Positive displacement pumps for continuous

[bluc]

Yea i have and every thread on continuous im 99% built, lwtcs has lots knowledge on the subject and was interested on his spin on this is all.....

[bluc]

Another question. I guess im gunna find out but why is exact flow into column so important? So long as your your not flooding the column at peak of pump flow, why do small fluctuations matter in a stripping still,?

Is it just a matter of stability?

[LWTCS]

Another question. I guess im gunna find out but why is exact flow into column so important? So long as your your not flooding the column at peak of pump flow, why do small fluctuations matter in a stripping still,?

Is it just a matter of stability?

Well, the closer you get to steady state the better the still does it's job.
If the flow rate bounces around there is a good chance the head temp at top of the beer column is also fluctuating. I use head temp to govern feed rate by the way. Others use effluent discharge temps to govern feed rate and those temps are likely influenced by feed rate as well. The closer you can keep your actual temp to the target temp the better the still will do its job. I want less than a degree difference between the target and actual head temp. I can live with a single degree but less than a degree is what I consider ideal.

There is some tolerance for a fluctuating flow rate as long as you are not completely overshooting and over stuffing the column with way too much juice. That will definitely waste some alcohol down the drain and also prevent your feedstock from going through its phase change cycles. Fluctuations can also make pressure within the column inconsistent.
If you incorporate extra precautions to help widen the operating range of the still then it can help better deal with fluctuations. As an example, extra space between plates, extra column diameter, pre heating feed stock. But all those things drive up the cost. And it is really hard to engineer in those precautions if you haven't made at least a half dozen mistakes that will allow you to understand how your still,,,thinks. Yeah ya kinda have to think like the still. Though I'd bet money that Steve Alexander would absolutely scoff at my last comment since he has done the maths for all kinds of projects in spite of actually never building or running anything.

Centrifugal pumps are cheap and are very service life friendly. But they are not self priming and therefore suck at metering. They are the most difficult to dial in and in my opinion are nearly impossible to run without employing a PID. Positive displacement pumps on the other hand are quite easy to run manually with a speed controller. They do not run at steady state but can still follow along with target temps as long as the still is set up to cope with the on again /off again feed rate. We usually find a range and set the VFD to allow the pump to always run at 25 or 30% and let the PID then control the actual feed. Auto tune is an amazing bit of voodoo.

Frankly, I am tired of dealing with the fussiness of centrifugal pumps however. I'm moving to FIPs even though the impeller heads have such a short service life.

[bluc]

Thanks mate

[drmiller100]

Another question. I guess im gunna find out but why is exact flow into column so important? So long as your your not flooding the column at peak of pump flow, why do small fluctuations matter in a stripping still,?

Is it just a matter of stability?

What lwcts said.

For small scale continuous you have to reclaim waste heat and use it to heat beer going in.
In my design is have a column above the beer insertion point and amd am pulling 95 percent out the top. .

Feed rate, heat going into the boiler, pull rate, heat exchange rate. Column size. Drain rate. Alcohol percent in the beer. Heat loss out the sides. All must be balanced.
The more variables you can remove the more stable the thing will be.

And it really doesn't want to be stable.

[shadylane]

Frankly, I am tired of dealing with the fussiness of centrifugal pumps however. I'm moving to FIPs even though the impeller heads have such a short service life.

I had to look up FIP
A Flexible Impeller Pump like outboard motors use to pump cooling water.
https://en.wikipedia.org/wiki/Flexible_impeller

[LWTCS]

Frankly, I am tired of dealing with the fussiness of centrifugal pumps however. I'm moving to FIPs even though the impeller heads have such a short service life.

I had to look up FIP
A Flexible Impeller Pump like outboard motors use to pump cooling water.
https://en.wikipedia.org/wiki/Flexible_impeller

Ah, thanks.
Yeah these do a nice job of metering grain solids (as long as there are no rocks) and can be reversed to un-jam a clog. Definitely a pump of choice for those that won't or can't put an agitator on their beer well to ensure uniform suspension of grain solids.
But as you can see by the moving cartoon on the Wikipedia the impeller head takes on quite a bit of stress so it's always best to have a spare impeller on the bench and ya don't want to run the pump dry either since it is the liquid being pumped that keeps the heat caused by friction down.

[bluc]

Why do I always find out these details after the fact(already purchased a pump). But very good info and if first attempt fails I will try one of these

[ThomasBrewer]

Any insights on perstaltic pumps for this application? are they a good choice @lwtcs?

I'm not sure if he's a member here, but user "tight" on YouTube has some good information about tubing material/flowrates/longitivy using peristaltic pumps.

[utube][/utube]