JP2626787B2 - Method for recovering sulfur from hydrogen sulfide-containing gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering elemental sulfur from a hydrogen sulfide-containing gas, and can reduce the size of an apparatus and save energy consumption.

2. Description of the Related Art The Claus-type sulfur recovery method recovers sulfur from a hydrogen sulfide-containing gas using a gas-phase Claus reaction 2H ₂ S + SO ₂ → 3S + 2H ₂ O [1] of the following formula [1]. It operates at a gas plant.

In the above formula [1], sulfurous acid gas (SO ₂ ) is used. However, when there is no other SO ₂ gas source, as shown in the following formula [2], a raw material containing hydrogen sulfide in a reaction combustion furnace is used. When the gas is partially burned with air to convert about one third of the hydrogen sulfide contained in the raw material gas into sulfur dioxide, the Claus reaction proceeds almost simultaneously with the combustion due to the high temperature of the combustion. Produces elemental sulfur.

When the sulfurous acid gas generation by the partial combustion of hydrogen sulfide and the Claus reaction are combined, the reaction represented by the above formula [3] is performed in the reaction combustion furnace.

The reaction gas is cooled by a waste heat boiler, and further cooled by a sulfur condenser to separate generated elemental sulfur from the reaction gas.

An example of a typical Claus reactor in the case where there is no other SO ₂ gas source will be described with reference to FIG.

The raw material gas 52 containing hydrogen sulfide and the air 50 pressurized by the air blower 2 (or the oxygen-enriched air 51 enriched by the oxygen concentrator 1) are fed into the reaction combustion furnace 5, and the above-mentioned [3] A thermal Claus reaction of the formula is caused, the reaction gas is cooled by a waste heat boiler 6 and elemental sulfur is separated by a first sulfur condenser 7. Symbol 4 is a raw material gas preheater, symbol 3 is an air preheater,
Use as needed.

Since the conversion rate of the Claus reaction in the reaction combustion furnace is insufficient, the reaction gas from which elemental sulfur has been separated by the first sulfur condenser 7 in order to increase the sulfur recovery rate is heated by the first auxiliary burner 8, and then activated alumina, etc. Into the first reactor 9 filled with, and catalytically causes a Claus reaction. The first reactor outlet gas is cooled again in the second sulfur condenser 10 to separate generated sulfur.

In a normal sulfur recovery apparatus, the second auxiliary burner 11, the second reactor 12, the third
A sulfur condenser 13, a third auxiliary burner 14, a third reactor 15, and a fourth sulfur condenser 16 are installed, and then heating-contact reaction-
The cycle of cooling is repeated once or twice. 93-95% when using a two-stage catalytic reactor, 96-98 when using three stages
% Overall sulfur recovery is obtained.

The sulfur separated in the first to fourth sulfur condensers is liquid sulfur 54.
Take out as.

Exhaust gas 53 (hereinafter referred to as tail gas) from the final sulfur condenser contains a small amount of hydrogen sulfide, sulfur dioxide, and organic sulfur compounds. After processing using the combustion air 55 and the combustion gas 56, the air is discharged from the chimney 19 to the atmosphere. When it is necessary to reduce the amount of sulfur compounds in the tail gas, it is sent to a tail gas processing device such as a Scott method for processing.

The weakness of such Claus-type sulfur recovery systems is caused by nitrogen in the combustion air. As described with reference to FIG. 1, nitrogen in the combustion air is introduced into the system in the reaction combustion furnace, flows through the apparatus, and finally is released again to the atmosphere. Despite being active, it is always present in a large amount in the system (nitrogen concentration in the tail gas is about 60 vol%), and the following disadvantages are given to the sulfur recovery device.

Since the gas flow rate in the system is increased, the size of the apparatus must be increased.

In the sulfur recovery device, the cooling gas-heating process of the reaction gas is repeated, so that energy is wasted due to an increase in the gas flow rate in the system.

Reduce the partial pressure of the reaction components due to the dilution effect of nitrogen gas,
As a result, the sulfur recovery rate has been reduced.

Problems to be Solved by the Invention In order to solve the above-mentioned drawbacks, it has been considered to reduce the amount of nitrogen introduced into the system by using oxygen-enriched air as combustion air. If the concentration is too high, the temperature of the reaction furnace becomes too high, so there is a limit in terms of the material of the refractory material of the furnace.

The present invention recovers sulfur from a hydrogen sulfide-containing gas, which, in addition to the associated nitrogen reduction effect of using oxygen-enriched air, further enables a reduction in the amount of nitrogen introduced into the system and a reduction in energy consumption. The aim is to provide a method.

B. Means for Solving the Problems A method for recovering sulfur from a hydrogen sulfide-containing gas according to the present invention comprises introducing a raw material gas containing hydrogen sulfide and an oxygen-containing gas into a reaction combustion furnace to carry out a thermal Claus reaction. After the reaction gas is cooled and the elemental sulfur is separated by a sulfur condenser, a contact Claus reaction is performed in a contact reactor.The reaction gas is cooled and the elemental sulfur is further separated by a sulfur condenser. In the Claus-type sulfur recovery method to increase the sulfur recovery rate,
Oxygen concentration of 30-
Using 50 mol% oxygen-enriched air, the amount of oxygen supplied by the oxygen-enriched air and used for the reaction with hydrogen sulfide is 40 to 45 mol% of the amount of hydrogen sulfide in the raw material gas, and the reaction combustion By rapidly cooling the gas at the furnace outlet to a temperature of 700 ° C. or less within 1 second, the hydrogen concentration in the exhaust gas discharged from the final sulfur condenser is set to 3% by volume or more.

The conventional sulfur recovery method uses the Claus reaction From the amount of combustion air to convert one third of H ₂ S in the raw material gas to SO ₂ and H ₂ O, ie, the total H ₂ S
Controlling to 50 mol% has been paramount.

In the method of the present invention, unlike the conventional method, the amount of oxygen supplied by oxygen-enriched air and used for the reaction with hydrogen sulfide is controlled to 40 to 45 mol% of the amount of hydrogen sulfide in the raw material gas, and The outlet gas is rapidly cooled to a temperature of 700 ° C. or less within one second.

This is because not only the thermal Clause reaction of 6H ₂ S + 3O ₂ → 6S + 6H ₂ O [3] but also the thermal decomposition reaction of hydrogen sulfide represented by H ₂ S → S + H ₂ [4] occur in the reaction combustion furnace. It is to make it.

When the amount of oxygen used for the reaction with hydrogen sulfide is set to 40 mol% of the amount of hydrogen sulfide in the raw material gas, theoretically, the thermal Claus reaction of the above formula [3] is 80%, and that of the formula [4] If the thermal decomposition reaction is carried out by 20% and the amount is 45 mol%, 90% of the thermal Claus reaction of the formula [3] is theoretically performed and 10% of the thermal decomposition reaction of the formula [4] is performed. .

Here, the term "amount of oxygen used for the reaction with hydrogen sulfide" refers to the amount of oxygen contained in the source gas containing hydrogen sulfide based on the amount of oxygen in the oxygen-enriched air sent to the reaction combustion furnace. It is the amount obtained by subtracting the amount of oxygen consumed to burn hydrocarbons. This is because hydrocarbons preferentially consume oxygen and burn.

Therefore, in the practice of the present invention, the amount of oxygen-enriched air sent to the reaction combustion furnace is controlled in consideration of the proportion of hydrocarbons contained in the raw material gas containing hydrogen sulfide.

Also, the rapid cooling of the reaction combustion furnace outlet gas to a temperature of 700 ° C. or less within 1 second is because elemental sulfur and hydrogen generated by the thermal decomposition of hydrogen sulfide according to the above formula [4] are recombined and returned to hydrogen sulfide. This is to suppress the situation.

In a conventional sulfur recovery apparatus, a reaction gas is cooled by generating steam using a waste heat boiler. Although a similar waste heat boiler can be used in the present invention, it is necessary to increase the gas linear velocity in the waste heat boiler compared to the conventional method. From the exhaust heat boiler inlet temperature
The average contact time up to 700 ° C. is desirably 1 second or less, preferably 0.5 second or less.

The oxygen concentration of the oxygen-enriched air to be used may be higher than that of ordinary air, but the oxygen concentration is usually 30 to
50% (mol%) oxygen-enriched air is used.

Because, for the purpose of reducing the amount of the reaction gas by reducing the introduced nitrogen, the effect of reducing the introduced nitrogen accompanying the increase in the oxygen concentration is remarkable in the range of the oxygen concentration of about 30 to 50%.
This is because, when the oxygen concentration exceeds 50%, the effect of the degree of decrease in the introduced nitrogen accompanying the increase in the oxygen concentration is reduced.

For example, when using oxygen-enriched air with an oxygen concentration of 50%, the nitrogen in the system can be reduced by about 75%. Only a decrease. On the other hand, enriching oxygen to 50% or more increases the production cost, which is against the purpose of cost reduction.

Oxygen-enriched air of 50% or less has recently become available at a low cost due to advances in membrane separation and adsorption separation techniques.

The source gas suitable for the present invention desirably contains hydrogen sulfide in an amount of 70 mol% or more. Below this range, it is difficult to obtain the combustion temperature required to advance the thermal Claus reaction and the thermal decomposition reaction of hydrogen sulfide. When processing a plurality of source gases, this criterion is applied to the hydrogen sulfide concentration after mixing. However, when the raw material gas contains a large amount of hydrocarbons, a desired combustion temperature can be reached even when the hydrogen sulfide concentration is 70 mol% or less.

In order to promote the thermal decomposition of H ₂ S, the combustion temperature in the reaction combustion furnace is preferably as high as possible, and preferably at least 1400 ° C. or higher. This is achieved by using oxygen-enriched air and a source gas having a hydrogen sulfide concentration of 70 mol% or more.

Higher temperatures are also advantageous in terms of the conversion of the Claus reaction. However, the upper limit is 20 due to the cost of furnace refractory.
It is practical to set the temperature to 00 ° C, and the normal operating condition is 1400
A range of 11800 ° C. is preferred.

If the predetermined combustion temperature is not reached depending on the H ₂ S concentration in the source gas, it is effective to preheat the source gas and / or the oxygen-enriched air.

Example 1 Using the apparatus shown in FIG. 1, the raw material gas having the composition shown in Table 1 was 240.0 kgmol / hr (H ₂ S: 210.91 kgmol / hr) and oxygen-enriched air (O ₂ concentration: 31%) ) 320.0Kg mol / hr (O ₂ : 99.2Kg)
Mol / hr) into the reaction combustion furnace to cause a thermal Claus reaction. The reaction gas is rapidly cooled to 700 ° C in the exhaust heat boiler in 0.2 seconds to separate elemental sulfur, and then the auxiliary burner (3 stages) Table 2 shows data obtained when the reaction gas was heated to perform a catalytic Claus reaction by using a total of 16.1 kgmol / hr of the raw material gas. In this case, the molar ratio between oxygen and hydrogen sulfide used for the reaction with hydrogen sulfide, excluding oxygen consumed for the combustion of methane in the raw material gas, of the oxygen fed to the reaction combustion furnace (O ₂ / H ₂ S molar ratio) is 0.407.

Example 2 The flow rate of oxygen-enriched air was set to 33.51 Kg mol / hr (O ₂ : 103.88 Kg mol / hr), and the reaction gas was heated to 700 ° C. with an exhaust heat boiler to 0.5 ° C.
Table 2 shows data obtained when the same test as in Example 1 was performed except that the sample was rapidly cooled in seconds. In this case, the molar ratio between oxygen and hydrogen sulfide used for the reaction with hydrogen sulfide, excluding oxygen consumed for the combustion of methane in the raw material gas, of the oxygen fed to the reaction combustion furnace Is 0.429.

Example 3 The flow rate of oxygen-enriched air was set to 345.7 kgmol / hr (O ₂ : 107.17 kgmol / hr), and the reaction gas was heated to 700 ° C. by a waste heat boiler to 0.7 ° C.
Table 2 shows data obtained when the same test as in Example 1 was performed except that the sample was rapidly cooled in seconds. In this case, the molar ratio between oxygen and hydrogen sulfide used for the reaction with hydrogen sulfide, excluding oxygen consumed for the combustion of methane in the raw material gas, of the oxygen fed to the reaction combustion furnace Is 0.445.

Comparative Example 1 The oxygen-enriched air flow rate was 366.8 Kg mol / hr (O ₂ : 113.71 Kg mol / hr), and the reaction gas was heated to 700 ° C. with an exhaust heat boiler at a temperature of 1.7 ° C.
Table 2 shows data obtained when the same test as in Example 1 was performed except for cooling in seconds. In this case, the molar ratio between oxygen and hydrogen sulfide used for the reaction with hydrogen sulfide, excluding oxygen consumed for the combustion of methane in the raw material gas, of the oxygen fed to the reaction combustion furnace Is 0.476.

From Table 2, it can be seen that the tail gas amount is clearly reduced in Examples 1, 2 and 3 as compared with the comparative example, and the apparatus itself can be made smaller. It can also be seen that the amount of fuel used in the insulator is greatly reduced. The reason why the reduction rate of the fuel gas is larger than the reduction rate of the tail gas is that a large amount of hydrogen is contained in the tail gas, and a part of the hydrogen is burned by the incinerator.

Even if the ratio of the amount of oxygen in the oxygen-enriched air supplied to the reaction combustion furnace to the ratio of hydrogen sulfide in the raw material gas is reduced, the sulfur recovery rate does not change, but rather increases.

Using oxygen-enriched air as the oxygen-containing gas to be introduced into the reaction combustion furnace, the amount of oxygen supplied by the oxygen-enriched air and used for the reaction with hydrogen sulfide is calculated as the amount of hydrogen sulfide in the raw material gas.
By setting the content to 40 to 45 mol%, the thermal decomposition reaction of hydrogen sulfide proceeds simultaneously with the thermal Claus reaction in the reaction combustion furnace, and the outlet gas of the reaction combustion furnace is rapidly cooled to a temperature of 700 ° C or less within 1 second. Thereby, the recombination of elemental sulfur and hydrogen generated by thermal decomposition to return to hydrogen sulfide is suppressed. As a result, the sulfur recovery rate does not decrease despite the decrease in the O ₂ / H ₂ S molar ratio, the gas amount in the reaction system decreases, and the apparatus becomes compact and energy consumption decreases.

C. Effect of the Invention The apparatus becomes compact because the amount of reaction gas is reduced.

Insulator fuel can be reduced.

Since hydrogen is produced as a by-product, there is no need to use a reducing gas in the tail gas treatment device.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a process flow of a Claus-type sulfur recovery device.

Claims (1)

(57) [Claims] A raw material gas containing hydrogen sulfide and an oxygen-containing gas are introduced into a reaction combustion furnace to cause a thermal Claus reaction,
After cooling the reaction gas and separating elemental sulfur with a sulfur condenser, a catalytic Claus reaction is performed in the contact reactor, and the reaction gas is cooled, and elemental sulfur is further separated with a sulfur condenser to recover sulfur. In a Claus-type sulfur recovery method that increases the oxygen concentration, the oxygen-containing gas
30 to 50 mol% of oxygen-enriched air is used, the amount of oxygen supplied by the oxygen-enriched air and used for the reaction with hydrogen sulfide is 40 to 45 mol% of the amount of hydrogen sulfide in the raw material gas, and The hydrogen concentration in the exhaust gas discharged from the final sulfur condenser is increased to 3% by volume or more by rapidly cooling the outlet gas of the reaction combustion furnace to a temperature of 700 ° C. or less within 1 second. How to collect.