Generally water contains certain percentage of dissolved solids. The percentage of impurities found in boiler water depends on the untreated feed water quality, the treatment process used and the boiler operating procedures.
As a general rule, the higher the boiler operating pressure, the greater will be the sensitivity to impurities. As the feed water materials evaporate into steam, dissolved solids concentrate in the boiler either in dissolved or in suspended state. Above a certain level of concentration, these solids encourage foaming and cause carryover of water into the steam. This leads to the formation of scaling inside the boilers, resulting in localized overheating and ending finally in boiler’s tube failure.
Blowdown is necessary to control the level of concentration of the solids and this is achieved by the process of ‘blowing down’, where a certain volume of water is blown off and is automatically replaced by feed water thus maintaining the optimum level of total dissolved solids (TDS) in the boiler water. Blowdown is necessary to protect the surfaces of the heat exchanger in the boiler. However, blow down can be a significant source of heat loss, if blowdown is not carried out properly.
Benefits of Carrying Blowdown in a boiler:
Good boiler blowdown control can significantly reduce treatment and operational costs of a boiler that include:
- Increased boiler life.
- Less make-up water consumption.
- Reduced maintenance downtime of a boiler.
- Lower consumption of treatment chemicals and
- Lower pre-treatment costs.