Recycling of papermaking black liquor - spray drying

The main components of plant stems are cellulose, hemicellulose and lignin, cellulose accounts for about 50%, hemicellulose accounts for 15% to 25%, and lignin accounts for 15% to 30%. The current chemical pulping method utilizes only cellulose and a part of hemicellulose, and abandons lignin and a part of hemicellulose, which not only wastes resources but also pollutes the environment.

The papermaking methods commonly used at the present include alkaline methods (using sodium hydroxide or sodium sulfide, hydrazine), acid methods (using calcium bisulfite, magnesium bisulfite, sodium sulfite, etc.), ammonium methods (using ammonium sulfite) and other new methods. Method (SFP method, mechanical refining method, blasting method).

The characteristics of the various black liquors (or red liquors) before spray drying are as follows: the liquid concentration is 40% to 55%; the amount of treatment is relatively large; 1 set of 10,000 tons/year scale paper mill, the black liquor treatment capacity is greater than 3 t/h; containing more ash, the so-called silicon interference; black liquor without desugar treatment, containing a lot of sodium saccharate and its derivatives; containing many small staple fibers; high viscosity at room temperature; lignin spontaneous combustion Sex.

Therefore, the following issues should be noted when performing spray drying: preheat the concentrated black liquor to 70°C or above to reduce the viscosity of the solution; use a rotary disc atomizer to avoid clogging of the orifice of the pressure atomizer. With the air atomizer, due to the low dry powder loading density, the atomization energy consumption increases the cost; in the paper mill with the power generation device, the power station vapor can be used as the heat source, and the coal-fired hot blast stove can be directly used as the heat source after dusting with the flue gas. When the inlet air temperature is higher than 280°C, it may easily cause combustion of accumulated material in the drying tower. Therefore, the inlet air temperature must not exceed 280°C. The feed rate must be strictly controlled to prevent poor atomization and sticky walls due to excessive feeding rate, leading to burning. The phenomenon occurs.