JPS6291408A - Method for dioxidizing oxygen-containing gaseous nitrogen - Google Patents

Abstract

PURPOSE:To obtain high-purity nitrogen with a simple device while conserving energy by mixing hydrogen into such low-purity nitrogen as obtained from air by a PSA method, burning the mixture in a catalytic combustor, cooling the combustion gas which is then passed through a dehumidification tower, and utilizing the heat retained by the combustion gas for the regeneration of the dehumidification tower. CONSTITUTION:Hydrogen is supplied as fuel into raw oxygen-contg. gaseous nitrogen (e.g., 90-98% purity) and the mixture is burned in the catalytic combustor. Then the outlet gas from the catalytic combustor is cooled to condense and separate water, then the gas contg. moisture remaining as saturated steam is passed through at least one of the two dehumidification towers and dehumidified, and gaseous nitrogen having an extremely low content of oxygen and moisture (e.g., 95-99% purity) is obtained. Meanwhile, raw oxygen-contg. gaseous nitrogen which is heated by the heat exchanger with the outlet gas from the catalytic combustor is supplied to the other dehumidification tower which is used in dehumidification and absorbs moisture to regenerate the dehumidification tower. The raw gas used in the regeneration and contg. oxygen is cooled to condense and separate water and used as raw gas.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for removing oxygen from nitrogen gas containing some oxygen, and in particular to a method for removing oxygen from air.
e 8wing Adsorption) to high purity (90-98%) nitrogen, such as that obtained by
95-99.9%).

(Prior Art) Conventionally, nitrogen (Nz) gas has been widely used as an inert gas for purging in equipment used in, for example, chemical factories.

Conventionally, one gas as this inert gas is high purity N (99.9% to 99.9
99%), the technology is well established, and the industrial results are too numerous to mention. However, the biggest drawback is the high equipment and running costs.

In addition, by completely burning hydrocarbons such as natural gas, naphtha, and kerosene in air, oxygen in the air is extinguished, and carbon dioxide gas (Cow) in the combustion exhaust gas is converted to CO using a wet absorption method.
There is also a method of removing , and finally removing +21 and leaving N and Ar. Although this method is cheaper to produce inert gas than the deep cooling method, it is not used much because of problems with the complete combustion technology.

Furthermore, the PSA method (Pres
Sure Swing Adsorption)
A method is being developed that uses air as a raw material and adsorbents specific to each manufacturer, such as oxygen-adsorbing adsorbents, to adsorb 02 in the air and convert the remaining gas into N and Ar. , the device is small and has little experience. The purity of product N2, which is stated in the mold list, is currently 95-99%. However, although this method technically can be concentrated to about 99% as an inert gas, the rate of acceleration increases as N (approximately 78%) and Ar (approximately 1%) in the air are concentrated. Separation efficiency also deteriorates, and the amount of adsorbent used also increases. Inefficiency means that a large amount of air is required to absorb the same amount of N. For example, the theoretical amount of air required to separate 1 m3 of N2+Ar is , but if high concentration is attempted, η will be on the order of 5 to 10.

Although air is phaseless, it is necessary to compress a large amount of air to dehumidify and remove carbon dioxide gas from the air before passing it through the adsorbent. Therefore, the current PSA method can compete with the cryogenic method (not suitable for small scales) for small-scale products, but when it comes to industrial scale (not clear, but 500 N"/T (or more)), it becomes uneconomical. However, the f# wire manufacturing purity of N in the PSA method is 95.
If it can be folded at ~98%, manufacturing costs will drop rapidly. However, in this case, there is a lot of residual oxygen, which limits the scope of use and reduces versatility.

(Problems to be Solved by the Invention) The present invention deals with N, gas (including Ar) obtained by the PSA method.
Gas) purity as mentioned above? In order to eliminate the drawback that manufacturing costs are low if it is around 5 to 98%, but if you try to achieve higher purity, the manufacturing costs will increase.
Purity 95-98%N.

Focusing on gas, the present invention aims to provide a method for deoxidizing N and gas at low cost.

(Another means to solve the problem) The present invention mixes hydrogen as a fuel into raw nitrogen gas containing oxygen, burns it in a catalytic combustor, cools the exit gas of the catalytic combustor, and condenses and separates moisture. After that, the gas containing moisture remaining as saturated steam is dehumidified by passing it through one of at least two dehumidification towers to obtain a gas with extremely low oxygen and moisture content. The other dehumidification tower is regenerated by supplying raw nitrogen gas containing oxygen heated by heat exchange with the catalytic combustor outlet gas, and the oxygen used for the regeneration is regenerated. This is a method for deoxidizing an oxygen-containing nitrogen gas, characterized in that the raw material gas containing is cooled and water is condensed and separated, and then used as a raw nitrogen gas.

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIG.

In Figure 1, an apparatus for separating nitrogen from air (e.g., a P
Nitrogen separation device by SA method) The nitrogen gas obtained in 1 contains some oxygen.

The raw material N2 gas containing oxygen has a pressure, which is caused by the valves 2 and 3.
．． When opening 4, the catalytic combustor 5 passes through the combustion mixer 7.
In order to combust the externally introduced oxygen, hydrogen passes through a valve 6 and is mixed with raw material N and gas in a fuel mixer 7, and then introduced into a catalytic combustor 5. The amount of hydrogen used as fuel is only required to combust the oxygen in the raw material Nt gas. That is, water is produced by reacting with oxygen+dhydrogen in the feed gas on the catalyst and burning, and the oxygen disappears.

As the catalyst of this catalytic combustor 5, a palladium-based catalyst is generally used. Combustion heat is generated in the catalyst layer in the catalytic combustor 5. This calorific value corresponds to a temperature rise of approximately 150 to 170° C. per 1% oxygen content in the raw material N and gas.

That is, if the allowable temperature limit of the catalyst is T°C, and the inlet temperature of the catalytic combustor 5 is t°C, then the oxygen content in the raw material N2 gas is T-
The limit of combustion is determined by t.

However, if the oxygen content exceeds the heat resistance temperature of the catalyst due to combustion of oxygen in the raw material N2 gas, a large number of cooling pipes are inserted into the catalytic packed bed of the catalytic combustor 5 to remove heat. Just do it.

The high temperature gas that does not contain oxygen leaving the catalytic combustor 5 is the first
In the heat exchanger 8, the raw material N containing oxygen is cooled by gas, and then in the second heat exchanger 9, it is brought to room temperature (10 to 45
℃).

During this cooling process, the moisture contained in the outlet gas of the heating pot 5 is removed, except for the moisture remaining in the form of saturated steam.
Condenses as droplets. The condensed water generated here is discharged to the outside of the system by the first separator 10.

The gas containing saturated water vapor that has exited the first separator 10 is then led to a dehumidifier (A') 11 in the adsorption process to remove moisture from the gas.
Completely remove by adsorption. In order to perform dehumidification continuously, multiple dehumidifiers are installed, and after moisture is removed from the oxygen-free gas and the moisture in the dehumidifier becomes saturated, the dehumidifier (A) 11 is connected to another dehumidifier ( B) Switch to 12.

The desiccant is filled with a substance that adsorbs water well, such as synthetic zeolite, activated alumina, or silica alumina gel.

Now, assuming that there are two dehumidifiers, one of the two dehumidifiers (A) is used for adsorption operation to adsorb moisture in the gas, while the other dehumidifier (B) 12 performs an operation to regenerate the desiccant that has already adsorbed moisture.

To regenerate the desiccant, (a) temperature swing adsorption (temperature swing adsorption that changes the intensity without changing the pressure) is used.
Swing Adsorption) law and (b
) There is a pressure swing adsorption method that changes the pressure without changing the temperature, but in the present invention, the former is adopted in order to effectively use the combustion heat from the catalytic combustor 5 as a regeneration heat source for the adsorbent. .

The temperature swing method requires hot gas to regenerate the desiccant. Raw material N containing oxygen in this gas source! using the gas itself,
This is heated to the temperature required for regeneration by exchanging heat with the high temperature gas discharged from the catalytic combustor 5 via the first heat exchanger 8.

The heated oxygen-containing raw material N2 gas passes through the valve 3 and enters the dehumidifier (
B) 12 to release moisture adsorbed by the desiccant.

Dehumidifier - (B) High temperature raw material N2 containing moisture coming out of 12
The gas is passed through the valve 4 by the third heat exchanger 13
0-45°C).

This cooling causes some moisture in the gas to condense, so the condensed water is separated by the second separator 14 and discharged to the outside of the system.

After the regeneration process of the dehumidifier (B) 12 is completed, it is necessary to cool the dehumidifier (B) 12 which is in a high temperature state in preparation for the next adsorption process. This cooling is performed by opening the valve 15 and closing the valve 2, so that the raw material N2 gas containing oxygen is transferred to the first heat exchanger 8.
The dehumidifier (B) 12 is cooled by flowing directly to the dehumidifier (B) 1.2 without passing through the dehumidifier (B) 1.2.

Once the dehumidifier (B) 12 has been cooled, the valves 17 and 18 are already closed, and by opening the valve 16 and then closing the valve 3.4, the raw material N2 gas containing oxygen is transferred to the dehumidifier (B) 12. Without passing through, valve 15. It flows directly to the catalytic combustor 5 via the valve 16 and the fuel mixer 7, and the dehumidifier (B) 12 is isolated from the system.

In FIG. 1, the route of the raw material N and gas containing oxygen to the fuel mixer 7 via the second separator 14 is shown by a solid line, but as shown by the dotted line, There is no need to go through valve 14; the point is to go through valve 15. The raw material N2 gas entering the system via the valve 16 may pass through the fuel mixer 7.

At this time, since the dehumidifier (B) 12 is filled with gas containing oxygen, the pressure is then reduced to atmospheric pressure by the valve 19, thereby releasing the gas containing oxygen in the dehumidifier 12. After this, valve 19 is closed.

By repeating this operation, the oxygen concentration remaining in the dehumidifier (B) 12 can be lowered.

Next, the valve 17 is opened, and a gas containing neither oxygen nor moisture, ie, product gas, is introduced into the dehumidifier (B) 12 and pressurized in the operating pressure trench, and then the valve 17 is closed. Subsequently, the gas in the dehumidifier (B) 12 is released to atmospheric pressure again by the valve 19, and the valve 19 is closed. This operation is called pressurized purge.

The number of pressurized purges is determined by the allowable oxygen concentration in the product gas. When the oxygen in the dehumidifier (B) 12 becomes sufficiently low, open the valve 18 and turn off the dehumidifier (B).
) 12 to equalize the pressure.

At this time, the more the number of pressurized purges increases, the more the dehumidifier (B) 12
The oxygen concentration within will decrease.

Once the regeneration is completed, the dehumidifier (B) 12 is then switched to adsorption operation. The operation is to open valve 17 and then open valve 2.
By closing 0.21, the dehumidifier (8) 11, which was currently in the process of dehumidifying the gas, is disconnected from the flow and subsequently switched to the regeneration process. The dehumidifier (A) 11 is regenerated in the same manner as the dehumidifier (B) 12 described above.

The gas exiting the dehumidifier (B) 12 has been sufficiently dehumidified and is nitrogen gas with almost no oxygen.

Each line in FIG.
0 kg/csa", which indicates the temperature of the oxygen-containing raw material gas at a temperature of 30°C. However, if the dehumidifier (A) 11 is in the dehumidification process,
This is a case where the dehumidifier (B) 12 is performing a regeneration process.

〔Effect of the invention〕

1. A small amount of oxygen, an impurity contained in nitrogen gas separated from air by the PSA method, can be removed with a simple device.

2. In the deoxidation method of the present invention, it is combined with a dehumidifier, but the raw material gas containing oxygen is used as the regeneration gas source without introducing any special gas from another, and oxygen is used as the regeneration heat source. This is an energy-saving process by using the combustion heat from combustion.

[Brief explanation of drawings]

FIG. 1 shows the flow of a method for deoxidizing oxygen-containing nitrogen gas as an embodiment of the present invention. Sub-Agents 1) Meifuku Agent Ryo Hagiwara - Sub-Agent Atsushi Anzai November 72, 1985

Claims (1)

[Claims] Hydrogen as a fuel is mixed into raw material nitrogen gas containing oxygen, combusted in a catalytic combustor, and the gas at the outlet of the catalytic combustor is cooled to condense and separate moisture, and then the remaining moisture-containing gas is converted into saturated steam. The gas is dehumidified through one of the at least two dehumidification towers to obtain a gas with extremely low oxygen and moisture content, while the other dehumidification tower used for dehumidification and adsorbing moisture contains the catalytic combustion regenerating the dehumidification tower by supplying raw material nitrogen gas containing oxygen heated by heat exchange with the outlet gas;
A method for deoxidizing an oxygen-containing nitrogen gas, characterized in that the oxygen-containing raw material gas used for the regeneration is cooled and moisture is condensed and separated, and then used as a raw nitrogen gas.