subject: Chemical Cleaning Of Boilers - To Clean Or Not To Clean [print this page] Chemical cleaning can play an important role in boiler maintenance. Proper chemical cleaning removes deposits from the inside of boiler tubes which improves the boiler heat rate, reduces tube failures and improves the stability of boiler chemistry.
1.Know When to Clean
It is important, therefore, to use chemical cleaning only when necessary. In fact, improvements in boiler and feedwater practices have reduced the need for chemical cleaning at many utilities, extending the period between cleanings by years
2.How to determine the need to clean
Two or three tube samples should be taken from high heat flux areas of the boiler and analyzed for deposit loading on the inside of the water wall tube. This is still the best way to determine the need to clean with chemicals, assuming there have been no major since the last chemical cleaning. Boiler tube removal becomes crucial when contamination incidents increase in period of time.
3.Time-Based Cleanings
Cleaning based on time either operating hours or number of years since the last chemical cleaning is probably the worst way to determine need. Deposits do not form on boiler tube walls at a uniform rate over time. Other factors, including frequency of start-up and shutdown and water chemistry, must be considered.
4.A Major Contamination Incident
Often overlooked, a chemical cleaning should be performed at the next opportunity when there is a major contamination of boiler water. It is best to do so before the unit is restarted. A common cause of boiler contamination is a condenser tube leak.
5.Removing Deposits
In low-pressure boilers, chemical cleaning typically removes calcium carbonate and other hard adherent scales. In higher-pressure boilers, the major deposit removed is magnetite and some copper.
Chemical cleaning can improve the boiler heat rate and reduce the number of tube failures. It typically improves the stability of boiler chemistry. However, there also are down sides to chemical cleaning.
6.Evaluating the Risks
When making the decision to clean your boiler with chemicals remembers that chemical cleaning is:
Expensive (vendor costs alone may be $50,000 $150,000)
Potentially dangerous to personnel and equipment
An environmental and chemical spill risk
7.Postponing Your Next Chemical Cleaning
The need to use chemical cleaning is the result of corrosion products building up on the boiler tube walls. The more corrosion products generated in the boiler and feedwater system, the more often the unit will require chemical cleaning. Reducing corrosion in these areas can improve overall boiler chemistry and extend the time between cleanings.
A large percentage of the corrosion products on boiler tube walls come in from the feedwater system during start-up. Improving lay-up and start-up practices can mean the difference between needing to clean with chemicals every three years and every 12 years.
Find a knowledgeable consultant or chemical vendor that will help you develop better lay-up and start-up practices and get out of the chemical cleaning cycle.
Chemical cleaning has been considered a necessary part of boiler maintenance for many years. The objective of a chemical cleaning is to safely remove all the deposits from the inside of the boiler tubes
