VM Take-off rate for 3" 2200W Packed Column

[Dave022]

I am running my new 3" SPP packed column using VM as take-off and a 2200W keg boiler.

I am currently getting Over 96% out (which I am happy about) but it only runs at approx 400ml / hour.

This seems really low to me, am I wrong?

[The Stig]

To go beyond 95.6%, you’d need chemical drying agents (e.g., molecular sieves), which are rarely used in home setups due to safety and legality

[Dave022]

sorry fat fingers, over 95%...

[GrumbleStill]

Agree 100% - that’s a very low take off rate from a 3” - especially as you are using spp. You should be able to get 1.5 - 2 lph with a setup like that at 2200W.
Can you provide any more info on your rig eg column height, RC setup, takeoff valve size etc?

Cheers

[Dave022]

Hi thanks for the reply.

Column is 1120 mm high with 980 mm packed SPP. There is a hammerhead condenser on the top and a 1/2" takeoff below that controlled with a silicone tube and hoffman clamp direct to a standard liebig condenser. water control is seperate for both condensers.

[GrumbleStill]

Ok - Makes sense now.

The 1/2” offtake is way too small for a 3” VM. The amount of product you get / reflux ratio is dictated by the size of the of the offtake compared to size of the column above it. A 1.5” gate valve might be a better idea.

If that’s not an option, it might be worth considering switching to an LM design.

Cheers

[Dave022]

I am running another 10% sugar wash through this now, still the same issue. if I use 2200W I get 444ml / hr.

If I reduce water flow to reflux condenser then I increase flow but vapour escapes past the reflux condenser.

I have played with reduced power and water flow adjustments but can't seem to find a balance, is there a systematic approach I should be taking?

[Dave022]

Ok - Makes sense now.

The 1/2” offtake is way too small for a 3” VM. The amount of product you get / reflux ratio is dictated by the size of the of the offtake compared to size of the column above it. A 1.5” gate valve might be a better idea.

If that’s not an option, it might be worth considering switching to an LM design.

Cheers

Didn't see this reply before writing last comment. Well I could use a 3" to 1.5" reducing elbow at take-off, but the liebig condenser is only 1/2". Now I have a 1.5" to 1/2" reducer and could put a valve either at the 1.5" or 1/2" end; but is this going to help my situation?

[GrumbleStill]

Yeah, I can see how that could be an issue.

Could be a really good excuse to upgrade to a 2” shotty for your product condenser ;-)

Another approach could be go old school and reduce the whole column at the off take.

There’s a nice illustration of the concept in this post viewtopic.php?f=57&t=3117

[Oblivion]

I am running another 10% sugar wash through this now, still the same issue. if I use 2200W I get 444ml / hr.

If I reduce water flow to reflux condenser then I increase flow but vapour escapes past the reflux condenser.

I have played with reduced power and water flow adjustments but can't seem to find a balance, is there a systematic approach I should be taking?

Dave, are you still around? Can you post a pic of your VM head? Just need to see the reflux condenser, the vapor take-off, the water lines (state the ID of the water lines) and tell us how you supply water to your condensers. Do you use a pump to recirculate water, do you use well water pressure or city water pressure?

I have a 3" VM with a 1" gate valve for the take-off. I operate at 2750W with a 5'-6' tall column packed with Lava Rock and I get approx 3-3.25 LPH take-off rate. 1-1/2" is way over sized and completely unnecessary for a take-off port for a 3" VM still.

You may have at least 2 or more bottlenecks with your current rig. If your reflux condenser cannot operate at 100% reflux at 2200W then that reflux condenser is inadequate and too weak for a 3" reflux column. If your water lines are very small or if your water flow rate is relatively low then that would be a problem, but that depends on exactly how you are supplying water to your rig. We need more info.

You would also do much better to increase the height of the column. Pack it with the SPP on top, but pack the lower section at least with rolls of copper mesh.