JPH05163933A - Denitration device - Google Patents

Abstract

PURPOSE:To achieve an excellent denitration treatment even if a temperature of exhaust gas is lower than a predetermined denitration temperature, for example, in starting or stopping by providing a preheater for increasing a temperature of the exhaust gas in the case where the temperature of the exhaust gas before being brought into contact with a catalyst is lower than a predetermined value. CONSTITUTION:Exhaust gas 12 from a burner 11 passes through an ammonia mixer 14 for mixing the exhaust gas with aqueous ammonia as a reducing agent in a predetermined ratio. The resultant mixture gas 18 is turned into nitrogen gas and steam in contact with a catalyst inside a reactor 15, to be discharged through a chimney 16. On a pipeline before the ammonia mixer 14, there is provided a preheater 22 for introducing combustion gas 21 from a low No.x burner 20 as preheating gas into the exhaust gas 12. In the case of starting when the catalyst inside the reactor 15 is completely cooled, the preheater is started for preheating an exhaust gas line by the combustion gas 21 to activate the catalyst inside the reactor 15 and inject the aqueous ammonia 13 into the ammonia mixer 14, for denitration. In this state, the burner 11 is started, and a load is gradually increased. Simultaneously, fuel of the preheater 22 is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention relates to a denitration apparatus for denitrating the NO _X in the exhaust gas of a combustion apparatus such as boilers and incinerators, good denitration even when particular exhaust gas temperature such as during start-stop is low The present invention relates to an improvement of a denitration device that can be performed in

[0002]

2. Description of the Related Art As nitrogen oxides, several kinds of compounds are known to exist depending on the bonding state of nitrogen (N) and oxygen (O). NO) and nitrogen dioxide (NO ₂ ), both of which are generally called nitrogen oxides (hereinafter referred to as NO _x ). In combustion devices such as boilers and diesel engines, the NO / NO _X ratio at the time of combustion gas discharge is 9 _% by volume.
It is about 0 to 95%, NO _X in the exhaust gas almost N
It is O.

NO is a colorless and odorless gas which is almost insoluble in water and is said to be less toxic than NO ₂ . NO ₂ is produced by NO being oxidized mainly by ozone (O ₃ ) existing in the atmosphere. The reaction rate is also affected by weather conditions such as wind speed, solar radiation, temperature, and other pollutants. NO ₂ is more water-soluble than NO, and has a reddish brown color and an odor when the concentration is high.

The sources of NO _x present in the atmosphere include both natural and artificial sources. The main sources of natural sources are lightning, volcanic eruptions, bacterial activities, etc.
There are various types of sources, which can be classified into mobile sources and small group sources.

In order to suppress the generation of NO _x , (1) use a fuel containing no organic nitrogen compound, (2) lower the oxygen concentration in the combustion region, and (3) in the high temperature region. shortening the residence time of the combustion gas, thereby achieving a reduction of the NO _X by the combination, to apply each of the principles, such as (4) (eliminating especially local high temperature zone) to lower the combustion temperature.

By the way, N generated by combustion of fuel
Most of the O _x is NO with low reactivity, so its removal is technically quite difficult. With the appropriate catalyst as a specific denitration method, a reducing agent is added to the exhaust gas, it is often used catalytic reduction method for reducing the NO _X. As the reducing agent, ammonia, hydrocarbon, hydrogen, carbon monoxide, etc. are used.

FIG. 3 is an explanatory view showing the structure of a conventional catalytic reduction type denitration apparatus. As shown in the figure, the exhaust gas 2 discharged from the combustion device 1 such as a boiler or a diesel engine passes through an ammonia mixing device 4 that mixes a predetermined amount with, for example, ammonia 3 as a reducing agent, and a mixed gas 8 is generated in a reactor 5. Contacting the catalyst, it becomes nitrogen gas and water vapor, and the stack 6
Discharged from. The heat of the gas leaving the reactor 5 is recovered by the exhaust gas boiler 7.

[0008]

As described above, in the conventional denitration apparatus, the temperature of the exhaust gas generated by the combustion apparatus 1 is raised and the catalyst such as zirconia reacts at the reaction temperature (about 300 ° C. or higher).
Then, ammonia was sprayed into the exhaust gas to cause a denitration reaction inside the catalyst, and NO _x was released to the atmosphere as N ₂ and H ₂ O, which are non-polluting.

By the way, since the denitrification treatment cannot be performed stably for about one hour after the start of the combustion device, the denitration equipment cannot be used effectively in facilities with frequent start / stop, and a large amount of NO _X is generated during the start / stop timing. It was released untreated. Although the amount of NO _X removed varies depending on the local regulations, it is not allowed to release a large amount of NO _X untreated even at the time of start-up, but it has not been possible with the denitration equipment to date.

It is an object of the present invention to provide a denitration device which can perform a denitration treatment favorably even when the exhaust gas temperature is low, such as when starting and stopping.

[0011]

In the denitration apparatus according to the invention described in claim 1, NO _x in the exhaust gas discharged from the combustion apparatus is mixed with a reducing gas and brought into contact with the catalyst to form a nitrogen gas. A denitration apparatus for reducing to steam is provided with a preheating means for raising the temperature of the exhaust gas before it is brought into contact with the catalyst is lower than a predetermined temperature.

Specifically, it is disclosed that the reducing gas is ammonia gas, the preheating means is provided with a low NO _x burner, and the combustion gas of the burner is introduced into the exhaust gas as preheating gas. ..

[0013]

In the present invention, since the exhaust gas before being brought into contact with the catalyst is provided with the preheating means for raising the temperature of the exhaust gas when the temperature is lower than the predetermined temperature, the temperature of the exhaust gas is controlled to a predetermined value, for example, at the time of start / stop. Even when the temperature is lower than the denitration temperature, the denitration treatment can be favorably performed.

According to the present invention, a combustion device, such as a diesel engine, which emits high-temperature exhaust gas and generates a larger amount of NO _X than at the time of start-up, and can be installed particularly in a device having a high start / stop frequency. good.

When the temperature of the exhaust gas contacting the catalyst is raised by the preheating means of the present invention and NO _{x in} the exhaust gas uses ammonia as a reducing agent, the following reaction is performed:
Reduced to nitrogen gas and water vapor. 4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O (1) 6NO + 4NH ₃ → 5N ₂ + 6H ₂ O (2) 6NO ₂ + 8NH ₃ → 7N ₂ + 12H ₂ O (3) When contacting the catalyst When the temperature is around 350 to 400 ° C, the reaction of the formula (1) preferentially proceeds.

As a concrete preheating means, the pipe itself for introducing the exhaust gas is heated, or the exhaust gas is introduced into the heating furnace and brought into combustion again before contacting with the catalyst,
Various means are taken, with low NO _X burner particular,
A means for introducing the combustion gas of the burner into the exhaust gas as a preheating gas can be attached to an existing denitration device,
Excellent facility cost, fuel cost, maintenance cost, etc.

These preheating means are used only when the exhaust gas temperature is lower than the denitration temperature, and the exhaust gas temperature is stable.
When the temperature exceeds the denitration temperature, the preheating means is stopped.
As described above, according to the device of the present invention, NO _x can be removed by denitration reaction from a low load when the combustion device is started.
In particular combustion apparatus of high NO _X as a diesel engine,
Further, it is effective in adding to an existing denitration device, which is a device with a high frequency of starting and stopping and in which the highness of the device itself cannot be drastically modified.

[0018]

EXAMPLE An outline of a denitration apparatus equipped with the preheating means of the present invention will be described below. In the present invention, the denitration device follows the exhaust gas system blow of the diesel power generator. FIG. 1 is an explanatory diagram showing the configuration of an embodiment of the denitration device of the present invention.

As shown in the figure, exhaust gas 12 discharged from a combustion device 11 such as a boiler or a diesel engine passes through an ammonia mixing device 14 which mixes a predetermined amount with, for example, ammonia 13 as a reducing agent, and is mixed in a reactor 15. The gas 18 comes into contact with the catalyst, becomes nitrogen gas and water vapor, and is discharged from the stack 16. The heat of the gas leaving the reactor 15 is recovered by the exhaust gas boiler 17. A low NO _x burner 2 is installed in the pipe before the ammonia mixing device 14 of this device.
A preheating device 22 for introducing the combustion gas 21 of 0 as a preheating gas into the exhaust gas 12 is provided. Low NO _x burner 2
The degree of combustion of 0 is controlled by the controller 23 by the exhaust gas temperature in the reactor 15.

In the operating procedure of the denitration apparatus as described above, in starting when the catalyst in the reactor 15 is completely cooled (for example, black start or start after long-term stop), the preheating apparatus 22 is first started. And exhaust gas line 400
Preheating with an exhaust gas of ˜500 ° C. activates the catalyst in the reactor 15 at a temperature of about 350 ° C. Therefore, denitration becomes possible by injecting the ammonia water 13 into the ammonia mixing device 14 in a required amount. In this state, a diesel engine (not shown) is started and the load is gradually increased. In parallel with this, the fuel of the preheating device 22 is also increased, and the reactor 15
Ensure the reaction temperature of the catalyst inside.

FIG. 2 is a diagram showing changes over time in the NO _x amount (A) at the reactor outlet, the reactor temperature and the engine output (B) when the preheater was driven or not driven. The vertical axis represents the NO _X amount, temperature and engine output rate, the horizontal axis represents time, and is the reactor outlet N when the preheating device is driven.
O _X amount, the reactor outlet _the amount of NO _X, the reactor outlet temperature when the reactor outlet temperature in the case of driving the preheater, the did not drive the preheating device when not driving the preheating device, Is the reactor inlet temperature when the preheater is not driven, is the engine outlet temperature, and is the engine output. In addition, since the time is variously extended depending on the capacity of the reactor,
It is just a reference time.

[0022] As shown in FIG. Otherwise, driving the pre-heating device, NO _X amount and temperature change, as can be seen from the gradual engine output to start the engine 100
%, The time required for the outlet temperature of the reactor 15 to reach or exceed the denitration reaction temperature and activate the catalyst of the reactor 15 (about 36 minutes). On the other hand, the amount of NO _X cannot be removed even though it has already exceeded 800 ppm 10 minutes after the start-up, and is emitted as exhaust gas. Further, even when the engine is stopped, the exhaust gas temperature is lowered by lowering the output of the engine in the same manner, and the reaction can hardly be performed at 300 ° C. or less, so that the injection of ammonia water is stopped. Therefore N
O _X is Since then discharged as exhaust gas.

When the preheating device is driven, the preheating device is driven before the engine is started to raise the temperature of the catalyst in the reactor 15 to a predetermined temperature. Therefore, immediately after the starting (5 minutes).
Ammonia can be injected to start the denitration reaction, the output of the preheating device is lowered as the output of the engine rises, and the preheating device is stopped when the denitration reaction can be performed only with the exhaust gas of the engine. Also, even when the engine is stopped, the preheater is restarted when the output starts to decrease, and the fuel amount of the low NO _X burner is gradually reduced as the engine output is decreased while securing the reaction temperature. The state is the same as when the engine was started in the previous graph.

When the device for discharging exhaust gas is stopped for a short period of time, after the engine is stopped, the preheating device is kept in the preheating operation state so that the temperature of the reactor does not decrease so much, and the catalyst temperature is set to 300. ~ 400 ° C (exhaust gas is 50
The temperature may be controlled at about 0 ° C. In addition, the preheating device is also stopped when it is stopped for a long period of time or when it is stopped for 10 hours or more. Since most of the diesel engine power generators and the like are equipped with an exhaust heat recovery boiler, 60 to 70% of the energy generated in the preheating device can be recovered, so energy is not wasted much.

The amount of gas in the low NO _x burner may be about 1/2 to 1/3 of the amount of gas at the rated output of the engine, and the gas temperature may be 500 ° C. (max). The required gas amount is obtained by the following formula. Required gas amount (kg / h) = 1.5 to 2 (kg / h) x rated output (ps) The heat amount for preheating while the engine is stopped is the exhaust gas pipe and NO.
_It may be capable of covering the heat released from the _X reactor.

[0026]

As described above, in the present invention, since the preheating means for raising the temperature of the exhaust gas before contacting with the catalyst is lower than a predetermined temperature, for example, at the time of starting and stopping, Even when the temperature of the exhaust gas is lower than the predetermined denitration temperature, the denitration treatment can be favorably performed.

Further, as a concrete preheating means, various means such as heating the pipe itself for introducing the exhaust gas, introducing the exhaust gas into the combustion device and bringing it into combustion again before contacting with the catalyst, various means are taken. but especially with low NO _X burner, means for introducing into the exhaust combustion gas of the burner as a preheating gas, it is possible to attached to existing denitration apparatus, equipment costs, fuel costs, excellent in maintenance costs, etc. ing.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of an example of a denitration device of the present invention.

FIG. 2 is a diagram showing changes over time in the NO _x amount (A) at the reactor outlet, the reactor temperature, and the engine output (B) when the preheating device was driven or not driven.

FIG. 3 is an explanatory diagram showing a configuration of a conventional catalytic reduction type denitration device.

Claims (3)

[Claims] 1. NO in exhaust gas discharged from a combustion device
_In a denitration device for mixing _X with a reducing gas and bringing it into contact with a catalyst to reduce it to nitrogen gas and water vapor, a preheating means for raising the temperature of the exhaust gas before contacting with the catalyst is lower than a predetermined temperature. A denitration device characterized by being equipped with. 2. The preheating means comprises a low NO _x burner,
The denitration apparatus according to claim 1, wherein the combustion gas of the burner is introduced into the exhaust gas as a preheating gas. 3. The denitration apparatus according to claim 1, wherein the reducing gas is ammonia gas.