JP2010194435A - Method and apparatus for protecting denitration catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent in a simple structure an abnormal temperature rise originated in combustion caused by adsorption of hydrocarbon components to a denitration catalyst. <P>SOLUTION: In a method for protecting a denitration catalyst by preventing the abnormal temperature rise of the nitrification catalyst for reducing nitrogen oxides in an exhaust gas containing the nitrogen oxides into which ammonia or urea is blown as a reduction agent, the amount of hydrocarbon adsorbed to the nitrification catalyst is sought by integrating for a predetermined time a product signal 108 obtained by multiplying the signal 106 of the total flow rate of an exhaust gas by the difference between hydrocarbon concentration signals 100, 102 of an exhaust gas inlet and an exhaust gas outlet of the denitration catalyst, and when the amount of hydrocarbon sought exceeds a predetermined set threshold value 112, the flow rate of the exhaust gas is controlled corresponding to the temperature signal 116 of the nitrification catalyst. Thus, the denitration catalyst is prevented from an abnormal temperature rise by vaporizing or even by burning the hydrocarbon adsorbed to the nitrification catalyst to increase the quantity of heat absorbed by the exhaust gas. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a protection method and a protection device for a denitration catalyst that reduces nitrogen oxides contained in combustion exhaust gas, and in particular, an abnormal temperature due to combustion of hydrocarbons such as fuel oil components in the exhaust gas adsorbed on the denitration catalyst. The present invention relates to a technique for preventing a rise.

  NOx in flue gas discharged from power plants, various factories, automobiles, etc. is a causative substance of photochemical smog and acid rain. As an effective removal method, selective catalytic reduction using ammonia or urea as a reducing agent The flue gas denitration method is widely used around the world, mainly in boiler exhaust gas treatment.

  In addition to the simple structure of the flue gas denitration device, the titanium oxide catalyst (Ti catalyst) containing vanadium V, molybdenum Mo, tungsten W, etc. as the active component has a very long life, so it is an environmental device. However, it is one of the easy maintenance and less trouble.

  However, even in a denitration system, oil mist (or steam) or unburned hydrocarbon gas is adsorbed by the catalyst when the fire is started or the ignition burner is used for a long time. In some cases, the catalyst may be exposed to high temperatures due to oxidation or burning at a time when gas is passed.

  In Patent Document 1, when hydrocarbon gas is detected in combustion exhaust gas, the adsorption and adhesion of hydrocarbon gas to the denitration catalyst can be prevented by controlling the FDF (push-in fan) and performing air purge. Are listed.

JP-A-2-275211

  However, the technique described in Patent Document 1 performs air purge by controlling the FDF (push-in fan) every time hydrocarbon gas is detected in the combustion exhaust gas. Control may be complicated.

  Accordingly, an object of the present invention is to prevent an abnormal temperature rise caused by adsorption and combustion of a hydrocarbon component on a denitration catalyst by simple control.

  The denitration catalyst protection method of the present invention prevents abnormal temperature rise of a denitration catalyst that reduces nitrogen oxides in exhaust gas containing nitrogen oxides in which ammonia or urea is blown as a reducing agent. In order to solve the problem, the amount of hydrocarbon adsorbed on the denitration catalyst is measured, and when the measured hydrocarbon amount exceeds a preset threshold, the flow rate of exhaust gas is controlled according to the temperature of the denitration catalyst. It is said.

  That is, the present invention does not suppress the adsorption of hydrocarbon gas to the denitration catalyst itself, but at the stage where hydrocarbons are adsorbed to some extent by the denitration catalyst, whether the flow rate of exhaust gas is maintained, for example, according to the temperature of the denitration catalyst Or it controls to increase. According to this, the amount of heat taken away by the exhaust gas can be increased even if the hydrocarbon adsorbed on the denitration catalyst is evaporated or burned. As a result, it is possible to easily suppress the denitration catalyst from rising to an abnormal temperature without complicated control.

  More specifically, when the measured hydrocarbon amount exceeds a preset threshold value and the temperature of the denitration catalyst is equal to or higher than the first set temperature or lower than the second set temperature that is lower than the first set temperature, When the flow rate of the exhaust gas is prohibited, the measured hydrocarbon amount exceeds the preset threshold value, and the temperature of the denitration catalyst exceeds the second set temperature and is lower than the first set temperature, the exhaust gas flow rate is reduced. The temperature can be raised to a preset value and the temperature of the denitration catalyst can be made higher than the first set temperature.

  According to this, even if hydrocarbons are adsorbed to some extent on the denitration catalyst, the hydrocarbon adsorbed on the denitration catalyst evaporates or the amount of heat taken up by the exhaust gas increases even if it is burned, thereby preventing an abnormal temperature rise. be able to.

  Also, instead of automatically controlling the flow rate of exhaust gas according to the temperature of the denitration catalyst, an alarm that the denitration catalyst may rise abnormally if the measured hydrocarbon amount exceeds a preset threshold When the temperature of the denitration catalyst is equal to or higher than the first set temperature or equal to or lower than the second set temperature that is lower than the first set temperature, the reduction of the exhaust gas flow rate is prohibited and the temperature of the denitration catalyst is set to the second temperature. When the temperature exceeds the preset temperature and is less than the first preset temperature, the flow rate of the exhaust gas is increased to a preset value, and an alarm is generated that indicates that the temperature of the denitration catalyst should be higher than the first preset temperature. it can.

  According to this, the worker who received the alarm can manually control the flow rate of the exhaust gas in accordance with the content of the alarm, and as a result, even if hydrocarbons are adsorbed to some extent on the denitration catalyst, Even if the adsorbed hydrocarbons evaporate or burn, the amount of heat taken up by the exhaust gas increases, so that it is possible to suppress an abnormal temperature rise.

  Further, the denitration catalyst protection device of the present invention prevents an abnormal temperature rise of the denitration catalyst that reduces nitrogen oxides in exhaust gas containing nitrogen oxides in which ammonia or urea is blown as a reducing agent. In order to solve the problem, a hydrocarbon meter that measures the concentration of hydrocarbons in the exhaust gas at the inlet and the outlet of the denitration catalyst, and a difference meter that calculates the difference in hydrocarbon concentration between the inlet and outlet of the exhaust gas of the denitration catalyst, A multiplier that multiplies the obtained difference by the exhaust gas flow rate obtained by the exhaust gas flow meter, an integrator that integrates the multiplication result obtained by the multiplier for a preset time, and an integrator. A comparator that compares the integration result with a preset threshold value, and controls the exhaust gas flow rate based on the comparison result obtained by the comparator and the temperature of the denitration catalyst obtained by the temperature sensor of the denitration catalyst. Constructed and a that control means.

  According to the present invention, it is possible to prevent an abnormal temperature rise caused by adsorption and combustion of a hydrocarbon component on a denitration catalyst by simple control.

It is a figure which shows the whole structure of the waste gas processing system comprised including a denitration catalyst protection apparatus. It is the figure which plotted the generation | occurrence | production amount of CO and CO2 accompanying combustion at the time of making it heat up, flowing air after making a typical denitration catalyst soak in 0.5 wt% of light oil. It is a figure which shows the content of the control signal of the denitration apparatus of this embodiment.

  Hereinafter, an embodiment of an exhaust gas treatment system including a denitration catalyst protection device to which the present invention is applied will be described. FIG. 1 is a diagram showing an overall configuration of an exhaust gas treatment system including a denitration catalyst protection device.

  As shown in FIG. 1, the exhaust gas treatment system includes a boiler 10 serving as an exhaust gas source, and ammonia (NH 3) or urea after being discharged from the boiler 10 as a reducing agent, and nitrogen oxidation from exhaust gas containing nitrogen oxides. A denitration catalyst reactor 12 having a denitration catalyst for reducing and detoxifying the product, an air preheater 14 for performing heat exchange between the exhaust gas from which nitrogen oxides have been reduced and removed in the denitration catalyst reactor 12, and air, and after the heat exchange The apparatus includes a dust collector 16 that collects particulate matter from exhaust gas, a desulfurization device 18 that removes sulfur oxide from the exhaust gas after dust collection, and a chimney 20 that discharges the desulfurized exhaust gas.

  By the way, in such an exhaust gas treatment system, an unburned fuel component (hydrocarbon) in the exhaust gas due to an accident, an operation error, or a combustion test exceeding the limit at the time of inspection of a boiler or a gas turbine which is an exhaust gas source. May be included as mist or steam. Then, hydrocarbons contained in the exhaust gas are adsorbed and accumulated on the denitration catalyst provided in the denitration catalyst reactor 12, and then suddenly burned, so that the denitration catalyst may increase in abnormal temperature and deteriorate.

  In this regard, the present inventors have found that even if hydrocarbon compounds such as fuel oil components are contained in the exhaust gas, in most cases, the temperature of the denitration catalyst does not rise abnormally and is abnormal only when certain conditions are satisfied. It has been found that the temperature rises and leads to deterioration of the denitration catalyst.

  On the other hand, the cause of the large amount of hydrocarbon compounds contained in the exhaust gas is that the burner misfires in a combustor such as a boiler, the use of an ignition burner with a large amount of unburned fuel for a long time, and the supply of fuel oil to the unignition burner due to malfunction Also, it is difficult to deal with a variety of types, such as tests in the unburned area by trial operation of the combustor.

  In view of such circumstances, in order to prevent abnormal temperature rise caused by adsorption and combustion of hydrocarbon components on the denitration catalyst with simple control, the present inventors have adsorbed hydrocarbon compounds adsorbed on the denitration catalyst. The present inventors have studied the combustion behavior and the process leading to an abnormal temperature rise from an engineering point of view. This phenomenon is listed as follows.

  (1) If the temperature is high and the flow rate of the exhaust gas is large even if the hydrocarbon compound is once adsorbed on the denitration catalyst, the amount of heat that the exhaust gas takes away even if it is evaporated or burned, so that the abnormal temperature rises. Absent. Conversely, if the flow rate is reduced or the gas flow is stopped, the amount of heat lost is reduced, leading to an abnormal temperature rise.

  (2) Even if the catalyst adsorbs hydrocarbons at a low temperature, if the temperature is raised with a sufficient amount of gas passing, the heat of combustion is deprived earlier and the abnormal temperature does not rise. When the temperature is raised under low flow conditions where the amount of heat taken is small, an accelerated temperature rise is caused.

  (3) FIG. 2 is a graph plotting the generation amounts of CO and CO2 accompanying combustion when the temperature is raised while flowing air after impregnating 0.5 wt% of light oil into a general denitration catalyst. As shown in FIG. 3, combustion starts around 300 ° C. and proceeds rapidly from 350 ° C. or higher. Therefore, the hydrocarbon component in the catalyst disappears if the catalyst is kept under the condition of a sufficient gas amount and 350 ° C. or more.

  In the present embodiment, based on these phenomena, the amount of hydrocarbons adsorbed on the denitration catalyst is measured, and when the measured hydrocarbon amount exceeds a preset threshold, the exhaust gas according to the temperature of the denitration catalyst is measured. The flow rate is controlled. Hereinafter, a denitration catalyst protection device and a protection method will be described.

  As shown in FIG. 1, the denitration catalyst protection device includes hydrocarbon meters 26 and 28 that measure the hydrocarbon concentration of exhaust gas led from sampling pipes 22 and 24 from the exhaust gas inlet and outlet of the denitration catalyst reactor 12. The differencer 30 that generates the difference signal 104 (100 signal−102 signal) between the hydrocarbon concentration signals 100 and 102 measured by the hydrocarbon meters 26 and 28, and the exhaust gas flow meter of the difference signal 104 and the denitration device control unit 32. Is provided with a multiplier 34 for generating a product signal 108 with the exhaust gas total flow rate signal 106 sent from.

  In addition, the product signal 108 from the multiplier 34 is integrated for a preset time to obtain the amount of adsorption of hydrocarbons on the catalyst layer, the integration signal 110 and the limit value of the adsorption concentration on the denitration catalyst (alarm). Level) and a preset threshold signal 112, and the comparison signal 114 and a temperature signal 116 sent from the temperature sensor 116 of the denitration catalyst of the denitration device control unit 32, the denitration device And a control signal generator 40 for generating a control signal 118.

  Here, as the hydrocarbon meters 26 and 28, general hydrocarbon meters such as an FID type hydrocarbon meter and an infrared type hydrocarbon meter can be used, but all of the FID type can easily obtain information proportional to the calorific value. Good results are obtained with a hydrocarbon meter.

  The obtained signal is calculated by calculating a hydrocarbon concentration signal 100-hydrocarbon concentration signal 102 by an analog or digital differencer to obtain a difference signal 104, and subsequently a product signal 108 of the exhaust gas total flow signal 106 and the difference signal 104. Is obtained by the multiplier 34. Further, the amount of hydrocarbon adsorbed on the catalyst layer is obtained by integrating the product signal 108 by the integrator 36 for a preset time. The content of the calculation here corresponds to obtaining the total amount of hydrocarbons adsorbed on the denitration catalyst by integrating the amount of adsorption to the denitration catalyst layer per unit time from the concentration change accompanying adsorption and the total exhaust gas flow rate.

  A comparison is made between the integrated signal 110, which is the total amount of hydrocarbons adsorbed on the catalyst layer, and a threshold signal 112, which is a level for warning that the denitration catalyst layer has reached a level causing an abnormal temperature rise phenomenon, and is set in advance. 38, when the integration signal 110 exceeds the threshold signal 112, this is generated as a comparison signal 114.

  Based on the comparison signal 114 and the denitration catalyst layer temperature signal 116 sent from the denitration device control unit 32, a denitration device control signal 118 is generated and sent to the denitration device via the denitration device control unit 32. In other words, when the integral signal 110 exceeds the threshold signal 112, the control signal 118 of the denitration device is generated in accordance with the temperature signal 116 of the denitration catalyst layer. Although the generated control signal 118 differs depending on the control method of the denitration apparatus, it is as shown in FIG. 3 in this embodiment.

  FIG. 3 is a diagram showing the contents of the control signal of the denitration apparatus of the present embodiment. As shown in FIG. 3, when the temperature condition of the denitration catalyst layer is 300 ° C. ± 50 ° C. or more, that is, the first set temperature is 350 ° C. or more or the second set temperature is 250 ° C. or less, It is determined that an exhaust gas flow rate sufficient to prevent an abnormal temperature rise is obtained, and a reduction in the exhaust gas flow rate is prohibited as exhaust gas flow rate control, and a stop of the apparatus is prohibited as a lock signal. In other words, at least the current flow rate of the exhaust gas is maintained.

  On the other hand, when the temperature condition of the denitration catalyst layer is less than 300 ° C. ± 50 ° C., that is, more than 250 ° C. which is the second set temperature and less than 350 ° C. which is the first set temperature, the exhaust gas flow rate is controlled as the exhaust gas flow rate control. The temperature is increased (increased) to a preset value, and the temperature of the denitration catalyst is set to 350 ° C. or higher which is the first set temperature. In other words, control is performed so that hydrocarbons are actively burned and the heat of combustion is lost. However, the temperature of the denitration catalyst is not increased to an abnormal temperature (for example, 650 ° C.). In order to increase the flow rate of the exhaust gas, for example, the rotational speed of the pushing fan (FDF) or the induction fan (IDF) may be increased.

  According to this, whether the flow rate of exhaust gas is maintained, for example, in accordance with the temperature of the denitration catalyst at the stage where hydrocarbons are adsorbed to the denitration catalyst to some extent, rather than suppressing the adsorption of hydrocarbon gas to the denitration catalyst itself. Alternatively, even if hydrocarbons are adsorbed to some extent on the denitration catalyst, the hydrocarbons adsorbed on the denitration catalyst can be easily evaporated without complicated control, or the amount of heat taken away by the exhaust gas can be increased even if burned. It can suppress reaching abnormal temperature rise.

  The denitration catalyst protection device and the denitration catalyst protection method of this embodiment have been described above, but the present invention is not limited to this embodiment. For example, this embodiment shows an embodiment in which the flow rate of exhaust gas is automatically controlled in accordance with a control signal 118 of the denitration apparatus. However, instead of automatically controlling the exhaust gas flow rate or the like, if the integral signal 110 exceeds the threshold signal 112, an alarm is generated that the denitration catalyst may rise abnormally, and depending on the temperature of the denitration catalyst. It is possible to generate an alarm as to how the flow rate of exhaust gas should be controlled.

  Specifically, when the temperature condition of the denitration catalyst layer is 350 ° C. or more which is the first set temperature or 250 ° C. or less which is the second set temperature, the reduction of the exhaust gas flow rate is prohibited as the exhaust gas flow rate control. , An alarm indicating that the stop of the apparatus should be prohibited is generated as a lock signal, and when the temperature condition of the denitration catalyst layer exceeds the second set temperature of 250 degrees and is less than the first set temperature of 350 degrees Celsius, As the exhaust gas flow rate control, the exhaust gas flow rate can be increased (increased) to a preset value, and a warning that the temperature of the denitration catalyst should be set to 350 ° C. or higher, which is the first preset temperature, can be generated.

  According to this, the worker who received the alarm can manually control the flow rate of the exhaust gas in accordance with the content of the alarm, and as a result, even if hydrocarbons are adsorbed to some extent on the denitration catalyst, Even if the adsorbed hydrocarbons evaporate or burn, the amount of heat taken up by the exhaust gas increases, so that it is possible to suppress an abnormal temperature rise.

  In addition, the integrator 36 used in the present embodiment provides a threshold value for the input signal in order to prevent malfunction due to accumulation of a small amount of hydrocarbons contained in normal exhaust gas. It can be integrated. In addition, when the temperature of the denitration catalyst is maintained at 350 ° C or higher for a certain time or longer, the integral value is reset so that sudden generation of hydrocarbons that does not lead to an abnormal temperature rise occurs. Are not accumulated, and the reliability of the alarm can be improved.

DESCRIPTION OF SYMBOLS 10 Boiler 12 Denitration catalyst reactor 26, 28 Hydrocarbon meter 30 Difference unit 32 Denitration device control unit 34 Multiplier 36 Integrator 38 Comparator 40 Control signal generator 100, 102 Hydrocarbon concentration signal 104 Difference signal 106 Exhaust gas total flow signal 108 product signal 110 integral signal 112 threshold signal 114 comparison signal 116 temperature signal 118 control signal

Claims (6)

A denitration catalyst protection method for preventing an abnormal temperature rise of a denitration catalyst for reducing the nitrogen oxide in exhaust gas containing nitrogen oxide blown with ammonia or urea as a reducing agent,
The amount of hydrocarbon adsorbed on the denitration catalyst is measured, and when the measured hydrocarbon amount exceeds a preset threshold, the flow rate of the exhaust gas is controlled according to the temperature of the denitration catalyst. A denitration catalyst protection method. The measured hydrocarbon amount exceeds a preset threshold,
When the temperature of the denitration catalyst is equal to or higher than the first set temperature or equal to or lower than the second set temperature lower than the first set temperature, the reduction of the exhaust gas flow rate is prohibited,
When the temperature of the denitration catalyst exceeds the second set temperature and is less than the first set temperature, the flow rate of the exhaust gas is increased to a preset value and the temperature of the denitration catalyst is set to the first set temperature. The method for protecting a denitration catalyst according to claim 1 as described above. When the measured hydrocarbon amount exceeds a preset threshold, an alarm is generated that the denitration catalyst may increase in abnormal temperature,
When the temperature of the denitration catalyst is equal to or higher than the first set temperature or equal to or lower than the second set temperature lower than the first set temperature, the reduction of the exhaust gas flow rate is prohibited,
When the temperature of the denitration catalyst exceeds the second set temperature and is less than the first set temperature, the flow rate of the exhaust gas is increased to a preset value and the temperature of the denitration catalyst is set to the first set temperature. The method for protecting a denitration catalyst according to claim 1, wherein an alarm having the above contents is generated. A denitration catalyst protection device for preventing an abnormal temperature rise of a denitration catalyst for reducing the nitrogen oxide in exhaust gas containing nitrogen oxide blown with ammonia or urea as a reducing agent,
A hydrocarbon meter that measures the concentration of hydrocarbons in the exhaust gas at the inlet and outlet of the exhaust gas of the denitration catalyst, and a difference meter that calculates a difference in the concentration of hydrocarbons at the exhaust gas inlet and outlet of the denitration catalyst. A multiplier that multiplies the difference by the exhaust gas flow rate obtained by the exhaust gas flow meter, an integrator that integrates a multiplication result obtained by the multiplier for a preset time, and an integral obtained by the integrator A comparator for comparing the result with a preset threshold value, and the flow rate of the exhaust gas is controlled based on the comparison result obtained by the comparator and the temperature of the denitration catalyst obtained by the temperature sensor of the denitration catalyst. A denitration catalyst protection device comprising a control means. The control means, the integration result obtained by the integrator by the comparator exceeds the preset threshold,
When the temperature of the denitration catalyst is equal to or higher than the first set temperature or equal to or lower than the second set temperature lower than the first set temperature, the reduction of the exhaust gas flow rate is prohibited,
When the temperature of the denitration catalyst exceeds the second set temperature and is less than the first set temperature, the flow rate of the exhaust gas is increased to a preset value and the temperature of the denitration catalyst is set to the first set temperature. The denitration catalyst protection device according to claim 4 as described above. The control means generates an alarm that the denitration catalyst may rise abnormally if the integration result obtained by the integrator exceeds the preset threshold value by the comparator,
When the temperature of the denitration catalyst is equal to or higher than the first set temperature or equal to or lower than the second set temperature lower than the first set temperature, the reduction of the exhaust gas flow rate is prohibited,
When the temperature of the denitration catalyst exceeds the second set temperature and is less than the first set temperature, the flow rate of the exhaust gas is increased to a preset value and the temperature of the denitration catalyst is set to the first set temperature. The method for protecting a denitration catalyst according to claim 4, wherein an alarm having the contents to be described above is generated.

Images