| The Drum Displacer - A Multistage Washer for Conserving Water | Finland | - | Full scale |
MANUFACTURE OF PAPER AND PAPER PRODUCTS # 25
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
New technology.
Cleaner Production Application
The Drum Displacer is a new multistage washer, where all washing stages are carried out with one drum. The washer consists of a rotating drum with sectors and of a housing around the drum. Further, the housing has been divided into various zones. One of the main components is the distribution valve.
Pulp is pumped at a consistency of 4-6% to the feed zone, where it is thickened approximately up to 10 t. Pulp is washed at this consistency, but is not diluted nor thickened during washing. In the thickening zone the pulp is de-watered by means of vacuum. Then the consistency rises approximately up to 15%. The pulp is discharged by compressed air.
The washing is carried out as a four stage displacement washing on the counter-current principle. The washing liquid is pumped to the fourth washing zone, from where the liquid passes through the pulp to the third washing zone. This is repeated in the second and first washing zones. The filtrate from the first zone flows to the filtrate tank.
The Enso-Gutzeit mill's washer capacity is 80 ADMTPD (air dry metric ton per day) and the Kymmene mill's is 200 ADMTPD. The raw material in both mills is sawdust of birch and pine.
The process discussed is commercially available. The washing machinery is specially designed for this application.
Environmental and Economic Benefits
The single unit process reduces the maintenance requirement to a minimum. The average maintenance time the washer has required is 8 hours/year.
The reduced number of equipment (25 vs. 100) enables installation in a smaller space. Pulp is not diluted between different washing stages. The quantity of liquid to be pumped and the energy needed for pumping decrease considerably. Pulp washing is carried out in a pressurised liquid phase resulting in more complete displacement. Pulp can be washed clean with a smaller water quantity. During washing the quantity of circulating wash liquid is small and the retention time short (3 min) compared to the filter washing line (more than 600 min). The washing is controlled almost without retention time.
Material/Energy Balances and Substitutions
| Material Category | QTY Before | QTY After |
| Waste Generation: | 100 | reduced (see water) |
| Feedstock Use: | 100 | 100 |
| Water Use: | 100 | 80 |
| Energy Use : | 100 | 50 |
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 submission, 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.height="6"