What is Black Liquor?
Black liquor is a by-product generated during the paper manufacturing process. In the paper making process, wood chips are dissolved in an aqueous solution or white liquor. This causes the chemical lignin, which binds the cellulose fiber in wood, and other organic matter to dissolve, forming the black liquor. The remaining cellulose pulp is harvested to make paper.
When released into the environment without being treated, this liquid waste can be extremely hazardous. To prevent environmental hazards, paper mills attempt a recovery process to recycle the waste.
How is Black Liquor recycled?
Conventionally, Tomlinson recovery boilers were used to recycle the black liquor. In its original form, black liquor has only 15% solid biomass and is not readily combustible. The recovery process begins by concentrating it. Concentrated Black liquor has about 70% solids, which are burnt in the recovery boiler. This process results in the formation of some gases and smelt. The smelt is further processed and reused as pulping chemicals while the gases are burnt to generate steam, which can be used to power the mills or move turbines to generate electricity.
What is Black Liquor Gasification?
The black liquor gasification process is an improvement over the recovery boilers. Gasification is an evolving process and several methods are in use. Of these, pressurized black liquor gasification with an integrated combined cycle (BLGCC) is very effective.
In this process, the black liquor is atomized and sprayed into a high temperature chamber in the presence of oxygen. The gasification process converts the organic substances in the black liquor into combustible gases like H2, CH4, CO2, which are then used to fire gas turbines to generate electricity. The inorganic material smelt is reused in the pulping process. This process doubles the electricity generation and yields better quality chemicals in the form of smelt.
How can Black Liquor Gasification benefit us?
Black liquor gasification process has the potential to reduce 25% of world’s fossil fuel consumption. Black liquor can be a great alternative fuel, which unlike bio fuels, does not have to be separately cultivated. Nor is there any competition for land used for growing food crops. It has the potential to make industries energy-efficient, to reduce costs and to protect the environment.
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