The conflict issue between feedwater pH and ammonia

This post was last edited by Yang Qing on 2020-9-9 at 14:31. With this concentration, it’s not clear whether it can be considered as complete ionization of ammonia; if the ionization is essentially complete, then such a process could theoretically work. However, if the feed water is not pure or its pH is already below 7, then what you are experiencing is normal. If there are limits on ammonia levels while the pH must meet certain standards, then other types of alkaline solutions can be considered. It is also necessary to consider whether the measuring instruments accurately reflect \"ammonia\" and \"pH value\" as mentioned in the question. Anyway, I don’t think it’s very appropriate to use ammonia to adjust the pH of demineralized water, especially considering there are limits on the ammonia concentration in ppm levels. I’m not sure what the purpose of the demineralized water is for the person who posted this question.

Desalinated water is mainly used as make-up water for boilers. I have observed a pattern: when the boiler is not generating steam, an ammonia concentration of around 0.5–0.8 mg/L is sufficient to keep the pH value of the feed water within the desired range; however, this situation changes once the boiler starts to generate steam

This post was last edited by Yang Qing on 2020-9-9 at 16:57. According to your description, if it is to be used for feeding boilers, can liquid alkali be used? Such a low concentration will not have a significant impact on costs. The boiler water must have a certain level of alkalinity to prevent scaling and reduce corrosion of the boiler. Since deionized water is being used, it is sufficient to ensure that the water hardness is within acceptable limits and to add an appropriate amount of alkalinity. The amount of alkalinity can be adjusted accordingly based on the total alkalinity level of the boiler water, which helps to ensure safe operation. Using ammonia does not seem to be a suitable option; could it not evaporate away along with the steam when gas is released? (Because ammonia is volatile, and based on your description there may also be environmental issues related to ammonia nitrogen.) These are just personal opinions for reference only.

This post was last edited by qugd on 2020-9-10 at 11:02. Ammonia is inherently a volatile component; when the boiler supplies steam externally, it can be lost along with the water, which causes the pH to drop. This is a normal phenomenon; ammonia needs to be added continuously depending on the operating conditions. When sodium hydroxide is used to adjust the pH of boiler feedwater, the pH is less likely to drop, but the amount of waste water discharged increases.

We use the Nessler’s reagent visual colorimetric method to determine the ammonia content. If ammonia is carried away by vapor, according to the ionization equilibrium, both the pH and ammonia levels should decrease; however, in reality only the pH decreases while the ammonia level remains unchanged

This post was last edited by Yang Qing on 2020-9-11 09:05. I’m not sure what method is used to add ammonia in your process, and what parameters determine the amount added? Online by pH value? Also, when you mention a decrease in pH, do you mean the boiler water or the feedwater? Where is the sampling point – in the cold water after ammonia addition, or in the preheated hot water before it enters the boiler? It is likely referring to feed water with a low temperature after ammonia addition, as the temperature and pH of the feed water prevent ammonia from evaporating (or only to a very small extent), or because the low pH of the feed water (deionized water) results in the formation of ammonium salts. Anyway, it seems that the original poster hasn’t clarified the questions raised, so it’s difficult to make a judgment. What are the water quality standards for the boiler feedwater and furnace water used by the poster? Generally, the pH of boiler water should be above 10; at such a pH level, ammonia loss is likely to be high. Also, you mentioned “deionized water” – how is this deionized water obtained? Anion and cation exchange + mixed-bed? What is the purity of the deionized water?

The method of addition involves pouring bottled ammonia into the dosing tank where it is mixed, and then the dosing pump is used to add this mixture to the water supply. The amount of ammonia added is determined primarily by the pH of the water supply; if the pH is high, less ammonia is added, while if it is low, more ammonia is added. pH measurement is carried out in the water analysis laboratory, about 400 meters away, by taking samples using plastic bottles from the sampling point located 7 meters away from the boiler, after which the bottle caps are tightened. A low pH indicates a low pH in the water supply, while the pH of the boiler water is adjusted using trisodium phosphate to keep it within normal ranges. Water sampling is taken at the inlet of the economizer; the location of the water treatment chemicals addition point is not specified. The control parameters for boiler feedwater are: pH 8.8–9.2, ammonia level 0.2–1 mg/L. The control parameters for boiler water are: pH 9–10. Deionized water is produced through a process that involves ultrafiltration, primary RO treatment, secondary RO treatment, and EDI; the resistivity of the resulting water is 17 MΩ·CM

It seems that your requirements for boiler feed water are quite high; if this deionized water can indeed achieve such a high resistance value, it is already pure enough. Stabilizing the pH of the boiler water using trisodium phosphate ensures a stable environment, thereby providing a basic guarantee for the safe operation of the boiler. Theoretically, if the quality of the feed water remains constant, and both the ammonia concentration and the amount added per unit volume stay unchanged, then the ammonia content and pH should also remain constant. However, in actual operation, what the poster described occurs: the standards are met when no gas is supplied, but when gas is supplied, there is a conflict between ammonia and pH – either the ammonia level is too high or the pH level is insufficient. I’m not sure what the purpose of setting standards for pH and ammonia levels in the water supply is; in any case, in practice, at certain times the quality of the deionized water is not very good, which leads to an increased need to add ammonia. Therefore, it is possible to observe whether the resistance value of deionized water remains stable, and whether this is due to parameter fluctuations in the deionization system when it is not operating continuously.