Black Liquor Evaporators – Equipment
Describes several different evaporator designs used to concentrate black liquor, including rising film evaporators, falling film evaporators, falling film concentrators, and forced circulation concentrators (crystallizers). Discusses scaling and boil outs, the role of the surface condenser, overall driving force and capacity, and removal of non-condensable gases (NCGs) from a multiple effect evaporator set.
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Course Details
Learning Objectives
• List the objectives of black liquor evaporators
• Differentiate between the designs and operation of several common types of black liquor evaporators and concentrators
• Define “scaling” and recognize the need of a “boil-out”
• Describe the role of the surface condenser
• Describe overall driving force and capacity
• State the importance of non-condensable gas (NCG) removal
Specs
Frequently Asked Questions
What is the primary purpose of black liquor evaporators?
Falling film evaporators have some advantages over rising film evaporators. What is their major disadvantage?
What is the difference between black liquor concentrators and evaporators?
What is the role of a surface condenser in a mulitple effect evaporator set?
How do non-condensible gases affect evaporator performance?
Sample Video Transcript
There are several different evaporator designs used to concentrate black liquor, and they all contain two major parts. The first is the heating element, usually a vertically-arranged heat exchanger where the vapor or steam condenses and transfers its heat to the black liquor. The second part is the vapor body, also referred to as the vapor head or dome, which provides space for the concentrated liquor and water vapor to separate. The heating element is designed to provide as much surface area as possible for the vapor to condense and transfer heat to the liquor. The more heating surface that is available, the more the solution can be heated. Sets of tubes or parallel plates are commonly used. Black liquor and vapor or steam are both continuously fed into the evaporator, and concentrated liquor, water vapor, and condensate are all continuously discharged.
