Method and apparatus for defibering and screening recycled fibre material

Abstract: A method and an apparatus for defibering and screening recycled fibre material. In the method, fibre mass is defibered in a primary pulper that is a vertical pulper operating at a high consistency. From the primary pulper the fibre mass is supplied along a transfer conduit (4) to a secondary pulper that is correspondingly a vertical pulper operating at a low consistency. The apparatus comprises a primary pulper that is a vertical pulper operating at a high consistency, and a secondary pulper that is a vertical pulper operating at a low consistency. Between the primary pulper and the secondary pulper there is a transfer conduit (4) along which the fibre mass flows from the primary pulper to the secondary pulper solely by the action of the pressure difference produced by the difference in the fluid levels of the pulpers.

Description: The invention relates to a method for defibering and screening recycled fibre material according to the preamble of claim 1. The invention further relates to an apparatus for defibering and screening recycled fibre material according to the preamble of claim 10. Recycled fibre material, i.e. waste paper or some other similar fibre material that has already been used, is defibered, purified and screened at present mainly by supplying the material in batches into a pulper where it is defibered simultaneously with the removal of impurities. Such arrangements are known e.g. from DE 2,757,580 and CH 617,734. Each reference discloses an arrangement where a fibre mass is supplied to a vertical pulper for disintegration, whereafter the mass is pumped from the pulper to the following stages of processing, such as the removal of refuse and separate post-processing that is carried out with a horizontal pulper. However, recycled material comprises a considerable amount of impurities that have different characteristics and behaviour and that must therefore be removed in different manners. Such impurities include, for example, heavy impurities, pieces of metal, stones of different shapes and sizes, and sand, and light impurities, such as plastic-based packaging materials and various glue-based substances. All of these cannot be removed with the same technique nor can they be separated at the same time as fibre bundles and more solid pieces of fibre. As recycling becomes more common and the requirements set for the use of material obtained from recycling increase, demands for defibering and purification also become more numerous and the processes and apparatuses become more and more expensive. Known vertical pulpers that operate on an intermittent basis require the use of large containers to provide the required capacity, since about half of the operating time is taken by the stages of emptying and filling. This also affects the process control and requires large apparatuses. Further, moving a fibre mass from one stage to another requires in all cases pumps that are capable of pumping the fibre mass and that consume a considerable amount of energy and require maintenance and repair. Conventionally, also vertical pulpers that operate on a batch basis are low consistency pulpers. The prior continuous high consistency pulpers in turn are exclusively drum pulpers that are large and expensive, since the degree to which they are filled during operation is only about 20 to 30% of their total volume. Further, drum pulpers are not capable of disintegrating such waste paper types that are difficult to process. WO-A-94/09202 discloses a method according to the preamble of claim 1 and an apparatus according to the preamble of claim 10. The purpose of the present invention is to provide a method and an apparatus with which it is as easy and effective as possible to defiber and screen a recycled fibre mass and to separate impurities on a continuous basis. The method according to the invention is characterized by the features defined in the characterizing portion of claim 1. The apparatus according to the invention is characterized by the features defined in the characterizing portion of claim 10. The basic idea of the invention is that recycled fibre material is processed in two successive vertical pulpers as a continuous process such that a thick fibre mass suspension that consists of water and the mass disintegrated in a primary or high consistency pulper is moved from the lower part of the primary pulper to a secondary or low consistency pulper, the suspension being simultaneously diluted with water, via only a transfer pipe provided between the pulpers without the aid of pumps by utilizing the principle of so-called communicating vessels. This means that the flow of the resulting fibre material is based entirely on the pressure difference that results from the difference in the fluid levels and that is produced by the recycled fibre mass and water supplied to the high consistency pulper. Further, another idea of the invention is that the fibre mass is screened immediately after the low consistency pulper preferably by using a low consistency pulper with an associated screen, whereupon the fraction rejected in the screening is returned to the high consistency pulper, which simultaneously also receives circulated water and chemicals that are mixed with the water and that were required for removing ink etc. The invention has the advantage that when a vertical pulper that operates as a high consistency pulper is used as the first pulper, for example the removal of ink can be achieved with a lower consumption of chemicals and steam than in conventional pulping. The invention also has the advantage that the forward flow of the fibre mass in the process can be controlled simply by adjusting the addition of water and the material to be defibered, whereupon the defibering can be carried out with effective vertical pulpers as a continuous process merely by removing fibre mass suspension from the low consistency pulper. Yet another advantage of the invention is that the consumption of energy is considerably lower than in known arrangements and when the reject and water that remain in the final stage of the defibering/screening process are returned to the high consistency pulper, the consumption of new water can also be decreased significantly compared to prior arrangements. The invention will be described in greater detail in the accompanying drawing, which schematically shows an apparatus according to the invention. The apparatus comprises a conveyor 1 for supplying material to be defibered 1a for processing. The apparatus further comprises a primary or high consistency pulper 2 to which the material to be defibered is supplied usually in the form of bales. Water is also supplied to the high consistency pulper 2 via a conduit 3. The rotor 2a of the high consistency pulper 2 is shaped and designed such that when the dry solids content is about 10 to 18%, the rotor disintegrates the recycled fibre material effectively. The rotor 2a is rotated in a manner known per se by means of a motor 2b shown schematically. The high consistency pulper 2 is connected from its lower end to a secondary or low consistency pulper 5 via a transfer conduit 4. Both the high consistency pulper 2 and the low consistency pulper 5 are vertical pulpers. The transfer conduit 4 does not comprise any pumps or the like, but the flow of the fibre mass from the high consistency pulper 2 to the low consistency pulper 5 is based on the principle of communicating vessels, whereupon the flow is adjusted solely by the pressure produced by the difference in the fluid levels of the pulpers, resulting from the material to be defibered and the water supplied to the pulper, and the fibre mass suspension removed from the low consistency pulper and the reject, respectively. If no new material or water is supplied, the fluid levels of the pulpers become even. The transfer conduit 4 comprises a separate refuse chute 6 to which the heavier material conveyed with the fibre mass suspension falls and from which it can be removed for example at suitable intervals or continuously, if desired. For this purpose, the chute can be provided, for example, with a discharge mechanism formed by different valves in a manner known per se, or the material can be removed for example by lifting it with a separate lifting device. The removal of the material from the refuse chute is known per se and therefore contains nothing unconventional. Correspondingly, above the refuse chute 6 there is a pipe 6a that has an open upper end and that extends a short distance above the fluid level of the low consistency pulper 5. For example material that is lighter than the fibre mass travels to this pipe and can be removed therefrom at suitable intervals, for example. In the low consistency pulper 5, the fibre mass suspension is further disintegrated at a low consistency, i.e. typically about 2 to 8%. This pulper is as described in Fl 82,493, for example, whereupon it is provided with a double screen 7 placed in the lower part thereof. Between the screen 7 and the low consistency pulper 5 there is a horizontal screen plate 7a that performs the coarse screening so that litter and large impurities cannot pass through it. Correspondingly, fibre mass suspension that has passed through the screen plate 7a must pass through another cylindrical screen surface 7b. The rotor 5a of the pulper 5 and blades 7c of the double screen 7 that sweep the screen surface are rotated by means of the same shaft by the motor 5b that is shown schematically. The fibre mass suspension that has passed through the screen surface 7b is removed from the screen 7 via a discharge conduit 8 for example to a mass container 9 and from there via a conduit 9a to the next processing stage. The part of the fibre mass suspension that does not pass through the second screen surface 7b is returned via a conduit 10 to the lower part of the high consistency pulper 2 to be defibered again in the pulper. Both water and chemicals are simultaneously returned to the pulper, so that there is less need to add water via the conduit 3. The material that does not pass through the screen plate 7a, i.e. the reject, is removed via a reject conduit 11 starting from the lower part of the low consistency pulper 5 to a separate reject pulper 12 that is typically a horizontal pulper. The rotor 12c of this horizontal pulper is correspondingly rotated by means of a motor 12b shown schematically. The removed reject disintegrates in the reject pulper 12 partly into a fibre material that passes through a screen plate 12a provided in the reject pulper 12 and is conducted through a conduit 13 to the mass container 9. Correspondingly, the part of the reject that does not pass through the screen plate 12a is conducted via a conduit 14 to a reject drum 15 where the reject is washed with water supplied from a spray pipe 15a such that the fibres that have been supplied with the reject are removed with the water into a collection vessel 15b. The obtained water that contains only a little fibre is gathered for example to a collection basin 16 from where it is supplied along the conduit 3 to the high consistency pulper 2. The same fibre-containing water can be supplied, if required, along conduits 3' and 3" to the transfer conduit 4, the screen 7, the reject conduit 11 and the conduit 14 to dilute the masses flowing therein. It is thus possible to circulate as large an amount of the water as possible inside the process and actual additional water is only needed in an amount that corresponds to the water discharged from the process with the removed mass. The invention is described above in the specification and in the drawing by way of example only, and it is not restricted thereto in any way. The reject pulper 12 may be any suitable pulper with which reject can be processed. The washing drum may also be any drum type suitable for the purpose. The essential factor is that the primary pulper and the secondary pulper are vertical pulpers and that between the pulpers there is a transfer conduit without pumps or the like, so that the transfer of the fibre mass from the primary pulper to the secondary pulper takes place solely by the action of the pressure difference produced by the mass and water supplied to the primary pulper.

Claims: A method for defibering and screening recycled fibre material, wherein the recycled fibre material is defibered with water, impurities are removed therefrom and the obtained fibre mass is screened, whereby the recycled fibre material to be defibered is supplied with water to a primary pulper which is a high consistency pulper where it is first defibered at a high consistency, the fibre mass suspension formed in the high consistency pulper is supplied from it without screening via a transfer conduit which leads from the lower part of the high consistency pulper to a secondary pulper, where the recycled fibre material is further defibered and the fibre mass suspension is only screened after being defibered in the secondary pulper, characterized in that both the primary and the secondary pulper are vertical pulpers, that the secondary pulper is a low consistency pulper (5), into which the fibre mass suspension formed in the high consistency pulper (2) diluted with water is supplied based on the principle of communicating vessels solely by the action of the pressure resulting from the difference in the fluid levels of the high consistency pulper (2) and the low consistency pulper (5). A method according to claim 1, characterized in that the fibre mass that flows from the high consistency pulper (2) to the low consistency pulper (5) is diluted by supplying dilution water to the fibre mass suspension to the end of the transfer conduit (4) provided between the pulpers (2, 5) on the side of the high consistency pulper (2). A method according to claim 2, characterized in that heavy impurities are separated from the fibre mass flowing from the high consistency pulper (2) to the low consistency pulper (5) by means of a refuse chute (6) placed in the transfer conduit (4). A method according to any one of the preceding claims, characterized in that the fibre mass suspension is screened by means of a screen (7) associated with the low consistency pulper (5), whereupon the fibre mass suspension that has passed through a screen plate (7a) provided between the screen (7) and the low consistency pulper (5) is further screened by means of a cylindrical screen surface (7b) placed in the screen (7), so that the fibre mass suspension that has passed through the screen surface (7b) is supplied for further processing and the part of the fibre mass suspension that has not passed through the surface is returned to the high consistency pulper (2), and that the reject that does not pass through the screen plate (7a) is conducted to a separate reject pulper (12) for further processing. A method according to claim 4, characterized in that the material that has passed through a screen plate (12a) provided in the reject pulper is supplied for further processing and the reject that has not passed through the plate is supplied for washing in a separate washing drum (15). A method according to claim 5, characterized in that the water used in the washing and the fibre material separated from the reject and mixed with the water are recovered and some of it is supplied to the high consistency pulper (2). A method according to claim 6, characterized in that some of said recovered water is supplied to the transfer conduit (4) between the pulpers (2, 5) as dilution water for the fibre mass suspension. A method according to claim 6 or 7, characterized in that all the additional water replacing the water that is discharged with the fibre mass suspension supplied for further processing is fed into the defibering stage in the form of washing water of the washing drum. A method according to any one of the preceding claims, characterized in that the fibre mass is disintegrated in the high consistency pulper such that the consistency is 10 to 18%, and that it is diluted such that the consistency in the low consistency pulper is 2 to 8%. An apparatus for defibering and screening recycled fibre material, the apparatus comprising means for defibering the fibre material and a screen for screening the obtained fibre mass suspension, whereby the means for defibering the recycled fibre material comprise two pulpers, the first of which is a high consistency pulper where the recycled fibre material and water are supplied and the pulpers are interconnected with a transfer conduit that leads from the lower part of the high consistency pulper to the second pulper, characterized in that both pulpers (2, 5) are vertical pulpers, that the second pulper (5) is a low consistency pulper where the fibre mass suspension formed in the high consistency pulper is supplied for further defibering, diluted with water, and pulpers (2, 5) are directly interconnected with the transfer conduit (4) based on the principle of communications vessels so, that the fibre mass suspension flows from the high consistency pulper (2) to the low consistency pulper (5) solely by the action of the pressure produced by the difference in the fluid levels of the high consistency pulper (2) and the low consistency pulper (5). An apparatus according to claim 10, characterized in that the transfer conduit (4) comprises a refuse chute (6) for removing impurities that are heavier than the fibre mass suspension from the fibre mass suspension when it flows from the high consistency pulper (2) to the low consistency pulper (5). An apparatus according to claim 10 or 11, characterized in that the means for screening the fibre mass suspension comprise a screen (7) that is associated with the low consistency pulper (5), so that between the low consistency pulper (5) and the screen (7) there is a screen plate (7a) through which the fibre mass suspension flows to the screen (7) for screening. An apparatus according to claim 12, characterized in that the screen (7) comprises a separate cylindrical screen surface (7b), the material that has passed through the surface being conducted for further processing, that the apparatus comprises a conduit (10) for returning the material that has not passed through the screen surface (7b) back to the high consistency pulper (2), and that the apparatus comprises a separate reject pulper (12), and that the reject pulper (12) is connected to the low consistency pulper (5) so that the material that does not pass through the screen plate (7a) flows from the low consistency pulper (5) to the reject pulper (12) to be further processed therein. An apparatus according to claim 13, characterized in that the reject pulper (12) comprises a screen plate (12a), the material that has passed through the plate being conducted for further processing, and that the apparatus comprises a washing drum (15) to which the material that has not passed through the screen plate (12a) is conducted for washing. An apparatus according to claim 14, characterized in that it comprises means for recovering the water used in the washing drum (15) and the fibre material mixed with the water, and for supplying some of the water and fibre to the high consistency pulper (2). An apparatus according to claim 15, characterized in that it comprises a conduit (3') for conducting the water recovered from the washing stage and the fibre material mixed with the water to the transfer conduit situated between the high consistency pulper (2) and the low consistency pulper (5) in order to dilute the fibre mass suspension for the low consistency pulper in the transfer conduit.

Inventors: HAUTALA JOUKO, HAUTALA, JOUKO
Applicants: METSO PAPER INC, METSO PAPER, INC.
Application year: 1997
Main classification: D21B1
IPC codes: D21B1