JP4969149B2 - Ammonia injection device and method for exhaust heat recovery boiler - Google Patents

Description

  The present invention relates to a combustion apparatus, and more particularly to an ammonia injection apparatus and method for an exhaust heat recovery boiler suitable for reducing nitrogen oxides in exhaust gas.

  FIG. 2 shows an ammonia injection device 21 for a denitration device 6 that uses ammonia water in a combined cycle plant (hereinafter sometimes referred to as a boiler plant) including an exhaust heat recovery boiler 1 that uses exhaust heat of gas turbine exhaust gas. It is a systematic diagram which shows an example of the prior art using the combustion exhaust gas 2 as a heat source.

  The exhaust gas 2 introduced into the exhaust heat recovery boiler 1 is supplied to the denitration device 6 together with ammonia from the ammonia injection nozzle 5 via the superheater 3 or an evaporator (not shown) arranged on the downstream side of the superheater 3. The denitrated gas 2 ′ is discharged from the chimney 4.

  Here, the ammonia water is sprayed from the ammonia injection nozzle 5 to the upstream side of the denitration device 6 in the exhaust heat recovery boiler 1 by the following ammonia injection device 21. That is, the ammonia injection device 21 is disposed adjacent to the exhaust heat recovery boiler 1, and a gas circulation pipe 19 for extracting a part of the exhaust gas 2 flowing in the exhaust heat recovery boiler 1 and an evaporator provided at the end of the gas circulation pipe 19. 15 is a fluid circulation system consisting of an evaporator outlet pipe connected to the ammonia injection nozzle 5 from the outlet of the evaporator 15. The gas circulation pipe 19 is provided with a switching damper 12, a gas circulation fan 13, and a flow meter 14, and an ammonia water pipe 17 is connected to the evaporator 15, and a plurality of two-fluid nozzles 16 are provided inside the evaporator 15. The ammonia water pipe 17 and the atomizing air pipe 18 are connected to the nozzle 16, the ammonia water is atomized by the action of the two-fluid nozzle 16, and the atomized ammonia water is exhausted from the outlet pipe of the evaporator 15. It is supplied into the recovery boiler 1.

When the exhaust heat recovery boiler 1 is started, the exhaust gas 2 of the exhaust heat recovery boiler 1 is sucked into the gas circulation pipe 19 by the gas circulation fan 13, and the high temperature exhaust gas 2 is circulated between the exhaust heat recovery boiler 1 and the evaporator 15. 15 is heated up. When the evaporator 15 is heated to a temperature that satisfies the ammonia injection conditions, ammonia water is introduced into the evaporator 15 via the ammonia water pipe 17. At this time, ammonia water is atomized by the action of the two-fluid nozzle 16, the atomized ammonia water is sprayed into the heated air flow, and evaporated by the thermal energy of the high-temperature exhaust gas 2 introduced from the gas circulation pipe 19, The evaporated ammonia water is injected as a mixed gas of ammonia gas, H ₂ O and air into the exhaust gas 2 flowing in the exhaust heat recovery boiler 1 from the ammonia injection nozzle 5 provided in the exhaust heat recovery boiler 1, and the ammonia is exhausted. It acts as a reducing agent for nitrogen oxides in the exhaust gas 2 of the heat recovery boiler 1.

  The flow rate of the exhaust gas 2 for heating the ammonia water is adjusted by a switching damper 12 provided in the gas circulation pipe 19 so that the ammonia water and the exhaust gas 2 have an appropriate mixing ratio, and after passing through the gas circulation fan 13, the orifice flow meter 14 It is measured. The extraction point of the exhaust gas 2 for heating ammonia water from the exhaust heat recovery boiler 1 to the gas circulation pipe 19 is set in consideration of the exhaust gas temperature and the piping material.

  In the prior art described above, since the circulation of the exhaust gas 2 for heating the ammonia water is stopped while the operation of the boiler plant 1 and the denitration device 6 is stopped, the internal temperature of the evaporator 15 is also reduced. Next, when the boiler plant 1 is restarted, ammonia water cannot be injected into the exhaust heat recovery boiler 1 until the outlet gas temperature of the evaporator 15 becomes equal to or higher than a specified value. The temperature of the evaporator 15 is increased by circulating the exhaust gas 2 to the evaporator 15. Since the exhaust gas 2 that has been reduced in temperature by exchanging heat in the superheater 3 is used, the ammonia 15 can be evaporated. It took a considerable amount of time to rise to the outlet temperature. Therefore, the exhaust gas denitration operation cannot be performed for a certain period of time after the boiler plant 1 is started. In particular, a boiler plant that operates DSS (Daily Start and Stop) or WSS (Weekly Start and Stop) is different from a continuous operation plant. Since the temperature raising operation of the evaporator 15 is required every time the boiler 1 is activated, the time during which the denitration operation cannot be performed becomes longer, so that the amount of high-concentration nitrogen oxides increases and the denitration device 6 can be activated. There was a problem that the plant had to be operated with a low load.

Japanese Patent Laid-Open No. 5-49856 discloses an exhaust gas denitration device that extracts high-temperature exhaust gas from an exhaust heat recovery boiler, evaporates ammonia water, and injects the obtained ammonia into the inlet of the denitration device of the exhaust heat recovery boiler. Although it is disclosed, at the start of the exhaust heat recovery boiler, as the evaporation heat source of ammonia water, instead of the high-temperature exhaust gas system from the boiler, the air introduced from the air fan is switched to the heated air system heated by the electric heater It is described to do.
Japanese Patent Laid-Open No. 5-49856

  In contrast to the prior art described in Patent Document 1, when the exhaust heat recovery boiler is started, an air fan and an electric heater system are selected, and it is necessary to start the heated air system before starting the gas turbine. A large amount of standby equipment maintenance and electricity usage are required. Further, in a plant such as a combined cycle plant that frequently starts and stops, a burden is imposed on the operator each time.

  The air system for heating the ammonia is a useful means for early start-up, but has an exhaust gas circulation fan and an air fan system with similar system configurations, and thus has a complicated system configuration and an air system. There is a problem in the reliability and stable operation of the system, such as an increase in maintenance of peripheral devices as well as fans, leading to an increase in electricity usage.

  The object of the present invention is to save power usage and reduce the start time of the denitration device without requiring special additional equipment, thereby enabling the plant exhaust gas denitration operation without time delay after the plant start-up. It is an object to provide an ammonia injection apparatus and method for an exhaust heat recovery boiler.

The above object is achieved by the following configuration.
That is, the invention according to claim 1 is a heat transfer tube group for recovering the heat of the combustion exhaust gas (2) discharged from the combustion device, and nitrogen oxides contained in the exhaust gas (2) into harmless nitrogen and water. A waste heat recovery boiler (1) in which a denitration device (6) for reduction and an ammonia spray section (5) provided in an upstream region of the denitration device (6) are arranged between the flow paths through which the exhaust gas (2) flows. On the other hand, for an exhaust heat recovery boiler comprising using ammonia water as an ammonia source and using exhaust gas (2) in the exhaust heat recovery boiler (1) as a heat source for evaporating the ammonia water. A first piping (19a) and a second piping (19b) for extracting an exhaust gas (2) from an inlet portion of an exhaust heat recovery boiler (1) and an inlet portion of a denitration device (6), respectively, which are ammonia injection devices (21). And the pipes (19a, 19b) A first switching damper (9a) and a second switching damper (9b) are provided respectively, and the gas circulation pipe (19c) connected by joining the two pipes (19a, 19b) is denitrated in the exhaust heat recovery boiler (1). An evaporator (15) connected to the inlet of the device (6) and evaporating ammonia introduced from the ammonia water supply pipe (17) using the exhaust gas (2) as a heat source at the intermediate part of the gas circulation pipe (19c) Gas temperature meters (7, 8, 11) are arranged at the inlet of the exhaust heat recovery boiler (1), the inlet of the denitration device (6), and the outlet of the evaporator (15), respectively, and the three gas temperatures Switching control of the gas (2) introduced into the evaporator (15) by switching between the first switching damper (9a) and the second switching damper (9b) based on the gas temperatures measured by the meters (7, 8, 11). And again Ammonia water is supplied from the ammonia water supply pipe (17) to the evaporator (15) based on the gas temperatures measured by the gas thermometers (8, 11) at the inlet of the denitration device (6) and at the outlet of the evaporator (15). It is an ammonia injection device for an exhaust heat recovery boiler provided with a control device (24) for performing control to be introduced.

  According to the second aspect of the present invention, a gas thermometer (23) is also arranged in the gas circulation pipe (19c), and the first switching damper (9a) and the first switching damper (9a) are arranged based on the exhaust gas temperature measured by the exhaust gas thermometer (23). The ammonia injection device for an exhaust heat recovery boiler according to claim 1, further comprising a control device (24) for adjusting the temperature of the exhaust gas (2) to be switched to the second switching damper (9b) and introduced into the evaporator (15). .

  The invention according to claim 3 is a gas circulation fan (13) that is started when the outlet gas temperature of the evaporator (15) becomes a predetermined temperature (eg, 200 ° C.) or less or when the exhaust heat recovery boiler (1) is started. It is an ammonia injection device for exhaust heat recovery boilers according to claim 1 or 2 provided in gas circulation piping (19c).

The invention according to claim 4 is a heat transfer tube group for recovering the heat of the combustion exhaust gas (2) discharged from the combustion device, and denitration for reducing nitrogen oxides contained in the exhaust gas (2) into harmless nitrogen and water. In contrast to an exhaust heat recovery boiler (1) having an apparatus (6) and an ammonia spray section (5) provided upstream of the denitration apparatus (6), an inlet portion or denitration of the exhaust heat recovery boiler (1) The exhaust gas (2) from which the exhaust gas (2) is extracted from the inlet of the device (6) is guided to the evaporator (15), and the ammonia water supplied into the evaporator (15) is evaporated by the exhaust gas (2). An ammonia injection method for a waste heat recovery boiler that supplies the obtained ammonia to an inlet portion of a denitration device (6) of a waste heat recovery boiler (1), and when the exhaust heat recovery boiler (1) is started, the exhaust heat recovery boiler Ratio extracted from the entrance of (1) The high temperature exhaust gas (2) is led to the evaporator (15) to raise the temperature in the evaporator (15), and the exhaust gas (2) at the inlet of the exhaust heat recovery boiler (1) is brought to a predetermined temperature (eg, 300 ° C.). When the gas temperature at the outlet of the evaporator (15) reaches a predetermined temperature (eg, 270 ° C.), the exhaust gas (2) introduced into the evaporator (15) is discharged into the exhaust gas (2) at the inlet of the exhaust heat recovery boiler (1). To the exhaust gas (2) at the inlet of the denitration device (6), and the exhaust gas temperature at the inlet of the denitration device (6) and the gas temperature at the outlet of the evaporator (15) are each equal to or higher than a predetermined temperature (eg, 270 ° C.). Then, ammonia water is introduced into the evaporator (15), and evaporated with the exhaust gas (2) while gradually increasing the amount of exhaust gas led to the evaporator (15) based on the gas temperature at the outlet of the evaporator (15). Resulting ammonia was supplied to the inlet portion of the denitration apparatus exhaust heat recovery boiler (1) (6), Oite during shutdown of the exhaust heat recovery boiler (1), the exhaust gas inlet portion of the exhaust heat recovery boiler (1) temperature of (2), the exhaust gas (2) as they become heat resistant temperature below the pipe to be introduced to the evaporator (15) (19c), denitrator exhaust gas (2) to be introduced into the evaporator (15) (6 ) Is switched from the exhaust gas (2) at the inlet to the exhaust gas (2) at the inlet of the exhaust heat recovery boiler (1), and at the same time, the amount of exhaust gas introduced into the evaporator (15) is controlled. It is.

  According to the fifth aspect of the present invention, there is a gas circulation in the pipe (19c) for introducing the exhaust gas (2) extracted from the inlet part of the exhaust heat recovery boiler (1) or the inlet part of the denitration device (6) into the evaporator (15). A fan (13) is provided, and when the exhaust heat recovery boiler (1) stops operating, the outlet gas temperature of the evaporator (15) falls below a predetermined temperature (eg, 200 ° C.) or the next exhaust heat recovery boiler (1) The exhaust fan (13) extracted from the inlet part of the exhaust heat recovery boiler (1) is circulated in the exhaust heat recovery boiler (1) at the inlet part of the denitration device (6) by starting the circulation fan (13) when starting The ammonia injection method for an exhaust heat recovery boiler according to claim 4, wherein the method is an ammonia injection method.

(Function)
When the combined cycled plant including the exhaust heat recovery boiler (1) is stopped (DSS and WSS), the gas circulation fan (13) can be started according to any control set temperature condition. And the operation of stopping and circulating the combustion exhaust gas (2) retained at a high temperature in the exhaust heat recovery boiler (1) between the exhaust heat recovery boiler (1) and the denitration device (6). As shown in the prior art evaporator (15) outlet temperature curve after stopping the boiler (1) shown, the outlet gas temperature of the evaporator (15) where the temperature drops due to atmospheric diffusion while the gas circulation fan (13) is stopped 3 can be suppressed like the curve of the outlet gas temperature of the evaporator (15) of the present invention after the boiler (1) is stopped as shown in FIG.
As a result, at the next startup of the boiler (1), the temperature difference from the ammonia injection permission condition is smaller than in the conventional case, so that ammonia injection in a short time can be realized.

  Depending on the control set temperature of the ammonia injection permission condition, the gas circulation fan (13) is started earlier than before, and the hot exhaust gas (2) is taken into the ammonia injection device (21), so that ammonia can be injected in a shorter time. It is also possible to establish a movable temperature condition, and it is possible to shorten the time during which the denitration operation can be performed after the exhaust heat recovery boiler (1) is started.

  In addition, when the plant containing the exhaust heat recovery boiler (1) stops for a long period of time, such as during regular inspections, the gas temperature in the exhaust heat recovery boiler (1) also decreases during the stop period. In the configuration in which the temperature of the ammonia injection device (21) is increased using heat, the effectiveness is low, and it is not necessary to start the gas circulation fan (13) in preparation for the next start of the boiler (1). Therefore, when the operation of the boiler plant (1) is stopped for a long time, it can be selected not to start the gas circulation fan (13) when the boiler (1) is stopped.

  Further, during the steady operation or long-term continuous operation of the exhaust heat recovery boiler (1), the combustion exhaust gas (2) at the inlet of the denitration device (6) is used as a heat source for the evaporation of ammonia water, and the exhaust heat recovery boiler (1). The system for exhaust gas suction can be switched according to the state of the exhaust heat recovery boiler (1) so that the combustion exhaust gas (2) at the inlet of the exhaust heat recovery boiler (1) is used as a heat source for evaporation of ammonia water at the time of startup.

 According to the second aspect of the invention, for example, when the temperature in the gas circulation pipe (19c) rises abnormally, the first switching damper (9a) on the high temperature side is closed and the second switching damper (9b) is opened. Then, a relatively low temperature gas (2) at the inlet of the denitration device (6) is introduced into the gas circulation pipe (19c) for cooling, and the evaporator (15) is operated so as to keep the warming temperature constant. As a result, the warming operation of the gas circulation pipe (19c) for warming up the gas circulation fan (13) is continued without affecting the heat resistance of the gas circulation fan (13), and the gas circulation fan ( In combination with the activation of 13), the conditions for injecting ammonia water into the evaporator (15) and injecting the evaporated ammonia to the upstream side of the denitration device (6) through the ammonia spraying part (5) are established.

  According to the third and fifth aspects of the present invention, when the operation of the exhaust heat recovery boiler (1) is stopped, it depends on the next start mode of the exhaust heat recovery boiler (1) or the outlet gas temperature of the evaporator (15). The gas circulation fan (13) provided in the gas circulation pipe (19c) is started / stopped, and the gas circulation fan (13) is started to remove the high temperature staying exhaust gas (2) in the exhaust heat recovery boiler (1). By circulating in the ammonia injection device (21), it is possible to suppress a decrease in the temperature of the ammonia injection device (21) as a whole, and to shorten the start-up time in the next activation of the exhaust heat recovery boiler (1).

According to the first and fourth aspects of the invention, when the boiler (1) is started, the difference between the gas temperature satisfying the ammonia injection permission condition and the boiler exhaust gas temperature is smaller than that in the prior art. Ammonia injection can be realized, and it is possible to shorten the denitration operation possible time after the start of the exhaust heat recovery boiler (1) and reduce the amount of air pollutants discharged when the boiler (1) is started.
Further, during the steady operation or long-term continuous operation of the exhaust heat recovery boiler (1), the combustion exhaust gas (2) at the inlet of the denitration device (6) is used as a heat source for evaporating ammonia water, thereby maintaining the low output. There is an effect of relaxation of control.

  According to the invention described in claim 2, since ammonia can be injected into the exhaust heat recovery boiler (1) in a timely manner without a time delay, the problem of exceeding the environmental regulation value of the nitrogen oxide concentration in the exhaust gas at start-up is solved. This reduces the burden on the operator and makes it possible to reduce the maintenance and ensure stable operation.

  According to the third and fifth aspects of the present invention, when the operation of the exhaust heat recovery boiler (1) is stopped, the start-up time can be shortened in the next activation of the exhaust heat recovery boiler (1), and the gas Only the exhaust gas (2) of the exhaust heat recovery boiler (1) is used for warming up the circulation pipe (19c), the electricity consumption is unnecessary, and the system is simple. The load is low, and stable operation is possible with reduced maintenance.

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a system diagram in which combustion exhaust gas 2 is used in an ammonia injection device 21 for a denitration device 6 using ammonia water in a combined cycle plant including an exhaust heat recovery boiler 1 of the present embodiment. In the system diagram shown in FIG. 1, members having the same functions as those in the system diagram of the prior art shown in FIG.

  The exhaust gas 2 introduced into the exhaust heat recovery boiler 1 is supplied to the denitration device 6 together with ammonia from the ammonia injection nozzle 5 via the superheater 3 or an evaporator (not shown) arranged on the downstream side of the superheater 3. The denitrated gas 2 ′ is discharged from the chimney 4.

  Exhaust gas extraction pipes 19a and 19b for extracting a part of the exhaust gas 2 flowing in the exhaust heat recovery boiler 1 are provided in the ammonia injection device 21 of the present embodiment disposed adjacent to the exhaust heat recovery boiler 1. The exhaust gas extraction pipes 19a and 19b are respectively provided at the inlet portion of the exhaust heat recovery boiler 1 and the downstream side of the superheater 3. The exhaust gas extraction pipes 19a and 19b are provided in the exhaust gas extraction pipes 19a and 19b, respectively. The switching dampers 9a and 9b merge at the downstream side gas circulation pipe 19c. A switching damper 12, a gas circulation fan 13, a flow meter 14, and an evaporator 15 are sequentially arranged from the upstream side in the gas circulation pipe 19c.

  Moreover, the opening degree of each switching damper 9a, 9b provided in the exhaust gas extraction pipes 19a, 19b respectively connected to the inlet part of the exhaust heat recovery boiler 1 and the inlet part of the NOx removal device 6 (the downstream side of the superheater 3) is The configuration is controlled by the control device 24 based on the measured values of the thermometers 7 and 8 that detect the exhaust gas temperature inside the exhaust heat recovery boiler 1 at the inlet portion of the exhaust heat recovery boiler 1 and the inlet portion of the denitration device 6. .

  Further, an ammonia water pipe 17 is connected to the evaporator 15, and a plurality of two-fluid nozzles 16 provided inside the evaporator 15 are connected to an ammonia water pipe 17 and an atomizing air pipe 18. As a result, the ammonia water is atomized, and the atomized ammonia water is formed inside the evaporator 15. At this time, an ammonia shut-off valve 10 provided in the ammonia water pipe 17 is provided, and opening and closing of the ammonia shut-off valve 10 detects a gas thermometer 8 at the inlet portion of the denitration device 6 and an evaporator 15 outlet gas temperature. Is controlled by the control device 24 based on the appropriate measured value (about 270 ° C.). The switching damper 12 and the gas circulation fan 13 are also controlled based on the gas temperature at the outlet of the evaporator 15 measured by the thermometer 11 at the outlet of the evaporator 15.

  In the ammonia injection device 21 of the present embodiment having the above-described configuration, the extraction position of the combustion exhaust gas 2 in the exhaust heat recovery boiler 1 is switched by operating the dampers 9a and 9b provided in the exhaust gas extraction pipes 19a and 19b. To control the exhaust gas temperature for heating ammonia water.

After the startup of the boiler plant including the exhaust heat recovery boiler 1, ammonia water can be injected from the ammonia water pipe 17 into the gas turbine exhaust gas 2 in the boiler 1, for example, the exhaust gas temperature on the inlet side of the denitration device 6 When the exhaust gas temperature in the exhaust heat recovery boiler 1 measured by the total 8 becomes about 270 ° C. and the outlet gas temperature of the evaporator 15 measured by the thermometer 11 of the evaporator 15 becomes about 270 ° C. It is. When this condition is satisfied, the control device 24 fully opens the ammonia injection shut-off valve 10 and starts injection of ammonia water into the evaporator 15 to evaporate the ammonia water. The obtained ammonia gas is supplied from the ammonia injection nozzle 5 into the boiler 1. The denitration is started in the denitration device 6.
The above conditions can be achieved in a short time when the boiler plant 1 is activated, and the following operation is performed in the ammonia injection device 21 of the present embodiment in order to shorten the activation time of the denitration device 6.
During normal operation of the exhaust heat recovery boiler 1, the system for sucking the exhaust gas 2 from the inlet of the denitration device 6 that can obtain sufficient exhaust gas temperature conditions for ammonia evaporation, that is, the switching damper 9a of the extraction pipe 19b is fully opened, In order to protect the circulation pipe 19c, the switching damper 9a of the extraction pipe 19a for introducing the high-temperature exhaust gas 2 at the inlet of the exhaust heat recovery boiler 1 into the ammonia injection device 21 is operated in a fully closed state.

  When the high-temperature exhaust gas 2 at the inlet of the exhaust heat recovery boiler 1 is constantly supplied to the ammonia injection device 21, it is necessary to increase the heat resistance temperature of the entire ammonia injection device 21 such as the gas circulation pipe 19 c, the gas circulation fan 13, and the evaporator 15. Therefore, it becomes a factor of considerable equipment cost increase.

  For this reason, in this embodiment, the switching dampers 9a and 9b can be switched so as not to increase the equipment cost. During normal operation, the exhaust gas 2 is introduced from the downstream side of the superheater 3 as in the prior art. Is operated in a system that supplies ammonia to the ammonia injection device 21.

  Further, when the operation of the exhaust heat recovery boiler 1 is stopped, the temperature of the exhaust gas 2 staying in the exhaust heat recovery boiler 1 gradually decreases. Therefore, an evaporator using a higher temperature exhaust gas 2 is used. It is necessary to suppress the temperature drop of 15. For this purpose, the exhaust gas temperature at the inlet of the exhaust heat recovery boiler 1 measured by the exhaust gas thermometer 7 provided at the inlet of the exhaust heat recovery boiler 1 is monitored. The system is switched to a system in which the exhaust gas 2 is sucked into the ammonia injection device 21 from the inlet of the heat recovery boiler 1. That is, by opening the switching damper 9a little by little and conversely closing the switching damper 9b little by little at the same time, a system for sucking the exhaust gas 2 into the ammonia injection device 21 from the exhaust gas 2 at the inlet of the denitration device 6 at normal time is used as an exhaust heat recovery boiler. Switch to exhaust gas 2 at 1 inlet. Finally, the switching damper 9b is closed and the switching damper 9a is fully opened. At this time, the damper 12 is operated while monitoring the gas thermometer 11 at the outlet of the evaporator 15.

  In the initial start-up of the exhaust heat recovery boiler 1, a system is used in which the evaporator 15 is heated using the high-temperature exhaust gas 2 from the inlet of the exhaust heat recovery boiler 1 in the same manner as when the exhaust heat recovery boiler 1 is stopped. As a result, the high-temperature exhaust gas 2 before passing through the superheater 3 can be sent to the ammonia injection device 21 when the exhaust heat recovery boiler 1 is started, and the evaporator 15 can be heated in a shorter time. To protect the gas circulation pipe 19c, the switching damper 9a is closed when the exhaust gas temperature at the inlet of the exhaust heat recovery boiler 1 exceeds a specified value or when the outlet gas temperature of the evaporator 15 rises above a certain value. On the contrary, the switching damper 9b is fully opened, and the system is switched from the inlet of the denitration device 6 to the system into which the exhaust gas 2 is introduced.

  Further, a thermometer 23 is installed in the gas circulation pipe 19c, and when the temperature in the gas circulation pipe 19c rises abnormally, the switching damper 9b is opened, and a relatively low temperature gas at the inlet of the denitration device 6 for cooling. 2 is introduced into the gas circulation pipe 19c and operated so as to keep the warming temperature of the evaporator 15 constant. When the temperature of the gas circulation pipe 19c exceeds the opening operation temperature of the switching damper 12, the switching damper 9a on the high temperature side is closed, and the switching damper 9b is opened based on the closing signal of the switching damper 9a. Let As a result, the warming operation of the gas circulation pipe 19c for warming up the gas circulation fan 13 is continued without affecting the heat resistance of the gas circulation fan 13, and the evaporator is activated within a short period of time. The condition is such that ammonia water is injected into 15 and the evaporated ammonia can be injected into the upstream side of the denitration device 6 via the ammonia injection nozzle 5.

  As described above, the conditions for injecting ammonia into the exhaust heat recovery boiler 1 are established before the ammonia injection start temperature and the standby state is established. Therefore, when the denitration in-service temperature is reached, the exhaust heat recovery boiler is timely without time delay. Since ammonia can be injected into 1, the problem of exceeding the environmental regulation value at the time of start-up can be solved. Further, only the exhaust gas 2 of the exhaust heat recovery boiler 1 is used for warming up the gas circulation pipe 19c, and no electric consumption is required and the system is simple, so the load on the operator is small. This enables stable operation combined with maintenance reduction.

Further, when the exhaust heat recovery boiler 1 is stopped, the switching damper 9b is fully closed, the switching damper 9a is fully opened, and the exhaust gas system to be introduced into the evaporator 15 is switched to the inlet side of the exhaust heat recovery boiler 1 to inject ammonia. Since the high temperature exhaust gas 2 staying inside the exhaust heat recovery boiler 1 does not circulate in the apparatus 21, the gas circulation fan 13 is operated according to the outlet temperature of the evaporator 15 in accordance with the switching operation of the exhaust gas system. When the outlet temperature of the evaporator 15 falls below an appropriate control set temperature (about 200 ° C.), the gas circulation fan 13 is activated and the high-temperature exhaust gas 2 on the inlet side of the exhaust heat recovery boiler 1 is circulated to the ammonia injection device 21. By doing so, it operates so that the temperature fall of the ammonia injection apparatus 21 whole can be suppressed and control control temperature can be maintained.
Since the high-temperature exhaust gas 2 is circulated through the evaporator 15 by the above operation, even when the operation of the exhaust heat recovery boiler 1 is stopped, it is possible to prevent a sudden temperature drop of the evaporator 15 and the exhaust gas flow path on the downstream side of the evaporator 15. it can.

  Further, when the boiler plant is stopped for a long time, the gas circulation fan 13 can be selected not to be activated by mode selection. Further, in order to prevent the gas circulation fan 13 from being damaged due to gas leakage during the operation of the dampers 9a, 9b, 12 and the like, the gas circulation fan when the inlet gas temperature of the exhaust heat recovery boiler 1 becomes a certain value or less. 13 is automatically stopped.

FIG. 3 shows data comparing the relationship between the start time and the outlet gas temperature of the evaporator 15 in the conventional method and the denitration processing of the present method. According to this embodiment, when the operation of the boiler plant 1 is stopped, the gas circulation fan 13 is also stopped. Therefore, the evaporator 15 outlet temperature begins to gradually decrease. When the outlet temperature of the evaporator 15 is lowered to an appropriate control set temperature (the temperature at this time is the temperature in the DSS and WSS modes, about 200 ° C.), the gas circulation fan 13 is restarted and the exhaust heat recovery boiler 1 is in the inlet side. The high temperature exhaust gas 2 is sucked into the ammonia injection device 21 to suppress a decrease in the outlet temperature of the evaporator 15. When the boiler plant 1 is restarted in this manner, the temperature T from the start of the plant to the start of the denitration apparatus is less than the time T ′ from the start of the prior art plant to the start of the denitration apparatus. small.
As described above, according to this embodiment, it is possible to provide the ammonia injection device 21 that is optimal for the exhaust heat recovery boiler plant denitration device 6.

  ADVANTAGE OF THE INVENTION According to this invention, the ammonia injection apparatus 21 suitable for the denitration apparatus of a waste heat recovery boiler plant can be provided.

1 is a system diagram showing an ammonia injection device and an exhaust heat recovery boiler according to an embodiment of the present invention. It is a systematic diagram which shows the ammonia injection device and waste heat recovery boiler of a prior art. It is a figure which shows the comparison of the denitration apparatus operation | movement and starting time in this invention and a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Waste heat recovery boiler 2 Exhaust gas 3 Superheater 4 Chimney 5 Ammonia injection nozzle 6 Denitration device 7, 8, 11, 23 Thermometer 9a, 9b Switching damper 10 Ammonia shut-off valve 12 Switching damper 13 Gas circulation fan 14 Flow meter 15 Evaporator 16 Two-fluid nozzle 17 Ammonia water piping 18 Atomized air piping 19a, 19b Exhaust gas extraction piping 19c Gas circulation piping 21 Ammonia injection device 24 Control device

Claims (5)

A heat transfer tube group that recovers the heat of combustion exhaust gas discharged from the combustion device, a denitration device that reduces nitrogen oxides contained in the exhaust gas to harmless nitrogen and water, and an upstream region of the denitration device With respect to the exhaust heat recovery boiler disposed in the flow path through which the exhaust gas flows with an ammonia spraying part, ammonia water is used as the ammonia source, and the exhaust heat recovery boiler in the exhaust heat recovery boiler is used as a heat source for causing the ammonia water to evaporate. An ammonia injection device for an exhaust heat recovery boiler comprising using exhaust gas,
A first switching damper and a second switching damper are provided in the first pipe, the second pipe, and the pipes respectively for extracting exhaust gas from the inlet part of the exhaust heat recovery boiler and the denitration apparatus inlet part;
Connect the gas circulation pipe connected by joining the two pipes to the denitration device inlet of the exhaust heat recovery boiler,
An evaporator for evaporating ammonia introduced from the ammonia water supply pipe using the exhaust gas as a heat source in the middle of the gas circulation pipe is disposed,
Gas thermometers are arranged at the inlet of the exhaust heat recovery boiler, the inlet of the denitration device and the outlet of the evaporator
Based on the gas temperatures measured by the three gas thermometers, the gas to be introduced into the evaporator is controlled by switching between the first switching damper and the second switching damper, and each of the denitration device inlet and the evaporator outlet is controlled. An ammonia injection device for an exhaust heat recovery boiler, characterized in that a control device is provided for performing control for introducing ammonia water from an ammonia water supply pipe to an evaporator based on each gas temperature measured by a gas thermometer.   A control device that arranges a gas thermometer also in the gas circulation pipe and adjusts the temperature of the exhaust gas introduced into the evaporator by switching the first switching damper and the second switching damper based on the exhaust gas temperature measured by the exhaust gas thermometer. The ammonia injection device for an exhaust heat recovery boiler according to claim 1, wherein the ammonia injection device is provided.   3. The exhaust gas heat recovery boiler for an exhaust heat recovery boiler according to claim 1 or 2, wherein a gas circulation fan is provided in the gas circulation pipe to be started when the evaporator outlet gas temperature becomes a predetermined temperature or lower or when the exhaust heat recovery boiler is started. Ammonia injection device. A heat transfer tube group that recovers the heat of the combustion exhaust gas discharged from the combustion device, a denitration device that reduces nitrogen oxides contained in the exhaust gas to harmless nitrogen and water, and an ammonia spray provided upstream of the denitration device For the exhaust heat recovery boiler having a section, the exhaust gas extracted from the inlet part of the exhaust heat recovery boiler or the inlet part of the denitration apparatus is led to an evaporator, and the ammonia water supplied into the evaporator is evaporated by the exhaust gas. An ammonia injection method for a waste heat recovery boiler that supplies ammonia obtained in this way to the denitration device inlet of the exhaust heat recovery boiler,
When the exhaust heat recovery boiler starts up, the temperature of the evaporator is increased by introducing the relatively high temperature exhaust gas extracted from the inlet of the exhaust heat recovery boiler to the evaporator.
When the exhaust gas at the inlet of the exhaust heat recovery boiler reaches a predetermined temperature or the gas temperature at the evaporator outlet reaches a predetermined temperature, the exhaust gas introduced into the evaporator is changed from the exhaust gas at the inlet of the exhaust heat recovery boiler to the exhaust gas at the inlet of the denitration device. switching,
When the exhaust gas temperature at the inlet of the denitration device and the gas temperature at the evaporator outlet exceed the specified temperatures, ammonia water is introduced into the evaporator, and the exhaust gas is evaporated while gradually increasing the amount of exhaust gas guided to the evaporator based on the gas temperature at the evaporator outlet. Supply ammonia to the denitration device inlet of the exhaust heat recovery boiler,
Oite during shutdown of the heat recovery steam generator, the temperature of the exhaust gas inlet portion of the exhaust heat recovery boiler, the exhaust gas when it becomes less than the heat resistance temperature of the pipe to be introduced to the evaporator, denitration unit exhaust gas to be introduced into the evaporator An ammonia injection method for an exhaust heat recovery boiler, characterized in that the exhaust gas at the inlet is switched to the exhaust gas at the inlet of the exhaust heat recovery boiler and at the same time the amount of exhaust gas introduced into the evaporator is controlled.   When the exhaust gas extracted from the exhaust heat recovery boiler inlet or the denitration equipment inlet is installed in the evaporator, a gas circulation fan is installed. When the exhaust heat recovery boiler stops operating, the evaporator outlet gas temperature falls below the specified temperature. The exhaust gas extracted from the inlet portion of the exhaust heat recovery boiler is circulated in the exhaust heat recovery boiler at the inlet portion of the denitration device by starting the circulation fan when the exhaust heat recovery boiler is started next time. An ammonia injection method for the exhaust heat recovery boiler as described.

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