JP4613156B2 - Method for removing NOx compounds accumulated in a cryogenic separation facility - Google Patents

Description

  The present invention relates to a method for removing NOx compounds accumulated in a cryogenic separation facility, and more particularly to a method for removing NOx compounds accumulated in a cryogenic separation facility while operating the cryogenic separation facility.

  Generally, petroleum cracking gas and coke oven gas contain a very small amount of NOx. Therefore, in a device that cools raw gas such as petroleum cracking gas and coke oven gas using a cryogenic separation facility and performs a gas-liquid separation operation, a very small amount of NOx present in the raw material gas is cryogenically separated. It is known that it condenses in the heat exchanger (cooler) and piping of the equipment and reacts with coexisting oxygen and hydrocarbons, particularly dienes, to generate explosive NOx compounds (Non-Patent Documents). 1 and 2).

  This explosive NOx compound gradually accumulates in the process flow path of the cryogenic separation facility, and when a considerable amount of NOx compound accumulates, it decomposes by impact such as thermal shock, impact, vibration, etc. It will cause an explosion.

  For this reason, when NOx compounds accumulate in the process flow path of the cryogenic separation facility, the operation of the cryogenic separation facility and further the operation of the entire process including the cryogenic separation facility are temporarily stopped, and an alkaline aqueous solution, methanol, etc. It is necessary to clean the heat exchanger (cooler) and piping of the cryogenic separation facility and remove the NOx compound using the polar solvent.

Haseba Michi, two others, “Danger of Nitric Oxide in Cryogenic Gas Separators”, Safety Engineering, Vol. 8, no. 1, p. 22-29 (1969) W. H. Henstock, "NOx in the Cryogenic Hydrogen Recovery Section of an Olefins Production Unit", Plant / Operations Progress, vol.5, No, 4, p232-237 (1986)

  As described above, when removing NOx compounds accumulated in the process flow path of the cryogenic separation facility, it is necessary to temporarily stop the cryogenic separation facility and the entire apparatus including the cryogenic separation facility. However, there is a problem that, for equipment industries such as petroleum refining and petrochemical, which are normally premised on continuous operation for one year or more, the shutdown of the equipment leads to a large loss. Therefore, regarding the removal of explosive NOx compounds accumulated in the cryogenic separation facility, there is a demand for a method for removing them efficiently without stopping the operation of the apparatus.

  Under such circumstances, an object of the present invention is to solve the above-described problems of the prior art and provide a method for removing NOx compounds accumulated in the cryogenic separation facility while operating the cryogenic separation facility. .

  As a result of intensive studies to achieve the above object, the inventors of the present invention conducted a deep cooling of light offgas (FCC offgas) containing olefins such as ethylene and propylene by-produced from a catalytic cracking apparatus (FCC apparatus). In an apparatus that cools using a separation facility and concentrates olefins, etc., an inlet for polar solvents such as methanol in the upstream and downstream piping of the process flow path of the heat exchanger (cooler) of the cryogenic separation facility In addition, an injection facility comprising a polar solvent storage tank and an injection pump is disposed in the cryogenic separation facility, and the polar solvent is continuously or intermittently controlled while controlling the injection amount using this injection facility. We found that explosive NOx compounds accumulated in the cryogenic separation facility can be removed by injecting and discharging from the discharge port without stopping the system. Was able to complete.

That is, the NOx compound removal method of the present invention includes a heat exchanger, a gas-liquid separation tank, a plurality of flow paths, and a flow path for injecting a polar solvent into at least one of the flow paths. Using a cryogenic separation facility,
The NOx-containing gas is introduced into the heat exchanger of the cryogenic separation facility, cooled, and separated into a gas component and a liquid component in the gas-liquid separation tank, and the cryogenic separation facility is operated. A polar solvent is injected to remove NOx compounds accumulated in the cryogenic separation facility , wherein the polar solvent is methanol having a concentration of 99.5% by mass or more .

In the first preferred embodiment of the NOx compound removal method of the present invention, heat exchange is performed between the heat exchanger, the gas-liquid separation tank, the flow path connecting the heat exchanger and the gas-liquid separation tank, and the NOx-containing gas. Using a cryogenic separation facility comprising a flow path for introducing the gas into the vessel and a flow path for injecting the polar solvent into the flow path for introducing the NOx-containing gas into the heat exchanger,
The NOx-containing gas is introduced into the heat exchanger of the cryogenic separation facility, cooled, and separated into a gas component and a liquid component in the gas-liquid separation tank, and the NOx-containing gas is operated into the heat exchanger while operating the cryogenic separation facility. A polar solvent is injected into the flow path for introduction to remove NOx compounds accumulated in the cryogenic separation facility, and the polar solvent is methanol having a concentration of 99.5% by mass or more .

In the second preferred embodiment of the method for removing NOx compounds of the present invention, a heat exchanger, a first gas-liquid separation tank, a second gas-liquid separation tank, and a NOx-containing gas are introduced into the heat exchanger. A flow path, a flow path for sending the NOx-containing gas cooled in the heat exchanger to the first gas-liquid separation tank, and a gas component separated in the first gas-liquid separation tank for reintroducing the heat exchanger , The flow path for sending the gas component cooled again in the heat exchanger to the second gas-liquid separation tank, and the gas component separated in the first gas-liquid separation tank are reintroduced into the heat exchanger A bypass line for connecting a flow path for use with the flow path for sending the gas component cooled again in the heat exchanger to the second gas-liquid separation tank, and for injecting a polar solvent into at least one of the flow paths Using a cryogenic separation facility with
The NOx-containing gas is introduced into the heat exchanger of the cryogenic separation facility, cooled, separated into gas and liquid in the first gas-liquid separation tank, and gas separated in the first gas-liquid separation tank through the bypass line At least a part of this is sent to the second gas-liquid separation tank without going through the heat exchanger, and the temperature of the heat exchanger is controlled. In operation, a polar solvent is injected into at least one of the flow paths to remove NOx compounds accumulated in the cryogenic separation facility , wherein the polar solvent has a concentration of 99.5% by mass or more. Of methanol .

  In another preferred embodiment of the method for removing NOx compounds of the present invention, the gas containing NOx is petroleum cracked gas or coke oven gas.

In the NOx compound removal method of the present invention, methanol is used as the polar solvent from the viewpoint of ease of handling. The concentration of the methanol is usually in terms of avoiding to solidify in heat exchanger moisture cryogenic separation facility contained in the methanol, 99.5% by mass or more.

  In another preferred embodiment of the method for removing NOx compounds of the present invention, the polar solvent is injected intermittently at intervals of 0.5 to 1 hour. In this case, the NOx compound removal effect can be easily confirmed.

  According to the present invention, it is possible to remove explosive NOx compounds accumulated in the process flow path of the cryogenic separation facility without stopping the operation of the apparatus, so that it is necessary to stop and start the facility. Loss of time, labor, and heat energy can be reduced, and as a result, operating costs can be reduced.

  Further, by providing a polar solvent injection facility in the cryogenic separation facility, the NOx compound can be cleaned and removed in a short time. Therefore, it is possible to take a quick response even in an emergency such as when NOx compounds accumulate in a short time.

  Furthermore, since it is possible to inject the polar solvent in a sealed state without opening the piping or the like, cleaning with the polar solvent can be performed regardless of the weather.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic view of an example of a cryogenic separation facility that can be used for carrying out the NOx compound removal method of the present invention. A cryogenic separation facility 1 shown in FIG. 1 includes a heat exchanger (cooler) 2, a first gas-liquid separation tank 3, and a second gas-liquid separation tank 4. The cryogenic separation facility 1 shown in FIG. 1 has one heat exchanger and two gas-liquid separation tanks, but the heat exchanger of the cryogenic separation facility to which the NOx compound removal method of the present invention is applied. The number of gas-liquid separation tanks is not limited to this.

  Further, the cryogenic separation facility 1 shown in FIG. 1 includes a flow path 5 for introducing the NOx-containing gas into the heat exchanger 2, and the NOx-containing gas cooled by the heat exchanger 2 in the first gas-liquid separation tank 3. The flow path 6 for sending to the heat exchanger, the flow path 7 for sending the liquid component separated in the first gas-liquid separation tank 3 to the heat exchanger 2, and the gas-liquid separation in the first gas-liquid separation tank 3 are performed. A flow channel 8 for reintroducing the gas component into the heat exchanger 2, a flow channel 9 for sending the gas component cooled again by the heat exchanger 2 to the second gas-liquid separation tank 4, and a second gas A flow path 10 for discharging the gas component separated in the liquid separation tank 4 to the outside of the cryogenic separation facility 1 and the liquid component separated in the second gas-liquid separation tank 4 are converted into the heat exchanger 2. And a flow path 12 and 13 for discharging cold gas to the heat exchanger 2 to discharge to the outside of the cryogenic separation facility 1.

  In the cryogenic separation facility 1 shown in FIG. 1, the raw material NOx-containing gas is introduced into the heat exchanger 2 through the flow path 5, and the NOx-containing gas is cooled in the heat exchanger 2. Here, the cooling temperature is appropriately set according to the purpose, and for example, a range of −10 to −65 ° C. is preferable.

In addition, as the raw material NOx-containing gas used in the method of the present invention, petroleum cracked gas and coke oven gas containing NOx are preferable. Examples of petroleum cracking gas include off-gas of FCC equipment, steam reforming method, pyrolysis gas of hydrogen production facility by partial oxidation method, and pyrolysis gas of visbreaking method and coking method. Here, the amount of the NOx-containing gas introduced into the cryogenic separation facility 1 varies depending on the scale of the cryogenic separation facility 1 and is not particularly limited. As an example, the processing capacity is 10,000 Nm ^3. / for about Hr, preferably a range of 5,000Nm ³ / Hr~11,000Nm ³ / Hr.

  The NOx-containing gas cooled by the heat exchanger 2 is sent to the first gas-liquid separation tank 3 through the flow path 6, and is separated into a gas component and a liquid component in the first gas-liquid separation tank 3.

  The liquid component separated in the first gas-liquid separation tank 3 is sent to the heat exchanger 2 through the flow path 7, and is returned to room temperature by supplying cold heat to the raw material NOx-containing gas to become a gas. .

  On the other hand, the gas component separated in the first gas-liquid separation tank 3 is reintroduced into the heat exchanger 2 through the flow path 8 and further cooled in the heat exchanger 2. Here, the cooling temperature is appropriately set according to the purpose, and for example, a range of −65 to −130 ° C. is preferable.

  The gas component cooled again by the heat exchanger 2 is sent to the second gas-liquid separation tank 4 through the flow path 9, and is separated again into the gas component and the liquid component in the second gas-liquid separation tank 4.

  The gas component separated in the second gas-liquid separation tank 4 usually contains methane, nitrogen, hydrogen, etc., and is discharged to the outside of the cryogenic separation facility 1 through the flow path 10.

  On the other hand, the liquid component separated in the second gas-liquid separation tank 4 is depressurized and sent as a refrigerant to the heat exchanger 2 through the flow path 11 and returned to room temperature to become a gas. The gas merges with the gas flowing through the flow path 7, the heat exchanger 2, and the flow path 12, and is discharged to the outside of the cryogenic separation facility 1 through the flow path 13. Here, the gas discharged to the outside of the cryogenic separation facility 1 includes ethylene, propylene, propane, and the like, and is sent to a rectifying apparatus at the subsequent stage via, for example, the tank 14 in FIG. 1 and separated into each component. Is done.

  In the cryogenic separation facility 1 shown in FIG. 1, another flow path 15 for injecting a polar solvent is connected to the flow path 5 for introducing the NOx-containing gas into the heat exchanger 2. Further, another flow path 16 for blowing is connected to the flow path 15, and the injection of the polar solvent can be assisted by blowing.

  Here, the polar solvent stored in the polar solvent storage tank 17 in FIG. 1 is injected into the flow path 5 through the flow path 15 by the injection pump 18, whereby the polar solvent can be added to the NOx-containing gas. The polar solvent storage tank 17 is preferably sealed with nitrogen having a purity of 99.99% by volume or more in order to keep the polar solvent in a dry state.

  In the cryogenic separation facility 1 shown in FIG. 1, NOx-containing gas is introduced into the heat exchanger 2 of the cryogenic separation facility 1 through the flow path 5 and cooled, and separated into gas and liquid in the gas-liquid separation tanks 3 and 4. Then, while operating the cryogenic separation facility 1, the polar solvent is injected through the flow path 15 into the flow path 5 for introducing the NOx-containing gas into the heat exchanger 2, and the mixture of the NOx-containing gas and the polar solvent is obtained. The NOx compounds accumulated in the cryogenic separation facility 1 are removed by flowing through the heat exchanger 2, the gas-liquid separation tank 3 and the flow paths 6, 7, 8, 9, 11, 12, 13 of the cryogenic separation facility 1. To do.

  In the cryogenic separation facility 1 shown in FIG. 1, a flow path 15 for injecting a polar solvent is connected to a flow path 5 for introducing a NOx-containing gas into the heat exchanger 2. The cryogenic separation equipment used in the invention may be connected to a flow path for injecting a polar solvent into at least one of the plurality of flow paths, or may be connected to another flow path. Here, the flow path for injecting the polar solvent is preferably connected to a flow path at which the operating temperature is −50 ° C. or less, in which NOx compounds may accumulate.

In the method of removing the NOx compounds of the present invention, the polar solvent used to wash removing NOx compounds, from the viewpoint of easy handling, it is methanol.

The concentration of methanol to be used is at least 99.5 wt%. If the concentration of methanol used is less than 99.5% by mass, the water normally contained in methanol solidifies in the heat exchanger 2 of the cryogenic separation facility 1 and causes trouble.

The injection rate of the polar solvent varies depending on the scale of the cryogenic separation facility 1 and is not particularly limited. As an example, when the processing capacity is 10,000 Nm ³ / Hr, 50 to 600 L / Hr It is preferable to inject the polar solvent at a rate of When the amount of the polar solvent injected is large, the concentration of the NOx compound contained in the cleaned polar solvent is lowered, and it is difficult to determine the end of the cleaning with the polar solvent. Moreover, when the injection amount of the polar solvent is extremely large, the heat balance of the heat exchanger 2 of the cryogenic separation facility 1 is affected, and the operation of the cryogenic separation facility 1 becomes difficult.

  In the NOx compound removal method of the present invention, the polar solvent may be injected intermittently or continuously, but in order to confirm the NOx compound removal effect, an interval of 0.5 to 1 hour is used. It is preferable to inject the polar solvent intermittently.

  Since the NOx compound removal method of the present invention performs cleaning with a polar solvent during operation of the apparatus, in the cryogenic separation facility 1 shown in FIG. 1, a heat exchanger that connects the flow path 8 and the flow path 9 Two bypass lines 19 are preferably provided. Then, at least a part of the gas separated in the first gas-liquid separation tank 3 through the flow path 8 and the bypass line 19 is introduced into the flow path 9 without passing through the heat exchanger 2, and the flow rate is controlled by a control valve or the like. It is preferable to adjust the operating conditions by controlling at -20, and to control the operating temperature of the heat exchanger 2 and the flow path to -20 to -80 ° C. In this case, it is possible to prevent the polar solvent injected in the second gas-liquid separation tank 4 and the flow paths 9 and 11 from solidifying.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

Example 1
H containing light offgas (FCC offgas, 10,000 Nm ³ / Hr) containing olefins such as ethylene and propylene by-produced from the FCC apparatus having the composition shown in Table 1 in an amine cleaning apparatus and a soda cleaning apparatus After removing ₂ S, CO _{2 and the} like, it was introduced into a cryogenic separation facility 1 equipped with an injection facility comprising a methanol storage tank 17 and an injection pump 18 as shown in FIG.

While operating the cryogenic separation facility 1, methanol was continuously injected through the flow path 15 at a rate of 500 L / Hr using a methanol injection pump 18. Methanol after washing the process flow path of the cryogenic separation facility 1 was recovered in the tank 14 in FIG. The recovered washing methanol was filtered to remove solids, and then the amount of NO ₂ in methanol was calculated according to the analysis method specified in JIS B 7953.

Further, the above methanol injection and washing were repeated twice (total 0.5 Hr injection x 3 times). It shows the NO ₂ amount of washing in methanol in Table 2. From the results in Table 2, it can be seen that NOx compounds accumulated in the cryogenic separation facility 1 can be removed by washing with methanol.

  Further, after the process gas in the tank 14 of FIG. 1 was passed through the absorption liquid, it was analyzed by GC-FID, and it was confirmed that methanol was not detected 80 minutes after the methanol injection was stopped (1 ppmw or less). . After the start of methanol injection, the time during which methanol was no longer detected in the process gas in the tank 14 was taken as a series of working hours for methanol cleaning. Table 2 shows the working time.

(Comparative Example 1)
H containing light offgas (FCC offgas, 10,000 Nm ³ / Hr) containing olefins such as ethylene and propylene by-produced from the FCC apparatus having the composition shown in Table 1 in an amine cleaning apparatus and a soda cleaning apparatus After removing ₂ S, CO _{2 and the} like, it was introduced into the cryogenic separation facility shown in FIG.

After stopping the cryogenic separation facility 1, methanol through flow path 16 for blowing in Figure 1 after 250L injected, the purity of 99.99% by volume or more nitrogen, through the channel 16 at a flow rate of 200 Nm ³ / Hr The methanol was poured into the tank 14 in FIG. Further, methanol after washing the process flow path of the cryogenic separation facility 1 was recovered in the tank 14 of FIG. 1 and the amount of NO ₂ contained was measured in the same manner as in Example 1.

Furthermore, the above methanol injection and washing were repeated twice (total 250 L injection × 3 times, and the total injection amount was the same as in Example 1). Table 2 shows the amount of NO ₂ in the recovered methanol. From the results in Table 2, it can be seen that NOx compounds accumulated in the cryogenic separation facility 1 can be removed by washing with methanol.

After NO ₂ was no longer detected in the recovered methanol, the cryogenic separation facility 1 was restarted.

  The process gas in the tank 14 of FIG. 1 was passed through the absorption liquid and analyzed by GC-FID, and it was confirmed that methanol was not detected after 80 minutes (1 ppmw or less). After the start of methanol injection, the time during which methanol was no longer detected in the process gas in the tank 14 was taken as a series of working hours for methanol cleaning. Table 2 shows the working time.

  From Table 2, using methanol injection equipment as in Example 1 and performing methanol cleaning without shutting down the apparatus, the apparatus is shut down and performing methanol cleaning (Comparative Example 1). It was found that the time required for methanol washing can be shortened by 26 hours.

It is the schematic of an example of the cryogenic separation equipment which can be utilized for implementation of the removal method of the NOx compound of this invention.

Explanation of symbols

1 Cryogenic separation equipment 2 Heat exchanger (cooler)
3 First Gas-Liquid Separation Tank 4 Second Gas-Liquid Separation Tank 5, 6, 7, 8, 9, 10, 11, 12, 13, 15, 16 Channel 14 Tank 17 Polar Solvent Tank 18 Injection Pump 19 Bypass Line

Claims (5)

Using a cryogenic separation facility comprising a heat exchanger, a gas-liquid separation tank, a plurality of flow paths, and a flow path for injecting a polar solvent into at least one of the flow paths,
The NOx-containing gas is introduced into the heat exchanger of the cryogenic separation facility, cooled, and separated into a gas component and a liquid component in the gas-liquid separation tank, and the cryogenic separation facility is operated. Injecting a polar solvent to remove NOx compounds accumulated in the cryogenic separation facility ,
The method for removing a NOx compound , wherein the polar solvent is methanol having a concentration of 99.5% by mass or more . A heat exchanger, a gas-liquid separation tank, a flow path connecting the heat exchanger and the gas-liquid separation tank, a flow path for introducing NOx-containing gas into the heat exchanger, and a NOx-containing gas heat exchanger Using a cryogenic separation facility comprising a flow path for injecting a polar solvent into a flow path for introduction into
The NOx-containing gas is introduced into the heat exchanger of the cryogenic separation facility, cooled, and separated into a gas component and a liquid component in the gas-liquid separation tank, and the NOx-containing gas is operated into the heat exchanger while operating the cryogenic separation facility. It is characterized by injecting a polar solvent into the flow path for introduction and removing NOx compounds accumulated in the cryogenic separation facility ,
The method for removing a NOx compound according to claim 1, wherein the polar solvent is methanol having a concentration of 99.5% by mass or more . The heat exchanger, the first gas-liquid separation tank, the second gas-liquid separation tank, the flow path for introducing the NOx-containing gas into the heat exchanger, and the NOx-containing gas cooled by the heat exchanger are the first A flow path for sending to the gas-liquid separation tank, a flow path for reintroducing the gas component separated in the first gas-liquid separation tank, and the gas content re-cooled in the heat exchanger The flow path for sending to the second gas-liquid separation tank, the flow path for re-introducing the gas component separated in the first gas-liquid separation tank and the gas component cooled again by the heat exchanger into the first Using a cryogenic separation facility comprising a bypass line connecting a flow path for sending to a two-gas liquid separation tank and a flow path for injecting a polar solvent into at least one of the flow paths,
The NOx-containing gas is introduced into the heat exchanger of the cryogenic separation facility, cooled, separated into gas and liquid in the first gas-liquid separation tank, and gas separated in the first gas-liquid separation tank through the bypass line At least a part of this is sent to the second gas-liquid separation tank without going through the heat exchanger, and the temperature of the heat exchanger is controlled. In operation, the polar solvent is injected into at least one of the flow paths to remove NOx compounds accumulated in the cryogenic separation facility ,
The method for removing a NOx compound according to claim 1, wherein the polar solvent is methanol having a concentration of 99.5% by mass or more .   The method for removing a NOx compound according to claim 1, wherein the gas containing NOx is petroleum cracked gas or coke oven gas.   The method for removing a NOx compound according to claim 1, wherein the polar solvent is injected intermittently at intervals of 0.5 to 1 hour.

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