Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – With squeezing – compression – rubbing – kneading
Patent
1994-02-28
1995-11-14
Lacey, David L.
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
With squeezing, compression, rubbing, kneading
162 18, 162 26, 162261, 3661711, 3661721, 366307, D21B 134
Patent
active
054663342
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to methods and apparatus for mixing a treatment agent with a pulp suspension. More particularly, the present invention relates to methods and apparatus for mixing such treatment agents which can be chemicals, such as bleaching chemicals, in a liquid or gaseous state.
BACKGROUND OF THE INVENTION
In connection with various types of chemical delignification, it is decisively important to obtain persistently uniform and proportional admixing of chemicals with the pulp in order to achieve acceptable results. With such uniform admixing it is then possible to obtain uniform results in terms of treatment, as well as optimum utilization of the chemicals to the smallest required extent, as well as the lowest required temperature and shortest required reaction time. In order to minimize the chemical demand, and to further reduce the energy demand, it is desirable to carry out this treatment at a relatively high pulp concentration, preferably from about 10 to 25%.
In connection with the known devices, however, such high pulp concentrations create problems of a uniform distribution of the chemicals in the pulp. Present such devices normally comprise rotary members, which intensively agitate the pulp while the chemicals are simultaneously added thereto. Presently available devices are also relatively large, and require a great deal of energy. A substantial portion of the energy supplied to these devices is transformed solely into heat, and is thus not utilized efficiently during the mixing operation itself.
SUMMARY OF THE INVENTION
In accordance with the present invention, these and other problems have now been overcome by the invention of a method for mixing a treatment agent with a pulp suspension comprising supplying the pulp suspension to a mixing chamber having a predetermined width, moving the pulp suspension through a mixing zone within the mixing chamber, the mixing zone having a predetermined height, and supplying the treatment agent to the moving pulp suspension across the entire predetermined width of the mixing chamber prior to the mixing zone, the predetermined height of the mixing zone being sufficiently small so that the pulp suspension and the treatment agent are subjected to kneading within the mixing zone in order to repeatedly stretch and compress fiber flocks in the pulp suspension. In a preferred embodiment, the pulp suspension has a concentration of between about 10 and 25%.
In accordance with one embodiment of the method of the present invention, the kneading in the mixing zone is carried out at an energy input of between about 0.5 and 5 kwh per ton of the pulp suspension. In another embodiment, the pulp suspension and the treatment agent pass through the mixing zone for a time period of about 1/100 to about 1/5 of a second.
In accordance with the present invention, apparatus has also been provided for mixing a treatment agent with a pulp suspension which comprises a housing having an inner wall and a predetermined width, a substantially cylindrical rotor rotatably mounted within the housing for rotation at a predetermined direction about an axis, the rotor having a predetermined axial length substantially corresponding to the predetermined width of the housing and having an outer surface including mixing members thereon, a mixing chamber defined by the space between the housing and the rotor, an inlet in the housing for providing the pulp suspension to the mixing chamber, an outlet in the housing for withdrawing the pulp suspension and treatment agent from the mixing chamber, a treatment agent inlet in the housing for providing the treatment agent to the mixing chamber, and stationary mixing means mounted on the inner wall of the housing for a predetermined distance therealong, thereby defining a mixing zone for the predetermined distance within the gap between the mixing means and the mixing members on the outer surface of the rotor.
In accordance with a preferred embodiment of the apparatus of the present invention, the treatment agent
REFERENCES:
patent: 4339206 (1982-07-01), Ahs
patent: 4416548 (1983-11-01), Carre et al.
patent: 4577974 (1986-03-01), Prough et al.
patent: 4834547 (1989-05-01), Niskanen
patent: 5088831 (1992-02-01), Reinhall
Forslund Kjell
Fredriksson Borje
Lacey David L.
Nguyen Dean T.
Sunds Defibrator Industries Aktiebolag
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