1-805-484-2992
Quotes - Engineering - SalesSterile after the still, sterile at the tap
The exchanger is the one place a sterile loop runs against something that is not
Sterile water is distilled or membrane-purified water that has been made free of viable organisms and is then kept that way, which in most plants means storing it hot at 176 F and circulating it continuously. Every point of use wants that water at 68 to 77 F for buffer make-up, media preparation, blood and plasma fractionation, equipment rinse or API formulation, and the cooler that gets it there has glycol on the other side of a tube wall.
The parent page covers what low-conductivity water does to stainless. This page is about sterility: how the cooler is sterilized, how it is kept from leaking inward, and how the same construction serves bio-kill and waste deactivation duties at the other end of the plant.
How a sterile water exchanger is built and run
Point-of-use coolers off a hot loop
The common arrangement is a hot loop at 176 F with a small cooler at each use point that runs only while the valve is open. Between draws the cooler must sit full of hot loop water, not cooled water at 77 F where a film grows in a day. HeatX arranges the cooler so the loop sweeps through it continuously and the chilled side is enabled only on demand.
A 20 gpm draw from 176 F to 77 F is about a million Btu/h for the few minutes it lasts, which is a much larger exchanger than the average load suggests. It is sized on the draw, not the average, with chilled water at 45 F and a 6 to 8 degree approach.
Keeping the utility out
Sterile water runs at a higher pressure than the glycol against it, so a pinhole leaks outward, and the tube joints are double tubesheet with the gap open to atmosphere so a weeping joint shows on the floor before it shows in a sample. The water side is orbital-welded 316L with no gasket from loop connection to outlet.
- Product-side design pressure 150 psig, utility side 150 psig, 250 F SIP on the water side
- Tubes 15 to 20 Ra electropolished, shell 32 Ra where the shell carries sterile condensate
- Instrument bosses and drains flush to the bore, sloped 1/8 in per foot to the low point
Bio-kill and waste deactivation
The other sterile water duty is the reverse: liquid waste from a biosafety suite, fermenter harvest or animal facility is heated to 250 to 285 F, held for the required log reduction, and cooled before drain. The heater is a steam-heated shell-and-tube, or a tube-in-tube where the waste carries solids; the cooler recovers heat to the incoming waste. The hold coil is sized on the slowest particle and the kill temperature is proven at its outlet with a diversion valve.
Materials on bio-kill duty follow the waste chemistry rather than the water: 316L is standard, 2205 duplex or AL-6XN where the waste carries chloride from saline media, and the product path is welded so the waste never sees a gasket at 285 F.
The common mistake
Buying a cooler that is sanitary but not sterilizable. It has tri-clamp ends and a polished bore, and it fails the first SIP because the tube joints were rolled, not welded, and 250 F steam finds the crevice; or it passes SIP and fails a month later when the chilled side is pressurized before the loop. A sterile water cooler is welded, double tubesheet, pressure-ordered and steamed with the loop it serves. Call and talk it through with an engineer: 1-805-484-2992
Sterile water process conditions
The rows describe coolers and heaters that keep the water sterile from the still to the last valve. Compare your use points and sterilization routine with them, then send both with the quote request.
| Condition | Detail |
| Fluid | Sterile water, WFI-grade or filtered purified water; buffers and media on the same class of exchanger |
| Flow range | 2 to 150 gpm point-of-use coolers; 20 to 400 gpm loop coolers; 1 to 20 gpm bio-kill |
| Temperatures in / out | 176 F loop to 68 to 77 F at the use point; 40 F where the recipe calls for cold water |
| Hold | None in the cooler; bio-kill holds 250 to 285 F for 30 seconds to several minutes |
| Utility | Chilled water or glycol; sterile condensate where the site allows nothing else near the loop |
| Approach | 5 to 10 degrees on chilled water; 15 on glycol at the cold end |
| Construction | Double tubesheet straight tube, product in the tubes; double-wall plate on small intermittent duties |
| Finish / class | 316L, 15 to 20 Ra electropolished, ASME BPE fittings; duplex, AL-6XN or titanium where the site names them |
| Pressure relationship | Water side held above utility side at all times, including start-up |
| CIP / SIP | SIP at 250 F for 30 minutes on the water side; CIP rarely needed, chemical sanitization on schedule |
Common FAQs
Where the utility is chilled water, glycol or plant steam, yes. A single tubesheet unit puts one joint between sterile water and tower water, and joints cycle. The double tubesheet with a vented gap is the standard on any loop whose water reaches a patient, a bioreactor or a final rinse.
A 5 degree approach on 85 F August tower water gives 90 F at the tap, not 77 F. Most sites use chilled water or glycol for the last stage and tower water only as a first stage on large draws.
With the loop: clean steam or hot water at 250 F through the water side for 30 minutes with the utility side drained. The exchanger is built for that cycle daily, with free-expanding straight tubes and no product-side bellows.
Shell diameters from 2 to 36 in and lengths to 65 ft in straight tube, U-tube, multi-pass and double tubesheet forms. A point-of-use cooler is usually a 3 or 4 in shell; a large loop cooler may be 12 to 16 in.
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