Heating efficiency of the furnace

In ordinary heating furnaces, the flue dampers are used to directly adjust the negative pressure in the furnace, keeping it around -30 Pa; this negative pressure has a significant impact on the furnace’s thermal efficiency as well. In order to improve the thermal efficiency of the furnace, we often set the negative pressure very low, sometimes even to a slight positive pressure. This does help to increase the furnace’s thermal efficiency, but it can easily lead to burns from backfire, and it is also harmful to the equipment; therefore, it is not recommended. The flue dampers can be controlled automatically or manually, with automatic control being the standard approach. However, adjusting the flue baffle also has some consequential effects on the exhaust gas temperature and the oxygen content in the furnace.

The flue dampers certainly have a significant impact on the thermal efficiency of the furnace; the opening degree of these dampers directly affects the flow rate of air entering the heating furnace.

The flue dampers certainly have an impact on the furnace’s thermal efficiency, but automatic control is used during normal operation. By setting the negative pressure of the furnace to a very low level, the furnace pressure can easily fluctuate to the positive pressure alarm threshold. Therefore, for the sake of ease of operation and safety, it is not advisable to deliberately reduce the furnace pressure in order to improve the furnace’s thermal efficiency.

The flue damper has a significant impact on the thermal efficiency of the furnace； The method to improve the thermal efficiency of a furnace is to ensure that the oxygen content remains between 2% and 3%, based on the heat required by the material being processed; this is achieved by adjusting the flue dampers, the amount of steam used for atomization, and the air valves, by using high-efficiency burners, and by installing waste heat recovery systems. Last edited by Zhongyuanren on 2009-4-16 20:30]

The opening degree of the flue baffle is directly related to the furnace’s thermal efficiency. If it is opened too wide, the negative pressure increases, more air enters, the flue gas temperature rises, and the volume of flue gas increases; as a result, more heat is carried away, leading to a decrease in the furnace’s thermal efficiency. On the other hand, if it is opened too narrow, it may cause positive pressure in the furnace chamber, posing a risk of backfire.

It matters a lot! The main factors affecting the thermal efficiency of a heating furnace are the combustion conditions and the exhaust gas conditions; good combustion and an appropriate exhaust gas temperature result in higher thermal efficiency. The opening degree of the flue baffle directly affects the furnace negative pressure and the excess air coefficient: a larger opening degree results in higher furnace negative pressure and excess air coefficient, which leads to better combustion, but it also increases the amount of flue gas, thereby carrying away a large amount of heat ； With a low opening degree, the negative pressure in the furnace and the excess air coefficient are low, resulting in poor combustion and fuel waste. Therefore, the opening degree of the flue baffle must be appropriate; generally, the negative pressure in the furnace is controlled at 20-50 kPa

The slight negative pressure in the furnace chamber of a heating furnace is related to the opening degree of the chimney dampers; when the opening degree is low, a positive pressure develops in the furnace, which can cause hot flue gases to escape, increasing heat losses. It may also lead to overheating or damage of the steel structures outside the furnace, triggering other accidents. When the opening is large, the negative pressure inside the furnace increases, allowing more air to leak in; as a result, the excess air coefficient rises, which **reduces the thermal efficiency of the heating furnace**. Our furnace chamber is maintained at -85 Pa (gauge pressure)

It matters a lot! There are two main factors that cause heat loss in heating furnaces: high flue gas temperature and incomplete combustion. The opening degree of the flue dampers has a direct impact on the negative pressure in the furnace and the excess air coefficient: a larger opening degree results in higher negative pressure in the furnace and a higher excess air coefficient. While this improves combustion, it also leads to an increased amount of flue gas, more air leaking in, and thus greater heat loss ； With a low opening degree, positive pressure develops in the furnace, and the oxygen content entering the furnace decreases, resulting in incomplete combustion of the fuel and a significant reduction in the furnace’s thermal efficiency. Therefore, the opening degree of the flue baffle must be appropriate.

Flue dampers certainly have a significant impact on the thermal efficiency of a furnace, but when it comes to thermal efficiency, the flue gas temperature is the main factor determining its level

Could someone explain the formula for calculating thermal efficiency?

Just control the furnace negative pressure, the residual oxygen level in the flue gas at 2–3%, and the color of the burner flame

It has a significant impact; it affects the negative pressure in the furnace, the exhaust gas temperature, and the oxygen content! !

Personally, I think in terms of safety, one must always keep in mind the issue of negative pressure in furnaces; of course, positive-pressure furnaces are another matter. For negative-pressure furnaces, it is sufficient to maintain a certain level of negative pressure; if this level is too low, more fuel must be used, which increases the costs. The pressure is too high; although the thermal efficiency improves, safety concerns arise. Therefore, finding the optimal pressure level is quite important for the thermal efficiency of the furnace.