JP4959742B2 - Digestion gas deoxygenation method and apparatus - Google Patents

Description

  The present invention relates to a digestion gas deoxygenation method and apparatus for removing oxygen remaining in methane gas purified from digestion gas generated by subjecting organic waste to methane fermentation.

Currently, methane fermentation treatment is frequently used to treat organic waste with relatively high water content. The gas generated by this methane fermentation treatment is usually called “digestion gas”, and the components in the digestion gas are about 60% by volume of methane and about 40% by volume of carbon dioxide. Furthermore, sulfur impurities such as 100 to 3000 ppm of hydrogen sulfide (hereinafter referred to as “H ₂ S”) and about 0.3% by volume of oxygen are also included as trace amounts of impurities. This digestion gas is used as a fuel gas. For example, it is a fuel such as a boiler for producing hot water or steam, such as a gas engine for power generation, a gas turbine, or a fuel cell. In recent years, it is highly desired that this digestion gas be further purified and supplied as city gas. However, in order to refine this digestion gas and use it as city gas, it is necessary to remove sulfur impurities such as H ₂ S and oxygen. Moreover, as a technique for removing the organic sulfur compound and oxygen, for example, a technique described in Patent Document 1 is known.

  The technique for removing the organic sulfur compound and oxygen disclosed in Patent Document 1 is as follows. This technique includes a first catalyst containing palladium in a reactor and a second catalyst containing at least one of molybdenum, nickel, or cobalt, and is heated at 300 to 450 ° C. from methane gas containing an organic sulfur compound and oxygen. The organic sulfur compound and oxygen are removed at the same time.

However, the technology for removing organic sulfur compounds and oxygen disclosed in Patent Document 1 first converts oxygen that inhibits desulfurization of organic sulfur compounds into water vapor on the first catalyst, and then organic sulfur on the second catalyst. Since the compound is to be converted to H ₂ S, the digestion gas is purified, and when oxygen remaining in the purified gas is removed, a high temperature is required, and H ₂ is contained in the purified gas. A lot of S remains. The applicant has already filed a new patent application as an invention for solving these problems (see Patent Document 2).

JP 58-215488 A Japanese Patent Application No. 2008-218511

According to the invention described in Patent Document 2, the digestion gas is purified by the high-pressure water absorption method, and the high temperature is not required when removing the oxygen remaining in the purified methane gas. In addition, H ₂ S and siloxane compounds that cannot be completely removed in the methane gas purified by this high-pressure water absorption method are very small.

However, even if H ₂ S is very small, if the catalyst packed in the catalyst tower is continuously poisoned, the performance of the catalyst gradually deteriorates. Deterioration of the catalyst performance in this way becomes an obstacle to extending the life of the digestion gas deoxygenation device.

The object of the present invention is to eliminate oxygen remaining in methane gas purified by the high-pressure water absorption method without requiring a high temperature and at least preventing the catalyst from deteriorating due to H ₂ S. An object of the present invention is to provide a digestion gas deoxygenation method and apparatus capable of extending the service life.

In order to achieve this object, the invention according to claim 1 of the present invention provides:
The digestion gas generated by subjecting the organic waste to methane fermentation is compressed and compressed by a compressor, the pressurized digestion gas is supplied to an absorption tower, and the digestion gas and water pressurized in the absorption tower are supplied. The step of purifying methane gas by dissolving carbon dioxide and sulfur-based impurities contained in the pressurized digestion gas in high-pressure water and separating the carbon dioxide and sulfur-based impurities from the pressurized digestion gas by contacting in a high-pressure state When,
By passing the purified methane gas (hereinafter referred to as “purified gas”) through a first dehumidifier having a function of removing at least H ₂ S together with moisture, H remaining in the purified gas without being completely removed. Removing ₂ S together with moisture;
Adding hydrogen to the purified gas that has passed through the first dehumidifier;
Supplying the purified gas added with hydrogen to a catalyst tower packed with a catalyst, and converting oxygen remaining in the purified gas added with hydrogen into water by catalytic reaction;
By passing the purified gas in which oxygen remaining in the catalyst tower has been converted to water through a second dehumidifier having a function of removing at least moisture, at least moisture from the purified gas in which the oxygen has been converted to water. Removing, and
A digestion gas deoxygenation method characterized by comprising:

The invention according to claim 2 is the invention according to claim 1,
In the step of removing the H2S remaining without being completely removed the refined gas with water, characterized in that the H2S and siloxane compounds using those having a function of removing with water before Symbol first dehumidifier .

The invention according to claim 3 is the invention according to claim 1 or 2,
A gas holder is interposed between the first dehumidifier and the catalyst tower, and the purified gas that has passed through the first dehumidifier is stored in the gas holder.

The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein the catalyst layer space velocity SV of the purified gas to which the hydrogen supplied to the catalyst tower is added is 7, 000h ⁻¹ or less (however, zero is not included).

  The invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein in the step of adding hydrogen to the purified gas that has passed through the first dehumidifier, The molar ratio is 2 or more with respect to the amount of oxygen remaining in the purified gas.

The invention described in claim 6
A compressor that compresses and pressurizes digestion gas generated by methane fermentation of organic waste;
The digestion gas and water pressurized by the compressor are received and contacted in a high-pressure state to dissolve carbon dioxide and sulfur impurities contained in the pressurized digestion gas in high-pressure water and from the pressurized digestion gas. An absorption tower for separating carbon dioxide and sulfur impurities and purifying methane gas;
A first dehumidifier having a function of receiving the purified methane gas (hereinafter referred to as “purified gas”) and removing at least H ₂ S remaining in the purified gas without being removed together with moisture;
Hydrogen supply means for adding hydrogen to the purified gas that has passed through the first dehumidifier;
A catalyst tower that receives a purified gas to which hydrogen has been added by the hydrogen supply means, and is filled with a catalyst for converting oxygen remaining in the purified gas to which hydrogen has been added into water by a catalytic reaction;
A second dehumidifier having a function of receiving a purified gas in which oxygen remaining in the catalyst tower is converted into water and removing at least moisture from the purified gas in which the oxygen is converted into water;
A digestion gas deoxygenation apparatus comprising:

The invention according to claim 7 is the invention according to claim 6 ,
Before SL first dehumidifier, characterized in that the H2S and siloxane compound has a function of removing with water.

The invention according to claim 8 is the invention according to claim 6 or 7 ,
It has a gas holder interposed between the first dehumidifier for storing the purified gas that has passed through the first dehumidifier and the catalyst tower.

The invention according to claim 9 is the invention according to any one of claims 6 to 8, wherein the catalyst layer space velocity SV of the purified gas to which the hydrogen supplied to the catalyst tower is added is 7, 000h ⁻¹ or less (however, zero is not included).

  According to a tenth aspect of the present invention, in the invention according to any one of the sixth to ninth aspects, the hydrogen supply means is provided for the amount of oxygen remaining in the purified gas that has passed through the first dehumidifier. The amount of hydrogen added is characterized by being 2 or more in molar ratio.

As described above, according to the digestion gas deoxygenation method of the present invention,
The digestion gas generated by subjecting the organic waste to methane fermentation is compressed and compressed by a compressor, the pressurized digestion gas is supplied to an absorption tower, and the digestion gas and water pressurized in the absorption tower are supplied. The step of purifying methane gas by dissolving carbon dioxide and sulfur-based impurities contained in the pressurized digestion gas in high-pressure water and separating the carbon dioxide and sulfur-based impurities from the pressurized digestion gas by contacting in a high-pressure state When,
By passing the purified methane gas (hereinafter referred to as “purified gas”) through a first dehumidifier having a function of removing at least H ₂ S together with moisture, H remaining in the purified gas without being completely removed. Removing ₂ S together with moisture;
Adding hydrogen to the purified gas that has passed through the first dehumidifier;
Supplying the purified gas added with hydrogen to a catalyst tower packed with a catalyst, and converting oxygen remaining in the purified gas added with hydrogen into water by catalytic reaction;
By passing the purified gas in which oxygen remaining in the catalyst tower has been converted to water through a second dehumidifier having a function of removing at least moisture, at least moisture from the purified gas in which the oxygen has been converted to water. Removing, and
Therefore, the following effects are achieved.
1) Since there is a step of previously separating carbon dioxide and sulfur-based impurities in digestion gas using a high-pressure water absorption method and purifying methane gas, it is not necessary to remove sulfur-based impurities and oxygen at the same time. Therefore, when oxygen remaining in the purified methane gas is removed, the catalytic reaction does not require a high temperature of 300 to 450 ° C., and sufficient deoxygenation is possible only by adding hydrogen and proceeding the catalytic reaction at room temperature. The method can be realized.
2) In addition, H ₂ S that cannot be completely removed in the methane gas purified by the high-pressure water absorption method can pass through the purified gas through the first dehumidifier provided at the rear stage of the absorption tower. In addition, since it has a step of removing in advance at least the H ₂ S remaining in the purified gas together with moisture, the catalyst is not poisoned by the H ₂ S, the catalyst is prevented from being deteriorated, and the catalyst has a long life. It is possible to realize a digestion gas deoxygenation method that makes it possible. In addition, H ₂ S that cannot be completely removed in the methane gas purified by the high-pressure water absorption method is removed in advance before entering the catalyst tower. As a result, high-purity methane gas is obtained in the final stage. It becomes possible.

Further, according to the digestion gas deoxygenation apparatus according to the present invention,
A compressor that compresses and pressurizes digestion gas generated by methane fermentation of organic waste;
The digestion gas and water pressurized by the compressor are received and contacted in a high-pressure state to dissolve carbon dioxide and sulfur impurities contained in the pressurized digestion gas in high-pressure water and from the pressurized digestion gas. An absorption tower for separating carbon dioxide and sulfur impurities and purifying methane gas;
A first dehumidifier having a function of receiving the purified methane gas (hereinafter referred to as “purified gas”) and removing at least H ₂ S remaining in the purified gas without being removed together with moisture;
Hydrogen supply means for adding hydrogen to the purified gas that has passed through the first dehumidifier;
A catalyst tower that receives a purified gas to which hydrogen has been added by the hydrogen supply means, and is filled with a catalyst for converting oxygen remaining in the purified gas to which hydrogen has been added into water by a catalytic reaction;
A second dehumidifier having a function of receiving a purified gas in which oxygen remaining in the catalyst tower is converted into water and removing at least moisture from the purified gas in which the oxygen is converted into water;
Therefore, the following effects are achieved.
1) Since the high-pressure water absorption method can be used to separate most of the carbon dioxide and sulfur-based impurities in the digestion gas in advance and purify methane gas in the absorption tower, it is necessary to remove sulfur-based impurities and oxygen simultaneously. Disappear. Therefore, when removing the oxygen remaining in the purified methane gas, it is possible to realize a deoxygenation apparatus that can add hydrogen and proceed the catalytic reaction at room temperature without requiring a high temperature of 300 to 450 ° C. in the catalyst tower. .
2) Further, H ₂ S that cannot be completely removed in the methane gas purified by the high-pressure water absorption method is also removed at least from the H ₂ S provided in the rear stage of the absorption tower together with moisture. By passing through the first dehumidifier having a possible function, H ₂ S that cannot be completely removed in the purified gas is removed in advance, so that the catalyst is not poisoned by the H ₂ S, and the catalyst It is possible to realize a digestion gas deoxygenation apparatus that prevents the deterioration of the catalyst and extends the life of the catalyst. In addition, H ₂ S that cannot be completely removed in the methane gas purified by the high-pressure water absorption method is removed in advance before entering the catalyst tower. As a result, high-purity methane gas is obtained in the final stage. It is possible to realize a digestion gas deoxygenation apparatus that can perform such a process.

It is explanatory drawing which illustrates typically the whole structure of the deoxidation apparatus of the digestive gas of Embodiment 1 of this invention. It is explanatory drawing which illustrates typically the whole structure of the deoxidation apparatus of the digestive gas of Embodiment 2 of this invention.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

(Embodiment 1)
FIG. 1 is an explanatory diagram schematically illustrating the overall configuration of a digestion gas deoxygenation apparatus according to Embodiment 1 for carrying out the digestion gas deoxygenation method of the present invention.

In FIG. 1, 1 is a mist separator, 2a and 2b are digestion gas compressors, 3 is an absorption tower (scrubber), 4 is a water supply tank, 5 is a water supply pump, 6 is a water electrolysis device as hydrogen supply means, 7 Is a palladium (Pd) catalyst, 8 is a catalyst tower packed with Pd catalyst 7, 9 is an adsorbent such as molecular sieve as a first dehumidifier having the function of removing H ₂ S and siloxane compounds together with moisture. The adsorption tower 10 used is an adsorption tower using an adsorbent such as a molecular sieve as a second dehumidifier having a function of removing at least moisture.

  Next, the operation of the digestion gas deoxygenation apparatus according to the present invention will be described with reference to FIG.

Digestion gas generated by methane fermentation of organic waste such as organic sludge and organic wastewater is removed by mist separator 1 from mist (water) and dust. The components in the digestion gas after passing through the mist separator 1 are about 60% by volume of methane, about 40% by volume of carbon dioxide, about 0.3% by volume of oxygen, and 100 to 100% of H ₂ S as a sulfur impurity. 3000 ppm, and other impurities (for example, siloxane compound) are extremely small. The digestion gas is compressed by digestion gas compressors 2a and 2b connected in series, and the pressure is increased to a predetermined pressure higher than the atmospheric pressure. The digestion gas pressurized by the digestion gas compressors 2 a and 2 b is introduced into the lower part of the absorption tower 3. On the other hand, from the upper part of the absorption tower 3, it is pumped up by a water supply pump 5 from a water supply tank 4 in which sand filtrate from a sand filtration facility of treated water provided downstream of the final sedimentation basin of the sewage treatment plant is stored. And is supplied in a boosted state. As water used at this time, in addition to using sand filtration water from the sand filtration facility of the treated water provided downstream of the final sedimentation basin of the sewage treatment plant, tap water, well water, or It is also possible to use treated water obtained by treating wastewater such as sewage.

  In this way, the digestion gas compressors 2a and 2b are pressurized and fed into the absorption tower 3 from the lower part thereof, and the water supply pump 5 is pressurized and fed into the absorption tower 3 from the upper part thereof. Thus, the inside of the absorption tower 3 is maintained in a high pressure state satisfying the range of 0.55 to 2.0 MPaG, and the digestion gas and water are brought into contact with each other in the high pressure state satisfying the pressure range in the absorption tower 3. The absorption tower 3 is filled with a packing such as Raschig ring in order to bring the digestion gas and water into sufficient contact.

Sulfur such as carbon dioxide and H ₂ S contained in the digestion gas in a gaseous state by bringing the digestion gas and water into contact with each other at a high pressure satisfying the range of 0.55 to 2.0 MPaG in the absorption tower 3. System impurities are dissolved and absorbed in high-pressure water, while methane gas is taken out from the top of the absorption tower 3 with almost no dissolution in high-pressure water. Further, when purifying methane gas by separating sulfur-based impurities such as carbon dioxide and H ₂ S from the digestion gas, the digestion gas and water are brought into contact in a high pressure state satisfying the range of 0.55 to 2.0 MPaG. Good. The low pressure atmosphere than this range, not carbon dioxide and H _{2 S} sulfur based impurities are sufficiently separated and removed, such as, also, the sulfur-based impurities such as carbon dioxide and H _{2 S} even in the high pressure atmosphere from this range The removal rate is not improved so much, which is not preferable from the viewpoints of operation cost and increase in apparatus cost due to high pressure specifications. In addition, it is more preferable to make digestion gas and water contact in the high pressure state which satisfy | fills the range of 0.7 MPaG or more and less than 1.0 MPaG from the point of a removal rate, an operating cost, and apparatus cost.

Note that most of the H ₂ S and the like from the purified gas having a high concentration of methane gas taken out from the top of the absorption tower 3 by bringing the digestion gas and water into contact at a high pressure of 0.55 MPaG or more as described above. Sulfur impurities and siloxane compounds are removed. However, about 0.3% by volume of oxygen still remains in the purified gas having a high concentration of methane gas taken out from the top of the absorption tower 3, so that it cannot be used as city gas as it is.

Further, in the purified gas having a high concentration of methane gas taken out from the top of the absorption tower 3, H ₂ S and a siloxane compound remain in a very small amount without being removed by the high-pressure water absorption method described above. As described above, if the Pd catalyst 7 in which the catalyst tower 8 is filled with H ₂ S or a siloxane compound is poisoned even if it is extremely small, the performance of the Pd catalyst 7 gradually deteriorates. This is an obstacle to extending the life of digester gas deoxygenation equipment.

Therefore, hydrogen (H ₂ ) is added from the water electrolysis apparatus 6 to the purified gas having a high concentration of methane gas taken out from the top of the absorption tower 3, and the purified gas to which the hydrogen is added is filled with the Pd catalyst 7. The catalyst 8 is sent to the tower 8 and a catalytic reaction as shown in the following formula (1) proceeds at room temperature, and the following treatment is performed in advance before the oxygen in the purified gas is converted to water.
O ₂ + 2H ₂ → 2H ₂ O ――― Formula (1)

That is, a purified gas having a high concentration of methane gas taken out from the top of the absorption tower 3 is passed through an adsorption tower 9 provided at the rear stage of the absorption tower 3, and H ₂ S and siloxane remaining without being completely removed in the purified gas. After removing the compound together with moisture, hydrogen is added from the water electrolysis device 6 and sent to the catalyst tower 8 filled with the Pd catalyst 7. By adopting such a configuration, the Pd catalyst 7 is not poisoned by the both substances, and the deterioration of the Pd catalyst 7 can be prevented. Such a configuration has a significant effect on extending the life of the digestion gas deoxygenation apparatus. In addition, the oxygen concentration in the purified gas can be removed to a predetermined required performance, for example, 0.01% by volume (100 ppm) or less.

  In addition, hydrogen must have a molar amount twice that of oxygen based on the above reaction formula (1). Therefore, it is possible to control oxygen remaining in the purified methane gas to 0.01 volume% (100 ppm) or less by adding hydrogen in a molar ratio of 2 or more with respect to oxygen. The amount of hydrogen added to oxygen is preferably 2 to about 3.3 in molar ratio. Thereby, it is possible to prevent excessive consumption of hydrogen while removing remaining oxygen to a predetermined reference value or less.

The Pd catalyst 7-layer space velocity (SV) of the purified gas to which hydrogen is added can be changed within a range of 7,000 h ⁻¹ or less (excluding zero), preferably 3,000. It is in the range of ˜6,000 h ⁻¹ . As a result, the amount of Pd catalyst 7 to be used is not unnecessarily increased while removing the remaining oxygen to a predetermined reference value or less. Therefore, the size of the catalyst tower 8 can be suppressed.

  This purified gas with reduced oxygen is sent to the adsorption tower 10, and after moisture is sufficiently adsorbed and removed, it is connected to a city gas conduit. The high-pressure water in which sulfur impurities such as carbon dioxide and hydrogen sulfide separated from the digestion gas are dissolved is extracted from the bottom of the absorption tower 3 and supplied to the water treatment facility via the valve V1.

Since it is the above structures, in the digestion gas deoxygenation method and apparatus which concern on this invention, there exist the following effects.
1) Since there is a step of previously separating carbon dioxide and sulfur-based impurities in digestion gas using a high-pressure water absorption method and purifying methane gas, it is not necessary to remove sulfur-based impurities and oxygen at the same time. Therefore, when oxygen remaining in the purified methane gas is removed, the catalytic reaction does not require a high temperature of 300 to 450 ° C., and sufficient deoxygenation is possible only by adding hydrogen and proceeding the catalytic reaction at room temperature. The method can be realized.
2) In addition, H ₂ S that cannot be completely removed in the methane gas purified by the high-pressure water absorption method can pass through the purified gas through the first dehumidifier provided at the rear stage of the absorption tower. In addition, since it has a step of removing in advance at least the H ₂ S remaining in the purified gas together with moisture, the catalyst is not poisoned by the H ₂ S, the catalyst is prevented from being deteriorated, and the catalyst has a long life. It is possible to realize a digestion gas deoxygenation method that makes it possible. In addition, H ₂ S that cannot be completely removed in the methane gas purified by the high-pressure water absorption method is removed in advance before entering the catalyst tower. As a result, high-purity methane gas is obtained in the final stage. It becomes possible.
3) Moreover, since hydrogen obtained by electrolysis of water has high purity, there is little mixing of impurities, and the purity of the purified methane gas can be easily maintained.

  The water electrolysis device 6 in the present embodiment can be used as long as it generates hydrogen, and a preferable water electrolysis device includes a water electrolysis hydrogen generation device using a solid polymer electrolyte membrane or the like. It is possible to use a water electrolysis type high purity hydrogen oxygen generator (trade name: HHOG) manufactured by Shinko Environmental Solution Co., Ltd., which generates high purity hydrogen and oxygen. By using this water electrolysis-type high-purity hydrogen oxygen generator, it is not necessary to store hydrogen in advance using a high-pressure hydrogen cylinder, and high-purity hydrogen is required when the power is turned on / off. It is safe to supply only a small amount. Further, it is possible to control the amount of hydrogen by detecting the concentration with respect to fluctuations in the oxygen concentration in methane gas. Thus, it is possible to control the amount of oxygen remaining in the purified methane gas. Further, as described later, high-purity oxygen can be supplied at the same time.

  In the present embodiment, a coalescer as a mist separator is not shown in front of the adsorption tower 9 and the adsorption tower 10, but it is preferable to install a coalescer. By doing so, scattered water can be removed.

Further, the purified gas in the present embodiment has been described as an example using a molecular sieve having a function of removing H _{2 S} and siloxane compound together with water in an adsorption column as dehumidifier, leaving the absorption tower 3 In the case where no siloxane compound remains, it is sufficient if it has a function of removing H ₂ S together with moisture. That is, the first dehumidifier only needs to have a function capable of removing at least H ₂ S together with moisture.

In the present embodiment, similarly to the adsorption tower 9, the adsorption tower 10 as a dehumidifier is described with an adsorption tower using a molecular sieve having a function of removing H ₂ S and a siloxane compound together with moisture as an example. However, the present invention is not necessarily limited to this, and if it is a molecular sieve, for example, it is possible to use any of molecular sieves 3A, 4A, 5A, and 13X having a function of removing at least moisture, As a necessary condition, any dehumidifier having a function of removing moisture may be used. In addition, the adsorbent is not an adsorbent such as a molecular sieve having the function of removing H ₂ S and siloxane compounds together with water, but for example, water adsorbent, silica light or acid treatment was applied as the H ₂ S adsorbent. A dehumidifier in which acid-treated silica gel is used as silicalite and siloxane compound adsorbent, and these adsorbents are placed in an adsorption tower may be used.

  Hereinafter, the following laboratory tests were conducted in order to confirm the effects of the present invention.

Example 1
In FIG. 1, a test was conducted to examine the relationship between the amount of hydrogen added to the purified gas that passed through the adsorption tower 9 and the amount of oxygen remaining in the purified gas exiting from the catalyst tower 8. Since H ₂ S and the siloxane compound are removed together with moisture from the purified gas that has passed through the adsorption tower 9, the oxygen concentration is 0.3 vol% and the hydrogen concentration is 0.55 to 1.0 vol% as the test gas. A dry gas composed of the remaining methane gas was used. In this test gas, those having hydrogen concentrations of 0.55, 0.6, 0.8, and 1.0% by volume were tested. 1, 2, 3, 4 (see Table 1 below). Other test conditions are as follows.
Size of catalyst tower 8: Diameter 27 mm-Length 300 mm
Volume of catalyst 7 layers: 67 mL (L means liter)
Flow rate of the test gas: 200 L / h (SV = 3,000 h ⁻¹ equivalent)
Pressure of the above test gas: 0.9 MPaG

  As shown in Table 1 above, when a test gas having a hydrogen concentration of 0.6, 0.8, 1.0% by volume (Test Nos. 2, 3, 4) was used, the test exited from the catalyst tower 8 The amount of oxygen remaining in the gas becomes 0 ppm, and oxygen can be removed to a predetermined required performance, for example, 0.01% by volume (100 ppm) or less. However, when the hydrogen concentration is 0.55% by volume (test No. 1), the amount of oxygen remaining in the test gas discharged from the catalyst tower 8 is 200 to 350 ppm, and the predetermined required performance cannot be satisfied. Therefore, the amount of hydrogen to be added needs to be 2 or more in molar ratio with respect to the amount of oxygen remaining in the purified gas. However, the amount of hydrogen added to oxygen is preferably 2 to about 3.3 in terms of molar ratio, considering that hydrogen is not consumed more than necessary.

(Example 2)
In FIG. 1, the amount of oxygen remaining in the purified gas exiting the catalyst tower 8 can satisfy a predetermined required performance (for example, 0.01% by volume (100 ppm or less)) based on a Pd catalyst 7 layer having a predetermined volume. No. conducted a test to examine how much purified gas passed through the adsorption tower 9 to which hydrogen was added. As in Example 1, H ₂ S and siloxane compound are removed together with moisture from the purified gas that has passed through the adsorption tower 9, so that the oxygen concentration is 0.3% by volume and the hydrogen concentration is 0.2% as the test gas. A dry gas composed of 6% by volume and the remaining methane gas was used. The test gas was controlled so that the gas amount was adjusted to SV of 3,000, 4,000, 6,000, and 7,000 h ⁻¹ , respectively. 5, 6, 7, and 8 (see Table 2 below). Other test conditions are the same as those in Example 1.

As shown in Table 2 above, when the SV of the test gas is 3,000, 4,000, 6,000 h ⁻¹ (test No. 5, 6, 7), the test gas exiting from the catalyst tower 8 The remaining oxygen amount is 0 ppm. When the SV of the test gas is 7,000 h ⁻¹ (Test No. 8), the amount of oxygen remaining in the test gas exiting from the catalyst tower 8 is 100 to 200 ppm. Therefore, the catalyst layer space velocity SV of the purified gas that has passed through the adsorption tower 9 to which hydrogen supplied to the catalyst tower 8 is added needs to be 7,000 h ⁻¹ or less (however, zero is not included). Preferably, SV is in the range of 3,000 to 6,000h- ¹ . As a result, the amount of the catalyst 7 to be used is not unnecessarily increased while removing the amount of oxygen remaining in the purified gas from the catalyst tower 8 to a predetermined reference value or less. Therefore, the size of the catalyst tower 8 can also be suppressed.

(Embodiment 2)
FIG. 2 is an explanatory diagram schematically illustrating the overall configuration of a digestion gas deoxygenation apparatus according to Embodiment 2 for carrying out the digestion gas deoxygenation method of the present invention. In the present embodiment, the same components as those in the first embodiment are given the same numbers, and detailed description thereof is omitted, and only different portions are described in detail.

  In FIG. 2, 11 is a gas holder. In the present embodiment, a portion that is significantly different from the first embodiment is that a gas holder 11 is installed between the adsorption tower 9 and the catalyst tower 8, and this part will be described in detail.

  Since the purified gas that has passed through the adsorption tower 9 is once stored by the gas holder 11, the flow rate of the purified gas to the catalyst tower 8 can be easily adjusted. Further, since the adsorption tower 9 is provided in the front stage of the gas holder 11, it is possible to prevent condensation and corrosion in the gas holder 11.

  Moreover, in this Embodiment, although the coalescer as a mist separator is not illustrated in front of the adsorption tower 9, it is preferable to install a coalescer. By doing so, scattered water can be removed.

  In the first and second embodiments, even if the deoxygenation reaction proceeds due to the catalytic reaction in the catalyst tower 8, the temperature of the purified gas containing moisture that has left the catalyst tower 8 rises so much due to the reaction heat. do not do. However, if the temperature rise due to the reaction heat of the purified gas containing moisture exiting the catalyst tower 8 is considerably large, a heat exchanger may be installed between the catalyst tower 8 and the adsorption tower 10. By adopting such a configuration, the purified gas containing moisture whose temperature has been raised can be cooled by a heat exchanger, the temperature can be lowered, and the moisture adsorption capacity in the adsorption tower 10 in the subsequent stage can be increased. Thus, if the water | moisture-content adsorption capacity in the adsorption tower 10 becomes high, it will also become possible to make the adsorption tower 10 as a 2nd dehumidifier compact. In addition, by reducing the temperature of the purified gas containing moisture that has exited the catalyst tower 8, a portion of the moisture in the purified gas is condensed, and a drain trap (see FIG. The amount of water in the purified gas introduced into the adsorption tower 10 is also reduced by separating it in the system and discharging it outside the system, so that the adsorption tower 10 as the second dehumidifier can be made more compact. It becomes possible.

  In addition, as the Pd catalyst 7 in the first and second embodiments, palladium compounds such as metal palladium, palladium oxide, and palladium hydroxide can be used. Further, any catalyst can be used as long as it has an action of promoting the reaction between oxygen and hydrogen at room temperature, such as platinum. Furthermore, those obtained by supporting these catalyst substances on a carrier such as alumina or zeolite can also be used.

DESCRIPTION OF SYMBOLS 1 Mist separator 2a, 2b Digestion gas compressor 3 Absorption tower 4 Water supply tank 5 Water supply pump 6 Water electrolysis apparatus 7 Pd catalyst 8 Catalyst tower 9, 10 Adsorption tower 11 Gas holder

Claims (10)

The digestion gas generated by subjecting the organic waste to methane fermentation is compressed and compressed by a compressor, the pressurized digestion gas is supplied to an absorption tower, and the digestion gas and water pressurized in the absorption tower are supplied. The step of purifying methane gas by dissolving carbon dioxide and sulfur-based impurities contained in the pressurized digestion gas in high-pressure water and separating the carbon dioxide and sulfur-based impurities from the pressurized digestion gas by contacting in a high-pressure state When,
By passing the purified methane gas (hereinafter referred to as “purified gas”) through a first dehumidifier having a function of removing at least H ₂ S together with moisture, H remaining in the purified gas without being completely removed. Removing ₂ S together with moisture;
Adding hydrogen to the purified gas that has passed through the first dehumidifier;
Supplying the purified gas added with hydrogen to a catalyst tower packed with a catalyst, and converting oxygen remaining in the purified gas added with hydrogen into water by catalytic reaction;
By passing the purified gas in which oxygen remaining in the catalyst tower has been converted to water through a second dehumidifier having a function of removing at least moisture, at least moisture from the purified gas in which the oxygen has been converted to water. Removing, and
A method for deoxidizing digestive gas, comprising: In the step of removing the H _{2 S} remaining without being completely removed the refined gas with water, that using those having a function of removing with water the H _{2 S} and siloxane compounds prior Symbol first dehumidifier The method for deoxidizing digestive gas according to claim 1.   A gas holder is interposed between the first dehumidifier and the catalyst tower, and the purified gas that has passed through the first dehumidifier is stored in the gas holder. Item 3. A method for deoxidizing digestion gas according to Item 1 or 2. The catalyst layer space velocity SV of the purified gas to which hydrogen is added to the catalyst tower is 7,000 h ^-1 or less (however, zero is not included). The method for deoxidizing digestion gas according to any one of the above.   In the step of adding hydrogen to the purified gas that has passed through the first dehumidifier, the amount of hydrogen added is set to 2 or more in a molar ratio with respect to the amount of oxygen remaining in the purified gas. Item 5. The digestion gas deoxygenation method according to any one of Items 1 to 4. A compressor that compresses and pressurizes digestion gas generated by methane fermentation of organic waste;
The digestion gas and water pressurized by the compressor are received and contacted in a high-pressure state to dissolve carbon dioxide and sulfur impurities contained in the pressurized digestion gas in high-pressure water and from the pressurized digestion gas. An absorption tower for separating carbon dioxide and sulfur impurities and purifying methane gas;
A first dehumidifier having a function of receiving the purified methane gas (hereinafter referred to as “purified gas”) and removing at least H ₂ S remaining in the purified gas without being removed together with moisture;
Hydrogen supply means for adding hydrogen to the purified gas that has passed through the first dehumidifier;
A catalyst tower that receives a purified gas to which hydrogen has been added by the hydrogen supply means, and is filled with a catalyst for converting oxygen remaining in the purified gas to which hydrogen has been added into water by a catalytic reaction;
A second dehumidifier having a function of receiving a purified gas in which oxygen remaining in the catalyst tower is converted into water and removing at least moisture from the purified gas in which the oxygen is converted into water;
A digestion gas deoxygenation apparatus comprising: Before SL first dehumidifier is deoxygenator digestion gas according to H 2 _S and siloxane compound to claim 6, characterized in that it has a function of removing with water.   The digestion according to claim 6 or 7, further comprising a gas holder interposed between the first dehumidifier for storing the purified gas that has passed through the first dehumidifier and the catalyst tower. Gas deoxygenator. 9. The catalyst layer space velocity SV of the purified gas to which hydrogen is added to the catalyst tower is 7,000 h ⁻¹ or less (however, zero is not included). The digestion gas deoxygenation apparatus of any one of Claims 1. 10. The amount of hydrogen added by the hydrogen supply means with respect to the amount of oxygen remaining in the purified gas that has passed through the first dehumidifier is 2 or more in molar ratio. The digestion gas deoxygenation apparatus of any one of Claims 1.

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