JP2006159193A - Gas refining method and method for utilizing refined gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas refining method, which can remove dimethylsiloxane from a methane-containing gas over a long period of time, and to provide a method for utilizing refined gas. <P>SOLUTION: When a methane-containing gas generated in the anaerobic fermentation of organic waste such as garbage or sewage sludge is supplied to and passed through a packed bed of activated carbon having pores with a mean pore size of 2.0 to 4.0 nm and a volume of pores with a size of not more than 1.0 nm of not more than 0.2 ml/g, dimethylsiloxane contained in the methane-containing gas is effectively adsorbed by the activated carbon. As a result, even if the methane-containing gas passed through the packed bed of activated carbon is burnt, the amount of SiO<SB>2</SB>generated is small. Therefore, the methane-containing gas can be utilized as fuel for a gas engine or the like, e.g., for power generation which requires long-time stable operation. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a gas purification method and a method for using the same. More specifically, the present invention removes dimethylsiloxane from methane-containing gas generated when anaerobic fermentation of organic waste such as garbage and sewage sludge. The present invention relates to a gas purification method using a methane-containing gas from which dimethylsiloxane has been removed as a fuel, and a method for using the same.

  As is well known, methane-containing gas is generated when anaerobic fermentation of organic waste such as garbage and sewage sludge. The use of the methane-containing gas generated in this way as a fuel for power generation is being actively promoted in Western countries, particularly in Germany. However, such a methane-containing gas contains substances as described later, and there is an urgent need to realize means for economically removing these substances.

  That is, it is known that a methane-containing gas generated from sewage sludge or the like contains a trace amount of an organic silicon compound generated by decomposition of shampoo or rinse. Among these organosilicon compounds, a dimethylsiloxane cyclic organic compound (hereinafter referred to as dimethylsiloxane) in which three or more unit structures of —Si (CH 3) 2 O— are bonded and cyclized is used when a methane-containing gas is used. Known to cause major obstacles. Dimethylsiloxane contained in the methane-containing gas (raw gas) has a low concentration of about 100 mg / m3 or less.

  However, for example, when power is generated by driving a gas engine using methane-containing gas containing dimethylsiloxane as fuel, dimethylsiloxane changes to solid SiO 2 in the gas engine. As a result, the gas engine is damaged (ignition failure due to adhesion to the spark plug, premature wear of the cylinder liner and piston, intake valve, exhaust valve, and SiO2 adhesion to the entire engine combustion chamber head). Becomes difficult. The reason why dimethylsiloxane changes to solid SiO2 in the gas engine is that the organic part (methyl group) of dimethylsiloxane in the gas engine burns and burns away, and the remaining SiO2 gradually grows in the gas engine. It is thought to be because. It is also considered that the same trouble occurs in other internal combustion engines such as gas turbines.

  In order to avoid the above-mentioned problems caused by dimethyl siloxane and to achieve a long-term stable operation of an internal combustion engine such as a gas engine, the following various dimethyl siloxane removal methods have been proposed.

(1) Method of adsorbing and removing dimethylsiloxane with an adsorbent such as activated carbon (2) Method of absorbing and removing dimethylsiloxane with a solvent rich in dimethylsiloxane absorption capacity (3) Cool the methane-containing gas to about -30 ° C By the way, as a specific example of the removal method for removing dimethylsiloxane from a methane-containing gas, a removal method for removing dimethylsiloxane using activated carbon is disclosed in Non-Patent Document 1, for example. ing. The conventional method for removing dimethylsiloxane with activated carbon is to supply activated carbon by supplying sewage digestion gas to activated carbon under the conditions of a filling height of activated carbon of 0.3 m and a gas superficial velocity of 0.15 m / s. The removal performance of dimethylsiloxane was investigated. In this case, the dimethylsiloxane removal rate from the sewage digestion gas is maintained at 90% or more until 550 hours, and dimethylsiloxane can be removed from the sewage digestion gas.
Proceedings of the 38th Sewerage Research Presentation (see page 695)

  However, in the above conventional example, as described above, dimethylsiloxane can be removed up to 550 hours, but it is considered difficult to remove dimethylsiloxane. In other words, the gas space velocity (SV) is 1800 m / h under the above processing conditions, and it is determined that the adsorption apparatus (adsorption tower) has a standard or slightly larger scale for the amount of gas to be processed. Nevertheless, the adsorbent used in this adsorption device has a short endurance time (removable time of dimethylsiloxane), so it is considered that frequent replacement of activated carbon is necessary, and it is difficult to say that it is an economical means. Is. In order to cope with the problem of durability in such an adsorption device according to the conventional example, there is no measure other than increasing the filling amount of activated carbon, and as a result, it is impossible to avoid an increase in the size of the adsorption device.

  Accordingly, an object of the present invention is to provide a gas purification method capable of removing dimethylsiloxane from a methane-containing gas over a long period of time, and a method for using the same.

  The present invention has been made in view of the above circumstances. Therefore, in order to solve the above problems, the means adopted by the gas purification method according to claim 1 of the present invention is a raw gas containing dimethylsiloxane. Is passed through a packed bed of activated carbon having pores with an average pore size of 2.0 to 4.0 nm and pores of 1.0 nm or less having a volume of 0.2 ml / g or less. It is characterized by adsorbing dimethylsiloxane.

  The means adopted by the gas purification method according to claim 2 of the present invention is the gas purification method according to claim 1, wherein the raw gas is a methane-containing gas generated from organic waste by anaerobic fermentation. It is characterized by being.

  The means adopted by the gas purification method according to claim 3 of the present invention is the gas purification method according to any one of claims 1 and 2, wherein the gas purification method according to any one of claims 1 and 2 is allowed to pass through the packed bed of activated carbon. The relative humidity of the raw gas is lowered.

  The means employed by the gas utilization method according to claim 4 of the present invention is that the raw gas containing dimethylsiloxane has pores having an average pore diameter of 2.0 to 4.0 nm and 1.0 nm or less. By passing through a packed bed of activated carbon having a pore volume of 0.2 ml / g or less, dimethylsiloxane is adsorbed on the activated carbon, and a processing gas from which dimethylsiloxane has been removed from the raw gas is used as a fuel. It is what.

  As described above, according to the gas purification method according to claims 1 to 3 of the present invention, the average inner diameter is 2.0 to 4.0 nm, and the pore volume of 1.0 nm or less is 0. By using activated carbon of 2 ml / g or less, dimethylsiloxane can be effectively removed for a longer time than in the conventional example. And since there are few pores with a small average inner diameter, the amount of adsorption of flammable substances such as H2 and CH4 and flammable substances such as O2 is small, and the risk of igniting activated carbon is reduced, so the activated carbon is easy to handle. There is also an effect of becoming.

  According to the gas purification method of the third aspect of the present invention, the methane-containing gas having a reduced relative humidity passes through the packed bed of activated carbon. Therefore, the amount of water trapped in the pores of the activated carbon is reduced, and more dimethylsiloxane can be trapped, so that the dimethylsiloxane removal performance of the activated carbon is improved.

  According to the gas utilization method according to claim 4 of the present invention, since dimethylsiloxane is reliably removed from the methane-containing gas, an internal combustion engine such as a gas engine or a gas turbine is driven without trouble for a long time. Electricity can be obtained, and it can be effectively used as fuel, such as being stored in a cylinder and used as fuel for automobiles.

  Hereinafter, an embodiment according to a gas purification method for removing dimethylsiloxane from a methane-containing gas (raw gas) according to the present invention will be described. That is, the inventors are superior to dimethylsiloxane in view of the fact that the conventional method for removing dimethylsiloxane with activated carbon has a problem that the durability (removable time of dimethylsiloxane) of activated carbon is short. In order to realize activated carbon that has both adsorption performance and durability, we have conducted extensive research. As a result, it was found that activated carbon having pores having an average pore diameter of 2.0 to 4.0 nm has excellent adsorption performance and durability.

  Dimethylsiloxane contained in the sewage digestion gas is known to have 3 to 6 unit structures of —Si (CH 3) 2 O—, and the molecular size of the unit structure is 0.7 to 1 Estimated to be 1 nm. On the other hand, since the average pore diameter of the pores of the activated carbon is usually 1.0 nm or more, activated carbon having pores with smaller average pore diameters is considered preferable. However, when the volume of the pores that greatly affects the durability is about the same, the average pore diameter of 2.0 to 4.0 nm is relatively larger than the activated carbon with many average pore diameters of 2.0 nm or less. It was found that the activated carbon having large pores has a larger adsorption performance for dimethylsiloxane.

  That is, it has been found that the activated carbon used for solvent recovery or the like has a larger average pore diameter than the activated carbon for gas treatment used for general deodorization and the like, and is preferable for adsorption of dimethylsiloxane. This is presumably because several molecules of dimethylsiloxane are condensed and trapped in the pores when dimethylsiloxane is adsorbed on the activated carbon. However, it has been found that activated carbon having pores with an average pore diameter exceeding 4.0 nm cannot provide sufficient dimethylsiloxane removal performance. It was also found that activated carbon having pores with an average pore diameter of 3.5 nm or less has the best dimethylsiloxane removal performance.

  By the way, when the pore diameter of the activated carbon is 1.0 nm or less, flammable substances such as H2 and CH4 and flammable substances such as O2 are adsorbed, which may increase the ignition risk of the activated carbon. is there. On the other hand, in the case of activated carbon that purifies the methane-containing gas targeted by the present invention, as described above, the average pore diameter is 2.0 to 4.0 nm, and there are few pores with small pore diameters. . Therefore, the amount of adsorption of combustible substances such as H2 and CH4 and combustion-supporting substances such as O2 is small, and the activated carbon according to the present invention has an effect of facilitating handling of the activated carbon because the ignition risk is reduced. In order to reduce the ignition risk of activated carbon, the pore volume of 1.0 nm or less is preferably 0.2 ml / g or less.

  Incidentally, an example in which the amount of H2 adsorbed that increases the risk of ignition increases when there are many pores of 1.0 nm or less is clearly shown. This is an examination of the adsorption amount of H2 under the temperature and pressure conditions of a temperature of 23 ° C. and a pressure of 1 MPa using activated carbons having the same average pore diameter and different pore volumes of 1.0 nm. In the activated carbon A having an average pore diameter of 2.13 nm and a pore volume of 1.0 nm or less of 0.15 ml / g, the adsorption amount of H2 was 0.18 (mol-H2 / kg-activated carbon). On the other hand, with activated carbon B having an average pore diameter of 2.06 nm and a pore volume of 1.0 nm or less of 0.23 ml / g, the adsorption amount of H2 is 0.33 (mol-H2 / kg-activated carbon. This activated carbon B has a larger amount of adsorption of H2 than the activated carbon A.

  The type of activated carbon according to the present invention is not particularly limited, and may be, for example, coconut shell or coal, and the average inner diameter of the pores is within the range of 2.0 to 4.0 nm of the present invention. If so, excellent dimethylsiloxane removal performance can be obtained. Further, the shape and molding method of the activated carbon are not particularly limited, and any of a pellet, a granular product, a pulverized product, and an extruded molded product may be selected as appropriate according to the purpose of use. Is.

  When dimethylsiloxane is removed from the methane-containing gas using the activated carbon according to the present invention, the object can be achieved by supplying the methane-containing gas to the adsorption tower packed with the activated carbon. However, when the methane-containing gas is a water saturated gas after passing through the scrubber, the pores of the activated carbon are saturated with water, and sufficient dimethylsiloxane removal performance cannot be obtained. Therefore, it is preferable to lower the relative humidity by a method such as heating the methane-containing gas or passing a hygroscopic agent, and then supplying the gas to the adsorption tower packed with activated carbon. Further, the air volume of the methane-containing gas supplied to the activated carbon is not particularly limited, and may be appropriately selected according to the purpose of use.

  As described above, the methane-containing gas having a low concentration of dimethylsiloxane can be used as a fuel by various methods. For example, it is possible to obtain heat and electricity by driving an internal combustion engine such as a gas engine or a gas turbine stably for a long time, and it can be stored in a cylinder and used as a fuel for various applications such as automobiles. It is also possible to do. That is, it is only necessary to select an optimal usage form in consideration of the amount of gas obtained, usage, regional conditions, and the like. Furthermore, the methane-containing gas is non-fossil fuel-based energy, so-called biomass energy, and its use of fuel is considered to have no CO2 emission.

(Example)
Hereinafter, an embodiment of the present invention will be described with reference to FIG. 1 of a schematic configuration diagram of a dimethylsiloxane adsorption test apparatus and FIG. 2 of a molecular structure diagram of dimethylsiloxane D4. However, the present embodiment is not intended to limit the present invention, and all modifications that do not depart from the technical idea of the present invention are included in the scope of the present invention.

  In this example, a dimethylsiloxane-containing gas was supplied to several types of activated carbon having pores with different average pore diameters, and the relationship between the average pore diameter and dimethylsiloxane removal performance was examined. More specifically, activated carbon having pores having an average pore diameter of 1.67 nm to 4.05 nm (obtained by analyzing a measured value measured by a nitrogen gas adsorption method) was used. These activated carbons are all 1/8 inch diameter extruded pellets, each having a specific surface area of 1000 to 1200 m / g and a pore volume of 0.50 to 0.60 ml / g. There is no significant difference between the activated carbons.

  As shown in FIG. 1, the above-mentioned activated carbon is filled in the adsorption tube 1 having an inner diameter of 30 mm to form a packed bed 2 having a height of 15 cm. And the simulation gas G adjusted to the composition mentioned later containing dimethylsiloxane was supplied to this packed bed 2 by the air volume 10.6 normal liter / min. The air volume (10.6 normal liters / min) of the simulated gas G corresponds to an empty space velocity (SV) of 6000 / h, and the gas supply amount per unit time and unit activated carbon volume is equal to the empty space velocity ( SV) is about 3.3 times that of the conventional example of 1800 / h.

  The simulated gas G supplied to the packed bed 2 vaporizes and vaporizes each dimethylsiloxane corresponding to 250 mg / Nm3 of dimethylsiloxane tetramer (D4) and 250 mg / Nm3 of pentamer (D5). The composition is adjusted by mixing nitrogen gas at a temperature of 30 ° C. and a relative humidity of 80%. In addition, the density | concentration of the dimethylsiloxane contained in the simulation gas G used in the present Example is about 6 times the density | concentration of the dimethylsiloxane contained in the dimethylsiloxane containing gas used in the prior art example. Incidentally, the molecular structure of the dimethylsiloxane tetramer (D4) is a structure in which four dimethylsiloxane unit structures are bonded as shown in FIG.

  As described above, the test conditions in this example are such that the gas supply amount per unit time and unit activated carbon volume is about 3.3 times that of the conventional example, and the concentration of dimethylsiloxane is about 6 times. When these are simply multiplied, it can be said that the activated carbon is evaluated under conditions that are about 20 times as severe as those of the conventional example. The removal performance of dimethylsiloxane by each activated carbon was examined by quantifying the D4 and D5 concentrations at the activated carbon outlet every hour with a gas chromatograph. Immediately after starting the simulation gas supply, dimethylsiloxane could not be detected from the gas flowing out from the outlet of the activated carbon in any activated carbon.

  The average pore diameter of the pores of each activated carbon (obtained by analyzing the measured value measured by the nitrogen gas adsorption method) and the time when the dimethylsiloxane removal rate was reduced to 90% under the above test conditions Is shown in Table 1. Table 2 shows the change in the dimethylsiloxane removal rate with respect to the treatment time of the activated carbon of Example 1 (average pore size 2.09 nm). In addition, the removal rate of dimethylsiloxane in a present Example is computed by the following formula.

  Removal rate of dimethylsiloxane (%) = {1- (sum of D4 and D5 concentrations in outlet gas) / (sum of supplied D4 and D5 concentrations)} × 100

  According to Table 1 above, in the case of the activated carbons of Examples 1 to 5 having pores with an average pore diameter of 2.09 to 3.73 nm, all of the pores with an average pore diameter of 1.67 nm and 4.05 nm were obtained. It can be seen that a longer time is required until the removal rate of dimethylcyclosan is reduced to 90% as compared with the case of the activated carbons of Comparative Examples 1 and 2 having. In addition, according to Table 2 above, 100% dimethylcyclosan by activated carbon according to Example 1 (Examples 2 to 5 are also shown as an example since the same tendency is shown) up to 27 hours. Can be seen to have been removed. Therefore, it can be said that the activated carbon according to the present invention is extremely excellent in durability. In this example, the time required for the dimethylcyclosan removal rate to drop to 90% is 29 to 44 hours, but this is converted to the conventional gas supply amount and dimethylsiloxane concentration conditions. 580 to 880 hours, which exceeds 550 hours of the conventional example.

  By the way, Example 1 is an example in which dimethylsiloxane was removed using a simulation gas G having a temperature of 30 ° C. and a relative humidity of 80%. On the other hand, assuming that the simulation gas G is heated (when the absolute humidity is the same (water vapor pressure 3.4 kPa) and the temperature and relative humidity are different), the simulation is performed at a temperature of 40 ° C. and a relative humidity of 46%. Gas G was passed through the packed bed of activated carbon of Example 1 to examine the removal performance of dimethylsiloxane.

  As a result, the time required for the dimethylsiloxane removal rate to decrease to 90% was 39 hours, which was 4 hours longer than the 35 hours of Example 1 above.

  That is, lowering the relative humidity by heating is preferable for improving the removal performance of dimethylsiloxane. In addition, this can be understood to be because the amount of water trapped in the pores of the activated carbon is reduced as described above.

  In the above description, the test apparatus in which activated carbon is packed in an adsorption tube having an inner diameter of 30 mm has been described as an example. However, even if the adsorption tube is a practical-scale adsorption tower, it is possible to obtain the same effect as the present embodiment. .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration explanatory diagram of a dimethylsiloxane adsorption test apparatus according to an embodiment of the present invention. It is molecular structure explanatory drawing of dimethylsiloxane D4.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Adsorption pipe | tube 2 ... Packing layer of activated carbon G ... Simulated gas.

Claims (4)

The raw gas containing dimethylsiloxane passes through a packed bed of activated carbon having pores with an average pore size of 2.0 to 4.0 nm and a pore size of 1.0 nm or less of 0.2 ml / g or less. A method for purifying a gas, wherein dimethylsiloxane is adsorbed on the activated carbon. The gas purification method according to claim 1, wherein the raw gas is a methane-containing gas generated from organic waste by anaerobic fermentation. 3. The gas purification method according to claim 1, wherein a relative humidity of the raw gas is lowered before passing through the packed bed of activated carbon. 4. The raw gas containing dimethylsiloxane passes through a packed bed of activated carbon having pores with an average pore size of 2.0 to 4.0 nm and a pore size of 1.0 nm or less of 0.2 ml / g or less. By using the activated carbon, dimethylsiloxane is adsorbed on the activated carbon, and the process gas from which the dimethylsiloxane has been removed from the raw gas is used as a fuel.

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