| The ORGANOCELL Process for Sulfur free Pulp and Lignin | Germany | - | Full scale |
MANUFACTURE OF PAPER AND PAPER PRODUCTS # 45
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 ORGANOCELL process is essentially an all-alkaline pulping process. In the operation of the demonstration plant the wood chips are initially impregnated at a temperature of 110-140oC with a mixture of alcohol and water. Either methanol or ethanol can be used in the process.
From the impregnation stage the softened wood chips are transported into the digester where alkali and catalytic amounts of anthraquinone (AQ) are added. The pulping liquor is indirectly heated to 165-170oC, which produces a pressure of approximately 13 bar in the dome above the chip pile inside the digester, due to the methanol, 25-30% by volume, in the aqueous pulping liquor. The wood chips are then cooked for a period of 120 minutes, the alkali charge and the cooking time depending on the degree of delignification of the wood chips desired.
From the cooking zone the delignified wood chips move inside the digester downward into the high-heat wash zone where they are washed countercurrently with wash liquor from the pulp washers following the in-digester wash zone.
Once discharged from the digester, the pulp is screened on a knotter screen to remove knots and coarse uncooked wood pieces and then sent to the bleach plant. In the first bleaching stage, oxygen and alkali are mixed with the pulp.
While in the oxygen stage the main objective is to remove residual lignin form the pulp fiber without imparting damage to the cellulose during the alkaline oxygen treatment, the bleaching stages following the oxygen stage bring the most brightness improvements.
Attached to the ORGANOCELL demonstration plant is an experimental plant for the electrolytic recovery of sodium ions form black liquor. The plant is being operated on an intermittent basis to collect sulfur-free lignin and also to gain operational experience in the operation of said plant.
The ORGANOCELL process is capable of producing a wide range of pulps from hardwoods, softwoods and annual pants. ORGANOCELL type pulps are equal in quality to Kraft pulp properties. These pulps are bleached without chlorine products to quite high brightness levels. AOX discharges from bleach plants are insignificant.
The operation of conventional pulp mills is characterized by the emission of sulfur containing products into the air. With the conversion of a mill to the ORGANOCELL process these emissions no longer exist. The ORGANOCELL process does not produce any hazardous waste by-products. Since no sulfur is used in the process, by-products form the process can either be used in other industries, e.g., cement industry, or can be disposed by burning.
It is anticipated that the amount of fresh water used in the process will be approximately 30 cubic meters per ton pulp produced. The mill will be energy self sufficient by burning the organic wood degradation products produced in the pulping process. Some natural gas will be required in the chemicals recovery area of the mill to reburn calcium carbonate to lime.
Environmental and Economic Benefits
The ORGANOCELL process is the first solvent pulping process commercially implemented for the use of softwoods. Investment cost as well as operational cost for an ORGANOCELL type pulp mill will be lower than those for a Kraft mill since no odor control equipment will be required. The chemicals recovery portion of the plant is also simpler than that of a Kraft mill due to the absence of sulfur from the process.
Operational and maintenance costs will be lower than for a conventional Kraft mill since no odor control equipment will have to operated or maintained.
The payback time will be the same, if not shorter, than for a conventional Kraft mill due to the lower investment cost for an ORGANOCELL type pulp mill.
The ORGANOCELL process produces a sulfur-free pulp as well as sulfur-free lignin. The pulp can be bleached to market-accepted brightness levels without any chlorine products.
Constraints
ORGANOCELL type pulps are processed in the demonstration plant in a manner similar to Kraft pulps. No special equipment is required and plant operating practices are similar to those of a Kraft mill. Pulp is washed inside the digester countercurrently with wash water from the brown stock washers.
Fresh water is applied to the last stage of the brown stock washers and the filtrate cascaded back into the high-heat wash zone of the digester and ultimately into the evaporators/chemicals recovery plant.
In the 5-year operation of the demonstration plant no unstable operating situations have ever been encountered.
Pulping trials with mixed North American hardwoods have produced pulps which have physical properties superior to those which are normally produced from the same fiber source by the Kraft process.
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"