JP3224605B2 - Exhaust gas denitration method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION This invention provides a boiler for burning various fuels, gas turbine, the NO _x in the exhaust gas discharged from a combustion furnace or the like is removed with high efficiency, and to discharge the NH ₃ unreacted The present invention relates to a method for denitration of exhaust gas so as not to cause any problem.

[0002]

As a method for removing the Related Art NO _x in the exhaust gas, the addition of NH ₃ (ammonia) in the exhaust gas on the catalyst to produce a reaction of the following formula N ₂ and H ₂ O to decompose the selective reduction denitration The method (SCR method) is widely applied to boiler exhaust gas for large-scale thermal power generation for business use.

[0003]

Embedded image

[0004] The above-mentioned denitration method has hitherto achieved a denitration rate of 80%.
%, But with the recent tightening of exhaust gas regulations, there is a demand for high-efficiency denitration with a denitration rate of 90% to 100%.

[0005]

As it is clear from the equation of the chemical formula 1 in order to perform a highly efficient denitration of [0005], close to equimolar addition amount of NH ₃ with respect to N Ox, or equimolar It is necessary to do above. However, when more than an equimolar amount of NH ₃ relative to NO _x, an excess of NH ₃ not reacted is that environmentally unfavorably discharged from the chimney and NO _x. Further, the consumption of NH ₃ for removing NO _x increases, which is not economically preferable.

An object of the present invention is to solve the above-mentioned problems and to provide a method for denitrifying smoke gas capable of reducing NO _x and NH ₃ in exhaust gas discharged to almost zero.

[0007]

Means for Solving the Problems] (1) denitration method of exhaust gas of the present invention, the NH ₃ in the above reaction equivalent of the NO _x in the exhaust gas is added to the exhaust gas upstream of the reducing denitration reactor of the NO _x In the reduction denitration reactor, NO _x in the exhaust gas is reacted with NH _3, and then unreacted NH ₃ remaining in the exhaust gas is converted to titanium oxide, alumina, silica-alumina,
Or titanium oxide as a carrier vanadium, molybdenum,
Temperature swing by adsorbent composed of tungsten based catalyst
The exhaust gas adsorbed in the adsorption / desorption device for performing the discharging method is discharged, and the NH ₃ adsorbed in the adsorption / desorption device is discharged to the reduction denitration reactor.
Desorption using high-temperature exhaust gas branched upstream of
The NH ₃ thus obtained is supplied to the exhaust gas upstream of the reductive denitration reactor, and the adsorbent having the NH ₃ desorbed therein is
The exhaust gas discharged after adsorption of NH ₃ from the adsorption / desorption device
₃ wherein the cooled prior adsorption. (2) Further, the denitration method of exhaust gas of the present invention, in the above invention (1), using the adsorption-desorption apparatus two or more tower adsorbent filled in NH _3, the adsorption of NH _3, desorption and adsorption The cooling operation of the agent is performed by switching the gas flow path. (3) In the method for denitrifying exhaust gas according to the present invention, the adsorbent charged in the adsorption / desorption device is divided into an NH ₃ adsorption zone, an NH ₃ desorption zone, and an adsorbent according to the present invention (1). The cooling zone is continuously or intermittently rotated and passed therethrough .

[0008]

[Action] In the present invention (1), by which the NH ₃ or more reactive equivalent of the NO _x in the exhaust gas upstream of the reducing denitration reactor of the NO _x is added to the exhaust gas, NO _x
In the reduction denitration reactor, NO _{x in} the exhaust gas is sufficiently and efficiently denitrated. NH ₃ remaining in the exhaust gas exiting from the NO _x reduction denitration reactor is subjected to the temperature swing method.
Adsorption is performed by the adsorption / desorption device. Therefore, the exhaust gas is NO _x
And NH ₃ are exhausted in a clean state with sufficient removal. On the other hand, NH ₃ adsorbed by the adsorption / desorption device is desorbed and supplied to the exhaust gas upstream of the NO _x reduction denitration reactor, whereby NH ₃ is effectively used. Also warm
Titanium oxide, alumina,
Vanadi with silica-alumina or titanium oxide as carrier
Adsorption composed of catalysts based on aluminum, molybdenum and tungsten
Of desorption of NH ₃ upstream of reduction denitration reactor
And by the high-temperature exhaust gas of the NH ₃ in the adsorption-desorption apparatus
Adsorption without the need for other heat sources due to desorption
Of desorbed NH ₃ to increase the thermal efficiency of the plant
Adsorbent that has desorbed NH ₃ and heated
Lower from the destination device of the discharged temperature after NH ₃ adsorption clean
Adsorption process by cooling before adsorption of NH ₃ with a simple exhaust gas
It can be prepared for.

In the present invention (2), in addition to the effect of the present invention (1), the NH 2 adsorbent filled with NH ₃ is used.
Since adsorption and desorption devices of more than a tower are used, and the operations of adsorption and desorption of NH ₃ and cooling of the adsorbent are performed by switching the gas flow furnace, the NO _x reduction and denitration reaction can be continuously performed by a simple operation. It is possible to adsorb and desorb NH _{3 in} the exhaust gas leaving the vessel.

In the present invention (3), in addition to the function of the present invention (1), the adsorbent filled in the adsorption / desorption apparatus is divided into a divided NH ₃ adsorption zone, an NH ₃ desorption zone and By rotating the adsorbent cooling zone continuously or intermittently, the adsorption and desorption of NH ₃ and the cooling of the adsorbent can be continuously performed by a simple apparatus.

[0011]

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIG. The present embodiment relates to a method for denitrifying 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 combustion exhaust gas of the gas turbine is sequentially introduced into the exhaust heat recovery boilers 5 and 6 on the upstream side and the downstream side, heats the condensate supplied to the exhaust heat boiler 6 from the condensate line 11, and further heats the condensate. The condensate supplied from 6 to the waste heat boiler 5 is heated and evaporated, and the steam is removed from the steam line 12.
It is further introduced into the steam turbine 9 to drive the generator 10.
The condensate of the steam turbine 9 is circulated from the condensate line 11 to the exhaust heat boiler 6 and then to the exhaust heat boiler 5 as described above.

A denitration reactor 7 for reducing and denitrating NO _x is provided in a flow path of the combustion exhaust gas between the exhaust heat boilers 5 and 6, and a combustion between the denitration reactor 7 and the exhaust heat boiler 5 is performed. An ammonia injection section 8 is provided in the flow path of the exhaust gas. Within the denitration reactor 7, it has been reduced catalyst is filled in NO _x, as the catalyst can be used vanadium and titanium oxide as a carrier, molybdenum, a catalyst tungsten-based or the like.

Downstream of the downstream exhaust heat boiler 6, 2
Temperature swing type adsorption / desorption devices 13 and 14 filled with the NH ₃ adsorbent of the column are provided.
The exhaust gas from the exhaust heat boiler 6 is introduced into one of the two. The flue gas that has exited the adsorption / desorption device 13 or 14 is discharged from the chimney 17 to the outside. Also,
The flue gas passes through the bypass line 15 from the upstream side of the exhaust heat boiler 5 on the upstream side, and the other exhaust / desorption device 13 or 14 to which the flue gas discharged from the exhaust heat boiler 6 is not supplied.
Through the upper bypass line 15 supplied to the exhaust heat boiler 5. Further, a part of the flue gas discharged from the one adsorption / desorption device 13 or 14 is:
Downstream of the upper adsorption / desorption device supplied to the other adsorption / desorption device, the exhaust gas is returned to the flow path of the combustion exhaust gas reaching the chimney 17, and 16 and 16 'denote circulation lines thereof.

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). As a result, in one adsorption / desorption device, NH in the exhaust gas discharged from the exhaust heat boiler
₃ adsorption step of adsorbing is performed, at the same time, on the other hand the adsorption-desorption apparatus, the desorption step is desorbed by the hot flue gas is NH ₃ adsorbed supplied via the bypass line 15, then the temperature by the combustion gas An adsorbent cooling step is performed in which the heated adsorbent is cooled by low-temperature combustion exhaust gas downstream of the adsorption / desorption device supplied through the circulation line 16. In addition, each of the above-described steps is sequentially and alternately performed in the two 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.

N charged in the adsorption / desorption devices 13 and 14
The adsorbent H _3, titanium oxide, alumina, silica - alumina, or materials used as the catalyst in the denitration reactor 7, i.e., vanadium titanium oxide was a carrier,
A catalyst such as molybdenum or tungsten can be used.

The air 18 heated by the heater 19 is supplied to the bypass line 15, and the heated air 18
May be supplied to the adsorption / desorption device 13 or 14 alone or together with the combustion exhaust gas from the upstream of the exhaust heat boiler 5. A device for absorbing and desorbing heated air 18 alone
Alternatively, when supplying to the air supply 14, the portion of the bypass line 15 from the upstream of the exhaust heat boiler 5 to the supply point of the air 18 is omitted.

In the present embodiment, approximately 5
The combustion exhaust gas having a temperature of about 00 ° to 600 ° C. is reduced in temperature by the exhaust heat recovery boiler 5, and has a NH ₃ / NO _x molar ratio equal to or more than the reaction equivalent to NO _x contained in the ammonia injection section 8, which is 1%. -About 2 NH ₃ is added. This N
The flue gas to which NH ₃ has been added in an amount equal to or greater than the reaction equivalent to O _x is denitrated by the catalyst packed in the denitration reactor 7, and almost all of the contained NO _x is removed.
Excess NH ₃ remains in the combustion exhaust gas.

The combustion exhaust gas in which the NH ₃ remains remains at a temperature of about 100 ° C. in the exhaust heat recovery boiler 6 and is introduced into one of the adsorption / desorption devices 13 and 14. NH ₃ is adsorbed on the adsorbent.

In this way, almost all of the NO _x and NH 3
_The flue gas that has become clean after removal of ₃ is the chimney 1
It is discharged from 7.

At the same time, in the other adsorption / desorption device, high-temperature flue 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 flue gas heated by the heater 19. The air 18 is introduced to desorb the NH ₃ adsorbed by the adsorbent, and the desorbed NH ₃ is returned to the upstream of the exhaust heat boiler 5 via the bypass line 15. Therefore, the adsorption / desorption device 13 or 14
NH ₃ adsorbed in is added to the flue gas exiting the gas turbine 3 at the upstream of the exhaust heat boiler 5, with NH ₃ added in the ammonia injection unit 8 enters the denitration reactor 7, effectively the denitration reaction Used.

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
On the other side of 4, the flow path is switched and clean combustion exhaust gas having a low temperature exiting one of the adsorption / desorption devices via the circulation line 16 is introduced, and the adsorbent heated in the desorption step is cooled, and the next adsorbent is cooled. This will prepare for the adsorption step. The flue gas which has cooled the adsorbent in the other side of the adsorption / desorption device is discharged from the chimney 17 via the circulation line 16 '.

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 flue gas discharged from the exhaust heat boiler 6 is introduced into the other of the adsorption and desorption devices. Adsorption of NH ₃ is performed, and desorption of NH ₃ and cooling of the adsorbent are performed in one of the adsorption / desorption devices. .

[0024] 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 tower sequentially continuously performed, the combustion exhaust gas is always discharged from the chimney Can be maintained in a clean state.

A second embodiment of the present invention will be described with reference to FIG. The present embodiment relates to a method for denitration of exhaust gas of a normal boiler plant, and is configured to denitrate combustion exhaust gas of a boiler 22 that burns with combustion air 21 preheated by an air preheater 25. .

The ammonia injection section 8, the denitration reactor 7, the adsorption / desorption devices 13 and 14 of the two towers, the bypass line 15, and the heater 19 for the air 18, which are provided in the flue gas flow path of the boiler 22, There is no difference from the embodiment.

In the present embodiment, an air preheater 25 for the combustion air 21 is provided in the flow path of the combustion exhaust gas between the denitration reactor 7 and the adsorption / desorption devices 13 and 14.
An electric precipitator 28 is provided between 3 and 14 and the chimney 17. In addition, the low-temperature combustion exhaust gas that has exited the electrostatic precipitator 28 is introduced into the adsorption / desorption devices 13 and 14 via the line 29 to cool the adsorbents of the adsorption / desorption devices 13 and 14 so that the adsorbent is cooled. Cooling flue gas into line 29 '
And is combined with the combustion air 21 that enters the air preheater 25 through the air preheater 25.

The present embodiment differs from the gas exhaust gas of the first embodiment in that the flue gas at the boiler outlet has a temperature of about 350 ° C. to 450 ° C. The addition of NH _{3 to} the combustion exhaust gas, the denitration of the combustion exhaust gas in the denitration reactor 7, the adsorption / desorption of NH _{3 in} the adsorption / desorption devices 13 and 14, and the cooling of the adsorbent are different from those in the first embodiment. But NO _x
And clean exhaust gas from which almost all of NH ₃ has been removed can be discharged from the chimney 17.

A third embodiment of the present invention will be described with reference to FIG. In this embodiment, a rotary adsorption / desorption device is used instead of the two-column adsorption / desorption device in the first and second embodiments.

In this rotary adsorption / desorption apparatus, a fixed adsorption zone A, a desorption zone B and a cooling zone C for the adsorbent are formed in a sector shape, and these zones are continuously or intermittently rotated and passed. A cylindrical body 30 having a circular cross section filled with an NH ₃ adsorbent is provided. The upper surface of the adsorption zone A is connected to a flow path a of the exhaust gas discharged from the exhaust heat boiler 6 or the air preheater 25, and the lower surface thereof is connected to a flow path b to a chimney 17. Wherein the lower surface and the upper surface of the desorbing zone B introduces gas to perform desorption of NH _3, and bypass line 15 for discharging the same time NH ₃ are connected. A circulation line 16 or line 29 for supplying a gas for cooling the adsorbent is connected to the lower surface of the cooling zone C, and a circulation line 16 'or line 29' is connected to the upper surface thereof.

In this embodiment, as the cylinder 30 rotates,
The adsorbent in the cylindrical body 30 is sequentially adsorption zone A, through the desorbing zone B and a cooling zone C, at the same time, and carried out continuously, the adsorption of NH _3, the desorption and cooling of the adsorbent of the NH ₃ be able to. In addition, the adsorption / desorption device does not require a valve for switching the flow path, and the above-described steps can be reliably performed with a simple device.

[0032]

[0033]

As described above, the present invention according to claim 1 removes almost all of NO _x in exhaust gas without wasting NH ₃ as a NO _x reducing agent, and , Excess NH ₃ is absorbed and desorbed by temperature swing method
More adsorbed, it can be made to discharge the exhaust gas containing no NO _x and NH ₃ most. Also temperature swing
In carrying out the method, titanium oxide, alumina, silica
Vanadium, molybdenum with alumina or titanium oxide as carrier
Uses an adsorbent consisting of a catalyst based on ribene and tungsten
The NH ₃ desorption is branched upstream of the reduction denitration reactor
Desorption of NH ₃ in the adsorption / desorption device by hot exhaust gas
Adsorbed without the need for other heat sources
Desorption of NH ₃ to increase the thermal efficiency of the plant
Adsorbent that desorbs NH ₃ and raises its temperature
Clean exhaust gas with low temperature discharged after adsorption of NH ₃ from
NH ₃ with the adsorption step followed by cooling before adsorption with the scan
Can be done.

Further, the present invention described in claims 2 and 3
In addition to the effect of the present invention as described in claim 1, excess NH ₃ can be continuously removed by a simple device, and the discharged exhaust gas can be kept in a clean state.

[0035]

[Brief description of the drawings]

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

FIG. 2 is a system diagram of a second embodiment of the present invention.

FIG. 3 is an explanatory view of a rotary adsorption / desorption device used in a third embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 3 gas turbine 5, 6 exhaust heat boiler 7 denitration reactor 9 steam turbine 13, 14, adsorption / desorption device 15 bypass line 16, 16 'circulation line 17 chimney 18 air 19 heater 22 boiler 25 air preheater 28 electric precipitator 29 , 29 'line 30 cylinder A adsorption zone B desorption zone C cooling zone

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshiaki Obayashi 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima-shi Inside the Hiroshima Laboratory, Mitsubishi Heavy Industries, Ltd. (72) Inventor Jun Morii 1-1, Akunouramachi, Nagasaki-shi Mitsubishi Heavy Industries Inside Nagasaki Shipyard Co., Ltd. (72) Akira Serizawa, Inventor 1-1 1-1 Akunouramachi, Nagasaki City Mitsubishi Heavy Industries, Ltd. Inside Nagasaki Shipyard, Inc. (72) Takako Kobayashi 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Heavy Industries, Ltd. (56) References JP-A-2-152523 (JP, A) JP-A-57-190640 (JP, A) JP-A-59-22631 (JP, A) JP-A-56-26523 (JP, A) A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B01D 53/04 B01D 53/06 B01D 53/34

Claims (3)

(57) [Claims] 1. A NO _x NO _x in the exhaust gas in the reducing denitration reactor reaction equivalent or more NH ₃ is added to the exhaust gas with the NO _x in the exhaust gas upstream of the reducing denitration reactor
Is reacted with NH _3, and then the unreacted NH ₃ remaining in the exhaust gas is converted to titanium oxide, alumina, silica-aluminum.
Vanadium, molybdenum with titanium or titanium oxide as carrier
Temperature due to the adsorbent composed of
The exhaust gas adsorbed in the adsorption / desorption device for performing the leaching method is discharged, and the NH ₃ adsorbed in the adsorption / desorption device is subjected to the reduction denitration reaction.
Desorption using high temperature exhaust gas branched upstream of the reactor
With supplying the NH ₃ which is deposited in the exhaust gas upstream of the reducing denitration reactor, the adsorbent to desorb NH ₃
Is the exhaust gas discharged after adsorption of NH ₃ from the adsorption / desorption device.
The method for denitration of exhaust gas, wherein the exhaust gas is cooled before NH ₃ adsorption . 2. Using the desorption apparatus adsorbent least two towers which are filled with NH _3, and performs adsorption NH _3, desorption and the operation of cooling the adsorbent by switching the gas flow path The method for denitration of exhaust gas according to claim 1. 3. The adsorbent charged in the adsorption / desorption device is rotated continuously or intermittently through the divided NH ₃ adsorption zone, NH ₃ desorption zone and adsorbent cooling zone. denitration method of exhaust gas according to claim 1, characterized in that.