Method and arrangement for the separation of tall oil products from black liquor

Abstract

A method and arrangement for separating tall oil products from a black liquor-containing boiling liquid that has been drained off, was produced within a kraft mill chip digester, and includes a fibrous cellulose material in a mixture with the black liquor and tall oil products, and where the boiling liquid is separated in a separation unit arranged to mechanically separate the boiling liquid into a fibrous cellulose material and a mixture of mixed black liquor and tall oil products, where the mixture of boiling liquid and tall oil products is brought to a separation tank, the separation tank being a gravity separation tank, and adapted to be emptied in a discontinuous manner of the tall oil product collected and concentrated therein, the tall oil products being floated on top of and above a fraction of mixed black liquor, where the tall oil products is brought to a centrifugal separator.

Claims

1. A method for the separation of tall oil products from a black liquor, comprising: draining off boiling liquid that has been produced in a kraft mill chip digester, where said boiling liquid comprises a fibrous cellulose material in a mixture with said black liquor and tall oil products; mechanically separating the boiling liquid in a separation unit for the production of the fibrous cellulose material and the mixture of black liquor and tall oil products; adapting the mixture of black liquor and tall oil products to a mixed black liquor by addition of intermediate black liquor; bringing the mixed black liquor to a gravity separation tank, adapted for being emptied of collected and concentrated tall oil products in a discontinuous manner; floating said tall oil products to become positioned above and resting on a fraction of the mixed black liquor; bringing said concentrated tall oil products from the separation tank to a mixing tank for mixing; pumping said concentrated tall oil products from the mixing tank, through a pumping unit, to a centrifuge separator; bringing the concentrated tall oil products and the mixed black liquor contained to an inlet of said centrifugal separator; and said centrifugal separator generating centrifugal forces, allowing concentration of the tall oil products to a solid structure, wherein the solid structure has a solid form that is too hard to be pumped in a simple manner, the solid form is adapted to be diluted with water to the extent that it can be pumped, the thus diluted tall oil products are pumped to a tank.

2. The method according to claim 1, further comprising homogenizing the diluted tall oil products in the tank.

3. The method according to claim 1, further comprising the separation tank, by addition of mixed black liquor, elevating concentrated tall oil products, which by said elevation flows through a skimmer to the mixing tank before, through a pumping unit, being pumped to the centrifuge separator.

4. The method according to claim 2, further comprising feeding the tall oil products separated from mixed black liquor, to a digestion facility which, through addition of an acid at a pH of approximately 3.5, forming raw tall oil and acid water, lignin and salts as rest products.

5. The method according to claim 2, further comprising choosing a proportion of raw tall oil of 50 to 70 wt %, as a mixture of the tall oil products and mixed black liquor downstream of the centrifugal separator.

6. The method according to claim 5, further comprising feeding separated mixed black liquor fractions from the centrifugal separator to the added mixture of mixed black liquor with tall oil products, or directly to a lower portion of the separation tank.

7. An apparatus for separation of tall oil products from a black liquor containing boiling liquid produced within a kraft mill chip digester, where said boiling liquid comprises a fibrous cellulose material in a mixture with said black liquor and tall oil products, adapted to a mixed black liquor by the addition of intermediate black liquor, where the arrangement comprises: a separation unit adapted to mechanically separate the boiling liquid from the fibrous cellulose material; a gravity separation tank adapted for being emptied of the tall oil products collected and concentrated therein in a discontinuous manner, said tall oil products being floated on top of and above a fraction of mixed black liquor; a mixing tank adapted to receive said concentrated tall oil products from the gravity separation tank; a centrifugal separator arranged to be fed with and further concentrate said concentrated tall oil products, and where the centrifugal separator is arranged to, through the generation of centrifugal forces, separate and further concentrate the tall oil products to such an extent that the tall oil products are available in a solid and hard structure, wherein the solid structure has a solid form which is too hard to be pumped in a simple manner; a mixer adapted to dilute the solid form with water so that it becomes possible to pump; and a pump arranged to pump the thus diluted tall oil products to a tank.

8. The apparatus according to claim 7, wherein said tank is a homogenization tank.

9. The apparatus according to claim 7, wherein said pump is a displacement pump.

10. The apparatus according to claim 8, wherein said tank is arranged to supply tall oil products, partly separated from mixed black liquor, to a digestion facility in the arrangement, which allows the formation of a raw tall oil and acid water, lignin and salts as rest products by the addition of an acid to a pH of 3.5.

11. The apparatus according to claim 7, wherein a mixture of tall oil and black liquor downstream of the centrifugal separator is chosen with a proportion of raw tall oil of 50 to 70 wt %.

12. The apparatus according to claim 11, wherein the centrifugal separator is arranged to feed separated fractions of mixed black liquor to the mixed black liquor in separation tank which comprises tall oil products, alternatively to the lower portion of the separation tank.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The prior art and a proposed embodiment that has the characterizing features of the invention, shall now be described in an example with reference to the attached drawing in which:

(2) FIG. 1 shows, as a schematic block diagram, a part of a known arrangement within a kraft mill and where mixed black liquor is added to a separation tank for gravity separation of concentrated tall oil products from said mixed black liquor,

(3) FIG. 2 shows, as a schematic block diagram, a part of a known arrangement for the separation of tall oil products from black liquor or mixed black liquor, that uses two buffer soap tanks and for addition of tall oil products to a digestion facility, and

(4) FIG. 3 shows, as a schematic block diagram, a method and an arrangement according the invention, for a stepwise separation and concentration of tall oil products from mixed black liquor through a centrifugal separator and where the two buffer soap tanks of FIG. 2 have been eliminated.

DEFINITIONS

(5) The current invention has as its main task to allow the concentration of a mixture of gravity-separated tall oil products (soap) and black liquor and mixed black liquor fractions mixed therein.

(6) For this purpose, the invention uses a compressing means which in the disclosed embodiment is illustrated by a centrifugal separator.

(7) Said tall oil products and the black liquor or mixed black liquor mixed therein will through this process be available with variable states of compression, where at least the following different grades of compression should be mentioned. a) A higher (the highest) state of compression where the included tall oil products (soap) and mixed black liquor mixed therein is in a solid form and as such displays a “sausage”-like structure and shall be considered to display a structure corresponding to a non-viscous fluid. b) A lower grade of compression where the included tall oil products (soap) and mixed black liquor mixed therein is present in a mousse- or slurry structure by the addition of water to the highest grade of compression and where this structure is adapted to only with difficulty be pumped with the aid of displacement pumps and similar.

(8) Description of a Prior Art Arrangement According to FIGS. and 1 and 2.

(9) FIG. 1 shows a schematic block diagram of a prior art arrangement “A” within a kraft mill plant, with a chip digester “K”.

(10) The chip digester K is fed with wooden chips through a conduit 1 and white liquor through conduit 2 in a manner that is previously known.

(11) Wooden chips and white liquor is then boiled in the chip digester “K”, whereupon the boiling liquid is drained off through conduit 3, to a mechanical separator unit “S” in order to separate the fibrous cellulose material, which through a conduit 4, is transported to a plant for the manufacturing of paper pulp.

(12) The separation unit “S” also separates tall oil products mixed with black liquor or mixed black liquor, through a conduit 5.

(13) The boiling liquid, having been separated from the fibers, is now referred to as weak black liquor, passes through conduit 5 and is mixed with intermediate black liquor 7 from an evaporator “I” in order to produce mixed black liquor through conduit 5a.

(14) The mixed black liquor (5a) also contains small amounts of fibrous material which can be concentrated in an evaporator “I” connected to conduit 7.

(15) The mixed black liquor (5a) with approximately 23 wt % tall oil products passes through the conduit 5a to a separation tank “SE”.

(16) FIG. 2 part A shows a known part of an arrangement between the separation tank “SE” and a first buffer soap tank “C1” while part B shows a following part of an arrangement between the first buffer soap tank C1 and a connecting and following homogenization tank and a digestion facility “SP”.

(17) FIG. 2 parts A and B shows that said separation tank “SE” by way of conduit 11 is connected to a buffer tank “B1” which in turn, by way of conduit 12, is serially connected to the first soap buffer tank “C1” which in turn, by way of conduit 13, is serially connected to a second soap buffer tank “C2”, which in turn, by way of conduit 14, is connected to digestion facility “SP” through a homogenization tank “H” and a conduit 15.

(18) The two soap buffer tanks “C1:C2” can be different or identical and with a chosen flow velocity so that the storage time will be in the magnitude of 3 to 4 weeks, with a gravity separation of and concentration of tall oil products (soap) within the top portion of the tanks while a mixed black liquor fraction and its black liquor fraction is collected in the lower portion of the tanks, which is being drained off as waste liquor.

(19) FIG. 2 parts A and B shows certain information regarding volumes and suitable tall oil product weight percentages of the soap.

(20) The present invention is based on, i. a. on the elimination of the two buffer soap tanks in FIG. 2.

DESCRIPTION OF A SUGGESTED EMBODIMENT

(21) The following is a description of a suggested embodiment, which shows the features of the invention. It should initially be pointed out that we have chosen the wording and the terminology of the description in order to make the idea of the invention clear.

(22) However, it should be said that the chosen expressions shall not be considered to be limited to the terminology used herein, but that it shall be understood, that every chosen term shall be interpreted to also include all technical equivalents that work in the same, or essentially the same, manner, in order to achieve the same or essentially the same technical effect.

(23) With reference to the attached FIGS. 1, 2 and 3, but in particular FIG. 3, it is thus shown, schematically and in detail, not only the features of the current invention but also the important peculiarities of the invention.

(24) Thus, FIG. 3 shows, with reference to FIGS. 1 and 2, the presence of a separation tank “SE” serially connected through conduit 21 with a mixing unit “BE” in the form of an initial or first homogenization tank, and which, through conduit 22, is connected to the inlet 23a of a centrifugal separator “CS” which allows the separation of light tall oil products from heavier black liquor or mixed black liquor products 28 and which through a piece of conduit (virtual conduit) 23 brings the tall oil products to a mixer “VB”.

(25) Since the form of, and the rheological properties of, the tall oil products which leaves the outlet 23b of the centrifugal separator “CS” in a compressed form, shall be chosen as to be so solid that the tall oil products cannot easily be pumped with the use of ordinary displacement pumps dimensioned for a fluid transport, but must be pumped with a special pump, it is suggested that the outlet 23b of the centrifugal separator is connected directly to the mixer “VB”.

(26) The tall oil products are mixed in the mixer with a very small portion of water (not black liquor or mixed black liquor) and are then pumped, through conduit 24, to a finalizing homogenization tank “H” for, as a mousse- or slurry structure, be brought to the digestion facility “SP” in the way indicated according to FIG. 2, part B.

(27) With regard to the method and the arrangement, the invention separates tall oil products (soap products) from a black liquor-containing boiling liquid that has been drained off, said boiling liquid having been produced within a kraft mill chip digester, where said boiling liquid comprises a fibrous cellulose material and a mixture of said black liquor and tall oil products, and where the boiling liquid is mechanically separated in a separator unit “S” into a fibrous cellulose material and a mixture of black liquor and tall oil products, and where the mixture of black liquor and tall oil products, after addition of intermediate black liquor, is brought to a separation tank “SE” where gravity separation takes place, said separation tank being adapted for being discontinuously emptied of collected and gravity-separated tall oil products “TP”, which through flotation are positioned above and floating on a black liquor and mixed black liquor fraction “SA”, and where said concentrated tall oil products are brought, through conduits 21 and 22 to a means for separating and concentrating tall oil products, here illustrated as a centrifugal separator “CS”.

(28) According to the invention described in FIG. 3, said concentrated tall oil products “TP” with a limited content of black liquor or mixed black liquor shall be brought to the inlet 23a of said centrifugal separator “CS”, said centrifugal separator being adapted to, through the generation of centrifugal forces, concentrate the tall oil products with its limited fraction of black liquor or mixed black liquor, so that it is available in a solid form or at least a form that is very viscous mousse- or slurry-form “MK” in the conduit part 23.

(29) The form shall be chosen to be so concentrated and hard as is practically possible, usually too hard to be pumped in a simple manner, the form having a high rheological units and can be adapted to be diluted with water or such, to a form that can be pumped, with only slightly lower rheological properties to be able to be pumped to a tank “H”.

(30) It is preferred that said tank “H” shall serve only as a homogenization tank with a stirrer.

(31) The separation tank “SE” can then be adapted to, through the addition of mixed black liquor elevate the concentrated tall oil products “TP” which by said elevation can flow to the mixing unit “BE” through a skimmer 21a, before they, by a pumping unit, is pumped to the inlet 23a of the centrifugal separator “CS”.

(32) The tall oil products, separated from black liquor and/or mixed black liquor will be fed from said homogenization tank “H” to a digestion facility “SP” which through the addition of an acid (H.sub.2SO.sub.4) with a pH of approximately 3.5 will form raw tall oil 27 and acid water, precipitated lignin and salts as rest products 26.

(33) The mixture of tall oil products and black liquor or mixed black liquor downstream of the centrifugal separator 23b, 23 is chosen such that the percentage of tall oil products in the soap is from 50 to 70%, preferably approximately 60 wt. %.

(34) Separated black liquor or mixed black liquor fractions 28 from the outlet 23c of the centrifugal separator “CS” is fed to the added mixed black liquor 5a, alternatively directly to the lower portion of the separation tank “SE”.

(35) It can be assumed that the tall oil products gathered by flotation in the top portion of the separation tank will assume a structured layering with a higher concentration of tall oil products at the top and a successively lower concentration of tall oil products thereunder.

(36) It is the intention of the invention to drive the compression of solid compressed tall oil products downstream of the centrifugal separator 23b, 23 as far as practically possible, in order to separate the tall oil products from mixed black liquor, even if it is not practically possible to allow the complete separation of tall oil products only.

(37) FIGS. 1 to 3 show the presence of several pumping units on selected conduits, however with no position numbers.

(38) The conduit 23 does not, however, comprise a physical pumping unit.

(39) However, it should be noted that it is of course possible, within the limits of the invention, to also for this conduit 23 have a purpose built pumping unit, designed and dimensioned for being able to pump and move very viscous material, between the outlet of the centrifugal separator “CS” to the inlet of the water mixer “VB”.

(40) Within the invention is also the insight that the material fed from the outlet 23b of the centrifugal separator shall have such a high concentration of solid tall oil products that is practically possible.

(41) Furthermore, FIGS. 1 to 3 show conduits 5 that transport weak black liquor or black liquor with 14-15% TS and tall oil products and a conduit 5a for mixed black liquor with 23% TS and tall oil products.

(42) The conduit 7 allows the transport of intermediate black liquor.

(43) FIGS. 2 and 3 show a number of conduits 10, 10a that transport mixed black liquor to an evaporator “I”, alternatively black liquor to waste liquor.

(44) The volume of added water in the water mixer “VB” shall be as small as possible, however enough to let the solid material 23 to obtain a mousse or slurry form that can be pumped.

(45) This small amount of water passes through the homogenization tank “H” and will be mixed with the added acid in the digestion facility “SP”.

(46) The design of the displacement pump can be chosen to be an ordinary displacement pump with a rotor and a stator, alternatively an equivalent displacement pump such as a gear pump, a lobe pump or similar.

(47) The invention is not limited to the embodiment given as an example above, but can be modified within the spirit of the invention as defined in the claims.

(48) In particular it should be noted that each shown unit and or circuit can be combined with every other unit and/or circuit within the limit in order to achieve the technical effect.