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Physical obstruction vs. Blower control
For most air-roasting people, decreasing blower power or reducing airflow during the roast just comes with the territory. The beans get lighter. The beans get larger. The beans start flying.
There are some recent threads discussing the potential to automate this process.....and the difficulties involved.
What is the best way to monitor the intensity of the bean movement?
What to do about controlling heat?
Will heat adjustments alter fluid velocity enough to create a feedback loop?

I've started experimenting (accidently) with physically controlling the bean movement instead of controlling with blower pressure.
In the process of increasing the capacity of my roaster, I built a larger roast chamber and created an internal aparatus to promote better bean movement inside this larger roast chamber. After some trial and error, It worked. I was able to get 10# moving, using the same blower and burner that I used for 5#.
Everything was wonderful....until I got to City+ . As the beans expanded, the load began stalling.

What had promoted better bean movement early in the roast was now causing it to stall. So, I started working back in the other direction.

I now have a 10# roast chamber that is better balanced , but not yet ideal. I currently reduce airflow a bit at the beginning of the roast, then increase a bit toward the end to keep the beans moving. That's still a bit backwards from the traditional dynamic.
I like to believe that I can remove that airflow variable completely.

Whenever possible, I like to throw it into HRO to see what comes back.
Here's a pic of the experimental roast chamber mid-section, including the vertical airfoil and baffle.(looking in from the top)
Has this already been done somewhere?

As always, I thank you all for any input. Cheers, Scott
JETROASTER attached the following image:
Scott this sounds very interesting.

So instead of needing to monitor bean movement and adjust the blower, you just have it set up in a way that does not require any blower adjustments?

My only concern would be that for the later stages of the roast, a higher blower setting might be required than in a normal roast chamber resulting in a less energy efficient roaster?? Or maybe I misunderstand?
Yes, exactly. If possible, I'd like to totally eliminate that need to dial down air pressure and the corresponding need to adjust heat.

I share the concern about too much airflow. I've come to see the bean mass as a lot more porous than I did before. I'm hoping that the restriction will force heat out through a greater cross section of the bean mass.
If I can get a load roasted in under 14 minutes I'll start feeling better about it.
So, a few more changes and more testing.
I need a bit more heat, so a little redo of the combustion liner should increase efficiency.
I'll open up and straighten the distribution jet a bit. It blasts a little off center.
Then I need to trim down the "wing" a bit to accelerate the bean return.
Here's a couple shots of the current performance.
Green. Heat is on, airflow is at max.

This is the same load, roasted and cooling. Airflow is still at max. Once this load cools a bit more, it will in fact stall.
Edited by JETROASTER on 02/01/2014 10:02 AM
Any positive tweaking results? Looking forward to where this leads.

Hey, did I see water level graduation lines on the inside of this experimental jet roaster?

1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
Yes, the water level lines. That is, in fact, a 55(?) cup percolator. I've used nearly all the parts for various creations....wierd little habit of mine.
I'll get some more video posted as soon as I can. The bean "fall" rate was increased by diminishing the wing. That helped increase the bean density in the bottom of the chamber.

Reduced restriction through vertical tube, and opened the diameter of the distributor by 1/8". Also added a screen to the deflector to reduce the bean noise.
Resulting so far in 10 minutes to City at 50% throttle(vs. 14 minutes at 100%). Much better than last week!
I'll get some more pics and stuff posted over the weekend.
Cheers, -Scott
......and the update. The changes to the vertical tube and wing have increased bean mass density in the lower roast chamber (RC) during the earlier stages of the roast. Beans are still flying around, but the new deflector helps. It has made a huge improvement RoR. It seems that the energy transfer is alot more effective.
I can dump in a full 10lb load and no longer be concerned about whether or not I have enough velocity to move it. In fact, it's become a sort of "set it and forget it" thing. Dump in the off fuel when done.
For light roasts, this is a very nice 10lb roaster. For darker seems to be a very nice 9lb roaster!!!
If I roast a full 10lbs, it will begin stalling at city+. For a 9lb load, dark roasts are no problem. Still, when cooling, a 10lb load will stall at 200dg. ....and when it stalls....that's it.
So, not perfect, but well enough to move onto getting the beans in and out more effectively. Once that is done, this could be 60lb per hour roaster.

It does seem (so far) that controlling the bean movement can be accomplished with means other than airflow. I'm not sure if bean movement is considered a Process Variable, but if that variable was eliminated/controlled, would that make anyones life easier? Would it change the ways in which people might automate the roasting process?
Cheers, -Scott
Edited by JETROASTER on 02/18/2014 9:37 AM


freshbeans wrote:
It does seem (so far) that controlling the bean movement can be accomplished with means other than airflow. I'm not sure if bean movement is considered a Process Variable, but if that variable was eliminated/controlled, would that make anyones life easier? Would it change the ways in which people might automate the roasting process?
Cheers, -Scott

Making the three or four blower reductions in my previous fluidbeds were not something that bugged me terribly but if I was roasting coffee in a production setting it would be a huge deal to me. When roasting in the 1 bag Sivetz we were continually making small air flow changes from the beginning of the browning phase through to the end of the roast and made it much more difficult to concentrate on controlling power level.

How's the coffee cupping in this roaster since making the change?

1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
Hi Allen,
It wasn't just the blower adjustments. The fuel adjustments were eliminated as well. I can start in at 65% throttle and just roll. That will produce City in 10 minutes. ....I can't lie, it's not the best cup.
The best cup is to go in at 50% throttle. That will produce City in 11:45 -12:00 minutes. Some of the best I've had.

Crossing that 60lbs per hour mark was just a project objective.
I'm gathering parts for the bean evacuator/loader. That's the better place for me to save time.
Cheers, -Scott
Well, I can't make any sense of it, but it seems that I'm now roasting 10lb loads, using 75% of the fuel that I used for 5lb loads before.
The bean mass actually seems looser than before, especially in the early stages. I haven't made any changes to the combustion liner yet. The warehouse is still hovering around 28dg. The combustion pressure is higher, but that was also true last week when I struggled to complete a 10lb load in under 14 minutes.
So, I opened up the distributor a bit, and changed the bean flow a little. Now I can crank out 10lbs in 8 minutes? (not very tasty BTW)
I'm not complaining, I just can't figure it out.
What would create such a dramatic change ?
Scott - I've came to the conclusion there is something 'magical' about a 12 minute fluid-bed roast. Lately I've been setting both the PV temperature and the RC exit air restriction before starting each roast, then make small adjustments to the air-flow during the roast.

My goal for each roast has been to set the lowest PVT required to finish about one minute after the end of first crack. Currently the PVT for 445 grams of Sidamo- Aletawendo- DP is 1100 watts for 520?F air and cooling is started at the 12 minute mark. It seems to be the 'smell' that's so outstanding.
No oil on my beans...
12 minutes does seem to be a sweet spot. I currently find myself targeting 12 minutes for all of it.....Light roast, City, City+. I'm liking the results, and I really like the simplicity of it. I choose the appropriate throttle level, dump in the load, and let it go.
50% throttle gives me City in 12min.
65-70% throttle gives me City+ in 12min. and so on....

Once I've nailed down the throttle settings a bit, I'll only have to make some minor compensations for ambient temp, bean type.
Cheers, -Scott
zombie girl
using red car, let us see what happens to this thread I am not clear on what may happen...
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