Natural water contains a variety of impurities, which can drop out of solution when heated, leaving behind deposits, which interfere with proper boiler performance, inhibiting heat transfer and water flow. Water is an excellent solvent, dissolving gases from the air, gases from organics in the soil, suspended matter from the earth, and minerals, chiefly calcium carbonate, magnesium carbonate, calcium sulfate, magnesium sulfate, silica (sand), sodium chloride, sodium sulfate, and small quantities of iron, manganese, fluorides, aluminum, etc. Waters which contain a large proportion of calcium and magnesium are considered "hard to wash with", hence the name hard water. The amount of hardness in natural water can vary from several parts per million to over 500 parts per million. Since calcium and magnesium compounds are relatively insoluble in water, when heated, they tend to precipitate (fall out) of solution, causing scale and corrosion. Since deposits insulate the pipes, they prevent the efficient transfer of heat, causing overheating. If the overheating is severe enough and and long enough, the metal fails. Boiler tube deposits can also cause plugging or partial obstruction of boiler tubes, also causing overheating. Corrosion can occur under the deposits, potentially leading to leaks in the tubes. Natural waters also contain varying levels of oxygen and carbon dioxide, which act as oxidizers, causing both weakening and failure of metal and corrosion byproduct, which add to the boiler deposits. Alken-Murray uses oxygen scavenging chemicals Alken® Treatment 52. to eliminate oxygen from the system and alkalinity boosters, such as Alken® Total series or Alken® Treatment 479 , to maintain the water in the range of 100 ppm to 600 ppm alkalinity. Daily testing by the boiler attendant allow the amount of chemical to be adjusted as needed. Condensate system corrosion is caused by carbon dioxide and oxygen carried into the system by the steam. Condensate corrosion is controlled by neutralizing amines, which neutralize the corrosive effect of the gases found in the return condensate piping and filming amines, which form a protective film on the interior surfaces of the return condensate piping. The Alken® Treatment J and HSN series contains a variety of amine formulas, selected by your Alken-Murray representative to compliment your particular water and its problems. When possible, it is best to obtain boiler feedwater from ground-water, as this water is more consistent in composition and contains less suspended matter than surface supplies, which are modified by rainfall and erosion. A 1/9 inch deposit of scale on the
waterside surface increases fuel consumption by 16%; while
a 1/8 inch deposit of scale on the waterside increases fuel consumption
by 20%. By measuring the difference between the stack temperature
and the temperature of the water can indicate the amount of scale that may
be present, assuming that the combustion side of the boiler is operating
efficiently (if not, Alken Even-Flo® can solve
most fireside problems). |
