France - Wheat Solubles
In many cases, off-gases from existing plant operations such as dryers or scrubbers contain valuable energy which may be recovered as the energy sources for gas heated evaporators. This essentially "free" energy provides for very low operating cost. Also, with the reduction of the waste gas stream exiting the evaporator, energy requirements are reduced downstream for the emissions handling equipment as well.
- Waste gas is made up of dry air and water vapor
- Wet bulb temperature gives Wt. water vapor /lb. dry air
- The btu’s are coming from the water vapor
- The higher the wet bulb temperature;
» The more water vapor condensed
» The more effects that can be used
» Or... the evaporator costs less
- Reduced volume exhaust gas on picture
There are cases in many plants where process vapors other than water vapor are generated. Rather than dissipating the latent heat of these vapors using cooling water in a condenser, they are often used as the energy source to drive evaporation.
In the Biofuel Industry, for example, ethanol vapor from rectification and molecular sieves is sometimes used as an energy source to drive the stillage evaporator. Given a sufficient quantity, flash vapors or turbine exhausts are also a welcome source of recoverable energy.
Another waste energy source that can exist in a plant environment is hot water (such as condensate). Dedert has designed and supplied evaporators that use the sensible heat from process streams as the energy source.
Waste Heat Recovery