Evaporation

Evaporation

• The purpose of the evaporation system is to remove water from the thin stillage.

• The evaporation system boils the thin stillage using a tube and shell heat exchanger called the Calandria, which has an attached separator. This is the first stage (effect) of the evaporation process.

• The stillage entering the system consists of approximately 92% water and 8% solids.

Evaporation

• The heat source for the evaporation system is the MVR (mechanical vapor re-compressor).

• The product is pumped from the Calandria to the North and South Finishers which are also tube and shell heat exchangers.

• From the finishers the product is sent to the syrup storage tank.

Evaporation

• The evaporation system produces syrup, (Condensed Distillers Soluble) which is thickened stillage. Through a process of heating the stillage and boiling off the water, the entrained liquid and vapor are separated and the syrup solids are concentrated. The syrup has a target of 30 to 32% solids in the final product.

Evap Preheater

• The evap pre-heater is a spiral scroll type heat exchanger.

• The evaporator pre-heater is used to preheat the thin stillage entering into the evaporator.

• The heat source for the pre-heater is evaporation condensate.

Evap Pre-heater• The pre-heater

can be bypassed for repair and cleaning if necessary.

• The evaporation process will work with out the pre–heater online, but will not operate as efficiently.

Evap Preheater

The Science of Evaporation

• The Calandria and finishers are falling film evaporators.

• In this type of evaporator, liquid and vapors flow downwards in parallel flow. The stillage is heated to a boiling temperature. An even thin film enters the heating tubes via a distribution device in the head (top) of the evaporator, flows downward at boiling temperature, and is partially evaporated.

The Science of Evaporation

• The weight of the liquid in the tubes as well as the downward movement of the vapor keeps the product moving downward.

• The successful operation depends on an even distribution of liquid at the top of the Calandria.

The First Stage of Evaporation

• The evaporation system boils the thin stillage using a tube and shell heat exchanger called the Calandria, which has an attached Separator tank.

• The stillage from the pre-heater is feed into the Calandria and re-circulated by four pumps.

The First Stage of Evaporation

• A liquid level is maintained in the bottom of the Calandria and Separator. This level can be checked with a sight glass located on the side of the Separator and should be less than 1/3rd the way up the sight glass. This liquid is re-circulated back through the Calandria, with a portion being drawn off and sent to the Finishers.

The Second Stage of Evaporation

• Instead of one exchanger and one separator like the first stage the second stage is setup with two exchangers and one separator.

• The two exchangers are also falling film type evaporators and are called the North and South Finishers.

• There is a tank between the Finishers that is the separator.

The Second Stage of Evaporation

• The heat exchangers and separator function in the same way as the first stage.

• A liquid level is maintained in the bottom of each Finisher and the separator tank.

• That liquid is re-circulated back to the top of the Finishers with a portion being drawn out and sent to the syrup storage tank.

The MVR

• MVR is an acronym for Mechanical Vapor Re-Compressor.

• During mechanical vapor recompression, the vapor of an evaporator is recompressed to a higher pressure by means of a mechanically driven compressor.

• Steam from the MVR is the heat source for evaporation.

The MVR

Evap Condensate

• Steam is injected on the shell side of the Calandria and Finishers.

• The steam is subsequently condensed as it transfers its energy to the stillage and the condensate is collected in the Evap Condensate tank.

• From here the condensate is pumped through the Evap pre-heater and to the Recycle water tank.

The Separator Tanks

• As mentioned before each stage of evaporation has a separator tank.

• The purpose of the separator is to remove the water droplets from the steam vapor as it is drawn out the top of the vessel to the suction of the MVR.

The Separator Tanks• The vapor is drawn up through Chevrons.• The Chevrons are mist eliminators that are are

highly effective in removing liquid entrainment from gas streams.

• They providing high efficiency and low pressure drop.

The Separator Tanks

• The chevrons can remove fine droplets with efficiencies approaching 100%.

• They also provide excellent resistance against fouling in applications with high solids loading.

Storage

• The process syrup tank is used to supply syrup to the wet feed.

• Syrup being drawn from the evaporators is pumped to the process syrup tank.

• The syrup tank works as a surge tank.• We pump the syrup we make into it and pump

out what we need for the wet feed.• What we don’t use is sold to various customers.