JP2006307134A - Method for separating C2 + fraction from light gas containing NOx - Google Patents

Abstract

A for NO _x containing light gases such as FCC off-gas, while suppressing the generation and accumulation of the NO _x gums, to separate and recover C2 + fraction.
SOLUTION: Gas-liquid separation tanks 31 to 34 for separating a raw material containing hydrogen, methane and C2 + into a gas phase component and a liquid phase component, and hydrogen for separating the gas phase component into a hydrogen fraction and a low pressure methane fraction A low-pressure methane separation tank 51, a demethanizer 61 for distilling the liquid phase component and separating the liquid phase component as a C2 + fraction, a top component of the demethanizer 61 is cooled, and a gas phase component is converted to high pressure methane. As a fraction, a part of the liquid phase component is separated as a medium pressure methane fraction, and the remainder is refluxed to the demethanizer 61, and the gas phase components from the gas-liquid separation tanks 31 to 34 are separated into hydrogen fractions. and in cryogenic system 1 that includes a deep cold heat exchanger 41 for cooling by heat exchange low-medium pressure and high pressure methane fraction, and supplies the NO _x containing light gas to NO _x containing light gas distillation column 62 The vapor phase component obtained by distillation is supplied to the demethanizer 61.
[Selection] Figure 2

Description

The present invention is, from the NO _x containing light gases such as FCC off-gas by-produced in the FCC process, such as oil refining process, ethylene, relates to a method of separating the C2 + fraction containing useful olefinic cut such as propylene.

  The FCC off-gas produced as a by-product in the fluid catalytic cracking (Fluid Catalytic Cracking: this is referred to as “FCC” as appropriate) processes such as petroleum refining processes are hydrocarbons containing 2 or more carbon atoms containing useful olefin fractions such as ethylene and propylene (This is appropriately referred to as “C2 + fraction”. In the following description, hydrocarbons having a carbon number of n or more are referred to as “Cn + fraction” with the lower limit of carbon number n attached thereto). Yes.

  Specifically, the off-gas generated from the FCC device is first (i) in the by-product gas recovery system, impurities such as hydrogen sulfide are removed and a part of the C3 + fraction is separated to produce a hydrogen-containing light gas (hydrogen , Methane, C2 + fraction, etc.). Subsequently, (ii) in the dehydration / deep cooling system, hydrogen and a part of methane are separated and become light gas (including methane, C2 + fraction, etc.) (see Non-Patent Document 1). In the present specification, a light gas obtained from the off-gas generated from the FCC apparatus through the above-mentioned (i) by-product gas recovery system and (ii) dehydration / deep cooling system is referred to as “FCC off-gas”.

  It has been proposed to separate and recover useful olefin fractions by supplying this FCC offgas to the compression process of an ethylene production plant (see Non-Patent Document 2).

“Petroleum Refining Process”, 2003, published by Kodansha, edited by The Japan Petroleum Institute, p. 154 Chemical Engineering, November 1996, p. 133-135

However, the FCC off-gas contains nitrogen oxide (this is referred to as “NO _x ” as appropriate) in addition to methane and C2 + fraction. If this is supplied as it is to the compression step of the ethylene production plant, it is different from the deep cooling system of the refining process provided in the subsequent stage (this is different from the “dehydration / deep cooling system” provided in the oil refining process described above. In the specification, when simply referring to “deep cooling system”, it is not the “dehydration / deep cooling system” of the petroleum refining process, but the application object of the present invention represented by the deep cooling system of the refining process of the ethylene production plant. is intended to refer to cryogenic system in.), gums NO _x is in explosive (hereinafter, may be referred to as "NO _x gums".) is formed, possibly this will be deposited in the deep cooling system is there.

Measures contrast, in Non-Patent Document 2 described above, by a technique such as alkali washing and dewatered, after decreasing concentrations of the NO _x in FCC off-gas to about 100 ppb, of supplying to the compressing process of ethylene production plant Has been proposed.

However, even when reduced concentration of NO _x FCC offgas, the NO _x in FCC off-gas is left, even slightly, when this brought to the compression process of ethylene production plant, the subsequent purification step cryogenic There is a risk that NO _x gum is generated and deposited in the system. Therefore, while more reliably suppress the generation and accumulation of the NO _x gums, a method of separating and recovering useful olefinic cut from an FCC off-gas has been demanded.

In the above description, a case of separating and recovering useful olefinic cut the FCC off-gas and petroleum refining process has been described as an example, not limited to this case, generally containing methane, C2 + fraction and NO _x In the case where the C2 + fraction is separated and recovered from the gas to be used (this is referred to as “NO _x- containing light gas” as appropriate), the same problem is widely caused.

The present invention has been made in view of the above problems. It is an object of the present invention, the NO _x containing light gases such as FCC off-gas, while suppressing the generation and accumulation of the NO _x gum is to provide a method for separating and recovering C2 + fraction.

As a result of intensive studies, the present inventors have focused on the fact that the existence of a cryogenic temperature region (about −160 ° C.) in the cryogenic gas-liquid separation tank causes the generation and deposition of NO _x gum. Then, another distillation column (NO _x containing light gas distillation column) provided in front of the demethanizer, and distilled NO _x containing light gas in the NO _x containing light gas distillation column, a liquid phase component and gaseous component while separated by configured to provide to the demethanizer cryogenic system the gas phase component obtained, it is possible to avoid this extremely low temperature region, to suppress the generation and accumulation of the NO _X gum However, it was found that the C2 + fraction could be separated and recovered, and the present invention was completed.

That is, the gist of the present invention is that C2 + distillation is performed from methane, a hydrocarbon having 2 or more carbon atoms (hereinafter referred to as “C2 +”), and a gas containing nitrogen oxide (hereinafter referred to as “NO _x- containing light gas”). (A) a gas-liquid separation tank which is supplied with a raw material containing hydrogen, methane and C2 + and separates it into a gas phase component and a liquid phase component; and (B) the gas-liquid separation method. A hydrogen / low pressure methane separation tank that separates the gas phase component separated by the separation tank into a hydrogen fraction and a methane fraction (hereinafter referred to as “low pressure methane fraction”); and (C) the gas-liquid separation tank. A demethanizer that distills the separated liquid phase component and separates the liquid phase component as a C2 + fraction; and (D) the top component of the demethanizer tower is cooled, and the gas phase component is converted into a methane fraction (hereinafter “ High-pressure methane fraction ”) and a part of the liquid phase components. A further separation as a tan fraction (hereinafter referred to as “medium pressure methane fraction”), the remainder being refluxed to the demethanizer tower, and (E) a gas phase component separated by the gas-liquid separation tank, Chilled heat exchange cooled by heat exchange with the hydrogen and low pressure methane fractions separated by the hydrogen / low pressure methane separation tank, and the medium pressure and high pressure methane fractions separated by the reflux tank In a deep-cooled system equipped with a vessel, the NO _x -containing light gas is supplied to a NO _x -containing light gas distillation column to be distilled and separated into a liquid phase component and a gas phase component. by supplying the dehydration demethanizer, characterized by being configured to separate the C2 + fraction of the NO _x containing light gas, resides in C2 + fraction separation methods from the NO _x containing light gas (according Item 1).

According to the present invention, the NO _x containing light gases such as FCC off-gas was distilled NO _x containing light gas distillation column, while separated into a liquid phase component and gaseous component, resulting gas phase components of the cryogenic system by configured to supply to the demethanizer, while taking the configuration of an existing cryogenic system, while suppressing the generation and accumulation of the NO _X gums, it is possible to separate the C2 + fraction. Further, it is possible to supply to the demethanizer from beforehand remove C2 + fraction contained in NO _x containing light gases, it is possible to reduce the load of the demethanizer. Further, it is possible to control the heat source provided in the heat source and the NO _x containing light gas distillation column provided demethanizer at different temperature levels, depending on the type of application to the plant, to obtain the effect of reducing such costs It becomes possible.

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the gist of the present invention.

  In the following description, as an embodiment of the present invention, a system including a cryogenic heat exchanger and a demethanizer provided in a purification process of an ethylene production plant that is a kind of chemical plant (this is appropriately referred to as “around the demethanizer tower”). A case where the present invention is applied to “deep cooling system” or simply “deep cooling system”) will be described as an example.

  As an example of a typical configuration of an ethylene production plant, a process of thermally decomposing raw materials such as naphtha in a cracking furnace (decomposition process), a process of quenching and rectifying the obtained cracked gas (quenching process), It includes a process for compressing the rapidly cooled and rectified cracked gas (compression process) and a process for separating and purifying the compressed cracked gas into its components to obtain ethylene, propylene, etc., which are the main products (purification process) Configuration.

  Of these, particularly in the purification process, the cracked gas that has been compressed in the previous compression process and from which moisture has been completely removed is cooled in a cryogenic heat exchanger, and a hydrogen fraction and a part of the methane fraction (low-pressure methane fraction). The distillate) is separated and fed to a demethanizer tower. In the demethanizer tower, the remaining methane fraction (medium-pressure methane fraction and high-pressure methane fraction) is separated from the top of the tower, and then the liquid at the bottom of the tower is sent to a subsequent process. In the post-process, each component is separated by passing through a distillation tower such as a deethanizer tower, an ethylene tower, a depropanizer tower, a propylene rectification tower, and a debutane tower. There are also processes in which the types and order of these distillation columns are different.

[I. First Embodiment (Reference Embodiment)]
FIG. 1 shows the depth around a demethanizer tower in a purification process of an ethylene plant provided with a configuration for carrying out a method for separating a C2 + fraction from a light gas containing NO _{x according} to an embodiment related to the present invention. It is a figure which shows typically an example of a structure of a cold system.

  1 includes a plurality of heat exchangers 21 to 25, multistage (four stages in the figure) gas-liquid separation tanks 31 to 34, a cryogenic heat exchanger 41, a hydrogen / low pressure methane separation tank 51, a desorption system. A methane tower 61, a reflux tank 71, and control valves 81 to 88 are provided.

  The cracked gas a sent from the previous stage (usually the compression step) (hereinafter, this cracked gas a may be referred to as a raw material) contains hydrogen, methane, and a hydrocarbon having 2 or more carbon atoms. The cracked gas a is cooled by the heat exchanger 21, partly condensed and liquefied (gas-liquid mixed phase fluid a ′), and sent to the first-stage gas-liquid separation tank 31.

  In the first-stage gas-liquid separation tank 31, the gas-liquid mixed phase fluid a ′ sent is separated into a liquid phase component b and a gas phase component c, and the liquid phase component b is sent to a demethanizer tower 61 described later. (Note that a flow control valve 81 for adjusting the flow rate of the liquid phase component b is usually provided on the path from the first-stage gas-liquid separation tank 31 to the demethanizer 61). On the other hand, the gas phase component c is sent to the cryogenic heat exchanger 41 to be cooled, and further cooled by the heat exchanger 22, and a part thereof is condensed and liquefied (gas-liquid mixed phase fluid c ′). It is sent to the two-stage gas-liquid separation tank 32.

  In the second-stage gas-liquid separation tank 32, the gas-liquid mixed phase fluid c ′ sent is separated into the liquid phase component d and the gas phase component e, and the liquid phase component d is sent to the demethanizer tower 61 described later. (Note that a flow rate adjusting valve 82 for adjusting the flow rate of the liquid phase component d is usually provided on the path from the second stage gas-liquid separation tank 32 to the demethanizer 61). On the other hand, the vapor phase component e is sent to the cryogenic heat exchanger 41 to be cooled, and further cooled by the heat exchanger 23, and a part thereof is condensed and liquefied (gas-liquid mixed phase fluid e ′). It is sent to the three-stage gas-liquid separation tank 33.

  In the third-stage gas-liquid separation tank 33, the gas-liquid mixed phase fluid e ′ sent is separated into the liquid phase component f and the gas phase component g, and the liquid phase component f is sent to the demethanizer tower 61 described later. (Note that a flow rate adjusting valve 83 for adjusting the flow rate of the liquid phase component f is usually provided on the path from the third-stage gas-liquid separation tank 33 to the demethanizer 61). On the other hand, the gas phase component g is sent to the cryogenic heat exchanger 41 to be cooled, and further cooled by the heat exchanger 24, and a part thereof is condensed and liquefied (gas-liquid mixed phase fluid g ′), It is sent to the fourth stage gas-liquid separation tank 34.

  In the gas-liquid separation tank 34 in the fourth stage (final stage), the gas-liquid mixed phase fluid g ′ sent is separated into a liquid phase component h and a gas phase component i, and the liquid phase component h is a demethanizer tower described later. (In addition, a flow rate adjusting valve 84 for adjusting the flow rate of the liquid phase component h is usually provided on the path from the fourth stage gas-liquid separation tank 34 to the demethanizer 61). On the other hand, the gas phase component i is sent to the cryogenic heat exchanger 41 to be cooled, and a part thereof is condensed and liquefied (gas-liquid mixed phase fluid i ′) and sent to the hydrogen / low pressure methane separation tank 51. .

  In the hydrogen / low pressure methane separation tank 51, the gas-liquid mixed phase fluid i ′ sent is separated into a liquid phase component j and a gas phase component k. The gas phase component j (mainly composed of hydrogen) is sent to the cryogenic heat exchanger 41 as a hydrogen fraction and used as a refrigerant. On the other hand, the liquid phase component g (mainly composed of methane) is flushed by the flow control valve 85 to reduce the pressure and temperature, and then sent to the deep heat exchanger 41 as a low-pressure methane fraction. It is also used as a refrigerant.

  In the demethanizer 61, the liquid phase components b, d, f, and h sent from the gas-liquid separation tanks 31 to 34 are distilled, and the C2 + fraction l is separated from the bottom of the tower and fed to the subsequent process. Is done. In addition, the component (top component) m separated from the top of the demethanizer 61 is sent to the top condenser (heat exchanger) 25 to be cooled and partially condensed / liquefied (gas-liquid). The mixed phase fluid m ′) is sent to the reflux tank 71 for gas-liquid separation. A part n of the separated liquid phase component is refluxed as a reflux liquid to the demethanizer tower 61 (note that the flow rate of the reflux liquid n is usually adjusted on the path from the reflux tank 71 to the demethanizer tower 61. A flow control valve 86 is provided for this purpose). The remainder o (mainly composed of methane) of the liquid phase component is flushed by the flow rate control valve 87, the pressure and temperature are lowered, and sent to the chilled heat exchanger 41 as an intermediate pressure methane fraction, as a refrigerant. Used. In addition, the gas phase component p (mainly composed of methane) separated in the reflux tank 71 is sent to the chilled heat exchanger 41 as a high-pressure methane fraction, and is also used as a refrigerant (note that it is used as a refrigerant from the reflux tank 71). A flow rate adjusting valve 88 for adjusting the flow rate of the high-pressure methane fraction p is usually provided on the path to the cold heat exchanger 41.)

Further, the cryogenic system 1 shown in FIG. 1 has a path for supplying NO _x -containing light gas (symbol x in the figure) to the demethanizer 61 as a component for carrying out the separation method of the present embodiment. A flow rate adjusting valve 91 and a heat exchanger 92 are provided on the path.

As described above, the NO _x -containing light gas is not particularly limited as long as it is a gas containing methane, a C2 + fraction and NO _x . An example is FCC off-gas in an oil refining process, again as described above.

The NO _x -containing light gas supplied from the outside is first supplied to the demethanizer 61. Preferably, the NO _x -containing light gas is supplied to a position where the NOx-containing light gas has almost the same value as the composition in the demethanizer 61. Further, before being supplied to the demethanizer 61, the pressure and temperature of the NO _x -containing light gas are adjusted so that the temperature and pressure at the supply position of the demethanizer 61 are substantially the same value. Therefore, the NO _x -containing light gas is subjected to pressure adjustment or flow rate adjustment by the compressor or the control valve 91 and cooling or heating by the heat exchanger 92 as necessary. In addition, although the example provided with the control valve 91 and the heat exchanger 92 is shown in FIG. 1 as mentioned above, it is not necessarily restricted to this structure.

  Specifically, the pressure of the demethanizer 61 is usually about 2.5 to 3.5 MPaG, and the temperature is usually about −10 ° C. to 10 ° C. near the tower bottom and about −110 ° C. to −90 ° C. near the top of the tower. .

After adjusting the pressure and temperature, the NO _x -containing light gas supplied to the demethanizer 61 and the liquid phase components b, d, f, and h obtained by the gas-liquid separation tanks 31 to 34 in the demethanizer 61. While being distilled, C2 + fraction l is separated from the bottom of the column.

Here, when comparing the conventional technique with this embodiment, in the conventional technique represented by the above-mentioned Non-Patent Document 2, since the NO _x- containing light gas is introduced into the compression process which is the previous stage, The cracked gas a sent contains NO _x , which passes through the gas-liquid separation tanks 31 to 34 and the hydrogen / low-pressure methane separation tank 51. The in-vessel temperatures of the gas-liquid separation tanks 31 to 34 and the hydrogen / low-pressure methane separation tank 51 become lower as the process proceeds to the subsequent stage, and in the hydrogen / low-pressure methane separation tank 51 (final stage), the in-vessel temperature is usually −165. It becomes extremely low temperature range of about ℃ (see "Reporton Activities of the NOx in Ethylene Recovery Task Group", DC Grenoble, Prepared for Presentation at the 2004 Spring AlChE National Meeting, April 25-29, New Orleans, LA). In contrast, NO _x because gum made usually easily generated as the temperature is low, if the NO _x during the decomposition gas a is present in trace amounts, NO in the hydrogen-pressure methane separation vessel 51 (the final stage) _x There is a risk of gum formation.

On the other hand, according to the cryogenic system 1 of the present embodiment, the NO _x -containing light gas is directly supplied to the demethanizer 61 after adjusting the pressure and temperature by the flow rate control valve 91 and the heat exchanger 92. The gas-liquid separation tanks 31 to 34 and the hydrogen / low-pressure methane separation tank 51 (particularly, the final stage hydrogen / low-pressure methane separation tank 51 in a cryogenic region) are not passed. In the path through which NO _x may pass, the lowest temperature is the medium pressure methane after being flushed by the control valve 87, and this is usually about −140 ° C. to −120 ° C. as described above. In addition, since it is higher than the hydrogen / low pressure methane separation tank 51, the generation and deposition of NO _x gum is greatly suppressed. Therefore, according to the cryogenic system 1 of this embodiment, it is possible to separate and recover C2 + fraction while suppressing the generation and accumulation of the NO _x gums.

In the arrangement of FIG. 1, although the flow control valve 91 and heat exchanger 92 is provided on a path NO _x containing light gas is supplied to the demethanizer 61, the type of the NO _x containing light gas Ya Depending on the separation performance of the demethanizer 61, a plurality of these components may be provided, the arrangement may be changed, or the components may be omitted. Moreover, you may provide another component (for example, gas-liquid separation tank etc.) on this path | route. Hereinafter, an embodiment with such a modification will be described.

[II. Second Embodiment (Embodiment of the Present Invention)]
FIG. 2 is a cryogenic system around a demethanizer tower in a purification process of an ethylene plant, which is provided with a configuration for carrying out a method for separating a C2 + fraction from a light gas containing NO _{x according} to an embodiment of the present invention. It is a figure which shows typically an example of a structure of. 2, the same components as those in FIG. 1 are denoted by the same reference numerals.

  2 is a plurality of heat exchangers 21 to 25, multistage (four stages in the figure) gas-liquid separation tanks 31 to 34, and a deep cold heat exchanger 41. , A hydrogen / low pressure methane separation tank 51, a demethanizer 61, a reflux tank 71, and control valves 81-88. Since these functions are the same as those in FIG. 1, the description thereof is omitted.

In the cryogenic system 1 ′ of FIG. 2, another distillation column (NO _x- containing light gas distillation column, NO _x- containing light gas stripper) is provided on the path through which the NO _x- containing light gas is supplied to the demethanizer 61. 62 is provided. The NO _x -containing light gas is first supplied to the NO _x -containing light gas stripper 62 and distilled. The gas phase component (mainly methane fraction) q obtained from the top of the NO _x -containing light gas stripper 62 is sent to the demethanizer 61 and the liquid phase components obtained by the gas-liquid separation tanks 31 to 34. Distilled with b, d, f, h. On the other hand, the C2 + fraction r is extracted from the bottom of the NO _x -containing light gas stripper 62 and fed to the subsequent process together with the C2 + fraction l obtained by the demethanizer 61.

By such configuration, the C2 + fraction contained in NO _x containing light gas can be supplied after removing in advance the demethanizer 61 in NO _x containing light gas stripper 62, it is possible to reduce the load of the demethanizer It becomes possible. In addition, since the heat source provided in the demethanizer 61 and the heat source provided in the NO _x -containing light gas stripper 62 can be controlled at different temperature levels, an effect such as cost reduction can be obtained depending on the type of plant to be applied. It can also be obtained.

[III. Third Embodiment (Reference Embodiment)]
FIG. 3 shows the depth around the demethanizer tower in the purification process of an ethylene plant provided with a configuration for carrying out a method for separating a C2 + fraction from a light gas containing NO _{x according} to an embodiment related to the present invention. It is a figure which shows typically an example of a structure of a cold system. In FIG. 3, the same components as those in FIGS. 1 and 2 are denoted by the same reference numerals.

3 is similar to the refrigeration system 1 ′ of FIG. 2, a plurality of heat exchangers 21 to 25, multistage (four stages in the figure) gas-liquid separation tanks 31 to 34, and a refrigeration heat exchanger. 41, hydrogen-pressure methane separation tank 51, demethanizer 61, NO _x containing light gas stripper 62, a reflux tank 71, and a regulating valve 81 to 88. these features similar to FIG. 1 and FIG. 2 Since there is, explanation is omitted.

In the refrigeration system 1 ″ of FIG. 3, the liquid phase component b obtained by the first-stage gas-liquid separation tank 31 is first supplied to the NO _x -containing light gas stripper 62, and the NO _x -containing light gas and After that, the vapor phase component (mainly methane fraction) q obtained from the top of the NO _x -containing light gas stripper 62 is removed from the demethanizer 61 as in the case of the refrigeration system 1 ′ of FIG. sent to each gas-liquid liquid phase component b obtained by separation tank 31 to 34, d, f, is distilled together with h. on the other hand, from the bottom of the NO _x containing light gas stripper 62 C2 + fraction r Is extracted and fed to the subsequent process together with the C2 + fraction l obtained by the demethanizer 61.

By such configuration, the composition of the NO _x containing light gases, temperature, can be reduced variations in operating conditions of the demethanizer 61 and NO _x containing light gas stripper 62 due to the variation of the pressure and the like. That is, in a situation where NO _x containing light gas (for example, FCC offgas) is supplied from a plant (for example, an oil refinery plant) different from the plant (for example, an ethylene plant) to which the cryogenic system 1 ″ belongs, FCC offgas is used for the convenience of the oil refinery plant. even or when the supply is stopped, and so the ethylene plant side, the supply of the liquid phase component from the gas-liquid separation tank NO _x containing light gas stripper 62 is continuing, the operation of the NO _x containing light gas stripper 62 Therefore, it is possible to reduce the influence of the ethylene plant from fluctuations in the operating conditions of the oil refinery plant.

In the cryogenic system 1 ″ of FIG. 3, the entire liquid phase component b obtained by the first-stage gas-liquid separation tank 31 is supplied to the NO _x -containing light gas stripper 62. In addition, only a part of the liquid phase component b, but not all, is supplied to the NO _x -containing light gas stripper 62, and the rest of the liquid phase component b is supplied directly to the demethanizer 61 as in the case of the cryogenic system 1 in FIG. may be configured to. the supply liquid phase component d obtained by the gas-liquid separation tank 32 to 34 other than the gas-liquid separation tank 31 of the first stage, f, and h to the NO _x containing light gas stripper 62 It is also possible to configure so as to.

[IV. Others]
As described above, as the embodiment of the present invention and related embodiments, the deep cooling system 1, 1 ′, 1 ″ shown in FIGS. 1 to 3 has been described. , 1 ′, 1 ″, and can be applied to any deep cooling system as long as it does not exceed the gist.

  For example, although FIGS. 1-3 demonstrated the case where the gas-liquid separation tanks 31-34 were four steps as mentioned above, the number of stages of a gas-liquid separation tank may differ. Also in this case, the gas-liquid mixed phase fluid sent from the previous stage is separated in the gas-liquid separation tank of each stage, and the liquid phase component is sent to the demethanizer tower, while the gas phase component is sent to the refrigeration heat exchanger (and It is cooled by a heat exchanger, and a part of it is condensed and liquefied (gas-liquid mixed phase fluid), and it is transferred to the next-stage gas-liquid separation tank (in the case of the last-stage gas-liquid separation tank, hydrogen / low-pressure methane) Configured to be sent to a separation tank). Similarly, in the case of a single-stage gas-liquid separation tank, cracked gas (raw material), which is a gas-liquid mixed phase fluid sent from the previous stage, is separated and the liquid phase component is sent to the demethanizer tower. The gas phase component is cooled by a deep cold heat exchanger (and a heat exchanger), and a part of the gas phase component is condensed and liquefied (gas-liquid mixed phase fluid) and is sent to a hydrogen / low pressure methane separation tank. .

  In addition, even when the number of stages of the gas-liquid separation tank is different, the temperature in the tank of the gas-liquid separation tank in the final stage (in the case of a single stage, the temperature in the tank) is usually an extremely low temperature range of about −165 ° C. (“ Report on Activities of the NOx in Ethylene Recovery Task Group ", DC Grenoble, Prepared for Presentation at the 2004 Spring AlChE National Meeting, April 25-29, New Orleans, LA). Therefore, the same effect can be obtained by applying the present invention.

  Moreover, in FIGS. 1-3, although the heat exchangers 21-24 are provided around the cryogenic heat exchanger 41 and the gas-liquid separation tanks 31-34 of each stage, the number, arrangement | positioning, etc. of a heat exchanger are arbitrary. It is. For example, some heat exchangers may be omitted between the gas-liquid separation tanks of each stage, and a plurality of heat exchangers may be provided.

  1 to 3, the gas components c, e, g, and i obtained from the gas-liquid separation tanks 31 to 34 are all cooled by a single deep heat exchanger 41. In other cases, the gas components c, e, g, and i may be separately cooled. For example, a gas component obtained by the first deep-cooling heat exchanger that cools the gas components c, e, and g obtained by the gas-liquid separation tanks 31 to 33 other than the final stage and the gas-liquid separation tank 34 of the final stage. The structure etc. which provide the 2nd deep-cooling heat exchanger which cools i separately independently are mentioned.

  In addition, when providing a several deep-cooling heat exchanger, you may use the same combination of refrigerant | coolants with all the deep-cooling heat exchangers, but the combination of the refrigerant | coolant used for every deep-cooling heat exchanger may be changed. For example, if the first and second deep heat exchangers are provided as described above, in the first deep heat exchanger, the hydrogen fraction i, the low pressure methane fraction k, the medium pressure methane fraction o, the high pressure While all of the methane fraction p is used as a refrigerant, the second cryogenic heat exchanger may be configured to use only the hydrogen fraction i and the low-pressure methane fraction k as the refrigerant.

1 to 3, all of the liquid phase components b, d, f, and h obtained by the gas-liquid separation tanks 31 to 34 are directly sent to the demethanizer 61 or the NO _x -containing light gas stripper 62. In some cases, these liquid phase components are subjected to treatment such as heat exchange and then sent to the demethanizer 61 or the NO _x -containing light gas stripper 62. For example, some or all of these liquid phase components b, d, f, and h are first sent to the cryogenic heat exchanger 41 and used as a refrigerant in the cryogenic heat exchanger 41, and then heated by heat exchange. In addition, a configuration in which these components b, d, f, and h are sent to the demethanizer 61 or the NO _x -containing light gas stripper 62 is exemplified.

  Furthermore, in addition to the hydrogen fraction i, the low-pressure methane fraction k, the medium-pressure methane fraction o, the high-pressure methane fraction p, the liquid phase components b, d, f, h of the gas-liquid separation tanks 31 to 34, etc. Moreover, it is good also as a structure which uses another fluid as refrigerant | coolants, such as the deep-cooling heat exchanger 41 grade | etc.,. Moreover, in this deep-cooling heat exchanger 41 grade | etc., It is good also as a structure which cools another fluid collectively.

  Moreover, in FIGS. 1-3, although it has the structure which adjusts the flow volume of various fluids, such as each methane fraction, by the flow control valves 81-88 etc., the number of these flow control valves, arrangement | positioning, the object to be adjusted, etc. In some cases, the method may be appropriately modified. Further, a liquid level control valve or the like may be provided instead of the flow rate control valve.

1 to 3, a single demethanizer 61 is provided, and all liquid phase components b, d, f, and h are sent to the demethanizer 61 (or the light gas stripper 62 containing NO _x ). Although it is configured to be distilled, a plurality of demethanizer towers may be provided. For example, in the configuration of FIG. 1, another demethanizer tower (pre-demethanizer tower) is provided in the front stage of the demethanizer tower 61, and the liquid phase component b obtained by the first-stage gas-liquid separation tank 31 is first added to this pre-methanizer tower 31. While the gas phase component obtained by distillation in the demethanizer tower is sent to the demethanizer tower 61 and distilled together with the liquid phase components d, f, and h obtained by the other gas-liquid separation tanks 32 to 34. Then, a configuration in which a C2 + fraction is extracted from the bottom of the column and is fed to a subsequent process together with the C2 + fraction obtained by the demethanizer 61 is exemplified. In addition, in the configuration in which the NO _x -containing light gas stripper 62 is provided as shown in FIGS. 2 and 3, a pre-demethanizer tower may be provided in addition to this, and further, the NO _x -containing light gas stripper 62 and the pre-degassing tower may be provided. A methane tower may be provided integrally.

  As described above, various modifications exist in the structure of the cryogenic system around the demethanizer tower in the refining process of the ethylene plant. In any of these modifications, hydrogen, methane, and a carbon number of 2 or more. When separating the raw material containing hydrocarbons in the gas-liquid separation tank, the vapor phase component is cooled by a deep-cooling heat exchanger, and as a refrigerant of the deep-cooling heat exchanger, a hydrogen fraction and a low-pressure methane fraction separated in the latter stage This is the same in that the medium-pressure methane fraction and the high-pressure methane fraction are used.

In any of the above modifications, the present invention may be applied with appropriate modifications depending on the configuration of the cryogenic system, the operating conditions, the type of the light gas containing NO _x , and the like. Basically, if a path for supplying the NO _x -containing light gas to the demethanizer tower is provided, it is possible to prevent NO _x from passing through the gas-liquid separation tank that is in the extremely low temperature range. while suppressing the generation and accumulation of the NO _x gums, it is possible to separate and recover C2 + fraction. When a plurality of demethanizer towers are provided, a route for supplying the NO _x -containing light gas to any of the demethanizer towers may be provided.

  In addition, the deep cooling system to which the present invention can be applied is not limited to the deep cooling system around the demethanizer tower in the purification process of the ethylene purification plant. When the raw material containing hydrogen, methane, and C2 + fraction is separated in the multistage gas-liquid separation tank, the vapor phase component is cooled by the cryogenic heat exchanger, and the hydrogen fraction separated in the latter stage is used as a refrigerant for the cryogenic heat exchanger. Can be used in various chemical plants and other various fields as long as it is configured to use water, low pressure methane fraction, medium pressure methane fraction, and high pressure methane fraction. The present invention can be applied.

Applications of the present invention is not particularly limited, but can be applied to various fields in which it is required to separate the C2 + fractions from the NO _x containing light gases, in particular, by-product in the FCC process of petroleum refining processes It is suitably used when separating useful olefin fractions such as ethylene and propylene from the FCC offgas.

Configuration of a cryogenic system around a demethanizer tower in a purification process of an ethylene plant, provided with a configuration for carrying out a method for separating a C2 + fraction from a light gas containing NO _{x according} to an embodiment related to the present invention FIG. An example of a configuration of a cryogenic system around a demethanizer tower in a purification process of an ethylene plant provided with a configuration for carrying out a method for separating a C2 + fraction from a NO _x -containing light gas according to an embodiment of the present invention FIG. Configuration of a cryogenic system around a demethanizer tower in a purification process of an ethylene plant, provided with a configuration for carrying out a method for separating a C2 + fraction from a light gas containing NO _{x according} to an embodiment related to the present invention FIG.

Explanation of symbols

1 deep cooling system 21～25,92 heat exchanger 31-34 multistage gas-liquid separation tank 41 deep cold heat exchanger 51 the hydrogen-pressure methane separation tank 61 demethanizer 62 NO _x containing light gas stripper (NO _x containing light gas distillation Tower)
71 Reflux tank 81-88, 91 Control valve

Claims (1)

A method for separating a C2 + fraction from methane, a hydrocarbon having 2 or more carbon atoms (hereinafter referred to as “C2 +”), and a gas containing nitrogen oxides (hereinafter referred to as “NO _x- containing light gas”). ,
(A) a gas-liquid separation tank which is supplied with raw materials containing hydrogen, methane and C2 + and separates the raw material into a gas phase component and a liquid phase component;
(B) a hydrogen / low pressure methane separation tank for separating a gas phase component separated by the gas-liquid separation tank into a hydrogen fraction and a methane fraction (hereinafter referred to as “low pressure methane fraction”);
(C) a demethanizer for distilling the liquid phase component separated by the gas-liquid separation tank and separating the liquid phase component as a C2 + fraction;
(D) The top component of the demethanizer tower is cooled, the gas phase component is separated as a methane fraction (hereinafter referred to as “high pressure methane fraction”), and a part of the liquid phase component is separated into a methane fraction ( Hereinafter referred to as “medium pressure methane fraction”), and a reflux tank for refluxing the remainder to the demethanizer tower;
(E) The gas phase component separated by the gas-liquid separation tank is divided into a hydrogen fraction and a low-pressure methane fraction separated by the hydrogen / low-pressure methane separation tank, and a medium-pressure methane fraction separated by the reflux tank. In a cryogenic system equipped with a cryogenic heat exchanger that cools by exchanging heat with a methane fraction and a high-pressure methane fraction,
By supplying the NO _x -containing light gas to the NO _x -containing light gas distillation column and distilling it, separating it into a liquid phase component and a gas phase component, and supplying the obtained gas phase component to the demethanizer tower, NO _x content is characterized by being configured to separate the C2 + fraction lighter gas, NO _x C2 + fraction separation methods from containing light gas.

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