DEFIBRATOR WITH SEPARATED BLOW VALVE

Abstract

The invention relates to a pulp refining system for mechanically refining of lignocellulosic material, comprising a defibrator, a defibrator housing, in which the defibratoris arranged, a blow valve having an inlet and an outlet and being adapted for regulating a flow of pulp therethrough, and a discharge pipe having an inlet, which is connected to the outlet (12) of the blow valve, wherein a mounting pipe having an inlet, which is connected to the defibrator housing, is arranged between the defibrator housing and the blow valve, said mounting pipe having a length of at least about 0.2 meter.

Description

TECHNICAL FIELD

The present invention relates generally to a defibrator used in the manufacture of pulp from lignocellulosic material, such as wood chips, and more particularly to a blow valve through which fibrous pulp leaves a defibrator housing, and even more particularly to a specific mounting arrangement for such a blow valve between a discharge pipe and a specially arranged mounting pipe connected to the defibrator housing.

BACKGROUND

A defibrator is a refining apparatus in which lignocellulosic materials, e.g., wood chips, saw dust and other fibrous materials from wood or plant, are ground between two refining elements in an environment of steam. A typical defibrator for processing fibrous materials is a disc-type refiner, wherein two refiner plates—which also are referred to as refiner discs—are positioned opposite to each and wherein at least one refiner plate rotates with respect to the other refiner plate. The lignocellulosic material to be refined is fed into a central inlet in at least one of the two refiner plates, and moves therefrom into a refining gap arranged between the two refiner plates. As at least one of the refiner plates rotates, centrifugal forces created by the relative rotation between the two refiner plates move the lignocellulosic material outwards and towards the periphery of the refiner plates. The opposing refiner plates have surfaces that include bars and grooves, and the lignocellulosic material is—in the refining gap provided between crossing bars of the opposing refiner plates—separated into fibers by forces created by the crossing bars as the refiner plates rotate in relation to each other. Another type of defibrator is a drum-type refiner, in which a refining gap is formed between an outer cylindrical drum and a rotor that rotates inside the outer cylindrical drum.

In the thermo-mechanical refining process referred to above, a considerable amount of energy is required to create and maintain the rotational movement that separates the lignocellulosic material into fibers, and a large part of this mechanical energy is converted into heat, whereby steam is generated in a defibrator housing in which the defibrator with its refining elements is arranged. The pulp created by the defibrator is fed out from the defibrator housing through a discharge pipe, and because of the pressurized atmosphere prevailing inside the defibrator housing, a blow valve—also referred to as a discharge valve—is arranged at the defibrator housing and is connected to the discharge pipe, and the pulp is fed through this blow valve before being fed into the discharge pipe for further transport and processing. An arrangement of this type is, for example, disclosed in the U.S. Pat. No. 4,163,525 to Reinhall.

As indicated above, the energy consumption in a defibrator is high, and there are always ongoing efforts to reduce this energy consumption and thereby the operating costs of a defibrator. This can, for example, involve more efficient use of the steam generated in the refining process. Another technical challenge is a substantial wear of components in a defibrator, which reduces the operating life-time of these components and leads to high operating costs. Examples of such wear-subjected components are the refining elements, e.g. refiner plates, and also the blow valve, which is arranged at the defibrator housing and through which pulp is fed out into a discharge pipe. An object of the present invention is therefore to reduce the energy consumption in a system comprising a defibrator. Another object is to increase the operational life time for a blow valve arranged at a defibrator housing by reducing the wear of this blow valve.

SUMMARY OF THE INVENTION

The above-mentioned objects are achieved with a pulp refining system comprising a defibrator, a defibrator housing and a blow valve according to the independent claim. Preferred embodiments are set forth in the dependent claims.

The invention relates to a pulp refining system comprising a defibrator arranged in a defibrator housing, which has a portion from which pulp is fed out to a discharge pipe. The pulp refining system comprises further a blow valve, which—according to the invention—is mounted before (as seen in the pulp transport direction) the discharge pipe and is connected to the defibrator housing by a mounting pipe having a length, which is at least about 0.2 meter, and more preferably at least about 0.5 m, and even more preferably about 0.7-1.5 m. In one embodiment of the invention, the mounting pipe has the same diameter at its inlet, which is connected to the defibrator housing, as at its outlet, which is connected to the inlet of the blow valve. This diameter is further preferably the same as the diameter of a flow channel through the blow valve when the blow valve is in a fully open position.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be further explained hereinafter by means of non-limiting examples and with reference to the appended drawings, wherein:

FIG. 1 is a schematic illustration of a pulp refining system according to the present invention.

FIG. 2 is a schematic illustration of a blow valve, a discharge pipe and a mounting pipe arranged in the pulp refining system illustrated in FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 illustrates schematically a refining system 1, which comprises a defibrator 2 with a first refining element 3 and a second refining element 4. In this example, the first refining element 3 is a stationary refining disc 3, while the second refining element 4 is a rotating refining disc 4. However, the type of refining elements is not crucial for the present invention, and the refining elements could, for example, instead of refining discs be a rotor that rotates within an outer drum. The defibrator 2 is arranged within a defibrator housing 5, which, because of the steam generated by the mechanical forces created when the lignocellulosic material is ground between the first refining element 3 and the second refining element 4, contains a pressurized atmosphere. Pulp, which has been ground between the two refining elements 3, 4, leaves the defibrator housing 5 at a house portion 6, and enters into a mounting pipe 7, whose inlet 8 is connected to the defibrator housing 5 and whose outlet 9 is connected to an inlet 10 of a blow valve 11, whose outlet 12 is connected to an inlet 13 of a discharge pipe 14.

The provision of a mounting pipe, such as mounting pipe 7, is a novel arrangement according to the invention, because the standard practice in the field is to arrange a blow valve, such as blow valve 11, in direct connection with a defibrator housing, such as defibrator housing 5. However, by providing the mounting pipe 7, which has non-negligible length, surprisingly positive effects have been achieved both regarding the energy consumption of the defibrator 2 and also regarding the wear of the blow valve 11. Without wishing to be bound be theory, it is believed that the provision of the mounting pipe 7 before the blow valve 11 creates a laminar pulp flow through the blow valve 11, i.e. the pulp flow at the exit from the defibrator housing 5, i.e. at the inlet 8 of the mounting pipe 7, is presumably highly turbulent, and by providing the mounting pipe 7, which has a non-negligible length, the pulp flow is “settling down” and a laminar flow is established at the outlet 9 of the mounting pipe 7. And it is further believed that this laminar pulp flow is less aggressive and exposes the inner surfaces of the blow valve 11 to less wear. The reduction of energy consumption in the defibrator 2 is more difficult to understand, but it could be that when a turbulent pulp flow encounters a blow valve—as is the case when a blow valve is mounted directly at a defibrator housing—shock waves are created which are transferred back through the pulp to the rotating refining element and counteract its movement, something which, in turn, requires energy to overcome. Thus, by creating a laminar pulp flow through a blow valve, these repercussioning shock waves are eliminated, which has a positive effect on the energy consumption.

To achieve a laminar pulp flow through the blow valve 11, the mounting pipe 7 has been given a length of at least about 0.2 m, and more preferably a length of at least about 0.5 m, and even more preferably of at least about 0.7 m. In FIG. 1, the length of the mounting pipe 7 is indicated by an “L”. The maximal length of a mounting pipe, such as mounting pipe 7, is not so crucial for practicing the present invention. However, if for some reasons the blow valve 11 is closed, pulp will plug and block the mounting pipe 7 and it may take a considerable time to remove this pulp and put the refining system 1 back into operation again. Furthermore, it is the steam pressure generated in the defibrator 2 that drives the refining system 1, i.e. the steam pressure forces the pulp forward and through the mounting pipe 7, the blow valve 11 and the discharge pipe 14 and also through further components and pipes which are not seen in the figures; and more specifically, it is the pressure drop over a pipe or component section, such as over mounting pipe 7, that creates a pulp flow through the section in question. Hence, a blow valve, such as blow valve 11, cannot be positioned so far from a pressure generating defibrator so that the pressure has dropped to zero or essentially zero. For at least these reasons, the length of the mounting pipe 7 should not be longer than necessary, and a suitable maximal length is about 1.5 m, i.e. 0.2 m≤L≤1.5 m. The mounting pipe 7, the blow valve 11 and the discharge pipe 14 are schematically illustrated in FIG. 2. The mounting pipe 7 has preferably a circular inner cross-section with an inner diameter d₁, which preferably is constant, i.e. the diameter d₁ is the same at the inlet 8 of the mounting pipe 7 as at the outlet 9 of the mounting pipe 7. Further, the blow valve 11 comprises a valve housing 15, which, inter alia, encloses a flow channel 16, through which the pulp is intended to flow. The cross-sectional area of the flow channel 16 can be regulated by a valve member 17, which can be introduced into the flow channel 16 to thereby reduce the size of the cross-sectional area of the flow channel 16, but according to the present invention, the cross-section of the flow channel 16 of the blow valve 11 is preferably equal to the cross-section of the mounting pipe 7. The latter is typically but not necessarily the case when the blow valve 11 is in its fully open position, i.e. when the valve member 17 has been retracted out of the flow channel 16 and does not restrict the pulp flow through the blow valve 11. The flow channel 16 has a preferably a circular cross-section with a diameter d₂, which is preferably equal, or at least approximately equal, to the diameter d₁ of the mounting pipe 7, which then preferably also has a circular cross-section with d₁≅d₂. If for some reasons, other cross-sectional shapes than circular are chosen for a mounting pipe and a flow channel through a blow valve, these cross-sectional shapes should be essentially equal for the mounting pipe and the flow channel, and the cross-sectional areas should also be essentially equal. By this arrangement, when the cross-section of the flow channel 16 through the blow valve 11 is equal, both in shape and size, to the inner cross-section of the mounting pipe 7, a laminar pulp flow is ensured through the blow valve 11, which, in turn, reduces wear on the blow valve 11. Also, the risk of micro-scale shock waves, which travel back through the pulp and counteract the rotational movement of the rotating refiner element 4, is reduced, which has a positive effect on the energy consumption of the refiner system 1.

Although the present invention has been described with reference to specific embodiments, also shown in the appended drawings, it will be apparent to those skilled in the art that many variations and modifications can be done within the scope of the invention as described in the specification and defined with reference to the claims below. It should in particular be noted that in the embodiment shown in FIG. 1 and FIG. 2, the mounting pipe 7 has been shown as a separate component. It is, however, within the scope of the invention that a mounting pipe is created as a prolonged inlet portion of a blow valve, i.e. the inlet portion is integrated with the blow valve. A mounting pipe according to the invention is therefore in this case configured as a mounting portion of a blow valve. A combination of a separate mounting pipe and a mounting portion of a blow valve is also within the scope of the invention. In any case, a length of a mounting pipe, such as the length L in FIG. 1, or a length of a mounting pipe which is configured as a mounting portion of a blow valve, or a length of a combination of a mounting pipe and a mounting portion, should always be measured from a defibrator housing to a first or closest side—as seen in the pulp transport direction—of a valve member arranged in a blow valve, which is connected to a discharge pipe.

Claims

1. A pulp refining system for mechanically refining of lignocellulosic material, comprising:

a defibrator,

a defibrator housing, in which the defibrator is arranged,

a blow valve having an inlet and an outlet and being adapted for regulating a flow of pulp therethrough, and

a discharge pipe having an inlet which is connected to the outlet of the blow valve, characterized in that a mounting pipe having an inlet, which is connected to the defibrator housing, is arranged between the defibrator housing and the blow valve, said mounting pipe having a length (L) of at least about 0.2 meter.

2. The pulp refining system according to claim 1, characterized in that the length (L) of the mounting pipe is at least about 0.5 meter.

3. The pulp refining system according to claim 1, characterized in that the length (L) of the mounting pipe is such that 0.2 m≤L≤1.5 m.

4. The pulp refining system according to claim 1, characterized in that the mounting pipe is provided as a separate component.

5. The pulp refining system according to claim 1, characterized in that the mounting pipe is configured as an inlet portion of the blow valve.

6. The pulp refining system according to claim 1, characterized in that the mounting pipe is configured as a combination of a separate component and an inlet portion of the blow valve.

7. The pulp refining system according to claim 1, characterized in that the length of the mounting pipe is measured from the defibrator housing to a closest side of a valve member arranged in the blow valve.

8. The pulp refining system according to claim 1, characterized in that the mounting pipe has a cross-section, which is essentially equal, both in shape and size, to the cross-section of an interior flow channel in the blow valve.