The boiler is burning under positive pressure – what’s the problem?
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Our unit installed a 4-ton steam boiler this year. During the first two months of operation, it worked normally, but later on pressure combustion occurred; whenever the boiler was turned on, dust filled the entire room. At first, it was thought that the flue was blocked, but an inspection showed that the flue was fine and the economizer was not blocked either. The front smoke box was inspected, and the smoke pipes were smooth. Later, the induced draft fan was checked, and its impeller was also in good condition with no blockages. The exhaust fan is operating normally, and the flue duct between the exhaust fan and the chimney is also in good condition with no blockages. I’m completely puzzled – why does such a thing happen? If the air supply volume is high, positive-pressure combustion should occur at the beginning of operation (since the blower does not have an adjustable damper). I would like to ask the experts and seniors for their help; is there anyone who can provide a reasonable explanation? Thank you!
A positive pressure in the furnace is naturally caused by an imbalance in the pressures of forced air and exhaust air. It is recommended to check the pressure at various points inside the furnace to determine where the zero-pressure point lies, and to compare this with the position of the zero-pressure point as specified in the boiler’s original design. Increasing the negative pressure for exhaust air and reducing the negative pressure for forced air can lower the pressure inside the furnace. Although, as you said, there is no ash accumulation or blockage in any parts of the boiler, and the air ducts and dampers are also in good condition, check whether the negative pressure for drawing in air has decreased.
How can I check the negative pressure of the exhaust fan?
Find out what type of boiler you have. There are many reasons for positive-pressure combustion in coal-fired boilers, and the cause must be determined based on the structure of your boiler. Here, I suggest that you check again the areas you have already inspected. Then, shut down the boiler and examine the air chamber baffles, the exhaust air baffles, the ash accumulation in the rear arch, the opening area of the secondary flue chambers, the degree of ash accumulation there, as well as the ash accumulation in the flue ducts and the chimney. Also, check how well the grate is conveying coal, whether there are any changes in the quality of the coal, and any changes in the thickness of the coal layer. If you need further assistance, please provide detailed information such as your boiler’s specific model, the type of coal used, the operating load, and the models of any auxiliary equipment. I’ll do my best to help you.
This is caused by the blower not having its air damper adjusted.
How does the poster handle the exhaust gases from the boiler? If water film dust removal is being used, this phenomenon can occur; in such cases it’s necessary to adjust the water volume or the amount of air drawn in. However, the biggest problem is likely ash accumulation and scaling in the economizer, so it’s recommended to conduct a thorough inspection.
Do you have air preheaters? This phenomenon has also occurred in our factory; it was later found that there were leaks in the air preheater
What’s your leakage ratio?
Please select: a) Circulating fluidized bed boiler b) Quarter-circle cut boiler c) Once-through boiler d) Other—————— (Please translation) IF: TO BE CONTINUED
Is water grinding effective for dust removal? For small boilers, is it possible to develop electrostatic dust removal or bag dust removal?
It is understandable for a negative-pressure boiler to have a slight positive pressure, but if the positive pressure becomes too high, then the issue of air supply needs to be considered. In the case of a balanced-ventilation boiler that uses both a blower and an exhaust fan, it is necessary to check whether the power of the exhaust fan is insufficient or whether there is a blockage in the flue. It can be said that an inadequate power level of the exhaust fan is a major problem
Boilers are such a pain. In the past, we were terrified whenever there was a problem with our boilers; now, steam is supplied from outside. There were also issues related to positive pressure in the boilers. Anyway, the mechanics are very skilled – they fixed it all in just one day!
Is it operating under overload, with insufficient air intake?
When a positive pressure occurs in the boiler, the harm it causes to production is self-evident. I believe that the problems should be investigated from the following aspects: 1. Check the water distribution in the water film dust remover to see if the return water flow is too low; if so, the water volume should be increased or an additional water source should be provided. 2. It is necessary to check the variation in the thickness of the furnace bed material layer; if the layer is too thin, positive pressure can easily occur, but it can return to normal within a very short time. 3. It is necessary to check the changes in resistance throughout the flue, such as in the narrower sections of the dust collector and areas prone to dust accumulation (including checking the baffles of the exhaust fan). 4. Check whether there are any leaks in the convective tube bundle; if there are, it will lead to increased accumulation of dust, which affects the gas flow rate and results in increased resistance and a positive pressure. 5. Check the entire flue system for any negative pressure leaks; if any are found, they should be sealed up.