Steam/Hot Water Boilers
Steam boilers have wide and extensive use for numerous applications. The energy contained in steam can drive a turbine for electric power, can be used for comfort heating in large buildings or homes, can be used in manufacturing processes, and the uses go on and on. The quality of the steam is important and becomes more critical as the pressure and temperature ranges in the boiler are increased. Contaminants in feedwater directly affect the quality of the steam and the condition and operations of the boilers and its systems over its operating life. Water, when heated and changed from the liquid state to the elevated state of steam, leaves behind any dissolved solids that were in the water, principally calcium, magnesium, silica, iron, etc. Water remaining in the boiler becomes more contracted with the contaminants as additional steam is generated. The concentrate must be removed to prevent deposition of scale as well as corrosion. The process of removing the concentrate is termed “blowdown”.
A good boiler program is prudent and will prevent corrosion and scale and other deposits in the boiler and condensate system. Pretreatment systems such as softeners, demineralizers and dealkalizers can be critical for many systems depending on the feedwater quality and other factors. Lack of good operations and control can result in unscheduled down time, excessive costs, poor reliability and potential safety problems in the boiler.
NuChem Corp and its team of professionals are ready to assist and help you with any problems relative to steam and hot water boilers. Our Boiler Treatment Products provide exceptional corrosion and deposit control to help ensure good heat transfer, efficiency and protection of the metal surfaces which permits the safe and efficient operation of your boiler and steam systems.
Questions About Boilers
1. How are steam and hot water boilers classified?
A. Steam and hot water boilers are generally classified by the operating "throttle" pressure. Boilers operating under 300 psig are classified as low pressure, those operating between 300 and 900 psig are classified as medium pressure and units operating between 900 and 1200 psig are designated as high pressure.
2. Why should we treat the water in our boiler?
A. 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/magnesium carbonates are considered “hard to wash with” hence the name hard water. They have an inverse solubility. When water containing the salts are heated, they are less soluble and precipitate from solution. 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 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 acts as oxidizers, causing both weakening and failure of metal and corrosion by-product, which add to the boiler deposits. NuChem uses oxygen-scavenging chemicals to eliminate oxygen from the system and alkalinity boosters to maintain the water in the range of 100 ppm to 600 ppm alkalinity. Daily testing by the boiler attendant allows the amount of chemical to be adjusted as needed. Condensate system corrosion is caused by carbon dioxide and oxygen carried into the system by makeup water, leaks, worn seals, etc. 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. NuChem manufactures and provides a number of corrosion control additives to complement your particular water and problem areas.
When possible, it is best to use boiler feedwater with low total dissolved solids, TDS, as the water is more consistent in composition and contains less overall solids thus minimizing scale problems.
At 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.
3. Does our boiler need treatment when it is out-of-service?
A. Unless idle boilers are stored properly, they will corrode. Wet layup of a boiler is possible as long as the ambient temperature remains above freezing. Before wet storage, the boiler should be inspected, cleaned if necessary, and refilled to the normal water level with deaerated feedwater. Add the correct dosage of chemical treatment while filling the boiler.
Test the boiler water several times while the boiler is shut-down and add additional treatment, as necessary, to maintain minimum levels. When chemicals are added, use an external pump to circulate the boiler water or reduce the water level to the normal operating level and steam the boiler for a short time. If the superheater cannot be drained, fill it with deaerated water and treat it in the same proportion as the boiler.
For dry layup, the boiler should be drained, cleaned and dried out. Close all vents, drains, etc. to prevent air from seeping in.