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Tag Archive: Pulp & Paper

  1. Defoamers for the Pulp & Paper Industry

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    Foam in the Pulp & Paper Industry

    Lignin, rosin and fatty acid soaps, and hemicellulose are commonly formed during the pulping process, resulting in high levels of foam. Excess foam will negatively impact process and equipment efficiency, leading to inferior or rejected paper. Defoamers and antifoams are a necessity to the entire paper making process.

    Why Are Defoamers Necessary in Pulp Mills?

    The black liquor formed during pulp production has a strong tendency to foam. The foaming tendency is due to the fact that 12% to 15% of black liquor solids are comprised of NaOH, Na2S, tall oil soap, rosin soap, lignin, hemicellulose and other organic compounds. Defoamers are necessary for pulp washing, screening, and bleaching. Foam problems cause safety issues and poor housekeeping along with the mentioned production problems.

    Why Are Defoamers Necessary for Paper Machines?

    Paper Mill Machine

    Foam is often generated through chemical interactions on the paper machine combined with the rapid motions involved in the paper making process. Some of these interactions may involve chemistries from:

    • Retention aids
    • Fillers
    • Sizing
    • Fines
    • Dry strength
    • Wet strength

    When paper machines generate foam and entrained air, it adversely affects production rates and paper quality. Defoamers facilitate the process of paper making and help to prevent the following issues:

    • Bacteria buildup
    • Poor sheet formation
    • Drainage issues
    • Pump cavitation
    • Poor housekeeping
    • Safety problems
    • Pulp consistency

    Slower production rates and inferior or rejected pulp and paper aren’t the only problems caused by foam. For both pulping and papermaking, other foaming issues can create costly outcomes. Foam is detrimental to the environment and can increase effluent COD, BOD, and color levels in the effluent. An excess of foam also creates workplace safety hazards and raises production costs. A few ways foam can increase operational costs:

    • Slower production rates
    • Increased deposits
    • Higher energy costs
    • Increasing makeup chemical costs
    • Increasing chemical demands on the paper machines

    Using defoamers makes the pulp and paper production process safer, more environmentally friendly, and increases overall production efficiency, all while reducing production costs.

    Defoamer Applications

    A variety of defoamer types serve different defoamer applications. Common applications include:

    • Brown stock washing and washing in general
    • Bleaching
    • Papermaking
    • Coatings
    • Effluent treatment

    Pulp Mill

    Utilized in brown stock washing, screen rooms, and bleach plants, pulp mill defoamers are effective at high temperatures and withstand high acid and alkaline conditions of the pulp mill process. Most mills use water-based silicone defoamers.

    However, pulping processes involving finished products, such as acetate dissolving pulp, will not tolerate silicone and/or silica. These processes use oil-based defoamers.

    Brown stock washing and pulp mill defoamers in general increase production rates by increasing washing efficiency. Increased washing efficiency is accomplished by improved drainage on the washer. Better washing reduces the pulp mill carry-over to the paper machine and will prevent deposits by washing the deposit forming compounds out of the pulp. This way, the deposit-causing compounds leave with the washed out liquor.

    Water-based and glycol-based defoamers may be used to control foam in both the screen room and bleach plant. Simultaneously, these defoamers improve drainage and bleaching efficiency by reducing entrained air.

    Papermaking

    Pulp and Paper Mill

    Paper machine defoamers are typically either water-based fatty alcohols or glycol-based products.

    Paper machine defoamers are necessary in order to run at or above the designed capacity of the machine. A good paper machine defoamer program will reduce entrained air in the head box and on the formation wire which further increases the drainage on the paper machine. It will also help reduce steam cost on the dryers over and above the capacity of retention and drainage aide programs.

    Coating

    In small amounts, defoamers are added to coating to prevent fish eyes, give an even coating film, and avoid streaks and holes. In addition to defoamers, other coating additives may include:

    • Wetting agents
    • Lubricants
    • Dispersants
    • Water-resistant agents
    • Water-retention and rheology modifiers

    Effluent Treatment

    Defoamers control the foam in effluent systems. Better foam control results in better-treated water before it is released into the environment. Foam control in the effluent system also prevents dried foam from forming on top of the effluent pond, which can be blown into the environment. Water based defoamers are typically used in this application to avoid oil slicks on the waterway the effluent is discharged into.

    Applied Material Solutions Defoamers for Pulp & Paper

    As paper products have the potential to become indirect food additives, defoamers intended for this application must meet a number of regulatory requirements. At AMS, all our defoamers meet one or more sections of the FDA regulation 21 CFR 176.170, 176.180, 176.200, 176.210.  AMS also has defoamers which meet global regulations such as Chinese GB 9685 and German BfR. Our experts are well-versed in federal and international regulations and can help ensure you meet the highest standards, no matter your location.

    AMS defoamers provide a significant reduction of foam and entrained air, and when properly applied, there is little impact on paper machine sizing. They’re an excellent choice for resellers looking for an economical, high-quality defoamer with a low environmental impact. Contact us today to find your ideal defoamer solution.

  2. What You Need to Know About Brown Stock Washing Defoamers

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    Brownstock washing is a complex, dynamic process in which dirty wash water or weak black liquor (dissolved organic and inorganic material obtained from the pulp cooking process) is separated from the pulp fibers1. The organic materials are recovered for their fuel value and the inorganic material is recovered for the sodium content to regenerate NaOH.

    Under-designed capital equipment can be augmented using chemical enhancements. In the case of brownstock washers, the application of defoamer is required to improve mat drainage and to control foam to enable overloaded washers to wash efficiently; this also allows pulp from the digesters to flow continuously to the bleach plant and/or the paper machine.2

    Washing efficiency directly correlates to pulp cleanliness. Cleaner pulp results in better chemical recovery, lower bleaching costs, fewer deposition issues, and more consistent pulp is sent to the paper machine.

    The following article provides an overview of brown stock washing deformers, outlining how they work, key benefits, and the types available.

    How Do Brown Stock Washing Defoamers Work?

    Brownstock washing defoamers have two purposes. First is to control the foam and prevent vats from overflowing onto the floor causing loss of product (the pulp) and housekeeping issues, while providing drainage on the washers which provides cleaner pulp and improves washing efficiency.

    Second is to recover valuable spent liquor. The black liquor is recovered for the fuel value and to regenerate NaOH by recovering sodium from the washing process.

    The foam level in the vat is not an indication of how well the defoamer is performing. If the foam is not spilling over on to the floor it is then purely cosmetic. The real indication of the defoamer’s performance is how well the foam is being released from the fiber. When the foam is released from the fiber it allows drainage.

    It is important to understand the defoamer must have a positive Entry Coefficient and a positive Spreading Coefficient. These are expressed in the following equations:

    (Entry Coefficient) E = γw/a + γw/o – γo/a

    Where γ is the surface tension or interfacial tension in dynes/cm2

    (Spreading Coefficient) S = γw/a – γw/o – γo/a

    Where “w” is water, “o” is oil, and “a” is air

    Brown Stock Washer Defoamers

    The equations briefly explained:

    The Entry Coefficient is equal to the surface tension of the black liquor + the interfacial tension between liquor and oil (i.e. the defoamer), minus the surface tension of the oil. This allows the defoamer droplet to enter the monolayer at the air/water interface.

    The same is true for the Spreading Coefficient: black liquor – the interfacial tension between liquor and oil, minus the surface tension of the oil. This causes the defoamer droplet to spread along the air/water interface forming a defoamer “lens.”

    How defoamers workHydrophobic particles within the defoamer facilitate the entering of the oil droplet into the surfactant monolayer at the air/water interface. With a positive Entry Coefficient, the defoamer droplet enters the surfactant monolayer at the air/water interface. Once the droplet is there, the positive Spreading Coefficient allows the defoamer droplet to spread across the monolayer forming a lens. The shape of the lens is altered by the movements in the foam. Stress occurs until the lens breaks and the foam lamella ruptures. This results in foam control throughout the pulp mill.

    On fiber, larger and larger bubbles are formed until the buoyancy of the bubble overcomes its adherence to the fiber and floats away from the fiber. The foam on the fiber causes an apparent increase in the fiber’s size. As the foam is removed from the fiber the apparent fiber size decreases creating a shorter path for the water to travel through the mat. The shorter path for the water results in improved drainage.

    It should be noted, when using defoamers in brown stock washing operations, it is important to understand that the defoamer must perform a balancing act, where the defoamer is sufficiently compatible in the black liquor to not cause deposition, yet incompatible (insoluble) enough to perform efficiently on the washer. A defoamer is never soluble in the medium it is defoaming.

    Benefits of Brown Stock Washing Defoamers

    A good defoamer program should facilitate production of the pulp, and add economic value to the pulp mill process by addressing the following:

    • Housekeeping issues
    • Increased chemical recovery
    • Reduced energy costs
    • Lower bleaching costs
    • The reduction of the environmental impact of the mill
    • Fewer safety hazards
    • Increased production rates
    • Increased quality of the end product
    • Lower reject rates3

    Types of Defoamers for Brown Stock Washing Operations

    Pulp and Paper MillBrown stock washing defoamers come in a variety of formulas and strengths to suit the needs of different pulp and paper processes. The types available include:

    • Oil-based defoamers
    • Water-extended, oil-based defoamers
    • Concentrated or water-based silicone defoamers
    • Polymer-based defoamers

    Oil-based and water-extended oil-based defoamers are less common than they were 15 to 20 years ago. They are used primarily in mills where silicone and/or silicates are not allowed.

    Brown Stock Washing Defoamer Solutions From AMS

    Brown stock washing defoamers are essential to both product and process quality. As a leading manufacturer and supplier of foam control products, Applied Materials Solutions has an extensive range of products suitable for use in these pulping applications. Our product offerings include:

    • Water-based silicone defoamers: (e.g. TRANS-2994 and TRANS-2931)
    • Oil-based defoamers: (e.g. TRANS-7285 and TRANS-7115)

    For additional information about our brown stock washing defoamers and other product solutions, contact us today.

     

    References

    Brownstock washing – A review of the literature, TAPPI Journal January 2014, Ricardo B. Santos and Peter W. Hart; page 9

    Brownstock Washing – Practices and Fundamentals. TAPPI Press, Peter Hart and Michael Brown, Chapter 15, page 545

    Brownstock Washing – Practices and Fundamentals. TAPPI Press, Peter Hart and Michael Brown, Chapter 15, page 562

     

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