A field study of a roof bolter canopy air curtain (2nd generation) for respirable coal mine dust control
|نوع نگارش مقاله||
scopus – master journals – JCR
۴٫۲۷۶ در سال ۲۰۲۰
۲۶ در سال ۲۰۲۱
۰٫۹۰۱ در سال ۲۰۲۰
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Q1 در سال ۲۰۲۰
خرید محصول توسط کلیه کارت های شتاب امکان پذیر است و بلافاصله پس از خرید، لینک دانلود محصول در اختیار شما قرار خواهد گرفت و هر گونه فروش در سایت های دیگر قابل پیگیری خواهد بود.
فهرست مطالب مقاله:
A ۲nd generation roof bolter canopy air curtain (CAC) design was tested by National Institute for Occupational Safety and Health (NIOSH) at a Midwestern underground coal mine. During the study, the roof bolter never operated downwind of the continuous miner. Using a combination of personal Data Rams (pDR) and gravimetric samplers, the dust control efficiency of the roof bolter CAC was ascer- tained. Performance evaluation was determined using three methods: (1) comparing roof bolter operator concentrations underneath the CAC to roof bolter concentrations outside the CAC, (2) comparing roof bol- ter operator concentrations underneath the CAC to the concentrations at the rear of the bolter, and finally, (3) using the gravimetric data directly underneath the CAC to correct roof bolter operator concentrations underneath the CAC and comparing them to the concentrations at the rear of the bolter. Method 1 dust control efficiencies ranged from ۵۳٫۹% to 60.4%. Method 2 efficiencies ranged from ۱۵۰٫۵% to 52.2%, and Method 3 efficiencies ranged from 40.7% to 91%. Reasons for negative and low dust control efficien- cies are provided in this paper and include: incorrect sampling locations, large distance between CAC and operator, and contamination of intake air from line curtain. Low dust concentrations encountered during the testing made it difficult to discern whether differences in concentrations were due to the CAC or due to variances inherent in experimental dust measurement. However, the analyses, especially the Method 3 analysis, show that the CAC can be an effective dust control device.
|بخشی از متن مقاله:|
Canopy air curtains (CAC) were originally developed for use on the cabs of continuous miners to protect miners from underground coalmine respirable dust in the mid-1970s by the U.S. Bureau of Mines (USBM). Once developed, field testing continuous miners at different underground coal mine sites demonstrated CAC dust control efficiencies ranging from 23% to ۶۹% . In the 1980s, the National Coal Board modified the USBM CAC and field tested it on a boom-type heading machine. Results of their testing demonstrated dust control efficiencies of 35%–۶۸% in blowing ven- tilation and 40%–۸۷% in exhausting ventilation . This field test- ing demonstrated the ability of the CAC to successfully protect miners from respirable coal mine dust.
The elimination of the cab on continuous miners occasioned the development for roof bolter operators. Laboratory testing of the roof bolter CAC has shown that the CAC can be an effective res-
pirable coal mine dust control for roof bolter operators. Laboratory test results demonstrated dust control efficiencies ranging from
14% up to ۷۵% [۳–۵]. Unfortunately, there is limited information on their effectiveness for controlling respirable coal mine dust in actual operating conditions at underground coal mining sites. Two underground tests of the CAC on roof bolters demonstrated dust control efficiencies of 35% and 53% before problems occurred with operation of the CAC . This study is the first to conduct field testing of the roof bolter CAC of sufficient duration to collect an adequate amount of data allowing analysis to demonstrate its effectiveness for roof bolter operators.
Very few studies of CAC have been completed outside of the USBM and NIOSH. A radial air curtain has been developed by the College of Mining and Safety Engineering at Shandong University of Science and Technology and is fully described in a Computa- tional Fluid Dynamic (CFD) study of the device [6–۸]. However, this device is radically different and is not a CAC which provides per- sonal protection to an individual mine equipment operator. This device is a tube that attaches to the blowing ventilation tubing and consists of slots to allow air to radially emanate from the
device. It provides airflow that creates a wall of air that essentially traps dust between the airwall and the face, protecting machinery operators who maybe outby the airwall. An exhaust ventilation tubing is required to remove the trapped dust at the face. These studies focused on the CFD analysis of the airflows showing its effectiveness. Field studies were conducted to show their curtain performance. However, there was minimal discussion of its effec- tiveness for personal protection. While the device provided protec- tion to mine equipment operators using airflow, the methodology of protection is very different from that of the CAC. Another version of an air curtain was designed to be installed on a longwall shearer body. This curtain created a wall of air which separated the venti- lation airflow into two channels. One kept dust contaminated air at the face while the other kept the clean air in the walkway. CFD analysis and field measurement comparisons were conducted to show its effectiveness . While effective, this methodology is also different from the CAC.
Since the implementation of the new respirable coal mine dust limit from 2.0 to ۱٫۵ mg/m3, roof bolter CACs are becoming more commonplace in underground coal mines as a dust control tool to prevent roof bolter operator overexposure to respirable coal mine dust . J.H. Fletcher & Co. has been instrumental in deliv- ering an effective design which incorporates the filter, blower, and canopy plenum seamlessly into the design of the roof bolter, resulting in a successful operational roof bolter CAC.
A field study was conducted by the NIOSH to test the effective- ness of the roof bolter CAC for respirable coal mine dust control. The study was conducted at Prairie State Energy’s underground coal mine; the Lively Grove Mine. The Lively Grove Mine is a room-and-pillar mine containing coal from the Herrin #6 seam. The mine produces approximately 7 million tons of coal per year to the adjacently located power plant. Testing was conducted on a roof bolter which operated in entries 7–۱۳ in a 13-entry main. The roof bolter is manufactured by J.H. Fletcher & Co. and is listed as serial #: 2015-306. The mine employed a blowing face ventila- tion system to the roof bolter machine during bolting operations. However, during this testing the roof bolter never operated down- wind of the continuous miner.
The CAC system is integrated into the roof bolter machine with the hydraulically driven fans and filter mounted on the roof bolter body and the plenum, which provides air over the operator, incor- porated into the roof bolter canopy. The fans are connected to the canopy via ۱۰٫۲-cm diameter hose. The left and right side of the roof bolter each had a CAC system in-place, which operated the entire time during roof bolter operation.
The shape of the canopy/plenum used at the mine site is shown in Fig. 1. This canopy is the 2nd generation design from J.H. Fletch- er’s original slotted CAC. The original slotted CAC had dust control efficiencies ranging from 14.2% to 24.5% in the laboratory . This
2nd generation CAC is an improvement upon NIOSH’s original design that uses uniform airflow across the plenum. The uniform filtered airflow provides protection to the roof bolter operator by flowing directly over the operator resulting in displacement of air contaminated by respirable dust from the operator’s breathing zone. The uniform filtered airflow also provides a column of air that prevents any entry ventilation airflow contaminated with res- pirable coal mine dust from penetrating. The ۲nd generation CAC also, implements recommendations from the NIOSH computa- tional fluid dynamics (CFD) evaluation conducted on the original design which recommended staggered slots or nozzles if perimeter outlets are to be used . This new design incorporates staggered perimeter nozzles to prevent infiltration of contaminated air into the CAC domain or the protection zone. The protection zone con- sists of an equally spaced pattern of holes providing airflow over the roof bolter operator at a lower velocity than the perimeter holes.
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