JP2939814B2 - Methane separation device and method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a methane separation apparatus and method for purifying and separating methane by performing liquefied rectification and separation using natural gas as a raw material.

[Conventional technology]

FIG. 2 shows a system of a conventional general methane separation device. This methane separation apparatus uses natural gas as a raw material, and contains nitrogen, ethane, hydrocarbons having 3 or more carbon atoms, carbon dioxide, moisture, and trace amounts of BTX (benzene,
In this method, toluene and xylene are separated and removed by an adsorption operation as a pretreatment and a liquefaction and rectification separation operation to purify and collect high-purity methane.

The raw natural gas from which carbon dioxide contained in advance has been removed by a washing method or the like is drawn into the compressor 2 from the raw material supply pipe 1, and after being pressurized to about 30 kg / cm ² G, the aftercooler 3, the precooler 4, It is introduced into the adsorption equipment 6 via the drain separator 5. In this adsorption equipment 6, a plurality of adsorbers (dryers) 7a and 7b to be used for switching are connected by switching valves 8a, 8b, 9a and 9b, and one adsorber 7a is used for the raw natural gas. During the adsorption step for removing impurities, the other adsorber 7b is in the regeneration step, and the regeneration of the adsorbent is performed by desorbing the impurity component adsorbed on the adsorbent by the regeneration gas described below and pre-cooling.

The raw natural gas introduced into one of the adsorbers 7a from the inlet valve 8a is purified and dried after removing the contained water, residual carbon dioxide gas, BTX, etc., and then is discharged into the cold box via the outlet valve 9a and the conduit 10. Introduced first heat exchanger 11, Freon cooler 1
The mixture is cooled in 2 and introduced into the gas-liquid separator 13 to separate low boiling components such as methane and ethane from other high boiling components. The raw material gas derived from the top of the gas-liquid separator 13 is further cooled by the second heat exchanger 14 and introduced into the lower part of the rectification column 15. Part of the methane gas rectified in the rectification tower 15 and led out from the top is branched into a conduit 16, and a valve 17, a subcooler 18,
After the cold heat is recovered through the second heat exchanger 14 and the first heat exchanger 11, the pre-cooler 4 is passed through the product gas conduit 19, the conduit 20, and the pre-cooler 4.
After being used as a cooling source, it is collected as product methane gas. Note that some of the product methane gas joins the product methane gas in the conduit 20 via the valve 21.

On the other hand, a liquefied gas containing about 50% of methane is led out from the bottom of the rectification column 15 and passed through the subcooler 18 and the valve 22 to the condenser 2.
Introduced in 3. In the condenser 23, the liquefied gas exchanges heat with the remainder of the methane gas led out from the top of the rectification column, and the methane gas is liquefied to become a reflux liquid of the rectification column 15.
The liquefied gas is partially vaporized and led out of the condenser 23 to the condenser outlet conduit 24, exits the second heat exchanger 14, and merges with the liquid phase part drawn out from the bottom of the gas-liquid separator 13. After that, it is led out of the cold box through the first heat exchanger 11 and
Collected as exhaust gas from 25. A part of this exhaust gas is branched from the conduit 25 to the conduit 26 for the regeneration gas, and is used as the regeneration gas in the adsorption equipment 6.

This regeneration gas is introduced into the heater 28 by the switching valve 27 at the time of the desorption operation at the beginning of the regeneration step, and after being heated to a predetermined temperature by steam or the like, is supplied from one of the regeneration valves 29a and 29b to the adsorber in the regeneration step. After flowing back, the impurities are introduced into the regeneration gas cooler 31 from one of the discharge valves 30a and 30b together with the exhaust gas and cooled, and then merge with the exhaust gas in the conduit 25. Further, the regeneration gas in the latter half of the regeneration step is not passed through the heater 28 but is passed from the switching valve 27 to the adsorbers 7a and 7b through the conduit 32 and the regeneration valves 29a and 29b.
And after pre-cooling of the adsorbent, merges with the exhaust gas in the same manner as described above.

[Problems to be solved by the invention]

However, in the methane separation process described above,
If the aim is to increase the methane recovery rate, for example, the mass balance [% by volume] shown in Table 1 is at a limit, and it is not possible to further improve the recovery rate.

This is based on the fact that the evaporation temperature of the methane-containing liquefied gas derived from the bottom of the rectification column 15 changes with the concentration of methane, and this change in the evaporation temperature changes the capacity of the condenser 23, that is, the condenser 23. Impact on the liquefaction capacity of methane gas in the sea. 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, but if the methane concentration is low, the evaporation temperature will be high and the methane gas in the condenser 23 will be high. The liquefaction capacity is reduced, and the reflux liquid in the rectification column 15 becomes insufficient, so that sufficient rectification cannot be performed.

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

Therefore, an object of the present invention is to provide a methane separation apparatus and a method thereof capable of improving the recovery rate without impairing the purity of the product methane after separation and purification.

[Means for solving the problem]

In order to achieve the above object, a methane separation apparatus of the present invention comprises a rectification column for liquefying and separating compressed, purified and cooled raw material natural gas, and one of the separated methane discharged from the top of the rectification column. In a methane separation device provided with a condenser for liquefying the separated methane by exchanging heat with the liquefied gas derived from the bottom of the rectification column and a liquefied gas, a gas-liquid separator is provided at a liquefied gas outlet of the condenser. In addition, a circulation system for introducing the gas separated by the gas-liquid separator into the raw material natural gas supply system is provided.

In the methane separation method of the present invention, the compressed, purified, and cooled raw natural gas is introduced into a rectification column to perform liquefied rectification and separation.
In the method for separating methane in the natural gas, a part of the separated methane derived from the top of the rectification column is collected as product methane, and the remaining methane and the liquefied gas derived from the bottom of the rectification column are collected. Is introduced into a condenser, and the two are heat-exchanged to liquefy the separated methane to obtain a reflux liquid of the rectification column, and a part of the liquefied gas is vaporized. And then introduced into the gas-liquid separator,
The gas separated at the upper part of the gas-liquid separator is introduced and circulated to the raw natural gas.

(Operation)

As described above, the gas-liquid separator is disposed at the liquefied gas outlet of the condenser, and the liquefied gas partially vaporized and derived by the condenser is subjected to gas-liquid separation, whereby the low boiling point contained in the liquefied gas is reduced. 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, it is possible to collect a portion of the methane conventionally entrained in the exhaust gas as product methane, thereby improving the yield. Can be achieved.

〔Example〕

Hereinafter, the present invention will be described in more detail based on one embodiment shown in the drawings. In the following description, the same elements as those in the conventional example shown in FIG. 2 are denoted by the same reference numerals, and detailed description is omitted.

In the apparatus of this embodiment, in addition to the above-described conventional apparatus, a condenser
A gas-liquid separator 41 disposed at the liquefied gas outlet of 23, a recovery circuit 42 for introducing gas derived from the top of the gas-liquid separator 41 into the raw material supply pipe 1, and a flow rate in the product gas conduit 19 The product gas flow meter (FIC A) 51 to be detected, the regeneration gas flow rate controller 52 (FIC B) provided in the flow path of the regeneration gas and linked to the product gas flow meter 51, A conduit 61 connecting the conduit 26 branched for gas, an automatic valve 62 provided in the conduit 61 and controlled by the regeneration gas flow rate controller 52, the conduit 10 on the outlet side of the adsorption equipment 7, and the regeneration gas And a valve 72 for connecting the product gas conduit 19 to the raw material supply pipe 1 and a conduit 81 for connecting the product gas conduit 19 and the raw material supply pipe 1 to each other. Valve 82
A pressure indicator 83 (PIC) for controlling the pressure is provided, and a thermometer 91 for measuring the temperature change of the adsorbent filled therein is provided near the outlet side of the adsorbers 7a and 7b. A controller 92 is provided for controlling the switching time of the valves 8a, 8b, 9a, 9b on the inlet and outlet sides of the adsorbers 7a, 7b based on the detection values of the product gas flow meter 51 and / or the thermometer 91. I have.

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 then introduced into the adsorption equipment 6 through the after cooler 3, the precooler 4, and the drain separator 5, and the impurity part is removed. Removal purification. Next, it is introduced into the cold box, and is introduced into the lower part of the rectification column 15 through the first heat exchanger 11, the CFC cooler 12, the gas-liquid separator 13, and the second heat exchanger 14, from the top of the rectification column. , High-purity purified methane gas is derived and part of it is collected as a product.
The remainder is liquefied in the condenser 23 and becomes the reflux liquid of the rectification column 15. In addition, the liquefied gas that is led out from the bottom of the rectification column and partially vaporized in the condenser 23 is introduced into the gas-liquid separator 41 from the condenser outlet conduit 24, and is separated into a gas phase and a liquid phase.

Among the liquefied gas components, the component that is vaporized in the condenser 23 is mainly methane gas having a low boiling point, and the methane gas is concentrated in the gas phase separated by the gas-liquid separator 41. For example,
The composition of the gas phase of the gas-liquid separator 41 is 96.5% methane,
The gas becomes 3.2% and nitrogen becomes 0.3%, which is a gas containing more methane than the raw material natural gas. Accordingly, 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 natural gas to the rectification separation step, whereby the gas is conventionally discharged as exhaust gas. It is possible to collect methane as a product. Thus, even if the methane concentration in the bottoms is increased, gas-liquid separation is performed at the outlet of the condenser 23, and the separated gas fraction (methane-rich gas) is compressed again and recycled to maintain the reflux liquid amount. At the same time, it was confirmed that the methane yield could be increased. On the other hand, in the liquid phase portion of the gas-liquid separator 41, the methane content decreases and the content of other components such as ethane relatively increases, and the exhaust gas passes through the second heat exchanger 14 and the first heat exchanger 11 as exhaust gas. After a part is used for the regeneration gas, it is recovered as exhaust gas from the conduit 25.

Here, in the above configuration, the composition is substantially the same as
The second is the mass balance when collecting the same amount of product methane.
It is shown in the table.

As is clear from Table 2 above, 53Nm ³ / h, which has been separated into the gas phase by the gas-liquid separator 41, is mixed with the raw natural gas and circulated out of the exhaust gas that has been conventionally discharged, thereby discharging it as exhaust gas. 158 Nm ³ / h from 105 Nm ³ / h to 105 Nm ³ / h, the concentration of methane contained in the exhaust gas can be reduced, and the amount of raw natural gas can be reduced. Can be improved. Also,
Since the methane in the liquefied gas can be recovered by the gas-liquid separator 41, by increasing the methane concentration of the liquefied gas derived from the bottom of the rectification column, lowering the evaporation temperature of the liquefied gas, and increasing the amount of liquefaction in the condenser 23, Also, the purity of the product methane can be improved by increasing the amount of reflux liquid in the rectification column 15. The gas-liquid interface in the gas-liquid separator 41 is maintained in a predetermined range by a liquid level controller 43.

On the other hand, in this type of separation device, the operation of reducing the weight to nearly 50% is performed. A problem when performing the reduction operation is securing of the regeneration gas in the adsorption equipment 6. In particular, in the case of increasing the yield of product methane as in the present invention, when the raw material gas composition is constant, the amount of exhaust gas relative to the raw natural gas is small, so that the gas that can be used as the regeneration gas in the adsorption facility 6 tends to be insufficient. is there. Therefore, the apparatus of the present embodiment is configured so that the amount of regeneration gas can be secured by linking the amount of product gas and the amount of regeneration gas. That is, the product gas flow rate is detected by the product gas flow meter 51, and the regeneration gas flow rate instruction controller 52 is operated based on the detection value of the flow meter 51, and the regeneration gas amount is changed to constantly reproduce the predetermined amount. Gas is supplied to the adsorption equipment 6. For example, when the amount of raw natural gas is reduced by performing a reduction 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 controller 52 controls the regeneration gas flow indication controller 52 in accordance with the decrease. Operate in the opening direction to increase the amount of regeneration gas with respect 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 regenerated gas can be introduced into the adsorption equipment 6,
The adsorbers 7a and 7b can be sufficiently regenerated.

Further, in the reduction operation, there is a problem whether the adsorbent in the adsorbers 7a and 7b is sufficiently used together with securing the amount of the regeneration gas. Therefore, in the present invention, a thermometer 91 for measuring the temperature of the adsorbent is provided in the middle of the adsorbers 7a, 7b, preferably between the outlet end and the center, and near the outlet end to measure the temperature change of the adsorbent. The switching time of the adsorbers 7a and 7b is adjusted by the switching time controller 92 by detecting the heat of adsorption generated when the adsorbent adsorbs the impurities (adsorbed substances), obtaining the degree of progress of the adsorption by this temperature rise. It is composed. As a result, the adsorbent can be used effectively and sufficiently even when the amount of the raw material natural gas is significantly reduced by the reduction operation. Further, by performing this means in combination with the means for securing the amount of the regenerated gas based on the product gas amount, a reliable adsorption removal function can be exhibited even during the reduction operation.

Further, a conduit 61 for connecting the conduit 19 for collecting the product and the conduit 26 for the regeneration gas is provided, and the conduit 61 is provided with an automatic valve 62 linked to the controller 52 for indicating the regeneration gas flow rate. If the required amount of regeneration gas is less than
The automatic valve 62 is opened by the operation of the regeneration gas flow rate controller 52, and a part of the product gas can be used as the regeneration gas.

As a result, a sufficient amount of regeneration gas can be secured even if the amount of exhaust gas is significantly reduced, and regeneration of the adsorbers 7a and 7b can be reliably performed. Also, by providing a conduit 71 and a valve 72 for connecting the conduit 10 on the outlet side of the adsorption facility and the conduit 26 for the regeneration gas, a part of the raw material natural gas purified in the adsorption facility 6 can be regenerated by the regeneration gas in the adsorption facility 6. Can be used as When the regeneration gas is insufficient due to the operating conditions, the regeneration gas can be increased by using a part of the product methane gas or a part of the purified raw natural gas. Can be played.

In addition, in order to further stabilize the weight reduction operation, a circulation path for the weight reduction operation connecting the product gas conduit 19 and the raw material supply pipe 1.
81, and the pressure in the product gas conduit 19 is
By opening and closing the automatic valve 82 based on this, when the demand for the product methane gas decreases and the pressure in the pipe 19 increases, the automatic valve 82 is opened and a part of the product methane gas is It can be circulated and joined to natural gas.
As a result, even when the product production volume is greatly reduced, the flow rate of each part of the apparatus can be maintained at a level higher than that required for stable operation, and the introduction of the product methane gas allows the raw material natural gas intake amount in the compressor 2 to be reduced. That is, the supply amount of the raw material can be automatically reduced.

In addition, the gas circulated to the raw material natural gas introduction system, including the circulating gas from the gas-liquid separator 41, can be combined with the raw material at an appropriate position depending on the flow rate and pressure, and the multistage compressor can be used. Can be joined at an intermediate stage.

〔The invention's effect〕

As described above, in the present invention, the gas-liquid separator is disposed at the liquefied gas outlet of the condenser, and the gas portion of the liquefied gas partially vaporized by the condenser is circulated. The rate can be increased 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 apparatus, so there is almost no increase in equipment cost and operation cost, and the cost of product methane can be significantly reduced.

In addition, by changing the ratio of the regeneration gas to the exhaust gas according to the flow rate of the product methane gas, the amount of the exhaust gas decreases with the improvement of the yield, and even if the regeneration gas in the adsorption equipment becomes insufficient, a sufficient amount of the regeneration gas can be obtained. Can be secured. Furthermore, by controlling the switching time of the adsorber based on a change in the product gas amount and a change in the temperature of the adsorbent, the adsorbent can be effectively used even when the amount of the raw material natural gas is reduced by the reduction operation. Further, by circulating a part of the product methane gas to the raw material supply system at the time of the weight reduction operation, the large weight reduction operation can be performed in a stable state.

[Brief description of the 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, 7
a, 7b …… Adsorber, 15… Rectification tower, 19… Product gas conduit,
23… Condenser, 24… Condenser outlet conduit, 41… Gas-liquid separator, 42… Recovery circuit, 51… Product gas flow meter, 52…
Regenerative gas flow rate controller, 91: thermometer, 92: switching time controller

Continuation of front page (58) Field surveyed (Int. Cl. ⁶ , DB name) F25J 1/00-5/00

Claims (10)

(57) [Claims] 1. A rectification column for liquefying and separating a compressed, purified and cooled raw natural gas, a portion of the separated methane derived from the top of the rectification column and a liquefied gas derived from the bottom of the rectification column And a methane separator provided with a condenser for liquefying the separated methane by exchanging heat with a gas-liquid separator provided at a liquefied gas outlet of the condenser, and separating the gas separated by the gas-liquid separator. A methane separation device comprising a circulation system for introducing a raw natural gas supply system. 2. The methane separation apparatus according to claim 1, wherein the raw material natural gas is purified by an adsorption facility, wherein a flow meter for detecting a flow rate of product methane collected as a product after separation is provided. A methane separation device comprising a regeneration gas amount adjusting means for adjusting a regeneration gas amount of the adsorption equipment according to a detected value. 3. The methane separation device according to claim 1, wherein the raw material natural gas is purified by an adsorption facility, wherein a flow meter for detecting a flow rate of product methane collected as a product after separation is provided. A methane separation device comprising an adsorber switching time control means for adjusting an adsorber switching time of the adsorption equipment according to a detected value. 4. The methane separation apparatus according to claim 1, wherein the raw material natural gas is purified by an adsorption facility, wherein a temperature detector is provided in an adsorber of the adsorption facility, and a temperature detector is provided in accordance with a detection value of the temperature detector. A methane separation device comprising an adsorber switching time control means for adjusting a switching time of an adsorber. 5. The methane separation device according to claim 1, wherein
A methane separation apparatus comprising a circulation system for introducing a part of product methane collected as a product after separation into a raw material natural gas supply system. 6. A method for introducing a compressed, purified and cooled raw natural gas into a rectification column for liquefied rectification and separation of methane in the natural gas, wherein the separation derived from the top of the rectification column is performed. Part of the methane is collected as product methane, the remainder of the separated methane and the liquefied gas derived from the bottom of the rectification column are introduced into a condenser, and the two are heat-exchanged to liquefy the separated methane and rectify. Obtaining the reflux liquid of the column and vaporizing a part of the liquefied gas, deriving the partially vaporized liquefied gas from the condenser, performing gas-liquid separation, and introducing and circulating the separated gas into the raw material natural gas. Characteristic methane separation method. 7. The methane separation method according to claim 6, wherein the purification of the raw material natural gas is performed by an adsorption facility, wherein the flow rate of the product methane collected as a product after the separation is detected and the flow rate of the product methane is determined according to the flow rate of the product methane. A method for separating methane, comprising adjusting a regeneration gas amount of the adsorption equipment. 8. The methane separation method according to claim 6, wherein the raw material natural gas is purified by an adsorption facility, wherein the flow rate of the product methane collected as a product after the separation is detected and the flow rate of the product methane is determined in accordance with the flow rate of the product methane. A method for separating methane, comprising controlling a switching time of an adsorber of the adsorption equipment. 9. The method for separating methane according to claim 6, wherein the raw material natural gas is purified by an adsorption facility, wherein a temperature of an intermediate portion of the adsorber of the adsorption facility is detected, and the temperature of the adsorber is determined in accordance with the detected temperature. A methane separation method characterized by controlling a switching time. 10. The method for separating methane according to claim 6, wherein when reducing the amount of product methane collected, a part of the product methane collected as a product after separation is introduced and circulated to the raw natural gas. Characteristic methane separation method.