Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – With regeneration – reclamation – reuse – recycling or...
Reexamination Certificate
1995-05-02
2002-01-08
Alvo, Steve (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
With regeneration, reclamation, reuse, recycling or...
C162S030100, C162S065000, C162S076000, C162S078000
Reexamination Certificate
active
06336994
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for producing pulp which is cooked under alkaline conditions and which is bleached without using chlorine-containing bleaching chemicals, with separate installations being used for recovering and for incinerating/gasifying filtrates from the cooking and the bleaching, respectively.
2. Description of Related Art
Bleaching pulp without using chlorine containing chemicals provides processing solutions which are of great interest from the environmental point of view. Thus, the discharge of impurities into the bleaching plant effluent can be reduced substantially and, in the optimum case, virtually eliminated by, in an appropriate manner, collecting up and concentrating the organic and inorganic compounds in the effluent and subsequently incinerating together the concentrates and the used chemicals from the cooking procedure. A process of this type has been reported in Swedish Patent Application no. 9201477-8.
Bleaching without chlorine-containing chemicals is carried out using hydrogen peroxide, sodium hydroxide and ozone, in particular. These bleaching chemicals are expensive, so that bleaching costs are significantly higher than in the case of conventional bleaching using chlorine and chlorine dioxide. It is therefore desirable, if possible, to be able to recover the bleaching chemicals, especially sodium hydroxide, separately. Sodium hydroxide is principally obtained in association with preparing chlorine gas by the electrolysis of sodium chloride. With decreasing use of chlorine gas, there is some risk of sodium hydroxide becoming an item in short supply.
The process, which is advantageous from the environmental point of view, of returning the used bleaching chemicals, and organic material released during the bleaching, to the system for recovering cooking chemicals can give rise to problems under certain circumstances. If the quantity of sodium compounds and sulphur-containing compounds in the bleaching plant effluent exceeds the requirement for “make-up” chemicals to cover losses, an imbalance arises in the Na/S ratio in the recovery cycle for cooking chemicals. This can lead to problems of having too high an emission of sulphur to the environment, and to other disturbances of the process as well. Another problem, which is equally serious, is that organic material in the bleaching plant effluent, which is incinerated in the works recovery boiler, leads to overloading of the boiler. A works recovery boiler is often utilized to maximum capacity. Overloading results in the production of pulp having to be decreased, which is an economic disadvantage. In those instances where transfer of used bleaching chemicals to the recovery cycle for cooking chemicals can lead to an imbalance in the Na/S ratio and/or overloading of an existing recovery boiler, a separate recovery cycle for the bleaching chemicals would be highly advantageous.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a solution, which is technically and economically advantageous, both to the requirement for recovering bleaching chemicals separately and to the problems of limited capacity in the recovery boiler.
In the following, the term bleaching also embraces oxygen delignification.
The invention relates to a process for producing bleached pulp comprising the steps of cooking unbleached pulp under alkaline conditions with a cooking chemical to delignify said unbleached pulp, recovering a filtrate containing a used cooking chemical in a first recovery installation, bleaching said unbleached delignified pulp with a chlorine-free bleaching chemical, and recovering a filtrate containing a used chlorine-free bleaching chemical in a second recovery installation. Preferably, the used cooking and bleaching chemicals are regenerated and reused.
REFERENCES:
patent: 3725194 (1973-04-01), Smith et al.
patent: 4039372 (1977-08-01), Reeve et al.
patent: 4372812 (1983-02-01), Phillips et al.
patent: 4595455 (1986-06-01), Mannbro
patent: 4601786 (1986-07-01), Santen et al.
patent: 5164043 (1992-11-01), Griggs et al.
patent: 5164044 (1992-11-01), Griggs et al.
patent: 5340440 (1994-08-01), Henricson
patent: 5374333 (1994-12-01), Nykanen et al.
patent: 1064206 (1979-10-01), None
patent: 6909674 (1973-09-01), None
patent: 9412720 (1994-06-01), None
Ahlstrom Brochure, “New Generation Kraft Pulping and Bleaching Technology” 1992.*
Emerging Technologies Today and in the Future, Copyright 1992, pp. 1-6.
1981 Oxidative Bleaching, Denver Hilton, Denvr, Co., Oct. 22, Copyright 1981, pp. 75-78.
Optimized Hydrogen Peroxide Bleaching In Closed White-Water Systems, Rolf Anderson, et al pp. 111-115.
Bleaching A Softwood Kraft Pulp Without Chlorine Compounds, N. Liebergott, et al. pp. 323-332.
Mannbro, “Closed-cycle recovery and combustion of bleachery filtrate”, Nordic Pulp and Paper Research Journal No. 3/1990, pp 134-141. No Trans.
Backlund Åke
Nilsson Bengt
Stigsson Lars
Alvo Steve
Kvaerner Pulping Aktiebolag
Manelli Denison & Selter PLLC
Melcher Jeffrey S.
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