CN101149147A - Dispersion Combustion Method for Fully Premixed Natural Gas Catalytic Combustion Device - Google Patents

Abstract

A fully premixed catalytic combustion device dispersion combustion method that integrates the advantages of staged combustion, non-directional radiation heat transfer of catalytic body and large flame directional radiation heat transfer technology. The invention includes a premixing chamber, a support plate with uniform holes and a medium-temperature honeycomb catalytic body. All the natural gas and air are passed into the premixing chamber, the wall temperature of the gas phase space downstream of the catalytic body is >800°C, the temperature of the catalytic body is 600-1000°C, the thickness of the catalytic body is 25-50mm and the time for the premixed gas to flow through the catalytic body is <0.1s, supply 2~ 3.75 times the air required for theoretical combustion. The proportion of gas consumed by catalytic combustion is proportional to the air supply. The temperature of the premixed gas flowing out of the catalytic body is >800°C and the oxygen concentration is <15%. The invention is simple and safe, with thermal efficiency > 98%, CO emission < 600ppm, and _NOx emission < 25ppm. Catalytic combustion boilers and kilns that burn natural gas or methane-rich gas can use the present invention.

Description

Dispersion Combustion Method for Fully Premixed Natural Gas Catalytic Combustion Device

technical field

The invention relates to a method for enlarging the flame volume of a fully premixed catalytic combustion device based on the principle of staged combustion, strengthening the non-directional radiation heat transfer of the catalytic body and the directional radiation heat transfer of the large flame in the gas phase space, which has safe and stable combustion, high efficiency and energy saving, and high combustion efficiency. Efficiency, low CO and _NOx emissions and other advantages, suitable for various industrial or civil catalytic combustion boilers or heating devices, high-temperature industrial furnaces and kilns that use natural gas or methane-rich gas for the purpose of energy saving and emission reduction.

Background technique

In the process of conventional flame combustion, the global warming effect and _NOx emission caused by _CO2 emission make the sustainable development of human beings face a severe test. According to statistics in 2003, my country's GDP only accounts for about 4% of the world's total, but its oil consumption accounts for about 7.4% of the world's total, and its coal consumption accounts for 31% of the world's total. In the next decade or so, China's domestic demand for coal will increase by about 9-10×10 ⁹ t. China's energy consumption accounts for 8-9% of the world, CO ₂ emissions rank second in the world, and NO _x emissions are 48% of Asia's. my country's high-temperature furnaces are the largest source of pollution that causes damage to the ecological environment. Smoke and dust emissions from large and medium-sized industrial kilns mostly exceed the standard, among which coal-fired furnaces are the most serious. The second is that _NOx emissions are also high, and even oil-fired stoves surpass coal-fired stoves. The reason is that the fuel is mainly heavy oil and the control level of excess air is low. The pollution discharge situation of kilns in the whole country is basically the same. Since the furnace temperature of most kilns is very high, the trend of _NOx rises sharply. There are more than 6,000 power generation boilers in the Ministry of Electric Power, thermal power plants in various provinces and cities, self-provided power plants in large enterprises, and recovery boilers in paper mills. There are nearly 1×10 ⁶ civil, industrial and domestic boilers below 20t/h in the country. Large-scale utilization of natural gas has become an important measure to improve my country's energy structure. After the use of natural gas instead of solid fuel coal, the atmospheric environment has been effectively improved, but there are still some important problems in the process of natural gas utilization. The vast majority of conventional boilers are based on the principle of non-premixed diffusion combustion. Before entering the furnace, the fuel and air are not mixed. After entering the furnace, the fuel and air are mixed and burned to form a flame visible to the naked eye. The size of the flame is small, the average temperature of the flame is not high, and the thermal efficiency of the device is not high; there is a local high temperature zone in the furnace, and the residence time of the mixture of fuel and air in the high temperature zone is very short, and the mixing of air and fuel is not sufficient, and the combustion reaction is not complete; The local high temperature zone creates conditions for the generation of NO _x , and the emission of NO _x is relatively high.

As a new type of combustion, catalytic combustion has multiple technical advantages: it can be used in a large range of gas ratio; it can reduce the activation energy of combustion reaction from the conventional level (100-200kJ/mol) to a lower level (40-80kJ/mol). /mol), the light-off temperature is reduced, the combustion is easy to reach and stable, and even after the light-off temperature is reached, the oxidation reaction can be completed without external heat transfer; it is beneficial to control _NOx emissions; the combustion reaction is complete; the temperature of the combustion plate is maintained at 1000 °C Level, significant thermal effect; no secondary pollution, low noise and moderate combustion. When the air is preheated to 1000°C and the oxygen volume concentration is reduced to less than 15% (diffuse combustion), it has new characteristics: blue or colorless flames appear, the flame volume expands, the flame peak temperature decreases, the temperature distribution is uniform, and the combustion temperature As the overall level increases, the heat release intensity of combustion decreases. The application of low-oxygen diffuse combustion in China's iron and steel industry has achieved good results such as energy-saving efficiency higher than 30%, and NO _x emission of 30-50ppm. Therefore, integrating the key technologies of catalytic combustion and low-oxygen diffuse combustion, overcoming the shortcomings of traditional flame combustion, and developing natural gas combustion technology with high efficiency, energy saving, and low _NOx and CO emissions will have significant environmental, economic, and social benefits.

Contents of the invention

In order to overcome the shortcomings of traditional flame combustion such as yellow flame, low thermal efficiency, and high CO and _NOx emissions, the present invention integrates catalytic combustion, diffuse combustion, staged combustion, non-directional radiation heat transfer and gas phase Taking advantage of technical advantages such as directional radiation heat transfer of a large space flame, a method for the dispersion combustion organization of a fully premixed natural gas catalytic combustion device is proposed.

The catalytic combustion device includes a premixing chamber, a uniform-porous support plate and a honeycomb medium-temperature catalytic body. All the gas and air are passed into the premixing chamber. The supporting plate forms the top wall of the premixing chamber. The catalytic body is placed on the supporting plate and the two The axes of the airflow passages are coincident.

When using the above device, feed all the fuel into the downstream of the catalytic body, set a 25-50mm thick catalytic body, the time for the premixed gas to flow through the catalytic body does not exceed 0.1s, supply 2-3.75 times the air required for theoretical combustion, and control the temperature of the catalytic body at In the range of 600-1000°C, the temperature of the wall surface of the gas phase space downstream of the catalytic body is adjusted to be above 800°C.

When the above-mentioned technical means are complete, the temperature of the premixed gas flowing out of the catalytic body is higher than 800°C and the oxygen concentration is lower than 15%, and the temperature of the wall surface of the gas phase space downstream of the catalytic body is higher than 800°C, which can organize diffuse combustion and consume the remaining gas.

The invention has the advantages of simple implementation, safe and stable combustion, safe use of the catalyst, energy saving and pollutant discharge indicators meeting the requirements of the national standard GB6932-2001, clean use and no black smoke. With the purpose of reducing combustion black smoke, CO and _NOx pollution and energy saving and consumption reduction, various catalytic combustion boilers, catalytic combustion heating devices, and high-temperature furnaces that burn natural gas or methane-rich gas can use the present invention.

Description of drawings

Figure 1 is a schematic diagram of the structure of a fully premixed natural gas catalytic combustion device.

The present invention will be further described below in conjunction with the accompanying drawings.

Detailed ways

As shown in FIG. 1 , the catalytic combustion device mainly includes a premixing chamber 1 , a uniform-porous support plate 2 and a honeycomb medium-temperature catalytic body 3 . All the gas and all the air pass into the premix chamber 3, and the support plate 2 forms the top wall of the premix chamber 1. The catalyst body 3 is placed on the support plate 2, the support plate 2 can support the weight of the catalyst body 3, and the pores are evenly distributed on the support plate 2, and the catalyst body 3 is provided with a honeycomb airflow channel for the combustion air premix to flow through. The central axes of the gas flow channels of the plate 2 and the catalytic body 3 coincide. The area downstream of the catalytic body 3 along the flow direction of the premixed gas flow is the gas phase space. The catalytic body 5 is a medium-temperature catalytic body, which can be a monolithic catalytic body or a coated catalytic body.

Natural gas and combustion-supporting air are all fed into the premix chamber 1 for full and uniform mixing. The premixed gas evenly flows through the gas flow channel of the catalytic body 3 through the support plate 2 . The temperature of the catalytic body 3 is 600-1000°C. The premixed gas absorbs heat while flowing in the gas flow channel of the catalytic body 2, so that the surface catalytic combustion reaction occurs when the temperature of the premixed gas flow is higher than the light-off temperature of natural gas. The temperature of the catalytic body 3 is 600-1000° C., which can effectively start the catalytic combustion reaction on the surface.

Part of the natural gas is consumed by the surface catalytic combustion reaction on the solid wall of the catalytic body 3, and the remaining natural gas and intermediate reaction combustible gas are consumed in the gas phase space downstream of the catalytic body 3 in the form of diffuse combustion. The thickness of the catalytic body 3 is 25-50 mm and the time for the premixed gas flowing out of the pre-mixing chamber 1 to pass through the catalytic body 3 is no more than 0.1 second, the actual air supply is 2 to 3.75 times the theoretical combustion air volume, and the pre-mixed gas passing through the honeycomb channel of the catalytic body 3 The concentration of the mixed combustible gas and the contact conditions between the premixed gas flow and the solid wall of the catalytic body 3 are all controlled. From the kinetic characteristics of the surface catalytic combustion, the percentage of natural gas consumed by the surface catalytic combustion can be controlled, and the final flow out of the catalytic body 3 The volume concentration of oxygen in the premixed gas flow can also be controlled. Catalytic combustion consumes 50% of natural gas when the actual air supply is twice the amount of air required for theoretical combustion (the air supply coefficient is 2). When the air supply coefficient is greater than 2, the percentage of natural gas consumed by catalytic combustion increases linearly with the increase of air supply coefficient. Catalytic combustion consumes all natural gas at an air supply factor of 3.75. Under these conditions, the oxygen volume concentration of the premix flowing out of the catalytic body 3 is lower than 15%, which meets the low-oxygen condition of the combustion-supporting gas stream required for diffuse combustion.

In the gas flow channel of the catalytic body 3, in addition to absorbing the sensible heat of the catalytic body 3, the premixed gas also absorbs the heat released by the catalytic combustion on the surface. When it leaves the catalytic body 3, the temperature can rise to more than 800°C, which meets the high temperature condition of the gas-supporting flow required for diffuse combustion. .

The thermal insulation performance of the wall surface of the gas phase space downstream of the catalytic body 3 is good and the heat load of the device is adjusted, so that the wall surface temperature of the gas phase space downstream of the catalytic body 3 is higher than 800°C, which meets the high temperature condition of the wall surface required for diffuse combustion.

When the premixed gas flows into the gas phase space downstream of the catalytic body 3, the fuel gas molecules and oxygen molecules have been uniformly mixed, the temperature of the premixed gas is higher than 800°C and the volume concentration of oxygen is lower than 15%, and the wall temperature is higher than 800°C, fully capable of dispersion The physical and chemical conditions required for combustion, the combustion speed is effectively controlled, and the volume of the combustion flame is expanded.

Natural gas with high purity or high calorific value must be burned under the condition of large air supply coefficient. The invention requires the air supply coefficient to be between 2 and 3.75. At this time, the volume percentage of natural gas in the premixing chamber 1 is lower than 5%, which is outside the deflagration range of natural gas. Therefore, there is no limit to the aperture size of the gas flow channel in the catalytic body 3, which can effectively The air flow resistance and the processing cost of the catalytic body 3 are reduced, and the combustion safety and stability are enhanced.

The invention organizes combustion in a staged combustion manner. The primary combustion is catalytic combustion, mainly based on the radiation heat transfer (non-directional radiation heat transfer) of the catalyst 3 solid wall and the small flame in the pore to the heating surface, and the secondary combustion is diffuse combustion, which is based on the radiation heat transfer of the large flame to the heating surface. Heat (directed radiation heat transfer) is dominant. The flame combustion in the traditional combustion device is replaced by the flameless combustion of the present invention, and the traditional flame directional radiation heat transfer is replaced by the "catalytic combustion pores and solid wall non-directional radiation heat transfer + diffuse combustion large-volume flame directional radiation heat transfer" of the present invention Or "catalytic combustion pores and non-directional radiation heat transfer on solid walls" instead, the comprehensive application of catalytic combustion and low-oxygen diffuse combustion technology improves the energy-saving performance of the device. The catalytic combustion boiler is based on the principle of premixed combustion. The air and fuel have been mixed before entering the furnace, and a blue or colorless flame appears; the catalyst reduces the activation energy of the combustion reaction; the volume of the diffuse combustion flame in the gas phase space becomes larger, and the range of the reaction zone is widened and extended. The residence time of the combustible gas in the high temperature reaction zone is determined. The three factors improve the combustion efficiency, make full use of fuel, eliminate the problem of burning black smoke, significantly reduce the CO content in the flue gas, and reduce environmental pollution. Catalytic combustion uses a selective catalyst that cannot reduce the activation energy required for the NO _x generation reaction. The combustion surface of catalytic combustion is wide, the heat release per unit area is reduced, and the peak flame temperature is reduced. The volume of the gas-phase space-dispersed combustion flame is large, the heat release per unit volume is reduced, and the peak temperature of the flame is reduced. The three-factor thermodynamic NO formation was suppressed.

Experimental tests show that: the inventive catalytic combustion is safe and stable, no black smoke phenomenon, the catalyst is safe to use, energy saving and pollutant emission indicators meet the requirements of the national standard GB6932-2001, the thermal efficiency exceeds 98%, the CO content of the flue gas is lower than 600ppm, and the NO _x content is low at 25ppm.

Claims (1)

1. catalytic combustion device dispersed combustion method, it is characterized in that: the cellular catalytic body thickness on the gripper shoe is set to 25～50mm earlier, again natural gas and combustion air are all fed the premixer of catalytic body upstream, and control catalytic body temperature is 600～1000 ℃ of scopes, regulate more than the catalytic body downstream gas-phase space wall surface temperature to 800 ℃, premixed flow is spent the catalytic body time and is controlled in the 0.1s, supplies 2～3.75 times of theoretical burning required airs.

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