In my opinion, the ...
Published by Ivan Tikhonov
In my opinion, the main drawbacks of reverse osmosis are the high cost and complexity of maintenance. I think the high cost of the equipment pays off quickly enough by the absence of continuous boiler purging and more reliable working of the steam- condensate track equipment (by reducing the amount of carbon dioxide in steam and condensate). But the wrong organization of reverse osmosis in the boiler water treatment technology can lead to bad consequences.
I think that for the preparation of water for low and medium pressure steam boilers in 90% of cases (depending on the composition of the source water) it is necessary to use a combined water treatment system, osmosis + softening. The boiler needs to feed with water containing sodium cation and bicarbonate ion. The Ca and Mg contained in the source water only reduce their salinity during osmosis. Even if the water hardness after osmosis can be obtained within the standard (which in practice is achieved very rarely), the lack of sodium will not allow to raise the pH of boiler water above 8.5. This will contribute to the strongest corrosion of the boiler and especially economizer. Of course, you can dose in osmotic water NaOH, but it is not a very good solution in the case of a steam boiler. It is better to organize the softening of osmotic water. At the same time, the filter cycle of such a softening system will be huge, the salt consumption for regeneration will be minimal, and the reliability and efficiency of the osmosis plant, deaerator, economizer, boiler and the steam- condensate track equipments will grow significantly.
As having considerable production experience I can say that in practice it is more convenient to operate water treatment systems when softening is ahead of osmosis. Yes, this salt is consumed even more than just Na-cation of feed water, taking into account the consumption of the concentrate. But on softened water you can get a very high osmosis reсovery or even work in two stages of concentrate. In this case, the concentrate, depending on the composition of the source water, can be used, for example, in the reverse water supply system of the enterprise.
It is obvious that the more condensate return to the deaerator, the less salt is contained in the feed water. With a large proportion of condensate return, the role of osmosis is not so significant. But even in this case, it can be quite significant. This is due to the working conditions of the steam and condensate line. This has already been said in the previous answers.
I apologize for such a long answer, but I would like to emphasize the prospects of osmosis is for water treatment of steam boilers as a powerful tool that can bring significant benefits or in case of improper operation to cause significant trouble. It is also necessary to develop competent guidance documents on the use of reverse osmosis in water treatment of steam boilers.