Mining Contract: Development of Dust Control Units for Underground Coal Mines

Contract Status & Impact

This contract is complete.

The contract resulted in two final reports—part 1 for a mobile dry scrubber, and part 2 for a mobile cuttings collector. To receive a copy of either or both parts of the final reports, send a request to mining@cdc.gov.

The overall objective of this contract with J.H. Fletcher & Co. was to reduce mine worker exposure to respirable coal and silica dust that can lead to the development of coal workers’ pneumoconiosis (CWP) and silicosis. To that end, two innovative concepts, described below, for collecting and containing rock and coal dust at the working face were developed and tested.

Mobile Dry Scrubber

The dry scrubber developed under this contract is a stand-alone, self-tramming, electrically powered unit that includes a 30 HP variable speed ventilation fan with two large, replaceable, commercially available, dry filter elements to collect dust from the ventilation air. The design is such that it can fit into a wide variety of mines and specific applications. The fan speed and resulting air flow is controlled by a variable frequency drive. This allows the mine to select an air flow through the dry scrubber which does not change the overall mine ventilation system. In addition, the variable frequency drive can be controlled with a feedback loop to automatically adjust the fan speed to maintain a constant air flow output as the filters are loaded with dust.

NIOSH provided laboratory testing facilities in a full-scale continuous miner test gallery and dust sampling equipment at the Pittsburgh facility to test the efficiency of the filtration system and overall operation of the machine. NIOSH also conducted underground testing of the system at the Alliance Resource Partners River View Mine in Waverly, KY. NIOSH lab tests showed that the scrubber averaged greater than 95% respirable coal dust removal efficiency while being operated at two fan airflow quantities of 3,000 and 9,000 cfm. Laboratory testing further indicated that the scrubber fan’s variable frequency drive speed controller maintained a relatively consistent airflow quantity during the first 10 hours of testing. Subsequent underground testing of the dry scrubber showed that it reduced the dust concentrations at a face location downstream of the continuous mining operations by 49.1%. This dust reduction was significantly lower than the dry scrubber dust collection efficiency in the lab because its operation induced and mixed some of the unfiltered return air with its filtered airflow into the face.

One of the possible benefits of this machine would be the ability to remove enough dust from the downstream airflow of a continuous miner such that the resulting ventilation air to roof bolter operators would meet current MSHA requirements of 1.5 mg/m³; however, this was not the stated goal of the contract.

Mobile Cuttings Collector

This unit was designed to operate in an underground coal mine in conjunction with a roof bolting machine. The concept of this design was to allow for a dust collection system to be located some distance away from the roof bolting machine and to collect the drill cuttings for a much longer period of time than is currently possible with roof bolters. The remote collection of cuttings would eliminate the need for frequent removal of the drill cuttings from the bolter and allow for the cuttings to be carried away and disposed of in a remote area of the mine.

Field testing of the prototype mobile cuttings collector indicated that it was capable of controlling dust from drilling as well as the standard dust collector. All gravimetric dust concentrations were less than 0.2 mg/m³ during testing, and no significant dust concentration differences were observed at the operator location, pre-dump location, and return location during drilling with the standard dust collector and the mobile cuttings collector. Size analysis of the drill cuttings material showed that the pre-dump removes most of the non-respirable sized dust from the cuttings, and the final classifiers inside the mobile cuttings collector and standard dust collector remove a substantial amount of the respirable-sized dust before reaching the final filter. About 10% of the material in the pre-dump was less than or equal to 10 microns in size (by volume), while about 90% and 70% of the dust in mobile cuttings collector final cyclone compartment and the standard dust collector vacuum bag, respectively, were less than 10 microns in size (by volume).

Although the prototype mobile cuttings collector controlled drilling dust as well as the standard roof bolter dust collector, some of its operational issues require further consideration before implementation at a producing continuous miner section. Additional design considerations for integrating the mobile cuttings collector operation into the bolting machine would be power cable handling, management of vacuum hoses, and engaging the mobile cuttings collector vacuum blower from the bolter operator location.