【Identify the Process from the Image】What is the purpose of introducing nitrogen into this electric heater?
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As shown in the figure above, the process medium is heat transfer oil, which needs to be heated to 300°C. For the electric heaters used, a protective cover has been installed over the exposed parts of the electric heating elements, and nitrogen is introduced for protection. This nitrogen is kept at a very low flow rate. May I ask everyone, what is the purpose of that? ? Similar electric heaters that heat air to 500°C can be seen in other sections, but they do not have such nitrogen protection devices. Please use it for discussion.
I guess it’s because combustible gases have a relatively low explosive lower limit, so an inert gas is introduced for protection. . It’s related to the medium, I guess
One purpose is to introduce an inert gas as a shield to prevent the heat transfer oil from catching fire.
The most likely reason is that the explosion-proof rating of this heat transfer oil heater is insufficient, which is why nitrogen is used as a remedial measure; once the explosion-proof rating is adequate, such a approach is generally not adopted. The original poster can ask the electrical staff in the workshop about the explosion-proof rating; normal heat transfer oil electric heating furnaces require a certain level of explosion-proof protection. See the explosion-proof junction box in the figure below. As for the other air heaters you’ve seen that don’t have this feature, you can also check their explosion-proof rating. For example, even though the medium used in your electric air heater is non-flammable, if it is installed in an area classified as a Class 1 explosion-proof zone, an explosion-proof wiring box is still necessary. . Looking at the English version of your flowchart, if it’s a foreign company that supplies the products, then that’s quite normal. Many foreign companies have their own unique approaches to these small details; some of them are gimmicks, while others represent lessons learned by the company over time. For example, it’s possible that the heat transfer oil leaks at the connections of the electric heaters, leading to fires; filling the area with nitrogen can provide good protection, and taking measures such as using explosion-proof wiring boxes adds an extra layer of safety (after all, it’s never a bad idea to be cautious when it comes to safety). All of these scenarios are possible.
Prevent the entry of flammable gases by introducing an inert gas for protection.
I understand what Brother Dao is saying, but this nitrogen protection cover is connected between the explosion-proof junction box and the exposed heating rod at the head of the vessel; usually a protective mesh is installed in that area. However, it turns out that this electric heater used for heating the heat transfer oil comes equipped with a special nitrogen protection cover. You can take a look at the drawings of this site: here, the explosion-proof junction box is separate, and the part filled with nitrogen is simply the exposed heating rod. And I checked that this nitrogen shield is sealed with silicone, and it seems to be separate from the outside of the heater.
Is it to prevent the heat transfer oil from catching fire upon coming into contact with the external electric heating element?
Hello, OP. It seems that the photos from the scene you posted, combined with my many years of experience in electric heating, can be used for analysis. The purpose of doing this is to cool down. The wiring box of this heater is located closer to the container through which the heat transfer oil flows compared to that of a regular heater; in other words, the non-heating zone is shorter. At the same time, heat transfer oil has a high specific heat capacity; as a result, prolonged operation leads to a gradual increase in temperature inside the junction box, which affects the efficiency of the wires and may even damage their insulation. A small amount of nitrogen introduced can continuously remove the heat from the middle, thereby protecting the junction box. A similar approach is also used in the application of viewports in some high-temperature furnaces; to prevent the acrylic viewports from being damaged by high temperatures, a certain flow rate of nitrogen is introduced in front of them as a cooling protection measure.
Another possibility is that due to certain errors, the heating element that is protected by nitrogen cooling also becomes a heat-generating area; nitrogen is introduced to cool it down in order to prevent prolonged dry burning. This usually only occurs as a result of errors during the production process, but the possibility of this happening is extremely low.