Flue gas recirculation system for wide-load nitrogen reduction of circulating fluidized bed boiler

Abstract

The utility model relates to the technical field of circulating fluidized beds, and particularly discloses a flue gas recirculation system for wide-load nitrogen reduction of a circulating fluidized bed boiler. One end of the recycling flue is connected with a primary fan, the other end of the recycling flue is connected with the output end of an induced draft fan, one end of the flue gas bypass is connected with the recycling flue, and the other end of the flue gas bypass is connected with the output end of a dust remover; a first shut-off baffle and a recirculation fan are sequentially arranged on the recirculation flue. The first turn-off baffle is arranged on the side close to the output end of the induced draft fan. A second shut-off baffle is arranged on the flue gas bypass. The flue gas recirculation technology is adopted, low-temperature flue gas exhausted by the boiler is extracted to replace primary air at the bottom of the boiler, enough fluidizing media can be provided, the fluidizing quality of materials in the boiler can be guaranteed, the amount of oxygen entering the boiler can be controlled, the reducing atmosphere of a main combustion area of the hearth can be built, and original generation of NOx can be restrained; and the problem of high original emission of NOx caused by too high bed temperature can be avoided.

Description

TECHNICAL FIELD

[0001] The utility model relates to circulating fluidized bed technical field more particularly, relate to a circulating fluidized bed boiler wide load nitrogen reduction flue gas recirculation system. BACKGROUND

[0002] Circulating fluidized bed boiler technology with its coal adaptability, low pollutant emission, high combustion efficiency advantage develops rapidly in the domestic, becomes one of the mainstream of coal power unit. However, after participating in the flexibility depth peak shaving, circulating fluidized bed boiler technology will also face environmental protection problem.

[0003] Circulating fluidized bed boiler in the depth of peak shaving flexibility low load operating condition, to ensure the good fluidization (if the fluidization quality is bad will lead to insufficient combustion, local coking, difficult deslagging, circulating material greatly reduces and so on influence the safe, stable operation problem) of furnace bed material, the primary air of furnace bottom needs to maintain the minimum air volume required for fluidization, and not only to meet the needs of fuel combustion, which leads to the primary air volume of furnace bottom at low load to be much larger than the primary air volume required for combustion, the lower part of the furnace is oxygen-rich atmosphere, and it is difficult to meet the low oxygen combustion requirement needed to suppress NOx generation. In addition, the low load furnace outlet flue gas temperature is relatively low, usually below 800 DEG C, which does not reach the SNCR reaction temperature, resulting in low SNCR denitration efficiency or even failure, and the SNCR cannot meet the requirements of ultra-low emission after being put into operation. Most of the early CFB boilers do not have pre-reserved SCR in the tail flue, and there is no space to add SCR. Even if there is originally reserved space for SCR, the problem of not being able to meet the SCR reaction temperature after the low load flue gas temperature decreases still exists.

[0004] In summary, the above factors lead to the fact that most of the circulating fluidized bed boilers in service at present cannot meet the current emission requirements under the depth of peak shaving flexibility operating condition. UTILITY MODEL CONTENTS

[0005] The utility model wants to solve the technical problem to provide a circulating fluidized bed boiler wide load nitrogen reduction flue gas recirculation system;

[0006] The utility model solves the technical problem and adopts the following solutions:

[0007] A circulating fluidized bed boiler wide load nitrogen reduction flue gas recirculation system, including one end with circulating fluidized bed boiler primary air blower connection and another end with the output end of circulating fluidized bed boiler induced draft fan connection's recirculation flue, one end with recirculation flue connection and another end with the output end of circulating fluidized bed boiler dust catcher connection's flue gas bypass;

[0008] Recirculation flue is provided with relevant break baffle one and recirculation fan in sequence along the direction of flue gas flow;

[0009] The shutoff baffle one is arranged on one side close to the output end of the induced draft fan; and the connection point of the flue gas bypass and the recirculation flue is arranged between the shutoff baffle one and the recirculation fan.

[0010] The shutoff baffle two is arranged on the flue gas bypass.

[0011] In some possible embodiments, the recirculation flue comprises an inlet pipe connected with the output end of the induced draft fan, an output pipe connected with the other end of the inlet pipe and the primary air fan respectively.

[0012] The shutoff baffle one and the recirculation fan are arranged on the inlet pipe in sequence along the flue gas flow direction.

[0013] In some possible embodiments, a pressure test device, a flow test device and a baffle assembly are arranged on the recirculation flue in sequence along the flue gas flow direction; the flow test device and the baffle assembly are arranged on the output pipe; and the pressure test device is arranged at the output end of the recirculation fan.

[0014] In some possible embodiments, the baffle assembly comprises an adjusting baffle and a shutoff baffle three arranged in sequence along the flue gas flow direction.

[0015] In some possible embodiments, the primary air fan is two groups, the output pipe is two groups and is connected with the inlet pipe in parallel, and the other end of the two groups of output pipes is connected with the two groups of primary air fans one by one.

[0016] In some possible embodiments, the induced draft fan is two groups, a pipe one is arranged at the output end of the dust collector in the circulating fluidized bed boiler, the two groups of induced draft fans are connected with the pipe one in parallel through the air inlet pipes, a pipe two is arranged at the inlet end of the chimney in the circulating fluidized bed boiler; and the two groups of induced draft fans are connected with the pipe two in parallel through the air outlet pipes.

[0017] In some possible embodiments, the pressure test device is one group and is arranged on the inlet pipe.

[0018] In some possible embodiments, the flue gas bypass is one group and one end of which is connected with the pipe one; and the inlet pipe is one group and is connected with the pipe two.

[0019] In some possible embodiments, the inlet pipe comprises two groups of inlet bypasses arranged with the shutoff baffle one respectively, and an inlet main pipe connected with the two groups of inlet bypasses respectively.

[0020] The other end of the two groups of inlet bypasses is connected with the two groups of air outlet pipes respectively; and the other end of the flue gas bypass is connected with the inlet main pipe.

[0021] In some possible implementation manners, the pressure testing devices are two groups and are arranged on two groups of output pipelines respectively; the flue gas bypasses and the inlet pipelines are two groups and are arranged in one-to-one correspondence with the two groups of induced draft fans; the two groups of flue gas bypasses are connected with the two groups of pipelines respectively; and the two groups of inlet pipelines are connected with the two groups of gas outlet pipes respectively.

[0022] Compared with the prior art, the utility model has the beneficial effects that:

[0023] The utility model discloses when the boiler participates in the flexible operation of depth peak regulation, effectively control the oxygen content of boiler operation is at 2% and below, for the coal quality sensitive to oxygen, can realize the original emission control of its NOx is within 50mg / Nm3;

[0024] The utility model discloses when the boiler is in high load operation, effectively delays the coal combustion time of low oxygen content flue gas of flue gas, reduces the temperature of furnace combustion area, thereby control the original emission of NOx;

[0025] The utility model discloses adopt partial flue gas to replace the primary air of furnace bottom, can increase the secondary air of dense phase area of furnace appropriately, thereby better realization the air staging required for low carbon combustion, further reduce the original generation of NOx;

[0026] The utility model discloses can adjust the oxygen content of boiler operation and bed temperature through the flow of flue gas, thereby improve the operation flexibility of circulating fluidized bed boiler. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 It is the structure schematic diagram of example 1 in the utility model;

[0028] Figure 2 It is the structure schematic diagram of example 2 in the utility model;

[0029] Figure 3 It is the structure schematic diagram of example 3 in the utility model;

[0030] Wherein: 1, recirculation flue; 2, flue gas bypass; 3, recirculation fan; 4, shut-off baffle one; 5, shut-off baffle two; 6, pressure testing device; 7, flow testing device; 8, adjusting baffle; 9, shut-off baffle three; 20, induced draft fan; 201, gas inlet pipe; 202, gas outlet pipe; 21, dust collector; 211, pipeline one; 22, preheater; 23, primary air fan; 24, cold primary air duct; 25, hot primary air duct; 26, chimney; 261, pipeline two. DETAILED DESCRIPTION

[0031] In the utility model, unless another definite provision and limitation, the terms "mount", "link", "connect", "fix" and so on should do the broad sense understanding, for example, can be fixed connection, also can be detachable connection, or be integrated;Can be direct connection, also can pass through the indirect connection of intermediate medium, can be the communication of two elements inside or the interaction of two elements.The "first", "second" and similar words mentioned in the application do not represent any order, quantity or importance, but only distinguish different components.Similarly, "one" or "a" and similar words do not represent quantity limit, but represent the existence of at least one.In the implementation of the application, the association relationship of the associated object is described, which means that there can be three kinds of relationships, for example, A and / or B can mean that A exists alone, A and B exist simultaneously and B exists alone.In the description of the embodiments of the application, unless otherwise specified, the meaning of "a plurality of" is two or more than two.For example, a plurality of positioning columns means two or more than two positioning columns.The specific meaning of the above terms in the utility model can be understood according to the specific circumstances for ordinary skilled in the art.

[0032] The utility model will be explained in detail below.

[0033] The circulating fluidized bed boiler is prior art, including hearth, separator, the vertical shaft that is internally provided with preheater 22, the dust catcher 21 that is communicated with the vertical shaft, the primary air fan 23 that is connected with preheater 22 through cold primary air duct 24, the induced draft fan 20 that is connected with the output end of dust catcher 21, and the chimney 26 that is connected with the output end of induced draft fan 20;A circulating fluidized bed boiler is provided with two groups of parallelly arranged induced draft fan 20;Preheater 22 is connected with the bottom air chamber of hearth through hot primary air duct 25.

[0034] Example 1

[0035] As Figure 1 As shown in a kind of circulating fluidized bed boiler wide load nitrogen reduction with flue gas recirculation system, including one end with the primary air fan 23 of connection in circulating fluidized bed boiler and another end with the output end of induced draft fan 20 in circulating fluidized bed boiler connection's recirculation flue 1, one end with recirculation flue 1 connection and another end with the output end of dust catcher 21 in circulating fluidized bed boiler connection's flue gas bypass 2;

[0036] Specifically, induced draft fan 20, primary air fan 23 are two groups;Two groups of induced draft fan 20, two groups of primary air fan 23 are parallelly arranged respectively;

[0037] The induced draft fan 20 is two groups, the output end of the dust collector 21 is provided with a pipeline 211, two groups of induced draft fan 20 are connected with the pipeline 211 in parallel through the air inlet pipe 201, the inlet end of the chimney 26 is provided with a pipeline 261; two groups of induced draft fan 20 are connected with the pipeline 261 in parallel through the air outlet pipe 202.

[0038] The recirculation flue 1 is provided with a recirculation fan 3 and a closing baffle 4 in sequence along the direction of the flue gas flow; the recirculation fan 3 is used to lift the pressure head of the flue gas, so that the flue gas is smoothly sent into the inlet of the primary fan 23 to mix with the cold primary air provided by the primary fan 23;

[0039] Specifically, the recirculation fan 3 is a circulating fan with a frequency converter, which is used to adjust the pressure head and flow of the recirculation flue gas to meet the operation requirements;

[0040] The closing baffle 4 is arranged on the side close to the output end of the induced draft fan 20; the connection point of the flue gas bypass 2 and the recirculation flue 1 is arranged between the closing baffle 4 and the recirculation fan 3;

[0041] The flue gas bypass 2 is provided with a closing baffle 5.

[0042] During normal operation, the closing baffle 1 is opened, the closing baffle 2 is closed, and the flue gas bypass 2 does not work; part of the flue gas treated by the dust collector 21 is transported to the primary fan 23 through the recirculation flue 1 by the induced draft fan 20, mixed with the cold primary air provided by the primary fan 23, and then transported to the preheater 22 through the cold primary pipeline, preheated by the preheater 22, and then transported to the bottom air chamber of the furnace through the hot primary pipeline, which is used as the fluidizing medium in the furnace; a part of the clean and low-temperature flue gas extracted from the dust collector 21 is used to replace part of the primary air at the bottom of the furnace, which can not only provide sufficient fluidizing medium to ensure the fluidization quality of the material in the furnace, but also control the amount of cold primary air, so as to effectively control the oxygen content of the furnace, create a reducing atmosphere in the main combustion zone of the furnace, and inhibit the original generation of NOx;

[0043] During shutdown, the closing baffle 2 is opened, the closing baffle 1 is closed, and the flue gas leaked from the outlet of the induced draft fan 20 into the recirculation flue 1 can pass through the flue gas bypass 2 and return to the induced draft fan 20 under the adsorption of the negative pressure at the inlet of the induced draft fan 20, so as to prevent the flue gas leaked into the recirculation flue 1 from stagnating in the system, thereby causing corrosion problems of the recirculation flue 1 and its accessories.

[0044] In some possible embodiments, the recirculation flue 1 includes an inlet pipeline connected with the output end of the induced draft fan 20, an output pipeline connected with the other end of the inlet pipeline and the primary fan 23 respectively;

[0045] The shutoff damper one 4 and the recirculation fan 3 are arranged in sequence on the inlet pipe along the flue gas flow direction; in normal operation, the shutoff damper one 4 is opened, and the recirculation fan 3 is started, and part of the flue gas will enter the inlet pipe and then enter the outlet pipe through the recirculation fan 3 to mix with the cold primary air extracted by the primary fan 23.

[0046] In some possible embodiments, a pressure testing device 6, a flow testing device 7 and a damper assembly are arranged in sequence on the recirculation flue 1 along the flue gas flow direction; the flow testing device 7 and the damper assembly are arranged on the outlet pipe; the pressure testing device 6 is arranged at the output end of the recirculation fan 3; the damper assembly includes an adjusting damper 8 and a shutoff damper three 9 arranged in sequence along the flue gas flow direction;

[0047] The pressure testing device 6 is used to monitor the pressure of the flue gas at the outlet of the recirculation fan 3, and the flow testing device 7 is used to monitor the flow of the flue gas, and is used in cooperation with the adjusting damper 8 to realize the adjustment of the flue gas flow;

[0048] The shutoff damper three 9 realizes the opening and closing of the outlet pipe, and the adjusting damper 8 is used to adjust the flow of the flue gas in the outlet pipe; in normal operation, the shutoff damper one 4 and the shutoff damper three 9 are opened, and the shutoff damper two 5 is closed.

[0049] In some possible embodiments, the outlet pipe is two groups and is connected in parallel with the inlet pipe, and the other end of the two groups of outlet pipes is connected with the two groups of primary fans 23 one by one; the other end of the two groups of primary fans 23 is connected with the preheater 22 through the cold primary air duct 24.

[0050] The pressure testing device 6 is one group and is arranged on the inlet pipe.

[0051] The flue gas bypass 2 is one group and one end is connected with the pipe one 211, and the other end of the flue gas bypass 2 is connected with the inlet pipe; the inlet pipe is one group and one end is connected with the pipe two 261.

[0052] The primary fan 23 is provided with a cold primary air inlet, and an adjusting valve is arranged on the cold primary air inlet, which is used to adjust the air intake of the cold primary air, so as to realize the control of the oxygen content.

[0053] The shutoff damper one 4, the shutoff damper two 5, the shutoff damper three 9 and the adjusting damper 8 can be manually or electrically controlled.

[0054] Example 2:

[0055] As Figure 2As shown, this embodiment is a further improvement on embodiment 1. Specifically, the inlet pipe includes two sets of inlet bypasses respectively equipped with baffles 4, and inlet main pipes respectively connected to the two sets of inlet bypasses; the other end of the two sets of inlet bypasses is respectively connected to the two sets of gas outlet pipes 202; one end of the flue gas bypass 2 is connected to pipe 211.

[0056] The other structures in this embodiment are the same as those in embodiment 1, and will not be described again here;

[0057] Example 3:

[0058] like Figure 3 As shown, this embodiment is a further improvement on embodiment 1. Compared with embodiment 1, the pressure testing device 6 is set to two sets and is respectively set on two sets of output pipes; the flue gas bypass 2 and the inlet pipe are both two sets and are set one-to-one with the two sets of induced draft fans 20; the two sets of flue gas bypass 2 are respectively connected to the two sets of pipes 211 and the other end is respectively connected to the two sets of inlet pipes; one end of the two sets of inlet pipes is respectively connected to the two sets of exhaust pipes 202; the two sets of inlet pipes are respectively connected to the two sets of output pipes and are set one-to-one.

[0059] The other structures in this embodiment are the same as in Embodiment 1, and will not be described again here.

[0060] According to Examples 1-3, when the unit participates in deep peak shaving and flexible operation, and it is necessary to control the original NOx emission by controlling the amount of operating oxygen, the recirculation fan 3 is turned on first, and then the shut-off damper 4 at the inlet of the recirculation flue 1 and the shut-off damper 9 at the outlet of the recirculation flue 1 are turned on. At this time, the shut-off damper 5 on the flue gas bypass 2 is kept closed. At the same time, the flow rate is monitored by the flow testing device 7 on the recirculation flue 1 and the flow testing device on the primary air duct (cold primary air duct 24, hot primary air duct 25) to obtain the flow rate of the flue gas. According to the flow rate of the flue gas, the amount of cold primary air is adjusted so that the total amount of fluidizing medium entering the bottom air chamber of the furnace remains unchanged.

[0061] Then, by adjusting the baffle 8, the opening of the recirculation flue 1 is gradually increased to increase the flue gas volume, while the cold primary air flow is gradually reduced to control the oxygen content until the boiler operating oxygen content is controlled at 2% or below. At the same time, the changes in boiler operating oxygen content, furnace bed pressure, and bed temperature need to be monitored: the oxygen content should be able to gradually decrease to a level of 2% or below without causing a large change in bed temperature; the bed pressure should be able to remain stable without large fluctuations; the bed temperature should be able to maintain stable combustion, and the bed temperature deviation should not increase significantly; the boiler parameters should be kept stable during the adjustment process.

[0062] This invention, by replacing some of the primary air at the bottom of the furnace with flue gas, increases the secondary air in the dense phase zone of the furnace, thereby better achieving the air staging required for low-carbon combustion and further reducing the initial formation of NOx; the low-temperature flue gas extracted by the recirculation fan 3 effectively delays the coal combustion time and reduces the temperature of the furnace combustion zone, thereby controlling the initial emission of NOx; by adjusting the flow rate of the flue gas, the oxygen content and bed temperature of the boiler are adjusted, thereby improving the operational flexibility of the circulating fluidized bed boiler.

[0063] When it is necessary to shut down the flue gas recirculation system, first gradually reduce the opening of the regulating damper 8 on the recirculation flue 1, and increase the cold primary air intake of the primary air fan 23 by adjusting the regulating valve to maintain the total flow rate of the fluidizing medium at the bottom of the furnace. At the same time, key parameters such as operating oxygen content, bed temperature, and bed pressure should be closely monitored.

[0064] When the opening of the regulating damper 8 is reduced to a certain extent, and the primary air volume has met the fluidization requirements, the recirculation fan 3 is turned off, and then the shut-off damper 3 9 at the outlet of the recirculation flue 1 and the shut-off damper 1 4 at the inlet of the recirculation flue 1 are closed, and the shut-off damper 2 5 of the flue gas bypass 2 is opened.

[0065] The flue gas that leaks into the recirculation flue 1 from the outlet of the induced draft fan 20 can be returned to the induced draft fan 20 through the flue gas bypass 2 under the adsorption effect of the negative pressure at the inlet of the induced draft fan 20, so as to prevent the flue gas that leaks into the recirculation flue 1 from stagnating in the system, thereby causing corrosion problems of the recirculation flue 1 and its accessories.

[0066] This invention employs flue gas recirculation technology to extract a portion of the clean, low-temperature flue gas after the boiler outlet to replace a portion of the primary air at the bottom of the furnace. This provides sufficient fluidizing medium to ensure the fluidization quality of the materials inside the furnace, while also controlling the amount of oxygen entering the furnace, creating a reducing atmosphere in the main combustion zone of the furnace, and suppressing the initial formation of NOx.

[0067] According to performance calculations, by adopting flue gas recirculation technology, the oxygen content of the boiler can be controlled to 2% or below. For oxygen-sensitive coal, this can achieve the goal of controlling the original NOx emissions to the current environmental protection requirements. At the same time, under certain specific conditions, the flue gas recirculation system can also be used to regulate the bed temperature at medium and high loads, avoiding the problem of high original NOx emissions caused by excessively high bed temperatures, and ultimately achieving the goal of reducing nitrogen emissions over a wide load range.

[0068] This invention is not limited to the specific embodiments described above. This invention extends to any new feature or combination disclosed in this specification, as well as any new method or process step or combination disclosed herein.

Claims

1. A flue gas recirculation system for a circulating fluidized bed boiler for wide load denitration, characterized by, The recirculation flue is connected with the primary air fan at one end and with the output end of the induced draft fan in the circulating fluidized bed boiler at the other end, the flue gas bypass is connected with the recirculation flue at one end and with the output end of the dust collector in the circulating fluidized bed boiler at the other end; A first shut-off baffle and a recirculation fan are arranged in sequence on the recirculation flue along the flue gas flow direction; The first shut-off baffle is arranged close to the output end of the induced draft fan, and the connection point of the flue gas bypass and the recirculation flue is arranged between the first shut-off baffle and the recirculation fan; A second shut-off baffle is arranged on the flue gas bypass.

2. A flue gas recirculation system for wide load denitration of a circulating fluidized bed boiler according to claim 1, characterized in that, The recirculation flue comprises an inlet pipe connected with the output end of the induced draft fan and an output pipe connected with the other end of the inlet pipe and the primary air fan respectively; The first shut-off baffle and the recirculation fan are arranged in sequence on the inlet pipe along the flue gas flow direction.

3. A flue gas recirculation system for wide load denitration of a circulating fluidized bed boiler according to claim 2, characterized in that, A pressure testing device, a flow testing device and a baffle assembly are arranged in sequence on the recirculation flue along the flue gas flow direction; the flow testing device and the baffle assembly are arranged on the output pipe; and the pressure testing device is arranged at the output end of the recirculation fan.

4. A flue gas recirculation system for wide load NOx reduction of a circulating fluidized bed boiler according to claim 3, characterized in that, The baffle assembly comprises an adjusting baffle and a third shut-off baffle arranged in sequence along the flue gas flow direction.

5. A flue gas recirculation system for wide load denitration of a circulating fluidized bed boiler according to claim 3 or 4, characterized in that, The primary air fan is two groups, the output pipe is two groups and is connected with the inlet pipe in parallel, and the other end of the two groups of output pipes is connected with the two groups of primary air fans one by one.

6. A flue gas recirculation system for wide load denitration of a circulating fluidized bed boiler according to claim 5, characterized in that, The induced draft fan is two groups, the output end of the dust collector in the circulating fluidized bed boiler is provided with a pipe one, the two groups of induced draft fans are connected with the pipe one in parallel through an inlet pipe, the inlet end of the chimney in the circulating fluidized bed boiler is provided with a pipe two, and the two groups of induced draft fans are connected with the pipe two in parallel through an outlet pipe.

7. A flue gas recirculation system for wide load NOx reduction of a circulating fluidized bed boiler according to claim 6, characterized in that, The pressure testing device is one group and is arranged on the inlet pipe.

8. A flue gas recirculation system for wide load NOx reduction of a circulating fluidized bed boiler according to claim 7, characterized in that, The flue gas bypass is one group and is connected with the pipe one at one end; and the inlet pipe is one group and is connected with the pipe two.

9. A flue gas recirculation system for wide load NOx reduction of a circulating fluidized bed boiler according to claim 8, characterized in that, The inlet pipe comprises two groups of inlet bypasses provided with a first shut-off baffle and an inlet main pipe connected with the two groups of inlet bypasses respectively; The other end of the two groups of inlet bypasses is connected with the two groups of outlet pipes respectively; and the other end of the flue gas bypass is connected with the inlet main pipe.

10. A flue gas recirculation system for wide load denitrification of a circulating fluidized bed boiler according to claim 6, characterized in that, The pressure testing device is two groups and is arranged on the two groups of output pipes respectively; the flue gas bypass and the inlet pipe are both two groups and are arranged one by one with the two groups of induced draft fans; the two groups of flue gas bypasses are connected with the two groups of pipes one respectively; and the two groups of inlet pipes are connected with the two groups of outlet pipes respectively.

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