In a kettle-type reactor with an internal coil, why is the temperature at the outlet of the coil lower than the temperature in the kettle?
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It is a kettle-type reactor with an internal coil; the coil is heated by heat transfer oil. The temperature inside the kettle is 220°C, while the temperature of the heat transfer oil is 240°C. However, the temperature at the exit of the heat transfer oil is 218°C. The reaction is exothermic, and the temperature of the feed material is around 80°C. Why is the temperature at the exit of the coil lower than the temperature inside the kettle?
1. It may be that the instrument’s measurements are inaccurate； 2. The heat generated by the exothermic reaction of the materials inside the reactor accumulates, and the temperature gauge measures the temperature in the high-temperature area.
3. The feed point is very close to the heat transfer oil outlet pipe
It depends on the temperature distribution, the location of measurement, and the accuracy of measurement.
I think this level of error is normal; the allowable error for measuring instruments is around 1%.
1. Is there a problem with the thermometer? 2. The installation location for temperature measurement might be inappropriate
It’s an exothermic reaction – why then has the temperature at the outlet of the heat transfer oil decreased?
Yes, I’m not sure what’s going on
It’s probably because the mixing isn’t sufficient; in a true counter-current setup, the temperature at the outlet of the heat transfer oil can approach 80°C, which is the temperature at the inlet of the material. The temperature inside the reactor is either a local temperature or an average temperature, and it’s possible for this to be lower than that temperature
If it’s not a problem with the thermometer, then it’s an issue with the design of the equipment (inconsistent mixing? Is the raw material feeding position incorrect? Is the coil layout unreasonable? Or it has not yet started to react). Furthermore, since it is an exothermic reaction, if the reaction has already taken place and the temperature in the reactor is 220 degrees, why is a heat transfer oil at 240 degrees being used? If there is no reaction, and the temperature of your raw materials is only 80 degrees while the reactor measures 220 degrees, with a heat transfer value of 240 degrees, the outlet temperature of the heat transfer oil might be below 220 degrees (depending on the location where the material is added and the setup of the coiled tubes).
The temperature of your reactor is high; another factor to consider is the heat radiation emitted by the equipment to its surroundings. Although it is exothermic, if the amount of heat released is less than the heat loss, heat may still need to be supplied. The temperature at the coil outlet is quite good; it’s normal for the temperature to be lower near the feed inlet.