JP5781737B2 - Low concentration methane removal method and low concentration methane removal device - Google Patents

Description

  The present invention removes methane from a gas containing a low concentration of methane that is lower than the lower limit of methane combustion limit (explosion limit) and does not enter the flammable range when mixed with air at any ratio, such as coal mine ventilation gas. The present invention relates to a removal method and apparatus.

  A large amount of methane is adsorbed in the coal bed, and its effective use is being promoted. Methane recovered by degassing from a coal bed before mining has a relatively high methane concentration of 30 to 95%, and it is relatively easy to use effectively by concentrating it. On the other hand, most of the gas released by the ventilation of the coal mine is diffused into the atmosphere because the methane concentration is as low as about 0.1 to 1%. Although methane is not harmful to the human body, it has a high global warming effect, so it is desired to reduce its emission. However, when concentrating a low-concentration gas such as a coal mine ventilation gas, it passes the methane explosion limit (5 to 15%) during the process, so there are great safety concerns and it is not realistic. . Therefore, a method of oxidizing and removing by using a method such as catalytic oxidation or the like as combustion air of a gas engine or a turbine has been proposed (Non-Patent Documents 1 and 2).

  In the treatment of gases containing low concentrations of organic compounds, a process in which an oxidation catalyst is combined with a heat exchanger, a preheated gas is passed through the catalyst, and organic compounds in the gas are removed by a catalytic oxidation reaction is generated from an industrial process. Widely used in the treatment of exhaust gases containing volatile organic compounds (VOC) (Non-patent Documents 3 and 4). In this process, a catalyst in which Pt or Pd is usually supported on an alumina carrier is used. The VOC treatment process is usually targeted for compounds that are relatively easily oxidized, such as toluene, acetone, ethyl acetate, etc., and these are easily oxidized at a low temperature of 350 ° C. or lower using the above catalyst. Can do.

  However, methane is the most stable compound among hydrocarbons, and it is difficult to oxidize and remove the catalyst at a low temperature of 400 ° C. or lower. For example, in Non-Patent Document 2, when the catalyst inlet temperature is set to 500 ° C., sufficient methane removal performance is not obtained unless the methane concentration is about 0.3%, and the methane concentration is 0.423%. Even in this case, it is indicated that sufficient methane removal performance cannot be obtained unless the catalyst inlet temperature is 490 ° C. or higher. In order to preheat a large amount of coal mine ventilation gas to about 500 ° C. at room temperature, a large-capacity heat exchanger is required, and there is a problem that economic efficiency deteriorates. Further, when the catalyst inlet temperature is about 500 ° C., the reaction heat of methane oxidation is added and the catalyst outlet temperature becomes about 600 ° C. to 700 ° C. This deteriorates the durability of the catalyst and also causes a problem that the cost of piping and heat exchanger increases due to the problem of heat-resistant temperature.

  Coal mine ventilation gas is derived from sulfur compounds in coal and contains trace amounts of sulfur compounds (hydrogen sulfide, methyl mercaptan, dimethyl sulfide, sulfur dioxide, etc.). These become strong catalyst poisons and make the catalytic oxidation of methane at low temperatures even more difficult. For example, Lee et al. Examined the effect of hydrogen sulfide on the oxidation of methane using a Pd catalyst, and when 26 ppm of hydrogen sulfide coexists, the 50% removal temperature of methane increases by more than 200 ° C. from 360 ° C. to 580 ° C. (Non-Patent Document 5).

  As a catalyst for removing oxidation of methane in combustion exhaust gas, a catalyst in which iridium and platinum are supported on a zirconia support and a catalyst in which iridium and platinum are supported on a titania support are known (Patent Documents 1 and 2). These catalysts can oxidize and remove methane at a relatively low temperature of about 350 to 400 ° C. even under conditions where sulfur dioxide coexists in addition to high-concentration water vapor. However, there are the following problems when applying this catalyst to the treatment of coal mine ventilation gas.

  First, it is necessary to ensure the durability of the catalyst against reducing sulfur compounds such as hydrogen sulfide and mercaptans. In general, in the poisoning with a sulfur compound, it is considered that a reducing sulfur compound in which a sulfur atom itself can coordinate to an active site is a stronger poison.

  Furthermore, the methane concentration in the coal mine ventilation gas fluctuates over a wide range of 0.1 to 1%, and it is difficult to predict the fluctuation. Therefore, simply combining a heat exchanger and a catalyst will reduce the methane concentration. If it drops rapidly, the gas temperature at the catalyst inlet will drop and sufficient removal performance will not be obtained. Conversely, if the methane concentration rises rapidly, the catalyst layer temperature will rise rapidly and recover. This will cause an impossibility of catalyst activity deterioration. In particular, when the methane concentration increases rapidly, the catalyst inlet temperature also increases due to the effect of heat exchange, which further increases the catalyst layer temperature, causing a rapid increase in the catalyst layer temperature within a short time. There is a risk of catastrophic destruction of the catalyst and heat exchanger. Gas preheating is combined with heat exchange in addition to heat exchange, and when the preheating temperature (= catalyst inlet temperature) rises above a certain level, combustion of the burner is stopped to stabilize the catalyst inlet temperature. A method is also known (Patent Document 3). However, this method requires fuel for the burner, so that the operation cost increases. When the methane concentration increases, the catalyst outlet temperature rises. Since the process goes up, the time delay from the increase in the methane concentration to the detection of the rise in the catalyst inlet temperature is large, and when the methane concentration fluctuates rapidly, deterioration of the catalyst activity cannot be avoided.

International Publication WO2002 / 040152 JP 2008-246473 A Japanese Patent Laid-Open No. Sho 62-254826

Shi Su et al., Progress in energy and combustion science, Vol. 31, 123-170 (2005) Shi Su and Jenny Agnew, Fuel 85, 1201-1210 (2006) Toshihiko Sakurai, Catalyst, 35, 304-311 (1993) Jensings et al., “Catalytic incineration for control of volatile organic compound emissions,” Noyes Publishing), New Jersey, USA (1985). Lee, et al., Catalysis Today, 47, 353-357 (1999).

  The present invention removes methane from a gas containing a low concentration of methane that is lower than the lower limit of methane combustion limit (explosion limit) and does not enter the flammable range when mixed with air at any ratio, such as coal mine ventilation gas. A methane removal method that ensures sufficient methane removal performance even when sulfur compounds coexist, and stable removal performance over a long period of time without degrading performance even if the methane concentration fluctuates greatly. And the main object is to provide a device.

〔Constitution〕
In order to achieve the above objective, the removal of low-concentration methane that contains reducing sulfur compounds and removes methane from gas to be treated that contains low-concentration methane that does not enter the flammable range when mixed with air in any proportion The characteristic configuration of the method is
The gas to be treated is preheated through a low-temperature channel of a heat exchanger, and then methane is catalytically oxidized through a catalyst having iridium and platinum supported on a support made of zirconia, titania or a mixture thereof, and the heat exchanger Supply heat to the discharge channel after heat recovery through heat exchange with the gas to be treated before reaction through the high temperature channel,
A part of the gas to be treated supplied to at least one of the low-temperature channel and the high-temperature channel leading to the heat exchanger is short-circuited between the upstream side and the downstream side of the heat exchanger in the channel. The remaining portion is circulated through the flow path leading to the heat exchanger, and the ratio of the gas to be treated that leads to the short-circuit flow path to the total amount of the gas to be treated is expressed as methane in the gas to be treated. The lower the concentration is, the lower the setting is, and the higher the methane concentration is, the higher the ratio is set, so that the oxidation catalyst inlet temperature is 350 ° C. or higher and the oxidation catalyst outlet temperature is 550 ° C. or lower. .

[Function and effect]
According to the characteristic configuration of the present invention, in order to employ a configuration including a heat exchanger and recovering heat generated by methane removal into a gas introduced into the oxidation catalyst, depending on the methane concentration of the gas to be processed The temperature of the oxidation catalyst can be appropriately maintained by changing the flow rate ratio leading to the short-circuit channel that short-circuits the heat exchanger. That is, for example, when the methane concentration is low, the flow rate leading to the short circuit that short-circuits the heat exchanger decreases, and conversely, when the methane concentration is high, the flow rate that leads to the short circuit that short-circuits the heat exchanger By increasing this, fluctuations in the temperature at the oxidation catalyst inlet can be suppressed.

  Thereby, high methane removal performance is obtained and the performance of the catalyst is maintained over a long period of time. In the present application, the temperature of the oxidation catalyst inlet or the temperature of the oxidation catalyst outlet both mean the gas temperature at the relevant part.

Then, as such oxidation catalyst used in the low-concentration methane removing method, zirconia or titania, or a catalyst, or carrying iridium and platinum on a support consisting of a mixture thereof, palladium and platinum on a support consisting of zirconia or titania, or mixtures thereof Is used.

These catalysts can oxidize methane even at a low temperature of about 350 ° C. to 400 ° C., and their activity decrease due to the sulfur compound is small. Therefore, it is not necessary to increase the capacity of the heat exchanger, and the economy is excellent.

  As will be described later with reference to FIGS. 9 and 11, in the configuration in which a heat exchanger is provided to recover the heat generated by the oxidation removal to the gas that leads to the oxidation catalyst, the entire amount of the gas to be treated is subjected to heat exchange. When it goes to the vessel, the temperature at the oxidation catalyst outlet rises as the methane concentration of the gas to be treated rises. As described above, when the temperature at the oxidation catalyst outlet rises above the allowable upper limit temperature, the oxidation catalyst deteriorates and the life becomes short. Also, special considerations are required for equipment such as heat exchangers. In contrast, according to the configuration of the present application, when a part of the gas to be treated is guided to the short-circuit channel that short-circuits the heat exchanger and the flow rate ratio leading to the short-circuit channel increases as the methane concentration increases, the temperature of the oxidation catalyst outlet Can be avoided. For this reason, the oxidation catalyst has a long life, and it is not necessary to take special measures against high temperatures in the heat exchanger or the like, and a good operation can be continued for a long time.

  A short-circuit channel that short-circuits the heat exchanger has the same effect whether it is provided on either the low temperature side (before the catalyst) or the high temperature side (after the catalyst) of the heat exchanger. This is advantageous because the valve does not require heat resistance.

As described above, the oxidation catalyst inlet temperature is 350 ° C. or higher and the oxidation catalyst outlet temperature is 550 ° C. or lower .

By setting it as such temperature conditions, the oxidation removal ability of methane can be maintained well even in the presence of a sulfur compound, and further, deterioration of the oxidation catalyst can be prevented .

〔Constitution〕
It is preferable that the to-be-processed gas containing the low concentration methane demonstrated so far is a gas discharge | released by ventilation of a coal mine.

[Function and effect]
The technology that can contribute to the prevention of global warming can be provided by treating the coal mine ventilation gas that has been conventionally released into the atmosphere using the method for removing low-concentration methane according to the present application.

The above-described method for removing low-concentration methane according to the present invention can be implemented by a low-concentration methane removal apparatus having the following configuration.
That is, zirconia or titania that catalytically oxidizes methane as a device for removing low-concentration methane from gas to be treated that contains reducible sulfur compounds and does not enter the flammable range even if mixed with air at any ratio Or, a support made of a mixture thereof is provided with an oxidation catalyst supporting iridium and platinum, a blower for introducing the gas to be treated into the oxidation catalyst, and a low-temperature flow path and a high-temperature flow path before and after communicating with the oxidation catalyst A heat exchanger that exchanges heat with
Furthermore, a short-circuit channel that short-circuits the upstream side and the downstream side of the heat exchanger in the channel is provided for at least one of the low-temperature channel and the high-temperature channel that communicates with the heat exchanger. In addition, while providing a part of the gas to be treated to the short-circuit flow path, a flow rate adjusting valve is provided for flowing the remainder to the flow path to the heat exchanger,
The ratio of the gas to be processed that leads to the short-circuit flow path to the total amount of the gas to be processed is set to be lower as the methane concentration in the gas to be processed is lower and higher as the methane concentration is higher. A control means can be provided in which the temperature is 350 ° C. or higher and the temperature at the oxidation catalyst outlet is 550 ° C. or lower.

[Function and effect]
By adopting this configuration, high methane removal performance can be obtained, and the performance of the catalyst can be maintained for a relatively long period of time, and the same actions and effects as described above can be obtained.

  In the methane removal method of the present invention, since a catalyst exhibiting very excellent resistance to activity inhibition by sulfur compounds can be used, various sulfur compounds (hydrogen sulfide, methyl mercaptan, dimethyl, etc., such as coal mine ventilation gas) can be used. Even if sulfide, sulfur dioxide, etc. are contained, methane can be removed from a temperature as low as about 350 ° C. Therefore, the capacity of the heat exchanger can be reduced as compared with the prior art, and the economic efficiency is greatly improved. Further, in the low concentration methane removal method of the present invention, even if the methane concentration in the gas to be treated fluctuates rapidly, the catalyst outlet temperature can always be kept stably at 550 ° C. or lower, so that the durability of the catalyst is improved. In addition to ensuring stable methane removal performance over a long period of time, there is no need to use expensive materials for piping and heat exchangers, and the economy is greatly improved.

It is a figure which shows an example of a structure of the methane removal apparatus of this invention. It is a figure which shows another example of a structure of the methane removal apparatus of this invention. It shows the time course of Ir-Pt / sulfur compounds zirconia catalyst _{(CH 3 SH 1.5 ppm + H} 2 S 1.5 ppm) methane removal performance and performance under co Ir-Pt / sulfur compounds zirconia catalyst (SO ₂ 3 ppm) shows changes with time of the methane removal performance and performance under co It shows the time course of pd-Pt / sulfur compounds alumina catalyst _{(CH 3 SH 1.5 ppm + H} 2 S 1.5 ppm) methane removal performance and performance under co Pd-Pt / sulfur compounds alumina catalyst (SO ₂ 3 ppm) shows changes with time of the methane removal performance and performance under co Ir-Pt / sulfur compounds titania catalyst (SO ₂ 3 ppm) shows changes with time of the methane removal performance and performance under co It shows the time course of pd-Pt / sulfur compounds zirconia catalyst _{(CH 3 SH 1.5 ppm + H} 2 S 1.5 ppm) methane removal performance and performance under co The figure which shows the relationship of the catalyst inlet_port | entrance and outlet temperature with respect to the methane density | concentration in the case of letting the whole amount of to-be-processed gas pass to a heat exchanger regardless of the methane density | concentration irrespective of the method of this invention The figure which shows an example of the relationship between the flow rate ratio which leads to the short circuit flow path which short-circuits a methane concentration and a heat exchanger in the method of this invention. The figure which shows the relationship of the catalyst inlet_port | entrance and outlet temperature with respect to the methane density | concentration in the case of making the flow rate ratio which leads to the short circuit flow path which short-circuits a heat exchanger according to the methane concentration according to the method of this invention.

  The apparatus 100 for removing low-concentration methane according to the present invention includes a blower 1 for introducing the gas G to be treated into the apparatus 100, an oxidation catalyst 2 for catalytically oxidizing methane (in FIG. 1, the oxidation catalyst is housed in a treatment cylinder). A heat exchanger 3 for exchanging heat between the gas Gin on the low-temperature channel 3a side before and after the oxidation catalyst 2 and the Gout on the high-temperature channel 3b side, and upstream of the oxidation catalyst 2 Detection means 4 such as a gas sensor for detecting the concentration of methane disposed is provided. Moreover, while providing the short circuit flow path 7 which short-circuits the upstream and downstream sides of the heat exchanger 3 in the low temperature flow path 3a, the short circuit flow which short-circuits the low temperature flow path 3a and the heat exchanger 3 through the heat exchanger 3 is provided. A flow rate adjusting valve 5 for adjusting a flow rate ratio with the passage 7 and a control means 6 for controlling a flow rate ratio leading to the short-circuit channel 7 according to a detection value of the detection means 4.

  As described above, the control unit 6 controls the flow rate control valve 5 in accordance with the methane concentration detection value of the detection unit 4, but the control mode of the control unit 6 according to the present application determines the flow rate ratio leading to the short-circuit channel 7. According to the methane concentration of the gas to be treated, the flow rate ratio when the methane concentration is high is increased with respect to the flow rate ratio when the methane concentration is low.

[Oxidation catalyst]
The oxidation catalyst 2 is preferably a catalyst in which iridium and platinum are supported on a support made of zirconia or titania or a mixture thereof, or a catalyst in which palladium and platinum are supported on a support made of zirconia, titania or a mixture thereof. These catalysts can oxidize and remove methane even at a low temperature of about 350 ° C. to 400 ° C., and their activity decrease is small even when a sulfur compound such as hydrogen sulfide or sulfur dioxide coexists.

Oxidation catalyst a
FIG. 3 shows a gas simulating coal mine ventilation gas on a zirconia support (BET specific surface area 17 m ² / g) on which 3 wt% of Ir and 2 wt% of Pt are supported (particle diameter: about 1 mm, 1.45 g). ₄ 1000 ppm, O ₂ 20%, H ₂ O 3%, balance N ₂ ) at a flow rate of 120 l / h (equivalent to space velocity per gas hour (GHSV) 80,000 h ⁻¹ )) The temperature dependence of the removal rate is shown. In the initial activity, a methane removal rate of 50% was obtained at 350 ° C., and it can be seen that the reaction starts sufficiently if the catalyst inlet temperature is about 350 ° C. Subsequently, when a sulfur compound (CH ₃ SH 1.5 ppm + H ₂ S 1.5 ppm) was added and the reaction was continued at 400 ° C., and the methane removal rate after 20 and 60 hours had elapsed, the activity was Although there was a slight decrease, methane removal rates of 38% (after 20 hours) and 35% (after 60 hours) were obtained at 350 ° C., and the decrease in activity was small even when a sulfur compound was present. Even if the sulfur compound is changed to 3 ppm of SO _2, the results are almost the same (FIG. 4), and it is confirmed that the catalyst having Ir and Pt supported on the zirconia support exhibits high methane removal performance regardless of the form of the sulfur compound. It was done.

Oxidation catalyst b
FIGS. 5 and 6 show the same for methane with a catalyst (particle size: about 1 mm, 1.45 g) in which Pd 3 wt% and Pt 2 wt% are supported on an alumina support (γ type, BET specific surface area 125 m ² / g). The result of evaluating the removal performance is shown (corresponding to GHSV 63,000 h ⁻¹ ). Conventionally, a catalyst in which Pd or Pt supported on VOC oxidation is supported on an alumina carrier has the same initial activity as a catalyst in which Ir and Pt are supported on a zirconia carrier, and is used in the low concentration methane removal apparatus of the present application. However, there is also a drawback that the methane removal performance is lost in a short period of time due to the coexistence of sulfur compounds.

Oxidation catalyst c
FIG. 7 shows the results of evaluating the methane removal performance of a catalyst (particle size: about 1 mm, 1.45 g) on which 3 wt% Ir and 2 wt% Pt are supported on a titania support (GHSV 50,000 h ^−1). Equivalent). In the initial activity, a methane removal rate of 90% was obtained at 350 ° C., and a methane removal rate of 59% was obtained even after 60 hours in the presence of SO ₂ .

Oxidation catalyst d
FIG. 8 shows the result of evaluating the methane removal performance in the same manner for a catalyst (particle size: about 1 mm, 1.45 g) supporting 3 wt% Pd and 2 wt% Pt on a zirconia support (GHSV 80,000 h ^−1). Equivalent). In the initial activity, a methane removal rate of 83% was obtained at 400 ° C., and a methane removal rate of 52% was obtained at 400 ° C. even after 60 hours in the presence of a sulfur compound. If the catalyst inlet temperature is set to 400 ° C. or higher, even if a sulfur compound coexists, the present catalyst works effectively.

  In the above test, the reaction was continued at 400 ° C. for 60 hours, but the catalytic activity after the reaction at higher temperatures (500 ° C., 550 ° C.) was also examined. As shown in Table 1, the activity of iridium and platinum supported on a zirconia or titania support (oxidation catalysts a and c) is not substantially reduced or increased rather than 500 ° C. At 550 ° C., the activity decreased slightly. In the catalyst conventionally used for VOC treatment, Pt / alumina can be used up to about 600 ° C. and Pd / alumina can be used up to about 700 ° C. However, in the case of a catalyst in which iridium and platinum are supported on a zirconia or titania support. It is understood that methane oxidation is possible at a lower temperature than the conventional catalyst, but the heat-resistant temperature of the catalyst is also lowered.

The shape of the oxidation catalyst 2 is not limited, but from the viewpoint of reducing the power of the blower 1 as much as possible, a honeycomb shape with a small pressure loss is preferable, and a shape in which a cordierite or metal honeycomb is wash-coated has high strength and heat resistance. Is also particularly preferred.
If the amount of the oxidation catalyst 2 used is too small, effective methane removal performance cannot be obtained, but if it is too large, it is economically disadvantageous, so that the space velocity per gas hour (GHSV) is 1,000 to It is preferable to use an amount of 200,000 h ⁻¹ , more preferably about 20,000 to 100,000 h ⁻¹ .

〔Heat exchanger〕
The heat exchanger 3 used in the present invention may be of any type as long as gas-to-gas heat exchange is possible and pressure loss is suppressed to a low level, but a plate-and-fin usually known as a compact heat exchanger 3 is used. A heat exchanger of the type or a rotary heat storage type heat exchanger is preferable. Although the heat transfer area of the heat exchanger to be used can be selected as appropriate, it is preferable to select the heat exchanger 3 so that the NTU is about 5 to 15 with respect to the discharge amount of the coal mine ventilation gas.

[Detection means]
The methane concentration detection means 4 used in the present invention may be of any type as long as it has sufficient responsiveness and stability. For example, a non-dispersive infrared methane concentration meter, a semiconductor gas sensor such as tin oxide, etc. Can be used.

The above is the description of the low-concentration methane removal apparatus 100 according to the present invention. Hereinafter, the low-concentration methane removal method according to the present invention will be described.
In the method for removing low-concentration methane according to the present invention, the gas to be treated G containing methane is preheated through the heat exchanger 3, then passed through the oxidation catalyst 2 for catalytic oxidation of methane, and again through the heat exchanger 3. In addition to performing heat recovery by heat exchange with the gas before the reaction, a part of the gas to be processed is passed through a short-circuit channel 7 provided by short-circuiting the heat exchanger 3 according to the methane concentration of the gas to be processed. The flow rate ratio led to the short-circuit channel 7 is changed in such a manner that the flow rate ratio when the methane concentration is high is increased with respect to the flow rate ratio when the methane concentration is low.

As an example, consider the treatment of coal mine ventilation gas (discharged 100 m ³ / s, 25 ° C.) that fluctuates between methane concentrations of 0.3-0.75%. In the case of this example, it is assumed that the amount of gas to be treated is maintained at a constant amount (100 m ³ / s).
Assuming that the NTU of the heat exchanger 3 is 10 and a heat dissipation loss of 25 kW occurs in the oxidation catalyst and the connecting pipes, the methane concentration The gas temperature at the catalyst inlet 2in and outlet 2out varies with respect to FIG. Actually, when the temperature at the inlet of the oxidation catalyst is lowered to 350 ° C. or lower (indicated by a one-dot chain line in FIGS. 9 and 11), the methane removal performance of the oxidation catalyst is lowered. On the other hand, if the temperature of the oxidation catalyst outlet exceeds 550 ° C. (indicated by a two-dot chain line in FIGS. 9 and 11), the catalyst cannot be recovered, so that methane removal can be performed stably stably. The methane concentration is only a very limited range of 0.3-0.4%.

  In contrast, the flow rate of the heat exchanger 3 in the short-circuit channel 7 according to the increase in methane concentration (0% when no gas flows through the short-circuit channel 7 and 100% when the entire amount flows through the short-circuit channel 7) % Corresponding to each%). As a result, when the flow rate ratio of the short-circuit channel 7 is controlled as shown in FIG. 10, for example, the catalyst inlet temperature can be maintained substantially constant up to a methane concentration of 0.3% to 0.75%, and the catalyst outlet It was found that the temperature could be maintained below 550 ° C. (FIG. 11).

[Another embodiment]
(1) In the above embodiment, the short-circuit channel 7 for short-circuiting the heat exchanger 3 is provided in the low-temperature channel 3 a of the heat exchanger 3, but the same is true even if provided in the high-temperature channel 3 b of the heat exchanger 3. (See FIG. 2). However, in this case, since the flow regulating valve 5 is exposed to a high temperature, it may be preferable to install it at the connection point on the downstream side of the short-circuit channel 7.
(2) The methane concentration detection means 4 is preferably installed in the vicinity of the inlet of the apparatus from the viewpoint of detecting a change in the methane concentration as quickly as possible, from the meaning of detecting the methane concentration of the gas to be treated. Is preferably provided in the suction tube 8. However, it is also possible to provide between the outlet of the blower 1 and the inlet of the heat exchanger 3 or between the outlet of the heat exchanger 3 and the inlet of the oxidation catalyst 2.
(3) The apparatus for removing low-concentration methane of the present invention may further be provided with means for measuring the gas temperature at the oxidation catalyst inlet and the oxidation catalyst outlet as necessary. As a result, even when an abnormality occurs in the methane concentration detection means 4, the apparatus can be stopped more safely.

  When removing methane from a gas containing low-concentration methane that does not enter the flammable range even if mixed with air at any ratio, such as coal mine ventilation gas, sufficient methane removal performance can be achieved even if sulfur compounds coexist. As a result, it was possible to provide a low-concentration methane removal method and apparatus capable of obtaining stable removal performance over a long period of time without degrading performance even when the methane concentration fluctuates greatly.

1: Air blower 2: Oxidation catalyst 3: Heat exchanger 4: Methane concentration detection means 5: Flow rate adjusting valve 6: Control means 7: Short circuit 8: Suction pipe

Claims (3)

A method for removing low-concentration methane that contains a reducing sulfur compound and removes methane from the gas to be treated containing low-concentration methane that does not enter the flammable range even if mixed with air at any ratio,
The gas to be treated is preheated through a low-temperature channel of a heat exchanger, and then methane is catalytically oxidized through a catalyst having iridium and platinum supported on a support made of zirconia, titania or a mixture thereof, and the heat exchanger Supply heat to the discharge channel after heat recovery through heat exchange with the gas to be treated before reaction through the high temperature channel,
A part of the gas to be treated supplied to at least one of the low-temperature channel and the high-temperature channel leading to the heat exchanger is short-circuited between the upstream side and the downstream side of the heat exchanger in the channel. The remaining portion is circulated through the flow path leading to the heat exchanger, and the ratio of the gas to be treated that leads to the short-circuit flow path to the total amount of the gas to be treated is expressed as methane in the gas to be treated. Low concentration methane is set so that the lower the concentration is, the higher the methane concentration is, and the higher the methane concentration is, the condition is that the oxidation catalyst inlet temperature is 350 ° C. or higher and the oxidation catalyst outlet temperature is 550 ° C. or lower. Removal method.   The method for removing low-concentration methane according to claim 1, wherein the gas containing low-concentration methane is a gas released by ventilation in a coal mine. A device for removing low-concentration methane from a gas to be treated containing low-concentration methane that contains a reducing sulfur compound and does not enter the flammable range even if mixed with air at any ratio,
Provided with an oxidation catalyst supporting iridium and platinum on a support made of zirconia or titania or a mixture thereof for catalytically oxidizing methane, a blower for introducing the gas to be treated into the oxidation catalyst, and before and after the oxidation catalyst A heat exchanger that exchanges heat between the low-temperature channel and the high-temperature channel is provided,
Furthermore, a short-circuit channel that short-circuits the upstream side and the downstream side of the heat exchanger in the channel is provided for at least one of the low-temperature channel and the high-temperature channel that communicates with the heat exchanger. In addition, while providing a part of the gas to be treated to the short-circuit flow path, a flow rate adjusting valve is provided for flowing the remainder to the flow path to the heat exchanger,
The ratio of the gas to be processed that leads to the short-circuit flow path to the total amount of the gas to be processed is set to be lower as the methane concentration in the gas to be processed is lower and higher as the methane concentration is higher. An apparatus for removing low-concentration methane, provided with a control means in which the temperature is 350 ° C. or higher and the temperature at the oxidation catalyst outlet is 550 ° C. or lower.

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