JP2008063392A - Method for recovering methane and apparatus for purifying digestive gas - Google Patents

Method for recovering methane and apparatus for purifying digestive gas Download PDF

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JP2008063392A
JP2008063392A JP2006240585A JP2006240585A JP2008063392A JP 2008063392 A JP2008063392 A JP 2008063392A JP 2006240585 A JP2006240585 A JP 2006240585A JP 2006240585 A JP2006240585 A JP 2006240585A JP 2008063392 A JP2008063392 A JP 2008063392A
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methane
digestion
absorption
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JP5112664B2 (en
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Kyozo Takenaka
恭三 竹中
Akihiro Konishi
章弘 小西
Hiroshi Teraoka
宏 寺岡
Shuichi Kiyama
秀一 木山
Hiroshi Miyamoto
博司 宮本
Tadashi Koyama
忠志 小山
Katsuo Matsumoto
勝生 松本
Shiro Toyohisa
志朗 豊久
Tomohiro Maruyama
智裕 丸山
Takeo Yoshigae
武男 吉ヶ江
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Shinko Pantec Co Ltd
National Research and Development Agency Public Works Research Institute
Kobe City
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Public Works Research Institute
Kobelco Eco Solutions Co Ltd
Kobe City
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for operating an apparatus for purifying a digestive gas designed to improve the recovery ratio of dissolved methane in absorbing water in a vacuum tank even when the amount of the absorbing water is increased by a rise in water temperature of the absorbing water and thereby easily maintain the methane concentration in purified gas constant. <P>SOLUTION: The method for operating the apparatus for purifying the digestive gas equipped with a digestive gas compressor for compressing the digestive gas fed from a digestive tank after removing mist and an absorption column for dissolving carbon dioxide, etc., in the digestive gas compressed with the digestive gas compressor in the absorbing water and removing the carbon dioxide, etc., is carried out as follows. The absorbing water taken out of the absorption column is fed and decompressed to diffuse a gas, which is returned to the digestive gas compressor. The absorbing water after diffusing the gas is drained to the outside of the system. In the method for operating the apparatus for purifying the digestive gas, the internal pressure of a pressure variable tank is decompressed to a lower pressure than the usual set pressure according to a temperature difference between the water temperature and the set temperature when the water temperature of the absorbing water exceeds the preset set temperature. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

本発明は、消化ガスからメタンを回収するメタン回収方法および消化ガス精製装置の改善に係り、より詳しくは、吸収水の水温の上昇により吸収水量を増加させても、減圧タンクの内圧を減圧させることにより、精製ガス中のメタン濃度およびメタン回収率を容易に一定に保持し得るようにしたメタン回収方法および消化ガス精製装置に関する。   The present invention relates to an improvement in a methane recovery method for recovering methane from digestion gas and a digestion gas purification apparatus. More specifically, the present invention reduces the internal pressure of a decompression tank even if the amount of absorbed water is increased by increasing the temperature of absorbed water. The present invention relates to a methane recovery method and a digestion gas purification device that can easily maintain a constant methane concentration and a methane recovery rate in a purified gas.

周知のとおり、下水処理等においては、最初沈殿池で回収される初沈汚泥や活性汚泥設備から発生する余剰汚泥は、例えば消化槽内でメタン菌等により嫌気性消化を行うことにより余剰汚泥を減容化している。上記のような減容化のための余剰汚泥の嫌気処理によりメタン（ＣＨ４）および二酸化炭素（ＣＯ２）を主成分とする消化ガス（ＣＨ４：約６０容量％、ＣＯ２：約４０容量％、Ｈ２Ｓ、シロキサン等：若干量）が発生する。このような消化ガスは、メタンガスが主成分であるため、従来、嫌気性消化処理を行う消化槽加温用のボイラ用燃料として有効利用されていた。この場合、消化槽加温用のボイラ用燃料として発生ガス量の５０％程度の消化ガスが有効利用されているが、ガス自体が５０００〜６０００ｋｃａｌ／Ｎｍ３と低カロリーであるため、余剰分は都市ガス原料等として有効利用されることもなく、焼却処分されていた。 As is well known, in sewage treatment etc., the initial sludge recovered in the first sedimentation basin and the excess sludge generated from the activated sludge equipment are removed by, for example, anaerobic digestion with methane bacteria in the digestion tank. Volume reduction. Digestion gas (CH 4 : about 60% by volume, CO 2 : about 40% by volume) mainly composed of methane (CH 4 ) and carbon dioxide (CO 2 ) by anaerobic treatment of excess sludge for volume reduction as described above. %, H 2 S, siloxane, etc .: some amount). Since such a digestion gas is mainly composed of methane gas, it has been conventionally used effectively as a boiler fuel for heating a digestion tank that performs anaerobic digestion. In this case, digestion gas of about 50% of the generated gas amount is effectively used as boiler fuel for digestion tank heating, but the gas itself has a low calorie of 5000 to 6000 kcal / Nm 3 , so the surplus is It was incinerated without being effectively used as a city gas raw material.

ところで、近年、環境負荷低減や省エネルギーの観点から、消化ガスの燃料としてのさらなる有効利用が注目されている。消化ガスの利用割合を向上させるには、二酸化炭素、Ｈ２Ｓ、シロキサン化合物等を可能な限り除去して、メタン含有率の高い精製ガスを安価に製造する必要がある。 By the way, in recent years, from the viewpoint of environmental load reduction and energy saving, further effective use of digestion gas as fuel has attracted attention. In order to improve the utilization ratio of digestion gas, it is necessary to remove carbon dioxide, H 2 S, siloxane compounds and the like as much as possible and to produce a purified gas having a high methane content at low cost.

消化ガスを精製することによって、精製メタンガスを製造する従来例に係る消化ガス精製設備（バイオガス精製設備）としては、例えば後述する構成になるものが公知である。
以下、この従来例に係る消化ガス精製設備を、その構成を示すフロー図の図５を参照しながら説明する。この従来例に係る消化ガス精製設備は、汚泥の嫌気性消化を行う消化槽（図示省略）と、脱硫塔５１と、ガスホルダー５２と、バイオガス精製装置である消化ガス精製装置とを備えている。また、この消化ガス精製装置は、コンプレッサー（消化ガス圧縮機）５３と、吸収塔５４と、放散塔（減圧タンク）５６と、ポンプ５５と、除湿器５７とから構成されている。より詳しくは、前記消化槽から脱硫塔５１に供給された消化ガス中の硫黄系化合物である硫化水素（Ｈ２Ｓ）は、前記脱硫塔５１内を通過する間に除去される。そして、Ｈ２Ｓが除去された脱硫後の消化ガスは、一旦低圧のガスホルダー５２に貯留される。ガスホルダー５２に貯留された貯留消化ガスの一部はボイラに供給されるが、残りの消化ガスは、都市ガスとして利用するために消化ガス精製装置の吸収塔５４に送られて精製される。 As a digestion gas purification facility (biogas purification facility) according to a conventional example for producing purified methane gas by purifying digestion gas, for example, one having a configuration described later is known.
Hereinafter, the digestion gas purification facility according to this conventional example will be described with reference to FIG. The conventional digestion gas purification facility includes a digestion tank (not shown) that performs anaerobic digestion of sludge, a desulfurization tower 51, a gas holder 52, and a digestion gas purification device that is a biogas purification device. Yes. The digestion gas purification apparatus includes a compressor (digestion gas compressor) 53, an absorption tower 54, a diffusion tower (decompression tank) 56, a pump 55, and a dehumidifier 57. More specifically, hydrogen sulfide (H 2 S), which is a sulfur compound in the digestion gas supplied from the digestion tank to the desulfurization tower 51, is removed while passing through the desulfurization tower 51. The digested gas after desulfurization from which H 2 S has been removed is temporarily stored in the low-pressure gas holder 52. A part of the stored digestion gas stored in the gas holder 52 is supplied to the boiler, but the remaining digestion gas is sent to the absorption tower 54 of the digestion gas purifier for purification as city gas.

即ち、消化ガスはコンプレッサー（消化ガス圧縮機に相当する）５３により圧縮されて吸収塔５４の塔底から供給される。この吸収塔５４の塔底から供給された消化ガスは、この吸収塔５４の内部に配設されたガス逆流防止板で仕切られた複数の充填層を通って塔頂に至る間中を継続して、この吸収塔５４の塔頂から供給されている吸収水との接触が繰返される。従って、消化ガス中の二酸化炭素等が吸収水に吸収（溶解）されて除去される。
次いで、吸収塔５４の塔頂から流出した二酸化炭素等が除去された消化ガスは、除湿器５７を経て精製メタンガスとして取出される。 That is, the digestion gas is compressed by a compressor (corresponding to a digestion gas compressor) 53 and supplied from the bottom of the absorption tower 54. The digestion gas supplied from the bottom of the absorption tower 54 continues throughout the period through the plurality of packed beds partitioned by the gas backflow prevention plates disposed inside the absorption tower 54 to reach the top of the tower. The contact with the absorption water supplied from the top of the absorption tower 54 is repeated. Accordingly, carbon dioxide or the like in the digestion gas is absorbed (dissolved) in the absorption water and removed.
Next, the digested gas from which carbon dioxide and the like flowing out from the top of the absorption tower 54 have been removed is taken out as purified methane gas via the dehumidifier 57.

一方、吸収塔５４の塔底から排出された二酸化炭素等を吸収した吸収水は放散塔５６の塔頂に送られる。この場合、この吸収塔５４の塔底から排出された吸収水は吸収塔５４と放散塔５６との間の圧力差により、ポンプを用いるまでもなく移送される。放散塔５６内の圧力は大気圧に設定されているので、吸収水に溶解している二酸化炭素等の不要ガス成分は、圧力差による放散により水から除去される。   On the other hand, the absorbed water that has absorbed carbon dioxide discharged from the bottom of the absorption tower 54 is sent to the top of the stripping tower 56. In this case, the absorption water discharged from the bottom of the absorption tower 54 is transferred without using a pump due to a pressure difference between the absorption tower 54 and the diffusion tower 56. Since the pressure in the stripping tower 56 is set to atmospheric pressure, unnecessary gas components such as carbon dioxide dissolved in the absorbed water are removed from the water by stripping due to the pressure difference.

不要ガス成分が除去された吸収水は、放散塔５６の下部の充填部に流下し、放散塔の塔底から供給される空気やメタンガス等のキャリヤガスと気液接触して、さらに多くの溶解ガスが除去される。吸収水から除去したガスを含んだキャリヤガスは、このキャリヤガスが空気である場合には燃焼用空気として、またメタンガスである場合には燃料ガスの一部としてボイラに送られる。そして、放散塔５６の塔底から排出されたガス除去後の吸収水は、ポンプ５５により加圧されて吸収塔５４に戻され、吸収水として再利用に供されるようになっている（例えば、特許文献１参照。）。
特開２００４−８３５４２号公報（図１） Absorbed water from which unnecessary gas components have been removed flows down to the packed portion at the bottom of the stripping tower 56 and comes into gas-liquid contact with carrier gas such as air or methane gas supplied from the bottom of the stripping tower, thereby further dissolving. Gas is removed. The carrier gas containing the gas removed from the absorbed water is sent to the boiler as combustion air when the carrier gas is air, or as part of the fuel gas when the carrier gas is methane gas. And the absorption water after the gas removal discharged | emitted from the tower bottom of the diffusion tower 56 is pressurized by the pump 55, is returned to the absorption tower 54, and is used for reuse as absorption water (for example, , See Patent Document 1).
Japanese Patent Laying-Open No. 2004-83542 (FIG. 1)

小規模な設備であって、かつ安価に大量の水の利用と排出が可能な下水処理場においては、このような消化ガス精製装置であって、減圧タンクからガス放散後の吸収水を排水する、吸収水を再使用しない吸収水一過式の消化ガス精製装置の適用により、設備費用および運転費用を抑えることが可能となる。この吸収水一過式の消化ガス精製装置の場合には、吸収塔に供給される吸収水の冷却に多大なエネルギーを要するため、通常吸収水の水温制御は行われていない。従って、吸収水の水温は季節や天候等の要件によって変動する。
そして、吸収水の水温が高温になると、ＣＯ２やＨ２Ｓの溶解度の低下により精製ガス中のＣＯ２やＨ２Ｓの含有率が増加する。 In a sewage treatment plant that is a small-scale facility and can use and discharge a large amount of water at low cost, it is such a digestion gas purification device that drains absorbed water after gas emission from a decompression tank. By using an absorption water transient digestion gas refining apparatus that does not reuse absorption water, it is possible to reduce facility costs and operation costs. In the case of this absorption water transient digestion gas purification apparatus, since a large amount of energy is required to cool the absorption water supplied to the absorption tower, the temperature control of the absorption water is not usually performed. Accordingly, the water temperature of the absorbed water varies depending on the requirements such as season and weather.
The temperature of the absorption water becomes a high temperature, CO 2 and H 2 S CO 2 and H 2 S content of the purified gas by a decrease in solubility of the increases.

その場合、二酸化炭素等を除去して、精製ガスのメタン含有率（例えば、９７容量％以上）を一定に維持するために、吸収水量を増加させる必要がある。ところが、吸収水の量を増加させると、吸収水に溶解して吸収塔から抜出されるメタン量が増大し、オフガスとして排出されるメタン量が増大するため、メタン回収率が低下する。即ち、精製ガスのメタン含有率を一定に維持するために吸収水量を増大させるにもかかわらず、メタン回収率を一定に維持することができなくなるという問題がある。   In that case, it is necessary to increase the amount of absorbed water in order to remove carbon dioxide and maintain a constant methane content (for example, 97% by volume or more) of the purified gas. However, when the amount of absorbed water is increased, the amount of methane dissolved in the absorbed water and extracted from the absorption tower increases, and the amount of methane discharged as off-gas increases, so the methane recovery rate decreases. That is, there is a problem that the methane recovery rate cannot be kept constant despite increasing the amount of absorbed water in order to keep the methane content of the purified gas constant.

従って、本発明の目的は、吸収水の水温の上昇により吸収水量を増加させても、減圧タンクの内圧を減圧させて吸収水中の溶存メタンの回収率を向上させ、減圧タンクから排出される吸収水中のメタン含有量を低減することにより、高いメタン回収率（例えば、９８％以上）を維持すると共に、精製ガス中のメタン濃度を容易に一定に保持することを可能ならしめるメタン回収方法および消化ガス精製装置を提供することである。   Therefore, the object of the present invention is to improve the recovery rate of dissolved methane in the absorption water by reducing the internal pressure of the vacuum tank even if the amount of absorbed water is increased by increasing the temperature of the absorption water, and the absorption discharged from the vacuum tank. A methane recovery method and digestion that can maintain a high methane recovery rate (for example, 98% or more) by reducing the methane content in water and can easily maintain a constant methane concentration in the purified gas. A gas purification apparatus is provided.

吸収水の水温上昇によるガス溶解度の低下を補うために吸収水量を増加させても、減圧タンクの内圧を減圧すれば、ガス溶解度の低下により溶存メタンを吸収水からより多く放散させ、この放散ガスを消化ガス圧縮機に戻すことができる。従って、吸収水量を増加させてもオフガスとなるメタンの全体量を減少させることができるから、メタンの回収率の低下を回避することができると考えて、本発明を具現したものである。   Even if the amount of absorbed water is increased to compensate for the decrease in gas solubility due to the rise in the water temperature of the absorbed water, if the internal pressure of the vacuum tank is reduced, dissolved methane will be dissipated more from the absorbed water due to the decrease in gas solubility. Can be returned to the digestion gas compressor. Accordingly, the present invention is embodied by assuming that the decrease in the recovery rate of methane can be avoided because the total amount of methane that becomes off-gas can be reduced even if the amount of absorbed water is increased.

本発明は、上記実情に鑑みてなされたものであって、従って上記課題を解決するために、本発明の請求項１に係るメタン回収方法が採用した手段の要旨は、メタンを主成分とする消化ガスを消化ガス圧縮機で圧縮し、圧縮した消化ガスを吸収塔に供給して、この吸収塔内の吸収水に消化ガス中の二酸化炭素等を溶解・除去して精製ガスを得る一方、前記吸収塔から抜出された吸収水を減圧タンクで減圧してガスを放散させ、放散させたガスを前記消化ガス圧縮機に戻すと共に、ガス放散後の吸収水を減圧タンク外に排出するメタン回収方法において、前記吸収水の水温が予め設定した設定温度を超えると、前記水温と設定温度との温度差に応じて前記減圧タンクの内圧を減圧することを特徴とするものである。   The present invention has been made in view of the above circumstances. Therefore, in order to solve the above problems, the gist of the means adopted by the methane recovery method according to claim 1 of the present invention is mainly composed of methane. While digestion gas is compressed with a digestion gas compressor, the compressed digestion gas is supplied to an absorption tower, and carbon dioxide in the digestion gas is dissolved and removed from the absorption water in the absorption tower to obtain purified gas, The methane that desorbs the absorbed water extracted from the absorption tower in a decompression tank to dissipate the gas, returns the diffused gas to the digestion gas compressor, and discharges the absorbed water after the gas dispersion to the outside of the decompression tank. In the recovery method, when the temperature of the absorbed water exceeds a preset temperature, the internal pressure of the decompression tank is reduced according to a temperature difference between the water temperature and the preset temperature.

本発明の請求項２に係るメタン回収方法が採用した手段の要旨は、メタンを主成分とする消化ガスを消化ガス圧縮機で圧縮し、圧縮した消化ガスを吸収塔に供給して、この吸収塔内の吸収水に消化ガス中の二酸化炭素等を溶解・除去して精製ガスを得る一方、前記吸収塔から抜出された吸収水を減圧タンクで減圧してガスを放散させ、放散させたガスを前記消化ガス圧縮機に戻すと共に、ガス放散後の吸収水を減圧タンク外に排出するメタン回収方法において、予め設定した一定時間内における消化ガスの流量およびメタン濃度の消化ガス測定データ、精製ガスの流量およびメタン濃度の精製ガス測定データ、およびオフガスの流量およびメタン濃度のオフガス測定データのうち、少なくとも何れか２組の測定データから求められるメタン回収率が予め設定した回収率以上の回収率になるように、前記減圧タンクの内圧を減圧することを特徴とするものである。   The gist of the means adopted by the methane recovery method according to claim 2 of the present invention is that the digestion gas mainly composed of methane is compressed by a digestion gas compressor, the compressed digestion gas is supplied to an absorption tower, and this absorption is performed. While purified gas is obtained by dissolving and removing carbon dioxide in the digestion gas in the absorption water in the tower, the absorption water extracted from the absorption tower is depressurized in a vacuum tank to dissipate and diffuse the gas. In the methane recovery method in which gas is returned to the digestion gas compressor and the absorbed water after gas emission is discharged out of the decompression tank, digestion gas flow rate and methane concentration digestion gas measurement data and purification within a predetermined period of time Refining gas measurement data of gas flow rate and methane concentration, and off-gas measurement data of off-gas flow rate and methane concentration. As the rate is preset recovery or recovery rate, and is characterized in that for reducing the internal pressure of the vacuum tank.

本発明の請求項３に係る消化ガス精製装置が採用した手段の要旨は、メタンを主成分とする消化ガスを圧縮する消化ガス圧縮機と、この消化ガス圧縮機で圧縮された消化ガスを受入れて消化ガス中の二酸化炭素等を吸収水に溶解・除去して精製ガスを得る吸収塔と、吸収水をこの吸収塔に供給するための吸収水供給ラインと、前記吸収塔から抜出された吸収水が供給されると共に、この吸収水を減圧する減圧タンクと、この減圧タンクでの減圧により吸収水から放散したガスを前記消化ガス圧縮機に戻す放散ガス戻しラインと、ガス放散後の吸収水を減圧タンク外に排出する吸収水排出ラインとからなり、前記吸収水供給ラインに吸収水の水温を測定する水温測定手段を設け、前記減圧タンクまたは前記放散ガス戻しラインに減圧タンクの圧力を測定する圧力測定手段を設け、放散ガス戻しラインに圧力調整弁を設けると共に、前記吸収水の水温が予め設定した設定温度を超えると、前記水温と設定温度との温度差に応じて前記減圧タンクの内圧を減圧するように放散ガス戻しラインに設けた前記圧力調整弁の開閉の制御を行う制御手段を設けたことを特徴とするものである。   The gist of the means employed by the digestion gas purification apparatus according to claim 3 of the present invention is that a digestion gas compressor that compresses digestion gas mainly composed of methane and digestion gas compressed by this digestion gas compressor are received. An absorption tower for obtaining purified gas by dissolving and removing carbon dioxide in the digestion gas in the absorption water, an absorption water supply line for supplying the absorption water to the absorption tower, and the absorption tower Absorption water is supplied, a decompression tank that decompresses the absorption water, a diffused gas return line that returns gas diffused from the absorbed water by decompression in the decompression tank to the digestion gas compressor, and absorption after gas dispersion An absorption water discharge line for discharging water out of the decompression tank, provided with a water temperature measuring means for measuring the temperature of the absorption water in the absorption water supply line, and the pressure of the decompression tank in the decompression tank or the emission gas return line. Pressure measuring means is provided, a pressure adjusting valve is provided in the diffused gas return line, and when the water temperature of the absorption water exceeds a preset temperature, the pressure reduction is performed according to a temperature difference between the water temperature and the preset temperature. Control means for controlling opening and closing of the pressure regulating valve provided in the diffused gas return line so as to reduce the internal pressure of the tank is provided.

本発明の請求項４に係る消化ガス精製装置が採用した手段の要旨は、メタンを主成分とする消化ガスを圧縮する消化ガス圧縮機と、この消化ガス圧縮機で圧縮された消化ガスを受入れて消化ガス中の二酸化炭素等を吸収水に溶解・除去して精製ガスを得る吸収塔と、吸収水をこの吸収塔に供給するための吸収水供給ラインと、前記吸収塔から抜出された吸収水が供給されると共に、この吸収水を減圧する減圧タンクと、この減圧タンクから減圧により吸収水から放散したガスを前記消化ガス圧縮機に戻す放散ガス戻しラインと、ガス放散後の吸収水を減圧タンク外に排出する吸収水排出ラインとからなり、消化ガスの流量およびメタン濃度を測定する第１測定手段、精製ガスの流量およびメタン濃度を測定する第３測定手段、およびオフガスの流量およびメタン濃度を測定する第２測定手段のうち、少なくとも何れか２組の測定手段を設け、前記減圧タンクまたは前記放散ガス戻しラインに減圧タンクの圧力を測定する圧力測定手段を設け、前記放散ガス戻しラインに圧力調整弁を設けると共に、前記測定手段による測定データから求められるメタン回収率が予め設定した回収率以上の回収率になるように、前記減圧タンクの内圧を減圧するように前記放散ガス戻しラインに設けた圧力調整弁の開閉の制御を行う制御手段を設けたことを特徴とするものである。   The gist of the means adopted by the digestion gas purification apparatus according to claim 4 of the present invention is that a digestion gas compressor that compresses digestion gas mainly composed of methane, and digestion gas compressed by this digestion gas compressor are received. An absorption tower for obtaining purified gas by dissolving and removing carbon dioxide in the digestion gas in the absorption water, an absorption water supply line for supplying the absorption water to the absorption tower, and the absorption tower Absorbed water is supplied, a decompression tank for decompressing the absorbed water, a diffused gas return line for returning the gas diffused from the absorbed water by decompression from the decompressed tank to the digestion gas compressor, and the absorbed water after the gas is diffused A first measuring means for measuring the digestion gas flow rate and methane concentration, a third measurement means for measuring the purified gas flow rate and methane concentration, and off-gas Among the second measurement means for measuring the flow rate and the methane concentration, at least any two sets of measurement means are provided, and the pressure measurement means for measuring the pressure of the pressure reduction tank is provided in the pressure reduction tank or the emission gas return line, and the diffusion A pressure regulating valve is provided in the gas return line, and the diffusion is performed so as to reduce the internal pressure of the decompression tank so that the methane recovery rate obtained from the measurement data obtained by the measuring means is equal to or higher than a recovery rate set in advance. Control means for controlling opening and closing of the pressure regulating valve provided in the gas return line is provided.

本発明の請求項１に係るメタン回収方法、または本発明の請求項３に係る消化ガス精製装置によれば、吸収水の水温が予め設定した設定温度を超えると、前記水温と設定温度との温度差に応じて減圧タンクの内圧が減圧されるため、吸収水の水温上昇によるガス溶解度の低下を補うために吸収水量を増加させても、減圧タンクで吸収塔から抜き出された吸収水に溶解していたメタンをより多く放散させて回収することができる。従って、吸収水の供給量を増加させてもオフガスとなるメタンの全体量の増加を回避することができるから、精製ガスのメタン濃度とメタンの回収率を一定に維持することができる。   According to the methane recovery method according to claim 1 of the present invention or the digestion gas purification apparatus according to claim 3 of the present invention, when the water temperature of the absorption water exceeds a preset temperature, the water temperature and the set temperature Since the internal pressure of the vacuum tank is reduced according to the temperature difference, even if the amount of absorbed water is increased to compensate for the decrease in gas solubility due to the increase in the temperature of the absorbed water, the absorbed water extracted from the absorption tower in the vacuum tank More dissolved methane can be released and recovered. Therefore, even if the supply amount of absorbed water is increased, an increase in the total amount of methane serving as off-gas can be avoided, so that the methane concentration of the purified gas and the methane recovery rate can be maintained constant.

本願発明の請求項２に係るメタン回収方法、または本発明の請求項４に係る消化ガス精製装置によれば、予め設定した一定時間内における消化ガスの流量およびメタン濃度の消化ガス測定データ、精製ガスの流量およびメタン濃度の精製ガス測定データ、およびオフガスの流量およびメタン濃度のオフガス測定データのうち、少なくとも何れか２組の測定データから求められるメタン回収率が予め設定された値以上になるように、減圧タンクの内圧が減圧される。従って、吸収水の水温上昇によるガス溶解度の低下を補うために吸収水の供給量を増加させても、減圧タンクで吸収塔から抜き出された吸収水に溶解していたメタンをより多く放散させて回収することができるため、オフガスとなるメタンの全体量の増加を回避することができるから、精製ガスのメタン濃度とメタンの回収率を一定に維持することができる。   According to the methane recovery method according to claim 2 of the present invention or the digestion gas purification device according to claim 4 of the present invention, digestion gas flow rate and digestion gas measurement data of methane concentration within a predetermined time period, purification The methane recovery rate determined from at least one of the two sets of measurement data of the gas flow rate and the purified gas measurement data of the methane concentration and the off-gas flow rate and the off-gas measurement data of the methane concentration is equal to or higher than a preset value. In addition, the internal pressure of the vacuum tank is reduced. Therefore, even if the supply amount of absorbed water is increased to compensate for a decrease in gas solubility due to an increase in the water temperature of the absorbed water, more methane dissolved in the absorbed water extracted from the absorption tower in the decompression tank is released. Therefore, it is possible to avoid an increase in the total amount of off-gas methane, so that the methane concentration of the purified gas and the methane recovery rate can be maintained constant.

以下、本発明のメタン回収方法を実施する消化ガス精製装置を、添付図面を参照しながら説明する。図１は本発明のメタン回収方法を実施する実施の形態１に係る消化ガス精製装置の模式的全体構成説明図である。また、図２は減圧タンクの圧力が０．４ＭＰａ（ゲージ圧力、以下同じ）の場合における吸収水の水温（℃）と、メタン回収率（％）の関係説明グラフ図、図３は吸収水の水温が２５℃の場合における減圧タンクの圧力（ゲージ圧力）とメタン回収率（％）の関係グラフ図である。   Hereinafter, a digestion gas purification apparatus for carrying out the methane recovery method of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic entire configuration explanatory view of a digestion gas purification apparatus according to Embodiment 1 for carrying out the methane recovery method of the present invention. FIG. 2 is a graph for explaining the relationship between the water temperature (° C.) of the absorbed water and the methane recovery rate (%) when the pressure in the decompression tank is 0.4 MPa (gauge pressure, the same applies hereinafter), and FIG. It is a graph of the relationship between the pressure (gauge pressure) of the decompression tank and the methane recovery rate (%) when the water temperature is 25 ° C.

なお、図２および図３は消化ガス量、消化ガス中のメタン濃度、精製ガス量、および精製ガス中のメタン濃度を計測し、消化ガス中のメタン量および精製ガス中のメタン量を算出して求めたメタン回収率をプロットして図示したものである。また、図２および図３に示すメタン回収率は、精製ガスのメタン含有率が９７容量％以上、かつ吸収塔圧力が０．９ＭＰａの場合のものであって、精製ガスのメタン含有率あるいは吸収塔の圧力が変われば、当然メタン回収率も変わるものである。   2 and 3 measure the digestion gas amount, the methane concentration in the digestion gas, the purified gas amount, and the methane concentration in the purified gas, and calculate the methane amount in the digested gas and the methane amount in the purified gas. The methane recovery rate obtained in this way is plotted and illustrated. The methane recovery rate shown in FIGS. 2 and 3 is that when the methane content of the refined gas is 97% by volume or more and the absorption tower pressure is 0.9 MPa. As the tower pressure changes, the methane recovery rate naturally changes.

先ず、図１を参照しながら、本発明のメタン回収方法を実施する実施の形態１に係る消化ガス精製装置を説明する。即ち、この消化ガス精製装置は、有機性汚泥、有機性廃水等の有機物の嫌気性消化を行う消化槽（図示省略）から消化ガス供給ライン１ａを介して流入する消化ガス、または脱硫（Ｈ２Ｓ除去）後の消化ガスのミスト（水滴）を除去するミストセパレータ１と、このミストセパレータ１を通過したミストが除去された消化ガスを圧縮する、第１段圧縮機２ａと第２段圧縮機２ｂとがシリーズ状に配置されてなる消化ガス圧縮機２を備えている。また、この消化ガス圧縮機２により圧縮されて塔底から導入される消化ガスから二酸化炭素、硫化水素、シロキサン化合物等を除去する吸収塔３を備えている。 First, a digestion gas purification apparatus according to Embodiment 1 for carrying out the methane recovery method of the present invention will be described with reference to FIG. That is, this digestion gas refining apparatus is a digestion gas that flows from a digestion tank (not shown) that performs anaerobic digestion of organic substances such as organic sludge and organic wastewater through the digestion gas supply line 1a, or desulfurization (H 2 The first stage compressor 2a and the second stage compressor that compress the digested gas from which the mist that has passed through the mist separator 1 is removed, and the mist separator 1 that removes the mist (water droplets) of the digested gas after the S removal) 2b is provided with a digestion gas compressor 2 arranged in series. Moreover, the absorption tower 3 which removes a carbon dioxide, a hydrogen sulfide, a siloxane compound, etc. from the digestion gas compressed by this digestion gas compressor 2 and introduce | transduced from the tower bottom is provided.

前記吸収塔３の内部には、分散板で仕切られた充填層３ａが設けられている。即ち、この吸収塔３は、塔底から導入される消化ガスが、充填層３ａを通って塔頂に至る間中を継続して、給水ポンプ４が介装された吸収水供給ライン４ａからこの吸収塔３の塔頂に供給される吸収水との接触を繰返させることにより、二酸化炭素、硫化水素等を吸収水に吸収させるように構成されている。また、消化ガス中にシロキサン化合物が含まれる場合は、高圧状態にすることにより凝縮され、吸収塔内で消化ガス中から除去される。なお、充填層３ａには、吸収水と消化ガスの接触効率を高めるための充填材が装入されている。   Inside the absorption tower 3, a packed bed 3a partitioned by a dispersion plate is provided. That is, the absorption tower 3 continues through the digestion gas introduced from the bottom of the tower through the packed bed 3a to the top of the tower from the absorption water supply line 4a in which the feed water pump 4 is interposed. By repeating the contact with the absorption water supplied to the top of the absorption tower 3, carbon dioxide, hydrogen sulfide and the like are absorbed in the absorption water. Moreover, when a siloxane compound is contained in digestion gas, it is condensed by making it a high pressure state, and is removed from digestion gas in an absorption tower. The packed bed 3a is filled with a filler for increasing the contact efficiency between the absorbed water and the digestion gas.

前記吸収塔３の塔頂から流出する二酸化炭素、硫化水素、シロキサン化合物等が除去された消化ガスは、除湿器６を経てメタンを主成分とする精製ガス（例えば、メタンガス濃度：９７容量％以上）として取出される。   The digestion gas from which carbon dioxide, hydrogen sulfide, siloxane compound, etc. flowing out from the top of the absorption tower 3 are removed is a purified gas (for example, methane gas concentration: 97 vol% or more) through the dehumidifier 6. ).

また、吸収塔３の塔底から抜出された二酸化炭素等を吸収した吸収水が供給される減圧タンク５を備えている。圧力測定手段Ｐｇで圧力が測定される減圧タンク５の圧力は前記吸収塔３の圧力よりも低圧に維持されるようになっているため、吸収水に溶解しているメタンの大部分が減圧タンク５内で放散される。減圧タンク５内において放散されたメタンは、減圧タンク５の上部から消化ガス圧縮機２のガス流入口、より具体的にはミストセパレータ１の消化ガスのガス流入口、または消化ガス圧縮機２の第２段圧縮機２ｂのガス流入口に、放散ガス戻しライン５ａを介して戻されるように構成されている。なお、この実施の形態１の場合には、圧力測定手段Ｐｇには減圧タンク５から圧力が導入されるように構成されているが、放散ガス戻しライン５ａから圧力が導入されるように構成されていてもよい。   In addition, a decompression tank 5 is provided to which absorbed water that has absorbed carbon dioxide extracted from the bottom of the absorption tower 3 is supplied. Since the pressure of the pressure reducing tank 5 whose pressure is measured by the pressure measuring means Pg is maintained at a lower pressure than the pressure of the absorption tower 3, most of the methane dissolved in the absorption water is the pressure reducing tank. Dissipated within 5. Methane diffused in the decompression tank 5 flows from the upper part of the decompression tank 5 into the gas inlet of the digestion gas compressor 2, more specifically, the digestion gas inlet of the mist separator 1, or the digestion gas compressor 2. It is configured to be returned to the gas inlet of the second stage compressor 2b via the diffused gas return line 5a. In the case of the first embodiment, the pressure measuring means Pg is configured to be introduced with pressure from the decompression tank 5, but is configured to be introduced with pressure from the diffused gas return line 5a. It may be.

そして、メタンの大部分が放散され、二酸化炭素等の不要ガス成分を吸収している吸収水は、減圧タンク５の底部から吸収水排出ライン５ｂを介して排出され、大気圧になる。
吸収水に溶解していた二酸化炭素等のガス成分はオフガスとして、必要に応じて硫黄系化合物が除去された後、オフガス排出ライン５ｃを介して系外に排出されるように構成されている。 And most of the methane is diffused, and the absorbed water absorbing the unnecessary gas components such as carbon dioxide is discharged from the bottom of the decompression tank 5 through the absorbed water discharge line 5b, and becomes atmospheric pressure.
A gas component such as carbon dioxide dissolved in the absorption water is configured as an off-gas, after the sulfur-based compound is removed as necessary, and then discharged out of the system via the off-gas discharge line 5c.

さらに、前記吸収水供給ライン４ａに吸収水の水温を測定する水温測定手段１０が設けられている。そして、前記圧力測定手段Ｐｇによって測定された減圧タンク５の圧力と、前記水温測定手段１０によって測定された吸収水の水温（測定値）が前記放散ガス戻しライン５ａに介装されてなる圧力調整弁Ｖ２の開閉を制御する制御手段であるコントローラ１１に入力されるように構成されている。つまり、前記コントローラ１１には予め吸収水の設定温度が入力されており、前記水温測定手段１０で測定された水温が設定温度を超えると、前記水温と設定温度との温度差に応じて前記減圧タンク５の内圧を減圧するように構成されている。 Furthermore, a water temperature measuring means 10 for measuring the water temperature of the absorbed water is provided in the absorbed water supply line 4a. And the pressure adjustment which the pressure of the pressure-reduction tank 5 measured by the said pressure measurement means Pg and the water temperature (measured value) of the absorption water measured by the said water temperature measurement means 10 are interposed by the said diffused gas return line 5a is configured to be input to the controller 11 is a control means for controlling the opening and closing of the valve V 2. That is, the preset temperature of absorbed water is input to the controller 11 in advance, and when the water temperature measured by the water temperature measuring means 10 exceeds the set temperature, the pressure reduction is performed according to the temperature difference between the water temperature and the set temperature. The internal pressure of the tank 5 is configured to be reduced.

以下、上記構成になる消化ガス精製装置の使用態様を、消化ガス精製装置に消化槽から消化ガスを直に（未脱硫で）導入する場合を例として説明する。即ち、汚泥の嫌気性消化を行う消化槽から消化ガス供給ライン１ａを介して供給される消化ガスは、ミストセパレータ１によりミスト（水滴）が除去され、ミスト除去後の消化ガスが消化ガス圧縮機２の第１，２段圧縮機２ａ，２ｂで所定の圧力に圧縮される。消化ガス圧縮機２により圧縮された消化ガスは、図示しない冷却器によって圧縮熱が除去されて吸収塔３の塔底に導入される。前記吸収塔３には、塔頂から給水ポンプ４で加圧された吸収水が供給されている。
なお、冷却によって消化ガスから発生する結露水は、フィルター等によって消化ガスから分離され、排水処理設備に送られるようになっている。また、吸収水としては、水道水、井水、下水等の排水を処理して得られた処理水等が用いられる。 Hereinafter, the usage mode of the digestion gas purification apparatus having the above-described configuration will be described by taking as an example a case where the digestion gas is directly introduced into the digestion gas purification apparatus from the digestion tank (undesulfurized). That is, the digestion gas supplied from the digester tank that performs anaerobic digestion of sludge through the digestion gas supply line 1a is removed from the mist (water droplets) by the mist separator 1, and the digested gas after the mist removal is used as a digestion gas compressor. The first and second stage compressors 2a and 2b are compressed to a predetermined pressure. The digestion gas compressed by the digestion gas compressor 2 is introduced into the bottom of the absorption tower 3 after the heat of compression is removed by a cooler (not shown). Absorption water pressurized by a feed water pump 4 is supplied to the absorption tower 3 from the top of the tower.
The condensed water generated from the digestion gas by cooling is separated from the digestion gas by a filter or the like and sent to a wastewater treatment facility. In addition, as the absorbed water, treated water obtained by treating drainage water such as tap water, well water, sewage, or the like is used.

上記のように、第１，２段圧縮機２ａ，２ｂで消化ガスを圧縮して塔底から吸収塔３内に導入すると共に、給水ポンプ４で加圧された吸収水を塔頂から供給することにより、吸収塔３内を０．５５〜２．０ＭＰａの範囲の高圧状態に保持する。そして、この吸収塔３内において、消化ガスと吸収水とを高圧状態で接触させる。   As described above, the digestion gas is compressed by the first and second stage compressors 2a and 2b and introduced into the absorption tower 3 from the bottom of the tower, and the absorption water pressurized by the feed water pump 4 is supplied from the top of the tower. Thus, the inside of the absorption tower 3 is maintained at a high pressure in the range of 0.55 to 2.0 MPa. And in this absorption tower 3, digestion gas and absorbed water are made to contact in a high-pressure state.

これにより、消化ガス中の二酸化炭素、および硫黄系化合物（例えば、Ｈ２Ｓ）が吸収水に溶解して吸収される。メタンは吸収水に殆ど溶解しないため、消化ガス中の殆どのメタンが精製ガスとして吸収塔３の頂部から取出されて除湿器６に導入される。そして、燃料として使用するときの圧力においても結露することがないように、大気圧における露点に換算して露点が、例えば−６０℃以下になるように除湿される。一方、消化ガス中に含まれているシロキサン化合物は、高圧状態であるため気体から液体に凝縮し、吸収塔３の内部を流下する高圧の吸収水と共に流下して吸収塔３の塔底に溜まる。 Thus, carbon dioxide in the biogas, and sulfur-based compounds (e.g., H 2 S) are absorbed and dissolved in the absorption water. Since methane hardly dissolves in the absorption water, most of the methane in the digestion gas is taken out from the top of the absorption tower 3 as purified gas and introduced into the dehumidifier 6. And it dehumidifies so that a dew point may be set to -60 degrees C or less, for example, converting into a dew point in atmospheric pressure so that it may not dew even in the pressure used as a fuel. On the other hand, since the siloxane compound contained in the digestion gas is in a high pressure state, it condenses from a gas to a liquid, flows down with the high-pressure absorption water flowing down inside the absorption tower 3, and accumulates at the bottom of the absorption tower 3. .

消化ガス中のメタンのごく一部が溶解し、二酸化炭素、および硫黄系化合物が溶解すると共に、凝縮したシロキサン化合物を含む吸収水は、弁Ｖ１の開弁により吸収塔３の底部から抜出され、底部付近から減圧タンク５に導入される。この減圧タンク５内の圧力は減圧されて、吸収塔３内の圧力より低圧になっている。例えば、吸収塔３内の圧力が０．９ＭＰａで、減圧タンク５内の圧力が０．４ＭＰａである場合には、減圧タンク５内の導入された吸収水に僅かに溶解しているメタンが放散されて分離される。 Withdrawing a small portion of the methane in the digestion gas is dissolved, carbon dioxide, and with a sulfur-based compound is dissolved, absorbed water containing condensed siloxane compound, from the bottom of the absorption tower 3 by the opening valve V 1 And introduced into the decompression tank 5 from near the bottom. The pressure in the decompression tank 5 is reduced to a pressure lower than the pressure in the absorption tower 3. For example, when the pressure in the absorption tower 3 is 0.9 MPa and the pressure in the decompression tank 5 is 0.4 MPa, methane slightly dissolved in the introduced absorption water in the decompression tank 5 is diffused. To be separated.

そして、吸収水から分離されたメタンは、メタン回収率を高めるため、圧力調整弁Ｖ２の開弁により放散ガス戻しライン５ａを介してミストセパレータ１の消化ガスのガス流入口、または消化ガス圧縮機２の第２段圧縮機２ｂのガス流入口に戻され、消化槽から導入された消化ガスと共に圧縮される。放散によりメタンが分離される一方、二酸化炭素、硫黄系化合物、シロキサン等を含んでいる吸収水は、弁Ｖ３の開弁により減圧タンク５の底部から吸収水排出ライン５ｂを介して図示しない排水処理設備に送られる。このとき、吸収水の圧力は大気圧になるため、二酸化炭素等が放散し、オフガスとして排出される。 The methane separated from the absorption water, to increase the methane recovery rate, the gas inlet of the digestion gas mist separator 1 via the stripping gas return line 5a by the opening pressure regulating valve V 2 or digestion gas compression, It returns to the gas inlet of the 2nd stage compressor 2b of the machine 2, and is compressed with the digestion gas introduced from the digester. While methane is separated by stripping, carbon dioxide, sulfur-based compounds, absorbing water containing siloxane or the like, not shown, via the absorption water discharge line 5b from the bottom of the vacuum tank 5 by opening the valve V 3 effluent Sent to processing facility. At this time, since the pressure of the absorbed water becomes atmospheric pressure, carbon dioxide and the like are diffused and discharged as off-gas.

この消化ガス精製装置では、通常上記のような運転により、消化ガスに含まれている二酸化炭素、硫黄系化合物、およびシロキサン化合物の殆どを除去し、９７容量％以上のメタンを含有する精製ガスを製造することができる。ところで、季節的要因により吸収水の水温が高温になると、ＣＯ２やＨ２Ｓの溶解度の低下により精製ガス中のＣＯ２やＨ２Ｓの含有率が増加するため、精製ガスのメタン含有率が低下する。そこで、精製ガスのメタン含有率を一定に維持するために、上記のとおり、吸収水の水量の増大によりＣＯ２やＨ２Ｓの除去量を多くしている。 In this digestion gas purification apparatus, most of the carbon dioxide, sulfur compounds and siloxane compounds contained in the digestion gas are usually removed by the operation as described above, and a purified gas containing 97% by volume or more of methane is removed. Can be manufactured. Incidentally, the water temperature of the absorption solution by seasonal factors becomes hot, since CO 2 and H 2 S CO 2 and H 2 S content of the purified gas by a decrease in solubility of the increases, the methane content of the purified gas Decreases. Therefore, in order to keep the methane content of the refined gas constant, as described above, the removal amount of CO 2 and H 2 S is increased by increasing the amount of absorbed water.

この場合にあっても、メタン回収率を向上させるために、上記のとおり、減圧タンク５に導入される吸収水に僅かに溶解しているメタンを放散させて回収するようにしている。
種々の試験を行った結果、吸収塔３から導入された０．９ＭＰａの吸収水の圧力を、減圧タンク５内において０．４ＭＰａに減圧する程度では、吸収水に溶解しているメタンの回収率が十分ではないことが分かった。つまり、たとえメタンの溶存量が僅かであっても、吸収水量の増量によりオフガスとして排出されるメタン量が増大し無視できないことが分かった。 Even in this case, in order to improve the methane recovery rate, as described above, methane slightly dissolved in the absorption water introduced into the decompression tank 5 is diffused and recovered.
As a result of various tests, the recovery rate of methane dissolved in the absorption water is such that the pressure of the absorption water of 0.9 MPa introduced from the absorption tower 3 is reduced to 0.4 MPa in the vacuum tank 5. Was not enough. In other words, it was found that even if the dissolved amount of methane is small, the amount of methane discharged as off-gas increases due to the increase in the amount of absorbed water and cannot be ignored.

例えば、減圧タンク５の圧力が０．４ＭＰａの場合には、吸収水の水温（℃）とメタン回収率（％）の関係は図２に示すとおりである。この図２によれば、吸収水の水温（℃）が２０℃を超えると、９８％のメタン回収率が低下し始め、２５℃になると０．７％程度減少して９７．３％程度になり、３０℃になると３％程度減少して９５％程度になることが分かる。   For example, when the pressure in the decompression tank 5 is 0.4 MPa, the relationship between the water temperature (° C.) of the absorbed water and the methane recovery rate (%) is as shown in FIG. According to FIG. 2, when the water temperature (° C.) of the absorption water exceeds 20 ° C., the methane recovery rate of 98% starts to decrease, and when it reaches 25 ° C., it decreases by about 0.7% to about 97.3%. It can be seen that at 30 ° C., it decreases by about 3% to about 95%.

また、例えば、吸収水の水温が２５℃の場合には、減圧タンク５の圧力（ゲージ圧力）とメタン回収率（％）の関係は図３に示すとおりである。この図３によれば、減圧タンク５の圧力が０．４ＭＰａの場合には、メタン回収率は９７．３％程度であるが、減圧タンク５の圧力が減圧されるに連れてほぼ直線的に増加し、０．２ＭＰａになると、９９．２％程度になることが分かる。   For example, when the water temperature of the absorption water is 25 ° C., the relationship between the pressure in the decompression tank 5 (gauge pressure) and the methane recovery rate (%) is as shown in FIG. According to FIG. 3, when the pressure in the decompression tank 5 is 0.4 MPa, the methane recovery rate is about 97.3%, but almost linearly as the pressure in the decompression tank 5 is reduced. When it increases and it becomes 0.2 Mpa, it turns out that it will be about 99.2%.

即ち、図２，図３には、減圧タンク５内の圧力を０．４ＭＰａで維持し続ける場合、吸収水の水温が２０℃を越えると、メタン回収率を９８％以上に維持することが困難になることが示唆されている。そして、吸収水の水温が２５℃である場合、減圧タンク５内の圧力を０．３３ＭＰａに減圧することにより、メタン回収率を９８％に維持することができるということが示唆されている。従って、水温測定手段１０で測定される吸収水の水温ｔ℃が、例えば設定温度２０℃を越えた場合、水温差Δｔ（ｔ−２０）℃に応じてコントローラ１１により圧力調整弁Ｖ２の開閉を制御して減圧タンク５内の圧力を減圧して、吸収水の設定温度範囲（２０℃以下）での所定圧力よりも低圧にすれば良いものである。 That is, in FIGS. 2 and 3, when the pressure in the decompression tank 5 is continuously maintained at 0.4 MPa, it is difficult to maintain the methane recovery rate at 98% or more when the water temperature of the absorbed water exceeds 20 ° C. It has been suggested that And when the water temperature of absorption water is 25 degreeC, it is suggested that a methane collection | recovery rate can be maintained at 98% by reducing the pressure in the decompression tank 5 to 0.33 MPa. Accordingly, when the water temperature t ° C. of the absorbed water measured by the water temperature measuring means 10 exceeds the set temperature 20 ° C., for example, the controller 11 opens and closes the pressure adjustment valve V 2 according to the water temperature difference Δt (t−20) ° C. And the pressure in the decompression tank 5 is reduced to a pressure lower than the predetermined pressure in the set temperature range of absorbed water (20 ° C. or less).

なお、特に水温差Δｔ℃に応じて連続的にきめ細かく減圧タンク５内の圧力を減圧する必要はない。例えば、吸収水の水温が２０℃を超え２５℃未満の場合に減圧タンク５内の圧力を０．３ＭＰａで維持し、吸収水の水温が２５℃を超え３０℃未満の場合に減圧タンク５内の圧力を０．２ＭＰａで維持するというように、吸収水の水温がある温度範囲にある場合に、減圧タンク５内の圧力を一定に維持するようにしても、同等の効果を得ることができる。   In particular, it is not necessary to reduce the pressure in the decompression tank 5 continuously and finely according to the water temperature difference Δt ° C. For example, when the water temperature of the absorption water is higher than 20 ° C. and lower than 25 ° C., the pressure in the vacuum tank 5 is maintained at 0.3 MPa, and when the water temperature of the absorption water is higher than 25 ° C. and lower than 30 ° C. Even if the pressure in the vacuum tank 5 is kept constant when the water temperature of the absorbed water is within a certain temperature range, such as maintaining the pressure at 0.2 MPa, the same effect can be obtained. .

本発明のメタン回収方法を実施する実施の形態２に係る消化ガス精製装置を、その模式的全体構成説明図の図４を参照しながら説明する。但し、本実施の形態２が上記実施の形態１と相違するところは、放散ガス戻しラインに介装されてなる圧力調整弁Ｖ２の開閉を制御するために、制御手段であるコントローラに測定値を入力する測定手段が相違するだけであるから、同一のものには同一符号を付し、その相違する点について説明する。 A digestion gas purification apparatus according to Embodiment 2 for carrying out the methane recovery method of the present invention will be described with reference to FIG. However, where the second embodiment differs from the first embodiment, in order to control the opening and closing of the pressure regulating valve V 2 composed is interposed stripped gas return line, measured values, which is a control unit controller The only difference is that the measuring means for inputting is the same, so the same symbols are attached to the same components, and the differences will be described.

消化ガス供給ライン１ａに、この消化ガス供給ライン１ａを流れる消化ガスの流量およびメタン濃度を測定する第１測定手段２０が設けられている。また、オフガス排出ライン５ｃにオフガスの流量およびメタン濃度を測定する第２測定手段２１が設けられている。
さらに、減圧タンク５に、この減圧タンク５の圧力を測定する圧力測定手段Ｐｇが設けられている。 The digestion gas supply line 1a is provided with first measurement means 20 for measuring the flow rate and methane concentration of the digestion gas flowing through the digestion gas supply line 1a. Further, a second measuring means 21 for measuring the off-gas flow rate and the methane concentration is provided in the off-gas discharge line 5c.
Furthermore, the pressure reducing means 5 for measuring the pressure in the pressure reducing tank 5 is provided in the pressure reducing tank 5.

そして、第１測定手段２０により測定された消化ガスの流量およびメタン濃度の消化ガス測定データ、第２測定手段２１により測定されたオフガスの流量およびメタン濃度のオフガス測定データ、圧力測定手段Ｐｇで測定された減圧タンク５の圧力データが、放散ガス戻しライン５ａに介装された圧力調整弁Ｖ２の開閉を制御する制御手段であるコントローラ２２に入力されるように構成されている。つまり、前記第１，２測定手段２０，２１による測定データから求められるメタン回収率が予め設定した回収率以上の回収率になるように、減圧タンク５の内圧を減圧するように前記圧力調整弁Ｖ２の開閉が制御されるようになっている。なお、この実施の形態２の場合も、上記実施の形態１の場合と同様、圧力測定手段Ｐｇには減圧タンク５から圧力が導入されるように構成されているが、放散ガス戻しライン５ａから圧力が導入されるように構成されていてもよい。 The digestion gas flow rate and methane concentration digestion gas measurement data measured by the first measurement means 20, the offgas flow rate and methane concentration offgas measurement data measured by the second measurement means 21, and the pressure measurement means Pg are measured. pressure data decompression tank 5 which is is configured to be input to the controller 22 is a control means for controlling the opening and closing of the stripped gas return pressure regulating valve V 2 interposed in the line 5a. That is, the pressure regulating valve is configured to reduce the internal pressure of the decompression tank 5 so that the methane recovery rate obtained from the measurement data obtained by the first and second measuring means 20 and 21 is equal to or higher than a recovery rate set in advance. opening and closing of the V 2 is adapted to be controlled. In the case of the second embodiment, as in the case of the first embodiment, the pressure measuring means Pg is configured to be introduced with pressure from the decompression tank 5, but from the diffused gas return line 5a. It may be configured to introduce pressure.

従って、これらデータをコントローラ２２に入力してメタン回収率を求め、この求めたメタン回収率が予め設定した回収率以上のメタン回収率になるように、前記減圧タンク５の内圧を減圧するという自動制御によってもメタン回収率を高率（例えば、９８％以上）で一定に維持することが可能である。本実施の形態２においては、メタン回収率の維持に消化ガスの流量およびメタン濃度の消化ガス測定データ、およびオフガスの流量およびメタン濃度のオフガス測定データを用いたがこれに限るものではない。   Therefore, these data are input to the controller 22 to obtain the methane recovery rate, and the internal pressure of the decompression tank 5 is reduced automatically so that the obtained methane recovery rate is equal to or higher than the preset recovery rate. It is possible to keep the methane recovery rate constant at a high rate (for example, 98% or more) even by control. In the second embodiment, digestion gas flow rate and methane concentration digestion gas measurement data and offgas flow rate and methane concentration offgas measurement data are used to maintain the methane recovery rate, but the present invention is not limited to this.

例えば、除湿器出口の精製ガスラインに精製ガスの流量およびメタン濃度の精製ガス測定データを測定する第３測定手段を設け、この第３測定手段で測定した精製ガス測定データと前記第１測定手段２０で測定した消化ガス測定データとを用いても、またこの第３測定手段で測定した精製ガス測定データと前記第２測定手段２１で測定したオフガス測定データとを用いても同等の効果を得ることができる。   For example, the purified gas line at the outlet of the dehumidifier is provided with third measurement means for measuring purified gas flow rate and purified gas measurement data of methane concentration, and the purified gas measurement data measured by the third measurement means and the first measurement means Even if the digestion gas measurement data measured at 20 is used, or the purified gas measurement data measured by the third measurement means and the off-gas measurement data measured by the second measurement means 21 are used, the same effect can be obtained. be able to.

ところで、この消化ガス精製装置の吸収塔３の場合は、上記のとおり、内圧を２．０ＭＰａにしても運転を継続し得るように設定されているから、吸収水の水温が高くなった場合、吸収塔３の内圧をより一層高圧にすることにより、吸収水量を増加させることなく二酸化炭素の吸収量を増加させることができる。その場合、減圧タンク５内の圧力を０．４ＭＰａに維持し続けても、メタン回収率を高率（例えば、９８％以上）で一定に維持することができると考えられる。しかしながら、消化ガス圧縮機２の駆動電力、給水ポンプの駆動力の増大によってランニングコストが嵩むので好ましくない。   By the way, in the case of the absorption tower 3 of this digestion gas purification apparatus, as described above, it is set so that the operation can be continued even if the internal pressure is 2.0 MPa. By making the internal pressure of the absorption tower 3 even higher, the amount of carbon dioxide absorbed can be increased without increasing the amount of absorbed water. In that case, even if the pressure in the decompression tank 5 is kept at 0.4 MPa, it is considered that the methane recovery rate can be kept constant at a high rate (eg, 98% or more). However, it is not preferable because the running cost increases due to an increase in driving power of the digestion gas compressor 2 and driving power of the feed water pump.

本発明のメタン回収方法を実施する実施の形態１に係る消化ガス精製装置の模式的全体構成説明図である。It is a typical whole structure explanatory view of the digestion gas refining device concerning Embodiment 1 which enforces the methane recovery method of the present invention. 減圧タンクの圧力が０．４ＭＰａ（ゲージ圧力）の場合における吸収水の水温（℃）とメタン回収率（％）の関係説明グラフ図である。It is a graph explaining the relationship between the water temperature (° C.) of absorbed water and the methane recovery rate (%) when the pressure in the decompression tank is 0.4 MPa (gauge pressure). 吸収水の水温が２５℃の場合における減圧タンクの圧力（ゲージ圧力）とメタン回収率（％）の関係グラフ図である。It is a relationship graph of the pressure (gauge pressure) of a pressure reduction tank in case water temperature of absorption water is 25 degreeC, and a methane recovery rate (%). 本発明のメタン回収方法を実施する実施の形態２に係る消化ガス精製装置の模式的全体構成説明図である。It is typical schematic structure explanatory drawing of the digestion gas refinement | purification apparatus which concerns on Embodiment 2 which implements the methane collection | recovery method of this invention. 従来例に係る消化ガス精製設備の構成を示すフロー図である。It is a flowchart which shows the structure of the digestion gas purification equipment which concerns on a prior art example.

符号の説明Explanation of symbols

１…ミストセパレータ，１ａ…消化ガス供給ライン
２…消化ガス圧縮機，２ａ…第１段圧縮機，２ｂ…第２段圧縮機
３…吸収塔，３ａ…充填層
４…給水ポンプ，４ａ…吸収水供給ライン
５…減圧タンク，５ａ…放散ガス戻しライン，５ｂ…吸収水排出ライン，５ｃ…オフガス排出ライン
６…除湿器
１０…水温測定手段，１１…コントローラ
２０…第１測定手段，２１…第２測定手段，２２…コントローラ
Ｐｇ…圧力測定手段
Ｖ１，Ｖ３…弁，Ｖ２…圧力調整弁 DESCRIPTION OF SYMBOLS 1 ... Mist separator, 1a ... Digestion gas supply line 2 ... Digestion gas compressor, 2a ... First stage compressor, 2b ... Second stage compressor 3 ... Absorption tower, 3a ... Packing bed 4 ... Feed water pump, 4a ... Absorption Water supply line 5 ... Depressurization tank, 5a ... Emission gas return line, 5b ... Absorbed water discharge line, 5c ... Off-gas discharge line 6 ... Dehumidifier 10 ... Water temperature measuring means, 11 ... Controller 20 ... First measuring means, 21 ... First 2 measuring means, 22 ... controller Pg ... pressure measuring means V 1 , V 3 ... valve, V 2 ... pressure regulating valve

Claims (4)

メタンを主成分とする消化ガスを消化ガス圧縮機で圧縮し、圧縮した消化ガスを吸収塔に供給して、この吸収塔内の吸収水に消化ガス中の二酸化炭素等を溶解・除去して精製ガスを得る一方、前記吸収塔から抜出された吸収水を減圧タンクで減圧してガスを放散させ、放散させたガスを前記消化ガス圧縮機に戻すと共に、ガス放散後の吸収水を減圧タンク外に排出するメタン回収方法において、前記吸収水の水温が予め設定した設定温度を超えると、前記水温と設定温度との温度差に応じて前記減圧タンクの内圧を減圧することを特徴とするメタン回収方法。   Digestion gas mainly composed of methane is compressed with a digestion gas compressor, the compressed digestion gas is supplied to the absorption tower, and the carbon dioxide in the digestion gas is dissolved and removed from the absorption water in the absorption tower. While obtaining purified gas, the absorbed water extracted from the absorption tower is depressurized in a decompression tank to dissipate the gas, and the diffused gas is returned to the digestion gas compressor, and the absorbed water after gas emission is depressurized. In the method for recovering methane discharged outside the tank, when the water temperature of the absorbed water exceeds a preset temperature, the internal pressure of the decompression tank is reduced according to a temperature difference between the water temperature and the preset temperature. Methane recovery method. メタンを主成分とする消化ガスを消化ガス圧縮機で圧縮し、圧縮した消化ガスを吸収塔に供給して、この吸収塔内の吸収水に消化ガス中の二酸化炭素等を溶解・除去して精製ガスを得る一方、前記吸収塔から抜出された吸収水を減圧タンクで減圧してガスを放散させ、放散させたガスを前記消化ガス圧縮機に戻すと共に、ガス放散後の吸収水を減圧タンク外に排出するメタン回収方法において、予め設定した一定時間内における消化ガスの流量およびメタン濃度の消化ガス測定データ、精製ガスの流量およびメタン濃度の精製ガス測定データ、およびオフガスの流量およびメタン濃度のオフガス測定データのうち、少なくとも何れか２組の測定データから求められるメタン回収率が予め設定した回収率以上の回収率になるように、前記減圧タンクの内圧を減圧することを特徴とするメタン回収方法。   Digestion gas mainly composed of methane is compressed with a digestion gas compressor, the compressed digestion gas is supplied to the absorption tower, and the carbon dioxide in the digestion gas is dissolved and removed from the absorption water in the absorption tower. While obtaining purified gas, the absorbed water extracted from the absorption tower is depressurized in a decompression tank to dissipate the gas, and the diffused gas is returned to the digestion gas compressor, and the absorbed water after gas emission is depressurized. In the method of recovering methane discharged out of the tank, digestion gas flow rate and methane concentration digestion gas measurement data, purified gas flow rate and methane concentration purification gas measurement data, and off-gas flow rate and methane concentration within a predetermined period of time Among the off-gas measurement data of at least one of the two sets of measurement data, the depressurization tag is set so that the methane recovery rate obtained is equal to or higher than a preset recovery rate. Methane recovery method characterized by depressurizing the internal pressure of the click. メタンを主成分とする消化ガスを圧縮する消化ガス圧縮機と、この消化ガス圧縮機で圧縮された消化ガスを受入れて消化ガス中の二酸化炭素等を吸収水に溶解・除去して精製ガスを得る吸収塔と、吸収水をこの吸収塔に供給するための吸収水供給ラインと、前記吸収塔から抜出された吸収水が供給されると共に、この吸収水を減圧する減圧タンクと、この減圧タンクでの減圧により吸収水から放散したガスを前記消化ガス圧縮機に戻す放散ガス戻しラインと、ガス放散後の吸収水を減圧タンク外に排出する吸収水排出ラインとからなり、前記吸収水供給ラインに吸収水の水温を測定する水温測定手段を設け、前記減圧タンクまたは前記放散ガス戻しラインに減圧タンクの圧力を測定する圧力測定手段を設け、放散ガス戻しラインに圧力調整弁を設けると共に、前記吸収水の水温が予め設定した設定温度を超えると、前記水温と設定温度との温度差に応じて前記減圧タンクの内圧を減圧するように放散ガス戻しラインに設けた前記圧力調整弁の開閉の制御を行う制御手段を設けたことを特徴とする消化ガス精製装置。   Digestion gas compressor that compresses digestion gas mainly composed of methane and digestion gas compressed by this digestion gas compressor, and dissolves and removes carbon dioxide etc. in digestion gas in absorbed water to remove purified gas An absorption tower to be obtained, an absorption water supply line for supplying the absorption water to the absorption tower, an absorption water extracted from the absorption tower and a decompression tank for decompressing the absorption water, and this decompression The absorption water supply comprising: a diffusion gas return line for returning the gas diffused from the absorption water due to depressurization in the tank to the digestion gas compressor; and an absorption water discharge line for discharging the absorption water after gas emission outside the pressure reduction tank A water temperature measuring means for measuring the water temperature of the absorbed water is provided in the line, a pressure measuring means for measuring the pressure of the pressure reducing tank is provided in the decompression tank or the diffused gas return line, and a pressure regulating valve is provided in the diffused gas return line. The pressure adjustment provided in the diffused gas return line so as to reduce the internal pressure of the vacuum tank according to the temperature difference between the water temperature and the set temperature when the water temperature of the absorbed water exceeds a preset set temperature A digestion gas purifier comprising a control means for controlling opening and closing of a valve. メタンを主成分とする消化ガスを圧縮する消化ガス圧縮機と、この消化ガス圧縮機で圧縮された消化ガスを受入れて消化ガス中の二酸化炭素等を吸収水に溶解・除去して精製ガスを得る吸収塔と、吸収水をこの吸収塔に供給するための吸収水供給ラインと、前記吸収塔から抜出された吸収水が供給されると共に、この吸収水を減圧する減圧タンクと、この減圧タンクから減圧により吸収水から放散したガスを前記消化ガス圧縮機に戻す放散ガス戻しラインと、ガス放散後の吸収水を減圧タンク外に排出する吸収水排出ラインとからなり、消化ガスの流量およびメタン濃度を測定する第１測定手段、精製ガスの流量およびメタン濃度を測定する第３測定手段、およびオフガスの流量およびメタン濃度を測定する第２測定手段のうち、少なくとも何れか２組の測定手段を設け、前記減圧タンクまたは前記放散ガス戻しラインに減圧タンクの圧力を測定する圧力測定手段を設け、前記放散ガス戻しラインに圧力調整弁を設けると共に、前記測定手段による測定データから求められるメタン回収率が予め設定した回収率以上の回収率になるように、前記減圧タンクの内圧を減圧するように前記放散ガス戻しラインに設けた圧力調整弁の開閉の制御を行う制御手段を設けたことを特徴とする消化ガス精製装置。   Digestion gas compressor that compresses digestion gas mainly composed of methane and digestion gas compressed by this digestion gas compressor, and dissolves and removes carbon dioxide etc. in digestion gas in absorbed water to remove purified gas An absorption tower to be obtained, an absorption water supply line for supplying the absorption water to the absorption tower, an absorption water extracted from the absorption tower and a decompression tank for decompressing the absorption water, and this decompression It comprises a diffusion gas return line for returning the gas diffused from the absorption water due to decompression from the tank to the digestion gas compressor, and an absorption water discharge line for discharging the absorption water after gas emission outside the decompression tank, and the flow rate of digestion gas and At least one of a first measuring means for measuring the methane concentration, a third measuring means for measuring the flow rate of the purified gas and the methane concentration, and a second measuring means for measuring the flow rate of the offgas and the methane concentration. Two sets of measuring means are provided, pressure measuring means for measuring the pressure of the pressure reducing tank is provided in the pressure reducing tank or the diffused gas return line, a pressure adjusting valve is provided in the diffused gas return line, and the measuring means The opening / closing of the pressure regulating valve provided in the emission gas return line is controlled so as to reduce the internal pressure of the decompression tank so that the methane recovery rate obtained from the measurement data is equal to or higher than the recovery rate set in advance. A digestion gas refining apparatus characterized by comprising a control means.
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