JPH01198687A - Recovering method of gas oil and naphthalene in coke oven gas - Google Patents

Abstract

PURPOSE:To obtain the title substance without using steam and corrosion to apparatus, by treating coke oven gas with an absorption oil, distilling under reduced pressure in a discharge tower, sending distillate to a side tower and recovering a gas oil from the top and naphthalene from the bottom of the side tower, respectively. CONSTITUTION:Coke oven gas containing a gas oil component and naphthalene component is countercurrently contacted with an absorption oil supplied from a top part of the tower by scrubbers 1 and 2 and the gas oil and the naphthalene are absorbed to the absorption oil which is then sent to a discharge tower 14 and distilled by a reboiler 15 provided in a bottom of the tower at an operating pressure of reduced pressure below 300Torr. The gas oil and naphthalene are distilled off from the top of the discharge tower 14 and the distillate oil is sent to a side tower 22, then the gas oil is recovered from the top of the side tower 22 and a bottom liquid from the bottom part of the side tower 22 is sent to a flash tower 25, thus naphthalene is recovered from the top of the tower.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention is directed to absorbing light oil (a mixture of benzene, toluene, and xylene) and naphthalene in coke oven gas (relatively heavy oils such as taleosote oil and anthracene oil). A mixture of aromatic oils or petroleum straw oil) is used to strip light oil and naphthalene from this absorbed oil without using steam or coke oven gas, resulting in a concentration of 80% by weight. A method for recovering light oil and naphthalene from coke oven gas that can efficiently and at low cost recover approximately 100% of naphthalene, and a method for efficiently removing NCN from the top oil of the ejection tower to prevent scaling and corrosion. The present invention relates to a method for recovering light oil and naphthalene from coke oven gas.

In the method of the present invention, naphthalene is concentrated and recovered to about 80% by weight, but once naphthalene of about 80% by weight is obtained, naphthalene of about 95% by weight is produced using a drum flaker and a screw press. becomes possible.

[Conventional technology]

Conventionally, when recovering light oil and naphthalene from coke oven gas, a method as shown in FIG. 6 has generally been used. That is, coke oven gas is introduced into the naphthalene scrubber 1 and then into the Penzol scrubber 2, and the absorbent oil (hereinafter referred to as
The coke oven gas is produced by spraying a countercurrent contact with the depentened absorbent oil (depenned absorption oil) to absorb and remove light oil, etc. Absorbed oil containing light oil and the like (hereinafter referred to as pen-containing absorbed oil) is heated in the heat exchanger 3 by exchanging heat with the hot depenned absorption oil, and then supplied to the dehydration tower 4, where it is heated at the top of the dehydration tower 4. The steam containing light oil and water released from the tank is supplied to the upper stage of the ejection tower B. The pen-containing absorbed oil coming out of the bottom of the dehydration tower 4 is heated to a heating furnace 5.
After being heated, it is supplied to the middle stage of the ejector tower B, which is operated at normal pressure, and is subjected to steam stripping. Most of the dependenized absorbed oil that exited the bottom of the ejection tower B is heat-recovered in the heat exchanger 3, and further cooled in the absorption oil cooler 7.
It is used in circulation for naphthalene scrubber 1 and penzol scrubber 2. A portion of the depenciled absorption oil from the bottom of the ejection tower B is supplied to the depitching tower 8, where the pitch accumulated in the circulating absorption oil is removed.

Light oil vapor containing naphthalene is distilled from the top of the ejection group 6 and is cooled and condensed in the ejection group condenser 10. Water is separated and removed from the condensate in the ejector reflux strum 11, a portion of the condensate is extracted as crude light oil, and the remainder of the condensate is returned to the top of the ejector column B as reflux. Naphthalene oil is extracted as a side stream from the middle stage of the ejector condensing section. In this case, the concentration of naphthalene in the naphthalene oil is generally about 50% by weight, and most of the remainder is an absorbed oil component having a boiling point higher than that of naphthalene.

Furthermore, as shown in Japanese Patent Publication No. 15675/1983, a method has been proposed in which a light oil expelling group is operated at normal pressure and coke oven gas from which light oil, etc. has been removed is used as an ejecting agent. .

[Problem that the invention seeks to solve]

The conventional method shown in FIG. 6, in which the light oil ejection group is operated at normal pressure and steam is used as the ejection agent, has the following disadvantages.

(11 Steam is used as an accompanying gas for light oil, etc., so most of the heat (latent heat) possessed by the steam is not utilized at all, resulting in an expensive waste of energy.

(2) Severe corrosion is promoted by condensation of steam within the ejection tower.

(3) When attempting to recover naphthalene, the crude gas oil distilled from the top of the ejection group contains a considerable amount of naphthalene, resulting in a low naphthalene recovery rate. - Examples are given in Table 1.

(Leaving space below) Table 1 (4) There is a large amount of absorbed oil that is accompanied by crude light oil and naphthalene oil, resulting in a large loss of absorbed oil.

Although the method described in Japanese Patent Publication No. 15675/1988 solves the disadvantages of the method shown in FIG. 6, it still has the following disadvantages.

fl) The light oil and coke oven gas discharged from the top of the ejection tower are cooled and the light oil and the like are condensed and separated, but the separated coke oven gas contains light oil and the like at a saturated concentration. Therefore, when this coke oven gas is used as a high-calorie fuel, the recovery rate of light oil and the like decreases.

(2) When the separated coke oven gas is mixed with the coke oven gas such as light oil at the inlet of the absorption bottle, the load on the absorption tower and the ejection unit increases.

(31wA A large amount of power is required to increase the pressure of coke oven gas as a propellant.

(4) Heat is carried out of the system by the coke oven gas, resulting in wasted energy (however, the amount of energy consumed is significantly lower than the conventional method shown in Figure 2).

(5) Since coke oven gas components are dissolved in the recovered light oil, etc., treatment such as degassing may be required.

The present invention was made to solve the above-mentioned disadvantages, and it uses absorption oil to absorb light oil and naphthalene in coke oven gas, without using steam or coke oven gas as a propellant. The object of the present invention is to provide a method capable of recovering light oil and naphthalene from coke oven gas at low cost by performing vacuum distillation using an expelling group.

However, in the method described above, in which light oil and naphthalene in coke oven gas are absorbed using absorption oil, and the light oil and naphthalene are recovered from the top of the column by distillation under reduced pressure with an ejector group, the light oil and naphthalene are absorbed from coke oven gas. Since trace amounts of HCN are mixed into the overhead oil of the ejection group, when this is heated, cyanide polymers are formed, causing scaling and corrosion of downstream conduits and equipment.

The invention of claim 3 of the present application has been made to solve this problem, and is a coke oven gas that efficiently removes IIcN from the top oil of the ejection group in a simple manner and prevents scaling and corrosion. The purpose of the present invention is to provide a method for recovering light oil and naphthalene in the fuel.

[Means and effects for solving the problem] In order to achieve the above object, the invention of claim 1 of the present application uses oil to absorb light oil and naphthalene in coke oven gas, as shown in FIG. In the method of ejecting and recovering light oil and naphthalene from the absorbed oil by introducing the absorbed oil into a discharging base, a reboiler 15 is installed at the bottom of the discharging base 14, and a reboiler 15 is installed at the bottom of the discharging base. The operation pressure is reduced to 300 Torr or less, and naphthalene is distilled out from the top of the ejection group along with light oil.The distilled oil is sent to the side column 22, and the light oil is recovered from the top of the side column. Naphthalene is recovered from the bottom of the tower.

Further, the invention of claim 2 of the present application is such that, as shown in FIG. 1, the bottom liquid of the side column 22 is further introduced into a flash column 25, and naphthalene is recovered from the top of the flash column. .

Furthermore, the invention of claim 3 of the present application, as shown in FIGS. 2 and 3, involves injecting water into the top oil of the ejection group 14 to extract and remove the HCN component in the top oil. This is how it was done.

In this case, it is possible to simply inject water, but it is more effective to add a mixing step after the injection.

The side column 22 and the flash column 25 are desirably operated at normal pressure or under reduced pressure, and the residual oil at the bottom of the flash column 25 may be returned to the upstream process.

In the method of the present invention, the operating pressure at the bottom of the ejection platform is reduced to 300 Torr (absolute pressure) or less as described above, but it is preferably 150 to 200 Torr (absolute pressure). In this case, cold water is required to condense the vapor at the top of the ejection base, and a refrigerator must be installed.On the other hand, if the temperature exceeds 200 Torr, the temperature at the bottom of the ejection base becomes high, causing deterioration of the absorbed oil. This is because (heaviness) is promoted.

Hereinafter, the present invention will be described in detail with reference to the drawings.

However, unless there is a specific description, the relative arrangement of the components shown in the drawings is not intended to limit the scope of the present invention thereto, and is merely an illustrative example.

In Fig. 1, coke oven gas containing light oil and naphthalene is brought into countercurrent contact with depentened absorption oil supplied from the top of the tower in naphthalene scrubber 1 and Henzol scrubber 2, and the light oil and naphthalene are removed. It is absorbed and removed and becomes refined coke oven gas. The pen-containing absorbent oil containing light oil and the like exchanges heat with the hot de-pencil absorbent oil in the first heat exchanger 12, is heated, and then is supplied to the dehydration tower 4. The moisture in the absorbed oil is removed in the dehydration tower 4, and the penned absorbed oil that exits the bottom of the dehydration tower is heated again with the depenned absorbed oil in the second heat exchanger 13, and then heated under reduced pressure of 300 Torr or less. It is supplied to the middle stage of the operated ejector tower 14, heated by a heating medium in the ejector reboiler 15, and the light oil and naphthalene components are ejected.

Most of the depenned absorbed oil that exited the bottom of the ejection platform is transferred to heat exchanger 1.
After the heat is recovered in step 3.12 and further cooled in the absorption oil cooler 7, it is recycled to the naphthalene scrubber 1 and the penzol scrubber 2.

A portion of the depenned absorbent oil is supplied to a depitching tower 8 to remove pitch accumulated in the circulated absorbent oil. Light oil and naphthalene vapor distilled from the top of the ejection platform are combined with light oil and vapor containing water coming out from the top of the dehydration tower, and are cooled and condensed in the ejection tower condenser 10.

Moisture is separated and removed from the condensed liquid in the ejection column reflux strum 11, a part of the condensed liquid is extracted as naphthalene-containing crude light oil, and the rest is returned to the top of the ejection platform as reflux. The degree of vacuum in the ejection tower 14 is maintained by a vacuum pump 17.

The depitching tower 8 is operated under a reduced pressure almost equal to that of the bottom of the ejection base, and is heated by a heating medium in the depitching tower reboiler 18 to extract pitch oil from the bottom of the tower, and components other than the pitch oil are converted into steam. It is returned to the base of the ejection platform. Since the reboiler 18 is installed at the bottom of the depitch tower 8 in this way, the depinch performance is good and the pitch concentration in the circulating absorption oil can be maintained low.

It is desirable that the ejection tower 14 be a packed tower, and the reason for this is as follows:
Compared to tray columns, packed columns have the advantage of being able to keep the bottom temperature low because of the smaller pressure loss within the column, preventing the absorbed oil from becoming heavier, and facilitating heat exchange in the reboiler. This is because there is.

Ejection tower reboiler 15 and depitching tower reboiler 18
Various types of heat exchangers and heating furnaces using organic thermal oil as a heat source can be used. When using organic thermal oil as the heat source, a thermosiphon type is preferable for the ejection tower reboiler.

Further, the dehydration tower 4 can be operated at either normal pressure or reduced pressure, and furthermore, it is also possible to omit the installation of a dehydration tower.

The naphthalene-containing crude gas oil from the ejection column 14 is heated by exchanging heat with the top vapor of the side column in the first side column condenser 20, then heated in the naphthalene condenser 21, and then transferred to the side column operated under normal pressure. 22 is fed to the top of the column. The top vapor of the side column from which heavy components such as naphthalene have been removed is cooled and condensed in a first side column condenser 20 and a second side column condenser 23, and then sent to a side column reflux drum 24. A part of the test solution a is sent to the top of the side column as reflux, and the remainder becomes the product crude light oil. The bottom oil of the side column is concentrated to about 80% by weight of naphthalene, but since it contains non-volatile components such as coloring components and pitch, it is re-evaporated under normal pressure in the flash column 25 and transferred to the naphthalene condenser 21. After shrinking LI11, it is recovered as about 80% by weight naphthalene. The side column reboiler 26 and flash column reboiler 27 are heated by a heat medium and serve as heat sources for the side column 22 and flash column 25. Further, since the bottom residual oil of the flash tower 25 contains a large amount of naphthalene, it can be recovered by returning it to an upstream process such as a depitching tower through a line 28 or the like. Note that there are cases where a flash tower is not installed. It is also possible to feed naphthalene-containing crude gas oil to the middle stage of the side column.

When the method described above is carried out according to the flow shown in FIG.
Since it contains 14 oppm, the first side column condenser 20
When heated in the naphthalene condenser 21, a cyanide polymer is produced.

For this reason, cyanide polymer (dark gray and sludge-like) is deposited in the conduits downstream of the first side column condenser 20 and naphthalene condenser 21, and in devices such as the first side column condenser 20, naphthalene condenser 21, and side column 22. ,
May cause blockage. In addition, if carbon steel is used as the material for conduits and equipment, the cyanide polymer deposits will be severely corroded (total corrosion). Therefore, it is necessary to use stainless steel, which is a high-grade material (the corrosivity of stainless steel is weak).

The mechanism of the HCN polymerization reaction has not been precisely elucidated, but when the HCN polymerization reaction occurs in the presence of sulfide (HlS in coke oven gas), a copolymer of cyanide and sulfide is formed. is reported to be generated. Table 2 shows an example of the elemental analysis of a deposit in the conduit downstream of the first side column condenser. In Table 2, this deposit is shown to be a typical cyanide polymer.

Table 2 is excluded.

In order to solve the above problems, water is injected into the top oil of the ejection group 14 to extract and remove HCN from the top oil water. Specifically, as shown in FIG.
Soft water is injected into the outlet side of the top oil transfer pump 30 downstream from the tower, and a mixer such as a static mixer 31 is provided downstream of this injection point.

32 is a partition plate, 33 is an ejection group reflux pump, 34
is a liquid reservoir. Note that there are cases where a mixer such as a static mixer is not provided. In this case, it is more effective to inject soft water into the suction side of the top oil transfer pump 30.

In addition, as shown in FIG. 3, the ejection group reflux bomb 3
It is also possible to inject soft water into the outlet side of the pump 3 and provide a mixer such as a static mixer 35 downstream of this injection point. Note that there are cases where a mixer such as a static mixer is not provided.

The above shows an example of the injection point of water (preferably soft water), but in the present invention, the injection point is not limited, and the point is that water is injected into the top oil of the ejection group 14. Just do it.

Next, the results of a cleaning test performed on the naphthalene-containing crude light oil condensed in the ejection group condenser 10 using soft water and waste ammonium water will be described. Here, waste ammonium water refers to waste ammonium water from a coke factory, from which free ammonia and acid gas components (H, S, HCN) have been removed using an ammonium water stripper.

The naphthalene-containing crude light oil and the cleaning liquid (soft water or Wan water) were mixed in a static mixer and separated by specific gravity in a separation tank. The compositions of the naphthalene-containing crude light oil and the cleaning liquid are shown in Table 3. Further, the cleaning test results are shown in FIGS. 4 and 5.

Table 3 The reason why soft water and Wan water were tested as cleaning fluids is that they are easily available in coke plants.

) 1 cH extraction ability is better with soft water, and since waste ammonia water contains Ct-, soft water is preferable as a cleaning liquid.Also, it is also possible to use hard water such as industrial water. If hard water is used, the naphthalene-containing crude gas oil has a high PU, so hard components will precipitate, causing scaling and causing failure of pumps, etc., so it is preferable to use soft water.

In the method of the present invention, if the HCN concentration in the naphthalene-containing crude gas oil is set to 25 to 50 pH or less, it is considered that cyanogenization hardly occurs.

It is also possible to wash only the naphthalene crude light oil in the side column with soft water, and as an example shown in Figure 3, a recycling line is installed from the ejection group reflux pump to the ejection group flux drum. You can also wash it here.

〔Example〕

Hereinafter, the present invention will be explained by giving examples.

Example 1 85.00ON+m3/H according to the flow shown in Figure 1
The coke oven gas was treated to obtain pen-containing absorbed oil from the penzol scrubber 2 and the naphthalene scrubber 1.

As shown in Table 4, this pen-containing absorbent oil has a light oil content of 1.
It contained 59 wt% and naphthalene content of 3.86 wt%.

The ejection group 14 has a pressure of 170 Torr at the top of the column and 185 Torr at the bottom of the column.
It was operated under a reduced pressure of 7 orr, and the light oil and naphthalene components were recovered as overhead fractions. As shown in Table 4 from the bottom of the ejection tower, the light oil content is 0.03 wt%, and the Natutalin content is 3.75%.
170 m”/H of dependenized absorbed oil containing wt% was recovered,
It was recycled and used in the Penzol Scrubber 2 and Naphthalene Scrubber 1 described above.

Ejection group reboiler 15 and depitching column reboiler 18
A 260°C heat medium was used as a heat source, and the temperature at the bottom of the ejection platform was 191°C, and the temperature at the bottom of the depitching column was 230°C. The operating pressure at this time is 185To at the bottom of the ejection platform.
rr, and the pressure at the top of the depitching tower was 188 Torr. The temperature of the dehydration tower 4 operated at normal pressure is 140°C, the temperature at the top of the ejection platform is 87°C, and the temperature at the ejection base reflux strum is 24°C.
Met. Further, the temperature of the pen-containing absorption oil introduced into the ejection group 14 was 171°C.

3.5 m3/H of naphthalene-containing crude light oil is extracted from the top of the ejection unit 14, and 60 kg/H of naphthalene-containing crude light oil is extracted from the bottom of the depitching tower 8.
H pitch oil was extracted from the system. 3.5m'/
After the naphthalene-containing crude light oil of It is heated to 100°C,
It was supplied to the side column 22. The top of the side tower is 0.02kg/c
aGS 120℃, tower bottom 0.1 kg/cjG,
The temperature was 229°C. 3.3+*2 from the top of side tower 22
/H crude light oil is extracted from the system, and the bottom liquid of the side column is introduced into the flash column 25, where 0.15 m3/) of naphthalene oil with a concentration of 81.8-t% is produced from the top of the flash column. ,
A residual oil of 0.05 m3/h was extracted from the bottom of the column. Note that the temperature of the side column refrunk strum 24 is 27°C, the pressure at the top of the flash column 25 is 0 kg 10 JG, and the temperature is 224°C.
The temperature of about 80 wt % naphthalene oil at the outlet of the naphthalene condenser 21 was 103°C. Further, the heat medium temperature of the side column reboiler 26 and flash column reboiler 27 was 260°C.

Further, the ejection unit 14 was a packed column, the side column 22 was a sheep tray, and the depitching column 8 and the flash column 25 were pan-flu trays.

Table 4 shows the results of the component analysis of the extracted oil from each part, and Table 5 shows the results of the component analysis of the gas around the naphthalene scrubber and Penzol scrubber. Note that C+ +H+. (Methylnaphthalene) is a representative component of absorbed oil components, "pre-distillate" refers to benzene pre-distillate, which is lighter than benzene, and "absorbed oil" refers to C1, Hl・(methylnaphthalene). Indicate what is included.

(Left below) Example 2 3 m3/H of soft water was injected into 8.5 m'/H of naphthalene-containing crude light oil between the ejection group condenser 10 and the ejection group reflux drum 11, and mixed with a static mixer 31. After that, light oil and water are separated by specific gravity in the ejection group reflow strum 11. Of the separated naphthalene-containing crude light oil, 3.5 a+"/H is transferred to the side via the first side column condenser 20 and the naphthalene condenser 21. The remaining 5 m'/H was returned as reflux to the ejection unit 14.The HCN concentration in the naphthalene-containing crude gas oil before soft water injection was 100 pp-, but after soft water injection HCN in crude naphthalene gas oil decreased to 21 pp-,
Cyanide polymerization no longer occurred.

〔Effect of the invention〕

According to the method of the present invention, the following effects can be achieved.

(11) Since no steam is used as an ejector, the energy saving effect is large.

(2) Since no steam is used as an ejection agent, corrosion caused by moisture condensation within the ejection tower can be prevented.

(3) Since the reboiler is installed at the bottom of the ejection group, the light oil stripping performance is good and the light oil concentration in the depenned absorbed oil can be maintained low. Therefore, the amount of light oil, etc. recovered from coke oven gas increases.

(4) By operating the ejection group under reduced pressure, the specific volatility of the absorbed oil with respect to light oil and naphthalene is improved, so the amount of absorbed oil that is distilled out together with the light oil and naphthalene is small, minimizing the loss of absorbed oil. It can be suppressed.

(5) Since the ejection group has good separation performance between naphthalene and absorbed oil components, and the side column also has good separation performance between light oil and naphthalene, naphthalene can be recovered as naphthalene oil of about 80% by weight. If naphthalene of about 80% by weight is obtained, it becomes possible to produce naphthalene of about 95% by weight using a drum flaker and a screw press.

(6) In the invention of claim 3, water (
Soft water is preferable) is injected to extract and remove the HCN component in the tower top oil before feeding it to the side tower, so even if heat is recovered and heated in the first side tower condenser or naphthalene condenser, cyan polymer will not be produced. is not generated. Therefore, the first
Since the side column feed line from the side column condenser to the side column will not be clogged or corroded, long-term stable operation is possible. In addition, carbon steel can be used as the material for the side column feed line and the side column from the first side column condenser to the side column, making it possible to reduce costs.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing an example of an apparatus for carrying out the method of recovering light oil and naphthalene from coke oven gas according to the present invention, and FIGS. Flowsheet detailing other examples, No. 4
5 and 5 show the results of experiments conducted by the present inventors, and FIG. 4 is a graph showing the relationship between the amount of cleaning liquid and the HCN concentration in the naphthalene-containing crude gas oil after washing, and FIG. 6 is a graph showing the relationship between cleaning liquid/naphthalene-containing crude light oil and removal rate, and FIG. 6 is a flow sheet showing a conventional example. 1... Naphthalene scrubber, 2... Penzol scrubber, 3... Heat exchanger, 4... Dehydration tower, 5...
・Heating furnace, 6... Ejection group, 7... Absorption oil cooler,
8... Depitching tower, 1... Ejection group condenser, 1
DESCRIPTION OF SYMBOLS 1... Ejection group reflux strum, 12... First heat exchanger, 13... Second heat exchanger, 14... Ejection group,
15... Ejection group reboiler, 17... Vacuum pump,
18... Depitching column reboiler, 20... First side column condenser, 21... Naphthalene condenser, 2
2... Side tower, 23... Second side tower condenser, 24
... Side column rerank strum, 25... Flash column, 26... Side column reboiler, 27... Flash column reboiler, 28... Line, 30... Tower oil transfer pump, 31. 35... Static mixer, 3
2... Partition plate, 33... Ejection group reflux pump, 34... Liquid reservoir Applicant: Kawasaki Heavy Industries, Ltd. Applicant: Mitsui Mining Co., Ltd.

Claims (1)

[Claims] 1. A method for absorbing light oil and naphthalene in coke oven gas using absorption oil, introducing the absorption oil into an ejection tower, and ejecting and recovering light oil and naphthalene from the absorption oil, A reboiler (15) is installed at the bottom of the ejection column (14), the operating pressure at the bottom of the ejection column is reduced to 300 Torr or less, and naphthalene is distilled out from the top of the ejection column together with light oil. Sending the distillate oil to a side column (22),
Method 2 for recovering light oil and naphthalene in coke oven gas, characterized by recovering light oil from the top of the side column and naphthalene from the bottom of the side column. Flash Tower (25
2. The method for recovering light oil and naphthalene from coke oven gas according to claim 1, wherein naphthalene is recovered from the top of a flash tower. 3. The method for recovering light oil and naphthalene in coke oven gas according to claim 1 or 2, wherein water is injected into the top oil of the ejection tower (14) to extract and remove HCN components in the top oil.