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1. Judgment based on the instruments: The criterion is that the outlet temperature of the heating furnace is within the specified process range. The temperature difference between various points within the furnace chamber of the cylindrical furnace should not exceed 30°C. Judging from the recorded curve: (1) The curve indicates normal operating conditions ； (2) The curve shows regular fluctuations with a stable center line, which generally indicates that the instrument or the scaling factor is too high and that the response is slow. (3) The center line of the curve is unstable, and the curve changes rapidly in an irregular manner, which usually indicates large fluctuations in fuel pressure or the presence of oil in the gaseous fuel. (4) The curve changes irregularly with a long bending period, but there is also a period of stability, which generally indicates changes in the feed rate or feed temperature. (5) The center line of the curve is unstable, with rapid changes over a short period of time; however, these changes follow a pattern, which generally indicates that the proportional-integral control is too strong. (6) A slow upward or downward movement of the line generally indicates a malfunction of the instrument. 2. Judging operation status from the sound of the heating furnace: Operators need to assess the operating conditions by listening to the sounds emitted by the furnace, focusing mainly on any changes in those sounds. The sound changes of the furnace can generally be categorized as follows: (1) The normal sound of a heating furnace, with a consistent level of noise ； (2) With a loud noise, the engine shuts down; the wind and power are cut off, and steam supply stops suddenly ； (3) The regular back-and-forth thudding sound is caused by improper proportional-integral control of the instrument ； (4) Irregular back-and-forth roaring noises are caused by improper operator adjustment, changes in feed volume and fuel oil pressure, or gas fuel containing oil. 3. Judging from the flame in the furnace chamber of the heating furnace, the flame combustion should meet the following criteria: multiple flames, short flames, even distribution, and uniform height. The flame of fuel oil should be apricot-colored, while the flame of gas should be sky-blue; the furnace chamber should be bright, combustion should be complete, the flame colors should be consistent, and no smoke should emerge from the chimney. The flame height is generally around 2 meters. Based on the above criteria, the abnormal phenomena in flame combustion include the following: (1) Incomplete combustion of the flame in the furnace; the flame is weak and limp, its base is dark black, and smoke may even emerge from the chimney. Reason: The ratio of fuel oil to steam is improper; there is too little steam, resulting in poor atomization. (2) The flame in the furnace does not burn completely; it spreads out chaotically, is weak and faint, colored black-red, or smoke emerges from the chimney. Reason: Insufficient steam and air volume. (3) The combustion of some flames does not meet the standards. Reason: Improper adjustment by the operator. (4) The furnace flame is prone to going out. Reason: Excessively high viscosity of the fuel oil along with water content, or a low opening degree of the oil valve; excessive steam volume along with water content. (5) The fuel exits the combustion channel at the nozzle and burns there. Reasons: Light fuel oil, excessive steam volume, excessive opening of the fuel valve, and insufficient air supply. (6) The flame is ejected in an unshaped form. Reason: The burner section is blocked, and the combustion channel of the burner is clogged with coke. (7) The duration of the flame cluster is short or long. Reason: Improper proportional-integral control of the instrument. (8) The flame is white and hard, with pulsating movement. Reason: Excessive steam and air volume. (9) Flash fire. Reason: The opening of the oil and vapor valves is too large, resulting in significant and regular fluctuations in fuel oil pressure. 4. Judgment from the heating furnace chimney: (1) It is normal if no smoke is visible coming from the furnace chimney. (2) Emitting intermittent small black smoke. Reason: Insufficient steam volume, poor atomization, incomplete combustion, or an improper oil-to-vapor ratio in some nozzles, as well as an excessive load on the heating furnace. (3) Emiting thick smoke. Reason: Sudden increase in fuel ； Instrument failure ； Sudden drop in steam pressure ； The furnace tube has burned through. (4) Emit large amounts of gray-black smoke. Reason: Sudden increase in gaseous fuel with oil contamination. (5) White smoke emission. Reason: Overheated steam pipe rupture. (6) Yellow smoke emission. Reason: Confused operations ； Improper adjustment ； This caused some nozzles to stop functioning ； Fuel oil vapor carries smoke out of the flue ； Incomplete combustion.