Bottom ash conveyor design change

[crusty1]

There is some talk about replacing our submerged ash drag chain conveyor with a dry bottom screw conveyor. Our plant is a stoker fired wood waste boiler. Does anyone have any experience with this design. I was trying to do some research on the internet and have yet to find any bottom ash conveyor manufacturers to use a screw design for this type of application.

 

[smckennz]

Hi Crusty1
I have played around with both, and prefer the wet bottom with drag chain (or belt). The things to watch for with a screw are bridging avoidance, bearing protection and gas sealing.
With low ash (no bark or mud) you may get away with a screw; I still use them on coal fired economic boiler refits, but much prefer wet handling if only to avoid the screeching of dry screws. If you go for a live base multiple screw arrangement with the screws supported at both ends dropping into a trough then you may have a winner. But there would have to be a good reason to do it, such as a flyash baghouse and pneumatically handled interpass deashing arrangement.
Also screws do not handle clinker as well as a drag chain.

Cheers

Steve

 

[rmw]

If your wood waste fuel has a significant of bark with dirt or mud (due both to dragging the logs through the woods, and/or wind borne deposits of dust into the growing bark, your screw flutes will experience a high rate of wear. Live base multiple screws as described above can be subject to material bridging, so be sure to have some 'poke hole ports' designed in so that a rod can be inserted and the bridging rodded out.

I haven't seen it done that way, but I have only seen 5-6 dozen wood fired boilers in my life, so my experience might be too limited.

I wouldn't do it.

rmw