When our customers tell me about the different places where CENCO and CSC Digital Moisture balances are used it always interests me.
A few weeks ago, I was asked if I understood the Black Liquor
When I responded with that they replied:
“No Art, it’s about a major process in pulping for paper making”.
As those of you in the paper industry know, Black Liquor is the lignin and hemicelluloses taken out of the wood chips, the spent chemicals that were used to separate them from the wood and a lot of water.
The lignin and hemicelluloses are removed from the wood chips to release the cellulose fiber needed for papermaking.
That’s very interesting, but So what? Who cares? It turns out that this residue is very important – you get several side products that have significant economic value.
Tall Oil is the first. It is skimmed off the Black Liquor before you start getting rid of the water. This by-product is used in adhesives, rubber, drilling fluids and inks. It’s also an ingredient in some cements, soaps and lubricants.
When you get most of the water out, a black, gooey mess of lignin and hemicelluloses results (it’s still called Black Liquor). This will burn. It is lit-off to produce steam for the generation of electric power for the plant.
The Black Liquor burn is accomplished in a recovery boiler. It’s called “recovery” because they recover the residual material that is left after the fire. This material consists of inorganic chemicals that are known as smelt (not to be confused with the type fish of the same name).
When mixed with water, this smelt, the recovered inorganic chemicals left after burning the Black Liquor, is known as Green Liquor.
It seems that booze is a common denominator in this Kraft process. The chemical mix that is the principal ingredient that causes the separation of the lignin, hemicelluloses and other components from wood chips is called White Liquor.
White Liquor to Black Liquor to Green Liquor. Now what?
Maybe you already knew this, but I was surprised – the Green Liquor that was produced in the recovery process is reconstituted as White Liquor to be used to start the pulping process all over again.
This is a case of use, recovery, power generation and material reuse. Recycling on a grand scale – Tall Oil, electric power and reused process chemicals.
I don’t know about you, but I found this small glimpse into the paper making process to be an intriguing story.
The whole thing started from a simple question about where our moisture balances are used. Maybe you can now see why I am continually mesmerized by the test equipment world.
I hope you found this little trip around the edges of papermaking interesting. If you did, feel free to share it with your friends and associates.
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By Art Gatenby