Enessco International concentrates on the ever increasing demands for improved quality from mills that use recovered paper in their furnish
July 2008
By Stanley Schiher, International Technical Manager and Steve Dumont, President, Enessco International
Recycle furnish quality and supply are deteriorating. Higher percentages of recycle in paper are not only “green” but in some countries legally required. Higher demand and use has led to a reduced supply and lower quality. This has resulted in additional problems for pulp and papermakers as well as creating a different and demanding market condition for recycled fiber globally.
Not only is recycled waste paper an issue, countries around the world are now economically, and in some cases governmentally, being required to close up water loops based on new environmental laws.
Both of these conditions cause increased operational costs and greater problems with the production of good quality pulp made from recovered fiber. Lower quality pulp can result in increasing paper quality problems and more deposition in and around the paper machine.
Worldwide, Enessco has seen an increasing need for treating the recycled waste paper to control contamination as well as improve the quality of effluent water from paper mills and deinking plants. The company’s technology is designed to reduce solvent cleaning, increase production, reduce breaks and improve paper quality easily. This can allow mills to use a lesser grade raw material and still keep the quality up to standards.
The technology is based upon its ability to enhance the performance of the stock prep cleaning and conditioning equipment. Increasing contaminant removal efficiencies allows for production of high quality recycle pulp and improved water loop cleanliness. With higher contaminant removal, cleaner and more "virgin like" fiber is sent forward to the paper machines. Cleaner furnish increases profitability via improved quality, production and machine runnability.
Contaminant Control Technology
Enessco treatment is a blend of surfactants and inorganic salt "polymers". These compounds change the physical behavior of the contaminant and the fiber to allow faster and cleaner separation between the two. It is designed to enhance the removal of hydrophobic contaminants by increasing removal efficiency rates in equipment designed to clean and condition recycled furnish. The quicker contaminants are released the larger they are, and larger particles are easier to remove. The more different in behavior a contaminant is from fiber the easier it is to remove.
Pulping: The treatment starts to work in the pulper with its surfactants (less than 10% of the formulation). These compounds reduce the surface tension of the water, much like soap, and speeds up the wetting out of the recycled fiber being added to the pulper. The faster the rewetting process the faster is the release of the contaminants. Labels, tape, stickers, etc cannot adhere to a wet surface.
Alone, the mechanical action of pulping uses primarily fiber-to-fiber collisions to break up recovered paper and separate contaminants, shreds “already been dried” material to smaller and smaller pieces until fibers wet out to the point of being small enough to flow through extraction plates in continuous pulpers, or become small enough to be “acceptable” in batch pulpers. It is claimed that the process becomes less harsh and more efficient by using the Enessco surfactant blend. Hydrophobic contaminants are more quickly and cleanly released from their fibrous surfaces. The quicker the release, the larger the particle; the larger the particle, the easier it is to remove.
Also, since hydrophobic materials do not stick to wet surfaces, the modified fiber now cleanly releases these contaminants, thus improving subsequent screening and cleaning removal efficiency and raw material yield. Pulping itself does not completely remove all the hydrophobic material from the fibers.
In some cases caustic or pulping aids are used to assist in pulping; however, severe alkalinity from caustic can cause fiber damage, and pulping aids can tend to over disperse inks and wax. Even discoloration of furnish is possible. Enessco claims to have none of these side effects. This improved pulping results in improved fiber quality, decreased fines and anionic trash and improved water quality.
Cleaning and screening: The function of the screens and cleaners is to separate fiber and contaminant. The greater the difference in physical character and behavior a contaminant is from fiber, the greater the mechanical efficiency of the screen and/or cleaner.
Centrifugal cleaners separate components based primarily upon density and flow characteristics of the feed material. Enessco modifies both allowing the cleaning equipment to distinguish between good fiber and rejectable contaminant, thus resulting in better accepts of fiber and higher removal of contaminant. Less contaminants travel downstream and more fiber is “accepted”, thus the quality of furnish and yield is improved.
Screening works by primarily size separation. If small and perhaps malleable enough, material will pass through the screen basket slots or holes. Screen designs, pressure differentials and reject flow rates determine reject removal efficiency and to a large part yield. Keeping the contaminants larger will improve removal efficiency in screening. The inorganic salt blend in Enessco bonds to all hydrophobic contaminants to increase their rigidity, also increasing screening reject efficiency.
Flotation and/or washing: In deinking mills, keeping particles large improves their removal efficiency. Ink particles with Enessco chemistry are not as dispersed and therefore floatation or deink cells have a much improved removal rate. Downstream washers will be less burdened and their efficiency will improve as well. In conjunction with this, the surfactant component of attaches existing process water air bubbles to the contaminants for improved lightweight removal.
Thermal dispersion: Some mills will install a thermal disperser that works, simply stated, as a hot screw press and causes the stickies and contamination to be exploded into micro particles so they can be an “acceptable” size. These stickies, hot melts and other small particle are still in the system and still very tacky. With high cost of energy and steam, in more than 50% of the cases using the Enessco treatment, the mill could eliminate the thermal disperser all together.
Pacification: For the small micro particles that do feed forward, the inorganic salts also detackifies and makes these contaminant materials less sticky and therefore less likely to deposit on surfaces, such as paper machine forming wires, press felts, dryer fabrics, wear surfaces or machine surfaces. Additionally, the detackified contaminants that do get trapped on surfaces are easier to remove. The Enessco web site has several case studies around this area as well as a TAPPI paper co-authored with SCA Tissue.
Water Loop Improvements
The more complete the removal of wax, stickies and ink, the cleaner the recycled fiber and the cleaner the process water used in the mill. The process water is the lifeblood of the mill. If the process water is allowed to cycle up with contaminants and ink, the more difficult it is to produce clean, bright, good quality furnish. Getting these materials out of the mill system always improves the quality of the process water, which will further improve the production of quality recycled furnish and will reduce effluent loadings.
Paper Machine Operational Benefits
Obviously, the most notable effects of recycled furnish are on the paper machine itself. Deposits on wire, felts, dryer fabrics and the sheet all cost money. Downtime, breaks, slower production rates, cleaning chemistry usage, yield and poor sheet quality are the typical areas contamination affects. Enessco’s value is improving the quality of recycled furnish to a more “virgin like” level. As recycle furnish deteriorates, paper mill profitability deteriorates as well. This is why there has been a sharp increase in demand from mills all over the world to resolve the negative effects of contaminants on paper mill profitability, productivity and paper quality.
Stanley Schiher is International Technical Manager; Steve Dumont is President, Enessco International. SWD International LLC, the parent company of Enessco International is based in Hampton NH, and has served the pulp and paper industry for more than 25 years.
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