Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – With agitation or forced circulation
Reexamination Certificate
1997-01-09
2001-06-05
Hoffmann, John (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
With agitation or forced circulation
C162S063000, C162S065000, C162S066000
Reexamination Certificate
active
06241852
ABSTRACT:
The present invention relates to a process and a device for mixing fluid into a pulp suspension of cellulose-containing fibre material, such as, for example, so-called MC (Medium Consistency) pulp having a dry matter content of 5-25%. The fluid can, for example, consist of ozone-containing gas, the admixture taking place with the aim of bleaching the pulp suspension with one or more bleaching agents which include ozone, supplied together with a carrier gas.
TECHNICAL BACKGROUND AND PROBLEMS
The mixing of, for example, ozone-containing gas into a pulp suspension, during ozone bleaching, usually takes place at a relatively high pressure since the prospects for the bleaching reaction are appreciably improved as the pressure in the reaction sector increases. Therefore, in order to be able to carry out ozone bleaching effectively, both the pulp suspension and the ozone-containing gas must be pressurized.
The apparatus required for pressurizing ozone constitutes by far the largest part of the investment costs associated with ozone delignification of pulp suspensions. The costs of such apparatus increases progressively in relation to increasing pressurization. When generating the gas, large quantities of energy are supplied to the carrier gas, for example pure oxygen, in ozone generators, in association with which a relatively small quantity of ozone is nevertheless formed since the carrier gas can only contain limited quantities of ozone. The total gas flow, which, as a consequence, is very large, is then compressed in so-called liquid ring compressors which are expensive and susceptible to disturbances.
In this context, the problem with currently known devices for bleaching pulp suspensions with ozone is that the reaction pressure which is possible is limited by the capacity of the compressors. In an example taken from a currently existing device, the compressors operate at an excess pressure of 10 bar. The pressure in the mixer may then, in practice, not exceed 7-8 bar excess pressure if blockage of the compressors at the slightest disturbance is to be avoided.
Nowadays, the admixture usually takes place by the pulp suspension being brought into rotation using a rotor surrounded by a coaxial stator, with the gas being supplied in the periphery of the rotating pulp suspension where the counter pressure for the compressors is greatest.
OBJECT OF THE INVENTION
The object of the present invention is to remove the abovementioned problems by developing a process and a device which make it possible to add the fluid, for example in the form of ozone-containing gas, at a lower pressure than the reaction pressure of the device.
TECHNICAL SOLUTION
The abovementioned object is achieved by the invention making available a process and a device for mixing ozone-containing gas into a pulp suspension of a cellulose-containing fibre material.
The solution proposed by the invention thus implies, in brief, that the fluid is supplied in the vicinity of the centre of the rotating pulp suspension where, owing to the fact that the centrifugal force increases radially outwards, the local pressure in the pulp suspension is lower than the reaction pressure prevailing at the periphery of the pulp suspension.
The solution makes it possible to increase the reaction pressure, which was previously limited by the compressors, while retaining the same compressor. Alternatively, a smaller, appreciably cheaper compressor can be used while maintaining the same reaction pressure in the device.
The invention therefore offers major advantages as compared with previously known technology.
REFERENCES:
patent: 881888 (1908-03-01), Atwood
patent: 3388037 (1968-06-01), Asplund et al.
patent: 3725193 (1973-04-01), Montigny et al.
patent: 4339206 (1982-07-01), Ahs
patent: 4577974 (1986-03-01), Prough et al.
patent: 4842690 (1989-06-01), Gazdik et al.
patent: 5405497 (1995-04-01), Torregrossa
patent: 5536368 (1996-07-01), Makela et al.
patent: 1283902 (1991-05-01), None
patent: 174 660 (1961-03-01), None
patent: 419 603 (1981-08-01), None
patent: 1139781 (1985-02-01), None
patent: 87/00450 (1987-01-01), None
patent: WO 92/16288 (1992-10-01), None
Ekholm Rolf
Jansson Ulf
Nystrom Per
Dorsey & Whitney LLP
Hoffmann John
Kvaerner Pulping AB
LandOfFree
Method and device for mixing of a fluid into a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and device for mixing of a fluid into a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and device for mixing of a fluid into a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2467576