JP5653768B2 - Gas purification equipment - Google Patents

Description

  The present invention relates to a gas purifier for purifying a purified gas mainly composed of methane from a raw material gas mainly composed of methane and carbon dioxide.

  Conventionally, as a gas purification apparatus in such a technical field, a cleaning unit that cleans a source gas and absorbs carbon dioxide, a separation membrane that separates the source gas cleaned by the cleaning unit into purified gas and off-gas, An apparatus including an off-gas return line that returns the off-gas separated by the separation membrane to the upstream side of the cleaning means is known (for example, see Patent Document 1).

JP 2010-174167 A

  In the gas purification apparatus, carbon dioxide is absorbed in the cleaning means, and the purified gas having a higher methane concentration is separated from the raw material gas having an increased methane concentration by the separation membrane. Further, since the purified gas is further separated from the off gas separated from the purified gas by the separation membrane and returned to the upstream side of the cleaning means, the recovery rate of the purified gas from the raw material gas is increased. However, since the cleaning means is provided in addition to the separation membrane, there is a problem that the equipment scale such as the installation space of the apparatus, the amount of cleaning water, the capacity of pumps and the like becomes large.

  Therefore, the present invention provides a gas purification apparatus that can purify a purified gas with a high methane concentration at a high recovery rate and reduce the equipment scale such as the installation space, the amount of washing water, and the capacity of pumps. Objective.

  The present inventors, the most important role of the cleaning means is not to increase the methane concentration in the previous stage of the separation membrane, but to prevent the increase of carbon dioxide circulating in the gas purification device, The present inventors have found that the place where the cleaning means is installed does not have to be in front of the separation membrane, and have reached the present invention.

Therefore, the gas purification apparatus according to the present invention is a gas purification apparatus for purifying a purified gas mainly composed of methane from a raw material gas mainly composed of methane and carbon dioxide, wherein the raw material gas is converted into purified gas and off gas. A separation membrane for separating, a cleaning means for cleaning off-gas separated by the separation membrane and absorbing carbon dioxide, an off-gas return line for returning the off-gas cleaned by the cleaning means to the upstream side of the separation membrane to supply the separation membrane; And a moisture removing means for removing moisture contained in the off gas and the raw material gas, which are provided in the preceding stage of the separation membrane and returned by the off gas return line .

  In such a gas purification apparatus, a purified gas having a high methane concentration is separated from the raw material gas by the separation membrane. The off gas separated from the purified gas is cleaned by the cleaning device, and returned to the upstream side of the separation membrane by the off gas return line. The purified gas is further separated from the off gas returned to the upstream side of the separation membrane by the separation membrane. For this reason, the purified gas can be purified with a high recovery rate. Further, the cleaning means only cleans off gas from which the purified gas is separated from the raw material gas, and since the amount of gas cleaned by the cleaning means is small, the cleaning means can be miniaturized. Furthermore, since the carbon dioxide concentration of the off gas is higher than the carbon dioxide concentration of the raw material gas, the carbon dioxide absorption efficiency in the cleaning means is high, and the cleaning means can be further downsized. Thereby, installation scales, such as the installation space of a gas purification apparatus, the amount of washing water, and the capability of pumps, can be reduced.

  Here, if the cleaning unit is configured to clean off-gas at normal pressure and absorb carbon dioxide, the amount of methane absorbed together with carbon dioxide in the cleaning unit is reduced, and the recovery rate of purified gas is increased.

  Further, when the cleaning means is configured to clean off-gas in a pressurized state and absorb carbon dioxide, the absorption efficiency of carbon dioxide increases compared to cleaning at normal pressure, and off-gas methane returns to the upstream side of the separation membrane. The concentration becomes high. Thereby, the purified gas can be purified with high efficiency. In addition, when it wash | cleans in a pressurized state, the quantity of the methane absorbed with a carbon dioxide will increase compared with washing | cleaning by a normal pressure. However, since the off-gas methane concentration is lower than the methane concentration of the source gas, even if the off-gas is washed in a pressurized state, methane is less likely to be absorbed than in the case where the source gas is washed in a pressurized state. For this reason, the fall of the recovery rate of refined gas is suppressed.

  According to the gas purification apparatus of the present invention, a purified gas having a high methane concentration can be purified with a high recovery rate, and the equipment scale such as installation space, the amount of washing water, and the capacity of pumps can be reduced.

It is a block diagram which shows one Embodiment of the gas purification apparatus which concerns on this invention. It is a block diagram which shows other embodiment of the gas purification apparatus which concerns on this invention.

  Hereinafter, a preferred embodiment of a gas purification apparatus according to the present invention will be described with reference to the accompanying drawings. Note that, in each drawing, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a configuration diagram showing a gas purification device 100 which is an embodiment of a gas purification device according to the present invention. As shown in FIG. 1, the gas purification device 100 includes a moisture removing device 1, a compressor 2, a moisture removing device 3, a separating device 4, a cleaning tower 5, and an offgas return line L <b> 1.

  The moisture removing apparatus 1 introduces a raw material gas mainly composed of methane and carbon dioxide, and removes moisture in the introduced gas. The compressor 2 pumps the gas from which moisture has been removed by the moisture removing device 1 toward the separating device 4 side. The moisture removing device 3 further removes moisture in the gas from the compressor 2 toward the separation device 4. As the moisture removing devices 1 and 3, for example, a device that cools the gas and condenses and removes moisture in the gas is employed.

  The separation device 4 is a device that introduces the gas from which moisture has been removed by the moisture removal device 3 and separates it into purified gas and off-gas. This separation device 4 has a separation membrane 6 that is easy to permeate carbon dioxide and difficult to permeate methane. The gas that has not permeated the separation membrane 6 becomes purified gas, and the gas that has permeated the separation membrane 6 is off-gas. It becomes. The separation membrane 6 is, for example, a polymer organic membrane such as polyimide, a zeolite membrane, or the like.

  The cleaning tower 5 cleans off-gas separated by the separation device 4 and absorbs carbon dioxide in the off-gas. The cleaning tower 5 introduces off-gas from the lower part and discharges it from the upper part, while introducing cleaning water from the upper part and discharges it from the lower part. As a result, the off gas and the cleaning water come into countercurrent contact, and a part of the carbon dioxide in the off gas is dissolved and absorbed in the cleaning water. Here, the inside of the cleaning tower 5 is at normal pressure, and is substantially equal to atmospheric pressure.

  The off-gas return line L <b> 1 returns the off-gas discharged from the upper part of the cleaning tower 5 to the moisture removing device 1.

  In such a gas purification apparatus 100, the raw material gas mainly composed of methane and carbon dioxide is introduced into the separation apparatus 4 after the moisture is removed by the moisture removing apparatus 1 and the moisture is further removed by the moisture removing apparatus 3. Is done. Here, the methane concentration of the source gas is, for example, about 60% by volume.

  Most of the carbon dioxide in the raw material gas introduced into the separation device 4 permeates the separation membrane 6. Methane in the raw material gas does not permeate the separation membrane 6 and remains upstream of the separation membrane 6, but a part of the methane permeates the separation membrane 6 together with carbon dioxide. As a result, a gas having a high methane concentration remains on the upstream side of the separation membrane 6, and this gas is recovered as a purified gas. The methane concentration of the purified gas recovered is, for example, about 98% by volume. Thus, according to the gas purification apparatus 100, a purified gas having a high methane concentration can be recovered. On the other hand, a gas with a high carbon dioxide concentration permeates from the separation membrane 6, and this gas is sent to the cleaning tower 5 as an off-gas. The off-gas methane concentration is, for example, about 30% by volume.

  The off-gas sent to the cleaning tower 5 comes into countercurrent contact with the cleaning water in the cleaning tower 5 and is discharged out of the cleaning tower 5. A part of the carbon dioxide in the off-gas is dissolved and absorbed in the cleaning water when coming into countercurrent contact with the cleaning water. The washing water that has absorbed carbon dioxide is discharged from the lower part to the outside of the washing tower 5. The off-gas methane concentration in which carbon dioxide is absorbed in the cleaning tower 5 is, for example, about 60% by volume. Thus, in this embodiment, the methane concentration of the off-gas is made substantially equal to the methane concentration of the source gas by the cleaning tower 5. Thereby, the methane concentration of the gas introduced into the separation device 4 is stabilized, and the methane concentration of the purified gas is stabilized.

  The off gas discharged from the cleaning tower 5 passes through the off gas return line L1, is returned to the moisture removing device 1, and is introduced into the moisture removing device 1 together with the raw material gas. Thereafter, the same operation is repeated, and the recovery of the purified gas from the off gas is repeated. Therefore, according to the gas purification apparatus 100, the purified gas can be purified with a high recovery rate.

  Further, according to the gas purification apparatus 100, the cleaning tower 5 cleans only the off-gas from which the purified gas is separated from the raw material gas, and the amount of gas cleaned by the cleaning tower 5 is small. 5 can be reduced in size. Furthermore, since the carbon dioxide concentration of the off gas is higher than the carbon dioxide concentration of the raw material gas, the carbon dioxide absorption efficiency in the cleaning tower 5 is high, and the cleaning tower 5 can be further downsized. Thereby, the installation scale of the gas purification apparatus 100, the amount of washing water, the capacity of pumps, etc. can be reduced.

  Moreover, since the inside of the washing tower 5 is set to normal pressure and the off-gas is washed at normal pressure, the amount of methane absorbed together with carbon dioxide is small, and the purified gas can be purified with a higher recovery rate.

  The preferred embodiment of the gas purification apparatus according to the present invention has been described above, but the present invention is not necessarily limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention.

  For example, as in the gas purification apparatus 200 shown in FIG. 2, a degassing device 7 that removes carbon dioxide dissolved in the washing water discharged from the lower part of the washing tower 5 and returns it to the upper part of the washing tower 5 is provided. It may be. In this case, since the cleaning water is repeatedly used, the consumption of the cleaning water is reduced.

  Moreover, in the gas purification apparatuses 100 and 200, although the one separation apparatus 4 is used, it is not restricted to this. For example, by using a plurality of separation devices 4, the gas remaining on the upstream side of the separation membrane 6 of the preceding separation device 4 is further introduced into the subsequent separation device 4, and upstream of the separation membrane 6 of the last separation device 4. The gas remaining on the side may be recovered as a purified gas.

  Moreover, in the gas purification apparatuses 100 and 200, the inside of the cleaning tower 5 is set to normal pressure, and the off gas introduced into the cleaning tower 5 is cleaned at normal pressure. However, the present invention is not limited to this. For example, the inside of the cleaning tower 5 may be pressurized, and the off gas introduced into the cleaning tower 5 may be cleaned in a pressurized state. In this case, the efficiency of absorbing carbon dioxide from off-gas is increased compared to cleaning at normal pressure, and the methane concentration of off-gas returning to the separation device 4 is increased. Thereby, the purified gas can be purified with high efficiency. When the off-gas is washed in a pressurized state, the amount of methane dissolved and absorbed in the washing water together with carbon dioxide increases as compared with washing at normal pressure. However, since the off-gas methane concentration is lower than the methane concentration of the source gas, even if the off-gas is washed in a pressurized state, methane is less likely to be absorbed than in the case where the source gas is washed in a pressurized state. For this reason, the fall of the recovery rate of refined gas is suppressed.

  5 ... Washing tower, 6 ... Separation membrane, 100 ... Gas purification device, L1 ... Off-gas return line.

Claims (3)

A gas purification apparatus for purifying a purified gas mainly containing methane from a raw material gas mainly containing methane and carbon dioxide,
A separation membrane for separating the source gas into the purified gas and off-gas;
A cleaning means for cleaning the off-gas separated by the separation membrane and absorbing carbon dioxide;
An off-gas return line for returning the off-gas cleaned by the cleaning means to the upstream side of the separation membrane to supply the separation membrane;
A gas purification apparatus comprising: a moisture removing unit that is provided in a preceding stage of the separation membrane and removes moisture contained in the off gas and the source gas returned by the off gas return line .   The gas purifier according to claim 1, wherein the cleaning means cleans the off-gas at normal pressure and absorbs carbon dioxide.   The gas purifier according to claim 1, wherein the cleaning means cleans the off-gas and absorbs carbon dioxide in a pressurized state.

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