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Homeroasters.org » BUILDING A ROASTER » Fluidbed Roaster
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Massive Fluidbed Heat Controls
allenb
Why not bail on the electric element and switch to a propane heat source? Surely this would be easier and provide plenty of headroom.


Designing a gas burner heat source for a top fired arrangement as yours might prove very challenging although I'm sure can be done. It's very possible that a 6 or 7 kw element could be wound on the existing former you have with an acceptable watt density but depends on a few things. What is the diameter of the coil form (insulated frame that the helical wire element is wrapped around)? What is the diameter of the wound element? Knowing this, we can calculate watt densities using various wire gauges and see if it's possible to pull off 6 or 7 kw without going over around 55 watts per square inch of element wire surface area. If possible, this would be much less headache than redesigning for gas.

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
Dowst
allenb wrote:

Why not bail on the electric element and switch to a propane heat source? Surely this would be easier and provide plenty of headroom.


Designing a gas burner heat source for a top fired arrangement as yours might prove very challenging although I'm sure can be done. It's very possible that a 6 or 7 kw element could be wound on the existing former you have with an acceptable watt density but depends on a few things. What is the diameter of the coil form (insulated frame that the helical wire element is wrapped around)? What is the diameter of the wound element? Knowing this, we can calculate watt densities using various wire gauges and see if it's possible to pull off 6 or 7 kw without going over around 55 watts per square inch of element wire surface area. If possible, this would be much less headache than redesigning for gas.

Allen


I was envisioning a jet nozzle that would blast downwards towards the impeller from the top a-la Flame Weeder style. We have a unit that we used to weed our 1.5 acre garden with--50,000btu/hr (equivalent to 14kW, I suppose) You could burn up a gas grill propane bottle in a day of two of weeding! Might even get the beans to third crack when the flame goes out and fills the super-heated roaster with propane!

Kidding aside, the core is 6" in diameter and 12" long, with cutouts spaced an inch apart to accommodate a 3/8" winding. So I guess we are looking at a rough total of 18' of wound 3/8" element--(18"circumference)(12 cutouts)/12=18'. Need to confirm actual length of straight wire in the coil on this element, but we can say 88.5' if it is .2ohm/ft. This would mean the straight length is 5 times longer than the coiled length. I have no idea if this is correct, but seems plausible.

Assuming an element is AWG15 NiCr 80 with .20 ohms/ft (17.7/.20=88.5), the surface area of the element calculates to 190 sq in (3.14*.057*88.5*12), providing a wattage density of 14.38 watts/sq in (2734/190=14.38). The PDF suggests 35watts/inch max in still air.

AWG11 NiCr80 wire at .078 ohms/ft would provide a total resistance of 6.9 ohms (88.5*.08=6.9), resulting in 33Amps and 7660 Watts. 303 sq in surface area, so 7600W/303sq inches equals 25watts/sq inch. Well within the 35watts/in limit for still air.

33 Amps leaves only 7 Amps to power the 5hp motor if I am going to use a 40A breaker. The motor is spec'd at 11.8 amps at 5HP (I doubt it will need 5hp to move 10lbs of beans, but who knows), but to run that 3phase 5HP on a single phase VFD max output, I need about 20amps. Our barn is wired from the main house with a 100A breaker. Really wish I had a better idea how many amps it will take to get 10lbs of bean moving. Probably will need a 60A breaker and 6/3 wire. Hope the electrician gives the okay for this setup.
Edited by Dowst on 05-27-2018 17:55
 
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allenb
I'm seeing 18 loops around the form, not 12 which would change things a bit but all one has to do is stretch the open coil helical gap between loops a bit wider in spacing to accommodate the additional distance in coil length. A watt density of 25 W/sq. in. is excellent for moving air and would last a lifetime.

A weed burner, as you mentioned, would do the trick for a down firing propane burner but accommodating the igniter and flame verification hardware for an electronic igniter controller which should be an absolute requirement for a design such as this can be troublesome to get it functioning just right. But, if electrical power is in short supply, might be worth the fuss.

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
Dowst
allenb wrote:

I'm seeing 18 loops around the form, not 12 which would change things a bit but all one has to do is stretch the open coil helical gap between loops a bit wider in spacing to accommodate the additional distance in coil length. A watt density of 25 W/sq. in. is excellent for moving air and would last a lifetime.

A weed burner, as you mentioned, would do the trick for a down firing propane burner but accommodating the igniter and flame verification hardware for an electronic igniter controller which should be an absolute requirement for a design such as this can be troublesome to get it functioning just right. But, if electrical power is in short supply, might be worth the fuss.

Allen


Now that I actually look at the picture that I posted, indeed 18 coils. Last night I just counted the number of cutouts on the printed drawings that I have, must have been looking at an older drawing!
 
allenb
A couple of companies who sell custom elements and wind to order:

This one has a $50 minimum

http://resistance...-elements/

Not sure about min orders from this one

https://www.keith...ments.html

For an affordable fan proving switch for control side of the works (40 mA max)

http://www.dwyer-...sMDA#specs

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
Dowst
Update!

I am currently recovering from a pretty serious back injury and haven't been able to dedicate the time and resources to this project as much as I'd like, but that is the way it goes and lately I have been making the time to keep this project moving along as best as possible.

I have now obtained most everything that I will need for heat and fan control. This includes:

- Fuji 5HP VFD/Phase Converter for fan power and flow control
- Fuji PXG5PYY1 with serial data output cable. This is spec'd for 0-10V voltage for
output control, as AllenB suggested, for use with the proportional SSR. 0-10V.
- Crydom Proportional 50A SSR
- Enormous heat sink for SSR

So the next step now will be fabricating a control box that will house all of the electronic devices and associated wiring, similar to how FransG did here: http://kostverlor...oller.html

I have a couple of questions which you all may be able to answer:

As I have been drawing out the wiring diagrams in preparation for assembly, I see that the Crydom SSR requires a power supply circuit of 8-30VDC/30mA max in addition to the control and load circuit. It doesn't appear that there would be a way to source this from the PXG, as mine is configured anyways (bought on eBay for a great price, configured with voltage as control output). I didn't realize I was going to need a separate power supply to run the SSR. What are my options for this power supply? The relay requires no additional power supply when using a 4-20mA control input, which I suppose would be the most ideal setup. Is it not worth it to try and use the PXG5 that I have, and just get one configured for 4-20mA output? I would like to use the one that I have, but don't want to reinvent the wheel to do it.

What would be the best thermocouple for this application? Looks like a K type Omega is a popular option? I am guessing a long, smaller diameter probe would be ideal?
Edited by Dowst on 06-29-2018 06:39
 
allenb
I didn't realize I was going to need a separate power supply to run the SSR. What are my options for this power supply?


My preference for control is 0-10 DC versus the 4-20 mA. If you can find an old laptop power pack or pick one up, they're very robust as well as very low cost. Many have had premature failures with the ultra low cost Chinese power supplys/converters off of ebay.

This would do the trick

https://www.amazo...4506637454

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
Dowst
allenb wrote:

I didn't realize I was going to need a separate power supply to run the SSR. What are my options for this power supply?


My preference for control is 0-10 DC versus the 4-20 mA. If you can find an old laptop power pack or pick one up, they're very robust as well as very low cost. Many have had premature failures with the ultra low cost Chinese power supplys/converters off of ebay.

This would do the trick

https://www.amazo...4506637454

Allen


I was hoping that there would be an easy solution for this! A quick search indicates that 230V chargers are common as well. Having everything run on 230V is a goal for the project. Why do you prefer the voltage control over the current control?

I drew up a wiring diagram for the roaster. Let me know what you think.
Dowst attached the following image:
img_0557_1.jpg
 
Dowst
Thanks again to everyone who has contributed to my effort in getting this project completed, there are many aspects of the control design that I do not think I would have arrived at alone. Having a supportive community with decades and decades of combined roasting experience is a true resource.

I am thinking about thermocouple placement. I know that a BT probe within the mass of levitated beans (placed through the wall of the roaster, 3" up) will not represent the actual temperature of the beans, but mostly the temperature of the air in the fluid bed, though influenced by the thermal mass of the beans.

I was originally thinking I would have three thermocouple (one at air inlet to element core, one after, and one within the bean mass). These would get data logged through a data acquisition board (arduino or phidgets, etc.) to a roast profile software like Artisan. Having all three temps would certainly give a decent idea about the how, when and wheres of temperature in the roaster, but even this will not provide a true BT.

For now, I know that I will have the one thermocouple driving the PXG unit. With the serial output from the PXG, I can monitor and log this data within Artisan.

I see that the Sivetz roasters have two thermocouple, one at air inlet and one at exhaust outlet. There really is not a "BT" like with a drum roaster--I watched a roast master begin the cooling sequence when the exhaust temp reached 466 degress. For a City/FC roast, obviously this temp is not an indicator of BT.

So I wonder where my thermocouple would best be placed to create some "actionable" data. In the case of this recirculative fluid bed design, it may be possible that temp above the bean mass will quickly stabilize to the inside temp of the roaster and provide an useless value.

At the moment I am thinking that I will place it above the mass and see what happens. I will set the PXG to heat the inlet air temp to 500-600F over the course of 5-10 minutes to preheat the unit and stabilize its temperature, drop the green beans and see how this temp reacts, and go from there.
 
allenb
I was hoping that there would be an easy solution for this! A quick search indicates that 230V chargers are common as well. Having everything run on 230V is a goal for the project. Why do you prefer the voltage control over the current control?


The reason I prefer 0-10 over 4-20 mA is due to the extra fiddling needed to ensure you've got a good current source when using components that may not already have an on board current source. If PID controller and analog power controller are already matched up and set up for 4-20 then it's a good way to control things especially if components are separated by long distances where voltage drops can distort things and if there may be a lot of electrical noise that can generate stray voltages on the lines. With one roaster with short wiring runs and with few high voltage lines to cause stray voltages, 0-10 is a good way to go with little fiddling required.

Either way can work fine depending on ambient factors.

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
Dowst
Check out this element winding jig!

https://youtu.be/...
 
allenb
I see that the Sivetz roasters have two thermocouple, one at air inlet and one at exhaust outlet. There really is not a "BT" like with a drum roaster--I watched a roast master begin the cooling sequence when the exhaust temp reached 466 degress. For a City/FC roast, obviously this temp is not an indicator of BT.


The two Sivetz roasters I've had experience with both had two sensors. One for hot air just before entering the roast chamber and one slightly above the top of the spouting beans, extending into the chamber from the front about 8" or so. Sivetz typically included a dial thermometer along side sheathed thermocouple. While this is, as many have stated, a mix of roasting air and beans, it will typically give one a first crack temp around 400 F. And there should be no need at all for trying to coax a more accurate reading. With your roaster design with it's inherently thinner bean bed depth, you may find a higher temperature at 1C but all will be relative. Before you drill holes and permanently mount your thermocouple, you'll need to try several locations to find the one least affected by the hot air stream. This can be quite a task to clamp fixtures inside the chamber to hold the thermocouple but well worth the effort to avoid drilling and mounting and then plugging the holes when they don't work out.
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
Dowst
Thought everyone might enjoy an update on this project, I am just about finished with getting the control box together, and have a 10kW element being wound with AWG11 NiCr80, 5.2Ohms and 43 Amps.

I assume there is a way to use the Fuji to cap max output to the element, right? Thinking that the 10kW element will provide good headroom for the future, but I don't think I want to be operating in that realm right off the bat.

Also, wondering if anyone has any input or constructive criticism about the execution or wiring of the controller. I have never worked with this level of electricity or put together a controller like this, so I have to say I am a little weary of what might happen when I plug it in. I could make a better wiring diagram if it is difficult to read. I will be adding a large terminal block instead of plugging everything into the 60A switch.

Thanks again for the interest in this project!
Dowst attached the following images:
2-img_0620_1.jpg 3-img_0621_1.jpg 1-img_0618_1.jpg

Edited by Dowst on 08-07-2018 11:07
 
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