In my Heat Recovery Surface Cleaning post I quoted the importance of keeping a process heater clean for optimum performance and how a soot blower can be an effective tool for this. Today, I'm going to delve into a little more detail about soot blowers in boilers. A friend of mine who has a lifetime's experience of working with industrial boilers recently sat down with me and explained some of the key principles and problems. It was truly fascinating!
Let's take coal fired boilers first. From what I understand, molten ash, or slag as it's often referred to, tends to accumulate in the furnace area and if this happens, two problems can arise:
1. Reduction of heat transfer efficiency
2. Failure of the boiler tubes due to increased tube metal temperature
Secondly, let's look at oil fired industrial boilers. Effectively the same problem occurs - ie. loss of heat transfer and general reduction of boiler efficiency. However, with oil fired boilers the material build-up is soot.
How can these problems be avoided? Well, for many years the accepted protocol has been to remove the ash or soot build-up by using soot blowers, in particular steam soot blowers, at intervals of 6 to 8 hours and they just blow away the build-up, thus bringing boiler efficiency back up to a better performance level. Many industrial boiler operations have benefited from the application of soot blowers in this way and continue to employ the technology today.
However, using steam soot blowers in boilers is by no means a perfect science and there are some disadvantages. For example:
a) because they do their blasting at fairly large intervals this allows slag or soot to build up in the meantime and by the time they blast again the soot blowers might only be cleaning the build-up from the leading edge of the steam tubes.
b) boiler tube corrosion and erosion can occur due to the continual effects of steam blasting.
This is apparently where the argument for sonic soot blowers has begun to emerge in recent years. Sonic soot blowers are employed much more frequently and by generating a rapid series of audiosonic pressure fluctuations, they can prevent the slag or soot from building up in the first place. Also, because there is no steam involved in the cleaning process, there is no risk of tube erosion or corrosion.
Boiler cleaning is a large and complex subject and there are some excellent, detailed articles online if you wish to learn more such as:
Mechanisms of Steam Soot Blower Erosion
Boiler Tube Failures
Boiler Cleaning Systems
