Sterile Water Heat Exchangers

Because the cooler sits full of 176 F loop water between draws, and the first water out is still near loop temperature when the chilled side comes on. A cooler holding 3 gallons clears in about 10 seconds at 20 gpm, so the flush is short but not optional: a batch recipe that wants 77 F water and gets 150 F for ten seconds is out of range. Set the flush at commissioning from the outlet temperature element and lock it in the sequence, not in the operator's hands.

Mostly by looking: the gap is open at the bottom, so a weeping joint shows as a drip or a stain on the walk-down. Where the cooler sits out of sight, a drip tray with a moisture sensor reports to the control system. The gap must never be plugged, insulated shut or painted over, because that turns the visible leak path back into a hidden crevice. Put the gap on the preventive maintenence round and record a dry check each week, so the day it is not dry has a date to compare against.

Yes, behind a double tubesheet with the water side at the higher pressure, and propylene glycol is the choice near pharmaceutical water. The glycol system's own pressure, including its expansion tank and the pump at shutoff, must stay below the water side at all times, so compare the glycol pump at shutoff with the lowest pressure the water side ever runs at, not with its normal running pressure. Glycol's lower heat capacity shows in the flow: a 20 gpm draw from 176 to 77 F is about a million Btu/h, which on chilled water at a 20 degree rise is about 100 gpm, and on 30 percent propylene glycol a little more. Most sites keep ethylene glycol out of the area even behind two barriers.

Keep the loop sweeping through its cooler at 176 F and include it in every sanitization; if the piping cannot keep loop water moving through it, remove the point. A seldom-used cooler is where loop excursions start, and a special procedure for one point is the kind of thing that lapses on a night shift. If the point must stay, pipe the cooler as a sub-loop with its own return so the water never stands.

The treated side. Recovery puts killed waste against incoming raw waste across one wall, and a leak must flow from treated to raw so live material can never reach the discharge. A pressure differential switch or the pump arrangement holds that order, and a double tubesheet on the recovery section gives the same visible leak path the sterile water coolers use. The raw side also fouls, with media solids and cell debris, so the recovery section is a straight tube or tube-in-tube that can be cleaned, not a plate, and the kill temperature at 250 to 285 F is proven at the hold outlet, not inferred from the recovery exchanger.

Through its own low-point drain and trap, with a temperature element at that drain proving 250 F for the full 30 minutes, because the drain is the coldest spot on the water side. Drain and vent the chilled side first; a tube wall backed by 45 F glycol condenses steam faster than it arrives and the water side never reaches temperature, which is the usual reason an SIP on a new cooler fails its first cycle. After the hold, refill with hot loop water rather than letting the cooler pull a vacuum and draw room air into the sterile path.