NOTE: This journal entry is a bit more technical then usual to give enough guidance to other distillers wanting to do something similar. If that's you, please note that pumping hot liquids is a dangerous business and our design is no guarantee of safety. If you can't calculate the technical requirements of your system then find someone that can.
As we grow and develop our distillery we maintain a list. It's a list of the things still to do to achieve our ultimate goal of zero waste.
This list is ranked, sadly not by ease of implementation, but by environmental impact. Way up there is waste heat.
Targeting zero waste
Distilling is a wasteful business. Our core role is to heat up liquid and cool it down again straight away. The specific heat capacity of water is 4185.5 J/(kg⋅K), which means it takes a LOT of energy to heat it up.
Once we've heated it up and boiled it for a while to extract the delicious, delicious ethanol, we're left with a volume of hot liquid (like, 98 degrees hot, called 'stillage') and a volume of hottish water used for cooling (60ish degrees, 'condenser water').
Now, we use a 100% renewable supply to heat it, but that doesn't mean we should be wasteful with that energy.
We need to strip out the heat energy for 2 reasons - 1) Our aim of zero waste includes heat energy that can be recovered and reused, and 2) all our liquid waste goes to our biodigester to be processed using green energy. Too much hot stillage would nuke the bacteria in the biodigester rendering it useless, and as we grow that's becoming an issue.
Build or buy?
Specialist heat recovery systems for distilleries tend to cost hundreds of thousands and are designed to suit distilleries which operate at full capacity five or seven days a week. Better for us to build one completely suited to our needs.
Ours essentially has three components:
An insulated thermal store. We discharge the stillage into this along with some of the condenser water - not too much of the condenser water as we have other uses for that and we want the temperature to be as high as possible for maximum efficiency. If we don't want to use the heat energy for a couple of days that's fine, it'll stay hot in the store for when we need it. If we don't have a use for it, then a radiator is plumbed into the store and will vent the heat slowly to the distillery over a week or so.
A wash feed circuit. This brings cool wash from the fermenter through 60m of coil in the thermal store which heats it up a bit, then through a plate heat exchanger where it picks up some more heat, and then to the still by which time it should be pretty hot.
A hot circuit. This pumps stillage out of the thermal store around the plate heat exchanger, both to warm the wash feed in the plate exchanger and to circulate the stillage in the thermal store to maintain efficient heat transfer
The net result of this is we bring the wash from a fermenter temperature of 12 degrees to 55 degrees in the still, while reducing the stillage temperature from 95 degrees to a balmy 40 degrees (ish).
It works like this. In Fill mode (below) the stillage is pumped from the still (through a filter to remove debris) into the thermal store holding vessel.
The stillage feeds into the top of the thermal store where there's also a fill point for condenser water here which doubles as a vent point (we can close this but it must never be sealed completely). The volume of the store is such that if we ONLY use stillage then the coil is covered completely.
When we're charging the still, the wash pump is pumping wash through the coil, through the plate heat exchanger, to the still.
The high temperature pump is circulating the stillage through the plate heat exchanger and around the thermal store.
When we're done, we have a still full of hot liquid ready to distll, and a thermal store full of warm liquid ready to be dumped to the biodigester.
Notes for Distillers
We mainly use this for stripping runs. You obviously don't want your fine spirit run to be hot too fast otherwise you won't get good separation of heads cuts.
Note we've mounted the plate exchanger on a few bits of timber so we can remove these easily and drop the exchanger off for maintenance.
Don't run you gin through this. It wouldn't be safe at that charge abv and it wont make for a nice spirit, but do use the gin stillage for heat recovery.
High-temperature Pump - Lowara Stainless Steel 415V from www.anchorpumps.com
High-temperature suction hose (from still to system) - www.ebay.co.uk/usr/hosemaster64
Plate heat exchanger - Wiltec Stainless Steel Heat Exchanger 60 Plates 130 kW
Thermal Store (See Below) - Custom build from www.worldheat.co.uk
Connections - www.ukpumpsupplies.co.uk & www.screwfix.co.uk