JPH0344802B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a liquid concentrating device,
In particular, the present invention relates to a concentrating device mainly used for concentrating dilute solutions such as white liquor, which is one of the raw materials for pulp production, and dilute alkaline solutions. [Prior Art] As is well known, a large amount of white liquor is used in pulp production. This white liquor is a dilute alkaline solution with a concentration of about 10-12%, for example
Approximately 10% as NaOH, Na ₂ S, Na ₂ CO ₃ ,
Contains about 2% Na ₂ SO ₄ , NaCl, etc. Incidentally, in recent years, in order to reduce pulp production costs, it has been required to slightly increase the concentration of this white liquor. First, the technical background will be explained. FIG. 3 is a system diagram showing the manufacturing process of kraft pulp. Reference numeral 14 is a digester, into which raw material chips and white liquor are introduced, and by steam heating, about 160
The chips are cooked in a heated and pressurized atmosphere at 9 Kg/cm ² at a temperature of 9 Kg/cm 2 . The white liquor is in the white liquor tank 10.
It is heated to about 85° C. inside the tank, and after being heated to about 120° C. by a heating device 12 using steam as a heat source, it is supplied to the digester 14. The reaction liquid from the digester 14 is once introduced into the flash drum 16 and released at atmospheric pressure, and flash steam is used for heat recovery. The reaction liquid returned to atmospheric pressure in the flash drum 16 is transferred to the washer 1.
8 and separated into cellulose and weak black liquor. The weak black liquor is introduced into the evaporator 20 and concentrated to become strong black liquor, which is then introduced as fuel into the boiler 22 where it is combusted together with heavy oil to generate steam.
This steam is supplied as heat source steam to the heating device 12 and the digester 14. In addition, the alkaline components contained in this black liquor mainly become Na ₂ CO ₃ and are removed from the causticizing reactor 24.
is introduced into NaOH, reacts with CaO, and is converted back to NaOH.
The white liquor is returned to the white liquor tank 10. In addition, in the causticizing reactor 24, CaO is changed to CaO ₃ ,
This CaCO ₃ is introduced into the kiln 26 and subjected to thermal decomposition treatment to become CaO, which is again subjected to a causticizing reaction. By the way, since the white liquor conventionally used for producing kraft pulp has a relatively low concentration of about 10 to 12%, a large amount of steam is released into the atmosphere from the flash drum 16, and the white liquor from the digester 14 is relatively low. For reasons such as an increase in the consumption of heating steam in the boiler 22, the consumption of heavy oil in the boiler 22 increases, causing an increase in pulp production costs. For these reasons, it has become desirable to increase the concentration of white liquor. Incidentally, a multi-effect evaporator is generally known as an apparatus for efficiently concentrating a solution. This multiple effect evaporator has a plurality of evaporators arranged in series, and vapor generated in the first evaporator is introduced into a second evaporator with a lower operating pressure to evaporate the liquid in the second evaporator. This is used as thermal energy and is repeated sequentially from the second evaporator onwards to perform multiple evaporations. Therefore, it is conceivable to apply this multi-effect evaporator to a white liquor concentrator. FIG. 2 shows one such example, which includes first to fifth evaporators 1 to 5. The stock solution is delivered to the stock solution pump 2.
8. The stock solution is introduced into the fifth evaporator 5 via the stock solution supply pipe 30, and is sequentially sent to the fourth, third, second, and first evaporators 4 to 1. Then, the concentrated liquid is taken out from the first evaporator 1 via the piping 32 and the concentrated liquid extraction pump 34. On the other hand, the steam for heating is introduced into the first evaporator 1 from the piping 36, and the steam generated in the first evaporator 1 is sent to the second evaporator 2 via the piping 38, and is sequentially sent to the lower stage. The side evaporator is fed in the same way. The vapor from the fifth evaporator is introduced via line 46 into a condenser 50 with an ejector system 48 and condensed. The rest of the configuration of the concentrating device shown in FIG. 2 is almost the same as that of the embodiment device described later, and the same members are given the same reference numerals and the explanation thereof will be omitted. [Problems to be Solved by the Invention] Although the multi-effect evaporation type concentrator configured as shown in Figure 2 is capable of reasonably efficient concentration, a concentrator with even higher efficiency and lower heat costs is expected. Ru. In addition, in the concentrating device shown in Fig. 2, since the concentrated liquid is at high temperature and high concentration in the first or second evaporator 1, 2, highly corrosion-resistant materials such as Ni or
SUS316L is used, but since the amount of evaporation in the first and second evaporators 1 and 2 is large, it is necessary to have a large surface area of the evaporation tubes of these first and second evaporators, resulting in high corrosion resistance. The amount of materials used also increases, which becomes a factor in increasing the device configuration cost. [Means for Solving the Problems] The liquid concentrating device of the present invention has the following features:
This is a multi-effect evaporation concentrator in which evaporators (n is 2 or more) are arranged in series, in which heat source steam is supplied to the first evaporator, and undiluted solution is supplied from the undiluted solution supply pipe to the n-th evaporator, which is the highest ranked evaporator. and sequentially introduce the vapor from the lower rank side evaporator into the higher rank side evaporator, and sequentially introduce the liquid to be evaporated in the higher rank side evaporator into the lower rank side evaporator, In a concentrator that extracts concentrated liquid from a first evaporator, a self-flashing evaporator is provided in the middle of the raw solution supply pipe, and this self-flashing vapor is introduced as heat source steam into any evaporator having a lower operating pressure than the self-flashing evaporator. It is structured as follows. [Function] In the concentrator of the present invention, the stock solution is once self-flash evaporated in an intermediate degree of vacuum, and the evaporated vapor is used as heat source vapor for an evaporator with a lower operating pressure. Therefore, according to the present invention, the amount of steam used as a heat source is reduced, and heating costs can be reduced. In addition, in an evaporator in which self-flashing steam is introduced, the amount of evaporation increases, so the amount of evaporation at the lower stage of low temperature and low concentration increases, and the amount of evaporation at the upper stage of high temperature and high concentration decreases. . Therefore, the surface area of the evaporation tube of the upper stage side evaporator can be reduced, the amount of highly corrosion resistant material used can be reduced, and the cost of the device configuration can be reduced. [Examples] Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a system diagram showing an embodiment in which a liquid concentrating device according to an embodiment of the present invention is applied as a white liquor concentrating device. In FIG. 1, this concentrator is equipped with first to fifth evaporators 1 to 5, and the first evaporator 1 on the uppermost side has a steam supply pipe 36 as a heating source and a condensate extraction pipe 36. Pipe 32 and concentrate extraction pump 34
is connected. The first to fifth evaporators 1 to 5 are equipped with a group of upright long-tube evaporation tubes 52, and the liquid to be concentrated is poured from the top of the tube group 52 and flows down in a thin film inside each tube. During this period, it is evaporated and concentrated. The generated steam enters the lower container 54 from the lower end of the tube group 52, and then passes through a droplet collector 56, such as a wire mesh type, to the steam extraction pipes 38 to 4.
It reaches 6. Further, the concentrated liquid is transferred to the evaporation tube group 52
falls into the container 54 from the lower end. The steam extraction pipes 38 to 44 are connected to the evaporation introduction sides of the lower evaporators 2 to 5, respectively, and heat the liquid in the tubes by passing between the evaporation tube group 52 of each evaporator. . The stock liquid is introduced into the flash evaporator 58 via the pump 28 and the supply pipe 30, where it flash evaporates, and the remaining liquid is introduced into the fifth evaporator 5 through the pipe 30, where it self-evaporates. The fifth evaporator 5 is provided with a piping 64 equipped with a pump 62 that connects the bottom of the container 54 and a liquid introduction chamber 60 formed at the top of the evaporation tube group 52 in a detour manner. The liquid is pushed up to the top of the evaporation tube group 52 and poured between the tubes of the evaporation tube group. The steam generated in the fifth evaporator 5 is sent from the pipe 46 to the condenser 50 and condensed. Further, the condensed liquid is discharged from the pipe 66 to the outside of the system via a tank 68 and a pump 70. The concentrated liquid in the evaporator 5 is transferred to a pipe 72, a pump 74,
The liquid is fed into the pipe 78 via the heat exchanger 76, into the liquid introduction chamber 60 at the top of the evaporator 4, flows down inside the evaporator tube group 52, and partially evaporates. The steam is sent from the pipe 44 to the fifth evaporator 5, and the condensate passes through the pipe 80, tank 82, and pump 84 and is discharged outside the system. Note that this condensed liquid is introduced into the heat exchanger 76 on the way, and is transferred from the fifth evaporator 15 to the fourth evaporator 76.
The liquid sent to the evaporator 4 is heated. The concentrated liquid in the fourth evaporator 4 is sent to the pipe 92 via the pipe 86, the pump 88, and the heat exchanger 90, and is introduced into the liquid introduction chamber 60 at the top of the third evaporator 3, and is then introduced into the evaporator tube group. 52. The steam evaporated while inside the evaporation tube group 52 is
The pipe 42 along with the steam sent from the pipe 126
It is sent to the fourth evaporator 4 via. The condensate is sent to the tank 82 via a pipe 94, a tank 96, and a pump 98, and is passed through a heat exchanger 90 along the way.
The liquid introduced into the third evaporator 3 is heated. The concentrated liquid in the third evaporator 3 is sent to the pipe 106 via the pipe 100, the pump 102, and the heat exchanger 104, and is sent to the liquid introduction chamber 6 at the top of the second evaporator 2.
0 and introduced between each tube of the evaporation tube group 52. The generated steam is sent to the third evaporator 3 via the pipe 40. Further, the condensate of the steam introduced from the pipe 38 is transferred to the pipe 10.
8. It is sent to the tank 96 via the tank 110 and the pump 112, and the heat exchanger 104 is sent to the tank 96 on the way.
The liquid introduced into the second evaporator 2 is heated. The concentrated liquid in the second evaporator 2 is sent to the pipe 120 via the pipe 114, the pump 116, and the heat exchanger 118, and is supplied to the liquid introduction chamber 60 of the first evaporator 1. The vapor then flows down inside the pipes of the evaporator tube group 52, during which time a portion of the vapor evaporates, and the generated vapor is sent from the pipe 38 to the second evaporator 2. The vapor condensate from the pipe 36 is sent to the tank 110 via the pipe 122 and the tank 124, and along the way it passes through a heat exchanger 118 to heat the liquid sent to the first evaporator 1. Therefore, the flash evaporator 58 is connected to a pipe 126 for extracting steam, and this pipe 126
is a pipe 42 connecting the third and fourth evaporators 4;
It has been merged with. Therefore, the flash evaporator 5
The steam of No. 8 passes through the pipes 126 and 42 and is introduced into the steam introduction side of the fourth evaporator 4 together with the steam from the third evaporator 4, and is used as a heat source in the fourth and fifth evaporators. In the concentrating device having such a configuration, compared to the concentrating device shown in FIG.
Since the amount of steam added as a heat source increases, a correspondingly larger amount of evaporation is performed in the fourth and fifth evaporators. Then, the amount of evaporation in the first to third evaporators can be reduced by that amount.
Therefore, it is possible to reduce the surface area of the evaporation tube on the upper side of high temperature and high concentration and increase the surface area of the evaporation tube on the lower side of low temperature concentration.
The amount of highly corrosion-resistant materials such as SUS316L is reduced,
It is possible to increase the amount of cheaper materials such as SUS304L. In addition, in the flash evaporator 58, the vapor is self-evaporated in an intermediate vacuum range, and the resulting vapor is used as heating steam in the fourth and fifth evaporators, so the sensible heat held by the stock solution is used as the evaporation heat source. The amount of heat source steam introduced into the first evaporator from the pipe 36 is also reduced. In addition, the concentration and temperature in each evaporator 1 to 5 when increasing white liquor with a concentration of 12.46% to 16.6%,
The amount of steam passing through the pipes 36 to 46, the temperature of the flash evaporator 58, etc. are entered in FIGS. 1 and 2. As is clear from this example, according to the apparatus of the embodiment shown in FIG. 1, the flow rate of steam introduced into the apparatus from the pipe 36 is reduced by about 20%, and it is clear that the evaporation process can be performed at a correspondingly lower heat cost. In addition, the surface area of the evaporation tube of each evaporator 1 to 5 is determined by the following
Shown in the table. As is clear from Table 1, the surface area of the evaporation tube of the first to third evaporators is approximately 15%.
The amount of Ni and SUS316L used is reduced accordingly, and the equipment configuration cost can be lowered by reducing the amount of expensive materials used.

[Table] Therefore, in order to apply the concentrating device of the present invention such as the embodiment shown in FIG. 1 to the kraft pulp manufacturing process shown in FIG. 3, it is sufficient to incorporate the concentrating device at the location A in FIG. 3. When the concentrator is installed in this way, the digester 14
The concentration of the white liquor introduced into the system can be increased and the temperature of the white liquor can be increased. Therefore, the amount of heating steam used in the digester 14 can be reduced. Furthermore, the amount of steam released into the atmosphere by the flash drum 16 is reduced, the amount of evaporation from the evaporator 20 is also reduced, and the steam load on the boiler 22 is reduced. Therefore, the amount of heavy oil consumed by the boiler 22 is reduced, and the manufacturing cost of kraft pulp can also be reduced. The device of the above embodiment is a self-flashing evaporator 5.
Although only one stage of 8 is provided, two or more stages may be provided in series so that each flash steam is used as heating steam for a separate evaporator. Further, the number n of evaporators installed may be 2 or more, and is not limited to that of the embodiment. The apparatus of the present invention can be suitably used not only for concentrating white liquor but also for concentrating various dilute liquids, especially dilute alkaline solutions. In addition, when applied to the concentration of a dilute alkaline solution, it is suitable for application to concentration of the solution to about 20% or less. [Effects of the Invention] As is clear from the above description, according to the concentrating device of the present invention, dilute alkaline solutions can be concentrated particularly efficiently, and the heat cost required for concentration can be reduced. Furthermore, the amount of highly corrosion-resistant material used is reduced, and the cost of configuring the device can also be reduced. Therefore, by incorporating the concentrating device of the present invention into the pulp manufacturing process, pulp manufacturing costs can be significantly reduced.

[Brief explanation of drawings]

FIG. 1 is a system diagram of an apparatus according to an embodiment of the present invention, FIG. 2 is a system diagram of a multi-effect evaporator, and FIG. 3 is a diagram of a manufacturing process for kraft pulp. 1-5... Evaporator, 30... Stock solution supply pipe, 36
...Steam supply pipe, 58...Self-flashing evaporator.

Claims (1)

[Claims] 1 A concentrating device using multiple effect evaporation in which first to nth evaporators (n is 2 or more) are arranged in series, in which heat source steam is supplied to the first evaporator, and the nth evaporator on the highest order side The stock solution is supplied to the can from the stock solution supply pipe, and the vapor from the low-rank evaporator is sequentially introduced into the high-rank evaporator, and the liquid to be evaporated in the high-rank evaporator is sequentially introduced into the low-rank evaporator. Introduced into the evaporator, the first
In a concentrating device that extracts concentrated liquid from an evaporator, a self-flashing evaporator is provided in the middle of the raw solution supply pipe, and this self-flashing vapor is supplied to the steam introduction side of any evaporator whose operating pressure is lower than that of the self-flashing evaporator. A liquid concentrating device characterized by: