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October 19, 2006 at 7:27 pm #4116
any suggestions on how to lower the amount of dust coming from the cokers? working on ideas and will post once finished but would love input. thx
October 31, 2006 at 8:37 am #7513
antonio saura CebrianParticipant
In the Old Discussion you can found some ideas or how the dust was generated. For example this was written for someone, but you can found other questions because the dust problem can be from the type of coke that you produce (operation condition, feed,etc) and the way that you cut the drum
“In no case is the pitch of cutter advance the ROOT cause of excessive fines. It may be, along with other variables such as the design of the cutting head, a proximate cause. Consider how fines are produced. First, all of the coke in the pilot hole gets pulverized to fines because the bigger chunks tend to sink to the bottom of the pilot hole and get beaten up until they are small enough to suspend. The inescapable conclusion is that the pilot hole should be made as small as possible by narrowing the included angle of the drilling jets. A smaller diameter pilot hole has the additional advantage that it offers less flow area for the water to drain out the bottom as the pilot hole approaches the bottom of the bed, retaining more water to fluidize the fines above the cutting head and reducing the area that has to be fluidized, reducing the likelihood of having the pilot hole fines slump around the drilling head. The angle of the pilot jets may be inexpensively modified by fabricating adapters with angular offset to screw into the cutting head in place of the nozzles, and then screwing the nozzles into the adapters.
Second, fines are produced when the coke bed is broken up by the high-velocity water. At first it appears counterintuitive that higher water velocity produces fewer fines, but it begins to make sense when you recognize that the higher the energy of the water, the more effect it has in shattering the coke bed rather than eroding it. Hence, use the highest water pressure available. Obviously, the higher the water pressure and the greater the shattering effect, the faster the pitch of cutting can and should be.
Third, fines are produced when chunks of coke already loosened from the matrix are subjected to repeated passes of the cutting jets. Picture what happens when a big chunk of coke is broken loose from the top of the coke matrix. The velocity of water flow across the horizontal surface of the bed toward the pilot hole is not great at the drum wall. As the water flows across the rough top surface of the bed, some of it drains down through the porous bed. The horizontal velocity is simply not great enough to transport all the larger chunks of coke to the pilot hole as soon as they are loosened, so those chunks lie on the bed until they are hit again and again by the water stream until they are reduced to particles small enough to be washed over to the pilot hole.
There are two solutions to this problem and the choice depends upon the nature of the coke being produced. The ideal solution, obviously, is to cut from the bottom of the drum, so that the chunks of coke fall out of the path of the cutting water as soon as they are shattered from the matrix. This incurs the risk of having part of the coke bed break loose and trap the cutting head. The stability of the remaining coke matrix can be increased by modifying the angle of the cutting jets to direct them to the steepest down angle that still gives sufficient velocity at the drum wall to blast the coke off. Start with 15 degrees below horizontal and then increase the angle stepwise until it is limited by the effectiveness of cleaning off the wall. As for the pilot nozzles, adapters produced in the local machine shop may be used to change the angle of the cutting nozzles without significant financial commitment while retaining the option to back up a step or two to optimize the angle. When the coke produced has so little mechanical integrity that it cannot be cut from the bottom even with the additional support afforded by down angle on the cutting jets, it has to be cut from top down. In that case, the movement of particles to the pilot hole can be facilitated by angling the cutting jets up to slope the top of the coke matrix toward the pilot hole. The biggest chunks will still see the cutting jet more than once, but the size of particle that can be washed to the center is obviously increased, reducing formation of fines. “
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