Method for controlling hydrophobic particles in aqueous environment in paper or board manufacture

Abstract

The invention relates to a method for controlling hydrophobic particles in aqueous environment in paper or board manufacture. The method comprises preparing an aqueous stock comprising natural fibrous material, feeding the stock to a wire section, where a fibrous web is formed by draining excess water through a wire, and adding a control chemical to aqueous environment at least in one dosage point between the preparation of the stock and the exit of the web from the wire section. The control chemical comprises performic acid, which is added to the aqueous stock, which has consistency of at least 3 weight-%.

Claims

1. A method for decreasing hydrophobic particles in aqueous environment in paper or board manufacture, the method comprising: preparing an aqueous stock comprising natural fibrous material, feeding the stock to a wire section, where a fibrous web is formed by draining excess water through a wire, adding a control chemical to aqueous environment at least in one dosage point between the preparation of the stock and the exit of the web from the wire section, wherein the control chemical comprises performic acid and it is added at least in one dosage point to the aqueous stock, which has consistency of at least 3 weight-%.

2. The method according to claim 1, wherein the hydrophobic particles are present in the aqueous environment at the time of addition of the control chemical.

3. The method according to claim 1, wherein the control chemical comprising performic acid is added to the aqueous environment in two or more dosage points.

4. The method according to claim 1, wherein at least 40%, preferably at least 45%, more preferably at least 50%, of the total amount of the control chemical is added to the aqueous stock having consistency of at least 3 weight-%, in one or more dosage points.

5. The method according to claim 1, wherein the method further comprises the steps filtering the water drained through the wire and adding control chemical also to superclear filtrate from the filtration in one or more dosage points.

6. The method according to claim 5, wherein at least 5%, preferably at least 10%, more preferably at least 15%, of the total amount of the control chemical is added to the superclear filtrate.

7. The method according to claim 1, wherein the control chemical is added in such amount that the total performic acid dosage is 0.2-2 kg/ton, preferably 0.5-1.5 kg/ton, more preferably 0.7-0.9 kg/ton.

8. The method according to claim 1, wherein the control chemical is added in two or more dosage points, whereby at least 50% of the total performic acid dosage is added to the aqueous stock having consistency of at least 3 weight-%.

9. The method according to claim 1, wherein the control chemical consists of an aqueous equilibrium solution of performic acid.

10. The method according to claim 1, wherein the paper manufacture process is a tissue process and that the produced fibrous web is a tissue web.

11. The method according to claim 10, wherein the aqueous environment has a pH value in the range of 7.0-8.2, preferably 7.5-8.0.

12. The method according to claim 1, wherein the produced fibrous web has a grammage of 11-45 g/m.sup.2, preferably 13-20 g/m.sup.2.

13. The method according to claim 1, wherein the natural fibrous material comprises recycled cellulosic fibres.

14. The method according to claim 1, wherein the amount of hydrophobic particles in the aqueous environment is monitored, and the addition of the control chemical is adjusted according to the monitored amount of hydrophobic particles.

15. The method according to claim 1, wherein at least one biocide, which is different from the control chemical, is added to at least one location, which is selected from the machine silo, headbox, mixing chest and broke chest.

Description

EXPERIMENTAL

[0029] An embodiment of invention is more closely described in the following non-limiting example.

Example 1

[0030] A trial was conducted in a tissue mill using a stock comprising 20-30 hardwood and 70-80% softwood. Hydrophobic particles were present in the water circulation of the tissue mill. Their amount and mean particle size was observed by using flow cytometry using selective fluorescence dye to stain the hydrophobic particles.

[0031] The control chemical tested was an equilibrium solution of performic acid, peracetic acid and peroxide.

[0032] In the trial the control chemical was added to the thick stock of the tissue mill, as well as to the superclear filtrate, the silo and overflow white water from the silo.

[0033] The total dosage of added control chemical was about 4 kg/ton dry stock in the start of the trial and then the dosage was gradually decreased to about 1.6 kg/ton dry stock.

[0034] The results are shown in FIG. 1, which shows the effect of addition of control chemical comprising performic acid to the total amount of hydrophobic particles in the short loop of the tissue machine. The start of the control chemical is indicated with an arrow. It can be see that amount of hydrophobic particles is lower and more stable than before the start of the feed. This means that the hydrophobic particles in the system are easier to manage and the risk for depositions are reduced.

[0035] Even if the invention was described with reference to what at present seems to be the most practical and preferred embodiments, it is appreciated that the invention shall not be limited to the embodiments described above, but the invention is intended to cover also different modifications and equivalent technical solutions within the scope of the enclosed claims.