By Brian Duffy, Senior Industry Development Manager, Board & Packaging Grades, and Brad Benz, Senior Industry Technical Consultant, Nalco CompanyMoving to lighter weights, strength, and energy costs are critical drivers in the board and packaging market. However, as the authors write, achieving the desired end-product performance to satisfy demand while maintaining and improving production efficiency can be a difficult task. Read Part I here .
The manufacturer wanted to run the machine at nominal basis weight or below while maintaining strength targets in ring crush and mullen. In addition, other key business drivers were increased production rates and reduced operating costs. Nalco understood that meeting these goals could prove difficult given the present and past operating conditions on the paper machine and that minimal impacts had been realized with previous changes.
Nalco's Industry Technical Consultants in cooperation with its on-site team performed a thorough mechanical, operational and chemical (MOC) audit. The team provided several recommendations in each area with a major focus on chemistry. From a chemistry standpoint, there was a need to address drainage on the fourdrinier without disrupting sheet formation. This particular machine has a very long forming section. The wet end chemistry and their injection point was not overly complex with the use of alum, starch, rosin size and cationic flocculant.
A review of audit findings was communicated to the manufacturer and a plan was proposed to improve machine speed and increase strength. Chemical recommendations were made to limit early fourdrinier drainage, focusing on vacuum drainage and pressing, as well as strength development.
Program design
As a first step, a high molecular weight cationic flocculant along with colloidal silica and a balance of thin versus thick stock starch provided necessary drainage on the fourdrinier. The ability to move the dry line on the fourdrinier was evident.
However, this particular chemical program did not result in increased machine speed or strength. Several parameters were adjusted on the fourdrinier and press section to take advantage of the drainage, but no adjustment provided sustained results. This was not a major setback as pre-trial audit findings suggested this was possibly due to water handling in the press section. The initial chemical program provided important technical information and demonstrated that the Nalco team had the ability to understand the papermaking process dynamics and provide a technical reason for the paper machine response observed as well as propose a solution.
The next step focused on a two-component polymer approach using a high molecular weight cationic flocculant in combination with a METRIX technology product. The technology was selected for this customer due to proven effectiveness with similar furnishes and also due to the inability of a traditional retention and drainage program to meet the mill's key business drivers.
In addition, METRIX technology provides additional strength to allow for reduction in basis weight and refining. Experience with the technology, along with a thorough understanding of the papermaking process at this manufacturer's facility, allowed Nalco to design a program that would provide maximum environmental and financial savings at the lowest sustainable cost. This program integration provides the customer an Environmental Return on Investment (eROI), delivering both environmental performance and financial payback.
In designing the feed strategy of step two, existing wet end additives were considered as well as their respective location to each unit operation. A feed location was selected that provided maximum retention with minimal interference from disruptive fines and colloidal material. The strategy incorporated a co-mix approach with high molecular weight cationic flocculant and METRIX technology. At this facility an overfeed situation occurred at 3.0 lb/ton (1.36 kg/ton) of METRIX technology; therefore, the team selected 2.0 lb/ton (0.91 kg/ton) as the final dosage.
Program results
Analysis was completed on 35# and 42# grades, running the paper machine at maximum steam consumption/speed optimization.
4-5% basis weight reduction 7-10% manufactured square footage increase 7-10% reel speed increase 1.5-2 ton per hour production increase 6% reduction in refining energy per unit ton on 42# (205 g/m2 ), no change on 35# (170 g/m2 ) Maintained target ring crush and mullen Optimum METRIX technology dosage - 2 to 2.5 lb/ton (0.91 to 1.13 kg/ton) Minimal dosage changes for existing wet end chemistry Customer ROI: $750/operating hour Saved 90,000 gallons/yr in flocculant makedown water The METRIX Technology response prior to a speed and basis weight change showed a 14% reduction in steam consumption and a 10% increase in both ring crush and mullen, grade dependent.
Conclusion
METRIX technology is a synergistic, multi-component program developed to enhance productivity, press section dewatering and strength development for paperboard manufacturers. It encompasses the use of a reactive polymer and one of Nalco's advanced retention and drainage programs. Program benefits are designed to include increased sheet strength and machine speed from enhanced dewatering during pressing and drying operations.
Literature
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