What is furnace negative pressure?
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At first, I didn’t understand what negative pressure in the furnace meant; today I finally got it. It turns out that the difference between the pressure inside the furnace and the atmospheric pressure outside is a reflection of the degree of draft in the furnace chamber. :lol
The draft in the furnace is determined by the height of the furnace chimney and the performance of the exhaust fan, primarily due to the density difference between the inside and outside of the chimney. This post was last edited by cswenhan on 2009-2-5 16:32]
Negative pressure anesthesia is created by a pressure difference, haha! For a heating furnace, it is very important to maintain negative pressure in the furnace chamber!
The negative pressure value is related to the opening degree of the dampers and flue baffles
In a naturally ventilated heating furnace that relies on chimney baffles to regulate draft, the generation of draft depends on the height of the furnace’s chimney and the conditions of the surrounding environment. For heating furnaces that are forced to ventilate using exhaust fans, the chimney is not relevant; the key is to adjust the \"three doors and one plate\" in order to regulate the negative pressure inside the furnace chamber
The resistance of the chimney is related to the velocity of the gas. High speed results in high resistance, but too low a speed leads to poor smoke exhaust. The gas velocity can reach 7–8 meters per second, but it should not be less than 5 meters per second to prevent air from flowing back into the chimney. The sum of these resistances is denoted by ∑ΔP. To ensure smooth smoke exhaust and maintain a certain negative pressure in the furnace, a force is needed to overcome the resulting resistance; when this resistance is high, mechanical ventilation is used. The capacity of the chimney exhaust fan should be determined based on the maximum volume of gas. It is generally overcome by using the chimney effect generated by natural convection. Its chimney draft must be equal to or greater than ∑ΔP. The draft in a chimney is caused by the difference in gas temperatures inside and outside the chimney, which leads to a difference in gas density. This density difference creates a pressure difference that constitutes the chimney’s draft; it overcomes resistances and drives the flow of smoke gases. It can be calculated using the following formula: ΔP = h (r_out – r_in), where: h is the height of the chimney, in meters; r_out is the density of the atmosphere outside the chimney, in kg/m3; r_in is the density of the gases inside the chimney, in kg/m3. As can be seen from this formula, the suction force ΔP exerted by the chimney is proportional to both the height of the chimney and the difference in gas densities. The higher the chimney, the greater the suction force ； The greater the difference in gas density, the greater the suction force. The difference in gas density is related to the temperatures of the gas inside and outside the chimney as follows: the greater the temperature difference, the larger the density difference, and thus the greater the suction force in the chimney. Due to process constraints, the temperature of the flue gas does not change significantly. Atmospheric temperature, on the other hand, changes with seasonal variations. When designing the chimney height, the most extreme summer conditions should be taken into account; when the process conditions remain unchanged, the flue dampers should be opened wider in summer and closed tighter in winter.
I’ve learned it,,, thank you so much!
The negative pressure in the furnace should be regulated using the \"three doors and one plate\" mechanism. For better smoke exhaust and for safety reasons, the furnace is usually kept at a slight negative pressure, so as to prevent the flame from causing injuries! It causes unnecessary safety accidents!