SE518536C2 - Method and apparatus for controlling the process temperature in the manufacture of a fiber web - Google Patents

Abstract

The present invention relates to a method and a plant for favourably increasing the processing temperature of a paper machine relative to previously known techniques and for providing precise regulation of the temperature of the paper machine process, where an evaporator is used in the process. The energy usage in the paper machine is clearly made effective by the process, in particular in a paper machines using wood product. Furthermore the method enables the quantity of fresh water required for the paper machine and of the waste water to be discharged to be reduced. Because of the processing temperature reached by the method the wood product washing efficiency of the method rises according to earlier patent applications for paper machines processing wood product.

Description

A problem that our invention this time seeks a solution to is the general heat economy of a paper machine or similar production machine or process. It is well known that the higher the temperature in the short cycle of a paper machine, the better the dewatering takes place in the wire and press sections, and the less heat is needed. parts optimally, as there were not sufficient amounts of steam available. In some cases, the backwater of the paper machine has been heated with high-pressure fresh steam, but in most cases it has been considered that the use of such steam is unprofitable with the drying section. however, the energy economy is not raised.

From the state of the art, it is known that the fresh water for the paper machine is heated in heat exchangers which usually use high-pressure steam as a heat source. It is also known from other contexts that the backwater of the paper machine is evaporated and that it is to some extent returned to the paper machine. In these applications, however, the possibility has not been considered that the temperature of the rear water could be raised by conducting condensate with a higher temperature from the evaporation plant to the recycled back water. It is also known to heat the paper mill's backwater by direct heating with steam, for example in the wire tank. However, it is also known and in practice accepted at all modern paper mills that the proportion of the backwater that is discharged to the wastewater from the paper machine is cooled, for example in seawater or seawater sprayers to a temperature required by biological treatment plants. Furthermore, in many paper mills, where on the other hand the heat demand is recognized, cooling towers are used to remove the "overflow heat" from the system. On the basis of the examples presented above, it is obvious that the heat economy at the paper mill is managed very randomly.

A starting point for our invention is that in paper machines which produce paper from mechanical pulp, at least part of the energy required by the evaporation using the process according to the invention is supplied in the form of high-pressure steam (above 2 bar) or low-pressure steam (below 2 bar), either from a pressurized or non-pressurized reject or main conveyor for mechanical pulp. Likewise, one can also take some of the energy that the evaporation plant requires from a pulp mill that may have been integrated in the paper mill, or from a power plant, in the form of either low-pressure or high-pressure steam.

Another starting point is to use at least part of the steam that is mainly used for heating at the paper machine via the evaporation plant.

In our invention we have gone into solving the above-mentioned problem, among other things, so that the steam which, for example from the above-mentioned sources, is first used for evaporating rear water from the combination of paper machine and refinery. In addition, by taking steam from the evaporator, advantageously from its last step, to heat the backwater of the paper machine, the backwater temperature can be raised to an optimum level with respect to papermaking. The temperature increase takes place with small costs, because in this procedure one can use energy (steam) which is also otherwise needed for heating the process. In the solution according to our invention, said heat is used in a new and more efficient way. As an example of such steam that is used, one can mention, among other things, the steam that is used in the heat exchangers to heat the fresh water that comes to the paper machine.

An advantage of the method according to the invention in controlling the temperature is also that with this method a particularly accurate control of the temperature is obtained as the temperature of the process water is regulated by the amount of heat for heating fresh water which passes the evaporator condenser and / or the rear water cooler.

Another problem on which our invention also provides a solution relates to the treatment of backwater at the refinery or TMP plant. This problem has to some extent been dealt with in Finnish patent application 980639. The problem dealt with in said patent application is the extracts which are bound to the carrier material or are present in the surrounding water in solution or colloidal form and which are transported by the pulp to the paper mill, these extracts also causes obvious quality problems in the paper in addition to clogging the wire surfaces, causing precipitation problems and problems running the process. The effect of the extract substances in the finished paper is perhaps most clearly seen as a reduced paper strength. In said patent application 980639 it is shown how to prevent said extract substances from being enriched in the process by arranging the press at such a place in the process that the extract substances are harmed in the filtrate from the press and thus no longer as such are returned to the process. Said filtrate is treated in a suitable separating device, which may be a membrane filter, an arc screen, a jet filter or the like, so that the extractor membranes remain in the liquid phase which is removed from the process. Said patent application does not take a position on how to remove extract substances from the liquid phase where they remained in the separation process.

The method and apparatus according to our invention offer as a solution to this problem to lead the liquid in question which contains extract substances into the backwater of the refinery and to treat it in the evaporation plant. The method and apparatus of the present invention seek to solve, inter alia, the above-described problems of the prior art so that the extracts are removed from the process at an early stage, substantially without the use of additional chemicals and by 536 use a high process temperature, whereby when washing the mechanical pulp the extracts and interfering substances accumulate in the waters of the plant for the production of mechanical pulp and can be removed from this water by evaporation. Inorganic interfering substances and most of the organic extracts and interfering substances in the water which are led to the evaporation plant can be removed to the concentrate of the evaporation plant. If necessary, the condensate from the evaporation plant can also be divided into so-called clean and dirty condensate. The dirty condensate accumulates substances with a boiling point under water, such as acids, alcohols and other interfering substances and substances that raise the COD level, and these substances can be removed from the process if necessary by using the process.

An additional problem that our invention offers a solution to relates to the water consumption in a corresponding machine or production process. The processes at the state of the art are characterized by either all backwater from the refinery being led back to nature through wastewater treatment, or that farskanga (with a pressure above 2 bar) is used for evaporation of the water, whereby the price of steam is so high in our opinion. , that evaporation by using farskanga does not pay off. The use of fresh steam in evaporation can only be justified when the supply of fresh water is an extreme shortage factor or limiting factor. paper machine or Approximate problems are solved so that the backwater from, for example, the paper machine and / or the refinery is led to the evaporation plant where water is evaporated from this water which replaces fresh water, by using, for example, secondary steam.

By using the method and apparatus according to the invention, the following advantages can be achieved, which for various reasons cannot necessarily be achieved in all processes: - the consumption of fresh water is reduced to a significant degree, - more efficient use of steam generated in a plant where mechanical pulp is produced, - a significantly improved reusability of process water, - the precipitation problems at both pulp and paper mills cease practically completely, - the clogging problems at both pulp and paper mills cease practically completely, - the waste water volume decreases significantly, - the paper quality increases, - the use of chemicals in the pulp mill can be reduced, and the temperature can be controlled as high as desired, with the result that - the microbial problems cease or at least decrease to a significant degree, - the driveability of the paper machine is improved, and - it becomes easier to separate interfering substances from the backwater of paper mills.

Characteristic features of the method and apparatus according to the invention appear from the appended claims.

In the following, the method and apparatus according to the invention are described in more detail with reference to the accompanying figures, in which Figure 1 shows schematically in the light of the energy consumption the liquid circuit in a combination of a TMP plant and a paper machine in the prior art. in a paper machine of the prior art, and Figure 3 shows in the light of the energy consumption a combination of a TMP plant and a paper machine according to an advantageous embodiment of the invention in a simple schematic diagram.

Figure 1 shows in a simple diagram, as an example of all the already mentioned different processes for manufacturing a fibrous web, a combination of a TMP plant and a paper machine according to the prior art which uses mechanical pulp for papermaking. The figure simply shows both the water cycle and the energy consumption in said combination. According to the clock, a total of 3.1 MWh / ADt of electrical energy E is supplied to the TMP array 30 and the paper machine 32, which is distributed so that the TMP plant 30 consumes 2.5 MWh / ADt and the paper machine 0.6 MWh / ADt. Of this energy, the TMP plant 30 consumes 1.5 MWh / ADt for mechanical work and 1.0 MWh / ADt is released as heat, which is conducted in the form of so-called primary steam along line 34 to the paper machine 32. The paper machine also receives steam from elsewhere , such as along line 36 from the bark burner. The water cycle of the combination is based on the paper machine 32 taking fresh water FW, which is eventually led to the TMP plant 30.

From the TMP plant 30, 11 m3 / ADt of backwater WW is removed along line 38 at a temperature of 75 ° C. On the other hand, in the case of Figure 1, the paper machine 32 needs sheep water FW in an amount of 12 m3 / ADt. According to the prior art, backwater WW from line 38 of the TMP plant 30 is used in the heat exchanger 40 to heat fresh water FW which is led to the paper machine 32. Assuming that the fresh water which is led from the outside to the paper machine 32 along line 42 has a temperature of 20 ° C that with backwater 10 15 20 25 30 35 518 536 WW is heated to about 52 ° C in line 44, whereby the temperature of the backwater in line 38 drops from 75 degrees to 40 degrees in line 46.

Figure 2 shows how to insert a conventional paper mill according to current technology into the heat exchanger 50, for example using fresh steam from line 52 to heat backwater coming from the paper mill along line 56. In the plant used throughout as an example in this application, approx. m3 / ADt of backwater at a temperature of about 55 degrees to line 56. In the heat exchanger 50, its temperature is raised to about 90 degrees, and the backwater is carried along line 58 back to the paper machine. Instead of 140-degree high-pressure steam, 115-degree low-pressure steam can also be used in the process, which otherwise would not necessarily be economically profitable to use in a paper mill. In such a case, it can be considered that the steam used in the evaporation in summer conditions is free and even in winter conditions extremely beneficial.

Figure 3 shows how primary or secondary steam from a suitable site is conducted along line 62 to the evaporation plant 60. According to a tedious embodiment of the invention, the site where the steam is generated is the TMP plant, which differs from at least most, if not all, prior art systems. in that the TMP plant's shrimp generator is also arranged to be under pressure, and thus it is possible to easily recover the steam and the energy bound in the steam which arises in the generator. Irrespective of the place where the steam is generated, it is led to the evaporation plant to a place that is suitable, taking into account its temperature and pressure. In the evaporator 60 the steam is used to evaporate the rear water WW which originally comes from the TMP plant along line 38. However, the rear water WW which comes along line 38 is first heated by means of hot concentrate which is returned to the evaporator 60 via line 66, heated in the evaporator and removed from the evaporator 60 along line 66 to the heat exchanger 68. Thus, the evaporator 60 is used to evaporate backwater originally generated in the paper machine and fed to the process via the refractors. In an example according to an advantageous embodiment of our invention, the treatment cycle for this water in the evaporator 60 is as follows. When we apply the example that was already used above in connection with the state of the art, we assume that the refining plant generates approx. Ll m3 / ADt of backwater. In the heat exchanger 68 this amount of water is heated from the temperature 75 degrees at the outlet from the reactors to a temperature of 107 degrees before the backwater is led to the evaporator 60. In the evaporator 60 about 4 m3 / ADt is evaporated as condensate, and the rest of the backwater 7 m3 / ADt whose temperature in the evaporator has further risen is conducted as a concentrate at a temperature of 135 degrees to the heat exchanger 68. In the heat exchanger 68 the temperature of the concentrate coming from the evaporator drops to 85 degrees, in which temperature the concentrate is conducted, along the line 70 to a second heat exchanger 72, where it is used to raise the temperature of the fresh water FW coming to the heat exchanger 72 along the line 42. In the process according to our invention, the need for fresh water FW is e.g. 8 ms / ADt, of the order of 12 m3 / ADt. Assuming that the temperature of the fresh water coming along line 42 is 20 degrees, the temperature of the fresh water teaching the heat exchanger 72 to line 74 will be 59 degrees, and the temperature of the concentrate going to line 76 will be 40 degrees. Thus, if desired, additional heat from the concentrate can be utilized by providing a friend exchanger in line 76.

Approximately 4 m3 / ADt of condensate is taken out from the evaporator 60 to line 78, from where via the expansion vessel 80 approx. the paper machine. Thus, the water conducted via line 44 to the paper machine, for example via injectors and chemical dilution, has a temperature of about 69 degrees, as in a process according to the prior art it was only about 52 degrees. In the expansion vessel 80, a part of the condensate, approx. 0.2 m3 / ADt, will evaporate, it still being available via line 84.

When the water heated in the manner described above is fed to a paper machine or corresponding production machine, for example in the form of injector water or water for chemical dilution, this water will, when filtered away from the web or otherwise end up among the wire water, raise the temperature of the paper machine short circuit. is possible to completely refrain from heating, for example, the wire water with fresh steam.

In exactly the same way, the temperatures of all the backwater of the paper machine rise, which also raises the temperature of the backwater carried from the paper machine to the pulp production and the production of mechanical pulp.

The above-mentioned case is only an example, and according to the presented principle one can change the ratio between the energy introduced into the process and the amount of evaporated water which replaces fresh water, even to a situation with closed water cycle.

From the above, however, it must be noted that the utilization of the steam from the shrimp refining must be taken only as an advantageous alternative and example of the invention. In a very similar manner, vapors which arise at any point in the mass or paper manufacturing process, regardless of whether they are of high or low value, can be fed to the evaporator, and used in the manner described above.

In other words, our invention makes it possible to transfer the steam which is still used nowadays for heating at a paper machine, to the evaporation plant where the temperature of the backwater can be raised so that it is no longer necessary to heat said place in the paper machine. In our experience, raising the temperature of the backwater in the evaporation plant is the most efficient way to increase the temperature of the paper machine's liquid cycle, which means that the availability of steam previously considered insufficient is now sufficient to raise the process temperature.

Figure 3 further shows the connection of the evaporator 60 to the rest of the rear water system, with which one can obtain a complete control of the liquid cycle in the paper machine. The higher upper corner shows how a part, approx. 3.6 m3 / ADt, of the paper machine's backwater (another part is dried, for example via the TMP plant and the evaporation plant to the process) is led at a temperature of approx. 88, to which, according to this form of dehydration, also leads both the steam line 84 from the expansion vessel 80 and (in this embodiment) the line for steam which is removed from the last step in the evaporator. In the condenser 88, which is advantageously of the jet condenser type, the steam from the line 84 will be condensed and at the same time raise the temperature of the backwater to about 90 degrees and amount to about 3.8 m3 / ADt, which backwater along the line 90 is returned to the paper machine. eg via dilution in the short circuit.

According to another advantageous embodiment of the invention, the steam which is removed from the last step of the evaporation plant is used to replace fresh steam in the paper machine, for example when drying the paper. According to another alternative, approximate steam is led to another use in the paper mill, even for use, for example, with another paper machine, or to some typical use of secondary steam, such as for heating buildings.

As can be seen from the above, we have developed a completely new and previously unknown method and apparatus for optimizing the heat economy of the process in the manufacture of a fi berbana, and for removing fat-soluble extract substances from the pulp. Although we have described in more detail above only a process alternative for a TMP paper machine, the method according to the invention can also be applied to other TMP processes and also PGW and GW processes, saint also to the various processes already mentioned above for manufacturing a fi berban . Thus, it should be borne in mind that although we have presented above the treatment of effluent in an evaporation plant in the manufacture of mechanical pulp, or at least the treatment of effluent carried from papermaking through the manufacture of mechanical pulp to an evaporation plant, it is clear that the backwater can also be direct paper mill backwater or common backwater from the paper and pulp mill, or backwater from the pulp department in a paper mill. Of course, in other corresponding processes one can also have exactly the same backwater, which can be treated with the method and apparatus according to our invention.

Claims (41)

Un w 20 518 536 10 PATENTKRAV A method of raising the temperature of a process for producing a fibrous web by utilizing steam obtained from the process, characterized in that the energy use of the production process is made more efficient by controlling at least a portion of the low or high pressure steam previously used to raise the process. temperature, so that it is used as an energy source for the backwater evaporation plant (60), the temperature of the production process being controlled and regulated with concentrate and / or with condensate and / or with steam from the evaporation plant. Method according to claim 1, characterized in that the temperature of the production process is controlled and regulated by raising the temperature of the water circulation of the process. Method according to claim 1, characterized in that the energy use of the production process is made more efficient by controlling at least a part of the low or high pressure steam "which occurs in the main or shrimp refining (24) in the production of" mechanical mass for the evaporation of backwater "in the production process. and / or the plant producing mechanical pulp. Method according to claim 1, characterized in that the energy use of the production process is made more efficient by controlling at least a part of the low or high pressure steam which occurs in the pulp mill and / or the power plant for the evaporation of backwater arising in 'Jr 10 20 5'I8 5356 11 and / or produces mechanical pulp. the production process plant as v Method according to Claim 3, characterized in that the rear water and / or the production of mechanical pulp is heated before the measurement to the evaporation plant from the production process with hot backwater which is diverted from the evaporator plant. Method according to claim 3, characterized in that said steam arising from the reject refining (24) is used to evaporate the backwater obtained from the production process and / or the plant producing mechanical pulp. Process according to Claim 1, characterized in that fresh water fed to the production process is heated hot from the evaporation plant. with concentrate being removed Process according to claim 1, with hot concentrate removed from the evaporation plant, first backwater is heated from the production of mechanical pulp and / or the production process before being fed to the evaporation plant, and then fresh water led to the production process. Method according to claim 1, characterized in that from the backwater of the evaporator (60), i.e. the condensate, to the proportion evaporated, whereby the production process, the use of which is characterized in that fresh water in the production process decreases by an amount corresponding to the evaporated proportion. ~ Method according to claim 1, characterized in that the proportion evaporated from the evaporation plant (60), i.e. the condensate, is returned to the production process at a temperature higher than the conventional temperature of the fresh water. 11. ll. characterized in that Process according to claim 1, the fresh steam in the production process. replaced by steam diverted from the final stage of the evaporation plant. Process according to Claim 11, characterized in that the steam from the last stage in the evaporator is used in drying the fibrous web. Process according to Claim 11, characterized in that the evaporation plant is used at a location for the steam from the last step b i which is typical for the use of secondary steam. characterized in that the rear water in the evaporator (60), i.e. the condensate, returned The method of claim 1, the proportion evaporated from to the production process via an expansion vessel (80), that the steam generated in the expansion vessel (80) is recovered, and that the steam is further used in the production process. the backwater iv 10 15 20 518 556 13 Method according to claim 14, characterized in that the steam generated in the expansion vessel (80) is led to. (88), the backwater of the production process is raised. a condenser \ where the temperature of 16. A process according to claim 1, 2, 3, 4 or 5, characterized in that the filtrate from the precipitation or pressing step in the production of mechanical pulp is divided into one. device i. a fiber fraction. and. a fraction containing extracts, and that the fraction containing extracts is passed via the backwater in the production of mechanical pulp along a flow path (38) to the evaporator (60), the extracts being removed from the process in the concentrate of the evaporator (60). Process according to Claim 1, 2, 3, 4 or 5, characterized in that the filtrate from the precipitation or pressing step in the production of a mechanical pulp is divided into one. device in a fiber fraction. and. a fraction containing extracts, and that the fraction containing extracts is passed via the backwater during preparation one. of mechanical: mass along a flow path (38) to the evaporator (60), the extracts being removed from the process in the dirty condensate of the evaporator (60). Process according to Claim 1, characterized in that the use of fresh water is reduced by replacing an all-incineration plant. part of or fresh water with condensate from 'Yes 10 15 20 518 536 14 Method according to claim 18, characterized in that the opportunity of the production machine. controlled raising of the temperature of process water is performed at the same Method according to claim 1, characterized in that the backwater of the production process is heated (88) by the heat exchangers in the condenser process. in the connections of the condenser in the evaporator (60) and Process according to Claim 1, characterized in that steam obtained either from the mechanical plant and / or and / or from the pulp mill is used as the heat source for pulp from the process at the paper machine evaporator (60). Process according to Claim 1, characterized in that low-grade vapors obtained from the production process are fed to (60) the steam is used - in the evaporator to be used at least as part of as the evaporator (60), which low-grade vapors have hitherto been used for either. directly or via a heat exchanger heat various objects in the production process. Process according to Claim 3, 4, 5 or 6, characterized in that the temperature in the precipitation or pressing step in the mechanical pulp process is raised by recirculating backwater, for the production of mechanical pulp, the temperature of the production machine, increasing the solubility of the extracts in the aqueous phase. . Un 10 20 _the second heat exchanger 518 536 15 Apparatus for controlling the temperature in a process for producing a fibrous web, which apparatus comprises at least (30), one fibrous web, for (32) and. an evaporation plant (38, 64) for the production of pulp and / or (32), which in addition has (66) (78) the evaporation plant and for steam (62) which comes into mass production plants a production machine for producing (60), for backwater is connected to the incoming line (30) of the production machine the devices for connections for concentrate and and condensate from to the evaporator and depart from there, characterized in that at least two heat exchangers (68, 72) are arranged in the concentrate line (66, 70, 76). Apparatus according to claim 24, characterized in that the first heat exchanger (68) (38, 64) which carries rear water WW to the evaporator (60). connected to the line Apparatus according to claim 24, characterized in that (72) (42, 74) which supplies fresh water FW to the process. connected to the line Apparatus for controlling the temperature in a process for producing a fibrous web, which apparatus for producing (32) and. an evaporation plant (38, 64) at least (30), a fibrous web, comprises devices mass a production machine for the production of (60), for backwater connected to the VaIS incoming line the devices (30) for the production of pulp and / or to the production machine (32) , and which also has connections for concentrate (66) and condensate (78) from the evaporation plant and for steam (62) which enters the evaporation plant and departs therefrom, characterized in that the condensate line (78) from the evaporation plant (60) ) connected to lead the condensate to be mixed with backwater scmx returned to the production process and / or that the connection for. steam discharged from the evaporation plant connected to (88) the backwater etc. is returned to the production process. devices for raising the temperature of Apparatus according to claim 27, characterized in that (80) from the evaporator (60). an expansion vessel arranged in the condensate line (78) Apparatus according to claim 27, characterized in that the expansion vessel (80) is connected on the one hand by a flow path (82) to the line (74, 44) as for fresh water FW to the production machine (32) and on the other hand by a flow path (84) to the condenser (88). Apparatus according to claim 29, characterized in that (88) an evaporator (60). the condenser is also disconnected from the steam line Apparatus according to claim 29, characterized in that a rear water line with (86) outgoing an incoming (32) production machine is also connected to the condenser (88). flow path from the production machine and with a flow path (90) to UI 10 20 30 518 536 17 Apparatus according to claim 24 or 27, characterized in that the production machine (32) is a paper or board machine. Apparatus according to claim 24 or 27, characterized in that the production machine '(32) is a cellulose dryer. Apparatus according to claim 24 or 27, characterized in that the production machine (32) is a machine for manufacturing fiberglass products. Apparatus according to claim 24 or 27, characterized in that the production machine (32) is a machine for manufacturing web-shaped cellulose products. 36. 27, characterized in that the devices for manufacturing Apparatus according to claim 24 or pulp include a plant for mechanical pulp, e.g. a TMP, GW or PGW facility. Apparatus according to claim 24 or 27, characterized in that the pulp production devices include a pulp section for the production machine, which pulp section prepares the pulp to be fed to the production machine, 27. 27, characterized in that the devices for manufacturing Apparatus according to claim 24 or pulp include a plant for producing chemical pulp or chemical mechanical pulp. UI 10 518 536 18 Apparatus according to claim 24 (38) of the evaporator. is connected to the devices or 27, characterized in that the line which carries back water to (30) for the production of pulp. Apparatus according to claim 24 or 27, characterized in that the line (62) which supplies steam to the evaporation plant '(60) is connected to the reject refiner (24) at the mechanical pulp plant (30). Apparatus according to claim 24 or 27, characterized in that the line (62) of steam for the evaporation plant (60) is connected to the main refiners of the mechanical pulp plant.