WO2004044324A1

WO2004044324A1 - Method for reducing deposits in water from pulp, paper or board making machines

Info

Publication number: WO2004044324A1
Application number: PCT/EP2002/012662
Authority: WO
Inventors: Alfred Pohlen; Gerhard Kern; Jeffrey Spedding
Original assignee: Alfred Pohlen; Gerhard Kern; Jeffrey Spedding
Priority date: 2002-11-12
Filing date: 2002-11-12
Publication date: 2004-05-27
Also published as: AU2002368355A1

Abstract

A method for reducing deposits in pulp, paper or board making machinery by adding as a shock dose or continually a solution of a stabilised bromine or bromine chloride in an amount ranging from 10 to 10.000 ppm based on the dry weight of solids contained in the (circulating) water in the machinery.

Description

METHOD FOR REDUCING DEPOSITS IN WATER FROM PULP , PAPER OR BOARD MAKING MACHINES

The present invention concerns a method for reducing deposits in water derived from or circulating in a pulp, paper or board making machinery.

Deposits forming within the water circuits in industrial plants are well known to cause problems. For instance scale forming on the surfaces of a heat-exchanger will reduce the efficiency of heat-transfer. In a cooling tower system, deposits can lead to mechanical breakdown of the cooling surfaces. Particularly in paper machines for example, deposits forming in the circuits can lead to detachment of these deposits and can lead to spots or defects in the paper sheet or to breaks in production. It can be clearly understood that a clean paper machine will have a significantly better runabil- ity than when contaminated with deposits and that the paper quality is enhanced.

Although the deposits which tend to form in paper machine water circuits can be caused by a variety of factors, in some machines, micro-organisms can be the main cause of deposits^' which lead to problems .

Micro-organisms often find ideal growing conditions in a^' paper machine due to the warm temperature and substances present which can act as nutrients. These micro-organisms do not only multiply in the circuit water but also can form slime or bio-films on surfaces. Fresh water can be an infection source of the micro-organisms, alternatively, raw materials used and especially waste paper used as secondary fibre can be further sources . When fresh water or certain qualities of treated circuit water are used for purposes such as anti-foam showers, at the point where such shower water comes into contact with the main circuit water or paper machine parts, then there is the possibility that certain micro-organisms, often of a filamentous nature, will form slime deposits. These are organisms that would not necessarily form slime exclusively in either the fresh water or process water but can find ideal combinations of for instance dissolved oxygen, nutrients and temperature somewhere at the interface between the liquid systems .

Some paper machines have large volume secondary water circuits such as intermediate storage tanks for cleaned white water, from a poly-disc or fibre recovery system for instance, whereby this water is re-used for stock preparation or for shower water on the machine.

It can also be that water left from a fibre recovery system is put into a large volume sedimentation tower or' funnel to further clean the water by sedimentation so that the water is more suitable for re-use.

Under these circumstances it can be that due to high levels of aerobic micro-organisms in the various circuit waters, any^' dissolved oxygen will rapidly be used up and lead eventually to anaerobic conditions especially in large vessels with slow throughput of circuit water. Intermediate storage vessels for return water or sedimentation funnels are typical of this. The anaerobic state that can develop in such vessels can lead to formation of fatty acids which can cause smell in the finished paper or to sulphides which can cause corrosion or disturb the chemical and biological equilibrium in the complex circuit system of the paper machine.

A significant reduction of the general microbiological activity in such machines can be of benefit in preventing unwanted smells, as well as reducing deposits caused by such microorganisms .

There are many ways to control micro-biological activity in paper machines.

In systems where a high microbe-count is not detrimental as the danger of an anaerobic situation is not present,, a: system can be used that does not necessarily reduce the number of non-sessile micro-organisms but prevents unwanted formation of slime colonies or over-thick bio-films. We are shown in EP 0 496 905 that lignosulphonates can be used for deposit control whereby it is said that the growth of microbes can be influenced to promote the presence of non-sessile microorganisms instead of slime building ones and thus reduce growth of colony-forming microbes. Thus teaching us that a high microbe count can reduce biological deposits.

Where high microbe counts would lead to rapid anaerobic conditions, conventional biocides could be used to reduce the microbe count thus reducing the biological oxygen demand in the circuits whilst at the same time reducing the chance of deposits from micro-organisms.

There are ways of reducing micro-organism levels and thus deposits due to biological slime by using oxidising biocides. Not only can use of oxidizing biocides reduce numbers of micro-organisms directly but also through oxidising ability can eliminate anaerobic conditions thus reducing the chances that anaerobic micro-organisms can grow. Anaerobic metabolism can be responsible for the production of low molecular weight fatty acid products which cause smell problems in papermak- ing. Further, such oxidizing biocides can directly react with and eliminate some products of anaerobic respiration such as sulphides which can also cause smells and in fact corrosion. These include processes such as the following: Addition of sodium bromide together with sodium hypochlorite as oxidant for the bromide. This system can produce hypobro- mous acid, hypochlorous acid or a mixture of both in the paper machine circuit as disinfectant.

Addition of bromo-chloro-dimethyl hydantoin (BCDMH) to the circuit whereby the product is a solid in tablet, granule or powder form and the product must dissolve in water to become active. Again, the product will produce hypobromous acid and hypochlorous acid depending on the conditions in the circuit water .

The disadvantage of such systems when used in paper machine circuits is that the oxidising power of the active halogen products in the system is high enough to not only kill microorganisms but also oxidise other substances used in the pa- permaking process such as dyes. Further, there can be problems with corrosion of the parts of the paper machine.

In the process as explained in US 5,976,386, we are taught that if an amine source such as ammonium bromide is mixed under strict conditions of pH and appropriate dilution with an oxidizing agent such as sodium hypochlorite, also at an appropriate concentration, a special halogenated biocidal product is formed which due to a lower oxidizing potential that hypochlorous acid or hypobromous acid can act as a biocide reducing the numbers of microbes in a system which contains other oxidisable substances without causing excessive oxidation of such substances and furthermore, with a low corrosive tendency. In practice however, it has been reported that the dosing equipment necessary to create the necessary biocidal product is very difficult to keep under perfect control and is very service intensive. If the process to produce the biocidal product is not kept under strict control then unwanted by-products can form leading to less of the required biocidal product being created and to more unwanted by-products that may cause corrosion or oxidative damage of other papermaking additives .

With ever increasing closure of the water circuits in paper machines to save fresh water, energy etc., the tendency for increases in deposit problems is significant. The time that process water resides in the circuits is longer for circuits that are more closed. This can mean that a biocide added into the circuit will also reside longer in the circuit. A biocide with a longer active life can therefore be dosed in one location but can remain active throughout the whole variety of interconnected circuits with the appropriate dosing level. Oxidizing biocides with a high oxidation potential such as sodium hypochlorite have a very short span of activity in a system such as a paper machine white water circuit where high levels of oxidizable substances are present.

The present invention is based on the problem of developing a process for control of micro-organisms and deposits connected thereof in the circuits of a pulp, paper or board machine whereby:

deposits on the surfaces of the circuit caused or influenced by micro-biological activity can be reduced

the number of micro-organisms in the circuit water can be reduced

the added products are safe and stable in storage and use

the added products can be dosed using simple pumps such as a diaphragm pump

the activity of the oxidising component of the products added should not be high enough to damage other papermaking additives the oxidising biocide component of the added products does not cause significant corrosion of the machine parts

any unwanted reducing substances in the circuit, such as for instance sulphides, can be oxidised to reduce anaerobic zones and reduce smells

the biocide remain active long enough in the system being treated to be effective but should finally break down to harmless by-products after a certain time and not cause production of AOX or other harmful substances

Surprisingly, it was found that a stabilised solution of bromine or bromine chloride when added to the circuits of a paper machine according to particular application techniques was successful in fulfilling these requirements.

Accordingly, object of the present invention is a method for reducing deposits in a pulp, paper or board making machinery by adding as a shock dose or continually a solution of a stabilised bromine in an amount ranging from 10 to 10.000 ppm based on the dry weight of solids contained in the (circulating) water in the machinery.

Accordingly, object of the present invention is a method for reducing deposits in a pulp, paper or board making machinery by adding as a shock dose or continually a solution of a stabilised bromine chloride in an amount ranging from 10 to 10.000 ppm based on the dry weight of solids contained in the (circulating) water in the machinery.

Preferred embodiments of the present invention can be derived from the subclaims . With the method of the invention the ad- vantages can be achieved which are described below and in the following examples.

The term deposits within the context of this invention means material which has accumulated or is present within the circuits, vessels and construction of paper, board or pulp making machinery and which can pose a threat to the quality of the paper or pulp being produced or to the runability of the machinery.

Typical locations for such deposits can be the inner surfaces of pipe-work, pumps or other devices carrying white-water, paper stock or pulp, the inside surfaces of the head-box, regions of the machinery where water is sprayed, inside surfaces of chests or holding tanks, formation-wire supports of de-watering foils and vacuum pumps.

Sources of such deposits can be due to the growth of microorganisms, especially slime-forming or filamentous bacteria and fungi. Deposits can also be caused by natural wood resins (pitch), synthetic resins, spun-fibres, stickies from adhesive contaminants in waste paper raw materials, certain papermaking additives, substances produced by chemical reactions in the circuit water and to inorganic scaling due to hardness of water.

The deposits can often be any combination of these biological, organic and inorganic materials.

"Reduction of deposits" within the context of this invention means the prevention, reduction or elimination of deposits which otherwise by their presence as a sessile growth or as particles set free into the circuits or process streams could adversely affect the quality of the paper of pulp being produced or affect the runability of the machinery. Total deposit reduction would mean that the surfaces of the machinery in contact with water or stock would be completely clean.

The method of this invention is primarily intended to reduce or stop microbiological activity whereby through reduction of the biological slime component of mixed deposits it can be that the whole deposit formation will loose its integrity and be dispersed or prevented from growing in the first place leading to a general reduction in many types of deposits not only purely those of biological origin.

Further, in many types of paper production, problems caused by deposits in the circuits are not only caused by microorganisms. Significant deposit problems can be caused by using re-cycle pulp (DIP) whereby stickies can be present or from mechanical pulp such as TMP with natural pitch contamination.

This can mean that although it may be necessary anyway^' to control microbial growth by using biocidal products to control fresh water infections or to prevent anaerobic zones forming, it can be also necessary to add other non-biocidal additives to the circuits to reduce deposits from resinous or chemical substances.

It was found that in a system where a combination of a hydrocarbon solvent together with a tenside was being added to a paper machine circuit with the intention of reducing resinous deposits and where a stabilised solution of bromine chloride was also added to the circuit, not only were the resinous deposits kept under control but also unwanted micro-biological growth was reduced as well giving improved runability. Further, the measured Redox potential in the circuit was increased and after a time, a rancid smell associated with byproducts from the metabolism of anaerobic micro-organisms disappeared. Laboratory trials showed that the invented process gave a longer lasting activity, as measured by available active halogen and by bacteria counts, against growth of microorganisms in a system which had a significant level of oxidizable substances (paper machine white-water) than some other oxidizing biocides that possessed a higher Redox potential in the white water.

Addition of a solution of stabilised bromine chloride to a paper machine as replacement of additions of a bromo-chloro hydantoin product (BCDMH tablets) to the white water circuits showed that with a simple, non-operator intensive application system, the deposit control achieved and the level of was studied as part of a machine trial. The BCDMH treatment, conducted via dissolving tablets of BCDMH in a brominator, was replaced by a single addition of a stabilised bromine chloride solution which was dosed from the original storage drum via a diaphragm pump into the white water circuit. A second deposit control product consisting of a combination of aliphatic solvent and a tenside was also in use and was kept as additional treatment.

The solution of stabilised bromine chloride as relating to the method of this invention can be dosed in appropriate quantities into the water circuits of pulp making machinery or into the aqueous circuits of paper or board machines and by measuring the effects in the ways described it has been possible to demonstrate that this method is able to successfully solve the problem as set out for this invention.

Addition levels of the solution of stabilised bromine chloride as a shock dose or continually to an aqueous system of a pulp, paper or board machine can be in the range of 10 to 10000 ppm based on the dry weight of solids contained in the aqueous system, preferably 50 to 1000 ppm but more typically 200 to 500 ppm. Examples

Example 1. Preparation of a stabilised bromine chloride solu- tion

A solution of stabilised bromine chloride was obtained which was prepared under industrial conditions by bringing together bromine and chlorine to form bromine chloride and adding this stream to an over-based sodium salt of sulphamic acid whilst cooling to remove the exothermically generated heat using a similar process to that described in US patent 6,068,861. The resultant product had a bromine chloride content of 11 % and a pH of 13.

The product so prepared had a mild odour, free of any intense halogen odour and was in the form of a low viscosity pale yellow liquid.

Example 2. Extended activity in a system with high levels of oxidizable substances

The stabilised bromine chloride product used for this example was a development product supplied under the name APIBROM L (API-Additives for Paper Industry GmbH) which was produced as in example 1.

(Lab test against hypochlorite and BCDMH- active residual halogen) Comparison of APIBROM L, sodium hypochlorite and BCDMH in PM white-water. Residue of free halogen, all additions equal, expressed as free chlorine

.NaOCI -APIBROM L

+ — BCDMH

Example 3. Reduction of microbial activity using stabilised bromine chloride

Influence of various active halogen containing substances in paper machine white-water; addition quantity 3 ppm calculated as total chlorine

Example 4. Effect on Redox potential

The stabilised bromine chloride product used for this example was a development product supplied under the name APIBROM L (API-Addit,ives for Paper Industry GmbH) which was produced as in example 1.

The following oxidising biocides were compared by measuring the Redox potential in a solution of the biocides dissolved in tap water with a Redox electrode.

Solutions were made from the various biocides to give free halogen values (expressed as total available chlorine) of around 4 ppm. A Redox electrode was placed in the same vessel . After the measured total available halogen value had stabilised, the sample was diluted with fresh water to a point where the total halogen was indicated as 3 ppm. At this point, the Redox potential was recorded. The test solution was further diluted and at successive free halogen values, the Redox 'potentials were recorded. The results were presented graphically as shown here.

Redox potential at various residual halogen levels (measured as total available CI2) for halogen- containing oxidizing biocides

Residual halogen (expressed as total chlorine in ppm) It was shown that the stabilised bromine chloride from example 1 exhibited a significantly lower Redox potential as a solution in fresh water at values of available halogen between zero and 3 ppm.

Example 5. Prevention of biological deposits in a wood-free fine paper machine

The stabilised bromine chloride product used for this example was a development product supplied under the name APIBROM L (API-Additives for Paper Industry GmbH) which was produced^' as in example 1.

A fine paper machine was producing special paper at a rate of approximately 80 tons per day. The white water circuits were already being treated by continual addition of a development product known as APICLEAN OR-N-0-3 into the white water I circuit. The product APICLEAN OR-N-0-3 (supplied by API- Additives for Paper Industry GmbH) constituted a solvent with ■a small addition • of tenside. A solution of bromo-chlόro dimethyl hydantoin (BCDMH) was being added into the head-box anti-foam shower water directly before the head-box. Experience had shown that without the treatment of BCDMH in this location, there was a tendency for slime to build up under the water surface on the walls of the head-box. Even with the^' combination of product from example 2 in the white water and the BCDMH dosage in the head-box, the head-box had to be cleaned at least every 10 days or deposits would start to show as spots in paper.

The use of BCDMH was achieved by filling a dissolving unit known as a "Brominator" every few days with tablets of BCDMH. This was seen as an unwanted task due to the corrosive dust from the tablets necessitating the use of gloves, breathing filters etc. during re-filling. During a period where the stabilized bromine chloride was added to the head-box shower water instead of the BCDMH solution, the machine ran for 20 days with no spot problems until a mechanical defect caused a necessary stop whereby, on opening the head-box, all surfaces under the water level were completely clean.

The performance benefits obtained were as follows:

Longer running period than normal before needing to stop for head-box cleaning.

Less handling problems as the liquid product was dosed from a drum using a diaphragm pump instead of the frequent handling problems experienced due to aggressive dust from BCDMH being present during repeated Brominator filling operations.

Claims

1. A method for reducing deposits in pulp, paper or board making machinery by adding as a shock dose or continually a solution of a stabilised bromine in an amount ranging from 10 to 10.000 ppm based on the dry weight of solids contained in the (circulating) water in the machinery.

2. A method for reducing deposits in pulp, paper or board making machinery by adding as a shock dose or continually a solution of a bromine chloride in an amount ranging from 10 to 10.000 ppm based on the dry weight of solids contained in the (circulating) water in the machinery.

3. The method of claim 1 or 2, characterised in that bromine or bromine chloride stabilised in a solution of over-based metal salt of sulfamic acid is added.

4. The method of claim 1 or 2 and 3, characterised in that the stabilised bromine or bromine chloride solution is added directly or indirectly into the white water I or II circuit of a papermachine.

5. The method of claims 1 or 2 to 4, characterised in that the stabilised bromine or bromine chloride solution is added in combination with another oxidising or non- oxidising biocide.

6. The method of any of claims 1 or 2 to 5, characterised in that the stabilised bromine or bromine chloride solution is added in combination with a combination of essentially water-insoluble organic solvent and tenside.

7. The method of claims 1 or 2 to 6, characterised in that the addition occurs into a system containing water leading into the white water I and II circuits of a paper or board machine or into the circuits of a pulp dewatering machine