JP3361827B2 - Exhaust gas denitration method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for denitration of exhaust gas, and more particularly to a fluid contacting method containing a gaseous denitration catalyst poisoning component.
The present invention relates to an exhaust gas denitration method suitable for reducing nitrogen compounds in high-temperature exhaust gas from a catalytic cracking furnace . [0002] Nitrogen oxides (hereinafter referred to as NOx) emitted from power plants, sintering furnaces, various chemical factories, automobiles, etc.
Is known as a causative substance of photochemical smog, and its emission regulations have been tightened year by year. In other words, the scope of regulation has been expanded to include those having relatively low NOx emission concentrations or those having small NOx emission concentrations, which have been excluded from the related art. For this reason, the demand for denitration equipment tends to increase in the future, from boilers in industrial plants and oil plants to heating furnaces and cracking furnaces. However, the exhaust gas discharged from these plants contains gaseous denitration catalyst poisoning components (hereinafter simply referred to as catalyst poisoning components), and the denitration catalysts are poisoned and deteriorated. A new problem is occurring. FIG.
FIG. 2 is a diagram showing an apparatus system of a conventional exhaust gas denitration method for decomposing NOx in exhaust gas of a regeneration tower of a petroleum cracking catalyst attached to a fluid catalytic cracking furnace (FCC). This device
An FCC plant 1; a denitration cooler 2 for cooling exhaust gas discharged from the FCC plant 1; a denitration device 4 provided downstream of the denitration cooler 2; It is mainly composed of a cooler 5, a dust collector 6, and a chimney 7 provided in order. Exhaust gas of, for example, 570 ° C. discharged from the FCC plant 1 is supplied to a denitration cooler 2.
At a temperature suitable for the denitration reaction, for example, 370
C., and then flows into the downstream denitration apparatus 4 together with the injected ammonia 13. The exhaust gas that has flowed into the denitration device 4 is subjected to the action of a denitration catalyst in the presence of ammonia, and about 90% of NOx is decomposed and removed. The exhaust gas from which most of the NOx has been removed in this way is supplied to the downstream cooler 5.
After cooling to, for example, 200 ° C., the dust flows into the dust collector 6, where the dust 12 is collected and removed, and then becomes a processing gas and is discharged to the atmosphere via the chimney 7. [0004] However, the above prior art does not take into consideration the prevention of deterioration of the denitration catalyst due to catalyst poisoning components, and the performance of the denitration catalyst is reduced in a short period of time.
There was a problem that it hindered the exhaust gas treatment operation. That is, the exhaust gas discharged from the FCC plant is a gas discharged when regenerating the petroleum cracking catalyst degraded by the catalyst poisoning component contained in the petroleum, and includes the petroleum cracking catalyst worn by the flow. Contains dust and gaseous catalyst poisoning components. The gaseous catalyst poisoning components adhere to the surface of the denitration catalyst and reduce the catalytic activity, which shortens the life of the catalyst, hinders the operation of the denitration equipment, and shortens the frequency of replacement of the catalyst. Disadvantages, such as an increase in As a method for removing such gaseous catalyst poisoning components, for example, it is conceivable to arrange a filter for adsorbing the poisoning components upstream of the denitration apparatus, but the amount of adsorption by the filter is limited. In addition, the time required for replacing the catalyst is not so different from the time required for replacing the denitration catalyst, so that it has not been put to practical use. Under such a background, there is a demand for the development of an exhaust gas denitration method capable of effectively treating even an exhaust gas containing a large amount of poisoning components of the denitration catalyst. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, to minimize catalyst poisoning by gaseous catalyst poisoning components, and to achieve high denitration over a long period of time. It is an object of the present invention to provide a method for denitration of exhaust gas from FCC, which can obtain a high efficiency. [0007] The object of the present invention is to cool exhaust gas introduced into a denitration apparatus to a temperature at which gaseous catalyst poisoning components condense, to adsorb and solidify the catalyst poisoning components in dust,
This can then be achieved by separating it with the dust. That is, the present invention relates to arsenic, selenium or te.
After adding ammonia as a reducing agent to high-temperature exhaust gas from a fluid catalytic cracking furnace containing gaseous catalyst poisoning components consisting of lulu and dust, it is introduced into a denitration catalyst device to remove nitrogen oxides in the exhaust gas. In the exhaust gas denitration method, after the exhaust gas is cooled to a temperature at which the gaseous catalyst poisoning component condenses, dust is removed, mixed with a predetermined amount of the high-temperature exhaust gas, and heated to a temperature suitable for a denitration reaction. It is characterized in that it is introduced together with the ammonia into a denitration catalyst device. By cooling a high-temperature exhaust gas containing a gaseous catalyst poisoning component and dust to a temperature at which the catalyst poisoning component condenses, the gaseous catalyst poisoning component contained in the exhaust gas condenses, It adheres to the accompanying dust and solidifies. Therefore, the catalyst poisoning component can be separated together with dust by removing the dust. The exhaust gas from which the catalyst poisoning components have been separated in this way is lower than the temperature suitable for the denitration reaction, and the required amount of untreated high-temperature exhaust gas is mixed with this to raise the temperature to the optimal denitration temperature. Can be. [0009] The high-temperature exhaust gas discharged from the FCC plant includes arsenic (As), selenium (Se), and tellurium (T).
e) and non-metals such as platinum (Pt), palladium (P
d) and a noble metal such as ruthenium (Rn).
The former inhibits the denitration reaction by adhering to the active site of the denitration catalyst,
The latter reduces the apparent denitration reaction rate by oxidizing the ammonia injected as a reducing agent at the surface of the denitration catalyst. In any case, each of the above-mentioned components is present in a gaseous state in high-temperature exhaust gas, and when passing through the denitration catalyst, it is adsorbed on the catalyst surface to reduce the catalytic activity. The amount of adsorption on the catalyst is related to the vapor pressure of the component gas in the exhaust gas. FIG. 2 shows a vapor pressure curve with respect to the temperature of As and Se having the highest vapor pressure among the catalyst poisoning components contained in the exhaust gas. In the figure, the vapor pressure of As and Se decreases rapidly at a temperature lower than 400 ° C.,
In the vicinity, the vapor pressure is almost zero. From this,
When the temperature of the exhaust gas falls below 300 ° C, gaseous As and S
It can be seen that e hardly exists and all become solid. That is, when the gas is cooled, most of the catalyst poisoning components in the exhaust gas containing dust solidify in a state where they are adsorbed by the accompanying dust, except for a part that solidifies as a single substance. Therefore, the gaseous catalyst poisoning component can be adsorbed and held on the dust by cooling the exhaust gas temperature to, for example, 300 ° C. or less before the denitration apparatus filled with the denitration catalyst. Then, if the dust adsorbing the catalyst poisoning component is separated from the exhaust gas, the catalyst poisoning component can be removed together with the dust, so that the influence of the catalyst poisoning component on the denitration catalyst device can be reduced. . FIG. 3 shows that the temperature of the exhaust gas at the inlet of the denitration apparatus is 370.
The graph shows the relationship between the exhaust gas cooling temperature at a constant temperature of ° C. and the mixing amount of untreated high-temperature exhaust gas mixed with the exhaust gas after dust removal after cooling. When the mixed exhaust gas amount increases, the gaseous catalyst poisoning component also increases, and accordingly, the catalyst poisoning component in the entire exhaust gas introduced into the denitration device also increases. Therefore, it is effective to lower the exhaust gas temperature at the outlet of the cooler to increase the removal rate of gaseous catalyst poisoning components that are separated together with dust. It must be understood that the amount of untreated high-temperature exhaust gas to be introduced must be increased in order to reduce the temperature of the exhaust gas. After all, from the viewpoint of minimizing the amount of catalyst poisoning components in the exhaust gas at the denitration apparatus after mixing the high-temperature exhaust gas, in the present invention, the cooling temperature of the exhaust gas is set to 200 to
Preferably, the temperature is 300 ° C. Next, the present invention will be described in detail with reference to examples. FIG. 1 is an apparatus system diagram of the exhaust gas denitration method of the present invention. In the figure, components denoted by the same reference numerals as those in FIG. 4 have the same functions with the same configuration. This device is shown in FIG.
The difference from the conventional apparatus is that instead of the denitration cooler 2, a denitration cooler 14 capable of cooling high-temperature exhaust gas to 300 ° C. or less, a dust removal device 8 downstream of the denitration cooler 2,
A bypass line 10 for branching exhaust gas at an inlet of the dust collector 8 and bypassing the exhaust gas to a downstream side of the dust remover 8, and a mixer 3 provided at a connection between the bypass line 10 and an outlet of the dust remover 8.
A temperature detector 11 disposed at an outlet of the mixer 3;
The point is that a flow control valve 9 provided in the bypass line 10 for adjusting the opening degree in response to a signal from the temperature detector 11 is provided. In such a configuration, most of the high-temperature exhaust gas containing gaseous catalyst poisoning components, for example, 570 ° C., discharged from the FCC plant 1 is mostly cooled by the cooler 14.
, Where it is cooled to a temperature at which the gaseous catalyst poisoning component condenses, for example, 260 ° C., and the catalyst poisoning component condenses, adsorbs on dust and solidifies. The cooling exhaust gas containing the dust that has been adsorbed and solidified by the catalyst poisoning component flows into the downstream dust removal device 8, where the dust that has adsorbed the catalyst poisoning component is separated. The low-temperature exhaust gas from which the catalyst poisoning components and dust have been removed flows into the gas mixer 3, where the signal from the temperature detector 11 disposed at the outlet of the gas mixer 3 receives a signal to adjust the flow rate. A predetermined amount of untreated hot exhaust gas (5) which is flow-regulated by the valve 9 and flows through the bypass line 10
70 ° C.) and a temperature suitable for denitration operation, for example 3
Adjusted to 70 ° C. The exhaust gas adjusted to the optimal denitration temperature flows into the downstream denitration device 4 and is denitrated in the presence of ammonia. The denitrated exhaust gas is the same as the conventional example,
It is released to the atmosphere via a cooler 5 and a dust collector 6. According to the present embodiment, after the exhaust gas discharged from the FCC plant 1 and containing the gaseous catalyst poisoning component is cooled to a temperature at which the catalyst poisoning component condenses, the dust is removed by the dust removing device. Since the required amount of untreated high-temperature exhaust gas is mixed and adjusted to the optimum temperature for denitration, the catalyst poisoning component is adsorbed on the dust and removed, so that the catalyst poisoning component in the process gas flowing into the denitration device is removed. Can be significantly reduced. Therefore, poisoning of the denitration catalyst by the catalyst poisoning component can be prevented, and stable denitration operation can be performed at an optimum temperature for a long period of time. In this embodiment, the effect of extending the life of the catalyst is calculated as follows, assuming that the deterioration of the denitration catalyst is proportional to the amount of the gaseous catalyst poisoning component in the exhaust gas. That is, since the exhaust gas temperature at the outlet of the denitration cooler 14 is 260 ° C., according to FIG.
%, And the amount of gas to be cooled is 70%. Therefore, the catalyst poisoning components in the exhaust gas, which account for 70% of the whole cooled to 260 ° C. in the cooler 14, flow into the denitration apparatus on the assumption that, for example, 95% thereof has been removed by the dust removal operation after cooling. The amount X of the catalyst poisoning component in the exhaust gas adjusted to the optimal temperature for denitration is as follows: X = 0.7 × (1−0.95) + 0.3 = 0.34 34% of ingredients
It can be seen that it can be reduced to Therefore, the life of the denitration catalyst can be extended about three times by simple calculation. According to the present embodiment, since the concentration of dust in the exhaust gas flowing into the denitration catalyst 4 is reduced together with the above-mentioned catalyst poisoning component, wear of the denitration catalyst is prevented, and the catalyst life can be extended from this point as well. effective. In the present embodiment, for example, a tubular heat exchanger is used as the denitration cooler 14. The tubular heat exchanger recovers the heat of the exhaust gas by passing water through the tube, and the temperature of the exhaust gas at the cooler outlet can be controlled by controlling the flow rate of the water in the tube. As the dust removing device 8, a simple dust removing device such as a cyclone is suitable. Fine dust that cannot be separated by the dust removing device is collected by the downstream dust collector 6 together with the dust in the high-temperature exhaust gas after the denitration process. In this embodiment, if the temperature of the exhaust gas at the denitration device is too low, the activity of the denitration catalyst is reduced. If the temperature is too high, the denitration catalyst is liable to be deteriorated. It is set in the range of 300 to 400 degrees . According to the present invention, even if the exhaust gas contains a gaseous catalyst poisoning component, the influence of the catalyst poisoning component can be reduced as much as possible. Activity can be kept high, and a highly reliable denitration operation can be performed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an apparatus system diagram of an exhaust gas denitration method according to the present invention. FIG. 2 is a diagram illustrating As and Se that are poisoning components of a denitration catalyst.
FIG. 4 is a diagram showing a vapor pressure with respect to a temperature of a sphere. FIG. 3 is a diagram showing the relationship between the temperature of a cooling exhaust gas and the amount of untreated high-temperature exhaust gas mixed with the cooling exhaust gas when the temperature of the exhaust gas at the inlet of the denitration apparatus is kept constant at 370 ° C. FIG. 4 is an explanatory diagram showing a conventional technique. [Description of Signs] 1 ... Fluidized catalytic cracking furnace (FCC) plant, 2 ... Cooler for denitration, 3 ... Mixer, 4 ... Denitration equipment, 5 ... Cooler, 6 ... Dust collector, 7 ... Chimney, 8 ... Dust remover, 9 ... flow control valve, 10
... bypass line, 11 ... temperature detector, 12 ... dust,
13 ... Ammonia, 14 ... Cooler for denitration.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B01D 53/86 F01N 3/08 F23J 15/00

Claims (1)

(57) [Claims 1] Gas consisting of arsenic, selenium or tellurium
In the exhaust gas denitration method, which adds ammonia as a reducing agent to high-temperature exhaust gas from a fluidized catalytic cracking furnace containing a catalyst poisoning component and dust, and then introduces it into a denitration catalyst device to remove nitrogen oxides in the exhaust gas After the exhaust gas is cooled to a temperature at which the gaseous catalyst poisoning component condenses, dust is removed, mixed with a predetermined amount of the high-temperature exhaust gas, heated to a temperature suitable for a denitration reaction, and then denitrated with the ammonia. An exhaust gas denitration method characterized by being introduced into a catalyst device.