JPH0114806B2 - - Google Patents

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, the combustion gas can be extracted as an inert gas.
There is an idea to use nitrogen in the air to produce inert gas, which is in high demand, while obtaining heat energy. However, the current combustion method using a burner, i.e. gaseous fuel such as LPG, LNG, naphtha, etc.
Fuels that are in a gaseous state during use, such as kerosene and liquefied coal, are mixed with air and burned so that the fuel concentration is within the explosive limit, that is, flammable combustion occurs, and the combustion gas is produced while obtaining the required thermal energy. In the method of obtaining , not only cannot it be used as an inert gas, but it is also impossible to avoid a decrease in efficiency in recovering thermal energy. That is, in the case of flaming combustion as described above, as is well known, the temperature of the flame is not uniform and locally high temperature areas are generated.
Large amounts of nitrogen oxides are produced from oxygen and nitrogen in the air. In addition, if the oxygen concentration in the combustion gas is reduced (for example, 1% or less) in an attempt to reduce the content of oxygen, which is an impurity, combustion is performed, incomplete combustion may occur, resulting in residual hydrocarbons. At the same time, incomplete combustion products such as carbon monoxide and hydrogen are produced. Therefore, for example, when LPG is used as fuel, the composition of the combustion gas is as shown in Table 1 below.

【table】

【table】

[Table] At this rate, it is difficult to use combustion gas as an inert gas. For example, attempts have been made to pass this combustion gas through water to remove water-soluble gases such as carbon monoxide, but this method is still far from being useful 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. The second feature is that catalytic combustion devices are installed in multiple stages, and in the second stage, fuel is mixed with the combustion exhaust gas from the previous stage to repeatedly perform catalytic combustion in the same manner. This system is designed to provide the desired effect and to extract inert gas with less impurity gas while efficiently recovering thermal energy. That is, the first is that by keeping the fuel concentration outside the explosive limit and contacting the catalyst,
By performing flameless combustion at a high temperature, for example, 1000°C or higher, it is possible to prevent the creation of a combustion environment where nitrogen oxides are easily produced, as in the case of flaming combustion using the burner, and to suppress the production of nitrogen oxides. This is what I did. 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 thermal efficiency. The high-temperature combustion suppresses the remaining unburned hydrocarbons and the generation of impure gases such as carbon monoxide and hydrogen due to incomplete combustion. Thirdly, by using multiple catalytic combustion devices and mixing fuel into the combustion exhaust gas from the first stage to repeatedly perform flameless combustion at high temperatures, the amount of oxygen in the air consumed by the first stage combustion can be reduced. The next stage of catalytic combustion is performed using a combustion exhaust gas with a smaller amount of oxygen, and the next stage of catalytic combustion is performed using a combustion exhaust gas with an even smaller amount of oxygen,
This is designed to bring the amount of oxygen in the combustion exhaust gas, which is ultimately used as an inert gas, close to zero. In addition to this, unburned components are combusted by repeated combustion of the combustion exhaust gas, thereby obtaining an inert gas with less 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 falls within the explosive limit, flame combustion occurs and combustion products such as nitrogen oxides are produced. However, if the combustion exhaust gas from the previous stage is used for repeated combustion, various adverse conditions such as those mentioned above can be avoided. This has the effect of overcoming this and bringing the amount of oxygen and other impurities in the combustion gas used as an inert gas close to zero. Table 2 shows an example of the composition of combustion exhaust gas obtained by three-stage catalytic combustion using LPG as fuel.As is clear from Table 1, carbon dioxide and water only slightly increase. Oxygen and other impurity gases are reduced to zero or significantly, indicating that they can be fully utilized as inert gases. Next, the present invention will be specifically explained using the embodiment diagram shown in FIG. In FIG. 1, A is a first catalytic combustion device, and 1 is its first mixer, which completely mixes the fuel fed by a blower 1a through an air introduction pipe 1b 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 fuel concentration will locally fall within the explosion limit and produce twisting products such as nitrogen oxides, so it is desirable to keep the preheating temperature below 600°C. Reference numeral 2 denotes a first catalytic combustor, which has a built-in catalyst with a lattice-like cross section, as shown in the cross-sectional view of FIG. 2, and flameless catalytic combustion occurs when the preheated mixture passes through this. , and combustion takes place at a temperature of 1000℃ or higher. 3 is the first heat exchange gas, which recovers thermal energy from the combustion gas. B is a second catalytic combustion device, and 4 is its second mixer, which mixes the combustion gas that has passed through the first heat exchanger 3 and the fuel from the fuel inlet pipe 4c so as to be outside the explosion limit; The first heat exchanger 3 adjusts the air-fuel mixture to a temperature of 600°C or less. 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, 7 is a third mixer and a fuel introduction pipe 7a
The fuel produced by
The second heat exchanger 6 adjusts the temperature to 600°C or less. 8 is a third contact combustor, 9 is a third heat exchanger, and the combustion gas thereof is sent to an extraction pipe 10. 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 drawings]

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,
1a...Air blower, 1b...Air introduction pipe, 1
c... Fuel introduction pipe, 2... First contact combustor, 3...
...First heat exchanger, B...Second catalytic combustor, 4...
Second mixer, 4a...Fuel introduction pipe, 5...Second catalytic combustor, 6...Second heat exchanger, C...Third catalytic combustion device, 7...Third mixer, 7a... Fuel introduction pipe, 8...Third contact combustor, 9...Third heat exchanger, 10...Inert gas extraction pipe.

Claims (1)

[Claims] 1 Multiple stages of catalytic combustion devices equipped with catalysts are provided, and a mixture of oxygen-containing gas and fuel is passed through the first stage catalytic combustion device so that the fuel concentration is outside the explosive limit, and flameless combustion is performed. In each of the following catalytic combustion devices, flameless combustion is performed sequentially using a mixture of fuel mixed with the combustion exhaust gas in the previous stage so that it is outside the explosion limit, and the amount of oxygen contained in the combustion exhaust gas is gradually reduced. A method for producing an inert gas by catalytic combustion, characterized in that it can be extracted as an inert gas with a low oxygen content.