A radiant tube
is a tube that extends in a straight line from the center in all directions. Refers to the non-central pipeline (or main pipe), which transports the substance of the main pipe to the designated or non-designated address. Radiant tubes are widely used in heating furnaces and are the main heating element of heating furnaces. The radiant tubes currently used are mainly divided into two categories: gas radiant tubes and electric heating radiant tubes. The thermal efficiency of the gas radiant tube is about double that of the electric heating radiant tube. Therefore, gas radiant tubes are the development trend of future radiant tubes
Radiant tubes are widely used in heating furnaces and are the main heating element of heating furnaces. The radiant tubes currently used are mainly divided into two categories: gas radiant tubes and electric heating radiant tubes. The thermal efficiency of the gas radiant tube is about double that of the electric heating radiant tube. Therefore, gas radiant tubes are the development trend of future radiant tubes. Under the conditions of the modern market economy, the competition of radiant tube
companies is becoming increasingly fierce. In order to increase market share, various companies have continuously improved radiant tubes. However, technological innovation is very difficult. To reduce the R & D cost of radiant tubes, the company's R & D personnel must accurately predict the development trend of the product, and adopt theoretical methods and tools to achieve product innovation and rapid design. Will do more with less.
The development of products and their technologies always follows certain objective laws, and the same rule is often applied repeatedly in different product technology areas, that is, the process of product improvement and technological change in any field is regular and all technologies can be followed. The creation and upgrading of the development are to the most powerful functions. TRIZ technology evolution theory is specialized in the evolution of technology systems. It has undergone three stages of traditional TRIZ evolution theory, TRIZ evolution theory development, and direct evolution theory. There are technology evolution theory (ET), technology evolution guidance theory (GTE), and direct evolution theory. Evolutionary theory (DE) and many other forms. TRIZ's theory of technological evolution is specialized in the evolution of technological systems. The theory of technological evolution reflects the important, stable and repetitive interactions between technological systems, components, systems and the environment during the evolution process, and each evolutionary law Each contains a different number of specific evolutionary routes and patterns.
The heat energy of the heating furnace is generally provided by the combustion of combustible gas such as natural gas, but the harmful gas generated during the combustion of the combustible gas will destroy the environment required for the heat treatment in the furnace. Therefore, a radiant tube was invented to burn the combustible gas in the radiant tube. Thermal energy is radiated into the furnace by the radiant tube, so that harmful gases will not damage the environment in the furnace. But because the radiant tube heats the workpiece through the tube wall radiation, its heating efficiency is related to the efficiency of heat treatment, so the heating efficiency of the radiant tube is one of the main characteristics of the radiant tube. The earliest radiant tube was invented and used by Germany in the 1930s. Its structure is a single-layer straight tube type that passes horizontally or vertically through the furnace; U-shaped radiant tubes
were not introduced until the early 1950s; For heating efficiency, W-type radiant tube was invented on the basis of U-type radiant tube; with the advancement of technology, P-type radiant tube, a typical type of radiant tube, appeared. In order to further improve the heating efficiency of radiant tubes, hemp surface radiant tubes were invented on the basis of various types of radiant tubes, the heating area of which was increased by more than 30% compared to smooth surface radiant tubes, which greatly improved the heating efficiency of radiant tubes. This process basically evolves along two technological evolution routes:
- The evolutionary path of geometric shapes:the shapes of subsystems and the shapes of subsystems and supersystems should be coordinated with each other. One of the evolutionary paths is the evolution of geometric shapes: straight lines → 2D lines → 3D lines → complex lines. Follow this evolutionary path to describe the evolution process of improving the heating efficiency of the radiant tube: The system is in the evolutionary 2D curve stage. The radiant tube can be designed as a 3D curve to improve the heating efficiency of the radiant tube, such as a radiant tube designed as a corrugated tube.
- Evolution of surface shape: smooth surface → convex surface → rough surface → active material. Follow this evolutionary path to describe the evolution process of improving the heating efficiency of the radiant tube: The system is in the stage of evolution with raised surfaces. You can increase the number of radiant tube surface protrusions or design the surface of the radiant tube as a rough surface to improve the radiant tube. Heating efficiency.
Uniformity of temperature distribution on the surface of the radiant tube:
The uniformity of the temperature distribution on the surface of the radiant tube is an important technical performance indicator for measuring the radiant tube. It affects the heating capacity, heating quality and service life of the radiant tube. At present, U and W-type radiant tubes are most widely used, so U-type and W-type radiant tubes are used as research objects.
The original radiant tube was only equipped with a burner at one end, and the temperature difference between the two ends of the radiant tube was large. In order to improve the uniformity of the temperature distribution on the surface of the radiant tube, a number of core blocks are arranged in the radiant tube. The core block fills the radiant tube with high-temperature gas, strengthens the convective heat transfer between the high-temperature gas and the tube wall, and the temperature at the tail is increased. Later, in order to improve the temperature uniformity of the radiant tube, burners were installed at both ends of the radiant tube, and the pulse combustion technology was used to improve the uniformity of the temperature distribution of the radiant tube. On the basis of pulse combustion, the uniformity of the temperature distribution of the radiant tube can be further improved by changing the combustion reversing time of the burner at both ends.
The uniformity of the temperature distribution on the surface of the radiant tube is closely related to the length of the flame. The initial burner can only perform one-stage combustion. Based on this, a two-stage burner is improved and designed. The control system can adjust the ratio of primary air and secondary air in the burner to effectively control the flame length. To improve the uniformity of the temperature distribution on the surface of the radiant tube.
The advent of regenerative combustion technology has greatly improved the temperature uniformity of the radiant tube. It was found through experiments that as the air preheating temperature increases, the maximum temperature difference on the surface of the radiant tube gradually decreases, and the temperature unevenness coefficient also decreases. There are two technological evolution routes in this process:
- Evolutionary path to supersystem: single system → dual system → multiple systems. According to this evolutionary route, the evolution process of improving the uniformity of the temperature distribution on the surface of the radiant tube (Note: the control system is changed to a heat storage body), the system is in the final stage of evolution.
- Frequency coordinated evolutionary path of a single object (flame): continuous motion → pulse → periodic action → increase frequency → resonance. According to this evolutionary path, describe the evolution process of improving the uniformity of the temperature distribution of the radiant tube. The system is in the cyclical stage of evolution, which can further improve the combustion cycle of the burners on both sides or develop in the direction of increasing frequency, such as increasing the burning on both sides The frequency of nozzles alternately burning to improve the uniformity of the temperature distribution of the radiant tube.
The number of radiant tubes used in the heating furnace is large and expensive. For example, a total of 128 radiant tubes used in an annealing furnace are priced at 37,000 yuan. If the service life of each radiant tube is increased by 0.5 to 1 year, a huge economy will be generated. benefit. Therefore, how to improve the service life of the radiant tube has great research value. The main factors affecting the life of a radiant tube are the material, structure and manufacturing process of the radiant tube, the combustion atmosphere in the radiant tube, the installation structure and maintenance, the uniformity of the temperature distribution on the surface of the radiant tube, the production process and the operation level.
Commonly used U-shaped or W-shaped radiant tube are relatively large in quality. In the process of use, under the combined effect of alternating thermal stress and their own mass, bending fatigue damage and creep deformation damage are prone to occur. In order to reduce the deformation of the radiation tube, a fixed support structure integrated with the radiation tube is provided at each elbow, and is supported on the furnace wall during installation. In order to adapt to the thermal expansion and cold shrink deformation of the radiant tube, an expansion joint is set between the outlet of the burner side and the furnace cover. Through the compensation of the expansion joint, the occurrence of cracks is avoided and the service life of the radiant tube is improved. At the same time, the fixed support at the elbow of the radiation tube was changed to a floating support, which further reduced the occurrence of cracks.
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