System and method for preventing boiler flue gas circulating flue from being corroded

Abstract

The invention discloses a system and method for preventing corrosion of a boiler flue gas circulation flue, the system comprises a boiler, a flue, an air flue, the flue gas circulation flue and a mixed smoke air flue, a flue gas outlet of the boiler is communicated with a waste heat recoverer through the flue, and a flue outlet is communicated with ambient air; the flue is further communicated with an inlet of the smoke circulating flue, an outlet of the smoke circulating flue and an outlet of the air flue are both communicated with an inlet of the mixed smoke air flue, and an outlet of the mixed smoke air flue is communicated with the boiler. The method comprises the steps that when flue gas circulation is put into operation, hot air enters the boiler by increasing the air volume of the air blower and opening the flue door, and meanwhile part of the hot air heats related equipment through the flue gas circulation flue. And when the flue gas circulation is stopped, the flue gas circulation fan is closed, meanwhile, the air volume of the air blower is increased, and part of hot air enters the flue gas circulation flue for purging. The flue gas circulation system can solve the problem of flue corrosion leakage caused by flue gas condensation, and the economical efficiency, safety and environment-friendly performance of boiler operation are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of industrial boilers, and in particular relates to a system and method for preventing boiler flue gas circulation from corroding. Background Art

[0002] During the operation of the boiler, in order to reduce the emission of nitrogen oxides, an atmospheric pollutant, flue gas circulation technology is generally used. Flue gas circulation technology is to transport part of the flue gas emitted by the boiler to the furnace through a circulating fan and a flue gas circulation pipe. After the flue gas is circulated back to the furnace, the generation of nitrogen oxides is reduced. The mechanism of this technology is as follows: Mechanism 1, the oxygen concentration in the flue gas is lower than the oxygen concentration in the combustion air. The flue gas circulation technology can reduce the oxygen concentration around the fuel in the furnace, creating a local reducing atmosphere, which is conducive to the conversion of fuel nitrogen in the fuel into nitrogen instead of nitrogen oxides; Mechanism 2, the oxygen concentration of the circulating flue gas is lower than the oxygen concentration in the combustion air. The flue gas circulation technology leads to a significant increase in the total flue gas volume generated by the complete combustion of the fuel, effectively reducing the temperature of the total flue gas during fuel combustion and the local flue gas temperature around the fuel. The reduction in flue gas temperature can inhibit the generation of thermal nitrogen oxides.

[0003] Based on the above-mentioned low NOx combustion mechanism, flue gas recycle technology is widely used in boilers that use fossil fuels, biomass fuels, and urban garbage as heat sources, including large pulverized coal power plant boilers and circulating fluidized bed power plant boilers, as well as small cogeneration boilers, biomass power plant boilers, and waste incinerators.

[0004] However, during the use of the flue gas circulation system of the boiler, there are problems of flue corrosion and leakage caused by flue gas condensation, as well as corrosion and contamination of the flue gas circulation fan impeller, which eventually lead to the failure of the flue gas circulation system to be used normally. The flue gas produced by the combustion of fossil fuels, biomass fuels and urban garbage contains water vapor and acidic gases, such as sulfur dioxide and hydrogen chloride. These acidic gases and water vapor condense after the flue gas temperature drops to a certain temperature, and eventually form acidic liquids on the surface of the flue gas duct, fan impellers and related equipment and components. These acidic liquids condense on the blades of the flue gas circulation fan, which not only causes corrosion of the blades, but also mixes with the dust deposited on the blades to cause blade contamination, resulting in reduced fan efficiency, increased vibration due to fan imbalance, and shortened fan life. If severe corrosion or contamination occurs, it may cause blade failure, leading to safety accidents.

[0005] The occurrence of condensation and corrosion problems is related to many factors. When the flue gas circulation is put into operation, the flue, fan and related equipment and components are at room temperature. When the flue gas containing water vapor and acidic gas is introduced into the flue gas circulation flue, condensation and corrosion will occur due to the decrease in flue gas temperature. When the flue gas circulation system is shut down, when there is a large amount of flue gas in the flue gas circulation pipeline, the circulating flue and circulating fan are closed. As the circulating flue and the flue gas therein cool, the water vapor in the flue gas condenses into water, and the acidic gases sulfur dioxide and hydrogen chloride in the flue gas will dissolve in the water to form acid liquid, causing corrosion of the flue gas circulation system. Summary of the invention

[0006] The object of the present invention is to provide a system and method for preventing boiler flue gas circulation from corroding, which can effectively solve the problem of flue gas corrosion and leakage caused by flue gas condensation.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A system for preventing corrosion of a boiler flue gas circulation duct comprises a boiler, a flue, an air duct, a flue gas circulation flue and a mixed smoke and air duct, wherein the flue gas outlet of the boiler is connected to a waste heat recovery device through the flue, and the flue outlet is connected to ambient air; the flue is also connected to the inlet of the flue gas circulation flue, and the outlet of the flue gas circulation flue and the outlet of the air duct are both connected to the inlet of the mixed smoke and air duct, a smoke and air volume meter is provided on the mixed smoke and air duct, and the outlet of the mixed smoke and air duct is connected to the boiler; the air duct, the flue gas circulation flue and the flue constitute a first loop, and when the flue gas circulation is started, hot air preheats the flue gas circulation flue through the first loop; when the flue gas circulation is stopped, hot air purges the flue gas circulation flue through the first loop; the flue, the flue gas circulation flue and the mixed smoke and air duct constitute a second loop, and when the flue gas circulates, a portion of the flue gas discharged from the flue re-enters the boiler for circulation through the flue gas circulation flue and the mixed smoke and air duct.

[0009] Furthermore, a blower is provided at the inlet of the air duct, and the air outlet direction of the blower is connected to the boiler through the air duct and the mixed smoke air duct. The air duct is sequentially provided with an air preheater for preheating air, a thermometer for monitoring the air temperature in the duct, an air volume meter for monitoring the air flow in the duct, and a duct door for adjusting the ventilation volume in the duct.

[0010] Furthermore, the inlet of the flue gas circulation duct is provided with a No. 1 flue gas thermometer for measuring the flue gas temperature and a dust collector, and the outlet is provided with a No. 2 flue gas thermometer for measuring the flue gas temperature, a flue door for controlling the flue gas flow rate, a flue gas volume meter for measuring the flue gas flow rate and a flue gas circulation fan in sequence; the flue gas inlet direction of the flue gas circulation fan is connected to the flue through the flue gas circulation duct, and the flue gas outlet direction of the flue gas circulation fan is connected to the boiler through the flue gas circulation duct and the mixed smoke and air duct.

[0011] Furthermore, the fuel supply port of the boiler is provided with a fuel machine for measuring the fuel supply.

[0012] Furthermore, the air preheater is provided with a heating medium inlet and a heating medium outlet.

[0013] The present invention also provides a method for preventing corrosion of the flue of boiler flue gas circulation. When the flue gas circulation is started, the combustion-supporting air provided by the blower is heated by the air preheater and then enters the boiler through the mixed smoke and air duct. At the same time, a part of the hot air directly enters the flue through the flue circulation flue. When the hot air passes through the flue circulation flue, it preheats the flue circulation flue, the No. 2 smoke thermometer, the flue door, the smoke volume meter, the flue circulation fan, the dust collector and the No. 1 smoke thermometer; when the flue gas circulation is operating normally, the combustion-supporting air provided by the blower is heated by the air preheater and then enters the boiler through the air duct and the mixed smoke and air duct; a part of the flue gas discharged from the boiler to the flue is used as the circulating flue gas and is discharged from the flue circulation flue through the flue circulation fan The hot air is transported to the mixed smoke and air duct by the blower, and the circulating smoke is mixed in the mixed smoke and air duct and then enters the boiler, and burns with the fuel input by the fuel machine to release heat. The smoke generated by the combustion enters the waste heat recovery device and releases part of the heat. The smoke after heat release enters the flue and is divided into two parts, one part of the smoke is returned to the boiler for circulation through the smoke circulation flue as the circulating smoke, and the other part of the smoke is finally discharged into the environment; when the smoke circulation is stopped, the combustion-supporting air provided by the blower is heated by the air preheater, and the hot air purges the smoke circulation flue, the No. 2 smoke temperature meter, the flue door, the smoke volume meter, the flue gas circulation fan, the dust collector and the No. 1 smoke temperature meter when passing through the smoke circulation flue.

[0014] Furthermore, when the flue gas circulation is put into operation, the air volume output of the blower is increased so that the hot air flow rate of the air duct measured by the air volume meter increases from the hot air flow rate value V when the boiler is operating normally. O，A Reach the hot air flow value V at the initial stage of flue gas circulation operation S，A , V O，A and V S，A The unit is Nm 3 / h; when V S，A =1.1V O，A ~1.3V O，A When the flue door is opened and the opening of the flue door is maintained at 1% to 30%, part of the hot air in the air duct enters the flue gas circulation flue, and the hot air is used to heat the flue gas circulation flue and the No. 2 smoke thermometer, flue door, smoke volume meter, flue gas circulation fan, dust collector and No. 1 smoke thermometer installed on the flue gas circulation flue; then increase the flue door opening and monitor the reading V of the smoke and air volume meter installed on the mixed smoke and air duct M，A , V M，A The unit is Nm 3 / h, as the flue door opening increases, the smoke and air volume meter reading V M，A Lower, when VM，A The value reaches V O，A When the temperature reaches 0.05 °C, stop increasing the opening of the flue door and keep the opening unchanged; at the same time, monitor the temperature value T measured by the No. 1 flue gas thermometer. g The temperature value T measured by the wind thermometer a , T a and T g The unit is ℃. When the flue gas circulation is started.

[0015] Furthermore, the steps of putting the flue gas circulation into operation are as follows: close the flue door, reduce the air volume output of the blower, so that the hot air flow rate of the air duct measured by the air volume meter is reduced to the hot air flow rate value V when the boiler is operating normally O，A Then start the flue gas circulation fan, open the flue door and keep the flue door opening at 1% to 30%, so that part of the flue gas flowing through the flue enters the heated flue gas circulation flue, then increase the flue door opening and the air volume output of the flue gas circulation fan, increase the amount of flue gas entering the flue gas circulation flue, monitor the flue gas flow value measured by the smoke meter, and when the flue gas flow value reaches the target flue gas circulation volume V RG,AIM =0.1V O，A ~0.5V O，A When the flue door opening and the air volume output of the flue gas circulation fan are maintained, the inlet flue gas temperature value T measured by the No. 1 flue gas thermometer of the flue gas circulation flue is monitored. g，in and the flue gas outlet temperature value T measured by the No. 2 smoke temperature meter g，out , T g，in and T g，out The unit is ℃; when the air volume output of the flue gas circulation fan continues for more than 30 minutes, if This means that the flue gas circulation volume is too small, and the flue gas temperature in some flue gas circulation flues is too low. The flue gas door opening and the air volume output of the flue gas circulation fan should be increased; when the circulating flue gas volume value measured by the smoke meter is less than VR G,AIM Under the upper limit condition, if This indicates that the temperature of the entire flue gas circulation flue is high enough, so the flue door opening and the air volume output of the flue gas circulation fan are maintained; when the circulating flue gas volume value measured by the smoke meter reaches V RG,AIM If the upper limit condition is This indicates that the flue gas temperature in some flue ducts of the flue gas circulation flue is too low, and the flue gas circulation should be stopped; when the operating load of the boiler is lower than 70% of the rated load of the boiler, the flue gas circulation should be stopped.

[0016] Furthermore, when the flue gas circulation is stopped, the air volume output of the flue gas circulation fan is reduced, and the opening of the flue door is reduced, so that the flue gas flow rate in the flue gas circulation flue measured by the smoke meter reaches the shut-down flue gas circulation volume V RG，C =5%V O，AAt this time, close the flue door and the flue gas circulation fan, and increase the air volume output of the blower, so that the air flow rate measured by the air flow meter in the air duct increases from the hot air flow value V when the boiler is operating normally. O，A The hot air flow value V required to achieve flue gas circulation and flue duct purge BL，A =1.1V O，A ~1.3V O，A , V BL，A The unit is Nm 3 / h, at this time, the opening of the flue door is increased, and the hot air from the flue enters the flue gas circulation flue and purges the hot flue gas circulation flue and the equipment on the flue gas circulation flue; at the same time, the reading V of the smoke and air volume meter set on the mixed smoke and air duct is monitored M，A , when V M，A The value reaches V O，A When the smoke is discharged, stop increasing the opening of the flue door and keep the opening unchanged. Continue to purge the smoke circulation flue for more than 15 minutes to blow the remaining smoke in the smoke circulation flue into the flue. Then reduce the opening of the flue door and the air duct door, reduce the air volume output of the smoke circulation fan, and check the reading V of the smoke and air volume meter. M,A , when V M,A =1.0V O,A ~1.05V O,A At the same time, maintain normal combustion of the boiler until the flue door is completely closed.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention forms a first loop through the air duct, the flue gas circulation flue and the flue. When the flue gas circulation is started, hot air preheats the flue gas circulation flue through the first loop to increase the temperature in the flue to be higher than the dew point temperature of the flue gas, thereby preventing water vapor condensation and reducing condensation. When the flue gas circulation is stopped, hot air purges the flue gas circulation flue through the first loop to remove residual flue gas and avoid the formation of corrosive deposits during the cooling process. In addition, the purge can also prevent the solid particles and impurities in the flue gas from being deposited during the cooling process.

[0019] When the flue gas circulation is put into operation, the air volume output of the blower is increased so that the air flow rate of the air duct reaches the hot air flow rate value at the initial stage of the flue gas circulation operation. Then the flue door is opened to allow the hot air to enter the boiler through the mixed smoke and air duct. At the same time, a part of the hot air directly enters the flue through the flue gas circulation flue, and the hot air is used to heat the flue gas circulation flue and the equipment installed on the flue gas circulation flue. When the flue gas circulation is operating normally, the combustion air provided by the blower enters the mixed smoke and air duct after being heated by the air preheater; the flue gas circulation fan extracts a part of the flue gas discharged from the boiler to the flue as circulating flue gas and transports it to the mixed smoke and air duct. The hot air and the circulating flue gas are mixed in the mixed smoke and air duct and then enter the boiler, and burn with the fuel input by the fuel machine to release heat. The flue gas generated by the combustion enters the waste heat recovery device and releases part of the heat. After the heat is released, the flue gas enters the flue and is divided into two parts. One part of the flue gas returns to the boiler again through the flue gas circulation pipeline as circulating flue gas, and the other part of the flue gas is finally discharged to the environment. When stopping the flue gas circulation, reduce the air volume output of the flue gas circulation fan and reduce the opening of the flue door so that the flue gas flow in the flue gas circulation reaches the shut-down flue gas circulation volume, and increase the air volume output of the blower to purge the flue gas circulation duct and the equipment installed on the flue gas circulation duct, and blow the remaining smoke in the flue gas circulation duct into the flue. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the process flow of the present invention;

[0021] In the figure: 100-boiler; 105-fuel engine; 110-waste heat recovery device; 120-flue; 123-mixed smoke and air duct; 126-smoke and air volume meter; 200-blower; 210-air duct; 220-air preheater; 223-heating medium inlet; 226-heating medium outlet; 230-air volume meter; 240-air duct door; 250-air temperature meter; 300-smoke circulation fan; 310-smoke circulation flue; 320-dust collector; 330-smoke volume meter; 340-flue duct door; 350-No. 1 smoke temperature meter; 355-No. 2 smoke temperature meter. DETAILED DESCRIPTION

[0022] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] like Figure 1As shown, a system for preventing boiler flue gas circulation from corroding in this embodiment includes a boiler 100, a flue 120, an air duct 210, a flue gas circulation flue 310, and a mixed smoke and air duct 123. The fuel supply port of the boiler 100 is provided with a fuel machine 105 for measuring the fuel supply, which can ensure that the amount of fuel input during the combustion process of the boiler 100 is appropriate, thereby maintaining the stability and efficiency of the combustion process. The flue gas outlet of the boiler 100 is connected to the waste heat recovery device 110 through the flue 120, and the outlet of the flue 120 is connected to the ambient air. The flue 120 is also connected to the inlet of the flue gas circulation flue 310, and the outlet of the flue gas circulation flue 310 and the outlet of the air duct 210 are both connected to the inlet of the mixed smoke and air duct 123. The mixed smoke and air duct 123 is provided with a smoke and air volume meter 126 for accurately measuring the flue gas flow in the mixed smoke and air duct 123, and the outlet of the mixed smoke and air duct 123 is connected to the boiler 100.

[0024] A blower 200 is provided at the inlet of the air duct 210, and the air outlet direction of the blower 200 is connected to the boiler 100 through the air duct 210 and the mixed smoke air duct 123. An air preheater 220, a wind temperature meter 250, an air volume meter 230 and an air duct door 240 are sequentially provided on the air duct 210. The blower 200 is used to deliver air to the air duct 210. The air preheater 220 is located behind the blower 200. The air delivered from the air outlet of the blower 200 passes through the air duct 210 and is preheated to a higher temperature when passing through the air preheater 220, thereby improving the combustion efficiency. In addition, the air preheater 220 is provided with a heating medium inlet 223 and a heating medium outlet 226. The heating medium is introduced into the air preheater 220 through the heating medium inlet 223. The heating medium contacts the passing air inside the air preheater 220, and the heat energy is transferred from the heating medium to the passing air, thereby preheating the air. After heat exchange, the heating medium exits the air preheater 220 through the heating medium outlet 226. The air temperature meter 250 and the air volume meter 230 are used to monitor the air temperature and flow rate of the air duct 210, respectively, and the air duct door 240 is used to adjust the ventilation volume of the air duct 210, thereby controlling air flow and distribution.

[0025] The inlet of the flue gas circulation flue 310 is provided with a No. 1 flue gas thermometer 350 for measuring the flue gas temperature and a dust collector 320. The dust collector 320 removes particulate matter and dust in the flue gas, thereby purifying the flue gas and protecting the equipment from wear; the outlet is provided with a No. 2 flue gas thermometer 355 for measuring the flue gas temperature, a flue door 340 for controlling the flue gas flow rate, a flue gas flow meter 330 for measuring the flue gas flow rate, and a flue gas circulation fan 300. The flue gas inlet direction of the flue gas circulation fan 300 is connected to the flue 120 through the flue gas circulation flue 310, and the flue gas outlet direction of the flue gas circulation fan 300 is connected to the boiler 100 through the flue gas circulation flue 310 and the mixed smoke and air duct 123.

[0026] A method for preventing boiler flue gas circulation from corroding comprises the following steps:

[0027] When the flue gas circulation is started, the combustion air provided by the blower 200 is heated by the air preheater 220 and enters the boiler 100 through the mixed smoke and air duct 123. At the same time, a part of the hot air directly enters the flue 120 through the flue gas circulation flue 310. When passing through the flue gas circulation flue 310, the hot air preheats the flue gas circulation flue 310 and the equipment on the flue gas circulation flue 310.

[0028] When the flue gas circulation is put into operation, the air volume output of the blower 200 is increased so that the hot air flow rate of the air duct 210 measured by the air volume meter 230 increases from the hot air flow rate value V when the boiler 100 is operating normally. O,A Reach the hot air flow value V at the initial stage of flue gas circulation operation S,A , V O,A and V S,A The unit is Nm 3 / h. When V S,A =1.1V O,A ~1.3V O,A When the flue door 340 is opened and the opening of the flue door 340 is maintained at 1% to 30%, part of the hot air from the air duct 210 enters the flue gas circulation flue 310, and the hot air is used to heat the flue gas circulation flue 310 and the second smoke temperature meter 355, the flue door 340, the smoke volume meter 330, the flue gas circulation fan 300, the dust collector 320 and the first smoke temperature meter 350 provided on the flue gas circulation flue 310; then the opening of the flue door 340 is increased and the reading V of the smoke and air volume meter 126 provided on the mixed smoke and air duct 123 is observed. M,A , V M,A The unit is Nm 3 / h, as the flue door 340 opens, the smoke and air volume meter 126 reads V M,A Lower, when V M,A The value reaches V O,A When the temperature of the flue door 340 is lowered, the temperature T measured by the No. 1 flue gas thermometer 350 is monitored. g The temperature value T measured by the wind thermometer 250 a , T a and T g The unit is ℃. When the flue gas circulation is put into operation, T s,GR To set the temperature difference coefficient, the value range is 5% to 10%.

[0029] By increasing the air volume output of the blower 200, preparations are made for hot air to blow the flue gas circulation duct 310 and the equipment on the flue gas circulation duct 310, so as to avoid the situation where, when the flue door 340 is opened, part of the hot air enters the flue 120 with lower pressure through the flue gas circulation duct 310, resulting in insufficient air entering the boiler 100 through the mixed smoke and air duct 123, which ultimately leads to incomplete combustion of the fuel, waste of energy, and increased emissions of atmospheric pollutants such as carbon monoxide.

[0030] Regarding the hot air flow rate V at the initial stage of flue gas circulation operation S，A If you set V S，A <1.1V O，A After the flue door 340 is opened, the hot air flow rate entering the flue 310 is small, and the hot air heats the flue 310 and the equipment on the flue 310 slowly, which will delay the commissioning of the flue gas circulation system. At the same time, considering the heat dissipation of the system, the flue gas circulation system may not be put into operation due to the failure to meet the temperature conditions for the commissioning of the flue gas circulation system. If V is set S，A >1.3V O，A , the air volume will exceed the output of the blower 200, resulting in the failure of the flue gas circulation system to operate; in addition, when the flue door 340 is opened, a large amount of hot air enters the flue 120 through the flue gas circulation flue 310, which will exceed the load of the flue and the subsequent equipment arranged in the flue. Therefore, V is set S，A The range is: V S，A =1.1V O，A ~1.3V O，A .

[0031] Before the flue door 340 is opened, the air temperature meter 250 measures the temperature of the hot air heated by the air preheater 220, which is generally greater than 150°C. At this time, the flue door 340 is closed, the flue gas circulation fan 300 is in a stopped state, and no hot air from the air duct 210 or hot flue gas from the flue 120 passes through the flue gas circulation flue 310. The temperature measured by the No. 1 flue gas temperature meter 350 is close to the ambient temperature. At this time, Much greater than 50%, greater than T S，GR .

[0032] After the flue door 340 is opened, the hot air from the air duct 210 enters the flue gas circulation flue 310 and heats the flue gas circulation flue 310 and the equipment on the flue gas circulation flue 310. The hot air temperature T measured by the thermometer 250 is a Maintain the same, the temperature T measured by the No. 1 smoke thermometer 350 g Start to rise, T g As the amount of hot air flowing through the flue gas circulation flue 310 increases, Tg The value gradually approaches T a The numerical value of Gradually decreases, due to the heat dissipation in the flue gas circulation flue 310, T g The value of T cannot reach a The numerical value of .

[0033] If T S，GR If the setting is too large, it means T g T a The hot air does not fully heat the flue gas circulation flue 310 and the equipment on the flue gas circulation flue 310. g Under lower temperature conditions, When the flue gas circulation operation conditions are met, the flue gas from the flue 120 is introduced into the flue gas circulation flue 310. The flue gas containing acidic gas and water vapor in the flue 120 may cause low-temperature condensation and corrosion in the flue gas circulation flue 310, causing the flue gas circulation flue 310 to be damaged by corrosion. S，GR If the setting is too small, T g Too T a Close, due to the heat dissipation of the flue gas circulation flue 310, it takes too long to meet Delaying the commissioning of the flue gas circulation system, or even failing to reach the set value, will cause the flue gas circulation system to be unable to be put into use. S,GR The value range is 5% to 10%.

[0034] When the flue gas circulation operates normally, the combustion-supporting air provided by the blower 200 is heated by the air preheater 220 and then enters the boiler 100 through the air duct 210 and the mixed smoke and air duct 123; a part of the flue gas discharged from the boiler 100 to the flue 120 is transported to the mixed smoke and air duct 123 by the flue gas circulation flue 310 through the flue gas circulation fan 300 as circulating flue gas, and the hot air and the circulating flue gas are mixed in the mixed smoke and air duct 123 and then enter the boiler 100, and are burned and released heat with the fuel input by the fuel engine 105, and the flue gas generated by the combustion enters the waste heat recovery device 110 and releases part of the heat. After the heat is released, the flue gas enters the flue 120 and is divided into two parts, one part of the flue gas is returned to the boiler 100 as circulating flue gas through the flue gas circulation flue 310 for circulation, and the other part of the flue gas is finally discharged into the environment.

[0035] The steps for commissioning flue gas recirculation are as follows:

[0036] Close the flue door 340, reduce the air volume output of the blower 200, so that the hot air flow rate of the air duct 210 measured by the air flow meter 230 is reduced to the hot air flow rate value V when the boiler 100 is operating normally. O,AThen, the flue gas circulation fan 300 is started, the flue door 340 is opened and the opening of the flue door 340 is maintained at 1% to 30%, so that part of the flue gas flowing through the flue 120 enters the heated flue gas circulation flue 310, and then the opening of the flue door 340 and the air volume output of the flue gas circulation fan 300 are increased, the amount of flue gas entering the flue gas circulation flue 310 increases, and the flue gas flow value measured by the smoke meter 330 is monitored. When the flue gas flow value reaches the target flue gas circulation volume V RG,AIM =0.1V O,A ~0.5V O,A When the flue door 340 is opened and the air volume output of the flue gas circulation fan 300 is maintained, the inlet flue gas temperature value T measured by the No. 1 flue gas temperature meter 350 of the flue gas circulation flue 310 is monitored. g,ib The flue gas outlet temperature value T measured by the No. 2 smoke temperature meter 355 g,out , T g,in and T g,out The unit is ℃; when the air volume output of the flue gas circulation fan 300 continues for more than 30 minutes, if This indicates that the smoke circulation volume is too small, and the smoke temperature in part of the smoke circulation duct 310 is too low. The opening of the flue door 340 and the air volume output of the smoke circulation fan 300 should be increased.

[0037] The circulating smoke volume value measured by the smoke meter 330 is less than V RG,AIM Under the upper limit condition, if This indicates that the temperature of the entire flue gas circulation flue 310 is high enough, so the opening of the flue door 340 and the air volume output of the flue gas circulation fan 300 are maintained; when the circulating flue gas volume value measured by the smoke meter 330 reaches V RG,AIM If the upper limit condition is This indicates that the flue gas temperature in part of the flue gas circulation duct 310 is too low and the flue gas circulation should be stopped.

[0038] When the operating load of the boiler 100 is lower than 70% of the rated load of the boiler 100, the flue gas circulation is stopped.

[0039] About the target flue gas circulation volume V RG,AIM The purpose of flue gas circulation is to control the amount of nitrogen oxides generated by the boiler 100. If V RG,AIM <0.1V O，A , the effect of reducing nitrogen oxides is not obvious due to the small amount of flue gas circulation; if V RG,AIM >0.5V O，A, since the amount of flue gas returning to the boiler 100 is too large, it will have an adverse effect on the stable combustion of the boiler 100; in addition, since the amount of flue gas entering the flue 120 and the waste heat recovery device 110 is too large, the flow rate of the flue gas is greatly increased, which not only accelerates the wear of the waste heat recovery device 110 and the flue 120, but also greatly increases the flow resistance of the flue gas and increases power consumption. Therefore, the target flue gas circulation volume V is set RG,AIM The range is: V RG,AIM =0.1V O，A ~0.5V O，A .

[0040] When the flue gas circulation is stopped, the combustion-supporting air provided by the blower 200 is heated by the air preheater 220, and the hot air, when passing through the flue gas circulation flue 310, purges the flue gas circulation flue 310, the No. 2 flue gas temperature meter 355, the flue door 340, the smoke volume meter 330, the flue gas circulation fan 300, the dust collector 320 and the No. 1 flue gas temperature meter 350.

[0041] When the flue gas circulation is stopped, the air volume output of the flue gas circulation fan 300 is reduced, and the opening of the flue door 340 is reduced, so that the flue gas flow rate of the flue gas circulation flue 310 measured by the smoke meter 330 reaches the shut-down flue gas circulation volume V RG，C =5%V O，A At this time, the flue door 340 and the flue gas circulation fan 300 are closed, and the air volume output of the blower 200 is increased, so that the air flow rate of the air duct 210 measured by the air volume meter 230 increases from the hot air flow rate value V when the boiler 100 is operating normally. O，A The hot air flow value V for purging the flue gas circulation flue 310 is reached BL，A =1.1V O，A ~1.3V O，A , V BL，A The unit is Nm 3 / h, at this time, the opening of the flue door 340 is increased, and the hot air from the flue 120 enters the flue gas circulation flue 310, and the hot flue gas circulation flue 310 and the equipment on the flue gas circulation flue 310 are purged; at the same time, the reading V of the smoke and air volume meter 126 set on the mixed smoke and air duct 123 is monitored. M，A , when V M，A The value reaches V O，A When the opening of the flue door 340 is stopped, the opening is maintained unchanged, and the flue gas circulation flue 310 is continuously purged for more than 15 minutes to purge the remaining flue gas in the flue gas circulation flue 310 into the flue 120; then the opening of the flue door 340 and the air duct door 240 is reduced, the air volume output of the flue gas circulation fan 300 is reduced, and the reading V of the smoke and air volume meter 126 is detected. M，A , when V M，A =1.0V O，A ~1.05V O，AWhen the boiler 100 is in normal combustion, the flue door 340 is completely closed.

[0042] About the shutdown flue gas circulation volume V RG，C The setting value should not be too large. If it is too large, it will have an adverse effect on the normal combustion of the boiler 100 when the flue gas circulation fan 300 is shut down, and will also cause pressure shock to the boiler 100, the flue 120 and the waste heat recovery device 110.

[0043] By increasing the air volume output of the blower 200, preparations are made for hot air to blow the flue gas circulation duct 310 and the equipment on the flue gas circulation duct 310, so as to avoid that when the flue door 340 is opened, part of the hot air enters the flue 120 with lower pressure through the flue gas circulation duct 310, resulting in insufficient air entering the boiler 100 through the mixed smoke and air duct 123, which ultimately leads to incomplete combustion of the fuel, waste of energy, and increased emissions of atmospheric pollutants such as carbon monoxide.

[0044] Hot air flow rate V for purge BL，A If you set V BL，A <1.1V O，A After the flue door 340 is opened, the hot air flow rate entering the flue gas circulation flue 310 is small, and the hot air purges the flue gas circulation flue 310 and the equipment on the flue gas circulation flue 310 at a slow speed, which will delay the shutdown of the flue gas circulation system. BL，A >1.3V O，A , the air volume may exceed the air volume output of the blower 200, resulting in the inability to shut down the flue gas circulation system; in addition, when the flue door 340 is opened, a large amount of hot air enters the flue 120 through the flue gas circulation flue 310, and a large amount of hot air enters the flue 120, which will exceed the air volume load of the flue and the subsequent equipment arranged in the flue. Therefore, the target flue gas circulation volume V is set BL，A The range is: V BL , A=1.1V O，A ~1.3V O，A .

Claims

1. A system for preventing boiler flue gas circulation from corroding, characterized in that: It comprises a boiler (100), a flue (120), an air duct (210), a flue gas circulation flue (310) and a mixed smoke and air duct (123), wherein the flue gas outlet of the boiler (100) is connected to a waste heat recovery device (110) through the flue (120), and the flue (120) outlet is connected to ambient air; The flue (120) is also connected to the inlet of the flue gas circulation flue (310), and the outlet of the flue gas circulation flue (310) and the outlet of the air duct (210) are both connected to the inlet of the mixed smoke and air duct (123). The mixed smoke and air duct (123) is provided with a smoke and air flow meter (126), and the outlet of the mixed smoke and air duct (123) is connected to the boiler (100); The air duct (210), the smoke circulation duct (310) and the smoke duct (120) form a first loop. When the smoke circulation is started, hot air passes through the first loop to preheat the smoke circulation duct (310); when the smoke circulation is stopped, hot air passes through the first loop to purge the smoke circulation duct (310); The flue (120), the flue gas circulation flue (310), and the mixed smoke and air duct (123) form a second loop. During the flue gas circulation, a portion of the flue gas discharged from the flue (120) re-enters the boiler (100) through the flue gas circulation flue (310) and the mixed smoke and air duct (123) for circulation.

2. A system for preventing boiler flue gas circulation from corroding according to claim 1, characterized in that: A blower (200) is provided at the inlet of the air duct (210); an air outlet direction of the blower (200) is connected to the boiler (100) through the air duct (210) and the mixed smoke air duct (123); and an air preheater (220) for preheating air, a temperature meter (250) for monitoring the air temperature of the air duct (210), an air volume meter (230) for monitoring the air flow rate of the air duct (210), and an air duct door (240) for adjusting the ventilation volume of the air duct (210) are sequentially provided on the air duct (210).

3. A system for preventing boiler flue gas circulation from corroding according to claim 2, characterized in that: The inlet of the flue gas circulation duct (310) is provided with a No. 1 flue gas temperature meter (350) for measuring the flue gas temperature and a dust collector (320), and the outlet is provided with a No. 2 flue gas temperature meter (355) for measuring the flue gas temperature, a flue door (340) for controlling the flue gas flow rate, a flue gas volume meter (330) for measuring the flue gas flow rate, and a flue gas circulation fan (300) in sequence; the flue gas inlet direction of the flue gas circulation fan (300) is connected to the flue (120) through the flue gas circulation duct (310), and the flue gas outlet direction of the flue gas circulation fan (300) is connected to the boiler (100) through the flue gas circulation duct (310) and the mixed smoke and air duct (123).

4. A system for preventing boiler flue gas circulation from corroding according to claim 3, characterized in that: The fuel supply port of the boiler (100) is provided with a fuel machine (105) for measuring the amount of fuel supplied.

5. A system for preventing boiler flue gas circulation from corroding according to claim 4, characterized in that: The air preheater (220) is provided with a heating medium inlet (223) and a heating medium outlet (226).

6. A method for preventing boiler flue gas circulation corrosion based on the system of claim 5, characterized in that: When the flue gas circulation is started, the combustion-supporting air provided by the blower (200) is heated by the air preheater (220) and then enters the boiler (100) through the mixed smoke and air duct (123). At the same time, a portion of the hot air directly enters the flue (120) through the flue gas circulation flue (310). When the hot air passes through the flue gas circulation flue (310), the flue gas circulation flue (310) and the second flue gas temperature meter (355), the flue door (340), the smoke volume meter (330), the flue gas circulation fan (300), the dust collector (320) and the first flue gas temperature meter (350) are preheated. When the flue gas circulation is operating normally, the combustion-supporting air provided by the blower (200) is heated by the air preheater (220) and then enters the boiler (100) through the air duct (210) and the mixed flue gas duct (123); a part of the flue gas discharged from the boiler (100) to the flue gas duct (120) is transported from the flue gas circulation flue (310) to the mixed flue gas duct (123) through the flue gas circulation fan (300) as circulating flue gas, the hot air and the circulating flue gas are mixed in the mixed flue gas duct (123) and then enter the boiler (100), and are burned and released heat with the fuel input by the fuel engine (105), the flue gas generated by the combustion enters the waste heat recovery device (110) and releases part of the heat, and the flue gas after heat release enters the flue gas duct (120) and is divided into two parts, one part of the flue gas is returned to the boiler (100) as circulating flue gas through the flue gas circulation flue (310) for circulation, and the other part of the flue gas is finally discharged to the environment; When the flue gas circulation is stopped, the combustion-supporting air provided by the blower (200) is heated by the air preheater (220), and the hot air, when passing through the flue gas circulation flue (310), purges the flue gas circulation flue (310), the second flue gas temperature meter (355), the flue door (340), the smoke volume meter (330), the flue gas circulation fan (300), the dust collector (320) and the first flue gas temperature meter (350).

7. A method for preventing boiler flue gas circulation from corroding according to claim 6, characterized in that: When the flue gas circulation is put into operation, the air volume output of the blower (200) is increased so that the hot air flow rate of the air duct (210) measured by the air volume meter (230) increases from the hot air flow rate value V when the boiler (100) is in normal operation. O,A Reach the hot air flow value V at the initial stage of flue gas circulation operation S,A , V O,A and V S,A The unit is Nm 3 / h; When V S,A =1.1V O,A ~1.3V O,A When the flue door (340) is opened and the opening of the flue door (340) is maintained at 1% to 30%, part of the hot air in the air duct (210) enters the flue gas circulation flue (310), and the hot air is used to heat the flue gas circulation flue (310) and the second smoke temperature meter (355), the flue door (340), the smoke volume meter (330), the smoke circulation fan (300), the dust collector (320) and the first smoke temperature meter (350) provided on the flue gas circulation flue (310); then, the opening of the flue door (340) is increased and the reading V of the smoke volume meter (126) provided on the mixed smoke and air duct (123) is monitored. M,A , V M,A The unit is Nm 3 / h, as the opening of the flue door (340) increases, the reading of the smoke and air volume meter (126) V M,A Lower, when V M,A The value reaches V O,A When the temperature of the flue door (340) is lowered, the temperature value T measured by the No. 1 flue gas temperature meter (350) is monitored. g The temperature value T measured by the wind thermometer (250) a , T a and T g The unit is ℃. When the flue gas circulation is put into operation, T S,GR To set the temperature difference coefficient, the value range is 5% to 10%.

8. A method for preventing boiler flue gas circulation from corroding according to claim 7, characterized in that: The steps of putting the flue gas circulation into operation are as follows: The flue door (340) is closed, and the air volume output of the blower (200) is reduced, so that the hot air flow rate of the air duct (210) measured by the air volume meter (230) is reduced to the hot air flow rate value V when the boiler (100) is operating normally. O,A Then, the smoke circulation fan (300) is started, the smoke duct door (340) is opened and the opening of the smoke duct door (340) is maintained at 1% to 30%, so that part of the smoke flowing through the smoke duct (120) enters the heated smoke circulation duct (310), and then the opening of the smoke duct door (340) and the air volume output of the smoke circulation fan (300) are increased, the amount of smoke entering the smoke circulation duct (310) increases, and the smoke flow value measured by the smoke meter (330) is monitored. When the smoke flow value reaches the target smoke circulation volume V RG,AIM =0.1V O,A ~0.5V O,A When the opening of the flue door (340) and the air volume output of the flue gas circulation fan (300) are maintained, the inlet flue gas temperature value T measured by the No. 1 flue gas temperature meter (350) of the flue gas circulation flue (310) is monitored. g,in and the flue gas outlet temperature value T measured by the No. 2 flue gas temperature meter (355) g,out , T g,in and T g,out The unit is ℃; when the air volume output of the flue gas circulation fan (300) continues for more than 30 minutes, if This indicates that the smoke circulation volume is too small, and the smoke temperature in part of the smoke circulation flue (310) is too low. The opening of the flue door (340) and the air volume output of the smoke circulation fan (300) should be increased. The circulating smoke volume value measured by the smoke meter (330) is less than V RG,AIM Under the upper limit condition, if This indicates that the temperature of the entire flue gas circulation duct (310) is high enough, so the opening of the flue gas duct door (340) and the air volume output of the flue gas circulation fan (300) are maintained; when the circulating flue gas volume value measured by the smoke meter (330) reaches V RG,AIM When the upper limit condition is It indicates that the flue gas temperature of part of the flue gas circulation flue (310) is too low and the flue gas circulation should be stopped; When the operating load of the boiler (100) is lower than 70% of the rated load of the boiler (100), the flue gas circulation is stopped.

9. A method for preventing boiler flue gas circulation from corroding according to claim 8, characterized in that: When the smoke circulation is stopped, the air volume output of the smoke circulation fan (300) is reduced, and the opening of the smoke duct door (340) is reduced, so that the smoke flow rate of the smoke circulation flue (310) measured by the smoke meter (330) reaches the stop smoke circulation volume V RG,C =5%V O,A At this time, the flue door (340) and the flue gas circulation fan (300) are closed, and the air volume output of the blower (200) is increased, so that the air flow rate of the air duct (210) measured by the air volume meter (230) increases from the hot air flow rate value V when the boiler (100) is operating normally. O,A The hot air flow value V required to purge the flue gas circulation flue (310) is reached BL,A =1.1V O,A ~1.3V O,A , V BL,A The unit is Nm 3 / h, at this time, the opening of the flue door (340) is increased, and the hot air from the flue (120) enters the flue gas circulation flue (310), and the hot flue gas circulation flue (310) and the equipment on the flue gas circulation flue (310) are purged; at the same time, the reading V of the smoke and air volume meter (126) provided on the mixed smoke and air duct (123) is monitored. M,A , when V M,A The value reaches V O,A When the smoke duct door (340) stops increasing its opening, the opening is maintained unchanged, and the smoke circulation duct (310) is continuously purged for more than fifteen minutes to purge the remaining smoke in the smoke circulation duct (310) into the smoke duct (120); Then, the openings of the flue door (340) and the air duct door (240) are reduced, the air volume output of the flue gas circulation fan (300) is reduced, and the reading V of the smoke and air volume meter (126) is detected. M,A , when V M,A =1.0V O,A ~1.05V O,A When the boiler (100) is in normal combustion, the flue door (340) is completely closed.

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