Method for preparing biomechanical unbleached pulp from wheat straw and full utilization of by-products thereof

A method for preparing biomechanical unbleached pulp from wheat straw and full utilization of by-products thereof, wherein the method comprises the following steps:

• (1) cutting a physically-screened and dust-removed wheat straw into small pieces of 1-8 cm as raw materials, putting them into a processor or a reactor, and performing a hot water treatment according to a liquid ratio of 1:4-1:8 for 15-90 min to obtain a mixture of hot water and a hot water treated wheat straw in the reactor or processor;
• meanwhile collecting rotten wheat straw which cannot be used for processing;
• (2) adding KOH to the mixture of hot water and the hot water treated wheat straw in the reactor or processor, adjusting pH of the hot water to 10-14, and performing a hydrothermal saturation and softening treatment on the wheat straw to obtain a hydrothermally saturated and softened wheat straw;
• collecting waste lye;
• (3) treating the hydrothermally saturated and softened wheat straw with an alkaline biological compound enzyme in a biological processor for 30-90 min in a liquid ratio of 1:3-1:8 (W/V) to obtain an enzyme treated wheat straw;
• collecting wastewater produced in an enzyme treatment stage;
• (4) refining the enzyme treated wheat straw after treatment in step (3) with a pulp refiner to obtain a refined wheat straw;
• and
• (5) washing the refined wheat straw to obtain a biomechanical pulp;
• disintegrating and mixing the biomechanical pulp homogeneously with a fiber disintegrator to obtain an unbleached pulp, collecting refining washing water;
• treating the waste lye, the wastewater produced in the enzyme treatment stage, and the refining washing water with a multi-effect evaporator to prepare residue by evaporation and concentration, and recycling heat energy for use in the hot water treatment stage of step (1);
• mixing the residue and the rotten wheat straw which cannot be used for processing in step (1) and adjusting pH thereof to prepare fertilizer.