Tubular air heaters are essential to maintaining the efficiency of a power plant. Their ability to control the temperature of incoming air is key to proper boiler functioning, which directly contributes to efficiency.
While minor decreases in efficiency due to tubular air heater degradation is to be expected as your heater unit ages, real problems result when physical damage occurs to the heating unit that causes noticeable decreases in efficiency.
Here, we’ll talk about the importance of preventing this damage so you can avoid repair and replacement costs down the road.
Types of Damage to Tubular Air Heaters
Tubular air heaters typically face three types of damage:
Erosion is typically found on the internal and external surfaces of the heater, as well as the tubesheets. There is a wide variety of causes of erosion, and most of them can be controlled if not outright prevented.
One cause of erosion that may not be preventable is the ash content of the fuel. A fuel with a high ash content will contribute to more erosion than low-ash fuels. Fuel sources for a power plant aren’t easily changed or replaced, so regular and frequent inspections are necessary.
Without proper intervention through regular monitoring, erosion will cause leakage.
Corrosion also attacks the surfaces of the air heater and results from chemical reactions caused by the flue gas. Anything from sulfuric acid (H2SO4) to nitric acid (HNO3) can cause corrosion if the temperature falls below the acid dewpoint.
Additionally, corrosion can be caused by the air heater having to deal with gases that are modified by emissions controls, like a selective catalytic reduction (SCR) system. Often, these air heaters weren’t designed with SCRs in mind.
One way to prevent corrosion is to make sure the tubular air heater is equipped to handle the change caused by an emissions control device. From a metallurgical standpoint, the materials used in construction need to be able to withstand the added chemicals in the flue gas from the emissions controls device.
Finally, fouling happens when ash in the flue gas condenses on the tubes and sticks, filling the tube and hindering heat transfer, whether it’s through altering the gas flow or reducing the total surface area of the tube.
Ongoing inspections constitute one of the best ways to stay on top of fouling and prevent it, short of changing fuel to go with a fuel with lower sulfur and lower ash content. This is similar to the approach used for erosion.
The Need for Frequent Inspections
In all three cases, frequent, regular inspections are the main ways you can prevent damage to your tubular air heaters. You need to check on the tubes to identify that a problem exists before you can stop it.
Defects are to be expected as an air heater goes through its operational lifespan. But when a unit isn’t regularly inspected, they will occur much more frequently because of corrosion, erosion, and fouling.
Ongoing maintenance is key because it may not be readily apparent that you have a problem just by observing the unit in action. Often, it’s too late when managers notice a problem, and an expensive repair or replacement is in order.
Southern Field inspects and maintains tubular air heaters for power plants. Contact us to learn more about our services and how we can help.