Modern Rock Dust Development and Evaluation

Recent events such as the Upper Big Branch Mine explosion where 29 miners lost their life brought to the forefront the need to evaluate the performance of rock dust and its ability to suppress explosions. In active workings of a coal mine, methane is kept at a level well below the explosive range. However, small pockets of methane may build up and reach the explosive range in an isolated area. If detonation occurs in this pocket, there is not much methane fuel throughout the rest of the mine to continue the propagation. However, there is an abundant source of coal dust throughout the mine which is highly explosive when suspended in air. The purpose of rock dust is to first not allow the coal dust to suspend in air, and second act as an inerting agent when suspended in air with the coal dust not allowing the flame front to propagate. Rock dust is the first, and only line of defense to extinguish the flame front in a coal dust explosion. Rock dust is applied to every exposed area of the mine (e.g. roof, floor, pillars) either by hand or by a machine. It is generally applied in a powder like form, dry dust, or mixed with water and sprayed on the exposed surfaces, wet dust. Technology has advanced to the point where the dust is mixed with water and proprietary additives and polymers which allow the dust to dry on the exposed surfaces with little caking, or clumping. Caking of rock dust is believed to greatly reduce the ability of the dust to suspend with the fine coal dust in the air and extinguish flame fronts. In underground coal mines, particularly thin seams, it is vital that an effective and efficient method of rock dusting is performed to ensure the utmost safety of coal miners in the event of an explosion. Limited facilities and resources are available to study coal dust and methane explosions in the United States. This proposal will enhance and continue research conducted by the Bureau of Mines and later NIOSH at the Bruceton Mine and Lake Lynn Experimental Mine. These facilities are currently very limited from a continued research perspective. By completing the objectives outlined in the proposed project, the Georgetown, Kentucky laboratory controlled by Dr. Lusk at the University of Kentucky will develop the technology and capability of performing research on coal dust and methane explosions. The lab already has a track record for sustained research on explosive events. UK has the personnel and facilities necessary to provide this capability to industry. The proposed project seeks to evaluate current technology for rock dust dispersion in underground coal mines. Several new technologies are emerging onto the market and need to be evaluated for inerting performance in coal dust applications. In total, six (6) rock dust types will be evaluated. The six types of rock dust include a new concept for hydrophobic rock dust, Dywidag Systems International (DSI) DYWI Dust, Strata Worldwide (Strata) FoamDust, a prototype rock dust by Minova North America, dry dust, and typical wet dust. The project will have three objectives. 1. Investigate a chemical absorption process for creating hydrophobic rock dust. 2. Determine the caking properties of the six types of rock dust and the resulting dispersion properties when subjected to explosions. 3. Evaluate the flame-front extinguishing performance of the new technologies developed by the Project Team and Independent Companies against typical dry-dust and wet-dust applications. For the first Objective, world-renowned mineral processing specialist Dr. Rick Honaker will develop and create a hydrophobic rock dust. His expertise in chemical additives and applications will yield a new, innovative product. His hypothesis involves the use of dry rock dust and a sprayed application of sodium oleate. This type of process should allow the rock dust to remain hydrophobic unless the chemical additive is worn away by abrasion. The concept is new, so several trials are expected to optimize the volume and application method of the additive. Hydrophobicity is desired for rock dust since water causes caking effects. Large clumps of rock dust from caking are believed to be detrimental for the ability of the rock dust to extinguish flame fronts created by explosions. In the second Objective, samples of the six rock dust types will be created. Each sample will be cycled through varying temperatures and humidities simulating underground coal mine environments. The dust samples will then be evaluated for caking effects by a sieve analysis where size distributions can be obtained. In addition to the laboratory testing, rock dust samples will be collected from coal mines with differing environmental conditions and exposure time to determine the level of caking produced in normal mining conditions. The coal mine samples will then be compared to laboratory caking results. The final task of Objective 2 will be quantification of rock dust dispersion when subjected to a blast wave. Samples will be placed in a shock tube and different pressure versus time waveforms will be generated from a detonated volume of high explosive inside the tube. Measurements including angle of ejection, volume loss, and others will be determined using various pieces of equipment (e.g. balances, high speed camera, etc). In the third Objective, the extinguishing properties of each rock dust will be determined and compared. A new chamber will be required to develop and produce explosions with flame fronts representative of mine explosions which include float coal dust. Advantages and disadvantages of each newer technology rock dust will be determined when compared to the typical dry or wet dusting applications. If the concerns regarding caking and dispersion effects for these polymerized rock dust applications can be abated and addressed, the safety in thin seam underground coal mines in Kentucky would be greatly enhanced. The polymerized or foam rock dust allows for more adequate application of the dust material and thus ensures more coverage of coal dust bearing surfaces. The space constraints in thin seam mines make efficient rock dust application methods particularly important. This project will require two years to allow for development and testing of six different variations of rock dust. The total cost to the Kentucky Department for Energy Development and Independence is $404,457. The first year will require $219,149 while the second will necessitate $185,308. Dr. Perry and Dr. Lusk have each committed to dedicate 3 months worth of salary toward the project while Dr. Honaker has committed 0.5 of a month. Personnel, faculty and two graduate students, will require $120,644 for the first year and $127,138 the second year for a total of $247,782, or approximately 61% of the total project cost. The remaining 39%, $156,675, is dedicated to equipment, supplies, tuition, and indirect costs at a 15% rate. DSI and Strata have, when combined, committed to cost-share to the amount of $$$$$, which represents a %%% match for a total project cost of $$$$$$. Minova has also been approached for cost sharing, but proposal submission date constraints did not allow inclusion.