In a well maintained, properly operating boiler system, condensate is almost pure water with low conductivity and minimal dissolved solids. Condensate contamination can be caused by heat exchanger leaks, boiler carryover, etc. and can be a perplexing problem. If approached logically, the source of contamination can be found out.
Consider the analogy of a tree with the boiler being the trunk and the steam/condensate system being the branches. When condensate contamination occurs, one should start at the trunk and work the way out one branch at a time until the source is found.
A good boiler water management program should include regular condensate testing by both the boiler operators and the contracted water management specialist. When condensate contamination is found, the following steps will lead to the source.
1. How is the boiler operating? Is the boiler operating within normal operational parameters? Is the steam load fluctuating significantly? If the boiler is over cycled, treatment chemicals are overfeed, or alkalinity is too high, carryover may occur. Fluctuating boiler water levels can be a cause too.
Boiler carryover is just as likely to have a mechanical cause as it is a chemical cause. Mechanical carryover causes include:
- Excessive movement of water in the steam drum.
- Spray or mist carryover from fine water droplets. (This usually occurs when separation devices are missing or damaged.)
- Steam production in excess of design rating.
- Sudden swings in steam load.
- High water level
- Changing boiler pressures
2. What is the contaminant? Use the testing tools on-hand to determine the nature of the contaminant. Typical parameters you should be able to easily check are conductivity, pH, hardness, orthophosphate, molybdate, nitrite, chlorides, and iron.
3. Are any of these contaminants unique to any of the steam uses in the plant? Hardness can come from a leaking hot water heat exchanger. Orthophosphate can come from a leaking heat exchanger in a phosphoric acid bath or boiler carryover.
Nitrite can come from a leaking heat exchanger in a closed hot water loop. Elevated pH may be attributed to an overfeed of neutralizing amine, the in leakage of caustic from a heated bath, or boiler carryover. Increased conductivity can be caused by any of the above. If you are lucky, the uniqueness of the contaminant will lead you directly to the source.
4. Check the condensate quality of the steam header as close to the boiler as possible and before any other possible contamination sources (including the neutralizing amine feed). You may be able to get a sample off the steam header''s steam trap. If you find contamination here, you most likely have boiler carryover occurring. This boiler carryover may either be the cause of the condensate contamination you see or be a result of it.
5. If you believe you have boiler carryover occurring, this must be corrected before you can further investigate the source of the contamination. Boiler carryover will contaminate the entire condensate system making any other condensate sampling a fruitless endeavor. A Boiler Blowdown Control System will maintain the Boiler TDS levels under control and ensure that this problem gets addressed.
6. After any carryover is under control and the condensate system has had time to clear itself of the carryover contamination, start testing the condensate returns system for the contamination. Start first with the condensate receivers closest to the boilers. When you find one that''s contaminated, work your way upstream from there. With any luck, you may be able to quickly find the source of the contamination.
Finding contamination sources can be tough sometimes. The offending piece of equipment may only operate sporadically. By the time condensate contamination is seen back at the boiler, the leaking piece of equipment may already be offline and any contaminated condensate flushed from its nearest condensate receiver.
Heated baths are often temperature controlled. When the bath reaches the set temperature, steam flow through the heat exchanger is turned off. The steam remaining inside the heat exchanger condenses and can form a negative pressure. If the heat exchanger has a leak, the outside liquid is sucked into the heat exchanger.
When steam flow is returned to the heat exchanger, a slug of contamination is sent back to the boiler system via the condensate. This can be an especially frustrating contamination source to find due to its intermittent nature, but can sometimes be easily spotted by a bubbling bath. If you see a heated bath bubbling near the heat exchanger, you most likely have steam leaking out of the heat exchanger.