JPH06228573A - Treatment of tail gas in coal gasification plant - Google Patents

Abstract

PURPOSE:To realize a treatment by a simple operation with high collecting efficiency, by converting the sulfur compound in the tail gas into an oxide and bringing the oxide into contact with an absorbent slurry containing Ca or Mg carbonate or hydroxide to fix it as the sulfate. CONSTITUTION:A flow 1 of an absorbent solvent having a sulfur compound absorbed by the contact with coal gasification gas is introduced into a heating regeneration tower 2, wherein it is brought into contact at the gas-liquid contact area 4 with a liquid heated by a heating source 3 provided in the lower part of the tower to release the sulfur compound and nitrogen compound. The regenerated absorbent solvent 5 is returned to an absorption tower for reuse. The regenerated gas 6 containing the sulfur compound and nitrogen compound is washed with water in a washing tower 7 to remove ammonia, chlorine, etc., by absorption. The washed tail gas 8 is introduced into a catalyst packed tower 9, where the sulfur compound is oxidized with heated air or oxygen 10 to a sulfur oxide. The gas 11 containing the sulfur oxide is brought into contact with a water slurry containing Ca or Mg carbonate or hydroxide at the gas- liquid contact area 14 in an absorption tower 12 to form calcium or magnesium sulfate crystals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tail gas treating method in a gas refining process of cracked gas obtained by gasifying coal. In particular, the present invention relates to a method for removing harmful substances in the tail gas generated in the step of regenerating the absorbing solvent by wet desulfurization with the absorbing solvent.

[0002]

2. Description of the Related Art Development of gasification technology for gasifying coal for various purposes by diversifying energy sources is in progress. The decomposition gas obtained by gasifying coal contains a sulfur-containing compound, a nitrogen-containing compound, a chlorine-containing compound, a fluorine compound, dust and the like. In order to gasify coal and effectively use it for multiple purposes, gas purification is performed to remove harmful substances. The gas purification process can be classified into a low temperature process performed by cooling coal gas and a dry process performed at a relatively high temperature. To effectively use the energy of coal gas, it is effective to remove harmful substances by a dry process, but it has not been put to practical use. Therefore, a wet process, which is a reliable gas purification process, has been put to practical use.

The wet desulfurization process applied to the gas purification of a coal gasification plant is carried out by an oxidation method, a physical absorption method and a chemical absorption method. At this time, as the absorbing solvent, a mixture of potassium carbonate and metavanadate, dimethyl ether of polyalkyl glycol (commonly known as selectol), amine compound and the like are used. In this wet desulfurization process, an absorbing solvent that has absorbed sulfur-containing compounds is introduced into the heating regeneration tower,
The absorbing solvent is regenerated and recycled.

The tail gas generated when the absorbing solvent is regenerated in the heating regeneration tower targeted by the present invention contains mainly hydrogen sulfide in a high concentration. Conventionally, this tail gas treatment method is performed by a Claus reaction in which hydrogen sulfide in the gas is partially oxidized to form sulfurous acid gas, hydrogen sulfide and sulfurous acid gas are reacted on a catalyst, and elemental sulfur is recovered. This method has a drawback that the molar ratio of hydrogen sulfide and sulfurous acid gas (2H ₂ S / SO ₂ ) needs to be strictly adjusted, and the conversion rate to elemental sulfur is low. Unreacted hydrogen sulfide or sulfurous acid gas in the Claus reactor has to be returned to the absorption step and absorbed again, which has a drawback that the refining process and the operation of adjusting the molar ratio of hydrogen sulfide and sulfurous acid gas are complicated.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides a desulfurization process in which sulfur compounds are oxidized into sulfurous acid gas, the sulfurous acid gas is absorbed by an absorbing liquid containing an alkaline substance, and fixed to sulfate as the above-mentioned tail gas treatment method. Especially.

[0006]

Means for Solving the Problems In the gas refining process in which coal gas from a coal gas plant is subjected to wet desulfurization with an absorbing solvent such as Selectol, the absorbing solvent absorbing a sulfur-containing compound is sent to a heating regeneration tower for heating. The present invention relates to a method of processing tail gas for regeneration and desorption.

The tail gas contains a nitrogen-containing compound such as ammonia and hydrogen cyanide, chlorine, etc. in addition to the sulfur-containing compound. First, the tail gas is introduced into the water washing tower and washed before being introduced into the catalytic oxidizer. The outlet gas from the water washing tower is introduced into the catalytic oxidation packed bed to oxidize hydrogen sulfide in the tail gas into sulfurous acid gas or sulfur trioxide. Oxidation of sulfur compounds in the tail gas to sulfurous acid gas and sulfur trioxide in the catalytic oxidation packed bed is carried out by entraining oxygen gas or air in the tail gas. At the outlet of the catalytic oxidizer, sulfur compounds (mainly hydrogen sulfide) in the tail gas are converted to sulfur dioxide (S
O ₂₎ or is oxidized to sulfur trioxide (SO _3). The sulfur oxide gas at the outlet of the catalytic oxidizer is brought into gas-liquid contact with a water slurry containing calcium, sodium or magnesium carbonate or hydroxide, and the sulfur compound is absorbed and fixed to sulfite or sulfate.

Sulfur oxide at the outlet of the catalytic oxidizer is once absorbed into water in the slurry as sulfurous acid or sulfuric acid, and finally crystallized as sulfite or sulfate. Sulfate crystallizes calcium sulfate (gypsum) when limestone is suspended in water, and magnesium sulfate crystallizes in the absorption reaction when it is suspended in water using magnesium hydroxide as an absorbent. Gypsum or magnesium sulfate can be collected by extracting a part of the absorption liquid from the absorption tower and precipitating and collecting the solid matter, and the supernatant liquid can be returned to the absorption tower for recycling. Therefore, the absorption tower is constantly supplied with calcium or magnesium carbonate or hydroxide in a chemical equivalent amount or more corresponding to the sulfur oxides entering the absorption tower.

[0009]

[Function] When coal is reduced or partially oxidized at high temperature to be gasified, in addition to hydrocarbons, carbon monoxide (CO), hydrogen (H ₂ ), hydrogen sulfide (H ₂ S), carbon dioxide (CO ₂ ),
Chlorine (Cl ₂ ), water vapor (H ₂ O), ammonia (NH
₃ ), decomposition gas containing nitrogen (N ₂ ), oxygen (O ₂ ) and the like is generated. This decomposed gas is then introduced into a wet desulfurization unit for gas purification. The absorption solvent in the wet desulfurization process is dimethyl ether of polyalkyl glycol (commonly known as
SELEXOL). In order to use SELEXOL as an absorbing solvent, the decomposition gas from the gasification furnace is cooled to about 50 ° C. or lower, and the absorption operation is performed near the pressure of the gas furnace. In this absorption reaction, the lower the temperature and the higher the pressure, the higher the absorption efficiency. Although the absorption efficiency of the sulfur-containing compound varies depending on the amount of treated gas and the contact ratio of the absorption liquid, it can be operated at a desulfurization rate of 95% or more. At this time, most of the sulfur compounds in the decomposed gas, ammonia and chlorine gas are absorbed by the absorbing solvent. The absorbing solvent that has absorbed the sulfur compound is supplied to the heating regeneration tower, and when the absorbing solvent is heated near 100 ° C., the sulfur compound,
Ammonia and chlorine gas are released. This desorbed gas is the tail gas of the coal gas refining process targeted by the present invention.

Since this tail gas contains ammonia, chlorine and the like in addition to hydrogen sulfide, it is washed in a water washing tower to selectively absorb the ammonia and chlorine gas. It is effective to raise the pH of the absorbing solution in the water washing tower in order to enhance the cleaning effect. The tail gas from which ammonia and chlorine gas have been removed is then introduced into a catalytic oxidizer, and sulfur compounds such as hydrogen sulfide contained in the tail gas are oxidized to sulfurous acid gas and sulfur trioxide gas to form sulfur oxides.

Oxidation catalysts containing sulfur compounds (H ₂ S) as sulfur oxides (SO ₂ or SO ₃ ) are Pt, Ag ₃ VO ₃ , C.
_{u 3 (VO 4) 2 -V} 2 O 5, Ag, WO 3, Fe 2 O 3, Fe 2
_{O 3 -Bi 2 O 3, Fe} 2 O 3 -K 2 O, Fe 2 O 3 -Sn
Oxidation catalysts of O ₂ and Cr ₂ O ₃ —SnO ₂ compounds alone or as a mixture have been developed. Each oxidation catalyst has an optimum temperature condition. For example, platinum-based oxidation catalysts have S
The highest conversion temperature that can oxidize O ₂ is 400 ℃
It is in the vicinity, and a higher conversion rate can be obtained at a lower temperature than other oxidation catalysts. Oxidized sulfur oxide (SO ₂ or SO ₃ ) is brought into contact with an absorbing solution prepared by suspending calcium or magnesium carbonate or hydroxide in water with a slurry, and sulfite or sulfate (calcium sulfate, magnesium sulfate, etc.) To be fixed as.

[0012]

【Example】

(Example 1) FIG. 1 shows an example of a typical tail gas treatment process of the present invention. The gas generated by coal gasification is brought into contact with an absorbing solvent selected from ethylene glycol-based, amine-based, or alkali carbonate-based compounds, and the absorbing solvent stream 1 that has absorbed the sulfur compound is introduced into the heating regeneration tower 2 for regeneration. . The operating temperature of the absorption tower is around 50 ° C, and the regeneration temperature of the heating regeneration tower is around 100 ° C. In the heating regeneration tower, the gas-liquid contact part 4 is brought into contact with the liquid heated by the heating source 3 at the lower part of the tower, so that the sulfur-containing compound and the nitrogen-containing compound are desorbed. Regenerated absorbent solvent is returned from stream 5 to the absorption tower for recycling. The regeneration gas 6 containing the sulfur-containing compound and the nitrogen-containing compound is supplied to the lower part of the water washing tower 7 and washed with water or a liquid in an alkaline state. The washing tower 7 mainly absorbs and removes ammonia and chlorine. The washed tail gas 8 is then introduced into the catalyst packed bed 9 to oxidize the sulfur compounds on the heated air or oxygen 10 and the oxidation catalyst.
Sulfur compounds are oxidized to sulfur oxides (SO ₂ or SO ₃ ).

In the oxidation catalyst unit 9, by constantly maintaining the temperature around 400 ° C. on the catalyst, conversion to high sulfur oxide can be performed. Gas containing sulfur oxide (SO ₂ or SO ₃ ) 11
Is in the absorption tower 12 in order to make gas-liquid contact with the absorbing liquid containing calcium or magnesium carbonate or hydroxide.
To introduce. In the absorption tower 12, an absorption liquid containing a carbonate or hydroxide of calcium or magnesium is supplied to the gas-liquid contact portion 14 by a circulation pump and brought into gas-liquid contact with the gas in the stream 11. In the absorption tower 12, the sulfur oxides are absorbed by the absorption liquid containing calcium or magnesium carbonate or hydroxide. Sulfur oxides in the gas of stream 11 are absorbed into the water in the absorbing solution as sulfurous acid and sulfuric acid, and the reaction proceeds to react with calcium or magnesium to form calcium sulfate (gypsum) or magnesium sulfate crystals and are fixed. . A carbonate or hydroxide of calcium or magnesium always flows in the absorption tower tank 19
Supplied from Calcium carbonate is limestone. It is also possible to intermittently supply air or oxygen gas to the absorption tower tank 19 to oxidize a part of sulfite to sulfate. A part of the absorption liquid is withdrawn from the absorption tower tank from the stream 16 and solid matter can be recovered by using gypsum or magnesium sulfate as a precipitate. The absorption tower 12 is replenished with water from stream 17 in order to keep the absorption conditions constant at all times. The gas of stream 18, which is detoxified, can be released to the atmosphere.

Example 2 The example of FIG. 2 shows the temperature of the absorbing solvent and the desulfurization rate of the sulfur-containing compound in the coal gas when dimethyl ether of polyalkyl glycol was used as the absorbing solvent. In the figure, A has a sulfur content of 400 ppm, B is 1
This is the case of 500 ppm. The desulfurization rate can be increased as the sulfur content in coal gas increases. Further, the desulfurization rate can be increased as the temperature of the absorbing solvent decreases. Therefore, the desulfurization rate at the time of gas refining coal gas can be made higher as the absorption temperature is lower, the system pressure is higher, and the amount of absorbing solvent brought into gas-liquid contact per unit gas treatment amount is larger. Therefore, the desulfurization rate can be adjusted efficiently by adjusting these operating conditions.

Example 3 The example of FIG. 3 shows the results of examining the heating regeneration characteristics of dimethyl ether of polyalkyl glycol having absorbed a sulfur compound, with respect to the heating temperature of the absorbing solvent. The regeneration condition is the regeneration efficiency when the condition is 1 at. The regeneration efficiency is increased in a shorter time as the regeneration temperature is higher.

(Embodiment 4) The embodiment of FIG.
The conversion rate to sulfurous acid gas was investigated on a platinum catalyst assuming a tail gas containing 000 ppm. The tail gas was mixed with 3% of O ₂ , and the balance gas was N ₂ . The conversion rate of H ₂ S increases from 380 ℃ to 420 as the reaction temperature rises.
It shows a maximum value between 0 ° C and tends to decrease when the reaction temperature becomes higher.

(Embodiment 5) After leaving the catalytic oxidizer shown in FIG. 1, the gas is brought into contact with an absorbent containing a carbonate or hydroxide of calcium or magnesium to absorb the sulfur oxide in the gas. Sulfur oxide is once fixed as sulfurous acid and sulfuric acid. Finally, it is fixed as sulfate.
An example in which absorption characteristics of a mixed gas of 3000 ppm of sulfurous acid gas and air in a limestone slurry was examined assuming a catalyst oxidizer outlet gas is shown in FIG. The pH of the absorbing solution was kept at 5.5 and 5.8 by adjusting the amount of limestone supplied. The desulfurization characteristics were measured by changing the supply amount of the absorbing liquid having pH of 5.5 and 5.8 per cubic meter of the gas to be treated.

The SO ₂ absorption efficiency (desulfurization rate) can be increased as the supply amount of the absorption liquid increases, and when the pH is kept constant at 5.8, the desulfurization performance is 17 to 18 liters per cubic meter of gas to be treated. By contacting,
A desulfurization rate of 98 or more could be achieved. Further, the desulfurization rate tends to decrease as the absorption liquid pH decreases. When the sulfur oxide in the gas to be treated is SO ₂ gas, it is fixed as sulfite in the absorbing liquid. When the sulfite is oxidized to sulfate by bubbling air through the absorbing solution to oxidize the sulfite, the desulfurization rate can be increased by 10 to 15%.

[0019]

INDUSTRIAL APPLICABILITY The present invention relates to a tail gas treatment in a gas refining process of a cracked gas obtained by gasifying coal, and more particularly to a treatment method of a tail gas generated in a process of wet desulfurization with an absorbing solvent and regenerating the absorbing solvent. Is. In the gas refining process of wet desulfurization of coal gas, the sulfur solvent in the tail gas (mainly hydrogen sulfide) in the catalytic oxidizer is used to process the tail gas generated by heating and regenerating the absorbing solvent that has absorbed the sulfur-containing compound in the heating regeneration tower. Oxidize to sulfurous acid gas (SO ₂ ) or sulfur trioxide (SO ₃ ) and absorb the carbonate or hydroxide of calcium or magnesium into water as a slurry to immobilize sulfur compounds on stable sulfate. Since this is the case, the collection efficiency is higher and the operation and process are simplified as compared with the conventional Claus reaction or the like. Therefore, the tail gas can be reliably processed.

[Brief description of drawings]

FIG. 1 is a system diagram of a tail gas treatment process in a coal gas refining process.

FIG. 2 is a characteristic diagram of removal of sulfur compounds from coal gas by an absorbing solvent.

FIG. 3 is a characteristic diagram of heating regeneration of an absorbing solvent that has absorbed a sulfur compound.

FIG. 4 is an explanatory diagram of a conversion rate of a sulfur compound to an oxide.

FIG. 5 is a characteristic diagram of desulfurization of sulfur oxide with limestone slurry.

[Explanation of symbols]

1 ... Heating regeneration tower, 2 ... Absorption solvent absorption tower, 3 ... Heating source,
6 ... Tail gas, 7 ... Washing tower, 9 ... Catalytic oxidizer, 10 ...
Air or oxygen gas, 12 ... Absorption tower using calcium or magnesium as an absorbent, 19 ... Absorption tower tank, 20 ...
Limestone supply line.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Miyadera 1-1-1, Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory

Claims (6)

[Claims] 1. A hydrogen sulfide-containing gas obtained by gasifying coal is brought into contact with an absorbing solution by wet desulfurization to absorb hydrogen sulfide gas, and the obtained absorbing solution is heated and regenerated to desorb hydrogen sulfide. In the method for treating hydrogen sulfide gas, the nitrogen-containing compound and chlorine gas are washed and removed from the gas generated when the absorption liquid is heated and regenerated to desorb hydrogen sulfide, and then hydrogen sulfide is oxidized and converted to sulfur oxides. A tail gas treatment method for a coal gasification plant, characterized in that the obtained gas is brought into contact with a water slurry absorbing solution containing calcium or magnesium carbonate or hydroxide to fix a sulfur-containing compound as sulfite or sulfate. . 2. The method according to claim 1, wherein the absorbing solvent is selected from ethylene glycol-based compounds, amine-based compounds and alkali carbonate-based compounds, and the sulfur-containing compound is absorbed by contacting with coal gas to absorb the sulfur-containing compound. The absorption solvent is sent to the heating and regeneration tower, the gas generated in the heating and regeneration tower is introduced into the water washing tower, and the nitrogen-containing compound and the chlorine-containing compound are absorbed and then introduced into the catalytic oxidation tower accompanied by air or oxygen, and sulfur. A tail gas treatment method with a coal gasification plant in which a gas obtained by converting a content compound into an oxide is subjected to gas-liquid contact with a water slurry containing calcium or magnesium carbonate or hydroxide to fix a sulfur-containing compound as sulfite or sulfate. . 3. The method according to claim 1, wherein the sulfur-containing compound is absorbed by contacting a gas obtained by gasifying coal with dimethyl ether of polyalkyl glycol as an absorbing solvent, and the absorption solvent absorbing the sulfur-containing compound is regenerated. Sent to the tower, the generated gas is introduced into the water washing tower to absorb the nitrogen-containing compound, and then air or oxygen is entrained and introduced into the catalytic oxidation tower to convert the sulfur-containing compound into oxide, and the gas of calcium or magnesium carbonate or A tail gas treatment method for a coal gasification plant, characterized in that it is brought into contact with a water slurry containing hydroxide to be fixed as a sulfite or a sulfate. 4. Pt, Ag ₃ VO ₃ , Cu ₃ (V
_{O 4) 2 -V 2 O 5} , Ag, WO 3, Fe 2 O 3, Fe 2 O 3 -
_{Bi 2 O 3, Fe 2 O} 3 -K 2 O, Fe 2 O 3 -SnO 2, Cr
_One or a mixture of ₂ O ₃ —SnO ₂ compounds and 350
After oxidizing the sulfur-containing compound to sulfurous acid gas or sulfur trioxide gas in the reaction field heated from ℃ to 700 ℃, the gas is brought into gas-liquid contact with a water slurry containing calcium or magnesium carbonate or hydroxide, or sulfite or Tail gas treatment method of coal gasification plant fixed as sulfate. 5. An absorption liquid prepared by suspending the sulfur-containing oxide according to claim 1 as a sulfite or a sulfate in water containing calcium or magnesium carbonate or hydroxide. The amount of sulfur oxide in the outlet gas of the catalytic oxidation tower is 3 to 2 per 1 cubic meter of gas to be treated.
A tail gas treatment method for a coal gasification plant, which is brought into contact with 5 liters. 6. The method according to claim 1, 2, 3, 4 or 5.
A tail gas treatment method for a coal gasification plant, in which sulfur-containing compounds are converted into sulfur oxides by catalytic oxidation and brought into gas-liquid contact with a water / slurry absorbent containing calcium and magnesium to fix sulfur oxides as sulfites or sulfates.