JPS6393B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved exhaust gas treatment method using a catalytic combustion method. Specifically, the present invention is a catalytic combustion method that completely oxidizes exhaust gas containing combustible organic compounds into harmless carbon dioxide and water through catalytic gas phase oxidation of exhaust gas discharged from paint factories, resin processing factories, etc. The present invention relates to an improved exhaust gas treatment method that can stably and efficiently make combustible compounds in the exhaust gas non-polluting despite changes in the concentration of the combustible compounds in the exhaust gas. Aromatic compounds such as benzene, toluene, and xylene, ketones such as acetone, alcohols such as ethanol, and even esters, which are contained in exhaust gas emitted from paint factories, adhesive processing plants, and other resin processing plants, Hydrocarbon compounds such as ethers are a cause of air pollution, and regulations on their emissions are becoming increasingly strict in recent years. If the concentration of these hydrocarbon compounds in exhaust gas is high enough, they may be recovered and reused by methods such as adsorption, but usually 5000 ppm
Because these hydrocarbon compounds are emitted at concentrations below (capacity), particularly 2000 ppm or less, recently these hydrocarbon compounds are often used by burning and recovering the generated heat. Among these, there is an exhaust gas treatment method using a catalytic combustion method, which is attracting attention as a method for removing harmful substances from exhaust gas in the recent resource and energy saving era. This method can be used if the exhaust gas to be treated contains combustible substances such as hydrocarbon compounds, and even if the concentration varies considerably, appropriate dilution is required taking into consideration the heat resistance of the equipment and catalyst. A gas (for example, air) is introduced and mixed, and the exhaust gas is supplied to a fixed bed type oxidation catalyst bed while controlling the temperature and flow rate of the exhaust gas, using a gas heater if necessary, to perform a complete oxidation reaction, This is a method in which heat is recovered from the heated reaction gas using a heat exchanger or the like. As a method to further improve the efficiency of heat recovery, a part of the high-temperature gas after treatment in the catalytic combustor is mixed directly with the raw material exhaust gas, raising the temperature of the raw material exhaust gas, and then supplying the raw material exhaust gas to the catalytic combustor again. has also been proposed (for example, see Platinum Metal Review, Vol. 2, p. 114 (1958)). This process eliminates the need for a large heat exchanger by simply satisfying the condition of increasing the amount of gas supplied to the catalytic combustor.
Moreover, there is an advantage that the efficiency of heating the raw material exhaust gas is ideally high. It has also become clear that by adopting this circulation method, it is possible to control the catalytic combustor inlet temperature extremely easily, which has been difficult in the past when the concentration of combustibles in the exhaust gas fluctuates widely. The present invention provides an improvement method for a catalytic combustion exhaust gas treatment method using such a gas circulation method, and in particular, the catalytic combustion reaction can be stably performed even when the concentration of combustible compounds contained in the exhaust gas fluctuates widely. To provide an exhaust gas treatment control method that is easy to operate and maintain safely. That is, the present invention was completed as a new and improved circulation method as a result of various studies aimed at improving the above-mentioned drawbacks. In particular, this method is adopted when the concentration of combustible substances in the exhaust gas is high and it is necessary to dilute it with diluent gas due to the heat resistance and safety of the catalyst and its filling device when burning it.It circulates the combustion heat of the exhaust gas. It has the advantage that it can be effectively used in a method, and is useful when the concentration of combustible substances fluctuates widely. Figure 1 shows the basic flow of this system, in which the exhaust gas is passed through the mixer, gas preheater, blower, and combustor in this order, and the exhaust gas supply line for circulation runs from the dilution gas supply line and the combustor outlet. is connected to the mixer, and a purge line is installed at the combustor outlet.In order to further control the processing conditions, the combustor inlet gas temperature or mixer outlet gas temperature is detected and the dilution gas supply amount is adjusted to control the combustor inlet temperature. The system is characterized in that it detects this and adjusts the amount of heating load on the gas preheater. In the method of the present invention, the installation of a mixer is particularly necessary in order to ensure uniform mixing of the exhaust gas, diluent gas, and circulating gas and to control the temperature at the mixer outlet. This is because if there is no mixer, the temperature in the gas tends to be non-uniform and sufficient control cannot be achieved. The combination of the gas preheater, the blower arrangement, and the control method of the present invention allows the blower suction gas temperature to be adjusted to a constant level even when the combustible substance concentration in the exhaust gas fluctuates widely, and therefore the amount of gas to be treated to be supplied is approximately constant. Therefore, the gas temperature at the combustor inlet is sufficiently uniform, allowing extremely good temperature control and combustion processing. Moreover, during this time, the amount of diluting gas is adjusted in accordance with the concentration of combustibles in the exhaust gas, and the amount of circulating gas (heat recovery) is also adjusted to perform the necessary heat recovery. If similar control was performed on the combustor inlet temperature in the arrangement of the blower gas preheater, when the concentration of combustibles in the exhaust gas is low,
In other words, when the gas preheater is in operation, the blower suction temperature fluctuates, and therefore the amount of gas to be treated changes, and the gas at the gas preheater outlet is not mixed sufficiently, so the combustor inlet temperature tends to become uneven, making it difficult to achieve satisfactory temperature control. It is not possible to carry out combustion treatment. Furthermore, when control is performed using the mixer outlet temperature, the temperature of the blower suction gas is kept constant, but the amount of heat consumed in the gas preheater increases, which is uneconomical. Hereinafter, embodiments of the present invention will be described based on the attached FIG. 1. The exhaust gases targeted by the present invention include paraffinic hydrocarbons such as methane, ethane, and butane; unsaturated hydrocarbons such as acetylene, ethylene, and propylene;
Naphthenic hydrocarbons such as cyclohexane, aromatic hydrocarbons such as benzene, toluene, and xylene, alcohol compounds such as methanol, ethanol, and butanol, ether compounds such as methyl ether, ethyl ether, and dioxane, and aldehydes such as formalin and acetaldehyde. compounds, ketone compounds such as acetone and methyl ethyl ketone, organic acids and their esters such as formic acid, acetic acid, and acrylic acid, as well as hydrocarbon compounds that are completely oxidized and rendered harmless by carbon dioxide gas and water, such as phenol and cresol. Preferably, those containing In addition, ammonia, hydrocyanic acid, acrylonitrile, aniline, pyridine, and other amines are not a problem as long as they are contained in small amounts, but when treating exhaust gas when they contain high concentrations, they may cause nitrogen oxides to be generated. Denitrification equipment may be required.
These exhaust gases are emitted from paint factories, resin processing factories, etc., as well as printing factories, ink and paint manufacturing factories, enamel wire and coil manufacturing factories, chemical factories, synthetic fiber factories,
Emitted by paper and pulp factories. A catalytic combustor is a fixed bed type complete oxidation catalyst, such as spherical, cylindrical, honeycomb, ribbon, etc.
It is formed into a shape such as a wire mesh, and is made by supporting active catalyst species such as platinum, copper, vanadium, or chromium on a carrier such as alumina, silica, silica-alumina, activated carbon, titanium oxide, silicon carbide, or heat-resistant metal. It has the ability to completely oxidize the above combustible compounds at a temperature of 150 to 400°C. The above exhaust gas is supplied to this combustor, but the oxidation reaction is an exothermic reaction, and for example, benzene, etc.
(by volume) If it is contained, the gas temperature will rise to over 100°C, and there is a risk that the temperature of the catalyst layer will rise too much and the catalyst activity will decrease. With this point in mind, the complete oxidation reaction is carried out by controlling the concentration (calorific value) of the gas passing through the catalyst layer. This reaction normally takes place at a space velocity of 10,000 to 100,000 hr ^-1 (STP), but with spherical or cylindrical catalysts, the space velocity is
30000hr ^-1 (STP), for honeycomb shaped catalysts etc.
Space velocities of 50,000 to 100,000 hr ^-1 (STP) are common. As shown in Fig. 1, the present invention connects a mixer, a gas preheater, a blower, and a catalytic combustor in series, circulates a part of the combustor outlet gas to the mixer, and purges the remaining gas. However, the mixer contains exhaust gas and diluent gas for combustion processing [temperature control of the raw material gas supplied to the combustor (mainly for cooling) and concentration control of the raw material gas (this is used in conjunction with circulating gas) ] is connected to the gas preheater, the combustor inlet temperature or mixer outlet gas temperature detection device is linked to the dilution gas supply valve, and the combustor inlet gas temperature detection device and the gas preheater are connected to each other. This is a control system for exhaust gas treatment that is linked to the fuel supply valve. According to the present invention, the temperature and combustible substance concentration of the raw material gas are controlled in the mixer.
The amount of heat used to raise the temperature comes from circulating gas from the combustor. When the temperature of the feed gas exceeds the rated range of the combustor inlet gas temperature (for example, exceeds 250°C), the dilution gas supply valve opens and dilution gas (usually air) at room temperature or lower enters the mixer. The amount of circulating gas is reduced accordingly. On the other hand, if simply circulating the combustor outlet gas is insufficient to raise the raw material gas temperature (for example, 150
℃)) The supply of diluent gas must be stopped and the temperature must be raised by a heater to the lowest rated temperature of the combustor inlet gas temperature. The blower should be operated at its rated capacity as much as possible during operation, and changes in air volume and gas temperature should be avoided as much as possible. The heater is activated when the combustor inlet gas temperature still does not reach the desired temperature even after maximizing the circulating gas amount and closing the dilution gas supply valve. Therefore, if a raw material gas containing sufficient combustible compounds can be prepared, the catalytic activity in the combustor can be maintained in a self-sustaining state, so there is no need to operate the heater. It is important to prepare a well-mixed raw material gas in a mixer. This is because by providing a region where the circulating gas supply amount and the diluent gas supply amount are simultaneously mixed with the exhaust gas, a good response can be achieved in terms of temperature control. If a mixing region as in the present invention is not provided by separately mixing the exhaust gas,
This is undesirable since the gas temperature up to the combustor inlet may be inaccurately detected. The operation of the method according to the invention is preferably set in accordance with the point in time when the maximum content of combustible substances in the exhaust gas to be treated is reached. This design condition makes it easy to control the temperature of the combustor inlet gas within the temperature range in which the catalyst works effectively and to operate the blower at its rated value. The mixer outlet gas temperature can be controlled. There is also the advantage that control followability is good even when the concentration of combustibles in exhaust gas fluctuates rapidly. Embodiments of the present invention will be described below. (Example 1) This is an example of a catalytic combustion device according to this method that processes exhaust gas amount of 50 Nm ³ /min (temperature 50° C., gas concentration fluctuates from 5000 to 0 ppm in terms of toluene, the rest is air). The maximum temperature at the combustor outlet was set at 550°C, taking into consideration factors such as the catalyst used, the durability of the equipment, heat resistance, fluctuations in gas concentration, and the amount of gas preheating. Therefore, the maximum amount of dilution air (at 20°C) required was approximately 12Nm ³ /min, and the amount of circulating gas was approximately 42Nm ³ /min. The combustor inlet gas temperature was set at 250°C. Under these conditions, the maximum temperature rise in the combustor is 300°C and the amount of gas to be treated passing through is approximately 104 Nm ³ /min. The maintenance control of the combustor inlet temperature (or mixer outlet temperature) was decided to be performed by adjusting the amount of dilution air (adjusting the amount of circulating gas) and the heating load amount of the propane gas ignition combustion type gas preheater. The combustor was filled with platinum-supported alumina as a catalyst. In this way, the exhaust gas was combusted, and despite the fluctuations in the exhaust gas concentration, the combustor inlet temperature and the amount of gas to be treated were controlled to be approximately constant, achieving sufficient combustion efficiency and effective heat recovery. The table below shows the relationship between exhaust gas conditions and operating conditions.

[Table] In this example, the treatment equipment self-combusts until the concentration of combustibles in the exhaust gas reaches 3078 ppm, and the heat consumption in the gas preheater is 0.
It can be seen that the amount of heat for gas preheating is entirely supplied from the circulating gas. The values shown in this example are the results under the above conditions. For example, if the combustor inlet temperature is set to 300℃, the amount of gas to be treated will be
It was found that the minimum combustibles concentration was 125Nm ³ /min and did not require heating with a gas preheater, and was 2660ppm.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing one example of an embodiment of the present invention. In the figure, 1 is a mixer, 2 is a gas preheater, 3 is a blower, and 4 is a combustor.

Claims (1)

[Scope of Claims] 1. In an exhaust gas treatment method using a catalytic combustion method in which exhaust gas containing combustible organic compounds is oxidized in a catalytic gas phase to render the combustibles harmless, the exhaust gas is processed into a mixer, a gas preheater, a blower and a combustion chamber. 1. A method for treating exhaust gas, characterized in that the diluent gas and a part of the high-temperature gas from the outlet of the combustor are supplied to a mixer. 2. The method according to claim 1, wherein the combustor inlet gas temperature or the mixer outlet gas temperature is detected to control the dilution gas supply amount and the gas preheater heating load amount.