Corrosion analysis of flue gas recovery equipment in natural gas boilers
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Natural gas flue gas: cooled from 800°C to 50°C, with waste heat recovery; severe corrosion occurs within just one winter – what’s going on? Help needed
Gas boilers reduce the flue gas temperature in an effort to improve the efficiency of gas utilization; however, this leads to the problem of corrosion caused by condensate water. If natural gas contains high levels of impurities, it will accelerate this corrosion process. For our company’s 20 d/h gas boiler, the design institute specified a temperature of 140 degrees, while the boiler manufacturer sets it at 90 degrees to prevent corrosion caused by low-temperature condensation. Your company may consider taking the following measures: reduce the water supply to the final heat exchanger, also known as the economizer, during winter, increase the flue gas temperature, adjust it according to the ambient temperature by selecting an appropriate temperature level, thereby reducing condensation-induced corrosion.
Inlet temperature: 800℃; after secondary heat exchange, outlet temperature: 50℃
Severe rusting, overall peeling; red rust present. Some areas are coated with anti-rust paint, while the uncoated areas continue to rust and end up falling off along with the paint
In less than three months, two coats of anti-corrosion paint were applied; repairs were carried out, and it ended in disaster
**The standard requires that the exhaust temperature be below 170°C, under conditions of a rated water temperature of 95°C and at full load. When the boiler water temperature is below 50°C, dew point corrosion inevitably occurs on the boiler’s convective heating surfaces. Therefore, this type of corrosion occurs in almost all heating boilers, though its progression can be fast or slow; in rapid cases, the boiler becomes unusable within a few months, mainly due to water leakage in the smoke pipes and the rear tube sheet. 10 years of slowness is no problem. So this question is worth exploring.
Low-temperature corrosion due to condensate water; the temperature shouldn’t drop too low