APPARATUS FOR LIQUID TREATMENT OF PULP

Abstract: The apparatus comprises an endless perforated steel belt (1). Devices (11) for the supply of treatment liquid are located above the belt, and containers (8) for the collection of liquid are located beneath the belt. Said containers (8) extend along the entire width of the belt (1). The containers (8) are provided with outlet (9) for liquid and outlet (10) for vapours and gases, which vapour outlet (10) is connected to the bottom of the containers (8). The vapour outlet (10) communicates with an internal passageway (21), which extends upwards to the upper portion of the containers (8) above a liquid level in the containers, and a screening is provided for preventing liquid to flow from the belt down into the vapour outlet (10).

Description: Apparatus for liquid treatment of pulp This invention relates to an apparatus for the liquid treatment , of pulp, comprising a stand with two end rolls, over which an endless liquid permeable web runs. The web consists ^ of a wire or perforated belt,for example steel belt. The web is driven by one of the end rolls and slides over perforated covers on containers located therebeneath. A head box for the supply of pulp is located at one end of the web, and means for the transfer of the treated pulp are located at the other end of the web. Means for supplying treatment liquid to the pulp are located above the web. The containers located beneath are intended for the collection of liquid. The said containers extend in cross-direction along the entire width of the web and are arranged one after the other in the running direction of the web. The width of the web, and therewith also of the containers, can be up to 6 m. In certain cases webs of stillvgreater width are used. The containers may also be sections of a greater trough. At the liquid treatment liquid in the pulp is driven out by supplied treatment liquid. The liquid driven out to¬ gether withivapours and gases are collected in the containers. It is desired to discharge vapours and liquid from the containers separately. This, however, involves difficulties, due to the extension of the containers in the cross-direction of the web and to the restricted space in the containers, which implies that the flow rate of the vapours is high and foam formation easily arises. The present invention has the object to solve this problem. * According to the invention, a very compact structural design in combination with low vapour rate and reduced risk of foam formation in the containers is obtained. The characterizing features of the invention are apparent from the attached claims. The invention is described in greater detail in the following, with reference to the accompanying Figures showing a preferred embodiment of the invention. Fig. 1 shows a liquid treatment system according to the invention. Fig. 2 shows a portion of a cross-section along II-II in Fig. 1. Fig. 3 is a section along III-III in Fig. 2. Fig. 4 shows a second embodiment in a section along II-II in Fig. 1. The embodiments shown comprise an endless perforated steel belt 1, which runs about a first and a second end roll 2 and, respectively, 3. The rolls are arranged in a stand 4. The first roll 2 is movable by means of a stretch¬ ing device, preferably hydraulic, for adjusting the belt tension. The belt is driven via the second roll 3, and both rolls are preferably coated with a friction increasing surface layer. At the first roll 2 a head box 6 is-.loeated for distrib¬ uting the cellulose pulp to a uniform layer on the belt 1. After the head box a plurality of containers 8 are arranged one after the other in the longitudinal direction of the belt. The containers are provided with perforated covers as a support for the belt 1. Outlets 9 and, respectively, 10 are connected to the containers 8 for the removal of liquid and, respectively, vapours and gases. The liquid outlet is located in the bottom of the containers 8 to ensure effective drainage. The liquid level in the containers is controlled by special means so that a small space for vapours and gases is maintained in the upper portion. The fall of the liquid from the belt 1 down into the containers thereby is small and reduces the foaming tendency. The outlet 10 for vapours and gases also is located in the bottom of the containers 8, preferably centrally beneath the containers in the cross-direction of the belt. The structural design, however, renders their location possible anywhere in the cross-direction of the containers. The outlet communicates with the space for vapours and gases in the containers 8 through an internal passageway 21. A screening 22 co-operates with said passageway and prevents liquid from the belt 1 to flow down into the outlet 10. Several outlets for vapour and gas may possibly be arranged beneath the containers, in which case they are placed in spaced relationship along the containers. Hereby the vapour and gas flow along the containers can be minimized and the gas rate be reduced so that a substantially laminar flow is obtained, which implies that liquid is not taken along and foaming is avoided. An effective separation of vapours and gases is hereby obtained in the containers. Due to the design * the containers can be utilized at maximum in their entire length in the cross-direction of the belt. According to the embodiment shown in Figs. 2 and 3, the passageway 21 is formed as a pipe, on which the screening 22 is attached. The passageway, however, can be formed in a different way, and the screening can be arranged, for example, in the walls or cover of the container. According to the embodiment shown in Fig. 4, the pass¬ ageway 21 is defined by a wall element and the screening 22 located in the cover of the container 8. The outlet 10 for vapours and gases communicates with a suitable exhausting device, for example a fan, whereby vapours and gases can be discharged directly or via a collecting vessel for liquid. In order to additionally improve the separation of vapours and gases, the outlets 10 from the containers 8 can be connected to a cyclone 24 via a conduit 23. The cyclone 24 is located to the side of the belt 1 on the same level as the outlets 10. Above the belt devices 11 for the supply of treatment liquid are arranged. A pressure difference is maintained above the pulp layer in order to effect liquid transport transversely through the pulp layer. The width of the pulp layer on the belt is limited by means 12. A hood 13 is placed over the belt. At the second roll 3 a transfer device 14 for the completely treated pulp layer is located,which, for example, has the form of a doctor blade. Below said blade a feed screw 15 is located for transporting the pulp to subsequent proc¬ essing steps. The steel belt used preferably shall have a thickness of 0,5 - 1,5 mm. The diameter of the end rolls must be adapted to the belt thickness, because the bending stress in the belt is directly proportional to the belt thickness and reciprocally proportional to the roll diameter. A suitable dimension of the rolls can be about 2 m diameter. The aperture size must be adapted to the pulp to be treated, but should be in the interval of 0,5 - 1,5 mm diameter. It can, of course, also be imagined to design the apertures as -slits. The open area under all conditions must be between 8 and 2555. The length and width of the belt are not critical, but can be chosen at option. The width desired can be obtained by longitudinally welding a number of narrow belts to a wider one, because it is not possible to directly manufacture steel belts of the widths required, which are, for example, about 6 m or wider. Steel belts normally are not manufactured with widths exceeding slightly one metre. The invention is not restricted to the embodiments shown, but can be varied within the scope of the invention idea.

Claims: Claims 1. Apparatus for the liquid treatment of pulp, comprising an endless perforated steel belt (1) for receiving a pulp suspension, devices (11) for the supply of treatment liquid above the belt, and containers (8) for the collection of liquid beneath the belt, which containers extend along the entire width of the belt, outlets (9), for liquid from the containers and at least one outlet (10) for vapours and gases from the containers (8), c h a r a c t ¬ e r i z e d i n that the said vapour outlet (10) is connected to the bottom of the containers (8), that the vapour outlet (10) communicates with an internal passageway (21), which extends upwards to the upper portion of the containers above a liquid level in the containers, and a screening (22) is provided to prevent liquid to flow from the belt down into the vapour outlet (10). 2. Apparatus as defined in claim 1, c h a r a c t e r ¬ i z e d i n that each container (8) is provided with a vapour outlet (10) located between the edges of the belt (1). 3. Apparatus as defined in claim 1, c h a r a c t e r ¬ i z e d i n that several vapour outlets (10) are provided from each container (8) and located in spaced relationship in the cross-direction of the belt (1). 4. Apparatus as defined in any one of the preceding claims, c h a r a c t e r i z e d i n that the vapour outlets (10) are connected via a conduit (23) to a cyclone (24) located to the side of the belt on the same level as the vapour outlets (10).

Inventors: LINDSTROEM ALF INGE, LINDSTROEM, ALF, INGE
Applicants: SUNDS DEFIBRATOR, SUNDS DEFIBRATOR AKTIEBOLAG
Application year: 1987
Main classification: D21C9
IPC codes: D21C9