Could the experienced workers tell me: what is the purpose of opening the furnace in the final step of heating it?
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(1) Before heating the furnace, all manholes, viewing doors, explosion-proof doors should be opened, and the chimney baffles should be removed to allow natural ventilation for more than 5 days, after which ignition to heat the furnace can begin. (2) When starting the furnace drying, open the chimney damper to about one-third. Once the temperature inside the furnace rises and the draft increases, open the chimney damper a little more. (3) Steam is introduced into the furnace tubes to start heating; once the temperature in the furnace reaches 130°C, the burners can be ignited to continue with the drying process. (4) When heating the furnace, gas fuel nozzles should be used as much as possible for diagonal ignition. (5) During the furnace drying process, the temperature should rise uniformly. The heating and cooling rates must follow the furnace drying curve, and the condition of the furnace walls should be monitored regularly. (6) Records should be kept during the furnace drying process, and the actual drying curve should be drawn after drying. (7) The furnace chamber is cooled at a rate of 20°C per hour. When the furnace temperature drops to 250°C, the fire is extinguished and the furnace is left to cool down to 100°C before natural ventilation is allowed. The above is the standard process for drying out the furnace, which is understandable; however, I would like to ask about the final step. The furnace has already finished heating – why turn on natural ventilation? Doesn’t the natural ventilation process allow air and moisture to enter the furnace again? Weren’t the ovens heated for nothing before? Shouldn’t it be time to start using it after the furnace has been dried out? Or should we keep it at over 100 degrees and wait to start working?
The purpose of the drying oven is to dry the free water and crystalline water contained in the thermal insulation materials inside the furnace. In the case of castable materials, it serves both as a drying and curing process. The heating process of the furnace is gradual, allowing the physical water and crystalline water contained in the thermal insulation materials to evaporate slowly, so as to prevent rapid evaporation that could cause the insulation materials to burst, especially in the case of cast materials. After the furnace is dried, it needs to be tested upon startup to check whether there is any insulation material that has fallen off and whether the casting material has cracked; if so, repairs are required. In a furnace that has been dried, during the natural ventilation process for cooling, water in the air cannot penetrate inside the insulation materials; it can only remain on the surface. By operating the furnace at a low temperature for a while after it is restarted, this issue can be addressed.
Is there any requirement regarding how long it can remain still after the furnace is turned off? If not, wouldn’t it mean that only new furnaces need to be baked? Is it still necessary to go through the entire furnace heating process up to 500 degrees when resuming operation after a short shutdown (such as half a month or a month) and starting to heat the furnace again? Do I just need to bake it at 130 degrees for a day?
Oven drying is only necessary for newly built ovens or those that have had their insulation layers repaired (especially those involving pouring processes). For ovens that are restarted after being shut down, as long as they have not been exposed to rain, there is no need for further oven drying, since when the oven is restarted, there are specific requirements regarding the rate at which it should be heated. In fact, furnace drying is the process of sintering and curing the insulation layer. Oven drying refers not only to the oven itself; for some chemical processing units that contain equipment with internal castings, drying, sintering, and curing operations are also required.
For a new furnace that has been out of use for a long time, it is sufficient to heat it up more slowly during the drying process; there is no need to repeat the entire drying procedure. The purpose of drying is to dry the pouring material, and since the pouring material is already dry, there is no need to dry it again.
Perhaps I misunderstood it earlier; the original unit is a small-scale unit that frequently starts up and shuts down. Every night before starting work, I heat the furnace to 100 degrees using a constant-burn light for an entire night; this is also done to remove the moisture from the refractory bricks. Thank you for your answer! !