JPS63253038A - Cooling and recovery of vapor - Google Patents

Abstract

PURPOSE:To cool and recover vapor advantageously, by directly bringing vapor such as unreacted styrene evolving from a vapor removal tank of a polystyrene plant into contact with a low-temperature circulating solvent, condensing the vapor by a wetted-wall cooler of water cooling type and further supercooling by a wetted-wall cooler of low-temperature cooling type. CONSTITUTION:In cooling and recovering vapor such as unreacted styrene evolving from a vapor removal tank of a polystyrene plant, a low-temperature circulating solvent is directly brought into contact with the vapor 36 at a direct contact part 32, the temperature of the vapor is lowered to the condensation temperature, the vapor and the solvent are introduced to a wetted-wall cooler 33 of water cooling type set under the direct contact part 32 to condense the vapor. Further the solvent and the condensed liquid are fed to a wetted-wall cooler 34 of low-temperature cooling type set under the wetted-wall cooler 33 of water cooling type and supercooled. The process is more simplified than a conventional procedure, the number of devices is reduced, capacity of refrigerators is saved, heat transfer performance is improved and the vapor is advantageously cooled and recovered.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for cooling and recovering steam, and particularly to a method for cooling and recovering unreacted styrene and solvent generated from a devolatilization tank of a polystyrene manufacturing plant.

[Prior Art] Polystyrene, which has a wide range of applications such as packaging containers and electrical parts, is produced by polymerizing styrene as a raw material. By the way, at the end of the polymerization process in a polystyrene manufacturing plant, there is a step in which unreacted styrene and solvent are evaporated and devolatilized from the polymerized polystyrene solution under vacuum, and then this gaseous unreacted styrene and solvent are collected by cooling and condensation. be.

The unreacted styrene contains a partially polymerized high-boiling substance called oligolimer, and when it is cooled and condensed using a shell tube type heat exchanger, which has been widely used in the past,
This high boiling point substance adheres to the cooling surface, reducing heat transfer performance and eventually causing clogging of the heat exchanger.

Conventionally, as a method for cooling and condensing unreacted styrene, the second
The one shown in the figure is known.

That is, high-temperature unreacted styrene, solvent, oligomer, etc., which are gasified and separated from the polymer by cooling and reducing the pressure in a devolatilization tank (not shown), are supplied from the steam supply line 1, In the condenser 2, the circulating solvent cooled by water in the first cooling B3 is sprayed through the first circulation line 4 and comes into direct contact with the solvent, the temperature is lowered, and most of the unreacted styrene and the like are condensed and recovered. Here, the condensate is the first
Most of the waste passes through the handling line 5 and is reused in the second circulation line 7 using the first circulation pump 6, while a portion is taken out of the system through the first barge line 8 and treated.

The uncondensed gas in the first condenser 2 is sent via line 9 to a second condenser 10 operated at a lower temperature;
The circulating solvent cooled by a refrigerant lower than water in the second cooler 11 is sprayed from the third circulation line 12 and comes into direct contact with the solvent, and the temperature is further lowered to condense and recover the remaining styrene and the like. This condensate passes through the withdrawal line 13 and is reused in the third circulation line 15 using the second circulation pump 14, and a portion is transferred from the second barge line 16 to the first condenser 2.
It merges with the first purge line 8 from the air and is discharged from the system through the discharge line 17. Here, the non-condensable matter in the second condenser 10 is the leaked air and a very small amount of styrene vapor, which is contained in the vacuum line 18 and the vacuum generator 1.
9 and is taken out of the yarn from the third barge line 20.

[Problems to be Solved by the Invention] However, the prior art has the following problems.

(1) The process is complex.

(2) Since there are many devices, the control and piping associated with them are also complex.

(3) Vapors of unreacted styrene, solvent oligomers, etc. are generally at a temperature of 200-240°C, and in order to recover condensate from this vapor, it is necessary to cool it to 5-10°C, which is removed as overt and latent heat. The amount of heat required is enormous. In conventional methods, this cooling is accomplished entirely through direct contact with the circulating solvent, which requires a large amount of circulating solvent (approximately 100 times the weight of steam). This increases the capacity of the condenser, circulation pump, heat exchanger, etc.

(4) When attempting to condense and recover styrene etc. by indirect cooling, oligomers may get onto the heat transfer surface and cause trouble.

The present invention has been made in view of the above circumstances, and provides a steam cooling and recovery method that simplifies the process compared to conventional methods, reduces the number of equipment, saves refrigerator capacity, and improves heat transfer performance. The purpose is to

[Means for Solving the Problems] The present invention provides a method for cooling and recovering vapors such as unreacted styrene generated from a devolatilization tank of a polystyrene plant, in which the vapors are brought into direct contact with a low-temperature circulating solvent to a condensing temperature. After lowering the temperature, the vapor and the solvent are introduced into a water-cooled wet wall cooler installed at the bottom of the direct contact area, and the vapor is condensed, and the solvent and condensate are then transferred to a low-temperature refrigerant installed at the bottom of the water-cooled wet wall cooler. The gist is to introduce it to a type wet wall cooler and supercool it.

[Function] According to the present invention, (1) The process is simplified, and the number of components is reduced to one condenser and one pump.

■Since the heat transfer coefficient of the 1-wall cooler section is large, the condenser becomes compact.

■Since most of the heat is removed by water cooling, the refrigerant chiller capacity becomes extremely small.

■The gas temperature in the cooling condenser can be brought closer to the refrigerant temperature, reducing the amount of styrene lost due to uncondensation.

[Example] Hereinafter, a system for a steam cooling and recovery method according to the present invention will be described with reference to FIG.

31 in the figure is a capacitor. This condenser 31 is a water-cooled type consisting of a direct contact part 32 provided at the top and a shell/tube type provided in the middle!
! It is composed of a wall hook 5 section 3, a low-temperature refrigerant type wet wall cooler section 34 provided at the bottom, and a liquid tank 35 provided at the bottom of this cooler section 34. The tube inlet is designed so that the fluid is uniformly dispersed in each tube, and the circulating solvent within the tube forms a liquid film on the inner surface of the tube wall and flows down.

A steam supply line 36 is connected to the direct contact section 32, and unreacted styrene, solvent, oligomer, etc. at 200 to 250°C are gasified in a devolatilization tank (not shown) and sent from the steam supply line 36. The steam is being sent.

The water-cooled two-wall cooler section 33 is connected to a supply line 37 for introducing cooling water and a first outlet line 38 for discharging the cooling water. The low temperature refrigerant type I wall section 34 has a supply line 39 for supplying refrigerant.
and a second outlet line 40 for discharging the refrigerant. A vacuum generating device 42 is connected to the liquid tank 35 via a vacuum line 41, and a purge line 43 is connected to the device 42. In addition, the liquid tank 35
A circulation pump 44 is connected via a liquid line 45 to
The circulation pump 44 and the direct contact section 32 are connected to the circulation line 4.
6. Note that 47 is an extraction line.

Next, the operation of the above system will be explained.

First, the vapor of unreacted styrene, etc. mentioned above is supplied from the vapor supply line 36, and a 5°C low-temperature circulating solvent is sprayed at the gas-liquid direct contact part 32 of the condenser 31 to directly contact the vapor, and due to the sensible heat of the solvent, the vapor is The temperature drops to the dew point at the pressure of direct contact. For example, at 10' Torr, the dew point is about 30°C.

Next, in order to condense and liquefy the steam, the water-cooled IIW cooler section 33 cools the steam using water. Here, steam and liquid flow down inside the tube of the liI wall roller section 33. Before&!
Cooling water is supplied to the shell side of the I-wall cooler section 33 through a supply line 3.
7 and flows out from the first outlet line 38. At this time, the solvent liquid film and vapor flowing down inside the tube are indirectly cooled and raised to a temperature of 25° C. to completely condense the vapor.

Next, the circulating solvent and condensate are passed through a low-temperature refrigerant type wet wall cooler section 34, and the refrigerant is passed from the supply line 39 to the second outlet line 4.
Cool while flowing to 0°C, and finally lower the temperature to 5°C.

Like this! The wall roller has the effect of increasing the heat transfer rate due to disturbance of the liquid film, and the overall heat transfer coefficient is 300 to 500.
It has a thick value of Kcal/mz -H-''C.

Yet another major feature of the wet wall cooler section is that the circulating solvent cleans the inner surface of the tube. The condensed steam contains oligomers, which are post-boiling point components, and when condensed, they become a sticky liquid, and if there is no cleaning liquid, they adhere to the inner surface of the tube, causing scale and tube clogging. However, in the present invention, since the solvent liquid always flows down within the tube while regulating the liquid film, the inside of the tube is always maintained in a clean state.

Furthermore, by dividing the wet wall cooler into two stages, the capacity of the refrigerator can be reduced by the amount of cooling of the refrigerant (for example, brine or chlorofluorocarbon).

Further, the fluid in the tube is finally cooled to 5° C. and stored in the liquid tank 35. A small amount of styrene vapor corresponding to the vapor pressure at this temperature and air leaking into the plant are discharged from the barge line 43 through the vacuum line 41 and the vacuum generator 42 to the outside of the system. The liquid in the liquid tank 35 passes through a liquid line 45 and a circulation pump 44, and part of it is supplied to the upper part of the condenser from a circulation line 46, and the rest is taken out of the system from a withdrawal line 47.

Next, an example using the above-described system will be described. First, the gas flow rate from the devolatilization tank, which is operated at 240°C and 10 Torr, is 560! ;l/H, and its composition is as follows.

Styrene 82゜2v01% Ethylbenzene 2.4vo1% Oligomer 14.3vo1% Others 1゜1v01% 9430Kg/H of circulating solvent at 5°C was sprayed from the upper part of the direct contact part of the condenser. This solvent is a liquid having approximately the same composition as the gas composition of the vapor. Next, 20°C water is supplied from the supply line 37 to the shell side of the water-cooled wet wall cooler unit 33, and 2°C water is supplied to the shell side of the low-temperature refrigerant type wet wall cooler unit 34.
prine was introduced from feed line 39. As a result,
The gas is cooled to 30°C in the direct contact area, the liquid at the outlet of the water-cooled wing wall cooler is cooled to 25°C, and the liquid at the outlet of the low-temperature refrigerant wet wall cooler is cooled to 5°C. Styrene, ethylbenzene, etc. were condensed and stored in a liquid tank 35. Further, the gas exhausted from the vacuum generator 42 was very small and consisted of 70% air and 30% styrene.

However, the present invention has the following effects.

■The process is simplified, and the number of components is reduced to one condenser and one pump.

■The heat transfer coefficient of the wet wall cooler section is large, making the condenser more compact.

■Since most of the body heat is absorbed through water cooling, the refrigerant capacity of the refrigerator becomes extremely small.

■The gas temperature in the cooling condenser can be brought closer to the refrigerant temperature, reducing the amount of styrene lost due to uncondensation.

■There is no adhesion of oligomers, etc. to the heat transfer surface, and the best heat transfer performance can always be demonstrated.

[Effects of the Invention] As detailed above, according to the present invention, the process is simpler than the conventional method, and various effects such as a reduction in the number of equipment, a reduction in refrigerator capacity, and an improvement in heat transfer performance can be achieved. It is possible to provide a method for cooling and recovering steam having the following characteristics.

[Brief explanation of the drawing]

The first factor is an explanatory diagram of a system of a steam cooling and recovery method according to the present invention, and FIG. 2 is an explanatory diagram of a system of a conventional steam cooling and recovery method. 31... Capacitor, 32... Direct contact part, 33
...Water-cooled wet wall cooler part, 34...Low temperature refrigerant type wet wall cooler part, 35...Liquid tank, 36...Steam supply line, 37.39...Supply line, 38.40.・・・
Outlet line, 41... Vacuum drawing line, 42... Vacuum generation 8m, 18... Verge line, 44... Circulation pump, 45... Liquid line, 46... Circulation line.

Claims (1)

[Claims] In a method for cooling and recovering vapor such as unreacted styrene generated from a devolatilization tank of a polystyrene plant, the vapor is brought into direct contact with a low-temperature circulating solvent to lower the temperature to condensation, and then the vapor and solvent are transferred to the lower part of the direct contact area. The steam is guided to a water-cooled wet wall cooler provided at the bottom of the water-cooled wall cooler and is condensed, and the solvent and condensate are further led to a low-temperature refrigerant-type wet wall cooler provided at the bottom of the water-cooled wet wall cooler for supercooling. Cooling recovery method.