JPS62213801A - Liquid concentration device - Google Patents

Abstract

PURPOSE:To reduce heating cost by installing a self-flashing evaporator halfway on a raw liquid supply tube as the supply source of heating source vapor in a concentration device of multiple effect evaporation method equipped with more than two evaporators for concentrating white liquor and the like used for manufacturing pulp. CONSTITUTION:Raw liquid is guided from a supply tube 30 into a flashing evaporator 58 for flashing evaporation. On the other hand, a concentration device is equipped with evaporation tubes 1-5, and a supply tube 36 and a removing tube 32 of concentrated liquid are installed in a first evaporator. Part of raw liquid is turned into vapor by a flash evaporator 58, flows through a tube 126 and joins vapor flowing through a tube 42 and sent to an evaporation tube 4. Raw liquid remaining unevaporated is guided from a tube 30 into evaporation tube 5 to be self-evaporated. Concentrated liquid in an evaporator 5 is sent through evaporators 4 3 2 1 and recovered out of the removing tube 32. As explained above, flashing vapor is utilized as the heat source for the evaporators 4 and 5, which reduces heating quantity of evaporators 1-3.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a liquid concentrating device, and is mainly used for concentrating dilute solutions such as white liquor, which is one of the raw materials for pulp production, and dilute alkaline solutions. The present invention relates to a concentrating device.

[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 to 12%, for example, about 10% as NaOH.
Around %, Na2S, Na2CO3, Na2S
O4, NaC! ; Contains about 2% of L, 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 denotes a digester, into which raw material chips and white liquor are introduced, and heated to about 160°C and 9 kg /
The chips are cooked in a heated and pressurized atmosphere maintained at 10 cm. After being heated to about 120° C. at 12, it is fed to a digester 14.

The reaction liquid from the digester 14 is once transferred to the flash drum 16.
The flash steam is used for heat recovery. The reaction liquid returned to atmospheric pressure in the flash drum 16 is introduced into the washer 18, and the 0-weak black liquor, which is separated into cellulose and weak black liquor, is introduced into the evaporator 20 where it is concentrated and becomes a strong liquid. It is introduced as fuel into the boiler 22 and burned together with heavy oil to generate steam.

This steam is supplied as heat source steam to the heating device 12 and the digester 14.

Further, the alkaline component contained in this black liquor becomes mainly Na 2 COa, which is introduced into the causticizing reactor 24, reacts with CaO, is returned to NaOH, and is returned to the white liquor tank 10. Note that in the causticizing reactor 24, C
aO changes to CaCO3, but this CaCO
3 is introduced into the kiln 26 and subjected to thermal decomposition treatment to become CaO
It is then subjected to a causticizing reaction again.

By the way, the white liquor conventionally used in the production of kraft pulp has a relatively low concentration of about 10-12%. 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 valve manufacturing 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 introduced into the fifth evaporator 5 via the stock solution pump 28 and the stock solution supply pipe 30, and is sequentially supplied to the fourth, third, second, and third evaporators.
It is fed into the first evaporators 4 to 1. Then, the concentrated liquid is taken out from the first evaporator l 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 l from the piping 36, and the steam generated in the first evaporator l 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 steam from the fifth evaporator is transferred in line 46 to a condenser 50 with an ejector system 48.
and condensed water.

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 concentrator shown in FIG. 2, since the concentrated liquid in the first or second evaporators 1 and 2 is at a high temperature and high concentration, a highly corrosion-resistant material such as Ni or 5US3161 is used. However, the first. Since the amount of evaporation in the second evaporator 1.2 is large, it is necessary to increase the surface area of the evaporator tubes of the first and second evaporators, which increases the amount of highly corrosion-resistant material used, and increases the equipment configuration cost. This contributes to an increase in

C. Means for Solving the Problem] The liquid concentrating device of the present invention is a multi-effect evaporating type concentrating device equipped with two or more evaporators, in which a self-flushing evaporator is provided in the middle of the stock solution supply pipe. The self-flashing steam is introduced as heat source steam into any evaporator having a lower operating pressure than the self-flashing steam.

[Operation] In the concentrator of the present invention, the stock solution is subjected to -H self-flash evaporation in an intermediate degree of vacuum, and the evaporated vapor is used as a 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 the evaporator in which self-flashing steam is introduced, the amount of evaporation increases, so the amount of evaporation in the lower stage of low temperature and low concentration increases, and the amount of evaporation in the upper stage of high temperature and high concentration decreases. . Therefore, the surface area of the evaporator tube of the upper evaporator can be reduced, and only a small amount of highly corrosion-resistant material is needed.
The device configuration cost can be reduced.

[Example] Embodiments 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. A pipe 32 and a pump 34 for extracting concentrated liquid are 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 inside each tube in the form of a thin film. 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 piping 3.
8 to 46.

Further, the concentrated liquid falls into the container 54 from the lower end of the evaporation tube group 52. The steam extraction pipes 38 to 44 are connected to the steam introduction sides of the lower evaporators 2 to 5, respectively, and pass between the evaporator tube groups 52 of each evaporator to heat the liquid in the tubes. .

The stock liquid is introduced into the flash evaporator 58 via the pump 28 and the supply pipe 30 and flash-evaporated, and the remaining liquid is introduced into the fifth evaporator 5 through the pipe 30 and 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 evaporator tube group 52 in a detour manner.
The liquid in the evaporator tube group 52 is pushed up to the top of the evaporator tube group 52 and flows between the tubes of the evaporator tube group 52. The steam generated in this fifth evaporator 5 is transferred from the pipe 46 to the condenser 5.
0 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 the pipe 72. The liquid is fed into a pipe 78 via a pump 74 and a heat exchanger 76, into a 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 midway, and heats the liquid sent from the fifth evaporator 5 to the fourth evaporator 4.

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, where it is introduced into the evaporator tube group. 52. The steam evaporated while flowing down in the evaporator tube group 52 is sent to the fourth evaporator 4 via the pipe 42 together with the X gas sent from the pipe 126. The condensate is transferred to piping 94 and tank 96. The liquid is pumped into the tank 82 via the pump 98, passes through a heat exchanger 90 on the way, and is introduced into the third evaporator 3 to heat the liquid.

The concentrated liquid in the third evaporator 3 is connected to a pipe 100 and a pump 102.
The liquid is fed into the pipe 106 via the heat exchanger 104, into the liquid introduction chamber 60 at the top of the second evaporator 2, and introduced between the tubes of the evaporator 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, is sent to the tank 96 via the tank 110 and the pump 112, and passes through the heat exchanger 104 on the way, and the second
The liquid introduced into the evaporator 2 is heated.

The concentrated liquid in the second evaporator 2 is transferred to the pipe 114 and the pump 116.
．． The liquid is fed into the pipe 120 via the heat exchanger 118 and supplied to the liquid introduction chamber 60 of the first evaporator l. 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 piping 38 to the second evaporator 2. The steam condensate from the pipe 36 is transferred to the pipe 122,
The liquid is sent to the tank 110 via the tank 124, passes through a heat exchanger 118 on the way, and is sent to the first evaporator 1 to heat the liquid.

Therefore, the flash evaporator 58 is connected to the steam extraction pipe 1.
26 is connected, and this piping 126 connects the third and fourth pipes.
The evaporator 4 is joined to a pipe 42 that connects the evaporator 4 to the evaporator 4. Therefore, the vapor in the flash evaporator 58 is transferred to the pipe 126.42.
through the fourth evaporator 4 together with the steam from the third evaporator.
and is used as a heat source in the fourth and fifth evaporators.

In the concentrator having such a configuration, the amount of steam added to the fourth and fifth evaporators 4.5 as a heat source is increased compared to the concentrator shown in FIG. This is done in the fifth evaporator. Then, the amount of evaporation in the first to third evaporators can be reduced by that amount.

Therefore, the surface area of the evaporator tube on the upper stage side of high temperature and high concentration can be reduced, and the surface area of the evaporator tube on the lower stage side of low temperature and low concentration can be increased, and the amount of highly corrosion resistant materials such as Ni and 5US316L used can be reduced. The usage of cheaper materials such as 5US304L can be increased.

In addition, in the flash evaporator 58, the vapor is self-evaporated in an intermediate vacuum range, and the 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, and piping 3 when increasing white liquor with a concentration of 12.46% to 16.6%.
The amount of steam passing through 6 to 46 and the temperature of the flash evaporator 58 are entered in FIGS. 1 and 2. As is clear from this example, according to the apparatus of the embodiment shown in FIG.
It is clear that the flow rate of steam introduced from No. 6 is reduced by about 20%, and the evaporation process can be performed at a correspondingly lower heat cost.

In addition, the surface area of the evaporator tube of each evaporator 1 to 5 is shown in Table 1 below.
In this evaporator, the surface area of the evaporator tube is reduced by about 15%, and the amount of Ni and 5US316L used is reduced accordingly.
By reducing the amount of expensive materials used, the device configuration cost can be reduced.

Table 1: Tube area However, 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. good.

When the concentrator is incorporated in this way, the concentration of the white liquor introduced into the digester 14 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 zO 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.

Although the steam embodiment apparatus is provided with only one stage of self-flash evaporator 58, it may be configured such that two or more stages are provided in series and each flash steam is used as heating steam for a separate evaporator. 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 solutions, especially dilute alkaline solutions.

When applied to the concentration of dilute alkaline solutions, approximately 20
It is suitable for application to concentration of solutions with a concentration of about 1.5% or less.

[Effects of the Invention] As is clear from the above description, according to the concentrating device of the present invention, a dilute alkaline solution 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.

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, 3
6... Steam supply pipe, 58... Self-flush evaporator.

Claims (1)

[Claims] A concentrating device using multiple effect evaporation in which first to nth (n is 2 or more) evaporators are arranged in series, the first evaporator is supplied with heat source steam, and the nth evaporator is supplied with a stock solution supply pipe. A concentrating device for supplying a stock solution from the stock solution, characterized in that a self-flash evaporator is provided in the middle of the stock solution supply pipe, and the self-flash vapor is supplied to the steam introduction side of any evaporator having a lower operating pressure than the self-flash evaporator. A device for concentrating liquids.