Mineapolis, MN: U.S. Department of the Interior, Bureau of Mines, TN 422, 1993 Sep; :1-2
Objective: Develop an alternative to water bath exhaust conditioners (water scrubbers) for permissible diesel equipment used in gassy mines. Background: Water scrubbers are a safety device used on diesel-powered vehicles in gassy mines. Exhaust from the engine passes through the scrubber, where it is cooled, and any flames or sparks present in the exhaust are extinguished. This prevents the ignition of combustible mine dust or methane that may be present. Unfortunately, water scrubbers consume large amounts of water and require frequent maintenance. Approach: Methods that do not require water replenishment and frequent maintenance were investigated. The dry exhaust conditioning system was selected for investigation because no water is consumed and existing heat exchanger technology can be adapted to underground mine vehicles. In accordance with U.S. Mine Safety and Health Administration (MSHA) requirements, the system was designed to cool exhaust and trap flames and sparks. The U.S. Bureau of Mines (USBM) developed and evaluated a system for large engines and evaluated a second system for smaller engines. Both systems were evaluated on an engine test bed; if warranted, the system was then tested underground. How It Works: The dry exhaust conditioning concept uses a heat exchanger with a mechanical flame and spark arrester. The exhaust gas passes through the heat exchanger where it is cooled, then through the flame and spark arresters. A larger vehicle cooling system than the one used in the conventional water scrubber system is needed to dissipate the exhaust heat. The dry exhaust conditioning system may require less maintenance than a water scrubber. A dry exhaust conditioning system was developed by the USBM for engines that power large equipment, such as that used in underground oil shale mines. Three heat exchangers and flame-spark arresters were needed to cool the high exhaust flow. A second dry exhaust conditioning system, for use on lower horsepower permissible equipment, typical of that used in coal mines, was evaluated by the USBM. The system was similar in concept to the one discussed above, but a ceramic diesel particulate filter was added. This filter, which was located downstream of the heat exchanger and flame arrester, captures diesel particulate. Results: After the dry exhaust conditioning system for large engines was evaluated at MSHA's Approval and Certification Center, the system was installed on a 50-short ton haul truck at a nongassy oil shale mine. The truck used a 650-horsepower engine. During the laboratory and in-mine evaluation of the large-engine system, the heat exchanger became "fouled" with diesel particulate (soot), causing the exhaust temperature to exceed the recommended limit of 204 degrees C (400 degrees F). While the individual components of the system withstood the rugged mine environment, more maintenance time than anticipated for cleaning the system was needed. Before the dry exhaust conditioning system can be used on large mining equipment, methods of preventing particulate fouling must be developed. The system for small engines was sized for a 150-horsepower engine. Only one heat exchanger and flame-spark arrester were required. The system was designed to reduce exhaust temperatures to below 150 degrees C (302 degrees F). The ceramic particulate filter was sized to operate for at least one shift before removal for cleaning. The small-engine system was first evaluated by the USBM. Diesel particulate emissions were reduced by over 97 pct during laboratory testing. However, the engine backpressure and exhaust temperature exceeded design limits because of particulate fouling of the heat exchanger. During subsequent testing by MSHA, the system failed to pass a test designed to · determine its effectiveness to extinguish sparks. The system was not evaluated in a mine. Current Status: The USBM has pioneered the development of dry exhaust conditioning systems for mine vehicles. Although MSHA certification of a system was not obtained, new information was gained that can be used for developing future exhaust systems.
Mineapolis, MN: U.S. Department of the Interior, Bureau of Mines, TN 422