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Building a small fluid bed roaster, need advice.
nijoe
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Posted on 04/23/2019 8:34 AM
Greetings everyone,after using a popcorn popper for a while, I decided to build something a bit bigger, ideally I would like to roast 100-200g batches, so I started getting necessary parts. Oh yeah, I forgot, I'm also a cheapskate.
So I got the following:
- heat proof glass tube 90mm OD, 200mm long
- 90mm ID funnel (40 smaller diameter)
- 2 x 350 Watt heater for hot air soldering station
- bestway air pump as seen here:https://www.amazon.co.uk/Bestway-Sidewinder-AC-Air-Pump/dp/B000A7J77K

I will get a thermometer and probably a cylone to remove chaff.
Now my question is: Is the air pump that I have to weak to agitate the beans? Would you recommend something stronger?
 
renatoa
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Posted on 04/23/2019 11:45 AM
If the pump is the 110W model, is good for 200 grams, managed to move satisfactory up to 250 without any heat applied.
 
nijoe
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Posted on 04/23/2019 1:09 PM
Yep, it's a 110W model/ 220V. I still have to find a pipe to put the funnel into. And then trdry test the whole thing.
 
nijoe
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Posted on 05/02/2019 1:31 PM
I haven't been able to test the blower as I cant find the adequate reduction piece as the funnel is 40mm and blower exhaust is 25mm.
I also became obsessed with the Idea of a cofee chute mechanism that would allow me to remove beans without removing the roasting chamber. So far, I haven't cume up with anything solid as the same tube used for blowing hot air up wold have to be used to pour the beans out.
 
renatoa
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Posted on 05/03/2019 3:06 AM
Looking for a pipe reducer for you, I found these... not what you want but, looking really cool Grin

https://www.aliba...27011.html
 
Sinobi
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Posted on 05/04/2019 1:33 AM

Quote


- bestway air pump as seen here:https://www.amazo...B000A7J77K
Now my question is: Is the air pump that I have to weak to agitate the beans? Would you recommend something stronger?

I would advice against using that air pump.
I build my FB roaster https://www.youtu...fOu7oM3Z1w last fall with a similar air pump, although 12 volt version, meaning it doesn't have a ac->dc power supply built in.
The motor inside is a brushed motor, and there in lye the problem.
The brushes will only last for 5-15 hours of roasting.
After that the brushes has deposited too much coal dust for the motor to work any more.
I've been through 3 motors in two blowers now, after 8 months of home roasting.
My last attempt was to remove the motor from the air pump and put in an large RC car motor I had lying around.
It too was a brushed motor, and is now about to die, even though I clean the brush contact area with a solvent every three roasts.
I have now ordered this instead
https://www.aliex...7d3fe1025d
that has roughly the same balance between flow and pressure as the cheep air pump, only twice as much, and more importantly is with a brushless motor.
It's rated to run for 8 hours and then one hour resting, and for 10000 hours!
Time will tell if this will be the final solution for me.
 
renatoa
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Posted on 05/05/2019 3:23 AM
If only a failure... could say it was a bad copy... but 3 in 8 months... hmmm.
However, most vacuum cleaners on the marked are using brushed motors and they last for years.
At least two members of our community are using similar pump motors for weekly roasts, in machine built 2-3 years ago, and didn't reported motor failure so far.
 
nijoe
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Posted on 05/05/2019 4:13 AM
Oh well, if my pump dies I'll look into other options. I didn't get the 12V DC version for simplicity's sake. I also tried to use parts that I can buy locally, so I could avoid 4-6 weeks shipping period that normally comes with goods from aliexpress. For example, the funnel is custom made, heaters come from electronic store 5 minutes away and the pump I got at Bauhaus.
So far the most difficult part to obtain is adequate piece of pipe.
 
BenKeith
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Posted on 05/05/2019 8:45 AM
Don't know anything about the air supply, but 2x350Watt heaters, that don't compute with anything I've ever tried. I don't think that's enough heat even with heavy recirculation. I don't use recirculation because I don't want all the smoke and other flavors dumped back into my beans. My little fluid bed does 150 grams running 2,400 watts, and it's maxed out once the beans get to about 340f and with enough air to keep the beans lifted some.
From about 15 years of messing with small fluid beds, all I can say is "good luck" on trying to use 700 watts. I don't see how you can heat enough air to keep the beans properly moving.
 
nijoe
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Posted on 05/13/2019 12:45 PM
It a sad state of affairs that it's cheaper to tear down a new heat gun than to get a new heating element. Ordered from aliexpress, now waiting.
 
BenKeith
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Posted on 05/13/2019 4:18 PM
As I said, don't know anything about his motor choice, but as for being a brushed motor, I don't see that as being a problem. I have a flow bench I've been running for over thirty years with 12, 107 CFM vacuum motors and have put hundreds, if not thousands, of hours on them and never had a one to fail. I've been running a brushed motor in my small fluid bed for 15 years and wouldn't even begin to guess how many roast it has done, and it's still going strong.
So, I don't see the fact that it's a brushed motor as being a problem. Now, when you get into those el cheapo Chinese motors, the quality of the brushes and the grade copper the armature is made of might be questionable. but not the fact that it's a brushed motor.

Well, I looked at the air pump referenced, sorry but that might move a few grams but I seriously doubt it will move anywhere near 150 grams. Most people use vacuum motors or those hot air popcorn poppers because you need the high CFM rating but one that also can deliver enough pressure to lift the beans.
The popcorn poppers might get you to 100 grams, the right vacuum motor with enough heat will get you to your 150, to 200 grams
Edited by BenKeith on 05/13/2019 4:35 PM
 
nijoe
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Posted on 05/14/2019 5:12 AM
I dry tested the pump, it moved 200g of roasted beans quite well just with me holding the fan inside the pipe, nothing was sealed. I still have to dry test it with heater in place and some raw beans. However, I believe the fan will be adequate.
 
Sinobi
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Posted on 05/30/2019 1:49 AM

Quote

BenKeith wrote:
Well, I looked at the air pump referenced, sorry but that might move a few grams but I seriously doubt it will move anywhere near 150 grams. Most people use vacuum motors or those hot air popcorn poppers because you need the high CFM rating but one that also can deliver enough pressure to lift the beans.
The popcorn poppers might get you to 100 grams, the right vacuum motor with enough heat will get you to your 150, to 200 grams

I might be tempted to say that you didn't look at my video above. At least the 75W 12 volts version have no problem lifting 200 grams in the video (and was in that video running at 70% in the beginning of the roast as the highest). The 75 W 12 volt version is rated "Blower PL-8103 12V 0.55PSI 300L/min", and with a 8cm dia. chamber with cocktail shaker top in the bottom with a kitchen sifting metal mesh in the bottom, the numbers match what is needed. at max speed it can sufficiently lift 300 grams. But my chamber is not high enough when the 300 grams are nearing the end of the roast, and they start to fly out the top.
True, if the diameter of the chamber, the diameter of the spout hole and the % block of the hole mesh does not match as good, you will need more pressure and/or more flow from the blower to lift something like 250 grams.
The blower that nijoe linked to might be this one http://www.powerl...d&id=1
It is PL8196B rated at 0.60PSI 450L/min so with the same dimensions on the chamber and all, it should be plenty, only the manufacture stats that you shouldn't use it for more than a few minutes at a time. I suspect it is because the blower design blocks the input ventilation holes in the front of the motor, so it doesn't have internal ventilation/cooling. They have compensated somewhat with two holes blowing air along the outside of the motor.


By the way, I have now done 5 roasts of 230 grams with the new brushless blower I linked to above. It is doing fantastic. It is designed to run for 8 hours non stop before one hour of cooling is needed. 1.01PSI 800Lmin so I can run it at a relatively low speed with lower noise, making it a lot easier to hear first crack. And it is a nice bit smaller too.
 
renatoa
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Posted on 05/30/2019 3:29 AM
A side note... I think there is a great misunderstanding about relationship between lifting capabilities of a blower and good roast.
A nice fountain isn't everything, you need also enough hot air volume, because heat comes from the air mass thermal energy. With less air you need to increase input temperature in order to have the same heat injected into system, and, when more than 270 C at input, this is a guaranteed recipe for scorching and tipping.
So I think the 6 liters for 1 kg greens rule from drum roasters should be valid for FB too.
This means that one liter glass roasting chamber should be filled with 166 grams of greens. Loading more just because your blower allows this, without monitor of hot air input temperature, could be risky for the beans health.
 
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