JPS5945035B2 - Coal gas purification method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying coal gas, and more particularly to a method for decomposing and removing ammonia contained in coal gas, and more specifically, a method for purifying coal gas in which ammonia is removed together with hydrogen sulfide. Relating to a gas purification method.

BACKGROUND ART The technology of synthesizing gaseous fuels consisting of hydrogen, carbon monoxide, methane, etc. by gasifying fossil fuels has been known for a long time.

In recent years, the use of coal as an energy source in place of oil has been reaffirmed, and power generation systems using coal as a fuel source are being considered.

However, in a power generation system using coal as a fuel source, it is economical and thermally efficient to burn the high-temperature gaseous fuel synthesized by coal gasification at a high temperature without lowering the temperature to operate the gas turbine. is considered an essential condition for process configuration.

The problem here is that sulfur and nitrogen, which are naturally contained in fossil fuels such as coal, turn into hydrogen sulfide and ammonia, respectively, during gasification, and each of them is released into the gaseous fuel after gasification. It is contained at a concentration of several percent from 11,000 pp.

Hydrogen sulfide is an extremely corrosive gas and is a serious source of pollution, and ammonia becomes nitrogen oxide when gaseous fuel is burned after gasification, which is also a serious source of pollution, so it is important to protect equipment such as gas turbines, For economical reasons, it must be removed before combustion.

Therefore, the development of technology for removing hydrogen sulfide and ammonia at high temperatures has been required as a key to the success of power generation systems using coal as a fuel source.

There are many examples in which the removal of hydrogen sulfide from high-temperature gases is required, not just synthetic fuels made from coal, but it is generally considered an extremely difficult technology.

Conventionally, a dry method using a solid removal agent formed into granules has been considered effective as a method for removing hydrogen sulfide from gas at high temperatures, and methods using calcium carbonate, dolomite, iron oxide, etc. Are known.

Among these removers, iron oxide is said to be the most excellent in terms of hydrogen sulfide removal rate, ease of recycling of the remover whose activity has deteriorated, and economic efficiency.

Iron oxide reacts with hydrogen sulfide at high temperatures to form iron sulfide as shown in equation (1).

Fe2O3 + 2H2S + H2 → 2FeS + 3H20 (1
) Iron oxide once converted to iron sulfide loses its ability to remove hydrogen sulfide, so it is required to be regenerated to restore its removal ability.

As a method for regenerating iron oxide, iron sulfide is brought into contact with air or a gas mixture of air and water vapor, and as shown in equations (2) and (3), it is returned to iron oxide with the by-product of sulfur dioxide gas or hydrogen sulfide. A method is being taken.

4FeS+70□→2 Fe 20s + 4 SO
2(2)2FeS+3H20→pe 20 a +
2 n 2 S + H2 (3) However, when removing hydrogen sulfide with iron oxide, water is produced as a by-product with the production of iron sulfide, so the moisture in the gas suppresses the hydrogen sulfide removal reaction shown by equation (1). Therefore, a certain concentration of hydrogen sulfide remains, which is determined by the gas temperature and the moisture concentration in the gas.

Further, the decomposition of ammonia by iron oxide is thought to be as shown in the following equation.

Fe2O3+3H2→2Fe+3H20(4)2Fex
N-+2xFe+N2 What is shown in FIG. 1 was made to demonstrate the mechanism of ammonia decomposition expressed by the above formulas (4) to (7).

That is, when a gas containing 1% ammonia is brought into contact with an iron oxide catalyst using helium gas, which does not participate in ammonia decomposition, as a diluent gas, A and a gas containing 10% hydrogen gas and 1% ammonia are obtained using helium gas as a diluent gas. This is a comparison of B when the two are in contact with each other.

When A is used for a gas that does not contain hydrogen gas, thermal decomposition of a small amount of ammonia occurs and hydrogen gas is generated.

This small amount of hydrogen gas reduces iron oxide to produce reduced iron according to equation (4), and the activity of this reduced iron decomposes ammonia according to equation (5), generating hydrogen gas that further reduces iron oxide.

In this way, reduced iron active in ammonia decomposition gradually increases, so that the ammonia decomposition rate increases until nearly 100% is decomposed.

On the other hand, in B, when the iron oxide is brought into contact with a gas containing hydrogen gas, which is a reducing gas, iron oxide is immediately reduced by the hydrogen and reduced iron that is active in decomposing ammonia is generated, so that the iron oxide is reduced to 100% within a short time after the start of gas contact. Nearby ammonia will now be decomposed.

Normally ammonia reacts with iron to form iron nitride, but at high temperatures iron nitride decomposes and separates into iron and nitrogen gas.

Therefore, when iron oxide is used for the decomposition of ammonia,
It was confirmed that reduced iron, which is produced when iron oxide is reduced with hydrogen, acts as a catalyst to decompose ammonia.

However, when iron oxide or a catalyst containing iron oxide, which is highly effective in removing hydrogen sulfide and decomposing ammonia, is applied to the decomposition of ammonia contained in real gas such as coal gas, serious problems occur and it is not practical. becomes inappropriate.

The cause of this serious problem is hydrogen sulfide and water, which are inevitably contained in coal gas and the like.

That is, hydrogen sulfide reacts with iron oxide according to equation (1) to form iron sulfide, and this iron sulfide has almost no activity for decomposing ammonia.

When ammonia is decomposed using iron oxide or a catalyst containing iron oxide, hydrogen sulfide can be removed using iron oxide etc. before starting the ammonia decomposition process, but 1
It is impossible to completely eliminate 00% from the viewpoint of reaction equilibrium.

Therefore, residual hydrogen sulfide that could not be removed in the hydrogen sulfide removal process using iron oxide, etc. flows directly into the ammonia decomposition process using iron oxide or a catalyst containing iron oxide, reacts with iron oxide, and becomes an inert substance for ammonia decomposition. Produces iron sulfide.

On the other hand, moisture in the coal gas interferes with the reduction reaction of iron oxide according to equation (4).

In other words, in the production reaction of reduced iron that is active against ammonia decomposition, since water is a byproduct, it greatly delays the reduction reaction of iron oxide according to equation (4), so that reduced iron is only produced gradually. I don't get it.

Figure 2 confirms the fact that hydrogen sulfide and water interfere with the ammonia decomposition reaction by iron oxide or a catalyst containing iron oxide. This shows the decomposition status of ammonia when brought into contact with.

Under condition C in Figure 2, although 14% hydrogen gas is contained, the iron oxide reduction reaction in equation (4) is delayed by the 5% water content, and ammonia is produced at a high decomposition rate. It appears that it takes a surprising amount of time before it begins to decompose.

Condition and Condition E are conditions in which hydrogen sulfide is contained in the CO gas, and the coal gas contains residual hydrogen sulfide.

Under condition E, the decomposition rate of ammonia gradually increases over time, but it settles at a low value of 30 to 40%, and a high decomposition rate cannot be expected.

This is because the reaction in which iron oxide is reduced with hydrogen is delayed by the presence of water, and iron oxide reacts with hydrogen sulfide during the reduction process to produce iron sulfide, which has sufficient activity against ammonia decomposition. It is based on the fact that it does not become reduced iron with .

Due to these unavoidable facts, a high decomposition rate cannot be expected when iron oxide or a catalyst containing iron oxide is applied to decompose ammonia in coal gas.

The present invention has been made in view of the above-mentioned points, and its purpose is to provide a coal gas purification method that can sufficiently increase the rate of decomposition and removal of ammonia contained in coal gas.

Another object of the present invention is to provide a method for purifying coal gas that can effectively remove hydrogen sulfide from coal gas and then decompose ammonia.

The present invention was made based on new facts discovered through detailed research on the mechanism of ammonia decomposition by iron oxide or a catalyst containing iron oxide, and supported by actual results based on the new facts. It has been experimentally determined that the cause of the extremely low decomposition rate of coal gas is the water and hydrogen sulfide contained in coal gas, and as a means to prevent interference from this water and hydrogen sulfide, the catalyst should be kept at least in a reduced iron state. For example, it is less susceptible to interference from water and hydrogen sulfide.
The first feature is to decompose ammonia in coal gas by bringing the catalyst in the reduced iron state into contact with coal gas, and further decompose hydrogen sulfide. The second feature is that the coal gas containing ammonia is brought into contact with a catalyst in an iron oxide state to remove hydrogen sulfide, and then the remaining coal gas is brought into contact with a catalyst in a reduced iron state to decompose ammonia. It is something.

The present invention will be explained below based on experimental data.

Figure 3 shows a packed bed reactor filled with a catalyst made of a granular mixture of alumina and iron oxide, and reduced with a reducing gas containing 10% hydrogen gas to completely convert the iron oxide into a reduced iron state. , 5% water and 250 ppr hydrogen sulfide at respective temperatures of 700°C (F) and 800°C (G).
This figure shows the change over time in the ammonia decomposition rate when ammonia was decomposed through coal gas having the composition shown in Table 2, including ri.

As shown in Figure 3, when a catalyst is used after converting to reduced iron, ammonia in the above composition is used to initiate contact, even though it contains hydrogen sulfide at a high concentration of 250 ppm and water at 5%. At the same time, it can be seen that it decomposes at a high decomposition rate of over 99% and maintains its decomposition ability for a long time.

When the contact was carried out at 800°C at 5v=ioooi/hr, it was confirmed that a high decomposition rate of 99% or more was maintained even after 45 hours.

Furthermore, Fig. 3H shows that coal gas having the composition shown in Table 3 containing 10% water and 250 ppm of hydrogen sulfide was produced at a temperature of 800°C after being made into a reduced iron state by the above-mentioned reduction operation using the same catalyst as above. This figure shows the change over time in the ammonia decomposition rate when ammonia is decomposed.

As shown in Figure 3H, if the iron oxide catalyst is once reduced and used in the reduced iron state, the ammonia decomposition rate hardly decreases even if the moisture content increases to 10%, and 98 %, and it is clear that the decomposition ability is maintained for a long time.

When contacted at 800° C. and SV=10001/hr, no change was observed in the decomposition rate even after 42 hours, confirming that a high decomposition rate was maintained.

): On the other hand, iron oxide was selected as the hydrogen sulfide remover, and a catalyst prepared by forming the mixture of alumina and oxide into granules was packed into a packed bed reactor, and water was removed in the iron oxide state without any reduction operation. 5-1
When passing coal gas having the composition shown in Table 4 containing 500 ppm of 0% hydrogen sulfide, ammonia is hardly decomposed, but is removed according to the reaction of hydrogen sulfide force x 1), and a small amount of hydrogen sulfide remains.

The residual hydrogen sulfide was as shown in Table 5, and maintained at a substantially constant value until just before the iron oxide contained in the catalyst packed in the packed bed was almost completely converted to iron sulfide.

The residual amount of hydrogen sulfide increases with the increase in moisture content and temperature, but it is all below 250 ppm.

When hydrogen sulfide is removed using iron oxide, the more hydrogen sulfide that remains, the more it will interfere with the decomposition of ammonia in the next step where ammonia is decomposed using a reduced iron-like catalyst. Hydrogen sulfide in gas 7
When removed using iron oxide at 00-800°C,
Since all remaining hydrogen sulfide is 250 ppm or less, the water concentration 5 containing 250 ppm hydrogen sulfide is
The fact that ammonia could be decomposed and removed from ~10% of coal gas at 700-800°C means that interfering factors were overcome under more severe conditions.

If the temperature of the coal gas to be purified by removing hydrogen sulfide and decomposing ammonia is high (and the moisture concentration is high), the concentration of hydrogen sulfide remaining after removing hydrogen sulfide using iron oxide will be high. However, when ammonia is subsequently decomposed using a catalyst in the reduced iron state, the rate of ammonia decomposition increases at higher temperatures, so the interfering effects of moisture and hydrogen sulfide on the reaction equilibrium are reduced. This does not pose a problem; in fact, the higher the temperature of the coal gas, the more advantageous it is to decomposing ammonia.

Furthermore, when the temperature of coal gas is relatively low, the absolute value of the concentration of hydrogen sulfide remaining after removing hydrogen sulfide using iron oxide is extremely small, regardless of the moisture concentration in the gas. Therefore, when ammonia is subsequently decomposed using a catalyst in the reduced iron state, the effect of the interfering factor becomes smaller, but the reaction rate of ammonia decomposition itself also becomes smaller, so it is possible to decompose and remove ammonia at a high decomposition rate. This requires a large amount of catalyst.

From a practical standpoint, the temperature at which ammonia can be decomposed at a sufficiently high decomposition rate with a sufficient amount of catalyst is 600°C or higher.

As mentioned above, if iron oxide or a catalyst mainly composed of iron oxide is once reduced and used in the reduced iron state, it is possible to overcome the interference of hydrogen sulfide and moisture and decompose ammonia at a sufficiently high decomposition rate. If hydrogen sulfide is removed using an iron oxide catalyst and then ammonia is decomposed using a reduced iron catalyst, hydrogen sulfide and ammonia in coal gas can be effectively removed. It is possible to achieve high-temperature purification and purification of coal gas.

In the above-mentioned experimental example, a catalyst prepared by molding a mixture of alumina and iron oxide into granules was filled into a reaction apparatus, and the catalyst was reduced with a reducing gas containing 10% hydrogen gas to completely transform the iron oxide into a reduced iron state. As mentioned above, it is the part in the reduced iron state that is active in decomposing ammonia, and alumina is added to carry iron and prevent sintering. It does not necessarily have to be a mixture of alumina and iron oxide (it can also be used; in addition to alumina, there are silica, viscosity, etc.).

Furthermore, since alumina does not play a role in the activity of decomposing ammonia, the amount added varies depending on the temperature required to prevent sintering.

The inventor found that if 50% alumina was added, the temperature would reach 900℃.
I know that it can be used up to

The hydrogen gas concentration of 10% is based on economic considerations and does not particularly limit the concentration, but if the hydrogen gas concentration is low, reduction will take a long time and is not economical, so a high concentration is preferable to a low concentration. .

Furthermore, it is not necessary to completely convert iron oxide into reduced iron; it is possible to decompose ammonia by partially converting it into reduced iron.

For example, coal gas contains hydrogen, so when coal gas is passed through iron oxide, the iron oxide is gradually reduced, partially producing reduced iron, and the ammonia in the coal gas is partially decomposed.

However, it takes a considerable amount of time to generate the amount of reduced iron necessary to decompose 90% or more of ammonia, and during this time, the decomposition of ammonia is insufficient and the iron is released.

Moreover, since the hydrogen sulfide contained in coal gas reacts with iron oxide in the process of being converted to reduced iron, iron sulfide, which is active against the decomposition of ammonia, is produced, and in the end, ammonia is not decomposed. The situation continues.

For this reason, in order to decompose ammonia with the highest efficiency for a given filling amount or weight, it is preferable that the iron be almost completely reduced to reduced iron.

Next, the present invention confirmed through the above experiments will be explained using some examples.

Figure 4 shows that because the temperature of the coal gas from which hydrogen sulfide and ammonia should be removed is high, the moisture and residual hydrogen sulfide in the coal gas have little effect of interfering with the ammonia removal process, and the reduced iron state for ammonia decomposition and removal is small. An example of the present invention applied to a system for removing hydrogen sulfide and ammonia when the activity of the catalyst is maintained for a long time with almost no deterioration and there is no need to regenerate the ammonia decomposition catalyst within the process. This is a sufrocess flow sheet.

Coal gas 1 generated in the gasifier is sent to a fluidized bed desulfurization reactor 31, where it comes into contact with iron oxide or a catalyst containing iron oxide, and hydrogen sulfide contained in the coal gas reacts with the iron oxide. The gas is removed and becomes the outlet gas 2.

The outlet gas 2 passes through two-stage cyclones 41 and 42, where entrained fine particles are separated, resulting in a gas 3 containing a small amount of residual hydrogen sulfide, which is sent to the ammonia decomposition reactor 33.

The fine particles separated from the outlet gas 2 leaving the desulfurization reactor 31 are returned to the desulfurization reactor 31 through 23.

The ammonia decomposition reactor 33 is filled with iron oxide or a catalyst containing iron oxide that has been reduced to a reduced iron state, and the ammonia contained in the coal gas 3 is decomposed and removed. Ru.

The gas 4 exiting the ammonia decomposition reactor 33 is purified coal gas from which hydrogen sulfide and ammonia have been removed.

In the desulfurization reactor 31, iron oxide partially converted to iron sulfide by reaction with hydrogen sulfide, or a catalyst containing iron oxide, is
1 and sent to an iron oxide regeneration reactor 32.

In the iron oxide regeneration reactor 32, iron sulfide is converted into (2) by supplying air or a mixed gas 11 of air and water vapor.
, (3), and iron oxide is regenerated.

The regenerated catalyst is extracted from 22 and sent to the desulfurization reactor 31.
It is returned to its original state and used in the hydrogen sulfide removal reaction.

The outlet gas 12 of the regeneration reactor 32 decomposes entrained fine particles in the cyclones 43 and 44, and then becomes regeneration gas 13 and is sent to the sulfur recovery step.

The fine particles separated from the gas 12 are returned to the regeneration reactor 32 via 24.

Next, regarding the example shown in FIG. 4, as an example of the operating conditions and results, the case where it was applied to coal gas 1 at 800° C. with the composition shown in Table 6 will be shown.

The iron oxide used for removing hydrogen sulfide in the desulfurization reactor 31 is a catalyst formed by forming a mixture of alumina and iron oxide into granules.

Hydrogen sulfide contained in the outlet gas 3 that exited the desulfurization reactor 31 was 200 ppm.

The ammonia decomposition reactor 33 is filled with a catalyst made of a granular mixture of alumina and iron oxide, and the iron oxide is reduced to a reduced iron state using a reducing gas containing hydrogen gas.

The coal gas 4 that exited the ammonia decomposition reactor 33 contains 90 ppm of ammonia and 200 ppm of hydrogen sulfide.
More than 99% of ammonia had been decomposed.

The mixture ratio of air and steam and temperature of the iron oxide regeneration gas 11 were adjusted so that the regeneration temperature was 800°C.

According to an embodiment of the present invention shown in FIG. 4, ammonia can be decomposed with sufficient desulfurization and a high decomposition rate through a very simple process, and coal gas can be purified at high temperatures. This makes it possible to realize a power generation system using coal and gas.

FIGS. 5 and 6 show other embodiments of the present invention, which differ from the embodiment shown in FIG. 4 in that the ammonia decomposition catalyst is regenerated within the process.

The embodiments shown in FIGS. 5 and 6 are used when tar in coal gas adheres to the ammonia decomposition catalyst and the ammonia decomposition ability deteriorates, or when the temperature of the coal gas itself is relatively low (residual sulfurization This is a flow sheet showing an example of applying the present invention to a case where the activity of an ammonia decomposition catalyst needs to be regenerated in a process, such as when the ammonia decomposition ability decreases due to the influence of hydrogen. FIG. 5 shows an example in which a packed bed type reactor is used as the ammonia decomposition reactor and the reduced iron regeneration reactor, and FIG. 6 shows an example in which a fluidized bed type reactor is applied to both.

First, the embodiment shown in FIG. 5 will be described.

Coal gas 1 generated in the gasifier enters the desulfurization reactor 31, where it reacts with iron oxide to remove hydrogen sulfide as iron sulfide.

In the outlet gas 2 of the desulfurization reactor 31, entrained solid particles are separated in cyclones 41 and 42 and returned to the desulfurization reactor 31 through 23, and the gas 3 is turned into a gas 3, which is passed through the valve 5 in the open state.
1 and enters the ammonia decomposition reactor 33.

The ammonia decomposition reactor 33 is filled with a catalyst in a reduced iron state produced by reducing iron oxide or a catalyst containing iron oxide.

Ammonia entering the ammonia decomposition reactor 33 is decomposed by this reduced iron.

The coal gas leaving the ammonia decomposition reactor 33 flows out through the open valve 53 and becomes purified coal gas 4.

The iron oxide catalyst, which has partially become iron sulfide through reaction with hydrogen sulfide in the desulfurization reactor 31, is taken out by 21 and enters the iron oxide regeneration reactor 32.

In the regeneration reactor 32, iron sulfide is oxidized by the regeneration gas 11, which is air or a mixed gas of air and water vapor (2
), iron oxide is regenerated as shown in the reaction formula (3).

The regenerated iron oxide catalyst is transferred to the regeneration reactor 32 through 22.
The hydrogen sulfide is taken out and sent to the desulfurization reactor 31, where it is used to remove hydrogen sulfide.

Regeneration gas 12 exiting regeneration reactor 32 passes through cyclone 43
The entrained solid particles are separated by 44 and returned to the regeneration reactor 32 through 24, where they become regeneration gas 13 and are sent to the sulfur recovery step.

In the reduced iron regeneration reactor 34, a reduced iron catalyst whose activity for ammonia decomposition has been partially reduced due to tar adhesion or production of iron sulfide is regenerated.

In the regeneration operation, first, tar or iron sulfide adhering to the reduced iron state catalyst is oxidized and removed using regeneration gas 15, which is air or a mixed gas mainly consisting of air and water vapor.
At the same time, the catalyst in the reduced iron state is also oxidized to iron oxide, and impurities and impurities are removed by oxidation.

At this time, the gas exiting the regeneration reactor passes through open valves 59, 62 and becomes regeneration gas 17, which is mixed with regeneration waste 13.

At this time, the valve is 55.6H! Closed.

When all the filling in the regeneration reactor 34 has been oxidized, the oxidation removal of impurities and the production of iron oxide have been completed, the valve 56.62
, open the valves 55 and 61, and supply the reducing gas 14 to the valve 55.
, 57 to the regeneration reactor 34.

In the regeneration reactor 34, the iron oxide is reduced to the reduced iron state, regaining sufficient activity for ammonia decomposition, and the gas exits as 16.

While ammonia is decomposed in the ammonia decomposition reactor 33 and reduced iron is regenerated in the regeneration reactor 34, the valves 51, 53, 57, and 59 are open, and the valves 52, 54,
58 and 60 are closed.

When the reduced iron regeneration operation in the regeneration reactor 34 is completed and a decreasing trend is observed in the ammonia decomposition activity in the ammonia decomposition reactor 33, the valves 51, 53, 57, 59 are closed, and the valves 52, 54, By opening 58 and 60, the operation is switched to decomposing ammonia in the regeneration reactor 34 and regenerating reduced iron in the ammonia decomposition reactor 33.

This switching operation is performed in rotation at appropriate intervals.

Next, the operating conditions and results of this example will be described based on an example.

Coal gas 1 has the composition shown in Table 7 at a temperature of 700°C.

When the hydrogen sulfide contained in the coal gas is removed using a catalyst made of a mixture of alumina and iron oxide shaped into granules, the amount of hydrogen sulfide remaining in the outlet gas 3 of the desulfurization reactor 31 is 7.
It was 5 ppm.

The ammonia decomposition reactor 33 is filled with a catalyst made of a granular mixture of alumina and iron oxide, and the iron oxide is reduced to a reduced iron state using a reducing gas containing hydrogen gas.

The coal gas 4 that exited the ammonia decomposition reactor 33 contains 85 ppm ammonia and 75 ppm hydrogen sulfide, which accounts for 99%
More ammonia had been decomposed.

The mixture ratio of air and steam and temperature of the iron oxide regeneration gas 11 were adjusted so that the regeneration temperature was 700°C.

The temperature of the reduced iron regeneration gas 15 and the mixing ratio of air and steam were adjusted so that the regeneration temperature was 600°C.

Further, as the iron oxide reducing gas 14, a reducing gas containing 10% hydrogen gas was used.

Next, the embodiment shown in FIG. 6 will be described.

Coal gas 1 generated in the gasifier enters the desulfurization reactor 31, where it reacts with iron oxide to remove hydrogen sulfide as iron sulfide.

The outlet gas 2 of the desulfurization reactor 31 flows through cyclones 41 and 42.
After separation of entrained solid fine particles by , and return operation by line 23 , it becomes desulfurized coal gas 3 and enters ammonia decomposition reactor 33 .

In the ammonia decomposition reactor 33, the reduced iron-like catalyst contacts the gas in a fluidized state and decomposes the ammonia in the gas.

The gas exiting the ammonia decomposition reactor 33 is transferred to the cyclone 4
At step 5.46, the entrained solid particles are separated and become purified coal gas 4.

The solid particles separated in the cyclones 45 and 46 pass through the line 28 and into the line 21 along with a part of the reduced iron catalyst in the ammonia decomposition reactor 33 which is extracted from the line 27.
from there to the iron oxide regeneration reactor 32.

The iron oxide catalyst, which has partially become iron sulfide through reaction with hydrogen sulfide in the desulfurization reactor 31 , is gradually extracted through the line 21 and sent to the iron oxide regeneration reactor 32 .

In the iron oxide regeneration reactor 32, particles coming from the desulfurization reactor 31 and the ammonia decomposition reactor 33 are oxidized, and iron oxide is regenerated and produced according to equations (2), (3) and the following equation.

4'Fe+30 −+ 2Fe203 (8)
A part of the iron oxide catalyst regenerated in the iron oxide regeneration reactor 32 is extracted from the line 22, sent to the desulfurization reactor 31, and used for removing hydrogen sulfide.

A portion is also extracted from the line 25 and sent to the reduced iron regeneration reactor 34.

In the reduced iron regeneration reactor 34, the reducing gas 14 and the iron oxide catalyst come into fluid contact, and the hydrogen contained in the reducing gas 14 reduces the iron oxide and converts it into a reduced iron state.

A portion of the regenerated catalyst converted into a reduced iron state is extracted from the regeneration reactor 34 through the line 26, sent to the ammonia decomposition reactor 33, and used as an ammonia decomposition catalyst.

The outlet gases 12.15 from the iron oxide regeneration reactor 32 and the reduced iron regeneration reactor 34 are fed into cyclones 43.4, respectively.
4 and 47 and 48, the solid particles are separated and returned to form regeneration gases 13 and 16, which are sent to the respective processing steps.

Next, the operating conditions and results of the example shown in FIG. 6 will be explained using an example.

Coal gas 1 has the composition shown in Table 8 at a temperature of 800°C.

The catalyst used throughout the system was a granular mixture of alumina and iron oxide.

Hydrogen sulfide remaining in the gas 3 exiting the desulfurization reactor 31 was 180 ppm.

The concentration of ammonia was almost the same as that in Coal Gas 1.

Ammonia was decomposed by contact with a reduced iron catalyst in the ammonia decomposition reactor 33, and the ammonia remaining in the outlet gas 4 was 45 ppm, meaning that 99.5% or more had been decomposed.

Hydrogen sulfide remained almost unchanged at 18 Qppm.

The iron oxide regeneration gas 11 and the reducing gas 14 were prepared in the same manner as in the example shown in FIG.

According to the embodiment of the present invention shown in FIG. 5, a high ammonia decomposition rate can be achieved relatively easily by adjusting the amount of catalyst packed in the ammonia decomposition reactor 33, which is a packed bed reactor. .

One embodiment of the present invention, shown in FIG. 6, has the advantage of utilizing the same catalyst throughout the system throughout desulfurization and ammonia decomposition, which can be effectively and economically combined with regeneration processes.

In the embodiments of the present invention shown in FIGS. 4, 5, and 6, catalysts manufactured by the same method can be used in the desulfurization section and the ammonia decomposition section, making the entire system economical. There is an effect that can be done.

Note that the present invention is not limited to the flow sheets specifically shown in FIGS. 4, 5, and 6.

According to the method for refining coal gas of the present invention as described above, ammonia is decomposed by a catalyst that is at least in the state of reduced iron, and ammonia in high-temperature coal gas can be decomposed at a high decomposition rate. By combining this method with the hydrogen sulfide removal operation using iron oxide, not only can the decomposition rate of ammonia be increased, but also effective purification of this type of gas can be performed in addition to hydrogen sulfide removal.

[Brief explanation of the drawings] Figure 1 is a characteristic diagram showing the relationship between the ammonia decomposition rate in ideal gas by iron oxide and changes over time based on the experimental results of the present inventor, and Figure 2 is a characteristic diagram showing the relationship between the rate of decomposition of ammonia in ideal gas by iron oxide and changes over time. Figure 3 is a characteristic diagram showing the relationship between the ammonia decomposition rate in coal gas and changes over time, and Figure 4 is a characteristic diagram showing the relationship between the ammonia decomposition rate in coal gas and changes over time. FIG. 5 and FIG. 6 are process flow sheets showing another embodiment of the present invention. 1... Coal gas, 11, 15... Regeneration gas, 14... Reducing gas, 31... Desulfurization reactor, 32... Iron oxide regeneration reactor, 33.
...Ammonia decomposition reactor, 34...Reduced iron regeneration reactor.

Claims (1)

[Claims] 1. A method for refining coal gas, which comprises bringing coal gas containing ammonia into contact with a catalyst containing at least iron in the state of reduced iron to decompose and remove the ammonia. . 2. A patent characterized in that the catalyst, whose activity for ammonia decomposition has decreased, is regenerated by oxidizing it using at least a mixed gas mainly composed of air, and then reducing it using a reducing gas containing hydrogen gas. Claim 1
Coal gas purification method described in section. 3. Bringing coal gas containing ammonia and hydrogen sulfide into contact with a catalyst containing at least iron oxide to remove the hydrogen sulfide, and then contacting the remaining coal gas with a catalyst containing at least iron in the state of reduced iron. A method for purifying coal gas, characterized in that the ammonia is decomposed and removed by contacting with the ammonia. 4 The catalyst with reduced activity for removing hydrogen sulfide,
Regeneration by oxidation using a mixed gas mainly consisting of at least air, and oxidizing the catalyst whose activity for ammonia decomposition has decreased using a mixed gas mainly consisting of at least air, and then containing hydrogen gas. 4. The method for refining coal gas according to claim 3, wherein the coal gas is regenerated by reduction using a reducing gas.