Canadian Mining Journal


DRY SCRUBBER: J.H. Fletcher offers new machine for a cleaner bolting experience

WEST VIRGINIA – J.H. Fletcher & Co. has created a new product to improve the operator environment on roof bolters. The machine, known as a dry scrubber, has the ability to operate in a variety of applications, making it a compliment to the Fletcher roof bolting product line.

The need for this product is evident, as dust concentrations downwind of continuous miners can exceed regulatory standards and overexpose roof bolter operators. In underground mining, on-board flooded bed scrubbers are used on continuous mining machines for respirable dust collection. Though these systems are proven, dust by-passing the continuous miner scrubber may expose roof bolter operators to high levels of respirable dust when working downwind of the continuous miner.

Fletcher’s new dry air scrubber meets all MSHA and NIOSH requirements.

Fletcher’s new dry air scrubber meets all MSHA and NIOSH requirements.

Fletcher’s research and development department developed the MSHA approved Fletcher dry air scrubber, a standalone, self-propelled, electrically powered ventilation fan.  The machine has two operating modes: tram and ventilation. While in tram mode, the fan cannot be operated. The dry air scrubber is engineered to be positioned between the rib and vent curtain. The unit then works to clean contaminated air before it enters the roof bolter work space, providing roof bolter operators with a cleaner air supply and lowering their exposure to respirable dust.

The design reflects Fletcher’s diversity in the underground mining sector, with the ability to fit into a wide variety of mines and applications. The dry scrubber is 5 metres in length and 1.4 metres wide, equipped with 305-mm crawler pads.

The dry scrubber pulls a portion (up to 9000 cfm) of the air flowing between the rib and the vent curtain into the filters on the inlet side of the fan. Filtered air is directed out of the machine and back into the main air stream. A pressure sensor arrangement is used to monitor filter conditions to alert the operator when the filters need replaced. A hydraulically operated hood and pivoting electrical controller allows access to the air filters. The fan speed and resulting airflow is controlled by a variable frequency drive (VFD). This allows the mine to select an airflow controlled with a feedback loop to automatically adjust the fan speed to maintain a constant airflow output as the filters are loaded with dust.

NIOSH laboratory tests found that the dry scrubber averaged greater than 95% respirable coal dust removal while being operated at two different fan airflow speed quantities of 3,000 to 9,000 cfm. Underground studies found a collection efficiency of 99.2%.

Other potential applications for the dry scrubber, include belt conveyor transfers, underground truck dumps, single entry air cleaning, and diesel particulate matter removal.

J.H. Fletcher products are available from Wajax Equipment in Montreal, 514-835-2030.

Please visit the manufacturer’s website at

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