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Quotes - Engineering - SalesPet food
A utility caustic heater for the wet side of an extruder line
The extruder barrel in a pet food plant is cleaned dry, by purging and pulling the screw. The CIP circuit lives on the wet side around it: meat slurry and emulsion tanks that feed the preconditioner, the slurry pumps and lines, the fat and digest coating system after the dryer, and the palatant tanks. The soil there is rendered animal fat, meat meal and blood plasma proteins, starch slurry, and a greasy coating-drum film that sets hard when the line cools. Fat is the dominant soil, and fat sets the temperature.
Tallow and poultry fat begin to melt around 100–115°F but saponify quickly only above 150°F, so pet food plants run their caustic strong and hot: sodium hydroxide at 2–3% and 165–170°F for 30–45 minutes. Meat meal brings calcium phosphate, and the water brings carbonate, so a phosphoric step at 1% and 130°F runs a few times a week. There is no sanitary program behind any of it. The loop is utility equipment, mill-finish stainless with flanged connections, and the plant wants it sized right rather than polished.
A 1,500-gallon tank taken from 60°F to 170°F in 45 minutes is about 1.8 MBtu/h, and that is the heater.
Fat saponifies above 150°F; below it the caustic just moves grease around
A pet food caustic tank that stalls at 140°F leaves a smear on every tank wall and a coating-drum film that thickens week by week. The heater is sized to reach and hold 170°F with the 1,500-gallon tank and the cold slurry tanks on the loop.
The circuit: strong caustic for fat, acid for the meal
The pet food wet-side wash is a saponification job. At 2–3% and 170°F, caustic turns rendered fat into soap that rinses away and carries the meal and plasma protein with it. The coating drum and the fat lines are the slow spots because the fat there was applied hot and has cooled into a varnish; sanitation often gives them the longest contact time of the cycle. Soap foam in the return is normal and tells you the chemistry is working.
Mineral comes from the meat meal, which is high in calcium and phosphate, and from the water. A 1% phosphoric step at 130°F for 15 minutes clears the gray phosphate film the caustic exposes. Nitric is rare in pet food plants, which keeps the gasket choice simple. Rinse water runs at 120–140°F; a hot sanitize is uncommon on this side of the line.
The heater: mill-finish 316L U-tube, flanged, sized for the tank and the cold steel
We recommend a U-tube shell-and-tube with steam inside the tubes and caustic on the shell side, in mill-finish 316L with flanged connections to match the plant's utility piping. The U-bundle takes the thermal cycling, the fat and soap film form on the shell side where the bundle pulls to clear them, and 125 psig steam at 353°F in the tubes keeps the bundle compact for 1.8 MBtu/h. The head gasket is EPDM, which is unaffected by 3% caustic and by phosphoric at 1%.
The sizing mistake we see in pet food plants is a heater that handles the tank heat-up and nothing more. Several thousand pounds of cold slurry tank, pump and pipe sit on the loop, and they absorb heat for the first 10 minutes of the caustic step. We size for the heat-up plus the recovery during the wash, with a fouling allowance of 0.001–0.002 for the soap film.
What to send for an extruder wet-side heater
A pet food heater is a utility job, and the quote is short. These items size the bundle and settle the connections; no finish or 3-A questions arise unless your plant has a program that asks for them.
- Caustic tank gallons, start temperature and the time allowed to reach 170°F
- Caustic strength and the acid used
- Tank loop flow in gpm and the line size
- Steam pressure at the heater
- Which equipment is on the circuit: slurry tanks, coating system, palatant tanks
- Flanged or tri-clamp, and whether the plant wants a spare bundle
Call and talk it through with an engineer: 1-805-484-2992
Pet food plant questions
On the solution side, yes. Hot 2–3% sodium hydroxide is fine on 316L indefinitely, and the acid step would attack a carbon steel shell in a season. The finish is where a utility plant saves: mill-finish stainless, flanged ends and no 3-A symbol do the job at a lower cost than a polished, tri-clamp build. Carbon steel appears only on a utility steam head, which the caustic never touches.
Melting is not removal. Melted fat spreads into a thin film and resets as soon as the surface cools, which is what a plant sees as a greasy coating drum after a 140°F wash. Saponification, where caustic converts the fat to water-soluble soap, runs quickly only above about 150°F. A 170°F set point gives margin for the heat the cold tanks take out of the loop.
Yes, one circuit at a time from the same tank. The slurry tanks are the larger heat sink because of their steel mass and the cold emulsion residue, so the heater sized for them has margin on the coating system. Sequence the circuits so the drum, with its varnish-like fat film, gets caustic after the tank is fully at 170°F rather than during the heat-up.
At 125 psig, around 1,900 lb/h during the 45-minute heat-up, tapering as the tank approaches 170°F. If the extruder's preconditioner and dryer are also drawing steam, the header may dip, so the pressure that matters is the one at the heater inlet during a wash. Tell us that figure and the bundle is sized for it rather than for the boiler nameplate.
For a plant that runs the wet side daily and cannot stop production for a week, a spare U-bundle is worth having. The soap and phosphate film on the shell side builds steadily, and swapping a clean bundle in takes an afternoon while the fouled one soaks in the caustic tank. We supply new bundles to the same drawing, so the spare drops into the existing shell without rework.
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