Question regarding phosphate dosing in boilers!
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Dear sea friends: Our company has boilers for waste liquids, waste gases, and waste solids, which generate steam at 50 barG and 20 barG pressures； There are also reactor waste heat boilers that produce steam at 20 barG, 6 barG, and 3 barG. The deaerator is used uniformly throughout the plant to supply water for all boilers. Is it feasible to plan to use a phosphate dosing unit to add chemicals uniformly at the outlet of the deaerator? Is it still necessary to use a dosing unit for each boiler separately? I hope fellow sailors can offer some advice. Thank you.
It depends on the quality of the make-up water and the purpose of the steam. In principle, the higher the steam pressure rating, the stricter the water quality requirements. If the water quality meets the requirements for a pressure range of 3.8–5.8 MPa, it will also satisfy the water quality requirements for lower-pressure boilers.
In principle, the plan proposed by your management is feasible; the water quality of each boiler can be well controlled through continuous or intermittent drainage. The problem is that it’s too cumbersome to operate
May I ask a question? Why is phosphate added to the boiler, rather than after the boiler feed pump, just like ammonia is added after the desalination pump to adjust the pH? Are there any design requirements for this?
For boilers with medium pressure and lower parameters, it is advisable to treat the feedwater with ammonia, while the boiler water should be treated with phosphates. Understanding: First, clearly understand the concepts of feedwater and boiler water ； Secondly, phosphates are added to form loose sludge, which must be removed through wastewater discharge. The water is circulated and heated in the boiler, a process that results in high temperatures and an accumulation of calcium and magnesium ions; therefore, it is better to add them to the boiler drum itself. This is my personal understanding for reference only.
Thank you. The management has decided to add phosphates uniformly at the deaerator outlet for use in the various boilers across the plant.
Hello. While searching for information, I encountered a new issue: if we have a large number of temperature reducers, the cooling water is supplied through the branch pipes of the feed water pump, after passing through the deaerator. At this point, can trisodium phosphate still be added to the feed water pump after the deaerator? ? Will it cause a significant decline in steam quality and excessive levels of sodium ions? We have extra-high voltage here, which is also used to drive steam turbines. Thank you.
Your analysis is correct; the quality of the water used for cooling should not affect the quality of the steam, and desalinated water is the best choice. The actual dosing pipelines and fittings have relatively small diameters; since there isn’t much money available, a single dosing unit can be shared, with flow meters added to the branch pipelines leading to each drum.