JPWO2009157434A1 - Carbon dioxide off-gas purification method, purification combustion catalyst, and natural gas production method - Google Patents

Abstract

In this carbon dioxide off-gas purification method, carbon dioxide off-gas is introduced into a catalytic combustor and subjected to oxidative decomposition treatment with a combustion catalyst to oxidatively decompose VOC and sulfur compounds contained in the carbon dioxide off-gas. The combustion catalyst is one or more metal oxides selected from the group consisting of zirconium oxide, titanium oxide and silicon oxide, and one or more noble metals selected from the group consisting of platinum, palladium and iridium. Including.

Description

The present invention relates to a method for purifying a gas containing carbon dioxide as a main component (hereinafter referred to as “carbon dioxide off-gas”), a combustion catalyst for purification, and a method for producing natural gas. More specifically, sulfur compounds such as hydrogen sulfide (H ₂ S) and mercaptans contained in carbon dioxide off-gas discharged from natural gas, oil-associated gas (hereinafter abbreviated as “natural gas”); benzene Sulfur compounds (excluding sulfur oxides) and VOCs in carbon dioxide off-gas by oxidative decomposition of volatile organic compounds (hereinafter referred to as "VOC") such as toluene, xylene, etc. with a combustion catalyst The present invention relates to a purification method and a purification combustion catalyst for reducing the concentration of the catalyst.
This application claims priority based on Japanese Patent Application No. 2008-162728 for which it applied to Japan on June 23, 2008, and uses the content here.

VOC is a gas in which light components such as organic solvents and petroleum products are released into the atmosphere, and is said to be a causative substance of photochemical smog and suspended particulate matter. For this reason, worldwide emission regulations have been put in place regarding VOCs.
In a conventional plant such as natural gas, off-gas is generated in a natural gas refining process for removing carbon dioxide and sulfur compounds contained in natural gas, and this off-gas contains hydrogen sulfide and VOC. VOC combustion catalysts are marketed by many manufacturers, but impurities such as hydrogen sulfide are generated in plants such as natural gas, so the off-gas purification method using VOC combustion catalysts has increased technical hurdles. The process was not established.
Therefore, at present, when the off-gas is released into the atmosphere, the off-gas is burned under a high temperature condition of about 900 ° C. by direct combustion (Thermal Incinerator) and then released into the atmosphere. However, the current off-gas treatment method by direct combustion is very expensive because the off-gas generated at room temperature is heated to about 900 ° C. and then burned.

  As a purification method of exhaust gas containing VOC, a purification method by catalytic combustion of exhaust gas containing organic silicon, VOC, carbon monoxide and the like is disclosed (for example, see Patent Document 1). Conventionally, organic silicon was considered as a poison for the combustion catalyst. However, in the exhaust gas purification method of Patent Document 1, the exhaust gas containing VOC is used for a long time by using a zeolite carrying a noble metal as a combustion catalyst. It became possible to purify. By the way, in plants such as natural gas, sulfur compounds such as hydrogen sulfide can be cited as poisoning substances for combustion catalysts. However, Patent Document 1 has not studied the resistance of combustion catalysts to sulfur compounds.

  Combustion catalysts for VOC decomposition include (1) those containing calcium salt, amorphous silica and copper compound, (2) those containing amorphous silica and copper compound, (3) crystalline silica and amorphous silica Those containing at least one of calcium salt and copper oxide, and (4) those containing at least one of crystalline silica and amorphous silica and copper oxide are disclosed (for example, see Patent Document 2). . Conventionally, noble metal catalysts such as platinum have been used for VOC combustion treatment. However, the combustion catalysts (1) to (4) can exhibit low-cost and equivalent combustion performance to noble metal catalysts. It became. However, even in Patent Document 2, the resistance of the combustion catalyst to the sulfur compound has not been studied.

  As a method of decomposing low-concentration methane emitted from plants such as natural gas and coal mines, preheat the mixed gas containing low-concentration methane to a temperature that allows catalytic combustion, then low-concentration methane in the mixed gas. Has been disclosed (see, for example, Patent Document 3). In this method, the amount of fuel input during preheating is reduced by using a cracked gas and a heat storage agent for preheating the mixed gas. As a result, methane can be released as carbon dioxide having a small warming potential without being released into the atmosphere as it is, and as a result, the total amount of greenhouse gas emissions can be reduced. Plants such as natural gas purify VOCs and sulfur compounds based on emission regulations (environmental standards). By the way, in patent document 3, the toxicity with respect to the combustion catalyst of the sulfur compound contained in the mixed gas containing low concentration methane and the decomposability | decomposability of a sulfur compound and VOC were not examined.

As a method of removing sulfur from a gas containing hydrogen sulfide, benzene, toluene, xylene, etc., in order to reduce leakage of sulfur compounds from the sulfur recovery device, carbonyl sulfide (COS) derived from hydrocarbons and carbon dioxide (2) A method of disposing at least one Claus catalyst imparted with hydrolytic ability of carbon sulfide (CS ₂ ) in a reactor is disclosed (for example, see Patent Document 4). In this method, as the Claus catalyst, a catalyst having at least one selected from alumina, titanium oxide and zirconia as a support and at least one selected from iron, cobalt, nickel, copper and vanadium as an active metal is used. It is done. However, in Patent Document 4, a Claus catalyst used in a sulfur recovery device is targeted, and the decomposability of VOC and sulfur compounds of gases mainly composed of carbon dioxide containing hydrogen sulfide and VOC has not been studied. .

Acid gas separation (AGR) for removing carbon dioxide in natural gas prevents co-absorbed VOC from evaporating in the low-pressure flash drum in front of the stripping tower (regeneration tower). A method of selectively evaporating and removing VOC while controlling temperature and pressure is disclosed (for example, see Patent Document 5). Since the VOC removed by this method is a self-combustible fuel, it is released into the atmosphere by a direct combustion process or is effectively used as a fuel. Further, in this method, the amine absorption liquid containing carbon dioxide and sulfur compound from which most of the VOC has been removed is converted into a gas containing a small amount of VOC, carbon dioxide and sulfur compound, and the amine absorption liquid in the diffusion tower. To be separated. The obtained gas is either directly burned or processed in a subsequent sulfur recovery device. When a sulfur recovery device is provided in the latter stage, if carbon dioxide and a small amount of VOC are supplied to the sulfur recovery device as they are, carbonyl sulfide (COS) and carbon disulfide (CS ₂ ) are by-produced, and the Claus catalyst Causes deterioration. When a hydrogen sulfide concentrating device is installed in the front stage of the sulfur recovery device and a gas mainly composed of carbon dioxide containing a small amount of VOC and hydrogen sulfide discharged from the upper part of the absorption tower is released to the atmosphere, about 900 ° C. It is necessary to directly burn the gas mainly composed of carbon dioxide under the high temperature conditions. Even when a sulfur recovery device is not provided in the subsequent stage, it is necessary to perform a direct combustion treatment as described above. Therefore, the method of Patent Document 5 involves a direct combustion process in the purification of VOCs and sulfur compounds contained in the above-mentioned gas containing carbon dioxide as a main component, and therefore has a high fuel consumption and a very high process cost. there were.

JP 2003-290626 A JP 2003-126696 A JP 2006-312143 A US Patent Application Publication No. 2004/0033192 US Pat. No. 6,605,138

Conventionally, mainly carbon dioxide containing sulfur compounds such as hydrogen sulfide, mercaptans, carbonyl sulfide, carbon disulfide, sulfur dioxide, VOC, or carbon monoxide, which are discharged from natural gas purification processes in plants such as natural gas. Carbon dioxide off-gas as a component had to be purified by thermal decomposition before being released into the atmosphere. For this reason, it is necessary to heat the gas having a temperature of about 40 ° C. to about 900 ° C. and directly burn it, which causes a high processing cost associated with a large amount of fuel consumption and a large amount of carbon dioxide emission. That was a problem.
Since the direct combustion method is a high-temperature treatment, it is necessary to use a heat-resistant material for the combustor and the heat exchanger, and the apparatus cost has been a problem.
The direct combustion method has a problem of thermal NOx generated by a process involving a flame.
In the direct combustion method with heat recovery, flue gas is circulated horizontally instead of vertically to recover heat, so the equipment occupies a large area, and there is a problem in plot layout in small plants and on-board plants. there were.
Furthermore, although VOC combustion catalysts are marketed by many manufacturers, they are resistant to sulfur compounds and there is no catalyst that can maintain a high purification rate of VOC and sulfur compounds for a long period of time. There was no established process.

Objects of the present invention include the following.
i) The concentration of the sulfur compound and VOC is lowered at a lower temperature than before by subjecting the carbon dioxide off-gas discharged from natural gas or the like to oxidative decomposition treatment with a combustion catalyst to the carbon dioxide off-gas containing sulfur compound and VOC.
ii) A high purification rate is maintained for a long time without generating thermal NOx.
iii) Reduce carbon dioxide emissions associated with large fuel consumption and lower processing costs.

  In the carbon dioxide off-gas purification method according to the present invention, a gas mainly containing carbon dioxide containing at least VOC and a sulfur compound of 50 ppmv or more and 10,000 ppmv or less is introduced into a catalytic combustor, and the catalyst combustor uses a combustion catalyst. By performing the oxidative decomposition treatment, the VOC and sulfur compound of the gas mainly containing carbon dioxide are oxidatively decomposed. The combustion catalyst is one or more metal oxides selected from the group consisting of zirconium oxide, titanium oxide and silicon oxide, and one or more noble metals selected from the group consisting of platinum, palladium and iridium. Including. The concentration of sulfur compounds (excluding sulfur oxides) in the gas after oxidative decomposition treatment is 5 ppmv or less.

In the present invention, the modes described below can be appropriately selected and combined.
The gas containing carbon dioxide as a main component may be exhausted in the purification of natural gas.
The reaction temperature of the oxidative decomposition treatment with the combustion catalyst is preferably 250 ° C. or higher and 650 ° C. or lower.
The pressure of the oxidative decomposition treatment with the combustion catalyst is preferably 0.01 MPa or more and 1 MPa or less.
It is preferable to decompose the VOC contained in the gas containing carbon dioxide as a main component into carbon dioxide by oxidative decomposition treatment.
The VOC preferably contains one or more selected from benzene, toluene, and xylene.

  By oxidizing and decomposing one or more selected from benzene, toluene and xylene contained in the gas containing carbon dioxide as a main component, the concentration of benzene in the gas containing carbon dioxide as a main component is 10 ppmv. The toluene concentration is preferably 50 ppmv or less or the xylene concentration is 50 ppmv or less.

It is preferable to supply the catalyst combustor after preheating the gas and / or air mainly composed of carbon dioxide.
Part or all of the preheating is selected from a heat exchanger using heat exchange with a combustion furnace, an electric line heater, a heat storage agent, and a gas mainly composed of carbon dioxide after oxidative decomposition treatment by a combustion catalyst. It is preferable to carry out by one or more means.
The catalytic combustor includes at least two catalytic combustion regions provided with a combustion catalyst when the upper limit of the reaction temperature is exceeded due to heat generation of the oxidative decomposition treatment, and between the catalytic combustion regions, after the oxidative decomposition treatment It is preferable to supply at least one selected from a gas mainly composed of carbon dioxide, air, and water, and to cool a gas mainly composed of carbon dioxide introduced into the catalytic combustor.

After removing mercury contained in the gas containing carbon dioxide as a main component, it is preferable to introduce a gas containing carbon dioxide as a main component after removing the mercury into the catalytic combustor.
The gas mainly composed of carbon dioxide is preferably a gas discharged from an acid gas separation device that separates and recovers an acid gas in a natural gas produced from a gas field by bringing the gas into contact with a liquid solvent.
The gas mainly composed of carbon dioxide is reduced in hydrogen sulfide by any one of a hydrogen sulfide concentrating device, a sulfur recovery device, and a tail gas processing device provided in a subsequent stage of the acidic gas separation device. The latter exhaust gas is preferred.

The combustion catalyst charged in the catalytic combustor preferably includes a base and a catalyst layer formed on the surface of the base and made of the metal oxide and the noble metal.
The substrate is preferably a honeycomb structure, a pellet body, or a sphere.
The substrate is preferably made of ceramics, metal oxide, or metal alloy.
The thickness of the catalyst layer is preferably 10 μm or more and 500 μm or less.
The content of the noble metal is preferably 0.1 g / liter or more and 10 g / liter or less per catalyst filling volume.
The specific surface area of the metal oxide is preferably 10 m ² / g or more and 300 m ² / g or less.
When the oxidative decomposition treatment using the combustion catalyst is performed, the oxygen concentration in the gas mainly composed of carbon dioxide is preferably 1% by volume or more and 15% by volume or less.

  The combustion catalyst for purifying carbon dioxide offgas according to the present invention is a combustion for subjecting at least a VOC and a sulfur compound contained in a gas mainly composed of carbon dioxide to an oxidative decomposition treatment at a reaction temperature of 250 ° C. or higher and 650 ° C. or lower. It is a catalyst. The combustion catalyst is one or more metal oxides selected from the group consisting of zirconium oxide, titanium oxide and silicon oxide, and one or more noble metals selected from the group consisting of platinum, palladium and iridium. Including.

The combustion catalyst includes a base and a catalyst layer formed on the surface of the base and made of the metal oxide and the noble metal, and the base is a honeycomb structure, a pellet, or a sphere. Is preferred.
The metal oxide is titanium oxide, and the content of the noble metal is preferably 0.1 g / liter or more and 10 g / liter or less per catalyst filling volume.
When the oxidative decomposition treatment using the combustion catalyst is performed, the oxygen concentration in the gas mainly composed of carbon dioxide is preferably 1% by volume or more and 15% by volume or less.

The combustion catalyst includes a honeycomb structure substrate having a large number of air passages, a metal oxide layer made of the metal oxide formed on the inner surface of the air passages, and at least a surface layer portion of the metal oxide layer. .1mg / cm ² or more, and a said noble metal is deposited at a density of 10 mg / cm ² or less, the substrate, the ceramic may be formed of a metal oxide, or a metal alloy.

The catalytic combustor includes a container having an inlet at one end and an outlet at the other end, and a plurality of combustion catalysts disposed in the container at an interval between the inlet and the outlet. Each of the combustion catalyst units has a honeycomb structure base provided with a large number of air passages through which carbon dioxide off gas passes, and a metal oxide formed of the metal oxide formed on the inner surface of the air passages. And the noble metal deposited at a density of 0.1 mg / cm ² or more and 10 mg / cm ² or less to at least the surface layer portion of the metal oxide layer, and the base is ceramic, metal oxide, or The inner diameter of the vent hole of the fuel catalyst unit that is made of a metal alloy and is close to the outlet port may be larger than the inner diameter of the fuel catalyst unit that is close to the inlet port.

  The method for producing natural gas according to the present invention includes a step of supplying raw natural gas to a slag catcher and separating the raw natural gas into a liquid phase and a vapor phase by the slag catcher, and carbon dioxide as a main component from the vapor phase. And an acid gas removing step for separating the carbon dioxide offgas containing VOC and sulfur compound, a moisture removing step for removing the condensed moisture by cooling the raw material gas after separating the carbon dioxide offgas, and after removing the moisture A heavy fraction removal step of fractionating a raw material gas by a distillation column to remove heavy hydrocarbons, and an offgas purification step of treating the carbon dioxide offgas by any of the carbon dioxide offgas purification methods described above. .

  According to the carbon dioxide off-gas purification method of the present invention, sulfur compounds having a strong toxic and irritating odor such as hydrogen sulfide and mercaptan contained in carbon dioxide off-gas can be purified and discharged as SOx. By using one or more metal oxides selected from the group consisting of zirconium oxide, titanium oxide, and silicon oxide as the combustion catalyst, the combustion catalyst is deteriorated by sulfation of SOx produced by oxidative decomposition treatment. Can be reduced. By using one or more kinds of noble metals selected from the group of platinum, palladium, and iridium as combustion catalysts, these noble metals have high oxidation activity in a low temperature range, and therefore carbon dioxide at a lower temperature than before. The off-gas oxidation reaction can proceed. Since metal oxides such as zirconium oxide, titanium oxide and silicon oxide have little sulfur adhesion to sulfur compounds and are not easily affected, they are stable with almost no change in form. The structure is maintained, the oxidative decomposition performance is less deteriorated with time, and the oxidative decomposition performance can be maintained over a long period. In addition, carbon dioxide off-gas can be oxidized and decomposed at low cost without generating thermal NOx and with low carbon dioxide emissions.

  Further, according to the method for producing natural gas according to the present invention, natural gas can be produced at low cost while efficiently treating off-gas.

It is the schematic which shows an example of the purification apparatus of the carbon dioxide off gas used in 1st embodiment of the purification method of the carbon dioxide off gas which concerns on this invention. It is the schematic which shows the 1st example of the collection | recovery apparatus of the carbon dioxide off gas processed with the purification method of this invention. It is the schematic which shows the 2nd example of the collection | recovery apparatus of the carbon dioxide off gas processed with the purification method of this invention. It is the schematic which shows the 3rd example of the collection | recovery apparatus of the carbon dioxide off gas processed with the purification method of this invention. It is the schematic which shows an example of the purification apparatus of the carbon dioxide off-gas used by 2nd embodiment of the purification method of this invention. It is the schematic which shows the carbon dioxide off gas purification apparatus of the direct combustion system used with the purification method of the conventional carbon dioxide off gas. 6 is a graph showing the relationship between the measured value and the calculated value of the reaction rate of the oxidation reaction of benzene by the combustion catalyst produced in Example 2. It is a graph which shows the relationship between the reaction temperature by the combustion catalyst produced in Example 2, and the conversion rate of benzene. It is the schematic which shows the test apparatus used for a combustion catalyst performance test. It is a graph which shows the relationship between the elapsed time from the reaction start by the combustion catalyst produced in Example 2 and Comparative Examples 2 and 4, and the conversion rate of benzene. It is a flowchart which shows one Embodiment of the manufacturing method of the natural gas which concerns on this invention. It is a longitudinal cross-sectional view which shows an example of the catalytic combustor which can be used for this invention. It is a perspective view of the combustion catalyst unit used for the catalyst combustor.

  Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments unless otherwise specified.

(1) First Embodiment FIG. 1 is a schematic view showing an example of a carbon dioxide off-gas purification apparatus used in the first embodiment of the carbon dioxide off-gas purification method of the present invention.
This carbon dioxide off-gas purification device (hereinafter abbreviated as “purification device”) 10 includes a heater 11 for heating a gas mainly composed of carbon dioxide (carbon dioxide off-gas) to a predetermined reaction temperature, and heating. Before introduction into the vessel 11, a preheater 12 for preheating carbon dioxide offgas and / or air and a combustion catalyst for subjecting the carbon dioxide offgas heated by the heater 11 to oxidative decomposition treatment were provided. The catalyst combustor 13 is connected to the catalyst combustor 13 and the flow paths 14 to 26 for flowing various gases.

As the heater 11, means such as a combustion furnace, an electric line heater, a heat storage agent, a heat exchanger using heat exchange with carbon dioxide off-gas after oxidative decomposition treatment by a combustion catalyst in the catalytic combustor 13 is used.
As the preheater 12, means such as a combustion furnace, an electric line heater, a heat storage agent, a heat exchanger using heat exchange with carbon dioxide off-gas after oxidative decomposition treatment by a combustion catalyst in the catalytic combustor 13 is used.

As the combustion catalyst filled in the catalytic combustor 13, a combustion catalyst including a base and a catalyst layer made of a metal oxide and a noble metal formed on the surface of the base is used.
An oximeter (not shown) is provided in the middle of the flow path 25 or 26 connected to the exhaust port of the catalytic combustor 13.

As the substrate, a honeycomb structure, a sphere, a pellet, or the like is used.
As the material of this substrate, cordierite (2MgO ₂ · 2Al ₂ O ₃ · 5SiO ₂ ), glass fiber, zirconia oxide, titanium oxide, fecroalloy, stainless steel and other ceramics excellent in heat resistance and substrate strength, metal oxide Or a metal alloy.
The magnitude | size of a base | substrate is not specifically limited, According to the amount of combustion catalysts required for the processing amount of one carbon dioxide off gas, it sets suitably.

  When the substrate is made of a honeycomb structure, a catalyst layer made of a metal oxide and a noble metal is formed on the inner wall surface of the cell of the honeycomb structure. When the substrate is made of pellets or spheres, a catalyst layer made of a metal oxide and a noble metal is formed on the outer surface of the substrate.

When a honeycomb structure is used, the number of cells is preferably 10 cpi ² (number of cells per inch square) or more and 1000 cpi ² or less, more preferably 100 cpi ² or more and 500 cpi ² or less.
When the number of cells of the honeycomb structure is less than 10 cpi ² , the total surface area of the catalyst layers provided on the inner wall surface of the cells becomes small, and the carbon dioxide off-gas cannot be efficiently oxidized and decomposed by the combustion catalyst. If the number of cells in the honeycomb structure exceeds 1000 cpi ² , the size of the cells decreases, it becomes difficult to form a catalyst layer on the inner wall surface of the cells, and the pressure loss in the honeycomb structure increases, resulting in The honeycomb structure may be damaged.

12 and 13 show an example of the catalytic combustor 13 that can be used in the present invention. The catalytic combustor 13 has a cylindrical or rectangular tube-shaped container 212 having an inlet 214 at one end (upper end in this example) and an outlet 216 at the other end (lower end). The inlet 214 is connected to the flow path 24 and the outlet 216 is connected to the flow path 25. The upper part and the lower part of the container 212 are tapered in a tapered shape toward the inlet port 214 and the outlet port 216. An annular flange 218 is formed at the upper and lower ends of the container 212 so that piping connection can be made. A plurality of combustion catalyst units 220A to 220I are disposed in the straight body portion of the container 212 at intervals in the longitudinal direction of the container, and the off-gas introduced from the inlet 214 is the combustion catalyst units 220A to 220I. , In order, and exit from the outlet 216. A gap is formed between adjacent combustion catalyst units.
When the catalyst substrate is a honeycomb structure, the air gap between these units serves to rectify the gas channeling. This is because when gas is fed to the honeycomb structure, the gas cannot diffuse in the direction perpendicular to the flow, but rectification can be improved by providing a gap between the units.
Moreover, you may connect the coolant supply path which is not shown in figure to each of these space | gap. Furthermore, through these coolant supply passages, at least one selected from gas, air, and water mainly composed of carbon dioxide after oxidative decomposition treatment is supplied, and the temperature of the downstream combustion catalyst unit is lowered, Reaction conditions may be controlled. This control may be feedback control by automatically opening and closing the valves of the respective coolant supply paths in accordance with the output of the temperature sensor provided downstream of the catalyst combustor 13 and controlling the supply amount of the cooling fluid. .

  Each of the combustion catalyst units 220A to 220I has a plate shape having a constant thickness, and is configured by arranging rectangular parallelepiped catalyst blocks 222 as shown in FIG. All of the catalyst blocks 222 are fixed to the inner wall of the container 212 by a support structure (not shown). The catalyst block 222 has a substrate composed of a square frame portion 224 and a honeycomb structure portion 226 arranged in a fine lattice pattern inside the frame portion 224. The honeycomb structure portion 226 in this example is a square lattice, but may be a hexagonal lattice, a triangular lattice, or a round hole. The inside of each lattice is a cell (air passage) that reaches a constant inner diameter from the upper end to the lower end, and off-gas flows evenly through these cells. The cell density is preferably in the above-mentioned range, but is not limited thereto. The base material may be as described above. By using the catalyst block 222 having such a honeycomb structure, the efficiency of the catalytic reaction can be enhanced while suppressing the gas flow path resistance.

  In this embodiment, the inner diameter of the air passage (cell) of the fuel catalyst unit near the outlet 216 is made larger than the inner diameter of the fuel catalyst unit near the inlet 214. More specifically, the cell inner diameter (channel cross-sectional area) increases in three stages in the order of the combustion catalyst units 220A to 220C, 220D to 220F, and 220G to 220I. As the cell inner diameter increases in this way, the flow resistance is reduced even when the offgas is heated by heat generation and the gas flow rate is accelerated in the process of the offgas flowing from the inlet 214 to the outlet 216. There is an advantage that can be suppressed. Since the combustible substance in the off gas burns when passing through the combustion catalyst units 220A to 220I, the off gas is heated and the flow rate is increased. For this reason, when the combustion catalyst units 220A to 220I have the same cell inner diameter, the flow resistance is increased in the downstream combustion catalyst unit, and the flow resistance of the catalyst combustor 13 as a whole is increased. .

  The rate of change of the inner diameter of the cell is S2 when the cross-sectional area of the individual cells of the most upstream combustion catalyst unit 220A is S1, and the cross-sectional area of the most downstream combustion catalyst unit 220I is S2. It is preferably about 1 to 1/5 times S1. More preferably, it is 1-1 / 3 times. In this embodiment, the cell inner diameter (channel cross-sectional area) is increased in three stages in the order of the combustion catalyst units 220A to 220C, 220D to 220F, and 220G to 220I. The total number of combustion catalyst units may be changed. In this embodiment, the number of combustion catalyst units 220 is nine, but the present invention is not limited to this. Generally, about 1 to 30 is preferable from the viewpoint of cost.

A metal oxide layer made of a metal oxide is formed on the surface of each of the combustion catalyst units 220A to 220I including the inner surface of each cell (air passage). The metal oxide is zirconium oxide _(ZrO 2), titanium oxide _(TiO 2), one kind or two or more materials selected from the group consisting of silicon oxide (SiO ₂₎ can be used. Particularly preferred is titanium oxide or zirconium oxide.

A noble metal is attached to at least the surface layer portion of the metal oxide layer at a density of 0.1 mg / cm ² or more and 10 mg / cm ² or less. The noble metal is preferably one or more selected from the group consisting of platinum (Pt), palladium (Pd), and iridium (Ir). Particularly preferred is platinum (Pt). Within the above range, the effect as a combustion catalyst is good. A more preferable noble metal adhesion density is 0.001 mg / cm ² or more and 0.1 mg / cm ² or less. Within this range, the performance is further enhanced.

Examples of combinations of noble metals and metal oxides include Pt / ZrO ₂ , Pt / CeO ₂ .ZrO ₂ , Pt / TiO ₂ , Pt / SiO ₂ , Pd / ZrO ₂ , Pd / CeO ₂ .ZrO ₂ , Pd / Examples include TiO ₂ , Pd / SiO ₂ , Ir / ZrO ₂ , Ir / CeO ₂ .ZrO ₂ , Ir / TiO ₂ , and Ir / SiO ₂ . Particularly preferred from the viewpoint of performance and cost are (Pt / ZrO ₂ , Pt / TiO ₂ ).

  The thickness of the catalyst layer composed of such a metal oxide and a noble metal is preferably 10 μm or more and 500 μm or less, more preferably 20 μm or more and 100 μm or less. When the thickness of the catalyst layer is less than 10 μm, it is difficult to efficiently disperse the noble metal on the support. If the distribution is non-uniform, it is difficult to improve the processing efficiency of the oxidative decomposition process using the combustion catalyst. When the thickness of the catalyst layer exceeds 500 μm, cost is increased, and the pressure loss increases because the inner diameter of the cell is reduced.

  The content (supported amount) of the noble metal is preferably 0.1 g / liter or more and 10 g / liter or less, more preferably 1 g / liter or more and 5 g / liter or less. When the content of the noble metal is less than 0.1 g / liter, the catalytic activity is lowered, and it is necessary to increase the reaction temperature of the oxidative decomposition treatment of carbon dioxide off gas, resulting in an increase in the treatment cost. When the content of the noble metal exceeds 10 g / liter, although the catalytic activity increases, the material cost increases and it is not practical.

  The noble metal does not form a dense film, but is preferably distributed on the surface and inside of the metal oxide as fine particles having a particle diameter of about 0.1 to 10 μm. The distribution of the noble metal may be attached only to the surface of the metal oxide layer, or may be distributed at a substantially uniform concentration throughout the thickness direction of the metal oxide layer, or in the thickness direction of the metal oxide layer. The concentration distribution may be such that the concentration is higher on the surface side, but the concentration is preferably higher on the surface side in terms of cost and reaction efficiency.

  The metal oxide preferably has an average particle size of 0.01 μm or more and 50 μm or less, more preferably 0.5 μm or more and 10 μm or less. When the average particle diameter of the metal oxide is less than 0.01 μm, the viscosity becomes high when it is made into a slurry when coating, which is not practical. When the average particle diameter of the metal oxide exceeds 50 μm, it is difficult to form a uniform slurry because the particles settle, and the coating layer is likely to be uneven when the slurry is supported, and the support is made of a noble metal made of a metal oxide. It becomes difficult to disperse uniformly with respect to the surface of the substrate, and the total surface area of the noble metals exposed on the surface of the support becomes small, resulting in a low catalytic activity.

The metal oxide preferably has a BET specific surface area (hereinafter referred to as “specific surface area”) of 10 m ² or more and 300 m ² or less, more preferably 10 m ² or more and 100 m ² or less. That is, the metal oxide layer is not a dense film but is microscopically porous. When the specific surface area of the metal oxide is less than 10 m ² , no improvement in the treatment efficiency of the oxidative decomposition treatment by the combustion catalyst is observed. Even if the specific surface area of the metal oxide exceeds 300 m ² , the noble metal can be supported, but the specific surface area decreases due to heat resistance, water resistance, change of form due to sulfur, etc. Therefore, the catalytic activity becomes low and is not practical.

  The combustion catalyst is not limited to the honeycomb structure as described above, and pellets, spheres, or irregularly shaped particles may be packed in a column with a gap between them. The type, concentration, thickness, and the like of the substrate, metal oxide, and noble metal may be the same as those of the honeycomb type catalyst described above. In this case, the size of the catalyst particles is preferably 0.1 mm or more and 50 mm or less as an average particle diameter, and more preferably 2 mm or more and 20 mm or less. When the average particle size is less than 0.1 mm, the contact efficiency between the carbon dioxide off-gas and the catalyst is high, but the pressure loss increases. When the average particle diameter exceeds 50 mm, the pressure loss can be kept low, but the contact efficiency between the carbon dioxide off-gas and the catalyst deteriorates and is not practical.

A method for producing the combustion catalyst will be described. A metal oxide, a sol (binder) of this metal oxide, and a polar solvent are mixed with a mortar, a lye machine, a kneader or the like to prepare a metal oxide-containing slurry. The blending mass ratio between the metal oxide and the sol (binder) of this metal oxide is preferably in the range of 95/5 to 30/70.
Water (pure water) is the best polar solvent, but polar organic solvents such as alcohols such as methanol, ethanol and propanol, ethers such as diethyl ether and tetrahydrofuran, esters, nitriles, amides and sulfoxides. Can also be used.

Metal oxide-containing slurry is applied to the surface of the substrate (inner wall surface for honeycomb structure, outer surface for sphere or pellet), and excess slurry is removed by air blowing. The substrate coated with the metal oxide-containing slurry is dried at 100 ° C. or higher and 200 ° C. or lower for 1 hour or longer with a dryer.
The substrate is baked in a baking furnace at 400 ° C. or more and 600 ° C. or less for 1 hour or more and 8 hours or less to form a layer made of a metal oxide on the surface of the substrate.
As the metal oxide, either an organic salt or an inorganic salt can be used. Examples of the organic salt include acetate, acetylacetonate, and cyanate. Examples of the inorganic salt include nitrate and chloride. Examples thereof include salts.

An aqueous solution of a noble metal compound (noble metal compound) and a polar solvent are mixed to prepare a noble metal compound solution having a predetermined concentration. As the noble metal compound, either an organic salt or an inorganic salt can be used. Examples of the organic salt include acetate, acetyl acetonate, and cyan salt, and examples of the inorganic salt include nitrate and chloride. Etc. are exemplified.
A noble metal compound solution is applied to the surface of the metal oxide layer, the layer made of the metal oxide absorbs this solution, and excess solution is removed by air blowing.
The substrate coated with the noble metal compound solution is dried at 100 ° C. or higher and 200 ° C. or lower for 1 hour or longer with a dryer.
This substrate is baked in a baking furnace at 400 ° C. or higher and 600 ° C. or lower for 1 hour or longer, and if necessary, reduced in a hydrogen stream at 400 ° C. or higher and 600 ° C. or lower, and the surface of the substrate is metal A combustion catalyst having a catalyst layer made of an oxide and a noble metal is obtained.

Next, a carbon dioxide off-gas purification method using the purification apparatus 10 will be described.
In the carbon dioxide off-gas purification method of this embodiment, carbon dioxide off-gas is introduced into the purification device 10 through the flow path 14 and air for auxiliary combustion (hereinafter referred to as “support combustion” from the flow path 18 into the purification device 10. Abbreviated as “air”).

Carbon dioxide off-gas is mainly composed of carbon dioxide, hydrogen sulfide (H ₂ S), mercaptan (R-SH, R is an organic group) of 50 ppmV or more and 10,000 ppmV or less, carbonyl sulfide (COS), carbon disulfide (CS ₂ ). ), A gas containing at least a sulfur compound such as sulfur dioxide (SO ₂ ).
Examples of the carbon dioxide off-gas include a gas discharged by a natural gas refining process in a natural gas or petroleum-related gas plant.
In addition to sulfur compounds, carbon dioxide off-gas includes VOCs such as benzene, toluene, and xylene, and may include carbon monoxide, methane, water, and the like.
The VOC contained in the carbon dioxide off gas contains at least one of 50 ppmv or more and 2000 ppmv or less of benzene, 100 ppmv or more and 2000 ppmv or less of toluene, and 100 ppmv or more and 2000 ppmv or less of xylene.

The auxiliary combustion air is used as an oxidant for the burner fuel of the heater 11 and then used as an oxidant for carbon dioxide off-gas in the catalytic combustor 13. In the burner of the heater 11, as compared with the catalytic combustor 13, containing a high concentration of oxygen is indispensable for achieving stable combustion. The catalytic combustor 13 can be combusted with a low concentration of oxygen compared to the burner combustion conditions.
Furthermore, in the heater 11, since the combustion exhaust gas and the carbon dioxide off gas are mixed, the heater 11 can be used for raising the temperature of the carbon dioxide off gas without losing the amount of heat held by the combustion exhaust gas, so that the thermal efficiency is high.
Therefore, the auxiliary combustion air is effectively used not only as an oxidant for carbon dioxide off-gas but also as an oxidant for the heater 11.

When the carbon dioxide off gas is not preheated (β = 1), the carbon dioxide off gas is supplied to the heater 11 through the flow path 16.
When the carbon dioxide off gas is preheated (β = 0), the carbon dioxide off gas is supplied to the preheater 12 via the flow path 15, and the preheater 12 preheats the carbon dioxide off gas to a predetermined temperature, Carbon dioxide off-gas is supplied to the heater 11 via the channel 17 and the channel 16. The preheating of the carbon dioxide off gas in the preheater 12 reduces the energy consumption (fuel consumption) when the temperature of the carbon dioxide off gas in the heater 11 is raised to a temperature higher than the oxidation decomposition treatment temperature by the combustion catalyst in the catalytic combustor 13. To be done.

When the auxiliary combustion air is not preheated (α = 1), the auxiliary combustion air is supplied to the heater 11 via the flow path 20.
When the auxiliary combustion air is preheated (α = 0), the auxiliary combustion air is supplied to the preheater 12 through the flow path 19, and after preheating the auxiliary combustion air to a predetermined temperature in the preheater 12, the flow path 21, The auxiliary combustion air is supplied to the heater 11 through the flow path 20. This preheating of the auxiliary combustion air in the preheater 12 reduces the energy consumption (fuel consumption) in the heater 11 when the auxiliary combustion air is heated to a temperature higher than the oxidation decomposition treatment temperature by the combustion catalyst in the catalytic combustor 13. Done for.

  In the preheating of the carbon dioxide off gas and the auxiliary combustion air in the preheater 12, either the carbon dioxide off gas or the auxiliary combustion air is preheated to a predetermined temperature, or both the carbon dioxide off gas and the auxiliary combustion air are preheated to a predetermined temperature. May be. In order to reduce the device cost, the preheater 12 may be omitted.

  The preheating temperature of the carbon dioxide off gas and the auxiliary combustion air in the preheater 12 is preferably 100 ° C. or higher and 400 ° C. or lower. When the preheating temperature of the carbon dioxide off gas and the auxiliary combustion air is low, the energy consumption (fuel consumption) when the temperature of the carbon dioxide off gas is raised above the oxidation decomposition treatment temperature by the combustion catalyst in the heater 11 increases. .

  In this embodiment, it is preferable to perform part or all of the carbon dioxide off-gas and the auxiliary combustion air in the preheater 12 by one or more means selected from the above means. Among these means, if a heat exchanger using heat exchange with the carbon dioxide off-gas after oxidative decomposition treatment by the combustion catalyst in the catalytic combustor 13 is used, it is not necessary to separately supply energy (heat) required for preheating. Therefore, it is excellent in thermal efficiency and processing costs can be reduced.

  In the heater 11, the fuel gas introduced into the purification device 10 through the flow path 22 becomes combustion exhaust gas after combustion in auxiliary combustion air, and then mixed with carbon dioxide off-gas, and the mixed gas is heated. Then, the temperature is raised to the reaction temperature (250 ° C. or higher, 650 ° C. or lower) of the oxidative decomposition treatment with the combustion catalyst in the catalytic combustor 13. Specifically, the temperature of the mixed gas is preferably 350 ° C. or more and 500 ° C. or less by the heater 11.

  The fuel gas is a gas containing methane, ethane, propane, n-butane, i-butane and the like.

  The mixed gas heated to a predetermined temperature by the heater 11 is supplied to the catalytic combustor 13 filled with the combustion catalyst, and the carbon dioxide off gas is brought into contact with the carbon dioxide off gas. To convert sulfur compounds such as hydrogen sulfide, mercaptan, carbonyl sulfide, carbon disulfide, and sulfur dioxide contained in the carbon dioxide off-gas into sulfur oxide (SOx). VOCs such as benzene, toluene and xylene contained in carbon dioxide off-gas are converted into carbon dioxide by oxidative decomposition treatment. When carbon monoxide is contained in the carbon dioxide off gas, the carbon monoxide is converted into carbon dioxide.

  In the oxidative decomposition treatment of carbon dioxide offgas by the combustion catalyst, the reaction temperature is preferably 250 ° C. or higher and 650 ° C. or lower, more preferably 350 ° C. or higher and 550 ° C. or lower. When the reaction temperature of the oxidative decomposition treatment with the combustion catalyst is less than 250 ° C., the oxidative decomposition reaction of the sulfur compound and VOC contained in the carbon dioxide off-gas does not proceed sufficiently. When the reaction temperature of the oxidative decomposition treatment with the combustion catalyst exceeds 650 ° C., the combustion catalyst is deteriorated by heat, and the purification rate of carbon dioxide off-gas cannot be kept high for a long time. The material of the catalytic combustor needs to be a heat-resistant material, which increases the material cost. The amount of fuel consumed for the oxidative decomposition treatment increases, the processing cost increases, and the amount of carbon dioxide emission increases. Furthermore, there is a possibility that thermal NOx is generated. In any embodiment, the difference between the temperature when entering the first combustion catalyst and the temperature when leaving the last combustion catalyst is about 30 to 300 ° C, more preferably about 50 to 200 ° C. preferable. If it is too large, the passage resistance will increase, resulting in adverse effects such as changing the pressure conditions of the upstream process and having to install a vacuum pump or a high chimney in the downstream.

  In the catalytic combustor 13, in the oxidative decomposition treatment of the carbon dioxide off gas, the pressure of the carbon dioxide off gas (the pressure of the carbon dioxide off gas supplied to the catalytic combustor 13) is preferably 0.01 MPa or more and 1 MPa or less, and more preferably. Is 0.05 MPa or more and 0.15 MPa or less. If the pressure of the carbon dioxide off gas is 0.2 MPa or more and 1 MPa or less, the volume of the carbon dioxide off gas is reduced, the residence time in the catalytic combustor 13 is shortened, the treatment efficiency is improved, and the treated carbon dioxide off gas is reduced. Since the power can be recovered by the gas expander before being released into the atmosphere, the processing cost can be reduced. When the pressure of the carbon dioxide off gas is less than 0.05 MPa, the volume of the carbon dioxide off gas is large, the residence time in the catalytic combustor 13 becomes long, and the processing efficiency deteriorates. When the pressure of the carbon dioxide off gas exceeds 1 MPa, the catalytic combustor 13 and its upstream equipment become pressure vessels, which increases the cost of the apparatus, necessitates compression power such as auxiliary combustion air, and increases the operating cost. Become.

The pressure of the carbon dioxide off gas is appropriately adjusted according to the carbon dioxide off gas recovery device to be described later and the release (discharge) destination of the treated carbon dioxide off gas.
In the conventional direct combustion type carbon dioxide off gas purification method, the treated carbon dioxide off gas is released into the atmosphere. Therefore, the carbon dioxide off-gas recovery device is operated at a pressure as close to atmospheric pressure as possible.
However, in some carbon dioxide off-gas recovery apparatuses, the amine solution is flashed at a high pressure of 0.5 to 1 MPa without using an amine regeneration tower, or about 180 ° C. using an amine solution with high heat resistance. The amine regeneration tower is operated at a high temperature of 0.5 to 1 MPa. In this case, a high-pressure carbon dioxide off-gas of 0.5 to 1 MPa is generated.

  In general, the higher the pressure, the smaller the gas volume, so the gas residence time in the catalytic combustor is shortened, and the catalytic combustor can be made smaller. Since the high-pressure gas can recover the power by the gas expander before being released into the atmosphere, the processing cost can be reduced. Therefore, when the carbon dioxide off-gas pressure in the catalytic combustor 13 is released into the atmosphere, the carbon dioxide off-gas pressure in the catalytic combustor 13 is 0.01 corresponding to the pressure of the carbon dioxide off-gas generated in the carbon dioxide off-gas recovery device. ˜1 MPa.

  By performing oxidative decomposition treatment with a combustion catalyst in the catalytic combustor 13, the concentration of sulfur compounds (excluding sulfur oxides) contained in the carbon dioxide off-gas becomes 5 ppmV or less. VOCs such as benzene, toluene, and xylene contained in the carbon dioxide off gas have a benzene concentration of 10 ppmV or less, a toluene concentration of 50 ppmV or less, and a xylene concentration of 50 ppmV or less by oxidative decomposition treatment.

  As the flow rate of the auxiliary combustion air supplied to the catalytic combustor 13 together with the carbon dioxide off-gas increases, the amount of fuel gas input for raising the temperature to the reaction temperature of the oxidative decomposition treatment increases and the thermal efficiency deteriorates. Catalytic combustion so that the concentration of oxygen contained in the treated carbon dioxide off-gas measured by an oxygen concentration meter provided in the latter stage is 0.5 to 15% by volume, more preferably 0.5 to 5% by volume. It is preferable to control the amount of auxiliary combustion air supplied to the vessel 13.

  The treated carbon dioxide off gas discharged from the catalyst combustor 13 is introduced into the preheater 12 through the flow path 25. When the preheater 12 is a heat exchanger, in this heat exchanger, either carbon dioxide off-gas after processing and carbon dioxide off-gas or auxiliary combustion air before processing, or carbon dioxide off-gas and auxiliary combustion before processing. Heat exchange with both of the air is performed, and the carbon dioxide off-gas or auxiliary combustion air before treatment is preheated to a predetermined temperature.

  The treated carbon dioxide off-gas (including sulfur oxide (SOx)) that has passed through the preheater 12 is discharged from the purification device 10 via the flow path 26.

In the carbon dioxide off-gas purification method of this embodiment, after removing mercury such as organic mercury, ionic mercury and elemental mercury contained in the carbon dioxide off-gas, catalytic combustion of the carbon dioxide off-gas after removing the mercury is performed. It is preferable to introduce into the vessel 13. The process of removing mercury contained in the carbon dioxide off gas is performed before introducing the carbon dioxide off gas into the purification apparatus 10 or before introducing the carbon dioxide off gas into the heater 11 in the purification apparatus 10. .
The removal process of mercury contained in the carbon dioxide off gas is performed by an adsorption process such as activated carbon.

  Thus, after removing mercury contained in carbon dioxide offgas in advance, by performing oxidative decomposition treatment of carbon dioxide offgas in the catalytic combustor 13, mercury contained in carbon dioxide offgas is released into the atmosphere. Thus, this mercury can be prevented from adversely affecting the human body and ecosystem.

Next, a method for recovering carbon dioxide offgas treated by the carbon dioxide offgas purification method of the present invention will be described.
The carbon dioxide off-gas treated by the carbon dioxide off-gas purification method of the present invention includes, for example, (1) acid gas separation in which acid gas in natural gas produced from a gas field is separated and recovered by contacting with a liquid solvent. Gas discharged from the apparatus, and (2) most of the hydrogen sulfide in any one of the hydrogen sulfide concentrating device, the sulfur recovery device, and the tail gas processing device provided in the subsequent stage of the acid gas separation device. Exhaust gas etc. after removing is mentioned.

  With reference to FIG. 2, a method for recovering carbon dioxide off-gas from natural gas produced from a gas field will be described. FIG. 2 is a schematic view showing a first example of a carbon dioxide off-gas recovery apparatus processed by the carbon dioxide off-gas purification method of the present invention. This carbon dioxide off-gas recovery device (hereinafter abbreviated as “recovery device”) 30 forms an acid gas separation device (Acid Gas Removal, AGR). In the carbon dioxide off-gas recovery method using the recovery device 30, first, natural gas produced from the gas field is supplied to the absorption tower 31 via the flow path 35.

In the absorption tower 31, carbon dioxide contained in natural gas is a main component, and hydrogen sulfide, trace amounts of sulfur compounds (mercaptan, carbonyl sulfide, carbon disulfide, sulfur dioxide), and VOC (benzene, toluene, xylene), etc. The impurity gas composed of hydrocarbons is selectively absorbed by the chemical absorption liquid or the physical absorption liquid (hereinafter collectively referred to as “absorption liquid”) in the absorption tower 31. The natural gas absorbed in the absorption liquid is discharged as a purified gas from the top of the absorption tower 31 via the flow path 36 and is collected in a product or another processing step.
The absorbing solution that has absorbed the impurity gas may be extracted from the bottom of the absorption tower 31 and then supplied to the flash drum 32 via the flow path 37 after the pressure is lowered. It may be lowered.
In the flash drum 32, light hydrocarbons are recovered through the flow path 38 as flash gas.
The absorption liquid from which the light hydrocarbons have been removed is extracted from the bottom of the flash drum 32 and supplied to the regeneration tower 33 via the flow path 39.
By heating the regeneration tower 33 to a predetermined temperature, the impurity gas is released from the absorbing liquid as carbon dioxide off gas, and the carbon dioxide off gas is supplied to the flash drum 34 via the flow path 40.
The absorption liquid from which the carbon dioxide off-gas has been released is extracted from the bottom of the regeneration tower 33, supplied to the absorption tower 31 via the flow path 41, and reused.
A part of the absorption liquid extracted from the bottom of the regeneration tower 33 is supplied to the regeneration tower 33 through the flow path 42 and again subjected to a treatment (heating) for releasing carbon dioxide off-gas.

In the flash drum 34, carbon dioxide off-gas is recovered as flash gas. The recovered carbon dioxide off-gas is discharged from the flash drum 34 via the flow path 43 and supplied to the purification device as shown in FIG.
A very small amount of absorption liquid mixed in the carbon dioxide off gas is extracted from the bottom of the flash drum 34 and supplied to the regeneration tower 33 via the flow path 44.

Referring to FIGS. 3 and 4, most of the hydrogen sulfide concentrating device, the sulfur recovery device, and the tail gas processing device provided in the subsequent stage of the acidic gas separation device shown in FIG. A method for recovering the exhaust gas after removing hydrogen sulfide as carbon dioxide off-gas will be described.
FIG. 3 is a schematic view showing a second example of the carbon dioxide off-gas recovery apparatus processed by the carbon dioxide off-gas purification method of the present invention. 3, the same components as those of the recovery apparatus shown in FIG. 2 are denoted by the same reference numerals, and the description thereof is omitted.

  In the carbon dioxide off-gas recovery method using the recovery device 50, first, the carbon dioxide off-gas A discharged from the recovery device 30 is sulfided through the flow path 43 together with the gas from which moisture has been removed after the tail gas treatment. It supplies to the absorption tower 51 of a hydrogen concentrator (Acid Gas, Enrichment, AGE).

In the absorption tower 51, an impurity gas comprising a large amount of hydrogen sulfide, a small amount of carbon dioxide, a sulfur compound (mercaptan, carbonyl sulfide, carbon disulfide), and VOC (benzene, toluene, xylene) contained in the carbon dioxide off-gas A. Are selectively absorbed by the chemical absorption liquid or the physical absorption liquid (hereinafter collectively referred to as “absorption liquid”) in the absorption tower 51. A carbon dioxide off-gas B containing a trace amount of a sulfur compound (hydrogen sulfide, mercaptan, carbonyl sulfide, carbon disulfide, sulfur dioxide), VOC, carbon monoxide and the like is discharged from the top of the absorption tower 51 through the flow path 56. , And supplied to the purification device as shown in FIG.
The absorbing solution that has absorbed the impurity gas is extracted from the bottom of the absorption tower 51 and supplied to the regeneration tower 52 of the hydrogen sulfide concentrating device via the flow path 57.

By heating the regeneration tower 52 to a predetermined temperature, the impurity gas is released from the absorption liquid as a hydrogen sulfide enriched gas, and this hydrogen sulfide enriched gas is supplied to the flash drum 53 via the flow path 58.
The absorption liquid from which the hydrogen sulfide-concentrated gas has been released is extracted from the bottom of the regeneration tower 52, supplied to the absorption tower 51 through the flow path 59, and reused.
A part of the absorption liquid extracted from the bottom of the regeneration tower 52 is supplied to the regeneration tower 52 via the flow path 60 and again subjected to a treatment (heating) for releasing the hydrogen sulfide-enriched gas. .

In the flash drum 53, the hydrogen sulfide concentrated gas is recovered as flash gas. The recovered hydrogen sulfide concentrated gas is discharged from the flash drum 53 via the flow path 61 and supplied to a sulfur recovery unit (Sulfur Recovery Unit, SRU) 54 including a combustor and a multistage Claus reactor. .
A very small amount of absorbing liquid mixed in the hydrogen sulfide concentrated gas is extracted from the tower bottom of the flash drum 53 and supplied to the regeneration tower 52 via the flow path 62.

In the sulfur recovery device 54, most of the sulfur content is recovered as single sulfur by the oxidative decomposition treatment of the hydrogen sulfide concentrated gas using the fuel gas and auxiliary combustion air supplied from the flow path 63 into the sulfur recovery device 54. .
A tail gas mainly composed of nitrogen containing a small amount of sulfur compound (hydrogen sulfide, carbonyl sulfide, carbon disulfide, sulfur dioxide) and carbon dioxide is discharged from the sulfur recovery device 54, and the fuel gas supplied from the flow path 64 and Auxiliary combustion air and hydrogen supplied from the flow path 65 are supplied to a tail gas treatment device (TGT) 55 including a hydrotreatment reactor via the flow path 66.

In the tail gas processing device 55, sulfur compounds other than hydrogen sulfide (carbonyl sulfide, carbon disulfide, sulfur dioxide) are reduced to hydrogen sulfide. The obtained hydrogen sulfide is discharged from the tail gas processing device 55, supplied to the absorption tower 51 via the flow path 67, and recirculated.
Water contained in the hydrogen sulfide discharged from the tail gas processing device 55 is discharged from a drainage channel 68 provided in the middle of the channel 67.

FIG. 4 is a schematic view showing a third example of the carbon dioxide off-gas recovery apparatus processed by the carbon dioxide off-gas purification method of the present invention.
In FIG. 4, the same components as those of the recovery device shown in FIGS. 2 and 3 are denoted by the same reference numerals, and the description thereof is omitted.

  In the carbon dioxide off-gas recovery method using the recovery device 70, first, the carbon dioxide off-gas A discharged from the recovery device 30 is sulfided through the flow path 43 together with the gas from which moisture has been removed after the tail gas treatment. It supplies to the absorption tower 51 of a hydrogen concentrator.

In the absorption tower 51, an impurity gas comprising a large amount of hydrogen sulfide, a small amount of carbon dioxide, a sulfur compound (mercaptan, carbonyl sulfide, carbon disulfide), and VOC (benzene, toluene, xylene) contained in the carbon dioxide off-gas A. Are selectively absorbed by the chemical absorption liquid or the physical absorption liquid (hereinafter collectively referred to as “absorption liquid”) in the absorption tower 51. A carbon dioxide off-gas B containing a trace amount of a sulfur compound (hydrogen sulfide, mercaptan, carbonyl sulfide, carbon disulfide, sulfur dioxide), VOC, carbon monoxide and the like is discharged from the top of the absorption tower 51 and passed through the flow path 56. And supplied to the channel 66.
The absorbing solution that has absorbed the impurity gas is extracted from the bottom of the absorption tower 51 and supplied to the regeneration tower 52 of the hydrogen sulfide concentrating device via the flow path 57.

By heating the regeneration tower 52 to a predetermined temperature, the impurity gas is released from the absorption liquid as a hydrogen sulfide enriched gas, and this hydrogen sulfide enriched gas is supplied to the flash drum 53 via the flow path 58.
The absorption liquid from which the hydrogen sulfide-concentrated gas has been released is extracted from the bottom of the regeneration tower 52, supplied to the absorption tower 51 through the flow path 59, and reused.
A part of the absorption liquid extracted from the bottom of the regeneration tower 52 is supplied to the regeneration tower 52 via the flow path 60 and again subjected to a treatment (heating) for releasing the hydrogen sulfide-enriched gas. . Further, a part of the absorption liquid extracted from the bottom of the regeneration tower 52 is supplied to the absorption tower 71 of the tail gas processing apparatus via the flow path 74.

In the flash drum 53, the hydrogen sulfide concentrated gas is recovered as flash gas. The recovered hydrogen sulfide concentrated gas is discharged from the flash drum 53 via the flow path 61 and supplied to the sulfur recovery device 54.
A very small amount of absorbing liquid mixed in the hydrogen sulfide concentrated gas is extracted from the tower bottom of the flash drum 53 and supplied to the regeneration tower 52 via the flow path 62.

In the sulfur recovery device 54, most of the sulfur content is recovered as single sulfur by the oxidative decomposition treatment of the hydrogen sulfide concentrated gas using the fuel gas and auxiliary combustion air supplied from the flow path 63 into the sulfur recovery device 54. .
A small amount of sulfur compounds (hydrogen sulfide, carbonyl sulfide, carbon disulfide, sulfur dioxide) and tail gas mainly composed of nitrogen containing carbon dioxide were discharged from the sulfur recovery device 54 and discharged from the top of the absorption tower 51. The carbon dioxide off gas B, the fuel gas and auxiliary combustion air supplied from the flow path 64, and the hydrogen supplied from the flow path 65 are supplied to the tail gas processing device 55 via the flow path 66.

In the tail gas processing device 55, sulfur compounds other than hydrogen sulfide (carbonyl sulfide, carbon disulfide, sulfur dioxide) contained in the tail gas and the carbon dioxide off gas B are reduced to hydrogen sulfide. The obtained tail gas containing hydrogen sulfide and carbon dioxide off-gas B are discharged from the tail gas processing device 55 and supplied to the absorption tower 71 of the tail gas processing device via the channel 67.
The water contained in the tail gas and the carbon dioxide off gas B discharged from the tail gas processing device 55 is discharged from a drainage channel 68 provided in the middle of the flow path 67.

In the absorption tower 71, hydrogen sulfide contained in the tail gas and the carbon dioxide off-gas B is selectively absorbed by a chemical absorption liquid or a physical absorption liquid (hereinafter collectively referred to as “absorption liquid”) in the absorption tower 71. The A carbon dioxide off-gas C containing a trace amount of a sulfur compound (hydrogen sulfide, mercaptan, carbonyl sulfide, carbon disulfide, sulfur dioxide), VOC, carbon monoxide and the like is discharged from the top of the absorption tower 71 through the flow path 72. , And supplied to the purification device as shown in FIG.
The absorption liquid that has absorbed hydrogen sulfide is extracted from the bottom of the absorption tower 71, supplied to the regeneration tower 52 via the flow path 73, and recirculated.

As described above, according to the carbon dioxide off-gas purification method of this embodiment, sulfur compounds that are highly toxic and irritating odors such as hydrogen sulfide and mercaptan contained in carbon dioxide off-gas are purified, and sulfur oxides ( SOx) and the concentration of sulfur compounds (excluding sulfur oxides) contained in the treated carbon dioxide off-gas can be reduced to 5 ppmV or less.
By using one or more metal oxides selected from the group consisting of zirconium oxide, titanium oxide, and silicon oxide as the combustion catalyst, the combustion catalyst is deteriorated by sulfation of SOx produced by oxidative decomposition treatment. Can be reduced.
By using one or more kinds of noble metals selected from the group of platinum, palladium, and iridium as combustion catalysts, these noble metals have high oxidation activity in a low temperature range, and therefore carbon dioxide at a lower temperature than before. The off-gas oxidation reaction can proceed.

VOCs such as benzene or toluene or xylene having carcinogenicity contained in carbon dioxide off gas can be reduced to a benzene concentration of 10 ppmV or less, a toluene concentration of 50 ppmV or less, or a xylene concentration of 50 ppmV or less by oxidative decomposition treatment with a combustion catalyst. , The influence of the VOC on the human body can be reduced. Photochemical smog and VOC, which are the cause of suspended particulate matter, can be purified and the environmental load can be reduced.
In addition, carbon dioxide off-gas can be oxidized and decomposed at low cost without generating thermal NOx and with low carbon dioxide emissions.

By the way, in the combustion reaction of benzene, toluene, and xylene using a conventional Pt / Al ₂ O ₃ , Pd / Al ₂ O ₃ based catalyst, when there is no sulfur compound, sufficient oxidative decomposition is performed at a temperature range of 200 ° C. or higher. Performance is obtained, but the presence of sulfur compounds causes performance degradation depending on the concentration. Normally, if the sulfur compound coexists for a short time or at a low concentration, the performance deterioration can be compensated by increasing the reaction temperature. However, when the concentration of the sulfur compound is high, when a conventional Pt / Al ₂ O ₃ or Pd / Al ₂ O ₃ based catalyst is used, sulfur acts on the support Al ₂ O ₃ and Al ₂ (SO ₄ ). ₃ is formed, and the surface area of the catalyst is reduced accordingly. When the surface area of the catalyst is reduced, platinum and palladium are aggregated, so that the degree of dispersion of these noble metals in the catalyst is reduced and the oxidative decomposition performance is reduced. As Al ₂ O ₃ changes to Al ₂ (SO ₄ ) ₃ , the bonding state of Pt—Al ₂ O ₃ is considered to have an influence on the oxidizing power of platinum, although it is slightly. This also contributes to a decrease in activity.

  Since the conventional Mn / CuO-based catalyst does not contain a noble metal and is inexpensive in price, the supported amount can be increased. However, this Mn / CuO-based catalyst exhibits high oxidative decomposition performance when used in the absence of a sulfur compound, but when a sulfur compound or halogen-based material is present, these materials, Mn salt, and Cu salt are produced. In addition, the oxidative decomposition performance is significantly reduced.

In contrast, the Pt / TiO ₂ catalyst used in the carbon dioxide off-gas purification method of the present invention has a form of TiO _{2 as} a carrier that is less affected by sulfur adhesion to sulfur compounds and is not easily affected. Stable with little change. Therefore, the Pt / TiO ₂ catalyst is a catalyst that maintains the initial catalyst structure and has little deterioration with time in oxidative decomposition performance.
Similarly, SiO ₂ and ZrO ₂ are also excellent in durability against sulfur, and combustion catalysts using these metal oxides can maintain oxidative decomposition performance over a long period of time.

(2) Second Embodiment Hereinafter, a second embodiment of the carbon dioxide off-gas purification method of the present invention will be described with reference to the drawings.
By the way, in the carbon dioxide off-gas purification method of the present invention, the configuration of the carbon dioxide off-gas purification device (hereinafter abbreviated as “purification device”) is adjusted to the concentration of combustible gas (such as methane) contained in the carbon dioxide off-gas. It is determined accordingly.
When the concentration of the combustible gas contained in the carbon dioxide off gas is within a range in which the reaction temperature can be controlled to 250 ° C. or more and 650 ° C. or less even after the heat generation due to the oxidative decomposition treatment of the carbon dioxide off gas, A purification device having a catalytic combustor provided with one catalytic combustion region provided with a combustion catalyst is used. When the combustible gas concentration contained in the carbon dioxide off-gas is in a range where the reaction temperature exceeds 650 ° C. due to heat generated by the oxidative decomposition treatment of the carbon dioxide off-gas, at least two catalytic combustion regions provided with combustion catalysts are provided. A catalytic combustor is provided, and at least one selected from carbon dioxide off-gas after oxidative decomposition treatment, air, and water is supplied between catalytic combustion regions, and carbon dioxide off-gas introduced into the catalytic combustor is supplied. A purification device configured to cool is used.

In this embodiment, a purification apparatus having a catalytic combustor having two catalytic combustion regions is illustrated in FIG. 5, and a carbon dioxide off-gas purification method will be described with reference to this drawing.
FIG. 5 is a schematic view showing an example of a purification apparatus used in the second embodiment of the carbon dioxide off-gas purification method of the present invention.
The carbon dioxide off-gas purification device 80 includes a heater 81 for heating the carbon dioxide off-gas to a predetermined reaction temperature, and a preheater 82 for preheating the carbon dioxide off-gas or air before being introduced into the heater 81. A catalyst combustor 83 including two catalytic combustion regions 83a and 83b provided with a combustion catalyst for subjecting the carbon dioxide off-gas heated by the heater 81 to oxidative decomposition treatment, and these, It is schematically configured from flow paths 84 to 97 for flowing various gases.

  As the heater 81, the thing similar to said heater 11 is used. As the preheater 82, the same one as the above preheater 12 is used.

  As the catalytic combustor 83, between the two catalytic combustion regions 83a and 83b and the two catalytic combustion regions 83a and 83b, the reaction temperature of the carbon dioxide off-gas oxidative decomposition treatment is set within a predetermined temperature range. And a quench fluid supply region 83c for supplying air for cooling the carbon dioxide off gas, and the catalyst combustion regions 83a and 83b are filled with the combustion catalyst. An oxygen concentration meter (not shown) is provided in the middle of the flow path 95 connected to the exhaust port of the catalytic combustor 83.

Next, a carbon dioxide off gas purification method using the purification device 80 will be described.
In the carbon dioxide off-gas purification method of this embodiment, carbon dioxide off-gas is introduced into the purification device 80 via the flow path 84 and auxiliary combustion air is introduced into the purification device 80 from the flow path 88.
In this embodiment, the concentration of flammable gases such as benzene, toluene, xylene and other VOCs and methane contained in the carbon dioxide off-gas is high.

When the carbon dioxide off gas is not preheated (β = 1), the carbon dioxide off gas is supplied to the heater 81 via the flow path 86.
When the carbon dioxide off gas is preheated (β = 0), the carbon dioxide off gas is supplied to the preheater 82 via the flow path 85, and the carbon dioxide offgas is preheated to a predetermined temperature in the preheater 82. Carbon dioxide off-gas is supplied to the heater 81 via the passage 87 and the passage 86. The preheating of the carbon dioxide off-gas in the preheater 82 is based on the energy consumption (fuel consumption) when the carbon dioxide offgas is heated to a temperature higher than the oxidation decomposition treatment temperature by the combustion catalyst in the catalytic combustor 83 in the heater 81. Done to reduce.

When the auxiliary combustion air is not preheated (α = 1), the auxiliary combustion air is supplied to the heater 81 through the flow path 90.
When the auxiliary combustion air is preheated (α = 0), the auxiliary combustion air is supplied to the preheater 82 via the flow path 89, and after preheating the auxiliary combustion air to a predetermined temperature in the preheater 82, the flow path 91, Carbon dioxide off-gas is supplied to the heater 81 through the flow path 90. The preheating of the auxiliary combustion air in the preheater 82 reduces the energy consumption (fuel consumption) when the auxiliary heater air is heated to a temperature higher than the oxidation decomposition treatment temperature by the combustion catalyst in the catalytic combustor 83 in the heater 81. Done for.

  In the preheating of the carbon dioxide off gas and the auxiliary combustion air in the preheater 82, either the carbon dioxide off gas or the auxiliary combustion air is preheated to a predetermined temperature, or both the carbon dioxide off gas and the auxiliary combustion air are increased to a predetermined temperature. You may preheat. In order to reduce the apparatus cost, the preheater 82 may be omitted.

The preheating temperature of the carbon dioxide off gas and the auxiliary combustion air in the preheater 82 is preferably 100 ° C. or higher and 400 ° C. or lower.
When the preheating temperature of the carbon dioxide off gas and the auxiliary combustion air is low, the energy consumption (fuel consumption) when the temperature of the carbon dioxide off gas is raised to the oxidative decomposition treatment temperature or higher by the combustion catalyst in the heater 81 increases. .

  In this heater 81, the fuel gas introduced into the purification device 80 via the flow path 92 becomes combustion exhaust gas after combustion by auxiliary combustion air, and subsequently mixed with carbon dioxide off-gas, and the mixed gas is heated. Then, the temperature is raised to the reaction temperature (250 ° C. or higher and 650 ° C. or lower) of the oxidative decomposition treatment with the combustion catalyst in the catalytic combustor 83. Specifically, the temperature of the mixed gas is preferably 350 ° C. or more and 500 ° C. or less by the heater 81.

  The mixed gas heated to a predetermined temperature by the heater 81 is supplied to the catalyst combustor 83 filled with the combustion catalyst, and the carbon dioxide off gas is brought into contact with the carbon dioxide off gas. To convert sulfur compounds such as hydrogen sulfide, mercaptan, carbonyl sulfide, carbon disulfide, and sulfur dioxide contained in the carbon dioxide off-gas into sulfur oxide (SOx). VOCs such as benzene, toluene and xylene contained in carbon dioxide off-gas are converted into carbon dioxide by oxidative decomposition treatment. When carbon monoxide is contained in the carbon dioxide off gas, the carbon monoxide is converted into carbon dioxide.

In the oxidative decomposition treatment of carbon dioxide offgas by the combustion catalyst, the reaction temperature is preferably 250 ° C. or higher and 650 ° C. or lower, more preferably 350 ° C. or higher and 500 ° C. or lower.
When the reaction temperature of the oxidative decomposition treatment with the combustion catalyst is less than 250 ° C., the oxidative decomposition reaction of the sulfur compound and VOC contained in the carbon dioxide off-gas does not proceed sufficiently. When the reaction temperature of the oxidative decomposition treatment with the combustion catalyst exceeds 650 ° C., the combustion catalyst is deteriorated by heat, and the purification rate of carbon dioxide off-gas cannot be kept high for a long time. The material of the catalytic combustor needs to be a heat-resistant material, which increases the material cost. The amount of fuel consumed for the oxidative decomposition treatment increases, the processing cost increases, and the amount of carbon dioxide emission increases. Furthermore, there is a possibility that thermal NOx is generated.

In the catalytic combustor 83, in the oxidative decomposition treatment of the carbon dioxide off gas, the pressure of the carbon dioxide off gas (the pressure of the carbon dioxide off gas supplied to the catalytic combustor 83) is preferably 0.01 MPa or more and 1 MPa or less, and more preferably. Is 0.05 MPa or more and 0.15 MPa or less.
When the pressure of the carbon dioxide off gas is 0.01 MPa or more and 1 MPa or less, the volume of the carbon dioxide off gas is reduced, the residence time in the catalytic combustor 83 is shortened, the treatment efficiency is improved, and the treated carbon dioxide off gas is reduced. Since the power can be recovered by the gas expander before being released into the atmosphere, the processing cost can be reduced.
When the pressure of the carbon dioxide off gas is less than 0.01 MPa, the volume of the carbon dioxide off gas is large, the residence time in the catalytic combustor 83 becomes long, and the processing efficiency is deteriorated. If the pressure of the carbon dioxide off gas exceeds 1 MPa, the catalytic combustor 83 and its upstream equipment become pressure vessels, resulting in high equipment costs, compression power such as auxiliary combustion air, and high operating costs. Become.

In this embodiment, since the combustible gas concentration contained in the carbon dioxide off gas is in a range where the reaction temperature in the oxidative decomposition treatment of the carbon dioxide off gas exceeds 650 ° C., the quench fluid supply region 83 c of the catalytic combustor 83 includes Auxiliary combustion air is supplied as a quench fluid through a flow path 97 branched from the middle of the flow path 90.
This auxiliary combustion air cools the carbon dioxide off-gas at the outlet of the catalytic combustion region 83a, suppresses the temperature in the catalytic combustion region 83b from excessively rising, and the reaction temperature in the oxidative decomposition treatment falls within the above temperature range. Control.

  By performing oxidative decomposition treatment with a combustion catalyst in the catalytic combustor 83, the concentration of sulfur compounds (excluding sulfur oxides) contained in the carbon dioxide off-gas becomes 5 ppmV or less. VOCs such as benzene, toluene, and xylene contained in the carbon dioxide off gas have a benzene concentration of 10 ppmV or less, a toluene concentration of 50 ppmV or less, and a xylene concentration of 50 ppmV or less by oxidative decomposition treatment.

  As the flow rate of the auxiliary combustion air supplied to the catalytic combustor 83 together with the carbon dioxide off-gas increases, the amount of fuel gas input for raising the temperature to the reaction temperature of the oxidative decomposition treatment increases and the thermal efficiency deteriorates. Catalytic combustion so that the concentration of oxygen contained in the treated carbon dioxide off-gas measured by an oxygen concentration meter provided in the latter stage is 0.5 to 15% by volume, more preferably 0.5 to 5% by volume. It is preferable to control the amount of auxiliary combustion air supplied to the vessel 83.

  The treated carbon dioxide off gas discharged from the catalyst combustor 83 is introduced into the preheater 82 via the flow path 95. For example, when the preheater 82 is a heat exchanger, in this heat exchanger, either carbon dioxide off-gas after treatment, carbon dioxide off-gas before treatment or auxiliary combustion air, or carbon dioxide off-gas before treatment. Then, heat exchange with both the auxiliary combustion air and the auxiliary combustion air is performed, and the carbon dioxide off-gas or auxiliary combustion air before treatment is preheated to a predetermined temperature.

  The treated carbon dioxide off-gas (including sulfur oxide (SOx)) that has passed through the preheater 82 is discharged from the purification device 80 via the flow path 96.

Even in the carbon dioxide off-gas purification method of this embodiment, after removing mercury such as organic mercury, ionic mercury, and elemental mercury contained in carbon dioxide off-gas, the carbon dioxide off-gas after removing the mercury Is preferably introduced into the catalytic combustor 83.
The treatment for removing mercury contained in the carbon dioxide off-gas is performed before introducing the carbon dioxide off-gas into the purification device 80, or before introducing the carbon dioxide off-gas into the heater 81 in the purification device 80. .
The removal process of mercury contained in the carbon dioxide off gas is performed by an adsorption process such as activated carbon.
(3) Embodiment of Natural Gas Production Method and Production Apparatus FIG. 11 is a flowchart showing an embodiment of a natural gas production method according to the present invention. This method includes a liquid phase removal step 200 in which a raw material natural gas collected from a well is first weighed and then supplied to a slag catcher to separate the raw natural gas into a liquid phase and a gas phase by the slag catcher or the like.

The gas phase from which the liquid phase has been removed is sent to an acid gas removal step 202, where carbon dioxide off gas containing carbon dioxide as a main component and containing VOC and sulfur compounds is separated. The separation method may be a conventionally known chemical absorption method, physical absorption method, or a combination thereof.
The raw material gas after separating the carbon dioxide off-gas is sent to the moisture removal step 204, where it is cooled to near the temperature at which the gas hydrate is formed, and the condensed moisture is removed.

The raw material gas from which moisture has been removed is sent to the mercury removing step 206, and the mercury concentration in the raw material gas is reduced to near 0.1 to 0.01 μm by an impregnated activated carbon adsorption method or the like.
The raw material gas from which mercury has been removed is sent to the heavy component removal step 208 and fractionated by a plurality of distillation towers to remove heavy hydrocarbons and the like that are pentane or higher to obtain natural gas. Further, the raw material gas from which the heavy hydrocarbons have been removed is sent to the liquefaction step 210, where it is cooled and compressed to fill the tank. The carbon dioxide off gas is sent to the off gas purification step 201, and the off gas is purified by the carbon dioxide off gas purification method of any one of the embodiments described above.

  According to such a method for producing natural gas, the exhaust gas can be purified while suppressing the amount of energy input, and the environmental load of natural gas production can be reduced.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited to a following example.

"Example 1"
In the catalytic combustion type carbon dioxide off-gas purification apparatus shown in FIG. 1, α = 1 and β = 1, carbon dioxide off-gas shown in Table 1, auxiliary combustion air shown in Table 2, and fuel gas shown in Table 3 are used. The carbon dioxide off-gas was oxidatively decomposed. As the catalyst, the catalyst prepared in Example 2 described later was used.
Table 4 shows the processing conditions and results.

"Comparative Example 1"
In the direct combustion type carbon dioxide off-gas purification apparatus shown in FIG. 6, α = 1 and β = 1, carbon dioxide off-gas shown in Table 1, auxiliary combustion air shown in Table 2, and fuel gas shown in Table 3 are used. The carbon dioxide off-gas was oxidatively decomposed.
Table 4 shows the processing conditions and results.

An outline of a carbon dioxide off-gas purification method using the purification apparatus 100 shown in FIG. 6 will be described.
In the carbon dioxide off-gas purification method using the purification device 100, the carbon dioxide off-gas is introduced into the purification device 100 through the flow path 104 and auxiliary combustion air is introduced into the purification device 100 from the flow path 108.

  When the carbon dioxide off gas is not preheated (β = 1), the carbon dioxide off gas is supplied to the combustor 101 via the flow path 106. When the carbon dioxide off gas is preheated (β = 0), the carbon dioxide off gas is supplied to the carbon dioxide off gas preheater 103 via the flow path 105, and the carbon dioxide off gas is heated to a predetermined temperature in the carbon dioxide off gas preheater 103. The carbon dioxide off gas is supplied to the combustor 101 through the flow path 107 and the flow path 106.

  When the auxiliary combustion air is not preheated (α = 1), the auxiliary combustion air is supplied to the combustor 101 via the flow path 110 and the flow path 111. When the auxiliary combustion air is preheated (α = 0), the auxiliary combustion air is supplied to the air preheater 102 via the flow path 109, and after the auxiliary combustion air is preheated to a predetermined temperature in the air preheater 102, The auxiliary combustion air is supplied to the combustor 101 via the line 111.

  Next, the carbon dioxide off-gas and auxiliary combustion air supplied to the combustor 101 are directly combusted in the combustor 101 together with the fuel gas introduced into the purification device 100 via the flow path 112. In this oxidative decomposition treatment of carbon dioxide off-gas by direct combustion, the reaction temperature is set to 900 ° C.

The treated carbon dioxide off-gas discharged from the combustor 101 is introduced into the air preheater 102 via the flow path 113 and further introduced into the carbon dioxide off-gas preheater 103 via the flow path 114.
When the air preheater 102 and the carbon dioxide offgas preheater 103 are heat exchangers, heat exchange between the treated carbon dioxide offgas and the auxiliary combustion air or carbon dioxide offgas before the treatment is performed in this heat exchanger. The auxiliary combustion air or carbon dioxide off gas before treatment is preheated to a predetermined temperature.

  The treated carbon dioxide off gas (including sulfur oxide (SOx)) that has passed through the carbon dioxide off gas preheater 103 is discharged from the purification device 100 via the flow path 115.

From the results of Table 4, the fuel consumption of the direct combustion method of Comparative Example 1 is 8,300 Nm ³ / h, whereas the fuel consumption of the catalytic combustion method of Example 1 is 2,200 Nm ³ / h. It was suggested that fuel consumption can be reduced by more than 70%.
In Example 1, since the combustion treatment was performed at a temperature lower than that of the conventional one, it was expected that the flammability of methane (CH ₄ ) contained in the carbon dioxide off-gas deteriorated. Therefore, in Example 1, the conversion rate of methane was assumed to be 0%, and the influence on the emission amount of carbon dioxide due to slippage of methane having a warming coefficient 21 times that of carbon dioxide was examined. The slip amount of methane is converted into carbon dioxide, and the amount of carbon dioxide emission ((a) + (b) in Table 4) associated with each combustion process is 10% in the direct combustion method of Comparative Example 1. While it was 900 Nm ³ / h, the carbon dioxide emission of the catalytic combustion system of Example 1 was 5,300 Nm ³ / h, suggesting that the carbon dioxide emission can be reduced by 50% or more.
Furthermore, considering the amount of carbon dioxide contained in the carbon dioxide off-gas, the total amount of carbon dioxide emission ((a) + (b) + (c) in Table 4) associated with each combustion process is The carbon dioxide emission amount of the direct combustion method is 103,300 Nm ³ / h, whereas the carbon dioxide emission amount of the catalytic combustion method of Example 1 is 97,700 Nm ³ / h, and the carbon dioxide emission amount is 5 % Reduction was suggested.

"Example 2"
58.6 g of titanium oxide powder (anatase type, trade name: PC-500, manufactured by Millennium), 138.0 g of titania sol (trade name: TA-15, manufactured by Nissan Chemical Industries), and 103.5 g of pure water Mixing was performed to prepare a slurry containing titanium oxide powder.
This titanium oxide powder-containing slurry was applied to the inner wall surface of a cordierite honeycomb (400 cpi ² , manufactured by NGK Corporation), and excess slurry was removed by air blowing.
The cordierite honeycomb coated with the titanium oxide powder-containing slurry was dried at 150 ° C. for 6 hours with a dryer.
This cordierite honeycomb was fired in a firing furnace at 500 ° C. for 2 hours to form a layer having a titanium oxide powder content of 50 g / liter.

88.89 g of a dinitrodiamine platinum aqueous solution (platinum content: 4.5 mass%) and 211.11 g of pure water were mixed to prepare a platinum aqueous solution having a platinum content of 1.33 mass%.
This platinum aqueous solution is applied to the inner wall surface of the cordierite honeycomb on which the layer made of titanium oxide powder is formed, and this solution is absorbed by the layer made of titanium oxide powder, and the excess solution is removed by air blowing to oxidize. The aqueous platinum solution was absorbed in the layer made of titanium oxide powder so that the content of the aqueous platinum solution in the layer made of titanium powder was 150 g / liter.
The cordierite honeycomb coated with the platinum aqueous solution was dried at 150 ° C. for 6 hours by a dryer.
This cordierite honeycomb was fired at 500 ° C. for 2 hours in a firing furnace, and further subjected to reduction treatment at 500 ° C. for 2 hours in a hydrogen atmosphere, and a Pt / TiO ₂ catalyst layer having a platinum content of 2 g / liter. And the combustion catalyst of Example 2 was obtained.

"Example 3"
In the same manner as in Example 2, a layer having a titanium oxide powder content of 52 g / liter was formed.
30 g of palladium nitrate aqueous solution (palladium content 10.0 mass%) and 270 g of pure water were mixed to prepare a palladium aqueous solution having a palladium content of 1.33 mass%.
This palladium aqueous solution is applied to the inner wall surface of the cordierite honeycomb on which the layer made of titanium oxide powder is formed, and this solution is absorbed by the layer made of titanium oxide powder, and the excess solution is removed by air blowing to oxidize. The aqueous palladium solution was absorbed in the layer made of titanium oxide powder so that the content of the aqueous palladium solution in the layer made of titanium powder was 150 g / liter.
The cordierite honeycomb coated with the aqueous palladium solution was dried at 150 ° C. for 6 hours with a dryer.
This cordierite honeycomb was fired in a firing furnace at 500 ° C. for 2 hours to form a Pd / TiO ₂ catalyst layer having a palladium content of 2 g / liter, and the combustion catalyst of Example 3 was obtained.

Example 4
Zirconium oxide powder (trade name: RC-100, manufactured by Daiichi Kagaku Kagaku Kogyo Co., Ltd.) 50.8 g, zirconia sol (trade name: NZS-30A, manufactured by Nissan Chemical Industries Co., Ltd.) 69.0 g, and pure water 180.2 g And a slurry containing zirconium oxide powder was prepared.
This zirconium oxide powder-containing slurry was applied to the inner wall surface of a cordierite honeycomb (400 cpi ² , manufactured by NGK Corporation), and excess slurry was removed by air blowing.
The cordierite honeycomb coated with the zirconium oxide powder-containing slurry was dried with a dryer at 150 ° C. for 6 hours.
This cordierite honeycomb was fired in a firing furnace at 500 ° C. for 2 hours to form a layer having a zirconium oxide powder content of 50 g / liter.

88.89 g of a dinitrodiamine platinum aqueous solution (platinum content: 4.5 mass%) and 211.11 g of pure water were mixed to prepare a platinum aqueous solution having a platinum content of 1.33 mass%.
This platinum aqueous solution is applied to the inner wall surface of the cordierite honeycomb on which the layer made of zirconium oxide powder is formed, and this solution is absorbed by the layer made of zirconium oxide powder, and the excess solution is removed by air blowing to oxidize. The platinum aqueous solution was absorbed in the layer made of zirconium oxide powder so that the content of the platinum aqueous solution in the layer made of zirconium powder was 150 g / liter.
The cordierite honeycomb coated with the platinum aqueous solution was dried at 150 ° C. for 6 hours by a dryer.
This cordierite honeycomb was fired at 500 ° C. for 2 hours in a firing furnace, and further subjected to reduction treatment at 500 ° C. for 2 hours in a hydrogen atmosphere to form a Pt / ZrO ₂ catalyst layer having a platinum content of 2 g / liter. The combustion catalyst of Example 4 was obtained.

"Comparative Example 2"
43.3 g of aluminum oxide powder (trade name: NST-5, manufactured by JGC Universal), 138.0 g of alumina sol (trade name: A-10, manufactured by Kawaken Fine Chemical Co., Ltd.) and 76.7 g of pure water were mixed. A slurry containing aluminum oxide powder was prepared.
This aluminum oxide powder-containing slurry was applied to the inner wall surface of a cordierite honeycomb (400 cpi ² , manufactured by NGK Corporation), and excess slurry was removed by air blowing.
The cordierite honeycomb coated with the aluminum oxide powder-containing slurry was dried with a dryer at 150 ° C. for 6 hours.
This cordierite honeycomb was fired in a firing furnace at 500 ° C. for 2 hours to form a layer having an aluminum oxide powder content of 50 g / liter.

88.89 g of a dinitrodiamine platinum aqueous solution (platinum content: 4.5 mass%) and 211.11 g of pure water were mixed to prepare a platinum aqueous solution having a platinum content of 1.33 mass%.
This platinum aqueous solution is applied to the inner wall surface of the cordierite honeycomb on which the layer made of aluminum oxide powder is formed, and this solution is absorbed by the layer made of aluminum oxide powder, and the excess solution is removed by air blowing to oxidize. The aqueous platinum solution was absorbed in the layer made of aluminum oxide powder so that the content of the aqueous platinum solution in the layer made of aluminum powder was 150 g / liter.
The cordierite honeycomb coated with the platinum aqueous solution was dried at 150 ° C. for 6 hours by a dryer.
This cordierite honeycomb was fired in a firing furnace at 500 ° C. for 2 hours, and further subjected to reduction treatment at 500 ° C. for 2 hours in a hydrogen atmosphere, so that a Pt / Al ₂ O ₃ catalyst having a platinum content of 2 g / liter. A layer was formed to obtain a combustion catalyst of Comparative Example 2.

“Comparative Example 3”
43.3 g of aluminum oxide powder (trade name: NST-5, manufactured by JGC Universal), 138.0 g of alumina sol (trade name: A-10, manufactured by Kawaken Fine Chemical Co., Ltd.) and 76.7 g of pure water were mixed. A slurry containing aluminum oxide powder was prepared.
This aluminum oxide powder-containing slurry was applied to the inner wall surface of a cordierite honeycomb (400 cpi ² , manufactured by NGK Corporation), and excess slurry was removed by air blowing.
The cordierite honeycomb coated with the aluminum oxide powder-containing slurry was dried with a dryer at 150 ° C. for 6 hours.
This cordierite honeycomb was fired in a firing furnace at 500 ° C. for 2 hours to form a layer having an aluminum oxide powder content of 50 g / liter.

30 g of palladium nitrate aqueous solution (palladium content 10.0 mass%) and 270 g of pure water were mixed to prepare a palladium aqueous solution having a palladium content of 1.33 mass%.
This palladium aqueous solution is applied to the inner wall surface of the cordierite honeycomb on which the layer made of aluminum oxide powder is formed, and this solution is absorbed by the layer made of aluminum oxide powder, and the excess solution is removed by air blowing to oxidize. The palladium aqueous solution was absorbed in the layer made of aluminum oxide powder so that the content of the aqueous palladium solution in the layer made of aluminum powder was 150 g / liter.
The cordierite honeycomb coated with the aqueous palladium solution was dried at 150 ° C. for 6 hours with a dryer.
This cordierite honeycomb was fired in a firing furnace at 500 ° C. for 2 hours to form a Pd / Al ₂ O ₃ catalyst layer having a palladium content of 2 g / liter, and a combustion catalyst of Comparative Example 3 was obtained.

“Comparative Example 4”
As Cu / Mn powder, 84.0 g of hopcalite powder (trade name: N-840, manufactured by Zude Chemie), 148.5 g of silica sol (trade name: Snowtex C, manufactured by Nissan Chemical Industries), and 67.5 g of pure water. Were mixed to prepare a slurry containing Cu / Mn powder.
This Cu / Mn powder-containing slurry was applied to the inner wall surface of a cordierite honeycomb (400 cpi ² , manufactured by NGK Corporation), and excess slurry was removed by air blowing.
The cordierite honeycomb coated with the Cu / Mn powder-containing slurry was dried at 150 ° C. for 6 hours with a dryer.
This cordierite honeycomb was fired in a firing furnace at 400 ° C. for 2 hours to form a Cu / Mn layer having a Cu / Mn powder content of 100 g / liter, and a combustion catalyst of Comparative Example 4 was obtained.

"Treatment rate of benzene with combustion catalyst"
When the oxidative decomposition treatment of hydrogen sulfide and benzene (C ₆ H ₆ ) was performed using a catalytic combustor having a combustion catalyst made of a cordierite honeycomb having a Pt / TiO ₂ catalyst layer produced in Example 2, Regarding the oxidation reaction of benzene (C ₆ H ₆ + 15 / 2O ₂ → 6CO ₂ + 3H ₂ O), the reaction rate was expressed by the following Langmuir-Hinshelwood equation (formula (1)).

In the formula (1), R is the reaction rate (mol / h / g-cat ), k is the reaction rate constant is dependent on the temperature T (K) (mol / h / g-cat / Pa base), P i the partial pressure of i component (Pa), _{K i} is the adsorption equilibrium constant of i component dependent on the temperature T (K) (1 / Pa ), the a and b shows the reaction order.
As a result of expressing the reaction rate by the above equation (1), it was confirmed that the measured value and the calculated value of the reaction rate almost coincided as shown in FIG.

"Sensitivity analysis of combustion catalyst by reaction rate equation"
A combustion catalyst comprising a cordierite honeycomb having a Pt / TiO ₂ catalyst layer produced in Example 2 with a GHSV (space velocity) of 30,000 h ⁻¹ , a benzene concentration of 500 ppm, and a pressure of the catalytic combustor of 1 atm. Fig. 5 shows the relationship between the reaction temperature and the conversion rate (decomposition rate) of benzene at the hydrogen sulfide concentration and oxygen concentration shown in Table 5 when hydrogen sulfide and benzene (C ₆ H ₆ ) are subjected to oxidative decomposition treatment. It is shown in FIG.
The conversion rate of benzene was defined by the following formula.
Conversion (%) = (1− (benzene concentration at the outlet side of the catalytic combustor / benzene concentration at the inlet side of the catalytic combustor) × 100

From the results of analysis examples 1 to 3 shown in FIG. 8, when the hydrogen sulfide concentration is 0 ppm, the oxidation reaction of benzene proceeds even at a reaction temperature of about 250 ° C. However, when a small amount of hydrogen sulfide is contained, the reaction activity decreases. It was suggested to do. That is, it was suggested that when the hydrogen sulfide concentration is 600 ppm, the reaction temperature needs to be raised by about 100 ° C. in order to proceed the same reaction as when the hydrogen sulfide concentration is 0 ppm. It was suggested that when the hydrogen sulfide concentration was 2,000 ppm, it was necessary to raise the reaction temperature by about 130 ° C. in order to proceed the same reaction as when the hydrogen sulfide concentration was 0 ppm.
From the results of Analysis Examples 2 and 4 shown in FIG. 8, it was suggested that when the oxygen concentration is reduced from 5.0% by volume to 2.0% by volume, the reaction activity in the oxidation reaction of benzene is reduced. That is, when the oxygen concentration is 2.0% by volume, it is necessary to increase the reaction temperature by about 20 ° C. in order to proceed the oxidation reaction of benzene as when the oxygen concentration is 5.0% by volume. It was suggested.
From the above results, the oxidation reaction of benzene using the combustion catalyst comprising a cordierite honeycomb provided with the Pt / TiO ₂ catalyst layer produced in Example 2 is affected by the concentration of coexisting hydrogen sulfide and oxygen. It was suggested. It was suggested that the reaction temperature should be 250 ° C. or higher in order to proceed the benzene oxidation reaction.

"Verification of upper limit of reaction temperature for oxidative decomposition treatment using combustion catalyst"
After the combustion catalyst comprising a cordierite honeycomb provided with the Pt / TiO ₂ catalyst layer produced in Example 2 was exposed to a high temperature atmosphere shown in Table 6, oxidative decomposition treatment of benzene under the reaction conditions shown in Table 7 Went.
The results are shown in Table 8.

From the results of Table 8, when the combustion catalyst of Example 2 is exposed to a high temperature atmosphere of 600 ° C. or higher, the reaction activity at 400 ° C. is reduced, and the reaction temperature needs to be increased compared to the conditions before exposure to the high temperature atmosphere. It has been suggested.
From the above results, in the benzene oxidation reaction using the combustion catalyst comprising the cordierite honeycomb provided with the Pt / TiO ₂ catalyst layer produced in Example 2, the upper limit of the reaction temperature is 650 from the viewpoint of the heat resistance of the catalyst. It was suggested that the temperature was about ° C.

"Combustion catalyst performance test"
Using the combustion catalysts prepared in Examples 2 to 4 and Comparative Examples 2 to 4, the basic performance of the combustion catalyst, the life performance of the combustion catalyst, and the relationship between the performance of the combustion catalyst and the reaction conditions were tested.
FIG. 9 is a schematic view showing a test apparatus used for the combustion catalyst performance test.
Using this test apparatus 120, the performance test of the combustion catalyst was performed by the following method.
First, a new combustion catalyst 122 was placed in the catalyst combustor 121 for each test condition, and a quartz crushed product 123 was placed in the previous stage (upstream side in the flow direction of the gas to be treated).

Carbon dioxide was supplied from the gas cylinder 124 to the catalytic combustor 121 while controlling the flow rate with the floating precision flow meter 125. At the same time, air was supplied from the gas cylinder 126 to the catalytic combustor 121 while controlling the flow rate with the floating ball type precision flow meter 127.
Carbon dioxide and air supplied to the catalytic combustor 121 were heated to a predetermined temperature by an electric furnace 128 disposed around the catalytic combustor 121.
The rotary pump 130 started supplying water from the container 129 containing water to the catalytic combustor 121.

  While controlling the flow rate by the mass flow controller 131, air is supplied from the gas cylinder 126 to the VOC (benzene, toluene, p-xylene) in the container 132, this VOC is volatilized, and a predetermined amount of VOC is supplied to the catalytic combustor 121. Supplied. Along with this, nitrogen containing a predetermined amount of hydrogen sulfide or mercaptan was supplied from the gas cylinder 134 to the catalytic combustor 121 while controlling the flow rate by the mass flow controller 135.

After a predetermined period of time, a Tedlar bag was installed at a sample collection port 136 provided on the outlet side of the catalytic combustor 121, and an outlet side gas sample was collected.
After the collection of the gas sample on the outlet side was completed, a Tedlar bag was installed at the sample collection port 137 provided on the inlet side of the catalytic combustor 121 to collect the inlet side gas sample.

For the outlet side gas sample and the inlet side gas sample, the benzene concentration or toluene concentration or p-xylene concentration is measured, the hydrogen sulfide concentration or mercaptan concentration, and the carbon monoxide concentration are measured, and the oxidation reaction of these gases is measured. The reaction rate and product were analyzed.
After collecting the gas sample, the supply of gases other than air and carbon dioxide was stopped, and the measurement was terminated.

The concentration of benzene, toluene or p-xylene contained in the gas to be treated was measured by gas chromatography.
As the gas chromatography, GC-14B (manufactured by Shimadzu Corporation) was used.
As the detector, FID (flame flame ionization detector) was used.
The concentration of hydrogen sulfide, mercaptan or carbon monoxide contained in the gas to be treated was measured with a gas detector manufactured by Gastec.

In the following combustion catalyst performance test, the conversion rate (decomposition rate) of benzene, toluene and p-xylene was defined by the following equation.
Conversion rate (%) = (1− (benzene concentration, toluene concentration, p-xylene concentration / benzene concentration, toluene concentration, p-xylene concentration at the inlet side of the catalytic combustor) × 100

(1) Basic Performance of Combustion Catalyst Using the combustion catalysts produced in Examples 2 to 4 and Comparative Examples 2 to 4, oxidative decomposition treatment of carbon dioxide containing sulfur compounds and VOCs was performed under the reaction conditions shown in Table 9 It was.
Table 10 shows the conversion rate of benzene.

From the results of Table 10, it was confirmed that the combustion catalysts of Examples 2 to 4 were suitable as a catalyst for oxidative decomposition treatment of carbon dioxide containing a sulfur compound and VOC.
The combustion catalyst using aluminum oxide (Al ₂ O ₃ ) of Comparative Examples 2 and ₃ was sulfated with sulfuric acid, which is an oxide of a sulfur compound, and stable oxidation even when the active metal species (platinum, palladium) were the same. It was confirmed that the decomposition performance could not be demonstrated.
Since the combustion catalyst of Comparative Example 4 did not use a noble metal as the active metal, it was confirmed that the reactivity at 350 ° C. and 400 ° C. was remarkably low under the reaction conditions shown in Table 9.

(2) Lifetime Performance of Combustion Catalyst Using the combustion catalyst produced in Example 2 and Comparative Examples 2 and 4, oxidative decomposition treatment of carbon dioxide containing a sulfur compound and VOC was performed under the reaction conditions shown in Table 11.
The conversion rate of benzene is shown in FIG.

From the results of FIG. 10, it was confirmed that the combustion catalyst of Example 2 was active for a long time as a catalyst for oxidative decomposition treatment of carbon dioxide containing a sulfur compound and VOC.
The combustion catalyst using aluminum oxide of Comparative Example 2 is gradually sulfated by SOx, which is an oxide of a sulfur compound, and even when the active metal species (platinum) is the same, the decrease in activity is quick and stable oxidative decomposition performance It was confirmed that it was not possible to demonstrate.
Also for the combustion catalyst of Comparative Example 4, it was confirmed that due to the influence of SOx, which is an oxide of a sulfur compound, the activity was rapidly reduced and stable oxidative decomposition performance could not be exhibited.

(3) Relationship between performance of combustion catalyst and reaction conditions (a) Reactivity when benzene, toluene and p-xylene are contained Using the combustion catalyst prepared in Example 2, sulfurization was performed according to the reaction conditions shown in Table 12. Oxidative decomposition treatment of hydrogen and carbon dioxide containing benzene, toluene and p-xylene was performed.
Table 13 shows the conversion rates of benzene, toluene, and p-xylene.

  From the results of Table 13, it was confirmed that the combustion catalyst of Example 2 has almost the same oxidative decomposition performance of benzene, toluene and p-xylene at 300 to 400 ° C.

(B) Reactivity in the case of containing sulfur compound Using the combustion catalyst produced in Example 2, oxidative decomposition treatment of carbon dioxide containing hydrogen sulfide, mercaptan, and benzene was performed under the reaction conditions shown in Table 14. .
The conversion rate of benzene is shown in Table 15.

  From the results in Table 15, it was confirmed that the combustion catalyst of Example 2 had very high oxidative decomposition performance of benzene at 350 ° C. and 400 ° C., regardless of the type of sulfur compound.

(C) Influence of Hydrogen Sulfide Concentration on Reactivity Using the combustion catalyst produced in Example 2, oxidative decomposition treatment of carbon dioxide containing hydrogen sulfide and benzene was performed under the reaction conditions shown in Table 16.
Table 17 shows the conversion of benzene.

  From the results shown in Table 17, although the reactivity of the oxidation reaction of benzene slightly decreases when the hydrogen sulfide concentration increases, the combustion catalyst of Example 2 can improve the reactivity by raising the reaction temperature. confirmed.

(D) Effect of oxygen concentration on reactivity Using the combustion catalyst produced in Example 2, oxidative decomposition treatment of carbon dioxide containing hydrogen sulfide and benzene was performed under the reaction conditions shown in Table 18.
Table 19 shows the conversion of benzene.

  From the results in Table 19, it was confirmed that the combustion catalyst of Example 2 can improve the reactivity of the oxidation reaction of benzene at 350 to 400 ° C. when the oxygen concentration is increased.

(E) Influence of platinum content in combustion catalyst on reactivity Using the combustion catalyst produced in Example 2, oxidative decomposition treatment of carbon dioxide containing hydrogen sulfide and benzene was performed under the reaction conditions shown in Table 20. .
The conversion rate of benzene is shown in Table 21.

  From the results of Table 21, it was confirmed that the combustion catalyst of Example 2 can improve the reactivity of the benzene oxidation reaction at 350 ° C. and 400 ° C. when the platinum content in the combustion catalyst is increased.

  According to the carbon dioxide off-gas purification method of the present invention, sulfur compounds that are highly toxic and irritating odors such as hydrogen sulfide and mercaptans contained in carbon dioxide off-gas can be purified and discharged as SOx, which is industrially applicable. Have sex.

10,80 Carbon dioxide off-gas purification device (purification device)
DESCRIPTION OF SYMBOLS 11,81 Heater 12,82 Preheater 13,83 Catalytic combustor 14-26,84-97 Flow path 212 Container 214 Inlet 216 Outlet 220A-220I Combustion catalyst unit

Claims (14)

A carbon dioxide off-gas purification method for oxidatively decomposing volatile organic compounds and sulfur compounds in a gas mainly composed of carbon dioxide,
Introducing into a catalytic combustor a carbon dioxide off-gas whose main component is carbon dioxide containing at least a volatile organic compound and a sulfur compound of 50 ppmv or more and 10,000 ppmv or less;
Comprising oxidatively decomposing the volatile organic compound and the sulfur compound with a combustion catalyst in the catalytic combustor,
The combustion catalyst is one or more metal oxides selected from the group consisting of zirconium oxide, titanium oxide and silicon oxide, and one or more noble metals selected from the group consisting of platinum, palladium and iridium. And
A carbon dioxide off-gas purification method in which the concentration of a sulfur compound excluding sulfur oxides in the gas after oxidative decomposition treatment is 5 ppmv or less.   The method for purifying carbon dioxide off-gas according to claim 1, wherein the gas and / or air containing carbon dioxide as a main component is preheated and then supplied to the catalytic combustor.   The catalytic combustor includes at least two catalytic combustion regions provided with a combustion catalyst, and is selected from gas, air, and water mainly composed of carbon dioxide after oxidative decomposition treatment between the catalytic combustion regions. The method for purifying carbon dioxide off-gas according to claim 1, wherein at least one kind is supplied and a gas mainly composed of carbon dioxide introduced into the catalytic combustor is cooled.   The carbon dioxide off-gas according to claim 1, wherein after removing mercury contained in the gas containing carbon dioxide as a main component, the gas containing carbon dioxide as a main component after removing the mercury is introduced into a catalytic combustor. Purification method.   The gas mainly composed of carbon dioxide is a gas discharged from an acid gas separation device that separates and recovers an acid gas in a natural gas produced from a gas field by contacting the gas with a liquid solvent. The carbon dioxide off-gas purification method as described.   The gas mainly composed of carbon dioxide is reduced in hydrogen sulfide by any one of a hydrogen sulfide concentrating device, a sulfur recovery device, and a tail gas processing device provided in a subsequent stage of the acidic gas separation device. The method for purifying carbon dioxide off-gas according to claim 5, which is a later exhaust gas. The combustion catalyst filled in the catalytic combustor includes a base and a catalyst layer formed on the surface of the base and made of the metal oxide and the noble metal, and the metal oxide has a specific surface area. The method for purifying carbon dioxide off-gas according to claim 1, wherein the purification method is 10 m ² / g or more and 300 m ² / g or less. The combustion catalyst includes a honeycomb structure substrate having a large number of air passages, a metal oxide layer made of the metal oxide formed on the inner surface of the air passages, and at least a surface layer portion of the metal oxide layer. .1mg / cm ² or more, and a said noble metal is deposited at a density of 10 mg / cm ² or less, the substrate, ceramics, carbon dioxide of the metal oxide, or claim 1, characterized in that formed in the metal alloy Off-gas purification method. The catalytic combustor includes a container having an inlet at one end and an outlet at the other end, and a plurality of combustion catalysts disposed in the container at an interval between the inlet and the outlet. Each of the combustion catalyst units has a honeycomb structure base provided with a large number of air passages through which carbon dioxide off gas passes, and a metal oxide formed of the metal oxide formed on the inner surface of the air passages. And the noble metal deposited at a density of 0.1 mg / cm ² or more and 10 mg / cm ² or less to at least the surface layer portion of the metal oxide layer, and the base is ceramic, metal oxide, or Made of metal alloy,
2. The carbon dioxide off-gas purification method according to claim 1, wherein an inner diameter of the vent of the fuel catalyst unit near the outlet is larger than an inner diameter of the fuel catalyst unit near the inlet. A combustion catalyst for subjecting at least a volatile organic compound and a sulfur compound contained in the gas containing carbon dioxide as a main component to an oxidative decomposition treatment at a reaction temperature of 250 ° C. or higher and 650 ° C. or lower,
The combustion catalyst is one or more metal oxides selected from the group consisting of zirconium oxide, titanium oxide and silicon oxide, and one or more noble metals selected from the group consisting of platinum, palladium and iridium. A combustion catalyst for purifying carbon dioxide off-gas containing   The combustion catalyst includes a base and a catalyst layer formed on the surface of the base and made of the metal oxide and the noble metal, and the base is a honeycomb structure, a pellet, or a sphere. Item 11. A combustion catalyst for purifying carbon dioxide offgas according to Item 10. The combustion catalyst includes a honeycomb structure substrate having a large number of air passages, a metal oxide layer made of the metal oxide formed on the inner surface of the air passages, and at least a surface layer portion of the metal oxide layer. .1mg / cm ² or more, and a said noble metal is deposited at a density of 10 mg / cm ² or less, the substrate is ceramic, according to claim 11, which is formed of a metal oxide or a metal alloy, dioxide Combustion catalyst for carbon offgas purification. The catalytic combustor includes a container having an inlet at one end and an outlet at the other end, and a plurality of combustion catalysts disposed in the container at an interval between the inlet and the outlet. Each of the combustion catalyst units has a honeycomb structure base provided with a large number of air passages through which carbon dioxide off gas passes, and a metal oxide formed of the metal oxide formed on the inner surface of the air passages. And the noble metal deposited at a density of 0.1 mg / cm ² or more and 10 mg / cm ² or less to at least the surface layer portion of the metal oxide layer, and the base is ceramic, metal oxide, or Made of metal alloy,
12. The combustion catalyst for purifying carbon dioxide offgas according to claim 11, wherein an inner diameter of the vent of the fuel catalyst unit near the outlet is larger than an inner diameter of the fuel catalyst unit near the inlet. A natural gas production method for producing natural gas from raw natural gas,
Supplying raw material natural gas to a slag catcher and separating the raw natural gas into a liquid phase and a gas phase by the slag catcher;
An acid gas removing step for separating carbon dioxide off-gas containing carbon dioxide as a main component and containing a volatile organic compound and a sulfur compound from the gas phase;
A moisture removal step of cooling the raw material gas after separating the carbon dioxide off gas to remove the condensed moisture;
A heavy fraction removal step of fractionating the raw material gas after removing moisture by a distillation tower to remove heavy hydrocarbons to obtain natural gas;
A natural gas production method comprising: an off-gas purification step of purifying the carbon dioxide off-gas by the carbon dioxide off-gas purification method according to claim 1.

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