LignoBoost® - the process
LignoBoost® is a patented process that produces lignin with characteristics that can be matched to the intended use. LignoBoost is fully integrated with the pulp mill’s processes and is designed to provide safe and reliable extraction of high-quality lignin.
High-quality lignin from a unique two-step process
LignoBoost is a patented extraction process divided into two steps: a separation step, followed by a washing step. Dividing the extraction into two steps makes it possible to optimize the conditions in each step and produce an extracted lignin of a very high quality. It also provides several options to adjust the lignin’s characteristics. LignoBoost was initially developed by universities and research institutes, but has been commercialized and further developed by Valmet.
Step 1: Separation
The first step in the LignoBoost process is to separate the lignin from the mill’s black liquor. Black liquor is taken from the evaporation, and the pH is lowered with CO2 and gas from the second step of the LignoBoost process. When the pH drops, lignin precipitates and is separated from the liquor with a press filter. The output of the first step is LignoBoost crude lignin.
Step 2: Washing
In the second step, the lignin is purified. The crude lignin is washed in a low pH solution and then dewatered in a second filter press. The results of washing the lignin greatly depend on the conditions during the washing step. LignoBoost is engineered to produce a very pure lignin. The quality of the lignin after the washing step is LignoBoost lignin.
Filter presses are key
The filter presses have a major influence on the lignin extraction process and the quality of the extracted lignin. The current design of the filters and their operation is a result of Valmet’s substantial experience in lignin extraction. The filters are engineered and fully integrated with the process’s two steps. This results in very high safety and reliability.
Return flow to the mill
Lignin lean black liquor and wash water are returned to the evaporation plant. The flow of wash water is low and can normally be handled with only minor changes to the mill’s operation.
Pulp mill sulfur balance
LignoBoost uses sulfuric acid to purify the lignin. Most of the sulfur in the acid is returned to the mill with the wash water and gas from the lignin extraction process. This may increase the amount of sulfur in the mill and may necessitate its removal from the pulp mill’s chemical cycle.
One way to remove sulfur is to remove the ash from the electrostatic precipitators. This ash is rich in sulfur, but it also contains sodium. Ash removal therefore leads to losses of sodium. Sooner or later, this loss must be replaced by make-up sodium, increasing the mill’s production costs.
Valmet’s sulfuric acid plant offers a good way to control the pulp mill’s sulfur balance. This plant can be operated in line with the need for sulfur removal. The produced acid can be used for lignin extraction, other purposes in the mill or sold.
Valmet’s solution for the production of sulfuric acid is proven. It ensures safe operation and high reliability. Valmet has built one sulfuric acid plant and has recently been awarded the contract for a second. To learn more about Valmet’s sulfuric acid plant technology, see here.
High operational safety
Valmet’s LignoBoost technology ensures reliable and safe handling of all the flows related to lignin extraction. This includes extracted black liquor, return liquor, wash water, extraction chemicals and gas from the process. When the pH of black liquor is reduced, H2S is released, and this makes the gas handling systems an important part of a lignin extraction plant. Valmet’s in-depth knowledge of the process reactions has resulted in several advanced gas handling solutions that are integrated with the LignoBoost technology and surrounding mill. LignoBoost is built for high safety.
The gas produced in the second step of the LignoBoost process is collected and used to reduce the pH of the incoming black liquor in the first step. This solution reduces the consumption of carbon dioxide in the first step and with it, the operating cost of lignin extraction.
Excess gas from the LignoBoost process falls into the DNCG category of gases in a chemical pulp mill. This gas is collected and sent to the mill for destruction. Valmet has many solutions for safe gas handling in pulp mills.
Extracted lignin needs to be stored and packaged for easy transportation to the mill’s customers. Valmet can help design solutions and supply equipment like conveyors, as well as drying and bagging systems, that ensure the simple and reliable handling of produced lignin.
Lignin as fuel in the lime kiln
Lignin is also an excellent fuel for the lime kiln. Valmet can supply modifications to the lime kiln burner and surrounding systems.
How much lignin can be removed from the black liquor?
Many pulp mills can extract up to around 25 percent of the lignin without modifying the existing mill equipment. The Stora Enso Sunila mill is designed to produce 50,000 metric tonnes of lignin per year, or 22 percent of the lignin. Lignin lean black liquor and wash water can be evaporated like a normal black liquor, and if the production of pulp is increased and the mill’s energy consumption is reduced, up to 70 percent of the lignin can be removed.
We bring our customers’ performance forward
Valmet is expert in lignin extraction and pulp mill processes. To discover how we can help you bring your lignin business forward, get in touch with us through the “contact us” pages or your local Valmet office.