Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Charging and/or discharging fibrous material
Reexamination Certificate
1998-01-23
2001-04-24
Alvo, Steve (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Charging and/or discharging fibrous material
C162S057000, C162S068000, C162S078000
Reexamination Certificate
active
06221208
ABSTRACT:
RELATED APPLICATIONS
This application claims the priority of PCT Application No. PCT/SE96/00280, filed Mar. 4, 1996, and Swedish Application No. 9501094-8, filed Mar. 28, 1995.
TECHNICAL FIELD
The invention relates to a method for treating a fibre pulp suspension, which comprises transporting the fibre pulp suspension from a maintenance vessel, in which there is atmospheric pressure or at most 1 bar overpressure and in which the temperature of the pulp suspension does not exceed 95° C., to a bleaching reactor and introducing the suspension into the bottom part of the reactor, which is at least 10 m high and at the top of which there is an overpressure exceeding the steam saturation pressure, in which reactor the pulp is subjected to a bleaching treatment under pressure at a reaction temperature which exceeds 100° C., in addition to which the pulp suspension, during transport from the maintenance vessel to the reactor, is heated to at least reaction temperature.
The invention also relates to equipment for treating a fibre pulp suspension, comprising means for transporting the pulp suspension from a maintenance vessel to a bleaching reactor and for introducing the pulp suspension into the bottom part of the reactor, and also means for increasing the temperature of the pulp suspension, during transportation, from a temperature which does not exceed 95° C. to a temperature of at least 100° C.
BACKGROUND TO THE INVENTION
In the bleaching departments of chemical pulp mills, the fibres are normally transported, in the form of a fibre pulp suspension, from a maintenance vessel, for example a so-called standpipe, using a pump which is directly connected to the maintenance vessel. This pump generates a pressure which is sufficiently high to enable the suspension to be transported to the reactor vessel and introduced through the bottom of the latter. On the way, aqueous steam is supplied in a mixer in order to heat the suspension from the said temperature which does not exceed 95° C., for example room temperature or normally approximately 70° C., to a temperature which is suited to the reaction and which is at least 100° C., normally greater. In order to achieve this, the pump pressure has to overcome the losses in pressure along the transportation distance, including a possible loss in pressure through the mixer, and, in particular, overcome the counterpressure in the bottom part of the reactor. This pressure can be considerable, since the reactors in question are tall, giving rise to a high static pressure at the bottom, and, in addition, a process pressure is applied to them. This means, in turn, that it is necessary, to achieve the heating, to use steam which is under a relatively high pressure, usually so-called medium-pressure steam which is available in the pulp mill and which is normally at a pressure of 9-12 bar. A disadvantage of this technique is that medium-pressure steam is expensive. Another limitation is the fact that it becomes difficult, or is rendered impossible, to use a mixer of the type which results in a pressure fall. This is a drawback, since these types of mixer possess certain advantageous properties, such as being relatively simple and cheap.
BRIEF ACCOUNT OF THE INVENTION
An object of the invention is to provide a method and equipment which enable low-pressure steam to be used for heating a fibre pulp suspension in the above-described environment. Low-pressure steam is a cheaper product than the more select medium-pressure steam. The overall economy of the integrated mill is improved if the consumption of medium-pressure steam can be reduced.
Another advantage of the invention is that any mixer type whatsoever, in which aqueous steam can be mixed into a fibre pulp suspension, can be used as the mixer, i.e. both differential pressure mixers of the type which do not contain any continuously moving parts, for example a mixer of the type which is described in WO 9521016 (PCT/SE95/00104), and more conventional mixer equipment containing rotatory members, for example a mixer of the type which is described in SE-B-419 603.
These, and other objects and advantages of the invention, can be achieved by means of the invention being characterized by that which is specified in the subsequent patent claims. Additional features and aspects, and also advantages, of the invention will be evident from the following description of a preferred embodiment.
REFERENCES:
patent: 5217575 (1993-06-01), Backlund
patent: 5690786 (1997-11-01), Cirucci et al.
patent: 24 41 579 (1975-03-01), None
Alvo Steve
Dorsey & Whitney LLP
Kvaerner Pulping AB
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