I just got clued in by Modelmaker that this thread was in play... sorry that I did not see it earlier!
I don't know if what I'm doing will apply directly or not... I did design and build my own FAB roaster. It's electric and can roast 2.5 to 14 lbs of beans in one batch.... with a slight modification we'll increase that to 20 lbs per batch.
For my roaster I have a 25kw 240V 3ph electric heater. ... it can raise the air temp from inlet to outlet by 880 degrees at 100scfm. I don't need to raise it that much, but I didn't want to run the heater at full bore all the time either.
That equates to roughly 85,000 BTU's in capability.
At 100 scfm the roaster will easily fluidize 3 lbs of beans and the heater will easily keep up with the heat requirements. But that heater is incredible overkill for 3 lbs of beans.
For your operation, if you only need 50 scfm to loft your 1 lb of beans (you'll have to measure that), I think you can get away with 29,000 BTU's to achieve a 500 degree temp output at the point where the air exits the heating element / chamber.
If you need more air velocity to loft your beans, you'll need more BTU's of course.
The trick is the blower... a typical 'fan' will probably not be able to generate enough pressure to loft the beans. A good 'squirrel cage' (Modelmaker, what say you here?) style fan can probably do it but a regenerative blower is more of a sure bet!
A blower that has a variable speed is also a good idea.... it takes a 20% velocity boost to get the beans lofted at the beginning of the roast than it does to keep them lofted once they're moving. Beans weigh more at the beginning of the roast than at the end... so if you can also degrade the speed of the blower by 20% over the span of the batch, you can get enough speed to loft the early part of the roast but slow it down so you're not shattering your beans on the top of the roaster... or shooting them into the ceiling at the end of the roast.
There is a whole lot more to this fluid air bed roasting than meets the eye.
My drum roaster took far less time and money ($50 and 3 days) to build than the FAB I'm in production with! But commercial production and home roasting are two different things!
There is much more that I could write on this topic but it's dinner time... gotta eat!
If there are specific questions or direction questions... I'll be happy to chime in. I'm not an engineer and I don't even play one on TV... so all I can tell you is what worked for me... and even then my information is somewhat circumspect.
Pete
