Cement Manufacturers Association (CMA)

Should the explosion venting not be self reclosing, e.g. by comprising rupture disks or rupture panels, the explosion venting would be counterproductive for the safety of the system. After having opened, ingress of atmospheric air and loss of emergency inerting gas through the system’s protection. Most coal grinding systems have a remote-control valve in the air in-feed duct of the mill. Damper is an often-used name for this valve, but using the word damper is not very well suiting. This valve plays a role in the emergency inerting concept for the system inhibiting dissipation of CO or N into the larger system, where the gas would be useless. This role of the valve has to be understood well by the process controllers and the controls that would enable the valve to play its role have to be in place. Sometimes a misunderstanding exists. That the valve can serve as a blockade designed as quick-acting is not true. Special EPSR explosion isolation valves exist, but these are not available in the larger sizes that would be necessary. They are parts of explosion isolation systems that respond to a sensor that notices the start of an explosion. They have to close extremely fast. For the duct diameters of air-swept coal mill systems the moving mass of the valves’ shutting mechanism would be too heavy as to be accelerated and decelerated fast enough as to be useful. The quick acting valves that can be found in the cement industry’s coal grinding systems are far too slow as to ever function as explosion isolation system. They have their function in the emergency inerting process and there is no need for them to be quick acting - Mill’s EPSR As often can be noticed with older systems, the need of EPSR of the VRM’s body, or of rotating cylinder is not always understood by the operators and their maintenance personnel. shortcut the opening and closing of away may dangerously compromise a mill’s EPSR. The rejects ejection of VRMs also very often is not correctly designed or installed. Such a system has to have 2 interlocked valves with the necessary EPSR, of which only one can be open at any given time. In case the ejected rejects are transported by a conveyor, it has to be ensured that the this path can do no harm. A conveyor eliminates the need for personnel to remove the rejects from where they are ejected from the mill, for which it otherwise would be necessary for the personnel to the VRM’s ejecting spout into the conveyor as well as the conveyor proper need to be that could harm workers and passers-by. Correct solutions for the transition of the VRM’s ejection into or onto conveyors are rare, in the industry. Lack of awareness of this need is ubiquitous. - VRM-to-DC or HBM-to-separator/ For the presently usual designs, the connection between a coal mill and the next downstream process vessel in case of a VRM is the system’s main baghouse (DC) and in Interconnected vessels are the reason why constructional explosion protection is not simple. Page 35