JP3229108B2 - 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. 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 with recent tightening of exhaust gas regulations. Therefore, there is a demand for high efficiency denitration with a denitration rate of 90% to 100%. 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. Also,
The consumption of NH ₃ for removing NOx increases, which is not economically favorable.

[0003] Therefore, the present inventors have solved the above-mentioned problem first as described below, and
The present invention provides a method for denitration of smoke gas capable of making x, NH ₃ almost zero. (Refer to Japanese Patent Application No. 4-233627.) That is, this denitration method uses NH _{3 in} an upstream of a NOx reduction denitration reactor in an amount equal to or higher than a reaction equivalent of NOx in exhaust gas.
Was added to the exhaust gas of NOx in the exhaust gas is reacted with NH ₃ in the reducing denitration reactor, and then after having adsorbed NH ₃ remaining unreacted in the exhaust gas at adsorption-desorption apparatus, the exhaust gas out of the system A method for denitration of exhaust gas which discharges and desorbs NH ₃ adsorbed by said adsorption / desorption apparatus and supplies it to exhaust gas upstream of said reductive denitration reactor, comprising two or more towers filled with an NH ₃ adsorbent. Using an adsorption / desorption device, NH ₃ in the adsorption / desorption device
Desorption using a high-temperature gas.

An embodiment of the above-mentioned system 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. 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,
Subsequently, the heat is circulated to the exhaust heat recovery boiler 5.
In the flow path of the combustion exhaust gas between the exhaust heat recovery boilers 5 and 6, a denitration reactor 7 for performing NOx reduction and denitration is installed,
An ammonia injection section 8 is provided in a flow path of the combustion exhaust gas between the denitration reactor 7 and the exhaust heat recovery boiler 5. The denitration reactor 7 is filled with a NOx reduction catalyst,
As this catalyst, vanadium using titanium oxide as a carrier,
Catalysts such as molybdenum and tungsten are commonly 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. The flue gas that has exited the adsorption / desorption device 13 or 14 is discharged from the chimney 17 to the outside. Further, the combustion exhaust gas is supplied to the exhaust heat recovery boiler 5 on the upstream side.
The exhaust gas from the exhaust heat recovery boiler 6 is supplied to the other adsorption / desorption device 13 or 14 which is not supplied from the upstream side of the exhaust heat recovery boiler 6 through the bypass line 15 and the bypass line 1
The heat is returned to the upstream of the exhaust heat recovery boiler 5 through 5 '. Further, the one adsorption / desorption device 13 or 14
A portion of the flue gas that has exited the chamber 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.
6 'indicates 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 6 is performed, and at the same time, in the other adsorption / desorption device, the adsorbed NH ₃ passes through the bypass line 15. Process in which the adsorbent heated by the exhaust gas is cooled by the low-temperature exhaust gas downstream of the adsorption / desorption device supplied through the circulation line 16. An agent cooling step is performed. In addition, each of the above-mentioned steps is sequentially and alternately performed in both adsorption / desorption devices 13 and 14 by switching the gas flow path.
And it is performed continuously. FIG.
5 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. As the NH ₃ adsorbent filled in the adsorption / desorption devices 13 and 14, titanium oxide, alumina, silica-alumina, zeolite, or a material used as a catalyst in the denitration reactor 7 is generally 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 to 600 ° C. is reduced by the exhaust heat recovery boiler 5 and the reaction equivalent of NOx contained in the ammonia injection section 8 is contained. NH ₃ / NOx
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, 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 high temperature Is introduced to desorb the NH ₃ adsorbed on the adsorbent, and the desorbed NH ₃ is returned to the upstream of the exhaust heat recovery boiler 5 via the bypass line 15 ′. Therefore, the adsorption / desorption device 1
The NH ₃ adsorbed by 3 or 14 is added to the combustion exhaust gas leaving the gas turbine 3 upstream of the exhaust heat recovery boiler 5, and together with the NH ₃ added by the ammonia 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 recovery 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.

[0010]

However, the above-mentioned proposed method has the following disadvantages. (1) Since the step of adsorbing and desorbing NH _{3 and} the step of cooling the adsorption tower are performed sequentially and sequentially, undesorbed NH ₃ accumulates in the adsorbent. Therefore, the NH ₃ adsorption capacity of the adsorbent decreases with time. (2) As a result, in order to establish the TSA cycle, the amount of the adsorbent had to be determined in consideration of the decrease in the adsorption capacity. The present invention is intended to provide the above to solve the problems, NOx in exhaust gas discharged denitration method smoke gas can be almost zero the NH _3.

[0011]

The present invention SUMMARY OF] is (1) exhaust gas of NH ₃ more than the reaction equivalent of NOx in the exhaust gas upstream of the reducing denitration reactor NOx by the reducing denitration reactor is added to the exhaust gas of NOx is reacted with NH _3, then the exhaust gas after having adsorbed NH ₃ remaining unreacted in the exhaust gas at adsorption-desorption apparatus was discharged out of the system, to desorb the NH ₃ adsorbed in the absorbent desorber the reduction denitration reactor a denitration method of exhaust gas supplied upstream in the exhaust gas, using the adsorption-desorption apparatus two or more tower adsorbent filled in NH _3, desorption of NH ₃ in the suction desorber Is performed using a high-temperature gas, a desorption step is provided after the desorption step, and the reduction is performed at 5 to 100 ° C. higher than the high-temperature gas for desorption to the adsorbent.
A high-temperature exhaust gas containing NOx upstream of the denitration reactor is introduced, and the adsorbent is further heated to completely discharge the NH ₃ accumulated in the adsorbent and regenerate the adsorbent. a denitration method of exhaust gas, and (2) most denitration method of the exhaust gas according to the above (1), characterized in that provided one adsorbent regeneration step after the repetition of 10 times the adsorption and desorption steps in, is there.

[0012]

In [act] The present invention (1), upstream of the reduction denitration reactor NOx, NOx by the addition of NH ₃ or more reactive equivalent of the NOx in the exhaust gas in the exhaust gas
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, an adsorbent regeneration step is provided after the desorption step, and a regeneration gas 5 to 100 ° C. higher than the desorption high-temperature gas is introduced. In this regeneration step, NH ₃ remaining in the adsorbent is almost completely removed even after the desorption step, so that the NH ₃ adsorption capacity of the adsorbent can be maintained at a higher level than in the past. Thus, NH into conventional adsorbents
₃ Adsorption performance can be stably repeated without deteriorating adsorption performance due to accumulation. Further, conventionally, the filling amount of the adsorbent is determined in consideration of the decrease in the adsorption performance. However, according to the present invention, the decrease in the adsorption capacity due to the adsorption of NH _{3 in the} adsorbent can be reduced. The amount of filling can be reduced.

According to the present invention (1) , in addition to the above-mentioned effects, N
Since the high-temperature gas containing Ox is passed through the adsorbent, NOx in the high-temperature gas for regeneration reacts with NH ₃ remaining in the adsorbent, and the regeneration of the adsorbent becomes faster and more complete. In the present invention (2) , in addition to the effect of the present invention (1 ), the regeneration of the adsorbent is carried out after repeating at most ten adsorption / desorption steps, so that the number of regeneration steps can be reduced. In addition, the amount of high temperature gas for regeneration can be reduced. Therefore, the thermal efficiency of the system can be increased.

[0014]

FIG. 1 shows an embodiment of the present invention.
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 focusing on the driving operation at the time of regeneration of the adsorbent in the adsorption / desorption devices 13 and 14. As mentioned above,
In the desorption process of NH ₃ , approximately 300 ° C. introduced from the upstream of the exhaust heat recovery boiler 5 through the bypass line 15.
More hot flue gas and / or the heater 19 hot air 18 heated by is introduced, is desorbed NH ₃ which has been adsorbed by the adsorbent, NH _3, which is the desorb the bypass line 15 ' After that, it is returned to the upstream of the exhaust heat recovery boiler 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 recovery boiler 5, and together with the NH ₃ added at the ammonia injection section 8, the denitration reactor 7 To be effectively used for the denitration reaction.

Here, as shown in FIG. 1, the adsorption / desorption device which has completed the desorption process is designated as 14. From here, the regeneration process of the adsorbent according to the present invention is started. Hot gas for desorption, that is,
Temperature set to the combustion flue gas of high temperature is introduced from the upstream of the exhaust heat recovery boiler 5 through the bypass line 15 becomes 5 to 100 ° C. higher than the temperature of the desorption step is introduced into desorption device 14 adsorption Heat the agent. Thereafter, the regeneration gas is returned to the upstream of the exhaust heat recovery boiler 5 via the bypass line 15 '. By this adsorbent regeneration step, NH ₃ conventionally accumulated after the adsorption / desorption step can be completely discharged, and the adsorbent N 3
H ₃ adsorption performance can be maintained at a higher level than before. Further, in this regeneration step, N
Since H ₃ is desorbed, by returning this NH ₃ to the denitration reactor 7, NH ₃ can be used more effectively than before. After this regeneration step, the same adsorption, desorption and cooling as in the prior art is repeated to recycle NH ₃ .

As described above, the regeneration step of the adsorbent is performed by the N
Since the H ₃ adsorption performance is maintained at a high level, it is possible to suppress the reduction of the allowable NH ₃ concentration breakthrough time in the adsorption step,
It is possible to repeat a stable cycle. Furthermore, by using a high-temperature exhaust gas containing NOx as the adsorbent regeneration gas, it is possible to quickly and efficiently regenerate the adsorbent. In addition, by performing regeneration of the adsorbent using high-temperature exhaust gas as the high-temperature gas for regeneration, the regeneration of the adsorbent is performed without the need for another heat source, and the thermal efficiency can be increased. Also, by performing the regeneration of the adsorbent after at most 10 repetitions of the adsorption / desorption step, the number of regeneration steps can be reduced, the amount of hot gas for regeneration can be reduced, and thus the thermal efficiency of the system can be increased. Can be.

[0017]

As described above, according to the first aspect,
The present invention relates to NH as a NOx reducing agent. _ThreeUselessly
To remove almost all of the NOx in the exhaust gas, and
NOx and NH_ThreeExhaust gas containing almost no
can do. Furthermore, adsorbent regeneration after desorption
Adsorbent NH depending on the process_ThreeKeep adsorption capacity at a high level
And shortens the adsorption time during the adsorption process
Can operate the adsorption / desorption device stably
You. Further, in consideration of the above-mentioned decrease in the adsorption capacity,
No need to determine the filling amount
The denitration method of this exhaust gas can be established with the amount of adsorbent.
You.

In addition , since the high-temperature gas containing NOx is passed through the adsorbent, NOx in the high-temperature gas for regeneration reacts with NH ₃ remaining in the adsorbent, and the regeneration of the adsorbent is completed more quickly and completely. Become.

Further, the present invention according to claim 2 has the effect of the present invention according to claim 1, and furthermore, the regeneration of the adsorbent is carried out after repeating the adsorption / desorption step at most ten times. The number of regeneration steps can be reduced, and the amount of high-temperature gas for regeneration can be reduced. Therefore, the thermal efficiency of the system can be increased.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of one embodiment of the present invention.

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI B01D 53/94 B01D 53/36 101A (72) Inventor Yoshiaki Obayashi 4-6-22 Kanonshinmachi, Nishi-ku, Hiroshima-shi, Hiroshima Mitsubishi Heavy Industries, Ltd. (72) Inventor Keiko Kobayashi 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Heavy Industries, Ltd. Headquarters (72) Inventor Jun Morii 1-1, Akunouramachi, Nagasaki City, Nagasaki Prefecture Mitsubishi Heavy Industries Co., Ltd. (72) Akira Serizawa, Inventor 1-1, Akunouracho, Nagasaki City, Nagasaki Prefecture Mitsubishi Heavy Industries, Ltd. (72) Inventor Osamu Naito 1-1, Akunouracho, Nagasaki City, Nagasaki Prefecture Mitsubishi Heavy Industries, Ltd. (72) Inventor Toshiyuki Onishi 1-1, Akunouramachi, Nagasaki City, Nagasaki Prefecture Mitsubishi Heavy Industries, Ltd.Nagasaki Shipyard (72) Invention Akiko Shimada 1-1-1, Akunoura-cho, Nagasaki City, Nagasaki Prefecture Mitsubishi Heavy Industries, Ltd. Nagasaki Shipyard (56) References JP-A-2-152523 (JP, A) JP-A-57-190640 (JP, A) JP-A Sho 53-103978 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 53/04 B01D 53/34-53/94

Claims (2)

(57) [Claims] NH NOx in the exhaust gas at 1. An upstream of the reduction denitration reactor NOx and NH ₃ in the above reaction equivalent of NOx in the exhaust gas is added to the exhaust gas the reducing denitration reactor
₃ and then unreacted NH remaining in the exhaust gas
₃ the discharge of exhaust gas after the adsorbed at desorption device to the outside of the system, there denitration method of the exhaust gas supplied upstream in an exhaust gas to desorb the NH ₃ adsorbed the reducing denitration reactor at a suction desorber Te, using the adsorption-desorption apparatus two or more tower adsorbent filled in NH _3, a method of performing desorption of NH ₃ in the intake desorber using a high-temperature gas, the adsorbent regeneration step after the desorption step NOx upstream of the reductive denitration reactor 5 to 100 ° C. higher than the high-temperature gas for desorption in the adsorbent
A denitration method for exhaust gas , comprising introducing a high-temperature exhaust gas containing the adsorbent and further raising the temperature of the adsorbent to completely discharge NH ₃ accumulated in the adsorbent and regenerating the adsorbent. 2. Repeating the adsorption / desorption step at most 10 times
Is followed by one adsorbent regeneration step
The method for denitration of exhaust gas according to claim 1.