Research Still

Scope

The research still was a request from the famous Philadelphia Distilling LLC.  Currently they do not have an accurate, repeatable way to test small batches of liquor without making over 100 gallons at a time.  The distillers want to be able to research and develop new liquors without the high cost of failure on a larger system. Anybody can buy a pre-built still and put a gas fire burner under it.  A big issue with this method is the high potential for scorching the bottom of the still and anything inside of it.  This is caused by direct flame’s inability to disperse heat evenly. Some will install a rummager to keep sediment moving on the bottom to reduce burning, but Oat Foundry had another idea:  Heat can evenly be introduced to the wash by means of low watt density heaters.  This also allows the unit to be used indoors without the risk of propane poisoning! This still was designed to use only electric heat.

Design

The initial design was simple: order a prebuilt copper still, outfit it with thermowells and RTDs, slap on some heaters and a controller and we are good to go!  Not so fast…the lead time on the still is 8 weeks and measurements need to be taken once the still is in hand to ensure the sensors and heaters will fit.

It may seem obvious, but it is always very important to order long lead time items as quickly as possible.  Sometimes this means ordering before there is even enough time to have a fully laid out bill of materials or refined design plan.  All hands were on deck to get together the preliminary design and spec out a still.  Once that was spec’d and ordered, the team can spend the time to get the details together surrounding the still.

Through prior experience in refrigeration, heat transfer and thermodynamics, the heat load was calculated to bring a 5 gallon wash to a boil in under 60 minutes.  Including losses to surroundings, the necessary amount of heat was calculated as 2800 watts.  One of the requirements for this still is that it can, under no circumstances, scorch the sediment from the wash as this would produce highly undesirable off-flavors.

Fabrication

Once the still came in and measurements were taken, next thing to do was order the heaters. The bottom of the still was a focus point because that is where the sediment will fall and have the highest potential to scorch. Through some research, silicone heaters fit the bill perfectly.  Low-density, flexible and impact resistant, these heaters would work well for this application.

A low watt-density heater was designed by Oat Foundry engineers and ordered from Tempco, a custom heater manufacturer.  A 12” diameter 1000 watt 240V heater was on its way (3 week lead time).  This comes out to 8.8 watts/sq.in. which in this case is a relatively low watt-density.  The additional 1800 watts must come from another source. Using the same heater material and a similar watt density, a 1” x 30’ silicone heater rated at 2400 Watts was selected.  This strip would wrap from the base of the still up to the handles.  This allows for evenly distributed heating of the wash.

The great thing about silicone heaters is how easy it is to apply them to the copper surface.  You may never have guessed but the best adhesive to use is actually high-temp silicone. The bottom heater took about 5 minutes to install. The heater wrapping took a bit longer because of added clamping and setting time for the silicone.  After everything was set, it was time to get some power to these heaters.

Wiring is always an interesting part of any electronic-related project.  The still could not be hard-wired to the electrical enclosure, because it needed the freedom to be rinsed and transported. A plug was installed between the still and the enclosure to allow for this. A distilling controller was added to the enclosure with a 240V solid state relay.  This relay would turn the heaters on or off depending on temperature. After everything was wired and insulated, it was time for a test.

In order to check for scorching oats were added to the water.  The entire 5 gallons and added oats came to a boil at 212F in 55 minutes. 212F is mentioned because the boiling point of an ethanol/water mixture is lower than 212F.  Actually ethanol boils at 173F, so the mixture is in between the two and is dependent on concentration.  The test proved no scorching! All that was left was the final touches.  HVAC duct tape was used to turn this into Sputnik.  Signed, sealed, delivered.

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