Mining Contract: Metering and Distribution Improvements to Increase the Effectiveness and Efficiency of Rock Dusters

Contract Status & Impact

This contract is complete. To receive a copy of the final report, send a request to mining@cdc.gov.

Rock dust is distributed throughout the mine to inert float coal dust, reducing the risk of a large-scale explosion. While rock dust is the primary mechanism for ensuring that float coal dust does not provide a continued fuel source to a small explosion or fire, it is critical that the rock dust meet very specific criteria in order to be effective. Technologies to measure the amount of liberated float coal dust and determine the necessary quantity of rock dust to be dispersed for proper inertion do not exist. Rather, mine operators generally estimate the amount of needed rock dust and then use visual inspection or the NIOSH-developed Coal Dust Explosibility Meter (CDEM) to determine if more rock dust is required.

ROHMAC, Inc., was contracted to demonstrate that dust monitors could be integrated into rock duster systems along with control algorithms that would result in rock dust quantities being automatically distributed in specific quantities based on real-time readings obtained from the dust sensor. Because a real-time float coal dust monitor does not currently exist, a commercially available dust monitor was used for the purpose of this contract. Because the system would be automated, additional improvements to application devices were warranted to ensure that coverage of rock dust on mine surfaces was sufficient independently of mine personnel being present.

The prototype rock dusting system was developed and tested at an active underground coal mine to evaluate the system performance and its ability to react in a timely manner to sudden changes in the air velocity and quantity of dust in the air stream. This “need-based” system successfully monitored the total amount of airborne dust in the mine entry, upwind of the rock duster, and sent a signal to the rock duster so that the amount of rock dust injected into the air was proportional to the measured amount of total coal dust. Furthermore, the efficiency and effectiveness of rock dust application was also achieved using a multipoint injection approach to help spread the rock dust across the cross section of the mine entry in an effort to improve mixing and distribution with the mine airflow. This technology could potentially provide mine operators with a fully automated system that will monitor the amount of float coal dust in the mine atmosphere, calculate the amount of rock dust required to inert the coal dust, dispense the required amount of rock dust, and send out an alert when the rock dust level in the system tank requires refilling.