JP3229102B2 - Exhaust gas denitration method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

Boiler The present invention relates to the combustion of various fuels, gas turbine, the NOx in the exhaust gas discharged from a combustion furnace or the like is removed with high efficiency, and can discharge the NH ₃ unreacted The present invention relates to a method for denitration of exhaust gas which is not required.

[0002]

2. Description of the Related Art As a method for removing NOx in exhaust gas, a selective reduction denitration method (SCR) is used in which NH ₃ is added to exhaust gas and the following reaction is generated on a catalyst to decompose it into N ₂ and H ₂ O.
Is widely applied to boiler exhaust gas for large-scale thermal power plants for business use.

Embedded image 4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O The above-mentioned denitration method has been operated at a denitration rate of about 80% until now, but recent exhaust gas regulations. There is a demand for a high-efficiency denitration with a denitration rate of 90% to 100% with the enhancement of the density. In order to perform highly efficient denitration, as is clear from the above equation, the amount of NH ₃ added needs to be close to equimolar or equal to or higher than NOx. However, if the added amount of NH ₃ is more than equimolar to NOx, excessive NH ₃ that does not react with NOx is discharged from the chimney, which is not environmentally preferable. NOx
The consumption of NH ₃ for removal increases, which is not economically favorable.

[0003] Therefore, the present inventors, as shown below,
The above-mentioned problems are solved in Japanese Patent Application No. 4-233627.
NOx, NH in exhaust gas_ThreeAlmost
To provide smoke gas denitration methods that can be
Was. That is, this denitration method is a NOx reduction denitration reactor
Upstream of the reaction equivalent to NOx in the exhaust gas
NH_ThreeIs added to the exhaust gas, and the exhaust gas is
NOx in gas_ThreeAnd then remain in the exhaust gas.
Unreacted NH _ThreeIs adsorbed by the adsorption / desorption device and then discharged.
The gas is discharged and the NH adsorbed by the adsorption / desorption device _ThreeDesorb
Exhaust gas to be supplied to the exhaust gas upstream of the reduction denitration reactor
A denitration method of_ThreePacked with adsorbent 2
Using an adsorption / desorption device of more than a column, NH in the adsorption / desorption device_Threeof
Desorption was performed by using a high-temperature gas.

One embodiment of the various systems will be described in more detail with reference to FIG. This embodiment relates to a method for denitration of exhaust gas from a gas turbine combined cycle plant. Combustion air 1 is compressed by a compressor 2 and supplied to a gas turbine 3 to burn fuel, and power is generated by the gas turbine 3. Machine 4 is driven. The exhaust gas from the gas turbine 3 is sequentially introduced into the exhaust heat recovery boilers 5 and 6 on the upstream side and the downstream side, and heats the condensate supplied from the condensate line 11 to the exhaust heat recovery boiler 6 and further heats the condensate. The condensed water supplied from the recovery boiler 6 to the exhaust heat recovery boiler 5 is heated and evaporated, and the steam is introduced from the steam line 12 into the steam turbine 9 to drive the generator 10. The condensate of the steam turbine 9 is condensed from the condensate line 11 as described above,
Next, the heat is circulated to the waste heat boiler 5.

[0005] A denitration reactor 7 for reducing and denitrifying NOx is installed in the flow path of the combustion exhaust gas between the exhaust heat recovery boilers 5 and 6, and is provided between the denitration reactor 7 and the exhaust heat recovery boiler 5. An NH ₃ injection unit 8 is provided in the flow path of the combustion exhaust gas. The NOx reduction reactor 7 is filled with a NOx reduction catalyst. As the catalyst, a catalyst such as vanadium, molybdenum, or tungsten using titanium oxide as a carrier can be used.

Downstream of the exhaust heat recovery boiler 6 on the downstream side, temperature swing type adsorption / desorption devices 13 and 14 filled with two towers of NH ₃ adsorbent are provided.
The combustion exhaust gas that has exited the exhaust heat recovery boiler 6 is introduced into one of 3 and 14. This adsorption / desorption device 13
Alternatively, the combustion exhaust gas that has exited from the outlet 14 is discharged from the chimney 17 to the outside. Further, the combustion exhaust gas is supplied from the upstream side of the exhaust heat recovery boiler 5 through the bypass line 15 to the other adsorption / desorption device 13 or 14 to which the combustion exhaust gas leaving the exhaust heat recovery boiler 6 is not supplied. Tagami bypass line 1
The air is returned to the upstream of the exhaust heat recovery boiler 5 through 5 '. Further, the one adsorption / desorption device 13 or 1
A part of the flue gas that has exited 4 is supplied to the other adsorption / desorption device, and is returned to the flow path of the combustion exhaust gas reaching the chimney 17 downstream of the adsorption / desorption device.
16 'shows the circulation line.

The supply of the combustion exhaust gas to one of the adsorption / desorption devices 13 and 14 and the supply of the combustion exhaust gas to the other of the adsorption / desorption device via a bypass line 15 and the supply of the combustion exhaust gas via a circulation line 16. Is performed by switching a gas flow path by a valve (not shown). Thus, in one adsorption / desorption device, an adsorption step of adsorbing NH ₃ in the flue gas discharged from the exhaust heat recovery boiler is performed. At the same time, in the other adsorption / desorption device, the adsorbed NH ₃ passes through the bypass line 15. Desorption process by the high temperature flue gas supplied through the desorption device, and the adsorbent heated by the flue gas is cooled by the low temperature flue gas downstream of the adsorption / desorption device supplied through the circulation line 16 An adsorbent cooling step is performed. In addition, the above-described steps are sequentially and alternately and continuously performed in the two adsorption / desorption devices 13 and 14 by switching the gas flow path. In addition,
FIG. 1 shows a state in which the adsorption / desorption device 13 performs the adsorption process, and the adsorption / desorption device 14 performs the desorption process and the adsorbent cooling process.

The N charged in the adsorption / desorption devices 13 and 14
As the H ₃ adsorbent, titanium oxide, alumina, silica-alumina, zeolite, or a material used as a catalyst in the denitration reactor 7 can be used. In addition, the air 18 heated by the heater 19 is supplied to the bypass line 15, and the heated air 18 is supplied to the adsorption / desorption device 13 or 14 alone or together with the combustion exhaust gas from the upstream of the exhaust heat recovery boiler 5. It can also be done. When the heated air 18 is supplied alone to the adsorption / desorption device 13 or 14, the portion of the bypass line 15 from the upstream of the exhaust heat recovery boiler 5 to the supply point of the air 18 is omitted.

In this embodiment, the temperature of the flue gas discharged from the gas turbine 3 at a temperature of about 500 ° C. to 600 ° C. is lowered by the exhaust heat recovery boiler 5 and then the NO ₃ contained in the NH ₃ injection section 8 is reduced. NH ₃ / NOx reactions or more equivalents of
NH ₃ is added in an amount of about 1.2 in a molar ratio of The flue gas to which NH ₃ is added in an amount equal to or more than the reaction equivalent to NOx is denitrated by the catalyst filled in the denitration reactor 7, and almost all of the contained NOx is removed.
Excess NH ₃ remains in the combustion exhaust gas. This NH ₃
The temperature of the combustion exhaust gas remaining is further reduced by the exhaust heat recovery boiler 6 to about 100 ° C.
14 and NH ₃ is adsorbed on the adsorbent in the adsorption / desorption apparatus. Thus, the clean exhaust gas from which almost all of the NOx and NH ₃ have been removed is discharged from the chimney 17. At the same time, in the other adsorption / desorption device, high-temperature combustion exhaust gas of about 300 ° C. or higher introduced from the upstream of the exhaust heat boiler 5 through the bypass line 15 and / or high-temperature air 18 heated by the heater 19 are produced. is introduced, the NH ₃ which has been adsorbed on the adsorbent is desorbed, NH ₃ which is the desorption-pass line 1
It is returned to the upstream of the waste heat boiler 5 through 5 '. Therefore, the NH ₃ adsorbed by the adsorption / desorption device 13 or 14 is added to the combustion exhaust gas exiting the gas turbine 3 upstream of the exhaust heat boiler 5, and together with the NH ₃ added at the NH ₃ injection section 8, the denitration reactor 7 To be effectively used for the denitration reaction.

When one of the adsorption and desorption devices 13 and 14 continues to adsorb the combustion exhaust gas, the adsorption and desorption devices 13 and 1
In the other side of 4, the flow path is switched and clean combustion exhaust gas having a low temperature exiting one of the adsorbers via the circulation line 16 is introduced, and the adsorbent heated in the desorption step is cooled, and the next adsorbent is cooled. It will be prepared for the process. The flue gas, which has cooled the adsorbent in the other side of the adsorption / desorption device, is supplied to the circulation line 1
It is discharged from the chimney 17 via 6 '. When the adsorption of the adsorbent in one of the adsorption and desorption devices 13 and 14 approaches saturation, the flow path is switched, and the combustion exhaust gas exiting the exhaust heat boiler 6 is introduced into the other of the adsorption and desorption devices, and NH ₃ is removed. Adsorption is performed, and desorption of NH ₃ and cooling of the adsorbent are performed in one of the adsorption / desorption devices. In this way, the adsorption process and NH ₃ desorption step and the cooling step of cooling agent of the NH ₃ alternately adsorption-desorption apparatus 2 column are sequentially performed continuously, always clean the combustion exhaust gas discharged from the chimney State can be maintained.

[0011]

However, the conventional method has the following disadvantages. (1) In order to desorb NH ₃ from the adsorbent, it is heated by the high temperature combustion exhaust gas of about 300 ° C. or higher introduced from the upstream of the exhaust heat recovery boiler 5 through the bypass line 15 and / or the heater 19. The temperature of the hot air 18
When supplied directly at about 300 ° C. or higher with little control, the concentration of the desorbed NH _{3 in} the bypass line 15 ′ changes with time in a pulsed manner, and the peak concentration of the pulse is extremely low. High, for example,
000 ppm or more. Therefore, such high NH
_{When the} concentration is added to the combustion exhaust gas exiting the gas turbine 3 upstream of the exhaust heat boiler 5 during the time period when the concentration is continued, N
Even if NH ₃ is not added in the H ₃ injection unit 8, the denitration reactor 7
The NH ₃ concentration immediately before being supplied to the
It will be equal to or greater than the predetermined reaction equivalent with Ox. Therefore, in this time zone, the residual N in the denitrated gas flowing out of the denitration reactor 7
The H ₃ concentration increases, and the time control of the adsorption process in the adsorption / desorption devices 13 and 14 becomes complicated. (2) Further, in the above-described change in the concentration of desorbed NH ₃ ,
Since the concentration change speed is rapid, the control of the amount of NH ₃ added in the NH ₃ injection section 8 is complicated and highly accurate.

An object of the present invention is to solve the above-mentioned problems and to provide a method for denitration of exhaust gas which can make NOx and NH ₃ in exhaust gas almost zero.

[0013]

The present invention SUMMARY OF] is (1) upstream of the reduction denitration reactor NOx, the exhaust gas by the reducing denitration reactor of NH ₃ more than the reaction equivalent of NOx in the exhaust gas is added to the exhaust gas The NOx contained therein is reacted with NH _3, and then the unreacted NH ₃ remaining in the exhaust gas is adsorbed by the adsorption / desorption device, and then the exhaust gas is discharged.
What is claimed is: 1. A method for denitration of exhaust gas for desorbing H ₃ and supplying it to exhaust gas upstream of said reductive denitration reactor, comprising using two or more adsorption / desorption devices filled with an NH ₃ adsorbent. The desorption of NH ₃ at high temperature using a high-temperature gas , wherein the high-temperature gas for the desorption is provided on the reductive denitration reactor.
Using the high temperature exhaust gas of the stream, the temperature at the time of supplying the high temperature gas is temporally controlled, and the rate of desorption of NH ₃ accumulated in the adsorbent is controlled by adjusting the rate of temperature rise of the adsorbent. Denitration method for exhaust gas, characterized in that the time change of the desorbed NH ₃ concentration is reduced to facilitate control of the amount of NH ₃ injected upstream of the reductive denitration reactor , (2) supply temperature of the high-temperature gas Is controlled by mixing a high-temperature gas and normal-temperature air , and the exhaust gas denitration method according to the above (1) , and (3) a supply temperature of the high-temperature gas is controlled by a heater and / or a cooler. denitration method of exhaust gas of the above (1), wherein the control using a.

[0014]

In [act] The present invention (1), by the NH ₃ above reaction equivalent of the NOx in the exhaust gas upstream of the reducing denitration reactor NOx added to the exhaust gas, NOx
In the reduction denitration reactor, NOx in exhaust gas is sufficiently and efficiently denitrated. NH ₃ remaining in the exhaust gas exiting the NOx reduction denitration reactor is adsorbed by the adsorption / desorption device. Therefore, the exhaust gas is discharged in a clean state from which NOx and NH ₃ have been sufficiently removed. On the other hand, NH ₃ adsorbed by the adsorption / desorption device is desorbed and supplied to the exhaust gas upstream of the NOx reduction denitration reactor, whereby NH 3
₃ is used effectively. Next, the supply temperature of the high-temperature gas for desorption to the adsorption / desorption device is temporally controlled, and the desorption rate of NH ₃ accumulated in the adsorbent is controlled by adjusting the rate of temperature rise of the adsorbent. , NH ₃ in desorbed gas
The time change of the concentration can be reduced, and the control of the amount of NH ₃ injected upstream of the reductive denitration reactor can be facilitated. For this reason, it is easy to keep the total amount of ammonia injected into the reduction denitration reactor constant, and it is possible to stably obtain a high denitration rate. Hot gas as hot gas
Desorption of NH ₃ in adsorption and desorption equipment using exhaust gas
Thus, the adsorbed NH ₃ without the need for another heat source
Is desorbed and the thermal efficiency can be increased.

In the present invention (2), in addition to the function of the present invention (1), the supply temperature of the high-temperature gas is controlled by mixing the high-temperature gas and the normal-temperature air. Can be reduced, and the thermal efficiency can be increased. In the present invention (3), in addition to the operation of the present invention (1), the supply temperature of the hot gas is controlled by using a heater and / or a cooler. It will be easier .

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIG. This embodiment relates to a method for denitration of exhaust gas of a gas turbine combined cycle plant, and the configuration of the apparatus, gas flow, and operation method of the entire apparatus are almost the same as those described in detail in the conventional example. . Hereinafter, the present invention will be described mainly with respect to a driving operation at the time of desorption by the adsorption / desorption devices 13 and 14. As mentioned above, NH
₃ In the desorption process, the combustion flue gas of a temperature higher than about 300 ° C., which is introduced from the upstream of the exhaust heat boiler 5 through the bypass line 15 is introduced, the NH ₃ which has been adsorbed by the adsorbent desorption Then, the desorbed NH ₃ is returned to the upstream of the exhaust heat boiler 5 via the bypass line 15 ′. Therefore, the NH ₃ adsorbed by the adsorption / desorption device 13 or 14 is added to the combustion exhaust gas that has exited the gas turbine 3 upstream of the exhaust heat boiler 5, and together with the NH ₃ added at the NH ₃ injection unit 8, the denitration reactor Step 7 is used effectively for the denitration reaction.

Here, as shown in FIG. 1, the adsorption / desorption device during the desorption process is denoted by 14. Hot gas for desorption, that is,
And controlling the temperature change in the combustion flue gas high temperature upstream of approximately 300 ° C. or higher, which is introduced from the exhaust heat boiler 5 through the bypass line 15, for example, as shown in FIG. 2 (a),
When the temperature finally rises to 400 ° C., the adsorbent is once heated to 300 ° C. at which the desorption rate of NH ₃ starts to increase, the NH ₃ concentration in the bypass line 15 ′ is once increased, and the change is small. Then, the hot gas is again
° C. the temperature was raised to, by heating the adsorbent to 400 ° C., figure NH ₃ concentration change in the bypass line 15 '2
Control can be performed so as to obtain the density change pattern shown in FIG. This concentration change pattern is relaxed to about half of the NH ₃ peak concentration shown in FIG. 3B, which occurs in the case of the operation of FIG. 3A in which the temperature change is not controlled in the conventional method, and the concentration change speed is also reduced. ing.

As a result, it becomes easier to control the amount of NH ₃ newly added to the flue gas discharged from the gas turbine 3 upstream of the exhaust heat recovery boiler 5 in the ammonia injection section 8 than in the conventional example. Further, the temperature of the hot gas for desorption can be controlled by adjusting the flow rate of the high-temperature combustion exhaust gas by a valve (not shown). Further, the temperature of the hot gas for desorption can be controlled, for example, by providing a heat exchanger on the bypass line 15 and heating or cooling the high-temperature combustion exhaust gas .

[0019]

As explained above, the present invention according to claim 1 removes almost all of NOx in exhaust gas without wasting NH ₃ as a NOx reducing agent, and
It can be made to discharge the exhaust gas containing no NOx and NH ₃ most. Furthermore, because it can control the concentration of NH ₃ to be returned to control the temperature increase changes in the adsorbent in the adsorption-desorption apparatus at the time of desorption depending on the reduction denitration apparatus in a proper range, almost the NH ₃ injection rate of total It can be kept constant, and as a result, a high denitration rate can be stably obtained. Also, N2 adsorbed without the need for another heat source
The desorption of H ₃ is performed, and the thermal efficiency can be increased. In addition, the present invention described in claim 2 can reduce the supply amount of the high-temperature gas for desorption and increase the thermal efficiency in addition to the effect of the present invention described in claim 1. The third aspect of the present invention facilitates the temperature control of the hot gas for desorption in addition to the effects of the first aspect of the present invention .

[Brief description of the drawings]

FIG. 1 is a system diagram of an embodiment of the present invention.

FIG. 2 is a table showing an example of temperature control during NH ₃ desorption according to the present invention and a measurement example of a change in the desorbed NH ₃ concentration at that time.

FIG. 3 shows a conventional temperature for desorption of NH ₃ and a desorption NH at that time.
₃ is a table showing a measurement example of a density change in FIG.

Continuation of the front page (51) Int.Cl. ⁷ Identification code FI F23J 15/00 ZAB F23J 15/00 ZABA (72) Inventor Yoshiaki Obayashi 4-6-22 Kanonshinmachi, Nishi-ku, Hiroshima-shi, Hiroshima Mitsubishi Heavy Industries, Ltd. Hiroshima Inside the research institute (72) Inventor Akira Johana 4-22, Kannonshinmachi, Nishi-ku, Hiroshima-shi, Hiroshima Mitsubishi Heavy Industries, Ltd.Hiroshima Research Institute (72) Inventor Jun Morii 1-1, Akunouracho, Nagasaki-shi, Nagasaki Mitsubishi Heavy Industries Inside Nagasaki Shipyard Co., Ltd. (72) Akira Serizawa, Inventor 1-1 1-1 Akunouramachi, Nagasaki City, Nagasaki Prefecture Mitsubishi Heavy Industries, Ltd.Nagasaki Shipyard Co., Ltd. (72) Takako Kobayashi 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Heavy Industry Co., Ltd. (72) Inventor Toshiyuki Onishi 1-1, Akunouracho, Nagasaki City, Nagasaki Prefecture Mitsubishi Heavy Industries, Ltd. Nagasaki Shipyard (72) Inventor Masashi Kiyozawa 1-1, Akunouracho Nagasaki City, Nagasaki Prefecture Mitsubishi Heavy Industries (72) Akiko Shimada, Inventor, Nagasaki Shipyard Co., Ltd. No. 1-1 Akunouramachi, Nagasaki City, Nagasaki City, Mitsubishi Heavy Industries, Ltd. Nagasaki Shipyard (56) Reference JP-A-2-152523 (JP, A) JP-A-57-190640 (JP, A) JP-A-51- 39972 (JP, A) JP-A-57-102224 (JP, A) JP-A-52-2867 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 53/04 B01D 53 / 34-53/94

Claims (3)

(57) [Claims] Upstream of 1. A NOx reducing denitration reactor, the NH ₃ above reaction equivalent of NOx in the exhaust gas is reacted with NH ₃ to NOx in the exhaust gas by the reducing denitration reactor is added to the exhaust gas, Next, after the unreacted NH ₃ remaining in the exhaust gas is adsorbed by the adsorption / desorption device, the exhaust gas is discharged,
What is claimed is: 1. A denitration method for exhaust gas, which desorbs NH ₃ adsorbed by said adsorption / desorption device and supplies it to exhaust gas upstream of said reductive denitration reactor, comprising two or more towers filled with an NH ₃ adsorbent. the use, in a method of performing desorption of NH ₃ in the intake desorber using a high-temperature gas, as a high-temperature gas dehydration wear
Using high temperature exhaust gas upstream of the reduction denitration reactor,
The temperature during the supply of gas temporally controlled, the time variation of the desorption NH ₃ concentration is controlled to the desorption rate of NH ₃ stored in the adsorbent by adjusting the heating rate of the adsorbent A method for denitration of exhaust gas, characterized by relaxing and easily controlling the amount of NH ₃ injected upstream of the reductive denitration reactor. 2. The exhaust gas denitration method according to claim 1, wherein the supply temperature of the high-temperature gas is controlled by mixing the high-temperature gas and room-temperature air. 3. The exhaust gas denitration method according to claim 1, wherein the supply temperature of the high-temperature gas is controlled using a heater and / or a cooler.