kraftprocessen

The kraft process, also known as the sulfate process, is the most common method for pulping wood to produce paper. It is a chemical pulping process that separates lignin from cellulose fibers. In this process, wood chips are cooked in a strong alkaline solution, primarily sodium hydroxide and sodium sulfide, in a large pressure vessel called a digester. This mixture is known as white liquor. The heat and chemicals break down the lignin, which acts as a binder holding the wood fibers together.

After cooking, the resulting slurry is a mixture of cellulose fibers and spent pulping chemicals, called black liquor. The black liquor is then washed from the fibers. The spent chemicals are recovered and regenerated in a complex chemical recovery system. The black liquor is concentrated and burned in a recovery boiler, which generates steam for the process and recovers inorganic chemicals. These chemicals are then reconstituted into white liquor for reuse.

The cellulose fibers, now separated and cleaned, are bleached to achieve the desired brightness for papermaking. The kraft process is highly efficient in lignin removal, producing strong paper fibers. However, it also generates significant amounts of byproducts, including sulfur compounds, which can lead to odors if not properly managed. The byproducts can also be a source of valuable chemicals, such as tall oil and turpentine. The strength of the resulting paper is a key advantage of the kraft process, making it suitable for a wide range of paper products, from packaging to printing paper.