Can inorganic membranes (ceramic membranes) be used for once-through brine filtration?

The ceramic membrane process for treating brine is a new brine filtration technology. This technology takes advantage of the unique physicochemical properties of inorganic ceramic membranes. It employs an efficient \"cross-flow\" filtration method: the raw salt is first dissolved by chemical treatment, and then purified agents such as soda ash and caustic soda are added and mixed thoroughly to form suspended particles. These particles are then fed directly into a Jiusi membrane filter for three-stage filtration and separation, thereby achieving the purification of brine. Compared to organic membrane filtration, this technology offers advantages such as a shorter process flow, less space requirement, and lower investment costs; it represents the future direction for brine treatment technologies. However, after some research and investigation, it turns out that this process is not performing well at present. A design institute in China also conducted some studies on the ceramic membrane process and concluded that it is still not mature enough and requires further improvement. I. Investment and operating costs (without a pre-treater and without sodium hypochlorite) 1. Since the treatment process using ceramic membranes relies primarily on the technology of circulating and filtering most of the brine. Therefore, the power consumption of the brine circulation pump accounts for a significant portion of the operating costs of ceramic membranes. At present, for the most widely used membrane types in China, namely Kai membrane and Gore membrane, the ratio of pump power to flow rate for saltwater high-cycle pumps is approximately 0.5:1 ； The ratio of the power rating to the flow rate of the saline circulation pump for ceramic membranes is 1:1. From this perspective alone, the operating cost of ceramic membranes is not lower than that of Kaimo and Gore membranes. However, the process used for ceramic membranes involves directly feeding the brine in the reaction tank into the filter for filtration; no pre-treatment unit is required, nor are multiple reaction steps necessary. This reduction in initial investment is one of the advantages of ceramic membranes. Therefore, compared to investment costs, ceramic membranes have significant advantages. 2. According to Nanjing Jiusi’s estimates, due to the lower number of required devices and reduced investment costs, the ceramic membrane process for producing 300,000 tons per year of ion-exchange membrane caustic soda can save 11 million yuan in investment costs compared to the organic membrane process; operating costs can also be reduced by nearly 2 million yuan per year. However, according to estimates from some companies in the chlor-alkali industry, the ceramic membrane process for producing 300,000 tons per year of ion-exchange membrane caustic soda can save an investment cost of 4 million yuan compared to the organic membrane process; yet the operating costs are about 730,000 yuan higher per year, which differs somewhat from the figures related to ceramic membranes. 3. The above data are based on conditions without a pre-treater and without the addition of sodium hypochlorite. The function of the pre-treater is mainly to remove Mg2+ and organic substances; magnesium hydroxide forms flocs, and when its concentration is high, both organic and inorganic membranes get clogged. In fact, organic membrane filtration can also perform well without a pre-treater, provided that the saltwater contains very low levels of Mg2+. Therefore, eliminating the pre-treater in ceramic membrane processes is also conditional. Furthermore, it is claimed that ceramic membranes overcome sensitivity to organic substances, but in practice manufacturers add sodium hypochlorite to the saline solution, which is different from what the ceramic membrane manufacturers claim. Upon discussion with the users, it was found that this is mainly done to eliminate the impact of organic substances on the performance of the membranes 【another purpose of adding sodium hypochlorite is to remove organic amines】. Based on the above analysis, if the ceramic membrane process also requires a pre-treater and sodium hypochlorite, it will not have an investment advantage, and its operating costs will be higher than those of the organic membrane method. II. Problems encountered during the use of ceramic membranes: In discussions with manufacturers of ceramic membranes, it was found that different manufacturers have all experienced membrane breakage. There are mainly two reasons for membrane rupture: one is the formation of a gas hammer effect due to valve failures or improper operation, and the other is that the casing of the initial installation was primarily made of steel lined with PO; due to the different rates of thermal expansion and contraction between the PO lining and the casing, bubbling occurs at operating temperatures of 50–60°C, which causes the nearby membrane tubes to crack. By analyzing these two causes of membrane rupture, ceramic membrane manufacturers have taken certain measures to address them. Adding a programmable valve and interlock control can help prevent the occurrence of air hammer phenomenon ； At Shandong Hengtong, measures such as replacing the casing of a set of equipment with all-titanium material have been taken. Since the modified device has not been in operation for a long time, it is still too early to draw conclusions regarding its actual performance; however, no membrane rupture has occurred in the modified device. III. Summary and analysis of experiences in examining ceramic membranes, as well as the problems that need to be addressed when using ceramic membranes. The process of using ceramic membranes for saltwater purification is a technology that is still in the process of development. A simplified process and fewer equipment are the common experience among manufacturers that use ceramic membranes. To use this process, it is necessary to understand several aspects in more detail: 1. The safety and reliability of the ceramic membrane process. At present, this process is not yet fully developed and requires further improvement. Whether a pre-treatment unit or chemicals are needed depends on the conditions of the saline solution; therefore, before deciding to use this process, it is essential to carefully assess the conditions of the saline solution in one’s own company as well as any potential changes in those conditions in the future. 2. It is necessary to clarify the service life of ceramic membranes. It is understood that the component that actually performs the filtering function in ceramic membrane filtration tubes is a layer of zirconia sintered on the wall of the ceramic tube. The service life of zirconia directly affects the lifespan of the ceramic membrane tube. Will the zirconia layer gradually thin out or even peel off due to continuous pickling, backwashing, and saline flushing? Some chlor-alkali manufacturers have reported that the membranes get scratched after a short period of use; however, the manufacturers guarantee a service life of 5 years for these membranes. 3. How to detect membrane rupture and the processing time. During the use of ceramic membranes, membrane breakage has occurred on multiple occasions; in some cases, there were only one or two membrane tubes remaining intact within a single filtration tube. Currently, monitoring is primarily carried out by installing turbidity meters at the Qingye outlet to determine whether there has been a rupture in the membrane tubes. Large-scale fractures in the membrane tubes occur; ceramic membrane manufacturers explain that this is mainly due to the use of two sealing rings at the connection point between the membrane tube and the partition inside the filtration tube. When one membrane tube breaks, if this is not detected in time and fluid continues to flow into the filter at a high rate, it causes the membrane tube to move around inside the filtration tube, thereby breaking adjacent membrane tubes as well. If one is broken, two are broken; if two are broken, four are broken, and soon all the membrane tubes will be damaged. Therefore, timely detection of membrane breakage and control of the processing time have a significant impact on the safety of the membrane tube and the system. 4. Among the manufacturers currently in operation, there are high demands for plate and frame filter presses; some of them install such filter presses in the main production process as key equipment (such as Jiujiang Xinkangda). Shandong Hengtong is equipped with large-area plate and frame filter presses (2×500㎡ plates per unit, with a capacity of 80kt/a). Therefore, how to match the ceramic membrane process with the area of the plate and frame is an issue that needs to be resolved. 5. The transportation issue of membrane tubes. Now, when ceramic membrane manufacturers supply complete sets of equipment, they have them installed in the factory before transporting them to the end-user. Therefore, damage to the membrane tube is inevitable during transportation. Therefore, it is recommended that manufacturers install the filter membrane tubes on-site. 6. The issue of no alternative for membrane replacement: At present, in China, the only company using ceramic membrane technology is Nanjing Jiusi; the lack of options for replacing these membranes is also a concern that needs to be taken into account.

The above information was provided by a friend; corrections and technical support are welcome.

Any processing method has its advantages and disadvantages, which depend on the conditions of raw salt in the region

Our company chose ceramic membranes for its 300,000-ton project. Has the original poster gone to conduct an inspection? Many of your questions can actually be answered through communication with users. For example, in the case of plate and frame filters, we have visited that company in Shandong several times and had thorough discussions with them. They use plate and frame filter presses that were discarded from their PVC production facilities; these filters have a large surface area, and it sometimes takes three days to remove one layer of sludge from them, especially when the water flow rate is low. This is not a drawback of the ceramic membrane process; it’s simply that this company is unwilling to purchase the appropriate plate and frame filters. That shop in Jiujiang, which uses a plate-and-frame design, was a fresh experience for me – it truly has its own distinct features. It’s a pity that, in order to promote its technology and reduce energy consumption, Kyogo Company did not design processes with plate-and-frame filters at the front stage for subsequent projects.

After conducting sampling tests, it is clear that the water quality produced by the ceramic membrane process is indeed superior to that of our current process; such high-quality brine really makes those of us in the technical field envious. The company of the poster uses refined salt, and using a ceramic membrane process should be very effective; good quality brine helps to extend the cycle for regenerating the secondary brine as well as the lifespan of the ion membranes, providing a long-term solution.

If the quality of the raw salt used by the poster is guaranteed, there should be no problems with inorganic membranes. When using membrane technology for nitrogen removal, the amount of salt sludge generated is very small; it’s estimated that the filter plates need to be removed only once every half month

1. Comparison of energy consumption: Here, for primary brine with a caustic soda consumption of 20W per ton per year, pump selection is carried out using either the Kaimo membrane/Gore membrane technology or the Jiusi membrane technology. Pumps with identical specifications are not included in this table; all pump selections are based on the models offered by Hangzhou Caipump. A. Kai/Membrane/Gore Membrane Process
Name, Model, Pump Manufacturer, Flow Rate, Head, Shaft Power, Number of Units:
Ferric chloride solution pump – IFK80-65-125, Hangzhou Alkali Pump; Flow rate: 25, Head: 5, Shaft power: 0.64, Number of units: 1
Ferric chloride lift pump – IFK50-32-160, Hangzhou Alkali Pump; Flow rate: 13, Head: 32, Shaft power: 3.24, Number of units: 1
Pressurization pump – IJ175-150-450, Hangzhou Alkali Pump; Flow rate: 240–360, Head: 48–67, Shaft power: 73.8, Number of units: 1
Feeding pump – IJ150-125-250, Hangzhou Alkali Pump; Flow rate: 150–300, Head: 13–23, Shaft power: 15.1, Number of units: 1
Total: 92.78

B. Jiusi Ceramic Membrane Process
Three ceramic membrane filters with a surface area of 100 m2 each are used; the circulation flow rate for each filter is 280 m3.
Name, Model, Pump Manufacturer, Flow Rate, Head, Shaft Power, Number of Units:
Feeding pump – IJ150-125-250, Hangzhou Alkali Pump; Flow rate: 150–300, Head: 13–23, Shaft power: 15.1, Number of units: 1
Circulation pump – IJ175-150-250, Hangzhou Alkali Pump; Flow rate: 240–360, Head: 13–21, Shaft power: 24.7, Number of units: 3
Total: 89.2

In addition, the Kai/Membrane/Gore Membrane Process uses a gravity-fed saline tank to feed the filters. If pumps are used to apply pressure for filtration, the energy consumption will be much higher than that of the process described above. With pump-assisted filtration, a return valve (No. 3) is installed in the Kai membrane filters to allow fluid to flow back to the intermediate tank. Without this return valve, as filtration proceeds and the filtration flux decreases, the filtration pressure rises. The Kai/Membrane/Gore Membrane Filters will automatically shut down when the filtration pressure reaches 0.15 MPa. 2. Regarding the preprocessor issue: The Kem membrane process can indeed do without a preprocessor, but this is only possible when the magnesium content is very low, practically zero. Given that your company uses vacuum salt production, the quality of the salt is excellent, so it is entirely possible to use the Kem membrane process without a preprocessor. However, problems will arise if the quality of the salt changes. Furthermore, the cost of producing salt by vacuum is quite high compared to other types of salt. Has your company decided to continue using this method for salt production? If the price of vacuum salt production rises at some point, your company may be forced to use other types of salt due to cost pressures, but without a pre-treatment system it will not be possible to operate. I believe that in such a situation, your company will find itself in a very awkward position. The Jiusi membrane filters do not require a pre-treatment unit regardless of the level of magnesium content. Currently, two sets of Jiusi membrane filters manufactured by Jiuguo Company are in use in the potash industry; the potassium salts used there are mostly domestic ones, which contain high levels of magnesium – sometimes the calcium-to-magnesium ratio is as high as 1:5 – yet the performance of these filters remains excellent. 3. Lifespan of ceramic membranes: Jiuwu Company guarantees a lifespan of 5 years for its ceramic membrane filtration elements. The scouring of the membrane tubes is mostly caused by inadequate pre-filtering. Currently, Jiuwu Company uses titanium mesh filter elements of Φ1mm in diameter and 1mm in thickness, which are produced by the company itself. The problem of incomplete coarse filtering has been completely resolved. 4. The irreplaceability of membrane replacement: Jiuguo Company is an enterprise backed by Nanjing University of Technology; all its technologies are in the hands of Chinese people, so it is not subject to foreign technological constraints. The ceramic membranes it produces enjoy full intellectual property rights.

I had been worried that the energy consumption of the Jiusi membrane filter would be higher than that of organic membranes. After checking the energy consumption comparison mentioned above, and also by referring to the pump models and specifications of Hangzhou alkali pumps when I got home, I found that the situation was roughly the same as what was described above – the difference between the two is not significant. On the other hand, if an organic membrane filter uses a pump to feed saline water into it for filtration, more power is required; this is because such a filter is equipped with a manual reflux valve (not valve No. 3 as mentioned above), which results in increased energy consumption. The performance parameters of Hangzhou alkali pumps can be found on their official website; those who are interested are welcome to check it out. Additionally, given the situation described by the original poster, if your company decides to use vacuum salt production under any circumstances, you can opt for an organic membrane system that does not include a pretreater. However, this will result in significant constraints regarding the quality of the raw salt used. If the quality of salt produced by vacuum methods declines, or if your company decides, for cost reasons, to use industrial salt or sea salt instead, then an organic membrane system without a pretreater will not be able to function.

The filtration principle of ceramic membranes differs from that of Gore membranes; the former uses cross-flow filtration, meaning there is a high flow rate parallel to the membrane surface, and under this flow the membrane surface does not develop a filter cake layer, allowing for stable operation； The latter is a dead-end filtration process; as filtration time progresses, impurities accumulate on the surface of the membrane, and backwashing is required during operation. At this point, filtration stops, and the filtrate flows in the reverse direction to wash away the filter cake before filtration can resume. Therefore, it is a discontinuous operation. The issue of the irreplaceability of membrane replacement is also something users need to take into consideration. Although there is a warranty period, once that period ends, if the replacement of membrane tubes is controlled by a single supplier, the prices will not go down. Therefore, it is recommended that users choose standard specifications for inorganic membranes, mainly in terms of external dimensions (outer diameter, length), the number of membrane channels, etc. (Currently, the common outer diameter is 41 mm with 37 channels and a length of 1 m; or an outer diameter of 25 mm with 19 channels, etc., to prevent suppliers from using proprietary specifications.)

The filtration principle of ceramic membranes differs from that of Gore membranes; the former uses cross-flow filtration, meaning there is a high flow rate parallel to the membrane surface, and under this flow the membrane surface does not develop a filter cake layer, allowing for stable operation； The latter is a dead-end filtration process; as filtration time progresses, impurities accumulate on the membrane surface, and backwashing is required during operation. At this point, filtration stops, and the filtrate flows in the reverse direction to wash away the filter cake before filtration can resume. Therefore, it is a discontinuous operation. The issue of the irreplaceability of membrane replacement is also something users need to take into consideration. Although there is a warranty period, once that period ends, if the replacement of membrane tubes is controlled by a single supplier, the prices will not go down. Therefore, it is recommended that users choose standard specifications for inorganic membranes, mainly in terms of external dimensions (outer diameter, length), the number of membrane channels, etc. (Currently, the common outer diameter is 41 mm with 37 channels and a length of 1 m; or an outer diameter of 25 mm with 19 channels, etc., to prevent suppliers from using proprietary specifications.)