Patent Application
20120018544
This invention relates to mining More specifically, it relates to dust control around a continuous miner or similar mining machine through the use of water spray applications.
Increased productivity and high out-of-coal seam dilution (25% to 30%) in the US and around the globe continue to generate dust control problems in mining areas. After a significant decrease in the number of incidents of coal worker's pneumoconiosis (CWP) over the last several decades, the number of reported cases in this decade is increasing. The primary cause of CWP is inhalation of respirable dust in a confined workplace; specifically, the inhalation of coal and quartz dust in a mine. The National Institute for Occupational Safety and Health recognizes this disease as being severely disabling, potentially lethal, and entirely preventable through respirable (less than 10 micron) dust control. The typical protocol for prevention of this disease has been monitoring mine workers for symptoms of this disease and, once a CWP diagnosis has been made, moving the miner to a low-dust exposure job. Prevention of this disease through a significant reduction in mine workers' exposure to respirable dust is a high priority. Additionally, several mines are now facing reduced dust standards due to high respirable quartz content in the dust. In underground US coal mines, miner operator (MO), haulage unit operator (HO), and roof bolting (RB) unit operator are typically overexposed to respirable dust.
The conventional approach to dust control in a mine has been the use of water sprays located on the mining machines to wet the coal. Approximately located and intuitively designed water sprays on the cutter drum and around the continuous miner chassis have been extensively used to control dust for the miner operator (MO), batch haulage unit operator (HO), haulage roadways, and material transfer points. A continuous miner or CM is extensively used for coal production in partial extraction mining areas. Typical spray systems, provided by manufacturers, have 15-45 sprays located across the top and the sides of the cutter boom (
Several studies over the last several decades have attempted to locate the source of and have attempted a solution to the dust problems in mining environments. The conventional wisdom is that presented by Chang and Zukovich (Cheng L and Zukovich P. P. 1973. Respirable dust adhering to run-of-face bituminous coals. Pittsburgh, Pa.: U.S. Department of the Interior, Bureau of Mines, RI 7765. NTIS No. PB 221-883.) Their position was that a large amount of dust created does not become airborne and stays attached to the broken material. Therefore, spraying more water on the broken material tends to reduce dust. Adding water directly at the cutting picks that gets mixed with fragmented coal is more important than creating a shroud of water around the miner or shearer. Based on this observation, the conventional practice of mixing the water uniformly with broken coal was developed. However, this approach alone has not been effective in mine dust control.
More recently it has been observed that water can be used to control dust through the wetting of broken material and capture of airborne dust. (Kissel, F., “Handbook for Dust Control in Mining”, NIOSH, Information Circulation (IC 9465), 2003, pp. 131.) Although the methods of wetting broken material have been more uniform throughout the industry, a haphazard approach has been taken to the capture of airborne dust through the use of water sprays. This is most likely due to the problem and sometimes conflicting proposed solutions. It is suggested that a large number of smaller-volume sprays is better for dust control than smaller number of larger-volume sprays. Jayaraman and others concluded that many spray systems can create turbulent airflow in the face area that can result in rollback of dust. (Jayaraman, N, Fred N. Kissel, and W. E. Schroder (1984), “Modify Spray Heads to Reduce Dust Rollback on Miners,” Coal Age, June 1984)
However, certain research has proven valuable in the design of water spray systems. Courtney and Cheng concluded that typical water sprays operating at 100 psi do not capture more than 30% airborne dust in an open environment. (Courtney W. G. & Cheng L. 1977. Control of respirable dust by improved water sprays. In: Respirable Dust Control—Proceedings of Technology Transfer Seminars, Pittsburgh, Pa., and St. Louis, Mo., IC 8753, pp. 92-108. NTIS No. PB 272 910.) Furthermore, inappropriately designed sprays can displace dust clouds rather than wet or capture airborne dust. Reducing the water droplet size through the use of atomizing or fogging sprays may temporarily improve the airborne dust capture efficiency. However, small droplets tend to collapse/evaporate easily and release the captured dust. (McCoy J., Melcher J., Valentine J., Monaghan D., Muldoon T. & Kelly J. 1983. Evaluation of charged water sprays for dust control. Waltham, Mass.: Foster-Miller, Inc. U.S. Bureau of Mines contract no. H0212012. NTIS No. PB83-210476.) Atomizing nozzles are most efficient in airborne dust capture followed by hollow cone, full cone, and flat sprays. Hollow cone sprays are less likely to clog due to larger orifice area.
Nozzles operating at higher pressures are likely more efficient in the use of water while providing similar airborne dust capture efficiency as those operating at lower pressures. However, high-pressure sprays tend to disperse more dust. Therefore, their use is more appropriate in a relatively confined environment.
Courtney and others reported that the primary release point for dust from a CM is from under the boom when the cutter head shears down. (Courtney, W. G, N. I. Jayaraman, and P. Behum (1978), “Effect of Water Sprays for Respirable Dust Suppression with Research Continuous Mining Machine”, BuMines RI-8283, 17 pp) Thus, under-boom sprays should be considered. However, location and maintenance of under-boom sprays presents significant problems. Jankowski reported results for an alternate under-boom spray system with about 25% improved dust reduction (Jankowski, Robert A, N. I. Jayaraman, and C. A. Babbitt (1987),” Water Spray System for Reducing Quartz Dust Exposure of the continuous Miner Operator, “Proceedings of the 3rd U.S. Mine Ventilation Symposium, Pennsylvania State University, PP 605-611.)
In spite of considerable excellent research by the U.S. Bureau of mines (USBM) and the National Institute of Occupational Safety and Health (NIOSH) over the last 40 years, there are significant limitations to the current practice. These include use of high water pressure on the chassis (100 psi or more); similar water pressure on the chassis and under-boom sprays leading to escape of airborne dust from the sides; only one point of dust control on the top of the chassis; no control on roll-back dust travel; use of only one type of sprays such as hollow-cone for all sprays; poor orientation of sprays, etc. There is a need to revisit the design concepts of sprays on continuous miners to control respirable dust (including quartz dust) in and around the mining face area.
In the industry there is a need for improving spray efficiency. A more reasoned and systematic design is needed that more effectively reduces the respirable dust around mining machinery.
FIG. 1A—A top view of a continuous miner featuring an exemplary conventional spray system.
FIG. 1B—A side view of the continuous miner of
FIG. 2A—A top view of a continuous miner featuring an embodiment of a spray configuration, with Second Line of Defense (SLD) sprays, and Third Line of Defense (TLD) sprays.
FIG. 2B—(a) An operator side view of the continuous miner of
FIG. 2C—A detailed view of the cutter boom of the continuous miner of
FIG. 3A—A side view of the dust containment of an exemplary conventional spray system around the cutter boom of a continuous miner
FIG. 3B—A side view of one embodiment of the dust containment spray system around the cutter boom of a continuous miner featuring a spray configuration including SLD sprays.
FIG. 4A—(a) A sectional view of the side head sprays block; (b) Another sectional view of the side head sprays block.
FIG. 4B—(a) A sectional view of the center head sprays block; (b) Another sectional view of the center head sprays block.
FIG. 4C—A top view of the center and side head sprays blocks.
FIG. 5—(a) A sectional view of the TLD scrubber side spray block; (b) Another sectional view of the TLD scrubber side spray block.
In order to revisit the sources of mine dust and to analyze how the conventional technology is failing to provide adequate control of mining dust, it is important to analyze the sources and locations of respirable dust around continuous miners in multiple environments. It is also important to identify several areas in the mine where dust control could be introduced or improved: along the roof level of the mine, at the location of the conventional spray blocks, at the sides and under the miner, and at transfer points near the last open crosscut return.
A high concentration of respirable dust occurs near and along the roof level. Location of boom sprays for the cutter drum, loading pan sprays, under-boom spray pressure, type of sprays used and high water spray pressure (˜100 psi) used can displace dust-laden air along the roof level, towards the sides, and back of the miner and results in roll-back on the miner chassis toward the miner operator and batch haulage unit operator. This dust-laden air is moving at a relatively high velocity based on water pressure used and seam height and, due to its fine size dust particles, is not captured by suction inlets of a scrubber.
Spatial location of sprays on the spray blocks and type of sprays used can typically result in significant interaction among sprays. These interactions (caused by different sprays colliding with each other) can result in droplet size increase after interaction. Conventional cutter drum head sprays are directed at the rotating drum and cutting bits at different angles in the horizontal plane so that air moves across the face and is directed in the return entry. In several cases, these sprays intercept each other upon discharge from the orifice resulting in not only larger droplets that negatively impact dust control, but also in wasted energy. Since the ability to capture dust requires that the water droplet size be near the size of the dust particle, this interaction significantly reduces the potential to wet the finer fractions of dust. Furthermore, most of the spray energy is dissipated in interactions rather than in wetting the dust.
The side sprays on the miner operator side tend to contain the dust in the face area. These sprays attempt to create a seal between the sides of the excavation and the continuous miner. However, the seals are generally incomplete due to the large distance between the sprays and the excavation sides and interactions between these side sprays and the boom and under-boom sprays. Again, dust is pushed towards the roof level, or to the sides, or underneath the miner
Most of the dust load in the scrubber is from the scrubber suction inlet at the bottom over the coal conveyor. Even if the scrubber does an excellent job of wetting the dust, the dust generated during the material discharge from the conveyor into the haulage unit significantly increases dust concentration in the last open crosscut return (LOXC). In an attempt to control dust at material discharge points, throat sprays may be located above the conveyor carrying the cut material to be discharged in the haulage unit. Since conveyor speed is very high, water discharged from throat sprays only wets the surface of coal and it is not uniformly distributed in the entire mass of the material. This results in significant dust creation when the material is dumped into the haulage unit.
Movements of batch haulage units around the face area further complicate dust concentration and turbulence in the face area and intake air flow to the face area.
In the industry there is a need for improving spray efficiency. Various embodiments of the present invention are designed for improving the dust suppression using hydraulic sprays on the continuous miner: utilizing appropriate spray pressures spatially to minimize pushing the dust toward the roof, sides, and underneath the miner; wet and surround the airborne dust to allow the scrubber to capture it; and further wet the airborne dust escaping the scrubber inlets area before it enters the area behind the miner and the LOXC.
Various embodiments of the present invention utilize spatial distribution, spray pressure and type of sprays to address the problems identified in the prior art. Principles on spray configurations include: solid-cone sprays are ideal for wetting the broken coal but not good for wetting the air-borne fine particle dust; hollow-cone sprays are more efficient for wetting the airborne dust than flat sprays; flat sprays are more efficient for creating a hydraulic curtain than wetting the dust; narrow-angle sprays at a particular pressure reach farther than wide-angle sprays; narrow angle sprays cover a small area and therefore more number of sprays is needed to cover an area; inappropriate spatial location of sprays can increase interaction among sprays that may result in increasing spray droplet size, wasted spray pressure energy, and hollow-cone behaving more like a solid cone spray; and using high pressure water sprays can decrease likelihood of contact between dust particles and water droplets and decrease residence time for wetting the dust and low water pressure results in larger droplet sizes that are not effective for wetting fine particle sizes.
The primary means of dust control should be preventing the dust generated at the cutting faces from becoming airborne. Hollow-cone or flat sprays directed into the bits and the cutting face should help achieve this objective and cool the cutting bits.
Once the dust is airborne, the flooded-bed scrubber is an efficient mechanism at the face to capture the dust and wet it within the scrubber. Hence, the goal should be to maximize the amount of airborne dust that gets directed into the scrubber. To accomplish this, appropriately angled flat sprays or wide-angle hollow-cone sprays on the boom behind the first set of sprays create a shroud containing the generated dust near the face area in a restricted volume.
Similarly, flat or hollow-cone sprays underneath the cutting boom may envelope the gap between the pan and the boom and contain the airborne dust such that the central suction port of the scrubber is able to draw it inside the scrubber. Some miners have under-boom sprays that are directed away from the face toward the conveyor. However, such sprays reduce the residence time or contact time between the dust and water rather than increase it. However, spraying water toward the face area into the loading pan where it can be mixed with the entire volume of cut coal would help reduce generation during material discharge and during transport to dump point.
Under-boom sprays should be operated at a slightly lower pressure (10-20 psi lower) than the chassis sprays on the top of the cutter drum. This will allow the dust laden air to be pushed into the conveyor throat and bottom scrubber suction inlet rather than be pushed toward the roof, sides, or bottom of the miner.
Once the dust is airborne, its capture using hydraulic sprays requires sprays producing droplet sizes in the range of the respirable dust particle sizes or slightly higher. Hence, really fine, misting or atomizing sprays need to be used subject to the constraints of available water pressures and more importantly the constraints involving very small spray orifice sizes which are likely to get plugged in a typical mine environment. These sprays will be placed at the back corner of the loading pan on both sides and directed inside the pan. These sprays are introduced to allow capture of some dust (respirable and coarser than respirable) even before it actually enters the scrubber.
Despite the created shroud of sprays, some of the dust will still escape due to gaps in the shroud where the sprays do not overlap and due to the fact that at times, the cut coal traveling to the conveyor may partially obstruct the central scrubber suction port. Hence, there is a need to employ an improved line of defenses on the side of the continuous miner. This line of defense is implemented in the form of sprays on the left side of the miner located behind the left side suction ports of the scrubber. These sprays should be wide-angle, hollow-cone sprays that essentially create a seal with water curtain from the continuous miner to the left rib and to the roof top to contain the dust such that it gets an opportunity to enter the side suction port. These sprays can be located only on the left side of the miner as the prevailing air flow pattern in the face carries the escaping dust from the right side over the top of the miner and through the area between the left side of the miner and the rib.
As discussed above, dust-laden air along the roof level is moving at a relatively high velocity based on water pressure used, seam height, and rotational speed of the cutting drum. This air is not captured by suction inlets of scrubbers. To capture the dust escaping over the top of the miner, a set of misting sprays may be installed on the top of the miner directed towards the roof and angled towards the face such that the escaping dust contacts the mist and is captured. Furthermore, such sprays contain the dust in the face area and allow time for it to be sucked by the side suction inlets. These Second Line of Defense sprays (SLD sprays) are located on the top, the side, and on the top and sides of the CM chassis and spray water toward the roof and are angled toward the face. An additional set of sprays referred to herein as a Third Line of Defense (TLD) sprays generally located proximate to a set of scrubber suction inlets. Collectively or interchangeably, the SLD sprays and TLD sprays are referred to as a first set of water sprays and a second set of water sprays depending on their position and function. Due to the low inertia of the mist droplets, the mist migrates away from the face concurrently with the air and the respirable dust increasing the residence time for the dust and mist droplets to come in contact and attach resulting in the dust-droplet aggregates to drop out and fall to the ground. The SLD sprays can be small-volume misting sprays and operate at an appropriate pressure so that the resulting water curtain creates a seal against the roof. Appropriate sprays are selected that utilize orifice diameters similar to those of the conventionally used miner sprays, but which produce a very fine mist of water. Spraying Systems Company, Inc. in Chicago, Ill. produces sprays; however, this is not limiting and other fine-misting types of sprays can be substituted.
The various embodiments of the present invention are further described in reference to the figures.
The second set of sprays that contain the dust emanating from the cutter boom area 90 are the outer bit-ring sprays 82; these sprays are oriented differently than conventional sprays so that there is no interference between adjacent sprays. The outer bit-ring sprays 82, as a whole, create air movement toward the face of the cutter drum to remove volatile gas and dust particles.
The third set of sprays around the cutter boom 90 are configured differently than conventional sprays. These sprays are designed to create a seal around the sides of the material loading pan 88 so that dust cannot escape and is wetted in the material loading pan 88 and sucked-in through the wet scrubber suction inlet 94 located on the top of the material transfer conveyor 96. These sprays are oriented to establish seal along the sides of the mining excavation over as large an area as possible. Furthermore, these sprays are directed slightly inward (between 5°-20°) toward the loading pan to push the dust toward the scrubber suction inlet 94.
On both sides of the CM behind the cutter drum, the TLD sprays prevent any dust not captured by the head sprays, the outer bit-ring sprays 82, or the side cutter-boom sprays 68 from reaching the miner operator or haulage unit operator. The TLD top spray block 51 creates a hydraulic curtain across the excavation between the miner chassis and the roof of the excavation so that escaping dust can be wetted in this area before leaving the face area and without affecting the miner operator, haulage unit operator and other workers working on the downwind side of the miner. The TLD operator side spray block 52 and scrubber side spray block 53 create a seal between the side chassis of the miner and the sides of the excavation. The TLD top spray block 51 is located on the top of the chassis or along the sides of the chassis to ensure that roof falls will not impair their operation. The TLD top spray block 51 consists of 2-3 sprays angled horizontally and vertically in such way that the miner operator can see the mining face cutting area. The operator side spray block 52 and scrubber side spray block 53 also consist of 2-3 sprays oriented vertically and horizontally away from the chassis to create a seal between the chassis and sides of the excavation; sectional view of these spray blocks are shown in greater detail in
One embodiment of the TLD spray system was installed in a Joy 14 CM, similar to the miner shown in
In
This application claims priority to an earlier filed co-pending Provisional Patent application No. 61,366,356 filed Jul. 21, 2010 entitled Innovative Water Sprays Applications for Dust Control on Mining Machines.
| Number | Date | Country | |
|---|---|---|---|
| 61366356 | Jul 2010 | US |
