Operación de deareadores

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Operation of Deaerators to Increase Boiler System Reliability
Background Those who are directly or indirectly involved in the water treatment aspects of operating steam boiler systems know the many obstacles to successful boileroperations. Table 1 lists 15 fairly common boiler system operational problems that are water-related. Insufficient deaeration represents 40 percent of the causes for these common problems. Oxygen and carbon dioxide corrosion, shown in Figure 1, are two examples of the corrosion problems eliminated with successful deaeration. A major difference between insufficient deaeration of feedwater problems, andother problems listed in Table 1, is that insufficient deaeration is not detected by standard daily monitoring procedures. Dissolved oxygen is seldom monitored, except in boiler systems that are operated above 600 psig. On the other hand, boiler feedwater hardness, pH and conductivity are widely used test and control parameters for most boiler operations at all operating pressures.

Figure 1:Condensate Line Corrosion Mechanical Deaeration The boiler feedwater deaerator shown in Figure 2 is an essential piece of equipment for the operation of modern steam boilers. Deaerators mechanically remove non-condensable gases (e.g., argon, carbon dioxide, nitrogen, neutralizing amines, oxygen) from water (e.g., boiler feedwater, steam condensate). Deaerators operate at pressures that range from afew inches of mercury absolute pressure (i.e., vacuu m) to 60 psig or higher,

depending on the design of the deaerator and plant requirements. Other benefits of deaeration are that the deaerator: • Provides a reserve quantity of hot water for the boiler in the event of power failure, production surges, as well as startups (Deaerated Water Storage Tank as depicted in Figure 2). • Reduces repairand replacement costs caused by oxygen and carbon dioxide corrosion in condensate and feedwater systems. Reduces chemical cleaning costs by reducing the quantity of iron, as well as copper in the boiler feedwater. • Reduces steam trap and receiver pump maintenance. Provides a surge tank for sudden increases in feedwater demand, as well as surges of condensate returns. • Reduces chemical costs bylowering the need for chemical oxygen scavengers and neutralizing amines. • Improves boiler system efficiency by using low-pressure steam such as feedwater turbine pump exhaust steam, as well as flash steam from blowdown recovery systems, to heat and deaerate the boiler feedwater.

Common Cause of Problem 1 2 3 4 Failure of Pretreatment Failure of Pretreatment Failure of Pretreatment Failure ofPretreatment/Failure of Boiler Water Chemistry Control 5 Insufficient Deaeration of Feedwater

Classification of Problem Loss of boiler efficiency due to adhesion of hardness and silica scale Expansion or bursting of boiler tubes due to heavy scale adhesion Leakage of hardness, as well as silica from softener or demineralizer Reduction of turbine efficiency by silica and other salts Corrosion...