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Quotes - Engineering - SalesDairy tank circuits
A heated vessel that cooks its own soil onto the wall
A cheese vat is a jacketed stainless vessel, open or enclosed, in which milk is set with rennet and the curd is cut, stirred and cooked. Cooking raises the curd and whey to 100–105°F for cheddar types and higher for cooked-curd cheeses, with hot water in the jacket pushing the wall above the whey temperature. Whey protein against that warm wall, plus fat released from the curd and a fine dust of curd particles, dries into a film tougher than its temperature suggests, and on the whey screen and knife shafts it builds into a crust. Mineral is high too, because the whey draws calcium and phosphate out of the curd.
Enclosed vats of 5,000 to 20,000 pounds of milk are washed as tank circuits through fixed spray devices in the cover, each taking 25–100 gpm, so a vat circuit runs 100–300 gpm with the drain and whey outlet carrying it back to the CIP return. The finishing tables and curd conveyors downstream are washed as separate circuits with their own sprays. Caustic at 1–2%, pushed toward 3% on fat-heavy vats, runs 160–170°F for 30–45 minutes, and because of the mineral load the acid step at 0.5–1.5% is run daily on most cheese floors.
The steam heater that gets caustic and acid to temperature between the CIP tank and the spray supply pump is what we build, and this page is about sizing it for the vat.
One vat circuit at 100 gpm needs about 3 MBtu/h of steam
A single-vat circuit at 100 gpm raised from 105°F return to 165°F supply needs about 3 MBtu/h, which condenses roughly 3,100 lb/h of 15 psig steam. Two vats washing together double it. The spray count, not the vat size, is what we need first.
How the vat circuit runs
The circuit is set by the sprays. Three devices at 100 gpm each on a large enclosed vat make a 300 gpm circuit, and a floor washing two vats at once can ask the CIP set for 400–600 gpm, which is why vat CIP is usually staggered. Pre-rinse at 100–120°F for 5–10 minutes clears curd fines before the caustic can cook them on. Caustic at 160–170°F for 30–45 minutes, intermediate rinse, acid at 120–140°F for 10–20 minutes, final rinse 120–140°F.
Return temperature on a vat circuit is better than on a cold silo because the vat was recently warm, but a vat that sat empty overnight pulls the first pass down 20–30°F. The caustic tank is large, 2,000–5,000 gallons, and held hot through the day between vats, so the heater sees a long holding load with short bursts of recovery as each vat comes on line.
The heater for a vat circuit
A steam-to-caustic U-tube shell-and-tube, 316L shell and bundle, steam inside 3/4-inch or 1-inch tubes, 150 psig at 250°F on the solution side. For a 100 gpm vat circuit lifted 60°F the duty is about 3 MBtu/h, around 3,100 lb/h of low-pressure steam; a two-vat circuit at 200 gpm is 6 MBtu/h and the bundle grows accordingly. Steam at 15–50 psig at the heater is typical on cheese floors, and at 15 psig the 250°F saturation still gives an 85°F approach above a 165°F target, so surface rather than steam temperature sets the size.
Curd fines are the thing to design around. They pass the whey screen, ride the return, and settle in the CIP tank and any low spot in the heater's shell, where they bake onto hot tube surfaces into exactly the whey film the wash was meant to remove. We specify shell-side velocity high enough to keep fines moving, a shell that drains fully, and a removable bundle so the fouled side is the one you can see. The daily acid step means an FKM head gasket if the plant runs nitric.
What a cheese floor should send us
Vat CIP is sized by the spray devices and how many vats wash at once.
- Number of vats washed together and spray devices per vat with gpm each
- CIP tank volume and the hold temperature through the day
- Caustic concentration and target, 160–170°F
- Acid chemistry, nitric or phosphoric, and that it runs daily
- Steam pressure at the heater inlet during the wash
- Return temperature on the first pass if you have measured it
- Finishing table and conveyor circuits, if the same heater serves them
Call and talk it through with an engineer: 1-805-484-2992
Cheese vat questions
The jacket water set is sized to warm 20,000 pounds of curd slowly and is usually a closed loop; routing caustic through it, or asking it to lift 100 gpm by 60°F in one pass, is not what it was built for.
Curd fines. They come back in the return, pass through the CIP tank, and land on the hot shell side of the heater where they cook on. A heater with a horizontal shell that does not drain, or with low shell-side velocity, collects them fastest.
If the two circuits run through one heater, yes: 200 gpm raised 60°F is about 6 MBtu/h, twice the single-vat figure. Many plants instead stagger the vats by fifteen minutes so one heater sized for 3 MBtu/h handles the recovery of each in turn while the tank rides through. Tell us which you intend; it is the largest factor in the heater's size.
Only the gasket. 316L shell, tubes and heads take nitric or phosphoric at 0.5–1.5% and 140°F every day without change. The head gasket on the solution side is EPDM for caustic-only service and FKM once nitric is daily, and on a cheese floor it nearly always is. The acid also cleans the shell side of the heater.
Most plants treat the vat CIP loop as utility, with the vat and the product lines being the sanitary equipment. The heater is then mill-finish 316L with flanged or tri-clamp connections as the piping dictates. Where the inspector treats the CIP supply as part of the product system, we build it self-draining with a 32 Ra finish; say so.
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