JP2011179756A - Method and device for purging exhaust gas piping - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a purging method for preventing condensation of exhaust gas in an exhaust gas main pipe where exhaust gas is collected, when purging an exhaust system for exhaust gas in a regenerative burner heating furnace by combustion air for each zone. <P>SOLUTION: When the burner is stopped for each zone in the regenerative burner heating furnace, combustion air is made to flow from combustion air piping connected to the burner to exhaust gas piping, and by sequentially feeding the combustion air to an exhaust gas carrying pipe 25 and the exhaust gas main pipe 26, exhaust gas in the exhaust gas carrying pipe 25 and the exhaust gas main pipe 26 is purged by the combustion air. During the purging, a temperature in the exhaust gas main pipe 26 is measured by a thermometer 31, and a flow rate of the combustion air for the purging is controlled by a flow rate control means 32 so that the temperature does not decrease below a dew point of the exhaust gas. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a purge method and a purge apparatus for exhaust gas piping in a regenerative burner heating furnace.

  Conventionally, a regenerative burner heating furnace (hereinafter, also simply referred to as “heating furnace”) is used for heating, for example, a steel plate. As shown in FIG. 4, the heat storage burner heating furnace includes a heat storage means 12 to which a combustion air pipe 10 for supplying combustion air (combustion air) and an exhaust gas pipe 11 for discharging exhaust gas generated after combustion are connected. Each has a plurality of burners 13 provided, and the paired burners 13 are configured to operate alternately.

  The piping 10 for combustion air and the piping 11 for exhaust gas are the common pipe part 14 which can flow both combustion air and exhaust gas in the downstream of the piping 10 for combustion air, and the upstream of the piping 11 for exhaust gas, It is connected to the heat storage means 12. The heat storage means 12 includes a heat storage chamber 15 to which the common pipe portion 14 of the combustion air pipe 10 and the exhaust gas pipe 11 is connected, and a heat storage body 16 that is filled in the heat storage chamber 15 and is heated by sensible heat of the exhaust gas. have.

  The plurality of burners 13 provided in the regenerative burner heating furnace are divided into a plurality of zones Z (sections) so as to include at least a pair of burners. A combustion air pipe 10 of each burner 13 arranged in a certain zone Z is connected to a combustion air supply pipe 18 via a zone header pipe 17 in the zone Z, and a combustion provided for each zone Z. An air supply pipe 18 is connected to a combustion air main pipe 19. A combustion air fan 20 for supplying combustion air to the combustion air main pipe 19 is disposed upstream of the combustion air main pipe 19.

  Each combustion air pipe 10 is provided with a combustion air switching valve 21 for supplying and stopping combustion air to the burner 13. The combustion air supply pipe 18 is sequentially provided with an orifice 22 for measuring the flow rate in the pipe and a combustion air flow rate adjusting valve 23 for adjusting the flow rate from the upstream side to the downstream side.

  On the other hand, the exhaust gas pipe 11 of each burner 13 disposed in the zone Z is connected to the exhaust gas transport pipe 25 via the zone header pipe 24 in the zone Z, and the exhaust gas transport provided for each zone Z. The pipes 25 are connected to the exhaust gas main pipe 26, respectively. On the downstream side of the exhaust gas main pipe 26, there are an induction fan (IDF) 27 for discharging the exhaust gas from the exhaust gas main pipe 26, and a chimney for radiating the exhaust gas after performing a predetermined treatment to the atmosphere ( (Not shown).

  Each exhaust gas pipe 11 is provided with an exhaust gas switching valve 28 for discharging and stopping the exhaust gas generated in each burner 13. The exhaust gas transfer pipe 25 is sequentially provided with an orifice 29 for measuring the flow rate in the pipe and an exhaust gas flow rate adjusting valve 30 for adjusting the flow rate from the upstream side to the downstream side.

  In the above configuration, at the time of combustion by one burner 13 of a pair of burners, the combustion air that has flowed into the combustion air main pipe 19 by the combustion air fan 20 is used as the combustion air supply pipe 18 and the combustion air use burner. The heat storage body 16 is passed through the pipe 10 and supplied to the burner 13. At this time, the combustion air switching valve 21 is open, and the exhaust gas switching valve 28 is closed.

  On the other hand, in the burner 13 at the time of heat storage of the other of the pair of burners, exhaust gas in the heat storage chamber 15 is conveyed to the exhaust gas main pipe 26 via the exhaust gas pipe 11 and the exhaust gas transport pipe 25 by the induction blower 27, and the chimney To the atmosphere. At this time, the exhaust gas switching valve 28 is open, and the combustion air switching valve 21 is closed.

  In the operation of such a regenerative burner heating furnace, when the pair of burners 13 to be thinned out is stopped by the thinning operation, the combustion air switching valve 21 of the combustion air pipe 10 of the stopped burner 13 and The exhaust gas switching valve 28 of the exhaust gas pipe 11 is closed. However, since the induction blower 27 used to attract the exhaust gas to the chimney is activated, a negative pressure acts on the exhaust gas pipe 11 on the downstream side of the exhaust gas switching valve 28. Normally, there is a leak (leakage) of about 1% in the exhaust gas switching valve 28. Therefore, when the exhaust gas flows into the exhaust gas pipe 11 due to the influence and the temperature decreases, dew condensation occurs and the degree is severe. Lead to corrosion. Further, since the amount of leakage of the exhaust gas switching valve 28 is small, the amount of exhaust gas sucked out by the induction blower 27 from the exhaust gas pipe 11, the zone header pipe 24 and the exhaust gas transport pipe 25 becomes small, and the exhaust gas stays for a long time. If this happens, the temperature may drop to below the condensation temperature. In particular, when a gas containing sulfur (S), such as COG (coke oven gas produced during coal dry distillation), is used as the heating fuel used in the heating furnace, the exhaust gas is caused by sulfuric acid produced by condensation. Corrosion of the piping 11 or the like occurs.

  In order to prevent such corrosion of the exhaust gas pipe, Patent Document 1 discloses a method of purging exhaust gas in the exhaust gas pipe with combustion air. The purge method disclosed in Patent Document 1 will be described with reference to FIG.

  In the purge method of Patent Document 1, after the combustion of the pair of burners 13 to be thinned is stopped, the combustion air switching valve 21 and the exhaust gas switching valve 28 are opened. The combustion air supplied from the combustion air main pipe 19 is caused to flow to the exhaust gas pipe 11 through the combustion air supply pipe 18, the zone header pipe 17 and the combustion air pipe 10. The exhaust gas is pushed downstream. Thereby, the exhaust gas in the exhaust gas pipe 11 can be purged with combustion air.

  By the way, in the operation of the regenerative burner heating furnace, the burner combustion is stopped as follows: (1) Stop in units of burners, (2) Stop in units of zones, (3) Stop in all zones There are three patterns. However, when combustion of the burner is stopped in units of zones, if purging is performed by the method of Patent Document 1 described above, the combustion air used for purging in units of zones is directly transferred from the exhaust gas transport pipe 25 to the exhaust gas main pipe 26. Flows in. On the other hand, the exhaust gas main pipe 26 is filled with exhaust gas from other operating zones. Therefore, depending on the temperature and flow rate of the combustion air used for purging, the temperature in the exhaust gas main pipe 26 may drop below the dew point of the exhaust gas and the exhaust gas may condense, causing corrosion in the exhaust gas main pipe 26. There is. Normally, the temperature of the exhaust gas is about 100 to 200 ° C., and the temperature of the combustion air is room temperature. Therefore, when the combustion air flows directly into the exhaust gas main pipe 26, the exhaust gas in the exhaust gas main pipe 26 is cooled. The temperature in the exhaust gas main pipe 26 decreases.

Japanese Patent Laid-Open No. 2005-272995

  The problem to be solved by the present invention is to prevent the exhaust gas from condensing in the exhaust gas main pipe where the exhaust gas is aggregated when purging the exhaust gas exhaust system of the regenerative burner heating furnace in units of zones with the combustion air. It is an object of the present invention to provide a purge method and a purge apparatus that can be used.

  The purge method of the present invention includes at least a pair of burners each including a plurality of burners each provided with a heat storage means connected to a combustion air pipe for supplying combustion air and an exhaust gas pipe for discharging exhaust gas generated after combustion. The burners that are paired with each other are operated alternately, and the exhaust gas pipes that discharge the exhaust gas from each burner are collected in the exhaust gas transport pipes provided for each zone. In a regenerative burner furnace in which the exhaust gas transfer pipe is integrated into the exhaust gas main pipe, with at least one zone operating, all the burners in at least one of the remaining zones are stopped The exhaust gas pipe is purged with the combustion air for exhaust gas in the exhaust gas pipe and the exhaust gas transport pipe, and combustion of each burner in the stopped zone is performed. Open the combustion air switching valve provided in the gas piping and the exhaust gas switching valve provided in the exhaust gas piping of each burner in the stopped zone so that the combustion air flows from the combustion air piping to the exhaust gas piping. The exhaust gas in the exhaust gas pipe and the exhaust gas transport pipe are purged with combustion air by sending the exhaust gas transfer pipe and the exhaust gas main pipe in this order, and the temperature in the exhaust gas main pipe is measured during the purge, Is characterized in that the flow rate of combustion air for purging the exhaust gas pipe and the exhaust gas transport pipe is adjusted so as not to fall below the dew point of the exhaust gas.

  Further, the purge device of the present invention comprises at least a pair of burners each provided with a plurality of burners each provided with a combustion air pipe for supplying combustion air and an exhaust gas pipe for discharging exhaust gas generated after combustion. Is divided into a plurality of zones so as to include, the paired burners operate alternately, exhaust gas pipes that exhaust the exhaust gas from each burner are aggregated in the exhaust gas transport pipe provided for each zone, In a regenerative burner heating furnace in which the exhaust gas transport pipes in each zone are integrated into the exhaust gas main pipe, the exhaust gas pipe and the exhaust gas pipe purge device for purging the exhaust gas in the exhaust gas transport pipe with combustion air, Combustion air switching valve provided in the combustion air piping of each burner, valve control means for controlling opening and closing of the exhaust gas switching valve provided in the exhaust gas piping of each burner, and the temperature in the exhaust gas main pipe A thermometer for measuring, and a flow rate adjusting means for adjusting the flow rate of combustion air for purging the exhaust gas pipe and the exhaust gas carrier pipe, and the remaining zones in a state where at least one zone is operating When all the burners in at least one zone are stopped, the valve control means includes a combustion air switching valve provided in the combustion air piping of each burner in the stopped zone, and the stopped zone The exhaust gas switching valve provided in the exhaust gas pipe of each burner is opened, and the exhaust gas piping and the exhaust gas transport pipe are arranged so that the temperature measured by the thermometer does not fall below the dew point of the exhaust gas. The flow rate of the combustion air for purging the gas is adjusted.

  In the present invention, the flow rate of the combustion air for purging the exhaust gas pipe and the exhaust gas transport pipe is specifically adjusted so that the temperature in the exhaust gas main pipe is equal to or lower than the temperature obtained by adding the specified value to the dew point of the exhaust gas. Then, the flow rate of the combustion air for purging can be reduced, so that the temperature in the exhaust gas main pipe does not fall below the dew point of the exhaust gas.

  In the present invention, the temperature in the exhaust gas main pipe is measured during the purge, and the flow rate of the combustion air for purging is adjusted so that the temperature does not fall below the dew point of the exhaust gas. Condensation can be prevented, and corrosion of the exhaust gas main pipe due to exhaust gas condensation can be prevented.

It is a block diagram which shows the principal part of the purge apparatus of this invention for implementing the purge method of this invention. In the purge method of the present invention, the temperature Tpv in the exhaust gas main pipe, the output value (L) of the flow rate adjusting means, the valve opening degree of the exhaust gas flow rate control valve and the combustion air flow rate control valve, and the purge flow rate (combustion air flow rate) The change over time is conceptually shown. FIG. 3 conceptually shows changes over time in a temperature Tpv in an exhaust gas main, a valve opening degree of an exhaust gas flow rate control valve and a combustion air flow rate control valve, and a purge flow rate (flow rate of combustion air) in a conventional purge method. The structure of the conventional heat storage type burner heating furnace is shown.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a configuration diagram showing a main part of a purge apparatus of the present invention for carrying out the purge method of the present invention. The present invention can be implemented by adding the configuration shown in FIG. 1 to the conventional regenerative burner heating furnace described in FIG.

  The configuration added in the present invention will be described with reference to FIG. As shown in FIG. 1, a thermometer 31 is provided in the exhaust gas main pipe 26, and the temperature in the exhaust gas main pipe 26 is measured by the thermometer 31. The flow rate adjusting means 32 is provided, and the flow rate of the combustion air for purging is adjusted by the flow rate adjusting means 32 so that the temperature in the exhaust gas main pipe 26 measured by the thermometer 31 does not fall below the dew point of the exhaust gas. Note that the installation position of the sensor unit of the thermometer 31 can be, for example, the exhaust gas main pipe 26 or the iron shell of the exhaust gas main pipe, but if the temperature in the exhaust gas main pipe 26 can be measured with a certain degree of accuracy, the installation position thereof may be used. The position is not limited.

  Hereinafter, the purge method of the present invention will be described with reference to FIGS. The purge method of the present invention is a purge method when the burner is stopped in zone units. That is, a purge method performed when all the burners in at least one zone Z among the remaining zones Z are stopped in a state where at least one zone Z is operating among the plurality of zones Z shown in FIG. It is.

  In the purge method of the present invention, after all the burners 13 in the zone to be stopped are stopped, the air setting associated with the combustion air flow control valve 23 provided in the combustion air supply pipe 18 in the zone is set. The switch 33 and the exhaust gas setting switch 34 associated with the exhaust gas flow control valve 30 provided in the exhaust gas transport pipe 25 in the zone are switched from the combustion mode (A) to the purge mode (B), respectively. In the combustion mode (A), the air flow rate controller 35 compares the set flow rate of the air flow rate setter 36 with the actual flow rate measured by the orifice 22 so that the set flow rate is obtained. While adjusting the opening, the exhaust gas flow rate controller 37 compares the set flow rate of the exhaust gas flow rate setter 38 with the actual flow rate measured by the orifice 29 to open the exhaust gas flow rate control valve 30 so that the set flow rate is obtained. In the purge mode (B), the flow rate adjusting means 32 adjusts the opening degree of the combustion air flow rate adjustment valve 23 and the exhaust gas flow rate adjustment valve 30 as will be described later.

  Next, the combustion air switching valve 21 and the exhaust gas switching valve 28 are opened. In addition, opening and closing of these valves can be performed by a well-known valve control means (not shown). The combustion air supplied from the combustion air main pipe 19 is caused to flow to the exhaust gas pipe 11 through the combustion air supply pipe 18, the zone header pipe 17 and the combustion air pipe 10, and the zone header pipe 24, the exhaust gas is supplied. The exhaust gas in the exhaust gas pipe 11, the zone header pipe 24, and the exhaust gas transport pipe 25 is purged with combustion air by sending the exhaust pipe 25 and the exhaust gas main pipe 26 in this order.

  In the present invention, the flow rate of combustion air for purging is adjusted so that the temperature Tpv in the exhaust gas main pipe 26 measured by the thermometer 31 during the purge does not fall below the dew point of the exhaust gas. The flow rate of the combustion air is adjusted by the flow rate adjusting means 32. In the flow rate adjusting means 32, a temperature obtained by adding a specified value (α) to the dew point of exhaust gas, that is, a dew condensation prevention lower limit temperature Tsv is set in advance. In other words, α is a margin, and a specific numerical value is not limited, but is 20 to 30 ° C., for example.

  The flow rate adjusting means 32 compares the temperature Tpv in the exhaust gas main pipe 26 with the dew condensation prevention lower limit temperature Tsv, and outputs 1 as an output value (L) when Tpv> Tsv, and an output value (when Tpv ≦ Tsv) A numerical value less than 1 is output as L). The output value (L) from the flow rate adjusting means 32 is input to the product calculator 39. A predetermined opening (standard opening) (K) of the exhaust gas flow rate control valve 30 at the time of purging is input to the product calculator 39 in advance, and the product calculator 39 receives the specified opening (K) and the flow rate. The product operation with the output value (L) of the adjusting means 32 is performed, and the opening degree of the exhaust gas flow rate adjusting valve 30 is set by the calculated value.

  The output value (L) of the flow rate adjusting means 32 is also input to the product calculator 40 on the combustion air flow rate adjusting valve 23 side. A predetermined opening (standard opening) (J) of the combustion air flow rate control valve 23 at the time of purging is input to the product calculator 40 in advance, and the product calculator 40 calculates the specified opening (J). Product calculation with the output value (L) of the flow rate adjusting means 32 is performed, and the opening degree of the combustion air flow rate adjusting valve 23 is set by the calculated value.

  As described above, when the temperature Tpv in the exhaust gas main pipe 26 is higher than the dew condensation prevention lower limit temperature Tsv (Tpv> Tsv), the flow rate adjusting means 32 outputs 1 as the output value (L). The opening setting values of the exhaust gas flow rate control valve 30 and the combustion air flow rate control valve 23 output via 39 and 40 remain at the specified opening levels, and purge is performed at a standard flow rate. On the other hand, when the temperature Tpv in the exhaust gas main pipe 26 is equal to or lower than the dew condensation prevention lower limit temperature Tsv (Tpv ≦ Tsv), the flow rate adjusting means 32 outputs a numerical value less than 1 as the output value (L). The opening setting values of the exhaust gas flow rate control valve 30 and the combustion air flow rate control valve 23 that are output via 40 become smaller than the specified opening, and the flow rate of the combustion air for purging decreases. Thereby, the fall of temperature Tpv in the exhaust gas main pipe 26 is suppressed, and the temperature Tpv can be prevented from falling below the dew point of the exhaust gas.

  In the purge method of the present invention, the temperature Tpv in the exhaust gas main pipe 26, the output value (L) of the flow rate adjusting means 32, the valve opening degree of the exhaust gas flow rate adjusting valve 30 and the combustion air flow rate adjusting valve 23, and the purge flow rate ( FIG. 2 conceptually shows changes with time in the flow rate of combustion air. As shown in FIG. 2, when the temperature Tpv in the exhaust gas main pipe 26 becomes equal to or lower than the dew condensation prevention lower limit temperature Tsv (Tpv ≦ Tsv), the flow rate adjusting means 32 decreases the output value (L). The valve openings of the control valve 30 and the combustion air flow control valve 23 are reduced, and the purge flow is reduced. If it does so, the fall of temperature Tpv in the exhaust gas main pipe 26 will become moderate, and it can prevent this temperature Tpv from falling below the dew point of exhaust gas. In addition, as shown in FIG. 2, the output value (L) of the flow rate adjusting means 32 can be gradually changed by PID control or the like so that the change does not become abrupt.

  On the other hand, FIG. 3 shows the temperature Tpv in the exhaust gas main pipe 26 in the conventional purge method, the valve opening degree of the exhaust gas flow rate control valve 30 and the combustion air flow rate control valve 23, and the purge flow rate (combustion air flow rate). The change over time is conceptually shown. In the conventional purge method, regardless of the temperature Tpv in the exhaust gas main pipe 26, the valve opening degrees of the exhaust gas flow rate adjustment valve 30 and the combustion air flow rate adjustment valve 23 are constant (specified opening degree), so the purge flow rate is also high. It is constant. As a result, the temperature Tpv in the exhaust gas main pipe 26 continues to decrease and may fall below the dew point of the exhaust gas. If the temperature Tpv in the exhaust gas main pipe 26 falls below the dew point of the exhaust gas, condensation may occur during that time (between the arrows in FIG. 3).

Here, the combustion air amount Vsv (Nm ³ ) used for purging in the present invention is the sum of the volumes of the exhaust gas pipe 11, the zone header pipe 24, and the exhaust gas transport pipe 25 in the purged zone as Ve (m ³ ). In this case, Vsv = Ve × n. Here, n is a coefficient and is normally set in the range of 4-7. If n is less than 4, the purge becomes insufficient, and if it exceeds 7, the purge effect is saturated, which is meaningless.

In the present invention, as described above, since the amount of combustion air used for purging changes with time, it is determined whether the amount of combustion air used for purging has reached the above Vsv (Nm ³ ) by measuring the purge time. It is difficult. Therefore, as shown in FIG. 1, an integrated flow meter 41 is provided, and the purge can be terminated when the integrated flow rate by the integrated flow meter 41 reaches the above Vsv (Nm ³ ). In addition, although the integrating | accumulating flow meter 41 of FIG. 1 is integrating | accumulating the flow volume by the signal from the orifice 29 provided in the exhaust gas conveyance pipe 25, the installation position is not limited to this, For example, supply for combustion air You may make it connect with the orifice 22 provided in the pipe | tube 18. FIG. In short, it is sufficient that the amount of combustion air used for purging can be integrated for each zone. When purging a plurality of zones at the same time, the end point of purging may be determined by an integrated flow meter provided in each zone.

DESCRIPTION OF SYMBOLS 10 Combustion air piping 11 Exhaust gas piping 12 Thermal storage means 13 Burner 14 Shared pipe part 15 Thermal storage chamber 16 Thermal storage body 17 Zone header pipe 18 Combustion air supply pipe 19 Combustion air main pipe 20 Combustion air fan 21 Switching for combustion air Valve 22 Orifice 23 Flow control valve for combustion air 24 Zone header pipe 25 Exhaust gas transfer pipe 26 Exhaust gas main pipe 27 Induction fan 28 Exhaust gas switching valve 29 Orifice 30 Exhaust gas flow control valve 31 Thermometer 32 Flow control means 33 Air setting Switch 34 Exhaust gas setting switch 35 Air flow rate controller 36 Air flow rate setter 37 Exhaust gas flow rate controller 38 Exhaust gas flow rate setter 39 Product calculator 40 Product calculator 41 Integrated flow meter

Claims (4)

A plurality of burners each provided with a heat storage means connected to a combustion air pipe for supplying combustion air and an exhaust gas pipe for discharging exhaust gas generated after combustion are divided into a plurality of zones so that at least a pair of burners are included. Separately arranged, paired burners operate alternately, exhaust gas pipes that discharge exhaust gas from each burner are aggregated in exhaust gas transport pipes provided for each zone, and exhaust gas transport pipes in each zone In the regenerative burner heating furnace that is integrated into the main pipe, when all the burners in at least one of the remaining zones are stopped while at least one of the zones is operating, the exhaust gas piping And a method for purging the exhaust gas pipe for purging the exhaust gas in the exhaust gas transfer pipe with combustion air,
The combustion air switching valve provided in the combustion air piping of each burner in the stopped zone and the exhaust gas switching valve provided in the exhaust gas piping of each burner in the stopped zone are opened to burn the combustion air Pour the exhaust gas in the exhaust gas pipe and the exhaust gas transport pipe with the combustion air by flowing from the air pipe to the exhaust gas pipe and sending in order of the exhaust gas transfer pipe and the exhaust gas main pipe,
The temperature in the exhaust gas main pipe is measured during the purge, and the exhaust gas pipe for adjusting the flow rate of the combustion air for purging the exhaust gas pipe and the exhaust gas transport pipe so that the temperature does not fall below the dew point of the exhaust gas Purge method.   When the temperature in the exhaust gas main pipe is equal to or lower than the temperature obtained by adding the specified value to the dew point of the exhaust gas, reduce the flow rate of combustion air for purging the exhaust gas pipe and the exhaust gas transfer pipe, The method for purging exhaust gas piping according to claim 1, wherein the temperature of the exhaust gas does not fall below the dew point of the exhaust gas. A plurality of burners each provided with a heat storage means connected to a combustion air pipe for supplying combustion air and an exhaust gas pipe for discharging exhaust gas generated after combustion are divided into a plurality of zones so that at least a pair of burners are included. Separately arranged, paired burners operate alternately, exhaust gas pipes that discharge exhaust gas from each burner are aggregated in exhaust gas transport pipes provided for each zone, and exhaust gas transport pipes in each zone In the regenerative burner heating furnace integrated in the main pipe for exhaust gas, the exhaust gas pipe and the exhaust gas pipe purge device for purging the exhaust gas in the exhaust gas carrier pipe with combustion air,
A valve control means for controlling the opening and closing of the combustion air switching valve provided in the combustion air piping of each burner and the exhaust gas switching valve provided in the exhaust gas piping of each burner;
A thermometer for measuring the temperature in the exhaust gas main,
A flow rate adjusting means for adjusting the flow rate of combustion air for purging the exhaust gas pipe and the exhaust gas carrier pipe,
When all burners in at least one of the remaining zones are stopped while at least one zone is in operation, the valve control means uses the combustion air for each burner in the stopped zone. The combustion air switching valve provided in the piping and the exhaust gas switching valve provided in the exhaust gas piping of each burner in the stopped zone are opened, and the temperature measured by the thermometer is the temperature measured by the thermometer. A purging device for exhaust gas piping that adjusts the flow rate of combustion air for purging the exhaust gas piping and the exhaust gas transport tube so as not to fall below the dew point.   When the temperature in the exhaust gas main pipe is equal to or lower than the temperature obtained by adding the specified value to the dew point of the exhaust gas, the flow rate adjusting means reduces the flow rate of the combustion air for purging the exhaust gas pipe and the exhaust gas carrier pipe. The purging device for exhaust gas piping according to claim 3, wherein the temperature in the exhaust gas main tube does not fall below the dew point of the exhaust gas.

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