JPH03255876A - Methane separation apparatus and method - Google Patents

Abstract

PURPOSE:To recover a product methane after separation and refining without impairing the purity by arranging a gas-liquid separator at a liquefied gas outlet of a condenser to circulate a gas separated with the gas-liquid separator being converged into a stock natural gas. CONSTITUTION:A component which is evaporated with a condenser 23 among liquefied gas components is a methane gas as low boiling point component mainly and the methane gas is concentrated at a gaseous phase part separated with a gas-liquid separator 41. Therefore, the gas separated with the gas-liquid separator 41 is led out to be introduced into a material supply pipe 1 from a recovery circulation path 42 and circulated to a fraction separating process together with a stock natural gas, which enables the collection of methane discharged as exhaust gas traditionally. This also allows the recovery of the methane in the liquefied gas with the gas-liquid separator 41. Thus, a methane concentration of the liquefied gas being led out of the bottom of a fraction column is raised to lower an evaporation temperature of the liquefied gas, causing an increase in level of liquefaction of the condenser 23 thereby achieving higher purity of a product methane with an increase in amount of reflux liquid within the fraction column 15.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a methane separation apparatus and method for purifying and separating methane by performing liquefaction rectification separation using natural gas as a raw material.

[Conventional technology]

FIG. 2 shows the system of a conventional general methane separation device. This methane separation device uses natural gas as a raw material to separate nitrogen and ethane contained in the natural gas.

Hydrocarbons with a carbon number of 3 or more, carbon dioxide, moisture, trace amounts of BTX (benzene, toluene, xylene), etc. are separated and removed by pre-treatment adsorption and liquefaction rectification separation, and purified. It is used to collect pure methane.

The raw material natural gas, from which the carbon dioxide contained in it has been removed in advance by a cleaning method or the like, is sucked into the compressor 2 from the raw material supply pipe 1, and after being pressurized to about 30 kg/c4G, it is sent to the aftercooler 3. Precooler 4. The water is introduced into the adsorption equipment 6 through the drain separator 5. This adsorption equipment 6 has valves 8a and 8 for switching a plurality of adsorbers (dryers) 7a and 7b that are used in a selective manner.
b, 9a.

9b, and while one adsorber 7a is in the adsorption process to remove impurities from the raw natural gas, the other adsorber 7b is in the regeneration process, and the impurities adsorbed to the adsorbent by the regeneration gas, which will be described later, are removed. Regeneration of the adsorbent is performed, consisting of desorption of components and pre-cooling.

The raw natural gas introduced from the large mouth valve 8a into one of the adsorbers 7a contains moisture and residual carbon dioxide.

After BTX etc. are removed and purified and dried, the outlet valve 9a
, into the cold box via conduit 10 and into the first heat exchanger 11 . It is cooled in a freon cooler 12 and introduced into a gas-liquid separator 13 where low-boiling components such as methane and ethane are separated from other high-boiling components. The raw material gas led out from the top of the gas-liquid separator 13 is further passed through the second heat exchanger 1
4 and then cooled and introduced into the lower part of the rectification column 15. A portion of the methane gas that has been rectified in the rectification column 15 and led out from the top is branched into a conduit 16, and a valve 17. Supercooler 18, second heat exchanger 14. After the cold heat is recovered through the first heat exchanger 11, the product gas conduit 19. After passing through the conduit 20 and the precooler 4 and being used as a cooling source for the precooler 4, it is collected as a product methane gas. In addition, some product methane gas is
It joins the product methane gas in the conduit 20.

On the other hand, a liquefied gas containing approximately 50% methane is drawn out from the bottom of the rectification column 5, and is introduced into a condenser 23 through an appropriate cooler 18° valve 22. In the condenser 23, this liquefied gas and the remainder of the methane gas drawn out from the top of the rectification column exchange heat, and the methane gas is liquefied and becomes the reflux liquid of the rectification column 15. A part of the liquefied gas is vaporized and sent to the condenser 2.
3 to the condenser outlet conduit 24 and connected to the second heat exchanger 1
4 and joins with the liquid phase led out from the bottom of the gas-liquid separator 13, then led out of the cold box via the first heat exchanger 11, and recovered as exhaust gas through the conduit 25. A part of this exhaust gas is transferred from the conduit 25 to the conduit 2 for regeneration gas.
6 and is used as regeneration gas for the adsorption equipment 6.

During the desorption operation at the beginning of the regeneration process, this regeneration gas is introduced into the heater 28 by the switching valve 27, heated to a predetermined temperature by steam or the like, and then passed through one of the regeneration valves 29a and 29b to the adsorber in the regeneration process. The gas flows backward, desorbs and entrains impurities, and is introduced into the regeneration gas cooler 31 through one of the discharge valves 30a and 30b, where it is cooled and then joins the exhaust gas in the conduit 25. In addition, the regeneration gas in the latter half of the regeneration process does not pass through the heater 28, but flows from the switching valve 27 to the conduit 32. Regeneration valve 29
The adsorbent is introduced into the adsorbers 7a and 7b via a and 29b, and after precooling the adsorbent, it joins the exhaust gas as described above.

[Problem to be solved by the invention]

However, in the above-mentioned methane separation process, when aiming to increase the methane recovery rate, a limit is reached at, for example, the mass balance [volume %] shown in Table 1, and the recovery rate cannot be improved any further.

This is because the evaporation temperature of the methane-containing liquefied gas led out from the bottom of the rectification column 15 changes depending on the methane concentration. By affecting the liquefaction ability of methane gas in For example, if the methane concentration in the liquefied gas is high, the evaporation temperature will be low, and a large amount of methane gas can be liquefied in the condenser 23. However, if the methane concentration is low, the evaporation temperature will be high, and the methane gas in the condenser 23 will be liquefied. The liquefaction capacity decreases and the reflux liquid in the rectification column 15 becomes insufficient,
It becomes impossible to perform sufficient rectification.

Therefore, it is necessary to contain methane at a certain concentration in the liquefied gas, and the purity and yield of the methane gas to be collected as product purified methane is optimized, including the pressure balance. The recovery rate shown in the table was the limit.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a methane separation device and method that can improve the recovery rate without impairing the purity of product methane after separation and purification.

[Means to solve the problem]

In order to achieve the above-mentioned object, the methane separation apparatus of the present invention includes a rectification column that liquefies and rectifies compressed, purified, and cooled raw material natural gas, and a part of the separated methane derived from the top of the rectification column. In a methane separation apparatus equipped with a condenser that liquefies the separated methane by exchanging heat between the separated methane and the liquefied gas led out from the bottom of the rectification column, a gas-liquid separator is disposed at the liquefied gas outlet of the condenser. In addition, a circulation system is provided for introducing the gas separated by the gas-liquid separator into the raw natural gas supply system.

In addition, the methane separation method of the present invention is a method in which compressed, purified and cooled raw natural gas is introduced into a rectification column to undergo liquefaction rectification separation, and methane in the natural gas is separated, from the top of the rectification column. A part of the separated methane separated is collected as product methane, and the remaining part of the separated methane and the liquefied gas drawn out from the bottom of the rectification column are introduced into a condenser, and the two are exchanged with heat to liquefy the separated methane. The reflux liquid of the rectification column is obtained, and a part of the liquefied gas is vaporized, and the partially vaporized liquefied gas is led out from the condenser and then introduced into the gas-liquid separator, and the upper part of the vapor-liquid separator is The method is characterized in that the separated gas is introduced and circulated into the raw material natural gas.

[For production]

As mentioned above, by installing a gas-liquid separator at the liquefied gas outlet of the condenser and performing gas-liquid separation of the liquefied gas that is partially vaporized and led out in the condenser, it is possible to reduce the boiling point contained in the liquefied gas. The component methane can be concentrated in the gas phase. Therefore, by combining the gas separated by the gas-liquid separator with the raw natural gas and circulating it, a part of the methane that was conventionally entrained in the exhaust gas can be collected as product methane, improving the yield. can be achieved.

〔Example〕

Hereinafter, the present invention will be explained in more detail based on an embodiment shown in the drawings. In the following description, the same elements as those in the conventional example shown in FIG.

In addition to the conventional device, the device of this embodiment has a condenser 23.
Detecting the flow rate in the gas-liquid separator 41 disposed at the liquefied gas outlet of the gas-liquid separator 41, the recovery circulation path 42 that introduces the gas discharged from the top of the gas-liquid separator 41 into the raw material supply pipe 1, and the product gas conduit 19. a product gas flow meter (FICA) 51 for the regeneration gas, a regeneration gas flow rate indicator controller 52 (FICB) provided in the regeneration gas flow path and linked to the product gas flowmeter 51, a product gas conduit 19 and a regeneration gas flow meter 52 for the regeneration gas. A conduit 61 connecting the branched conduit 26, an automatic valve 62 provided in the conduit 61 and controlled by the regeneration gas flow rate indicating controller 52, a conduit 10 on the outlet side of the adsorption installation 7, and a regeneration gas conduit. 26, a conduit 81 that connects the product gas conduit 19 and the raw material supply pipe 1, and an automatic valve 82 provided in the conduit 81 to detect the pressure inside the product gas conduit 19. A pressure indicating regulator 83 (PIC) is installed to control the pressure, and a thermometer 91 is installed near the outlet side of the adsorbers 7a and 7b to measure the temperature change of the adsorbent filled inside.
Valves 8a and 8b are provided at the inlet and outlet sides of the adsorbers 7a and 7b according to the detected values of the product gas flowmeter 51 and/or thermometer 91.

A controller 92 is provided to control the switching time of 9a and 9b.

First, the raw material natural gas is supplied from the raw material supply pipe 1 and compressed by the compressor 2 in the same manner as described above, and is then compressed by the aftercooler 3. Precooler 4. The water is introduced into an adsorption facility 6 through a drain separator 5 and purified to remove impurities. Then introduced into the cold box and the first heat exchanger 11. Freon cooler 12. Gas-liquid separator 13. It is introduced into the lower part of the rectification column 15 via the second heat exchanger 14. Highly purified methane gas is led out from the top of the rectification column, a part of which is collected as a product, and the remainder is liquefied in the condenser 23 and sent to the rectification column 15.
becomes the reflux liquid. In addition, the liquefied gas led out from the bottom of the rectification column and partially vaporized in the condenser 23 is transferred to the condenser outlet conduit 2
4 into a gas-liquid separator 41, where it is separated into a gas phase and a liquid phase.

Among the liquefied gas components, the component vaporized in the condenser 23 is mainly methane gas, which is a low boiling point component, and the gas-liquid separator 41
Methane gas is concentrated in the gas phase separated by . For example, the composition of the gas phase of the gas-liquid separator 41 is 96.5% methane.
, ethane 3.2%.

The nitrogen content is 0.3%, resulting in a gas containing more methane than the raw natural gas. Therefore, the gas separated by the gas-liquid separator 41 is led out, introduced into the raw material supply pipe 1 from the recovery circulation path 42, and circulated together with the raw material natural gas to the rectification separation process, which would otherwise be discharged as exhaust gas. This makes it possible to extract methane as a product. Even if the methane concentration in the bottoms is increased in this way, the amount of reflux liquid can be maintained by performing gas-liquid separation at the outlet of the condenser 23, compressing the separated gas fraction (methane-rich gas) again, and recycling it. At the same time, it was confirmed that the yield of methane could be increased.

On the other hand, in the liquid phase part of the gas-liquid separator 41, the methane content decreases and the content of other components such as ethane relatively increases, and the liquid phase part passes through the second heat exchanger 14 and the first heat exchanger 11 as exhaust gas. After a portion is used as regeneration gas, it is recovered as exhaust gas through conduit 25.

Here, in the above configuration, the mass balance when collecting the same amount of product methane with the road composition and the same amount as the conventional example is shown in Table 2.

As is clear from Table 2 above, 53Nrr of the conventionally discharged exhaust gas was separated into the gas phase by the gas-liquid separator 41.
By combining r/h with raw natural gas and circulating it, the amount emitted as exhaust gas is reduced from 158 N/h to 105 Nrrl'/h, and the concentration of methane contained in the exhaust gas is reduced. Furthermore, since the amount of raw natural gas can be reduced, the yield of the product methane can be significantly improved. In addition, since methane in the liquefied gas can be recovered by the gas-liquid separator 41, the methane concentration of the liquefied gas derived from the bottom of the rectification column is increased, the evaporation temperature of the liquefied gas is lowered, and the amount of liquefied in the condenser 23 is increased. By doing so, it is also possible to increase the amount of reflux liquid in the rectification column 15 and improve the purity of the product methane. Note that the gas-liquid interface in the gas-liquid separator 41 is maintained within a predetermined range by a liquid level controller 43.

On the other hand, this type of separator is operated with a reduction of nearly 50%. A problem that arises when carrying out this reduction operation is securing regeneration gas for the adsorption equipment 6. In particular, in the case of the product with a high yield of methane as in the present invention, if the raw gas composition is constant, the amount of exhaust gas relative to the raw natural gas is small, so there is a tendency for there to be a shortage of gas that can be used as regeneration gas for the adsorption equipment 6. be. Therefore, the apparatus of this embodiment is configured to ensure the amount of regenerated gas by linking the amount of product gas and the amount of regenerated gas. That is, the product gas flow rate is detected by the product gas flow meter 51, and the flow meter 51
Based on the detected value, the regeneration gas flow rate indicator controller 52 is operated to change the amount of regeneration gas to constantly supply a predetermined amount of regeneration gas to the adsorption equipment 6. For example, if the amount of raw natural gas is reduced by reducing the amount of operation due to a decrease in product demand,
The product gas flow meter 51 detects a decrease in the amount of product gas, and the regeneration gas flow rate indicator controller 52 is operated in the opening direction in accordance with this decrease amount to increase the amount of regeneration gas relative to the total amount of exhaust gas. Thereby, even if the amount of exhaust gas increases or decreases due to an increase or decrease in the amount of product methane gas collected, a predetermined amount of regeneration gas can be introduced into the adsorption stage *6, so that the adsorbers 7a and 7b can be sufficiently regenerated.

In addition, in the reduction operation, it is a problem whether the amount of regeneration gas is secured and whether the adsorbent in the adsorbers 7a and 7b is sufficiently utilized. Therefore, in the present invention, a thermometer 91 for measuring the temperature of the adsorbent is provided in the middle part of the adsorbers 7a and 7b, preferably between the outlet end and the center part, and near the outlet end to measure the temperature change of the adsorbent. , detects the adsorption heat generated when the adsorbent adsorbs impurities (adsorbed substances), determines the progress of adsorption based on this temperature rise, and controls the adsorption unit 7 by the switching time controller 92.
It is configured to adjust the switching time of a and 7b. This allows the adsorbent to be effectively and fully utilized even when the amount of raw natural gas is significantly reduced due to the reduction operation. Furthermore, by combining this means with the means for ensuring the amount of regeneration gas based on the amount of product gas, a reliable adsorption and removal function can be exhibited even during the reduction operation.

Further, by providing a conduit 61 that connects the product collection conduit 19 and the regeneration gas conduit 26, and providing the conduit 61 with an automatic valve 62 that is linked to the regeneration gas flow rate indicator 52, the amount of exhaust gas can be reduced. If the required amount of regeneration gas is not reached, the regeneration gas flow rate indicating controller 52 is operated to open the automatic valve 62 to use a portion of the product gas as regeneration gas.

Thereby, even if the amount of exhaust gas decreases significantly, a sufficient amount of regeneration gas can be secured, and the adsorber 7a, 7b can be regenerated reliably. In addition, by providing a conduit 71 and a valve 72 that connect the conduit 10 on the outlet side of the adsorption equipment and the regeneration gas conduit 26, a part of the raw natural gas purified in the adsorption equipment 6 is transferred to the regeneration gas of the adsorption equipment 6. Can be used as When there is a shortage of regenerated gas due to operating conditions, the amount of regenerated gas can be increased using part of the product methane gas or part of the raw material natural gas after refinement, so even if the amount of exhaust gas decreases, the adsorbent can be reliably used. can be played.

In addition, in order to further stabilize the reduction operation, a reduction operation circulation path 81 is provided that connects the product gas conduit 19 and the raw material supply pipe 1, and the pressure inside the product gas conduit 19 is detected by a pressure indicating regulator 83. By opening and closing the automatic valve 82 based on this, when the demand for product methane gas decreases and the pressure inside the pipe 19 increases, the automatic valve 82 is opened and a part of the product methane gas is converted into raw material natural gas. It is possible to merge the circulation. As a result, even if the product production volume decreases significantly, the flow rate of each part of the equipment can be maintained above the amount required for stable operation.Moreover, by introducing product methane gas,
The amount of natural gas sucked into the compressor 2, that is, the amount of raw material supplied can be automatically reduced.

In addition, the gas to be circulated to the raw material natural gas introduction system, including the circulating gas from the gas-liquid separator 41, can be made to join the raw material at an appropriate position depending on its flow rate and pressure, and They can also be merged at an intermediate stage.

〔Effect of the invention〕

As explained above, in the present invention, a gas-liquid separator is disposed at the liquefied gas outlet of the condenser, and the gas part of the liquefied gas, which is partially vaporized in the condenser, is circulated. The ratio can be improved from the conventional 89% to about 96%. In particular, in terms of equipment, it is only necessary to add a gas-liquid separator to the conventional equipment, so there is almost no increase in equipment cost or operating cost, and the cost of product methane can be significantly reduced.

In addition, by changing the ratio of regeneration gas to exhaust gas according to the flow rate of product methane gas, the amount of exhaust gas decreases as the yield improves, and even when there is a shortage of regeneration gas in the adsorption equipment, a sufficient amount of regeneration gas can be maintained. Can be secured. Furthermore, by controlling the switching time of the adsorber based on changes in the amount of product gas and changes in the temperature of the adsorbent, the adsorbent can be used effectively even when the amount of raw natural gas decreases in the reduction operation. Further, by circulating a part of the product methane gas to the raw material supply system during the reduction operation, it is possible to perform a large reduction operation in a stable state.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing one embodiment of the present invention, and FIG. 2 is a system diagram showing a conventional example. 1... Raw material supply pipe 2... Compressor 6... Adsorption equipment 7a, 7b... Adsorber 15... Fractionation column 19... Product gas conduit 23... Condenser 2
4... Condenser outlet conduit 41... Gas-liquid separator
42... Recovery circulation path 51... Product gas flow meter
52...Regeneration gas flow rate indicator controller 91...Thermometer 92...Switching time controller

Claims (1)

[Claims] 1. A rectification column for liquefying and rectifying compressed, purified, and cooled raw material natural gas, and a part of the separated methane extracted from the top of the rectification column and a part of the separated methane extracted from the bottom of the rectification column. In the methane separation apparatus equipped with a condenser that liquefies the separated methane by heat exchange with the liquefied gas, a gas-liquid separator is disposed at the liquefied gas outlet of the condenser, and the gas-liquid separator separates the separated methane. A methane separation device characterized by having a circulation system for introducing the extracted gas into a raw material natural gas supply system. 2. The methane separation apparatus according to claim 1, wherein the raw material natural gas is purified by adsorption equipment, wherein a flow meter is provided to detect the flow rate of product methane collected as a product after separation, and the detected value of the flow meter is A methane separation apparatus characterized in that a regeneration gas amount adjusting means is provided for adjusting the amount of regeneration gas in the adsorption equipment accordingly. 3. The methane separation apparatus according to claim 1, wherein the raw material natural gas is purified by adsorption equipment, wherein a flow meter is provided to detect the flow rate of the product methane collected as a product after separation, and the detected value of the flow meter is A methane separation apparatus characterized in that an adsorption device switching time control means is provided for adjusting an adsorption device switching time of the adsorption equipment accordingly. 4. In the methane separation apparatus according to claim 1, wherein the raw material natural gas is purified by an adsorption facility, a temperature detector is provided in the adsorber of the adsorption facility, and the temperature of the adsorber is adjusted according to the detected value of the temperature detector. A methane separator characterized in that it is provided with an adsorber switching time control means for adjusting the switching time. 5. The methane separator according to claim 1, further comprising a circulation system for introducing a part of the product methane collected as a product after separation into the raw material natural gas supply system. 6. In a method of introducing compressed, purified, and cooled raw material natural gas into a rectification column and separating it by liquefaction rectification to separate methane from the natural gas, part of the separated methane derived from the top of the rectification column is The remainder of the separated methane and the liquefied gas drawn out from the bottom of the rectification tower are introduced into a condenser, and the two are exchanged with heat to liquefy the separated methane and reflux it in the rectification tower. The method is characterized in that while obtaining a liquid, a part of the liquefied gas is vaporized, the partially vaporized liquefied gas is led out from a condenser and then separated into gas and liquid, and the separated gas is introduced into the raw material natural gas and circulated. Methane separation method. 7. The methane separation method according to claim 6, wherein the raw material natural gas is purified by adsorption equipment, in which the flow rate of the product methane collected as a product after separation is detected, and the adsorption equipment is adjusted according to the flow rate of the product methane. A methane separation method characterized by adjusting the amount of regeneration gas. 8. The methane separation method according to claim 6, wherein the raw material natural gas is purified by adsorption equipment, in which the flow rate of the product methane collected as a product after separation is detected, and the adsorption equipment is adjusted according to the flow rate of the product methane. A methane separation method characterized by controlling the switching time of an adsorber. 9. The methane separation method according to claim 6, wherein the raw material natural gas is purified by an adsorption facility, in which the temperature at an intermediate portion of the adsorber of the adsorption facility is detected, and the adsorption device switching time is adjusted according to the temperature. A methane separation method characterized by controlling. 10. The methane separation method according to claim 6, characterized in that when reducing the amount of product methane to be collected, a part of the product methane collected as a product after separation is introduced and recycled into the raw material natural gas. Methane separation method.