As the source water is sprayed into the vessel, steam flows cross or counter to the water flow. The water is heated to the full saturation temperature corresponding to the steam pressure in the deaerator and causes the gases to have reduced solubility and be vented out to atmosphere. This piece of equipment uses steam to remove non-condensable gases from makeup and condensate streams. The most effective way to do this is with a deaerator. The first step to reducing dissolved oxygen should be through mechanical means. There are several ways to minimize corrosion in a boiler system and protect the metal surfaces throughout. Corrosion management - mechanical oxygen removal Pitting and other types of corrosion in the feedwater tank can also indicate the boiler's health. Metal loss in the feedwater does not have adverse performance effects however, it can affect the boiler, as stated above. On the other hand, if corrosion occurs in the boiler, different areas on the tubes or wall will have a material loss, which can cause, in severe cases, a tube leak or failure, particularly with high-pressure watertube boilers. Deposits can come from corrosion within the boiler or be pumped in from corrosion in the feedwater. This can even cause the boiler tubes to overheat and lose structural integrity. This requires the boiler to fire harder to achieve the same heat exchange, which reduces the boiler's efficiency. This kind of corrosion will cause grooving on the condensate piping.Īs corrosion occurs, material released from the anode will deposit on any metal surface. Iron deposition will attach to and effectively insulate the tubes in a boiler. Higher makeup alkalinity will increase the likelihood of this, making a condensate pipe more susceptible to carbonic acid attack. In the condensate piping, corrosion is mainly caused by the formation of carbonic acid. When the condensate travels back to the feedwater, CO 2 (carbon dioxide) absorbs into the water and forms H 2CO 3 (carbonic acid). With such high-purity water in the condensate, it does not take much dissolved CO 2 to lower the pH to a corrosive range. However, unnecessary turbulence can increase the absorption of oxygen in makeup water. Water will absorb oxygen directly from the atmosphere and introduce it to the feedwater tank through makeup. In the feedwater and boiler, dissolved oxygen is the perpetrator of corrosion. Different corrosive properties threaten the various stages throughout a boiler system. Several different characteristics of the water determine the corrosion rate: dissolved oxygen, pH and temperature all affect corrosion severity and speed. Throughout a boiler system, the primary cause of corrosion is the presence of dissolved oxygen in the water, causing a reaction that forms iron oxide (rust). Co-occurring, these combined reactions result in a net loss of base metal. A corrosion cell has two components: the cathode and the anode. The cathodic reaction is a reduction of oxygen to the hydroxide ion at the surface of the metal, and the anodic reaction is the oxidization of the metal into soluble ions. This article will focus on the corrosion aspect of boiler operation, and methods for mitigation and monitoring.Īn explanation of corrosion and its effectsĬorrosion is the gradual deterioration and loss of a material by electrochemical reactions with its environment a natural process that converts a refined metal into a more stable oxide. ![]() While the former typically is a result of inadequate or improper pre-treatment, the latter is typically a result of improper internal chemistry treatment and/or associated mechanical equipment. Within the water treatment segment of boiler operation, two main mechanisms affect their efficiency and longevity – scale/deposition and corrosion. Items such as water pre-treatment and boiler internal treatment, fuel pre-treatment, flue gas after-treatment and mechanical maintenance all play a role in the long-term reliable operation of boilers. While this process of steam production is relatively straightforward (an external source of heat energy applied to water, either directly or indirectly), the secondary processes involved must be monitored with just as much criticality. From heating to chemical manufacturing to electric power generation, there is no questioning the importance steam production plays in the creation of a vast amount of goods we all use. ![]() ![]() Industrial boilers play a foundational role in the operation of modern society.
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