Black Liquor Evaporators - Principles

SKU: C-497Duration: 13 Minutes

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Evaporators Series (Details)
Includes 5 courses for $299/year.

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Includes 72 courses for $1,499/year.

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Course Details


Training Time: 13 minutes

Compatibility: Desktop, Tablet, Phone

Based on: Industry Standards and Best Practices

Languages: English, Portuguese, French

The Black Liquor Evaporators - Principles course begins by describing how evaporators generally function and then lists the objectives of black liquor evaporators installed at kraft pulp mills. Next, it introduces some steam theory topics, including the relationship between steam pressure and temperature, flashing, and boiling point rise. It concludes by examining the impact of steam theory on evaporator size and the number of effects in a multiple effect evaporator set.

Learning Objectives

  • Describe the purpose of evaporators
  • List the objectives of black liquor evaporators
  • Describe the key principles of steam theory, including the relationship between temperature and pressure, and flashing
  • Describe the effect of concentration on boiling point rise
  • Describe why evaporator body sizes are not all the same

Key Questions

The following key questions are answered in this module:

What is boiling?
Boiling is the conversion a liquid to a gas by the addition of heat.

What happens to the solids in a water solution when the solution is boiled?
As water boils into steam, the solids in the solution do not boil away. As the amount of liquid water in the solution becomes smaller, the concentration of solids in the solution increases.

How can the boiling temperature of water be changed?
The boiling temperature of water is dependent on its pressure. As the pressure above a body of water decreases, so does the boiling temperature.

What is latent heat?
Latent heat is the heat which is absorbed or released during a phase change, such as when water is boiled to create steam.

Why are the final effects in multiple effect evaporators sometimes larger than the initial effects?
The pressures in the later effects of a multiple effect evaporators are lower than the initial effects. Gases expand as the pressure drops, so the later stages are made larger in an attempt to keep gas velocities down.

Sample Video Transcript

Below is a transcript of the video sample provided for this module:

At a kraft pulp mill, evaporators are used to remove water from the used pulping chemical solution in order to concentrate it. This is the first step in the process that is used to recover the chemicals so that they can be reused in the pulping process. Black liquor evaporators have several objectives. One, efficiently heat and remove water from the black liquor so that it can be fired into the recovery boiler. Two, avoid scale formation inside the evaporators. Three, produce condensate or warm water that is clean enough for reuse in the pulp mill and recausticizing area in order to reduce fresh water usage. And four, safely remove any volatile components and NCGs or non-condensable gases that are produced.
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