MANUFACTURE OF PAPER AND PAPER PRODUCTS # 13

Background

The SEP pulping process produces hardwood/softwood pulp of a strength comparable to that of low yield hardwood kraft pulp. In addition, the SEP process uses appreciably less refining energy than the conventional chemi-mechanical pulping processes. The environmental aspect of SEP process is similar to that of ultra-high yield CMP as far as cooking effluent is concerned and is about 50 % lower in bleaching effluents.

Cleaner Production Principle

Process modification

Cleaner Production Application

The steam explosion pulping process consists of the chemical impregnation of chips, a short time steam cooking, pressure release, refining and bleaching. In order to protect the chips against oxidation during the cooking stage and to simultaneously develop hydrophilic groups on the fiber surface during the steam treatment, the impregnation solution contains antioxidant agents like Na₂SO₃. To assure good swelling of chips and at the same time to prevent acid hydrolysis leading to yield loss, swelling agents such as NaOH, Na₂CO₃ or NaHCO₃ are present especially during hardwood cooking. The chemical up-take is from 8% to 10%. Short cooking time varying from 30 seconds to 6 minutes at temperatures varying from 170^oC to 210^oC leads to ultra-high-yield (90%+) explosion pulps of excellent pulp and paper properties.

Properties of exploded aspen, birch, maple or eucalyptus pulps are substantially better than those of corresponding ultra-high yield CTMP or CMP and can approach those of equivalent low yield kraft pulps.

The brightness of exploded aspen pulps (60%+) can be increased to 80%+ level by application of 4% H₂O₂.

In the case of hardwood pulps, the explosion pulps lead to considerably stronger papers when compared to equivalent CMP/CTMP pulps but using substantially lower refining energy. The strength can be up to 50% superior and the refining energy requirement up to 50% less than those of conventional pulps.

Scale of Operation: In the experiments reported, eight tonnes of aspen chips were impregnated with sulfite and caustic. Mills of 100 000 tons of pulp per year have been evaluated by several consulting companies like NLK, Nystrom Lee and Kobyashi, etc.

Stage of Development: Pilot stage.

Level of Commercialization

The technology is ready for commercialization via Stake Technology Ltd, Toronto, Canada.

Environmental and Economic Benefits

Bleaching with one stage H₂O₂ is environmentally acceptable. Primary and secondary treatment of effluents decreases BOD, solid substances and toxicity to very low levels.

Investment costs, operational and maintenance costs and payback time are available from Stake Technology Ltd.

The SEP require considerably lower capital investment (1/2) as well as operating cost than low yield hardwood kraft pulping. The SEP process can be economical in much smaller size (100 t/day).

Constraints

The new technology has to be proven on industrial scale. The same proven equipment used in conventional CMP processes are completed with a continuous Stake-Tech Digester already being used on industrial scale in biomass production (the continuous Stake Tech reactor replaces one refiner, therefore the capital cost of SEP is comparable to that of CMP).

Contacts

Name and Location of Company

Universite du Quebec a Trois-Rivieres

Center de recherche en pates et papiers

C.P.500, Trois-Rivieres,

Qc G9A 5H7 Canada

Tel : +1 819 376-5075; Fax : +1 819 376-5148

Type of Source material

Journal article and a book (Additional information on the experimental procedures as well as pulp properties is available in the source material.)

Citation

1. Barbe, M.C., Kokta, B.V., Lavallee, H-C. and Taylor, J., Aspen pulping: A comparison of Stake explosion and conventional chemi-mechanical pulping processes, Pulp & Paper Canada, 91:12 (1990), pp. 142-151
2. Kokta, B.V., Steam Explosion Pulping, book: Foc her, B., Marzetti, A. and Crescenzi, V.(ed.), Steam explosion techniques, Fundamentals and Industrial Applications, Gordon and Breach Science Publishers, 1991, pp. 163-206

Industry/Program Contact and Address

Bohuslav V. Kokta, Dr., Universite du Quebec a Trois

Rivieres, Center de recherche en pates et papiers,

C.P.500, Trois-Rivieres, Qc G9A 5H7 CANADA, phone: +1

(819)376-5075, fax: +1 (819)376-5148

John Taylor, President, Stake Technology, 2838 HwY7,

Norval, Ont, 2051KO, phone: 1-416 455 1990, fax: 1-416 455 2529

Review Status

This case study was submitted to UNEP IE by the Working Group on Cleaner Production in Pulp and Paper Industries : the Technical Research Center of Finland, located at PO Box 205, SF-02151 ESPOO, FINLAND (Tel: +358 0 456 6594, Fax: +358 0 460 493, e-mail: rabbe.thun@vtt.fi). The results were reported in December 1990. The case study was reviewed and edited by UNEP IE in August 1996. It has not undergone a formal technical review.

Subsequently the case study has undergone another technical review by Dr Prasad Modak at Environmental Management Centre, Mumbai, India, in September 1998.