JP6149821B2 - Coke oven gas purification method - Google Patents

Description

  The present invention relates to a method for refining coke oven gas, and more particularly to a method for refining coke oven gas that can reduce the load on wastewater treatment equipment and can reduce the amount of industrial water used.

Conventionally, a gas (hereinafter referred to as “C gas”) generated when coal is inserted into a coking chamber of a coke oven and dry-distilled (hereinafter referred to as “C gas”) contains a large amount of fuel components such as hydrogen, methane, and carbon monoxide, and is 20000 kJ / m. ^{Since it} has a high heat quantity exceeding ³ , it is recovered and reused as fuel gas for blast furnaces, coke ovens, heating furnaces, and boilers.

  At that time, various substances such as tar, water, ammonia, hydrogen sulfide, and cyan are mixed in the C gas discharged from the coke oven. Substances and harmful substances need to be removed. Therefore, it is customary to use fuel gas through purification to remove these combustion-inhibiting substances and harmful substances (see, for example, Patent Document 1).

  Further, in the C gas purification process, a large amount of coal-derived water is generated as waste water. Since this waste water contains a large amount of ammonia and organic matter, it is discharged into the sea after ammonia and organic matter are removed by the waste water treatment facility.

FIG. 1 is a diagram showing a general purification flow of C gas. Specifically, the purification of C gas into fuel gas is performed as follows. That is, first, after cooling C gas discharged from a coke oven (not shown), C gas 1 from which naphthalene causing equipment blockage is recovered is introduced into the desulfurization facility 2 to remove hydrogen sulfide (desulfurization). Process). Next, the C gas 3 from which hydrogen sulfide has been removed is introduced into the deammonia facility 4 to remove the ammonia component that causes nitrogen oxides (NO _x ) from the C gas 3 (deammonia process). Thereafter, the C gas 5 from which ammonia has been removed is cooled, the light oil content in the C gas 5 is recovered, and the C gas discharged from the coke oven is purified into fuel gas.

  As the desulfurization method in the desulfurization step, a wet desulfurization method such as a Takahax method or a Fumax method in which an absorbing solution such as an alkaline aqueous solution is brought into contact with C gas and hydrogen sulfide contained in C gas is absorbed into the absorbing solution is known. ing. Further, as these wet desulfurization methods, the absorbing liquid is sprayed into an absorption tower having a packed bed, and C gas is allowed to pass through the absorption tower so that the sprayed alkaline aqueous solution absorbs hydrogen sulfide in the C gas. Methods for desulfurization are known.

FIG. 2 is a diagram illustrating an example of a desulfurization facility based on such a wet desulfurization method. Desulfurization 2 shown in this figure, strike the absorption column 21 to absorb hydrogen sulfide contained in the C gas 1 into the absorbing liquid L _1, the hydrogen sulfide from the absorbing liquid L ₁ having no activity to absorb hydrogen sulfide And a regeneration tower 22 for regenerating by ripping (removing).

The desulfurization process of the C gas 1 in the desulfurization facility 2 is performed as follows. That is, first, an alkaline absorbing liquid L ₁ such as ammonia water is guided to the upper part of the absorption tower 21 and sprayed by spraying, and the C gas 1 introduced into the absorption tower 21 and the absorbing liquid L ₁ are brought into contact with each other in countercurrent. Let Then, since the absorbing liquid L ₁ having alkalinity has the ability to absorb hydrogen sulfide, it absorbs hydrogen sulfide contained in the C gas 1 and falls into the absorbing liquid L ₁ staying in the lower part of the absorption tower 21. Thus, the absorption liquid L ₁ is circulated in the absorption tower 21, the hydrogen sulfide contained in the C gas 1 is absorbed by the sprayed absorption liquid L ₁ , and the C gas 3 from which hydrogen sulfide has been removed is absorbed in the absorption tower 21. Drain from the top.

On the other hand, it stays at the bottom of the absorption tower 21 leads to a part of the absorbing liquid L ₁ became to inert absorbing hydrogen sulfide to the regenerator 22 by introducing regeneration air G _A to the regenerator 22, the absorption Play absorbing liquid L ₁ by removing the hydrogen sulfide absorbed in the liquid L _1. Removing hydrogen sulfide is discharged to the column outside as waste air G _B, regenerated active absorbing liquid L ₁ is used to absorb the upper portion guided by again hydrogen sulfide absorption tower 21. Thus, C gas 1 can be continuously desulfurized by circulating the absorbing liquid L ₁ between the absorption tower 21 and the regeneration tower 22.

In the desulfurization equipment 2 described above, in order to keep the properties of the absorbent L absorbing liquid L ₁ by extracting impurities or the like contained in ₁ constant desulfurization predetermined amount of the discharged absorbing liquid L ₁ from the absorption tower 21 Typically, it is taken out of 2 (ammonia-containing wastewater) and used as a raw material for sulfuric acid or ammonium sulfate. Then, in order to replenish the withdrawn absorption liquid L _1, industrial water is added. Further, ammonia water is also added separately in order to increase the hydrogen sulfide absorption efficiency of the absorption liquid L ₁ .

  Further, as an ammonia removal method in the deammonia step, C gas and dilute sulfuric acid are reacted and recovered as ammonium sulfate (hereinafter referred to as “ammonium sulfate”). FIG. 3 is a diagram illustrating an example of a deammonia facility. The deammonia facility 4 shown in this figure has an ammonium sulfate saturation tower 41, a mother liquor circulation tank 42, and a pump 43.

In this deammonia facility 4, the C gas 3 from which hydrogen sulfide has been removed through the desulfurization step is introduced into the ammonium sulfate saturated column 41, and the dilute sulfuric acid is sprayed by spraying to introduce the C gas 3 introduced into the ammonium sulfate saturated column 41. Contact with countercurrent. Then, by absorbing ammonia contained in C gas 3, stays to fall to the bottom of the ammonium sulfate saturation tower 41 as ammonium sulfate mother liquor L _2.

Here, a part of the ammonium sulfate mother liquor L ₂ staying in the lower part of the ammonium sulfate saturation column 41 is recovered in the mother liquor circulation tank 42, and after adding concentrated sulfuric acid S in the mother liquor circulation tank 42, the ammonium sulfate saturation tower is pumped by the pump 43. It is guided to the upper part of 41 and sprayed again. Thus, the ammonium sulfate mother liquor L ₂ is circulated between the ammonium sulfate saturation column 41 and the mother liquor circulation tank 42 to continuously remove the ammonia content in the C gas 3, and the C gas 5 from which the ammonia has been removed is removed from the ammonium sulfate saturation column 41. To discharge from.

On the other hand, the remainder of the ammonium sulfate mother liquor L ₂ staying in the lower part of the ammonium sulfate saturated column 41 is discharged from the ammonium sulfate saturated column 41, and the discharged ammonium sulfate mother liquor 6 is introduced into the ammonium sulfate crystallizer, and the ammonium sulfate contained in the ammonium sulfate mother liquor 6 is removed. Crystallized and recovered as crystalline ammonium sulfate. FIG. 4 shows an example of an ammonium sulfate crystallization apparatus for crystallizing ammonium sulfate contained in the ammonium sulfate mother liquor 6. The ammonium sulfate crystallization apparatus 7 shown in this figure has an ammonium sulfate crystallization tank 71, a heater 72, an evaporation tank 73, and a condenser 74.

  In the ammonium sulfate crystallization apparatus 7, the ammonium sulfate mother liquor 6 discharged from the ammonium sulfate saturation tower 41 is introduced into an ammonium sulfate crystallization tank 71. The introduced ammonium sulfate mother liquor 6 is heated by the heater 72 and supplied to the evaporation tank 73, and the water contained in the ammonium sulfate mother liquor 6 is evaporated and concentrated. The concentrated ammonium sulfate mother liquor 6 is returned to the ammonium sulfate crystallization tank 71, and ammonium sulfate is crystallized and precipitated by circulating the ammonium sulfate mother liquor 6 between the ammonium sulfate laminate 71 and the evaporation tank 73. The slurry containing the precipitated ammonium sulfate is discharged from the lower part of the ammonium sulfate precipitation tank 71, conveyed to an ammonium sulfate drying facility (not shown), and dried using a centrifugal separator, a drier, etc. Can be recovered.

  In the evaporation tank 73, the vapor 8 containing ammonium sulfate is discharged from the top of the evaporation tank 73. The discharged ammonium sulfate-containing steam 8 is condensed by the condenser 74, and the obtained ammonium sulfate-containing condensed water (hereinafter referred to as “ammonium sulfate condensed water”) 9 is sent to the wastewater treatment facility 10 and included in the ammonium sulfate condensed water 9. After decomposing ammonia, it is discharged into the sea as discharge water 11.

JP 2001-81479 A

  The ammonium sulfate condensate 9 obtained by the condenser 74 contains a large amount of free ammonia derived from the ammonium sulfate mother liquor 6. When such ammonium sulfate condensate 9 is treated in the wastewater treatment facility 10, the wastewater treatment facility 10. The problem was that the load on the site increased. And in recent years, from the viewpoint of environmental conservation, nitrogen emission regulation of the discharged water 11 has become stricter. And this regulation is expected to continue in the future, and it is expected that the load of the exhaust treatment facility 10 of each factory will increase more and more.

Furthermore, particularly in industrial areas, a shortage of industrial water has become apparent, and reducing the amount of industrial water used has been a problem for factories.
Therefore, an object of the present invention is to propose a method for purifying C gas that can reduce the load on the wastewater treatment facility and can reduce the amount of industrial water used.

  The inventors diligently studied how to solve the above problems. As a result, it has been found that it is extremely effective to replenish at least a part of the ammonium sulfate condensate that has been supplied to the wastewater treatment facility as a hydrogen sulfide absorbing liquid in the desulfurization process, and the present invention has been completed. It was.

That is, the gist of the present invention is as follows.
(1) The coke oven gas discharged from the coke oven is brought into contact with an absorbing solution that absorbs hydrogen sulfide to absorb the hydrogen sulfide contained in the coke oven gas into the absorbing solution, and then the hydrogen sulfide is recovered. In refining the coke oven gas to fuel gas, the dilute sulfuric acid is sprayed on the recovered coke oven gas to recover ammonia by absorbing ammonia contained in the coke oven gas from which the hydrogen sulfide has been recovered. Supply at least part of ammonium sulfate condensed water containing ammonia, which is generated when crystallizing ammonium sulfate from the dilute sulfuric acid that has absorbed ammonia, as supplementary water for absorbing liquid when recovering hydrogen sulfide from the coke oven gas A method for purifying coke oven gas.

(2) The method for purifying coke oven gas according to (1), wherein the absorption liquid is ammonia water.

  According to the present invention, the ammonium sulfate condensate that has been supplied to the wastewater treatment facility has been replenished as a hydrogen sulfide absorbing liquid in the desulfurization process, so that the load on the wastewater treatment facility can be reduced and industrial water can be used. The amount can be reduced.

It is a flowchart of the purification method of the conventional C gas. It is a figure which shows an example of a desulfurization installation. It is a figure which shows an example of a deammonia installation. It is a figure which shows an example of an ammonium sulfate crystallization apparatus. It is a flowchart of the purification method of C gas which concerns on this invention.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 5 shows a flow diagram of the method for purifying C gas according to the present invention. In addition, the same code | symbol is attached | subjected to the structure same as the structure shown by FIG. As shown in this figure, the method for purifying C gas according to the present invention is such that at least a part of the ammonium sulfate condensate 9 produced when crystallizing ammonium sulfate from dilute sulfuric acid that has absorbed ammonia in the deammonia step is used in the desulfurization step. It is characterized in that it is replenished as an absorbing liquid L ₁ when hydrogen sulfide is recovered from the coke oven gas 1 from which naphthalene has been recovered.

  As described above, in the conventional C gas purification method, the ammonium sulfate condensate 9 obtained by the condenser 74 is introduced into the wastewater treatment facility 10 and decomposes the ammonia contained in the ammonium sulfate condensate 9. It was released into the sea. However, the ammonium sulfate condensate 9 obtained by the condenser 74 contains a large amount of free ammonia derived from the ammonium sulfate mother liquor 6. When such ammonium sulfate condensate 9 is processed by the wastewater treatment facility 10, the wastewater treatment facility The load of 10 may increase and ammonia may not be decomposed sufficiently.

Therefore, the inventors diligently studied how to avoid treating all of the ammonium sulfate condensate 9 with the wastewater treatment facility 10. As a result, it was conceived that a part of the ammonium sulfate condensate 9 was replenished as supplementary water for the absorbing liquid L ₁ in the desulfurization process. That is, the ammonium sulfate condensate 9 contains a large amount of free ammonia that absorbs hydrogen sulfide contained in the C gas 1 in the desulfurization process, as described above. In addition, the ammonium sulfate condensate 9 contains oil and sludge that cause blockage of the equipment, but these amounts are very small, and the ammonium sulfate condensate 9 is used as makeup water for the absorbing liquid L ₁ in the desulfurization process. There is no problem.

  When the ammonium sulfate condensate 9 is supplied to the desulfurization facility 2, it is circulated through the absorption tower 21 and the regeneration tower 22, and finally discharged from the desulfurization facility 2 and recovered as ammonium sulfate. Therefore, by supplying at least a part of the ammonium sulfate condensate 9 to the desulfurization facility 2, the load on the wastewater treatment facility 10 can be reduced.

Further, as described above, industrial water is used in the desulfurization facility 2 as make-up water for the absorbing liquid L ₁ that is partially discharged. Therefore, when supplied to the desulfurization 2 ammonium sulfate condensed water 9 as makeup water for the absorbing liquid L _1, it is also possible to reduce the amount of industrial water to be subjected to the desulfurization step.

Further, as described above, not only industrial water is supplied to the desulfurization facility 2 but also ammonia water is added to the absorbent L ₁ in order to increase the absorption efficiency of hydrogen sulfide. Therefore, by supplementing the ammonium sulfate condensed water 9, not only industrial water but also the amount of ammonia water used can be reduced. Hereinafter, each process of the purification method of C gas of this invention is demonstrated.

  First, since the coke oven gas discharged from the coke oven has a high temperature of about 1000 ° C., it is cooled directly by contacting ammonia water (anhydrous water) with a dry main, and then directly and / or indirectly by a primary cooler or the like. Cool to about 35 ° C.

  Next, the cooled C gas is introduced into a naphthalene recovery facility, and naphthalene that causes equipment blockage is recovered from the cooled C gas. As a method for recovering naphthalene, a removal method using an absorbing oil is widely known and can be used in the present invention.

Subsequently, the C gas 1 from which naphthalene has been removed is introduced into the desulfurization facility 1 to remove hydrogen sulfide contained in the C gas 1. A specific desulfurization method using the desulfurization facility 2 shown in FIG. 2 is as described above, and a description thereof will be omitted. As shown in FIG. 1, in the conventional method, industrial water was used as make-up water for the absorbing liquid L _{1. In} the present invention, as shown in FIG. The ammonium sulfate condensate 9 is supplied as make-up water for the absorbent L ₁ . Thereby, the usage-amount of the industrial water used as make-up water and the ammonia water added for improving the absorption efficiency of hydrogen sulfide can be reduced.

Thereafter, the C gas 3 from which hydrogen sulfide has been removed is introduced into the deammonia facility 4 to remove the ammonia contained in the C gas 3. A specific deammonification method using the deammonification equipment 4 shown in FIG. 3 is as described above, and the description thereof is omitted. In the conventional method shown in FIG. 1, all of the ammonium sulfate condensate 9 obtained by the condenser 74 is supplied to the wastewater treatment facility 10 for treatment. In the present invention, as shown in FIG. At least a part of the ammonium sulfate condensed water 9 is supplied to the desulfurization facility 2 as make-up water for the absorbing liquid L ₁ in the desulfurization process. Thereby, the load of the waste water treatment facility 10 can be reduced.

  Thereafter, the C gas 5 from which ammonia has been removed discharged from the top of the ammonium sulfate saturation tower 41 is introduced into a light oil recovery facility (not shown), and the light oil contained in the C gas 5 is recovered. As a method for recovering the light oil, it is generally performed by an absorption method using absorption oil. The gas oil contained in the C gas 5 is physically converted into the absorption oil by bringing the C gas 5 and the absorption oil into countercurrent contact. Absorb.

  In this way, at least a part of the ammonium sulfate condensate that has been supplied to the wastewater treatment facility has been replenished as supplementary water for the hydrogen sulfide absorption liquid in the desulfurization process, so that the load on the wastewater treatment facility can be reduced, and industrial Coke oven gas can be purified by reducing the amount of water used.

(Invention example)
Examples of the present invention will be described below.
The coke oven gas was purified according to the C gas purification flow shown in FIG. That is, first, C gas 1 discharged from a coke oven and cooled to remove naphthalene was introduced into the desulfurization facility 2 to remove hydrogen sulfide.
Next, the C gas 3 from which hydrogen sulfide was removed was introduced into the deammonia facility 4 to remove the ammonia component that causes nitrogen oxides from the C gas 3 from which hydrogen sulfide was removed. At that time, 2640 tons of ammonia water (24 mass%) was supplied to the desulfurization facility 2 per day.
The ammonium sulfate mother liquor 6 discharged from the de-saturation saturation column of the deammonia facility 4 was introduced into an ammonium sulfate crystallizer 7 to crystallize ammonium sulfate contained in the ammonium sulfate mother liquor 6 to obtain crystalline ammonium sulfate. At that time, the ammonium sulfate-containing steam 8 discharged from the evaporation tank is condensed by a condenser, and 139 tons of the ammonium sulfate condensate 9 (312 tons) obtained per day is replenished to the absorption liquid L ₁ of the desulfurization facility 2. The remaining 173 tons were introduced into the waste water treatment facility 10 to decompose ammonia contained in the ammonium sulfate condensate 9 and then discharged into the sea as discharge water 11.
On the other hand, the C gas 5 from which ammonia was removed, which was discharged from the ammonium sulfate saturation tower of the deammonia facility 4, was cooled, and then the light oil contained in the C gas 5 was removed. Thus, the C gas discharged from the coke oven was refined into fuel gas. Table 1 shows the conditions for C gas purification.

(Comparative example)
The C gas G ₀ discharged from the coke oven 11 was purified according to the C gas purification flow shown in FIG. That is, all of the ammonium sulfate condensate 9 obtained in the inventive example was supplied to the wastewater treatment facility 10. The desulfurization facility 2 was supplied with 151 ton and 4800 tonnes of industrial water and ammonia water (24% by mass) per day, respectively. Other conditions are the same as those of the invention examples. Table 1 shows the conditions for C gas purification.

  As can be seen from Table 1, in the inventive example, it is not necessary to supply industrial water to the desulfurization facility 2, and the amount of ammonia water to be supplied can be reduced as compared with the comparative example. It can also be seen that the amount of ammonium sulfate condensed water 9 introduced into the wastewater treatment facility 10 can be reduced, and the load on the wastewater treatment facility 10 can be reduced. Thus, it turns out that the example of an invention can reduce the load of the waste water treatment facility 10, and can also reduce the usage-amount of industrial water and ammonia water compared with a comparative example.

  According to the present invention, at least a part of the ammonium sulfate condensate that has been supplied to the wastewater treatment facility can be supplied as supplementary water for the hydrogen sulfide absorption liquid in the desulfurization process, thereby reducing the load on the wastewater treatment facility. In addition, since the amount of industrial water used can be reduced, it is useful in the steel industry.

1,3,5 C gas 2 desulfurization equipment 4 deammonia equipment 6 ammonium sulphate mother liquor 7 ammonium sulphate crystallizer 8 ammonium sulphate-containing steam 9 ammonium sulphate condensate 10 wastewater treatment equipment 11 effluent water 21 absorption tower 22 regeneration tower 41 ammonium sulphate saturation tower 42 mother liquor circulation bath 43 pump 71 ammonium sulfate crystallization vessel 72 heater 73 evaporates tank 74 condenser G _A regeneration air G _B waste air L ₁ absorption liquid L ₂ ammonium sulfate mother liquor

Claims (2)

The coke oven gas discharged from the coke oven is brought into contact with an absorption liquid that absorbs hydrogen sulfide, and the hydrogen sulfide contained in the coke oven gas is absorbed into the absorption liquid and recovered, and then the coke that recovered the hydrogen sulfide is recovered. In refining the coke oven gas to fuel gas, the ammonia contained in the coke oven gas that has recovered the hydrogen sulfide by spraying dilute sulfuric acid to the furnace gas is absorbed into the dilute sulfuric acid and recovered.
Supply at least part of ammonium sulfate condensed water containing ammonia, which is generated when crystallizing ammonium sulfate from the dilute sulfuric acid that has absorbed ammonia, as supplementary water for absorbing liquid when recovering hydrogen sulfide from the coke oven gas A method for purifying coke oven gas.   The method for purifying coke oven gas according to claim 1, wherein the absorbing liquid is ammonia water.

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