Before boiler feedwater is passed into the boiler, it must be chemically treated to remove the corrosive elements that may be present and would ultimately corrode the boiler as well as affect the quality of steam required within a process.
Chemicals entering the boiler via the feedwater must be removed from the boiler. Failure to do so can result in the boiler system suffering from scale formation, corrosion, brittle and cracking metal, carry-over and foaming.
Therefore a proper chemical balance must be maintained within the boiler itself.
This is achieved through blowdown control. This process involves activating the blowdown valve mechanism situated on the boiler drum and drawing off a small percentage of the boiler water (containing the dissolved solids and non-dissolved sediments) from below the surface of the water in the boiler.
In order to retain a chemical balance within the boiler, the quantity of chemicals removed from the drum via blowdown must be equal to the quantity of chemicals that enter through feedwater. As steam loads vary, the rate of feedwater changes and so does the rate of blowdown.
On the other hand, excessive blowdown leads to inefficient running of the boiler plant, as each blowdown causes heat contained within the expelled water to be lost. The cost of fuel can be directly related to this heat loss. The cost of water and chemicals should also be taken into account. A balance has to be established between the requirements of removing the dissolved solids from the boiler system and running the boiler plant cost effectively.
