1. How to choose a circulating electric heater?
The selection and maintenance of circulating electric heaters must have certain experience in the electrical, mechanical and chemical fields. Many large companies or design institutes often artificially divide the designers into electrical, mechanical and heat transfer groups, designing electric heaters. Or choose to have at least one person involved. Of course, large-scale and powerful manufacturers can provide relevant technical support. Some manufacturers have developed professional design software. Therefore, electric heater design cannot be regarded as too simple or too complicated.
2. What causes the failure of the circulating electric heater?
The main causes of damage to electric heaters are the following five aspects:
1, cut off: In the case of a broken flow, if the temperature control of the electric heater is controlled by the outlet temperature, the sensor signal can not provide the correct signal, and always requires heating, the electric heater becomes more and more hot, if the over-temperature sensor works, It can also cut off the power supply. If the over-temperature sensor does not work, either the heating element is burned out or the container cracks or melts. No matter what happens, explosion-proof situations may have unpredictable consequences.
2. The position of the over-temperature sensor is not correct: If the position of the sensor is not close to the electric heater, the other circuit is heating up. The over-temperature sensor cannot detect the correct temperature or delay.
3. The wiring of the over-temperature sensor is not correct: When multiple electric heaters are used together on the same block, the wires may be miscrossed. For example: There are three electric heaters to heat natural gas in parallel, 1# and 2# heaters are running, 3# heaters are not used, if the overheat sensor of 2# heater crosses with the 3# heater and is misconnected, such as a sudden stop flow, The 3# sensor cannot always turn off the #2 heater and eventually the heater burns out.
4. Cracking of electric heating elements: Many heat exchangers have invested a lot of experience in tube cracking of shell-and-tube heat exchangers. However, there are few papers on the cracking of electric heater components, because the internals of electric heating elements are believed to be solid. Magnesium oxide powder can be cracked. In high pressure applications, magnesium oxide powder can be driven out into the wiring chamber, causing electrical leakage.
5, short circuit: high temperature magnesium oxide powder is a good thermal conductive material and insulating material, but magnesium oxide powder is easy to absorb moisture and reduce the electrical insulation, the main reason for moisture absorption is mainly due to the water vapor in the environment or a long time to place or open the wiring time is too long Etc., such as power, the circuit breaker did not cut off in time, may break through the heating element.
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3. Why does the gas wall heating temperature calculation and overtemperature protection device pay special attention in gas heating applications?
Most circulating electric heater cylinders are made of steel pipes. Under no-flow conditions and over-temperature non-operation, the temperature of the container will become hotter and hotter. It is only due to the radiation from the electric heating element, which is in off-flow and pressure. Under the circumstances, the cracking of the container leads to the leakage of the process gas and causes an accident. It is generally recommended that the wall temperature of the container be calculated without protection of the flow switch, and it is recommended to add over-temperature protection to the container.
4. Why does the on/off control shorten the service life of the electric heater?
Switch control or step control can cause the heating element to be turned on (heated) and disconnected (cooled). As a result, the heating element expands and contracts. Each expansion and contraction can weaken the small heating wire inside the heating element. The use of an overall thyristor power regulation can maintain a constant temperature on the surface of the heating element and extend the service life of the electric heater.
5. What is the maximum operating temperature of carbon steel containers and stainless steel containers?
The highest recommended temperature for carbon steel materials is 480°C, and stainless steel is 700°C. Refer to GB150 standard or similar standards for the operating temperature and pressure rating for specific applications.
6. What is the maximum recommended temperature for different heating element materials?
The highest recommended operating temperature for electric heating elements: Copper material: 175°C; Carbon steel material: 400°C; Stainless steel: 760°C; Monel: 480°C;Incoloy: 920°C; Inconel: 980
STAINLESS STEEL PRODUCTS
Stainless steel is a corrosion resistant steel alloy with a minimum of 10% chromium. There are different grades and surface finishes of stainless steel produced to accommodate the environment in which the material will be implemented. Unlike carbon steel, stainless steel does not rust when exposed to air and moisture due to the sufficient amount of chromium present. The chromium creates an invisible passive film of chromium oxide that will not let oxygen attack the surface and prevents rusting of the iron base.
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