A kind of lye multistage recovery process

Abstract

An alkali liquid multi-stage recovery process is disclosed, belonging to the technical field of viscose fiber production, papermaking, and the like. The process includes first-stage dilution, first-stage filtration, second-stage dilution, first-stage temperature rising, second-stage filtration, second-stage temperature rising, third-stage filtration, third-stage dilution and fourth-stage filtration. Different devices are adopted by combination of process characteristics, namely different nanofiltration systems are adopted in different process stages so that the process adapts to alkali liquidrecovery better. Multi-stage dilution and temperature rising and other types of treatment are adopted to reduce the viscosity of fed liquid, increase the net liquid flux, and reduce differential pressure among films, thus ensuring controllable, stable and efficient alkali liquid recovery.

Description

Technical field[0001]The invention relates to a lye recovery process, in particular to a lye multi-stage recovery process, belonging to the technical fields of viscose fiber production, papermaking and the like.Background technique[0002]In the production of viscose fiber and the paper industry, the raw pulp needs to be impregnated, and the treatment method is generally: dissolve the semi-fiber, resin, ash, etc. in the pulp by using lye to form porridge, and then press The method removes the semi-fiber, resin, ash, etc. in the porridge, and reuses the squeezed lye containing semi-fiber, resin, ash, etc. in the impregnation. However, after repeated use of the lye, the content of semi-fiber, resin, ash, etc. in the lye will gradually increase. When the semi-fiber, resin, ash, etc. reach a certain concentration (ie "black liquor"), the lye will Can not be reused, and form waste lye. Nowadays, under the multiple requirements of environmental protection and energy saving, most companies r...

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Problems solved by technology

[0004] In the filter residue of the recovery process, the concentration of sodium hydroxide is continuously decreasing, and the concentration of hemifiber is continuously increasing, and in the process of increasing the concentration of hemicellulose, the viscosity of waste lye is also continuously increasing, so the penetration of the coarse filtrate in the nanofiltration membrane As the pressure keeps dropping, the concentration polarization on the surface of the membrane layer also keeps increasing, resulting in a drop in filtration efficiency. When the efficiency drops to a certain limit, the entire alkali recovery system will have the following problems:

[0005] 1. The viscosity of waste lye rises, and the pressure difference between the inlet and outlet of the nanofiltration membrane is large, causing serious damage to the membrane core (the membrane system’s inlet and outlet membrane pressure difference exceeds 3bar, which will cause damage to the membrane core);

[0006] 2. The high content of hemicellulose in the waste lye causes serious concentration polarization of the membrane layer, which makes the membrane layer seriously polluted, thereby reducing the filtration efficiency of the membrane

The viscosity of the spent lye increases, the osmotic pressure of the membrane layer decreases, and the flux of the filtrate also decreases, which makes the filtration efficiency low and cannot meet the needs of industrial production.

[0007] Due to the above technical problems, the current average recovery rate of spent lye is lower than 60%. Some staple fiber factories even use the concentrated solution of spent lye directly for yellowing, sacrificing product quality to reduce the concentrated solution of spent lye emissions

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