Flue gas whitening system suitable for coal-fired units

Abstract

The present invention provides a flue gas whitening system suitable for a coal-fired unit, comprising: a tail flue arranged between a desulfurization tower outlet and a chimney; a flue gas heating bypass arranged on the tail flue and parallel to the tail flue, wherein a flue gas heating bypass inlet baffle, a flue gas circulation fan, a flue gas heat exchanger and a flue gas heating bypass outlet baffle are sequentially arranged through a pipeline; wherein the critical temperature for producing white smoke when the flue gas is discharged is T 1 The flue gas temperature at the outlet of the desulfurization tower is T 2 , when T 2 <T 1 When T 2 ≥T 1 When the flue gas heating bypass is disconnected, the flue gas directly passes through the tail flue to reach the chimney for discharge. The flue gas whitening system for coal-fired units provided by the present invention does not increase the flue resistance and is suitable for units with small induced draft fan margins; it is easy to switch on and off, and when the ambient temperature is high, the heating system can be exited without affecting the economic operation of the unit.

Description

Technical Field

[0001] The invention belongs to the field of thermal power generation, and in particular relates to a flue gas whitening system suitable for a coal-fired unit. Background Art

[0002] At present, the desulfurization systems of most coal-fired power plants in China adopt the wet desulfurization process of limestone-gypsum. After desulfurization, the flue gas temperature drops to 45~55℃. At this time, the flue gas is saturated wet flue gas, which contains a lot of water vapor. If the flue gas is directly discharged through the chimney and enters a low temperature environment, the water vapor in the flue gas will condense to form "white plume" when it encounters cold. The simple "white plume" will not affect the environmental quality, but it weakens the public's "sense of gain" in environmental protection work. In addition, the tiny water droplets condensed from the wet flue gas will also have a certain impact on the lives of surrounding residents. Therefore, many local governments have begun to write the elimination of "white plume" (abbreviated as "white plume elimination") into local environmental protection standards.

[0003] According to the formation mechanism of "white smoke plume", there are currently various technical routes for its treatment. Chinese patent application number 201710550580.5 discloses a flue gas treatment system for desulfurization, dehydration and mist reduction in power plants. It can significantly reduce the white mist pollution of flue gas in power plants by applying high-temperature heat pump technology to cool and dehydrate the flue gas and to heat and dehumidify the flue gas. However, the technical system is complex and requires a large maintenance workload. In addition, a flue gas heating and dehumidifying device must be added to the flue, which will significantly increase the resistance of the tail flue and affect the output of the induced draft fan and even its safe operation. Patent application number 201720168606.5 discloses a flue gas whitening system for wet flue gas desulfurization. The system reduces the moisture content and temperature of the flue gas through slurry cooling, and increases the flue gas temperature at the chimney outlet through flue gas heating and cooling heat exchangers and a heat medium water circulation system. Therefore, the "white smoke plume" can be effectively eliminated through condensation + reheating technology. However, the system also adds a flue gas heating heat exchanger and a flue gas cooling heat exchanger in the tail flue, which increases the resistance of the tail flue. It is not applicable to thermal power units with insufficient induced draft fan margin. Summary of the invention

[0004] An object of the present invention is to provide a flue gas whitening system suitable for a coal-fired unit and to provide at least the advantages to be described below.

[0005] Another object of the present invention is to provide a flue gas whitening system suitable for coal-fired units, which adds a flue gas heating bypass on the basis of the original equipment, simplifies the system, and reduces the maintenance workload of the whitening system in normal times; it does not increase the flue resistance, is suitable for units after the induced draft fan is combined, especially units with limited induced draft fan pressure head margin, and does not require modification or replacement of the original fan; the whitening system is flexible to switch on and off, and operates according to the ambient temperature and changing working conditions, and does not affect the energy consumption of the unit when it is not put into operation.

[0006] The technical solution of the present invention is as follows:

[0007] The flue gas whitening system applicable to coal-fired units includes:

[0008] The tail flue is arranged between the outlet of the desulfurization tower and the chimney;

[0009] A flue gas heating bypass arranged on and in parallel with the tail flue is provided with a flue gas heating bypass inlet baffle, a flue gas circulation fan, a flue gas heat exchanger and a flue gas heating bypass outlet baffle in sequence through a pipeline;

[0010] in,

[0011] The critical temperature for producing white smoke during flue gas discharge is T1, and the flue gas temperature at the outlet of the desulfurization tower is T2. When T2<T1, the flue gas heating bypass is connected, and the flue gas is heated and then returns to the tail flue to reach the chimney for discharge; when T2≥T1, the flue gas heating bypass is disconnected, and the flue gas directly passes through the tail flue to reach the chimney for discharge.

[0012] Preferably, in the flue gas whitening system applicable to coal-fired units,

[0013] The flue gas heat exchanger comprises a first heat source inlet and a second heat source inlet, wherein the first heat source inlet is connected to the outlet of the condensate heating device;

[0014] The condensate heating device comprises a first low-pressure heater, a second low-pressure heater and a deaerator which are sequentially arranged along the condensate circulation pipeline, the first low-pressure heater, the second low-pressure heater and the deaerator are respectively connected to the condensate pipeline through a first condensate branch pipe, a second condensate branch pipe and a third condensate branch pipe to be connected to the first heat source inlet, and the first condensate branch pipe, the second condensate branch pipe and the condensate branch pipe are respectively provided with a first valve, a second valve and a third valve;

[0015] The steam heating device comprises a steam branch pipe arranged between a steam heat source and an inlet of the second heat source, and a steam valve is arranged on the steam branch pipe.

[0016] Preferably, in the flue gas whitening system applicable to coal-fired units,

[0017] The opening priorities of the first valve, the second valve, and the third valve decrease in sequence;

[0018] The condensed water temperature at the inlet of the first heat source is ≥120°C.

[0019] Preferably, in the flue gas whitening system applicable to coal-fired units,

[0020] The steam heat source is steam extraction from the unit or exhaust steam from the unit operation;

[0021] When the unit is extracting steam, the opening priority of the steam valve is lower than that of the third valve;

[0022] When the unit is operated to exhaust steam, the opening priority of the steam valve is higher than that of the first valve.

[0023] Preferably, in the flue gas deoxidation system applicable to coal-fired units, the flue gas heating bypass adopts a countercurrent arrangement.

[0024] Preferably, in the flue gas whitening system applicable to coal-fired units, a guide device is provided in the tail flue.

[0025] Preferably, in the flue gas whitening system applicable to coal-fired units, the flue gas circulation fan adopts frequency conversion control and fan guide vane or moving blade adjustment.

[0026] Preferably, in the flue gas desulfurization system applicable to coal-fired units, a slurry circulation pipeline is provided between the slurry outlet and the flue gas outlet of the desulfurization tower, a slurry circulation pump and a condenser are provided on the slurry circulation pipeline, and an inlet valve and an outlet valve are respectively provided at the cold source inlet and outlet of the condenser.

[0027] Preferably, in the flue gas desulfurization system applicable to coal-fired units, a dust collector and an induced draft fan are also provided before the desulfurization tower.

[0028] The present invention has the following beneficial effects:

[0029] By extracting part of the flue gas, heating it in the flue gas heat exchanger and returning it to the tail flue to mix with the original flue gas, the flue gas temperature at the chimney outlet can be increased to eliminate the white smoke plume.

[0030] The heat source at the flue gas heat exchanger is mainly condensed water heating, and when the heat exchange load is high, the unit extraction steam is used for auxiliary heating;

[0031] The system is flexible in switching on and off and does not increase the resistance of the tail flue. It is especially suitable for units with small induced draft fan margin after the induced draft fan is combined.

[0032] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic structural diagram of an embodiment of a flue gas whitening system applicable to a coal-fired unit provided by the present invention;

[0034] Figure 2A schematic structural diagram of another embodiment of a flue gas whitening system applicable to a coal-fired unit provided by the present invention. DETAILED DESCRIPTION

[0035] The present invention is further described in detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0036] It should be understood that terms such as “having”, “including” and “comprising” used herein do not specify the existence or addition of one or more other elements or combinations thereof.

[0037] The prior art has the following disadvantages:

[0038] 1. The system is complex and the maintenance workload is large;

[0039] 2. It increases the tail flue resistance, which is not applicable to thermal power units with small induced draft fan pressure head margin;

[0040] 3. When the ambient temperature is high and the deoxidation system is not needed, the newly added heat exchanger will still affect the resistance of the tail flue, increase the output of the induced draft fan, and have a poor energy-saving effect.

[0041] like Figure 1 As shown, the present invention provides a flue gas whitening system suitable for a coal-fired unit, which comprises:

[0042] The tail flue is arranged between the outlet of the desulfurization tower 6 and the chimney 8;

[0043] A flue gas heating bypass arranged on and in parallel with the tail flue is provided with a flue gas heating bypass inlet baffle 15, a flue gas circulation fan 10, a flue gas heat exchanger 9 and a flue gas heating bypass outlet baffle 16 in sequence through a pipeline;

[0044] in,

[0045] The critical temperature for flue gas to produce white smoke is T1, and the flue gas temperature at the outlet of the desulfurization tower 6 is T2. When T2<T1, the flue gas heating bypass is connected, and the flue gas is heated and then returns to the tail flue to reach the chimney 8 for discharge; when T2≥T1, the flue gas heating bypass is disconnected, and the flue gas directly passes through the tail flue to reach the chimney 8 for discharge. The determination of the critical temperature T1 belongs to the prior art, and those skilled in the art can determine it according to the flue gas temperature, ambient temperature and humidity at the outlet of the desulfurization tower, and there is no need to elaborate on it in detail.

[0046] In one embodiment of the flue gas whitening system applicable to a coal-fired unit provided by the present invention,

[0047] The flue gas heat exchanger 9 includes a first heat source inlet and a second heat source inlet, wherein the first heat source inlet is connected to the outlet of the condensate heating device;

[0048] The condensate heating device comprises a first low-pressure heater 1, a second low-pressure heater 2 and a deaerator 3 which are sequentially arranged along the condensate circulation pipeline. The first low-pressure heater 1, the second low-pressure heater 2 and the deaerator 3 are respectively connected to the condensate pipeline through a first condensate branch pipe, a second condensate branch pipe and a third condensate branch pipe to be connected to the first heat source inlet. The first condensate branch pipe, the second condensate branch pipe and the condensate branch pipe are respectively provided with a first valve 11, a second valve 12 and a third valve 13; part of the condensate of the original unit heats the flue gas through a flue gas heat exchanger 9, and the condensate after heat exchange is recovered to the condensate pipeline;

[0049] The steam heating device comprises a steam branch pipe arranged between the steam heat source and the inlet of the second heat source, a steam valve 14 is arranged on the steam branch pipe, and the cooled water is recovered to the condensate water pipeline.

[0050] In one embodiment of the flue gas whitening system applicable to a coal-fired unit provided by the present invention,

[0051] The opening priorities of the first valve 11, the second valve 12, and the third valve 13 decrease in sequence;

[0052] The condensed water temperature at the inlet of the first heat source is ≥120°C.

[0053] In one embodiment of the flue gas whitening system applicable to a coal-fired unit provided by the present invention,

[0054] The steam heat source is steam extraction from the unit or exhaust steam from the unit operation;

[0055] When the unit is using steam extraction, the opening priority of the steam valve 14 is lower than that of the third valve 13;

[0056] When the unit is operated to exhaust steam, the opening priority of the steam valve 14 is higher than that of the first valve 11 .

[0057] In one embodiment of the flue gas deoxidation system applicable to coal-fired units provided by the present invention, the flue gas heating bypass adopts a countercurrent arrangement, and the flue gas heat exchanger 9 is made of corrosion-resistant materials, such as duplex steel or stainless steel.

[0058] In one embodiment of the flue gas deoxidation system applicable to coal-fired units provided by the present invention, a guide device is provided in the tail flue to allow the cold and hot flue gases to be mixed evenly. The specific structure does not need to be described in detail here, and a conventional guide device can be used.

[0059] In one embodiment of the flue gas deoxidation system applicable to coal-fired units provided by the present invention, the flue gas circulation fan 10 adopts frequency conversion control and fan guide vane or moving blade adjustment to control the flow rate of the heated flue gas.

[0060] In one embodiment of the flue gas desulfurization system applicable to a coal-fired unit provided by the present invention, a dust collector 5 and an induced draft fan 4 are further arranged before the desulfurization tower 6 .

[0061] The flue gas generated by the original unit of the system is first processed by the dust collector 4 and then connected to the induced draft fan 5. After being pressurized by the induced draft fan 5, it is sent to the desulfurization tower 6 for desulfurization. The slurry circulation pump 7 circulates the slurry in the desulfurization tower 6. A part of the desulfurized flue gas is sent to the flue gas circulation fan 10 for pressurization through the flue gas heating bypass inlet baffle 15 and then enters the flue gas heat exchanger 9 for heat exchange. The heated flue gas returns to the flue through the flue gas heating bypass outlet baffle 16, mixes with the original flue gas, and is discharged into the atmosphere through the chimney 8.

[0062] The flue gas whitening system for coal-fired units provided by the present invention can be used alone or in combination with other patented technologies, such as Figure 2 As shown, in one embodiment of the flue gas deoxidation system applicable to coal-fired units provided by the present invention, a slurry circulation pipeline is arranged between the slurry outlet and the flue gas outlet of the desulfurization tower 6, a slurry circulation pump 7 and a condenser 17 are arranged on the slurry circulation pipeline, and an inlet valve 18 and an outlet valve 19 are respectively arranged at the cold source inlet and outlet of the condenser 17, thus forming a flue gas condensation + heating flue gas deoxidation system.

[0063] Implementation Case 1:

[0064] A 600MW supercritical unit has no booster fan in the tail flue, and the margin of the induced draft fan is very limited. The conventional MGGH desulfurization scheme cannot be implemented, so this scheme is considered. The scheme is as follows: the maximum flue gas volume under BMCR operating conditions is 2290000Nm3 / h, the flue gas temperature at the desulfurization outlet is 45℃, the design point is selected as the ambient temperature of 5℃, the relative humidity is 50%, the flue gas temperature at the chimney outlet is heated to 70℃ (the hot flue gas temperature at the flue gas heat exchanger outlet is set to 100℃), the heat load of the flue gas heat exchanger is about 22.7MW, and the power consumption of the flue gas circulation fan is 230kW (calculated according to the flue resistance of 500Pa). Using condensate for heating is equivalent to increasing the unit's steam extraction load, reducing the unit's power generation by about 3760kW, and the flue gas desulfurization system increases the unit's power consumption by about 3925KW; when the ambient temperature is high, the desulfurization system can be exited, which has no effect on the operating energy consumption of the original unit.

[0065] The flue gas whitening system provided by the present invention is suitable for coal-fired units and does not increase the flue resistance. It is suitable for units with a small induced draft fan margin. It is easy to switch on and off. When the ambient temperature is high, the heating system can be exited without affecting the economic operation of the unit (the flue resistance is not affected, and the induced draft fan output is not increased compared to before the transformation).

[0066] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes, and they can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the illustrations shown and described herein.

Claims

1. Applicable to the flue gas whitening system of coal-fired units, characterized by: include: The tail flue is arranged between the outlet of the desulfurization tower and the chimney; A flue gas heating bypass arranged on and in parallel with the tail flue is provided with a flue gas heating bypass inlet baffle, a flue gas circulation fan, a flue gas heat exchanger and a flue gas heating bypass outlet baffle in sequence through a pipeline; in, The flue gas heat exchanger comprises a first heat source inlet and a second heat source inlet, wherein the first heat source inlet is connected to the outlet of the condensate heating device; The condensate heating device comprises a first low-pressure heater, a second low-pressure heater and a deaerator which are sequentially arranged along the condensate circulation pipeline, the first low-pressure heater, the second low-pressure heater and the deaerator are respectively connected to the condensate pipeline through a first condensate branch pipe, a second condensate branch pipe and a third condensate branch pipe to be connected to the first heat source inlet, and the first condensate branch pipe, the second condensate branch pipe and the third condensate branch pipe are respectively provided with a first valve, a second valve and a third valve; A steam branch pipe is provided between the steam heat source and the inlet of the second heat source, and a steam valve is provided on the steam branch pipe; The critical temperature for producing white smoke when the flue gas is discharged is T1, and the flue gas temperature at the outlet of the desulfurization tower is T2. When T2<T1, the flue gas heating bypass is connected, and the flue gas is heated and then returns to the tail flue to be discharged from the chimney; when T2≥T1, the flue gas heating bypass is disconnected, and the flue gas directly passes through the tail flue to be discharged from the chimney The opening priorities of the first valve, the second valve, and the third valve decrease in sequence; The condensate temperature at the inlet of the first heat source is ≥120°C; The steam heat source is steam extraction from the unit or exhaust steam from the unit operation; When the unit is extracting steam, the opening priority of the steam valve is lower than that of the third valve; When the unit is operated to exhaust steam, the opening priority of the steam valve is higher than that of the first valve.

2. The flue gas whitening system suitable for coal-fired units according to claim 1, characterized in that: The flue gas heating bypass adopts a countercurrent arrangement.

3. The flue gas whitening system suitable for coal-fired units according to claim 1, characterized in that: A flow guide device is arranged in the tail flue.

4. The flue gas whitening system suitable for coal-fired units according to claim 1, characterized in that: The flue gas circulation fan adopts frequency conversion control and fan guide vane or moving blade adjustment.

5. The flue gas whitening system suitable for coal-fired units according to claim 1, characterized in that: A slurry circulation pipeline is arranged between the slurry outlet and the flue gas outlet of the desulfurization tower, a slurry circulation pump and a condenser are arranged on the slurry circulation pipeline, and an inlet valve and an outlet valve are respectively arranged at the cold source inlet and outlet of the condenser.

6. The flue gas whitening system suitable for coal-fired units according to claim 1, characterized in that: A dust collector and an induced draft fan are also arranged before the desulfurization tower.

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