Indirect heating systems
The heating medium and product are not in direct contact, but separated by equipment contact surfaces. Several types of heat exchangers are applicable:
- scraped surface
Plate Heat Exchangers
Similar to that used in HTST but operating pressures are limited by gaskets. Liquid velocities are low which could lead to uneven heating and burn-on. This method is economical in floor space, easily inspected, and allows for potential regeneration.
Tubular Heat Exchangers
There are several types:
- shell and tube
- shell and coil
- double tube
- triple tube
All of these tubular heat exchangers have fewer seals involved than with plates. This allows for higher pressures, thus higher flow rates and higher temperatures. The heating is more uniform but difficult to inspect.
Scraped Surface Heat Exchangers
The product flows through a jacketed tube, which contains the heating medium, and is scraped from the sides with a rotating knife. This method is suitable for viscous products and particulates (< 1 cm) such as fruit sauces, and can be adjusted for different products by changing configuration of rotor. There is a problem with larger particulates; the long process time for particulates would mean long holding sections which are impractical. This may lead to damaged solids and overprocessing of sauce.