JP4365392B2 - Treatment of residual gas in ammonia tank - Google Patents

Description

  The present invention relates to a method for treating residual gas in an ammonia tank. More specifically, the present invention relates to a method for treating residual gas in an ammonia tank that can efficiently detoxify ammonia gas remaining in the tank when the liquid ammonia storage tank is opened and inspected.

In a tank that stores liquid ammonia, such as an ammonia production plant or a thermal power boiler plant, it is obliged to periodically open the tank for inspection and repair. When performing such inspections and repairs, the liquid ammonia stored in the tank is first transferred to another storage container. In this state, the tank is full of ammonia gas and enters the tank. The inspection and repair work cannot be performed.
Therefore, conventionally, after transferring liquid ammonia, the operation of filling the tank with water, absorbing the ammonia gas and recovering it as ammonia water was repeated to open the tank. However, this method has a problem that not only is the operation complicated and time-consuming, but also a large amount of ammonia water is generated as industrial waste, and ammonia gas is volatilized around and causes environmental pollution.
As a method for disposing of ammonia water generated as a waste liquid, there is a method of diluting and discharging in accordance with discharge standards, but there are restrictions from the viewpoint of complying with the total amount of ammonia nitrogen in a closed water area. In addition, there are existing treatment methods such as oxidative decomposition treatment and stripping treatment with chlorinated chemicals as treatment methods for ammonia water, both of which take time and expense and treat residual gas in the liquid ammonia storage tank. As a series of techniques, it is not practical.
As a conventional technique, Patent Document 1 discloses a method of injecting an inert gas to discharge ammonia in a liquefied ammonia storage container. Patent Document 2 and Patent Document 3 disclose a method of driving off residual flammable gas in a liquefied gas tank with an inert gas.
In these documents, by adjusting the flow rate of the ammonia gas or the effluent gas mixture to the catalytic combustion apparatus, a predetermined temperature in the catalyst tower determined by the type of catalyst is maintained, and the reaction of the catalytic combustion apparatus is controlled. A configuration for suppressing runaway is not disclosed.
JP-A-47-7208 JP-A-49-51617 Japanese Patent Laid-Open No. 10-160098

  The present invention solves these problems of the prior art, and the ammonia gas remaining in the liquid ammonia storage tank can be safely processed by simple operation using simple equipment. The purpose is to provide a processing method.

As a result of intensive studies to solve the above problems, the inventors of the present invention extracted ammonia gas remaining in the liquid ammonia storage tank using the internal pressure of the tank, and led it to an ammonia treatment device for treatment. By injecting an inert gas into the tank and diluting and flowing out the remaining ammonia gas, the effluent gas mixture is led to an ammonia treatment device and processed, so that liquid ammonia can be stored without generating a large amount of ammonia water. It has been found that ammonia gas remaining in the tank can be efficiently treated, and the present invention has been completed based on this finding.
That is, the present invention
(1) In the method of extracting and decomposing ammonia gas remaining in the liquid ammonia storage tank out of the tank, the ammonia gas extracted using the internal pressure of the tank is led to a catalytic combustion apparatus having a catalyst tower and processed. Then, an inert gas is injected into the tank to dilute and flow out the remaining ammonia gas, and the effluent gas mixture is led to a catalytic combustion apparatus having a catalyst tower for treatment, and the ammonia gas or the effluent gas mixture A method for treating residual gas in an ammonia tank, wherein the flow rate to the catalytic combustion device is adjusted by the temperature in the catalyst tower;
(2) A method for treating residual gas in an ammonia tank as described in item 1, wherein ammonia gas or effluent gas mixture is mixed with air at the inlet of the catalytic combustion device;
(3) The method for treating residual gas in an ammonia tank as described in item 1, wherein the inert gas is nitrogen gas, and
(4) The inert gas is injected into the tank to dilute and flow out the remaining ammonia gas, and then water is poured into the tank to recover the slightly remaining ammonia gas as ammonia water. Treatment method of residual gas in ammonia tank,
Is to provide.

  According to the method for treating residual gas in an ammonia tank of the present invention, ammonia remaining in the ammonia tank and the accompanying equipment system can be efficiently treated, and ammonia-containing water required for wastewater treatment is not generated. The odor of ammonia does not leak to the outside, and the environmental load can be greatly improved by shortening the construction period and reducing waste.

In the method for treating the residual gas in the ammonia tank of the present invention, the ammonia gas remaining in the liquid ammonia storage tank is taken out of the tank for treatment, and the ammonia gas drawn out using the internal pressure of the tank is treated with ammonia. After being guided to the apparatus and processed, an inert gas is injected into the tank to dilute and flow out the remaining ammonia gas, and the effluent gas mixture is guided to the ammonia processing apparatus for processing.
FIG. 1 is a process flow diagram of one embodiment of the method of the present invention. During normal operation, the liquid ammonia storage tank 1 is maintained at a pressure of about 1,000 to 1,500 kPa, and the stored liquid ammonia is heated to several tens of degrees Celsius in the evaporator 2 to be gasified, and the accumulator 3 and then supplied to the equipment continuously or intermittently as needed via the equipment delivery pipe 4. When inspecting or repairing the liquid ammonia storage tank, it is necessary that no ammonia gas exist in the tank. First, liquid ammonia stored in the tank is transferred to another storage container via the valve 10 and the valve 11. In this state, the tank is filled with ammonia gas, and the tank internal pressure is often about several hundred kPa. This remaining ammonia gas can be treated by the method of the present invention.

There is no restriction | limiting in particular in the ammonia processing apparatus used for this invention method, For example, an ammonia decomposition apparatus, an ammonia absorption apparatus, etc. can be mentioned. Examples of the ammonia decomposing apparatus include an oxidative decomposing apparatus using an oxidizing agent and a catalytic combustion apparatus. The ammonia decomposition apparatus is preferably an apparatus that directly decomposes ammonia gas, and among them, a catalytic combustion apparatus can be used particularly suitably. Examples of the ammonia absorber include a device that uses water as an absorbing solution and a device that uses acidic water as an absorbing solution. When acidic water is used as the absorbing solution, the absorption rate can be increased.
In the embodiment shown in FIG. 1, a catalytic combustion apparatus is used as the ammonia processing apparatus. A temporary pipe is connected by a valve 17 from the equipment discharge pipe 4 and connected to the catalytic combustion device 8 via the ammonia processing pipe 5, the valve 18, the flow meter 6 and the gas mixer 7. In carrying out the method of the present invention, after starting the catalytic combustion device and raising the temperature, the ammonia gas is sent out using the internal pressure of the tank, and the ammonia gas flow rate is adjusted using the valve 18 while being controlled by the flow meter 6. Then, it is mixed with air by the gas mixer 7 and sent to the catalytic combustion device 8. In the catalytic combustion apparatus, ammonia gas reacts with oxygen gas in the air according to the following formula to generate nitrogen gas and water.
4NH ₃ + 3O ₂ → 2N ₂ + 6H ₂ O

  When the internal pressure of the liquid ammonia storage tank drops to near normal pressure, the valve 10 is closed, the valve 9 is opened, an inert gas is injected into the tank, and the ammonia gas remaining in the tank is diluted. Next, the valve 10 is opened to let out a mixed gas of ammonia gas and inert gas, and the ammonia gas remaining in the evaporator and the accumulator 3 is made to flow out through the evaporator 2 and the accumulator 3 in the same manner. Air can be injected and mixed with a gas mixer, and ammonia gas can be oxidatively decomposed with a catalytic combustion apparatus. When the internal pressure of the liquid ammonia storage tank drops to near normal pressure, it is preferable to repeatedly dilute the remaining ammonia gas by injecting the inert gas into the tank and to flow out the mixed gas. Further, after that, the inert gas supply pipe is connected to the valve 11 or the valve 14 to supply the inert gas in a continuous or batch manner, and the ammonia gas still remaining in the evaporator and the accumulator is surely expelled to perform catalytic combustion. Preferably it leads to the device.

Further, when the ammonia remaining in the liquid ammonia storage tank 1 is processed, the ammonia processing pipe 5 is connected to the valve 11 instead of the valve 17 to process only the ammonia gas remaining in the liquid ammonia storage tank, The inert gas supply pipe is connected to the valve 11 and the ammonia treatment pipe is connected to the valve 14 to treat the ammonia gas in the evaporator 2, and the inert gas supply pipe is connected to the valve 14 and the ammonia treatment pipe is connected to the valve 14. It is also possible to treat the ammonia gas in the accumulator 3 by connecting to 17.
In the method of the present invention, the inert gas can be supplied by connecting an inert gas supply pipe to an inert gas supply line of a factory, or can be supplied by connecting to an inert gas cylinder. In the embodiment shown in FIG. 1, the inert gas supply pipe is connected to the liquid ammonia storage tank 1, but it is preferable that the inert gas supply pipe can be connected to a joint pipe having a valve 11 and a joint pipe having a valve 14. One end of the ammonia treatment pipe is connected to the catalytic combustion apparatus, and the other end is connected to the joint pipe having the valve 17, but the other end is also connected to the pipe having the valve 11 and the pipe having the valve 14. Preferably it is possible.

In the method of the present invention, after the ammonia gas remaining in the liquid ammonia storage tank is extracted using the internal pressure of the tank, the inert gas is injected into the tank to dilute and flow out the remaining ammonia gas. There is no risk of air flowing into the ammonia storage tank, and there is no risk of generating an explosive gas mixture by mixing with air. There is no restriction | limiting in particular in the inert gas used for this invention method, For example, nitrogen gas, a carbon dioxide, helium, neon, argon, krypton, xenon, radon etc. can be mentioned. Of these, nitrogen gas is particularly suitable because it is readily available.
In the method of the present invention, the ammonia gas remaining in the liquid ammonia storage tank is allowed to flow out in a gas state, so that a large amount of ammonia water that needs to be treated as industrial waste is not generated. Further, by using a catalytic combustion apparatus as an ammonia treatment apparatus, ammonia gas is oxidized and decomposed into nitrogen gas and water, and nitrogen oxides are not generated, so there is no possibility of polluting the environment.

FIG. 2 is an explanatory diagram of an embodiment of a gas mixer used in the method of the present invention. Air is sent from the damper 20 to the square-shaped mixing pipe 19, and ammonia gas or an outflow mixed gas of ammonia gas and inert gas is sent from the damper 21. In the figure, the upper right pipe is closed, and ammonia gas is mixed with air and sent out from the lower right pipe to the catalytic combustion apparatus. Instead of air, a gas having a high oxygen gas concentration can be sent.
FIG. 3 is an explanatory view of one embodiment of the catalytic combustion apparatus used in the method of the present invention. A mixed gas of ammonia gas and air is sent to the heat exchanger 23 by the blower 22 and preheated, and then heated to a predetermined temperature by the electric heater 24 and sent to the catalyst tower 25. Ammonia and oxygen gas react in the catalyst tower, and ammonia is oxidized and decomposed into harmless nitrogen gas and water. The gas flowing out from the catalyst tower is sent to the heat exchanger 23, where waste heat is recovered and then released into the atmosphere.

  Examples of the catalyst used in the method of the present invention include a shaped catalyst obtained by shaping a metal or a compound thereof into an arbitrary shape, a metal supported catalyst supported on a carrier, and the like. Examples of the metal include base metals such as iron and manganese, noble metals such as gold, silver, ruthenium, rhodium, palladium, osmium, iridium and platinum, and oxides and alloys of these metals. Among these, iron and manganese-based catalysts can be used particularly preferably because they can decompose ammonia at a relatively low temperature. Examples of the carrier on which the metal is supported include alumina, silica, titania, zirconia, zeolite, silicon carbide and the like. Among these, titania, zirconia and silicon carbide can be preferably used. The temperature of the catalyst tower is, for example, preferably 150 to 350 ° C, and preferably 180 to 280 ° C.

In the method of the present invention, after injecting an inert gas into a liquid ammonia storage tank to dilute and flow out the remaining ammonia gas, water is filled until the tank is filled with water, and a slight amount of remaining ammonia gas is added to the ammonia water. It is preferable to collect as. By filling the tank with water, the internal ammonia gas can be completely discharged and removed. When water is filled in the tank, it is preferable that the gas pushed out of the tank is also sent to the ammonia treatment apparatus and treated in the same manner. Since the tank is provided with a manhole that allows workers to enter and exit, water can be supplied into the tank through the manhole. Also, drainage can be performed from a manhole using a submersible pump. If there is a pipe at the bottom of the tank, the pipe can be used to drain water. By repeating the operation of injecting an inert gas into the liquid ammonia storage tank and diluting the remaining ammonia gas, the ammonia concentration absorbed in the tension water becomes sufficiently low, and the recovered ammonia water is used as a regular drainage in the public water area. Can be discharged.
According to the method of the present invention, the ammonia gas remaining in the liquid ammonia storage tank is processed in a gaseous state, so that the residual gas can be processed at a low cost in a short time without discharging any harmful waste. .

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
Example 1
For the liquid ammonia storage tank system shown in FIG. 1, the residual gas in the ammonia tank was treated. The capacity of the liquid ammonia storage tank was 135 m ³ , and after transferring the liquid ammonia in the tank out of the system, the amount of ammonia remaining in the ammonia tank and the accompanying equipment system was about 300 kg.
The catalytic combustion apparatus 8 having a catalyst tower filled with 1,200 L of iron and manganese forming catalyst was started, and the temperature in the catalyst tower was raised to 180 ° C. Next, by opening the valve 17 and adjusting the valve 18, ammonia gas is pushed out at an internal pressure of 320 kPa of the system, and this is mixed with a gas in which air is sucked at a flow rate of 1,800 m ³ (Normal) / h. It was poured into the vessel and mixed. The flow rate of ammonia gas was controlled by the temperature in the catalyst tower, and the flow rate of ammonia gas was adjusted so that the temperature in the tower did not exceed 280 ° C.
After 22 hours, since the internal pressure of the liquid ammonia storage tank dropped to 50 kPa, the valve 10 was closed and nitrogen gas was press-fitted into the tank to 470 kPa. Next, by opening the valve 17 and adjusting the valve 18, the mixed gas of ammonia gas and nitrogen gas is pushed out by the internal pressure of the system, and air is sucked by the blower at a flow rate of 1,800 m ³ (Normal) / h. The mixture was injected into the gas mixer. The flow rate of the mixed gas of ammonia gas and nitrogen gas was controlled at the catalyst tower temperature, and the mixed gas flow rate was adjusted so that the tower temperature did not exceed 280 ° C. It took 11 hours for the internal pressure of the tank to drop to 50 kPa.
Similarly, the injection of nitrogen gas into the liquid ammonia storage tank and the treatment of ammonia gas by aeration of the mixed gas to the catalytic combustion apparatus were repeated twice more. The third treatment took 5 hours and the fourth treatment took 4 hours.
Subsequently, industrial water was filled up to 135 m ³ of full water in a liquid ammonia storage tank. In addition, the gas pushed out when filling industrial water was similarly ventilated to the catalytic combustion apparatus. Since the total nitrogen concentration in the tension water was 10.6 mg / L and the ammonia concentration was confirmed to be less than 20 mg / L, the tension water was discharged. It took a total of 28 hours to put industrial water, analyze the total nitrogen in the tension water, and discharge the tension water.
Further, nitrogen gas was sent from the valve 11 to the evaporator 2, and a flowing mixed gas of ammonia gas and nitrogen gas was vented to the catalytic combustion device via the valve 14 to oxidize and decompose ammonia. Since the ammonia concentration in the mixed gas flowing out from the evaporator after about 6 hours became less than 20 ppm (volume ratio), the supply of nitrogen gas to the evaporator was stopped. Subsequently, nitrogen gas was sent from the valve 14 to the accumulator 3, and a mixed gas of ammonia gas and nitrogen gas flowing out was vented to the catalytic combustion device via the valve 17 to oxidize and decompose ammonia. Since the ammonia concentration in the mixed gas flowing out from the accumulator after about 6 hours became less than 20 ppm (volume ratio), the supply of nitrogen gas to the accumulator was stopped.
A total of 42 hours were required for the treatment of the ammonia gas remaining in the liquid ammonia storage tank system. Throughout the entire working time, no odor of ammonia was felt in the working environment, and the ammonia concentration in the working environment was less than 20 ppm (volume ratio).
The results of Example 1 are shown in Table 1.

In the conventional treatment method in which the ammonia gas remaining in the liquid ammonia storage tank is extracted using the internal pressure of the tank, and then industrial water is immediately put into the tank and extracted, until the worker can enter the tank. In addition, it was necessary to repeat the insertion and extraction of industrial water twice, 270 m ³ of industrial water was consumed, and the same amount of ammonia-containing water required for wastewater treatment was generated. Further, when diluting and discharging the generated ammonia-containing water, about 12,500 m ³ of diluted water and a corresponding time were required.
According to the method of the present invention, compared to the conventional method described above, the total treatment time is shortened, the amount of industrial water used is greatly reduced, ammonia-containing water required for wastewater treatment is not generated, and ammonia gas is reduced. All can be converted into harmless nitrogen gas and water.

  According to the method of the present invention, when checking or repairing a liquid ammonia storage tank, it is possible to efficiently treat the ammonia gas remaining in the liquid ammonia storage tank system, shorten the construction period, and suppress the generation of industrial waste. .

It is a process flow diagram of one mode of implementation of a method of the present invention. It is explanatory drawing of the one aspect | mode of the gas mixer used for the method of this invention. It is explanatory drawing of the one aspect | mode of the catalytic combustion apparatus used for this invention method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid ammonia storage tank 2 Evaporator 3 Accumulator 4 This equipment discharge piping 5 Ammonia processing piping 6 Flowmeter 7 Gas mixer 8 Catalytic combustion apparatus 9-18 Valve 19 Mixing piping 20 Damper 21 Damper 22 Blower 23 Heat exchanger 24 Electric heater 25 Catalyst tower

Claims (4)

  In the method of extracting and decomposing ammonia gas remaining in the liquid ammonia storage tank out of the tank, the ammonia gas extracted using the internal pressure of the tank is guided to a catalytic combustion apparatus having a catalyst tower and processed. An inert gas is injected into the reactor to dilute and flow out the remaining ammonia gas, and the effluent mixed gas is guided to a catalytic combustion apparatus having a catalyst tower for treatment, and the catalytic combustion apparatus for ammonia gas or the effluent mixed gas A method for treating residual gas in an ammonia tank, characterized in that the flow rate to the tank is adjusted by the temperature in the catalyst tower.   The method for treating residual gas in an ammonia tank according to claim 1, wherein ammonia gas or effluent gas mixture is mixed with air at the inlet of the catalytic combustion apparatus.   The method for treating residual gas in an ammonia tank according to claim 1, wherein the inert gas is nitrogen gas.   2. An ammonia tank according to claim 1, wherein an inert gas is injected into the tank to dilute and flow out the remaining ammonia gas, and then water is poured into the tank to recover the slightly remaining ammonia gas as ammonia water. Residual gas treatment method.

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