Softener Breakthrough and Foaming Carryover
A 200 hp, 150 psig boiler uses a sodium zeolite softener. Recent tests show feedwater hardness 1.8 gpg (as CaCO3), feedwater chloride 45 ppm, boiler water chloride 1,800 ppm, boiler water TDS 5,200 ppm, alkalinity 700 ppm, and silica 80 ppm. Blowdown is set at 4% of feedwater. The sight glass shows a foamy water line, and steam is carrying moisture into the process. The softener regenerates on a timer every 8 hours regardless of throughput, and brine strength is occasionally low. The operator proposes increasing continuous blowdown to 8%.
1. Calculate cycles of concentration from chloride and assess the blowdown.
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Chloride cycles = boiler water chloride / feedwater chloride = 1,800/45 = 40. That is very high for this boiler. With continuous blowdown and no other losses, 4% blowdown would suggest about 1/0.04 = 25 cycles, so the 40-cycle chloride result and the stated blowdown do not agree. Either the blowdown is not truly continuous, sampling is inconsistent, or there are other water losses. Either way, the boiler is overconcentrated. A more reasonable target might be about 15 to 20 cycles, which would require roughly 5% to 6.7% blowdown plus operating margin, but the target should be set from the limiting boiler-water parameter and confirmed by testing.
2. Why is the softener the likely root cause, and what risk does increasing blowdown alone pose?
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Feedwater hardness of 1.8 gpg is about 31 ppm as CaCO3. At 40 cycles, that hardness load is concentrated enormously in the boiler and will precipitate as scale on tubes and shell surfaces. A softener that regenerates on a fixed timer can pass hardness when throughput is high, and low brine strength causes incomplete regeneration. Increasing blowdown to 8% will lower cycles and help with foam and TDS, but it does not remove existing scale and does not stop hardness leakage. It also increases makeup, energy, and chemical consumption. Blowdown alone treats the symptom, not the scaling mechanism.
3. Recommend immediate and long-term actions.
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Immediately reduce boiler-water concentration by blowing down to a safe target, verify the gauge glass and carryover, and test hardness, chloride, TDS, alkalinity, and silica after each step. Do not rely on antifoam as a permanent fix. Long-term, repair or re-program the softener: regenerate on volume or hardness breakthrough, not only time; verify brine strength, salt level, injector, and resin condition; test softened-water hardness after each regeneration; and add a hardness alarm or online monitor. Inspect the boiler for scale and carryover deposits at the next opportunity, and adjust blowdown to hold the limiting parameter within the boiler manufacturer's recommended range.