Issues with boiler water quality parameters

The main reason for controlling the pH of the feedwater and boiler water is to reduce corrosion in the feedwater pipes and within the boiler; by maintaining it at **standard values, corrosion can be kept at a relatively low level. Since the boiler water is concentrated feedwater, its pH is naturally higher than that of the feedwater. By adding ammonia to the feedwater and trisodium phosphate to the boiler water, it is possible to ensure that the pH of the boiler water remains higher than that of the feedwater.

Thank you for the positive response. I have another question: By adding ammonia, the pH value of the feedwater can be increased from around 7, which is the pH of demineralized water, to 8–9.5. But will these substances such as ammonia, which are used to raise the pH of the feedwater, evaporate due to the high temperatures inside the boiler and drum and end up in the steam? Also, is adding trisodium phosphate to the boiler water done solely for hard water removal? Does it also play a role in regulating the pH value of the boiler water?

First, the pH value of the feed water is not 8–9.5, but rather 8.8–9.2. Second, the pH value of the feed water is adjusted by adding ammonia, primarily to prevent corrosion in the pipelines from the demineralized water station to the deaerator. Third, ammonia may volatilize in the deaerator, but this will not be a serious issue, as the pH value of the deoxygenated water generally does not drop much after deoxygenation. Fourth, sodium tripolyphosphate added to the boiler water is a strong base weak acid salt; it undergoes hydrolysis to produce an alkaline environment, thereby increasing the pH value of the boiler water. It ensures that the pH value of the boiler water is higher than that of the feedwater. Fifth, after deoxidation in the deaerator, volatile ammonia is present in very small amounts, and little of it is carried in the steam. Sixth, based on personal experience, as long as the pH value of the water supply is greater than 9.2 (in systems without copper), it is possible to ensure that the pH value of the deoxygenated water remains above 9.0. And a pH value of deoxygenated water above 9.0 ensures that the pH value of the boiler water stays above 9.0 as well.

After chemicals are added to the furnace, the pH value of the furnace water is higher than that of the feedwater.

It is appropriate to maintain the pH level of the boiler water between 9.0 and 10.5; values that are too high or too low can cause corrosion in the boiler tubes. Studies have shown that keeping the pH of the boiler water within the range of 9.0–11.5 results in the least corrosion of carbon steel by the boiler water. The pH value of the boiler water affects the formation of scale; when the pH is between 9 and 11, the reaction between PO43- and Ca2+ in the boiler water results in the formation of sludge that can be easily removed. However, when the pH drops to between 7.5 and 8.0, the reaction between these two ions leads to the formation of Ca3(PO4)2 scale. Furthermore, by properly controlling the pH value of the boiler water, it is possible to reduce the amount of silicic acid carried in the steam, thereby improving the quality of the steam.