JP4859797B2 - Pulverized coal fired boiler - Google Patents

Description

  The present invention relates to a pulverized coal fired boiler that burns pulverized coal as fuel.

  As a conventional pulverized coal-fired boiler, a pulverized coal-fired boiler that burns pulverized coal as fuel is pulverized into fine pulverized coal having a fine particle size by a mill as described in JP-A-2004-190981 Then, it is supplied into the furnace from the burner installed in the furnace of the boiler and burned.

  The boiler furnace is equipped with an after-air port that blows out combustion air that burns the pulverized coal supplied from the burner. Combustion gas generated by the combustion of the pulverized coal in the furnace flows down the furnace. A technique is disclosed in which a part of the discharged combustion exhaust gas is recirculated and mixed with the combustion air in the after-air port to reduce the generation amount of thermal NOx.

  In addition, as described in Japanese Patent Application Laid-Open No. 2004-190981, in a conventional pulverized coal fired boiler, a part of the combustion exhaust gas discharged from the boiler furnace is recirculated and supplied to the after-air port of the furnace. A method of reducing the amount of thermal NOx generated by completely burning unburned combustion gas by mixing with air for combustion in an air port and supplying it into a furnace is disclosed.

  In the pulverized coal-fired boiler described in Japanese Patent Application Laid-Open No. 2004-190981, a recirculated flue gas having a low oxygen concentration is supplied to the mixing interface between the combustion air and the reducing gas in the after air port, Suppresses the generation of NOx. The recirculated flue gas is a cooled flue gas at about 250 ° C. to 350 ° C. discharged from the furnace through the heat transfer tube group.

  By the way, in order to return the combustion exhaust gas to be recirculated from the downstream in the furnace to the after-air port of the furnace, a long pipe for circulating the combustion exhaust gas and a large capacity recirculation fan for supplying the combustion exhaust gas are required.

  Further, in the conventional pulverized coal fired boiler described in Japanese Patent Laid-Open No. 2005-265299, the combustion exhaust gas in the furnace is directly recirculated to the after-air port of the furnace by arranging an air injector or a surge tank and a blower. A method is disclosed.

Japanese Patent Laid-Open No. 2004-190981 JP 2005-265299 A

  By the way, in the conventional pulverized coal-fired boiler, as described in JP-A No. 2004-190981, if the temperature of the recirculated flue gas is relatively low, about 250 ° C. to 350 ° C., ash adhesion can be avoided. , It is necessary to install a long piping in the piping that recirculates the flue gas discharged from the furnace to the after-air port of the furnace, and to install a large-capacity recirculation fan. There is a growing problem.

  On the other hand, in a conventional pulverized coal-fired boiler, as described in JP-A-2005-265299, in order to extract the high-temperature combustion exhaust gas in the furnace and recirculate it to the furnace in order to shorten the pipe length, High-temperature (about 900 ° C.) combustion exhaust gas containing a large amount of fly ash flows through the pipe for recirculating the combustion exhaust gas inside.

  When the high-temperature combustion exhaust gas exceeding 700 ° C. is caused to flow down to the pipe for recirculation, there is a problem that the pipe is likely to be blocked due to ash adhering to the inner wall surface of the pipe.

  An object of the present invention is to provide a pulverized coal-fired boiler that reduces the size of equipment for flowing down combustion exhaust gas and prevents ash from adhering to the pipe through which the combustion exhaust gas flows down, thereby avoiding blockage of the pipe.

  A pulverized coal fired boiler according to the present invention includes a furnace, a plurality of burners installed on a wall surface of the furnace to supply pulverized coal into the furnace and combust it to generate reducing combustion exhaust gas, and a furnace above the burner. An after air port installed on the wall surface to supply combustion air and completely burn the reducing combustion gas generated in the burner to generate combustion exhaust gas, and the furnace air flowed down in the furnace downstream from the after air port A part of the combustion exhaust gas is extracted from the wall surface of the furnace and mixed with the combustion air supplied to the after-air port, and the combustion exhaust gas installed in the return pipe and flowing through the return pipe A cooling device for supplying a cooling fluid to be cooled is provided.

  According to the present invention, it is possible to realize a pulverized coal fired boiler that reduces the size of equipment for flowing down combustion exhaust gas and prevents ash from adhering to the pipe through which the combustion exhaust gas flows down, thereby avoiding blockage of the pipe.

  A pulverized coal burning boiler according to an embodiment of the present invention will be described below with reference to the drawings.

  The whole structure of the pulverized coal burning boiler of 1st Example which is one Example of this invention is shown in FIG.

  In the pulverized coal fired boiler according to the first embodiment of the present invention shown in FIG. 1, the furnace 1 constituting the boiler is an opposed combustion type furnace.

  In this embodiment, the wall on the flue side (right side of FIG. 1) of the furnace 1 is referred to as the can, and the opposite side (left side of FIG. 1) is referred to as the front of the can, and the wall surface in the depth direction of the furnace 1 in FIG. Call it.

  In the pulverized coal fired boiler of this embodiment, the upper and lower two-stage burners 2 are arranged in the width direction on the front wall 1a on the front side of the boiler of the boiler 1 and on the rear wall 1b on the rear side of the can (left and right direction in FIG. 1). A plurality are arranged in the depth direction of the figure.

  The fuel pulverized coal supplied to the burner 2 is pulverized into fine pulverized powder (about several tens of μm) by a mill (not shown) to be pulverized coal, and supplied from the pulverized coal transport blower 7. It is transported through the coal supply pipe 31 by the transporting air and supplied to the burner 2.

  The combustion air is blown from the combustion air blower 8 through the air supply pipe 32.

  The combustion air is preheated to about 300 ° C. by a heat exchanger (not shown) from the viewpoint of promoting combustion, and then burner window box 5 and after-airport window box 6 through air supply pipe 32. Are supplied respectively.

  The burner 2 is surrounded on the outside by a burner window box 5, and combustion air is fed into the burner 2 from the burner window box 5.

  As with the burner 2, the jet nozzle 3 of the after air port 3 a is also surrounded by a wind box 6 for the after air port, and combustion air is sent from the wind box 6 for the after air port to the jet nozzle 3. .

  The flow rate of the combustion air supplied to the burner 2 is adjusted by the flow rate control valve 9 so that the pulverized coal ejected from the burner 2 is reduced and burned in the furnace near the burner.

  The amount of combustion air supplied to the burner 2 is about 80% of the amount of air required for the pulverized coal supplied to the burner 2 to be completely burned in the furnace.

  And the pulverized coal supplied from the burner 2 is burned in the furnace 1 by supplying this combustion air.

  As the pulverized coal supplied from the burner 2 burns in the furnace 1, combustion gas 2 b of 1000 ° C. or more is generated in the furnace 1.

  The reducing combustion gas 2b generated after the pulverized coal is burned is first ejected toward the center of the furnace 1, and then collides with the reducing combustion gas 2a generated from the opposing burner 2 to rise in the furnace 1. .

  The rising combustion gas 2b is mixed with the combustion air jetted from the jet nozzle 3 of the after air port 3a above the burner 2 and burns completely, and rises in the furnace 1.

  A combustion method for oxidizing after reduction is known as a combustion method (two-stage combustion) for suppressing generation of unburned components such as nitrogen oxides and carbon monoxide.

  Combustion exhaust gas that has completely burned the reducing combustion gas 2b by the combustion air supplied into the furnace 1 from the jet nozzle 3 of the after-air port 3a flows up in the furnace 1 and flows in the upper part of the furnace 1. After heat is exchanged with water flowing through the heat tube group 10 to generate steam and recover the heat, it is discharged as exhaust gas into the flue 11 downstream of the furnace 1.

  In addition, a water-cooled tube group (not shown) is disposed on the inner surface of each wall of the front wall 1a, the rear wall 1b, and the side wall 1c constituting the furnace 1, and fuel burns in the furnace 1. The water or steam flowing through these water-cooled tube groups is heated by absorbing heat generated by the water.

  Here, when the combustion air ejected from the jet nozzle 3 of the after air port 3a is mixed with the reducing combustion gas 2b generated after combustion in the burner 2, an oxidation reaction occurs rapidly.

  Due to this oxidation reaction, the temperature of the combustion gas 2b rises rapidly, and thermal NOx is generated in the mixing region, but a larger amount of thermal NOx is generated when the gas temperature is higher.

  In boilers, the ratio of thermal NOx to the total amount of generated nitrogen oxides is large, so the reduction of thermal NOx leads to the reduction of the total generated amount of nitrogen oxides.

  The inventors have obtained the knowledge that thermal NOx is reduced when combustion exhaust gas is mixed with combustion air jetted from the jet nozzle 3 of the after-air port 3a and burned by basic experiments.

  The reason why the thermal NOx decreases when combustion exhaust gas is mixed and burned is that the temperature of the combustion flame is lower when the combustion exhaust gas is mixed than when the combustion exhaust gas is not mixed.

  Therefore, in the pulverized coal fired boiler of the present embodiment, a part of the combustion exhaust gas flowing down in the furnace 1 from the wall surface of the side wall 1c of the furnace 1 downstream from the after-air port 3a of the furnace 1 is extracted as the combustion exhaust gas 12. A return pipe 4 for supplying the combustion exhaust gas 12 to the combustion air flowing through the jet nozzle 3 of the after-air port 3a of the furnace 1 and mixing it is provided.

  If the pressure on the after-air port 3a side of the return pipe 4 is lower than the pressure in the furnace 1 where the combustion exhaust gas 12 is extracted from the furnace 1 side, the extracted combustion exhaust gas 12 passes through the return pipe 4 downward from above. And is supplied to the jet nozzle 3 of the after air port 3a to be recirculated.

  In the pulverized coal fired boiler shown in FIG. 1, the recirculated flue gas 12 is extracted from the side wall 1c at a position downstream of the upper air port 3a in the upper part of the furnace 1 and returned to the jet nozzle 3 of the after air port 3a. Through.

  FIG. 2 is a partially enlarged view showing the structure of the after-air port 3a in the pulverized coal burning boiler of this embodiment shown in FIG. 1 including the wind box.

  In the after air port 3a of the pulverized coal burning boiler of this embodiment shown in FIG. 2, the combustion exhaust gas 12 extracted from the wall surface of the side wall 1c of the furnace 1 is disposed so as to be recirculated to the jet nozzle 3 of the after air port 3a. The return pipe 4 was a double pipe structure composed of an inner pipe 4a and an outer pipe 4b covering the inner pipe 4a.

  When the return pipe 4 has a double-pipe structure as shown in FIG. 2, the recirculated combustion exhaust gas 12 flows down inside the return pipe inner pipe 4a, and between the inner pipe 4a and the outer pipe 4b. Water and steam 13 which are cooling fluids for cooling the inner pipe 4a flow down in the flow path formed in the above.

  The combustion exhaust gas 12 flowing into the inner pipe 4a of the return pipe 4 is considered to be around 1000 ° C., but the cooling capacity for cooling the combustion exhaust gas 12 flowing through the inner pipe 4a of the return pipe is based on water or steam 13 as a cooling fluid. The flow rate, pressure, temperature, etc. can be adjusted.

  If the tube wall of the inner tube 4a of the return pipe 4 is not sufficiently cooled, it becomes easy for ash to adhere to the inner wall of the inner tube 4a, and ash adheres to the tube wall of the inner tube 4a of the return pipe 4. In this case, since the ash has a low thermal conductivity and the attached ash is not removed and remains on the tube wall of the inner tube 4a, the cooling effect of the tube wall of the inner tube 4a is further reduced, and the ash is deposited on the tube wall of the inner tube 4a. The surface temperature of the attached ash will rise.

  Furthermore, since the ash is softened by the rise in the surface temperature of the ash, the ash is more easily attached to the tube wall of the inner tube 4a of the return pipe 4, and the thickness of the ash attached to the tube wall of the inner tube 4a is increased. .

  If ash adheres to the tube wall of the inner tube 4a of the return pipe 4, the piping of the inner tube 4a may be blocked. Therefore, as described above, as described above, the inner tube 4a and the outer tube of the return pipe 4 may be blocked. 4b, which is a cooling fluid, for example, water of about 200 to 300 ° C. or steam 13 is flowed to cool the wall of the inner pipe 4a flowing down the combustion exhaust gas 12, and the return pipe is cooled. The surface temperature of the tube wall of the 4 inner tube 4a is suppressed to be a temperature of about 400 ° C. or less to prevent ash from adhering to the inner tube 4a.

  Since the ash is in a dry powdery state at a temperature of about 400 ° C., there is no problem of adhering to the tube wall of the inner tube 4a. However, the temperature of the inner surface of the inner tube 4a is the dew point of the combustion exhaust gas 12. It is better not to be below.

  The reason is that when the temperature of the combustion exhaust gas 12 becomes lower than the dew point, moisture may condense in the inner pipe 4a of the return pipe 4 and lead to corrosion of the pipe.

  When the steam 13 is supplied as a cooling fluid to the flow path between the inner pipe 4a and the outer pipe 4b of the return pipe 4 to cool the pipe wall of the inner pipe 4a, the front wall 1a constituting the furnace 1 is used. Further, it is preferable to use steam generated by a water-cooled tube group disposed on the inner wall surface of each wall of the rear wall 1b and the side wall 1c.

  If it does so, since the calorie | heat amount discharge | released out of the system among the calorie | heat amount which the combustion exhaust gas 12 to recirculate can be reduced as much as possible, it becomes possible to reduce the fall of thermal efficiency.

  The structure of the after air port 3a and the mechanism for lowering the pressure on the after air port side of the return pipe 4 will be described with reference to FIG.

  As shown in FIG. 2, a wind box 6 for an after air port is installed on the wall surface of the front wall 1 a and the rear wall 1 b of the furnace 1, and after-air of combustion air is placed inside the wind box 6 in the furnace 1. The jet nozzle 3 of the after-air port 3a which jets in is installed.

  Although only one jet nozzle 3 is shown in FIG. 2, the jet nozzles 3 are actually arranged in a plurality of rows in the depth direction of the figure.

  The combustion air supplied into the wind box 6 for the after air port 3a is jetted into the furnace 1 from the jet nozzle 3 of the after air port 3a.

  Further, in the pulverized coal fired boiler of this embodiment, the jet nozzle 3 of the after air port 3a includes an inner peripheral jet nozzle 14 and an outer peripheral jet nozzle 15 installed on the outer periphery of the inner peripheral jet nozzle 14. It has a double structure.

  Further, swirl vanes 17 are installed on the outer peripheral side jet nozzle 15 of the jet nozzle 3, and a swirl component is given to the combustion air supplied into the furnace 1 from the after air port 3a.

  In addition, the inner peripheral jet nozzle 14 has a structure in which combustion air is taken into the inside through several holes 16 formed in the outer periphery.

  In the jet nozzle 3 of the after-air port 3a of the present embodiment, the mixing effect of the combustion air is improved by the swirling of the swirling blades 17 provided in the outer peripheral jet nozzle 15 and supplied from the jet nozzle 3 into the furnace 1. The combustion rate of the unburned matter contained in the combustion exhaust gas 12 is improved.

  2 schematically shows a jet of the combustion exhaust gas 12 blown into the furnace 1.

  Since the inner diameter of the inner peripheral jet nozzle 14 constituting the jet nozzle 3 of the after-air port 3a is smaller than the cross-sectional area of the combustion air suction port 16, the flow velocity of the combustion air flowing inside becomes faster.

  The flow rate of the combustion air varies depending on the combustion conditions and the furnace 1, but is approximately 20 to 50 m / s.

  From Bernoulli's law, the pressure drops approximately in proportion to the square of the flow velocity, so one end of the return pipe 4 is connected to the portion of the inner peripheral jet nozzle 14 where the pressure has dropped.

  As a result, the combustion exhaust gas 12 can be returned from the furnace 1 side to the after-air port 3a and recirculated.

  In the pulverized coal fired boiler of this embodiment, the return pipe 4 is installed so as to take in the outer periphery of the inner peripheral side jet nozzle 14 constituting the jet nozzle 3 of the after air port 3a. Several holes may be opened and connected.

  The installation position of the side wall 1c of the furnace 1 on the furnace 1 side of the return pipe 4 is important that there is little unburned content in the combustion exhaust gas 12 to be extracted.

  If the combustion exhaust gas 12 to be extracted has a large amount of unburned fuel, rapid combustion occurs in the jet nozzle 3 of the after air port 3a to which the combustion exhaust gas 12 is supplied, leading to a failure of the structure of the after air port 3a. This is because there is a possibility.

  The position of the side wall 1c of the furnace 1 where the return pipe 4 is provided and the combustion exhaust gas 12 is extracted from the furnace 1 is that the upper region of the furnace 1 has a relatively higher static pressure than the surroundings based on the combustion analysis of the furnace 1. And the side wall of the furnace 1 downstream of the after-air port 3a of the furnace 1 because it is known that the combustion gas flowing through the furnace 1 is mostly oxidized and the combustion gas flowing in the furnace 1 is small. A part of the combustion gas is extracted as the combustion exhaust gas 12 through the return pipe 4 from the wall surface 1c and is recirculated to the jet nozzle 3 of the after air port 3a.

  According to the embodiment of the present invention, the piping for flowing the combustion exhaust gas is shortened, the equipment that does not require the blower fan for flowing the combustion exhaust gas is downsized, and the piping for supplying the cooling fluid to flow the combustion exhaust gas is cooled. By doing so, it is possible to realize a pulverized coal fired boiler that can prevent the ash from adhering to the pipe and avoid the blockage of the pipe.

  Next, a pulverized coal burning boiler according to a second embodiment which is an embodiment of the present invention will be described with reference to FIGS.

  In this embodiment, since the basic configuration is common to the pulverized coal fired boiler of the first embodiment shown in FIGS. 1 and 2, the description of the common configuration will be omitted and only different portions will be described. .

  In the present embodiment shown in FIG. 3, a cooling water spray device 18, which is a device for flowing cooling water 19 of cooling fluid into the return pipe 4, is installed in the return pipe 4 as a structure for cooling the return pipe 4. Is.

  When the cooling water 19 is blown from the water spraying device 18 into the combustion exhaust gas 12 flowing down the return pipe 4, the water evaporates in addition to the heat of the sensible heat required when the temperature of the evaporated water rises. Since the latent heat of vaporization required for this can be used, the cooling capacity increases.

  It is better to blow the spray water 19 from the upstream of the recirculated combustion exhaust gas 12 as much as possible. By blowing the spray water 19 upstream, it is possible to cool the combustion exhaust gas 12 and sufficiently reduce the wall temperature of the return pipe 4. Therefore, it is not necessary to double the wall of the return pipe 4.

  As a result, the piping structure of the return pipe 4 can be simplified, leading to a reduction in the cost of manufacturing the return pipe 4 for recirculating the combustion exhaust gas 12.

  The water spraying device 18 is preferably a spray generating device in which the particle size of the sprayed water 19 to be sprayed is reduced from the viewpoint of shortening the evaporation distance.

  Since the water spray device 18 is also exposed to a high temperature, it is better to have a structure for cooling the water spray device 18 itself.

  Similarly, in FIG. 4, as the structure for cooling the return pipe 4, a cooling water spray device 20, which is a device for flowing the cooling water 19 of the cooling fluid into the return pipe 4, is installed in the return pipe 4.

  In FIG. 4, an example in which two cooling water spray devices 20 installed on the return pipe 4 are installed in the upper and lower directions is shown, but three or more may be installed around the return pipe 4.

  When the cooling water is sprayed near the pipe wall of the return pipe 4, the spray water 19 flows in the vicinity of the pipe wall, so that the pipe wall of the return pipe 4 can be efficiently cooled.

  Further, since the spray water 19 flows in the vicinity of the wall of the return pipe 4 and the combustion exhaust gas 12 containing a lot of fly ash flows in the center of the axis of the return pipe 4, the fly ash hardly adheres to the vicinity of the wall of the return pipe 4. .

  In particular, in the region where the temperature of the combustion exhaust gas 12 is high, the adhesion force of the ash becomes large, so it is important to make the ash difficult to catch the return pipe 4 upstream of the return pipe 4.

  In addition, it has been confirmed through basic experiments that when water is introduced from the water spray device 20 into the combustion exhaust gas 12 in the return pipe 4, the thermal NOx is lowered. The effect of introducing moisture into the combustion exhaust gas is as follows. large.

  According to the embodiment of the present invention, the piping for flowing the combustion exhaust gas is shortened, the equipment that does not require the blower fan for flowing the combustion exhaust gas is downsized, and the piping for supplying the cooling fluid to flow the combustion exhaust gas is cooled. By doing so, it is possible to realize a pulverized coal fired boiler that can prevent the ash from adhering to the pipe and avoid the blockage of the pipe.

  Next, a pulverized coal burning boiler according to a third embodiment which is an embodiment of the present invention will be described with reference to FIGS.

  In this embodiment, since the basic configuration is common to the pulverized coal fired boiler of the first embodiment shown in FIGS. 1 and 2, the description of the common configuration will be omitted and only different portions will be described. .

  The structure of the after-air port 3a in the pulverized coal burning boiler of this embodiment shown in FIG. 5 shows another structure of the junction between the return pipe 4 and the jet nozzle 3 of the after-air port 3a. A constricted portion 21 with a part of the conduit being constricted is provided in the inner peripheral jet nozzle 14 constituting the jet nozzle 3, and the return pipe 4 is joined to the outer periphery of the constricted portion 21.

  If a part of the pipe line of the jet nozzle 14 is narrowed, the cross-sectional area of the jet nozzle 14 is reduced and the flow velocity of the combustion air flowing inside can be increased. Therefore, the jet flow is increased by increasing the flow velocity of the combustion air as described above. The pressure in the pipe line of the nozzle 14 can be reduced.

  Accordingly, the smaller the diameter of the throttle portion 21 of the pipe line of the jet nozzle 14, the greater the pressure drop, and the combustion exhaust gas 12 flowing down the return pipe 4 connected to the throttle portion 21 and flowing into the jet nozzle 14. And the combustion exhaust gas 12 is supplied from the jet nozzle 14 into the furnace 1 and recirculated.

  The structure of the after-air port 3a in the pulverized coal burning boiler of this embodiment shown in FIG. 6 shows still another structure of the junction of the return pipe 4 and the jet nozzle 3 of the after-air port 3a. A structure 22 for narrowing the flow path is installed inside the pipe line of the jet nozzle 14 on the inner circumferential side constituting the jet nozzle 3 of the air port 3a, and the return pipe 4 is joined to the outer circumference of the pipe line with the narrowed flow path. is doing.

  By narrowing the channel of the jet nozzle 14, the flow velocity inside the jet nozzle 14 increases and the pressure inside the jet nozzle 14 decreases.

  Then, the return pipe 4 is joined to the outer periphery of the position where the structure 22 for narrowing the flow path is disposed, and the combustion exhaust gas 12 flows into the jet nozzle 14 through the return pipe 4 and is supplied into the furnace 1 for recirculation. Let

  The present embodiment shown in FIGS. 5 and 6 is an effective means for increasing the flow rate of the recirculated flue gas 12.

  The approximate value of the pressure difference at the inlet / outlet of the return pipe 4 can be calculated by the following method.

  First, assuming that the pipe cross-sectional area is 10% smaller than the pipe cross-sectional area of the jet nozzle 14 of the original after-air port 3a using a structure that narrows the throttle portion 21 and the flow path, the flow rate is fixed. The flow velocity in the jet nozzle 14 constituting the jet nozzle 3 of the after air port 3a is 111%.

  If the pressure value on the furnace 1 side of the return pipe 4 does not change, the square of the flow velocity is proportional to the pressure, so the inlet / outlet pressure difference of the return pipe 4 is 123% of the original.

  Further, in the structure of the after-air port 3a in the pulverized coal burning boiler of the present embodiment shown in FIG. 7, another structure of the joint portion between the return pipe 4 and the jet nozzle 3 of the after-air port 3a is shown. The return pipe 4 is joined to the outermost peripheral jet nozzle 15 constituting the jet nozzle 3 of the port 3a.

  The principle that the pressure at the joined portion of the return pipe 4 is lowered is the same as that when the return pipe is joined to the inner jet nozzle 14.

  If the combustion air and the reducing combustion gas are in direct contact with each other in the furnace 1, there is a possibility that a rapid reaction occurs at the interface between the combustion air and the reducing combustion gas, the temperature rapidly rises, and a large amount of thermal NOx is generated. Will increase.

  Accordingly, in the present embodiment shown in FIG. 7, the exhaust pipe 12 is jetted through the return pipe 4 by disposing the return pipe 4 on the outermost peripheral jet nozzle 15 constituting the spray nozzle 3 of the after air port 3a. The combustion air flowing through the nozzle 15 is supplied, and the combustion air containing a large amount of the combustion exhaust gas 12 is introduced into the furnace 1.

  Since the flue gas 12 blown from the outermost jet nozzle 15 flows so as to surround the inner combustion air as indicated by the wavy line on the right side of FIG. The temperature does not rapidly increase in the vicinity of the interface between the combustion air ejected from 3a and the reducing combustion gas, and the amount of thermal NOx generated can be suppressed.

  According to the embodiment of the present invention, the piping for flowing the combustion exhaust gas is shortened, the equipment that does not require the blower fan for flowing the combustion exhaust gas is downsized, and the piping for supplying the cooling fluid to flow the combustion exhaust gas is cooled. By doing so, it is possible to realize a pulverized coal fired boiler that can prevent the ash from adhering to the pipe and avoid the blockage of the pipe.

  Next, a pulverized coal fired boiler according to a fourth embodiment which is an embodiment of the present invention will be described with reference to FIG.

  In this embodiment, since the basic configuration is common to the pulverized coal fired boiler of the first embodiment shown in FIGS. 1 and 2, the description of the common configuration will be omitted and only different portions will be described. .

  In the piping configuration of the return pipe 4 of this embodiment shown in FIG. 8, a branch pipe 4 c is provided in the middle of the return pipe 4.

  The branch pipe 4c branched from the return pipe 4 is provided with a circulation fan 24 for sending the combustion exhaust gas 12 and a flow rate adjusting valve 23 for adjusting the flow rate of the combustion exhaust gas 12.

  In FIG. 8, for convenience of explanation, the return pipe 4 and the branch pipe 4c of the return pipe 4 are connected only to the after air port 3a in the front of the can 1a. The pipe 4 and the branch pipe 4c are connected.

  During normal operation of the pulverized coal fired boiler, the flow rate control valve 23 installed in the branch pipe 4c is closed and the circulation fan 24 is not activated, so that the pipe of the return pipe 4 where the circulation fan 24 is not installed is used. The combustion exhaust gas 12 flows.

  By the way, when the amount of combustion air is small at the start of operation of the pulverized coal fired boiler or at the time of partial load, the pressure difference between the furnace 1 side and the after air port 3a side of the return pipe 4 becomes small. It becomes impossible to send the combustion exhaust gas 12 to.

  Therefore, if the opening degree of the flow control valve 23 installed in the branch pipe 4c is opened and the circulation fan 24 is started, the combustion exhaust gas 12 flows through the branch pipe 4c in which the circulation fan 24 is installed.

  At this time, the flow rate of the flue gas 12 to flow down can be adjusted by operating the opening degree of the flow rate adjusting valve 23.

  According to the embodiment of the present invention, the piping for flowing the combustion exhaust gas is shortened, the equipment that does not require the blower fan for flowing the combustion exhaust gas is downsized, and the piping for supplying the cooling fluid to flow the combustion exhaust gas is cooled. By doing so, it is possible to realize a pulverized coal fired boiler that can prevent the ash from adhering to the pipe and avoid the blockage of the pipe.

  Next, a pulverized coal burning boiler according to a fifth embodiment which is an embodiment of the present invention will be described with reference to FIG.

  In this embodiment, since the basic configuration is common to the pulverized coal fired boiler of the first embodiment shown in FIGS. 1 and 2, the description of the common configuration will be omitted and only different portions will be described. .

  In the piping configuration of the return pipe 4 of this embodiment shown in FIG. 9, the combustion state in the furnace 1 of the pulverized coal fired boiler is controlled by using the flow rate control valve 26 installed in the middle of the return pipe 4. Yes.

  In other words, during operation of a pulverized coal-fired boiler, the nitrogen oxide concentration in the combustion gas at the boiler outlet may deviate from the design value due to the influence of the fuel composition, etc. It needs to be close.

  Therefore, a nitrogen oxide concentration measuring device 27 is installed at the boiler outlet, and the nitrogen oxide concentration data in the combustion gas is acquired by the measuring device 27.

  Then, the obtained data of the nitrogen oxide concentration in the combustion gas is converted into an electric signal from the measuring device 27 and taken into the control device 25, and the measured value of the nitrogen oxide concentration in the combustion gas measured by the control device 25. Compared with the design value, a command signal for adjusting the valve opening degree of the flow control valve 26 installed in the middle of the return pipe 4 is output based on the deviation signal of both.

  Changes in the nitrogen oxide concentration over time at the boiler outlet during operation of the pulverized coal-fired boiler and deviation from the design value are monitored by the output device 28.

  When the nitrogen oxide concentration at the boiler outlet deviates from the design value by the control of the control device 25, the valve opening degree of the flow control valve 26 installed in the middle of the return pipe 4 is adjusted to regenerate the combustion exhaust gas 12. By adjusting the circulation amount, the nitrogen oxide concentration in the combustion gas is controlled to approach the design value.

  If the nitrogen oxide concentration and the sensitivity of the valve opening degree of the flow control valve 26 are examined and set in advance at the time of operation adjustment, the control of the control device 25 becomes easy.

  According to the embodiment of the present invention, the piping for flowing the combustion exhaust gas is shortened, the equipment that does not require the blower fan for flowing the combustion exhaust gas is downsized, and the piping for supplying the cooling fluid to flow the combustion exhaust gas is cooled. By doing so, it is possible to realize a pulverized coal fired boiler that can prevent the ash from adhering to the pipe and avoid the blockage of the pipe.

  The present invention is applicable to a pulverized coal fired boiler that burns pulverized coal as fuel.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram which shows the whole of the pulverized coal burning boiler which is 1st Example of this invention. The fragmentary sectional view which shows the after air port which has arrange | positioned the return pipe in the Example of this invention shown in FIG. The fragmentary sectional view which shows the after air port which arrange | positioned the return pipe | tube provided with the cooling device in the pulverized coal burning boiler which is 2nd Example of this invention. The fragmentary sectional view which shows the after air port which arrange | positioned the return pipe | tube provided with the cooling device used as the modification of FIG. 3 in the pulverized coal burning boiler which is 2nd Example of this invention. The fragmentary sectional view which shows the structure of the jet nozzle of the after air port which has arrange | positioned the return pipe to the pulverized coal burning boiler which is 3rd Example of this invention. The fragmentary sectional view which shows the other structure of the jet nozzle of the after air port which has arrange | positioned the return pipe of the modification of FIG. 5 to the pulverized coal burning boiler which is 3rd Example of this invention. The fragmentary sectional view which shows the structure of the jet nozzle of the after air port which has arrange | positioned the return pipe of another modification of FIG. 5 to the pulverized coal burning boiler which is 3rd Example of this invention. The schematic block diagram which shows the whole of the pulverized coal burning boiler which is 4th Example of this invention. The schematic block diagram which shows the whole of the pulverized coal burning boiler which is 5th Example of this invention.

Explanation of symbols

  1: furnace, 1a: front wall, 1b: rear wall, 1c: side wall, 2: burner, 3: jet nozzle, 3a: after air port, 4: return pipe, 4a: inner pipe, 4b: outer pipe, 4c: Branch pipe, 5: Wind box for burner, 6: Wind box for after-air port, 10: Heat transfer tube group, 12: Combustion exhaust gas, 13: Steam for cooling, 14, 15: Spray nozzle, 17: Swivel blade, 18, 20: water spraying device, 21: throttle part, 22: structure, 23: branch pipe flow rate control valve, 25: control device, 26: flow rate control valve, 27: measuring device.

Claims (7)

  A furnace, a plurality of burners installed on the wall of the furnace, supplying pulverized coal into the furnace and burning it to generate reducing flue gas, and a combustion air installed on the furnace wall above the burner An after air port that completely burns reducing combustion gas generated in the burner to generate combustion exhaust gas, and a part of the combustion exhaust gas that has flowed down in the furnace downstream from the after air port And a cooling device that supplies cooling fluid that cools the flue gas that is installed in the return pipe and flows through the return pipe. A pulverized coal-fired boiler characterized by comprising:   The pulverized coal fired boiler according to claim 1, wherein the return pipe has a double pipe structure of an inner pipe and an outer pipe disposed so as to cover the inner pipe, and the combustion exhaust gas flows down into the inner pipe, and A pulverized coal fired boiler, characterized in that the cooling fluid supplied from the cooling device is caused to flow down in a flow path formed between the inner pipe and the outer pipe.   The pulverized coal fired boiler according to claim 1, wherein steam generated in a water-cooled tube group constituting a wall surface of a furnace is used as a cooling fluid supplied from the cooling device.   2. The pulverized coal fired boiler according to claim 1, wherein a water spray device for spraying water of a cooling fluid for cooling the combustion exhaust gas flowing through the return pipe is used as the cooling device.   The pulverized coal fired boiler according to claim 1, wherein a portion where the return pipe is disposed on the after air port side is connected to a throttle portion formed in a spray nozzle for supplying combustion air to the after air port. A pulverized coal fired boiler, characterized in that the ends are connected.   The pulverized coal fired boiler according to claim 1, wherein the return pipe is provided with a branch pipe branched from the middle of the pipe, and the branched pipe is circulated to supply combustion exhaust gas flowing through the branch pipe. A pulverized coal fired boiler comprising a branch pipe flow rate control valve for adjusting a flow rate of a fan and combustion exhaust gas.   The pulverized coal fired boiler according to claim 1, wherein a flow rate adjusting valve for adjusting the flow rate of the combustion exhaust gas flowing through the return pipe is installed in the middle of the return pipe, and flows down in the furnace 1 at the outlet side of the furnace 1 Combustion exhaust gas flowing through the return pipe by installing a measuring device for measuring the nitrogen oxide concentration of the combustion exhaust gas to be adjusted and adjusting the opening of the flow control valve based on the nitrogen oxide concentration of the combustion exhaust gas measured by this measurement device A pulverized coal fired boiler comprising a control device for controlling the flow rate of coal.

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