JP7708028B2 - Hydrocarbon production method, reduction furnace operation method, and pig iron production method - Google Patents

Description

The present invention relates to a method for producing hydrocarbons by separating and recovering high-purity CO2 from by-product gases, such as the top gas of a blast furnace or converter, particularly from by-product gases containing _CO2 and sulfur compounds such as _H2S and COS, by removing impurities other _{than CO2} , a method for operating a reduction furnace using the hydrocarbons produced by this method, and a method for producing pig iron by this operation method.

In recent years, there has been a demand to reduce carbon dioxide (CO ₂ ) emissions to prevent global warming, and suppressing CO ₂ emissions is an important issue in steelworks, which are large-scale emission sources, especially in blast furnaces. In a typical blast furnace, high-temperature air is blown in from the tuyere as blast gas, which reacts with reducing agents such as coke and pulverized coal to obtain carbon monoxide and hydrogen, which are then used to reduce iron ore. CO ₂ is generated in this process. In order to reduce CO ₂ emissions, it is necessary to capture the CO ₂ in the blast furnace gas and store or reuse it.

A known method for reusing _CO2 in steelworks is to use a catalyst to react _CO2 with _H2 to convert it into hydrocarbons such as methane ( _CH4 ), which is then reused as a reducing agent in the furnace. For example, Patent Document 1 describes a method in which _CO2 in the exhaust gas from a combustion furnace such as a hot stove is separated, then converted into _CH4 , and reused as a reducing agent in a blast furnace.

As a related technique for by-product gas processing, Patent Document 2 discloses a desulfurization process using a dry desulfurization agent that uses iron oxide. Similarly, Patent Document 3 discloses a _CO2 separation process that uses an amine-based absorbing solution.

JP 2014-5510 A Special Publication No. 6-31350 JP 2014-156379 A

The invention described in Patent Document 1 is configured to separate CO ₂ in steelworks gas and convert it to CH ₄ using a catalyst or the like. Steelworks gas also contains sulfur compounds such as hydrogen sulfide (H ₂ S), carbonyl sulfide (COS), and sulfur oxides (SOx) derived from coal used as a raw material. Here, Ni-based catalysts are known as CH ₄ conversion catalysts. It is known that the performance of this Ni-based catalyst deteriorates due to the flow of sulfur compounds. Therefore, when these sulfur compounds are mixed into the separated CO ₂ , not only does frequent catalyst replacement become necessary, but the instability of operation becomes a problem. Furthermore, since Ni-based catalysts are prone to catalyst deterioration due to carbon deposition in a CO atmosphere, in addition to desulfurization, CO removal is also required.

On the other hand, Patent Document 2 shows a desulfurization process using a dry desulfurization agent that uses iron oxide, but it is difficult to remove CO in conjunction with desulfurization, and there remains the problem that CO cannot be sufficiently removed.

Similarly, in the _CO2 separation process using an amine-based absorbing liquid described in Patent Document 3, it is difficult to remove _H2S and COS and separate _CO2 , and there remains a problem in that these impurities cannot be sufficiently removed.

Therefore, an object of the present invention is to solve the above problems and to propose a method for efficiently converting CO ₂ having a low concentration of sulfur compounds into hydrocarbons.

1. A gas separation step of separating _CO2 gas having a low concentration of sulfur compounds from a by-product gas containing _CO2 and sulfur;
A _CO2 conversion process for producing hydrocarbons by converting _CO2 contained in the _CO2 gas from the gas separation process using a catalyst,
The gas separation step includes:
an absorption tower withdrawal step of contacting the methanol absorption liquid supplied to the inside of the absorption tower with the by-product gas introduced into the absorption tower to cause the methanol absorption liquid to absorb components of the by-product gas, withdrawing a _CO2 -rich/S-rich absorption liquid having a large amount of _CO2 and sulfur compounds absorbed at a lower stage of the absorption tower, and withdrawing a _CO2 -rich absorption liquid having a large amount of _CO2 absorption at a middle stage of the absorption tower;
A _CO2 desorption step of introducing the CO2-rich/S-rich absorbing liquid into the middle part of _{a CO2} desorption tower, heating the CO2 _- rich/S-rich absorbing liquid to separate _CO2 and sulfur compound-containing gas, contacting the _CO2 and sulfur compound-containing gas with the _CO2 -rich absorbing liquid introduced into the upper part of the _CO2 desorption tower to absorb the sulfur compounds and extract _CO2 gas having a low sulfur compound concentration, and combining the liquid having absorbed the sulfur compounds with the _CO2- rich/S-rich absorbing liquid and heating it to obtain an S-rich absorbing liquid having a high _sulfur compound absorption amount;
A desorption tower extraction step of extracting the S-rich absorption liquid having a large amount of sulfur compounds obtained by the _CO2 desorption step at a lower stage of the _CO2 desorption tower;
A method for producing a hydrocarbon having the formula:

2. A sulfur compound desorption step of introducing the S-rich absorbent discharged from the lower stage of the _CO2 desorption tower into an S desorption tower to desorb sulfur compounds from the S-rich absorbent;
2. The method for producing hydrocarbons according to claim 1, further comprising:

3. The method for producing hydrocarbons according to 2 above, wherein in the sulfur compound desorption step, _N2 gas separated from air is blown into the S desorption tower.

4. The method for producing hydrocarbons according to 3 above, in which the _N2 gas is obtained by cryogenic separation of air, and heat exchange is performed between one or both of the _N2 and _O2 separated from the air and one or both of the various absorption liquids and various gases in the gas separation step.

5. The method for producing hydrocarbons according to any one of the above items 1 to 4, wherein in the _CO2 conversion step, the _CO2 gas from the _CO2 desorption step is mixed with _H2 gas to convert it into hydrocarbons ( _CH4 ).

6. The method for producing hydrocarbons according to any one of claims 1 to 5, wherein _H2 gas is introduced into the _CO2 desorption tower in the _CO2 desorption step.

7. The method for producing hydrocarbons according to 5 or 6, wherein the _H2 gas is obtained by vaporizing liquefied _H2 , and heat exchange is carried out between the liquefied _H2 and an absorption liquid discharged from the sulfur compound desorption step.

8. The method for producing hydrocarbons according to any one of 1 to 7, wherein the hydrocarbons obtained in the _CO2 conversion step are introduced into the _CO2 desorption step.

9. A method for operating a reduction furnace, comprising injecting the hydrocarbon obtained by the method according to any one of 1 to 8 into the reduction furnace as a _CO2 -derived reducing agent.

10. A method for producing pig iron, in which the reduction furnace is a blast furnace, and pig iron is produced by the reduction furnace operation method described in 9.

According to the method of the present invention, in a configuration in which _CO2 in a by-product gas, for example, blast furnace gas, is recovered and reused, it is possible to suppress the inflow of sulfur compounds into a _CO2 conversion facility, stabilize operations, and reduce the frequency of catalyst replacement. Furthermore, the obtained high-purity _CO2 is recovered and converted to produce hydrocarbons, which are then reused in a reduction furnace as a _CO2- derived reducing agent, thereby realizing the operation of a steelworks or the like that reduces _CO2 emissions.

FIG. 1 is a flow diagram showing a first embodiment of the present invention. FIG. 11 is a flow diagram showing a second embodiment of the present invention.

The process for producing hydrocarbons according to the present invention will now be described in detail with reference to FIG.
[First embodiment]
FIG. 1 shows a flow diagram of the process for separating and recovering high-purity _CO2 gas from by-product gas discharged from a reducing furnace such as a blast furnace or a converter.
As shown in FIG. 1, a by-product gas (hereinafter referred to as a raw material gas) G01 containing CO, CO ₂ , H ₂ S, and COS discharged from a reduction furnace A08 is compressed by a compressor A01, moisture in the gas is removed by a condenser A02, and the gas is introduced into an absorption tower A03.

In the absorption tower A03, methanol, which easily absorbs both _H2S and COS, is used as an absorbing liquid, and this methanol absorbing liquid (not shown) is introduced in advance from the top of the absorption tower A03. By using this methanol absorbing liquid, the introduced raw material gas G01 comes into contact with the methanol absorbing liquid in the absorption tower A03, and _H2S , COS, etc. contained in the raw material gas G01 are efficiently absorbed by the methanol absorbing liquid, making it possible to remove _H2S , COS, etc.

When the raw gas G01 is introduced into the absorption tower A03 and the gas comes into contact with the methanol absorption liquid, the sulfur compounds in the gas G01 are mainly absorbed into methanol in the lower part of the absorption tower A03, and _CO2 is mainly absorbed into methanol in the middle to upper parts of the absorption tower A03. As a result, gas G02 from which _CO2 and sulfur compounds have been removed is obtained at the top of the absorption tower A03. Since this gas G02 contains a large amount of CO and _H2 , it can be used for purposes such as obtaining heat by combustion, obtaining electricity by thermal power generation, and obtaining valuable materials by conversion using a catalyst.

Since _H2S and COS are more easily absorbed by methanol than _CO2 , the absorbing solution that accumulates at the bottom of the absorption tower A03 is a _CO2 -rich/S-rich absorbing solution with a large amount of _CO2 , _H2S , and COS absorbed. On the other hand, in the middle to upper stages of the absorption tower A03, the gas passing through the absorption tower A03 contains almost no _H2S or COS, so the amount of _{H2S and COS} absorbed is small, resulting in a _CO2 -rich absorbing solution with a large amount of _CO2 absorbed. These two types of absorbing solutions are extracted from the absorption tower A03 and supplied to the _CO2 desorption tower A04 in order to desorb the CO2 contained therein and obtain high-purity _CO2 gas, and it is necessary to separate _CO2 from _H2S and COS in this _CO2 desorption tower A04.

Here, the lower, middle, and upper stages of the absorption tower A03 refer to, for example, the middle stage in the height direction of the tower, from 0.3 to 0.7, with the lower stage being below this stage and the upper stage being above it.

The _CO2 desorption tower A04 is equipped with a heating device A04-02 such as a reboiler that heats the absorption liquid at the bottom of the tower. The _CO2 -rich absorption liquid extracted from the middle of the absorption tower A03 is transported to the top of the _CO2 desorption tower A04, and the _CO2- rich and S-rich absorption liquid extracted from the bottom of the absorption tower A03 is transported to the middle of the _CO2 desorption tower A04. That is, the CO2 _- rich absorption liquid is used to absorb the desorbed sulfur compound gas described below, so it is preferable that the temperature is low, but methanol vapor is generated by heating at the bottom of the desorption tower and the vapor moves to the top of the tower, resulting in heating the top of the tower. In order to alleviate this heating, it is preferable to introduce the _CO2- rich and S-rich absorption liquid from the middle of the _CO2 desorption tower A04 to contact it with methanol vapor, and to re-liquefy the methanol by cooling the vapor.

In the _CO2 desorption tower A04, the CO2 _- rich/S-rich absorbing solution and the _CO2 -rich absorbing solution are combined while repeatedly undergoing reactions of absorbing or desorbing _CO2 and S gases, and all of the combined absorbing solutions are heated here toward the heating device A04-02. In this heating process, mainly _CO2 and some sulfur compounds are desorbed from the combined absorbing solution. The _CO2 gas and sulfur compound gas after the desorption process are returned to the _CO2 desorption tower A04 and rise inside the tower. In this rising process, the sulfur compound gas is absorbed by the _CO2 -rich absorbing solution introduced from the top of the _CO2 desorption tower A04, and this absorbing solution falls toward the bottom of the tower A04, merges with the CO2 _- rich/S-rich absorbing solution at the middle of the tower A04, and is introduced again into the heating device A04-02. By repeating the above steps in the _CO2 desorption tower A04 and the heating equipment A04-02, the desorption of _CO2 from the absorbing liquid progresses and a CO2 _- rich gas is generated above the tower A04, while the sulfur compounds are reabsorbed into the absorbing liquid, and an S-rich absorbing liquid with a high sulfur compound concentration is generated on the heating equipment A04-02 side.

As described above, the _CO2- rich gas comes into contact with the CO2 _- rich absorbing solution from the middle of the absorption tower A03 at the upper stage of the _CO2 desorption tower A04, and the sulfur compounds are absorbed again by the absorbing solution. Here, the _CO2- rich absorbing solution from the middle of the absorption tower A03 contains very little _H2S and COS, so it is capable of absorbing _H2S and COS. Therefore, if the _CO2 gas and sulfur compound gas (which is CO2 _- rich but still contains _H2S and COS) rising from the lower stage of the _CO2 desorption tower A04 are brought into contact with the _CO2- rich absorbing solution, the _H2S and COS can be selectively absorbed and used to remove the _H2S and COS from the CO2 _- rich gas after the desorption process.

Therefore, as described above, the absorption tower A03 is provided with a structure that allows the absorption liquid to be extracted from the middle and lower stages of the absorption tower, so that the CO2 _- rich absorption liquid can be extracted from the middle stage and the CO2 _- rich and S-rich absorption liquid can be extracted from the tower bottom (lower stage). The extraction position from the middle stage of the absorption tower can be changed appropriately according to the degree of absorption of _H2S and COS.

In this manner, by contacting the CO2 _- rich gas generated from the lower stage of the _CO2 desorption tower A04 with the _CO2 -rich absorbing liquid in the upper stage of the tower, the _sulfur compound concentration in the CO2-rich gas G03 discharged from the top of the _CO2 desorption tower A04 can be sufficiently reduced.

It is preferable that the _CO2- rich gas G03 having a low concentration of sulfur compounds is converted into a hydrocarbon-rich gas G09 containing _CH4 in the _CO2 conversion equipment A11 and supplied to the reduction furnace A08 as a reducing agent. Specifically, the liquefied _H2 G07 is vaporized in the vaporizer A10, mixed with the CO2 _- rich gas G03, converted into a hydrocarbon-rich gas G09 containing _CH4 in the _CO2 conversion equipment A11, and can be blown into the reduction furnace A08 as a _CO2 -derived reducing agent. When the reduction furnace A08 is a blast furnace, pig iron can be produced by the operation method of blowing a _CO2- derived reducing agent into the blast furnace as described above.

On the other hand, the S-rich absorbing solution having a high concentration of sulfur compounds produced in the lower section (heating equipment A04-02) of the _CO2 desorption column A04 is transported to the upper section of the S desorption column A05.

This S desorption tower A05 is configured to circulate _N2- rich gas G06 from the bottom of the tower, and may further include a heating device A05-02 such as a reboiler that heats the absorption liquid at the bottom of the tower, as shown in the figure. The S-rich absorption liquid is transported to the top of the S desorption tower A05, where sulfur compounds are desorbed by contact with the _N2 -rich gas G06, and S-rich gas G04 is discharged from the top of the tower. This S-rich gas G04 may be released into the atmosphere after environmental load reduction treatment such as dilution, or may be partially oxidized by the Claus process or the like to recover it as sulfur.

On the other hand, a lean absorbent from which sulfur compounds have been desorbed is obtained at the bottom of the S desorption tower A05. The lean absorbent discharged from the S desorption tower A05 is cooled in a cooler A06 and is used again as an absorbent for absorbing _CO2 and sulfur compounds in the absorption tower A03.

The _N2- rich gas G06 circulated through the S desorption tower A05 can be, for example, N2 _- rich gas G06 purified from air G05 using an air separator A07. The _O2- rich gas G07 purified at the same time can be used in the reduction furnace A08. This configuration not only increases the temperature of the reduction furnace A08 to stabilize the operation of the reduction furnace, but also reduces the _N2 concentration in the _CO2- containing gas discharged from the reduction furnace A08, thereby increasing the _CO2 concentration.

The pressure in the absorption tower A03 is preferably 0.1 MPa or more and 5 MPa or less, more preferably 0.3 MPa or more and 0.99 MPa or less. By setting the pressure in this range, it is possible to promote the absorption of _CO2 and sulfur compounds while suppressing the absorption of impurities such as CO.

The _CO2 desorption tower A04 preferably has a pressure adjustment mechanism such as a back pressure valve. The pressure inside the _CO2 desorption tower A04 is preferably 0.01 MPa or more and 0.99 MPa or less, more preferably 0.1 MPa or more and 0.5 MPa or less. By setting the pressure in this range, it is possible to desorb _CO2 while suppressing evaporation of the absorbing solution.

Next, a second embodiment of the present invention will be described in detail with reference to FIG.
[Second embodiment]
Fig. 2 shows a flow diagram of a process for separating and recovering high-purity _CO2 gas from a raw material gas from a reduction furnace in an embodiment different from the embodiment shown in Fig. 1. Note that the same components as those shown in Fig. 1 are given the same reference numerals and will not be described.
That is, in the second embodiment, in addition to the configuration of the first embodiment shown in FIG. 1, the air separator A07 is a cryogenic separation type, and includes a _N2 heat exchanger A09 that exchanges heat with _N2 discharged from the air separator A07, a vaporizer A10 for liquefied _H2 G08, a _CO2 conversion facility A11, and a liquefied _H2 heat exchanger A12 that exchanges heat with the liquefied _H2 G08.

Here, the _N2 heat exchanger A09 and the liquefied _H2 heat exchanger A12 can perform heat exchange with the lean absorbing liquid discharged from the S desorption tower A05, for example, at the inlet side of the cooler A06, by a connection system not shown. That is, in the second embodiment, the lean absorbing liquid can be cooled by the cold heat of _N2 obtained by cryogenic separation (through the _N2 heat exchanger A09) and the cold heat obtained from the liquefied _H2 G08 (through the liquefied _H2 heat exchanger A12), and the load on the cooler A06 can be reduced.

Furthermore, the _CO2 desorption tower A04 is configured to introduce a portion of the hydrocarbon-rich gas G09 discharged from the _CO2 conversion equipment A11 and _H2 , thereby reducing the _CO2 partial pressure inside the _CO2 desorption tower A04 and promoting _CO2 desorption.

The _CO2- rich gas G03 discharged from the _CO2 desorption tower A04 flows into the _CO2 conversion equipment A11, where it is converted into hydrocarbons and the like, and a hydrocarbon-rich gas G09 is discharged. This gas G09 has a larger specific heat than when a mixed gas of only _CO2 and _H2 is used, and therefore has the effect of suppressing the temperature rise associated with the CO2 conversion in the _CO2 conversion equipment _A11 .

A part of the hydrocarbon-rich gas G09 is introduced again into the _CO2 desorption tower, and the remaining part is used in the reduction furnace A08. In this configuration, the use of the recovered _CO2 makes it possible to reduce the overall _CO2 emission amount.

In addition to the first and second embodiments described above, a flash facility may be provided to reduce the pressure of the liquid discharged from the absorption tower A03 to desorb the absorbed gas, and a compressor may be provided to circulate the desorbed gas back to the absorption tower A03. This configuration can further reduce the concentration of impurities such as CO.

Hydrocarbons were produced from the feed gas with the following composition according to the diagrams shown in Figures 1 and 2. The method of the present invention is characterized by the withdrawal of the absorbing liquid from the middle stage of the absorption tower A03. Therefore, the following calculations were performed to investigate the effect of withdrawing the absorbing liquid from the middle stage of the absorption tower.

That is, the composition of the raw material gas G01 is H ₂ : 31.0%, CO: 45.0%, CO ₂ : 23.0%, N ₂ : 1.0%, H ₂ S: 11 ppm, COS: 12 ppm in volume concentration. The operation conditions are: the flow rate of the raw material gas G01 is 430000 Nm ³ /h, the outlet pressure of the compressor A01 is 0.8 MPa, methanol is used as the absorption liquid, and it is introduced into the upper part of the absorption tower A03 at a flow rate of 3840 ton / h. The liquid withdrawal in the middle stage of the absorption tower is in the range of 0 to 80%, the temperature of the CO ₂ desorption tower reboiler A04-02 is 90 ° C, the temperature of the S desorption tower reboiler A05-02 is 95 ° C, and the liquid temperature at the outlet of the cooler A06 is -40 ° C.

Table 1 shows the correlation between the amount of liquid discharged from the middle stage of the absorption tower A03 and the CO concentration, _H2S concentration, and COS concentration in _{the CO2-} rich gas G03. As shown in Table 1, the CO concentration is reduced to 1% at each liquid discharge amount, which is 1/40 or less of the CO concentration in the raw gas. Therefore, it is presumed that when the CO2 _- rich gas G03 obtained according to the present invention is used, the deterioration of the catalyst due to CO in the _CO2 conversion equipment A11 can be sufficiently suppressed.

On the other hand, in Comparative Example 1, where the withdrawal amount was 0%, i.e., no withdrawal, both the _H2S concentration and the COS concentration were higher than those of the feed gas, and it is presumed that the catalyst installed in the downstream _CO2 conversion equipment would deteriorate quickly. In contrast, in Invention Examples 1, 2, 3, and 4, in which the absorption liquid was withdrawn from the middle of the tower, both the _H2S concentration and the COS concentration were reduced to 0.1 ppm or less, and catalyst deterioration could be sufficiently suppressed.

(Comparative Example 2)
When the raw gas G1 was subjected to chemical absorption by amine to separate _CO2 , the components of the gas obtained by this _CO2 separation were investigated in the same manner as above, and the results are shown in Table 2. As shown in the table, the gas obtained by _CO2 separation can have a _CO2 concentration of 99.9% or more and a CO concentration of 0.1% or less. However, since _H2S and COS are concentrated along with _CO2 , the sulfur concentration in the gas is high, and it is unavoidable that the catalyst in the downstream _CO2 conversion facility will be deteriorated.

(Comparative Example 3)
When dry desulfurization using iron oxide and copper oxide was applied to the raw gas G1 to separate _CO2 , the components of the gas obtained by this _CO2 separation were investigated in the same manner as above, and the results are shown in Table 2. As shown in the table, it is possible to reduce the _H2S and COS concentrations to 0.01 ppm or less. However, since the CO concentration is not reduced in this method, it is unavoidable to deteriorate the catalyst in the downstream _CO2 conversion equipment.

A01 Compressor A02 Condenser A03 Absorption tower A04 _CO2 desorption tower A05 S desorption tower A06 Cooler A07 Air separator A08 Reduction furnace A09 _N2 heat exchanger A10 Vaporizer A11 _CO2 conversion equipment A12 Liquefied _H2 heat exchanger A12
G01 Raw material gas G02 _CO2 , sulfur removal gas G03 _CO2- rich gas G04 S-rich gas G05 Air G06 _N2- rich gas G07 _O2- rich gas G08 Liquefied _H2
G09 Hydrocarbon-rich gas

Claims (11)

A gas separation step of separating _CO2 gas having a low concentration of sulfur compounds from a by-product gas containing _CO2 and sulfur;
A _CO2 conversion process for producing hydrocarbons by converting _CO2 contained in the _CO2 gas from the gas separation process using a catalyst,
The gas separation step includes:
an absorption tower withdrawal step of contacting the methanol absorption liquid supplied to the inside of the absorption tower with the by-product gas introduced into the absorption tower to cause the methanol absorption liquid to absorb components of the by-product gas, withdrawing a _CO2 -rich/S-rich absorption liquid having a large amount of _CO2 and sulfur compounds absorbed at a lower stage of the absorption tower, and withdrawing a _CO2 -rich absorption liquid having a large amount of _CO2 absorption at a middle stage of the absorption tower;
A _CO2 desorption step of introducing the CO2-rich/S-rich absorbing liquid into the middle part of _{a CO2} desorption tower, heating the CO2 _- rich/S-rich absorbing liquid to separate _CO2 and sulfur compound-containing gas, contacting the _CO2 and sulfur compound-containing gas with the _CO2 -rich absorbing liquid introduced into the upper part of the _CO2 desorption tower to absorb the sulfur compounds and extract _CO2 gas having a low sulfur compound concentration, and combining the liquid having absorbed the sulfur compounds with the _CO2- rich/S-rich absorbing liquid and heating it to obtain an S-rich absorbing liquid having a high _sulfur compound absorption amount;
A desorption tower extraction step of extracting the S-rich absorption liquid having a large amount of sulfur compounds obtained by the _CO2 desorption step at a lower stage of the _CO2 desorption tower;
having
A method for producing hydrocarbons, wherein _H2 gas is introduced into the CO2 desorption tower _{in the CO2} desorption step _. A sulfur compound desorption step of introducing the S-rich absorbent discharged from the lower stage of the _CO2 desorption tower into an S desorption tower to desorb sulfur compounds from the S-rich absorbent;
The method for producing hydrocarbons according to claim 1, further comprising: The method for producing hydrocarbons according to claim 2, wherein in the sulfur compound desorption step, _N2 gas separated from air is blown into the S desorption tower. The method for producing hydrocarbons according to claim 3, wherein the _N2 gas is obtained by cryogenic separation of air, and heat exchange is performed between one or both of _N2 and _O2 separated from air and one or both of various absorption liquids and various gases in the gas separation process. The method for producing hydrocarbons according to any one of claims 1 to 4, wherein in the _CO2 conversion step, the _CO2 gas from the _CO2 desorption step is mixed with _H2 gas to convert the CO2 gas into hydrocarbons ( _CH4 ). The method for producing hydrocarbons according to claim 5 , wherein the _H2 gas is obtained by vaporizing liquefied _H2 , and heat exchange is carried out between the liquefied _H2 and an absorption liquid discharged from the sulfur compound desorption process. A gas separation step of separating CO2 gas _having a low concentration of sulfur compounds from a by-product gas containing CO2 _and sulfur;
A _CO2 conversion process for producing hydrocarbons by converting _CO2 contained in the CO2 gas _from the gas separation process using a catalyst,
The gas separation step includes:
an absorption tower withdrawal step of contacting the methanol absorption liquid supplied to the inside of the absorption tower with the by-product gas introduced into the absorption tower to cause the methanol absorption liquid to absorb components of the by-product gas, withdrawing a CO2-rich/S-rich absorption liquid having a large amount of CO2 and sulfur compounds absorbed at a lower stage of the absorption tower _{, and} withdrawing a CO2-rich absorption liquid _having a large amount of CO2 absorption _at a middle stage of the absorption tower ;
A _CO2 desorption step of introducing the CO2 -rich/S-rich absorbing liquid into the middle part of a CO2 _desorption tower, heating the CO2-rich/S-rich absorbing liquid to separate CO2 _and sulfur compound-containing gas, contacting the CO2 _{and sulfur} compound-containing gas with the _CO2 -rich absorbing liquid introduced into the upper part of the _CO2 desorption tower to absorb the sulfur compounds and extract CO2 gas having a low sulfur compound concentration _, and combining the liquid having absorbed the sulfur compounds with the CO2 _- rich/S-rich absorbing liquid and heating it to obtain an S-rich absorbing liquid having a high sulfur compound absorption _amount ;
A desorption tower extraction step of extracting the S-rich absorption liquid having a large amount of sulfur compounds obtained by the CO2 desorption step at a lower stage of the _CO2 desorption tower _;
A sulfur compound desorption step of introducing the S-rich absorbent discharged from the lower stage of _the CO2 desorption tower into an S desorption tower to desorb sulfur compounds from the S-rich absorbent;
having
In the sulfur compound desorption step, _N2 gas separated from air is blown into the S desorption tower, and the N2 _gas is obtained by cryogenic separation of air. A method for producing hydrocarbons, in which heat exchange is performed between one or both of the N2 and O2 separated from the air _and one _or both of the various absorption liquids and various gases in the gas separation step . A gas separation step of separating CO2 gas _having a low concentration of sulfur compounds from a by-product gas containing CO2 _and sulfur;
A _CO2 conversion process for producing hydrocarbons by converting _CO2 contained in the CO2 gas _from the gas separation process using a catalyst,
The gas separation step includes:
an absorption tower withdrawal step of contacting the methanol absorption liquid supplied to the inside of the absorption tower with the by-product gas introduced into the absorption tower to cause the methanol absorption liquid to absorb components of the by-product gas, withdrawing a CO2-rich/S-rich absorption liquid having a large amount of CO2 and sulfur compounds absorbed at a lower stage of the absorption tower _{, and} withdrawing a CO2-rich absorption liquid _having a large amount of CO2 absorption _at a middle stage of the absorption tower ;
A _CO2 desorption step of introducing the CO2 -rich/S-rich absorbing liquid into the middle part of a CO2 _desorption tower, heating the CO2-rich/S-rich absorbing liquid to separate CO2 _and sulfur compound-containing gas, contacting the CO2 _{and sulfur} compound-containing gas with the _CO2 -rich absorbing liquid introduced into the upper part of the _CO2 desorption tower to absorb the sulfur compounds and extract CO2 gas having a low sulfur compound concentration _, and combining the liquid having absorbed the sulfur compounds with the CO2 _- rich/S-rich absorbing liquid and heating it to obtain an S-rich absorbing liquid having a high sulfur compound absorption _amount ;
A desorption tower extraction step of extracting the S-rich absorption liquid having a large amount of sulfur compounds obtained by the CO2 desorption step at a lower stage of the _CO2 desorption tower _;
having
In the CO2 conversion process, the _CO2 gas from the CO2 desorption process _is mixed with H2 gas to convert it into a hydrocarbon ₍ CH4 _{) ;
The} H2 gas is obtained by vaporizing liquefied H2 _, and heat exchange is carried out between the liquefied H2 _and the absorption liquid discharged from the sulfur compound desorption step . CO ₂ and sulfur-containing by-product gas to produce CO with low sulfur compound concentration. ₂ a gas separation step of separating gas;
The CO from the gas separation process ₂ CO contained in gas ₂ to produce hydrocarbons by catalytic conversion of CO ₂ A converting step,
The gas separation step includes:
The methanol absorbing liquid supplied to the inside of the absorption tower is brought into contact with the by-product gas introduced into the absorption tower, so that the components of the by-product gas are absorbed into the methanol absorbing liquid, and CO is discharged from the lower stage of the absorption tower. ₂ and CO, which absorbs a large amount of sulfur compounds. ₂ The rich and S-rich absorbing liquid is extracted, and the CO ₂ High absorption of CO ₂ an absorption tower withdrawal step of withdrawing a rich absorption liquid;
The CO ₂ Rich/S-rich absorbent solution ₂ The CO ₂ Heating the rich and S-rich absorbing solution ₂ Separating sulfur-containing gas and ₂ Sulfur compound-containing gas is treated with the CO ₂ The CO introduced into the upper stage of the desorption column ₂ The CO having a low concentration of sulfur compounds is produced by contacting the CO with a rich absorption liquid to absorb the sulfur compounds. ₂ The gas is extracted, and the liquid in which the sulfur compounds have been absorbed is ₂ The S-rich absorbent is mixed with the CO-rich and S-rich absorbent and heated to obtain an S-rich absorbent with a high sulfur compound absorption capacity. ₂ A desorption step;
The CO ₂ The S-rich absorbing liquid having a high sulfur compound absorption amount obtained in the desorption step is ₂ a desorption column withdrawal step of withdrawing the desorption column from a lower stage of the desorption column;
having
The CO ₂ In the desorption step, ₂ A process for the production of hydrocarbons, comprising introducing the hydrocarbons obtained in the conversion step. A method for operating a reduction furnace, comprising injecting hydrocarbons obtained by the method for producing hydrocarbons according to any one of claims 1 to 4 into the reduction furnace as a _CO2 -derived reducing agent. A method for producing pig iron, comprising the steps of: The reduction furnace according to claim 10 is a blast furnace; and The reduction furnace according to claim 10 is a blast furnace.