JP3645417B2 - Liquid transfer method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid transfer method.
[0002]
[Prior art]
In general, a chemical process consists of a plurality of process equipment used for unit operations such as reaction and separation, connected by lines such as pipes, and raw materials in the state of gas, liquid or solid using the lines. And intermediate reactants are transferred and processed by each process equipment to produce a final product.
[0003]
Process substances that are transferred in a liquid state are generally pumped using a pump provided in the line, but the problem is that the equipment is damaged due to the phenomenon of bubbles in the liquid (cavitation). There is a point.
For example, when a polymer such as polypropylene is produced by polymerizing a monomer such as propylene in the presence of a liquid phase, the polymerization heat cools and condenses a part of the vaporized liquid phase (vaporized vapor). The condensate is removed using a reflux condenser that returns the polymerized liquid to the polymerization tank. The vaporized vapor is stirred in the polymerization tank, and a part of the vapor is extracted from the polymerization tank together with the polymer suspension. In some cases, it may enter the suction pipe of the pump used for pumping to the next process such as the recovery process, causing cavitation.
[0004]
Alternatively, there is a problem when pumping out the liquid extracted from the degassing tank for recovering the raw material monomer and additive by reducing the pressure from the polymer suspension.
Moreover, the above problems are not limited to the case where the suspension is transferred from a stirring tank such as a polymerization tank or a degassing tank. For example, the clarified liquid is separated from the suspension using a separation device such as a liquid cyclone. Even if it is transferred, the pressure drops due to the centrifugal action of the hydrocyclone and its resistance, making it easier to vaporize, and the proportion of vaporized vapor on the clarified liquid side increases, and it is installed in the clarified liquid transfer line. This is often a problem even in the pumps used.
[0005]
Generally, when installing a pump, the conditions for generating vaporized vapor at the pump inlet are judged, and the model is selected and arranged. However, vaporized vapor (bubbles) generated in the process equipment of the transfer source ) Is difficult to predict how much will be caught in the suction pipe. In some cases, it is necessary to operate under conditions other than the operating conditions when the pump is installed.
[0006]
As a method of preventing cavitation, for example, a method of installing a vortex breaker at the outlet of the process equipment, or a double line as an extraction line from the process equipment, by letting an extraction liquid flow into the inner pipe and a cooling medium to flow outside. Examples include a method of cooling the suspension and reducing bubbles.
However, even if a vortex breaker is installed, the effect of preventing air bubbles from mixing is not sufficient. In addition, in the method of cooling with a double pipe, the length of the transfer line from the process equipment to the pump becomes long, or a very low temperature cooling medium is required, so that the cost required for the cooling becomes high. There is a problem that. Even in the method of cooling with a multi-tube heat exchanger, there is a problem that the heat exchanger is blocked or the overall heat transfer coefficient is reduced due to the adhesion of scale.
[0007]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for transferring a liquid while preventing the occurrence of cavitation of a pump attached to the transfer line.
[0008]
[Means for Solving the Problems]
That is, the gist of the present invention is that when a liquid is pumped from a process device using a pump installed in a transfer line, the liquid to be transferred is a suspension of a polymer , and the source process device and the pump The liquid transfer method is characterized in that a line for injecting liquid is provided in the transfer line between and the liquid, and the liquid injected from the injection line is a raw material monomer of the polymer .
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
In the method of the present invention, when a liquid mixture extracted from various process equipment such as a polymerization tank and a stirring tank is transferred using a transfer line attached to a pump, the liquid is injected from the transfer line, thereby cavitation of the pump. It is a thing to move while suppressing.
[0010]
The liquid to be transferred may be a mixed liquid or a suspension, and is not particularly limited, but it is suitable for application to a highly volatile liquid because it has a large effect, and is suitable for polymers such as propylene and vinyl chloride. Examples include raw material monomers.
The liquid injected from the transfer line may be selected such that the vapor pressure of the liquid mixture of itself and the transferred liquid is lower than the vapor pressure of the transferred liquid before injection, From the viewpoint of using the sensible heat of the liquid, it is preferable to use a liquid having a temperature lower than that of the liquid to be transferred because the temperature of the liquid mixture after mixing is lowered and the effect of eliminating bubbles is further increased. Considering operations such as separation and purification in the above, the same main component as the liquid to be transferred is more preferably selected.
The type of pump is not particularly limited, and may be selected according to the process conditions such as the type of liquid to be transferred and the pressure.
[0011]
In addition, the transfer source process equipment may be any equipment that is used in the liquid processing process, but it is applicable to equipment that easily generates vaporized vapor such as a stirring tank, polymerization tank, degassing tank, and liquid cyclone. The effect of inhibiting cavitation due to the reduction of bubbles is great and preferable.
Hereinafter, an example in which the present invention is applied to an actual process will be described in detail with reference to the drawings.
[0012]
FIG. 1 is an explanatory view showing an example in which the present invention is applied to transfer of a suspension of a polymer.
The polymerization reaction of the liquid monomer is performed while being stirred by the stirring device 2 in the liquid phase portion in the polymerization tank 1. A part of the liquid phase is vaporized by the polymerization heat to become vapor, and the vaporized vapor is sucked by the blower 6, cooled by the condenser 4, and separated into a condensed liquid and a non-condensed gas. The condensate and non-condensable gas are circulated to the polymerization tank 1 via a condensate line 8 and non-condensation lines 5 and 7, respectively.
In the liquid phase part of the polymerization system as shown in FIG. 1 above, vaporized vapor generated by polymerization heat and non-condensed gas circulated from the condenser and returned to the liquid phase part exist as bubbles, After stirring and mixing in the phase part and staying in the liquid phase while splitting and coalescing, etc., a part of the gas part is discharged to the gas phase part, and the remaining part is withdrawn as a suspension together with the polymer. By introducing a liquid from the liquid injection line 10 installed in, bubbles are eliminated or reduced.
[0013]
The polymer suspension extracted from the pump suction line 9 is transferred to the subsequent process through the transfer line 12 by the transfer pump 11. Examples of the subsequent process as the transfer destination include a subsequent polymerization tank and an unreacted gas recovery tank. Or you may circulate to the superposition | polymerization tank 1 itself via a cooler, a classifier, etc. Further, the transfer destination may be a single process or a plurality of processes. In such an example, as the liquid injected from the transfer line, the raw material is simply used from the viewpoint of eliminating unnecessary operations in the separation / purification process after transfer or not inhibiting the polymerization when recycled to the polymerization system. The mer itself is exemplified as a preferred embodiment.
[0014]
FIG. 2 is an explanatory diagram when the present invention is applied to the transfer of the suspension in the degassing tank 13 for recovering the unreacted gas after the polymerization reaction. The degassing tank 13 is sucked by the compressor 18. The vaporized steam is introduced into the cooler 16 from the vaporized vapor line 3 and separated into a condensed liquid and a non-condensed gas. The non-condensed gas is sent to a recovery system or the like via lines 17 and 19 , and the condensed liquid is returned to the degassing tank 13 via line 8. Suspension Nigoeki in the degassing tank 13 is transported to the subsequent process by the transfer pump 11 through a pump suction line 9 with a portion of the vaporized steam. A liquid injection line 10 is installed in the pump suction line 9 to introduce a liquid for eliminating or reducing bubbles in the suspension.
[0015]
FIG. 3 is an example in which in the case of the polymerization system of FIG. 1, the liquid injection line 10 is connected to the condensation line 8 and a part of the condensate in the condenser is applied as the liquid injected from the liquid injection line 10. In such a case, it is preferable to constitute a circulation system in terms of cooling efficiency of the polymerization system.
As described with reference to FIGS. 1 to 3, when the present invention is applied to the polymerization process, examples of the liquid injected into the transfer line include liquids such as raw material monomers introduced into the polymerization tank. . Generally, the liquid introduced into these polymerization tanks is lower than the polymerization reaction temperature, so it is the easiest method to use a part of the liquid. Furthermore, when a circulation system is formed, what is originally introduced directly into the polymerization tank is merely introduced into the polymerization tank via this circulation system, and the coolant can be used without waste. It becomes possible.
[0016]
【Example】
Next, specific embodiments of the method of the present invention will be described using examples, but the present invention is not limited by the following examples unless it exceeds the gist.
<Example 1>
In the polymerization tank shown in FIG. 1, solution polymerization of liquid propylene was carried out continuously with the polymerization temperature in the tank controlled at 65 ° C. The amount of the polymer suspension extracted from the pump suction line 10 is 5.7 ton / h, and is supplied as a raw material monomer from the liquid injection line 10 provided in the pump suction line 9 to the polymerization tank. The same propylene having a temperature of 35 ° C. was injected into the pump suction line 9, and the gas circulation rate of the condenser cooler circulation gas blower was gradually increased to change the bubble ratio in the polymerization tank. By installing a density measuring device in the vicinity of the polymerization tank liquid outlet of the pump suction line 9 and in the vicinity of the pump suction port, the density of the turbid liquid in the pipe is continuously measured, and the bubble rate is calculated from the suspension density. (Volume volume) was measured.
[0017]
FIG. 4 shows the relationship between the amount of liquid injected from the liquid injection line 10 and the bubble rate of the suspension flowing through the pump suction line 9. As the liquid is injected, the bubble rate of the suspension decreases and then disappears. The reduction of bubbles is significant even when a small amount of suspension is injected. From this result, it can be seen that there is a correlation between the injection amount of the suspension and the bubble erasing rate.
[0018]
<Comparative Example 1>
The polymerization reaction was carried out in the same manner as in Example 1 except that the cooling liquid was not introduced between the liquid phase extraction outlet of the polymerization tank and the transfer pump, and the bubble rate was measured. FIG. 5 shows the time change of the current value of the transfer pump 11 and the bubble ratio in the vicinity of the pump suction port. The bubble rate gradually increased, and when it exceeded 20 vol%, the absolute value of the current value tended to decrease, and at the same time, the current value fluctuated and showed signs of cavitation. Judging that it was possible, the gas circulation rate of the condenser cooler circulation gas blower was reduced. FIG. 6 shows a change in the pump discharge flow rate in the same time zone as in FIG. 5, but it is shown that the decrease in the pump discharge flow rate is large.
[0019]
<Comparative example 2>
Example 1 except that a double pipe type cooler was installed between the polymerization tank liquid outlet and the suction of the transfer pump, and the turbid liquid was cooled by flowing cooling water through the outer pipe of the double pipe. The polymerization reaction was performed in the same manner, and the bubble rate was measured. FIG. 7 shows the correlation between the bubble ratio in the vicinity of the pump inlet when the bubble ratio in the vicinity of the polymerization tank outlet is 20 vol%, the cooler heat removal amount obtained from the cooling water inlet / outlet temperature and the amount of cooling water. . As a result, it is apparent that the bubbles can be reduced and further eliminated by cooling the turbid solution, and that there is a correlation between the amount of heat removal from the cooler and the elimination rate of the bubbles.
[0020]
In Comparative Example 1, an example is shown in which the pump reaches cavitation due to mixing of bubbles by vaporized vapor. In Comparative Example 2, an example in which the bubble rate is lowered by cooling to avoid cavitation is also shown. However, Example 1 shows that air bubbles can be easily reduced and cavitation can be avoided by using the method of the present invention without installing ancillary equipment such as a cooler.
[0021]
【The invention's effect】
According to the method of the present invention, the liquid can be transferred while preventing the occurrence of cavitation of the pump incidental to the transfer line, the possibility of damage to the pump can be reduced, and the polymerization tank which is the connection source of the transfer line Etc. can be operated stably.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an example in which the present invention is applied to the transfer of a polymer suspension. FIG. 2 is an explanatory diagram illustrating another example in which the present invention is applied to a transfer of a polymer suspension. 3 is an explanatory view showing another example in which the present invention is applied to the transfer of a polymer suspension. FIG. 4 is a graph showing an example of the relationship between the liquid injection amount and the bubble rate when the present invention is applied. 5] Trend graph of the current value during the transfer of the polymer suspension in the conventional technology and the corresponding bubble ratio [Fig. 6] Trend graph of the suspension flow rate during the transfer of the polymer suspension in the conventional technology [ FIG. 7 is a graph showing the relationship between the amount of heat removed from the cooler and the bubble rate in the prior art.
DESCRIPTION OF SYMBOLS 1 Polymerization tank 2 Stirrer 3 Vaporization vapor line 4 Reflux condenser 5, 7 Non-condensing gas line 6 Blower 8 Condensate line 9 Pump suction line 10 Liquid injection line 11 Transfer pump 12 Liquid transport line 13 Degassing tank
16 cooler
17, 19 Recovery gas line
18 compressors

Claims (5)

When the liquid is pumped from the process equipment using a pump installed in the transfer line, the liquid to be transferred is a suspension of the polymer, and the liquid is transferred to the transfer line between the source process equipment and the pump. A liquid transfer method characterized in that a line for injecting the liquid is provided and the liquid injected from the injection line is a raw material monomer of the polymer . Polymer is polypropylene, the transfer method of a liquid according to claim 1 the raw material monomer is propylene. The liquid transfer method according to claim 1 or 2 , wherein a transfer source of the transfer line is a polymerization tank. The liquid transfer method according to claim 1 or 2 , wherein a transfer source of the transfer line is a degas tank for removing a gas component after the polymerization reaction. The liquid transfer method according to claim 1 or 2 , wherein a transfer source of the transfer line is a liquid cyclone.

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