JP2012132622A - Method for diagnosis of furnace air preheater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diagnosis method capable of finding the occurrence of damage of an air preheater irrespective of whether a damaged portion is on an exhaust gas inlet side or an exhaust gas outlet side, and capable of estimating the position of the damaged portion.SOLUTION: In the method for diagnosis of a furnace air preheater, when diagnosing damage of the air preheater arranged in an exhaust passage of the furnace, respective exhaust gas temperatures of the exhaust gas inlet side and the exhaust gas outlet side with respect to the air preheater in the exhaust passage are measured under a condition of an operation temperature and an operation load of predetermined values or more; the measured exhaust gas temperatures are compared with a pre-measured exhaust gas temperature when the air preheater is not damaged; and if the measured exhaust gas temperature is lower a predetermined temperature or more from the exhaust gas temperature when the air preheater is not damaged, it is determined that there is an air leak from the air preheater due to damage of the air preheater.

Description

  The present invention relates to a diagnostic method for early detection of damage to an air preheater (recuperator) of a furnace such as a heating furnace or a heat treatment furnace.

  A furnace such as a heating furnace or a heat treatment furnace usually exchanges heat between high-temperature exhaust gas discharged from the furnace through an exhaust passage such as a flue or an exhaust duct and combustion air supplied into the furnace. In order to save energy by preheating combustion air, it is equipped with an air preheater placed in the exhaust passage such as the flue or exhaust duct, and such an air preheater is generally damaged by deterioration. Since the preheating temperature of the combustion air decreases, conventionally, the air preheater is routinely managed using the temperature of the preheated combustion air as a management index.

  In addition, as a conventional technique for determining the repair time of the air preheater for the heating furnace, for example, the increase in the pressure loss of the flue due to the leaked air from the air preheater arranged in the flue is calculated from the survey results, A method for preventing the operation limit of the furnace equipment from being reached is also known (see Patent Document 1).

Japanese Patent Application Laid-Open No. 08-338697

  However, with regard to the former method of monitoring preheated combustion air, damage to the air preheater does not necessarily occur on the exhaust gas inlet side (high temperature side), but may occur on the exhaust gas outlet side (low temperature side). is there. In this case, since the exhaust gas temperature is lowered after the air preheater by the air flowing into the exhaust passage from the air preheater, there is almost no temperature change of the preheated combustion air. For this reason, it is difficult to find damage on the exhaust gas outlet side (low temperature side) with this method of monitoring the preheated combustion air.

  On the other hand, with respect to the latter method using pressure loss as a criterion, this method is not a technique for evaluating changes in the performance of the air preheater from the viewpoint of energy saving, and this method also does not allow rough estimation of the damaged site. Further, when there is a margin in the exhaust capacity of the chimney or the exhaust fan, it is determined that the replacement is not required even if the air preheater is damaged and the pressure loss of the flue increases. Furthermore, even in the case of a furnace that has been modified by introducing a regenerative burner or the like, the initial chimney will have an excessive exhaust capacity in the subsequent flue displacement. For this reason, the method using this pressure loss as a criterion is also inappropriate for diagnosing damage to the air preheater.

  In order to solve the above-described problems, the present invention has an object to provide a diagnostic method that can detect the occurrence of damage to the air preheater regardless of whether the damaged portion is on the exhaust gas inlet side or the exhaust gas outlet side. . Furthermore, an object of the present invention is to provide a diagnostic method capable of estimating a damaged site.

  The method for diagnosing an air preheater of a furnace according to the present invention that achieves the above-described object is as follows.When diagnosing damage to the air preheater disposed in the exhaust passage of the furnace, Measure the exhaust gas temperature on the exhaust gas inlet side and the exhaust gas outlet side of the air preheater in the exhaust passage, and measure the measured exhaust gas temperature with the pre-measured exhaust gas temperature of the air preheater when it is healthy. In comparison, if the measured exhaust gas temperature falls below a predetermined temperature from the exhaust gas temperature when the air preheater is healthy, it is judged that air leakage from the air preheater has occurred due to damage to the air preheater. It is characterized by doing.

  Further, another method for diagnosing a furnace air preheater according to the present invention that achieves the above object includes an air preheater together with the exhaust gas temperatures on the exhaust gas inlet side and the exhaust gas outlet side of the air preheater in the exhaust passage. Measure the temperature of the preheated air coming out from the air periodically, and if it is determined that the air preheater is leaking due to the damage of the air preheater due to the exhaust gas temperature drop as described above When the preheated air temperature measured is compared with the preheated air temperature when the air preheater is healthy, and the measured preheated air temperature is not lower than the predetermined temperature from the preheated air temperature when the air preheater is healthy Is characterized in that it is determined that the air preheater is damaged on the exhaust gas outlet side.

  According to the former diagnosis method of the present invention, the temperature of the exhaust gas in the exhaust passage is used instead of the temperature of the preheated combustion air as a criterion for the presence or absence of air leakage. And the exhaust gas temperature at the exhaust gas outlet side is measured, and the measured exhaust gas temperature is compared with the pre-measured exhaust gas temperature when the air preheater is healthy. When the exhaust gas temperature drops below a certain level from the normal exhaust gas temperature, it is determined that air leakage from the air preheater has occurred due to damage to the air preheater. The occurrence of air leakage due to the damage can be surely diagnosed regardless of the exhaust side or the exhaust gas outlet side.

  According to the latter diagnostic method of the present invention, when it is determined that air leakage from the air preheater has occurred due to damage to the air preheater due to a decrease in exhaust gas temperature, the measured preheated air temperature is Compared with the measured preheated air temperature of the air preheater, if the measured preheated air temperature has not decreased by more than the specified temperature from the preheated air temperature of the air preheater when Since it is determined that the air preheater is damaged, the damaged portion can be estimated when the damaged portion of the air preheater is on the exhaust gas outlet side.

  If the measured preheated air temperature is lower than the preheated air temperature when the air preheater is healthy by a predetermined temperature or more, the heat exchange efficiency may be lower than when the air preheater is healthy, Because the temperature of the exhaust gas flowing around the air preheater is considered to have decreased, the heat exchange efficiency of the air preheater will decrease due to contamination, etc. If the exhaust gas temperature is lower than the specified temperature, and it is determined that air leakage from the air preheater has occurred, It can be assumed that the air preheater is damaged.

  Therefore, it is classified according to the combination of whether or not the measured exhaust gas temperature is lower than the predetermined temperature and whether or not the measured preheated air temperature is lower than the predetermined temperature from the preheated air temperature when the air preheater is healthy. Then, the state of the air preheater and the damaged part can be estimated with higher accuracy.

  Here, in the former method for diagnosing a furnace air preheater according to the present invention, a correlation diagram between the measured exhaust gas temperatures on the exhaust gas inlet side and the exhaust gas outlet side measured and a regression equation showing the correlation are prepared. In the correlation diagram, the regression line of the exhaust gas temperature on the exhaust gas outlet side as a whole falls below a predetermined temperature from the regression line of the exhaust gas temperature on the exhaust gas outlet side when the air preheater is healthy. If the result continues, it is preferable to determine that air leakage from the air preheater has occurred due to damage to the air preheater.

  In this way, it is determined that an air leak has occurred when the measured exhaust gas temperature is lowered by a predetermined temperature or more from the exhaust gas temperature when the air preheater is healthy over a wide temperature range. It is possible to prevent erroneous determination due to variations in measured values at the temperature of the part and to increase the certainty of determination.

  In the latter method of diagnosing a furnace air preheater according to the present invention, a correlation diagram between the exhaust gas temperature on the exhaust gas inlet side with respect to the measured air preheater and the preheated air temperature and a regression equation indicating the correlation are provided. When it is determined that air leakage from the air preheater has occurred due to damage to the air preheater, the straight line of the regression equation of the preheated air temperature in the correlation diagram is the soundness of the air preheater as a whole. It is preferable to determine that the air preheater is damaged on the exhaust gas outlet side when the temperature does not decrease by a predetermined temperature or more from the regression line of the preheating air temperature at that time.

  In this way, when it is determined that air leakage from the air preheater has occurred due to damage to the air preheater, the measured preheating is performed using the preheated combustion air temperature as the criterion for determining the damaged portion. The air preheater is damaged on the exhaust gas outlet side when the temperature of the burned combustion air does not fall below a predetermined temperature from the preheated combustion air temperature when the air preheater is healthy over a wide temperature range. Therefore, it is possible to prevent misjudgment due to variations in measured values at some temperatures and to increase the certainty of estimation of a damaged site.

It is sectional drawing which shows the continuous heating furnace which applied one Example of the diagnostic method of the air preheater of the furnace of this invention. Correlation showing a straight line based on the measurement results of the exhaust gas temperature on the exhaust gas inlet side and the exhaust gas outlet side with respect to the air preheater in the flue and the regression equation showing the correlation in the diagnostic method of the furnace air preheater of the above embodiment FIG. Correlation showing a straight line based on the measurement result of the exhaust gas inlet side exhaust gas temperature and the preheating air temperature for the air preheater in the flue and the preheating air temperature in the diagnosis method of the furnace air preheater of the above embodiment FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view showing a continuous heating furnace to which an embodiment of a method for diagnosing an air preheater of a furnace according to the present invention is applied. In FIG. 1, reference numeral 1 denotes a continuous heating furnace.

  The continuous heating furnace 1 conveys the material to be heated M inserted in the furnace bottom 3 in the furnace 1 from the insertion port 2 to the right in FIG. 1 by the walking beam device, and the material to be heated M is conveyed during the conveyance. Is preheated in the pretropical zone 4, heated in the heating zone 5, and further heated in the soaking zone 6 with no unevenness in heating, and then unloaded from the carry-out port 7. The furnace bottom 3 has a continuous heating furnace In order to exhaust the exhaust gas G such as combustion gas and atmospheric gas used in 1 to the outside of the furnace, a flue 8 is connected as an exhaust passage connected to the base of a chimney (not shown).

  In the flue 8, a heat exchange pipe of the air preheater 9 is arranged so as to extend across the extending direction of the flue 8. The combustion air that has entered is heat-exchanged with the high-temperature exhaust gas G discharged from the continuous heating furnace 1 to the flue 8 and preheated, and then comes out of the combustion air outlet 11 and is continuously heated. 1, while the hot exhaust gas G discharged into the flue 8 enters the passage between the combustion air outlet 11 side and the heat exchange pipe of the air preheater 9, and is on the combustion air inlet 10 side Go out of the passage and head towards the base of the chimney. As a result, the air preheater 9 can increase the temperature of the combustion air with the heat of the high-temperature exhaust gas G before supplying the combustion air into the continuous heating furnace 1. Can be planned.

  By the way, when the air preheater 9 is generally damaged due to deterioration or the like, the combustion air leaks to the flue 8, and the preheating temperature of the combustion air is lowered, and the energy saving effect may not be sufficiently obtained. For this reason, in the diagnosis method of this embodiment, the air preheater 9 is diagnosed as follows.

  That is, in the method for diagnosing the air preheater in the furnace of this embodiment, when diagnosing damage to the air preheater 9 disposed in the flue 8 of the continuous heating furnace 1, the combustion of the air preheater 9 in the flue 8 is performed. For example, a temperature sensor 12 having a thermocouple is provided at a position on the air outlet 11 side, that is, a position on the side where the high-temperature exhaust gas G enters the passage between the heat exchange pipes of the air preheater 9 (exhaust gas input side). The low-temperature exhaust gas after the heat exchange with the combustion air from the position on the combustion air inlet 10 side of the air preheater 9 in the flue 8, that is, the passage between the heat exchange pipes of the air preheater 9. For example, a temperature sensor 13 having a thermocouple is arranged at a position where G is emitted (exhaust gas outlet side), and these temperatures are set under conditions of an operating temperature and an operating load of the continuous heating furnace 1 or more. Exhaust gas inlet and exhaust gas outlet by sensors 12 and 13 The exhaust gas temperature at each position is measured, and the measured exhaust gas temperatures are compared with the exhaust gas temperatures at the exhaust gas inlet side and exhaust gas outlet side positions of the air preheater 9 measured in advance when the air preheater 9 is healthy. When the measured exhaust gas temperature falls below a predetermined temperature, for example, 30 ° C. or more, from the exhaust gas temperature when the air preheater 9 is healthy, the air preheater 9 causes damage to the inside of the flue 8. It is determined that there is an air leak.

  Specifically, in the method for diagnosing a furnace air preheater according to this embodiment, the air preheating in the flue 8 is performed under conditions of an operating temperature and an operating load that are normal conditions of the continuous heating furnace 1 or more. The exhaust gas temperatures on the exhaust gas inlet side and the exhaust gas outlet side with respect to the heat exchange pipe of the vessel 9 are periodically measured by the temperature sensors 12 and 13, and as shown in FIG. 2, the measured exhaust gas inlet side A correlation diagram showing the correlation between the exhaust gas temperature and the exhaust gas outlet side exhaust gas temperature is created, and a regression equation showing the correlation is created by, for example, the least square method.

  In FIG. 2, ○ indicates the measured value of the exhaust gas temperature when the air preheater 9 is healthy, △ indicates the measured value of the exhaust gas temperature when the air preheater 9 is abnormal (before deterioration update, etc.), and □ indicates the measured value This is a measured value of the exhaust gas temperature at the time of (diagnosis), and a straight line A is a regression line showing a correlation of exhaust gas temperature when the air preheater 9 is healthy, and a straight line B is an exhaust gas when the air preheater 9 is abnormal A straight line based on a regression equation indicating a correlation between temperatures, and a straight line C are a straight line based on a regression equation indicating a correlation between exhaust gas temperatures during measurement (diagnosis).

  Here, assuming that the exhaust gas inlet side exhaust gas temperature is Tg1 (° C.) and the exhaust gas outlet side exhaust gas temperature is Tg2 (° C.), for example, the regression equation at the time of healthy is Tg2 = 0.162 × Tg1 + 331, the regression at the time of abnormality The equation can be Tg2 = 0.131 × Tg1 + 257, and the regression equation at the time of measurement (diagnosis) can be Tg2 = 0.144 × Tg1 + 310. In this case, for example, the exhaust gas inlet side exhaust gas temperature is 600 ° C. to 900 ° C. Over the period, the exhaust gas temperature when the air preheater 9 is healthy is generally reduced to a predetermined temperature, for example, 30 ° C. or more, and approaches the exhaust gas temperature when the air preheater 9 is abnormal. From this, it can be determined that the exhaust gas temperature at the time of measurement (diagnosis) indicates the occurrence of air leakage from the air preheater 9 into the flue 8 due to damage to the air preheater 9.

  Therefore, according to the diagnosis method of this embodiment, the temperature of the exhaust gas G in the flue 8 is used instead of the temperature of the preheated combustion air as a criterion for the presence or absence of air leakage. The exhaust gas temperatures at the gas inlet side and the exhaust gas outlet side are measured, and the measured exhaust gas temperature is compared with the exhaust gas temperature at the time of soundness of the air preheater 9 measured in advance, and the measured exhaust gas is measured. When the temperature drops below a predetermined temperature from the exhaust gas temperature when the air preheater 9 is healthy, it is determined that air leakage from the air preheater 9 into the flue 8 has occurred due to damage to the air preheater 9. Therefore, regardless of whether the damaged portion of the air preheater 9 is the exhaust gas inlet side or the exhaust gas outlet side, it is possible to reliably diagnose the occurrence of air leakage due to the damage.

  In addition, according to the diagnosis method of this embodiment, the exhaust gas temperature when the air preheater 9 is healthy over the wide temperature range from 600 ° C. to 900 ° C. of the exhaust gas inlet side exhaust gas temperature is measured. Therefore, it is determined that air leakage has occurred, so that erroneous determination due to variation in measured values at some temperatures can be prevented and the certainty of determination can be improved.

  Further, in the method for diagnosing a furnace air preheater of this embodiment, as shown in FIG. 1, for example, a thermocouple is provided at a position in the combustion air (preheated air) outlet 11 of the heat exchange pipe of the air preheater 9. The temperature sensor 14 is arranged to periodically measure the temperature of the preheated air exiting from the air preheater 9 together with the exhaust gas temperatures on the exhaust gas inlet side and the exhaust gas outlet side of the air preheater 9 in the flue 8. As shown in FIG. 3, a correlation diagram showing the correlation between the measured exhaust gas inlet side exhaust gas temperature and the preheated air temperature is created, and for example, a regression equation showing the correlation by the least square method is created. create.

  In FIG. 3, ◯ indicates the measured exhaust gas temperature and preheated air temperature when the air preheater 9 is healthy, and △ indicates the exhaust gas temperature when there is an abnormality (damage) on the exhaust gas inlet side of the air preheater 9. And □ are the measured values of the exhaust gas temperature and the preheated air temperature at the time of measurement (diagnosis), and the straight line D is a regression equation showing the correlation of the exhaust gas temperature when the air preheater 9 is healthy. A straight line by E, a straight line E is a regression line showing a correlation of exhaust gas temperature when there is an abnormality (damage) on the exhaust gas inlet side of the air preheater 9, and a straight line F is a temperature It is the straight line by the regression equation which shows a correlation.

  As shown in FIG. 2, since the measured exhaust gas temperature is lower than the exhaust gas temperature when the air preheater 9 is healthy by a predetermined temperature or more, the air preheater 9 to the flue 8 is damaged by the damage of the air preheater 9. When it is determined that air leakage into the air has occurred, as shown in FIG. 3, for example, the preheated air when the air preheater 9 is healthy over the exhaust gas inlet side exhaust gas temperature of 600 ° C. to 900 ° C. When the preheating air temperature at the time of measurement is not lower than the predetermined temperature, for example, 30 ° C. or more as a whole, the air preheater 9 is damaged on the exhaust gas outlet side during this measurement (diagnosis). Can be determined.

  Therefore, according to the diagnostic method of this embodiment, when it is determined that air leakage from the air preheater 9 due to damage to the air preheater 9 has occurred, the combustion air preheated according to the determination criteria for the damaged portion is determined. When the temperature of the preheated combustion air measured using the temperature is not lowered from the temperature of the preheated combustion air when the air preheater 9 is healthy over a wide temperature range by a predetermined temperature or more, for example, 30 ° C or more Since it is determined that the air preheater 9 is damaged on the exhaust gas outlet side, it can be estimated when the damaged portion of the air preheater 9 is on the exhaust gas outlet side. It is possible to prevent erroneous determination due to variations in measured values at temperature and to reliably estimate the damaged site.

  It should be noted that the regression line of the preheating air temperature in the correlation diagram between the exhaust gas temperature on the exhaust gas inlet side with respect to the air preheater 9 and the preheated air temperature is entirely the regression of the preheated air temperature when the air preheater 9 is healthy. When the temperature is lower than a predetermined temperature, for example, 30 ° C. or more, from the straight line of the equation, the heat exchange efficiency is lower than when the air preheater 9 is healthy or the heat exchange of the air preheater 9 in the flue 8 Since it is considered that the temperature of the exhaust gas G flowing through the passage around the pipe is lowered, the heat exchange efficiency of the air preheater 9 is lowered due to contamination or the like when the exhaust gas temperature is not lower than a predetermined temperature. If it is determined that air leakage from the air preheater 9 has occurred because the exhaust gas temperature is lower than the predetermined temperature, the exhaust gas inlet side or the central portion For example, air precautions at parts other than the exhaust gas outlet side. Damage vessel 9 can be estimated to have occurred.

  These diagnostic results are shown in Table 1 below. Therefore, it is classified according to the combination of whether or not the measured exhaust gas temperature is lower than the predetermined temperature and whether or not the measured preheated air temperature is lower than the predetermined temperature from the preheated air temperature when the air preheater is healthy. By doing so, the state and damaged part of the air preheater 9 can be estimated with higher accuracy.

  Although the present invention has been described above based on the embodiments, the present invention is not limited to the above-described examples. For example, a furnace to which the method of the present invention can be applied is not limited to a continuous heating furnace, and heating and leveling of a material to be heated can be performed. Other types of furnaces for heat may be used.

  Further, the exhaust passage of the furnace to which the method of the present invention can be applied is not limited to the flue, and may be another passage such as an exhaust duct as long as it is a passage that guides high-temperature exhaust gas in the furnace to the outside.

  Thus, according to the former method for diagnosing the air preheater of the furnace of the present invention, the temperature of the exhaust gas in the exhaust passage is used instead of the temperature of the combustion air preheated as a criterion for the presence or absence of air leakage. Measure the exhaust gas temperature on the exhaust gas inlet side and exhaust gas outlet side with respect to the preheater, compare the measured exhaust gas temperature with the pre-measured exhaust gas temperature of the air preheater and measure it If the exhaust gas temperature falls below a certain level from the exhaust gas temperature when the air preheater is healthy, it is determined that air leakage from the air preheater has occurred due to damage to the air preheater. Regardless of whether the damaged portion is on the exhaust gas inlet side or the exhaust gas outlet side, the occurrence of air leakage due to the damage can be reliably diagnosed.

  In addition, according to the latter method of diagnosing an air preheater of the present invention, measurement was performed when it was determined that air leakage from the air preheater due to damage to the air preheater occurred due to a decrease in exhaust gas temperature. When the preheated air temperature is compared with the preheated air temperature when the air preheater is healthy, and the measured preheated air temperature is not lower than the predetermined temperature from the preheated air temperature when the air preheater is healthy Since it is determined that the air preheater is damaged on the exhaust gas outlet side, the damaged portion can be estimated when the damaged portion of the air preheater is on the exhaust gas outlet side.

DESCRIPTION OF SYMBOLS 1 Continuous heating furnace 2 Insertion port 3 Furnace bottom 4 Pre-tropical zone 5 Heating zone 6 Soaking zone 7 Carriage outlet 8 Chimney 9 Air preheater 10 Combustion air inlet 11 Combustion air outlet 12, 13, 14 Temperature sensor G Exhaust gas M Heated material

Claims (4)

In diagnosing damage to the air preheater located in the furnace exhaust passage,
Measure the exhaust gas temperature on the exhaust gas inlet side and the exhaust gas outlet side with respect to the air preheater in the exhaust passage under the condition of the operating temperature and operating load above the predetermined level,
When the measured exhaust gas temperature is compared with the exhaust gas temperature when the air preheater is healthy when measured in advance, and the measured exhaust gas temperature falls below a predetermined temperature from the exhaust gas temperature when the air preheater is healthy In addition, it is determined that air leakage from the air preheater due to damage to the air preheater occurs. Create a correlation diagram between the measured exhaust gas temperature on the exhaust gas inlet side and the exhaust gas outlet side and a regression equation showing the correlation,
In the correlation diagram, the exhaust gas temperature regression line on the exhaust gas outlet side generally falls below a predetermined temperature from the exhaust gas temperature regression line on the exhaust gas outlet side when the air preheater is healthy. 2. The method for diagnosing an air preheater in a furnace according to claim 1, wherein when the air preheater continues, it is determined that air leakage from the air preheater due to damage to the air preheater occurs. Regularly measure the temperature of the preheated air coming out of the air preheater along with the exhaust gas temperature on the exhaust gas inlet side and the exhaust gas outlet side of the air preheater in the exhaust passage,
When it is determined from the decrease in the exhaust gas temperature that air leakage from the air preheater due to damage to the air preheater has occurred, the measured preheated air temperature is measured in advance. If the measured preheated air temperature is not lower than the preheated air temperature when the air preheater is healthy, the air preheater is damaged on the exhaust gas outlet side compared to the air temperature. The method for diagnosing a furnace air preheater according to claim 1 or 2, characterized in that: Create a correlation diagram between the exhaust gas temperature on the exhaust gas inlet side with respect to the measured air preheater and the preheated air temperature and a regression equation showing the correlation,
When it is determined that air leakage from the air preheater has occurred due to damage to the air preheater, the straight line of the regression equation of the preheated air temperature in the correlation diagram is entirely the preheated air when the air preheater is healthy. 4. The furnace air preheating according to claim 3, wherein it is determined that the air preheater is damaged on the exhaust gas outlet side when the temperature does not fall below a predetermined temperature from a straight line of the temperature regression equation. Diagnosis method.

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