Patent Application
20150224449
The present invention relates to a method of processing papermaking wastewater and equipment therefor, and more particularly to a method of processing black liquor and equipment therefor which lowers operation cost in papermaking and recycles lye and concentrated black liquor.
Black liquor is one of pollution sources in papermaking industry, wherein at least 90% of pollutants in pulp manufacturing process come from COD and BOD, and 70% of solids in black liquor are organic compounds, inclusive of lignin, polysaccharides, humic acid and cellulose degradations. In addition, 30% of solids are inorganic substances, including the free salt (base) and compounds containing silicon.
Typically, the black liquor is processed by means of a lye recycling method, wherein the lye recycling method contains dehydrating the black liquor by ways of an evaporator so as to produce concentrated black liquor. Due to lignin and hemicellulose exist in concentrated black liquor at high proportion, they are burned by an alkali recovery boiler so as to become ashes with Na2Co3, and water is added to ashes to produce green liquid with small amount of iron ions, and then slaked lime is added to have recausticizing, thus generating NaOH. Finally, NaOH is recycled and used in pulp cooking process.
However, the evaporator is driven by burning coals to cause high production cost and to burn valued organics (such as lignin, turpentine, and saponified substances.
A membrane separation is served to recycle lignin in the black liquor, wherein lignin and solids are maintained by filtration membranes at a certain pressure so as to lower COD and BOD in liquor. Nevertheless, content of the solids in the black liquor is high and sticky, so filtrate liquidity decreases quickly and concentration increases to block the filtration membrane, thereby lowering recycle efficiency of lignin and increasing production cost.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.
The primary object of the present invention is to provide a method of processing black liquor which removes solids from UF membranes by ways of aeration disturbing, shear force resulting from rotating the UF membranes, and periodically scrapping the UF membranes, hence the UF membranes are not blocked so as to prolong service life and to decrease using cost of the UF membranes.
Another object of the present invention is to provide an equipment of processing black liquor which prevents the UF membranes from obstruction and prolongs service life of the UF membranes.
To obtain the above objective, a method of processing black liquor contains steps of:
A. flowing waste black liquor, which is chemically boiled, into a treatment tank, wherein the treatment tank has at least one rotary flat membrane unit formed in a circle shape and disposed in the treatment tank;
B. aerating and floating the waste black liquor in the treatment tank so as to eliminate macromolecule staple fibers and solids;
C. solid-liquor separating the waste black liquor which passes through a plurality of circularly flat UF membranes by means of vacuum pressure difference so that organic solids in the waste black liquor are remained in the treatment tank, and permeating liquor passing through the plurality of circularly flat UF membranes forms treated water;
D. periodically scrapping adhesive layers on the plurality of circularly flat UF membranes when the plurality of circularly flat UF membranes rotate so as to remove the solids and colloidal from the plurality of circularly flat UF membranes;
E. concentrating the treated water which flows through plural rear UF membranes by ways of a NF membrane so as to produce recycling lye for producing paper pulp and recyclable concentrated black liquor with high concentrations of lignin.
Also, an equipment of processing black liquor provided by the present invention contains:
a treatment tank which is an open tank for receiving waste black liquor for producing paper pulp;
at least one rotary flat membrane unit formed in a circle shape and horizontally soaked in the treatment tank, each rotary flat membrane unit having a plurality of circularly flat UF membranes equidistantly formed thereon and a water tube arranged along central positions of the plurality of circularly flat UF membranes, wherein the water tube is driven by a power unit to rotate, and a vacuum pressure difference facilitates the waste black liquor to be solid-liquor separated through the plurality of circularly flat UF membranes so as to form treated water, thereafter the treated water is flowed into the water tube by a vacuum pump;
an ultrafiltration tank mounted behind the at least one rotary flat membrane unit and communicating with the water tube so as to collect the treated water;
a scraping unit including plural rotating disks connected with the plurality of circularly flat UF membranes, a plurality of brushers radially extending outwardly from the plural rotating disks, and plural stop bars corresponding to the plurality of brushers, wherein each brusher contacts with the plurality of circularly flat UF membranes, when the plurality of circularly flat UF membranes rotate with the water tube, the plurality of brushers are stopped by the plural stop bars so that the plurality of brushers scrap the plurality of circularly flat UF membranes;
a NF membrane unit fixed behind the ultrafiltration tank so as to produce recycling lye and recyclable concentrated black liquor.
With reference to
A. Flowing waste black liquor, which is chemically boiled, into a treatment tank 10, wherein the treatment tank 10 has an open top surface, at least one rotary flat membrane unit 20 formed in a circle shape and disposed in the treatment tank 10, and an aeration unit 30 mounted on a bottom end of the treatment tank 10. Each rotary flat membrane unit 10 does not have a cover and is a horizontally open structure (i.e., an open flat membrane plate) soaked in the treatment tank 10. Also, each rotary flat membrane unit 20 has a plurality of circularly flat UF membranes 21 equidistantly formed thereon and a water tube 22 arranged along central positions of the plurality of circularly flat UF membranes 21.
B. Aerating and floating the waste black liquor by ways of the aeration unit 30, wherein the aeration unit 30 sprays pressurized microbubbles so as to eliminate macromolecule staple fibers and solids and to aerate and stir the plurality of circularly flat UF membranes 21. Moreover, in an aeration treatment, the plurality of circularly flat UF membranes 21 is driven by a power unit 23 (such as a motor) to rotate, and the power unit 23 is fixed on one end of the water tube 22, such that the water tube 22 and the plurality of circularly flat UF membranes 21 rotate concentrically so as to form a shear flow for scrubbing the plurality of circularly flat UF membranes 21, thus decreasing a growth of a gel layer (i.e., a filter cake) on surfaces of the plurality of circularly flat UF membranes 21 and maintaining water flux of the plurality of circularly flat UF membranes 21.
C. Ultrafiltrating the waste black liquor in the treatment tank 10 by means of two-stage ultrafiltration membrane separations, wherein a first-stage ultrafiltration membrane separation is used to process the plurality of circularly flat UF membranes 21 in the treatment tank 10, for example, the water tube 22 is vacuumed by a vacuum pump 40 so as to generate vacuum pressure difference, such that the waste black liquor is solid-liquor separated through the plurality of circularly flat UF membranes 21, and organic solids (such as lignin, free silica) in the waste black liquor are remained in the treatment tank 10, then permeating liquor passing through the plurality of circularly flat UF membranes 21 is flowed into a rear ultrafiltration unit 50 outside the treatment tank 10 via the water tube 22, thereafter the permeating liquor is membrane separation concentrated by using a water pump 40 and is flowed into an ultrafiltration tank 60 from the rear ultrafiltration unit 50.
D. Periodically scrapping adhesive layers on the plurality of circularly flat UF membranes 21 when the plurality of circularly flat UF membranes 21 rotate so as to remove the solids and colloidal from the plurality of circularly flat UF membranes 21. Referring to
As shown in
It is to be noted that 80% of solids in the waste black liquor are remained by/on the plurality of circularly flat UF membranes 21, the plural rear UF membranes 51 will not be obstructed, thus eliminating membrane scrapping process to the plural rear UF membranes 51.
E. Concentrating treated water which flows through the plural rear UF membranes 51 by ways of a NF membrane of a NF membrane unit 90 (as illustrated in
Thereby, the method of processing black liquor and equipment therefor is applicable for concentrated black liquor in paper industry and is served to separate the lye from the waste black liquor so that the lye is made into the paper pulp. Furthermore, the concentrated black liquor contains high concentrations of lignin. The waste black liquor is ultrafiltrated and concentrated by means of aeration disturbing, shear force resulting from rotating the UF membranes, and periodically scrapping the UF membranes so as to remove solids and colloidal from the UF membranes, thereby enhancing turbidity resistance of the waste black liquor and preventing the UF membranes from obstruction.
Preferably, each rotary flat membrane unit does not have the housing and is a horizontally open structure so as to be cleaned by water without causing obstruction, thus prolonging its service life.
As illustrated in
While the preferred embodiments of the invention have been set forth for the purpose of disclosure, modifications of the disclosed embodiments of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments which do not depart from the spirit and scope of the invention.
