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View Thread » BUILDING A ROASTER » Fluidbed Roaster
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Bake-a-Round build with heat recovery
After doing heat gun roasting for 6 years and 80 lb of Sweet Maria’s finest, I decided it was time for a fluidized bed roaster. This build owes a great deal to oldgearhead’s work. Here’s what’s similar:
Ametek Lamb with DC speed controller (KBIC-125, slightly higher current model than used by OGH). The blower never runs much over half speed, the DC controller is super.
single 1700 W heat gun element (Master HAS-043K, 120 V)
Bake-a-round RC--What a deal!
hot air recycling
I sandwiched the heat gun element between two soft firebricks (the type made for kiln construction, not the fireplace variety). It was easy to cut a channel in the brick, and it’s an excellent insulator for electric current and heat. I still used the mica insulation that comes from Master, but it’s not strictly necessary. (picture 1, 1a). The bricks are mortared together as the next pictures show, and the recess for the 3.5” SS tube is cut with a hole saw (top of picture 1, picture 3b)
I used an Ametek Lamb two-stage 2-stage blower (97 CFM, 8.3Amp, 120 V, [1000W electrical] model 116392) vacuum blower with a tangential bypass. I like to keep the motor cooled by ambient air, and the tangential bypass makes it easy to make connections to the heater assembly. (picture #2).
No cocktail shaker. I connected the Bake-a-Round RC to the heater assembly using 3.5 in stainless steel tubing (0.065” /16 ga wall thickness) with a stainless V-flange to allow very easy disassembly for dumping coffee and cleaning. (picture 3, 3b) The Bake-a-Round is affixed using a flexible layer of high temp silicone sealant (Permatex 81878 Ultra Copper) nearly 1 mm thick. This compensates for the big difference in thermal expansion between the stainless steel and the Pyrex, the glass would crack if it was tightly sealed. The thermocouple positions are visible here, the one in the RC (BT) is about 2” above the perf plate, the ET is just below the perf plate. I use the same 19 hole perf plate pattern as OGH. Nothing is machined or welded, the 20 ga. SS perf plate is silver brazed to the SS tube, and even that isn’t really necessary, you could just use the silicone sealant (soldering is a pain, the thermal distortion works against you). The flanges are a tight fit over the SS tube and stay put (I silver brazed the lower one, again, not really needed.)
The heated air recycling is done using 4” metal ductwork form the local home supply, I don’t like to heat PVC routinely, especially around food (picture 4). The chaff collection is easy with the wye-connection to return the air to the vacuum intake. The straight arm dead ends, and the chaff collects there (an internal screen keeps most of it from the intake box) above a gate valve from a shop dust collection system; just open that when done and the chaff dumps out. The air return uses a standard shop vac filter element to prevent chaff from being pulled back into the heater (pictures 4a-4c). I plan to insulate the duct with some old quilt or bath towel at some point. The whole recirculation duct just lifts right off, which I do when I’m cooling the beans (picture 5). The box is just 3/8” scrap plywood, there’s an opening on the side not visible in picture 4 for the motor cooling flow. Noise is quite tolerable, the firebrick insulation means the wood doesn’t get heated notably.
The system is working nicely with 350 g loads at about 1500 W on the heater (measured with clamp-on ammeter), hitting FC around 9-10 minutes. I have separate cords on the heater and blower, but the combined current is less than 20 A at 120 V, so I could run them off the same circuit (I don’t).
I’m beginning to grasp how to control my profile better. My setup doesn’t recycle heat as efficiently as OGH’s, but it suits my needs, I prefer somewhat smaller batches. Insulation on the hot air return may lower the heater power somewhat. I will add in an Arduino with three thermocouple mini-boards (Adafruit MAX 31855, the third one is to monitor recycled air) with an LCD screen and a datalogging board when I next have the time to build, replacing my current thermocouple readout. Eventually I may let the Arduino try to control the fan speed, but I’m not in a rush there, I am my own PID for now.
Final cost US $500-600, including tax & shipping.
Edited by Brewin_Bruin on 03-10-2018 16:14
These are 1, 1a & 2, showing details of heater and blower assembly.
Brewin_Bruin attached the following images:
picture_1_2.gif picture_1a_2.gif picture_2_2.gif

Edited by Brewin_Bruin on 03-06-2018 09:31
OK, here is the RC #3
Brewin_Bruin attached the following image:

Edited by Brewin_Bruin on 03-06-2018 09:37
Overall view (#4a & 4) The heat recycling tubing is visible here (on right) and the shop vacuum cleaner filter element is shown on left.
Brewin_Bruin attached the following images:
picture_4a.gif picture_4.gif

Edited by Brewin_Bruin on 03-06-2018 04:09
pictures 4c & 5 details. The heat recycling tubing simply lifts right off.
Brewin_Bruin attached the following images:
picture_4c_1.gif picture_5_1.gif

Edited by Brewin_Bruin on 03-06-2018 04:09
Brewin_Bruin wrote:

These are 1, 1a & 2, showing details of heater and blower assembly.

very nice did you make the hole in the fire brick?
This sort of firebrick is extremely soft, ordinary woodworking tools cut it easily. In order to make a pilot hole for a spade bit to follow, I first scored a shallow cut down the center of each brick on a tablesaw; a number of simpler tools such as a hacksaw could do the trick.
The two bricks are clamped together, with the scored channel in the middle, this guides the drilling. On one side I used a hole saw to cut a channel for the 3.5" stainless tube to rest in, guided by the center channel. The hole saw cut doesn't need to be perfect, you can slide the tube into the groove and wiggle it back and forth to seat it nicely. (The SS tube gets sealed into place when mounting the RC using the same high temp silicone sealant). Then I used a spade bit on a drill press for the center hole, and flipped the bricks over to drill from both sides. The pilot channel down the middle helps ensure the bored holes meet nicely, it keeps the point of the spade bit from wandering. On the opposite end from the SS tube, I rebored the center hole a bit larger for a short distance to fit the copper adapter that connects it to the blower, it just happened to be the perfect size. You can see the profiles in picture 1. After fitting, firebrick mortar is used to join the bricks permanently.
The firebrick feels comfortably warm to a bare hand with the heater on, and I don't have to worry about shorting the electrical connections. The insulated wire enters from the cool end, and has not been bothered.
Having roasted a number of batches with this unit, the performance is meeting all my hopes. Today I did a 450 g batch of Nicaraguan with 1550 W on the heater (Sweet Maria's site suggests that's probably wet processed, but I'm unclear). That means I with my 1700 W heater I can readily do 500-550g of beans, about the limit for the Bake-a-Round RC. The roast profile is attached, first crack was at about 9 minutes, 2nd crack at about 14, I let that stretch a little for development. Still experimenting but I'm enjoying what I'm producing and so are my friends (not an objective criterion, but ultimately what matters most, I think).
The unit behaves very much as oldgearhead describes: it IS the PID. I played with the air very minimally on the roast below, not touching it at all until 9 minutes, and then very small tweaks. The heater power was just left constant. I'm getting tuned to how much power is needed for different batch sizes, basically 50 g change in green beans is about a 25 W change on the heater, over the 300-450 g range.
Preheating to 140 C seems to be doing the job nicely: set the power at the estimated value (using a clamp-on ammeter) for the bean load, and then use the air to make the temp stabilize in the RC at 140 C (takes just a minute or two) ; this is slightly less than the amount of air to get the bean moving properly once loaded, but it in the ballpark. Once the beans are moving then the profile turns out pretty much as desired with minimal intervention.
Chaff collection using the wye junction at the bottom of the air return as a "dead end" (assisted by a screen in the wye) works really well. There is no discernible chaff in the beans themselves, and it's simple to empty because there's a gate valve right there.
Bean cooling is extremely easy in the RC, and removing the heat return duct (it just lifts off) speeds this a great deal, note the graph. No need to play with the air flow, it speeds up modestly with the return removed, and no beans get launched into orbit. No need for a dump mechanism. I can easily remove the RC because of the V-flange connection to empty out the beans. I may implement a J-tube as OGH has shown in his "Brewer to Roaster" thread to pull the beans straight into a container. The vacuum intake on the unit itself will do the job, no need to hook up the shop vac also.
I don't see roast defects now: no under-roasted quakers, no tipping, no divots (got some tipping when I preheated too high, got divots by cooling too aggressively). Terrific uniformity.
Multiple profiles recorded this month also posted for comparison.
Brewin_Bruin attached the following images:
450_g_roast_profile.gif roast_profiles_mar_2018.jpg

Edited by Brewin_Bruin on 03-16-2018 14:50
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