JPH0634902B2 - Exhaust gas denitration method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Object of the Invention" (Industrial field of application) The present invention relates to a catalytic denitration method for removing NOx in exhaust gas, in which NOx in exhaust gas is blocked or corroded in a catalytic reaction tower. It is intended to provide a method which can be efficiently removed under the preferable reaction conditions which have been eliminated and which has less trouble.

(Prior Art) There are two methods widely used as a catalytic denitration method for removing NOx contained in exhaust gas. One is a method in which liquid ammonia or ammonia gas is used as a raw material, and gaseous ammonia is blown into the exhaust gas flue upstream of the catalytic reaction tower to react with NOx in the exhaust gas. This method does not have a denitration problem, but since it handles liquid ammonia that is easily vaporized, it is not easy to handle because it is subject to legal regulations such as the High Pressure Gas Control Law, and there is a risk of gas leaks in pipes, etc. Or, there is a defect that a problem in the work environment is likely to occur when a gas leak occurs when repairing related equipment. The other is a method in which ammonia water is sprayed and blown into the exhaust gas flue on the upstream side of the catalytic reaction column in the same manner as the above method. This method is less problematic in terms of odor or safety, but when the temperature of the exhaust gas is low, ammonia in the droplets reacts with SO ₂ , SO ₃ etc. in the exhaust gas until the mist vaporizes, and 2NH ₄ OH + SO ₃ → (NH ₄ ) ₂ SO ₄ + H ₂ O, NH ₄ OH + SO ₃ → NH
₄ HSO ₄ , 2NH ₄ OH + SO ₂ → (NH ₄ ) ₂ SO ₃ + H ₂ O, NH ₄ OH +
Compounds such as SO ₂ → NH ₄ HSO ₃ are produced, and these are not completely decomposed by the time they reach the catalytic reaction tower and are deposited and accumulated on the catalyst to reduce the effective surface area of the catalyst and reduce the desulfurization efficiency. However, if it is continued, it has a defect such as blocking the catalyst layer.

Further, in Japanese Patent Laid-Open No. 53-11162, it is announced that the ammonia water to be used is heated and vaporized by utilizing the heat amount of the exhaust gas after denitration in the spraying of the ammonia water. ing.

Incidentally, in JP-A-54-135672, NOx
In the treatment step of catalytically reducing and removing the above in the presence of a denitration catalyst, the time required for the ammonia water as a reducing agent to reach the catalyst in a droplet state with a maximum particle size of 300 μ or less is 2 to
It has been announced that it will be added 10 seconds before.

(Problems to be Solved by the Invention) Among the above-mentioned conventional techniques, a method using ammonia water is preferable. When the ammonia water is used, the spray method described above and Japanese Patent Laid-Open No. 53-
In any of the methods of 11162, it is necessary to perform a dust collecting process in order to avoid blockage due to dust or the like contained in the exhaust gas in the catalytic reaction tower, and in such a case, the exhaust gas temperature is required to operate the dust collector properly. It is generally necessary to carry out at a low temperature such as 300 ° C. or lower, and a problem remains when the exhaust gas temperature becomes 300 ° C. or lower.

That is, the reaction temperature in the exhaust gas denitration method is generally 700 to 1000 ° C. in the case of no catalyst and 300 to 400 ° C. in the case of the catalytic method.
In the case of having to carry out at 0 to 300 ° C., it takes 3 to 4 seconds to vaporize the mist generated at the time of spraying in the ammonia water spray method, so that the above-mentioned problem due to compound formation easily occurs. Even if ammonia gas is blown in, the reaction with SOx as described above can be considered, but if the exhaust gas temperature is 230 ° C or higher, the reaction is hard to occur.
It is said that almost no reaction occurs at temperatures above ℃.

Also in the case of the method of Japanese Patent Laid-Open No. 53-11162, this technique uses the high temperature of exhaust gas (flue gas) to vaporize ammonia water, and it is premised that the exhaust gas temperature is high at 300 to 450 ° C. If the condition is satisfied, and it is unavoidable to carry out under the condition of 300 ° C. or lower, the effect cannot be obtained. That is, there is a disadvantage in that another denitration technique must be duplicated when assuming an exhaust gas temperature condition of at least 300 ° C. or less.
In addition, safety due to corrosion of a heater provided in the exhaust gas is unavoidable.

Since the reaction of SOx and ammonia in the gas phase is extremely slow in JP-A-54-135672, SOx is absorbed in the ammonia water and reacted in the liquid before the reaction of the gas phase ammonia vaporized by the ammonia water. The size of the ammonia water particles is regulated in this case.In this case, it takes a certain amount of time for the ammonia droplets to receive the heat supply from the surrounding exhaust gas and to rise in temperature, during which SOx in the exhaust gas is It is absorbed by the liquid droplets to form ammonium sulfate compounds,
Such a solution adheres to the catalyst and the device and causes deterioration of catalyst performance and corrosion. That is, the catalytic reaction is hindered and the durability of the equipment is impaired. Further, the addition of the catalyst 2 to 10 seconds before reaching the catalyst has a disadvantage in that it is unavoidably long as an actual facility of this kind.

“Structure of the Invention” (Means for Solving Problems) The present invention was devised in view of the above-mentioned current situation,
By using ammonia water, which is relatively easy to handle, and heating and pressurizing it with steam, etc., and blowing it into the flue upstream of the catalytic reaction tower, it is possible to remove the compound as described above against exhaust gas at temperatures of 300 ° C or lower. The desired reaction with suppressed generation was solved, and problems such as clogging of the catalyst layer due to the reaction product with SOx generated by the spray of conventional ammonia water were solved, and the catalytic reaction was achieved even when the exhaust gas temperature in the flue was low or during the process. Prevents the formation of reaction products such as ammonium sulfate, ammonium sulfite, and acidic ammonium sulfate adhering to the tower, and also prevents clogging of the catalyst layer due to dust in the exhaust gas, as well as effective corrosion prevention and catalyst performance deterioration prevention. It has succeeded in achieving it, and is as follows.

In a denitration method using a catalyst, ammonia water is heated and pressurized outside the exhaust gas flue at a temperature of 300 ° C. or lower on the upstream side of the catalytic reaction tower, and at the same time, some small droplets are vaporized at once. A method for denitrifying exhaust gas, characterized in that the pressure is adjusted and blown in as described above.

(Function) As described above, the drawback of using ammonia water is that when the temperature of the flue gas is low, such as 300 ° C. or lower, it takes time to vaporize when small droplets are present when the ammonia water is sprayed. Also, the fact that preferable vaporization cannot be obtained by heating with this exhaust gas causes reaction products such as ammonium sulfate to cause clogging and corrosion, but in the present invention, ammonia water is heated by steam and blown under pressure. As a result, even if some small droplets are present, they are vaporized all at once and a temperature condition higher than the reaction equilibrium constant is formed to avoid the formation of ammonium sulfate or acidic ammonium sulfate and effectively eliminate these disadvantages. Ammonia water, whose pressure is adjusted to ² kg / cm ² or more with a pressure control valve, is pressure-adjusted and blown to evenly disperse and add it to the gas in the exhaust gas flue, speeding up the reaction and achieving efficient NOx in the exhaust gas. Try to remove. The upper limit of this pressure is 20 kg /
The cm ² makes it possible to overcome the difficulty in equipment and operation.

As a mode of blowing the heated ammonia water, a pressure control valve is provided between the heater of the ammonia water and the flue to heat in a pressurized state. Even if small droplets are present, they are sufficiently dispersed so that they are vaporized all at once, and it does not take time to evaporate the droplets as in the past, and ammonium sulfite, etc. adheres to the catalyst layer and causes clogging. Almost no corrosion of equipment can be effectively prevented. Although steam as a heat source for heating can be easily adopted in factory equipment or the like that requires such denitration, electric heat or high temperature exhaust gas may be adopted depending on the case.

As described above, since the flue gas temperature is 300 ° C or lower, it can be effectively used for the exhaust gas in the process of appropriately collecting the dust by installing a dust collector, and therefore the clogging of the catalyst layer due to the dust in the exhaust gas is also appropriate. As a result, it is possible to continuously and stably treat exhaust gas in combination with elimination of blockage by reaction products such as ammonium sulfate-based compounds and prevention of corrosion as described above.

(Example) It was carried out by an ammonia water addition mechanism to the exhaust gas flue of the waste incineration treatment facility having the configuration shown in FIG. That is, the ammonia water having a concentration of 30% is introduced into the flue 6 from the incinerator having a throughput of 100 tons / day, the gas flow rate change (20000) in the flue 6 from the tank 1 through the supply pipe 2, the pump 3 and the flow control valve 4. To 40,000 Nm ³ / H) and the flow rate is adjusted to 7 to 14 / H in a state substantially proportional to the heater 5
Sent to. Steam of 150 to 180 ° C. is used as a heat source of the heater 5, and the pressure inside the heater 5 is adjusted to ² to 20 kg / cm ² by a pressure control valve 7 provided in front of the exhaust gas flue 6. That is, the pressure is adjusted in response to changes in gas temperature and flow rate from the start-up of the incinerator in the flue 6 as described above, and ammonia water having a concentration of 30% is started at 40 ° C. to 140 ° C. as described above. It was heated to the range of and was injected into the flue 6.

The ammonia water exiting the pressure control valve 7 is instantaneously decompressed,
Through the entire process of operation in the incineration facility as described above, the ammonia that is effectively gasified and mixed in the exhaust gas, and ejected from the pressure control valve 7 provided 10 m before the catalytic reaction tower 8 using the catalyst of titanium oxide and vanadium is At least up to the reaction tower 8, it was completely gasified. Average 3
In the case of the above equipment that uses 10 / h ammonia water (concentration 30%) for exhaust gas amount of 0000 Nm ³ / hr, at least once a month when spraying without heating by the conventional method. It was necessary to remove deposits such as ammonium sulfite on the catalyst layer and to remove the clogging by dusts, etc. However, by implementing the method of the present invention, the deposits were greatly reduced, and only once every six months. . Again 6
Even with the result of continuous operation for 20 months with a once-month decommissioning, the corrosion in the equipment after the catalytic reaction tower 8 was slight, and the flue was 12 to 18 months after the conventional method,
We have found that the corrosion resistance of the denitration reaction tower and other parts that required repairs and replacement was greatly improved.

"Effects of the Invention" In the case of the present invention as described in detail above, NOx in exhaust gas
In the catalytic denitration method that removes ammonia gas, by heating and pressurizing ammonia water, which is relatively easy to handle, and adjusting the pressure to vaporize at a dash even if some liquid droplets are present And a flue gas whose temperature is lowered to 300 ° C or less are formed, and a dust collector or the like is sufficiently operated to cause troubles in the conventional reaction tower due to exhaust gas dust and ammonium sulfate caused by mist generated during ammonia water spraying. Effectively eliminates both clogging and corrosion due to system compounds, etc., and can prevent deterioration of catalyst performance. Furthermore, since the heater is installed outside the exhaust gas flue, its durability can be improved. Therefore, it can be said that this is an extremely large invention in terms of environmental management.

[Brief description of drawings]

The drawings are schematic views showing an embodiment of the present invention, and FIG. 1 is an explanatory view showing an outline of equipment for carrying out the method of the present invention. However, the reference numerals in this drawing are as follows. 1: Ammonia water tank 2: Ammonia water supply pipe 3: Pump 4: Flow control valve 5: Heater 6: Exhaust gas flue 7: Pressure control valve 8: Catalytic reaction tower 9: Steam

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Takashi Yokoyama 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. (72) Takao Minami 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Date Inside the Steel Pipe Co., Ltd. (72) Inventor Tsuyoshi Nakao 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Inside the Nippon Steel Pipe Co., Ltd. (56) Reference JP-A-54-136572 (JP, A)

Claims (1)

[Claims] 1. In a denitration method using a catalyst, an exhaust gas flue at a temperature of 300 ° C. or lower upstream of a catalytic reaction tower,
A method for denitrifying exhaust gas, which comprises heating and pressurizing ammonia water outside the exhaust gas flue and adjusting the pressure so that even a few small droplets are vaporized at once and blowing.