Method for preventing scale formation

Abstract

The present invention provides a method for preventing or decreasing scale formation on process surfaces in manufacturing process of paper, board or the like, in which method performic acid is used as an antiscaling agent.

Claims

1. Method for preventing or decreasing scale formation on process surfaces in manufacturing process of paper, board or the like characterized in using performic acid as an antiscaling agent.

2. Method according to claim 1, characterized in adding performic acid to process water at least one process location comprising machine chest, mixing chest, white water channel, wire silo, short circulation loop, white water storage tank, fiber recovery system and/or shower water system.

3. Method according to claim 1, characterized in adding performic acid to unfiltered process water and/or fresh water entering the process.

4. Method according to claim 1, characterized in adding performic acid continuously to the process water at at least one process location.

5. Method according to claim 1, characterized in that the pH of the process water is >7, preferably 7.3, more preferably 7.5-8.5.

6. Method according to claim 1, characterized in that the pH value of the process water changes less than 1, preferably less than 0.5, more preferably less than 0.3, pH units after the addition of performic acid.

7. Method according to claim 1, characterized in that the addition of the performic acid is in the range of 0.1-150 mg/l, preferably 0.3-100 mg/l, more preferably 0.5-50 mg/l, even more preferably 0.7-20 mg/l.

8. Method according to claim 1, characterized in using performic acid for preventing calcium carbonate scale formation.

9. Method according to claim 8, characterized in that the calcium concentration in the circulating water is in the range of 100-1000 mg/l, preferably 200-800 mg/l, more preferably 400-600 mg/l.

10. Method according to claim 1, characterized in that the process is free of acid wash steps.

11. Method according to claim 1, characterized in that the concentration of performic acid in the process water is detected, and the addition of performic acid is automatically adjusted according to the information obtained about the concentration.

12. Method according to claim 1, characterized in using performic acid as an antiscaling agent in manufacture of printing paper, writing paper, packaging paper or tissue paper, preferably tissue paper.

13. Method according to claim 12, characterized in that tissue paper has a grammage in the range of 10-40 g/m.sup.2, preferably 15-35 g/m.sup.2.

14. Method according to claim 1, characterized in that the manufacturing process uses a fibre stock, which comprises at least 50%, preferably at least 75 weight-%, recycled fibre material, calculated on basis of dry fibre weight.

15. Method according to claim 1, characterized in using performic acid as an antiscaling agent for preventing scale formation on process surfaces, which are selected from paper machine surfaces, roll surfaces, process fabrics, wires and/or felts.

Description

EXPERIMENTAL

[0027] Some embodiments of the invention are described in the following non-limiting examples.

Example 1

Full-Scale Test in a Tissue Machine

[0028] A tissue machine in Western Europe is making tissue grades from 100% deinked pulp. The machine was experiencing severe dirt issues in final tissue product due to extensive carbonate scaling on process surfaces. A sample of hard scale was scraped off from machine surfaces and analysed to contain 96.8% calcium carbonate.

[0029] Performic acid was dosed to white water channel, machine chest and to a fibre recovery system of the machine, i.e. to circulating process water circuits only. No performic acid addition was made in broke flow or other storage systems. During the experiment period visual inspections showed that scaling was reduced and earlier regular acid washes of the machine could be omitted.

[0030] pH data from the process water before the experiment was collected on three different days during five months preceding the performic acid treatment. The data during the performic acid treatment was collected on about 40 separate days during first nine months of the treatment. Table 1 shows that the average pH of the paper making system increased after the performic acid treatment started. This demonstrates that the surprising effect of reduced carbonate scaling due to performic acid was not due to reduced pH of the system.

TABLE-US-00001 TABLE 1 pH before and during performic acid treatment. Average pH Before During treatment treatment Final stock chest 7.1 7.5 Machine chest 7.0 7.4 Flow Box 7.4 7.9 White water 7.5 8.1 Fiber recovery system 1, Feed 7.4 7.7 Fiber recovery system 1, Clear filtrate 7.2 7.6 Fiber recovery system 2, Feed 7.5 8.0 Fiber recovery system 2, Clear filtrate 7.2 8.0 Average 7.3 8.0

[0031] 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.