Study on W-type radiant tube burner

The W-type radiant tube burner is studied. The radiant tube heating technology based on the indirect heating principle effectively avoids the oxidation and decarburization of the surface of the heated parts, creates conditions for heat treatment in a protective atmosphere, and will not cause combustion gas and product pollution and affect the product quality. It is especially suitable for occasions with high requirements for product quality. The radiant tube furnace was invented and used in Germany in the 1930s. Its structure is a single-layer straight tube type, which passes through the furnace horizontally or vertically. Until the advent of U-shaped radiant tube in the early 1950s, W-type, casing I-type, exhaust gas recirculation p-type and O-type were developed on this basis [2]. Compared with other types of radiant tubes, W-type radiant tubes have the advantages of large combustion space, large heat transfer area and high thermal efficiency. But at the same time, due to the long tube pass, there are many factors affecting the flame length in the tube, and the poor temperature uniformity along the length of the radiant tube has become a difficult problem in the development of the radiant tube burner. Radiant tube burner is the core component of radiant tube heating device, which controls the heating power, temperature distribution, thermal efficiency and service life of radiant tube. The proper burner structure shall make the air and gas in the radiant tube mix to the appropriate strength. If air. The gas mixing intensity is too low, the mixing time is prolonged, the flame is prolonged, and the gas is not completely burned, resulting in unnecessary waste. Even the combustion flame may escape from the exhaust port of the radiant tube, reduce the thermal efficiency of the radiant tube, resulting in uneven temperature distribution on the surface of the radiant tube; If air. The gas mixing intensity is too large, the mixing time is shortened, the flame is too short, the end of the radiation tube cannot be completely heated, and the temperature distribution on the surface of the radiation tube is uneven. According to the needs of the technical transformation of the production line, a coaxial parallel jet diffusion combustion W-type radiant tube burner with stable performance and uniform heating temperature is developed. The W-type radiant tube burner is studied. The radiant tube heating technology based on the indirect heating principle effectively avoids the oxidation and decarburization of the surface of the heated parts, creates conditions for heat treatment in a protective atmosphere, and will not cause combustion gas and product pollution and affect the product quality. It is especially suitable for occasions with high requirements for product quality. If air. The gas mixing intensity is too low, the mixing time is prolonged, the flame is prolonged, and the gas is not completely burned, resulting in unnecessary waste. Even the combustion flame may escape from the exhaust port of the radiant tube, reduce the thermal efficiency of the radiant tube, resulting in uneven temperature distribution on the surface of the radiant tube; If air. The gas mixing intensity is too large, the mixing time is shortened, the flame is too short, the end of the radiation tube cannot be completely heated, and the temperature distribution on the surface of the radiation tube is uneven.

According to the needs of the technical transformation of the production line, a coaxial parallel jet diffusion combustion W-type radiant tube burner with stable performance and uniform heating temperature is developed.

1. Test the burner.

The test burner is mainly composed of gas pipe, gas nozzle, air pipe, air nozzle, combustion cylinder and ignition electricity. The combustion is organized through coaxial parallel jet diffusion combustion. The main combustion gas burns along the axial direction of the radiant tube, a gas nozzle is opened laterally, and a small amount of gas flows out along the radial direction of the radiant tube. The combustion air is fired coaxially and parallel with the main gas along the periphery of the gas pipe. The combustion pipe is divided into primary air (main gas) and secondary air to participate in combustion. The central outlet of the burner is provided with ignition power and. When the central air stream is in contact with the air stream automatically absorbed around it, the gas and air molecules on the interface diffuse with each other. After reaching the chemical equivalence ratio, once ignited, a flame will be formed.

2. Test device and test system.

Device system used in burner test. In order to simulate the thermal insulation and heat transfer conditions in the actual heating furnace, a 2.2mx1 5m × The inner wall of 1m test furnace is lined with 100mm thick asbestos fiber blanket, and thermocouple (No. 1 thermocouple) is installed in the furnace to measure the furnace temperature. The radiant tube is vertically installed in the furnace, 25 temperature measuring thermocouples are evenly arranged on the outer wall of the tube, the temperature distribution of the tube is continuously monitored, the bin burner is installed at the end of one side of the radiant tube, and the combustion supporting air is supplied by the blower. The calorific value of the test gas is 6688 ~ 7106kj / m. Gas composition of converter gas. The combustion waste gas is extracted from the other end of the radiation pipe through the smoke extractor, and the zero pressure surface detection point is set at the outlet of the combustion nozzle to control the opening of the smoke extractor valve. The test air and air flow are measured by LZB rotameter; The pressure of gas medium is measured by electronic pressure gauge, and the pipeline temperature and furnace temperature are continuously displayed and stored by multi-point temperature recorder. The flue gas composition is analyzed online by German MRU flue gas analyzer.

3. Test results.

3.1 burner ignition performance test.

The test burner is equipped with automatic ignition device. During the ignition test, touch the ignition controller switch, the ignition power and start discharge ignition, the gas solenoid valve and gas solenoid valve will open automatically, the gas and combustion air flow into the burner, mix at the burner outlet, and encounter spark combustion. When the flame detection probe detects a stable flame, if the fire indicator light is on, it indicates that the burner is ignited successfully. If the fire indicator goes out, it indicates that the fire has failed, and the gas solenoid valve and gas solenoid valve will be cut off automatically. The results show that the burner ignition is convenient, the combustion is stable, and the ignition time is ≤ 1s.

3.2 test the flow characteristics of burner.

Test burner air. When the design capacity of the burner is 150KW, the air pressure in front of the burner is 1340pa and the air pressure in front of the burner is 370pa. Under the test conditions, the small heat load of the burner is 30kW, the adjustment ratio of the burner is 1:5, and the combustion capacity of the burner meets the design requirements.

3.3 analysis of flue gas composition.

Test the stable combustion of the burner within the regulation ratio range, track and monitor the combustion flue gas composition outside the radiant tube, and check the combustion effect of the burner. The test data are shown in Table 3. Under the test conditions, the test burner can burn stably and completely, and the volume fraction of oxygen in flue gas does not exceed 2.44. Co volume fraction not exceeding 21 × 1o1。 N volume fraction not exceeding 98 × 1o~。 It can be seen that the test burner has good combustion effect and low harmful gas emission. The test burner burns stably under the design capacity (150KW), changes the intake flow of combustion air, adjusts the air consumption coefficient, and tracks and monitors the composition of combustion flue gas outside the radiant tube. When the air consumption coefficient is greater than 1.0, the test burner can burn stably and completely, and the emission of CO in flue gas is low. 3.4 radiant tube surface temperature uniformity test the burner burns stably under the design capacity (150KW).