KR100270088B1 - Coke gas purification method using slaked lime - Google Patents

Abstract

The present invention relates to a method for purifying coke gas generated in a coke oven of a mill, and to recovering the cyan compound in question from wastewater generated in the coke gas refining process so that it can be used as a useful chemical and thereby wastewater. It is an object of the present invention to provide a method for refining coke gas using slaked lime which can simultaneously solve the problem of waste gas generated in the process of oxidizing to sulfur by recovering hydrogen sulfide.

In the present invention, in the coke gas purification method, coke gas in which water and tar, naphthalene and fine tar particles are sequentially removed is sent from the hydrogen cyanide absorption tower 20 to react hydrogen cyanide in the coke gas with ammonium polysulfide in the liquid. Absorption is carried out by thiocyanic ammonium, and the hydrogen cyanide-free gas is sent to the hydrogen sulfide absorption tower (7) to absorb and remove hydrogen sulfide. Then, the gas is sent to the ammonia absorption tower (8) to absorb and remove ammonia, and then cooled. Sent to the absorption tower (10) to remove benzene, toluene and xylene to discharge to the outside; The absorption liquid discharged from the hydrogen cyanide absorption tower 20 is evaporated in the crystallizer 21 to form thiocyanium ammonium crystals, the crystals are separated, and the absorption liquid is circulated to the hydrogen cyanide absorption tower 20; After sending the absorbing liquid discharged from the hydrogen sulfide absorption tower 7 to the oxidation tower 22 through which oxygen is circulated, the hydrogen sulfide is oxidized, and then solid-liquid separation in the solid-liquid separator 23, and then the insoluble solid is heated in the sulfur evaporator 24. To evaporate the sulfur and then discharge it into slag, and send some of the liquid to the ammonia saturator 25 to saturate with ammonia, supply sulfur, and then send it to the hydrogen cyanide absorption tower 20 to supplement with hydrogen cyanide absorption liquid. Send the remainder of the liquid to the slurry replenishment tower 26 to replenish the slaked lime slurry and then to the hydrogen sulfide absorption tower 7; The main point is a method for purifying coke gas using slaked lime which is configured to distill the absorbing liquid discharged from the ammonia absorption tower 8 to separate ammonia and to send a part of the ammonia to the ammonia saturator 25.

Description

Coke gas purification method using slaked lime

1 is a process chart showing a conventional coke gas purification method using a wet oxidation method of hydrogen sulfide.

2 is a process chart showing a process for purifying coke gas according to the present invention.

* Explanation of symbols for main parts of the drawings

7: hydrogen sulfide absorption tower 8: ammonia absorption tower

10: benzol absorption tower 20: hydrogen cyanide absorption tower

21: crystallizer 22: oxidation tower

23: solid-liquid separator 24: sulfur evaporator

25: ammonia saturator 26: slurry supplement tower

The present invention relates to a method for purifying coke gas generated in a coke oven of an ironworks, and more particularly, to a method for refining coke gas using calcined lime that collects hydrogen cyanide and then absorbs and oxidizes hydrogen sulfide.

Coke gas is a gas produced by distilling coal into coke, and when it is purified, various chemicals can be obtained as by-products, and the purified gas can be used as fuel gas.

Conventional methods used for the purification of coke gas have been used to remove ammonia and absorb it in sulfuric acid solution or to decompose in cracking furnace and dissipate in air. At this time, when ammonia is decomposed in the cracking furnace, when ammonia and hydrogen sulfide are mixed, sulfur oxides are included in the cracking furnace gas, which causes a problem of being discharged as a pollutant. Another method of removing ammonia is the ginseng method, which is absorbed in a phosphate solution and recovered as pure ammonia.

However, hydrogen sulfide and hydrogen cyanide are more difficult to remove and cause pollution than ammonia, and numerous processes have been developed to remove them. Hydrogen sulfide was started by absorbing and removing limestone and wet process was developed to overcome the disadvantages of dry oxidation and dry oxidation process by oxidizing iron oxide and removing it with sulfur. The basic objectives are necessary land area and requirements. It was developed to reduce manpower and increase the purity of sulfur produced. In this method, hydrogen sulfide is absorbed into an alkaline solution and then removed by oxidizing hydrogen sulfide using an oxygen carrier. At this time, while absorbing hydrogen sulfide by the catalyst in the absorption tower to increase the hydrogen sulfide absorption rate, the catalyst is regenerated in the regeneration tower. Representative of the wet hydrogen sulfide removal method is the Fumnnks Process (Aromatics 27, 174,1975) developed in Japan, which uses picric acid as an oxygen carrier catalyst and similar Takahax process (Takahax Process, Chemical Economy). Engineering Review 2,27,1970) uses naphthoquinone-2-sulfonic acid natzate as a catalyst.

The wet hydrogen sulfide will be described in detail with reference to FIG. 1 as follows. As shown in FIG. 1, the coke gas discharged from the coke oven is collected and cooled in the coke gas collecting pipe (1) to condense water and tar, and the condensed water and tar are separated and processed in the gas-liquid separator (2). After the gas is cooled in the cooling tower 3, the naphthalene is removed from the naphthalene absorption tower 4 and sent to the electrostatic precipitator 6 via the blower 5.

The fine particle tar condensed in the electrostatic precipitator 6 is removed and the gas from which the fine tar particles have been removed is moved to the hydrogen sulfide absorption tower 7 to absorb and remove hydrogen sulfide and hydrogen cyanide, and then ammonia is removed from the ammonia collector 8. After the cooling is performed in the cooling tower 9, the benzene, toluene, xylene, and the like are removed from the benzol absorption tower 10 and then discharged to the outside.

In addition, the absorbing liquid discharged from the hydrogen sulfide absorption tower 7 is oxidized in the oxidation tower 11 and the sulfur is separated in the solid-liquid separator 13, and then some of the liquid is waste-treated, and most of the liquid is recycled to the absorbing liquid.

The waste air from the oxidation tower 11 is treated by the waste air treatment facility 12.

On the other hand, the tar and condensate separated in the gas-liquid separator 2 is separated from the condensate and tar in the anhydrous tar separator 15, the ammonia is distilled from the distillation column 14, the distilled gas is combined with coke gas and the condensate is Sent to the wastewater treatment unit.

However, since the wet process uses an expensive catalyst, an oxidation and regeneration tower for regenerating the catalyst is required, and thus, side effects due to the accumulation of various compounds in the circulation process occur. Representative accumulations are thiosulfate and thiocyanate. In order to remove this, a part of the circulating fluid is removed and discarded, or a method of oxidizing thiosulfate to sulfate with hydrogen peroxide. However, the only way to keep the thiocyanate below a certain concentration is to discard part of the solution. In this process, the generation of wastewater is imperative and thiocyanate is biologically difficult to decompose, which leads to the difficulty of treating wastewater. In addition, in the above method, a large amount of waste gas is generated during operation of the air regeneration tower by air, and thus there is a difficulty in treating the waste gas.

In order to solve the drawback of not recovering the cyanide compounds separately in the above method, a process for recovering sodium cyanate (NaCNS) by absorbing it in sodium polysulfide (NaSx) solution has recently been developed. (Coke and Chemistry, No. 5, pp. 20-22, 1984).

However, since the process was developed with the main purpose of recovering thiocyanate and phenol, pollutants such as CN ^- ions and CNS ^- ions generated during the recovery and treatment of hydrogen sulfide are generated.

Accordingly, the present inventors have conducted research to solve the above-mentioned problems of the conventional methods, and based on the results, the present invention proposes the present invention, which is a problem in the wastewater generated in the coke gas purification process. By recovering the compounds separately, they can be used as useful chemicals, thereby solving the problem of wastewater treatment and simultaneously recovering hydrogen sulfide, thereby reducing the problem of waste gas in the process of oxidizing to sulfur. To provide a method for purifying the coke gas used, the purpose is.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The present invention is condensed coke gas to separate the water and tar, and after cooling the coke gas separated water and tar, remove naphthalene from the naphthalene absorption tower, remove the condensed fine particles tar, in the hydrogen sulfide absorption tower Absorbs and removes hydrogen sulfide and hydrogen cyanide; Oxidizing the absorbed liquid discharged from the hydrogen sulfide absorption tower in an oxidation tower to oxidize hydrogen sulfide to sulfur, separating sulfur in a solid-liquid separator, and then recycling the waste liquid and recycling the absorbed liquid; The gas from the hydrogen sulfide absorption tower is sent to an ammonia collector to remove ammonia, cooled, and then sent to a benzol absorption tower to remove benzene, toluene, xylene, and the like, and to discharge the coke gas to the outside. In the process, the coke gas from which water and tar, naphthalene and fine tar particles are sequentially removed is sent to a hydrogen cyanide absorption tower to react with hydrogen cyanide in the coke gas and ammonium polysulfide in the liquid to absorb and remove the thiocyanate, The hydrogen cyanide-free gas is sent to a hydrogen sulfide absorption tower to absorb and remove hydrogen sulfide, then to an ammonia absorption tower to absorb and remove ammonia, and then cooled to a benzol absorption tower to remove benzene, toluene and xylene to the outside. Exhaust; The absorption liquid discharged from the hydrogen cyanide absorption tower is evaporated in a crystallizer to form thiocyanate ammonium crystals, the crystals are separated, and the absorption liquid is circulated to the hydrogenation absorption column; The absorbed liquid discharged from the hydrogen sulfide absorption tower is sent to an oxidation tower through which oxygen is circulated to oxidize hydrogen sulfide, and then solid-liquid separation is carried out in a solid-liquid separator. The insoluble solid is heated to evaporate sulfur and then discharged into slag. Part of is sent to ammonia saturator, saturated with ammonia, supplied with sulfur, then sent to hydrogen cyanide absorption tower to replenish with hydrogen cyanide absorption liquid, and the remainder of the liquid is sent to slurry replenishment tower to replenish calcined lime slurry, and then hydrogen sulfide absorption Send it to the tower; The present invention relates to a method for purifying coke gas using slaked lime which is configured to distill an absorbent liquid discharged from the ammonia absorption tower to separate ammonia and send a portion of the ammonia to the ammonia saturator.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

As shown in FIG. 2, the coke gas discharged from the coke oven is collected and cooled in the coke gas collecting pipe (1) to condense moisture and tar, and the condensed water and tar are separated and treated in the gas-liquid separator (2). After the gas is cooled in the cooling tower (3), the naphthalene is removed from the naphthalene absorption tower (4) and sent to the electrostatic precipitator through the blower (5).

The fine particle tar condensed in the electrostatic precipitator 6 is removed, and the fine tar is removed, and the gas is sent to the hydrogen cyanide absorption tower 20 to react hydrogen cyanide in the coke gas with ammonium polysulfide in the liquid to be absorbed as thiocyanate. It is removed and only a part of it becomes calcium thiocyanate.

As described above, the gas from which hydrogen cyanide is removed is sent to the hydrogen sulfide absorption tower 7 to absorb and remove hydrogen sulfide. In the hydrogen sulfide absorption tower 7, hydrogen sulfide reacts with the slaked lime supplied from the slurry supplement tower 26 to be absorbed and removed in the form of Ca (SH) ₂ .

As described above, the hydrogen sulfide-free gas is sent to the ammonia absorption tower (8) to absorb and remove the ammonia using a phosphate solution, and then cooled in the cooling tower (9), and then sent to the benzol absorption tower (10) such as benzene, toluene and xylene, etc. After removing, discharge to the outside.

The absorbent liquid discharged from the hydrogen cyanide absorption tower 20 is evaporated as much water is received from the hydrogen sulfide absorption tower 7 in the crystallizer 21 to form a thiocyanate ammonium crystal, and then separated from the crystal. Circulated to the hydrogen cyanide absorption tower 20.

The absorbing liquid discharged from the hydrogen sulfide absorption tower 7 is moved to the oxidation tower 22 where oxygen is circulated to oxidize hydrogen sulfide, and then solid-liquid separated in the solid-liquid separator 23, and then the insoluble solid is heated in the sulfur evaporator 24. Sulfur is evaporated and then discharged into slag, and a portion of the liquid is transferred to the ammonia saturator 25, saturated with ammonia, and supplied with sulfur, and then sent to the hydrogen cyanide absorption tower 20 to be replenished with hydrogen cyanide absorption liquid, and The remainder of the liquid is sent to the slurry replenishment tower 26 to replenish the slaked lime slurry and then to the hydrogen sulfide absorption tower 7.

The flow rate of the absorbent liquid from the hydrogen sulfide absorption tower to the hydrogen cyanide absorption tower is preferably at least 1.2 L per 1 g of hydrogen cyanide, because the amount of ammonium polysulfide or calcium polysulfide is saturated by ammonia saturation and sulfur supplementation. It must be supplied in sufficient quantity to react with, because the flow rate can not supply as much as required.

The absorption liquid discharged from the ammonia absorption tower 8 is distilled in the ammonia distillation unit 23 to separate ammonia, and a part of this ammonia is sent to the ammonia saturator 25.

On the other hand, the tar and condensate separated in the gas-liquid separator (2), as in the conventional method, the condensate and tar is separated in the ordough tar separator (5), the condensate is distilled from the distillation column (14), the distilled gas It is combined with coke gas and condensate is sent to the wastewater treatment unit.

As described above, the present invention has an absorption tower 20 for removing hydrogen cyanide to prevent the accumulation of thiocyanate in the oxidation tower, and recovers it as thiocyanate and removes hydrogen cyanide. The gas was allowed to enter the hydrogen sulfide absorption tower (7). At this time, when the absorbent liquid is partially absorbed from the absorption column of the hydrogen sulfide absorption tower and added to the hydrogen cyanide absorption tower absorbent, calcined lime added to the hydrogen sulfide absorption liquid and calcium polysulfide or ammonia sulfide combined with ammonia and sulfur in the absorbent liquid are supplied. The hydrogen cyanide is absorbed and converted into calcium thiocyanate or ammonia thiocyanate by reaction with calcium polysulfide or ammonia sulfide supplied from a hydrogen sulfide absorption tower. The absorbing liquid supplied from the hydrogen sulfide absorption tower was saturated in the ammonia supplied from the ammonia absorption tower in the ammonia saturator 25 to supply the insufficient sulfur and thus reacted with the hydrogen cyanide even if a small amount was supplied. Sufficient ammonia and sulfur will be supplied. Calcium thiocyanate and ammonia thiocyanate accumulated in the absorbent liquid are crystallized in the crystallization unit 21 to separate crystals, and the absorbent liquid from which the crystals are separated is recycled.

In the crystallizer, a method of heating and evaporating moisture is used to continuously receive the hydrogen sulfide absorbing liquid without generating waste water. In the hydrogen sulfide absorption tower, hydrated lime slurry was used. When oxidizing hydrogen sulfide absorbed in the slurry in the sintered slurry in the oxidation tower 22, the exhaust gas from the oxidation tower 22 was recycled again using pure oxygen to prevent emission of waste gas. It can be used. The absorbent liquid from the oxidation tower 22 was separated from the solid phase and the liquid phase in the solid-liquid separator, and the liquid was replenished in the slurry replenishment tower 26 to supplement the slurry of slaked lime so that the entire volume was recycled to be sent to the hydrogen sulfide absorption tower and no waste water was generated. . The solid separated in the solid-liquid separator contains hydrated lime slurry, sulfuric acid sulfuric acid, sulfur, and the like. The sulfur was recovered in a sulfur distiller and the rest was disposed of as slag. Ammonia was absorbed and removed using the ginseng method, and the ammonia generated therefrom was supplied to the hydrogen cyanide absorption tower.

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

EXAMPLE

Using nitrogen gas as the base gas, a mixed gas containing 5g / Nm3, 5g / Nm3 and 1.5g / Nm3 of ammonia, hydrogen sulfide and hydrogen cyanide was used for the experiment and the gas flow rate was 70Nm3 / h. The experiment was carried out. The absorption towers were all stratified towers.

At this time, the absorption liquid flow rate passing through the absorption tower was 110L / h. At the beginning of the absorption tower operation, the absorbent liquid was artificially prepared. Sodium sulfide was dissolved to 4.5g / L concentration, sulfur was added to 15g / L, and heated to make about 200L of sodium sulfide solution. Once the operation is started, a part of the absorbed liquid separated from the solid-liquid separator of the hydrogen sulfide absorption tower is passed through the ammonia saturator to supply the sodium sulfide to be consumed, and then supplied with ammonia and supplied at a flow rate of 4 L / h. Calcium sulfide or polysulfide ammonia was supplied. The ammonia saturator was also allowed to be fed continuously in an amount of 122 g / h in order to feed shortage of sulfur. Once the steady state was reached, the amount of crystals recovered with thiocyanate and ammonia thiocyanate was about 310 g / h including impurities.

In the hydrogen cyanide absorption tower and in the hydrogen sulfide absorption tower, the absorption rate was very high because it was operated in a highly alkaline state and absorbed and reacted at the same time, and the hydrogen cyanide was absorbed from the hydrogen cyanide absorption tower. The concentration of hydrogen dropped to 0.002 g / Nm 3.

After passing through the hydrogen sulfide absorption tower, the concentration of hydrogen sulfide in the mixed gas dropped to 0.01 g / Nm 3. The absorbent flow rate of the absorption tower passing through the hydrogen sulfide absorption tower was 250 L / h, and a solution obtained by mixing the lime with 10% of the absorbent solution was initially used. The fine powdered slaked lime was supplied to the slaked lime slurry replenishment tower. The lime was allowed to be supplied to the absorption tower in the form of slurry. At this time, the amount of calcined lime fed 3.1kg / h was supplied every 30 minutes. When condensation of sulfur vapor was collected, the amount was about 305 g / h and the slag discharged was 2.5 kg / h. At this time, the ammonia absorption rate in the ammonia absorption tower was also very high and the final discharge concentration was 0.01 g / Nm3.

As described above, in the present invention, since hydrogen cyanide can be separated separately, the thiocyanate is not accumulated in the hydrogen sulfide absorbing liquid, and the calcium sulfate produced as a by-product can be removed in the form of slag because the solubility is very low. Partial elimination with calcium thiosulfate allows the generation of wastewater for control of their concentration to be partially removed by recycling the absorbents at all times without authorization, so that the absorbents can always be recycled and used without generating any wastewater for controlling their concentration. In addition, it has the advantage of recovering calcium thiocyanate or ammonia thiocyanate, which can be used as an expensive chemical raw material, using calcium sulfide or ammonia from its own process without using any other raw materials. Because it uses oxygen instead of air Baesunhwan to the total amount of oxygen is discharged will not be effective to solve the problem of the waste gases generated in the conventional oxidation tower.

Claims (2)

After condensing coke gas to separate water and tar and cooling the coke gas from which water and tar are separated, the naphthalene is removed from the naphthalene absorption tower 4, and then the condensed fine particle tar is removed. Absorb and remove hydrogen sulfide and hydrogen cyanide in 7); Oxidizing the absorbed liquid discharged from the hydrogen sulfide absorption tower 7 in an oxidation tower to oxidize hydrogen sulfide to sulfur, separating sulfur in a solid-liquid separator, and then recycling the waste liquid and recycling the absorbed liquid; And removing the ammonia by sending the gas from the hydrogen sulfide absorption tower (7) to the ammonia collector, and then cooling and then sending the gas to the benzol absorption tower (10) to remove benzene, toluene, xylene, etc. In the coke gas purification method, the coke gas from which water and tar, naphthalene and fine tar particles are sequentially removed is sent to the hydrogen cyanide absorption tower 20 to react hydrogen cyanide in the coke gas with ammonium polysulfide in the liquid. Absorption is carried out by thiocyanic ammonium, and the hydrogen cyanide-free gas is sent to the hydrogen sulfide absorption tower (7) to absorb and remove hydrogen sulfide, which is then sent to the ammonia absorption tower (8) to absorb and remove the ammonia, and then cooled, It is sent to the absorption tower (10) to remove benzene, toluene and xylene to be discharged to the outside, the hydrogen cyanide absorption tower 20 The evaporation of the absorbing solution is in the crystallizer (21) ammonium thiocyanate and which is separating the crystals was formed, and then a decision cycle the absorbent to the hydrogen cyanide absorption column 20; The absorbed liquid discharged from the hydrogen sulfide absorption tower 7 is sent to the oxidation tower 22 through which oxygen is circulated to oxidize hydrogen sulfide, and then solid-liquid separation is carried out in the solid-liquid separator 23, and then an insoluble solid is separated from the sulfur evaporator 24. After heating, the sulfur is evaporated and discharged into slag, and a part of the liquid is sent to the ammonia saturator 25 to saturate with ammonia, and sulfur is supplied. Then, the sulfur cyanide absorption tower 20 is sent to the hydrogen cyanide absorption liquid. Replenish and send the remainder of the liquid to the slurry replenishment tower 26 to replenish the hydrated lime slurry and then to the hydrogen sulfide absorption tower 7; And distilling the absorbent liquid discharged from the ammonia absorption tower (8) to separate ammonia, and to send a portion of the ammonia to the ammonia saturator (25). The method of claim 1, wherein the flow rate of the absorption liquid supplied from the ammonia saturator (25) to the hydrogen cyanide absorption tower (20) is 1.2L or more per 1 g of hydrogen cyanide.