In the waste heat boiler, the phosphate level is high while the pH of the boiler water is low. Seeking advice from all the experts! ! !
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1. Our plant has two 25-ton waste heat boilers with a pressure of 1.0 MPa. The boiler feedwater is demineralized water, with a pH value of around 8.5. 2. Recently, in Unit 2, there has been an increase in phosphate levels in the boiler water along with a decrease in the pH value. (A similar situation occurs in Furnace No. 1, but the change in water quality is not significant. ) These two boilers have been in operation for about 10 years. In the early days, trisodium phosphate was added to adjust the pH level of the boiler water and prevent scale formation. Last year, we started using an organic chemical with similar effects instead. Under normal circumstances, the phosphate level in boiler water is around 1 mg/L. A couple of days ago, the pH value of the boiler water suddenly dropped from 10 to around 8. Meanwhile, the phosphate level rose rapidly, peaking at 20 mg/L. 3. The method for detecting phosphate in boiler water is to use a spectrophotometer; the result is then calculated according to a formula. I’d like to ask all the experts: What’s going on here, and how can it be resolved?
The increase in phosphate content and the decrease in pH value in the boiler water may be caused by several factors. Below are several possible causes of this phenomenon, along with corresponding solutions: 1. Poor water quality: – If the amount of impurities in the feedwater increases, especially if it contains metal ions that can be phosphorylated, phosphorous compounds may form in the boiler. This, in turn, leads to an increase in the concentration of phosphate ions. It is necessary to re-examine and analyze the composition of the feed water to ensure the proper operation of the demineralization or water softening systems, as well as to carry out proper pretreatment. 2. Chemical dosing issues: - The replacement of chemicals may have altered the chemical balance of the boiler water, resulting in a decrease in pH. It is necessary to re-evaluate the dosage and frequency of the new medication; consult the pharmaceutical provider and professionals if needed. At the same time, verify that the chemical mixing and dosing equipment is operating normally, with no malfunctions. 3. Internal contamination or corrosion of the boiler: – Prolonged operation of the boiler leads to the accumulation of dirt and corrosion products. If cleaning and maintenance are inadequate, it may result in a decrease in pH levels and an increase in phosphate levels. A thorough inspection and cleaning of the boiler is required to remove scale and contaminants. 4. Operational errors or equipment malfunctions: - Check the operation logs to determine whether any operational errors led to an excessive dosage of chemicals or a malfunction in the control system. At the same time, check whether all instruments and equipment related to the control of boiler water pH and phosphate levels are accurate and functioning properly. 5. Accuracy of the analytical method: – Verify whether the calibration and operating procedures of the spectrophotometer are accurate, so as to prevent incorrect judgments caused by measurement errors. Considering all these possible causes, you can take the following steps to address the issue: A. Compare the water quality changes in both boilers, identify any differences, and analyze the potential causes ； B. Re-verify the spectrophotometer and recheck the test results for phosphate ； C. Inspect and verify the effectiveness of the water treatment system to ensure that the water quality meets standards ； D. Adjust the chemical dosing plan and control strategy according to the recommendations of the boiler manufacturer and chemical supplier ； E. Perform internal inspection and cleaning of the boiler to eliminate dirt and corrosion issues ； F. Strictly implement operating procedures to ensure that all control parameters and equipment operating conditions remain in their optimal states ； If the problem remains unresolved after performing the above checks and adjustments, it is recommended to contact a professional boiler chemical treatment company for further inspection and diagnosis. .
It is recommended that the poster verify the normal indicator values of the boiler water. According to GBT 16811, for a boiler operating at 1.0 MPa, a pH value of 10–12 and a phosphate concentration of 10–30 mg/L for the boiler water are within the normal range. The current issue is that the pH value of the boiler water is on the low side (observing the continuous blowdown, it seems to be slightly reddish). It is recommended to verify whether the feed water pH value is indeed 8.5 and if there are any fluctuations (I can’t recall ever seeing a situation where the pH of the boiler water was lower than that of the feedwater.) If there are still problems, they most likely stem from the chemical dosing process.
Due to the replacement with organic chemicals, the phosphate level in the boiler water is now very low. The national standard is established based on the phosphate treatment process. These days, the phosphate level rises only after the pH of the boiler water decreases. On our end, it’s sufficient to keep the pH value of the boiler water above 10. Regarding the feedwater, monitoring has been ongoing since issues arose with the boiler water; the values have all been around 8.5. Previously, trisodium phosphate was used; now it’s unclear whether the phosphate ions originate from the salt deposits in the furnace or are introduced via the feedwater. Today, I’m considering whether to install an online pH detector at the water supply end.
Does your testing method measure total phosphorus or phosphate? It seems that organic phosphate cannot be detected using this method. Additionally, what kind of changes occur in the electrical conductivity?
Learned*: victory: