Maintaining high TDS levels in the boiler drum results in water carryover and foaming. This leads to wet steam and lower heat transfer efficiencies to the process.
As boiler generates steam, impurities which are in the boiler feedwater and which do not boil off with the steam concentrate in the boiler drum water.
As the concentration of impurities increases, the steam bubbles rising from the bottom of the drum tend to become more stable, failing to burst as they reach the water surface of the boiler.
There comes a point where a substantial part of the steam space in the boiler becomes filled with bubbles and this foam is carried over into the steam main.
Presence of moisture reduces the heat exchange rate, increasing the process time. Thus it is also wastage of fuel as only steam participates in heat exchange in the process. High TDS levels in the boiler drum also lead to increased water side scaling.
Eg: The incremental fuel consumed due to high level of TDS maintained in the boiler is illustrated below.
Modern blowdown control systems are available to ensure TDS levels in the boiler are always maintained within set parameters.