Chemical aspects of reducing fresh water consumption

 There are many motifs to reduce the amount of fresh water consumed in paper/board production, from availability, cost, and energy savings to new more stringent government regulations and corporate “good citizen” image. Whatever the motifs, reducing fresh water consumption raises questions and fears about its impact on productivity, efficiency, and product quality. Pruszynski Paper Chemistry Consulting offers initial answers to those embarking on this journey. We are available to review the selection and application of wet-end chemistry to overcome some of the detrimental aspects of mill closure and delay significant capital investments. With 30+ years of global industry experience in process stabilization and impact of water chemistry on chemical programs, we bring unique perspectives on mill closure problems - academic and practical mill experience from 100+ paper machines in each corner of the world. Numerous papers, conference contributions, and the TAPPI book chapter have documented this interest over the years. Experiences gathered in European mills from the late 1990s to early 2000s, when mill closure projects were very active, are particularly relevant.

Reducing fresh water consumption can be modeled as a box with an input and output for potential contaminants with some degree of recirculation. For the system where the volume of freshwater inputs is equal to the total system volume (no recirculation), the degree of closure

r =0, and the concentration of any substance in the box remains identical to the concentration in the input flow - no accumulation or enrichment occurs. With increasing internal recirculation, freshwater represents a lower portion of the total system volume as more water is recirculated within the process box. Simple Alexander and Dobbin’s equation describes the Enrichment Factor (EF) as a function of the degree of closure r. The degree of closure (r) can be estimated from the freshwater flow and total system volume:

EF=1/(1-r) 

This equation was later modified by Xu and Deng, by adding the affinity tacoer K, describing the affinity of any species for the sheet. 

EF=1/(1-r+rK)  

Affinity factor reduces the EF at any given degree of closure r.  

The enrichment factor (EF) allows for predicting the impact of the freshwater reduction on the steady-state concentration of any substance added to the process box with all its sources. The shape of the plot of EF vs. r plot resembles the hockey stick, with the steep part at a high degree of closure. The response to the initial stage of freshwater reduction will depend on which part of this hockey stick mill finds itself at the beginning of the project. It is essential to ensure that we include only fresh water in contact with the papermaking process in these calculations. Otherwise, we underestimate the r value and place ourselves in the flatter range of EF change. If we use the total volume of freshwater usage, we need to put it in two categories – water used in contact with the fiber and water without such contact. 

Once we estimated the new level of wet-end chemistry contamination at any mill freshwater reduction, our experience allowed us to predict the scale of issues facing paper machine performance and product quality. Our experience includes operating under high conductivity conditions, high cationic demand, and hardness. These factors can critically affect retention, drainage, strength, sizing, and machine cleanliness. The recommendations of wet-end chemistry selection or changes in the application of existing chemistry may improve the performance, recover performance, and delay costly capital investments.  

  The dry strength properties of paper and board products are crucial to their performance. Various dry strength tests are always at the top of the quality specifications of each board and packaging grade. The fiber-fiber bonding characteristics always affect the paper products' strength. For a given fiber selection and its mechanical development through refining, papermaker can increase strength further by applying dry strength agents - typically various starches or synthetic dry-strength polymers.. 

   The performance of cationic dry-strength products is highly affected by increased levels of contamination associated with increased mill water circuit closure. Amphoteric additives (cationic and anionic charge) with their multiple adsorption options and higher resistance to increase conductivity levels are more robust in highly closed mills and using poor quality recycled fibers. A recent  joint paper published with ARAKAWA and Westrock R&D demonstrated the performance of amphoteric dry strength product Polystron and indicated interesting synergy with cationic GPAM. If interested, please look for this paper in the publication section of this website. 

This technology has been under development for at least 20 years and represents a very specific molecular weight and its distribution, amount of charge, charge ratio, and distribution. An earlier paper presented at TAPPICon in 2018 provided details of the molecular structure responsible for forming intra- and extra-molecular ionic complexes and improving retention on the fiber 

  Pruszynski Paper Consulting and the Arakawa Team would be available for the technical presentation describing all aspects of amphoteric dry strength technology marketed as Polystron.

This presentation would include all relevant technical, performance, and application details and product availability, service, support, and pricing. We would also perform a mill system survey to select addition points for the product. We then prepare a proposal for a short (1-2 days) mill trial to demonstrate product performance. Depending on customer request, additional lab testing could be done prior to short trial. 

Pruszynski Paper Chemistry Consulting Group provides technical support to the ARAKAWA team in the North American (US and Canada) market. Please get in touch with us for any technical information. We will re-direct commercial inquiries to ARAKAWA US team.