Let me appreciate first the manner in which you have described your problem here. Such details really help one to understand the problem with better clarity.

It appears to me that you are taking the correct line of action. Balancing the coal-air velocity at four corners would be the most important corrective action that needs to be taken in your system conditions. But don’t just rely on the DAVT results. Try to map the gas temperatures at four corners at different elevations to check for the balancing. You can do that with the help of the hand held laser guns till you manage to install a dependable pyrometer.

In addition to mill combination, I would also suggest different mill fines setting. Since you would be taking trials; why don’t you try that? Try with less % of fine on upper elevation mills and gradually increase towards the lower elevation mills.

Also, after you correct your SADC defects, you can try with changing the vertical bias of auxiliary air; with less in the lower elevation and gradually increasing as you go up.

Confirm if the spray is more when you are using coal with higher percentage of VM. If so, then what I have suggested above should help. Try to increase the SA/ PA ratio without increasing the total air as much as the system allows.

All the best