Why does the pH value drop after desalinated water is used?
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The demineralized water used in our plant is used to remove the heat generated during reactions, producing steam at 1.6 MP pressure, which is equivalent to a boiler operating at 1.6 MP. We have found that the pH value of the wastewater is about 1.5 lower than that of the incoming water. Does anyone know why this is?
The boiler water is kept slightly alkaline (pH 9-12) to prevent corrosion and scaling; the pH of the boiler water is generally controlled by adding mildly alkaline phosphate agents, as well as through regular and continuous blowdown. In the boiler, in alkaline water, the Ca2+ ions present in the non-carbonate hardness react with PO43- to form Na3PO4: 10Ca2++6PO43-+2OH-——Ca10(OH)2(PO4)6. The resulting basic phosphates is a soft sludge that can be removed during wastewater discharge. In my opinion, as can be seen from the above equation, the consumption of OH ions may lead to a decrease in pH.
In desalinated water, the pH value is generally adjusted using liquid ammonia; when steam is generated, some of the ammonia evaporates, so the pH value decreases slightly.
The pH value of demineralized water is generally adjusted using ammonia, with a value kept between 8.5 and 9.2. After steam is generated, some of the ammonia evaporates, which causes the pH value to decrease slightly.