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Quotes - Engineering - SalesThe Utility Is Half the Selection
The product side gets the attention, but the utility side decides how big the unit is, how it is controlled and whether the product comes out the far end unharmed. A hotter utility gives a larger temperature difference and a smaller exchanger, and also a hotter wall. On water that does not matter. On milk, egg, juice, wort and protein solutions it matters more than the size, because a wall 40 F above the product cooks a layer onto itself in the first hour and the exchanger is fouled by lunch.
This page runs through the four common utilities, the temperatures they are normally supplied at, how each is controlled, and which products each suits.
The four utilities and their normal supply temperatures
- Plant steam: 15 to 150 psig, 250 to 366 F saturated; the hottest and least gentle
- Culinary steam: filtered plant steam from an approved boiler chemistry, used where steam may contact product
- Hot water set: a closed loop at 185 to 195 F, steam-heated, for gentle and precise heating
- Chilled water: 34 to 40 F supply, 10 F rise, for cooling to storage temperature
- Propylene glycol: 20 to 30 F for wort, juice and beer, food-grade, where chilled water cannot reach the outlet
- Low-temperature glycol or refrigerant: minus 20 to minus 40 F for extraction, cold traps and solvent recovery
Plant steam at 150 psigAgainst milk at 150°F that steam drives the wall above 300°F and protein deposits within minutes, while 190°F water holds the wall near 175°F for a full shift.
Wall Temperature and Burn-on
The wall of a sanitary exchanger sits between the product temperature and the utility temperature, weighted toward whichever side has the higher film coefficient. With condensing steam on the utility side the coefficient there is very high and the wall runs close to the steam temperature. Milk at 150 F against 150 psig steam at 366 F sees a wall over 300 F, and denatured protein and calcium phosphate deposit on it within minutes. The same milk against 190 F water sees a wall around 175 F and runs a full shift.
The working rule on dairy, egg and protein products is to keep the wall within 15 to 20 F of the product, which in practice means a hot water loop, or steam throttled by a modulating valve to a low enough pressure that its saturation temperature is close to the product outlet.
- Milk, cream, whey, egg, plant milks: hot water at 185 to 195 F, or steam throttled below 5 psig on the last section
- Juice, wort, beer, soft drinks: hot water for heating; glycol at 20 to 30 F for cooling below 45 F
- Sauces, tomato, viscous product in tube-in-tube: steam in the jacket is normal, throttled to hold the wall within limits
- CIP solution heating: plant steam directly, the product is caustic and does not care about wall temperature
- WFI, purified water, point-of-use: plant steam or clean steam for heating, chilled water for cooling, double tubesheet
- Extraction and solvent recovery: glycol or refrigerant at minus 40 F, construction and gaskets rated for it
Hotter utility, smaller unit, hotter wall, and the wall is what fouls.
- Hot water set at 185 to 195°F for dairy and egg
- Keep the wall within 15 to 20°F of the product
- Propylene glycol 20 to 30°F below where chilled water reaches
Steam, Water and Glycol, One at a Time
Plant steam is the cheapest heat in the building and the hardest to use gently. At 150 psig it is 366 F; even at 15 psig it is 250 F. A modulating steam valve on the inlet throttles the pressure down until the saturation temperature is where the wall needs to be, and a condensate trap and a vacuum breaker keep the shell from filling or pulling a vacuum on shutdown. Steam belongs on a shell side or in a tube-in-tube jacket, never in a gasketed plate at plant pressure. It is the right utility for CIP heating, for clean steam generation, for viscous product in tube-in-tube where the coefficient is low enough that the wall stays reasonable, and for any duty where the product is not heat-sensitive.
Culinary steam is plant steam filtered to remove particulates and produced from a boiler whose treatment chemicals are on the approved list for incidental food contact. It is required wherever steam could contact the product or the product contact surface, which includes direct injection and any SIP of product lines, and it is the sensible specification on any sanitary exchanger where a tube leak would put steam into the product. On the exchanger it behaves exactly as plant steam does; the difference is upstream, and it costs a filter and a boiler chemistry review rather than a different exchanger.
The hot water set is how heat-sensitive product is heated at scale. A closed loop of water is heated by plant steam in its own exchanger and pumped through the product exchanger at 185 to 195 F, returning 10 to 15 F cooler. The loop temperature is controlled by the steam valve on the water heater, and the product outlet by a valve on the water flow or a three-way blend. The wall never sees more than the loop temperature, so a milk heater runs its shift without burn-on. It costs a second exchanger, a pump and a control loop, and it lowers the LMTD compared with steam, so the product exchanger is larger. On dairy, egg and juice the trade is made without hesitation.
Hot water also changes control. Steam valves control pressure and therefore temperature; a hot water loop controls flow and therefore approach. On a pasteurizer with a legal minimum the water loop is easier to keep stable, and the flow diversion valve trips less often. On a batch process where the product starts cold and needs to be brought up quickly then held, a loop with a wide flow turndown does the job; steam does it faster but overshoots.
Chilled water at 34 to 40 F is the cooling utility for storage temperatures of 38 to 45 F. It is usually a plant loop with a 10 F rise, so the utility flow is set by the duty: a 1.18 MMBtu/h milk cooler without regeneration needs about 236 gpm of it. The product approach on plates is 2 to 3 F, so 36 F water cools milk to 38 or 39 F comfortably. It cannot cool anything to 33 F, and it will not cool wort from 200 F to 50 F in one pass on a hot day without a very large unit, which is why breweries and juice plants add a glycol section.
Propylene glycol at 20 to 30 F is the food-grade cold utility. It is usually 30 to 35% glycol in water, which has a lower specific heat and higher viscosity than water, so the utility flow is higher and the utility-side coefficient is lower for the same duty; the exchanger is sized for that. Wort coolers use it on the second stage to reach pitching temperature, juice plants use it to hold product below 40 F, and dairies use it where the chilled water loop is short of capacity. Ethylene glycol is not used on sanitary duty because it is toxic, and the specification should say propylene, food-grade, and the concentration.
Extraction, solvent recovery and cold traps run at minus 20 to minus 40 F on low-temperature glycol or direct refrigerant. The construction is rated for it: gaskets that stay flexible, materials with low-temperature impact properties, and a design that takes the thermal shock of a warm solvent meeting a cold wall. The product side is often an ethanol or hydrocarbon solvent rather than a food, so the sanitary finish matters less than the seal design and the pressure rating. Tell us the coldest utility temperature and the warmest product temperature and the unit is built for the range. Call and talk it through with an engineer: 1-805-484-2992
Milk against 150 psig steam sees a wall over 300 F and fouls in minutes; against 190 F water it runs a full shift.
Request a QuoteCommon FAQs
In a shell-and-tube or tube-in-tube, yes, with a modulating valve throttling the steam so the saturation temperature stays within 15 to 20 F of the product outlet, and usually with culinary steam. A hot water set is the more common and more controllable choice for pasteurizing duty.
One hundred eighty-five to 195 F supply with a 10 to 15 F drop across the product exchanger. High enough for a sound LMTD on a 165 F pasteurizer, low enough that the wall does not burn product on.
When the product outlet has to be below about 40 F, when the chilled water loop cannot spare the flow, or when a hot product like wort has to be brought down to pitching temperature in one pass. Propylene glycol at 20 to 30 F is the standard food-grade answer.
Yes. A 30 to 35% propylene glycol solution has a lower specific heat and higher viscosity than water, so the utility flow is higher and the utility-side coefficient lower. The unit is sized for glycol from the start; a chilled water unit switched to glycol later will fall short of duty.
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