Distillation and Alcohol Heat Exchangers

Ethanol vapor leaves through the vent until the steam is cut, so the cut has to be automatic. A pot still on a 600,000 Btu/h jacket is making about 600 lb/h of vapor; with no water on the shell, that vapor goes straight out the vent at 173 to 190 F. A flow switch on the cooling water and a high-temperature switch on the condenser outlet should both close the steam valve, and the vent should terminate outdoors well away from the still house air intake. A check valve on the water supply keeps a pressure dip from draining the shell backward. The interlock costs a fraction of one lost run, and insurance surveyors increasingly ask to see it.

Because air and CO2 that cannot condense blanket tube surface and make a good condenser look undersized. Wash carries dissolved CO2 from fermentation and the still draws air at every charge, and that gas collects at the cold end of the tubes where the vapor has already condensed. A vent at that point lets it leave continuously; a vent run into a long common header, or throttled to save ethanol, backs gas into the bundle instead. The symptom is a condenser that holds through the heads and floods during the tails. Check the vent before adding tubes.

Inspect it on a schedule, clean it with citric acid, and budget to replace it. Copper does its flavor work by reacting with sulfur compounds in the vapor, and every ounce of copper sulfide that forms came out of the tube wall, so the tubes thin over years of service. Keep the hot caustic used on the stainless mash side off the copper; a citric wash removes the black sulfide film. Measure wall thickness at the vapor inlet, where attack is fastest, at each opening.

Yes, but only through a unit that passes spent grain; a plate exchanger will not. Whole stillage leaves the beer still near 212 F with the grain in it, so the recovery exchanger is a 2 inch bore tube-in-tube or a multi-tube with stillage in the tubes and process water or incoming wash in the annulus or shell. Thin stillage after a screen or decanter is clean enough for a wide-gap plate. The economics work only if the heated water has somewhere to go on the same shift, such as the next mash-in or CIP make-up; heating a tank that cools overnight recovers nothing. As a scale, 1,000 gallons of stillage dropped from 200 F to 120 F gives up about 670,000 Btu, enough to lift 1,000 gallons of strike water from 60 F to 140 F. Send the stillage rate, its solids content and what the recovered heat would feed.

On vapor temperature at the top of the column, not on a fixed water flow. The vapor shifts from heads near 173 F to tails toward 212 F, so a water flow that gave the right reflux ratio at the start gives too little later and spirit proof drifts down through the hearts. A temperature controller on the dephlegmator vapor outlet modulating the water valve holds proof steady, with a manual override so the distiller can still make cuts by taste. The dephlegmator is sized generously and throttled down, never sized tight and opened up, because its area is the ceiling on reflux.

Yes, at the hot inlet where gelatinized starch and protein first meet the wall, and it stays clean by flushing before anything dries. Mash at 15 to 25 percent solids and 500 to 2,000 cP leaves a film on the first few feet of tube every transfer; a husk plug at the inlet is the other failure. A water flush right after each run, then caustic at 160 F, keeps the film from baking into the next batch. On a single tube-in-tube or multi-tube the tubes can be brushed or pigged when a plug forms, which is the reason plates are kept off grain-in mash despite their lower price. A pressure guage on each end of the cooler shows a plug forming hours before the fermenter fill falls behind.