Improving fiber yield through borate autocausticizing.

Editor's Note: This series of articles is a result of the Forest, Wood and Paper Industry's Agenda 2020 Program, which is focused on providing technology for a robust and sustainable future. Summarized here is one of the six platforms of Agenda--Breakthrough Manufacturing Technologies.

New technology has continually transformed the pulp and paper industry throughout its long history. Today, we are looking for the breakthrough technologies that will drive change in our new century.

The goal of the "Breakthrough Manufacturing Technologies" platform of Agenda 2020 is to utilize new technology to achieve a 35% reduction in manufacturing costs by targeting three key goals for significant process changes:

* A 50% enhancement of fiber functionality

* A 50% reduction in energy use

* A 33% reduction in fiber and materials consumption

Three key sessions at Technology Summit II, held in May 2004, focused on these breakthrough goals:

1. Reducing the complexity of paper drying

2. Retaining and improving fiber functionality

3. Increasing fiber yield

This report centers on the results, forward paths, and subsequent progress for the Increasing Fiber Yield session.

FIBER YIELD SESSION GOAL, ORGANIZATION, AND PROCESS

The goal of the session was to identify key activities and individuals who will remove barriers to the development and deployment of higher yield, cost effective processes within existing pulp and paper mills.

To this end, 10 session participants from producer companies, suppliers, and academia reviewed a portfolio of projects developed in partnership with the U.S. Department of Energy's Industrial Technologies Program. The review's objective was to select one or two project technologies around which an alliance of interested companies might be formed to accelerate deployment. Criteria for selection were:

1. Promising benefits in fiber, energy, and capital costs

2. Proximity to deployment as evidenced by pilot activity and/or mill trials

3. Strong interest by companies and individuals to form an alliance to remove any remaining barriers to technical success.

Reviewed projects were:

* Directed green liquor utilization pulping (DGLV)

* Borate autocausticizing to supplement lime kiln and causticizing capacities

* Two projects on high selectivity oxygen delignification

Of these technologies, borate autocausticizing was selected for an immediate, informal deployment alliance. Especially if implemented as a 100% replacement of the lime and causticizing cycles, this technology has the greatest potential for yield improvement, elimination of fossil fuel dependence (1), reduction of process complexity, and avoidance of future capital investment (2). Borate autocausticizing has also established a recent track record of mill trials and long-term usage as a partial supplement to the production of kraft cooking liquors.

OVERVIEW AND STATUS

This technology is an alternate and simpler means of producing sodium hydroxide in kraft white liquor. Sodium borates are added to the liquor cycle to expel carbon dioxide from sodium carbonate, forming trisodium borate in the recovery boiler smelt. The latter compound when hydrated in the smelt dissolving tank forms caustic and sodium metaborate, which remains soluble through the white and black liquor cycle. The metaborate continues to form caustic when it returns to the recovery boiler. The following equations summarize the autocausticizing chemistry:

NaB[O.sub.2] + [Na.sub.2]C[O.sub.3] [left and right arrow] [Na.sub.3]B[O.sub.3] + C[O.sub.2] Recovery Boiler (1)

[Na.sub.3]B[O.sub.3] + [H.sub.2]O [left and right arrow] 2NaOH + NaB[O.sub.2] Dissolving Tank (2)

This borate causticizing chemistry is now being used to partially supplement white liquor production by conventional processes where there is a lime kiln or causticizing restraint. Typically, in mill applications of partial autocausticizing, 10-20% of the required caustic is provided by borate addition.

The evolution of partial borate autocausticizing is shown in Figure 1. In some instances, both laboratory and extended mill trials have indicated that a 1 to 2% yield increase may accompany this technology due to the presence of borate in pulping liquors. For more information on borate autocausticizing, please refer to John Cameron's publication in TAPPI JOURNAL [3(6), p. 3-6, June 2004].

100% BORATE AUTOCAUSTICIZING

The primary interest of the informal alliance formed around borate autocausticizing technology is the eventual elimination of conventional calcining and causticizing operations by 100% regeneration of white liquor caustic in the recovery boiler and dissolving tank. This goal is illustrated in Figure 2 and represents a major reduction in fossil fuel use, process complexity, and capital expenditures. It is also possible that more consistent and higher yields will be realized at high concentrations of borate in cooking liquors.

[FIGURE 2 OMITTED]

As a result of Technology Summit II, the informal alliance mentioned above was formed to further the development of 100% borate autocausticizing. The alliance companies are International Paper, US Borax, Mead-Westvaco, and Weyerhaeuser.

PROGRESS SINCE SUMMIT II

The alliance had its first meeting in Cincinnati, Ohio, USA in June 2004. Company experts in pulping and recovery reviewed the state of knowledge around borate autocausticizing and generated a gap analysis for 100% borate autocausticizing. Key gaps are:

* percent autocausticizing achievable in practice

* potential yield increases for southern pine

* recovery boiler issues as borate levels approach the 100% case

* black liquor properties as borate levels approach the 100% case

* synergy with new pulping and recovery technologies

The major outcome of this meeting and gap analysis was the decision by alliance members to fund development of a material and energy balance model for a kraft mill using 100% borate autocausticizing technology. Model development is now underway.

NEXT STEPS

Assuming the material and energy model indicates an attractive case for 100% borate autocausticizing, the alliance will develop a formal consortium, including research partners, to prepare proposals and seek government funding to conduct research and develop 100% borate autocausticizing.

1979-1998       1998-2000     2000-2002         2002-Present
Early           Concept       Technology        Commercialization
investigation   testing       refinement

* One trial in  * Six trials  * Five trials  * Eight trials around the
  Europe          in N.         in N.          globe:     1 successful
* Laboratory      America       America      N. America:  1 unsuccessful
  work          * Chemistry   * Operational  Europe:      1 successful
* New             proven        issues       S.           2 on-going
  chemistry     * Modified      uncovered    America:     1 on-going
  proposed        analytical  * Screening    Asia/        1 successful
                  process       criteria     Pacific:     1 planned
                  developed     developed

Figure 1. Chronological summary of major development activities in
borate autocausticizing.

WHAT YOU WILL LEARN

* The goal of the "Breakthrough Technologies" platform of Agenda 2020.

* Why borate autocausticizing was selected as a key "breakthrough technology."

* The additional steps needed to implement 100% borate autocausticizing.

ADDITIONAL RESOURCES

* Initial results from Technology Summit II: www.tappi.org/redirects/techsummit.asp.

* "Technology Summit II targets the challenge of deployment," Solutions!, June 2004. To access this article, enter the following product code in the search field on www.tappi.org: 04JUNSO49.

* "Setting the Industry's Technology Agenda," edited by Gerard Closset. Product Code: 0101R307

(1) It has been estimated that the lime cycle consumes approximately 2 MMBTU per ton of pulp (1.7 MMBTU per ton of pulp from fossil fuel) for a 350,000 ton per year plant.

(2) The installed costs for a kiln and recausticizing plant have been estimated at US $50 million.

ABOUT THE AUTHORS:

Bob Eckert (not pictured) is director, strategic technology for Weyerhaeuser Co., Federal Way, Washington, USA; contact him by email at [e-mail].

David Turpin is director, process and product development for MeadWestvaco Research, Chillicothe, Ohio; contact him by email at [e-mail].

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Josh Dunn is business development manager, autocausticizing for U.S. Borax Inc., Valencia; California. Email: [e-mail].

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