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Quotes - Engineering - SalesSauce kettles
The heater behind a kettle circuit with burnt-on soil
A sauce kettle is the hardest soil in a food plant to wash in place. Starch thickeners, tomato solids, cheese and cream all scorch where the jacket is hottest, and the burnt ring at the heat-transfer line is a mix of carbonized sugar, denatured protein and fat that caustic has to lift one layer at a time. Sanitation answers with the strongest wash on the site: sodium hydroxide up to 3% at 165–175°F, often with a chelant, for 30–45 minutes, followed by acid for the mineral and a hot rinse.
Kettle circuits are tank circuits. Two spray devices at 40–60 gpm each put roughly 100 gpm onto the kettle wall, and the return pump sends it back to the CIP tank through a line that was sized for sauce, not water. What makes the kettle different from a silo is thermal mass. A jacketed, insulated 300-gallon kettle holds several hundred pounds of stainless and a jacket full of cold condensate, and the first minutes of caustic that hit it leave at 120°F no matter how hot they arrived.
The heater on the CIP tank has to replace that heat while the wash is running, not just before it starts. Lifting 100 gpm by 60°F is about 3 MBtu/h, which condenses around 3,100 lb/h of 15 psig steam, and that is the figure a kettle-room heater is built around.
A cold jacketed kettle pulls 60°F out of the first caustic
Sizing the kettle heater for the standing tank alone leaves the wash short. We size for 100 gpm through two spray devices with a 60°F recovery, about 3 MBtu/h, so the return climbs back to 170°F before the burnt ring has a chance to set again.
The circuit: 3% caustic, 170°F, carbonized soil
Burnt sauce is removed in stages. Hot caustic swells the starch and saponifies the fat, which exposes the carbonized sugar layer beneath; the chelant in the formulation keeps calcium from binding the protein back onto the wall. Below about 160°F the process slows to the point where sanitation adds a manual scrape, and that is the failure mode we hear most: a kettle room where the wash cycle is long enough but the caustic arrives too cool to finish.
Acid follows caustic more often in a sauce plant than in a dairy because tomato and dairy-based sauces leave calcium phosphate and oxalate. Nitric or phosphoric at 1–1.5% and 130–140°F for 10–20 minutes, run several times a week, keeps the mineral from building a base for the next scorch. Rinse water runs at 120–140°F and sanitize at 180°F or above.
The heater: a U-tube bundle sized to the kettle, not the tank
The construction is a U-tube shell-and-tube with steam in the tubes and caustic on the shell side. Starch gel and saponified fat carried back from the kettle coat the shell side, the steam side stays clean, and the bundle pulls when the film gets thick. The shell, bundle and heads are 316L, and the EPDM head gasket is swapped for FKM where the acid step uses nitric at the hot end of the range. The surface carries a fouling allowance of 0.001–0.002.
On 15 psig steam the tubes run at 250°F, enough for 170°F caustic with margin; at 50 psig the heater is smaller for the same 3 MBtu/h. The one trap we see in kettle rooms is a heater sized for heat-up of the tank only, which reaches 170°F in the tank and then watches the return fall to 140°F for the whole wash.
What to send for a kettle circuit heater
The kettles themselves set the duty. Send us the kettle count, size and jacket type along with the chemistry, and we will size for the recovery during the wash rather than for the tank sitting idle.
- Number of kettles washed at once, gallons each, jacketed or not
- Spray device count per kettle and the gpm they were set for
- Caustic strength and wash temperature from the sanitation program
- Acid type, strength and how many times a week it runs
- Steam pressure at the kettle room
- Full unit or a replacement bundle for an existing heater
Call and talk it through with an engineer: 1-805-484-2992
Sauce kettle questions
Nothing with the tank. The kettle steel and the cold jacket are absorbing the difference, and the heater is not adding heat fast enough during the wash to keep up. Sizing the heater for the recirculating duty, around 3 MBtu/h at 100 gpm with a 60°F recovery, brings the return up within the first ten minutes. Draining the jacket before CIP also helps.
Not the metal. 316L is unaffected by sodium hydroxide at that strength and temperature. The gaskets are the only elastomer in the solution path, and EPDM handles 3% caustic indefinitely. Where the plant uses a chelated caustic blend, check that the chelant is compatible with EPDM; most are. The steam side has no elastomer at all.
Yes, if it is sized for the larger duty, which is nearly always the kettles. A filler loop on a 3-inch line at 70 gpm with no cold mass behind it asks far less of the heater than two spray devices on a cold kettle. Run the circuits one at a time from the same tank and the kettle sizing covers both.
Not as the steam heater. Starch gel and saponified fat plug the narrow plate channels, and 3% caustic at 175°F on one side with steam cycling on the other is hard on gasket life. A plate pack earns it's place in a sauce plant on the return-to-makeup recovery duty, where it is solution against water at modest pressure and the gaskets stay cool.
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