Wow thats a lot of charcoal! And a lot of energy lost! Keep in mind there is a lot of energy lost in the makeing of charcoal, this energy you get back if you burn the charcoal producet but if you slip it trugh you loose quite some efficiancy. Do you return the sliped char in the hopper?
Big gas velocitys are important for 2 reasons. One is to achive a turbolent gas pattetn trugh the whole heart, this turbolence mixes and swils all the gases and solids.
The other is to rip the ash off the surface of char as soon as it apears IN THE WHOLE HEART, from nozzles to grate, never leting it to settle. Imagine a peace of glowing char in a BBQ. The charcoal burns but since there isnt enough air velocity, you just end up with a pile of ash in place of that char. Now, if you blow on it, you blow all the ash stright away. This allso presents a CLEAN, reactive surface.
The grate can now have small openings to alow this high velocity gas/ash suspension to go trugh without ash settling on top of the grate, while the biger char peaces stay in.
In the otherhand, any turbolence is more drag on the system.
Thats why lmbert dimensions are so precise and inportant. A carefull equalibrium between turbolence and drag.
As for chardust, there was a interasting pattent in WW2, called the Käle gasifier, that returned the cyclone soot back in the primary air. Its an interasting prospecrive