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The modified direct method: a solution for obtaining accurate coal desorption measurements.
Diamond WP; Schatzel SJ; Garcia F; Ulery JP
Proceedings of the International Coalbed Methane Symposium, May 14-18, 2001, Tuscaloosa, Alabama. Tuscaloosa, AL: University of Alabama, 2001 May; :331-342
The direct method test was developed for general mine safety applications by the U.S. Bureau of Mines in the early 1970's to measure the gas content of coal samples obtained from the relatively shallow depths of eastern U.S. coal mines. Over time, applications for gas content data evolved which required increasingly accurate desorption values. It became evident that some of the inherent weaknesses in the original direct method test could best be addressed by abandoning the water displacement based desorbed gas volume measurements. The ideal gas law based modified direct method (MDM) and associated desorbed gas volume measurement apparatus was developed to provide the most accurate desorption values possible for rock samples obtained from any gas-bearing strata. The MOM baS a number of significant advantages, including: (1) increased accuracy, especially for low gas content samples, (2) a test apparatus with an integral sampling port to facilitate the collection of uncontaminated gas samples, (3) an inherent head space effect correction in the periodic MDM desorbed gas volume calculations, (4) measurement of positive and negative desorbed gas volumes, (5) elimination of differential gas solubility effects as a source of error inherent in the water displacement methods, and (6) a compact and rugged test apparatus that along with the elimination of the "glassware" required for the water displacement methods, facilitates its use in the field.
Mining industry; Mine gases; Gas sampling; Gas meters; Gases; Gas chromatography; Gas detectors
Proceedings of the International Coalbed Methane Symposium, May 14-18, 2001, Tuscaloosa, Alabama
Page last reviewed: July 9, 2021
Content source: National Institute for Occupational Safety and Health Education and Information Division