When will the induced draft fan be put into use?
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The operating procedures state that once the blower is put into use and the oxygen level is under proper control, the exhaust fan should be activated when the temperature of the flue gas at the chimney reaches 260°C. 1. Are the drum blowers started with the inlet butterfly valves fully closed to avoid excessive starting current? 2. What is the reason for starting to operate the exhaust fan once the flue gas temperature in the chimney reaches 260°C? On the technician operation test questions, it states that \"for forced-air heating furnaces, in order to effectively dry the lining of the air preheater ducts, the exhaust fan should be started when the temperature of the flue gas at the inlet reaches 260°C, so as to ensure air circulation inside the preheater.\" ” Are the answers to these two questions correct?
The first question is correct – start-up with no load. For the second question, it may vary depending on the device; generally, the drum blower is started first before ignition. 260°C may be a maximum limit to prevent dry burning of the preheater
1. Closing the inlet is to prevent startup under load, which would result in excessive current. 2. I have doubts regarding the second issue: how can negative pressure be created in the furnace if the fan is not started, and how can normal combustion of the flame be ensured? Why can the drying of the flue duct be carried out during the furnace drying stage once the temperature of the flue gas at the chimney reaches 260°C?
With the inlet valve fully open and the outlet valve closed, it is a no-load start.
The second point should be considered in conjunction with low-temperature dew point corrosion
If this is an exam question, take the person who created it outside and kill them 10 times. Before starting the furnace and igniting it, it is necessary to turn on the exhaust fan in order to ventilate the furnace chamber. During ignition, the inlet valve of the exhaust fan can be closed; it is important to maintain a negative pressure in the furnace chamber. For furnaces equipped with blowers, these also need to be started before ignition, and their outlet valves should be closed during ignition as well. Establishing circulation within the furnace chamber is an essential condition. If it is due to dew point corrosion, the amount of fuel used when starting up the furnace can be ignored; modern large-scale installations use stainless steel for their exhaust fans, and chimneys should have an internal anti-corrosion coating. It’s fine if the pipeline is corroded; just repair or replace it.
The furnace itself has a chimney that creates negative pressure for ventilation; activating the exhaust fan essentially means switching between the exhaust fan and the flue damper. The reason why the exhaust fan is not activated from the beginning is to avoid dew point corrosion – the furnace may take some time to heat up, and if smoke remains at low temperatures for an extended period, it can indeed cause corrosion in the waste heat recovery system.