Thread Content
Furnace negative pressure is an important parameter that reflects the stability of the combustion conditions, and it is one of the key parameters that need to be controlled and monitored during operation. Once the combustion conditions inside the furnace change, the negative pressure in the furnace chamber changes accordingly. When there is a fault or abnormality in the boiler’s combustion system, it is first reflected in the negative pressure within the furnace; followed by changes in the flame detection systems and the flame itself, with changes in steam parameters occurring last. Therefore, monitoring and controlling the negative pressure in the furnace is of extreme importance for ensuring the stability of combustion conditions inside the furnace, analyzing those combustion conditions as well as the operation of the flue gas system, and determining the causes of certain accidents. Most boilers use balanced ventilation to keep the pressure of the flue gases inside the furnace equal to the external atmospheric pressure; in other words, there is a negative pressure of the flue gases inside the furnace. The area with the highest flue gas pressure inside the furnace is the top of the furnace chamber. The so-called furnace negative pressure refers to the pressure of the flue gas at the top of the furnace. When the negative pressure in the furnace is too high, the air leakage increases, leading to higher power consumption of the exhaust fan, greater losses due to incomplete combustion, and higher heat losses from the exhaust gases. It can even make the combustion unstable, cause the furnace to operate under negative pressure or even under positive pressure; as a result, flames and fly ash will escape through any gaps in the furnace, worsening the combustion process and posing a risk to human safety and equipment integrity. Therefore, the negative pressure in the furnace chamber should be maintained within the normal range. A major cause of fluctuations in the negative pressure inside the furnace during operation is changes in the combustion conditions. With the intake and exhaust fans remaining unchanged, minor variations occur due to these changes in combustion conditions, which results in fluctuations in the negative pressure within the furnace. When combustion is unstable, the furnace pressure experiences severe fluctuations, and accordingly, the negative pressure within the furnace also sees large and sharp variations. When the furnace pressure experiences severe fluctuations, it is often a precursor to fire out; in such cases, it is necessary to enhance monitoring and inspection of the combustion conditions inside the furnace, analyze the causes, and take prompt corrective actions. At the same time, as the flue gas passes through each pair of convective heating surfaces, it must overcome flow resistance; therefore, the negative pressure at various points along the flue gas path increases gradually. At different loads, due to changes in the amount of flue gas, the negative pressure at various points in the flue also changes accordingly; for example, as the load increases, the negative pressure at those points increases as well ； Conversely, it decreases accordingly. Under normal operation, the negative pressure at various points in the flue maintains a certain pattern of variation in relation to the load. When slagging, ash accumulation, or local blockages occur on certain sections of the heating surfaces, the cross-sectional area through which the flue gas flows decreases, resulting in an increase in the flow velocity of the flue gas and a rise in resistance. As a consequence, the pressure difference between the inlet and outlet, as well as the negative pressure at the outlet, increase accordingly. By monitoring the changes in negative pressure at various points in the flue, as well as the temperature of the flue gas, it is possible to detect promptly any issues such as ash accumulation, blockages, leaks on the heating surfaces, or incidents of secondary combustion. Therefore, under normal conditions, the negative pressure in the furnace chamber and that in each flue have roughly the same range of variation. During operation, if any abnormal changes in the numerical values are detected, a thorough analysis should be conducted to identify the cause and take timely action to prevent various abnormalities and accidents, thereby ensuring the safe operation of the furnace