Status of demineralized water in various plants
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Medium-pressure boilers all use deionized water. Our plant’s water treatment process is relatively old: raw water – electrodialysis – first-stage mixed-bed resins – deionized water, with the conductivity of the output water being less than 10 μS. I understand that many new systems use reverse osmosis desalination technology, and I’m very interested in knowing: are the operating results satisfactory? What are the problems? Everyone is welcome to discuss. :lol
Our company uses an RO + anion/cation exchange process, and the overall operation is satisfactory. Compared to electrodialysis, the initial investment is higher. The key to the operation of an RO system is raw water treatment. I actually have an article on this forum that you can take a look at.
Our company’s desalinated water is produced in a dedicated production facility, with an output of 300 T/h; this water is mainly supplied to thermal power plants, sulfuric acid plants, caustic soda plants, as well as for external distribution. The production process is as follows: industrial tap water → raw water pump → addition of oxidant → self-cleaning filter → plate heat exchanger → ultrafiltration → addition of reductant → addition of scale inhibitor → safety filter → high-pressure pump → reverse osmosis membrane module → carbon dioxide remover → intermediate water tank → intermediate water pump → cation exchanger → anion exchanger → mixed-bed reactor → desalinated water tank → desalinated water pump → end users. Quality of the final product water: hardness: ≈0 μmol/l; silica: ≤20 μg/l; conductivity: ≤0.2 μS/cm
We use a cation/anion exchange process; the quality of the water output is poor, with a relatively high conductivity, below 5 μS/cm. The quality of the steam is also poor, leading to rapid scaling of the turbines, with silicon being the main component of this scale. We are currently carrying out modifications to improve water quality by installing mixed-bed filters.
May I ask, chx8965, what is the role of the plate exchanger in the above process? Thank you!
The plate heat exchanger is used to heat the raw water with steam; if the temperature of the raw water is below 15°C, open the steam inlet valve and the condensate valve of the plate heat exchanger； Open the main steam inlet valve and adjust the steam control valve so that the outlet temperature of the plate heat exchanger displays around 25°C. This is done with regard to the performance of the ultrafiltration membrane, in order to ensure its filtering efficiency and prevent a decrease in water production. This post was last edited by chx8965 on 2007-12-16 12:59.]
We used the acid cooler replaced by an old unit to heat the raw water. The water production rate can be increased by about 5–10%.
We use a cation/anion exchange process, along with a mixed-bed system, with a conductivity of less than 0.2 μS/cm. Since it is fully manual, manual analysis of the cation exchange resin columns is cumbersome; I would like to know how to simply determine which column has failed
My experience: Do not wait until it stops working before carrying out regeneration. Instead, determine an appropriate production rate per cycle through testing and calculations, supplemented by manual analysis, in order to ensure stable and reliable operation.
“The saying “Don’t wait until it fails before regenerating it” is absolutely true, but we haven’t fully followed this advice; we hope for good monitoring tools that allow the process to be completed easily with just a few steps
Using the periodic water production volume as an operational indicator is very reliable.
When producing demineralized water using RO, it is generally not necessary to install a decarburization device.
Hello, our company has a system of 80, which follows a process similar to that of your company; we just add decarburization as an additional step. We would like to purchase another set of 320 models. Could you please tell us which company’s equipment your company uses, what the performance is like, and what the water production rate is? Thank you.
If only cation-anion resins are used for treatment, the quality of the effluent water is generally not good. Considering medium-pressure boilers, it is recommended to add mixed-bed treatment as well. With the current water quality from the anion exchange bed, it should be possible to treat at least 3,000 times the volume of resin. The silicon content in the effluent is around 10 ppb. Please contact us if needed.
Now, online monitoring is done using sodium meters. It’s very convenient.
This definitely won’t work. First of all, you can’t ensure that the quality of the water entering the system remains constant; especially during winter and summer, there are significant changes in water quality. Additionally, you can’t guarantee that the regeneration process of the columns is consistent each time – the degree of regeneration of the resin isn’t always the same, unless you ignore the factors related to acid and alkali consumption.
In fact, fully automatic operation is also possible at present; the effluent from the cation exchange resin bed is monitored using a sodium meter, while the effluent from the anion exchange resin bed is monitored using a conductivity meter and a silicon meter. If the parameters exceed the set limits, the regeneration process is initiated automatically.
How is the concentration of the acid produced by you and the control steps automated?
There are concentration meters for measuring the concentration of acids and bases; these can be either domestic or imported. In general, water treatment in power plants is often controlled by programs. For example, when a filter bed fails, the system switches to the regeneration mode via the computer, and it operates automatically according to the established procedures: how many seconds for backwashing, how many seconds of rest, how many seconds for draining water, how many seconds for pre-injection, how many seconds for adding acid, what the concentration should be, how many seconds for regeneration, how many seconds for rinsing, and so on. This is quite simple; the only thing to consider is the cost. Unless cost is not a concern, private companies generally do not opt for fully automatic operation.
Measure the pH value; it remains stable when not defective, but rises when defective.
What is the water production rate? Are there any data on operating costs and investment?