JPS597756B2 - Wet desulfurization method for coke oven gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wet desulfurization method for coke oven gas, and its object is to desulfurize coke oven gas without producing sulfur.

Coke oven gas usually contains 2-6 g/N 7F+'' hydrogen sulfide and 0.5-3 g/N 771'' hydrogen cyanide.

Hydrogen sulfide burns and becomes sulfur dioxide gas, which pollutes the atmosphere, so it must be removed during the purification process.

Methods for removing hydrogen sulfide from coke oven gas include a method of absorbing ammonia in the gas as an alkali source, and a method of absorbing gas from which ammonia has been removed in advance using caustic soda as an alkali source, but both methods absorb hydrogen sulfide. When the oxidized liquid is oxidized with a gas containing oxygen, a redox catalyst such as a quinone derivative, naphthoquinone derivative, anthraquinone derivative, or picric acid is used to generate mainly elemental sulfur, thiocyanide, and as a side reaction, thiosulfate and sulfate. Elemental sulfur is separated and the absorption liquid is recirculated. A portion is extracted to prevent the salt concentration from rising in the absorption liquid and supplementary water, catalyst, and alkali are added.

This method is a so-called redox reaction type wet desulfurization method for coke oven gas, and both use a catalyst to efficiently oxidize l{2S or HS- ions absorbed in the absorption liquid to elemental sulfur. Elemental sulfur suspended in the desulfurization solution was mainly removed by physical means such as Todori centrifugation.

However, as a new treatment method for desulfurization liquid was developed, a method was developed in which wet oxidation was carried out at high temperature and high pressure, and all of the elemental sulfur and sulfur compounds were eventually converted to sulfates, and the method of generating elemental sulfur became meaningless, and the method of generating elemental sulfur became meaningless. Elemental sulfur causes clogging of the desulfurization liquid circulation system and desulfurization tower.

In particular, in the desulfurization method where the coke oven gas desulfurization process is installed before the removal of light oil and naphthalene, the heavy unsaturated hydrocarbons contained in the coke oven gas combine with the generated elemental sulfur to form a highly viscous oily sulfur compound. This was a major cause of clogging, such as adhesion to the packed bed of the desulfurization tower.

Furthermore, the generated elemental sulfur is not desirable because it causes clogging of heat exchangers and local abnormal oxidation reactions even in the wet oxidation process, which is a treatment facility for desulfurization liquid.

Furthermore, in the desulfurization solution treatment process/wet oxidation, all of this elemental sulfur becomes sulfuric acid, which has the effect of making the reaction product strongly acidic, so it is necessary to add alkali such as ammonia, which is necessary for neutralization. Since sulfur starts to oxidize at low temperatures and has a high calorific value, there are strong restrictions on the concentration that can be charged to wet oxidation equipment.

On the other hand, one method of desulfurization operation that does not generate elemental sulfur is to limit the amount of oxygen supplied during the oxidation and regeneration process of the catalyst.
Alternatively, an operating method is used in which the concentration of the added catalyst is reduced to limit the oxidation of HS- ions to HSx or S20x-, thereby minimizing the generation of elemental sulfur.

However, even with this method, it is impossible to operate without generating elemental sulfur at all due to fluctuations in the hydrogen sulfide concentration of coke oven gas and gas flow rate, and furthermore, the oxidation regeneration of the catalyst in the oxidation process becomes poor, which has the effect of lowering the desulfurization rate. There were drawbacks that made it difficult to say that it was an efficient desulfurization method.

The present invention was made to solve the problems of the prior art, and involves bringing coke oven gas into contact with an alkali-containing absorption liquid, and removing hydrogen sulfide contained in the absorbed liquid using a redox catalyst. In the method of desulfurizing coke oven gas by using and oxidizing the alkali and regenerating and circulating the alkali, the gas drain generated from the coke oven is appropriately added during desulfurization, or the desulfurization liquid is added without adding a specific catalyst substance. It is characterized by absorbing and concentrating the catalytic substances contained in the coke oven gas itself into the desulfurization liquid by contacting and absorbing the coke oven gas for a long period of time.

That is, as a result of a detailed study of concentrated ammonia water (hereinafter referred to as ammonium water) generated from coke oven gas and the desulfurization liquid during operation of the wet desulfurization equipment, the present inventors found that there is a trace amount of ammonia in coke oven gas. found that it contains a substance that exhibits catalytic performance in redox reaction type desulfurization, and furthermore, when this substance is used as a catalyst in redox reaction type desulfurization method, the desulfurization rate and desulfurization rate increase without generating any problematic elemental sulfur. We obtained the knowledge that it is possible to maintain operations that are no different from conventional catalyst-added desulfurization in terms of cyanide content.

In particular, when the catalytic substance contained in ammonium chloride is used, no elemental sulfur is generated in the catalyst oxidation regeneration process even at redox potentials (-200 to -300 mV') where elemental sulfur is likely to be generated in the past. It has been found that the conversion rate to thiosulfuric acid and sulfuric acid can be maintained extremely high, making it extremely advantageous in post-treatment processes (wet oxidation processes, etc.) of waste desulfurization liquid.

Figure 1 shows a comparison of the oxidation selectivity characteristics of HS-1 catalysts.

As shown in Figure 1, when the conventional catalyst β-naphthoquinone sodium sulfonate NQ is used, the redox potential is -2.
At 00 to -300 mV, the generation of elemental sulfur is significant, but when the ammonium water according to the present invention is used as a catalyst, no unit sulfur is generated.

In addition, in the conventional method using NQ as a catalyst, s2o,j and SO
:- The amount of generated is small, but when the ammonium water according to the present invention is used as a catalyst, the oxidation-reduction potential is s2 within the above range.
It can be seen that there are significantly more o:j- and SO2,-.

The catalytic substances contained in the coke oven gas in small amounts in the redox reaction according to the present invention are water-revealable substances such as side chain phenols, cyclic polyhydric phenols, and quinones, and as tar acid components. It is a relatively high boiling point substance that is quantified.

This substance mainly exists in large amounts in the ammonium water flushed into the dry main of the coke oven or in the ammonium water condensed in the primary cooler, and is also present in trace amounts in the coke oven gas after the primary cooler.

It is also clear that the condensed water from the coke oven gas after the primary cooler exhibits redox catalytic performance, albeit to a small extent.

Next, the catalytic ability of the redox catalytic substance contained in the coke oven gas will be explained.

Add 2 ml of 7.5-carbon sodium sulfide solution to 200 ml of oxygen-saturated water, and add 10 ml of ammonium water, 0.1 mol, cooled and condensed from coke oven gas as a catalyst.
/m3 β-Naphthoquinone sulfonate sodium 10ml and pure water 10Tll were added separately, kept at a temperature of 30°C, and stirred at the same speed in a sealed state to prevent air from entering.The dissolved oxygen concentration was measured using a oxygen meter. The catalytic ability to oxidize sodium sulfide was investigated by comparatively measuring changes over time.

Figure 2 shows the results. As shown in Figure 2, dissolved oxygen hardly decreases in pure water, but when 10 TLl of ammonium water is added, dissolved oxygen disappears in about 7 minutes.

Sodium β-naphthoquinone sulfonate which is a redox catalyst 0. In a 1 mol/711 solution, free oxygen disappears in about 6 minutes.

The time required to reduce the free oxygen by 1 m9/l is approximately 50 seconds for sodium β-naphthoquinone sulfonate and approximately 60 seconds for ammonium sulfate, and the catalytic ability to oxidize sodium/cum sulfide is 0. 1
It can be seen that there is not much difference in the catalytic ability between sodium β-naphthoquinone sulfonate and ammonium water at a concentration of mol/m''.

FIG. 3 shows an operational system diagram for extracting and separating the catalytic substances in the ammonium water obtained by cooling and condensing the coke oven gas.

As can be seen from this figure, the catalytic substances contained in ammonium water cooled and condensed from coke oven gas are water-soluble substances with a relatively high boiling point and are extracted and separated as so-called tar acid components extracted with caustic soda.

FIG. 4 is a process diagram illustrating a redox reaction type coke oven gas wet desulfurization apparatus according to the present invention.

In the figure, 1 is undesulfurized coke oven gas. This gas 1 is led to an absorption tower 2, and in the absorption tower 2 it comes into contact with an absorption liquid 3 to absorb hydrogen sulfide in the gas 1. Furnace gas 4
become.

On the other hand, in the oxidation tower 5, hydrogen sulfide is oxidized by an oxygen-containing gas 6 and a catalyst, and in the absorption tower 2, thiocyanide, elemental sulfur, which is an oxide of hydrogen sulfide, and thiosulfuric acid react with hydrogen cyanide absorbed simultaneously. It becomes water-soluble salts of compounds and sulfates.

In order to maintain the desulfurization rate, a portion of the absorption liquid 3 is extracted as a blow 10 so as not to increase the salt concentration, and a catalyst 7 such as β-naphthoquinone sodium sulfonate, make-up water 8, and an alkali source 9 are replenished.

Since the blow 10 has a high COD, it is treated by wet oxidation/reduction combustion, etc.

Example 1 In the equipment shown in Fig. 4, ammonium thiocyanate, ammonium thiosulfate, and ammonium sulfate were added as a catalyst to the absorption liquid 3, and ammonium thiocyanate, ammonium thiosulfate, and ammonium sulfate were added at 60 g/l and 5 g/l, respectively. 1,40 g/L and using an absorption liquid containing 8 g/L of ammonia, the desulfurization rate and
The cyanide removal rate was investigated.

Air is used as the gas supplied to the oxidation tower 5, and the air ratio is 0.05 (
Air/C O G ) The temperature of the absorption liquid and gas was 35° C., and ammonia in coke oven gas was used as an alkali source for the absorption liquid.

Ammonia in undesulfurized coke oven gas is 8~1.0g
/Nm3 Hydrogen sulfide was 2 to 3 g/N7ri:, and hydrogen cyanide was 0.6 to 1.1 g/Ntri:.

For comparison, tests were also conducted without the addition of a catalyst and with sodium β-naphthoquinone sulfonate.

Table 1 shows the desulfurization rate and cyanide removal rate. The sulfur in the absorption liquid and the HS concentration before and after the oxidation tower are shown.

As shown in Table 1, when aqueous ammonia is used as the absorption liquid and no catalyst is added, almost no desulfurization occurs (approximately 12%), but when ammonium water obtained by cooling and condensing coke oven gas is added to the absorption liquid, the desulfurization rate increases. is approximately 97%.

Desulfurization efficiency also decreases when the proportion of ammonium water added to the absorption liquid is reduced, but even when the proportion of ammonium water added is 10 parts, the desulfurization rate is over 80 parts, and when ammonium water is used, no sulfur is generated in any case. Ta.

9.2m of β-naphthoquinone sulfonic acid sodium in the absorption liquid
ol/m" showed a desulfurization rate of about 96% under the same conditions, but generated 0.4 g/l of elemental sulfur.

Hydrogen sulfide at the outlet of the oxidation tower, which indicates the oxidation ability of the catalyst, is 0.04 when aqueous ammonia without catalyst is used as the absorption liquid.
7 g/l, but with ammonium water added it is 0.0 0
This is the same as when using sodium β-naphthoquinone sulfonate at 8 g/l, which shows that ammonia water has the catalytic ability to oxidize hydrogen sulfide. Example 2 Using the same absorption equipment as in Example 1, 0.2 mol/m' of sodium β-naphthoquinone sulfonate was added to water as an absorption liquid, and 10 parts of ammonium was added to the absorption liquid, and ammonia (N
H3) 8 j! An absorption liquid containing /l was prepared and a continuous absorption experiment was conducted under the same conditions as in Example 1 to investigate the composition of the absorption liquid.

Table 2 shows the composition of the absorption liquid after 8 days.

As shown in Table 2, when an experiment was carried out under the same conditions with the addition of sodium β-naphthoquinone sulfonate at a concentration of 0.2 mol/m3 to the absorption liquid, 35.1 g/l of thiosulfate was produced.
It is higher than sulfates, with elemental sulfur at 0.69/l.
Occurred.

However, when the ammonium water of the present invention is added at 10%, the thiosulfate is 4.
The amount was 7 g/l, and there were many sulfates, and no elemental sulfur was generated.

Furthermore, the same effect was obtained by using ammonia water that had been in contact with coke oven gas for one month.

As described above, it can be seen that according to the present invention, the oxidation of the absorption liquid progresses, and the treatment in the next step (wet oxidation, etc.) becomes easier.

As explained above, the method of the present invention is a redox reaction type wet desulfurization method for coke oven gas, in which the gas drain generated from the coke oven is appropriately added to the desulfurization solution without adding a specific catalyst substance, or the desulfurization solution is added to the desulfurization solution. By contacting and absorbing coke oven gas for a long period of time, the catalytic substances contained in the coke oven gas itself are absorbed and concentrated in the desulfurization liquid, and desulfurization can be performed.

Furthermore, according to the method of the present invention, in the conventional redox reaction type coke oven gas wet desulfurization method, there is no need to add a specific catalyst and no elemental sulfur is generated. This product prevents clogging of other equipment due to elemental sulfur, and at the same time provides extremely large economic effects such as improving the processing efficiency of the wet oxidation method in the desulfurization liquid treatment process, ensuring stable operation, and eliminating the need for the addition of ammonia water. It is.

Furthermore, if the method of the present invention is applied to condensed ammonium water from a preheated coal coke oven, the generated high COD and high rhodane liquid can be effectively treated and recovered as sulfuric acid, ammonium sulfate, etc. by COG desulfurization liquid treatment, so that the ammonium water treatment process can be improved. This method eliminates the need for activated sludge treatment, making it a more economical method.

[Brief explanation of drawings]

Figure 1 is a diagram showing a comparison of the characteristics of the oxidation selectivity of HS- using a catalyst, Figure 2 is a diagram showing changes in dissolved oxygen in a Na2S solution over time due to a catalyst, and Figure 3 is a diagram showing a comparison of the characteristics of the oxidation selectivity of HS- using a catalyst. Fig. 4 is a process diagram illustrating the redox reaction type coke oven gas wet desulfurization apparatus according to the present invention.
4: desulfurization coke oven gas, 5: oxidation tower, 6: gas containing oxygen, 7: catalyst, 8: makeup water, 9: water containing alkali,
10: Blow liquid, 11: Exhaust.

Claims (1)

[Claims] 1. A method for desulfurizing coke oven gas by bringing coke oven gas into contact with an absorption liquid containing an alkali, oxidizing hydrogen sulfide contained in the absorbed liquid using a redox catalyst, and regenerating and circulating the alkali. The catalytic properties contained in the coke oven gas itself can be removed by adding the gas drain generated from the coke oven to the desulfurization solution, or by allowing the desulfurization solution to contact and absorb the coke oven gas for a long period of time without adding a specific catalyst substance. A wet desulfurization method for coke oven gas characterized by absorbing and concentrating substances in a desulfurization liquid.