Manufacture of fiberboard according to the wet method with closed backwater system

Abstract

An improved method for the manufacture of wood fiberboard according to the wet system with a closed white water system includes the steps of drying the incoming lignocellulose containing material, prior to the dilution step, to a dryness, or solid consistency, which is higher than the dryness of the wet lap or sheet before final drying to produce the fiberboard product. Formaldehyde is added to the resulting white water which is homogenized to atomize occurring precipitations through efficient agitation and dispersion prior to being recirculated for use for diluting the incoming fiber material. Thus, there is obtained an efficient closed white water system which results in a reduction of environmentally harmful discharge of polluted water as well as the production of fiberboard with enhanced appearance.

We claim: 
     
       1. In the method of manufacturing wood fibreboard according to the wet system with closed white water system including defibrating lignocellulose material, diluting the defibrated material in water serving as the transporting medium, forming wet sheets from the diluted pulp, mechanically separating white water obtained from the formation of wet sheets and recirculating it to the dilution stage and final drying by evaporation of water from the wet sheets, the production of fibreboard having enhanced appearance while maintaining a closed white water system with reduced discharge of pollutants to the environment including drying the incoming lignocellulose material, prior to the dilution step, to a .[.dry content from 60 percent to 75 percent.]. .Iadd.dryness .Iaddend.which is higher than the dryness of the wet sheet prior to the time it enters the final drying stage, the improvement comprising adding formaldehyde to the white water, homogenizing the white water containing said formaldehyde to a degree such that occurring precipitations are atomized prior to using it for dilution of incoming fibre material. 
     
     
       2. An improved method according to claim 1, in which the homogenization of the white water occurs in the white water chests. 
     
     
       3. An improved method according to claim 1, in which the homogenization is brought about by agitation and dispersion through the use of a stirrer. 
     
     
       4. An improved method according to claim 1, wherein the formaldehyde is added in the amount of 0.02-0.5 percent based on the fibre weight.