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How to control a fluidbed roast profile?
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| tamarian |
Posted on 06/04/2012 14:38
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1/4 Pounder
Posts: 96
Joined: 01/21/2012 00:44
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After roasting with GeneCafe for a while, then heatgun/bowl, I'm now starting with a fluidbed. Build is almost done, a 1600 watts vacume blower, and a 4000 watts electric coiled wire, both controlled with dimmer switches. The blower seems too powerful and I just need it on 20% to get the beans circulating properly.
The heating element reaches 150C in 3-4 minutes, then starts to stall and barely rises more than 3C/minute. When I recycle the air, it jumps to first crack within 3 minutes. This is on 1 Kg batch.
So I wanted to check how do you folks control your profile? I mean what adjustments do you make through the roast. Do you control the temperature by varying the speed? Do you need to to turn down the heat prior to first crack? |
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| Dan |
Posted on 06/04/2012 14:47
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Founder - Member
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Joined: 10/24/2005 17:09
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I don't have a fluid bed roaster, but I am familiar with machine control. I would adjust the blower speed to keep the bed just barely fluidized. This uses less heat because the air volume is less. Keep in mind that as the beans begin to dry out and expand you can reduce the blower speed, which has the effect of increasing temperature, too.
However, throughout the roast I'd adjust the heater directly. I'd use a programmable PID for that function. If using a dimmer switch, I'd want an air inlet thermometer to read. |
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| oldgearhead |
Posted on 06/04/2012 16:32
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Pounder Plus
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Joined: 02/10/2011 15:16
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I'm a bit surprised you can get enough 'turn'down' with a dimmer switch.
I switched to a DC drive quite early is the project. A DC drive gives me much more control of my universal motor.
I haven't automated my fluid-bed roaster yet. I really haven't seen the need. However, if I did automate, I would probably use an A/B SLC504
PLC (because I have one), and I would step down the blower speed at the
3, 6, 8, and 10 minuite points during the roast. I would control the heater by rate of rise.
Currently I control the the blower speed with a pot attached to the DC drive, and the heater manually through a standard PID (I don't use PID)
controller. Roasts are 410 grams (because it will fit in a one-quart Mason jar.
Drying phase:
T=0m - 70% blower, 1000 watts, recycle set to 17%
T=3m - 50% blower, 1000 watts, recycle set to 17%
T=4m - 50% blower, 1300 watts, recycle set to 40%
Ramp to FC:
T=6m - 40% blower, 1300 watts, recycle set to 40%
T=8m - 30% blower, 1100 watts, recycle set to 17%
Finish:
Around T=12m - 25% blower, 1100 watts, recycle set to 17%.
..as you can see, I turn the heat UP prior to FC, and DOWN when it gets rolling. Hint: putting four 1/4" 'bleed' holes in my manifold between the heating element and the blower smoothed things out quite well...
oldgearhead attached the following image:
Edited by oldgearhead on 06/04/2012 16:41
"Development of flavor, aroma, and body in the coffee bean is a chemical process which requires absorption of a definite number of heat units per pound of coffee-in the shortest possible time and the lowest possible temperature." - Sivetz
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| lmclaren |
Posted on 06/05/2012 04:07
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1/4 Pounder
Posts: 156
Joined: 03/19/2011 22:17
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How much coffee are you trying to roast at a time?
I would expect you should be able to do between 200 - 400 grams easy with 4kw with no recycling.
I normally set the beans to a bit more than just floating. What sort of air temps are you getting after the element with the beans floating?
When pushing hard I hit about 330c but normally about +70c on the bean temp for a medium ror. Mine is PID controlled but I suspect If you can't get 330c at the normal air rate then you have a problem.
btw, I have a bleed hole in the air box so that I can let some of the air out before the element, that way you will be able to have the air set higher and have finer control.
Lee |
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| greencardigan |
Posted on 06/05/2012 04:46
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Pounder Plus
Posts: 538
Joined: 11/21/2010 20:23
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I also have my heater on a PID controller but still need to keep reducing the blower speed throughout the roast.
4kW should do 1kg without recirculating of you can if you can lower the blower enough.
What shape roast chamber and perforated plate setup do you have?
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| freshbeans |
Posted on 06/05/2012 06:29
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Super Admin
Reasonable
Posts: 1400
Joined: 03/06/2010 11:10
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tamarian wrote:
The blower seems too powerful and I just need it on 20% to get the beans circulating properly.
what adjustments do you make through the roast. Do you control the temperature by varying the speed? Do you need to to turn down the heat prior to first crack?
Hi Tamarian,
That is alot of blower! OGH suggested bleeding off some of that air(prior to heat). That's a great place to start. You can still use the dimmer to make minor adjustments, rather than using it as a brake.
For me, adjustments through the roast are fairly minor. I start out at 357c (675f) at the inlet. I do reduce air delivery as the roast looses weight, but I would normally reduce heat as well, to maintain my 357c.
Some beans get a more, or less aggressive treatment, but typically no radical changes through the roast....unless I screw up...or get distracted!
Post a couple pics, it will help. Good luck! -Scott |
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| seedlings |
Posted on 06/05/2012 09:15
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Administrator EMERITUS
Posts: 4295
Joined: 06/27/2007 11:39
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Dan wrote:
I don't have a fluid bed roaster, but I am familiar with machine control. I would adjust the blower speed to keep the bed just barely fluidized. This uses less heat because the air volume is less. Keep in mind that as the beans begin to dry out and expand you can reduce the blower speed, which has the effect of increasing temperature, too.
This is exactly how I do it. I only have 3600W of heat, so it is on full until just after 1st crack, and - when the weather is warm - then the heat can be turned down. Blower control is significantly more useful than heater control.
CHAD
Don't put the cart before the horse. Put the horse in the cart and listen to him say "weeeee" all the way down the hill.
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| tamarian |
Posted on 06/06/2012 00:55
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1/4 Pounder
Posts: 96
Joined: 01/21/2012 00:44
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Thanks for sharing guys, all the folks I've been reading for a couple of months :)
Here are some pics:
tamarian attached the following images:
Edited by tamarian on 06/06/2012 01:04
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| tamarian |
Posted on 06/06/2012 01:44
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1/4 Pounder
Posts: 96
Joined: 01/21/2012 00:44
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The right side of this cart is for my old 1/2 kg heatgun/bowl and an egg beater for agitation (egg beater is below, stuffed in a box filled with cloth to align it properly. I'm keeping it for small batches.
Hanging on the right is an exhaust fan for cooling. It used to go on top until I made place for the fluidbed. Plan to make it in a drawer. Now it rests on a large tile supported with a bucket on top of a funnel :)
The left side is obviously the fluidbed. The heat chamber is an 8 inch stainless steel milk pot insulated with cement and formed inside as a pipe going from 4 inches to 6.25 inches. Inside is a large tile cut as a 2 sided comb to wrap the coiled wire around it. Heat chamber has a short 4 inche aluminium pipe below, hooked to a can that connects the blower, whitch is covered from the top with an inverted aluminium bucket.
The roast chamber is a 5L jar, it became around 4L after I sawed off the bottom. It holds 1 KG a bit tight, so may reduce to 750 grams, if needed. The base is just stainless steel bowels sawed off and attached with high temp silicon, and a 2 holes for the thermocouples. One goes on top of the heat chamber, the other digs into the bean mass. BMT reads exactly as my heatgun on first crack, so it's a good location. Inlet location I'm not sure as I'm new to fluidbeds.
The support bowel is lined up with thin layer of silicon to allow aligning the RC. Was planning on adding bolts to hold it in place, but it is quite heavy and supports itself. The bowl at the top is for the handle, under construction.
Recycling so far is controlled by positioning the distance from blower inlet. But I'm working on a more controllable door.
De chaffing so far is poor, a screen that keeps plugging, so it's under construction, but it is needed, otherwise I can see sparks going up in the RC and may damage the motor. |
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| tamarian |
Posted on 06/06/2012 04:21
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1/4 Pounder
Posts: 96
Joined: 01/21/2012 00:44
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If I insert a 4 inch bowl inside the 6.25 inch RC, inverted, to reflect the hot air back on the beans before exiting/recycling. Would this increase the heat. I'll test it today with a small inverted cup, to save me from ripping the sillicon to install the inverted bowl. Added advantage is that I can increase the air flow when I need to turn down the heat without the beans shooting out of the RC.
I couldn't wait, tested with a small cup, on 750g and reached 2nd crack in 13 minutes, WITHOUT recycling. Ambient temp of 40 C might have helped.
So I'll go ahead and rip the sillicone.
Here's a pic of the cup
tamarian attached the following image:
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| Dan |
Posted on 06/06/2012 05:27
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Founder - Member
Posts: 1803
Joined: 10/24/2005 17:09
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That roaster looks like a disembodied Tin Man! |
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| seedlings |
Posted on 06/06/2012 06:53
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Administrator EMERITUS
Posts: 4295
Joined: 06/27/2007 11:39
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LOVE the roaster! Exceptional re-purposing of parts!
CHAD
Don't put the cart before the horse. Put the horse in the cart and listen to him say "weeeee" all the way down the hill.
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| oldgearhead |
Posted on 06/06/2012 08:21
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Pounder Plus
Posts: 485
Joined: 02/10/2011 15:16
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After doing some work with a baffle separater, I've settled with using a
30 mesh screen at the top of the RC and a 120 mesh screen over the blower inlet. At the end of each roast I tap the 30 mesh screen, all the chaff drops on top of beans, and I simply vacuum off the chaff.
oldgearhead attached the following image:
"Development of flavor, aroma, and body in the coffee bean is a chemical process which requires absorption of a definite number of heat units per pound of coffee-in the shortest possible time and the lowest possible temperature." - Sivetz
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| tamarian |
Posted on 06/07/2012 14:57
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1/4 Pounder
Posts: 96
Joined: 01/21/2012 00:44
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Thanks for help everyone. I'm getting there.
I've made some changes, added some element wire to reach 260 C inlet temp. This required adding another tile to wrap the extra wire and a 3rd tile to separate the two.
I've also removed the recycling stuff. It will make profile control a lot easier.
A minor cosmetic change, I've put the heating chamber below the table.
Tested the heating without beans and cooling. The roasting chamber cannot be used for cooling as the insulation resulted in taking 6-7 minutes to cool down the inlet close to ambient.
I plan on getting rid of my exhaust fan and just use the suction of the blower to cool the beans.
Will post a pic of of the new adjustment after running a test.
One question though, is pre-heating needed or useful in warm weather? |
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| lmclaren |
Posted on 06/08/2012 16:30
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1/4 Pounder
Posts: 156
Joined: 03/19/2011 22:17
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Hi Tamarian,
Have you considered using mica sheet instead of the tiles? It may help you lower your heating element inertia.
http://www.homero...post_30593
The mica sheet is the same stuff they use to replace the waveguide covers on microwave ovens. Some ovens have the top of the cooking chamber made of mica.
The sheet I used was 300mm x 300mm. If you are interested, I will describe the construction in detail.
best regards
Lee |
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| tamarian |
Posted on 06/08/2012 21:25
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1/4 Pounder
Posts: 96
Joined: 01/21/2012 00:44
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Hi Lee, very interested. The tiles have a few more problems. The teeth I cut in the tile become a weak point. If I re-wire the heat element, some of these cut teeth simply fall off. I'll make some calls and see if I can source mica sheets locally. Your heating element looks very elegant!
Update: The additional wire bring the heating element to 5kw, but still wasn't enough to eliminate recycling. I'm starting to think the perforated sheet I'm using has too many holes?
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| oldgearhead |
Posted on 06/08/2012 21:43
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Posts: 485
Joined: 02/10/2011 15:16
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tamarian wrote:
One question though, is pre-heating needed or useful in warm weather?
I don't preheat at all. However, the drying phase for the 'cold' batch will usually take 2 minutes longer than the 2nd batch of the same bean,
unless I equalize things by setting the ambient air temperature gate to allow less ambient air into the box for the 'cold batch'..then the times are equal...
oldgearhead attached the following image:
"Development of flavor, aroma, and body in the coffee bean is a chemical process which requires absorption of a definite number of heat units per pound of coffee-in the shortest possible time and the lowest possible temperature." - Sivetz
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| tamarian |
Posted on 06/08/2012 21:56
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1/4 Pounder
Posts: 96
Joined: 01/21/2012 00:44
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OGH, since I'm back to recycling, how is your "door" designed to control the mixture of ambient air and recycled hot air? |
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| greencardigan |
Posted on 06/09/2012 03:40
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Pounder Plus
Posts: 538
Joined: 11/21/2010 20:23
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5kW should definitely not require recycling for 1kg green.
Can you get a short video clip of the beans circulating?
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| RoasterRob |
Posted on 06/09/2012 05:32
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1/2 Pounder
Posts: 318
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Hi Tamarian
Your bean bed depth is is too short. I am roasting 6 kg of green with 12kw gas. (sievert 2941 burner 7kw at 2bar 12kw at 4bar). IMO your perf plate is too big. I go for perf plate about 20 to 25% of RC area. I also go for bigger holes about 3.2mm. I have blithered on infinitum in past posts about perf plates etc.
With a taller bean bed your beans are in the heated air flow longer before it is lost to the atmosphere. I realize to change this you would need to redesign your RC.
I am building an electric roaster that will hopefully do 650gram minimum with 2kw electric, will post here when I get it going.
Most of my profiling is done by turning the airflow down throughout the roast. I only need to change the heat at about 4 mins and then need to play with it a little in the last 3mins or so.
Rob
VBM Minimax 2gp, 1gp Reneka Techno, 2 gp la Pavoni Pub, la Cimbali M28, SJ Maz, FB 6kg HM roaster and other stuff
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thanks for joining.
Marco.....