JP2008128542A - METHOD OF DETECTING NOx COMPOUND ACCUMULATED IN CRYOGENIC SEPARATION FACILITY - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of detecting a NOx compound accumulated in cryogenic separation facilities with high accuracy. <P>SOLUTION: In the cryogenic separation facilities 1 comprising a heat exchanger 2 with which one or more pairs of introduction flow channels 5, 7, 8, 11 and discharge flow channels 6, 9, 12, 13 are connected, and gas-liquid separation tanks 4, 5, pressures in one or more pairs of introduction flow channels 5, 7, 8, 11 and discharge flow channels 6, 9, 12, 13 of the heat exchanger 2 are respectively measured, and pressure loss between the introduction flow channels 5, 7, 8, 11 and the discharge flow channels 6, 9, 12, 13 is calculated to detect the NOx compound accumulated in the cryogenic separation facilities 1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for detecting NOx compounds accumulated in a cryogenic separation facility, in particular, a method for accurately determining the presence or absence of accumulation of NOx compounds in the cryogenic separation facility, and further a NOx compound in the cryogenic separation facility. The present invention relates to a method for accurately measuring the amount of accumulation.

  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, in order to operate the cryogenic separation facility safely, the amount of NOx compound accumulated in the cryogenic separation facility is measured, and when a certain amount or more of NOx compound accumulates, the polarity of alkaline aqueous solution, methanol, etc. It is necessary to wash the heat exchanger (cooler) and piping of the cryogenic separation facility with a solvent to remove NOx compounds.

  On the other hand, as a means for measuring the amount of NOx compound accumulated in the cryogenic separation facility, conventionally, the NOx accumulated in the cryogenic separation facility is obtained by taking the material balance of IN / OUT of the cryogenic separation facility for NOx. A method for estimating the amount of a compound and a method for measuring pressure loss for a device of a cryogenic separation facility have been adopted (Non-patent Document 3).

Haseba, 2 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) W. H. Isalski and B. Pacalowska, "A novel process recovers olefins from cracker offgas", Chemical engineering, vol.103, p133-136 (1996)

  However, for the method of estimating the amount of accumulated NOx compounds by taking the IN / OUT mass balance of the cryogenic separation facility, the IN / OUT of the cryogenic separation facility is analyzed frequently (at least once / day). It is necessary and the load of analysis is large. In addition, this method has a problem that the analysis error is large and the analysis cannot be performed online, so that the accuracy of the estimation result of the NOx compound accumulation amount is low.

  On the other hand, regarding the method of measuring the pressure loss for the equipment of the cryogenic separation facility, a valve for controlling the normal pressure and / or the liquid level is installed in the process flow path of the cryogenic separation facility, and a considerable amount of NOx compound is present. Until accumulation, it was difficult to detect as an increase in pressure loss.

  Accordingly, an object of the present invention is to solve the above-described problems of the prior art and provide a method for accurately detecting NOx compounds accumulated in a 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., there is a possibility of accumulation of NOx compounds. A plurality of nozzles are installed in the flow path (IN / OUT process flow path), and the same pressure gauge is connected to this nozzle to measure the pressure loss between the introduction flow path and the discharge flow path. The present inventors have found that NOx compounds accumulated in the process flow path of the cold separation facility can be detected with high accuracy, and have completed the present invention based on this knowledge.

That is, the NOx compound detection method of the present invention is a method of detecting NOx compounds accumulated in a cryogenic separation facility comprising a heat exchanger in which a pair of introduction flow paths and discharge flow paths are connected, and a gas-liquid separation tank. A detection method,
Measure the pressures of one or more inlet and outlet channels of the heat exchanger, calculate the pressure loss between the inlet and outlet channels, and store the NOx compounds accumulated in the cryogenic separation facility. It is characterized by detecting.

  In the NOx compound detection method of the present invention, it is preferable that at least one of the introduction flow path and the discharge flow path is −50 ° C. or lower in the pair of the introduction flow path and the discharge flow path for calculating the pressure loss.

  In another preferred embodiment of the method for detecting a NOx compound of the present invention, a pressure gauge used for measuring the pressure of the introduction flow path in the pair of the introduction flow path and the discharge flow path for calculating the pressure loss is provided in the discharge flow path. It is the same as the pressure gauge used to measure pressure.

  According to the present invention, by measuring the pressure loss between the introduction flow path and the discharge flow path of the heat exchanger of the cryogenic separation facility, the presence or absence of NOx compound accumulation, and further the accumulation location of NOx compound can be immediately determined. Can be identified. Further, the accumulated amount of NOx compound can be obtained from the pressure loss value.

  In addition, by using the same pressure gauge, the reliability of the pressure loss value is improved, and the accumulated NOx compounds can be detected accurately from the increase in the pressure loss value, and the cryogenic separation equipment can be safely operated. It becomes possible to drive.

  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 to which the NOx compound detection method of the present invention can be applied. 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. The heat exchanger of the cryogenic separation facility to which the NOx compound detection 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 discharges the NOx-containing gas cooled by the heat exchanger 2 from the introduction channel 5 for introducing the NOx-containing gas into the heat exchanger 2 and the heat exchanger 2. A discharge passage 6 for introducing the liquid, and an introduction passage 7 for introducing the liquid component separated in the first gas-liquid separation tank 3 into the heat exchanger 2, and a gas-liquid in the first gas-liquid separation tank 3. An introduction flow path 8 for reintroducing the separated gas component into the heat exchanger 2, a discharge flow channel 9 for discharging the gas component cooled again by the heat exchanger 2 from the heat exchanger 2, and Heat exchange is performed between the liquid component separated in the second gas-liquid separation tank 4 and the flow path 10 for discharging the gas component separated in the second gas-liquid separation tank 4 to the outside of the cryogenic separation facility 1. In order to form a pair with the introduction flow path 11 and the introduction flow path 7 for introduction into the heat exchanger 2, to supply cold heat to the heat exchanger 2, and to discharge the gas at normal temperature from the heat exchanger 2. And the discharge passage 12, without the introduction passage 11 a pair, the gas became fed normal temperature cold heat to the heat exchanger 2 comprises a discharge channel 13 for discharging from the heat exchanger 2. Note that the discharge flow path 12 and the discharge flow path 13 are combined and connected to the flow path 14.

  Further, in the cryogenic separation facility 1 shown in FIG. 1, a liquid level gauge 3A is installed in the first gas-liquid separation tank 3, and the valve 7A disposed in the introduction flow path 7 is controlled to control the first gas. The liquid level of the liquid separation tank 3 can be controlled. Further, a liquid level gauge 4A is installed in the second gas-liquid separation tank 4, and the liquid level of the second gas-liquid separation tank 4 is controlled by controlling the valve 11A disposed in the introduction flow path 11. be able to.

  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 introduction 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 is in the range of −10 to −65 ° C., for example.

As the raw material NOx-containing gas, petroleum cracking 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. Further, the amount of 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 discharged from the discharge flow path 6 to the outside of the heat exchanger 2 and sent to the first gas-liquid separation tank 3 through the discharge flow path 6. In the separation tank 3, it is separated into a gas component and a liquid component.

  The liquid component separated in the first gas-liquid separation tank 3 is introduced into the heat exchanger 2 through the introduction flow path 7, and is returned to room temperature by supplying cold heat to the raw material NOx-containing gas to become a gas. Then, the heat is discharged from the discharge channel 12 to the outside of the heat exchanger 2.

  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 introduction flow path 8 and further cooled in the heat exchanger 2. Here, the cooling temperature is appropriately set according to the purpose, and is, for example, in the range of −65 to −130 ° C.

  The gas component cooled again by the heat exchanger 2 is discharged from the discharge channel 9 to the outside of the heat exchanger 2 and is sent to the second gas-liquid separation tank 4 through the discharge channel 9, so that the second gas-liquid is discharged. In the separation tank 4, the gas and liquid are separated again.

  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 decompressed and introduced as a refrigerant into the heat exchanger 2 through the introduction channel 11, is returned to room temperature, becomes a gas, and is heated from the discharge channel 13. It is discharged outside the exchanger 2. The gas discharged from the discharge flow path 13 merges with the gas discharged from the discharge flow path 12, and is discharged to the outside of the cryogenic separation facility 1 through the flow path 14. 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 15 in FIG. 1 and separated into each component. Is done.

  In the cryogenic separation facility 1 shown in FIG. 1, a nozzle 5B for connecting a pressure gauge is installed in the introduction flow path 5, and the pressure in the introduction flow path 5 is obtained by connecting the pressure gauge to the nozzle 5B. Can be measured. The discharge channel 6 is provided with a nozzle 6B for connecting a pressure gauge. The introduction channel 7 is provided with a nozzle 7B for connecting a pressure gauge. The nozzle 8B for connecting the pressure gauge is installed, the nozzle 9B for connecting the pressure gauge is installed in the discharge channel 9, and the pressure gauge is installed in the introduction channel 11. A nozzle 11B for connection is installed, a nozzle 12B for connecting a pressure gauge is installed in the discharge flow path 12, and a nozzle 13B for connecting a pressure gauge is connected to the discharge flow path 13. In the flow path 14, a nozzle 14B for connecting a pressure gauge is installed, and a pressure gauge is connected to each nozzle 6B, 7B, 8B, 9B, 11B, 12B, 13B, 14B. Thus, each flow path 6, 7, 8, 9, 11, 12 Pressure 13, 14 can be measured. In FIG. 1, it is assumed that the tips of the nozzles 6B, 7B, 8B, 9B, 11B, 12B, and 13B are located outside the cryogenic separation facility 1.

  In the cryogenic separation facility 1 shown in FIG. 1, the introduction flow path 5 and the discharge flow path 6 are paired with the heat exchanger 2 interposed therebetween, and the pressures of the introduction flow path 5 and the discharge flow path 6 are measured. Thereby, the pressure loss between the introduction flow path 5 and the discharge flow path 6 can be measured. In addition, the introduction flow path 7 and the discharge flow path 12 are paired, and the pressure loss between the introduction flow path 7 and the discharge flow path 12 is reduced by measuring the pressure of the introduction flow path 7 and the discharge flow path 12 respectively. Can be measured. Furthermore, the introduction flow path 8 and the discharge flow path 9 also form a pair, and the pressure loss between the introduction flow path 8 and the discharge flow path 9 is measured by measuring the pressures of the introduction flow path 8 and the discharge flow path 9 respectively. Can be measured. Furthermore, the inlet channel 11 and the outlet channel 13 are also paired, and the pressure loss between the inlet channel 11 and the outlet channel 13 is reduced by measuring the pressure of the inlet channel 11 and the outlet channel 13 respectively. Can be measured.

  In the cryogenic separation facility 1 shown in FIG. 1, according to the present invention, the pressures of the introduction channel 5 and the discharge channel 6, the pressures of the introduction channel 7 and the discharge channel 12, the introduction channel 8 and the discharge, respectively. By measuring the respective pressures in the flow channel 9 and the respective pressures in the introduction flow channel 11 and the discharge flow channel 13, the introduction flow channels 5, 7, 8, 11 and the discharge flow channels 6, 12, 9, 13 are It is possible to determine the presence or absence and accumulation location of NOx compounds by respectively calculating the pressure loss between them. Further, the accumulated amount of NOx compound can also be determined from the magnitude of pressure loss.

  In the present invention, the pressure of the pair of the introduction flow path and the discharge flow path at which at least one of the introduction flow path and the discharge flow path of the heat exchanger 2 is −50 ° C. or less is measured, respectively. It is preferable to determine the presence or absence of NOx compound accumulation and the amount of NOx compound accumulation by monitoring the pressure loss during the period. For example, in FIG. 1, since the temperature of the introduction flow path 11 is particularly low, it is preferable to measure the pressure of the pair of the introduction flow path 11 and the discharge flow path 13. Since there is a high possibility that NOx compounds will accumulate in channels that are below -50 ° C, the presence or absence of NOx compounds and the amount of NOx compounds accumulated can be monitored by monitoring the pressure loss in channels that are below -50 ° C. Can be determined early. Further, the cryogenic separation facility 1 can be safely operated by appropriately removing the accumulated NOx compound.

  In the present invention, the pressure gauge used for measuring the pressure of the introduction flow path in the pair of the introduction flow path and the discharge flow path for calculating the pressure loss is the same as the pressure gauge used for measuring the pressure of the discharge flow path. Preferably there is. In this case, an error due to the pressure gauge can be eliminated, and the pressure loss between the paired introduction flow path and discharge flow path can be obtained with high accuracy. Moreover, it is necessary to use the pressure gauge to check the accuracy of the indicated value.

  In the present invention, the number of nozzles for connecting the pressure gauges is preferably large. However, if the number of nozzles is large, the chance of losing the cold heat of the heat exchanger 2 increases. It is preferable to install only portions where pressures of 7, 8, 11 and the discharge channels 6, 12, 9, 13 can be measured.

  Moreover, since the nozzle which attaches a pressure gauge contacts external air, it is also a part which loses the cold heat of the heat exchanger 2. FIG. For this reason, it is preferable to minimize the length of the nozzle. Furthermore, it is preferable that the nozzle to which the pressure gauge is attached collects the installation place by devising the layout in order to make the pressure loss measurement short.

  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, the pressure measuring nozzles 5B of the introduction flow paths 5, 7, 8, 11 and the discharge flow paths 6, 9, 12, 13 of the heat exchanger 2 as shown in FIG. It introduced into the cryogenic separation equipment 1 provided with 6B, 7B, 8B, 9B, 11B, 12B, 13B.

  The cryogenic separation facility was continuously operated under process conditions, the pressures of the introduction flow paths 5, 7, 8, 11 and the discharge flow paths 6, 9, 12, 13 of the heat exchanger 2 were measured, and the pressure loss was calculated. The results are shown in Tables 2 and 3.

From the results in Table 3, an increase in the differential pressure between the introduction flow path 11 (measured at the nozzle 11B) and the discharge flow path 13 (measured at the nozzle 13B) in FIG. 1 was observed after operating for 3 months. Then, the introduction flow path 11 and the discharge flow path 13 and the space between them were washed with methanol, and the washing liquid was collected in the tank 15 of 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. As a result, it was confirmed that NO ₂ was dissolved at a concentration of 160 ppmw in 50 L of washing methanol, and NOx compounds were accumulated in the introduction flow path 11 and the discharge flow path 13 and any of them.

(Comparative Example 1)
As a comparative example, Table 4 shows changes over time in the differential pressure (the difference in pressure measured by the nozzle 5B and the nozzle 14B in FIG. 1) in the entire cryogenic separation facility 1.

  Since the change in the differential pressure in the entire cryogenic separation facility 1 is smaller than the differential pressure between the introduction flow path 11 and the discharge flow path 13 of the heat exchanger 2, From the measurement, it can be seen that it is difficult to determine whether or not NOx compounds are accumulated. In addition, as a matter of course, from the measurement of the differential pressure in the entire cryogenic separation facility 1, when there are a plurality of flow paths in the heat exchanger 2, it is determined which of the flow paths contains NOx compounds. I can't judge.

It is the schematic of an example of the cryogenic separation equipment which can apply the detection 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, 7, 8, 11 Introduction flow path 6, 9, 12, 13 Discharge flow path 10, 14 flow path 3A, 4A Level gauge 7A, 11A Valve 5B , 6B, 7B, 8B, 9B, 11B, 12B, 13B, 14B Nozzle 15 tank

Claims (3)

A method for detecting NOx compounds accumulated in a cryogenic separation facility comprising a heat exchanger in which a pair of introduction flow paths and discharge flow paths are connected, and a gas-liquid separation tank,
Measure the pressures of one or more inlet and outlet channels of the heat exchanger, calculate the pressure loss between the inlet and outlet channels, and store the NOx compounds accumulated in the cryogenic separation facility. A method for detecting a NOx compound, comprising detecting the NOx compound.   2. The method for detecting a NOx compound according to claim 1, wherein the pair of the introduction flow path and the discharge flow path for calculating the pressure loss is such that at least one of the introduction flow path and the discharge flow path is −50 ° C. or lower. .   The pressure gauge used for measuring the pressure of the introduction flow path in the pair of the introduction flow path and the discharge flow path for calculating the pressure loss is the same as the pressure gauge used for measuring the pressure of the discharge flow path. The method for detecting a NOx compound according to claim 1.

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