Tubular air heaters (or preheaters) are vital pieces of equipment when you’re trying to keep thermal efficiency as high as possible.
Available in vertical or horizontal configurations, tubular air heaters increase thermal efficiency by recuperating heat from the exit flue gases. This heat is used to preheat the air coming into the boiler unit, which means it takes less energy to achieve proper temperatures – resulting in better thermal efficiency.
Here, we’ll discuss all the benefits of having tubular air heaters and how you can protect them from the most common types of damage these pieces of equipment face in the field.
Benefits of Tubular Air Heaters
Tubular air heaters have a wide variety of benefits. Using these heaters results in lower fuel costs, since you have to burn less fuel to get air temperature to where it needs to be. Higher temperatures lead to better fuel consumption, which also leads to less ash.
You can better control the consistency and volume of your exit flue gases. Also, you benefit from lower fan amperages.
The biggest benefit is in boiler efficiency, which every plant manager wants to get as high as possible. For every 40°F that you increase the inlet air temperature, you’ll see a 1% increase in boiler efficiency.
Common Causes of Damage
Tubular air heaters are robust pieces of equipment thanks to their relatively-simple design, but that doesn’t mean they can’t be damaged.
There are three types of damage that are most often seen with tubular air heaters: corrosion; erosion; and mechanical.
Corrosion generally happens when temperature of the fresh air drops below the acid dew point, which is typically between 225°F and 285°F. The acid dew point can be as high as 325°F if ammonia bisulfate is present.
Erosion is caused by flue gases, fly ash, and fan velocity. Any of these three variables can cause the material making up the tubes to erode, which decreases efficiency. And dealing with any of these three causes almost always means inspecting and fixing another system in the plant (such as ash handling for fly ash and air handling for fan velocity and flue gases).
Finally, there are several types of mechanical damage that can be inflicted on your air heaters, from high temperature warping to chemical injection and soot blower damage.
Repairing and Maintaining Tubular Air Heaters
The best defense against damage is regular, ongoing inspections. You need to be able to spot signs of damage while it’s early, so it doesn’t grow into needing a full-scale replacement.
We use a variety of methods to inspect tubular air heaters, such as visual, UT measuring, pressure testing, and eddy current testing. Visual inspection can be the best way to spot early signs of damage, but it alone won’t tell you when a problem could or will develop.
If damage occurs, there are several ways to repair it, from plugging and plating to sleeving, partially re-tubing the array, fully re-tubing the array, and conducting a full tube sheet replacement. The later damage is detected, the more likely it’ll be that you’ll have to have a full tube sheet replacement.
Tubular air heaters are important pieces of equipment that can bring a lot of benefits to your plant. Installing them is only part of the battle; the rest of it involves keeping them operating at max efficiency.
Southern Field performs vital plant maintenance and repairs for a variety of industries. Contact the team of specialists for more information.