Cement Manufacturers Association (CMA)

Page 44 This means that the explosion isolation system between DC and pump pre-hopper(s) presently only can be a rotary valve, with the necessary gap width feature being lost over time. What needs to be done here is to ensure that the screw conveyor connection between the DC’s funnel hopper and the vertical drop pipe above the pump pre-hopper is an EPSR pipe screw conveyor and not a U-through screw conveyor. In many cases the screw conveyors for the transfer of the DC’s output are U-through screw conveyors without EPSR, which are not suitable for the application. The reasons have already been given in U-through screw conveyors will not have EPSR. Deformation or separation of their formation of a dust cloud in the vicinity of the damaged spot. The air borne ground coal is perfect fuel for explosive combustion outside of the screw conveyor and often the location will cause the dust cloud to form inside a structure or building. The 2 nd reason why U-through screw conveyors should not be used for PF is that unobstructed channel for the transfer of conveyor. Screw conveyors with a pipe body and the necessary EPSR are what has to be installed. The combination of EPSR pipe body screw as explosion isolation system when new is an acceptable solution.After the gap width between rotor vane tips and body bore has widened as result of wear the combination of rotary valve and EPSR pipe body screw conveyor will still provide for explosion isolation. Again, this then is in the grey area of constructional explosion protection. In case of multiple DC funnel hoppers, the complex and explosion isolation in most cases will have to be installed under each funnel hopper outlet, which is another reason why DC’s with multiple funnel hoppers should not be installed, in coal grinding systems. Often, pump pre-hoppers are connected de-aeration air. This is wrong, since the result of it is that another set of interconnected vessels in which a dust explosion can be ignited is created. This seems not to have been understood by most system designers. protected correctly, a number of explosion isolating and explosion de-coupling features would have to be installed. What should be done is installing a small on the market. A vessel like a pre-hopper with EPSR good for 9 or 10 bar g should not be connected with another vessel. That the screw conveyor connection between the DC and the pre-hopper needs explosion isolation in it is challenging enough. Other types of explosion isolation presently. Possible would be EPSR valve locks with 2 valves with alternating valve movements that ensure that always one of the 2 valves is closed at any given time.Presently no supplier has worked out the design and done the necessary type tests that would make qualifying equipment available to the market.