Characteristics of pulverized coal during coalbed methane drainage in Hancheng block, Shaanxi Province, China

Pulverized coal is one of the main controlling factors constraining the capacity of coal-bed methane wells during CBM drainage. The characteristics of pulverized coal can be used to identify the sources of the pulverized coal particles and to develop reasonable means of controlling pulverized coal output. Using light transmission microscopy, laser particle size testing, X-ray diffraction, reflection polarized optical microscopy, and scanning electron microscopy with energy dispersive X, the characteristics of pulverized coal collected during CBM drainage in the Hancheng block were analyzed for concentration, particle size, composition, and morphology. These traits were used to identify the sources of pulverized coal. The results showed that coal body structure (structural damage) was a primary control factor of pulverized coal output. The sizes of the pulverized coal particles tended to be around 100 mu m. The main components of pulverized coal were vitrinite and clay minerals. The pulverized coals were divided into groups based on their columnar, flaky, or granular morphology. Columnar pulverized coal may involve the formation of the native structure coal or the fragmented coal that later sustains erosive damage. Flaky pulverized coal may be produced by the flaking of scaled coal or leaf coal. In this way, granular pulverized coal may be produced from granulated coal. Therefore, the morphology of the pulverized coal was found to be related to its coal body structure and to late mechanical destruction.