Backyard vapour compression distillation

[diyfarmer]

My wife and I make a bit of maple syrup every spring in a traditional wood fired evaporator. I am intrigued by the vapour compression distillation process and am trying to figure out how I could build a small setup. The biggest stumbling block is what to use for a compressor. The only idea I have so far is a vacuum motor from a central vac unit. Are there any other options that are easily available and inexpensive?

 

[Compositepro]

Start with a process diagram of how you want your process to work, then select the equipment to do it. Will the syrup be at sub-ambient pressure or positive? The problem with sub-ambient is that any leakage will be air into your system, which will interfere with condensation and has to be removed. The advantage of sub-ambient evaporation is that the syrup will see less heat. A diaphragm type piston compressor that can tolerate steam would probably be the most suitable, but may not tolerate vacuum on the suction stroke and pressure on the exhaust stroke due to fatigue of the diaphragm. A roots type blower could also work but it has seals that can leak.
So, what will be your evaporator pressure/temperature and your condenser pressure/temperature. A vacuum cleaner motor is completely unsuitable because the motor will be in your process flow and also it is designed for high flow at low pressure differential. You need adequate pressure differential to create the enough temperature differential so that heat will flow between the hot compressed steam to your syrup. I would guess you need at least 5 to 10 psi of compression.

 

[moltenmetal]

Part of the flavour of maple syrup comes from caramelization, so it takes heat, and time while hot.

The conventional approach for getting rid of water first is much better, and more efficient than vapour recompression- it's reverse osmosis. That takes care of all the water you can get rid of, leaving only the finishing step to develop the required syrup consistency and flavour.

Best of luck!

 

[diyfarmer]

Thanks for the replies, you've given me some starting points to look at.

 

[chicopee]

Instead of a vapor compression about just creating a vacuum over the sap to get rid of the water. The process may be slower than using an wood fired evaportor though.