Evaporators

Evaporators are used in many industries to reduce the water content of a product by the use of steam heat. Paper, food, textile, chemical and steel manufacturing all employ evaporators.

Evaporators are shell and tube heat exchangers that house steam in the shell and pump product through the tubes. After leaving the heat exchanger, the product is forced into a separating chamber where the vapor is drawn off and may be used elsewhere. The product concentrate is then pumped out. In single effect units the concentrate is piped to other areas of the plant.

When greater concentration of the product is required, a multiple effect evaporator is used. In these cases, the vapor is cascaded to provide heat in subsequent evaporator heat exchangers. The product concentrate flows through successive tubes and separators until the desired concentration is achieved. The vapor from the final effect may be used to preheat the incoming product, or piped off to perform some other service such as heating water.

In general, there are a number of common considerations when employing steam evaporators:

• They run continuously and have large, uniform condensate loads
• Later effects have lower differentials than earlier effects
• The evacuation of air and contaminants is important at each effect
• Only condensate from the first effect can be returned to the boiler