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Black liquor's transformation journey: Why is it the best choice for biofuel?
In industrial chemistry, black liquor is a by-product produced when making pulp from wood through the Kraft process. It is mainly used to remove lignin, hemicellulose and other extractable components in wood, and ultimately to extract cellulose. The composition of black liquor makes it a relatively promising source of biofuels, but as environmental concerns become more severe, the way it is used continues to transform.
The composition of black liquor
For every ton of pulp produced, seven tons of black liquor are produced. Black liquor is an aqueous suspension of lignin residues, hemicelluloses and inorganic chemicals used in the process. Black liquor contains about 15% solids, and its organic matter accounts for about 40-45%, mainly composed of soap, lignin and other organic matter.
With the advancement of black liquor treatment technology, many traditional sewage treatment methods no longer meet the needs of modern environmental protection.
Looking at the development of black liquor from history
Early Kraft pulp mills would discharge black liquor into waters, which caused serious threats to aquatic life and darkened the color of the water. The Kraft process advanced significantly with the invention of G.H. Tomlinson's recovery boiler in the 1930s. By the 1990s, most Kraft plants were able to consume their own black liquor, such as recycled cooking chemicals, to reduce water pollution.
Energy Utilization of Black Liquor
Not only is black liquor a by-product of the pulp film manufacturing process, it also contains more than half the energy content of the raw wood material. The black liquor is typically concentrated to 65% to 80% via a multi-effect evaporator and burned in a recovery boiler to produce energy and recover cooking chemicals. This approach has allowed pulp mills to become almost energy self-sufficient, especially in the United States, where paper companies have consumed almost entirely their own black liquor production since the 1990s.
The pulp industry has become a major producer of carbon-neutral renewable energy in the United States, generating approximately 28.5 terawatt hours of electricity annually.
Biofuel applications of black liquor
With the emergence of new technologies, the way black liquor is utilized has changed. The development of gasification technology has made black liquor a potential biofuel feedstock. After gasification, it can generate energy-rich syngas, which can be used in gas turbines or converted into chemicals and fuels.
Dual challenges of environment and economic development
From the past black liquor discharge to today's recycling, the balance between environmental protection and economic benefits has become the key. However, there are still small Kraft plants that fail to achieve effective recovery of black liquor, which has caused pollution in some environments, which also shows the urgency of industrial upgrading.
U.S. tax incentives
In 2005, the U.S. Congress enacted a tax incentive to support the use of liquid alternative fuels, which was subsequently expanded in 2007 to include biomass-derived liquid alternative fuels. This policy has greatly promoted the commercial application of black liquor, and the results have been impressive for many large companies.
The future prospects of black liquor
Black Liquor’s journey of reinvention continues. From a simple fuel source to a potential multifunctional biomaterial, with the deepening of scientific research, the application of black liquor will become more extensive. This is not only a response to the demand for renewable energy in the manufacturing industry, but also a commitment to environmental protection.
As global demand for renewable energy grows, could black liquor become one of the core elements of the future energy revolution?
