seeking feedback on solids drying application -- tray vs rotary

[leakyseal]

Folks,

Seeking solutions for the processing of a 35% solids slurry (metal plating wastes) where it is desired to evaporate the free liquid completely. My thinking had been along the lines of an internally agitated batch mixer/dryer or rotary dryer with internal flights, to allow good surface renewal and hence enhanced MT, and some degree of comminution of the final product to assist with flowablity and packaging.

My client is rejecting these technologies (e.g. Littleford, Ross, AVA etc) due to high cost and perceived complexity and wants to know why he can't just put a bunch of pans in a large oven. The extra labour in handling does not seem to concern him at all. My gut feeling was that this form of evaporation would be hugely inefficient and hence prohibitive from an energy point of view, but some quick and dirty heat balances (given flux values from oven vendors, assuming thin liquid layers (say 1" sheets), tabulated heat-of-vap values and an arbitrary 50% efficiency) seem to indicate that this approach is not as wrongheaded as I first thought.

Anyone have any experience with these kinds of systems and can share their opinions? What else do I need to be thinking about?

 

[StoneCold]

leakyseal
We have both types of technologies. I can tell you that the ovens are quite a bit slower. However it is really solid dependant. Some solids clump up and crust over and that makes the drying very slow. The mixer dryers are expensive but they are faster. Why not go with a sludge press and blow air through it until it is semi-dry and call it good? Or one of the continuous belt presses? Or a rotating vacuum drum filter? Then putting it into an oven to get a final loss on drying number would not be bad.

Regards

StoneCold

 

[leakyseal]

StoneCold,

Thanks for the feedback.

We kicked around the idea of a filter press or belt press, but the feed has some surfactant residue in it which blinds off press cloths pretty quickly. We might be able to optimize the screen media but the client is pretty twitchy about the idea since they really messed up their bench press in tests.

I wrote a memo detailing their options with advantages and disadvantages---we shall see what we shall see.