Scale deposits in steam boilers can cause serious problems including higher fuel use, increased maintenance and unexpected failure. The high costs associated with boiler scale highlights the importance of good water treatment to keep waterside surfaces clean. These costs can also be used to evaluate investments to improve program results. For example, the costs can be used to calculate the payback on cleaning a scaled boiler, installing more reliable softeners, or upgrading the chemical feed and blowdown control system.
Scaled Boilers Require More Fuel
The problems associated with boiler scale largely stem from its insulating properties. In a boiler, fuel (natural gas, oil, wood, etc.) is burned to generate heat energy. From an energy efficiency standpoint, the objective is to transfer as much heat as possible from the hot combustion gases to the boiler water.
Since scale deposits are insulating, they reduce how efficiently heat is transferred through the metal boiler tubes to the water. The reduced heat transfer efficiency, in a dirty boiler, means more of the heat goes out the stack instead of being converted into steam. This also means more fuel must be burned to produce the required amount of steam; accompanied by more greenhouse gas emissions.
However, not all scale deposits are the same. Some deposits are much more insulating than others. For example, 1/32” of “normal” scale reduces heat transfer efficiency by 2%; 1/32” of a high iron and high silica scale reduces efficiency by 7%. This makes a tremendous difference in the excess fuel costs and greenhouse gas emissions associated with the deposit. Scale composition can also provide insights into why the deposits formed.
Scaled Boilers Are More Likely To Fail
Because boiler deposits are insulating, the fireside/waterside metal temperatures are much hotter in a dirty boiler than in a clean one. The increased metal temperatures in turn increase the potential for tube overheating and tube failure.
Scale deposits in water tube boilers are prone to “slough off” inside the tubes and block water flow. When circulation is lost, the tubes will fail rapidly due to overheating. Scale can also cause overheating and failure in firetube boilers, especially if deposits can cause tubes to become bridged or if a heavy buildup of scale is allowed to accumulate in the belly of the boiler. A deposit buildup at the tube sheet can be particularly damaging since the metal is not readily cooled. In both instances, the boiler will have to be taken out of service for repair.
The end result of boiler deposits is invariably higher fuel and maintenance costs, with unexpected failure being a very real possibility. Chem-Aqua experts can help you evaluate opportunities to maximize the life, efficiency, and reliability of your boiler systems. To learn more, visit Chem-Aqua online today!