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Carryover - a classic water chemistry problem.
Dissolved solids and particles entering a boiler through the make-up water will remain behind when steam is generated. During operation the concentration of solids builds up and finally a concentration level is reached where operation of the boiler becomes impossible. If solids are not purged from the boiler they can lead to scale formation, carryover, corrosion and embrittlement. Chemical treatments and continuous surface blowdowns are commonly used to eliminate solids at the same rate as they are added from make-up water. In general short frequent blowdowns are more effective in removing boiler water sludge than a one, long, infrequent blowdown.
When the boiler water chemistry is out of balance the most likely culprits are high TDS (Total Dissolved Solids), high TSS (Total Suspended Solids) and/or Alkalinity levels. The TDS should be below 2000-2500 PPM (3000-3750 µS/cm), TSS should be negligible or zero and the Total "P" Alkalinity should be below 500 PPM for boilers operating under 15 psig. The cycles of concentration should be such that none of these three limits are exceeded. These values are recommended by the ABMA (American Boiler Manufactures Association) and ASME (American Society of Mechanical Engineers).
Other factors like chemical over treatment, scale, oil and suspended solids can also cause carryover. Oxygen and/or air infiltration is a big factor that contributes to high TDS readings and must be addressed. Vacuum return systems are notorious for "air leaks" in the system. These leaks will cause corrosion and high TDS levels. A good way to quickly check for a chemistry imbalance is to beat or whisk a sample of the boiler blowdown water. If bubbles form and do not immediately dissipate there is most likely a chemistry imbalance that can and will cause carryover.
If the carryover problem is not solved you will be hard pressed to find a pump big enough to replace the water fast enough to keep up the water entrained with the steam. This will add excessive amounts of fresh untreated water into your steam system. Carryover can be confirmed by testing the return water chemistry.
