JPS61129001A - Recover of heat from vented gas in concentration process of liquid having large amount of gas dissolved therein - Google Patents

Abstract

PURPOSE:To effectively recover heat from vented gas, by introducing the vented gas into a preheater or a high concn. evaporation boiler. CONSTITUTION:A raw solution is supplied to a preheater from a line 1 while the vent gas exhausted from an evaporation boiler 11 is also supplied to the preheater 7 through a line 8. The raw solution is raised in its temp. through the heat exchange with steam accompanied by the vent gas in the preheater 7 to be guided to the evaporation boiler 11 through a line 3. As a result, the vented gas can be utilized as the heat source for preheating the raw solution. By supplying the raw solution and the vented gas to the high concn. evaporation boiler, the vented gas can be utilized as the heat source for highly concentrating the raw solution concentrate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for recovering heat from vent gas, and more specifically, a method for recovering heat from vent gas, in particular, dissolving a large amount of gas. This article relates to an effective heat recovery method for vent gas discharged outside the system when a liquid is processed in a concentration process using an evaporative vapor recompression method.

[Prior art] Liquid containing a large amount of dissolved gas, such as desulfurization waste liquid discharged from the wet desulfurization process of coke oven gas, is subjected to a steam heating method or an evaporative vapor recompression method before being combusted. In the latter case, the generated vapor is compressed and heated, used as a heating source, and then cooled and condensed with cooling water. This will be explained based on FIG. 3 as follows.

A liquid in which a large amount of gas is dissolved (sometimes referred to as "undiluted solution" for convenience) is introduced from line 1 into evaporator 11 . Also, from the line 17, vapor for auxiliary evaporation is supplied. The raw solution exchanges heat with the evaporated steam, and a portion of it evaporates. At this time, the dissolved gas in the stock solution is compressed together with the water vapor generated by degassing.
After being absorbed by &12 and compressed and heated, it is supplied again to the evaporator 11 as a heat source.

In the first agricultural contraction process that employs such an evaporative vapor recompression method, the dissolved gas accompanying the water vapor is continuously and reliably discharged from the evaporator 11 through the vibro to the outside of the system without allowing it to remain on the heating side of the heat transfer element. is important in maintaining heat transfer performance.

For this reason, conventionally, the vent gas discharged from line 6 contains 5 to 40% by weight of inert gas.
If it contains a relatively large amount of
3, a large amount of entrained water vapor is condensed in a large-capacity condenser 13 and then discharged to the outside of the system.

However, the implementation of the conventional evaporative vapor recompression method requires a large amount of cooling water for the condenser, and has the disadvantage that the amount of heat contained in the steam accompanying the vent gas is wasted out of the system.

[Purpose] The present invention mainly aims to reduce the effective heat of the vent gas discharged outside the system in the concentration process of the evaporative vapor recompression method of a liquid in which a large amount of gas (e.g. NH, Co, etc.) is dissolved as described above. It provides a collection method.

[Configuration] The present invention uses the vent gas discharged outside the system from the concentration process of the evaporative vapor recompression method to preheat the stock solution or to further highly concentrate the concentrated solution of the stock solution (liquid obtained by concentration processing). The vent gas heat recovery method is characterized in that the heat source for the vent gas is introduced into a preheater or a highly concentrated evaporator having a plate type or multi-tubular heat transfer surface.

Hereinafter, the present invention will be explained in more detail in comparison with a conventional method based on the accompanying drawings.

FIG. 1 is a system diagram of an apparatus that uses a heat source of vent gas to preheat the stock solution, and the stock solution is passed from line l to preheater 1
7. On the other hand, vent gas discharged from the evaporator 11 is also supplied to the preheater 17 through the line 8.

The preheater 17 has a structure having a plate type or multi-tube type heat transfer surface. Therefore, in the preheater 17, the stock solution is heated by exchanging heat with the steam entrained in the vent gas and heated, and then is led to the evaporator 11 through the line 3.

The evaporator (11) is of the type that recycles the evaporation paper led through the pipe (14), compresses it in the compressor (I2) and uses it as heated steam, and has two evaporating surfaces. A heating element (15) rn is provided, and the heated steam is injected into the interior of the heating element (15), and the undiluted solution falling from the upper distributor (19) is heated through the circulation pipe (2). Heat exchange occurs by flowing down the outer surface of the element (15), and water is evaporated and concentrated. Evaporator (11)
The paper evaporated inside is led out through a pipe (14), compressed and heated by a compressor (12), and then injected into the heating element (I5) as heated vapor. The concentrated liquid flows down the outer surface of the heating element (15) and is extracted from the bottom through a pipe (5), and sent through a pipe (7) to a combustion furnace (not shown) for combustion treatment. Note that there is a line (
17) to supply auxiliary steam.

The vent gas discharged from line 8 contains inert gas 5
It is included in the range of 40% by weight.

Further, mainly inert gas is supplied from the preheater 17 to the condenser 19 through the line 9.

Now, using the apparatus shown in Fig. 1, the amount of dissolved gas in the stock solution is 150 kg/hr,
When the temperature and pressure of the vent gas discharged through the line 8 are 95° C. and 1740 Torr, the amount of entrained steam supplied to the preheater 17 through the line 8 is 769 kg/hr. On the other hand, when the inert gas is discharged from the preheater 17 through the pipe 9 under conditions of 80° C. and 720 Torr, 125 kg/hr of water vapor is entrained in the inert gas.

Therefore, in this case, 644 kg/hr of entrained steam was used in the preheater 17 for preheating the stock solution.

FIG. 2 is a system diagram of an apparatus that uses a heat source of vent gas for highly concentrating a concentrated liquid. The stock solution is supplied from pipe 1 to evaporator 11, and then passes through line 4 to high concentration can 1.
8. on the other hand.

Evaporator l
The contained vent gas is also passed through line 8 to highly concentrated canister 18.
supplied to High concentration can [8 is preheater 1 shown in Figure 1]
7, it has a structure having a plate type or multi-tubular heat transfer surface.

The highly concentrated liquid is extracted from the system through line 20 and is burned. In addition, gas mainly consisting of inert gas is sent from line 9, and water vapor is sent from line 10 to condenser 19.
is led out of the system through Here, the vent gas is effectively used as a heat source for the highly concentrated can 18, and the stock solution is further concentrated.

Now, in Figure 2, the amount of dissolved gas in the stock solution is L50kg.
/hr, and the temperature of the vent gas supplied from the evaporator 11 through the line 8 to the high concentration can I8.

Under pressure conditions of 95° C. and 740 Torr, the amount of entrained water vapor supplied to the high concentration can 18 through line 8 is 769 kg/hr. On the other hand, when the inert gas is discharged from the highly concentrated can 18 through the line 9 under conditions of 80° C. and 720 Torr, 125 kg/hr of water vapor is entrained in the inert gas.

Therefore, in this case as well, 644 kg/hr of entrained steam was used in the high concentration can 18 for concentrating the raw treatment liquid, and about 700 kg in the high concentration can [8]
/h is evaporated.

On the other hand, in the conventional system shown in Fig. 3, the dissolved gas in the stock solution supplied from line 1 is 150 kg/h (
Average molecular weight 21) If it existed, when the inert gas was discharged from the evaporator 11 to the outside of the system through the line 6 under conditions of 95°C and 740 Torr, a large amount of water vapor of 769 kg/hr would be entrained in the inert gas. .

This water vapor is condensed by a large capacity condenser 13.

The concentrated liquid or highly concentrated liquid is treated by known means such as combustion treatment to recover sulfuric acid or gypsum.

Until now, the explanation has been based on desulfurization waste liquid as the target of treatment, but
Of course, the object to be processed is not limited to this. When a concentrated food is desired, the concentrated liquid and highly concentrated liquid themselves become the product.

[Effects] According to the present invention, the steam accompanying the vent gas discharged from the evaporator II is used for preheating the stock solution.

In addition, it is effectively used for highly concentrating the stock treatment solution.

In addition, as a side effect of the present invention, in the conventional method, it was necessary to condense a large amount of water vapor in the condenser 13, but according to the present invention, only a small amount of water vapor needs to be condensed, and the capacity of the condenser 19 can be reduced. It is possible to reduce the size to about 1/6 of the conventional size, and furthermore, the shaft power of compression 11!1112 can be significantly reduced.

In order to obtain a certain amount of evaporation and final concentration, the amount of steam handled by the compressor [2] is smaller than in the conventional method, and the high-concentration canister 18 is used for high-concentration concentration with a high increase in boiling point. This is due to the fact that the intermediate concentration method (11) handled by the compressor 12 requires a low concentration concentration operation with a low increase in boiling point, so the compression ratio of the compressor [2] can be reduced.

The present invention makes it possible to design an economical concentrator using an evaporative vapor recompression method with low running costs even for treated liquids (undiluted liquids) with relatively high boiling points.

[Brief explanation of the drawing]

1 and 2 are system diagrams showing two sides of an apparatus useful for carrying out the method of the present invention, and FIG. 3 is a system diagram for explaining the conventional method. 11... Evaporator 12... Compressor 1
3.19...Condenser 17...Preheater 1
8... Highly concentrated can 21.22, 23, 24, 25, 26, 27, 28, 2
9, 30.31... pump 32.33, 34, 35,
36, 37, 38, 39. 40, 41, 42...Condensate line patent applicant Sumitomo Heavy Industries, Ltd. Kan 3 Ward

Claims (1)

[Claims] 1. The vent gas discharged outside the system from the concentration step of the evaporative vapor recompression method is used as a heat source for preheating a liquid in which a large amount of gas is dissolved or for further concentrating a concentrated liquid of the liquid, A method for recovering heat from vent gas, characterized by introducing the heat into a preheater or highly concentrated evaporator having a plate-type or multi-tubular heat transfer surface. 2. The method according to claim 1, wherein the vent gas contains 5 to 40% by weight of Menato gas.