A steam boiler requires softened, filtered water – crystal clear, and free of impurities.
If the available water comes from a well, it will be necessary to filter it through a silica sand filter and additionally, if it contains chlorine or odors, through an activated carbon filter, in order to eliminate all of the unwanted elements. It is also recommended to check the hardness of the available water and if greater than 80 parts per million (ppm), to run it through a water softener.
Note: If the water comes from the main water line and is already clean and clear with a hardness of lower than 80 ppm, you may be able to avoid having to install a water softener and instead, treat the water with a chemical treatment and a system of scheduled blowdowns.
If the available water is free of impurities and contains little chlorine, but has a hardness of greater than 80 ppm, running it through a water softener is recommended.
Water softeners require a minimum pressure of 15 PSI to operate effectively and, depending on the size, may require a pressure of up to 45 PSI.
Once the otherwise pure water has been softened, it gets deposited via a control valve into the condensate receiver tank, from which, with the help of a feedwater pump, it is injected into the boiler.
It is called a “condensate tank” because in addition to receiving the softened water, the tank collects condensates which result from the steam that the boiler supplies to the heat exchangers or processes, once the steam transfers its heat or energy and changes from vapor to liquid water condensate.
The boiler feedwater pump sucks the water from the condensate take and injects it with pressure into the boiler.
The heat transfer is carried out in a steam boiler. Fuel is put into a burner, which then generates a flame and combustion gases. The boiler water cools down the heat transfer surface area as its own temperature rises until it is converted into saturated steam upon reaching the operating pressure of the boiler.
For example: If the boiler is working at a gauge pressure of 85 PSI, the boiler would be at an absolute pressure of approximately 99 PSI, producing steam with a temperature of approximately 327°F.
Definition of BHP (Boiler Horse Power):
Boiler horse power is a theoretical term defined as “the production of 34.5 pounds of saturated steam per hour at atmospheric pressure and a temperature of 212°F, using boiler feedwater (in the condensate tank) at the same temperature.” It is equivalent to a heat transmission of 8,436.56 Kcal/hour or 33,479 BTU/hour or 9.81 kW.
This calculation is entirely theoretical since boilers are normally fed water with a temperature of 158°F (when there is a good rate of condensate return in the tank) and operate at a higher pressure which requires a higher temperature to evaporate.
Saturated steam, generated by the boiler, is sent to different end users. Normally, it passes through heat exchangers where it gives off its heat indirectly, and can as such achieve 100% condensate return.
*Note on Condensate Return: The amount of condensate that returns to the boiler is of utmost importance, requiring the installation of a good steam filter and a reliable steam trap in good working order. The boiler operator must continuously check that the trap is functioning correctly and that the condensates are successfully returning – uncontaminated – to the condensate tank.
A good rate of condensate return – free of any type of contamination – enables the boiler to achieve a higher level of operating efficiency, reducing the consumption of soft water, chemical treatments, energy (as the condensates return hot), and fuel, and improving the evaporation capacity of the boiler.
If upon selecting the required boiler, you are aware that it will operate efficiently, with a high rate of condensate return, it is recommended that you order a larger condensate tank at the onset so as to avoid condensate spills in the future.
Boiler Water Quality Control:
It is critical to carefully monitor boiler water. It should not contain even minimal amounts of acidity (corrosion), hardness (scale), contaminants, nor be subject to an ill-advised chemical treatment, as any of the above can lead to the formation of binding masses which prevent the internal surfaces of the boiler heat transfer area from cooling down. This, in turn, can cause serious damage to the boiler.
A good boiler water quality control system should include weekly, biweekly, or monthly reviews by a qualified chemical engineer, as well as the administering of a customized chemical treatment. Additionally, a scheduled system of purges is required to rid the water of sludge and chemical products resulting from preexisting contamination.
Blowdown Separator Tank:
The blowdown separator tank is a pressure vessel that receives the sludge and residuals extracted during the blowdowns. The extracted elements leave the boiler at the boiler working pressure and as a result, are quite dangerous.
For example: If the boiler is working at a gauge pressure of 99 PSI, then the blowdown materials leave the boiler at this pressure, the equivalent of a 230 foot column of water, which can cause serious damage to the boiler piping.
The blowdown separator tank is a high risk pressure vessel, necessary in the operation of a steam boiler and whose construction must be carried out in strict accordance with the guidelines stipulated in the ASME Code. In order to bear the force of the output of the blowdowns, it must be able to expand in small space, lowering the pressure to the drain. The hot flash steam rises and is expelled safely through the wide upper connection of the blowdown tank.