New process extracts lignin from pulp mill black liquor
LignoBoost works in conjunction with evaporation. It all starts with lignin being precipitated from the black liquor by lowering the pH with CO2. The precipitate is then dewatered using a filter press. LignoBoost then overcomes conventional filtering and sodium separation problems by redissolving the lignin in spent wash water and acid. The resulting slurry is once again dewatered and washed, with acidified wash water, to produce virtually pure lignin cakes. The lignin can be exported or, after final drying, be used as fuel in the lime kiln.
Extracted lignin has numerous profitable uses. Lignin is an outstanding biofuel with high heat value. It can be used at mill, for instance
- as a fuel in a power boiler
- to replace oil in a lime kiln
When it comes to lime kilns the potential savings of using lignin are as much as 50 liters (13 gallons) of fuel oil per ton of pulp. For a mill with an annual production of 200 000 tons of pulp the savings potential is 10 000 m3 (2.6 million gallons) of oil.
Green energy produced from lignin can be profitably exported as process steam or power, or simply sold as fuel in the form of pellets or powder. Lignin is also a good raw material for making specialty chemicals, making it a very interesting substance for the chemical industry where many companies are looking for renewable raw materials. In addition, there have been successful trials at making carbon fibers from lignin. Both exporting lignin as fuel and selling it on for further refining give pulp mills opportunities for new sources of income.