JP2020121267A - Exhaust gas treatment equipment - Google Patents

Abstract

To provide an exhaust gas purifier which satisfactorily suppresses production of acidic ammonium sulfate at exhaust gas low temperature time with simple configuration.SOLUTION: A denitration catalyst packed layer for reducing and removing nitrogen oxide in exhaust gas with ammonia or urea as a reductant is located in a gas flow passage 18 in which exhaust gas, which has been discharged from a furnace of a circulation type drum boiler 1 for heating water derived from a drum 4 by the furnace and returning the same to the drum 4, flows. Ammonia or urea is injected into exhaust gas flowing in the gas flow passage on an upstream side of the denitration catalyst packed layer. A heat exchanger 30 is located in the gas flow passage 18 on the upstream side of the denitration catalyst packed layer (denitration device 20), and a heat medium introduction pipe 33 introduces water in the drum 4 into the heat exchanger 30. Water introduced from the heat medium introduction pipe 33 flows in the heat exchanger 30 as a heat medium.SELECTED DRAWING: Figure 1

Description

The present invention relates to an exhaust gas treatment device for purifying exhaust gas from a boiler.

In a thermal power plant that burns fuel in a boiler to generate power, exhaust gas from the boiler is purified by a smoke treatment system and then discharged into the atmosphere. The flue gas treatment system includes a denitrification device that reduces and removes nitrogen oxides (NOx) in exhaust gas, an air preheater that heats combustion air by heat exchange with exhaust gas, and dust (combustion ash) in exhaust gas. An electric dust collector or the like for collecting and removing is provided.

Further, in Patent Document 1, there are two examples (first and second examples) as a boiler starting device that raises the exhaust gas temperature at the denitration device inlet at the time of starting the boiler in which the denitration device is installed in the flue of the boiler outlet part. ) Is described. In the first example, when the boiler is activated, a bypass damper that bypasses a part of the heat transfer surface is opened to raise the exhaust gas temperature at the inlet of the denitration device. In the second example, part of the steam supplied from the brackish water separator to the turbine side is supplied to the exhaust gas superheater installed at the inlet of the denitration device.

JP-A-3-51601

In the case of a denitration device using a catalyst that uses ammonia or urea as a reducing agent, if the temperature of the exhaust gas flowing into the denitration device (exhaust gas temperature before passing through the denitration catalyst) is low, the S content and reducing agent contained in the exhaust gas Is reacted with ammonia to produce acidic ammonium sulfate (ammonium hydrogen sulfate: NH ₄ HSO ₄ ). This causes the performance of the denitration catalyst to deteriorate. In addition, the generated acidic ammonium sulfate may be deposited and deposited on a device (for example, an air preheater) on the downstream side of the denitration device, resulting in deterioration or malfunction of the device (for example, clogging of the air preheater). For example, during low-load operation of the boiler for adjusting (suppressing the power supply amount to be low), the exhaust gas temperature is lowered and acid ammonium sulfate is easily generated.

On the other hand, as in the first example of Patent Document 1, in an exhaust gas treatment device in which a bypass duct that bypasses a part of the heat transfer surface (for example, a economizer) is provided and the bypass duct can be opened and closed by a bypass damper When the temperature of the exhaust gas flowing into the denitration device is low, the exhaust gas temperature at the inlet of the denitration device can be raised by opening the bypass damper. In addition, as in the second example, in the exhaust gas treatment device that supplies part of the steam supplied from the brackish water separator (drum) to the turbine side to the exhaust gas superheater (heat exchanger) on the inlet side of the denitration device. If the temperature of the exhaust gas flowing into the denitration device is low, the exhaust gas temperature at the denitration device inlet can be raised by the heat exchanger. For this reason, acid ammonium sulfate is less likely to be generated, and the adhesion and deposition of acid ammonium sulfate on the equipment downstream of the denitration device can be suppressed.

However, when the exhaust gas treatment device of the first example is applied to an existing boiler that does not have a bypass duct, large-scale construction of adding a bypass duct is required. In addition, there is a space problem for disposing a large bypass duct. For these reasons, it is often difficult to apply the exhaust gas treatment device of the first example to an existing boiler without a bypass duct, and an exhaust gas treatment that can be easily applied to an existing boiler without a bypass duct. A device is needed.

Further, in the exhaust gas treating apparatus of the second example, since the steam from the drum is used as a heat medium, the amount of power generation tends to be lowered, and pulsation may occur due to condensation in the heat exchanger.

Therefore, it is an object of the present invention to suitably suppress acidic ammonium sulfate generated at a low temperature of exhaust gas with a simple configuration.

In order to achieve the above object, the exhaust gas purifying apparatus according to the present invention is provided in a circulation type drum boiler that heats water drawn from a drum in a furnace and returns it to the drum. In the gas flow passage through which the exhaust gas discharged from the furnace flows, a denitration catalyst packed layer that reduces and removes nitrogen oxides in the exhaust gas by using ammonia or urea as a reducing agent is arranged, and gas distribution on the upstream side of the denitration catalyst packed layer Ammonia or urea is injected into the exhaust gas flowing through the passage.

An exhaust gas purifying apparatus according to a first aspect of the present invention includes a heat exchanger arranged in a gas flow passage on an upstream side of a denitration catalyst packed bed, and a heat medium introducing pipe for introducing water in a drum into the heat exchanger. Equipped with. The water introduced from the heat medium introduction pipe flows as a heat medium inside the heat exchanger.

In the above configuration, the water in the drum becomes hot due to the operation of the circulation type drum boiler (boiler), the hot water in the drum (drain water, falling water) is extracted from the drum, and heat exchange is performed via the heat medium introduction pipe. Since it is introduced into the reactor, the temperature of the exhaust gas before passing through the denitration catalyst (denitration catalyst packed bed) rises due to heat exchange with high-temperature drain water. For example, during low-load operation of the boiler, the exhaust gas temperature is lower than during non-low-load operation (for example, during normal operation), but with a circulating drum boiler for power generation, the steam pressure is increased to improve plant efficiency. .. Therefore, the high-temperature water in the drum becomes higher than the temperature of the exhaust gas passing through the denitration catalyst, and the exhaust gas heated by the heat exchanger can be introduced into the denitration catalyst during the low load operation.

Further, the heat exchanger is arranged in the gas flow passage on the upstream side of the denitration catalyst, and the heat medium introducing pipe for introducing the water in the drum to the heat exchanger is provided, which is a simple structure and has a wide width such as a bypass duct. Since it does not require an installation space, it can be easily applied to an existing circulating drum boiler without a bypass duct.

Further, since the high temperature drain water from the drum is used as the heat medium, it is less likely to cause a decrease in the amount of power generation as compared with the case where steam is used as the heat medium, and it may cause pulsation due to condensation in the heat exchanger. Absent.

A second aspect of the present invention is the exhaust gas treatment apparatus of the first aspect, which includes a heat medium recovery pipe that returns water flowing out from the heat exchanger to the water supply route or the water circulation route of the circulating drum boiler.

In the above configuration, since the drain water flowing out from the heat exchanger is returned to the boiler water supply path or the water circulation path, it is possible to recover the residual heat of the drain water that has passed through the heat exchanger and improve the boiler efficiency.

A third aspect of the present invention is the exhaust gas treatment apparatus according to the first or second aspect, which includes an introduction amount control valve that is provided in the heat medium introduction pipe and controls the introduction amount of water to the heat exchanger. ..

In the above configuration, the amount of drain water introduced can be increased or decreased depending on the operating state of the circulation boiler (may include fully closed without drain water introduced), while increasing the boiler efficiency while suppressing the production of acidic ammonium sulfate. be able to. For example, the upper limit (threshold temperature) of the temperature range in which acid ammonium sulfate is likely to be generated is obtained in advance, the temperature of the exhaust gas passing through the denitration catalyst is detected, and the detected exhaust gas temperature (exhaust gas detection temperature) is the threshold value. Drain water is introduced when the temperature is below the temperature (or below the threshold temperature), and when the exhaust gas detection temperature exceeds the threshold temperature (or above the threshold temperature), the introduction of drain water is stopped to generate acidic ammonium sulfate. It is possible to improve boiler efficiency while suppressing the above.

According to the present invention, it is possible to preferably suppress the production of acidic ammonium sulfate at a low temperature of exhaust gas with a simple configuration.

It is a schematic diagram which shows the smoke emission processing system which concerns on one Embodiment of this invention. It is a schematic diagram which shows the heat exchanger and the denitration apparatus of FIG.

An exhaust gas treatment apparatus according to an embodiment of the present invention will be described with reference to the drawings. The white arrows in the figure indicate the exhaust gas flow direction. In the present embodiment, an example in which the exhaust gas treatment device of the present invention is applied to a coal-fired natural circulation drum boiler (hereinafter simply referred to as a boiler) 1 for power generation will be described. It should be noted that the boiler 1 may be a boiler other than a boiler for power generation, a boiler other than coal-cooking, or a forced circulation type drum boiler.

As shown in FIG. 1, water in a drum (brackish water separating drum, brackish water separator) 4 is introduced into a water wall pipe 3 forming a furnace of a boiler 1 through a downcomer pipe 5. The water in the water wall pipe 3 receives the combustion heat of the fuel in the combustion chamber 2 of the furnace to generate steam, returns to the drum 4 via the rising pipe 6, and is separated into water and steam by the drum 4. The drum 4, the downcomer pipe 5, the water wall pipe 3 and the rising pipe 6 constitute a water circulation path of the boiler 1, and the water separated by the drum 4 is again introduced from the downcomer pipe 5 to the water wall pipe 3 and circulated. To do. The steam separated by the drum 4 is supplied to a turbine (not shown) for power generation via a saturated steam pipe 7, a superheater 8 and a superheated steam pipe 9. In addition, in FIG. 1, illustration of the connecting portion between the downcomer pipe 5 and the rising pipe 6 and the water wall pipe 3 is omitted.

Water in a water supply tank (not shown) is supplied to the drum 4 by a water supply pump 11 via a water supply pipe 10. A economizer 12 is provided in the middle of the water supply pipe 10, and water heated by the economizer 12 is supplied to the drum 4. That is, the water supply pipe 10, the water supply pump 11, and the economizer 12 constitute a water supply path of the boiler 1.

Fuel (coal) is finely pulverized by a mill (not shown), is carried by the primary air flowing through the primary air duct 13, and is introduced into the combustion chamber (internal space of the furnace) 2 from the burner 14 together with the primary air. Further, the combustion chamber 2 is supplied with secondary air (combustion air) heated by an air preheater (air heater) 15 from a burner 14 through a secondary air duct 16. Note that part or all of the primary air may be heated by the air preheater 15, and the secondary air may be supplied to the combustion chamber 2 from other than the burner 14 (for example, an after air port or the like).

The exhaust gas generated by the combustion of the fuel flows through the flue 17 and is discharged from the chimney (not shown). In the exhaust gas flow passage (gas flow passage 18) from the furnace of the boiler 1 to the chimney, the superheater 8, the economizer 12, the heat exchanger 30, the denitration device 20, and the air flow from the upstream side to the downstream side. A preheater 15 is provided.

In the superheater 8, the saturated steam separated by the drum 4 is heated by the exhaust gas to generate superheated steam. In the economizer 12, the water supplied to the drum 4 is heated by the exhaust gas, and in the air preheater 15, the secondary air supplied to the combustion chamber 2 is heated by the exhaust gas.

As shown in FIG. 2, the denitration device 20 includes a catalyst layer (denitration catalyst filling layer) 21 and a plurality of reducing agent injection nozzles (reducing agent injection means) 22. The catalyst layer 21 and the reducing agent injection nozzle 22 are fixedly provided in the gas flow passage 18.

The catalyst layer 21 is composed of a denitration catalyst that reduces and removes nitrogen oxides in exhaust gas by using ammonia or urea as a reducing agent, and a carrier that supports the denitration catalyst. The catalyst layer 21 may be a single layer (one step) or a plurality of layers (a plurality of steps).

The reducing agent injection nozzle 22 is arranged in the gas flow passage 18 on the upstream side of the catalyst layer 21, and injects ammonia or urea into the exhaust gas flowing through the gas flow passage 18. The reducing agent injection nozzle 22 may be arranged in the gas flow passage 18 in the flue 17 between the boiler 1 and the denitration device 20.

A gas temperature sensor (exhaust gas temperature detection means) 23 that detects the temperature of the exhaust gas passing through the denitration catalyst is provided on the upstream side of the catalyst layer 21. The location of the gas temperature sensor 23 is not limited to the upstream side of the catalyst layer 21, and may be the downstream side of the catalyst layer 21, for example.

As shown in FIGS. 1 and 2, the heat exchanger 30 is arranged in the gas flow passage 18 on the upstream side of the denitration device 20 (catalyst layer 21), and the heat medium inlet 31 of the heat exchanger 30 has The downstream end of the medium introduction pipe 33 is connected. The heat medium introduction pipe 33 has one or a plurality of drain extraction pipes 36 for extracting water in the drum 4 at the upstream end, and introduces the water in the drum 4 into the heat exchanger 30. High-temperature water (drain water, falling water) introduced from the heat medium introduction pipe 33 flows through the inside of the heat exchanger 30 as a heat medium. The upstream end of the heat medium introducing pipe 33 may be connected to the downfall pipe 5 instead of being connected to the drum 4.

An introduction amount control valve 34 for controlling the introduction amount of water to the heat exchanger 30 is provided in the middle of the heat medium introduction pipe 33. The introduction amount control valve 34 is set to, for example, an arbitrary opening between fully open and fully closed. The opening degree of the introduction amount control valve 34 (the introduction amount of drain water per unit time) is the temperature of the exhaust gas passing through the denitration catalyst (catalyst layer 21) (the temperature of the exhaust gas detected by the gas temperature sensor 23 (exhaust gas detection temperature)). ). The introduction amount control valve 34 may be opened and closed by a manual operation or an automatic control.

The upstream end of the heat medium recovery pipe 35 is connected to the heat medium outlet 32 of the heat exchanger 30. The downstream end of the heat medium recovery pipe 35 is connected to the water supply pipe 10 on the upstream side of the water supply pump 11, and the drain water flowing out from the heat exchanger 30 is returned to the water supply path of the boiler 1 by the heat medium recovery pipe 35. The downstream end of the heat medium recovery pipe 35 may be connected to the pipe of the water circulation path or the drum 4 so that the drain water flowing out from the heat exchanger 30 is returned to the water circulation path of the boiler 1.

The heat exchanger 30 is arranged at a lower position than the drum 4 so that drain water flows from the drum 4 to the heat exchanger 30 by gravity. In addition, it is preferable to arrange the heat medium outlet 32 at a position lower than the heat medium inlet 31 so that the drain water flows by gravity in the heat exchanger 30 (see FIG. 2 ). Further, it is preferable to arrange the heat exchanger 30 so that the flow direction of the exhaust gas and the flow direction of the drain water (heat medium) intersect.

According to the present embodiment, the water in the drum 4 becomes hot due to the operation of the boiler 1, the hot water (drain water) in the drum 4 is extracted from the drum 4, and the heat exchanger is introduced via the heat medium introducing pipe 33. Since it is introduced into 30, the exhaust gas before passing through the denitration catalyst (catalyst layer 21) rises in temperature by heat exchange with high-temperature drain water. For example, during low-load operation of the boiler 1, the exhaust gas temperature is lower than during non-low-load operation (for example, during normal operation), but by increasing the steam pressure to improve plant efficiency, the water temperature in the drum 4 is reduced. The temperature becomes higher than the temperature of the exhaust gas before passing through the denitration catalyst (on the upstream side of the heat exchanger 30). Therefore, during such a low load operation, the exhaust gas heated by the heat exchanger 30 can be introduced into the denitration catalyst. Accordingly, the deposition of ammonium ammonium sulfate in the pores of the denitration catalyst can be prevented or suppressed, and the deposition of ammonium ammonium sulfate on the downstream equipment (eg, air preheater 15) of the denitration catalyst can be suppressed.

The heat exchanger 30 is arranged in the gas flow passage 18 on the upstream side of the denitration catalyst, and the heat medium introducing pipe 33 that introduces the water in the drum 4 into the heat exchanger 30 is provided. Since it does not require such a large space, it can be easily applied to an existing circulating drum boiler without a bypass duct.

Since the high-temperature drain water from the drum 4 is used as the heat medium, it is less likely to cause a decrease in the amount of power generation as compared with the case where steam is used as the heat medium, and pulsation due to condensation in the heat exchanger 30 is not caused ..

Since the drain water flowing out from the heat exchanger 30 is returned to the water supply path of the boiler 1, the residual heat of the drain water passing through the heat exchanger 30 can be recovered and the boiler efficiency can be improved.

The amount of heat supplied from the heat exchanger 30 to the exhaust gas is recovered by the air preheater 15 and input to the boiler 1, so that the amount of heat that is lost can be suppressed to a small amount, and a decrease in boiler efficiency can be suppressed.

When switching from low-load operation to high-load operation (normal operation), the temperature of the exhaust gas passing through the denitration catalyst can be raised in a short time, so the time required to obtain performance during high-load operation can be shortened. it can.

Since it is not necessary to perform the boiler load increasing operation for the purpose of removing ammonium acid sulfate during the low load operation, the low load operation can be continued.

In addition, by opening and closing the introduction amount control valve 34, the introduction amount of the high temperature drain water can be increased or decreased according to the operating state of the boiler 1 (fully closed without drain water may be included). Boiler efficiency can be improved while suppressing generation. For example, the upper limit (threshold temperature) of the temperature range in which acidic ammonium sulfate is likely to be generated is obtained in advance, the temperature of the exhaust gas passing through the denitration catalyst is detected by the gas temperature sensor 23, and the exhaust gas is detected by the gas temperature sensor 23. By introducing drain water when the temperature is below the threshold temperature (or below the threshold temperature) and stopping the introduction of drain water when the exhaust gas detection temperature exceeds the threshold temperature (or above the threshold temperature), the acid Boiler efficiency can be improved while suppressing the production of ammonium sulfate.

The present invention is not limited to the above-described embodiments and modifications described as examples, and is not limited to the above-described embodiments and the like as long as the technical idea of the present invention is not deviated. Various modifications are possible according to the design, etc. For example, the circulation type drum boiler 1 includes a natural circulation type and a forced circulation type, and the present invention is applicable to both.

1: Circulation type drum boiler 2: Combustion chamber 3: Water wall pipe 4: Drum 5: Precipitation pipe 6: Rise pipe 7: Saturated steam pipe 8: Superheater 9: Superheated steam pipe 10: Water supply pipe 11: Water supply pump 12: Economizer
13: Primary air duct 14: Burner 15: Air preheater (air heater)
16: Secondary air duct 17: Flue 18: Gas flow passage 20: Denitration device 21: Catalyst layer (Denitration catalyst packed layer)
22: reducing agent injection nozzle 23: gas temperature sensor 30: heat exchanger 31: heat medium inlet 32: heat medium outlet 33: heat medium introduction pipe 34: introduction amount control valve 35: heat medium recovery pipe 36: drain extraction tube

Claims (3)

The water discharged from the drum is heated in the furnace and returned to the drum. In the gas flow passage through which the exhaust gas discharged from the furnace of the circulating drum boiler flows, the nitrogen oxides in the exhaust gas are reduced using ammonia or urea as a reducing agent. An exhaust gas purifying apparatus for arranging a denitration catalyst packed layer to be removed, for injecting ammonia or urea into the exhaust gas flowing through the gas flow passage on the upstream side of the denitration catalyst packed layer,
A heat exchanger arranged in the gas flow passage on the upstream side of the denitration catalyst packed bed;
A heat medium introducing pipe for introducing water in the drum to the heat exchanger,
The exhaust gas purifying apparatus, wherein the water introduced from the heat medium introducing pipe flows through the inside of the heat exchanger as a heat medium. The exhaust gas purifying apparatus according to claim 1,
An exhaust gas purifying apparatus comprising: a heat medium recovery pipe that returns water flowing out from the heat exchanger to a water supply path or a water circulation path of the circulating drum boiler. The exhaust gas purifying apparatus according to claim 1 or 2, wherein
An exhaust gas purification apparatus, comprising: an introduction amount control valve that is provided in the heat medium introduction pipe and controls the introduction amount of water into the heat exchanger.

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