Steam Boilers

A steam boiler heats feedwater until it turns to steam, which leaves the boiler and carries heat to the plant. The dissolved solids in the feedwater stay behind in the boiler water and become more concentrated as steam is raised. Blowdown removes some of this concentrated water, and fresh feedwater replaces what was lost as steam and as blowdown.

How does a steam boiler system work?

Treated make-up water and returned condensate are mixed and usually deaerated before the feed pump sends them to the boiler. Inside the boiler, heat from the fire side passes through metal surfaces into the water. Steam leaves through the steam header, and some water is removed by blowdown to control concentration. Each stage affects the next, so the quality of the feedwater determines the condition of the boiler internals.

What are the water-chemistry risks?

• Scale and deposits: hardness, silica and iron that reach the boiler can form insulating deposits on hot surfaces, which reduce heat transfer, raise metal temperature and may lead to overheating.
• Oxygen corrosion: dissolved oxygen in the feedwater pits boiler metal and feed lines, especially during idle periods.
• Alkalinity and pH: water that is too acidic attacks metal, while an unsuitable alkaline balance can promote carryover or deposits.
• Carryover: foam and entrained water can reach the steam and damage downstream equipment.
• Metal transport: iron and copper from corroded condensate lines settle in the boiler and add to deposits.

How is a steam boiler monitored?

Monitoring covers the pH of the boiler water, conductivity or total dissolved solids to control blowdown, hardness of the feedwater, residual of the oxygen scavenger and indicators of corrosion such as iron in samples. Inspection of the boiler internals at shutdown shows what the chemistry has actually done. Records of blowdown and make-up help to spot a change early.

Which chemical categories are relevant?

Our datasheets describe a boiler pH booster, a boiler scale and corrosion inhibitor, a multipurpose boiler product and a neutralizing amine for steam and condensate, alongside the oxygen scavengers used in feedwater. Treatment rates are set by our technical team from the water analysis and the operating conditions, fed with a chemical metering pump.

Points to take into account when treating a steam boiler. These are qualitative guidance and not a recommendation for a specific boiler.

• Boiler type and operating pressure class, which affect the feedwater purity the boiler needs.
• Feedwater quality and the performance of softening, RO or deaeration ahead of the boiler.
• Condensate return share and its condition, since returned iron and copper end up in the boiler.
• Where steam contacts product or people, which limits which chemicals may be considered.
• Load pattern, because frequent start-up and shutdown increases idle-period corrosion risk.
• Blowdown practice and heat recovery, which affect both cost and chemistry.
• Lay-up during long shutdowns, which needs its own plan.

Our technical team reviews the water analysis and boiler details before any program is proposed.