JPS58241A - Production of inert gas by catalytic combustion - Google Patents

Abstract

PURPOSE:To produce an inert gas while recovering heat energy with good efficiency in plural catalytic burners provided with catalysts by repeating catalytic combustion wherein the concn. of fuel is kept out of the explosion limit. CONSTITUTION:Plural catalytic burners A-C provided with catalysts are provided. First, a gaseous mixture of an oxygen-contg. gas and fuel is subjected to flameless combustion out of the explosion limit, and after heat exchanging, the waste combustion gas is fed to the catalytic combustion device of the next stage where it is mixed with fuel to the concn. outside the explosion limit in the same manner and is subjected to flameless combustion. In this way, the amts. of the oxygen contained are decreased successively and the inert gas is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an inert gas by catalytic combustion, which makes it possible to utilize combustion gas as a high-quality inert gas while efficiently recovering thermal energy.

In power generation plants that use gaseous fuels such as LPG, in order to prevent pollution caused by nitrogen oxides contained in the exhaust combustion gas, it is necessary to extract the combustion gas as an inert gas (secondly, to prevent heat generation). There is an idea to use nitrogen in the air to produce inert gas, which is in high demand while also obtaining energy.

However, the current combustion method using a burner, i.e., gaseous fuel such as LPG, LNG, naphtha, kerosene, liquefied coal, etc., is a fuel that becomes gaseous when used, but the fuel concentration is within the explosive limit, that is, flammable combustion occurs. By mixing it with air and burning it to obtain combustion gas while obtaining the required thermal energy, not only can it not be used as an inert gas, but it is also possible to avoid a decrease in efficiency when recovering thermal energy. I can't. In other words, when flaming combustion is carried out as described above, as is well known, the temperature of the flame is not uniform and locally high-temperature areas occur, resulting in a large amount of nitrogen oxides being produced from the oxygen and nitrogen in the air. generated. In addition, if the oxygen concentration in the combustion gas is reduced (for example, less than 1) in an attempt to reduce the content of oxygen, which is an impurity, combustion will occur, resulting in incomplete combustion and the remaining hydrocarbons. At the same time, it also leads to the production of carbon monoxide and hydrogen, which are incomplete combustion products. Therefore, for example, when LPG is used as fuel, the composition of the combustion gas is as shown in Table 1 below.
Table 2 In this case, it is difficult to use combustion gas as an inert gas. Therefore, attempts have been made to remove water-soluble gases such as carbon monoxide by passing the combustion gas through water.
However, it is still far from being used as an inert gas. In addition, in the method using a burner, it is difficult to adjust the combustion gas temperature without causing incomplete combustion. Therefore, it is difficult to obtain combustion gas at the required temperature and recover thermal energy at the required temperature, and a decrease in thermal efficiency cannot be avoided.

The present invention provides a manufacturing method that can efficiently recover thermal energy at the required temperature from combustion gas while extracting combustion exhaust gas as an inert gas containing little impurity gas such as oxygen, thereby preventing pollution based on nitrogen oxides, etc. This design allows for effective use of thermal energy. Next, the details will be explained using the drawings.

The features of the present invention are as follows. The first method is to set the fuel concentration outside the explosion limit (the explosion limit is sometimes called the flammability limit, and according to this expression, it is within the flammability limit in the case of the burner method), and to conduct catalytic combustion using a catalyst. The first feature is that it is passed through an apparatus and burned at a high enough temperature, for example, 1000° C. or higher, to promote the oxidation reaction. Second, multiple stages of catalytic combustion equipment are installed,
The second stage is characterized by the fact that fuel is mixed with the combustion exhaust gas from the previous stage and the same catalytic combustion is repeated repeatedly, thereby achieving the following effects and converting thermal energy. This makes it possible to extract inert gas with less impurity gas while efficiently recovering it. The first is combustion that facilitates the production of nitrogen oxides, such as flaming combustion using a burner, by setting the fuel concentration outside the explosive limit and causing flameless combustion at a high temperature, for example, 1000°C or higher, through contact with a catalyst. This prevents the formation of an environment and suppresses the production of nitrogen oxides. Secondly, in catalytic combustion, the catalytic combustion temperature can be easily adjusted by adjusting the mixture ratio of air and fuel.

Therefore, by using catalytic combustion, it is possible to obtain combustion gas at the required temperature and recover thermal energy at the required temperature without causing incomplete combustion as in the burner method, improving the thermal efficiency. High-temperature combustion (= more incomplete combustion that suppresses the remaining unburned hydrocarbons and the generation of impurity gases such as carbon monoxide and hydrogen. Thirdly, multiple catalytic combustion devices are used. By mixing fuel into the combustion exhaust gas of the first stage and repeatedly performing flameless combustion at high temperature, the combustion exhaust gas with an amount of oxygen less than the amount of oxygen in the air consumed in the first stage combustion is used to generate the next combustion. The catalytic combustion of one stage is carried out, and the catalytic combustion of the next stage is carried out using a combustion exhaust gas with an even smaller amount of oxygen, thereby reducing the amount of oxygen in the combustion exhaust gas that is finally used as an inert gas. In addition to this, unburned components are combusted by repeated combustion of the flue gas, thereby obtaining an inert gas with few impurities. In other words, when fuel is supplied so that all the oxygen contained in the air is consumed by one catalytic combustion device, the inside of the combustion device becomes too high and is damaged, and at the same time, the catalyst becomes unable to withstand the temperature. When the fuel concentration is within the explosive limit, flame combustion occurs and combustion products such as nitrogen oxides are produced, but if the combustion exhaust gas from the previous stage is used for repeated combustion, the various evils mentioned above can be avoided. This has the effect of overcoming the above conditions and bringing the amount of oxygen and other impurities in the combustion gas used as an inert gas close to zero.Table 2 shows the combustion exhaust gas obtained by three-stage catalytic combustion using LPG as fuel. As is clear from Table 1, carbon dioxide and water only increase slightly, while oxygen and other impurity gases decrease to zero or to a large extent, which is sufficient as an inert gas. It shows that it is available.

Next, the present invention will be specifically explained using the embodiment diagram shown in FIG. In FIG. 1, A is the first catalytic combustion device, (1)
In the first mixer, the fuel is completely mixed with the fuel fed by the blower (la) through the air introduction pipe (lb) so that the concentration is outside the explosion limit. In this case, it is desirable to preheat the catalytic combustion, and it is preferable to use, for example, a heat exchanger as described below as the heat source. In this case, if the preheating temperature exceeds 600°C, the local fuel concentration will reach the explosive limit and combustion products such as nitrogen oxides will be produced, so it is desirable to keep the preheating temperature below 600°C. (2) is the first catalytic combustor, which has a built-in catalyst with a lattice-like cross section, as shown in the cross-sectional view in Fig. 2, and when the preheated air-fuel mixture passes through this, flameless catalytic combustion occurs. and the combustion takes place at a temperature of 1000°C or higher. (3) is the first heat exchange air, which recovers thermal energy from the combustion gas. B is a second catalytic combustion device, and (4) is its second mixer, which makes the combustion gas that has passed through the first heat exchanger (3) and the fuel that flows through the fuel introduction pipe (4C) out of the explosion limit. The mixture is mixed in such a way that the temperature of the mixture is 600° C. or less, and the first heat exchanger (8) is used to adjust the temperature of the mixture. (5) is a second catalytic combustor, and (6) is a second heat exchanger, which recovers the thermal energy of the combustion gas obtained by catalytic combustion.

C is the third catalytic combustion device, and (7) is the third mixer, which mixes the fuel from the fuel introduction pipe (7a) and the combustion exhaust gas that has passed through the second heat exchanger (6) in the preceding stage so that it is outside the explosion limit. A second heat exchanger (6) to mix and maintain the temperature below 600°C.
Adjust with. (8) is the 8th catalytic combustor, (9) is the 8th catalytic combustor
In the heat exchanger, the combustion gas is sent to the take-off pipe Ql.

As is clear from the above description, according to the present invention, inert gas at a required temperature can be easily obtained, and thermal energy at a required temperature can be easily recovered.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of an embodiment of the present invention, and FIG. 2 is a sectional view showing an example of a catalyst. A...First catalytic combustion device, (1)...First mixer, (la)...Air blower 1 (1b)...
・Air introduction pipe, (lc)...Fuel introduction pipe, (2)
...first contact combustor, (3)--first heat exchanger,
B...Second contact combustor, (4)...Second mixer, (4a)...Fuel introduction pipe, (5)...
Second contact combustor, (6)...Second heat exchanger, C.
...Eighth catalytic combustion device, (7)...Eighth mixer, (7a)...Fuel introduction pipe, (8)...Third
Contact combustor, (9)...8th heat exchanger, α1...
...Inert gas extraction pipe. Patent applicant: Patent attorney, Central Research Institute of Electric Power Industry, Otsuka, 1 external person

Claims (1)

[Claims] A plurality of stages of catalytic combustion devices equipped with catalysts are installed, and each of the second and subsequent stages of catalytic combustion devices performs flameless combustion using a mixture of fuel mixed with the combustion exhaust gas of the previous stage so as to be outside the explosion limit. A method for producing an inert gas by catalytic combustion, characterized in that the steps are performed sequentially to gradually reduce the amount of oxygen contained in the combustion exhaust gas, so that the combustion exhaust gas can be extracted as an inert gas containing a small amount of oxygen.