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Homeroasters - Home Roasting Coffee Community » BUILDING A ROASTER » Fluidbed Roaster

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Gas Fluidbed Ignition
makrsnak	#1 Posted on 03/14/2020 2:24 PM
Newbie Posts: 12 Joined: January 07, 2017	Finally finishing up my fluidbed build. Had a long hiatus... Getting really close to a first test run. How are you/others igniting natural gas/propane in your build? I have a 120V stove igniter and could easily run down the street and grab a piezo electric lighter. My concern is the build could easily turn into a projectile launcher. Everything may just be a sequence of operation: 1. Remove roast chamber 2. Fan off 3. Open valve to lighting position 4. Light with Piezo Ignition OR 1. Remove roast chamber 2. Fan off 3. Allow 120V Stove igniter to heat up 4. Open valve to lighting position Both 5. Turn fan to low speed or open bypass valve to relieve air pressure 6. Replace roasting chamber If enough gas builds before ignition, the 2in pipe turns into a propane powered launcher. Attached is basic drawing setup. Vacuum fan blower on the bottom, through a stainless 2in tube, to the conical roast chamber. Gas control valve is a normally closed Clippard EPV 0-10. I sourced a pwm to 0-10v converter for about $10 on either amazon or ebay. Also attached is the control board. It is setup for TC4/Artisan or manual control. Ideas? makrsnak attached the following images: Edited by makrsnak on 03/14/2020 2:38 PM


pisanoal	#2 Posted on 03/16/2020 9:46 AM
1/4 Pounder Posts: 97 Joined: October 11, 2019	I used a piezo electric igniter on both of my builds. They work great as long as they are positioned properly. One question on your sequence. Why are you turning your fan OFF before lighting? Its pretty standard practice to have airflow interlocks prior to lighting a burner in any furnace type setting (everything from your furnace at home to huge industrial boilers). Meaning if there is no air flow, the gas solenoids won't even be allowed to open. There is also generally a "purge sequence" after failed ignition or flame out, where the fans run for a set period of time before allowing re-ignition. The reasoning is two fold. First have enough air for ignition, second to not have gases build up high enough in the chamber that a large volume of air enters into the flammable range. The idea is keep the flammable region only close to the burner. If your fan is off, a large portion of your 2" chamber can go flammable thus creating the scenario you are wanting to avoid. My advice for sequence would be: 1. Remove RC (if necessary) 2. Fan On to low/med speed 3. Open valve to lighting position 4. Light with piezo electric ignitor Or vice versa on 3 and 4 if using a stove ignitor which should be just fine.


allenb	#3 Posted on 03/16/2020 5:08 PM
Administrator Posts: 3858 Joined: February 23, 2010	pisanoal is correct. And for additional emphasis. NEVER NEVER NEVER try to light a fluidbed roaster without first confirming at least a minimum airflow. If a particular burner design isn't able to be lit with air flowing then one must tweak the design. No explosions allowed! 1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana


pisanoal	#4 Posted on 03/17/2020 9:10 AM
1/4 Pounder Posts: 97 Joined: October 11, 2019	Another thing I noticed in your drawing is your ET probe is below your burner. This is measuring ambient air temp, and not what is traditionally referred to as ET which would be the air temperature that is entering the Roast Chamber for a fluid bed. For this measurement, locate your ET probe just below your perf plate (1" or so). If you are intending to measure ambient air or if you are recircing flue gas and need to keep an eye on return air temp, then ignore this. But ET is a very helpful control parameter. Also, if you have not included it already, I highly recommend a baffle or air mixer between your flame and your perf plate. Insufficient air/heat mixing can cause a lot of issues in fluid bed roasters.


Scorchy	#5 Posted on 04/18/2020 9:41 AM
Newbie Posts: 12 Joined: January 12, 2020	Thanks for sharing, makrsnak- looking forward to further progress reports and pictures! May I inquire as to what material you constructed your furnace chamber out of? I'm looking for ideas there; I've thought about a 6" stainless pipe, but finding that (and for a reasonable price) isn't exactly easy. Pisanoal, can you expand on your concept of the baffle/air mixer? This isn't something I'd seen before in my perusing of the designs on this site. Very interested!


pisanoal	#6 Posted on 04/19/2020 4:43 PM
1/4 Pounder Posts: 97 Joined: October 11, 2019	Quote Scorchy wrote: Pisanoal, can you expand on your concept of the baffle/air mixer? This isn't something I'd seen before in my perusing of the designs on this site. Very interested! Sure. Basically you need to make sure the heat from the flame is evenly mixed. I have had several issues, especially with larger roasters, with seemingly high ET due to uneven heat. Essentially the way ive solved that is to place a baffle above the burner to create some turbulence. Ive usually done two baffles so the air has to flow from left to right to left again before going through the perf plate. Ive had really good success with bringing down ETs that way (thermocouple placed below right below perf plate). When i was building a 5 lb roaster for a friend of mine i was having high ET issues and looked around at several other threads and noticed the same thing. Several of them never got past this issue and ended up roasting smaller batch sizes instead of the full design size to get around it so its a pretty common issue. If this doesn't make let me know. Ive got some more discussion on it and some rough drawn pictures i think in my thread titled something like 5lb perf plate design.


Scorchy	#7 Posted on 04/19/2020 6:00 PM
Newbie Posts: 12 Joined: January 12, 2020	Very interesting, and once again you have been very helpful - I had no idea about this problem before now. I will be sure to incorporate something in this regard. Thank you!

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