Collection of Papers on Chlor-alkali Industry

I have it; what’s the point of asking for it? I can fax you any article you want

Mainly papers on electrolyzers and ion membranes, thank you.

Could those papers be shared?

Yeah, let everyone learn* learn*.:lol

Is there an electronic version? If you have any, please share them; I want to learn too* learn*!

Yes, post it online so everyone can share it; good deeds should be spread widely

Find a way to create an electronic version and upload it for everyone to share.

【Keywords】 Chlorine drying, process flow, tower equipment, optimized design 【Abstract】 This paper analyzes and summarizes the current operating status of chlorine drying units in China. Drawing on years of practical experience in the design, manufacture, and installation of such units, it focuses on the optimized design of the chlorine drying process flow and the main tower equipment, as well as new technologies, along with an introduction to the Tohni drying process. Preface: Chlorine drying is a crucial link in chlor-alkali production, serving as a bridge between preceding and subsequent processes. The quality of chlorine after drying has a direct impact on the safe operation of chlorine compressors and other equipment that utilize chlorine in later stages; it is thus an essential process. Chlorine compressor failures occur due to the quality of chlorine (primarily high moisture content in chlorine along with sulfate impurities), which in turn leads to frequent blockages and corrosion in equipment that uses chlorine. In recent years, relying on the adoption of advanced chlorine drying technology, and with the efforts of renowned domestic experts in tower design, chlor-alkali technology, as well as teams of specialized engineers, Dongri Company has designed, manufactured, installed, and commissioned over a dozen high-performance chlorine drying units for various chlor-alkali enterprises. It offers significant advantages in terms of cost-effectiveness, energy conservation and environmental protection, as well as technological advancement. 1. Current status of chlorine drying equipment in China and the impact of moisture content in chlorine on chlorine compressors. At present, among the nearly 200 chlor-alkali enterprises in China, the performance of the chlorine drying equipment in use varies widely. The process flows can be generally divided into three categories: single tower, double tower, and multi-tower (3–4 towers). The most common tower types are packed towers, bubble columns, or combinations of these two types; bubble columns are less used nowadays due to their limited operational flexibility. The level of moisture content in the chlorine after treatment also varies; in most units, the mass fraction of moisture in the chlorine ranges between 200–400 PPm, while in a few units with advanced technical specifications, this value can reach

Chlorine gas； Chlorine drying ； Packed tower ； Tower packing ； Liquid distributor ； Gas distributor ； Internal components of towers: This section introduces the application of modern packing tower technology in chlorine drying processes, including the selection of tower packing, the proper use of internal components such as liquid distributors and gas distributors, key aspects for the optimized design of chlorine drying towers, and examples of the industrial application of chlorine drying systems. I. Overview Over the past decade, China’s chlor-alkali industry has experienced rapid development, with an annual production of caustic soda exceeding 12 million tons, ranking first in the world. However, the chlorine drying process is relatively backward; the moisture content in chlorine is high, with many manufacturers having levels above 0.01% (w), and the problem of mist removal is not adequately resolved. To change this situation, we have made unremitting efforts, and this article introduces the application of modern packed tower technology in chlorine drying. Considering the characteristics of the chlorine drying process: (1) High requirements are placed on drying, with the moisture content needing to reach international standards, below 0.002% ； (2) The system operates at a slight negative pressure, with a limited allowable pressure drop, generally kept at no more than 10 Kpa ； (3) The operating load may experience significant fluctuations; therefore, the device is required to have a high degree of operational flexibility ； (4) Chlorine is a highly toxic substance with strong corrosivity, requiring strict safety protocols; any leakage of this toxic material is absolutely not permitted. Packed towers have advantages such as high efficiency, large throughput, low pressure drop, great operational flexibility, low liquid holdup, and strong adaptability, enabling them to meet all the requirements of the chlorine drying process. However, meeting these requirements and achieving stable control of various process parameters in actual production is no easy task. In addition to maintaining production stability and strictly controlling the various operational parameters throughout the process, the proper application of packed tower technology is a crucial factor. The significant progress in packed tower technology over the past 20-plus years has provided the theoretical and practical basis for this. II. Application of modern packed tower technology in chlorine drying. As one of the most commonly used gas-liquid mass transfer devices in chemical production, its structure appears simple; however, upon closer examination, its theoretical aspects are quite complex, involving research on the random flow and mass transfer of the gas and liquid phases within the packed layer, the patterns of pre-distribution of gas as it enters the tower, the methods for ensuring uniform distribution of liquid in the liquid distributor, and the impact of the packed layer’s structure on gas and liquid flow, among many other topics. To this end, we have spent over 20 years in exploration, and in the past 10 years we have completed the design, fabrication, and application of more than a hundred large and medium-sized industrial chlorine drying towers; below are some brief insights on this topic. 1. Proper selection of tower packing – plastic short-step rings and metal plate corrugated packing. Metal plate corrugated and short-step ring packings were first developed by Zhejiang University of Technology in 1982 and 1996 and applied in chlorine drying towers. The former is a recognized highly efficient structured packing, while the latter boasts advantages such as a reasonable geometric structure, large specific surface area, high porosity, high pressure resistance of the bed layer, and low susceptibility to damage. As a result, it exhibits good fluid distribution, high mass transfer efficiency, high throughput, low pressure drop, and low liquid holding capacity; it is therefore a bulk packing with excellent overall performance. Years of practical use have shown that these types of packings are suitable for use in chlorine drying towers. There are various materials available, such as polypropylene (PP), polyvinyl chloride (PVC), and chlorinated polyvinyl chloride (CPVC). PP is suitable for use in dryers with a sulfuric acid concentration of around 80%; it is inexpensive and has a low specific gravity ； PVC is suitable for concentrated sulfuric acid, and it will not become brittle even after years of use ； When the temperature is above 60°C, CPVC is the preferred choice. Practice has shown that the service life of fillers selected in this way is over 4 years. When the moisture content in chlorine gas is reduced to very low levels (such as around 0.01%), its water vapor partial pressure becomes extremely low, which in turn results in a very low driving force for mass transfer during the drying process; this makes the progress of the process quite difficult. To address this issue, we used high-efficiency metal plate corrugated fillers of different types in the last tower, and three years of practical use have shown that this approach is effective. 2. Selecting an appropriate liquid distributor: In the design of a packed tower, while the choice of packing is indeed important, the internal components of the tower that complement it, especially the liquid distributor, are equally crucial. This is particularly true for large towers; the proper selection of a liquid distributor often determines the success or failure of the tower. There are three reasons for this: (1) An improper initial distribution of the liquid inevitably leads to a sharp decline in drying efficiency ； (2) An unfavorable initial distribution makes it difficult to achieve the natural flow distribution in the packing layer ； (3) New types of high-efficiency fillers generally have a smaller radial diffusion coefficient, and therefore rely more on a good initial distribution. There are five criteria for evaluating the performance of liquid distributors: (1) operational feasibility ； (2) Even distribution, with the criterion being: sufficient density of distribution points ； Geometric uniformity of the distribution of points ； Uniformity of traffic between distribution points ； (3) Appropriate operational flexibility ； (4) Sufficient airflow channels ； (5) Simple and compact structure with a reasonable price. There are a wide variety of liquid distributor types with different structures. To suit the design of drying towers, over the past decade we have designed and developed dozens of specialized liquid distributor series for chlorine drying towers, made from various materials and suitable for towers of different diameters, in many different styles and structures. These distributors have been used in more than 100 towers, achieving satisfactory results in all cases. 3. Installation of the gas distributor in the tower: The packing dryers used in production in the past had a very simple gas inlet design, with gas entering almost always from the side. Experimental studies have shown that this design results in an uneven initial distribution of the gas flow; once the gas enters the packing layer, it continues to flow in a biased manner. This type of flow has a particularly significant impact on chlorine drying towers. Production experience has shown that it not only reduces the efficiency of moisture removal but also increases the amount of acid mist carried out at the outlet, causing substantial losses in the purification of chlorine. The literature indicates that the criterion for evaluating the performance of the inlet structure in a packed tower is good uniformity of distribution ； Low flow resistance ； Small space requirement ； Liquids can fall freely, which facilitates mass transfer between the gas and liquid phases ； Simple structure, easy to install. Based on the characteristics of the drying process, we have developed two types of gas distributors: grid-type and radial-type. Figure 1 shows schematic diagrams of the structures of these two types of gas distributors. The grid-type distributor consists of support beams and baffle plates, while the radial-type distributor includes upper and lower baffle plates, radial distribution plates, and liquid discharge pipes. The principle of even distribution in the two types of distributors is different; the grid-type utilizes a special baffle design to intercept, redirect, and divide the airflow directed toward the tower walls. The radial type achieves redistribution through bend redirection, baffle interception, and distributor plate diversion; the quality of the even distribution depends on the size ratios of various components. The lateral air intake and the flow streamline patterns after passing through the distributor are shown in Figure 2. a. Grid type b. Radial type Figure 1: Schematics of the two types of distributors. a. Grid-type air inlet b. Radial-type air inlet c. Lateral air inlet Figure 2: Flow pattern diagrams for various air inlet methods. The characteristics are briefly described as follows: a. Grid type: In the grid-type distributor, baffles are placed at different distances along the inlet jet flow, causing the airflow to be divided along its path. This prevents internal circulation that occurs at the bottom and sides, thereby improving the airflow distribution. Additionally, due to the guiding effect of the baffles, the regularity of the airflow increases, and the flow resistance is reduced compared to lateral air inlet. This type of distributor has a simple structure and does not occupy valuable space inside the tower, making it particularly suitable for technical upgrades of existing towers. Its drawback is that it requires higher technical skills for installation, and its uniformity performance is inferior to that of the radial type. b. Radial type: The advantage of the radial type is its excellent uniformity in gas distribution; the size of the space above and below the distributor has little impact on this uniformity. Moreover, our unique design prevents the mixing of gas and liquid. In addition, it features a simple structure, making it easy to manufacture and install. Its disadvantages include higher flow resistance compared to the grid type, and the need to occupy more space inside the tower. 4. Rational design of packing support plates – Application of gas-jet type packing support plates. The perforated plates used in the early stages had a porosity of only 10%–25%; when gas and liquid flowed counterflow, a liquid layer of a certain thickness would accumulate on these plates (Figure 3). This led to mixing between gas and liquid, causing flooding to occur prematurely in the support area and then spreading upward throughout the entire packing layer, thereby disrupting the normal operation of the entire tower. Figure 3 shows the gas and liquid flow conditions in the two types of packing support plates. The gas-jet type packing support plate is a type of bulk packing support plate with excellent comprehensive performance, which can be constructed by combining a certain number of perforated corrugated plates depending on the tower diameter; its structure is shown in Figure 4. Advantages: three-dimensional structure, with a porosity of up to 100% ； Gas-liquid separation prevents the mutual entrainment of the two phases ； Filler particles or fragments do not easily clog the orifices ； It saves materials, is lightweight, and is easy to install and maintain. It is a bulk packing support plate with excellent comprehensive performance, and has been used in chlorine drying towers for 10 years with satisfactory results. A series of products made from three materials – carbon steel, fiberglass-reinforced plastic, and rigid polyvinyl chloride – with tower diameters ranging from 1.0m to 2.4m. Figure 4. Structures of gas-jet type packing support plates for three materials. 5. Fixing of the packing layer – packing retaining plates and packing compression rods. Under normal operation, the empty-tower velocity in the chlorine drying tower is well below the flooding point; the packing bed is a fixed bed, and it does not become loose, fluidized, or experience collisions due to gas and liquid flow, nor is the packing carried out of the tower by the gas flow. However, abnormalities can inevitably occur in production, such as emergency shutdowns due to accident handling, flooding inside the tower caused by overloading, and system pressure fluctuations and temperature swings resulting from sudden changes in process conditions. The sudden changes in the conditions inside the tower have an impact on the bed that is hard to imagine; they can cause the bed to expand, become fluidized, or result in the deformation or fragmentation of the packing. In some cases, large amounts of packing may be carried away by the airflow and end up in the liquid distributor, and even in other equipment outside the tower. For regularly arranged packing, its orderly pattern will be disrupted. Therefore, to maintain the effectiveness and integrity of the packing bed and prevent accidents from damaging it, effective fixation must be applied after the packing is filled. Figures 5 (plastic) and 6 (metal) show two types of filler retaining plate structures used to secure bulk fillers. These structures consist of a frame and a mesh, and they are fixed to the top layer of the filler through multiple lugs welded to the tower wall, thereby preventing the filler from escaping while not hindering the normal flow of gas and liquid. For structured packing, packing compression rods are used to press the top layer of plates horizontally, thereby preventing the packing layer from becoming loose. Figure 5 Plastic filler restriction plate Figure 6 Metal filler restriction plate 6. Key points of the optimized design for chlorine gas drying towers The chlorine gas drying tower can be divided into 5 sections: a. Acid storage section—from the bottom of the tower to the height of the sulfuric acid overflow port ； b. Intake section—maximum allowable liquid level of sulfuric acid (overflow port) to the underside of the packing support plate ； c. Drying section—i.e., the height of the packing layer ； d. Liquid distribution section—from the inlet pipe to the top surface of the packing layer ； e. Demisting section—from above the liquid inlet pipe to the gas outlet pipe. Optimization design techniques include two aspects: the determination of appropriate operating conditions for each section, and the selection of tower internals along with their mutual coordination. These aspects are not isolated from one another but are rather interconnected. The determination of the tower internals was introduced earlier; the following briefly discusses other issues. (1) Determination of tower diameter and packing layer height: According to conventional design, the tower diameter is calculated based on the size of the foam point ； The height of the packing layer is determined by the mass transfer performance. However, the chlorine drying tower has its special aspects, requiring consideration of the effect of gas velocity on the liquid load as well as issues related to the removal of trace amounts of moisture. Therefore, the results obtained from conventional calculations must also be multiplied by a safety factor determined based on the designer’s experience. (2) Selection of spray density: Given that the system operates under gas film control, it is theoretically assumed that the mass transfer coefficient is independent of the liquid flow rate; therefore, the spray density should be set at the lowest value sufficient to wet the surface of the packing. In fact, the impact of uneven liquid distribution on the wetted packing also needs to be taken into account; generally, a spray density of 15–30 m3/h·m2 is selected. (3) Regarding the issue of uniform gas-liquid distribution: For efficient packed-bed absorbers used to remove trace amounts of water, ensuring uniform gas-liquid distribution inside the tower during operation is a critical issue. This must first be addressed through proper design, and it is also closely related to the manufacturing and installation of the equipment; any negligence at any stage can render all previous efforts futile. Regarding design issues, these mainly pertain to the proper selection and design of liquid distributors, redistributors, and gas distributors. Some literature provides an overview on this topic, but most of the information available is in the form of internal company patents. (4) Whether to install a liquid (gas) redistributor. The principle of segmenting the packing into sections, proposed by the renowned scholar Homer, is that the layer height should be 7m ； Equivalent to a height of 10 mass transfer units ； 6 to 8 times the tower diameter in height. The lowest height among the three is taken as the segmentation criterion; in addition, the maximum load-bearing capacity of the support plate and the filler itself must also be considered ； Based on this principle, since the height of the packing layer in the drying tower is only about 5 meters, it is unnecessary to divide it into sections or install liquid (gas) redistributors. (5) Reasonable arrangement of sections: In addition to each section needing to have sufficient height, the connection between sections is also crucial. When the system is operating stably, both the liquid level in the acid storage sections of each tower and the sulfuric acid concentration remain constant; theoretically, the amount of acid stored, and thus the liquid level, has no impact on the operation process. However, unstable factors are inevitable in the actual production process. The greater the acid storage volume once such factors arise, the stronger the system’s resistance to interference, which is certainly conducive to maintaining stable dryness levels at the chlorine outlet. For example, intermittent addition of concentrated sulfuric acid can cause an increase in the acid temperature; changes in the sulfuric acid concentration in turn affect whether the moisture content of the chlorine gas at the outlet meets the specified standards, and these changes can be significant if the amount of acid stored is too small. Therefore, the acid storage section must have sufficient height to facilitate operation. Special studies have been conducted on the impact of the intake structure on airflow distribution. In short, the simpler the intake structure, the greater the height required to achieve a uniform airflow distribution; to reduce this height, it is necessary to add gas distributors, and the required height is determined by the type of distributor chosen and its design methodology. Determining the height of the packing layer is a complex issue; theoretically, it can be determined by the product of the number of mass transfer units and the height of each mass transfer unit. In practice, however, the calculated value should be multiplied by a sufficiently large safety factor. As for the height of the liquid distribution section, it consists of the height of the distributor itself plus the distance from the liquid discharge port to the top surface of the packing layer; the former is determined by the design of the distributor, while the determination of the latter height has been discussed in separate articles. Determining the height of the demisting section is relatively difficult; increasing this height always helps with the separation of mist. It can be appropriately increased when conditions permit. III. Application Examples: Starting from the summer of 1994, we applied modern packed tower technology to the chlor-alkali industry. More recently, by combining the non-metallic equipment developed by Hangzhou Dongri Fiberglass Co., Ltd. with the metal equipment and tower packing production techniques of other companies, we have helped more than 40 large and medium-sized enterprises in China carry out technical upgrades, expansions, and new construction projects, earning high praise from both within and outside the industry. The table below shows just a few examples. The newly established Hangzhou Zhonghao Technology Co., Ltd. brings together well-known domestic experts in tower equipment, specialists in the chlor-alkali industry, as well as professional engineering and technical personnel, and is capable of providing services in design, manufacturing, installation, and commissioning. In recent years, by studying the development trends in equipment imports within China’s chlor-alkali industry as well as the quality requirements for chlorine gas, various parties have collaborated to develop a set of advanced technical solutions for chlorine gas drying systems in China. Table: Some Application Examples
Serial Number | Company Name | Abbreviated Process Flow | Construction and Operation Period | Remarks
1 | Zhejiang Juhua Co., Ltd. Electrochemical Plant | 4-tower process | 1994–2005 | Renovation and new construction
2 | Zhejiang Jiahua Industrial Co., Ltd. | 2-tower process | 1996–2005 | Renovation and new construction
3 | Jiangsu Meilan Chemical Co., Ltd. | 4-tower process | 1999–2005 | New construction
4 | Jiangsu Xinpu Chemical Co., Ltd. | 2-tower process | 2000–2005 | Renovation
5 | Jiangsu GreenAipu Chemical Co., Ltd. | 3-tower process | 2002–2005 | Renovation
6 | Jiangsu Yangnong Chemical Group Ruixiang Chemical Plant | 4-tower process | 2005 | Under construction
7 | Sinopec Nanjing Chemical Plant | 2-tower process | 2002–2005 | New construction
8 | Anhui Wuhu Shanjiang Chemical Co., Ltd. | 2-tower process | 2005 | Under construction
9 | Hunan Jiantao (Hengyang) Industrial Co., Ltd. | 3-tower process | 2004–2005 | New construction
10 | Leshan Juxing Chemical Yongxiang Resin Factory | 2-tower process | 2004–2005 | New construction
11 | Xi’an Xihua Thermal Power Chemical Co., Ltd. | 2-tower process | 2005 | New construction
12 | Nanning Chemical Group Co., Ltd. | 3-tower process | 2004–2005 | New construction
13 | Guizhou Zunyi Alkali Plant | 3-tower process | 2004–2005 | Renovation and new construction

References
Dong Yiren, Zhang Wenmin. Performance Study and Industrial Application of Polypropylene Short-Step Ring Packings. Chemical Engineering, 1996, 24(4): 21.
National Chemical Engineering Design Technology Center Station. Handbook for the Design Selection of Tower Packings and Internal Components. 2000, 6.
Xu Chongsi, Dong Yiren, Jiang Qingquan. Performance Study of Metal-Pressed Orifice Plate Ripple Packings. Chemical Engineering, 1982, 10(5): 35.
Edited by Lanzhou Petroleum Machinery Research Institute. Modern Tower Technology. Sinopec Press, 2005.
Dong Yiren, Xu Chongsi. Analysis of Liquid Distributors in Packing Towers. Chemical Engineering, 1996, 24(4): 25.
Dong Yiren. Air Inlet Structures in Packing Towers and Their Design. Chemical Engineering Design, 1993, 3(3): 1.

Author Introduction:
1. Dong Yiren, Professor, School of Chemistry and Materials Science, Zhejiang University of Technology. Phone: 0571-85815643
2. Huang Huadong, Engineer, Hangzhou Zhonghao Technology Co., Ltd. Phone: 0571-86189188; 13185716803. Address: 12th Floor, Ningbo Building, No. 46 Tianmu Mountain Road, Hangzhou. Postal Code: 310012

Those on the 12th floor and the 13th floor, thank you so much; this is really helpful to me. Thanks!