Ash Conveying

This isn't exactly the information you are requesting (I don't have experience with pneumatic conveying), but you might find it pertinent.

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Have you studied the actual fuel value of the unburned carbon? The reason I ask, is because in even moderate temperature combustion, glasses tend to form from Si0₂ Al₂O₃, CaO, and Fe₂O₃. These glasses may form a barrier that severely limits any heat that might be obtained from attempting to burn the ash again.

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If that does seem to be the case, it might help to run the returning ash through a section of pipe that is acting as a ball mill....turning with hard media inside to crush the glass, exposing any unburned carbon.....

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The unburned ash also might have high water content.... not sure, but it would be worth investigating. Burning the ash again could be a good idea, as long as it actually causes more of it to be burnt, and doesn't require extra fuel to be consumed.

Do a study to determine the amount of savings this return system will generate for your company, assuming the 10kg/h return rate is a significant enough number compared to the initial fuel input rate.

If the savings is significant enough, hire a mechanical engineer with the proper experience or hire one that can design the system without resorting to asking total strangers for help.

Truth is not a compromise

Thank you for your answer. We have done all kind of studies before starting to design this process. From what I've been told from the guys in the lab that were doing the tests, there weren't any problems burning that part of ash. The fuel value is much higher than that of initial fuel (can't remember the exact value though).

Lyn

That's exactly what I am trying to do. But to do that I need to know how much the system will cost us. And to know that I have to contact the vendors to get the prices for all the equipment we will need, so I need to know at least approximately what we will need. Usually we do a preliminary design by ourselves before hiring someone.

At this point just take some educated guesses. Err on the high side, so you have a justifiable estimate.

I noticed that you have cyclones. Is it any difference in form and density (not bulk) between the "carbon rich" ash and the other ash ? If yes iy could be possible to make the separation by "air floating" and adapted cyclones for this kind of operation.

I can't help with much here but I did learn a thing or two when designing the pipe bridges that carried flyash piping. The lined piping was designed for easy replacement, even to the extent that we included walkways and monorails the full length of the bridges. Sorry, all that tells you is that the piping is high maintenance and that it was lined. I know there were several sources of resistant pipe.

The cross section of the bridge was similar to a soccer goal with a monorail hung directly below the cross bar, and with brackets on the inner side of the posts to carry the piping. Each piping length sat on at least two brackets so that it could stay in place when adjacent ones were removed for replacement. The monorail system ran continuously to a couple of drop zones in the thousand plus yard length of the bridges.