JP2012093013A - Boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a boiler inhibiting ammonia of a reducing agent injected into a boiler furnace from flowing out of the furnace and surely reducing NOx in exhaust gas.SOLUTION: The boiler includes a plurality of burners burning fossil fuel at a stoichiometric air-fuel ratio or less, and an after air nozzle on a downstream side of the burners for supplying combustion air of a deficiency in the burners into the furnace. In the boiler, a reducing agent injection nozzle with at least one outlet hole is arranged in the wall face of the furnace in a region between the burner situated at the uppermost stage and the after air nozzle, and a mixed fluid of a fluid containing the reducing agent and a fluid containing oxygen is supplied into the furnace from the outlet hole of the reducing agent injection nozzle.

Description

  The present invention relates to a boiler that burns fossil fuel such as pulverized coal or petroleum, and particularly relates to a boiler that reduces nitrogen oxides (NOx) by introducing a reducing agent into a furnace of the boiler.

  In a boiler that burns fossil fuel, it is required to suppress the concentration of NOx contained in the combustion gas generated when the fuel is burned in the boiler, and a two-stage combustion method is generally adopted as a countermeasure.

  As a boiler to which the two-stage combustion method is applied, for example, as disclosed in Japanese Patent Application Laid-Open No. 9-310807, a pulverized coal burner is disposed in a furnace of a pulverized coal burning boiler, and an after-air nozzle is provided downstream of the pulverized coal burner. The pulverized coal burner is supplied with fuel pulverized coal and combustion air, and only the combustion air is supplied from the after-air nozzle to burn the fuel pulverized coal.

Furthermore, a non-catalytic denitration method is used for the purpose of reducing NOx in the boiler furnace. For example, as disclosed in Japanese Patent Application Laid-Open No. 2006-64291, ammonia as a reducing agent is injected into a region where the gas temperature is about 1000 ° C. in the oxidation region downstream of the after air, and NOx is reduced to N ₂ to reduce NOx. A method for reducing the above is disclosed.

  Also, WO2005 / 001338 discloses a nozzle structure that uniformly blows urea into the furnace.

Japanese Patent Laid-Open No. 9-310807 JP 2006-64291 A WO2005 / 001338

  In the non-catalytic denitration method in which the reducing agent is injected into the oxidation region downstream of the after air, the temperature range in which NOx is reduced is narrow, so the denitration efficiency is poor in a boiler having a temperature distribution. Further, when the amount of reducing agent input is increased to reduce NOx, unreacted ammonia flows out of the furnace.

Ammonia reacts with sulfur trioxide (SO ₃ ) in the combustion gas to form ammonium sulfate, adheres to the air heater, causes clogging, and reacts with hydrogen chloride to produce white smoke. Further, in the prior art in which urea is injected near the burner, detailed denitration conditions such as the urea injection position and the gas temperature at the injection position are not clear.

  An object of the present invention is to provide a boiler that can suppress the outflow of ammonia, which is a reducing agent injected into a boiler furnace, to the outside of the furnace and reliably reduce NOx in exhaust gas.

  The boiler of the present invention is a boiler comprising a plurality of burners for burning fossil fuel at a theoretical air ratio or less, and an after-air nozzle for supplying combustion air in the burner to a downstream side of the burner into the furnace. A reducing agent injection nozzle having at least one outlet hole is disposed on a wall surface of the furnace in a region between the burner located at the uppermost stage and the after air nozzle, and the reduction is performed from the outlet hole of the reducing agent injection nozzle. A mixed fluid of a fluid containing an agent and a fluid containing oxygen is configured to be supplied into the furnace.

  Further, the boiler of the present invention includes a plurality of burners for burning fossil fuel at a theoretical air ratio or less, and an after-air nozzle for supplying combustion air in the burner at a downstream side of the burner into the furnace. In the boiler, a reducing agent injection nozzle having a plurality of outlet holes is disposed on the wall surface of the furnace in the region between the burner located at the uppermost stage and the after air nozzle, and the fluid containing the reducing agent and oxygen are supplied. The contained fluid is supplied to the furnace from different outlet holes of the reducing agent injection nozzle, respectively.

  ADVANTAGE OF THE INVENTION According to this invention, even if it introduce | transduces a reducing agent in a boiler furnace, it suppresses discharge | emission of ammonia outside a furnace, and implement | achieves the boiler which made it possible to reduce NOx in exhaust gas reliably. it can.

BRIEF DESCRIPTION OF THE DRAWINGS The block diagram which shows schematic structure of the boiler which is 1st Example of this invention. The block diagram which shows an experimental furnace. _NH 3 / NOx molar ratio and characteristic diagram showing the relationship between the outlet NOx of this embodiment. NOx in the present embodiment, characteristic diagram showing the relationship between the NH ₃ remaining rate. _O 2 / NH ₃ molar ratio and the characteristic diagram showing the relationship between the outlet NOx of this embodiment. The block diagram which shows schematic structure of the boiler which is 2nd Example of this invention. The block diagram which shows schematic structure of the boiler which is 3rd Example of this invention. The block diagram which shows schematic structure of the boiler which is 4th Example of this invention. An example which shows the reducing agent injection | pouring nozzle used in 1st Example thru | or 4th Example. Another example showing a reducing agent injection nozzle used in the first to fourth embodiments. The block diagram which shows schematic structure of the boiler which is 5th Example of this invention.

  The boiler which is an Example of this invention is demonstrated below with reference to drawings.

  The boiler which is 1st Example of this invention is demonstrated using FIG. In the boiler 50 according to the first embodiment of the present invention shown in FIG. 1, fossil fuel such as pulverized coal or petroleum and combustion air are both put on the wall surface of the lower part of the furnace 1 constituting the boiler 50. A plurality of burners 2 to be supplied and combusted are installed in a plurality of stages in the vertical direction, and combustion air is supplied from the burner 2 to the furnace 1 in an amount equal to or less than the theoretical air ratio required for complete combustion of the fuel. The fuel is burned in the state of air shortage by supplying it into the inside, and NOx generated by combustion by the burner 2 is reduced to nitrogen to suppress generation of NOx contained in the burner part combustion gas 5 generated in the furnace 2. .

  An after air nozzle 3 for supplying combustion air into the furnace 1 as the after air is installed on the wall surface of the upper portion of the furnace 1 located on the downstream side of the combustion gas with respect to the burner 2. The exhaust gas 6 completely burned in the furnace 1 by the after air 7 supplied into the furnace 1 from the after air nozzle 3 passes through the heat exchanger 8 installed on the downstream side of the furnace 1 of the boiler 50 and passes through the heat exchanger 8. Steam is generated at 8 and then discharged through the flue 9 from the chimney 10 to the atmosphere.

A reducing agent that reduces NOx contained in the burner portion combustion gas 5 to nitrogen (N ₂ ) in a region between the burner 2 and the after air nozzle 3 on the wall surface of the furnace 1 constituting the boiler 50 of the present embodiment. Is disposed in the furnace 1. In this embodiment, the reducing agent injected into the furnace 1 from the reducing agent injection nozzle 4 is ammonia gas. Although only one reducing agent injection nozzle 4 is shown in the embodiment shown in FIG. 1, a plurality of the reducing agent injection nozzles 4 are used in order to uniformly mix the reducing agent with the burner part combustion gas 5. It is desirable to install.

  The reducing agent injection nozzle 4 is connected to a reducing agent supply system 18 that supplies a fluid containing ammonia gas as a reducing agent and an air supply system 14 that supplies air. The reducing agent supply system 18 is configured to supply ammonia gas as a reducing agent from the ammonia gas tank 15, and the supplied ammonia gas flow rate is a flow rate provided in the reducing agent supply system 18 by a control signal 16 from the control device 40. The opening amount of the control valve 17 is operated to supply a necessary amount of ammonia gas flow when necessary and injected into the furnace 1 from the reducing agent injection nozzle 4.

  The reducing agent stored in the ammonia gas tank 15 may be not only ammonia gas but also ammonia gas mixed and diluted with an inert gas such as nitrogen or argon. Further, the inert gas may be mixed with the reducing agent supply system 18 through another system to dilute the ammonia gas (not shown).

  Air is supplied from the blower 12 to the air supply system 14, and the supplied air flow rate is necessary when necessary by operating the opening degree of the flow control valve 13 provided in the air supply system 14 by the control signal 11 from the control device 40. Is supplied from the reducing agent injection nozzle 4 into the furnace 1.

  In order to determine the conditions for efficiently denitrating NOx contained in the burner part combustion gas 5 by injecting the reducing agent into the furnace 1 from the reducing agent injection nozzle 4, a combustion experiment was performed using the experimental furnace 60 shown in FIG. 2. .

The experimental furnace 60 of FIG. 2 performed two-stage combustion in the same manner as the actual boiler, with the burner 2 disposed at the lower part of the furnace 1 and the after air nozzle 3 disposed downstream of the burner 2. Propane was used as the fuel supplied from the burner 2 and burned. A reducing agent injection nozzle 4 for injecting a reducing agent is arranged in a region between the burner 2 and the after air nozzle 3 which is the wall surface of the furnace 1.
A reducing agent supply system 18 that supplies ammonia gas and an air supply system 14 that supplies air are connected to the reducing agent injection nozzle 4. The exhaust gas 6 completely burned in the furnace 1 by the after air 7 supplied into the furnace 1 from the after air nozzle 3 is cooled by the heat exchanger 33 and released to the outdoors. The concentration of NOx at the outlet of the furnace 1 was measured at a position 32 on the downstream side where the reaction was stopped after being sufficiently cooled downstream of the heat exchanger 33.

  The optimum denitration conditions will be described below from the results of combustion experiments in the experimental furnace 60.

FIG. 3 shows the influence of the ambient gas temperature at which ammonia is injected as a reducing agent in the experimental furnace 60 shown in FIG. The horizontal axis is the nozzle NH ₃ / NOx molar ratio, and the vertical axis is the outlet NOx. The outlet NOx is shown on the basis of no NH ₃ injection.

The ambient gas temperature was measured at a position 30 in the furnace 1 in the experimental furnace 60 of FIG. If the gas temperature is less than 1200 ° C., NOx in the exhaust gas 6 does not decrease even if NH ₃ is injected, and a gas temperature of 1200 ° C. or higher is necessary for denitration of NOx in the exhaust gas 6. The higher the temperature, the better the thermal decomposition of NH ₃ , so the higher the combustion gas temperature at the position of the reducing agent injection nozzle 4, the better.

  In conventional non-catalytic denitration, NOx is reduced only in a narrow temperature range of about 800 to 900 ° C. in the oxidation region in the furnace 1 downstream of the after air nozzle 3. Ammonia may be injected into the temperature region. The flame temperature of the burner portion is about 1600 ° C. or higher, and the gas temperature is high in the reduction region of the burner 2 and the after air nozzle 3.

Next, the amount of NH ₃ injected, as shown in FIG. 3, NOx is minimized in the vicinity of the NH ₃ / NOx molar ratio of 1 to 2, and the NOx tends to increase as the NH ₃ / NOx molar ratio increases. .

The range of the NH ₃ / NOx molar ratio in which NOx in the exhaust gas 6 is reduced is in the range of 0.5 to 3.0 indicated by L, and the optimum value is in the range of 1.0 to 2.0.

Here, the NOx mole on the horizontal axis was calculated from the average NOx concentration at the position 31 in the furnace 1 in the upstream region of the reducing agent injection nozzle 4 shown in FIG. Also in the boiler of the embodiment shown in FIG. 1, NOx in the exhaust gas 6 is reduced by injecting the amount of NH _{3 in the} range L shown in FIG. 3 into the furnace 1 from the reducing agent injection nozzle 4.

  By the way, in the reduction area in the furnace 1 on the downstream side of the burner 2 and the upstream side of the after-air nozzle 3, combustion is caused by air shortage, and this is an oxygen shortage area. In the present invention, ammonia as a reducing agent is injected into the furnace 1 from the outside by the reducing agent injection nozzle 4 in the reduction zone, thereby increasing the reducing agent and reducing NOx in the exhaust gas 6.

Under reducing zone the ammonia will react with OH radicals, NH ₂ radical becomes NH ₂ radicals react with NO, (1) formula, is reduced to nitrogen (N2) of NO as in (2) below.

NH ₃ + OH → NH ₂ + H ₂ O (1)
NH ₂ + NO → N ₂ + H ₂ O (2)
As can be seen from the above formula, in order to reduce NO to nitrogen, it is important to react with OH radicals to generate NH ₂ radicals.

  By the way, the OH radical concentration in the reduction region depends on the burner air ratio, and the higher the burner air ratio, that is, the more air supplied to the burner part, the more OH radicals are generated.

FIG. 4 shows the residual ratio of NOx and NH ₃ after ammonia injection due to the difference in the reduction zone. Gas sampling was performed in the space in the reduction zone immediately upstream of the after-air nozzle 3 in the experimental furnace 60 of FIG. 2, and NOx and NH ₃ concentrations were measured. For NOx, the NOx concentration when NH ₃ was not injected was taken as 100%, and the residual rate was calculated from the NOx concentration at the measurement position. For NH _3, the concentration at which NH ₃ was injected was set to 100%, and the residual ratio was calculated from the NH ₃ concentration at the measurement position. The amount of ammonia injected was equimolar with the NOx mole optimal for denitration. The weak reduction region on the horizontal axis shows a case where the burner air ratio is higher than 0.8, and the strong reduction region shows a case where the burner air ratio is 0.8 or less.

As can be understood from FIG. 4, it is shown that NH ₃ remains without being decomposed in the strong reduction region as compared with the weak reduction region. NH ₃ remaining in the reduction zone is oxidized by the air supplied from the after-air nozzle 3 and converted to NOx. Therefore, if NH ₃ remains at a high concentration in the reduction zone, the NOx removal rate decreases because the outlet NOx increases.

This is because the OH radical is small in the strong reduction region as described above. FIG. 4 shows the remaining rate when air is added. By adding a small amount of O ₂ (oxygen) under the condition of a strong reduction region and increasing OH radicals, the decomposition of NH ₃ is promoted, and the residual rate of NH ₃ is lowered. Therefore, the NOx conversion rate in the after-air portion can be reduced and the denitration effect can be enhanced.

FIG. 5 shows the influence of O ₂ injection. A small amount of air was injected at the time of injection of equimolar amounts of NH ₃ and NOx under the conditions of the strong reduction region. As shown in FIG. 5, it can be seen that NOx is minimized when the O ₂ / NH ₃ molar ratio is around 1.0. The range of 0.5 to 1.5 indicated by M in the figure is the optimum range of the O ₂ injection amount. By injecting a small amount of oxygen even in the strong reduction region in this way, OH radicals are increased, decomposition of NH ₃ is promoted, and outlet NOx is reduced.

In the experiment, the condition is a strong reduction region, but the effect of promoting the decomposition of NH ₃ by injecting a small amount of oxygen is the same even in the weak reduction region. As injection volume of _{O 2} even in the boiler of the embodiment of FIG. 1 is the optimum range of range of _O 2 / NH ₃ 0.5 to 1.5 as described above in a molar ratio, in the air through the air supply line 14 NOx is reduced by injecting air containing O ₂ into the furnace 1.

As described above, according to the boiler of this embodiment, the opening degree of the flow control valve 17 installed in the reducing agent supply system 18 is controlled by the command signal from the control device 40 and the flow control valve installed in the intake supply system 14. by controlling the 13 opening of the injection amount of the NH ₃ in the range showing the NH ₃ in FIG. 3 described above _is, NH 3 / NOx molar ratio range of 0.5 to 3.0 as described above, the optimum the range with adjusted to the range of 1.0 to 2.0, injection volume of _{O 2} and _{O 2} is the optimum range shown in FIG. 5 described above is described above in _O 2 / NH ₃ molar ratio By adjusting to be in the range of 0.5 to 1.5 and injecting it into the reduction zone in the furnace 1, NOx in the exhaust gas 6 can be efficiently reduced. Further, the NH ₃ injection position in the boiler of the present embodiment is upstream of the after air nozzle 3, and unreacted NH ₃ is oxidized by the air of the after air 7 and converted into NOx, so that the outflow of NH ₃ to the outside of the furnace is prevented. Absent.

Therefore, since no ammonia is present in the combustion gas 6, the air heater (not shown) disposed on the downstream side of the furnace 1 is not blocked and white smoke is not generated. Further, it is sufficient to inject a small amount of oxygen contained in the air or the exhaust gas 6 without injecting expensive chemicals or the like for promoting the decomposition of NH ₃ , and an effect can be obtained at low cost.

  According to the present embodiment, even if a reducing agent is introduced into the boiler furnace, ammonia is prevented from being discharged outside the furnace, and a boiler capable of reliably reducing NOx in the exhaust gas is realized. Can do.

  Next, the boiler 50 which is 1st Example of this invention is demonstrated using FIG. The boiler 50 according to the second embodiment of the present invention shown in FIG. 6 has the same basic configuration as the boiler according to the first embodiment shown in FIG. The differences will be described below.

  In the boiler 50 of this embodiment shown in FIG. 6, an exhaust gas supply system 23 that supplies a part of the exhaust gas 6 to the reducing agent injection nozzle 4 via the branch system 19 branched from the flue 9 is connected. A blower 20 is installed in the exhaust gas supply system 23, and a part of the exhaust gas 6 containing oxygen is sucked from the branch system 19 connected to the flue 9, and the control from the control device 40 is performed as in the first embodiment. The signal 21 adjusts the opening degree of the flow control valve 22 provided in the exhaust gas supply system 23 to control the supply amount of the exhaust gas, and the exhaust gas 6 containing oxygen is supplied to the reducing agent injection nozzle 4 through the exhaust gas supply system 23. It is supplied and injected into the furnace 1.

  By the way, the oxygen concentration contained in the exhaust gas 6 is about 2 to 3%, which is about 1/10 of the oxygen concentration of air 21%. When supplying the same oxygen concentration, the exhaust gas 6 has a flow rate about 10 times that of air. Therefore, compared with the air supply in the boiler of 1st Example, since the flow volume of the fluid containing the oxygen inject | poured in the furnace 1 from the said reducing agent injection | pouring nozzle 4 increases, momentum increases and the burner part in the furnace 1 increases. Mixing with the burner part combustion gas 5 which rises from is accelerated | stimulated.

Also in the boiler 50 of the present embodiment, the opening degree of the flow control valve 17 installed in the reducing agent supply system 18 is controlled by the command signal 16 from the control device 40, and also via the branch system 19 branched from the flue 9. Te by controlling the opening degree of the flow rate adjusting valve 22 installed in an exhaust gas supply system 23 for supplying a part of exhaust gas 6, the injection amount of the NH ₃ in the range showing the NH ₃ in FIG. 3 described above, NH ₃ / NOx molar ratio was adjusted to the above-mentioned range of 0.5 to 3.0, and the optimum range was 1.0 to 2.0, and O ₂ was optimized as shown in FIG. by injection volume of O ₂ is in the range injects adjusted to be in the range of 0.5 to 1.5 as described above with O _{2 /} NH ₃ molar ratio in the reduction zone of the furnace 1, efficient exhaust gas NOx in 6 can be reduced.

Further, the NH ₃ injection position in the boiler of the present embodiment is upstream of the after air nozzle 3, and unreacted NH ₃ is oxidized by the air of the after air 7 and converted into NOx, so that the outflow of NH ₃ to the outside of the furnace is prevented. Absent. Therefore, since no ammonia is present in the combustion gas 6, the air heater (not shown) disposed on the downstream side of the furnace 1 is not blocked and white smoke is not generated.

  According to the boiler of the present embodiment, the same effect as that of the boiler of the first embodiment is obtained, and further, mixing of the reducing agent ammonia and the combustion gas 5 is promoted and mixed uniformly in a short time. There is a merit that the NOx reduction rate of NO increases.

  According to the present embodiment, even if a reducing agent is introduced into the boiler furnace, ammonia is prevented from being discharged outside the furnace, and a boiler capable of reliably reducing NOx in the exhaust gas is realized. Can do.

  Next, the boiler which is 3rd Example of this invention is demonstrated using FIG. The boiler 50 according to the third embodiment of the present invention shown in FIG. 7 has the same basic configuration as the boiler according to the first embodiment shown in FIG. The differences will be described below.

  The boiler 50 of this embodiment shown in FIG. 7 is connected to an air supply system 14 for supplying air in addition to an exhaust gas supply system 23 for supplying a part of the exhaust gas 6 to the reducing agent injection nozzle 4. The method for supplying the reducing agent is the same as in the first embodiment.

Also in the boiler 50 of the present embodiment, the opening degree of the flow control valve 17 installed in the reducing agent supply system 18 is controlled by a command signal from the control device 40, and via the branch system 19 branched from the flue 9. By controlling the opening degree of the flow control valve 22 installed in the exhaust gas supply system 23 that supplies a part of the exhaust gas 6 and the opening degree of the flow control valve 13 to the air supply system 14 that supplies oxygen-containing air, respectively. , injection volume of NH ₃ in the range showing the NH ₃ in FIG. 3 described above _is, NH 3 / NOx molar ratio range of 0.5 to 3.0 as described above, the as optimal range 1.0 to 2. with adjusted to the range of 0, 0.5 to 1.5 range of the injection amount of _{O 2} to _{O 2} is optimum range shown in FIG. 5 described above is described above in _O 2 / NH ₃ molar ratio Adjusted so that Doing, it is possible to reduce the NOx efficiently in exhaust gas 6.

Further, the NH ₃ injection position in the boiler of the present embodiment is upstream of the after air nozzle 3, and unreacted NH ₃ is oxidized by the air of the after air 7 and converted into NOx, so that the outflow of NH ₃ to the outside of the furnace is prevented. Absent. Therefore, since no ammonia is present in the combustion gas 6, the air heater (not shown) disposed on the downstream side of the furnace 1 is not blocked and white smoke is not generated.

  That is, both the air containing oxygen and the exhaust gas 6 containing oxygen are mixed and supplied to the reducing agent injection nozzle 4, thereby adjusting the flow rate of the fluid containing oxygen supplied from the reducing agent injection nozzle 4 over a wide range. Even when the load of the boiler 50 fluctuates and the flow rate of the combustion gas 5 changes, the opening degree of the flow rate control valves 13 and 22 can be adjusted to an optimum flow rate for mixing with the combustion gas 5 and efficiently. It becomes possible to promote mixing.

  According to this embodiment, the same effect as that of the boiler of the first embodiment can be obtained, and furthermore, the reducing agent injected from the reducing agent injection nozzle can be efficiently mixed with the combustion gas 5 in response to the load fluctuation of the boiler. There is an advantage that the NOx reduction rate increases.

  According to the present embodiment, even if a reducing agent is introduced into the boiler furnace, ammonia is prevented from being discharged outside the furnace, and a boiler capable of reliably reducing NOx in the exhaust gas is realized. Can do.

  Next, the boiler which is 4th Example of this invention is demonstrated using FIG. The boiler 50 according to the fourth embodiment of the present invention shown in FIG. 8 has the same basic configuration as the boiler according to the first embodiment shown in FIG. The differences will be described below.

  In the boiler 50 of the present embodiment shown in FIG. 8, the after air nozzle 3 of the furnace 1 is configured in two stages up and down. According to this configuration, after-air (air) can be supplied from the after-air nozzle 3 into the furnace 1 in a more uniformly dispersed manner, so that mixing of the after-air and the combustion gas 5 is promoted, and complete combustion can be performed quickly. In the case of CO or coal combustion in the exhaust gas 6, the unburned content is reduced and the combustion efficiency is increased.

Also in the boiler 50 of the present embodiment, the opening degree of the flow control valve 17 installed in the reducing agent supply system 18 is controlled by a command signal from the control device 40, and via the branch system 19 branched from the flue 9. By controlling the opening degree of the flow control valve 22 installed in the exhaust gas supply system 23 that supplies a part of the exhaust gas 6 and the opening degree of the flow control valve 13 to the air supply system 14 that supplies oxygen-containing air, respectively. , injection volume of NH ₃ in the range showing the NH ₃ in FIG. 3 described above _is, NH 3 / NOx molar ratio range of 0.5 to 3.0 as described above, the as optimal range 1.0 to 2. with adjusted to the range of 0, 0.5 to 1.5 range of the injection amount of _{O 2} to _{O 2} is optimum range shown in FIG. 5 described above is described above in _O 2 / NH ₃ molar ratio Adjusted so that Doing, it is possible to reduce the NOx efficiently in exhaust gas 6.

Further, the NH ₃ injection position in the boiler of the present embodiment is upstream of the after air nozzle 3, and unreacted NH ₃ is oxidized by the air of the after air 7 and converted into NOx, so that the outflow of NH ₃ to the outside of the furnace is prevented. Absent. Therefore, since no ammonia is present in the combustion gas 6, the air heater (not shown) disposed on the downstream side of the furnace 1 is not blocked and white smoke is not generated.

  This configuration in which the after air nozzles 3 are arranged in two stages in the vertical direction can be applied to the boilers of the first to third embodiments, and the same effect can be obtained.

  According to the boiler 50 of the present embodiment, not only the same effects as the first to third embodiments can be obtained, but also the CO and unburned components in the exhaust gas can be reduced, and the combustion efficiency is improved. There is.

  Next, FIGS. 9 and 10 show examples of the structure of the reducing agent injection nozzle 4 applied to the boilers of the first to fourth embodiments. The reducing agent injection nozzle 4 shown in FIG. 9 has a single nozzle outlet hole 41 for jetting the reducing agent fluid 42, and the reducing agent injection nozzle 4 shown in FIG. 10 jets the reducing agent fluid 42. The structure in the case of having two nozzle outlet holes of the nozzle outlet hole 41a and the nozzle outlet hole 41b to be shown is shown.

  Since the reducing agent injection nozzle 4 shown in FIGS. 9 and 10 is installed in a high temperature field, a flow path through which the cooling water 43 flows is formed inside the reducing agent injection nozzle 4 so that the nozzle does not melt.

  Further, the reducing agent injection nozzle 4 shown in FIG. 10 may supply the same fluid in which the reducing agent and oxygen are mixed to the two nozzle outlet holes of the nozzle outlet hole 41a and the nozzle outlet hole 41b, or You may make it supply separately the fluid containing a reducing agent, and the fluid containing oxygen.

  According to the present embodiment, even if a reducing agent is introduced into the boiler furnace, ammonia is prevented from being discharged outside the furnace, and a boiler capable of reliably reducing NOx in the exhaust gas is realized. Can do.

  Next, the boiler which is 5th Example of this invention is demonstrated using FIG. The boiler 50 according to the fifth embodiment of the present invention shown in FIG. 11 has the same basic configuration as the boiler of the first embodiment shown in FIG. The differences will be described below.

In the boiler 50 of the present embodiment shown in FIG. 11, a reducing agent supply system 28 that supplies ammonia water or urea water instead of ammonia gas as a reducing agent is connected to the reducing agent injection nozzle 4. Ammonia water or urea water is fed from the reducing agent tank 24 by the pump 25, and the flow rate is controlled by the flow rate adjusting valve 27 provided in the reducing agent supply system 28. The opening degree of the flow control valve 27 is operated by a control signal 26 from the control device 40.
It is desirable that the liquid droplets injected into the furnace 1 from the reducing agent injection nozzle 4 are not vaporized quickly and are mixed with the combustion gas 5 without being refined so that the reducing agent reaches the center of the furnace.
A one-fluid nozzle and a two-fluid nozzle may be used by using the nozzle structure of the reducing agent injection nozzle 4 shown in FIGS.

In the case of using a one-fluid nozzle, it is desirable that the liquid containing the reducing agent is pressurized with a pump or the like and supplied to the one-fluid nozzle, and the gas containing oxygen is supplied from another nozzle.
When a two-fluid nozzle is used, a liquid containing a reducing agent and a gas containing oxygen are supplied to the two-fluid nozzle by increasing the pressure to a predetermined pressure, and the gas and liquid are mixed and injected into the furnace by the nozzle. . In the two-fluid nozzle, the smaller the amount of gas with respect to the amount of liquid, the coarser the droplet. Therefore, by adjusting the supply amount of the exhaust gas 6 having a low air and oxygen concentration, it can be injected into the furnace with a desired droplet diameter, and the mixing of the reducing agent and the combustion gas is promoted.

  By the way, urea water is an aqueous solution in which urea is dissolved in water, and is safe and easy to handle. Urea water is decomposed into ammonia as shown in formula (3) in a high temperature field, and acts as a reducing agent.

CO (NH ₂ ) 2 + H ₂ O → 2NH ₃ + CO ₂ (3)
Further, since the aqueous solution is injected into the furnace, the combustion gas temperature is lowered by the latent heat of evaporation of water, thermal NOx generated by after-air combustion is reduced, and the outlet NOx is lowered.

Also in the boiler 50 of the present embodiment, the opening degree of the flow control valve 27 installed in the reducing agent supply system 28 for supplying ammonia water or urea water from the reducing agent tank 24 is controlled by a command signal from the control device 40, and To the air supply system 14 for supplying air containing oxygen and the opening degree of the flow control valve 22 installed in the exhaust gas supply system 23 for supplying a part of the exhaust gas 6 via the branch system 19 branched from the flue 9 by controlling the degree of opening of the flow control valve 13, respectively, the injection amount of the NH ₃ in the range showing the NH ₃ in FIG. 3 described above _is described above in NH 3 / NOx molar ratio from 0.5 to 3.0 range, as well as adjusted to the range of 1.0 to 2.0 as the optimum range, the injection quantity of _{O 2} is _O 2 / NH ₃ molar is optimal range shown an _{O 2} in FIG. 5 described above 0.5 above in the ratio By injecting adjusted to such a range of 1.5 to reduction zone of the furnace 1, it is possible to reduce the NOx efficiently in exhaust gas 6.

Further, the NH ₃ injection position in the boiler of the present embodiment is upstream of the after air nozzle 3, and unreacted NH ₃ is oxidized by the air of the after air 7 and converted into NOx, so that the outflow of NH ₃ to the outside of the furnace is prevented. Absent. Therefore, since no ammonia is present in the combustion gas 6, the air heater (not shown) disposed on the downstream side of the furnace 1 is not blocked and white smoke is not generated.

  According to this embodiment, not only the same effect as the boiler of the first embodiment can be obtained, but also there is a merit that thermal NOx is further reduced.

  According to the present embodiment, even if a reducing agent is introduced into the boiler furnace, ammonia is prevented from being discharged outside the furnace, and a boiler capable of reliably reducing NOx in the exhaust gas is realized. Can do.

  The present invention can be applied to a boiler that reduces NOx suitable for combustion of fossil fuel.

  1: furnace, 2: burner, 3: after air nozzle, 4: reducing agent injection nozzle, 41, 41a, 41b: nozzle outlet hole, 42: fluid in nozzle, 43: cooling water for nozzle, 5: burner part combustion gas, 6: exhaust gas, 7: after air, 8, 33: heat exchanger, 9: flue, 10: chimney, 11, 16, 21, 26: control signal, 13, 17, 22, 27: flow control valve, 12, 20 ,: Blower, 15: Ammonia gas tank, 18: Reductant supply system, 23: Exhaust gas supply system, 24: Ammonia water and urea water tank, 25: Pump, 30, 31, 32: Measurement location, L, M: Optimal Range, 40: control device, 50: boiler, 60: experimental furnace.

Claims (8)

In a boiler comprising a plurality of burners for burning fossil fuel at a theoretical air ratio or less, and an after air nozzle for supplying combustion air in the burner to the downstream side of the burner into the furnace,
A reducing agent injection nozzle having at least one outlet hole is disposed on the wall surface of the furnace in a region between the burner located at the uppermost stage and the after air nozzle, and the reducing agent is provided from the outlet hole of the reducing agent injection nozzle. A boiler configured to supply a mixed fluid of a fluid containing oxygen and a fluid containing oxygen into the furnace. In a boiler comprising a plurality of burners for burning fossil fuel at a theoretical air ratio or less, and an after air nozzle for supplying combustion air in the burner to the downstream side of the burner into the furnace,
A reducing agent injection nozzle having a plurality of outlet holes is provided on the wall surface of the furnace in a region between the burner positioned at the uppermost stage and the after air nozzle, and a fluid containing a reducing agent and a fluid containing oxygen Is supplied to the furnace from different outlet holes of the reducing agent injection nozzle. In the boiler according to claim 1 or claim 2,
The reducing agent supplied to the reducing agent injection nozzle is ammonia gas, ammonia water, or urea water, and the amount of the reducing agent supplied to the reducing agent injection nozzle is nitrogen in the combustion gas generated in the furnace. A boiler characterized by being set in a range of 0.5 to 3 moles per mole of oxide (NOx). In the boiler according to claim 1 or claim 2,
The fluid containing oxygen supplied to the reducing agent injection nozzle is air, combustion exhaust gas, or a mixed fluid of air and combustion exhaust gas, and the amount of oxygen supplied is based on 1 mol of the reducing agent supplied. A boiler characterized by being set in a range of 0.5 to 1.5 mol. In the boiler according to claim 1 or claim 2,
The oxygen-containing fluid supplied to the reducing agent injection nozzle is air, combustion exhaust gas, or a mixed fluid of air and combustion exhaust gas. When the reducing agent injection nozzle is a two-fluid nozzle, the fluid is sprayed. The boiler is characterized in that the amount of oxygen to be supplied is set in the range of 0.5 to 1.5 mol with respect to 1 mol of the reducing agent to be supplied. In the boiler according to claim 1 or claim 2,
A boiler characterized in that the after-air nozzle is arranged in a plurality of stages on the wall surface of the furnace. In the boiler according to claim 3,
By controlling the flow rate of the fluid containing the reducing agent supplied to the reducing agent injection nozzle, the amount of the reducing agent to be supplied is set to 0. 1 mol of nitrogen oxide (NOx) in the combustion gas generated in the furnace. A boiler comprising: a flow rate adjusting valve installed in the reducing agent injection nozzle so as to be in a range of 5 to 3 mol; and a control device for adjusting an opening degree of the flow rate adjusting valve. In the boiler according to claim 4,
By controlling the flow rate of the fluid containing oxygen supplied to the reducing agent injection nozzle, the amount of supplied oxygen is generated in the furnace in the range of 0.5 to 1.5 mol with respect to 1 mol of reducing agent supplied. The flow rate control valve installed in the reducing agent injection nozzle and the opening of the flow rate control valve are adjusted so that the range is 0.5 to 3 moles per mole of nitrogen oxide (NOx) in the combustion gas. A boiler having a control device installed therein.

Images