The problem of scaling in boiler feedwater pipes
Thread Content
Steam drum, 5 MPa; after 8 months of operation, it was observed that the water addition rate had decreased. Upon inspecting the pipes, scaling was found inside them. Analysis of the scale revealed that its main components were Fe: 15.16, SiO2: 1.07, CaO: 0.36, MgO: 38.94, Al2O3: 0.6, and P: 14.424. Assistance is sought in determining the cause of this scaling. The chemicals used for routine treatment are ammonia solution, dimethyldithiooxime, and trisodium phosphate
1. According to the analysis, the main component of the impurities in your case is iron, which indicates that the pipes before starting up the furnace were not properly cleaned with acid. Similar situations occur in pipes that have been cleaned with acid, but to a much lesser extent! 2. Does your boiler have a system for reusing condensate water? Attention should also be paid to this aspect; carrying out slag removal at the lowest point of the reuse pipeline helps to reduce the impurity content in the condensate water!
I think there’s an issue with the water treatment process for refilling your boilers; is deionized water being used?
The boiler is fed with softened water to remove calcium and magnesium ions with high hardness; also, are the pipes made of stainless steel?
The dimethyl oxime solution used had a hardness of 2750 mg/L
Are the parameters of the boiler feed water and furnace water normal? Is the continuous and periodic drainage functioning properly? Abnormal periodic drainage can prevent the phosphates in the furnace water from being removed, leading to scaling.
Are the parameters of the boiler feed water and furnace water normal? Is the continuous and periodic drainage functioning properly? Abnormal periodic drainage can prevent the phosphates in the furnace water from being removed, leading to scaling.
Scaling in water supply pipes has little to do with regular or continuous drainage. It mainly depends on the location where chemicals are added to the feed water and whether the quality of the feed water is satisfactory. Also, it matters whether the material of the water supply pipes is appropriate, and whether the maintenance work before and during operation is carried out properly.
The dosage of the chemical added does not match the level of calcium, magnesium, and iron ions in the water; adding such chemicals can only reduce the ion levels but cannot eliminate them completely. It is recommended to carry out desalination treatment on the water, and if possible, replace the pipes with stainless steel ones.