EP2083216A1 - Pulverized coal boiler - Google Patents
Pulverized coal boiler Download PDFInfo
- Publication number
- EP2083216A1 EP2083216A1 EP07831257A EP07831257A EP2083216A1 EP 2083216 A1 EP2083216 A1 EP 2083216A1 EP 07831257 A EP07831257 A EP 07831257A EP 07831257 A EP07831257 A EP 07831257A EP 2083216 A1 EP2083216 A1 EP 2083216A1
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- EP
- European Patent Office
- Prior art keywords
- furnace
- pulverized coal
- air
- steam
- water
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23L—SUPPLYING AIR OR NON-COMBUSTIBLE LIQUIDS OR GASES TO COMBUSTION APPARATUS IN GENERAL ; VALVES OR DAMPERS SPECIALLY ADAPTED FOR CONTROLLING AIR SUPPLY OR DRAUGHT IN COMBUSTION APPARATUS; INDUCING DRAUGHT IN COMBUSTION APPARATUS; TOPS FOR CHIMNEYS OR VENTILATING SHAFTS; TERMINALS FOR FLUES
- F23L7/00—Supplying non-combustible liquids or gases, other than air, to the fire, e.g. oxygen, steam
- F23L7/002—Supplying water
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN A CARRIER GAS OR AIR
- F23C7/00—Combustion apparatus characterised by arrangements for air supply
- F23C7/02—Disposition of air supply not passing through burner
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23L—SUPPLYING AIR OR NON-COMBUSTIBLE LIQUIDS OR GASES TO COMBUSTION APPARATUS IN GENERAL ; VALVES OR DAMPERS SPECIALLY ADAPTED FOR CONTROLLING AIR SUPPLY OR DRAUGHT IN COMBUSTION APPARATUS; INDUCING DRAUGHT IN COMBUSTION APPARATUS; TOPS FOR CHIMNEYS OR VENTILATING SHAFTS; TERMINALS FOR FLUES
- F23L9/00—Passages or apertures for delivering secondary air for completing combustion of fuel
- F23L9/02—Passages or apertures for delivering secondary air for completing combustion of fuel by discharging the air above the fire
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES
- F23J2215/00—Preventing emissions
- F23J2215/10—Nitrogen; Compounds thereof
- F23J2215/101—Nitrous oxide (N2O)
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23L—SUPPLYING AIR OR NON-COMBUSTIBLE LIQUIDS OR GASES TO COMBUSTION APPARATUS IN GENERAL ; VALVES OR DAMPERS SPECIALLY ADAPTED FOR CONTROLLING AIR SUPPLY OR DRAUGHT IN COMBUSTION APPARATUS; INDUCING DRAUGHT IN COMBUSTION APPARATUS; TOPS FOR CHIMNEYS OR VENTILATING SHAFTS; TERMINALS FOR FLUES
- F23L2900/00—Special arrangements for supplying or treating air or oxidant for combustion; Injecting inert gas, water or steam into the combustion chamber
- F23L2900/07008—Injection of water into the combustion chamber
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23L—SUPPLYING AIR OR NON-COMBUSTIBLE LIQUIDS OR GASES TO COMBUSTION APPARATUS IN GENERAL ; VALVES OR DAMPERS SPECIALLY ADAPTED FOR CONTROLLING AIR SUPPLY OR DRAUGHT IN COMBUSTION APPARATUS; INDUCING DRAUGHT IN COMBUSTION APPARATUS; TOPS FOR CHIMNEYS OR VENTILATING SHAFTS; TERMINALS FOR FLUES
- F23L2900/00—Special arrangements for supplying or treating air or oxidant for combustion; Injecting inert gas, water or steam into the combustion chamber
- F23L2900/07009—Injection of steam into the combustion chamber
Definitions
- the present invention relates to a pulverized coal boiler that uses pulverized coal as a fuel, more particularly to a pulverized coal boiler that suppresses the generation of thermal nitrogen oxides.
- Pulverized coal boilers use the two-stage combustion method because the concentrations of NOx generated during the combustion of pulverized coal used as a fuel need to be reduced.
- the two-stage combustion method is applied to pulverized coal boilers in which pulverized coal burners are provided in the furnace of the pulverized coal boiler and after-air ports are also provided downstream of the burners, as disclosed in Japanese Patent Laid-open No. Hei 6(1994)-201105 ; pulverized coal used as a fuel and combustion air is supplied from the burners, and combustion air is supplied from the after-air ports.
- combustion air is supplied from the burners by an amount by which the theoretical stoichiometric ratio necessary for complete combustion of the pulverized coal used as a fuel is not exceeded, the combustion air being supplied together with the pulverized coal as a fuel gas; the pulverized coal included in the fuel gas is burnt in a state in which air is insufficient in the furnace so that a reducing atmosphere is created, and NOx generated during the combustion is reduced to nitrogen to suppress the generation of NOx.
- unburnt pulverized coal is left in the fuel gas supplied from the burners into the furnace due to the oxygen insufficiency, generating CO (carbon monoxide).
- CO carbon monoxide
- combustion air is supplied from the after-air ports located downstream of the burners to the furnace by an amount a little more than the amount of air equivalent to an insufficiency relative to the theoretical stoichiometric ratio, so that the unburnt pulverized coal and CO are burnt to reduce the generation of NOx and CO.
- the combustion gas resulting from the combustion of the pulverized coal included in the fuel is directed down in the furnace so that the combustion gas exchanges heat with a heat exchanger (not shown) installed in the furnace to extract heat from the combustion gas; the combustion gas is then cooled and expelled from the furnace to the outside of the pulverized coal boiler as an exhaust gas.
- a heat exchanger not shown
- NOx gases generated in boilers are broadly classified into fuel NOx and thermal NOx.
- Fuel NOx is generated when nitrogen compounds included in coal used as a fuel are oxidized. This type of fuel NOx is substantially reduced by improved technologies applied to combustion in burners.
- Thermal NOx is generated when nitrogen included in the air is oxidized at high temperature.
- thermal NOx As fuel NOx has been reduced, the amount of thermal NOx generated can be no longer neglected in recent years. To further reduce NOx, thermal NOx must be reduced.
- the spray nozzle Since it is also necessary to have the spray nozzle include the driving unit for retracting and inserting the spray nozzle through which water or steam is supplied, the structure of the spray nozzle becomes complex, increasing costs for the maintenance and other services for the unit. It is also conceivable in terms of reliability that if the spray nozzle is kept inserted into the inside of the furnace for a long period of time, the spray nozzle may not withstand prolonged use due to ash adhering to the spray nozzle and structural member deformation caused by a contact with the combustion gas at high temperature.
- An object of the present invention is to provide a highly reliable pulverized coal boiler that ensures suppression of a rise in flame temperature caused during the combustion of an unburnt gas in a furnace when combustion air is supplied from after-air ports so as to reduce the concentration of thermal NOx generated during the combustion.
- a pulverized coal boiler comprising a furnace, a burner provided on a wall of the furnace for supplying pulverized coal to the inside of the furnace and burning the pulverized coal, and an after-air port provided on the wall of the furnace at a position downstream of the burner for supplying combustion air to the inside of the furnace, wherein a plurality of after-air ports are disposed in the furnace in a combustion gas flow-direction; and at least one of the plurality of after-air ports disposed upstream in the combustion gas flow direction in the furnace supplies the water, the steam, or the two fluids including water and steam to the inside of the furnace.
- the spray nozzle 6 which is a single-fluid nozzle, is disposed on the after-air port 3.
- the pulverized coal boiler 100 in FIG. 1 has a furnace 1, on the wall of which a plurality of burners 2 are disposed; a fuel gas, in which pulverized coal used as a fuel and combustion air are mixed, is supplied from the plurality of burners 2.
- a plurality of after-air ports 3 are provided at positions downstream of the burners 2 on the wall of the furnace 1.
- Coal used as a fuel in the pulverized coal boiler 100 is crushed into powder by a plurality of mills 7, resulting in pulverized coal.
- the pulverized coal is then supplied through pipes 7b to the burners 2, and further supplied from the burners 2 to the inside of the furnace 1 together with combustion air supplied by a blower 12 through a duct pipe 14, as a fuel gas, and the fuel gas is burnt therein.
- Part of the hot air resulting from the heat exchange is adjusted for the amount to be apportioned by dampers 8 disposed at intermediate points on the duct pipe 14.
- the apportioned air is supplied to each wind box 4, which is provided on the wall of the furnace 1 and internally includes burners 2, and further supplied from the wind box 4 to the inside of the furnace 1 as outer circumferential air of the burners 2.
- the apportioned air is supplied to a wind box 5, which is provided on the wall of the furnace 1 and internally includes the after-air port 3, and further supplied from the wind box 5 through the after-air port 3 to the inside of the furnace 1 as the combustion air, as described above.
- a combustion gas 10 resulting from the combustion of the pulverized coal included in the furnace 1 flows in the furnace 1 toward the downstream side and is exhausted through a pipe 14b to the outside of the furnace 1, as an exhaust gas 11. Since the heat exchanger 13 is disposed in the pipe 14b, a heat exchange occurs in the heat exchanger 13 between the exhaust gas 11 and the combustion air. Denitrification and desulfurization (not shown) are then performed for the combustion air, after which the exhaust gas 11 is released from a chimney 15 with which the pipe 14b connects.
- the spray nozzle 6 is disposed in the after-air port 3 provided on the wall of the furnace 1.
- Water 18, which is a cooling fluid for suppressing the generation of thermal NOx during the combustion of the combustion gas, is supplied from a pump 16 through a pipe 42 to the spray nozzle 6.
- the flow rate of the water 18 (cooling fluid) to be sprayed from the spray nozzle 6 toward the inside of the furnace 1 is adjusted based on the NOx concentration of the exhaust gas 11, the NOx concentration being detected by a NOx detector 55 provided in the pipe 14b though which the exhaust gas 11 from the furnace 1 is exhausted to the outside.
- a NOx concentration signal about the exhaust gas 11 detected by the NOx detector 55 is input to a controller 50.
- the controller 50 compares the NOx concentration with a desired NOx setting, calculates a flow rate command signal about the cooling fluid to be sprayed from the spray nozzles 6 toward the inside of the furnace 1 so that the NOx concentration of the exhaust gas 11 is maintained at the desired setting, and outputs the command signal to a valve 17 used for flow rate adjustment, which is provided in a pipe 42, through which the water 18 (cooling fluid) is supplied to the spray nozzles 6.
- the opening of the valve 17 is adjusted in response to the flow rate command signal calculated by the controller 50 to raise the flow rate of the water 18 (cooling fluid) to be supplied from the spray nozzles 6, so that a rise in the flame temperature is suppressed and NOx is reduced.
- the opening of the valve 17 is adjusted in response to the flow rate command signal calculated by the controller 50 to lower the flow rate of the water 18 (cooling fluid) or the supply of the water 18 is stopped, so that an appropriate amount of water is sprayed from the spray nozzle 6 and an efficient operation is performed.
- the flow rate of the water 18 (cooling fluid) to be sprayed from the spray nozzles 6 toward the inside of the furnace 1 may be controlled based on the load of the pulverized coal boiler 100.
- the load of the pulverized coal boiler 100 is structured so that the flow rate of the water 18 (cooling fluid) to be sprayed from the spray nozzles 6 toward the inside of the furnace 1 is adjusted based on a boiler load signal commanded from a control room.
- the boiler load signal commanded from the control room is entered to the controller 50, and then the controller 50 calculates a flow rate command signal about the cooling fluid to be sprayed from the spray nozzles 6 toward the inside of the furnace 1.
- the command signal is output from the controller 50 to the valve 17, used for flow rate adjustment, which is disposed on the pipe 42 for supplying the cooling fluid to the spray nozzles 6 so that the flow rate of the cooling fluid is adjusted.
- the flow rate of the water 18 (cooling fluid) to be sprayed from the spray nozzles 6 is adjusted so that if the load of the pulverized coal boiler 100 is low, the opening of the valve 17 is adjusted to lower the flow rate of the water 18, or if the load is high, the opening is adjusted to raise the flow rate of the water 18. Then, it becomes possible to spray an appropriate amount of cooling fluid and perform an efficient operation.
- FIG. 15 is a block diagram showing the structure of the controller 50.
- the controller 50 includes a spray amount calculator 53 to which the boiler load signal and the NOx detection value of the exhaust gas 11, which is detected by the NOx detector 55, are input.
- the controller 50 also includes a boiler load setting unit 51 for setting an operation load for the boiler and a NOx concentration setting unit 52 for setting a NOx concentration.
- the spray amount calculator 53 in the controller 50 compares the boiler load signal with the load setting (threshold) in the boiler load setting unit 51. If the detected value exceeds the setting, the spray amount calculator 53 calculates the flow rate of the water 18 (cooling fluid) that corresponds to the difference between the setting and detected value, and outputs an opening of the valve 17, which corresponds to the calculated spray amount, to the valve 17 as a command signal so that the flow rate of the water 18 to be sprayed from the spray nozzles 6 toward the inside of the furnace 1 is adjusted.
- FIGs. 16A and 16B are graphs indicating characteristics for controlling the valve that adjusts the flow rate of the cooling fluid.
- the vertical axis indicates the detected NOx concentration of the exhaust gas 11
- the horizontal axis indicates the opening of the valve 17
- the dashed line indicates a setting and the solid line indicates opening characteristics of the valve 17 with respect to the detected NOx concentration.
- the vertical axis indicates the boiler load and the horizontal axis indicates the opening of the valve 17, while the dashed line indicates a setting and the solid line indicates the opening characteristics of the valve 17 with respect to the boiler load.
- the opening of the valve 17 is set to 0 (closed) to stop the water from being sprayed from the spray nozzles 6. If the value of the detected NOx concentration exceeds the setting, the valve 17 is opened based on the opening of the valve 17, which corresponds to a calculated spray amount based on a difference from the setting, so that the spray of the water from the spray nozzles 6 is controlled.
- FIG. 2 is an enlarged view showing part of the structure of the after-air port 3, which has a spray nozzle, the after-air port 3 being used in the pulverized coal boiler, shown in FIG. 1 , in this embodiment of the present invention.
- the after-air port 3 in this embodiment is provided on the wind box 5 at one end; at the other end, the after-air port 3 has a straight flow path 30, which is cylindrical and communicates with an opening 3a of the after-air port 3, which is formed in the wall of the furnace 1.
- the after-air port 3 also has a swirl flow path 31, which has a truncated cone shape, on the outer circumference of the straight flow path 30; an end of the swirl flow path 31 is connected to the wall of the furnace 1, forming an external edge of the opening 3a of the after-air port 3.
- a swirl flow 36 which is also part of the combustion air, is adjusted for its swirl intensity by means of a register 32 provided in the swirl flow path 31, which has a truncated cone shape and is formed around the outer circumference of the straight flow path 30, and supplied from the opening at the end of the swirl flow path 31 to the inside of the furnace 1.
- a jet flow 40 of combustion air is formed in the inside of the furnace 1, the inside communicating with the opening 3a of the after-air port 3; the jet flow 40 spreads from the opening 3a toward the center of the furnace 1, as shown in FIG. 2 , by the combustion air supplied from the straight flow path 30 and swirl flow path 31 formed in the after-air port 3.
- the unburnt gas 10a is burnt as a result of mixing the combustion air supplied as the jet flow 40 and the unburnt gas 10a; when the temperature of a generated flame rises, thermal NOx is generated.
- the latent heat and sensible heat of the water 18 sprayed in the spray area 18a overlapping the mixed area 41 deprive the heat of the flame resulting from the combustion of the unburnt gas 10a in the mixed area 41, suppressing the flame temperature from rising.
- the generation of thermal NOx can then be reduced in the mixed area 41 in which thermal NOx is most easily generated.
- the spray nozzle 6 in this embodiment is disposed near the opening 3a of the after-air port 3, it becomes possible to prevent ash from adhering to the spray nozzle and the structural members from being deformed due to contact with the combustion gas at high temperature and thereby obtain a highly reliable spray nozzle that can withstand prolonged use.
- FIG. 3 shows the opening 3a of the after-air port 3 having the spray nozzle 6, as viewed along line A-A in FIG. 2 .
- the water 18 (cooling fluid) is sprayed so that it spreads concentrically from the spray nozzle 6, as one form of the spray range 18a overlapping the mixed area 41, where the jet flow 40 of combustion air supplied from the opening 3a of the after-air port 3 shown in FIG. 2 is mixed with the unburnt gas 10a.
- FIGs. 5 and 6 show part of the structure of an after-air port in another embodiment that is used in the pulverized coal boiler shown in FIG. 1 , which embodies the present invention.
- the basic structure of the after-air port 3 in this embodiment shown in FIGs. 5 and 6 is the same as the basic structure of the after-air port 3 in the embodiment shown in FIGs. 2 to 4 , so the explanation of the same basic structure will be omitted and only different parts will be described.
- each spray nozzle 6 for spraying water is positioned near the opening 3a of the after-air port 3, as in the structure of the after-air port 3 shown in the embodiment shown in FIG. 2 .
- the water 18 (cooling fluid) can be precisely sprayed from the spray nozzles 6 in the spray range 18a overlapping the mixed area 41, where the jet flow 40 of combustion air and the unburnt gas 10a are mixed, the jet flow 40 being jetted from the after-air port 3 to the inside of the furnace 1, the inside communicating with the opening 3a of the after-air port 3.
- FIGs. 7 and 8 show part of the structure of an after-air port in other embodiment that is used in the pulverized coal boiler shown in FIG. 1 , which embodies the present invention.
- FIG. 7 shows the structure of the after-air port, having spray nozzles, in the other embodiment.
- FIG. 8 shows a section as viewed along line C-C in FIG. 7 .
- a pulverized coal boiler in which the after-air port 3 in this embodiment is used has the same structure as the pulverized coal boiler 100 in the embodiment shown in FIG. 1 , so the explanation of the pulverized coal boiler including the after-air port 3 in this embodiment will be omitted.
- the spray nozzles 6 in this embodiment are also disposed near the opening 3a of the after-air port 3, it becomes possible to prevent ash from adhering to the spray nozzles and the structural members from being deformed due to contact with the combustion gas at high temperature. Furthermore, since a plurality of spray nozzle are provided, even if some of the plurality of spray nozzles are clogged, a necessary amount of cooling fluid can still be sprayed by the remaining spray nozzles, so it becomes possible to obtain highly reliable spray nozzles that can withstand prolonged use.
- the basic structure of the after-air ports 3 in this embodiment shown in FIGs. 9 and 10 are the same as the basic structure of the after-air ports 3 in the embodiments shown in FIGs. 5 and 7 , so the explanation of the same basic structure will be omitted and only different parts will be described.
- each spray nozzle 6, included in the after-air port 3 in each embodiment, from which the water 18 (cooling fluid) is sprayed, is disposed so that the end of the spray nozzle 6 is positioned near the wall of the wind box 5 rather than the opening 3a of the after-air port 3 to leave a distance from the furnace 1; the end of the spray nozzle 6 is located, in the after-air port 3, at an upstream position of the jet flow 40 of combustion air, relative to the opening 3a of the after-air port 3.
- the water 18 (cooling fluid) is sprayed from each spray nozzle 6 at an upstream position of the jet flow 40 of combustion air supplied from the opening 3a of the after-air port 3 into the inside of the furnace 1, and vaporized so that moisture is further evenly mixed with the jet flow 40 of combustion air supplied from the after-air port 3, adding the moisture to the jet flow 40 itself of the combustion air supplied from the after-air port 3. Accordingly, the moisture can be more precisely supplied to the spray range 18a overlapping the mixed area 41, where the jet flow 40 and the unburnt gas 10a are mixed, and thereby a rise in flame temperature can be more surely suppressed.
- control of the cooling fluid by the spray nozzles 6 in the after-air ports 3 in this embodiment, shown in FIGs. 9 and 10 can be carried out by having the controller 50 adjust the flow rate of the cooling fluid as in the embodiments described above.
- the above embodiments in the present invention can also achieve a highly reliable pulverized coal boiler that ensures suppression of a flame temperature rise that is caused during the combustion of an unburnt gas in a furnace when combustion air is supplied from after-air ports so as to reduce the concentration of thermal NOx generated during the combustion.
- a two-fluid nozzle which can spray two fluids including water 18 and steam 20 is used as the spray nozzle 6 disposed in the after-air port 3.
- a system for supplying the water 18 to the spray nozzles 6, each of which sprays the two fluids including water 18 and steam 20 as the cooling fluid uses the same the pipe 42 and the valve 17 as shown in FIG. 1 .
- a system for supplying the steam 20 to the spray nozzles 6, each of which sprays the two fluids, has a steam tank 21 to which part of steam used in a power generation plant is supplied for storage purposes, the pressure in the steam tank 21 being set to a prescribed value.
- the system also has a pipe 43 through which the steam 20 stored in the steam tank 21 is supplied to the spray nozzles 6, a valve 22 for adjusting the flow rate of the steam 20 supplied is provided on the pipe 43.
- the opening of the valve 22, which adjusts the flow rate of the steam 20 sprayed from the two-fluid spray nozzles 6 into the inside of the furnace 1, is controlled by the controller 50.
- the spray amount calculator 53 in the controller 50 compares a boiler load and the NOx emission concentration of the exhaust gas 11, which is detected by the NOx detector 55, with the setting in the boiler load setting unit 51 and the setting in the NOx concentration setting unit 52, respectively. Then, the spray amount calculator 53 calculates the amount of the steam 20 that needs to be supplied.
- the opening of the valve 22 that corresponds to the amount of steam is commanded as an opening signal by the spray amount calculator 53 in the controller 50 for the valve 22 so that the necessary amount of steam 20 is sprayed from the spray nozzles 6.
- the opening of the valve 22 is controlled by the controller 50 in the same way as the opening of the valve 17 is controlled by the controller 50 as shown in FIGs. 16A and 16B .
- the above embodiment in the present invention can also achieve a highly reliable pulverized coal boiler that ensures suppression of a flame temperature rise that is caused during the combustion of an unburnt gas in a furnace when combustion air is supplied from after-air ports so as to reduce the concentration of thermal NOx generated during the combustion.
- the basic structure of the pulverized coal boiler in this embodiment is the same as the basic structure of the pulverized coal boiler 100 in the embodiment shown in FIG. 1 , so the explanation of the same basic structure will be omitted and only different parts will be described.
- the jet flow 40 of combustion air with which the water 18 (cooling fluid) sprayed from the spray nozzle 6 into the wind box 5 and vaporized is mixed, can be precisely and evenly sprayed in the mixed area 41, where the jet flow 40 of combustion air and the unburnt gas 10a are mixed, the jet flow 40 being jetted toward the inside of the furnace 1, the inside communicating with the opening 3a of the after-air port 3.
- the latent heat and sensible heat of the water 18 sprayed from the spray nozzle 6 deprive the heat of the flame resulting from the combustion of the unburnt gas 10a in the mixed area 41, so it is possible to suppress the flame temperature to about 1600K or below, preferably about 1600K to about 1400K.
- the concentration of NOx generated in the boiler can thereby be reduced by about 10% to 30%.
- FIG. 17 is a schematic diagram indicating the structure of a pulverized coal boiler 100 in other embodiment of the present invention.
- the pulverized coal boiler 100 comprises burners 2 for burning pulverized coal used as a fuel, after-air ports 3 for supplying combustion air, and spray nozzles 6 for spraying water (cooling fluid) into a duct pipe 14 through which the combustion air is supplied to the after-air ports 3.
- the basic structure of the pulverized coal boiler in this embodiment is the same as the basic structure of the pulverized coal boiler 100 in the embodiment shown in FIG. 1 , so the explanation of the same basic structure will be omitted and only different parts will be described.
- the ratio of the vaporization of the water 18 sprayed from the spray nozzle 6 is increased and lessens drainage water, and thereby the water 18 (cooling fluid) sprayed from the spray nozzle 6 is more efficiently vaporized.
- the steam 20 or two fluids including the water and steam may be sprayed instead of the water.
- control of the cooling fluid by the spray nozzles 6 disposed in the wind boxes 5 in this embodiment can be carried out by having the controller 50 adjust the flow rate of the cooling fluid as in the embodiments described above.
- the basic structure of the pulverized coal boiler in this embodiment is the same as the basic structure of the pulverized coal boiler 100 in the embodiment shown in FIG. 17 , so the explanation of the same basic structure will be omitted and only different parts will be described.
- the sub after-air ports 60 are disposed in the direction in which the combustion gas 10 flows in the furnace 1 on the upstream side and main after-air ports 61 are disposed on the downstream side.
- the sub-after port 60 has the spray nozzle 6, from which water or both water and steam is sprayed.
- the amount of air supplied from the sub after-air port 60 is smaller than the amount of air supplied from the main after-air port 61.
- the air flows 62 supplied from the sub-after ports 60 into the inside of the furnace 1 by being sprayed are directed toward the downstream side along the inner wall of the furnace 1 because the amount of air sprayed is small.
- the combustion gas 10a While flowing from downstream to upstream in the furnace 1, the combustion gas 10a is mixed with the air flows 62 and 63. Near the wall of the furnace 1, the temperature of the combustion gas 10a mixed with the air flow 62 on the upstream side is higher than the temperature of the combustion gas 10a mixed with the air flow 63 on the downstream side.
- the pulverized coal boiler 100 in this embodiment is structured so that water is sprayed from the spray nozzles 6 disposed in the sub after-air ports 60 on the upstream side, the air flow 62 includes much moisture supplied from the sub after-air port 60 toward the inside of the furnace 1.
- part of the air flow 62 is further mixed with the air flow 63 jetted from the main after-air port 61 located downstream of the air flow 62.
- part of the air flow 62 including moisture is mixed with the air flow 63, part of a gas already burnt in an inner wall vicinity 64 in the furnace 1 is involved in the air flow 63 jetted from the main after-air port 61, so a burnt gas including moisture flows along the outermost circumference of the air flow 63.
- the combustion temperature can be reduced due to the specific heats of the moisture included in the burnt gas.
- the amount of thermal NOx generated at the central part of the furnace 1 can be reduced.
- the air flow jetted from the after air port and the combustion gas 10a are mixed, as described above, the air flow including much moisture and the burnt gas including moisture are supplied to the inner wall vicinity 64 in the furnace 1 in a relatively upstream region, the central part 65 of the furnace 1, and other parts where high temperature is easily reached, enabling the amount of thermal NOx generated to be suppressed to a small value.
- thermal efficiency is lowered by the supplied water, since thermal NOx is suppressed, it is possible to suppress, at a downstream site of the furnace 1, power for operating units to reduce NOx and the amount of chemicals supplied.
- the steam 20 or two fluids including water 18 and steam 20 may be sprayed instead of water 18.
- the swirl flow causes much of the water 18 jetted from the spray nozzle 6 to flow around the outer circumference of the air flow 62, so much moisture is included in the mixture of the combustion gas 10a and the air flow 62. Accordingly, the concentration of the thermal NOx can be reduced with a small amount of water.
- the cooling fluid sprayed from the spray nozzle 6 disposed in the sub after-air port 60 is controlled by the controller 50, as in the embodiments described above.
- a NOx concentration signal about the exhaust gas 11 detected by the NOx detector 55 is entered to the controller 50.
- the controller 50 compares the NOx concentration with a desired NOx setting, calculates a flow rate command signal about the cooling fluid to be sprayed from the spray nozzles 6 toward the inside of the furnace 1 so that the NOx concentration of the exhaust gas 11 is maintained at the desired setting, and outputs the command signal to the valve 17 used for flow rate adjustment, which is disposed in the pipe 42, through which the water 18 (cooling fluid) is supplied to the spray nozzles 6.
- This arrangement enables the flow rate of the cooling fluid to be appropriately controlled and thereby the thermal NOx concentration to be reduced.
- the pulverized coal boiler 100 described above can be a highly reliable pulverized coal boiler that ensures suppression of a flame temperature rise that is caused during the combustion of an unburnt gas in a furnace when combustion air is supplied from after-air ports so as to reduce the concentration of thermal NOx generated during the combustion.
- the present invention can be applied to a pulverized coal boiler that uses pulverized coal as a fuel, more particularly to a pulverized coal boiler that suppresses the generation of thermal nitrogen oxides.
- the present invention can also be applied to conventional pulverized boilers with ease.
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Abstract
Description
- The present invention relates to a pulverized coal boiler that uses pulverized coal as a fuel, more particularly to a pulverized coal boiler that suppresses the generation of thermal nitrogen oxides.
- Pulverized coal boilers use the two-stage combustion method because the concentrations of NOx generated during the combustion of pulverized coal used as a fuel need to be reduced.
- The two-stage combustion method is applied to pulverized coal boilers in which pulverized coal burners are provided in the furnace of the pulverized coal boiler and after-air ports are also provided downstream of the burners, as disclosed in Japanese Patent Laid-open No.
Hei 6(1994)-201105 - Specifically, for the combustion in the burner section, combustion air is supplied from the burners by an amount by which the theoretical stoichiometric ratio necessary for complete combustion of the pulverized coal used as a fuel is not exceeded, the combustion air being supplied together with the pulverized coal as a fuel gas; the pulverized coal included in the fuel gas is burnt in a state in which air is insufficient in the furnace so that a reducing atmosphere is created, and NOx generated during the combustion is reduced to nitrogen to suppress the generation of NOx.
- In the reducing atmosphere, unburnt pulverized coal is left in the fuel gas supplied from the burners into the furnace due to the oxygen insufficiency, generating CO (carbon monoxide). To completely burn the unburnt pulverized coal and CO generated in the reducing atmosphere, combustion air is supplied from the after-air ports located downstream of the burners to the furnace by an amount a little more than the amount of air equivalent to an insufficiency relative to the theoretical stoichiometric ratio, so that the unburnt pulverized coal and CO are burnt to reduce the generation of NOx and CO.
- The combustion gas resulting from the combustion of the pulverized coal included in the fuel is directed down in the furnace so that the combustion gas exchanges heat with a heat exchanger (not shown) installed in the furnace to extract heat from the combustion gas; the combustion gas is then cooled and expelled from the furnace to the outside of the pulverized coal boiler as an exhaust gas.
- NOx gases generated in boilers are broadly classified into fuel NOx and thermal NOx. Fuel NOx is generated when nitrogen compounds included in coal used as a fuel are oxidized. This type of fuel NOx is substantially reduced by improved technologies applied to combustion in burners. Thermal NOx is generated when nitrogen included in the air is oxidized at high temperature.
- As fuel NOx has been reduced, the amount of thermal NOx generated can be no longer neglected in recent years. To further reduce NOx, thermal NOx must be reduced.
- Japanese Patent Laid-open No.
2003-322310 -
- Patent Document 1: Japanese Patent Laid-open No.
Hei 6 (1994) -201105 - Patent Document 2: Japanese Patent Laid-open No.
2003-322310 - In the technology disclosed in Japanese Patent Laid-open No.
2003-322310 - Since it is also necessary to have the spray nozzle include the driving unit for retracting and inserting the spray nozzle through which water or steam is supplied, the structure of the spray nozzle becomes complex, increasing costs for the maintenance and other services for the unit. It is also conceivable in terms of reliability that if the spray nozzle is kept inserted into the inside of the furnace for a long period of time, the spray nozzle may not withstand prolonged use due to ash adhering to the spray nozzle and structural member deformation caused by a contact with the combustion gas at high temperature.
- An object of the present invention is to provide a highly reliable pulverized coal boiler that ensures suppression of a rise in flame temperature caused during the combustion of an unburnt gas in a furnace when combustion air is supplied from after-air ports so as to reduce the concentration of thermal NOx generated during the combustion.
- A pulverized coal boiler according to the present invention comprising a furnace, a burner provided on the wall of the furnace for supplying pulverized coal to the inside of the furnace and burning the pulverized coal, and an after-air port provided on the wall of the furnace at a position downstream of the burner for supplying combustion air to the inside of the furnace, the pulverized coal boiler further comprising: a spray nozzle disposed near a jet port of the after-air port for supplying water, steam, or two fluids including water and steam to the inside of the furnace; whereby the water, the steam, or the two fluids including water and steam sprayed from the spray nozzle are supplied to the inside of the furnace together with the combustion air supplied from the after-air port.
- A pulverized coal boiler according to the present invention comprising a furnace, a burner provided on a wall of the furnace for supplying pulverized coal to the inside of the furnace and burning the pulverized coal, and an after-air port provided on the wall of the furnace at a position downstream of the burner for supplying combustion air to the inside of the furnace, wherein a plurality of after-air ports are disposed in the furnace in a combustion gas flow-direction; and at least one of the plurality of after-air ports disposed upstream in the combustion gas flow direction in the furnace supplies the water, the steam, or the two fluids including water and steam to the inside of the furnace.
- In the pulverized coal boiler according to the present invention, wherein at least one of the plurality of after-air ports disposed upstream in the combustion gas flow direction in the furnace supplies combustion air less than that of combustion air supplied from the after-air ports disposed downstream in the combustion gas flow direction.
- In the pulverized coal boiler according to the present invention, wherein each of the after-air ports for supplying the water, the steam, or the two fluids including water and steam is provided with a straight flow path for jetting the combustion air as a straight flow, and a swirl flow path formed around an outer circumference of the straight flow path for jetting the combustion air as a swirl flow, internally; and the water, the steam, or the two fluids including water and steam are jetted from the swirl flow path.
- A pulverized coal boiler according to the present invention comprising a furnace, burners provided on a wall of the furnace for supplying pulverized coal to the inside of the furnace and burning the pulverized coal, an after-air port provided on the wall of the furnace at a position downstream of the burner for supplying combustion air to the inside of the furnace, a wind box having the after-air port, and a duct pipe for externally supplying the combustion air into the wind box,
the pulverized coal boiler further comprising: - a spray nozzle disposed in the wind box or in the duct pipe for supplying water, steam, or the two fluids including water and steam; whereby the water, the steam, or the two fluids including water and steam sprayed from the spray nozzle into the inside of the wind box or the duct pipe are supplied to the inside of the furnace together with the combustion air supplied from a jet port of the after-air port.
- The present invention can achieve a highly reliable pulverized coal boiler that ensures suppression of a rise in flame temperature caused during the combustion of an unburnt gas in a furnace when combustion air is supplied from after-air ports so as to reduce the concentration of thermal NOx generated during the combustion.
-
-
FIG. 1 is a schematic diagram indicating the structure of a pulverized coal boiler in an embodiment of the present invention. -
FIG. 2 is a cross sectional view showing the structure of an after-air port having a spray nozzle, the after-air port being applied to the pulverized coal boiler in the embodiment shown inFIG. 1 . -
FIG. 3 shows the cross section of the after-air port having a spray nozzle, as viewed along line A-A inFIG. 2 . -
FIG. 4 shows an exemplary spray pattern of the spray nozzle disposed in the after-air port shown inFIG. 2 . -
FIG. 5 is a cross sectional view showing the structure of another after-air port having spray nozzles, the after-air port being applied to the pulverized coal boiler in the embodiment shown inFIG. 1 . -
FIG. 6 shows the cross section of the after-air port having spray nozzles, as viewed along line B-B inFIG. 5 . -
FIG. 7 is also a cross sectional view showing the structure of other after-air port having spray nozzles, the after-air port being applied to the pulverized coal boiler in the embodiment shown inFIG. 1 . -
FIG. 8 shows the cross section of the after-air port having spray nozzles, as viewed along line C-C inFIG. 7 . -
FIG. 9 is also a cross sectional view showing the structure of other after-air port having spray nozzles, the after-air port being applied to the pulverized coal boiler in the embodiment shown inFIG. 1 . -
FIG. 10 is also a cross sectional view showing the structure of other after-air port having spray nozzles, the after-air port being applied to the pulverized coal boiler in the embodiment shown inFIG. 1 . -
FIG. 11 is a schematic diagram indicating the structure of a pulverized coal boiler in another embodiment of the present invention. -
FIG. 12 is also a schematic diagram indicating the structure of a pulverized coal boiler in other embodiment of the present invention. -
FIG. 13 is a cross sectional view of a wind box, which has spray nozzles, applied to the pulverized coal boiler in another embodiment shown inFIG. 12 . -
FIG. 14 is the cross section of the wind box having spray nozzles, as viewed along line D-D inFIG. 13 . -
FIG. 15 is a block diagram showing the structure of a controller disposed in the pulverized coal boiler in the embodiment shown inFIG. 1 of the present invention to control the amount of cooling fluid sprayed. -
FIGs. 16A and 16B are graphs indicating characteristics - for controlling a valve that adjusts the flow rate of the cooling fluid in the controller shown inFIG. 15. FIG. 16A shows a relation ship between the NOx concentration of an exhaust gas and the opening of the valve.FIG. 16B shows a relationship between a boiler load and the opening of the valve. -
FIG. 17 is a schematic diagram indicating the structure of a pulverized coal boiler in other embodiment of the present invention. -
FIG. 18 is also a schematic diagram indicating the structure of a pulverized coal boiler in other embodiment of the present invention. - 1: Furnace, 2: Burner, 3: After-air port, 3a: Opening of the after-air port, 4: Wind box of the burner, 5, 5a: Wind box of the after-air port, 6: Spray nozzle, 7: Mill, 8, 9: Damper, 10: Combustion gas, 10a: Unburnt gas, 11: Exhaust gas, 12: Blower, 13: Heat exchanger, 14: Duct pipe, 15: Chimney, 16: Pump, 17, 22: Valve, 18: Water, 18a: Spray range, 20: Steam, 21: Steam tank, 30: Straight flow path, 31: Swirl flow path, 33, 34: Damper, 40: Jet flow, 41: Mixed area, 42, 43: Pipe, 50: Controller, 51: Boiler load setting unit, 52: NOx concentration setting unit, 53: Spray amount calculator, 55: NOx detector, 60: sub after air port, 61: main after-air port, 100: Pulverized coal boiler.
- Next, a pulverized coal boiler in an embodiment of the present invention will be described with reference to the drawings.
-
FIG. 1 is a schematic diagram indicating the structure of a pulverized coal boiler, in a first embodiment of the present invention, that burns pulverized coal used as a fuel. The pulverizedcoal boiler 100 comprises, on the wall of afurnace 1,burners 2, and after-air ports 3, each of which has aspray nozzle 6 for spraying water, to supply combustion air. - In the pulverized
coal boiler 100 in the embodiment inFIG. 1 , thespray nozzle 6, which is a single-fluid nozzle, is disposed on the after-air port 3. - The pulverized
coal boiler 100 inFIG. 1 has afurnace 1, on the wall of which a plurality ofburners 2 are disposed; a fuel gas, in which pulverized coal used as a fuel and combustion air are mixed, is supplied from the plurality ofburners 2. - The
burners 2 supply the combustion air by an amount by which the theoretical stoichiometric ratio necessary for complete combustion of the pulverized coal used as a fuel is not exceeded, the combustion air being supplied together with the pulverized coal as a fuel gas to the inside of thefurnace 1; the fuel gas is burnt in a state in which there is an insufficient amount of air in the furnace so that a reducing atmosphere is created, and NOx generated during the combustion is reduced to nitrogen to suppress the generation of NOx. - A plurality of after-
air ports 3 are provided at positions downstream of theburners 2 on the wall of thefurnace 1. - Part of the fuel gas supplied from the
burners 2 to the inside of thefurnace 1 is left as anunburnt gas 10a, which has not been burnt due to the insufficient oxygen in the reducing atmosphere. To completely burn theunburnt gas 10a and CO generated in the reducing atmosphere, combustion air is supplied from the after-air ports 3 to the inside of thefurnace 1 by an amount a little more than the amount of air equivalent to an insufficiency relative to the theoretical stoichiometric ratio, so that the pulverized coal included in theunburnt gas 10a and CO are burnt to reduce the generation of NOx and CO. - Coal used as a fuel in the pulverized
coal boiler 100 is crushed into powder by a plurality ofmills 7, resulting in pulverized coal. The pulverized coal is then supplied throughpipes 7b to theburners 2, and further supplied from theburners 2 to the inside of thefurnace 1 together with combustion air supplied by ablower 12 through aduct pipe 14, as a fuel gas, and the fuel gas is burnt therein. - The combustion air for burning the
unburnt gas 10a, which is part of the fuel gas supplied from theburners 2 to the inside of thefurnace 1 and left unburnt, is externally supplied by theblower 12 to aheat exchanger 13, where a heat exchange occurs between the combustion air and hot exhaust gas 11 exhausted from thefurnace 1, heating the combustion air to about 300°C. The heated combustion air is then supplied to the after-air ports 3 through theduct pipe 14. - Part of the hot air resulting from the heat exchange is adjusted for the amount to be apportioned by
dampers 8 disposed at intermediate points on theduct pipe 14. The apportioned air is supplied to eachwind box 4, which is provided on the wall of thefurnace 1 and internally includesburners 2, and further supplied from thewind box 4 to the inside of thefurnace 1 as outer circumferential air of theburners 2. - Another part of the hot air is also adjusted for the amount to be apportioned by
dampers 9. The apportioned air is supplied to awind box 5, which is provided on the wall of thefurnace 1 and internally includes the after-air port 3, and further supplied from thewind box 5 through the after-air port 3 to the inside of thefurnace 1 as the combustion air, as described above. - A
combustion gas 10 resulting from the combustion of the pulverized coal included in thefurnace 1 flows in thefurnace 1 toward the downstream side and is exhausted through apipe 14b to the outside of thefurnace 1, as an exhaust gas 11. Since theheat exchanger 13 is disposed in thepipe 14b, a heat exchange occurs in theheat exchanger 13 between the exhaust gas 11 and the combustion air.
Denitrification and desulfurization (not shown) are then performed for the combustion air, after which the exhaust gas 11 is released from achimney 15 with which thepipe 14b connects. - The
spray nozzle 6 is disposed in the after-air port 3 provided on the wall of thefurnace 1.Water 18, which is a cooling fluid for suppressing the generation of thermal NOx during the combustion of the combustion gas, is supplied from apump 16 through apipe 42 to thespray nozzle 6. - The flow rate of the water 18 (cooling fluid) to be sprayed from the
spray nozzle 6 toward the inside of thefurnace 1 is adjusted based on the NOx concentration of the exhaust gas 11, the NOx concentration being detected by aNOx detector 55 provided in thepipe 14b though which the exhaust gas 11 from thefurnace 1 is exhausted to the outside. - Specifically, a NOx concentration signal about the exhaust gas 11 detected by the
NOx detector 55 is input to acontroller 50. Thecontroller 50 then compares the NOx concentration with a desired NOx setting, calculates a flow rate command signal about the cooling fluid to be sprayed from thespray nozzles 6 toward the inside of thefurnace 1 so that the NOx concentration of the exhaust gas 11 is maintained at the desired setting, and outputs the command signal to avalve 17 used for flow rate adjustment, which is provided in apipe 42, through which the water 18 (cooling fluid) is supplied to thespray nozzles 6. - If the
NOx detector 55 detects, from the exhaust gas 11, a higher NOx value than the desired setting, the opening of thevalve 17 is adjusted in response to the flow rate command signal calculated by thecontroller 50 to raise the flow rate of the water 18 (cooling fluid) to be supplied from thespray nozzles 6, so that a rise in the flame temperature is suppressed and NOx is reduced. - If the
NOx detector 55 detects, from the exhaust gas 11, a lower NOx value than the desired setting, the opening of thevalve 17 is adjusted in response to the flow rate command signal calculated by thecontroller 50 to lower the flow rate of the water 18 (cooling fluid) or the supply of thewater 18 is stopped, so that an appropriate amount of water is sprayed from thespray nozzle 6 and an efficient operation is performed. - In addition to responding to the NOx concentration of the exhaust gas 11, the flow rate of the water 18 (cooling fluid) to be sprayed from the
spray nozzles 6 toward the inside of thefurnace 1 may be controlled based on the load of the pulverizedcoal boiler 100. - In this case, the load of the pulverized
coal boiler 100 is structured so that the flow rate of the water 18 (cooling fluid) to be sprayed from thespray nozzles 6 toward the inside of thefurnace 1 is adjusted based on a boiler load signal commanded from a control room. - Specifically, the boiler load signal commanded from the control room is entered to the
controller 50, and then thecontroller 50 calculates a flow rate command signal about the cooling fluid to be sprayed from thespray nozzles 6 toward the inside of thefurnace 1. The command signal is output from thecontroller 50 to thevalve 17, used for flow rate adjustment, which is disposed on thepipe 42 for supplying the cooling fluid to thespray nozzles 6 so that the flow rate of the cooling fluid is adjusted. - The flow rate of the water 18 (cooling fluid) to be sprayed from the
spray nozzles 6 is adjusted so that if the load of the pulverizedcoal boiler 100 is low, the opening of thevalve 17 is adjusted to lower the flow rate of thewater 18, or if the load is high, the opening is adjusted to raise the flow rate of thewater 18. Then, it becomes possible to spray an appropriate amount of cooling fluid and perform an efficient operation. - The structure of the
controller 50, which calculates the flow rate command signal about the cooling fluid to be sprayed from thespray nozzles 6 and outputs a command signal about a valve opening to thevalve 17 to control the flow rate of the cooling fluid, will be described below.FIG. 15 is a block diagram showing the structure of thecontroller 50. As shown in the drawing, thecontroller 50 includes aspray amount calculator 53 to which the boiler load signal and the NOx detection value of the exhaust gas 11, which is detected by theNOx detector 55, are input. - The
controller 50 also includes a boilerload setting unit 51 for setting an operation load for the boiler and a NOxconcentration setting unit 52 for setting a NOx concentration. - The
spray amount calculator 53 in thecontroller 50 compares the boiler load signal with the load setting (threshold) in the boilerload setting unit 51. If the detected value exceeds the setting, thespray amount calculator 53 calculates the flow rate of the water 18 (cooling fluid) that corresponds to the difference between the setting and detected value, and outputs an opening of thevalve 17, which corresponds to the calculated spray amount, to thevalve 17 as a command signal so that the flow rate of thewater 18 to be sprayed from thespray nozzles 6 toward the inside of thefurnace 1 is adjusted. - Similarly, the
spray amount calculator 53 in thecontroller 50 compares the NOx detection signal, detected by theNOx detector 55, about the exhaust gas 11 with a NOx setting (threshold) in the NOxconcentration setting unit 52. If the detected value exceeds the setting, thespray amount calculator 53 calculates the flow rate of the water 18 (cooling fluid) that corresponds to the difference between the setting and detected value, and outputs an opening of thevalve 17, which corresponds to the calculated spray amount, to thevalve 17 as a command signal so that the flow rate of thewater 18 to be sprayed from thespray nozzles 6 toward the inside of thefurnace 1 is adjusted. - The opening of the
valve 17 operated by thecontroller 50 to adjust the flow rate of thewater 18 to be sprayed will be described below.FIGs. 16A and 16B are graphs indicating characteristics for controlling the valve that adjusts the flow rate of the cooling fluid. InFIG. 16A , the vertical axis indicates the detected NOx concentration of the exhaust gas 11, and the horizontal axis indicates the opening of thevalve 17, while the dashed line indicates a setting and the solid line indicates opening characteristics of thevalve 17 with respect to the detected NOx concentration. - In
FIG. 16B , the vertical axis indicates the boiler load and the horizontal axis indicates the opening of thevalve 17, while the dashed line indicates a setting and the solid line indicates the opening characteristics of thevalve 17 with respect to the boiler load. - As seen from the characteristic chart in
FIG. 16A , if the value of the detected NOx concentration of the exhaust gas 11 is lowered to or below the setting (an NOx emission standard, for example) as a result of control by thecontroller 50, the opening of thevalve 17 is set to 0 (closed) to stop the water from being sprayed from thespray nozzles 6. If the value of the detected NOx concentration exceeds the setting, thevalve 17 is opened based on the opening of thevalve 17, which corresponds to a calculated spray amount based on a difference from the setting, so that the spray of the water from thespray nozzles 6 is controlled. Although, in the drawing, there is a proportional relationship between the NOx concentration and the opening of thevalve 17, this is not a limitation. - Similarly, as seen from the characteristic chart in
FIG. 16B , when the boiler load is lowered due to control by thecontroller 50, the opening of thevalve 17 is set to 0 (closed) to stop the water from being sprayed from thespray nozzles 6 because the amount of NOx emissions is originally small. As the boiler load is increased and brought close to a rated load, the amount of NOx emissions also increases. Accordingly, as the boiler load increases, the water spray from thespray nozzles 6 is controlled by opening thevalve 17 based on the opening of thevalve 17, which corresponds to a calculated spray amount based on a difference from the setting. Although, in the drawing, there is a proportional relationship between the NOx concentration and the opening of thevalve 17, this is not a limitation. - Even when the boiler load is high, if the NOx concentration of the exhaust gas is lower than or equal to the setting (emission standard) shown in
FIG. 16A , there is no need to reduce the NOx concentration to a lower value than necessary by further spraying water from thespray nozzles 6. - Accordingly, when the boiler load is raised (near the rating) due to control by the
controller 50 and the NOx concentration of the exhaust gas is high, if water is sprayed from thespray nozzles 6, the boiler can be operated in an efficient manner. - Next, the after-
air port 3 used in the pulverized coal boiler in this embodiment of the present invention will be described in detail. -
FIG. 2 is an enlarged view showing part of the structure of the after-air port 3, which has a spray nozzle, the after-air port 3 being used in the pulverized coal boiler, shown inFIG. 1 , in this embodiment of the present invention. InFIG. 2 , the after-air port 3 in this embodiment is provided on thewind box 5 at one end; at the other end, the after-air port 3 has astraight flow path 30, which is cylindrical and communicates with anopening 3a of the after-air port 3, which is formed in the wall of thefurnace 1. - The after-
air port 3 also has aswirl flow path 31, which has a truncated cone shape, on the outer circumference of thestraight flow path 30; an end of theswirl flow path 31 is connected to the wall of thefurnace 1, forming an external edge of theopening 3a of the after-air port 3. - A
straight flow 35, which is part of the combustion air, is led from a hole formed in the barrel of thestraight flow path 30 to the inside of thestraight flow path 30, and supplied from an opening at the end of thestraight flow path 30 to the inside of thefurnace 1. - A
swirl flow 36, which is also part of the combustion air, is adjusted for its swirl intensity by means of aregister 32 provided in theswirl flow path 31, which has a truncated cone shape and is formed around the outer circumference of thestraight flow path 30, and supplied from the opening at the end of theswirl flow path 31 to the inside of thefurnace 1. - A
movable damper 33 is provided outside the hole formed in the barrel of thestraight flow path 30, and anothermovable damper 34 is also provided upstream of theswirl flow path 31. The apportionment of the flow rate of the combustion air flowing down in thestraight flow path 30 is adjusted by operating thedamper 33. Similarly, the apportionment of the flow rate of the combustion air flowing down in theswirl flow path 31 is adjusted by operating thedamper 34. - The
spray nozzle 6 is disposed in the jet port at the end of the cylindricalstraight flow path 30 formed in the after-air port 3. Thespray nozzle 6 is placed along the center of the axis of thestraight flow path 30 so that the end of thespray nozzle 6 is positioned near theopening 3a of the after-air port 3. The water 18 (cooling fluid) is sprayed from the end of thespray nozzle 6 toward the inside of thefurnace 1 to suppress NOx generation. - When the water 18 (cooling fluid) is sprayed from the
spray nozzle 6 toward the inside of thefurnace 1, the effect of suppressing NOx generation is obtained as described below. - A
jet flow 40 of combustion air is formed in the inside of thefurnace 1, the inside communicating with theopening 3a of the after-air port 3; thejet flow 40 spreads from theopening 3a toward the center of thefurnace 1, as shown inFIG. 2 , by the combustion air supplied from thestraight flow path 30 andswirl flow path 31 formed in the after-air port 3. - When the
jet flow 40 of combustion air is supplied from thestraight flow path 30 andswirl flow path 31 through theopening 3a of the after-air port 3 to the inside of thefurnace 1, thejet flow 40 is mixed with theunburnt gas 10a, including unburnt pulverized coal, which flows down from theburners 2 to the after-air port 3 on the downstream side in the inside of thefurnace 1, together with thecombustion gas 10, forming amixed area 41 along the outer edge of thejet flow 40 of combustion air. - In the
mixed area 41, theunburnt gas 10a is burnt as a result of mixing the combustion air supplied as thejet flow 40 and theunburnt gas 10a; when the temperature of a generated flame rises, thermal NOx is generated. - The amount of thermal NOx generated is univocally determined by the flame temperature. When the flame temperature reaches about 1700K, the generation of thermal NOx starts. The amount of thermal NOx generated is approximately proportional to the square of the flame temperature rise; the higher the temperature is, the more the amount of generation increases significantly.
Accordingly, in this embodiment, the water 18 (a cooling fluid), which has been led through thepipe 42 from thespray nozzle 6 disposed near theopening 3a of the after-air port 3, is sprayed in aspray range 18a that overlaps themixed area 41. The latent heat and sensible heat of thewater 18 sprayed in thespray area 18a overlapping themixed area 41 deprive the heat of the flame resulting from the combustion of theunburnt gas 10a in themixed area 41, suppressing the flame temperature from rising. The generation of thermal NOx can then be reduced in themixed area 41 in which thermal NOx is most easily generated. - According to this embodiment, the
water 18 can be sprayed with precision in thespray area 18a overlapping themixed area 41 from thespray nozzle 6, so it is possible to suppress the flame temperature of theunburnt gas 10a burnt in themixed area 41 to about 1600K or below, preferably about 1600K to about 1400K. The concentration of NOx generated in the boiler can thereby be reduced by about 10% to 30%. - Since the
spray nozzle 6 in this embodiment is disposed near theopening 3a of the after-air port 3, it becomes possible to prevent ash from adhering to the spray nozzle and the structural members from being deformed due to contact with the combustion gas at high temperature and thereby obtain a highly reliable spray nozzle that can withstand prolonged use. - The water 18 (cooling fluid) is sprayed in the
spray area 18a, from thespray nozzle 6 toward themixed area 41 formed in thefurnace 1, as described above. To have thewater 18 precisely sprayed in thespray area 18a overlapping themixed area 41, where thewater 18 is mixed with theunburnt gas 10a, according to the spread and shape of thejet flow 40 of combustion air supplied from the after-air port 3, thespray nozzle 6 may be structured so that it can be turned and move fore and aft in the axial direction. -
FIG. 3 shows theopening 3a of the after-air port 3 having thespray nozzle 6, as viewed along line A-A inFIG. 2 . InFIG. 3 , the water 18 (cooling fluid) is sprayed so that it spreads concentrically from thespray nozzle 6, as one form of thespray range 18a overlapping themixed area 41, where thejet flow 40 of combustion air supplied from theopening 3a of the after-air port 3 shown inFIG. 2 is mixed with theunburnt gas 10a. - Even if, as another form of the
spray range 18a, as shown inFIG. 4 , a spray pattern different from inFIG. 3 is used by changing the shape of the end of thespray nozzle 6 so that thewater 18 is sprayed in a cone-like shape, the same effect is obtained because the moisture of the water 18 (cooling fluid) is supplied to thespray range 18a overlapping themixed area 41, where thejet flow 40 of combustion air and theunburnt gas 10a are mixed, which is the area where NOx is generated. - The above embodiment in the present invention can achieve a highly reliable pulverized coal boiler that ensures suppression of a flame temperature rise that is caused during the combustion of an unburnt gas in a furnace when combustion air is supplied from after-air ports, so as to reduce the concentration of thermal NOx generated during the combustion.
- Next,
FIGs. 5 and 6 show part of the structure of an after-air port in another embodiment that is used in the pulverized coal boiler shown inFIG. 1 , which embodies the present invention. -
FIG. 5 shows the structure of the after-air port, having spray nozzles, in the other embodiment.FIG. 6 shows a section as viewed along line B-B inFIG. 5 . A pulverized coal boiler in which the after-air port 3 in this embodiment is used has the same structure as the pulverizedcoal boiler 100 in the embodiment shown inFIG. 1 , so the explanation of the pulverized coal boiler including the after-air port 3 in this embodiment will be omitted. - The basic structure of the after-
air port 3 in this embodiment shown inFIGs. 5 and 6 is the same as the basic structure of the after-air port 3 in the embodiment shown inFIGs. 2 to 4 , so the explanation of the same basic structure will be omitted and only different parts will be described. - In the after-
air port 3 in this embodiment shown inFIGs. 5 and 6 , in which spray nozzles used in the pulverized coal boiler are included, a plurality ofspray nozzles 6 are provided in the opening in theswirl flow path 31, which is formed around the outer circumference of thestraight flow path 30. The end of eachspray nozzle 6 for spraying water (cooling fluid) is positioned near theopening 3a of the after-air port 3, as in the structure of the after-air port 3 shown in the embodiment shown inFIG. 2 . - In the after-
air port 3 in this embodiment as well, the water 18 (cooling fluid) can be precisely sprayed from thespray nozzles 6 in thespray range 18a overlapping themixed area 41, where thejet flow 40 of combustion air and theunburnt gas 10a are mixed, thejet flow 40 being jetted from the after-air port 3 to the inside of thefurnace 1, the inside communicating with theopening 3a of the after-air port 3. - Accordingly, in this embodiment, the latent heat and sensible heat of the sprayed
water 18 deprive the heat of the flame resulting from the combustion of theunburnt gas 10a in themixed area 41, so it is possible to suppress the flame temperature to about 1600K or below, preferably about 1600K to about 1400K. The concentration of NOx generated in the boiler can thereby be reduced by about 10% to 30%. - Since the
spray nozzles 6 in this embodiment are also disposed near theopening 3a of the after-air port 3, it becomes possible to prevent ash from adhering to the spray nozzles and the structural members from being deformed due to contact with the combustion gas at high temperature and thereby obtain a highly reliable spray nozzle that can withstand prolonged use. Furthermore, since a plurality of spray nozzles are provided, even if some of the plurality of spray nozzles are clogged, a necessary amount of cooling fluid can still be sprayed by the remaining spray nozzles, so it becomes possible to obtain highly reliable spray nozzles that can withstand prolonged use. - Next,
FIGs. 7 and 8 show part of the structure of an after-air port in other embodiment that is used in the pulverized coal boiler shown inFIG. 1 , which embodies the present invention. -
FIG. 7 shows the structure of the after-air port, having spray nozzles, in the other embodiment.FIG. 8 shows a section as viewed along line C-C inFIG. 7 . A pulverized coal boiler in which the after-air port 3 in this embodiment is used has the same structure as the pulverizedcoal boiler 100 in the embodiment shown inFIG. 1 , so the explanation of the pulverized coal boiler including the after-air port 3 in this embodiment will be omitted. - The basic structure of the after-
air port 3 in this embodiment shown inFIGs. 7 and 8 is the same as the basic structure of the after-air port 3 in the embodiment shown inFIGs. 2 to 4 , so the explanation of the same basic structure will be omitted and only different parts will be described. - In the after-
air port 3 in this embodiment shown inFIGs. 7 and 8 , in which spray nozzles used in the pulverized-coal boiler are 3 included, a plurality ofspray nozzles 6 for spraying water (cooling fluid) are provided in the opening inside thestraight flow path 30 and the opening in theswirl flow path 31, which is formed around the outer circumference of thestraight flow path 30. The end of eachspray nozzle 6 is positioned near theopening 3a of the after-air port 3, as in the structure of the after-air port 3 shown in the embodiment shown inFIG. 2 . - In the after-
air port 3 in this embodiment as well, the water 18 (cooling fluid) can be precisely and evenly sprayed from the plurality ofspray nozzles 6 in thespray range 18a overlapping themixed area 41, where thejet flow 40 of combustion air and theunburnt gas 10a are mixed, thejet flow 40 being jetted from the after-air port 3 to the inside of thefurnace 1, the inside communicating with theopening 3a of the after-air port 3. - Accordingly, in this embodiment, the latent heat and sensible heat of the sprayed
water 18 deprive the heat of the flame resulting from the combustion of theunburnt gas 10a in themixed area 41, so it is possible to precisely suppress the flame temperature to about 1600K or below, preferably about 1600K to about 1400K. The concentration of NOx generated in the boiler can thereby be reduced by about 10% to 30%. - Since the
spray nozzles 6 in this embodiment are also disposed near theopening 3a of the after-air port 3, it becomes possible to prevent ash from adhering to the spray nozzles and the structural members from being deformed due to contact with the combustion gas at high temperature. Furthermore, since a plurality of spray nozzle are provided, even if some of the plurality of spray nozzles are clogged, a necessary amount of cooling fluid can still be sprayed by the remaining spray nozzles, so it becomes possible to obtain highly reliable spray nozzles that can withstand prolonged use. - Next,
FIGs. 9 and 10 show part of the structures of after-air ports in other embodiments that are used in the pulverized coal boiler shown inFIG. 1 , which embodies the present invention. -
FIGs. 9 and 10 show the structures of the after-air ports, having spray nozzles, in the other embodiments. Pulverized coal boilers in which the after-air ports 3 in this embodiment are used have the same structure as the pulverizedcoal boiler 100 in the embodiment.shown inFIG. 1 , so the explanation of the pulverized coal boilers including the after-air ports 3 in this embodiment will be omitted. - The basic structure of the after-
air ports 3 in this embodiment shown inFIGs. 9 and 10 are the same as the basic structure of the after-air ports 3 in the embodiments shown inFIGs. 5 and7 , so the explanation of the same basic structure will be omitted and only different parts will be described. - In
FIGs. 9 and 10 , eachspray nozzle 6, included in the after-air port 3 in each embodiment, from which the water 18 (cooling fluid) is sprayed, is disposed so that the end of thespray nozzle 6 is positioned near the wall of thewind box 5 rather than theopening 3a of the after-air port 3 to leave a distance from thefurnace 1; the end of thespray nozzle 6 is located, in the after-air port 3, at an upstream position of thejet flow 40 of combustion air, relative to theopening 3a of the after-air port 3. - According to this embodiment, the water 18 (cooling fluid) is sprayed from each
spray nozzle 6 at an upstream position of thejet flow 40 of combustion air supplied from theopening 3a of the after-air port 3 into the inside of thefurnace 1, and vaporized so that moisture is further evenly mixed with thejet flow 40 of combustion air supplied from the after-air port 3, adding the moisture to thejet flow 40 itself of the combustion air supplied from the after-air port 3. Accordingly, the moisture can be more precisely supplied to thespray range 18a overlapping themixed area 41, where thejet flow 40 and theunburnt gas 10a are mixed, and thereby a rise in flame temperature can be more surely suppressed. - Although the
spray nozzles 6 disposed in the after-air ports 3 in this embodiment have been indicated as one-fluid spray nozzles that spray thewater 18 as the cooling fluid, the embodiment can also be applied to a two-fluid spray nozzle that sprays a coolingliquid including water 18 andsteam 20. - Although not described, control of the cooling fluid by the
spray nozzles 6 in the after-air ports 3 in this embodiment, shown inFIGs. 9 and 10 , can be carried out by having thecontroller 50 adjust the flow rate of the cooling fluid as in the embodiments described above. - The above embodiments in the present invention can also achieve a highly reliable pulverized coal boiler that ensures suppression of a flame temperature rise that is caused during the combustion of an unburnt gas in a furnace when combustion air is supplied from after-air ports so as to reduce the concentration of thermal NOx generated during the combustion.
- Next, a pulverized coal boiler in another embodiment of the present invention will be described with reference to the drawings.
-
FIG. 11 is a schematic diagram indicating the structure of a pulverizedcoal boiler 100 in another embodiment of the present invention. The pulverizedcoal boiler 100 comprises, on the wall of afurnace 1,burners 2 for burning pulverized coal used as a fuel and after-air ports 3, each of which has aspray nozzle 6 for spraying both water and steam. - The basic structure of the pulverized coal boiler in this embodiment is the same as the basic structure of the pulverized
coal boiler 100 in the embodiment shown inFIG. 1 , so the explanation of the same basic structure will be omitted and only different parts will be described. - In the pulverized
coal boiler 100 in this embodiment shown inFIG. 11 , a two-fluid nozzle, which can spray twofluids including water 18 andsteam 20 is used as thespray nozzle 6 disposed in the after-air port 3. - A system for supplying the
water 18 to thespray nozzles 6, each of which sprays the twofluids including water 18 andsteam 20 as the cooling fluid uses the same thepipe 42 and thevalve 17 as shown inFIG. 1 . - A system for supplying the
steam 20 to thespray nozzles 6, each of which sprays the two fluids, has asteam tank 21 to which part of steam used in a power generation plant is supplied for storage purposes, the pressure in thesteam tank 21 being set to a prescribed value. The system also has apipe 43 through which thesteam 20 stored in thesteam tank 21 is supplied to thespray nozzles 6, avalve 22 for adjusting the flow rate of thesteam 20 supplied is provided on thepipe 43. - The opening of the
valve 22, which adjusts the flow rate of thesteam 20 sprayed from the two-fluid spray nozzles 6 into the inside of thefurnace 1, is controlled by thecontroller 50. Specifically, as with control of the opening of thevalve 17 for adjusting the amount of spray of thewater 18, thespray amount calculator 53 in thecontroller 50 compares a boiler load and the NOx emission concentration of the exhaust gas 11, which is detected by theNOx detector 55, with the setting in the boilerload setting unit 51 and the setting in the NOxconcentration setting unit 52, respectively. Then, thespray amount calculator 53 calculates the amount of thesteam 20 that needs to be supplied. The opening of thevalve 22 that corresponds to the amount of steam is commanded as an opening signal by thespray amount calculator 53 in thecontroller 50 for thevalve 22 so that the necessary amount ofsteam 20 is sprayed from thespray nozzles 6. - The
steam 20 is sprayed from the two-fluid spray nozzle 6 toward the inside of thefurnace 1 in a form similar to thespray range 18a, which overlapsmixed area 41, extending from thespray nozzle 6 shown inFIGs. 2 to 4 . - The opening of the
valve 22 is controlled by thecontroller 50 in the same way as the opening of thevalve 17 is controlled by thecontroller 50 as shown inFIGs. 16A and 16B . - Due to the above arrangement in this embodiment, the flow rate of the
steam 20 sprayed from thespray nozzles 6, -which spray twofluids including water 18 andsteam 20 can follow a change in the flow rate of thewater 18 sprayed. - Accordingly, when the two-
fluid spray nozzle 6 in this embodiment is used, droplets of the cooling fluid sprayed toward the inside of thefurnace 1 become finer and evaporation of the water is facilitated, quickly suppressing the rise in the flame temperature. - The above embodiment in the present invention can also achieve a highly reliable pulverized coal boiler that ensures suppression of a flame temperature rise that is caused during the combustion of an unburnt gas in a furnace when combustion air is supplied from after-air ports so as to reduce the concentration of thermal NOx generated during the combustion.
- Next, a pulverized coal boiler in another embodiment of the present invention will be described with reference to the drawings.
-
FIG. 12 is a schematic diagram indicating the structure of a pulverizedcoal boiler 100 in other embodiment of the present invention. The pulverizedcoal boiler 100 comprisesburners 2 for burning pulverized coal used as a fuel, after-air ports 3 for supplying combustion air, andspray nozzles 6 for spraying water (cooling fluid) into the after-air ports 3. - The basic structure of the pulverized coal boiler in this embodiment is the same as the basic structure of the pulverized
coal boiler 100 in the embodiment shown inFIG. 1 , so the explanation of the same basic structure will be omitted and only different parts will be described. -
FIG. 13 shows the structure of thewind box 5, which includes the after-air ports 3 used in the pulverizedcoal boiler 100 in the embodiment of the present invention shown inFIG. 12 .FIG. 14 shows a section as viewed along line D-D inFIG. 13 . - In this embodiment, the
spray nozzles 6 are provided on the wall of thewind box 5 as shown inFIGs. 13 and 14 . The water 18 (cooling fluid) is sprayed from thespray nozzles 6 toward thespray range 18a in thewind box 5. - When combustion air is supplied from the
opening 3a of each after-air port 3 disposed in thewind box 5 into the inside of thefurnace 1 as thejet flow 40, the temperature of the combustion air is about 300°C in thewind box 5, which is sufficiently high for combustion air to vaporize thewater 18 sprayed from thespray nozzle 6 into thespray area 18a in thewind box 5. - After being vaporized in the
wind box 5, thewater 18 is adequately and evenly mixed with the flow of combustion air in thewind box 5, and the mixture of thewater 18 and the flow of combustion air is supplied, as part of thejet flow 40 of combustion air, from theopening 3a of the after-air port 3 toward the inside of thefurnace 1. Then, the mixture is supplied to themixed area 41, where thejet flow 40 of combustion air and theunburnt gas 10a are mixed, reducing the temperature of the flame in the combustion of theunburnt gas 10a. - In this embodiment as well, the
jet flow 40 of combustion air, with which the water 18 (cooling fluid) sprayed from thespray nozzle 6 into thewind box 5 and vaporized is mixed, can be precisely and evenly sprayed in themixed area 41, where thejet flow 40 of combustion air and theunburnt gas 10a are mixed, thejet flow 40 being jetted toward the inside of thefurnace 1, the inside communicating with theopening 3a of the after-air port 3. - Accordingly, in this embodiment, the latent heat and sensible heat of the
water 18 sprayed from thespray nozzle 6 deprive the heat of the flame resulting from the combustion of theunburnt gas 10a in themixed area 41, so it is possible to suppress the flame temperature to about 1600K or below, preferably about 1600K to about 1400K. The concentration of NOx generated in the boiler can thereby be reduced by about 10% to 30%. - In this embodiment, any spray pattern is allowed if the water 18 (cooling fluid) sprayed from the
spray nozzle 6 in thewind box 5 is vaporized. It is not necessary that the sprayedwater 18 is completely vaporized. Thewater 18 remaining in thewind box 5 without being vaporized may be collected as drain water and reused. - According to this embodiment, since the
water 18 sprayed from thespray nozzle 6 is vaporized in thewind box 5 and moisture is evenly mixed with thejet flow 40 itself supplied from the after-air port 3 into the inside of thefurnace 1, the moisture can be precisely supplied to themixed area 41, suppressing a flame temperature rise that is caused during combustion in themixed area 41. - Due to the evaporation of the sprayed moisture, the temperature of the combustion air in the
wind box 5 is lowered and thereby thejet flow 40 itself supplied from the after-air port 3 into the inside of thefurnace 1 becomes cold, more precisely suppressing the flame temperature rise that is caused during combustion in themixed area 41. - Although a case in which the
water 18 is used as the cooling fluid sprayed from thespray nozzle 6 has been described in this embodiment, thesteam 20 or two fluids including the water and steam may be sprayed instead of the water. - Although not described, control of the cooling fluid by the
spray nozzles 6 disposed in thewind boxes 5 in this embodiment can be carried out by having thecontroller 50 adjust the flow rate of the cooling fluid as in the embodiments described above. - The above embodiment in the present invention can also achieve a highly reliable pulverized coal boiler that ensures suppression of a flame temperature rise that is caused during the combustion of an unburnt gas in a furnace when combustion air is supplied from after-air ports so as to reduce the concentration of thermal NOx generated during the combustion.
- Next, a pulverized coal boiler in other embodiment of the present invention will be described with reference to the drawings.
-
FIG. 17 is a schematic diagram indicating the structure of a pulverizedcoal boiler 100 in other embodiment of the present invention. The pulverizedcoal boiler 100 comprisesburners 2 for burning pulverized coal used as a fuel, after-air ports 3 for supplying combustion air, andspray nozzles 6 for spraying water (cooling fluid) into aduct pipe 14 through which the combustion air is supplied to the after-air ports 3. - The basic structure of the pulverized coal boiler in this embodiment is the same as the basic structure of the pulverized
coal boiler 100 in the embodiment shown inFIG. 1 , so the explanation of the same basic structure will be omitted and only different parts will be described. - In this embodiment, the
spray nozzles 6 are disposed in thepipe 14 positioned further upstream than thewind boxes 5 through which combustion air is supplied to the after-air ports 3, and the water 18 (cooling fluid) is sprayed from thesespray nozzles 6 to the combustion air flowing in thepipe 14, so the sprayedwater 18 is mixed with the combustion air. Accordingly, thewater 18 stays in the combustion air at high temperature, which is supplied to the after-air ports 3, for an increased period of time. - As a result, the ratio of the vaporization of the
water 18 sprayed from thespray nozzle 6 is increased and lessens drainage water, and thereby the water 18 (cooling fluid) sprayed from thespray nozzle 6 is more efficiently vaporized. - According to this embodiment, since the
water 18 sprayed from thespray nozzle 6 is vaporized in thepipe 14 disposed upstream of thewind box 5 and moisture is evenly mixed with thejet flow 40 itself supplied from the after-air port 3 into the inside of thefurnace 1, the moisture can be precisely supplied to themixed area 41, suppressing a flame temperature rise that is caused during combustion in themixed area 41. - Due to the evaporation of the sprayed moisture, the temperature of the combustion air supplied to the inside of the
wind box 5 is lowered and thereby thejet flow 40 itself supplied from the afterair port 3 into the inside of thefurnace 1 becomes cold, more precisely suppressing the flame temperature rise that is caused during combustion in themixed area 41. - Although a case in which the
water 18 is used as the cooling fluid sprayed from thespray nozzle 6 has been described in this embodiment, thesteam 20 or two fluids including the water and steam may be sprayed instead of the water. - Although not described, control of the cooling fluid by the
spray nozzles 6 disposed in thewind boxes 5 in this embodiment can be carried out by having thecontroller 50 adjust the flow rate of the cooling fluid as in the embodiments described above. - Accordingly, in this embodiment, the latent heat and sensible heat of the
water 18 sprayed from thespray nozzle 6 deprive the heat of the flame resulting from the combustion of theunburnt gas 10a in themixed area 41, so it is possible to suppress the flame temperature to about 1600K or below, preferably about 1600K to about 1400K. The concentration of NOx generated in the boiler can thereby be reduced by about 10% to 30%. - The above embodiment in the present invention can also achieve a highly reliable pulverized coal boiler that ensures suppression of a flame temperature rise that is caused during the combustion of an unburnt gas in a furnace when combustion air is supplied from after-air ports so as to reduce the concentration of thermal NOx generated during the combustion.
- Next, a pulverized coal boiler in other embodiment of the present invention will be described with reference to the drawings.
-
FIG. 18 is a schematic diagram indicating the structure of a pulverizedcoal boiler 100 in other embodiment of the present invention. The pulverizedcoal boiler 100 comprises, on the wall of thefurnace 1,burners 2 for spraying and burning pulverized coal used as a fuel, main after-air ports 61 for supplying combustion air, and sub after-air ports 60, each of which has thespray nozzle 6 for spraying both water and steam to supply combustion air. - The basic structure of the pulverized coal boiler in this embodiment is the same as the basic structure of the pulverized
coal boiler 100 in the embodiment shown inFIG. 17 , so the explanation of the same basic structure will be omitted and only different parts will be described. - On the wall of the
furnace 1 in the pulverizedcoal boiler 100 in this embodiment shown inFIG. 18 , the sub after-air ports 60 are disposed in the direction in which thecombustion gas 10 flows in thefurnace 1 on the upstream side and main after-air ports 61 are disposed on the downstream side. - The
sub-after port 60 has thespray nozzle 6, from which water or both water and steam is sprayed. - In the pulverized
coal boiler 100 in this embodiment, the amount of air supplied from the sub after-air port 60 is smaller than the amount of air supplied from the main after-air port 61. - In the pulverized
coal boiler 100 structured as described above, air sprayed from thesub-after ports 60 into the inside of thefurnace 1 flows as air flows 62 and air sprayed from the main after-air ports 61 into the inside of thefurnace 1 flows as air flows 63, as schematically shown inFIG. 18 . - The air flows 62 supplied from the
sub-after ports 60 into the inside of thefurnace 1 by being sprayed are directed toward the downstream side along the inner wall of thefurnace 1 because the amount of air sprayed is small. - The air flows 63 supplied from the main after
ports 61 into the inside of thefurnace 1 by being sprayed reaches the central part of thefurnace 1 because the amount of air sprayed is large. - While flowing from downstream to upstream in the
furnace 1, thecombustion gas 10a is mixed with the air flows 62 and 63. Near the wall of thefurnace 1, the temperature of thecombustion gas 10a mixed with theair flow 62 on the upstream side is higher than the temperature of thecombustion gas 10a mixed with theair flow 63 on the downstream side. - The temperature of the
combustion gas 10a is highest at the central part of thefurnace 1 because it is distant from the wall. - When the
hot combustion gas 10a including the unburnt gas is mixed with the supplied air, a combustion reaction proceeds and the temperature of the mixture of thecombustion gas 10a and the supplied air is raised. At that time, nitrogen gas in the air or thecombustion gas 10a is oxidized in a hot oxidization atmosphere, generating nitrogen oxides (NOx), which is so-called thermal NOx. The higher the temperature is, the more thermal NOx is generated. - Since the pulverized
coal boiler 100 in this embodiment is structured so that water is sprayed from thespray nozzles 6 disposed in the sub after-air ports 60 on the upstream side, theair flow 62 includes much moisture supplied from the sub after-air port 60 toward the inside of thefurnace 1. - The water sprayed from the
spray nozzle 6 deprives evaporation heat from the surrounding air during the evaporation, lowering the temperature of the air. - Since the
air flow 62 includes much moisture, its specific heat is raised. Accordingly, when thecombustion gas 10a is mixed with theair flow 62 jetted from the sub after-air ports 60, it is possible to suppress the combustion reaction by the amount of moisture included in theair flow 62 and thereby the combustion temperature can be reduced - Therefore, the amount of thermal NOx generated during the combustion reaction can be reduced.
- In the pulverized
coal boiler 100 in this embodiment, after theair flow 62 including moisture has been mixed with thecombustion gas 10a, part of theair flow 62 is further mixed with theair flow 63 jetted from the main after-air port 61 located downstream of theair flow 62. - When the part of the
air flow 62 including moisture is mixed with theair flow 63, part of a gas already burnt in aninner wall vicinity 64 in thefurnace 1 is involved in theair flow 63 jetted from the main after-air port 61, so a burnt gas including moisture flows along the outermost circumference of theair flow 63. - Accordingly, when the unburnt gas including moisture, the
air flow 63, and thecombustion gas 10a are mixed, the combustion temperature can be reduced due to the specific heats of the moisture included in the burnt gas. As a result, the amount of thermal NOx generated at the central part of thefurnace 1 can be reduced. - When the air flow jetted from the after air port and the
combustion gas 10a are mixed, as described above, the air flow including much moisture and the burnt gas including moisture are supplied to theinner wall vicinity 64 in thefurnace 1 in a relatively upstream region, thecentral part 65 of thefurnace 1, and other parts where high temperature is easily reached, enabling the amount of thermal NOx generated to be suppressed to a small value. - Since the burnt gas including much moisture is involved in the outermost circumferential part of the
air flow 63, both reduction in the amount of water supply and suppression of thermal NOx can be achieved. - Although the thermal efficiency is lowered by the supplied water, since thermal NOx is suppressed, it is possible to suppress, at a downstream site of the
furnace 1, power for operating units to reduce NOx and the amount of chemicals supplied. - In this embodiment, a situation in which the amount of air in the
air flow 62 supplied from the sub after-air port 60 disposed upstream of thefurnace 1 is smaller than the amount of air in theair flow 63 supplied from the main after-air port 61 disposed downstream has been described. However, even if the amount of air in theair flow 62 supplied from the sub after-air port 60 disposed upstream of thefurnace 1 is larger than the amount of air in theair flow 63 supplied from the main after-air port 61, almost the same effect can be obtained. - To reduce thermal NOx generated in this case, it is clear as described above that much more water must be sprayed from the
spray nozzle 6 disposed in the sub after-air port 60 than described above. - However, since much air of the
air flow 62 supplied from the sub after-air port 60 is mixed with thecombustion gas 10a upstream of thefurnace 1, the amount of unburnt gas can be reduced at the exit of thefurnace 1. - Although a case in which the
water 18 is used as the cooling fluid sprayed from thespray nozzle 6 has been described in this embodiment, thesteam 20 or twofluids including water 18 andsteam 20 may be sprayed instead ofwater 18. - In this embodiment, a case in which the end of the
spray nozzle 6 is positioned in the opening of the sub after-air port 60 has been described. Even if, however, thespray nozzle 6 is disposed in- awind box 5a, which accommodates the sub after-air port 60, or thepipe 14, through which air is supplied to thewind box 5a, as in the sixth embodiment shown inFIG. 12 and the seventh embodiment shown inFIG. 17 , the same effect as describe above can be obtained. - The effect obtained when the
spray nozzle 6 is disposed at one of the above positions is the same as in the sixth embodiment shown inFIG. 7 and the seventh embodiment shown inFIG. 17 . - It is also possible to dispose the
spray nozzle 6 in the opening in theswirl flow path 31, which is formed around the outer circumference of thestraight flow path 30, as in the second embodiment of the present invention shown inFIGs. 5 and 6 . - In this case, the swirl flow causes much of the
water 18 jetted from thespray nozzle 6 to flow around the outer circumference of theair flow 62, so much moisture is included in the mixture of thecombustion gas 10a and theair flow 62. Accordingly, the concentration of the thermal NOx can be reduced with a small amount of water. - In the pulverized
coal boiler 100 in this embodiment the cooling fluid sprayed from thespray nozzle 6 disposed in the sub after-air port 60 is controlled by thecontroller 50, as in the embodiments described above. - Specifically, a NOx concentration signal about the exhaust gas 11 detected by the
NOx detector 55 is entered to thecontroller 50. Thecontroller 50 then compares the NOx concentration with a desired NOx setting, calculates a flow rate command signal about the cooling fluid to be sprayed from thespray nozzles 6 toward the inside of thefurnace 1 so that the NOx concentration of the exhaust gas 11 is maintained at the desired setting, and outputs the command signal to thevalve 17 used for flow rate adjustment, which is disposed in thepipe 42, through which the water 18 (cooling fluid) is supplied to thespray nozzles 6. This arrangement enables the flow rate of the cooling fluid to be appropriately controlled and thereby the thermal NOx concentration to be reduced. - The pulverized
coal boiler 100 described above can be a highly reliable pulverized coal boiler that ensures suppression of a flame temperature rise that is caused during the combustion of an unburnt gas in a furnace when combustion air is supplied from after-air ports so as to reduce the concentration of thermal NOx generated during the combustion. - The present invention can be applied to a pulverized coal boiler that uses pulverized coal as a fuel, more particularly to a pulverized coal boiler that suppresses the generation of thermal nitrogen oxides. The present invention can also be applied to conventional pulverized boilers with ease.
Claims (10)
- A pulverized coal boiler comprising a furnace, a burner provided on a wall of the furnace for supplying pulverized coal to the inside of the furnace and burning the pulverized coal, and an after-air port provided on the wall of the furnace at a position downstream of the burner for supplying combustion air to the inside of the furnace,
the pulverized coal boiler further comprising:
a spray nozzle disposed near a jet port of the after-air port for supplying water, steam, or two fluids including water and steam to the inside of the furnace; whereby the water, the steam, or the two fluids including water and steam sprayed from the spray nozzle are supplied to the inside of the furnace together with the combustion air supplied from the after-air port. - The pulverized coal boiler according to claim 1, wherein a plurality of after-air ports are disposed in the furnace in a combustion gas flow direction; and
at least one of the plurality of after-air ports disposed upstream in the combustion gas flow direction in the furnace supplies the water, the steam, or the two fluids including water and steam to the inside of the furnace. - The pulverized coal boiler according to claim 2, wherein at least one of the plurality of after-air port disposed upstream in the combustion gas flow direction in the furnace supplies combustion air less than that of combustion air supplied from the after-air ports disposed downstream in the combustion gas flow direction.
- The pulverized coal boiler according to claim 2 or 3, wherein each of the after-air ports for supplying the water, the steam, or the two fluids including water and steam is provided with a straight flow path for jetting the combustion air as a straight flow, and a swirl flow path formed around an outer circumference of the straight flow path for jetting the combustion air as a swirl flow, internally; and the water, the steam, or the two fluids including water and steam are jetted from the swirl flow path.
- The pulverized coal boiler according to any one of claims 1 to 4, further comprising:a NOx detector for detecting a NOx concentration of an exhaust gas exhausted from the pulverized coal boiler; anda controller for controlling a flow rate of the water, the steam, or the two fluids including water and steam, which are supplied from the spray nozzle to the inside of the furnace, based on the NOx concentration detected by the NOx detector.
- The pulverized coal boiler according to any one of claims 1 to 4, further comprising a controller for controlling a flow rate of the water, the steam, or the two fluids including water and steam, which are supplied from the spray nozzle to the inside of the furnace, based on a load of the pulverized coal boiler.
- The pulverized coal boiler according to claim 1, wherein a jet port of the spray nozzle for supplying the water, the steam, or the two fluids including water and steam into the inside of the furnace is disposed upstream in a jet flow of combustion air jetted from the jet port of the after-air port.
- A pulverized coal boiler comprising a furnace, a burner provided on a wall of the furnace for supplying pulverized coal to the inside of the furnace and burning the pulverized coal, an after-air port provided on the wall of the furnace at a position downstream of the burner for supplying combustion air to the inside of the furnace, a wind box for supplying the combustion air into the after-air port, and a duct pipe for externally supplying the combustion air into the wind box,
the pulverized coal boiler further comprising:a spray nozzle disposed in the wind box or in the duct pipe for supplying water, steam, or two fluids including water and steam; whereby the water, the steam, or the two fluids including water and steam sprayed from the spray nozzle into the inside of the wind box or the duct pipe ar supplied to the inside of the furnace together with the combustion air supplied from a jet port of the after-air port. - The pulverized coal boiler according to claim 8, further comprising:a NOx detector for detecting a NOx concentration of an exhaust gas exhausted from the pulverized coal boiler; anda controller for controlling a flow rate of the water, the steam, or the two fluids including water and steam, which are supplied from the spray nozzle to the inside of the furnace, based on the NOx concentration detected by the NOx detector.
- The pulverized coal boiler according to claim 8, further comprising a controller for controlling a flow rate of the water, the steam, or the two fluids including water and steam, which are supplied from the spray nozzle to the inside of the furnace, based on a load of the pulverized coal boiler.
Applications Claiming Priority (2)
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JP2006302881 | 2006-11-08 | ||
PCT/JP2007/071525 WO2008056650A1 (en) | 2006-11-08 | 2007-11-06 | Pulverized coal boiler |
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EP2083216A1 true EP2083216A1 (en) | 2009-07-29 |
EP2083216A4 EP2083216A4 (en) | 2013-03-06 |
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US (1) | US20100031858A1 (en) |
EP (1) | EP2083216A4 (en) |
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CN105003912A (en) * | 2015-07-24 | 2015-10-28 | 湖南高华环保股份有限公司 | Low-NOx combustion method and low-NOx combustion system |
CN105003912B (en) * | 2015-07-24 | 2017-10-27 | 湖南高华环保股份有限公司 | Low nox combustion method and low nox combustion system |
Also Published As
Publication number | Publication date |
---|---|
EP2083216A4 (en) | 2013-03-06 |
JPWO2008056650A1 (en) | 2010-02-25 |
JP5095628B2 (en) | 2012-12-12 |
WO2008056650A1 (en) | 2008-05-15 |
US20100031858A1 (en) | 2010-02-11 |
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