Brainstorming theoretical fluid bed build - Page 4

Discuss roast levels and profiles for espresso, equipment for roasting coffee.

Postby false1001 » May 10, 2019, 7:18 pm

If you can cut your own circles out of stainless steel sheet and have access to a drill press I'd suggest trialing out multiple spout designs. Spout geometry can make or break your air speed/heat ratio (i.e. the sweet spot where you have enough airflow to loft beans but not overwhelm the heating element), and varies widely depending on the roaster. I've found success with a cluster of holes around the middle and one ring of smaller holes around the edge. I suggest reducing airflow to the minimum required to loft your goal weight, higher pressure in the heating chamber will increase heating efficiency.


Postby Elfmaze » May 15, 2019, 6:27 am

First test fire is a success! although my controller seems backwards(100% to turn off and 0% appears to be full power...) Have to try figure out what I did wrong there. I'm worried about the gasket in the exit of the heat tube to the roasting chamber. It will have the highest heat so I'm working on making a ring out of copper to hold between the two sections.

Still not sure what I'm going to do about the temp probe in the funnel. Probably do a run with a second probe attached to the side low and see what the temp disparity is in different spots before I start cutting anything. I relocated the screen down to the triclamp spot and cut a wheel of stainless steel screen to sit on top. Nice tight fit and I'm sure my beans will not be able to make it into the heating coil now.




Postby Elfmaze » May 15, 2019, 12:10 pm

First test of the blower system! Used 420grams of old dead beans to simulate a full loft 500gram batch. Its quite quiet, and the blower is not installed in the can yet and was still pleasantly quiet. I have good control of the blower motor with a router speed controller(SSR), BUT I have to be careful It is QUITE capable of blowing the beans clear out of the chamber in half a second... I know because it happened... I wish i would have got the volcano of coffee beans on slow motion... It was beautiful!

I can add an additional section of 4" to the top for a bit more head room. I'm surprised how much the beans filled the hopper.


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Postby yakster » May 15, 2019, 1:28 pm

Congrats, that's impressive.

I wired up my own bare Variac in a case with a power cord and an outlet and managed to wire it backwards, where 0% is full and 100% is off but I didn't want to pull it apart to re-wire it so I just left it as is.

Are you referencing the Hot lead instead of the Neutral lead as the return with your controller, that might reverse things.

LMWDP # 272


Postby Elfmaze » May 19, 2019, 8:47 am


Did my first full run on manual control with 250grams of Espresso blend from Sweet Marias.

BT thermometer was a complete fail. I was getting temps that were 40* below the bean temp taken with infrared from the top. The hobby lobby thermometers did not work at all as well, I was reading way lower on my heater thermometer than I was at the top of the beans. So I was flying a bit blind on the heater setting.

The bigger problem was I ran out of throttle. In the beginning it wasn't going too badly. I was using one of Almico's curves for a general guide to ramp speed. I got to about 350* and ran out of throttle. About a min later I started reducing the bean loft to the absolute minimum to try get the heat up. I was right on the edge of the beans not moving and had to bump the airflow back up a few times to get them moving again. In the end it took about 14mins to hit FC and at 16 mins got to 446* and hit cooling cycle. Only took about 3 mins to cool in the chamber.


problem 1 measurements:
Not quite sure where to go from here. Need to find a new way to measure BT, the hole I drilled in the heater should be fairly easy to stick a proper thermocouple in for ET. A wider cone would help to get out of jet flow but I know guys are using 2-4" columns so there has to be a solution out there. I figure a thermocouple sticking a half inch into the lower cone might work? Or I zip off the thermowell and stick the naked TC directly into the side a half an inch in.

Problem 2 heat:
I need to get a clamp meter on the wires to see how many amps I'm pushing into the 2000 watt heater, but the element was running at about 1000*f per the soft red glow. I should have plenty of head space (nearly 7000watts available) on the wiring and controller side. I can insulate the side of the heater tube, but honestly it wasn't that hot to the touch. I doubt I was loosing too much energy through the sides. false1001 mentioned changing the flow pattern to reduce the number of holes, I can drill a restrictor plate easy enough, just worried about beans getting stuck at the edges.

All in all I did FINALLY get them to temp(444*) after 16 mins... :(


Postby Elfmaze » May 19, 2019, 9:07 am

Something like this might be the next step up in heating elements ... SwukZcAT9M


Postby EddyQ » May 19, 2019, 10:29 am

Elfmaze wrote:BT thermometer was a complete fail. I was getting temps that were 40* below the bean temp taken with infrared from the top.

The best reference for temperatures are the sensory changes as the beans roast. Where they yellow, tan and first crack. IR is certainly not a great reference, since it too could be influenced by other factors. Getting a decent BT for fluid bed roasters is always a trick and takes some fussing. Keep at it, your first attempt looks promising to me.


Postby Elfmaze » May 19, 2019, 11:58 am

So according to ohms law... as my heater coil is reading 23-24 ohms, chances are I'm only getting 220v not 240v. That would put my heater at 2000watts with 220v.... But I plugged my heater straight into the mains without my controller and I'm only reading an 1100watt jump on my sense home energy meter, maybe it pulls more as the coil heats up.

I looked up the roast from last night and seems about right at 2000watts, . lower line is at about 1700watts and while the roaster was running I got ~3700 watts so about 2000watts going into the roast.


If I understand ohms law correctly I need to cut some of the coil off... that would lower the resistance and increase power. 19 ohms would get me 2500watts and 16 ohms would pull 3000watts. But this will vastly increase surface temp of the remaining coil two fold. not sure how fast it will break down at higher temps. I would need to cut off just under a third of the coil.

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Postby tamarian » May 23, 2019, 8:41 pm

Nice build. I would recommend replacing the perforation with much smaller holes, to avoid wasting energy, and take the thermocouple out of the center/air flow, to avoid measuring hot air. Place it higher on the side where beans are accumulating on their down path.


Postby Elfmaze » Jul 18, 2019, 2:59 pm

As an update. I have roasted a few pounds through the machine so far. Works well after the 3500watt element and 250 gram batches. going to try for 500grams again once I finish mounting the air pump inside the barrel.

The bean direction funnel has been more difficult to source than I thought it would be. Ive gotten quotes as high as $500 for the one part and haven't figured out how to make it myself yet. I have choked the air inlet down to 1" with a SS washer and have a metal ring acting as a pseudo funnel... But I fear beans can still get caught on the edges.

For the BT probe I cut off the thermowell and I'm using the hole to pass the wire into the roast chamber. the probe sits against the wall(but not touching) just below the old well. Seems to respond nicely and eventually I will screw the probe to the wall with a thermal insulator.