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12 kg Roaster Design
allenb
If my mental calculations are correct, using Pi x diameter/4 in steps 1 and 2 instead of Pi x diameter will give you a vane pitch that's less than 45 degrees but I'm not sure how much less. The math needed to adjust the formulas to end up with x degree pitch is over my head. My guess is if we use Pi x diameter/5, we'd be pretty close to a 30 degree pitch but someone would need to give it a try to verify it.

By small drum I'm thinking of a drum less than around 14" diameter but to be sure, one needs to break out the graph paper and draw the drum with vanes and see if there's room between front bearing flange and reverse vane for a trier to comfortably fit in.

I've only seen the L12 in person and photos of other drums but I'll bet all models will be similar. A 24 x 24 would not be considered small in relation to needing another arrangement for the trier.

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
Axel
I'm probably going to bolt the vanes to the drum wall and just wing the pitch at 40 degrees(I like the number 40). Is that for both the horizontal and vertical angle?
how do I determine the height of the vane from the wall?

after some more calculation and preliminary cut drawings for my CNC table, it looks like i'll be going with a 22"outside diameter drum. much more efficiency of material. still thinking of making it 24"long but not sure if that would be a benefit.

Also I haven't been able to find any conclusive info on wall thicknesses for double wall drums of this size. waiting to hear back from Probat...
Thinking about using 18 or 20Gauge with 1/4" air space.

the burners are 90,000BTU each
I already have one since someone was selling an extra for a great price
 
allenb

Quote

Axel wrote:

I'm probably going to bolt the vanes to the drum wall and just wing the pitch at 40 degrees(I like the number 40). Is that for both the horizontal and vertical angle?
how do I determine the height of the vane from the wall?

after some more calculation and preliminary cut drawings for my CNC table, it looks like i'll be going with a 22"outside diameter drum. much more efficiency of material. still thinking of making it 24"long but not sure if that would be a benefit.

Also I haven't been able to find any conclusive info on wall thicknesses for double wall drums of this size. waiting to hear back from Probat...
Thinking about using 18 or 20Gauge with 1/4" air space.

the burners are 90,000BTU each
I already have one since someone was selling an extra for a great price


40 degrees should be fine. The vane angle is based on the shaft line. So, shaft is 0 degrees, front plate of the roaster is 90 degrees.

From my calculations, a 22 x 22 will be sufficient for a 12 to 13.5 kilo batch.

From my experience, getting a response from Probat on questions related to design aspects of their roasters that's not already published is next to impossible unless you know someone on the inside. I think you'll be good with the 1/4" airspace gap.

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

Quote

how do I determine the height of the vane from the wall?


From memory, the forward vanes on the L12 were around 2 to 2 1/4" tall and many of the older drum roasters used wider reverse vanes compared to the forward which makes sense if you consider they are grabbing less coffee at the height they're at. If I were designing a 12 kilo drum roaster I would use around 2 1/4" for the forward and 2 1/2 or 2 3/4 for the reverse vanes. I would also place the reverse no more than 1/4" or so above the forward vanes for good mixing.

Different manufacturers differ widely on vane shape, size and placement.

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
Axel
Thank you Allen.

Any last thoughts on drum wall thickness?
I'm about to order the sheet metal for the two layers.
aiming at 18Gauge..
there should be plenty of BTUs (180,000) so maybe even 16gauge would work, however i'm worried that the responsiveness when lowering the temperature would be delayed with the thicker metal.
The benefit of thicker layers seems to be that the temperature drop would be lessened when the beans go in.

in the continued design optimization of the sheet and plate metals I'm heading back towards a 24" outside diameter and 24" depth.
 
ginny
Axel:

had you done any information gathering before coming here? just curious.


ginny

roar
 
Axel

Quote

ginny wrote:

Axel:

had you done any information gathering before coming here? just curious.


ginny

roar


Yes.
far and wide.
just got a copy of the Coffee Roaster's Companion by Scott Rao.
so far I feel that most of the fundamental information it contains is that which I have already found the long way.
It would have saved me a great deal of time to get the book first...

Still, there are some things that are fundamental which I am not completely certain about since there is a lack of conclusive data.
Double wall drum wall gauge/thickness is one such factor.
I've seen it mentioned as being an important part of roaster design but nothing more specific than "it shouldn't be too thick or too thin"
Edited by Axel on 08/22/2015 12:00 PM
 
allenb

Quote

Axel wrote:

Thank you Allen.

Any last thoughts on drum wall thickness?
I'm about to order the sheet metal for the two layers.
aiming at 18Gauge..
there should be plenty of BTUs (180,000) so maybe even 16gauge would work, however i'm worried that the responsiveness when lowering the temperature would be delayed with the thicker metal.
The benefit of thicker layers seems to be that the temperature drop would be lessened when the beans go in.

in the continued design optimization of the sheet and plate metals I'm heading back towards a 24" outside diameter and 24" depth.


Whether it be 10 gauge or 24 gauge, the thermal inertia and response to burner output changes will be pretty much the same so I would base your decision on which gauge to use on what is easier to form and work with. If you can work with 18 gauge or even 16 gauge then definitely go with thicker metal as it will be easier to mount things to without deforming.

For you to see a noticeable increase in response time lag you would have to be using thicker than 1/8".

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

Quote

allenb wrote:


Whether it be 10 gauge or 24 gauge, the thermal inertia and response to burner output changes will be pretty much the same so I would base your decision on which gauge to use on what is easier to form and work with. If you can work with 18 gauge or even 16 gauge then definitely go with thicker metal as it will be easier to mount things to without deforming.

For you to see a noticeable increase in response time lag you would have to be using thicker than 1/8".



Excellent,
seems like there is plenty of margin so I can stop stressing so much about making a terrible mistake with choosing the gauge.
I'm having my metal supply company roll the sheet and spot weld it for the drum so maybe I'll see what the 16gauge will cost and then decide.
 
Axel
With a 24"x24" drum, what might be the optimal space between the outside of the outer drum layer and the inner layer of housing?(I'm planning to do two layers of housing about 2" apart and maybe adding insulation or baffles inside...)

also, how much space at the back of the drum so that some of the hot air going in through the perforated back of the drum is forced to travel up the sides before going in? I'm guessing that if there is too much space the air will just all go in at the base of the drum and not spread the heat up the sides as well?
I'm hoping that by constricting the flow a bit, the heating should be more efficient?
 
allenb

Quote

allenb wrote:

Quote

how do I determine the height of the vane from the wall?


From memory, the forward vanes on the L12 were around 2 to 2 1/4" tall and many of the older drum roasters used wider reverse vanes compared to the forward which makes sense if you consider they are grabbing less coffee at the height they're at. If I were designing a 12 kilo drum roaster I would use around 2 1/4" for the forward and 2 1/2 or 2 3/4 for the reverse vanes. I would also place the reverse no more than 1/4" or so above the forward vanes for good mixing.

Different manufacturers differ widely on vane shape, size and placement.

Allen


Well, I'm 99% certain that the 1980's vintage Probat L-12 I was able to examine a few years ago had vanes in the ballpark of the dimensions I stated above but I'm wondering if they vary them from time to time? Because, Mark (Chimpy74) was nice enough to oblige me and take measurements of his Probat L-12's vanes and email them to me.

Hi allen sorry its taken while, i measured the drum vanes tonight.

The forward vanes are 38mm high and sit 55mm from front edge of drum.
The actual arms (Drum to shaft ) sit 30mm back from front edge of drum.
The reverse vanes are 60mm height.
Hope this helps, always happy to help.

Regards mark


So this makes his L-12's forward vanes 1.5" tall and reverse vanes 2.36" tall.

As I stated in an earlier post, there's quite a wide range of vane dimensions and placement scenarios between roaster models and different manufacturers even in the same capacity category but thought I'd share Mark's L-12 dimensions so we could see actual numbers from a real Probat.

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

Quote

allenb wrote:



So this makes his L-12's forward vanes 1.5" tall and reverse vanes 2.36" tall.

As I stated in an earlier post, there's quite a wide range of vane dimensions and placement scenarios between roaster models and different manufacturers even in the same capacity category but thought I'd share Mark's L-12 dimensions so we could see actual numbers from a real Probat.

Allen


wow this is fantastic insight!
Thank You!
so combined, the forward and reverse vanes stand 3.86"?
I'm guessing they're not spaced apart?
and so the trier must be located closer to the shaft?

Also, any thoughts on the spacing around the outside(sides and back) of the drum?

and something that I'm just starting to research is which magnehelic gauges to get for propane and exhaust pressure respectively.
as I understand, the propane operating pressure will be about .25" of water column so 0 to .50" should be good?
what range gauge should I choose for the exhaust air pressure pre exhaust blower?
in the link is a list of the available magnehelics:
http://www.dwyer-...Series2000
Edited by Axel on 08/28/2015 10:48 PM
 
allenb
While some Probats and other manufacturers leave little to no gap between forward and reverse vanes, it appears the L-12 has a pretty sizable gap and my estimate from viewing photos is around 1/2" to 3/4".

Don't locate the trier until you've spun the drum at design rpm with an acrylic, see through front panel and a full batch of green coffee to locate the optimum point to catch falling beans. Vane angle, height and rpm will affect this greatly. You'll want to shoot for an rpm that creates a bean travel arc where the center of the falling mass of beans is hitting the shaft.

On spacing between drum and inside skin, I've never measured this but from all I've seen you'd be in the right ballpark going for around 2 1/2" and same for space between back of drum and inner rear plate. Also, same for space between inner and outer skin. Use a good mineral wool for insulation between the two skins. A good mineral wool won't smoke during the first few warmups.

Quote

how much space at the back of the drum so that some of the hot air going in through the perforated back of the drum is forced to travel up the sides before going in? I'm guessing that if there is too much space the air will just all go in at the base of the drum and not spread the heat up the sides as well?
I'm hoping that by constricting the flow a bit, the heating should be more efficient?


No need to try and come up with what seems like an optimum spacing for coaxing the hot air to travel up before entering the rear of the drum. As long as you're greater than 2", it will flow up well past the half way point before being drawn back to the rear of the drum and heat transfer will be plenty efficient. Actually, constricting the flow would do just the opposite.
allenb attached the following image:
12011_l12_disassembly_20130706_0357.jpg

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

Quote

and something that I'm just starting to research is which magnehelic gauges to get for propane and exhaust pressure respectively.
as I understand, the propane operating pressure will be about .25" of water column so 0 to .50" should be good?
what range gauge should I choose for the exhaust air pressure pre exhaust blower?
in the link is a list of the available magnehelics:
http://www.dwyer-...Series2000


Propane regulators on gas grills and most commercial heating equipment gives you around 11" h20 which is what you'll want for supplying your modulating gas valve as in the Maxitrol Selectra series. The valves typically chosen for drum roaster control have a modulation span of 10". Other manufacturers of modulating gas valves meant to be used in combination with a pilot ignition safety valve (as with the selectra), should be fairly similar in how they operate. The 2015 model Magnehelic will most likely be a good choice for you (0-15" h2O) but I'd wait till you finalize your gas valve controls design to be certain.

As for a magnehelic gauge for measuring the exhaust negative pressure? The needed pressure range for the gauge can't possibly be known until you've got the roaster built and operating. At that time, you'll need to get your hands on a loaner gauge from someone to find the pressure range needed. No amount of calculations will give you that value.

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
okmed
Axel, Google "u-tube monometer" and build a simple water u-tube monometer to determine the range of the magnehelic gauge you will require.
RAF-1 Extreme (modified B-2K) Hottop with HTC+TC4C, HG-One grinder, Bezzera Strega.
 
broeker

Quote

okmed wrote:

Axel, Google "u-tube monometer" and build a simple water u-tube monometer to determine the range of the magnehelic gauge you will require.


I used a home built "Manometer" on my roasters to figure out the actual operating pressures and pressure range while roasting......... its then a simple calculation to figure out what "gauge" and pressure range you require...... don't buy one till you have everything up & going...... the gauge I ended up with a range of (0-2.5kpa from a LPG bottle etc...) was much lower than we had imagined.....
 
allenb
Great idea on building your own test U-tube manometer!

Something else to consider in sizing of burner components is to get your gas regulator, pilot ignition safety valve and modulating valve put together first and size your burner jet orifice afterwards based on the maximum pressure delivered by the modulating control valve. If you already have a packaged burner assembly with venturi/jet included, you may have to up-size or down-size the jet orifice to give you a suitable throttling range.

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

Quote

allenb wrote:

Great idea on building your own test U-tube manometer!

Something else to consider in sizing of burner components is to get your gas regulator, pilot ignition safety valve and modulating valve put together first and size your burner jet orifice afterwards based on the maximum pressure delivered by the modulating control valve. If you already have a packaged burner assembly with venturi/jet included, you may have to up-size or down-size the jet orifice to give you a suitable throttling range.

Allen


I plan to use orifices and Polidoro burners sold as parts for a commercial pool heater. still looking for a good valve to use.
Any suggestions?
Axel attached the following image:
raypak_pool_heater.png

Edited by Axel on 08/30/2015 10:18 PM
 
Axel

Quote

broeker wrote:

Quote

okmed wrote:

Axel, Google "u-tube monometer" and build a simple water u-tube monometer to determine the range of the magnehelic gauge you will require.


I used a home built "Manometer" on my roasters to figure out the actual operating pressures and pressure range while roasting......... its then a simple calculation to figure out what "gauge" and pressure range you require...... don't buy one till you have everything up & going...... the gauge I ended up with a range of (0-2.5kpa from a LPG bottle etc...) was much lower than we had imagined.....

Thanks for the advice okmed and broeker, i'm planning to look more closely at setting up a u-tube manometer once ready.
 
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