Design of the hottest high temperature air combust

2022-09-21
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High temperature air combustion technology and natural gas heat treatment technology equipment

Abstract: This paper briefly discusses the development status of heat treatment energy technology at home and abroad, and focuses on the current situation and development trend of high temperature air combustion technology and natural gas energy technology; At the same time, the development and application prediction, research, key technologies and key equipment of high temperature chamber gas combustion technology and natural gas energy technology in China's heat treatment industry are discussed

key words: high temperature chamber gas combustion technology, natural gas, gas heat treatment technology and equipment

1 overview

China's heat treatment industry is a major energy consumer in the machinery industry, and the proportion of heat treatment electricity in China's machinery manufacturing plants accounts for 25% - 30% of the whole plant. There are about 120000 heat treatment furnaces in the national heat treatment industry, of which more than 90% use electricity. The annual power consumption is about 10billion kwh. The average power consumption of heat treatment production in China is 700kwh/t, which is about twice that of Japan and Europe. The average power consumption of heat treatment production in Japan is about 323kwh/t, and the average power consumption of heat treatment production in European industrial countries is (300 ~ 450) kwh/T; The thermal efficiency of Japan's heat treatment production is 49.8%, while that of China's heat treatment and continuous production for 5 minutes is about 29%, which is a big gap

we know that electricity is a secondary energy. The power generation efficiency of general fuels is about 36%, and the upper limit of thermal efficiency of electric energy is about 80%, so the upper limit of thermal efficiency of fuels is about 29%. Natural gas energy is a primary energy, and natural gas is purified before being provided to users, so it is a cleaner energy [7]. Under the current general technology, the upper limit of its thermal efficiency is about 50.5%, which is nearly twice as high as the thermal efficiency of electric energy. In recent years, many large-scale natural gas field structures have been found in China, with a total reserves of more than 38 trillion m3. With the western development and international cooperation in the development of natural gas fields, China's natural gas production during the Tenth Five Year Plan period can reach more than 64.5 billion m3 from 23.8 billion m3 in 1999 [8], creating conditions for China to develop natural gas energy, change the single energy structure of heat treatment, improve energy utilization and realize comprehensive energy utilization

high temperature air combustion technology (HTAC) is a new type of combustion technology that has been widely promoted and applied in developed countries since the 1990s. It has multiple advantages of high-efficiency flue gas recovery, high-temperature preheated air and low NOx emission. China has also begun to take steps in this technical field in recent years, and has achieved significant technical and economic benefits in industrial production. China will further develop and promote this high-efficiency, energy-saving Advanced combustion technology with low pollution is imperative and has broad prospects for development

2 development status, trend and market demand analysis of energy technology at home and abroad

2.1 overview of heat treatment energy technology at home and abroad

overview of heat treatment energy technology at home and abroad is shown in Table 1. Table 1 overview of heat treatment energy technology at home and abroad

2.2 overview of natural gas energy technology development at home and abroad

overview of natural gas energy technology development at home and abroad is shown in Table 2. Table 2 overview of natural gas energy technology development at home and abroad

note: natural gas energy accounts for 24% of all kinds of energy in the world

2.3 development status, trend and market demand analysis of energy and combustion technology at home and abroad

compared with the production level of Europe, Japan and the United States, which makes rational use of energy and attaches great importance to heat treatment production and energy-saving technology, China has a significant gap. The energy structure of China's heat treatment industry is unreasonable, and the use of electric energy accounts for more than 90%, resulting in a great waste of primary energy, unreasonable utilization, and low thermal efficiency of fuel. There is still a large gap between China's fuel furnace and its burners, accessories design, manufacturing, computer control technology, intelligent instruments and other complete technologies and foreign advanced technologies

high temperature air combustion technology is an advanced combustion technology with high efficiency, energy saving and environmental protection that developed rapidly in the 1990s. Compared with traditional combustion technology, high temperature air combustion technology can make the air preheating temperature reach 95% of the flue gas temperature through regenerative flue gas waste heat recovery, and the furnace temperature uniformity is 5C, and its combustion thermal efficiency can be as high as 80%. High temperature air combustion technology through h, we also provide precise evaluation tools to better understand the equipment status and encounter potential problems. TAC burner and recovery device can save more than 60% energy: thus, CO2 emissions can be reduced by more than 60%. At the same time, high temperature air combustion technology can realize combustion in oxygen poor areas, so that NOx emissions can be greatly reduced, up to 40% × The order of magnitude (40mg ~ 50mg)/m3 is 1//20 of the traditional combustion technology. In addition, high temperature air combustion technology has low combustion noise and reduces noise pollution. High temperature air combustion technology has developed several high temperature air burners (regenerative burner heating system), which have been used in production in Japan, the United States and Europe. The development and application of this technology has reached maturity, and its technical and economic benefits are remarkable. In recent years, China has developed several kinds of regenerative burners and device systems in this technical field, which have been successfully applied to industrial production, with huge technical and economic benefits and superior environmental protection performance [6]

during the Tenth Five Year Plan period in China, a large number of heat treatment equipment should be updated and transformed. Advanced energy-saving, efficient, high-quality, clean and pollution-free heat treatment furnace (production line) equipment with computer control should be used to replace the heat treatment equipment with obsolete equipment, high energy consumption, low efficiency and serious pollution. According to the requirements of the tenth five year plan, China needs at least 2500 sets of advanced heat treatment equipment (sealed box furnace, vacuum furnace, continuous heat treatment furnace, induction heating heat treatment production line, etc.). It is estimated that if the technical transformation centered on less and no oxidation and clean heat treatment is basically completed in 2015, at least 5000 ~ 8000 sets of advanced equipment will be required. If one third of them adopts natural gas energy, at least one set of gas-fired heat treatment equipment with high-temperature air combustion technology will be required

it should be particularly pointed out that the use of natural gas energy also brings benefits to the heat treatment industry to improve product quality, because natural gas itself is a reducing protective atmosphere, and the preparation of endothermic atmosphere with natural gas is the mainstream technical method of carburization abroad. Due to the less development and utilization of natural gas in China, the controllable atmosphere heat treatment and carburization technology in the heat treatment industry have to adopt more propane Acetone and nitrogen based atmosphere heat treatment, etc. [5]. If natural gas is widely used as energy in the heat treatment industry, it will undoubtedly contribute to improving China's heat treatment production with less oxidation heating, because the main 10000 parts of natural gas are hydrocarbons, which is itself a protective gas. The use of natural gas energy is a great good thing for the heat treatment industry, which can greatly improve the economic benefits of heat treatment production. Our advanced technology deserves the attention of customers, and can greatly improve the degree of less and no oxidation heating in China's heat treatment industry, so as to contribute to improving the quality of heat treatment products

3 research and development of high temperature air combustion technology in heat treatment industry key technologies and equipment for natural gas energy application

research and development of key technologies and equipment for natural gas energy application in heat treatment industry mainly include the following points, which we will introduce respectively

(1) the optimal combustion ratio of gas/air and precise control technology. By establishing the mathematical model of pressure and temperature of natural gas combustion system, an intelligent and precise control system of gas furnace temperature is developed

(2) research and development of high temperature air combustion technology, high efficiency, low noise, low NOx and low Sox combustion technology

(3) high efficiency gas radiant tube technology

(4) waste heat utilization technology

3.1 optimal combustion ratio of gas/air and precise control technology

we know that for gas-fired heat treatment furnace, under the condition of a certain amount of charging, the furnace temperature T depends on the sum of natural gas flow LN and air flow LG and the ratio of natural gas flow LN and air flow LG μ, In order to ensure the best combustion, the excess air coefficient must be guaranteed α= Between 1.02 and 1.10, for this reason, the system must control the residual oxygen O2 and CO content in the flue [8]. The automatic regulation and control of residual oxygen is the core of realizing the optimal combustion ratio and accurate control of gas/air. The optimal combustion ratio is also an important measure to save energy and reduce burning loss, as illustrated by an example

the system is composed of ibm-286 microcomputer, high-speed nozzle, air preheater, ddz-11 series temperature control instruments and high-precision flue gas analysis. The double cross control mode is adopted to ensure the best gas/air mixing ratio. The monitoring instrument adopts oxygen probe, and the infrared instrument measures the residual oxygen to control the gas/air mixing ratio. The system uses specific boundary conditions to establish the mathematical model of the instantaneous temperature field of the workpiece in the process, The computer application software of the core temperature of the workpiece is compiled, and the difficult problem of the process temperature control of the gas furnace is solved. Further, the optimized heating rate and real-time control are realized. Figure 1 shows that the diameter of d=360mm, l=1850mm, and the major axis is 3m in Luoshan mine × Comparison between measured and simulated values of 6m large trolley type gas heating furnace. The experimental results show that the average relative error of the determination is ± 1.0%, i.e. ≤± 7 ° C, which meets the requirements of precise process control

Figure 1 Comparison of measured and simulated heating values of 3m~6m large trolley type gas furnace

3.2 high temperature air combustion technology, research and development of high-efficiency low-noise, low NOx, low Sox burner technology

high temperature air combustion technology is a new type of combustion technology developed and promoted by industrial developed countries since the 1990s. It has multiple advantages of high-efficiency waste heat recovery, high-temperature preheating air and low NOx emission. Nearly 900 sets of several types of high temperature air burners (burners) have been developed. By 1995, more than 800 fuel furnaces have applied this technology [6]

the principle of this technology is briefly introduced as follows

Figure 2 preheating air temperature and oxygen concentration and NOx generation

in order to reduce the high NOx emissions caused by high-temperature combustion, it can be seen from Figure 2 that reducing the oxygen concentration in the combustion space and creating oxygen poor combustion conditions are the most economical and effective way

Figure 3 gives the schematic structure diagram of ultra-low NOx burner. The fuel is fed into the furnace in two ways: primary fuel F1 and secondary fuel F2. The primary fuel quantity F1 is much less than F2. F1 combustion belongs to oxygen enriched combustion, which will be completed quickly under high temperature conditions. After flowing through the optimized nozzle, a high-speed flue gas jet and the surrounding entrainment reflux flow will be formed. A large amount of fuel is injected into the high-temperature flue gas with an oxygen content of less than 15% (or even less than 5%) through the secondary fuel path F2. At this time, the combustion of fuel belongs to controlled diffusion combustion reaction, and there is no longer a local hot high-temperature zone with excess air coefficient close to 1 in the flame front of traditional diffusion combustion. With this staged combustion method similar to that on coal-fired boilers, the generation of NOx is fundamentally inhibited and the emission of NOx is greatly reduced

Figure 3 working principle of ultra-low NOx burner

the flame characteristics formed under the condition of high temperature and oxygen deficiency are quite different from the traditional combustion flame. The latter is a static flame with local hot spots; The former results from the reaction at uniform high temperature and has the following characteristics

there is no static flame, the volume is significantly increased until doubled (or even expanded to the entire combustion space), the brightness radiation is reduced, the common incandescent flame area disappears (so it is called flameless electronic type, which is a new product combination developed in recent years), the flame presents a variety of colors, sometimes invisible to the naked eye, the temperature gradient and density are very small, the peak flame temperature decreases, and the heat dissipation distribution is uniform, The temperature in the whole furnace is evenly distributed. This feature will effectively reduce NOx emissions. Low noise during combustion

3.3 high efficiency gas radiant tube technology

application of domestic gas radiant tubes in production

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