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Quotes - Engineering - SalesWhat the percentage means
Regeneration percentage is the share of the total temperature rise that raw milk picks up from hot pasteurized milk before the heater does the rest. With raw milk entering at 38°F and a holding temperature of 163°F, the total rise is 125°F. At 90% regeneration the raw side leaves the regenerator at 150.5°F, and the heater only has to add the last 12.5°F.
Choosing the number
The same arithmetic runs on the cooling side. Pasteurized milk leaving the holding tube at 163°F gives up 112.5°F in the regenerator and reaches the cooler near 50.5°F, so the cooler takes it down the final 12.5°F to 38°F. With equal flows on both sides, the regenerator spares the heater and the cooler the same amount of work.
That is why HTST milk plants run 85–94%, and why 90% is so common: the heater and the cooler shrink to a tenth of their once-through duty.
What pushes regeneration up or down
- Long daily run hours and high energy cost push it up
- Frame length, floor space and pump head hold it down
- Short runs and frequent product changes favor a lower figure
- Cultured bases held hot for minutes give back less
- A separator or homogenizer between stages splits the section in two
- Double-wall regenerators usually settle a few points lower
Common HTST milk regenerationAt 90% the heater and cooler each carry about a tenth of the once-through load, which is why most fluid milk plants settle there.
Plates against percentage
For a balanced milk-to-milk regenerator, the thermal length needed climbs steeply as the percentage rises. The number of transfer units (NTU) for regeneration R in a balanced counterflow section is R divided by (1 minus R), and the surface rises roughly in step with it:
- 85% regeneration: NTU about 5.7
- 90% regeneration: NTU 9, about 1.6 times the 85% section
- 94% regeneration: NTU about 15.7, about 1.7 times the 90% section
- Near the top, each point costs more plates than the point before it
Call and talk it through with an engineer: 1-805-484-2992
Working out the payback
Payback sets the cost of the extra regenerator plates against the heating and cooling they save per operating hour. Take a line running 3,000 gal/h of whole milk, about 25,800 lb/h at 8.6 lb per gallon, with a specific heat near 0.93 BTU/lb°F. Once-through, the heater would carry about 3.0 million BTU/h to take that milk through the full 125°F rise.
Every point of regeneration is 1% of 125°F, or 1.25°F. At this flow that is about 30,000 BTU/h off the heater and about the same off the cooler, which is 2.5 tons of refrigeration while the line runs. Over 4,000 operating hours a year, one point is roughly 120 million BTU of heat and the same again of cooling.
Price that against your own steam and refrigeration cost and against the plates the step needs. Moving from 85% to 90% gains five points for roughly 60% more regenerator surface; moving from 90% to 94% gains four points for about 74% more. The first step usually pays inside a normal budget horizon; the second often pays only on lines that run long days, six or seven days a week.
A note on equal flows: the clean arithmetic above assumes the same product flow and specific heat on both sides of the regenerator. Where cream is separated out between stages, or standardization sends a different stream back, the two sides no longer match and the percentage differs from one side to the other. We size each stage on its real flows.
Once-through is a legitimate answer. A plant pasteurizing a few hours a week, a pilot line, or a heater serving a cultured base that stays hot in a holding tank has little to recover. In those cases a compact heater and cooler, each sized for the full load, cost less to buy and to clean, and a multi-section frame can still hold both in one press.
Each point of regeneration is a fixed slice of the heating and cooling load.
Send your run hours per year and we will show the plate count at two or three regeneration figures.
Request a QuoteRegeneration questions
Indirectly. At high regeneration the heater makes a small final step, so any drift in regenerator performance, from fouling or a flow change, moves the heater inlet and the hot-water loop has to follow it. Lines above about 92% should have a hot-water set with margin, so the recorder still holds setpoint late in a long run.
Yes, and it is a common layout. The regenerator is split in to two stages; raw milk leaves the first warm enough for the separator or homogenizer, then returns to the second stage before the heater. Each stage is sized on its own temperatures, and the pressure margin has to hold across both, which affects where the booster pump sits.
Usually less than on milk. Viscous product on both sides of a wide-gap plate transfers less heat per plate, so the pack grows quickly as the percentage climbs, and pressure drop rises with it. We size two or three figures for cream and mix so the plant can see where the extra plates stop paying for themselves.
If the carrying bars have length left and the plate pattern is still available, yes. Adding plates lowers velocity per channel unless the pass arrangement changes, so we recheck the whole section, not just the new plates. We supply the new plates and gaskets; the frame is rechecked against the new pack length and the plate-pack tightening dimension.
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