Summaries of October 2004 peer-reviewed papers.

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BLACK LIQUOR RECOVERY

RELEASE OF NITROGEN SPECIES FROM THE RECOVERY PROCESSES OF THREE KRAFT PULP MILLS

APPLICATION: Mills with malodorous vent gases can reduce the total nitrogenous gas emissions by combusting the gases in a controlled way.

Nitrogen enters the pulp mill with wood chips and is extracted during pulping as nitrogen-containing organic compounds and ammonia. The organic nitrogen compounds and some of the ammonia leave the washing process with the black liquor. While [N.sub.2] and NOx are the primary gaseous products from black liquor combustion, a significant portion of the original nitrogen remains in the char and exits the recovery boiler with the smelt.

This study centers on gaseous nitrogenous emissions found in the recovery boiler and the causticizing area at three kraft mills. Mass balances were carried out to calculate the nitrogen flow with the smelt. These data were compared to the nitrogen flow with the black liquor based on black liquor analysis and mill process data. This research provided information regarding nitrogen distribution during black liquor combustion at the three mills. It also resulted in information about the flow of cyanate and ammonia in the causticizing plants of the three mills, including the flow of ammonia with vent gases from recausticizing. View this paper online at http://www.tappi.org/index.asp?pid=30750

Nikolai DeMartini, Mikael Forssen, and Mikko Hupa are with Abo Akademi University, Process Chemistry Centre, Piispankatu 8, FI-20500 Turku, Finland. Klaus Niemela is with KCL, P.O. Box 70, FI-02151 Espoo, Finland. Asa Samuelsson is with STFI-Packforsk AB, Drottning Kristinas Vag 61, SE-11428, Stockholm, Sweden. Email DeMartini at [e-mail].

DELIGNIFICATION

RELATIONSHIP BETWEEN THE KAPPA NUMBER AND THE PERMANGANATE NUMBER OF THE WESTERN HEMLOCK KRAFT PULP

The kappa number of western hemlock kraft pulp can be calculated from its permanganate number and vice versa.

To study the relationship between the kappa and permanganate numbers of kraft pulp, the authors analyzed the experimental results of other research on kraft delignification of western hemlock wood. They found both semi-logarithmic and natural logarithmic relationships between kappa number and permanganate number. The kappa and permanganate numbers calculated fit well with the experimental values already determined. The kappa number of western hemlock kraft pulp can be calculated from its permanganate number and vice versa. View this paper online at http://www.tappi.org/index.asp?pid=30751

Vlado Masura is a former researcher, now retired from the Pulp and Paper Research Institute, Bratislava, Lamacska str. No. 3, 815 20 Bratislava, Slovak Republic.

NONWOOD FIBERS

RESPONSE OF BAGASSE AND WHEAT STRAW RECYCLED PULPS TO REFINING

APPLICATION: Bagasse and wheat straw are potential fibrous raw materials for countries short of forest-based fiber supplies. This investigation shows the effect of refining as a means of strength enhancement of recycled pulps of bagasse and wheat straw.

The effect of refining on the recycled chemical bleached pulps of bagasse and wheat straw has been evaluated. Refining in PFI mill is capable of recovering the tensile strength of recycled pulps to a large extent but with a sharp decrease in freeness. Reduction in freeness due to refining is more severe for wheat straw pulp than for bagasse pulp. High content of very fine particles in the wheat straw pulp contributes to a great deal in its slowness. An alkali treatment of pulps prior to refining reduces decrease in freeness. A 50:50 mixture of refined coarse fraction and unrefined fines fraction of the recycled pulps can be prepared to have much higher freeness than the refined whole pulp for equivalent strength values. View this paper online at http://www.tappi.org/index.asp?pid=30752

Mayank Garg and Surendra Pal Singh are with the Department of Paper Technology, Saharanpur Campus, Indian Institute of Technology Roorkee, India. Email Garg at [e-mail] or Singh at [e-mail].

TESTING

ACCELERATED LIGHT EXPOSURE OF WOOD-CONTAINING PULPS. PART I: EFFECTS OF WAVELENGTH AND INTENSITY

APPLICATION: This study shows the need for more reliable methods to test the light stability of wood-containing papers.

Mills increasingly use high yield pulps in higher-value papers where color stability is an important quality issue. While this is an attractive market for high-yield pulp producers, the lack of a credible method to test light stability impedes their ability to exploit this opportunity.

We examined the effects of wavelength distribution and intensity of the light source on the aging of peroxide-bleached softwood thermomechanical pulp (BTMP) and peroxide-bleached hardwood chemithermomechanical pulp (BCTMP). Accelerated aging protocols usually use light sources that have higher intensity or enhanced ultraviolet (UV) output compared to fluorescent office lighting. Our results show that these conditions do not reliably predict the performance of pulps treated with yellowing inhibitors. Even the relative ranking of different types of inhibitors can change as light intensity changes.

Our results suggest that accelerated aging protocols that use high-intensity broadband light or any light source with a strong UV component would significantly underestimate the light stability of papers containing mechanical pulp. Until a more thorough understanding of wavelength and intensity effects is achieved, testing methods using high-UV and high intensity illumination cannot be considered reliable in the absence of corresponding exposure tests under ambient conditions. View this paper online at http://www.tappi.org/index.asp?pid=30753

Peter F. McGarry, John A. Schmidt, and Cyril Heitner are with Paprican, Pointe-Claire, Quebec, Canada. Email Schmidt at [e-mail].

RECOVERY BOILERS

THE SINTERING TENDENCY OF RECOVERY BOILER PRECIPITATOR DUST

APPLICATION: Understanding the factors that cause fireside deposits to sinter and become resistant to sootblowing can help boiler operators to devise better strategies for minimizing fouling and plugging problems.

Blockage of flue gas passages by alkali salt deposits has been a problem in recovery boilers for many years. These deposits reduce heat transfer efficiency and lower overall black liquor burning capacity. Much progress has been made toward minimizing carryover deposit problems in the superheater region, but fouling and blockage of boiler bank gas passages by fine, sub-micron size fume or dust particles has persisted as a problem. These fume deposits are initially soft and are easily removed by sootblowing. However, they may harden rapidly and become strong enough that sootblowing is not effective in removing them.

A new method has been developed to rapidly characterize the sintering behavior of recovery boiler precipitator dust. Sixty-one dust samples from more than 40 recovery boilers of various types have been characterized, and their sintering tendencies have been ranked according to an index that relates to the strength of the sintered dust.

The results show that chloride and potassium contents had the most significant effects on dust sintering, while highly sulfated dusts did not sinter appreciably below 600[degrees]C. The sintering tendency of a particular sample was strongly related to the first melting temperature and the uncompacted bulk density of the dust. Black liquor firing load, solids contents, and sulfidity also had an effect on the sintering tendencies of the various samples. View this paper online at http://www.tappi.org/index.asp?pid=30754

Melanie Duhamel and Honghi Tran are with the Pulp & Paper Centre, University of Toronto, Toronto, ON, Canada. W. James Frederick, Jr. is with The Institute of Paper Science and Technology at Georgia Tech, Atlanta, GA. Email Tran at [e-mail].

ONLINE EXCLUSIVE PULPING

RAPID ESTIMATION OF SEASONING IN LOGS AND WOOD CHIPS BY ENZYMATIC COLORIMETRIC DETERMINATION OF GLYCERIDES

APPLICATION: Mills could use this quick test to sort wood chips and logs for seasoning or pulping and reduce pitch deposition problems.

A simple and fast procedure for estimating the elapsed time since tree felling (seasoning time) has been developed. The procedure is suitable for logs or wood chips. The method involves squeezing wood chips at high pressure and analyzing the resultant exudate for its glycerides content by an enzymatic colorimetric test. Fully seasoned chips yield a yellow coloration whereas fresh or partially seasoned chips yield a pink coloration, the intensity of which is a function of the seasoning time. Results can be obtained in about 20 minutes. The procedure can distinguish between fresh and seasoned wood. It was used to monitor laboratory seasoning of several wood species. View this paper online at http://www.tappi.org/index.asp?pid=30755

B. Bruce Sithole and Lawrence H. Allen are with Paprican, 570 Boul. St.-Jean, Pointe Claire, Quebec, Canada. Email Sithole at [e-mail].

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