Wet lime/limestone flue gas desulfurization
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The wet FGD process is a desulfurization technique used after coal combustion. It is characterized by the fact that the entire desulfurization system is located after the air preheater and dust collector; the desulfurization process takes place in a solution, with both the desulfurizing agent and the by-products being in liquid form. The reaction temperature during this desulfurization process is below the dew point, which means that the flue gas after desulfurization generally needs to be reheated before it can be emitted through the chimney. Question: Why is reheating necessary? Is it because there is a fear that the liquefaction of water could cause \"water hammer,\" or is there some other reason? Solve
Flue gas dew point corrosion occurs because sulfur in the fuel is converted into SO2 and SO3 during combustion; when the outer surface temperature of the heat exchange surface is lower than the temperature of the flue gas, sulfuric acid mist droplets form on that surface, leading to corrosion of the heat exchange surface.
This post was last edited by qugd on 2011-9-9 10:53. Reducing corrosion is just a small part of the reasons. The main reason is that if the flue gas after desulfurization is not heated, it cannot rise on its own into the flue; since this gas contains a high amount of carbon dioxide and is therefore dense, its density decreases only when the temperature rises, allowing it to be discharged upward. The main reason why the temperature of flue gas does not drop very low is to ensure smooth emission.
Reply to 4# qugd: I’m not sure what the relationship is between carbon dioxide density and temperature, but if that’s the reason, it’s completely possible to use a fan for extraction. In the sulfuric acid industry, heat from exhaust gases is fully utilized before they are released; there is no record of heating the gases further prior to emission. Personal opinion
Reply to 5# yusmile: Go and take a look at the design of the heating furnace and the smoke exhaust system, and you’ll understand. Any self-ventilating flue is more efficient and energy-saving than one using a fan, and making use of waste heat is the simplest approach. Have you ever seen flue gas that is at the same temperature as the environment?
Reply to 6# qugd: Indeed, in comparison, self-arranging types are more energy-efficient. Of course, if the flue gas coming from the system has a certain pressure, it’s not clear whether this is still necessary.
The desulfurized flue gas is highly corrosive; discharging it directly through a chimney can cause corrosion. It is necessary to apply anti-corrosion measures to the chimney and to heat the flue gas in order to raise its dew point, with either of these two approaches being available