The role of water and steam chemistry in the performance and lifespan of boiler systems is of paramount importance. Water and steam are not mere carriers of heat in such systems, but active participants in various physical and chemical processes that influence boiler efficiency, safety, and durability. These processes include the formation of deposits, dissolution and redeposition of materials, particularly where water evaporates to form steam or condenses back to water. Understanding and effectively controlling the quality and treatment of water within boiler systems is therefore crucial to their successful operation. This paper will explore the key parameters to be controlled, the necessary treatments to maintain water quality, and the importance of operator training and understanding in managing these complex systems.
Main parameters to control:
The three key parameters to control in any steam supply system are: pH, Electro-Chemical Potential (ECP), and the presence of specific deleterious species. These parameters are directly influenced by the quality and treatment of the water used in the boiler and can impact the formation of deposits, the dissolution of materials, the efficiency and lifespan of the boiler itself.
Key factors to be considered:
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Water Treatment: water used in boilers must be purified and treated to prevent scale formation, corrosion, and contamination by impurities. This process involves purification of make-up water, condensate polishing, deaeration, blowdown, and the addition of certain chemicals to control pH, ECP, and oxygen concentration. Through these processes, boiler efficiency can be improved, maintenance reduced, and the life of the boiler system extended.
Training and Understanding: Operator training and understanding of boiler water chemistry guidelines is essential to effectively manage these systems. This knowledge extends to how impurities, treatment chemicals, and boiler components interact. Early detection and management of chemistry upsets can be achieved through such understanding, reducing the potential for catastrophic failures and enhancing system performance.
Chemistry-Boiler Interactions and Boiler Types: Understanding the interaction between boiler circuitry and the steam generation process helps to control boiler water chemistry more effectively. Different boiler types – drum boilers and once-through boilers – require unique water chemistry and control strategies. Once-through boilers, for instance, require feedwater of high quality due to their complete conversion of water to steam without recirculation.
Control of Boiler Water Chemistry: Control of boiler water chemistry involves minimizing the introduction of impurities into the boiler, such as sodium hydroxide (NaOH), sodium carbonate (Na2CO3), or acid-forming salts like magnesium chloride (MgCl2) or sulfate (MgSO4), which can cause corrosion. Additionally, oxygen and carbon dioxide need to be controlled as these gases can also cause corrosion in the boiler system.