Method and device for feeding at least one chemical substance into a main process stream

Abstract

The present invention concerns a method and a device for feeding at least one chemical substance into a main process stream. The method of the invention comprises the steps of providing a concentrated stream of said chemical substance, mixing said concentrated stream with a diluent stream to provided a diluted stream of said chemical substance, injecting said diluted stream of said chemical substance into said main process stream, wherein said mixing of said concentrated stream with said diluent stream is effected by injecting a jet of either one of said concentrated stream or said diluent stream into the respective other stream. The device of the invention comprises a first pipe segment (21) having a first inlet (22) for a first fluid and a first outlet (23) for a mixed fluid, a second pipe segment (24) having a second inlet (25) for a second fluid and a second outlet (26) connected to and leading into said first pipe segment (21) between said first inlet (23) and said first outlet (24), and first connection means (27) for connecting said first outlet (23) of said first pipe section (21) to a main pipe (14) of said main process stream, wherein said second pipe segment (24) comprises at least one nozzle (28) for generating a jet (29) of said second fluid arranged upstream of said second outlet (26).

Claims

1. A method of feeding at least one chemical substance into a main process stream of a paper making process, the main process stream comprising a pulp suspension, the method comprising: mixing a concentrated liquid stream of at least one chemical substance selected from the group consisting of a retention chemical and other additive for improving and/or modifying paper properties with a diluent liquid stream to obtain a diluted liquid stream of said chemical substance; and injecting a jet of said diluted liquid stream of said chemical substance into a main process stream comprising a pulp suspension, wherein said mixing of said concentrated liquid stream with said diluent liquid stream is effected by injecting a jet of either one of said concentrated liquid stream or said diluent liquid stream into the respective other stream at an injection angle of from 15 to 90 through a nozzle having a spray angle in the range of 10 to 120 selected such that said spray angle of said injected jet essentially covers the diameter of said respective other stream, and wherein said diluent liquid stream is not supplied by diverting a portion from said main process stream.

2. The method of claim 1, wherein said diluent liquid stream is injected into said concentrated liquid stream of said chemical substance.

3. The method of claim 1, wherein more than one diluted liquid stream is injected into said main process stream.

4. The method of claim 3, wherein said more than one diluted liquid stream is injected into the main process stream at locations which are offset with respect to each other.

5. A device for feeding at least one chemical substance into a main process stream of a paper making unit, the main process stream comprising a pulp suspension; the device comprising: a first pipe segment having a first inlet for a first fluid and a first outlet for a mixed fluid; a second pipe segment having a second inlet for a second fluid and a second outlet connected to and leading into said first pipe segment between said first inlet and said first outlet, wherein said second pipe segment is connected to said first pipe segment at an injection angle of from 15 to 90; and a first connector for connecting said first outlet of said first pipe segment to a main pipe of said main process stream, wherein said first connector comprises a first exchangeable connection flange housing an injection nozzle for generating a jet of said mixed fluid, wherein said second pipe segment comprises at least one spray nozzle having a spray angle in the range of 10 to 120 for generating a jet of said second fluid arranged upstream of said second outlet, said spray angle being selected such that spray angel of said injected jet essentially covers the diameter of said respective other stream, and wherein said second fluid is not supplied to the second pipe segment from said main pipe.

6. The device of claim 5, wherein said spray nozzle is a flat fan nozzle, a hollow cone nozzle or a full cone nozzle.

7. The device of claim 5, wherein said second inlet of said second pipe segment comprises a second connector for connecting said second pipe segment to a feed pipe for said second fluid.

8. The device of claim 7, wherein said second connector comprises a second exchangeable connection flange housing said spray nozzle for generating a jet of said second fluid.

9. The device of claim 5, wherein the spray angle of said spray nozzle is approximately 150.

10. The device of claim 5, wherein said second pipe segment is connected to said first pipe segment at an injection angle of approximately 45.

11. The device of claim 5, wherein the distance between said spray nozzle opening and the center of the other stream is 10 to 30 times the diameter of said spray nozzle.

Description

IN THE DRAWINGS

(1) FIG. 1 is a very schematic drawing of a paper machine fed with a pulp suspension through a main process pipe; and

(2) FIG. 2 depicts a device according to a preferred embodiment of the invention for feeding a retention chemical to the pulp suspension, shown in a cross-sectional view perpendicular to the main process pipe.

(3) FIG. 1 depicts very schematically a paper machine 10 which is merely exemplified by a headbox 11, a roll 12 and a paper web 13. The headbox 11 is fed with a pulp suspension via a main process pipe 14. The usual water circulation, suspension preparation and mixing tanks, pumps, filters, gas separation tanks etc. used in the paper manufacturing process are not depicted for the sake of simplicity. A retention chemical is prepared as concentrate solution in a concentrate tank 15 and fed via concentrate feed pipe 16 towards main process pipe 14. Before reaching the main process pipe 14, the concentrated solution is diluted at a pre-mixing point 17 by injecting a diluent stream vial diluent line 18 into the concentrate stream. The diluent line 18 can be connected to a water supply or can be branched off from main process line 14. The diluted stream is fed to the main process pipe 14 via pipe segment 19.

(4) In FIG. 2, a device according to a preferred embodiment of the invention for feeding a retention chemical the pulp suspension is described in more detail. Specifically, the device of the invention is installed at the pre-mixing point 17 of the scheme of FIG. 1 for diluting the concentrate stream of the retention chemical.

(5) The device of the invention is generally denoted by reference sign 20 and comprises a first pipe segment 21 having a first inlet 22 for the concentrated retention chemical stream which is connected to concentrate feed pipe 16 and a first outlet 23 for the diluted retention chemical which is connected via pipe 19 to the main process pipe 14 which is depicted in a cross-sectional view. A second pipe segment 24 is permanently connected to the first pipe segment 21 at an injection angle of 45 and has a second inlet 25 for a diluent which is connected to diluent feed pipe 18 and a second outlet 26 which leads into the first pipe segment 21 between said first inlet 22 and said first outlet 23. First connection means 27 are provided for connecting the first outlet 23 of the first pipe section 21 to the main pipe 14 of the main process stream.

(6) The second pipe segment 24 comprises at least one spray nozzle 28 for generating a jet 29 of the diluent stream which is injected into the concentrated stream of the retention chemical. The spray nozzle 28 is arranged upstream of the second outlet 26. In the present case, the nozzle is a flat fan nozzle generating a spray angle of approximately 15.

(7) The first connection means 27 comprises an exchangeable connection flange 30 housing an injection nozzle 31 for injecting a jet of said mixed, diluted fluid into said main process pipe 14. The injection nozzle can be made as insert so that the same connection flange can be used for different nozzles.

(8) The second inlet 25 of said second pipe segment 24 comprises second connections means 32 for connecting said second pipe segment to the diluent feed pipe 18. The second connection means comprise a second exchangeable connection flange 33 which houses the spray nozzle 28 for generating a jet of the diluent stream.

(9) In the embodiment of FIG. 2, two identical devices 20, 20 are used to inject diluted streams of retention chemicals into the main process pipe 14. As can be taken from the drawing, rather than being both directed towards the center 34 of the main process pipe 14, the devices 20, 20 are eccentrically arranged so that that the jets of diluted fluid injected into the main process stream do not directly point at each other. The device 20 is identical to device 20 and will therefore not be explained in further detail here.

(10) Due to effective pre-mixing when diluting the concentrated stream of retention chemical, it is possible to reduce the diluent stream by 50 to 70% thus minimizing costs for diluent water and reducing associated investment and operating costs for pumps and pipeline configuration. Despite the reduced diluent stream, an effective mixing of the diluted retention chemical stream with the pulp suspension of the main process stream can be achieved which allows the injection point to be transferred closer to the headbox. Thus loss of efficiency of the retention chemical is prevented and the total amount of retention chemical can also be reduced. Further, the injection point can be optimized to allow for sufficient time for flock formation while prevention flock degradation due to shear forces in the pipe leading to the headbox.