WO2009065829A1

WO2009065829A1 - Deposit control

Info

Publication number: WO2009065829A1
Application number: PCT/EP2008/065755
Authority: WO
Inventors: Kari Takala; Pekka Kultalahti
Original assignee: Bim Kemi Ab
Priority date: 2007-11-22
Filing date: 2008-11-18
Publication date: 2009-05-28
Also published as: SE531688C2; EP2212470B1; RU2471031C2; SE0702601L; RU2010124948A; EP2212470A1

Abstract

The invention relates to an agent for preventing deposits in a papermaking system, said agent comprising (a) a first component at least comprising a water soluble sulphonated polymer; and (b) a second component at least comprising hypochlorite. The invention also relates to a method for preventing deposits in a papermaking system using said agent. By obtaining information about the composition of a deposit formed in the papermaking system, a deposit control agent may be applied which is designed to efficiently prevent the formation of similar deposits. Thus, the invention allows more efficient use of deposit control agents.

Description

DEPOSIT CONTROL

Technical field

The present invention relates to the field of papermaking, in particular to the prevention and control of deposits formed within the papermaking equipment.

Background of the invention

Modern paper production is a sensitive process requiring clean machine surfaces to produce a paper product of acceptable quality and cost- effectiveness. Detrimental deposits are formed to varying degree by deposi- tion of three types of material onto machine surfaces. The first type of deposit is organic fatty deposit originating from the wood or organic substances such as man-made additives entering the process with recycled paper. The second type is microbiological deposit formed by growth of microorganisms such as bacteria, fungi and algae in the process water. A microbial deposit is some- times termed "biofilm" or "biofouling". The third type is inorganic deposit formed by precipitation of salt, e.g. various calcium salts and barium sulphate. Quite often all three deposit types are present in a deposit.

Deposits formed on the surfaces of a papermaking machine reduces the productivity, as the paper machine eventually must be stopped and cleaned. Also, machine surface deposits negatively affect the quality of the paper produced, resulting in breaks, holes and spots in the paper.

Various types of deposits and the conventional methods used to address the problems of paper machine deposits are described in detail in Hassler, T, "The Source and control of Paper Machine Deposits", Applications of Wet End Paper Chemistry, Blackie Academic & Professional (1995).

The conventional approach has been to treat the above three types of deposits separately. The relative ratio between the above components of a deposit may vary greatly, and, in an extreme case, each component may be present at a content of from 1 to 99 % by dry weight. In a more typical situation the content of each component is between 5 and 90 % by dry weight. Finally in some cases each component may be present in equal amounts.

WO 2006/097578 A1 discloses a method to control biofilm formation using a combination of hypochlorite and a substance called BCDMH. The use of ammonium bromide or ammonium sulphate in combination with hypochlorite is also a well-known strategy for preventing biofilm formation.

The article New Microbiological Growth Control Treatment Programme for the Pulp and Paper Industry; Paper Technology ¹VoI 48, No 3 pp 38-40 (2007) describes a method to control biofilm formation using a composition comprising sulphonated lignin and a surfactant.

US 5 282 976, US 6 355 214 and US 6 144 950 all disclose methods to control formation of scale formed by precipitation of salt on surfaces. These references examplify the use of certain polymers which are known in the art for their efficacy in controlling formation of scale. Such products are called scale inhibitors.

Typically, control of mixed composition deposit today involves the use of four different products. Moreover, it is also good practice to remove deposits during production stop with cleaning chemicals, involving the use of yet other products. Thus, there is a need in the art for improved methods for preventing and controlling deposits in paper production systems.

Summary of the invention

It is an object of the present invention to provide means for improved control of deposit formation. In particular, it is an object of the present invention to provide an improved method for preventing the formation of deposits, and an agent for use in such a method.

In one aspect, the invention relates to an agent for preventing paper machine deposits, said agent comprising a first component comprising a water soluble sulphonated polymer, and a second component comprising hypochlorite. Said first component is preferably selected from the group consisting of lignosulphonate and a polymerization product of formaldehyde and naphtalene sulphonate, and combinations thereof.

The use of the agent according to the invention involves a reduction in the number of chemical products used in the production of paper and paper board for preventing and controlling machine deposits. As a result, the production process is rendered safer, more cost-effective, and more convenient.

The agent according to the invention has also proven to be particularly effective in preventing deposition on paper and board machines.

Optionally, said first component further comprises a surfactant and/or a bromide salt. Optionally, said second component further comprises a surfactant and/or a bromide salt and/or a scale inhibitor.

By adjusting the composition of the first and second components, respectively, a combined effect on the deposit, which typically consists of several different deposit species, may be obtained which improves the performance of the agent.

When a bromide salt is used in the first and/or the second component, the bromide salt is preferably selected from the group consisting of ammonium bromide and sodium bromide. In another aspect, the invention relates to the use of said agent for preventing formation of deposit in a papermaking system.

In another aspect, the invention relates to a method for preventing paper machine deposits in a papermaking system comprising the steps of

- identifying a composition of a deposit; - selecting a first component which at least comprises a water soluble sulphonated polymer;

- selecting a second component which at least comprises hypochlorite; and

- adding said first component and said second component to said papermaking system during operation of said system.

By obtaining information about the composition of a deposit formed in the papermaking system, and thus identifying the different deposit components and their respective amount, a deposit control agent may be applied which is designed to efficiently prevent the formation of similar deposits. Thus, the method of the invention allows more efficient use of deposit control agents and achieves a more satisfactory result.

Preferably, said first and second components are added simultaneously to the papermaking system. By simultaneous or near simultaneous addition of the components, an improved combination effect of the components of the agent according to the invention is achieved.

Detailed description of the invention

The inventors have surprisingly found that deposits consisting of all three different deposit types, i.e., organic content, inorganic content, and microbiological content, may be successfully treated using an agent which is a combination of two compositions. This agent comprises a first component comprising a water soluble sulphonated polymer and a second component comprising hypochlorite. Furthermore, the inventors have developed a method for controlling paper machine deposits in a papermaking system comprising the use of such an agent.

In general, the method according to the invention comprises the following consecutive steps:

(i) Obtaining information about (i.e., identifying) the composition of the deposit; (ii) Selecting the proper ingredients for the two components based on the information obtained in step (i) above; and (iii) Feeding the two components simultaneously into the paper or board making system.

Optionally, step (iii) may be followed by verifying the efficacy of the method and subsequent adjustment of the ingredients of the first component and/or the second component. Identification of the composition of the deposit typically involves chemical and/or physical characterization of a deposit sample. Examples of methods which may be used include conventional organic analytical techniques, such as infrared spectroscopy, various chromotographic techniques (e.g., gas chromatography and size exclusion chromatography), NMR and C¹³, X-ray spectroscopy and other conventional wet chemical methods. Conventional microbiological methods may also be used.

The sample to be analyzed may be collected at any point in the paper- making process. In particular, a sample may be collected at a location which is known to be susceptible of deposit formation, such as a surface of the white water tank, or a surface of the headbox of a papermaking machine.

Based on the above identification of deposit composition, a first component and a second component of the agent according to the invention are selected. Thus, the respective compositions of the two components are selected with regard to the composition of the deposit to be prevented so as to optimize their performance. Also, the relative addition rates of the first and second components are typically set with regard to the composition of the deposit. The composition of the components and the proper selection thereof will be described below.

Thus, the agent according to the invention may be regarded as a kit comprising a first component and a second component.

Typically, the first component comprises an aqueous solution of a sulphonated polymer. For example, lignosulphonate or a polymerisation product of sulphonated naphtalene and formaldehyde may be used as the sulphonated polymer. The sulphonated polymer may be present in the agent according to the invention at a content of 1 to 55 % by total weight of the agent. In embodiments of the invention, additional substances may be in- eluded in the first component. For example, a bromide salt, such as ammonium bromide or sodium bromide, may be included in the first component. For example, a bromide content of the first component may be in the range of 0 to 20 % by total weight of the agent.

In embodiments of the invention, a surfactant may be included in the first component to enhance the performance of the agent according to the invention in certain applications. Typically, the surfactant is anionic or non- ionic. It is also within the scope of the invention to use a combination of surfactants, such as a combination of an anionic and a nonionic surfactant. An example of a suitable surfactant is an alcohol ethoxylate made by reaction of cetyl alcohol with ethylene oxide. The surfactant may be present in the first component at a content in the range of from 0 to 20 % by total weight of the agent.

Thus, in addition to the sulphonated polymer, the first component may further comprise a bromide salt and/or a surfactant. As indicated above, the second component of the agent of the invention comprises hypochlorite. Hypochlorite is a common general cleaning agent for household use as well as industrial applications. Furthermore, due to the oxidizing activity of hypochlorite, the second component comprising hypochlorite should preferably be formulated separately from the first com- ponent in order to retain the activity of both components. The hypochlorite content of the second component of the agent according to the invention may be in the range of from 1 to 18 % by total weight of the agent.

Furthermore, any conventional scale inhibitor or combination of polymers known to inhibit scale formation may also be included in the second component. Examples of conventional scale inhibitors comprise polymers, such as low molecular weight polymers, and chelating agents, such as EDTA and DTPA. A scale inhibitor may be present at a content of from 0 to 20 % by total weight of the agent.

In embodiments of the invention, a bromide salt may also be included in the second component of the invention. A bromide content of the second component may be in the range of from 0 to 20 % by total weight of the agent. Furthermore, one or more surfactants known to both be stable in hypochlorite solution and also known to enhance the cleaning properties of hypochlorite may be included in the second component. The surfactant content of the second component of the agent according to the invention may be up to 5 % by total weight of the agent. Examples of suitable surfactants comprise amine oxides.

The composition of the microbiological material should form a basis for the choice and amount of the sulphonated polymer of the first component. Microbiological species which are particularly prone to forming deposits are well known in the art. Thus, as a general rule, if the deposit sample is found to contain high amounts of certains micobiological material, then the content of the sulphonated polymer used in the first component should preferably be high. Conversely, if the deposit sample is found to have a lesser content of microbiological material, the sulphonated polymer content of the first compon- ent is typically reduced.

The composition of any scale content should form a basis for the choice of scale inhibitor used, and how much of this scale inhibitor preferably should be used in the method according to the invention. Thus, as a general rule, the higher scale content in the deposit, the higher should be the content of scale inhibitor in the second component.

Similarly, the composition and content of the material extractable in organic solvents should form a basis for the choice of type and amount of surfactant used.

Furthermore, the papermaking system to be treated and the quality of the paper to be produced therein should influence the choice of first and second components. For example, a papermaking system operating at high speed is more sensitive to deposit formation than a system operating at lower speed, and may require a deposit control agent of higher concentrations. Likewise, a thin paper web is more susceptible to damage caused by deposits than a thicker web, and may thus require a deposit control agent of high concentrations.

According to the method of the invention, the agent is fed into the papermaking system. Preferably, the first and second components are fed simultaneously or only at short intervals into the system, so as to allow mixing of the two components in the papermaking system.The addition may be made at any point in the papermaking process. Since the process water is recycled and reused the exact position of the addition point is not critical. However, since it is generally more important to have clean surfaces in the short circulation around the forming section of a paper machine, addition to or shortly before this part of the process is advantageous. It is preferable to have some residual hypochlorite concentration in the water at the forming section of a paper machine. The agent of the invention is preferably fed into the papermaking system during operation of the system, and thus enables treatment of the system without interrupting the papermaking process. It may also be desirable to add one or both components at a secondary addition point to achieve a machine wide control of deposition. The agent and/or the method according to the invention may also be used for preventing depositions in a system for preparing pulp, for example in an up-take machine for market pulp. Thus, as used herein, the term "paper- making system" is meant to encompass a machine for preparation of wood or paper pulp. In embodments of the invention, a fourth step of confirming the efficacy of the steps (i) to (iii). Such a step may comprise the analysis of a wet or dry sample taken from a machine surface. In the event that a deposit has been formed in spite of the application of the agent of the invention, the composition of that deposit is preferably identified, and the composition of the first and second component may then be suitably adjusted in order to further reduce the extent of deposit formation.

The invention will be further illustrated by the following examples.

Examples

Example 1

A sample of deposited material is collected from the headbox of a paper machine. The composition of the deposit sample is determined using a combination of conventional methods for quantification and characterization of the deposit with respect to inorganic constituents, organic constituents, and microbiological constituents.

The dry deposit sample has an organic fatty content of about 30 %, a microbiological content of about 50 % and an inorganic salt content of 10 % by weight. The inorganic salt content essentially consists of calcium oxalate. The remaining 10 % of the deposit is wood fibres incorporated in the matrix.

A deposit control agent is prepared as follows: a first component is formulated by dissolving in water 25 % lignosulphonate, 10 % ammonium bromide and 15 % decanol reacted with 15 moles etylene oxide to form a nonionic surfactant; and a second component is fomulated by combining 5 % of the hypochlorite stable surfactant Triton W 30 (DOW Chemicals), 10 % of a scale inhibitor known to prevent calcium oxalate deposition and 15 % hypochlorite in water (the remaining 20 %). All percentages are by total weight of the deposit control agent. The first component and the second component are simultaneously added to a paper machine right before the fan pump during continuous operation of the papermaking process.

Example 2 A sample of deposited material is collected from a white water tank of a tissue machine using recyled fiber. The composition of the deposit sample is determined using the methods of example 1. The dry deposit sample has an organic content of 65 % by weight comprising a composition of hotmelts and glues, and a microbiological content of 25 % by weight. Essentially no in- organic matter is present in the deposit. Wood fibres incorporated in the matrix constitute the remaining 10 %.

A deposit control agent is prepared as follows: A first component is formulated by combining 30 % of a polymer prepared by reacting sulphonated naphtalene with formaldehyde with 10 % of a surfactant prepared by reacting oleic acid with polyethylene glycol to make a diester based surfactant. A second component is formulated by adding 10 % sodium bromide to 15 % hypochlorite solution. All percentages are by total weight of the deposit control agent. No scale inhibitoris used in either composition, since scale is not present in the deposit. The first component and the second component are simultaneously added to the inlet of the white water tank during operation of the papermaking process.

The above examples may be used as references for the preparation of an agent according to the invention. As indicated above, the respective con- tents of the ingredients of the first component and the ingredients of the second component should be adjusted on the basis of information about the deposit composition and the sensitivity of the paper or the papermaking system.

Claims

1. Agent for preventing deposits in a papermaking system, said agent comprising (a) a first component at least comprising a water soluble sulphonated polymer; and (b) a second component at least comprising hypochlorite.

2. Agent according to claim 1 , wherein said first component is selected from the group consisting of lignosulphonate, a polymerization product of formaldehyde and naphtalene sulphonate, and combinations thereof.

3. Agent according to claim 1 or 2, wherein said first component further comprises a surfactant.

4. Agent according to any one of the preceding claims, wherein said second component comprises a surfactant.

5. Agent according to any one of the preceding claims, wherein said first component and/or said second component comprise(s) at least one bromide salt.

6. Agent according to claim 5, wherein said bromide salt is selected from the group consisting of ammonium bromide, sodium bromide and combinations thereof.

7. Agent according to any one of the preceding claims, wherein said second component comprises a scale inhibitor.

8. Use of an agent according to any one of the preceding claims for preventing formation of deposit in a papermaking system.

9. Method for controlling formation of deposits in a papermaking system, said method comprising the following steps of i. obtaining information about a composition of a deposit; ii. selecting a first component according to any one of the claims 1 to 7 based on the information obtained above; iii. selecting a second component according to any one of the claims 1 to 7 based on the information obtained above; and iv. adding said first component and said second component to said papermaking system during operation of said system.

10. Method according to claim 9, wherein said first and second components are added simultaneously to said papermaking system.