Circular utilization method in pulping and papermaking processes with straw

A circular utilization method in pulping and papermaking processes with straw, wherein the method comprises the following steps:

• (1) among raw materials from farm planting, greenhouse planting and garden, selecting straw raw material that is suitable for pulping, obtaining straw raw material for pulping through stock preparation, obtaining a pulp with a hardness of Kappa number 24-50 by digestion, then obtaining pulp by extruding and washing, performing post-treatment for pulp to obtain paper pulp, and manufacturing paper product;
• (2) extracting a black liquor during extruding and washing the pulp with a hardness of Kappa number 24-50, and obtaining a concentrated black liquor by evaporation and concentration, which is used as a first fertilizer for circularly returning to farm planting, greenhouse planting and garden for utilization;
• (3) generating ammonium sulfite by mixing a contaminated condensate obtained by evaporation and concentration of the black liquor with gas desulfurization, and circularly using the ammonium sulfite in digestion;
• (4) in step (1), obtaining a waste after stock preparation, mixing the waste with the contaminated condensate, obtaining a second fertilizer by fermentation, returning the second fertilizer to farm planting, greenhouse planting and garden for utilization, which can result in the circular availability of straw raw material;
• (5) using recycled water from mid-phase water processing in corresponding phases in a whole pulping process,
• the mid-phase water processing including filtration, flocculation settling, biochemical treatment, and advanced treatment,
• the advanced treatment including a precipitation separation step;
• the flocculation settling being performed by up-flow physical and chemical bed (UPCB) treatment;
• the UPCB treatment including:
• at first a wastewater mixed with flocculants being introduced into a hybrid reaction layer of a UPCB reactor;
• then facultative, aerobic and cyclic sludge being added into the wastewater at a boundary between the hybrid reaction layer and an augmented reaction layer;
• after the reaction in the augmented reaction layer, flocculants being added or not added into the wastewater, and the wastewater being delivered into an adsorption filtration layer in UPCB;
• the post-treatment including defibering and oxygen delignification;
• wherein the wastewater mixed with the flocculants enters a bottom of the UPCB reactor along a tangent, with an upward declination angle of 15-45°;
• and
• a hydraulic retention time is controlled within 4-10 hours.