CBD Extraction Heat Exchangers

Chiller, miscella, condenser and glycol

The solvent chiller: sized on the glycol side

Ethanol is easy to chill; the fluid chilling it is not. At -40 F ethanol is about 4.5 cP, while 60 percent propylene glycol at -50 F is over 100 cP and creeping. The plate exchanger that chills 20 gpm of ethanol from 70 F to -40 F, about 190,000 Btu/h, is sized almost entirely by the glycol film, and the fix is flow: 2 to 3 times the ethanol flow on the glycol side, a high-theta chevron plate to force turbulence, and a 10 F approach rather than the 3 F a water duty would get. A potassium formate or silicone fluid cuts the viscosity five to ten times and halves the plate count; HeatX quotes the exchanger both ways so the plant can see the difference.

Miscella and crude: the cold, thick, dirty streams

After extraction the ethanol carries cannabinoids, some wax, fine biomass and water pulled from the plant. Kept cold on the way to the filter and the evaporator it stays clean; let it warm and the waxes redissolve into the crude. An in-line miscella cooler is a tube-in-tube, because the stream drops wax onto a cold wall and a plate channel plugs in a shift. The same applies to winterization, where crude in ethanol at 10 to 1 is chilled to -20 to -40 F for a day in a tube-in-tube or a jacketed tank. Wall temperature matters more than bulk: glycol at -60 F freezes wax onto the tube even with bulk ethanol at -20 F, so the glycol is tempered to a few degrees below target.

The recovery condenser on the evaporator

A falling-film or rising-film evaporator strips ethanol at 100 to 500 lb/h, under vacuum at 100 to 120 F or at atmospheric pressure at 173 F. The condenser is sized on that vapor rate, the pressure and the cooling fluid, with a sub-cooling section that brings the condensate 20 F below its boiling point so the receiver vent does not carry ethanol to the vacuum pump. Under vacuum the condensing temperature is close to summer tower water and the condenser needs chilled water or the evaporator rate falls every July. It is a vertical shell-and-tube with vapor on the shell, a vent at the top and a drain at the bottom, 316L on the ethanol side because the condensate meets product again. Recovery condensers for ethanol and other extraction solvents are covered in more depth on our solvent recovery condenser pages.

The common mistake

Buying a chiller by tonnage and the exchanger by area, separately, and finding at commissioning that the two do not meet. A 20 ton chiller at -50 F delivers perhaps 8 tons, and an exchanger with a 3 F approach on 100 cP glycol uses half of that. The line makes 60 percent of its rated batches and the operators blame the chiller. Glycol temperature, flow and fluid are chosen first, the exchanger is sized on them, and the chiller is bought to deliver that glycol with the real derating.

Send HeatX the ethanol flow, evaporator rating and chiller fluid and temperature, and the four exchangers are sized as a set. Call and talk it through with an engineer: 1-805-484-2992