It depends on water quality. I would inspect the boiler tube waterside surfaces and check for deposit build-up. If you have a distinct build-up of deposits, these should be removed to improve heat transfer and to avoid damaging the tube material from long term overheating.
Can you describe what the pictures would show? Would they be of scale deposits in the tubes?
I think I have photos (not electronic) of scale deposits so thick that when they came out of the tubes, they looked themselves like pieces of tubing. When the tubing cleaners finished running, the workers cleaned up the chips of scale with shovels.
Knowing what the composition of the deposited material is is very important in order to decide what process and chemical cleaning solution to use. If you have the ability to analyze the deposits I suggest you do so.
The Betz (now GE Water) and Nalco industrial water conditioning handbooks have good general information on chemical cleaning of industrial boilers. Specific parameters such as the type of agents, solution concentration, recirculation time, cleaning system configuration, recirculation rate, and solution temperature will have to be determined by someone with expertise in this area.
The amount of iron in the deposit is troubling. Looks like you either have or have had corrosion in either the condensate recovery or boiler feedwater systems (possibly both). Deposited iron scale will lead to under-deposit corrosion and pitting of the boiler water-sides.
The Ca, Mg, & Si in the deposit are indicative of a inoperative, malfuctioning or non-existant make-up water pre-treatment system. Pre-treatment of the make-up water and possibly condensate polishing are critical. Feeding treatment chemicals to compensate for poor feedwater quality is cost prohibitive and marginally effective.
You will have to take steps to improve the feedwater quality or be faced with periodic mechanical and chemical cleaning of the boiler water-sides along with a significantly reduced service life.
Thank you
That’s right, but our feed water quality isn’t troubling now (Conduct:6~7). However the feed water quality was very worrying 4 years ago.
Since we use dispersant based on inorganic phosphates, the deposits is soft and non- adherent.
what is our problem?
Thank you for your attention
It's impossible to tell what the problems are without performing a site survey. However, if you are still getting scale and sludge formation in the boiler water-sides there is a problem with the feed-water pre-tretment and/or the application of the internal treatment program.
As posted above nothing beats an on site inspection. Here are a few items to consider.
Did you clean the boiler when you begin the current water treatment process? If not your present treatment maybe altering the physical properties of an existing scale.
What are your blowdown parameters?
What size is you boiler and is it amenable to chemical or mechanical cleaning?
Have you discussed your problem with your chemical supplier? There could be some alteration to your present chemical treatment that might mitigate your problem.
Is everything with the make-up water system and the water treatment system normal and by the book?
Worst scaled boiler I ever saw was in a plant where they pumped their make-up water (and they had a high make-up percentage) from a nearby stream to a holding pond on the plant site and took the boiler make-up from there. The plant got cited for violating rules about discharging their boiler blowdown into a public waterway and the mental midget plant manager ordered that the boiler blowdown just be re-routed to the holding pond. Problem solved!!!!
It took a while for the detrimental effects to show up and when they did, it wasn't pretty - but it did feed my children for a while, though.
