ENERGY ECONOMY AND RECOVERY
Process optimization has long been one of Dedert’s specialties. Each Dedert Evaporator system is systematically configured to provide the Customer with the quickest return on their investment with the lowest operating cost.
As the price of energy has risen over the years so have efforts increased to find reusable energy. Dedert has long been a pioneer in waste heat recovery and was granted the us patent for an evaporator chest with built in scrubber for the corn wet milling industry.
ENERGY SOURCES FOR EVAPORATION
Steam Heated Multiple Effect
The energy source is steam at a condensing temperature above that which exists on the process side of the heat transfer surface. For cases where evaporation requirements are small or steam is relatively inexpensive, single effect evaporators are used. In this case, the vapors produced are rejected to a condenser. For higher evaporative duties or when steam is relatively expensive, additional “effects” are used and the process vapors are condensed in subsequent effects operating at lower pressures.
Mechanical Vapor Recompression
Dedert originally introduced mechanical vapor recompression to the grain processing industry decades ago.
These evaporator components are similar to steam driven machinery with the addition of a mechanical compressor. Mechanical energy supplied via a compressor or fan compresses the process vapor to a higher pressure (and condensing temperature) where it is reused as the heating steam. Steam and cooling water requirements are significantly reduced and are eliminated in many cases. MVR evaporators use electricity. With increased gas prices, the operating costs of MVR evaporators are significantly lower.. Fewer vessels are required than in steam powered multiple effect systems; therefore, installation costs are lower. The replacement of required steam with recycled vapor results in lower operating costs making this a viable choice in many applications. This is a very attractive option for larger evaporation rates.
Thermal Vapor Recompression
As a way to reduce energy consumption, a thermocompressor which uses high pressure steam as a motive fluid is added to a typical steam heated evaporator. The motive steam at approximately 150 psig enters the thermocompressor and expands as it passes through a diffuser. This in turn entrains recycled vapor and discharges it at an intermediate pressure while providing a steam rate reduction. Steam is once again the source of energy. Economics and product characteristics determine the suitability of thermal vapor recompression operation.. This design provides improved steam economy with less costly equipment than straight steam heated designs but requires higher pressure steam.
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.
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.