| The SRP Process for Reduced Energy Consumption | France | - | Full scale |
MANUFACTURE OF PAPER AND PAPER PRODUCTS # 38
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
This bivis process, called SRP process (sulfite reducing peroxide), is characterized by the following sequence:
| Pretreatment of chips with a chelating agent and washing. |
| Impregnation with a sodium sulfite solution containing a more electronegative reducing agent than the sulfite ions. Afterwards heating in the absence of air at a temperature above 100oC during 3 to 30 minutes. |
| Washing and bleaching of the sulfonated pulp with hydrogen peroxide in alkaline medium. |
The second step is the key point of the process; the impregnation must be carried out at ambient temperature in the absence of air. The reducing agent is added to the sulfonation liquor just before the impregnation. The most efficient agent is sodium borohydrite used in the form of alkaline solution containing 12% of sodium borohydrite and 40% of caustic soda. The molar ratio Na2SO3/NaBH4 should be higher than 8.
The pilot unit is running continuously producing pulp lots for paper and board trials. It includes principally two bivis machines and a double discs refiner operating in series. Chips defiberizing and sulfonation in reducing medium is carried out in the first machine, washing and bleaching in the second bivis machine. The bleaching reaction is carried out in a storage chest during one hour at 90oC. Then the bleached pulp is refined, screened and dewatered on the wet lap machine ready for use on a paper machine.
The installation also includes equipment for white waters recovery and their recycling in the process and for the preparation of chemicals mixtures for sulfonation and bleaching.
Bleached bivis pulps have been manufactured from softwoods chips (mixture of fir, spruce, sawmill waste) and from hardwoods (poplar).
Material/Energy Balances and Substitutions
| Material Category | QTY Before | QTY After |
| Waste Generation: | N/A | N/A |
| Feedstock Use : | N/A | N/A |
| Water Use: | N/A | 6-7 m3/t of pulp |
| Energy Use: | N/A | 1700-1800 kWh/T of |
| pulp (softwoods) 1600-1700 kWh/T of pulp (hardwoods |
Environmental and Economic Benefits
Total investment for a CTMP green field mill based on BIVIS technology:
| pulp capacity: 50 t/f (cotton); 20 million US$, (machinery: 6,5 million US$) |
| pulp capacity: 75 t/d (wood): 23,5 million US$, (machinery: 7,5 million US$) |
Operational and Maintenance Costs
| wood consumption: 1,76 t of wood/t of pulp AD (process yield: 92% |
| cotton consumption: 1,38 t of cotton/t of pulp AD (process yield: 87%) |
| kWh: 1,700-1,800 kWh/t (softwood), 1600-1700 kWh/t (hardwood) |
Chemicals:
| sodium hydroxide: 40 kg/t of pulp AD |
| sodium sulfite: 40 kg/t of pulp AD |
| hydrogen peroxide: 30-40 kg/t of pulp AD |
| maintenance costs |
| operating supplies: 8 US$/t of pulp AD |
| maintenance costs: 4% of investment cost/year. |
The Center Technique du Papier (Grenoble) has been studying this new bleached high yield pulping process with reduced energy consumption for several years. The equipment is well adapted to use the new bleaching process developed by Atochem (chemical group) for the manufacture of softwoods and hardwoods pulps. The bleaching is carried out with hydrogen peroxide. Both brightness of the unbleached CTMP pulp and the hydrogen peroxide response to bleaching are greatly improved. Furthermore it is possible to produce very strong pulps at high brightness levels because the brightening ability of sodium borohydrite allows the use of higher levels of caustic in the sulfite treatment. Chemicals could be saved when very high brightness is required.
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.