Boiler Systems

Addressing scale formation & depositions in boiler systems

In steam-powered processes, the treatment of feedwater or makeup water before steam generation is a complex issue to tackle, and a thorough understanding of boiler water chemistry is key to upkeep operational and production efficiency belonging to boilers and steam-use equipment. Unlike other processes, i.e., thermal desalination, reverse osmosis, good quality municipal or plant water meant for domestic use is rarely acceptable for boiler feedwater. 

Feedwater from these sources of makeup goes through rigorous treatment to reduce contaminants to industry standards. Corrective additives are applied later to neutralize the adverse effects of the remaining trace contaminants that are not captured or removed by the previous treatment processes. The desired quality of the finished feedwater should not contribute to deposition, corrosion, or carryover. 

The complexity of problems in boiler systems 

Boiler systems operate under high-temperature and high-pressure conditions, and the allowance of deposit formation can result in poor heat transfer between the boiler tubes and the feedwater in the process of steam generation. For intermediate and high-pressure boilers, the presence of a thin film of deposition can easily lead to a significant increase in the temperature of the tube metal. 

The temperature will increase in line with continuous scale formations, exceeding the safe maximum temperature of the tube metal and ultimately leading to failure. Feedwater circulating through the tubes also conducts heat away from the metal and is hindered when there is increasing insulation of tube metal but the layer of deposits. 

Scale formations & deposits in boiler systems

Formations favor water-washed equipment surfaces such as boiler tubes, where the application of heat can easily upset equilibrium conditions of the feedwater coming into contact with these surfaces. The commonly encountered scale formations and depositions are calcium phosphate, calcium carbonate (for low-pressure boilers), magnesium hydroxide, magnesium silicate, and alumina. 

Deposits can originate from scale or chemicals that have precipitated upon application for treatment. In low-velocity areas of the boiler system, these deposits compact to form an agglomerate of sludge. Iron particulates returning from the condensate systems can also deposit if not managed correctly. 

The application of CrestoGuard™ 452 addresses the problem of calcium phosphate, calcium carbonate, metal silicate deposition, and disperses iron particulate to mitigate the issue of deposition formation leading to poor heat transfer efficiencies and system failures. 

In steam-driven boilers used in the food and beverage industry, there is a possibility where the generated steam comes into contact with food or food-related products. Under these circumstances, treatment chemicals will need to be FDA-approved. CrestoGuard™ 452 is also FDA-approved chemistry for use in applications where steam may come into contact with food or food-related products. 

Corrosion in boiler systems

Corrosion in boiler systems is attributed to the process of attack by oxygen and can occur in pre-boiler systems, boilers, condensate return lines, and parts of the steam cycle where oxygen is present. 

When poor mechanical and chemical deaeration takes place in the pre-treatment process, it allows oxygen to enter the feedwater going into the boiler. Oxygen in trace amounts as low as 1-5 ppm (parts per million) under the boiler operating temperatures can accelerate corrosivity. 

Oxygen under elevated temperatures forms localized corrosion pits and can rapidly deteriorate a metal surface, leading to metal fatigue and failure. As the process of oxygen corrosion continues, it dissolves the iron surface and sends dissolved iron into the boiler systems. This dissolved iron can deposit onto boiler tubes, exacerbating the process of deposition. 

The application of CrestoGuard™ 206 effectively removes any oxygen remaining from the process of mechanical and chemical deaeration, to prevent the escalation of corrosion in boiler systems.