Treatment of Yellow River water
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The industrial circulating water used in our company is a mixture of water from the Yellow River and water from nearby deep wells. The Yellow River water has relatively high alkalinity and chloride levels, while the water from deep wells has slightly higher alkalinity; its chloride level is acceptable (below 20 mg/l). At present, our company is planning to treat the raw water, mainly by reducing alkalinity and chloride levels. Alkalinity is relatively easy to reduce, while lowering chloride levels is more difficult. To my knowledge, there are four treatment techniques available: the first is cation-anion resin exchange technology, which requires moderate investment but results in high consumption of acids and bases, leading to higher operating costs. The second is coagulation technology; the investment is low, but an appropriate coagulant has not been found (please advise experts). Third is reverse osmosis technology (reverse osmosis membranes), but it requires significant investment, and pre-treatment through filtration is necessary first. Fourth is ultrafiltration technology; discussions with other technicians have shown that this technology has little effect on Cl ions. I would like to ask the experts for their evaluations of these four technologies? If there is a better technique, please share it? Urgent!
It depends on your requirements regarding chloride ions. If the requirements aren’t very high, a mixed-bed system using both cations and anions is still a good option; if the requirements are strict, then reverse osmosis is the better choice. Reverse osmosis technology is now quite mature, and its operation is reliable. I’m also interested in coagulation – please let me know what you know about it as well
Reverse osmosis technology is a good choice; our factory uses this technology. However, the raw water must first undergo precipitation and purification, pass through two stages of filtration before entering the reverse osmosis system, and be treated with chemicals as well.
Coagulation cannot remove chloride ions; its mechanism relies on the compression of the double electric layer and bridging effects of coagulants to eliminate colloids and large molecular organic substances, but it has little effect on chlorine. The same is true for ultrafiltration, whose mechanism is mechanical screening, and it also cannot remove chloride ions. To remove chloride ions, ion exchange, reverse osmosis, or electrodialysis is required. Ion exchange has high operating costs and is complicated to operate due to the need for acids and bases during regeneration. The reverse osmosis process is relatively better, but the initial investment is high. For you to use as circulating water, it is sufficient to select an appropriate proportion of raw water and subject it to RO desalination, followed by mixing to meet the chloride ion requirements for circulating water; this will reduce the investment cost. Specifically, this can be determined after comparing the investment costs of an ion exchange system and an RO system.
Our factory also uses reverse osmosis technology!
May I ask, do the moderators upstairs also use reverse osmosis to treat the circulating water? Or produce boiler make-up water?
Based on the characteristics of the water, it is necessary to remove alkalinity and Cl ions. Regarding alkalinity, the methods for removal are relatively simple; it can be handled using lime, ion exchange, reverse osmosis, or even by adding acid directly ； As for Cl ions, they can only be treated through ion exchange or reverse osmosis; coagulation and ultrafiltration processes are ineffective against dissolved Cl ions. For Yellow River water, the cost of acid-base regeneration through ion exchange is too high; from the perspective of energy conservation and clean production, it is not suitable ； Using reverse osmosis to remove Cl ions is the better option in terms of operating costs. Moreover, the price of reverse osmosis membranes is currently quite low, so the investment required for this method is also acceptable. Additionally, it is possible to consider mixing some reverse osmosis-produced water with treated Yellow River water, which would reduce the investment required for reverse osmosis systems.
Activated carbon has good adsorption capacity for chloride ions, but it is necessary to choose activated carbon with high performance indicators, good strength, and superior quality.
How much Cl should be removed on the 1st floor? An adsorptive coagulant can remove 49% of Cl ions. talmh@126.com
What kind of coagulant is it? Chloride ions can be removed
20 ppm for chloride ions is not high; even 50 ppm is not considered high. Of course, it mainly depends on the concentration ratio of the circulating water. If, after reaching that concentration ratio, the chloride ion level is 300 ppm, it’s still not considered high. Only when it exceeds that level does further treatment become necessary. Corrosion caused by chloride ions can be addressed by adding corrosion inhibitors, both organic and inorganic; this poses no major problem for carbon steel systems, but it does not work for stainless steel systems. Therefore, the chloride ion level in carbon steel systems can be higher, which results in lower costs compared to using chlorination equipment and associated operating expenses. The equipment used for removing chloride ions depends on the concentration of chloride ions in the incoming water as well as that in the outgoing water. It’s not true that the best equipment is necessarily the most suitable one; rather, the most appropriate equipment is the one that offers the best cost-effectiveness. Most choose RO membranes due to their durability.
May I ask, for office 0#, could you tell me which manufacturer produces the synthetic anionic coagulant? Is it imported or domestically produced?
Reverse osmosis technology is a suitable choice, as its cost-performance ratio has improved significantly compared to before.
It’s membrane treatment, haha. Isn’t reverse osmosis a bit rough?
Hehe, our factory also uses reverse osmosis technology: lol
Does your company use boiler water or circulating water? In my opinion, a chloride content of 20 mg/l in circulating water is sufficient; pitting of the steel can be disregarded in such cases. Ion exchange and reverse osmosis are not required. Generally, water treated by reverse osmosis can be used as make-up water for boilers.
If your system is made of 304 stainless steel and 70-1A brass, keep the chloride ions below 300 mg/L； For materials such as carbon steel, B, AB copper, brass, or 316L stainless steel, there are no such strict requirements regarding chloride ions. Removing chloride ions is essentially a laborious and costly process in all methods; it’s best to avoid doing it. Besides, the chloride level in the Yellow River water ranges from 80 to 140; when mixed with groundwater, it drops to around 5 or 6. It’s no problem to concentrate it by a factor of three or five. Therefore, chloride ions do not need to be treated, and it will have no impact.
From the perspective of water conservation and environmental protection, I think reverse osmosis is a better option; moreover, the technology behind it is well-developed. Ion exchange generates acidic and alkaline wastewater, and even if no such wastewater is produced, some other form of treatment is still required
Ultrafiltration can only be used as a pretreatment for reverse osmosis; it cannot remove ions on its own