines Research Institute with the temperature program controlled manually with a chromel-alumel thermocouple readout. The signal from the thermocouple was monitored by a Radiometer pH/mV meter and outputed to a calibrated laboratory recorder. Gas collection was either metered or collected over water by using a mercury manostat instead of solenoids (6). 

It has been noted that shale oil properties can vary with the percentage yield of a thermal process. The percentage of oil recovery compared with the Fischer assay is presented in Table III, which shows some more characteristics of the retorting runs of Table II. The data... 

Table II. Characteristics of Microwave-Produced Oil and Oil from the Modified Fischer Assay of Divided Oil Shale Samples...

Low Ethylene Ethane Ratio. Examination of the C2 fraction indicated an ethylene ethane ratio of 0.5 for the total gas, projected retorting indicies would suggest a longer residence time, or an effective temperature slightly higher than Fischer assay (18). 

Goodfellow, L. Atwood, M. T. Fischer Assay of Oil Shale—Procedures... 

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