JP3390116B2 - Prevention of adhesion inside the separator - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an evaporator for obtaining a molten urea of 96 wt% or more by concentrating an aqueous urea solution of about 70 wt% or more in one stage and a plurality of stages of 2-3 under reduced pressure. And a method for preventing urea from adhering to the inside of a separator in a concentration step having a gas-liquid separator (hereinafter, simply referred to as a separator).

[0002]

2. Description of the Related Art Conventionally, in a urea process or a large-grain urea process, for example, in order to obtain a molten urea of 96 wt% or more by concentrating an aqueous solution of urea of 70 wt% or more in one stage and a plurality of stages of 2-3 under reduced pressure. There was a concentration step consisting of an evaporator and a separator. Usually, in the urea process, 99.5 wt% or more of molten urea is obtained from the urea aqueous solution, and in the large-grain urea process, 96 wt% or more of molten urea is obtained and supplied separately to the large-grain urea production process. Is well known. By the way, when the urea aqueous solution is concentrated in a plurality of stages, the concentration at the outlet of each stage is appropriately determined for each process.

Regardless of the number of stages used, a part of the urea aqueous solution supplied to the separator as described above may be entrained in each stage and urea may adhere inside the separator.
FIG. 2 schematically shows the final stage as a representative example of these states. Details will be described below with reference to this figure. Normally, in the urea process, the urea aqueous solution 3 concentrated to about 94 to 98 wt% is separately supplied from the line 10 to the evaporator 2 operated under reduced pressure. The vapor evaporated from the urea aqueous solution in the evaporator 2 and the generated molten urea are collected in the line 11
Is introduced into the separator 1 (for example, tangential) operated under the same reduced pressure as the evaporator 2. The separator is operated at a temperature of 138 ° C. and a reduced pressure of 25 mmHg, for example. At this time, 99.5 wt% or more of molten urea is obtained from the bottom of the separator. In the large-grain urea process, the concentration of the urea aqueous solution 3 in the line 10 is, for example, 70
~ 85wt%, same as the urea process except that 96wt% or more of molten urea is obtained from the bottom of the separator and the operating conditions are different. In either process, the top of the separator is connected to the vacuum generator 7,
The water vapor generated inside the separator is guided to the vacuum generator 7. At this time, the urea 4 entrained in the water vapor may adhere to the inner wall of the upper part of the separator and solidify to grow the deposit 4.

There are cases in which problems such as blockage of the bottom of the separator due to the fall of the deposit 4 and stop of a pump for discharging molten urea from the bottom, which is not shown in the figure, may occur.

However, even if such a problem occurs,
Currently, there are no specific measures other than stopping the operation and removing the deposits.

Under these circumstances, hammer rings, knockers, vibrators, etc. have been installed and regularly treated as part of countermeasures, but no remarkable effect has been observed.

[0007]

As described above, according to the prior art, the separation efficiency is lowered by the adhered substance solidified inside the separator and the bottom of the separator is clogged due to the irregular fall of the adhered substance. However, problems such as the stop of the pump that discharges the molten urea from the bottom may occur.

An object of the present invention is to provide means for solving the above-mentioned problems.

[0009]

Means for Solving the Problems The inventors of the present invention have made extensive studies in view of the above problems. As a result, when the deposit 4 is removed at the time of attachment, it is extremely easy to remove, as compared with the case where there is a temporal change with time.
Furthermore, it was confirmed that the adhered matter was hard to adhere to the inner wall of the separator when it was always wet. The present invention is based on the above findings.

That is, according to the present invention, in the separator in the concentration step having the evaporator and the separator for concentrating the urea aqueous solution under reduced pressure, the inner wall above the raw material supply port, the horizontal portion of the shielding plate and the vertical portion of the shielding plate are provided. A method for preventing adhesion inside the separator, characterized in that water vapor is sprayed from a plurality of holes formed in the pipe installed in the section so as to wet the inner wall above the raw material supply port and the shielding plate, and ammonia as water vapor. it is the separator unit's internal antiadhesive how to use the water vapor containing.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention is shown in FIG.
The present invention will be described with reference to FIG. 1 by taking the urea process as an example. It should be noted that FIG. 1 is an example of the final stage in order to simplify the description. Needless to say, the present invention can also be applied to the large-grain urea process.

The separator 1 is connected to a vacuum generator 7 for reducing the pressure, and is operated at a pressure of 20 to 40 mmHg and a temperature of 136 to 145 ° C.

The pipe 6 installed on the inner wall above the raw material supply port of the separator, the horizontal portion 5 of the shield plate and the vertical portion 50 of the shield plate is
Has multiple holes. When using water vapor described below, the holes of at least the uppermost one of the pipes of the pipe are provided so that the inner wall on the tower top side and the inner wall on the tower bottom side of the separator are wetted. It is opened in both directions on the bottom. The hole of the pipe provided in the inner wall of the separator on the tower top side of the horizontal portion 5 of the shield plate and the vertical portion 50 of the shield plate is opened on the bottom side of the tower so as to hit the inner wall. Shield horizontal part 5 and shield vertical part
The pipe provided in 50 is opened so as to wet the surfaces of the horizontal portion of the shield plate and the vertical portion of the shield plate.

The number of the pipes to be installed requires at least three, one for each of the inner wall of the separator, the horizontal part of the shield plate and the vertical part of the shield plate located above the horizontal part of the shield plate. Multiple separators may be provided on the inner wall of the separator located at the upper portion.
The choice of number is empirically chosen from the size of the separators, usually four or five may be chosen.

When a plurality of separators are provided on the inner wall of the separator located above the horizontal portion of the shielding plate, the pipes are installed at intervals such that when water vapor is used alone, urea aqueous solution or molten urea is used alone. For the combination of
In any case, it is set to 2 to 3 m.

The clearance between the pipe and the inner wall of the separator located above the horizontal portion of the shield plate, the horizontal portion of the shield plate, and the vertical portion of the shield plate will be described later.

[0017] When used alone water vapor, the diameter of the holes provided in the pipe is usually selected from 1 to 3 mm. If the diameter of the hole is less than 1 mm, a pressure difference is likely to occur, and
If it exceeds 3 mm, the amount of water vapor consumed increases, which is not preferable.

The outlet flow velocity of the holes is set to 50 to 300 m / sec. If it is less than 50 m / sec, it depends on the diameter of the hole,
The steam curtain effect may be reduced to 300
The effect does not change even if it exceeds m / sec.

The pitch of the holes on the pipe is selected from 10 to 50 mm. If it is less than 10 mm, the effect does not change even if the amount of steam used increases, while if it exceeds 50 mm, the steam curtain effect may decrease, so it is preferable to avoid it.

When the pipe is used as it is, the clearance between the pipe and the inner wall of the separator is selected from, for example, 5 to 15 mm, and the clearance between the pipe and the shielding plate is selected from 1 to 10 mm. These clearances are for installing and fixing pipe supports and the like. Alternatively, the pipe may be divided in half and directly fixed by welding or the like. Forming a Steam curtain be to employ any, Ru der to blow away to force those entrained.

Water vapor having an original pressure of 3 bar or more is used. Incidentally, in the vacuum concentration method, burettes may be generated more often than in the normal atmospheric concentration method. To prevent this, there is a method to introduce ammonia separately,
It is also effective to use the condensate containing ammonia as a steam source by a method such as heating separately. In this case, ammonia may be contained in an amount of 2 wt% or more .
Your name, usually, such a condensate is set in one place, is intended to be handled separately, not good if using a part of.

[0022]

The present invention has been described above, but the present invention will be described in more detail with reference to examples.

Needless to say, the present invention is not limited to the examples described below. Example 1 An example in which steam is used to prevent adhesion to the final stage separator 1 shown in FIG. 1 will be described. The original pressure of steam was 3 bar. The separator 1 is connected to a vacuum generator 7 for reducing the pressure,
It was operated at a pressure of 25 mmHg and a temperature of 138 ° C. The feed urea solution concentration supplied to the separator was 94 wt% and the molten urea concentration was 99.5 wt% or more. Inside the separator, pipes 6 are placed every 2 m on the inner wall of the separator located above the horizontal part 5 of the shield, a total of 2 places, one on the horizontal part of the shield 5 and one on the vertical part 50 of the shield, respectively. We have installed a total of four locations. The clearance between the pipe and the inner wall of the separator is 10 mm, and the clearance between the pipe and the horizontal part 5 of the shield plate and the vertical part 50 of the shield plate is 5 mm.
It was each.

The diameter of the hole provided in the pipe was selected to be 1 mm. The pitch of the holes on the pipe was 50 mm. The exit flow velocity of the hole was set to 300 m / sec. The operation result is clogged
The number of outages per year due to Ri et al. Example 2 The hole diameter of Example 1 was 1 mm, the hole pitch on the pipe was 50 mm, and the outlet flow velocity of the holes was 300 m / sec. 3 mm, 10 mm and 50, respectively.
The same procedure as in Example 1 was carried out except that m / sec was changed. result
The number of outages per year was 0 due to clogging. Comparative Example 1 As a result of operating with the water vapor of Example 1 stopped, it was found that clogging occurred.
The number of outages per year was 5-10.

[0025]

According to the method of preventing adhesion inside the separator of the present invention, the following effects can be obtained. (1) It is not necessary to stop the plant to remove the deposits. Since long-term continuous operation is possible, the production volume becomes constant and the product can be supplied stably. (2) As a result of stable operation, the energy used during unstable operation is not consumed, thus saving energy.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing an embodiment of the prior art.

[Explanation of symbols]

1 separator 2 evaporator 3 Urea aqueous solution 4 attached matter 5 Shield horizontal part 50 Shield plate vertical part 6 piping 7 Vacuum generator 8 Raw material supply port 10 to 13 lines

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Claims (2)

(57) [Claims] 1. In a separator in a concentration step having an evaporator and a separator for concentrating an aqueous urea solution under reduced pressure, the separator is installed on an inner wall above a raw material supply port, a horizontal portion of a shielding plate, and a vertical portion of the shielding plate. A method for preventing adhesion inside a separator, characterized in that steam is sprayed from a plurality of holes formed in the pipe so as to wet the inner wall above the raw material supply port and the shielding plate. 2. The method for preventing adhesion inside a separator according to claim 1, wherein steam containing ammonia is used as the steam.