JP2008037901A - Method and device for removing siloxane in sewage gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and device for removing siloxane in sewage gas, capable of easily removing the siloxane in the sewage gas based on pressure and temperature, reducing a cost required for the removal and also suitably applicable in a system with a built-in electric power generation device equipped with a thermal engine such as a gas engine, gas turbine, etc., and capable of removing the siloxane reasonably in the system. <P>SOLUTION: This device for removing the siloxane from the sewage gas is provided by installing a compression device 1 for compression-treating the sewage gas and a cooling device 2 for cool-treating the sewage gas after the compression treatment from the upstream to downstream of flowing direction of the sewage gas one by one. The device is equipped with the electric power generation device 3 operated with the sewage gas, and the compression device is constituted by a turbo charger 1a run by the exhaust gas of the electric power generation device. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention can easily remove siloxane in digestion gas based on pressure and temperature, can reduce the cost required for removal, and incorporates a power generation device including a heat engine such as a gas engine or a gas turbine. The present invention relates to a method and an apparatus for removing siloxane in digestion gas, which can be suitably applied to a system and can reasonably remove siloxane in the system.

A cogeneration system in which combustible digestion gas obtained by subjecting organic matter such as sewage sludge to anaerobic fermentation is burned by a heat engine such as a gas engine or a gas turbine so that it can generate electricity as well as heat. Is attracting attention. However, the digestion gas contains siloxane (inorganic or organic silicon), and when the digestion gas is burned, silica (SiO ₂ ) is generated from the siloxane by an oxidation reaction, and this silica is contained in the gas engine or the like. It deposits as a combustion residue on the machine, etc., and adversely affects machine parts.

  Specifically, silica is a hard solid substance that causes sticking to the combustion chamber, biting between the exhaust valve and piston and cylinder liner, inflow and adhering to the admission valve, and mixing into the lubricating oil. As a result, the service life of the parts is shortened, and further, the maintenance interval for those defects is shortened. Further, when a NOx converter is installed at the rear stage of the heat engine, silica may adhere to the catalyst surface, which may cause a decrease in the NOx removal rate and an increase in pressure loss.

  For example, Patent Documents 1 to 3 are known as techniques for removing siloxane from the digestion gas. In the “digestion gas power generation device” of Patent Document 1, the digestion gas is introduced into a portion of the digestion gas pretreatment device having a depth of 200 mm or less and bubbled to remove water-soluble components in the retained water. The digested gas after bubbling is made to flow through the gas flow space of the pretreatment device at a low speed of 0.1 m / sec or less to remove water-insoluble mist-like foreign matters.

  In the “system and method for removing siloxane compound in digestion gas” of Patent Document 2, the digestion gas containing the siloxane compound is introduced into a temperature reducing device and cooled, and the cooled digestion gas is supplied to the digestion gas purification device. The digestion gas is introduced and brought into countercurrent contact with water, and the digestion gas treated by the digestion gas purification apparatus is heated by a heater.

Patent Document 3 “Digestion Gas Purification Device and Method” discloses a digestion gas purification device having a siloxane compound removal unit and a methane concentration unit downstream thereof, wherein the siloxane compound removal unit is a siloxane compound adsorbent. A pressure swing or thermal swing adsorption device having a regeneration means for regeneration is provided, and the gas generated by the regeneration treatment of the methane concentrating unit is used as a purge gas during regeneration of the siloxane adsorbent I am doing so.
JP 2006-8875 A JP 2006-45247 A JP 2006-83311 A

  As for siloxane removal, as in Patent Document 3, adsorption removal using an adsorbent is the mainstream, but in addition to the equipment cost of the adsorption apparatus itself, the adsorbent needs to be replaced as appropriate, and the running cost also increases. There was a problem. Moreover, like patent document 1 and 2, making digestion gas contact water had the subject that pre-processing was needed with respect to the subsequent combustion utilization with a gas engine etc.

  The present invention was devised in view of the above-described conventional problems, and can easily remove siloxane in digestion gas based on pressure and temperature, and can reduce the cost required for removal. A method and apparatus for removing siloxane in digestion gas that can be suitably applied to a system incorporating a power generation device including a heat engine such as an engine or a gas turbine, and can rationally remove siloxane in the system. The purpose is to provide.

  The method for removing siloxane in digestion gas according to the present invention is a method for removing siloxane from digestion gas, characterized by compressing the digestion gas and then cooling the digestion gas.

  The power generation apparatus operated with the digestion gas is used, and the digestion gas is compressed with the exhaust gas pressure from the power generation apparatus. The power generation apparatus operated by the digestion gas is used, and the digestion gas is compressed by the rotational output from the power generation apparatus. The power generation apparatus operated with the digestion gas is used, and the digestion gas is compressed with the electric power generated by the power generation apparatus.

  The apparatus for removing siloxane in digestion gas according to the present invention is an apparatus for removing siloxane from digestion gas, the compression apparatus sequentially compressing the digestion gas from the upstream in the flow direction of the digestion gas, and the compression treatment A cooling device for cooling the digestion gas later is provided.

  The power generation device is operated by the digestion gas, and the compression device is a turbocharger that is operated by the exhaust gas of the power generation device. The power generation device is operated by the digestion gas, and the compression device is a supercharger that is operated by being connected to a rotation output shaft of the power generation device. The compressor is a compressor driven by electric power.

  In the method and apparatus for removing siloxane in digestion gas according to the present invention, siloxane in digestion gas can be easily removed based on pressure and temperature, and the cost required for removal can be reduced. The present invention can be suitably applied to a system incorporating a power generation apparatus including a heat engine such as a gas turbine, and siloxane can be rationally removed in the system.

  Hereinafter, preferred embodiments of a method and apparatus for removing siloxane in digestion gas according to the present invention will be described in detail with reference to the accompanying drawings. The apparatus for removing siloxane in digestion gas according to the first embodiment is basically an apparatus for removing siloxane from digestion gas, as shown in FIG. 1, and sequentially digestion gas from upstream to downstream in the flow direction of digestion gas. And a cooling device 2 for cooling the digested gas after the compression processing.

  In addition, a power generation device 3 that is operated by digestion gas is provided, and a turbocharger 1 a that is operated by exhaust gas from the power generation device 3 is used as the compression device 1. The cooling device 2 is provided with an absorption chiller 2a that uses the exhaust gas of the power generation device 3 as a heat source. A decompression device 4 that decompresses digestion gas is provided downstream of the cooling device 2.

  Digestion gas is generated by anaerobic fermentation treatment of high water content biomass such as sewage sludge in a fermenter or the like. Digestion gas is produced as a combustible gas mainly composed of methane and carbon dioxide. This digestion gas contains siloxane. Siloxane is thought to originate mainly from shampoos, rinses and skin care products.

Siloxane is a general term for those having Si—O— as the main skeleton and having an organic group such as a methyl group in the side chain. The digestion gas contains a large amount of [(CH ₃ ) ₂ SiO] _n having a polymerization degree of 3 to 6. These include a chain type (L3 to L6) and a cyclic type (D3 to D6), and most of the siloxane in the digestion gas is D4 (octamethyl-cyclo-tetrasiloxane: [(CH ₃ ) ₂ SiO]. ₄ ) and D5 (decamethyl-cyclo-pentasiloxane: [(CH ₃ ) ₂ SiO] ₅ ).

  In this embodiment, the combustible digestion gas produced | generated with the fermenter is supplied to the gas engine generator 3a which is an example of the electric power generating apparatus 3, and the gas engine generator 3a combusts digestion gas. It is designed to convert heat energy and electrical energy.

  Between the fermenter which is not shown in figure and the gas engine generator 3a, the supply system 6 which connects these and distribute | circulates digestion gas is provided. The supply system 6 is provided with a compression device 1 for compressing digestion gas by being positioned upstream in the flow direction of the digestion gas sent from the fermenter and supplied to the gas engine generator 3a. A cooling device 2 is provided for cooling and condensing digestion gas, and the compression device 1 and the cooling device 2 are connected via a supply system 6. A pressure reducing valve 4 a capable of adjusting the degree of pressure reduction is connected to the downstream of the cooling device 2 as a pressure reducing device 4 through a supply system 6. The pressure reducing valve 4a is provided for reducing the pressure of digestion gas flowing from the cooling device 2 to end the condensation treatment of siloxane and adjusting the pressure for introducing the digestion gas into the gas engine generator 3a.

  A gas engine generator 3a is connected to the downstream of the pressure reducing valve 4a through a supply system 6. Further, a pipe 7 for supplying digestion gas to another gas utilization destination is connected downstream of the pressure reducing valve 4a as necessary.

  The pressure reducing valve 4a may be provided as necessary. Further, it is desirable that the supply system 6 is provided with a filter that is located upstream of the compression device 1 and previously removes dust in the digestion gas.

  In the first embodiment, the compression device 1 is constituted by a turbocharger 1a that is operated by the exhaust gas of the gas engine generator 3a. The turbocharger 1a is interposed in the exhaust gas system 8 of the gas engine generator 3a. The turbocharger 1a is rotationally driven by exhaust gas and compresses digestion gas. The exhaust gas system 8 is provided with a bypass system 9 that bypasses the turbocharger 1a, and the bypass system 9 is provided with a bypass control valve 9a whose opening degree can be adjusted. The exhaust gas system 8 is provided with a first control valve 10a which is positioned between the bypass system 9 and the inlet side of the turbocharger 1a and whose opening degree can be adjusted. The exhaust gas system 8 is provided with a second control valve 10b which is located on the outlet side of the turbocharger 1a and downstream of the bypass system 9 and whose opening degree can be adjusted.

  In the first embodiment, the cooling device 2 includes the heat exchanger 2b that cools the digestion gas with the circulating refrigerant, and the absorption refrigerator 2a that cools the refrigerant and circulates between the heat exchanger 2b. It consists of. The absorption refrigeration machine 2a is interposed in the exhaust gas system 8 downstream of the turbocharger 1a, is supplied with exhaust gas as a heat source, and cools the refrigerant by the exhaust heat of the exhaust gas. The inlet side of the absorption refrigerator 2a is connected to the exhaust gas system 8 on the upstream side of the second control valve 10b, and an exhaust gas adjustment valve 11 whose opening degree can be adjusted is provided on the inlet side. The outlet side of the absorption chiller 2a is connected to the exhaust gas system 8 on the downstream side of the second control valve 10b. The exhaust gas discharged from the absorption refrigeration machine 2a and the turbocharger 1a is sent out through the exhaust gas system 8 to recover exhaust heat or dissipate into the atmosphere.

  The first control valve 10a, the second control valve 10b, the bypass control valve 9a, and the exhaust gas adjustment valve 11 are appropriately adjusted in opening according to the operating state of the gas engine generator 3a, so that the turbocharger 1a and the absorption refrigeration machine The amount of exhaust gas supplied to both 2a is adjusted, and as a result, their operation is controlled.

  The method for removing siloxane in the digestion gas according to the first embodiment will be described. Basically, the digestion gas is first compressed and then cooled. The amount of siloxane contained in the digestion gas that can exist as a gas state in the digestion gas depends on the saturation vapor pressure depending on the temperature. On the other hand, the saturated vapor pressure does not depend on the pressure.

For example, taking D5 as an example, the amount that D5 can exist in the gas state in the digestion gas is 2171 mg / m ³ N at a saturated vapor pressure of 13.3 Pa (0.1 mmHg) at 20 ° C. and saturated at 5 ° C. It is 21.8 mg / m ³ N at a vapor pressure of 0.133 Pa (0.001 mmHg). As an example, if the amount of D5 in the digestion gas is 50 mg / m ³ N, when the gas temperature is 20 ° C., there is a relationship of 50 mg / m ³ N <2171 mg / m ³ N (saturated vapor pressure). , D5 does not condense, but when cooled to 5 ° C., a relationship of 50 mg / m ³ N> 21.8 mg / m ³ N (saturated vapor pressure) is established, and 28.2 mg / m ³ N (= 50-21. 8) Condensate. The removal rate at this time is 56.4%.

When the digestion gas is compressed in advance before cooling, for example, when the digestion gas is compressed from about 0.1 MPa to about 1 MPa, the amount of D5 in the digestion gas to be condensed is reduced to 500 mg / m ³ N (<2171 mg / m ³ N (saturated vapor pressure)), and when the digested gas thus compressed is cooled to 5 ° C., the amount is 478.2 mg / m ³ N (500-21.8). D5 can be condensed. The removal rate at this time is 95.6%.

The compression treatment is performed for the purpose of increasing the siloxane partial pressure in the digestion gas, and is set to a pressure that does not exceed the amount of gaseous siloxane that can be included in the saturated vapor pressure at the temperature during the compression treatment. In the case of D4, the amount that can be present in the digestion gas at 5 ° C. is about 270 mg / m ³ N, and as in D5, it is initially 50 mg / m ³ N and is compressed to 500 mg / m ³ N. If m ³ N, only 230 mg / m ³ N (= 500-270) can be removed.

In 1st Embodiment, after using the turbocharger 1a operated with the exhaust gas pressure of the gas engine generator 3a as the compression apparatus 1, the digestion gas produced | generated with the fermenter removes dust with a filter, It is introduced into the turbocharger 1a via the supply system 6. Hereinafter, for the sake of convenience, the concentration of siloxane in the digestion gas is the amount of digestion gas in the standard state obtained by converting the concentration in the actual digestion gas amount A (m ³ / h) per unit time to 0 ° C. and 0.1 MPa (normal). The gas amount is explained as the concentration in B (m ³ N / h). The siloxane concentration in the digestion gas of the gas amount A (m ³ / h) (= B (m ³ N / h)) delivered from the fermentor is 0.05 g / m ³ N for D4 and 0.05 g / m for D5. Assuming m ³ N, the following description is given. For example, before being introduced into the turbocharger 1a, digestion gas having a gas temperature of 20 ° C. and a gas pressure of 0.1 MPa is compressed by the turbocharger 1a so that the gas pressure is increased to 1 MPa at a gas temperature of 20 ° C. Is done. Thereby, the siloxane content (siloxane concentration) per unit volume is increased about 10 times (the amount of gas becomes 0.1 A (m ³ / h) by compression). The compression rate of digestion gas by the turbocharger 1a is adjusted by exhaust gas flow rate control by adjusting the opening of the first and second control valves 10a, 10b, the bypass control valve 9a, and the like.

The saturated vapor pressure related to the condensation action of siloxane does not change even if the pressure is changed, and depends only on the temperature. Therefore, the compression action by the turbocharger 1a does not cause the condensation action of siloxane. Digested gas compressed by the turbocharger 1a is sent via a supply system 6 to a heat exchanger 2b to which a refrigerant is supplied from an absorption refrigeration machine 2a that uses the exhaust gas of the gas engine generator 3a as a heat source. It is cooled to 0 ° C. (the amount of gas becomes 0.095 A (m ³ / h) by cooling). Adjustment of the refrigerant temperature to the heat exchanger 2 b is performed by exhaust gas flow rate control by adjusting the opening degree of the exhaust gas adjustment valve 11. When digestion gas is cooled, the siloxane content in the digestion gas is an amount corresponding to the saturation vapor pressure, i.e. D4 of about 0.027 g / m ³ N becomes, D5 becomes about 0.002 g / m ³ N , D4 and D5, the difference between about 0.023 g / m ³ N and about 0.048 mg / m ³ N is removed from the digestion gas as a condensate in the heat exchanger 2b portion.

Thereafter, the digestion gas is fed into the pressure reducing valve 4a through the supply system 6, and the gas pressure is reduced to 0.1 MPa at a gas temperature of 5 ° C. (the gas amount is reduced to 0.95 A (m ³ / h) by the reduced pressure). Become). By the pressure reducing operation by the pressure reducing valve 4a, the condensation action of siloxane is terminated and the subsequent condensation is prevented, and the introduction pressure of digestion gas to the gas engine generator 3a is optimized. The digestion gas decompressed by the pressure reducing valve 4a is sent to the gas engine generator 3a through the supply system 6. If necessary, the digestion gas is supplied from the pipe 7 to another gas utilization destination.

  The digested gas sent to the gas engine generator 3a is burned in the gas engine portion to drive the generator portion, thereby being converted into electric energy, and also cooling water etc. for cooling the gas engine generator 3a. It is also recovered as heat energy by heating. Further, the exhaust gas containing the thermal energy of the digestion gas is sent to the turbocharger 1a through the exhaust gas system 8, and the turbocharger 1a is rotationally driven to compress the digestion gas. The exhaust gas is sent to the absorption refrigeration machine 2a through the exhaust gas system 8, and is used as a heat source for cooling the refrigerant circulated to the heat exchanger 2b. The exhaust gas that has circulated through the exhaust gas system 8 is finally discharged from the turbocharger 1a, the absorption chiller 2a, etc., and is recovered as exhaust heat or dissipated into the atmosphere.

  In the first embodiment, since the turbocharger 1a operated with exhaust gas and the absorption refrigeration machine 2a using exhaust gas as a heat source are used, until a sufficient amount of exhaust gas is obtained, It is preferable to provide a starting device such as starting the gas engine generator 3a with LPG. However, if the siloxane removal is not necessary for a short period such as during the start-up period, it is needless to say that the removal device may be operated with the above configuration.

  In the method and apparatus for removing siloxane in digestion gas according to the first embodiment described above, since the cooling process is performed after compression, the siloxane is condensed by the cooling process and efficiently extracted from the digestion gas. The siloxane can be removed from the digestion gas more easily and efficiently because the siloxane can be condensed after increasing the amount of siloxane in the unit flow rate of the digestion gas by the pre-compression operation as well as removing the siloxane. can do.

  That is, since the saturated vapor pressure of siloxane depends only on the temperature and not on the pressure, the digestion gas is within the range as long as the amount of siloxane by compression does not exceed the amount of siloxane that can be included in the saturated vapor pressure at the temperature at the time of compression. By compressing the siloxane, the siloxane can be removed at a very high removal rate by the subsequent cooling treatment while preventing the condensation of the siloxane in the turbocharger 1a.

  Also about a cooling process, the condensation rate of a siloxane can be raised by setting as low temperature as possible as needed. This increases the equipment cost and running cost of the adsorber itself as in the above background art, and requires a pretreatment for combustion use in a gas engine or the like in order to bring digestion gas into contact with water As compared with the above, the cost required for removing siloxane can be reduced. When the removal device according to the present embodiment is added to the upstream side of the adsorption device of the digestion gas power generation facility in which the adsorption device is installed, the removal amount in the adsorption device can be reduced, so that the adsorbent replacement cycle can be reduced. Needless to say, the maintenance work can be reduced and the running cost can be reduced.

  Since the turbocharger 1a using the exhaust gas of the gas engine generator 3a operated by digestion gas is adopted as the digestion gas compression device 1, compared to the case of using a compression device driven by another drive source, The digestion gas can be compressed using the thermal energy of the digestion gas that is the object to be processed, and the compression treatment can be performed reasonably and efficiently. In addition, since the digestion gas cooling device 2 includes an absorption refrigeration machine 2a that uses the exhaust gas of the gas engine generator 3a operated by the digestion gas as a heat source, compared to a case where a cooling device that cools with a separate heat source is used. Like the turbocharger 1a, the digestion gas can be cooled using the thermal energy of the digestion gas that is the object to be processed, and the cooling process can be performed rationally and efficiently.

  Since the digestion gas is depressurized by the pressure reducing valve 4a after the digestion gas is cooled, the condensation action of siloxane after passing through the heat exchanger 2b can be prevented, and the digestion gas introduction pressure to the gas engine generator 3a, etc. Can be set appropriately.

  2 and 3 show a second embodiment and a third embodiment of the method and apparatus for removing siloxane in digestion gas according to the present invention, respectively. In the second embodiment, as the compressor 1, a supercharger connected to the rotation output shaft 3b of the gas engine generator 3a instead of the turbocharger 1a and rotationally driven by the rotation output from the gas engine generator 3a. Charger 1b is employed. In the second embodiment, although the power generation efficiency is reduced, the equipment configuration such as piping can be simplified. In the third embodiment, a compressor 1c that is driven using commercial power or power generated by the gas engine generator 3a is employed as the compression device 1. In the third embodiment, although the power consumption is increased, the equipment configuration such as piping can be simplified, and unlike the case of the turbocharger 1a and the supercharger 1b, these are operated for start-up. There is an advantage that it is not necessary to prepare another drive source.

  In any of the above-described embodiments, the gas engine generator 3a has been described as an example of the power generator 3. However, the generator is not limited to the gas engine, and may be a generator incorporating another heat engine such as a gas turbine. . The apparatus for circulating the refrigerant to the heat exchanger 2b is not limited to the absorption chiller 2a that uses exhaust heat of exhaust gas, but may be a cooling device that uses other heat sources or the like. In addition, the initial temperature and initial pressure of the digestion gas, the compression rate by the turbocharger 1a, the supercharger 1b, and the compressor 1c, the cooling temperature by the heat exchanger 2b, the pressure reduction rate by the pressure reducing valve 4a, etc. are limited to the description of the above embodiment. You may set suitably, without being performed. Further, on the upstream side of the power generator 3 such as the gas engine generator 3a, a heater or the like for raising the digestion gas temperature may be installed in order to meet the gas inlet conditions of the heat engine that drives the power generator 3. Good.

It is a schematic block diagram which shows 1st Embodiment of the siloxane removal apparatus concerning this invention. It is a schematic block diagram which shows 2nd Embodiment of the siloxane removal apparatus concerning this invention. It is a schematic block diagram which shows 3rd Embodiment of the siloxane removal apparatus concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Compressor 1a Turbocharger 1b Supercharger 1c Compressor 2 Cooling device 2a Absorption refrigerator 2b Heat exchanger 3 Power generation device 3a Gas engine generator 3b Rotation output shaft of power generation device 4 Pressure reduction device 4a Pressure reduction valve

Claims (8)

  A method for removing siloxane from a digestion gas, comprising compressing the digestion gas and then cooling the digestion gas.   2. The method for removing siloxane in digestion gas according to claim 1, wherein the digestion gas is compressed with an exhaust gas pressure from the power generation device using the power generation device operated with the digestion gas.   2. The method for removing siloxane in digestion gas according to claim 1, wherein the digestion gas is compressed with rotational output from the power generation device using the power generation device operated with the digestion gas.   The method for removing siloxane in digestion gas according to claim 1, wherein the digestion gas is compressed with the electric power generated by the power generation device using the power generation device operated with the digestion gas.   An apparatus for removing siloxane from digestion gas, comprising: a compression device that compresses the digestion gas sequentially from upstream to downstream in the flow direction of the digestion gas; and a cooling device that cools the digestion gas after compression processing An apparatus for removing siloxane in digestion gas, characterized in that   The apparatus for removing siloxane in digestion gas according to claim 5, comprising a power generation device operated by the digestion gas, wherein the compression device is a turbocharger operated by exhaust gas of the power generation device.   6. The siloxane in digestion gas according to claim 5, further comprising a power generation device operated by the digestion gas, wherein the compression device is a supercharger operated by being connected to a rotation output shaft of the power generation device. Removal device.   6. The apparatus for removing siloxane in digestion gas according to claim 5, wherein the compressor is a compressor driven by electric power.

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