| Super Batch Cooking - An Extended Delignification Process | Finland | 1992 | Full scale |
MANUFACTURE OF PAPER AND PAPER PRODUCTS # 36
Background
This case study was submitted on the part of the Working Group on Cleaner Production in Pulp and Paper Industries in the framework of the UNEP IE/PAC Cleaner Production Program with the support of the Technical Research Center of Finland's Non-Waste Technology Research Unit.
Cleaner Production Principle
Process modification
Cleaner Production Application
"Super Batch" is a cooking process based on the principles of extended delignification. This technology has been developed to reduce the chlorinated compounds in the discharge of bleach plant effluent.
The "Super Batch" cooking system was originally developed to make batch cooking more energy efficient. The system has been modified to achieve extended delignification in some mills. Environmental influence of effluents from bleaching of modified pulps is reported to be reduced if compared to conventional pulps.
Extended delignification refers to modifications of pulping processes, particularly the kraft processes, so as to prolong or extend the cooking to lower pulp lignin content or the kappa number in the digester. The main operational drawbacks to extended delignification are increased steam consumption and cooking time. These drawbacks have been overcome by coupling this technology with "Super Batch" cooking.
In the "Super Batch" system the chips are pre-impregnated and preheated with warm black liquor. Impregnation improves air removal from the chips. The digester will be hydraulically filled with liquor thus resulting in more uniform cooking.
Impregnation is followed by displacement with hot black and white liquor which gives very uniform pulp quality, high strength, low shives content, good heat economy, higher yield and makes extended cooking with good pulp properties possible.
Displacement with wash liquor at the end of cooking stops cooking reactions, cools the pulp and improves pulp washing by lowering the final black liquor solids.
Extensive mill-scale test runs have been performed in a Scandinavian pulp mill to observe the effects of extended cooking on the entire fiber line. The capacity of this mill is 900-1000 AD metric tons/day of bleachable-grade softwood or hardwood sulfate pulp.
The amount of Super Batch type pulp for the paper machine test runs was about 700 tons.
This process is fully implemented, with the first "Super Batch" mill having started in 1992.
The "Super Batch" process has been developed by Sunds Defibrator AB, Sweden. The equipment is readily available. Quantitative figures are based on actual mill
Environmental and Economic Benefits
The "Super Batch" cooking system enables very low steam consumption, washing in the digester and above all significantly improves the pulp quality and pulp yield.
| Material Category | QTY Before | QTY After (in bleaching effluent) |
| Waste Generation : AOX | 3,0 kg/t of softwood pulp | <1,0 kg/t of softwood pulp |
| COD | 70 kg/t of softwood pulp | <30 kg/t of softwood pulp |
| Feedstock Use: | N/A | N/A |
| Water Use: | N/A | N/A |
| Energy Use : | N/A | Reduction in steam consumption 70% |
Constraints
None reported.
Contacts
Review Status
This case study was submitted by the UNEP Working Group on Cleaner Production in the Pulp and Paper Industries, based at the Technical Research Center of Finland (address above) in 1992, as part of a contract for UNEP IE. Before submissions the case studies were reviewed at the Center. They were edited for the ICPIC diskette in June 1997.
Subsequently the case study has undergone another technical review by Dr Prasad Modak at Environmental Management Centre, Mumbai, India, in September 1998.