Retention/drainage technology reduces chemical cost.

Uncoated alkaline freesheet producers typically play a juggling game to maintain sheet quality, minimize furnish costs, and lower overall operating costs, while at the same time working to prevent production upsets. A Southern U.S. uncoated freesheet mill recently wanted to assess its ability to reduce machine operating and chemical costs but maintain or improve product quality.

The mill produces 650 tons/day of offset, envelope, linerboard, and cup stock on two machines using a furnish mix of softwood, hardwood, broke, and precipitated calcium carbonate. The machines run at a pH of 7.5 and a temperature of 110[degrees] F.

The mill's previous program used cationic polyacrylamide (CPAM) and bentonite and was meeting performance needs, but the need to reduce costs led the mill to investigate alternatives. A trial was run using a combination of alum, CPAM, and a competitive micropolymer with some positive results.

Hercules experts were asked to evaluate the system, and they recommended a program using alum and PerForm[R] SP9232 structured particulate, a newly re-engineered retention technology. This specially-designed technology provides superior retention, drainage, and formation and is used for a variety of neutral and alkaline paper grades. During an initial trial at the mill, the combination of the alum (added into the thin stock) and PerForm SP9232 were used to replace the existing retention and drainage program.

PerForm technology uses an anionic, organic particulate with a three-dimensional structure. The high charge and small size of this structured particulate make it efficient at delivering high performance on the machine. The structured particulate interacts with cationic sites on fibers, fines, and fillers to form microflocs. These microflocs provide retention but enable higher levels of drainage compared with traditional flocculants that create larger, more difficult to dry flocs.

Cationic sites are provided by additives such as alum, PAC (polyaluminum chloride), cationic flocculants, cationic starch, and/or polyamide wet strength resins. The sites with the strongest influence on the PerForm SP particulate are created by sources of aluminum, such as alum and PAC. Low levels of these additives used in conjunction with the PerForm SP particulate provide high levels of retention and drainage. In some programs, cationic flocculants are used in addition to or in place of alum or PAC to provide additional cationic sites to boost performance.

Numerous grades of paper, including coated and uncoated fine papers, LWC mechanical papers, white top board, recycled packaging board, bleached board, and towel grades, can benefit from this technology. Under proper conditions, the technology has also been effective in acid pH bleached board and acid pH unbleached packaging grades.

MILL RESULTS

The mill trial indicated that first pass ash retention had increased while maintaining good machine drainage, justifying conversion to the PerForm SP9232 technology. Further fine-tuning by Hercules and the mill helped improve first quality tons by 28% since initial conversion. Hercules' recommendations to change retention aid and PCC addition locations dramatically reduced sheet holes, which led to several mill production records.

Other benefits to the mill included: an overall cost reduction of 7.3% compared with the previous program; increased first pass ash retention; and elimination of handling and feed issues associated with bentonite.

The benefits achieved by this mill complement similar successes at other freesheet mills. A Northeast U.S. fine paper producer recently was asked by a new customer to develop a grade that had 25% to 27% sheet ash. The barrier for the producer was that its existing silica-based program--using an anionic flocculent, borosilicate, and alum--could not provide consistent ash retention beyond 22% sheet ash.

Based on an assessment and recommendations by Hercules, the mill trialed and converted to a program using a different flocculent combined with the PerForm SP9232 technology. The mill trial indicated that first pass ash retention had increased significantly with lower dosages of flocculent. The new program consistently maintained target sheet ash of 25% to 27% and controlled tray solids. The mill also realized an improvement in drainage with the new program, even though this was not the reason for running the trial.

For this mill, the ash content increase represents a US$ 10/ton saving in fiber cost alone. Also, the overall white water solids reduction allowed the clarifiers to operate with 50% less flocculent, and on grades with a basis weight of 70-lb., the need for flocculent was eliminated. These objectives were met at 30% less cost to the mill.

ABOUT THE AUTHOR:

James H. Woodward (Jamie) is a product development manager for Hercules Pulp and Paper Division. Woodward has been with Hercules for more than 11 years and has held a number of jobs within the company, including sales, applications, and product promotion positions. Most recently, he was responsible for leading one of the most successful product launches in Hercules' history. Contact him by email at [e-mail].

[ILLUSTRATION OMITTED]