System coal sampling

About one half of the coal samples used in the above study (61) have been investigated by workers in Gulf Research and Development Company, using a continuous flow reactor (63). The throughput was about 1 kg./h of coal/solvent slurry, the solvent was a partly hydrogenated anthracene oil, temperatures of 440 and 455°C were used, and the system was pressurized with hydrogen to 20.69 MPa. 

Radical Generation. The ESR spectrometer, flow system, and general procedure have been described (46). The apparatus was calibrated with freshly prepared diphenyl picrylhydrazyl (DPPH) solutions. The peroxy radical concentrations were determined by double integration of derivative spectra. A standard coal sample in the dual cavity allowed corrections to be made for changes in cavity Q. The rates of decay of the less reactive radicals were determined by stopped-flow techniques with manually or electrically operated valves. The decay was recorded... 

Irradiation I. The samples and standards (with appropriate flux monitors) are individually exposed to a neutron flux of 1 X 1013 neutrons cm"2 sec-1 for periods of V2 min for fly ash and 1 min for coal via a pneumatic rabbit system. The samples are irradiated and counted individually because of the short half-life of the (n/y) products of some of the elements and the requirement of counting at a specific time after irradiation. A copper flux monitor is irradiated with each sample to allow... 

For each run, coal samples of approximately 50 grams were dried, at 100°C. for 4 hours and weighed after cooling in a desiccator for % hour. In the early experiments, coal and solvent were mixed in the autoclave, and runs were performed. It was found that the time necessary for the autoclave and mixture to be heated from room temperature to reaction temperature was 1 hours. When extraction fraction vs. time was plotted, it showed that at higher temperatures more than 80% of the total possible extraction of coal dissolved before the system reached the reaction temperature. Consequently, the data obtained in the first 2 hours were incorrect. 

The issue of testing for bias in a coal sampling system (ASTM D-6518 ISO 13 909) is an essential part of coal analysis and is of significant importance (Gould and Visman, 1981). Accordingly, the term bias represents the occurrence of a systematic error (or errors) that is (are) of practical importance. 

ASTM D-6518. Standard Practice for Bias Testing a Mechanical Coal Sampling System. 

ASTM D-4702. Standard Guide for Inspecting Crosscut, Sweep-Arm, and Auger Mechanical Coal-Sampling Systems for Conformance with Current ASTM Standards. 

ASTM D-6315. Standard Practice for Manual Sampling of Coal from Tops of Barges. ASTM D-6518. Standard Practice for Bias Testing a Mechanical Coal Sampling System. 

Scanning electron microscopy with an energy-dispersive x-ray system accessory has been used to identify the composition and nature of minerals in coals and to determine the associations of minerals with each other. Examinations can be made on samples resulting from ashing techniques or whole coal. With this technique it is possible to identify the elemental components and deduce the mineral types present in coal samples. Computerized systems to evaluate scanning electron microscopy images have been developed and are useful in characterizing the minerals in coal mine dusts and in coal. 

In addition to these samples, several coal samples were provided by TRW Systems, Inc., from the San Juan Capistrano test plant in California. The samples included Illinois No. 6 and Pittsburgh No. 8 coals before and after treatment by the Gravimelt Process. The raw Illinois and Pittsburgh coals were -14 mesh and -6 mesh, respectively. 

In the coal samples, usually one of the two phases is coal, and the other is pores, which are considered to contain air. Sometimes, however, the effects of the mineral matter in the coal must be considered. The system then contains three phases. Our scattering data from the coals suggest that the pores and mineral matter scatter independently of each other, so that when the contribution of the minerals to the scattering must be considered, the coals can be taken to be two independent systems—one made up of coal and air, and the other consisting of coal and mineral matter. As we will explain below in more detail, we have estimated the contribution of the mineral matter to the scattering from several of the coals and have concluded that this scattering is small and often can be completely neglected.. ... 

The emission measurements during this testing included N0X, smoke, particulate and PNA. N0X was determined by a non-disper-sive infrared analyzer, and smoke by the Bacharach test. Both the particulates and PNA were sampled by a source assessment sampling system (SASS). The SASS system isokinetically samples a fraction of the stack gas and traps particulates in a series of cyclones, which classify the particulate by size. Final filtration is through a fiberglass filter mounted in an oven heated to 200°C to prevent condensation of acids. In this program, the cyclones were not used, since previous work (3) had shown the particulate from coal-derived fuel oils to be small, with an average diameter on the order of 0.4 /um. The PNA which is not deposited on the particulate is collected on XAD-2 resin after the gas has been cooled to 15-20°C. PNA analyses were carried out on a combined extract from the particulate, XAD-2 resin, other condensates in the system, and the solvent rinses used to clean the SASS system. 

Results from SAXS analysis and GA (using COp gas) for the same coal samples are shown below in Table I. From the results of SAXS analysis it may be concluded that the investigated Victorian brown coal possesses an extensive micropore system containing between 10 to 10 pores per gram. Additionally, according to the shape hypothesis these pores may be either slit-like (thin discs with large diameters) or filament-like (long narrow cylinders) and are... 

Mineralogical composition of ash samples and model systems was determined by XRD. X-ray fluorescence (XRF) analysis was also used for bulk elemental analysis of the ash. Raw coal analysis was performed by XRF and neutron activation (NAA). XRF elemental analyses of raw coal samples are listed in Table I. The neutron activation analyses were performed at North Carolina State University. 

The thermobalance is an apparatus capable of continuously weighing a coal sample which is undergoing reaction in a gaseous environment of desired composition at a constant pressure. The temperature can be kept constant or varied (10°F/min is the maximum rate for the apparatus used at IGT). The nature of gas-solid contact with the apparatus used in this study is shown in Figure 1. The coal sample is contained in the annular space of a wire mesh basket bounded on the inside by a hollow, stainless steel tube and on the outside by a wire mesh screen. To facilitate mass and heat transfer between the bed and its environment, the thickness of the bed is only 2-3 particle diameters when using —20+40 US sieve-size particles. Gas flow rates used with this system are sufficiently... 

A schematic drawing of the sensor system employed in the Sortex Ash Monitor is shown in Figure 4. The x-rays emitted by the Pu source irradiate the coal sample and penetrate up to 38 mm. This radiation is absorbed and scattered the fraction backscattered is counted with a gas proportional counter. The aluminum filter is used to compensate for iron fluorescent x-rays, which are excited by the incident x-rays. The filter preferentially absorbs most of the iron fluorescent x-rays ( 6 KeV), and its thickness is chosen based upon the iron content of the coal samples. The aluminum filter also compensates for sulfur variations in the coal. This occurs because a major fraction of sulfur is present as pyrite and the decrease in x-ray backscatter intensity due to sulfur is partially offset by an increase in iron fluorescence. Organic sulfur is generally constant, and it is corrected for in the calibration of the instrument ( 5). 

Figure 5. Typical coal sampling system and flow path.

The ignition temperature of the coal samples is about 340°C according to spontaneous combustion characteristics experiments of coal samples of the 065-2 working face in gushan mine. The spontaneous combustion index gas system with CO for main index gas and C2H4 for auxiliary was established when the effective forecasting temperature was below 220°C. 

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