Should cooling towers use a fillless technology?

Filler-free atomization technology: Whether it is a forced-air counter-current filled cooling tower, an exhaust-air counter-current filled cooling tower, or an exhaust-air cross-flow filled cooling tower, they all share one thing in common – fillers are installed inside the tower (although their materials and forms vary). Its function is to cause the water sprayed by the water distribution device to drip down along the slats in the form of droplets, or for the water to come into contact with air as a thin film on the surface of the packing; this increases the contact area between water and air, thereby enhancing the cooling effect. However, during operation, due to the deposition of calcium and magnesium ions, sediment, algae, microorganisms, etc. on the packing, as well as the accumulation and growth of scale on the surface of the packing, water tends to flow rather than forming a water film or droplets. Especially as the operational time of the production system increases, issues such as dead zones and channeling caused by filler aging, deformation, cracking, collapse, blockages, or clogs in the water distribution nozzles will inevitably lead to an increase in system resistance. 　　As can be seen from the aerodynamic performance curve of the axial flow fan, due to the increase in system resistance, that is, the increase in the fan’s total pressure, the fan’s air volume will inevitably decrease significantly, and uneven temperature distribution at the cooling points inside the tower will occur. As the air-water ratio in the system decreases and there is insufficient air supply, it becomes difficult to meet the requirements of the cooling process. This not only **reduces the cooling capacity and efficiency of the packed tower, but also requires shutdown in order to clean, replace, or replenish the packing or water distribution nozzles, thereby reducing operational time and increasing maintenance costs. Especially in closed circulating water systems, the brittle fragmentation of the packing can easily cause blockages in the heat exchange devices, pumps, and other equipment as well as in the delivery pipelines within the production system, forcing companies to suspend operations for cleaning these blockages. For example, in the Gaorun section of Sinopec’s Maoming Petrochemical Company, filler fragments blocked the heat exchanger tubes, forcing the plant to shut down for repairs and causing immeasurable losses to production. In summary, the packed tower has numerous insurmountable disadvantages during the production process, especially these disadvantages become more prominent as the production runtime increases. ◆Due to the increase in system resistance, the total pressure of the fan rises, which inevitably leads to a significant decrease in the fan’s air volume. As a result, the air-water ratio is reduced, **which lowers the cooling capacity and efficiency of the packed tower. ◆The uneven temperature at the cooling points inside the tower directly affects its cooling efficiency. ◆The current of the accompanying fan increases, resulting in higher power consumption. ◆Due to the aging of the packing, which leads to deformation, cracking, and collapse, the equipment and pipelines in the closed-loop circulating water system become blocked, forcing shutdowns for cleaning and maintenance. As a result, the production cycle is shortened, and the costs associated with maintenance and repairs increase. 　　 The key to completely overcoming the numerous drawbacks of fill-type cooling towers lies in addressing the issue of increasing system resistance as production runs continue for longer periods of time. And the filler is one of the main factors causing an increase in system resistance. Therefore, after years of dedicated research, we have specifically designed and manufactured a high-efficiency low-pressure centrifugal atomization device as a cooling element, to replace the packing and water distribution systems in packed cooling towers. The functions and characteristics of the high-efficiency low-pressure centrifugal atomization device are as follows: ◆ Since there is no packing, the gas-water ratio increases. By eliminating the packing, the entire tower essentially becomes an empty tower, which not only simplifies the structure of the cooling tower but also reduces the resistance of the tower; in other words, the total pressure required by the fan decreases. As can be seen from the aerodynamic curve of the fan, a decrease in total pressure inevitably leads to a significant increase in air flow, thereby increasing the gas-water ratio in the cooling system. ◆Atomizing the cooling medium: After removing the packing, how can the water to be cooled be dispersed within the tower to facilitate heat and mass transfer and exchange? Since the heat and mass transfer rate in a water-air system is proportional to the mass transfer area, to improve the cooling efficiency of a cooling tower, it is necessary to increase the mass transfer area. The calculated total mass transfer area for 1 m3 of water dispersed into spherical droplets of different particle sizes is shown in the table. Particle size (m): 0.020, 0.015, 0.010, 0.008, 0.006, 0.004, 0.002, 0.001; Area (m2): 300, 400, 600, 750, 1000, 1500, 3000, 6000. As can be seen from the table, the smaller the particle size, the larger the mass transfer area. Spraying water in a mist form is a more effective and economical way to increase the mass transfer area. Therefore, we adopted self-developed dispersion jet components that are at the advanced level in China, to disperse and spray the cooled medium under certain pressure into uniform, tiny mist particles with a larger specific surface area. Figure 1 is a diagram of the atomization device. ◆Low pressure: At a constant flow rate, the higher the pressure of the cooling medium, the better the atomization effect. At present, in industries such as petrochemicals, large-scale chemical manufacturing, and large-scale fertilizer production in our country, as well as in the cooling of turbine condensate water in thermal power plants, closed-loop circulation systems are used; the pressure of the water returning under pressure at the ±0.00 level is only 0.08–0.12 MPa. If the pressure is to be increased, it must be pressurized using a pump, which means an increase in energy consumption. Therefore, in order to avoid increased energy consumption, improvements were made to the design and numerous tests were conducted based on the actual conditions of these industries, so that the atomization device can achieve the most optimal atomization effect at a low pressure of 0.025–0.030 MPa. ◆The residence time of the growing fog particles in the tower: The height of the atomization determines the length of time that the fog particles remain in the tower, which in turn determines the duration of heat and mass transfer in the water-air system. The higher the atomization height, the longer the fog particles remain in the tower. Therefore, necessary measures were taken during design to ensure that the atomization device can achieve the highest atomization height at low pressures, thereby increasing the residence time of the fog particles inside the tower. ◆ Avoid short-circuiting in the heat exchange process of the gas-water system. The overlapping of fog zones can lead to short-circuiting in this heat exchange process, which has an adverse effect on it; the more overlapping areas there are among the fog zones, the more severe the short-circuiting in the gas-water system’s heat exchange process becomes. During design, improvements are made not only to the spray angle and spray radius of the atomization device, but also the devices are arranged in opposite directions within the tower, in order to minimize the overlapping area of the fog zones and thus avoid short-circuiting in the heat exchange process of the gas-water system. During the design of the piping system, pressure equalizing devices were added to ensure that the pressure at various points in the system is balanced, thereby enabling the fillless spray cooling tower to operate under ideal conditions with optimal cooling efficiency. ★ Anti-drift water technology: The resistance of the tower is **reduced** after the use of filler-free atomization technology. Thereby increasing the cross-sectional flow velocity. How can we prevent water from escaping at the top of the tower during operation? To address this issue, a new anti-drift water technology has been developed. In other words, an atomization zone has been added to the upper part of the WSFL-type filler-free spray cooling tower. Moreover, in view of the increased gas-water ratio and higher cross-sectional flow velocity, a specially developed collector made of flame-retardant fiberglass – the SB double-ripple collector, which is different from the collectors used in filler towers – has been installed above this atomization zone. The radius of the curved surface of the water collector was increased, and the distance between the individual pieces was adjusted during assembly; this prevented the upward airflow from moving in a straight line unimpeded, forcing it to follow the curve of the curved surface. As a result, the upward speed of the airflow was reduced, causing the water droplets carried by the airflow to grow larger as they rose, before falling back into the tower. Thus, the occurrence of water splashing is completely avoided. This not only reduces water loss but also prevents pollution of the surrounding environment, playing a positive role in protecting the environment and ecological balance.

Brother upstairs, let’s talk about whether well-known foreign cooling tower companies such as Malley and Hammon are also developing fillless towers. Has CTI in the United States mentioned anything or stated anything regarding the testing of fillless towers? Theory still matters. Well-known domestic experts in cooling towers such as Zhao Zhenguo and Li Dexing – which of these experts recommended the use of fillless towers? To be honest, the fillless tower is a development stage of the filled tower; it has become obsolete and is a product of China’s special historical circumstances. Objectively speaking, it can be considered a step backward in terms of technology. The above are my personal opinions; please point out any mistakes.

I don’t quite agree with the views of the gentleman upstairs. For discussion purposes, there’s no need to bring up foreign countries. Ordinary cooling towers do not involve any complex theories in terms of structure or principle, and I believe everyone agrees with this. You say that the filler-free technology is a step backward; this should be analyzed objectively. The filler-free differential principle we are discussing now is adopted following breakthroughs in the technical principles of nozzles. In the past, to divide water into small droplets, nozzles had to use methods such as creating small holes, like those found in shower heads; however, such nozzles could not be used in industrial applications because industrial circulating water contains impurities, which would cause these nozzles to get clogged immediately. However, with the development of nozzle technology and the adoption of swirl atomization technology in nozzles, large-diameter nozzles have become possible, with a diameter at the nozzle outlet of around 30 mm, which ensures good water dispersion. In principle, we all know that the mechanism of fillers involves breaking down water into \"films\" so that air can come into contact with them and carry away heat, as well as facilitate heat evaporation to cool the water. The \"differential\" mechanism, on the other hand, involves dispersing water into tiny particles, allowing air to come into contact with these small water droplets from all sides, which further aids in heat removal. However, one prerequisite for this is that the atomization must be effective. Here we can have a practical experience: while taking a shower under the showerhead, let’s check the difference in water temperature near the showerhead and at a distance from it.

This is difficult to define; for example, a spray tower is an empty tower that is primarily used for absorption and cooling. Of course, if you want to cool the substance, you will need a large amount of water (return fluid) for cooling; theoretically, this is possible. But you need to know whether your nozzle can achieve the desired results

That is, there is an algorithm for the air-water ratio here; could you provide the theoretical basis for calculating the air-water ratio in spray towers? In which manuals is this information recorded? Are there any authoritative organizations that have tested this type of cooling tower? What is the actual situation?

Personally, I think it’s necessary to adapt the approach to local conditions, as there are many factors at play: whether the cooling medium is clean, whether the temperature difference for cooling is significant, and so on – all of these need to be taken into full consideration.

The so-called air-to-water ratio refers to the ratio of the amount of air in the tower per hour to the amount of water per hour. This basic concept surely doesn’t require an expert’s evaluation, right?

Abroad, great emphasis is placed on the optimization of water distribution systems and the experimental research on nozzles. After numerous tests and modifications, American Malley Cooling Tower Company developed a type of nozzle. This nozzle is integrally injection-molded and is made of polypropylene. Water enters each nozzle from the tangential direction; the nozzle is connected to a diffuser ring, whose material is polypropylene filled with glass fibers. The nozzle spreads the water into a solid conical distribution pattern, while the diffuser ring ensures proper cutting and dispersion of the water. The diameter of all channels and holes is at least 2.54 cm (1 in), which prevents clogging, and the sprinkler operates at low inlet water pressure. Excerpted from: Petroleum Processing and Petrochemicals, 1997, Vol. 28, No. 7. The Current Status and Development of Cooling Tower Technology by Yang Likun

It still depends on the cooling medium and the purpose of cooling; not all tray sprays are suitable

Sir, what is the key factor determining the cooling efficiency of a cooling tower? It is likely you haven’t fully understood this yet. Professor Zhao Zhenguo, a seasoned expert in domestic cooling towers, discusses cooling tower fillers in his book titled \"Cooling Towers\" as follows: \"Fillers are an important component of cooling towers, and the temperature drop they induce accounts for 60% to 70% of the total temperature drop in the cooling tower.\" ； Hydrophilic materials should be used to form a water film on the surface of the filler, allowing water to flow down slowly and providing sufficient time for heat dissipation, thereby improving the efficiency of heat dissipation. ”(See page 41 of “Cooling Towers”.) Do the nozzles you mentioned also have the ability to reduce the temperature of the entire cooling tower by 60% to 70% of its total temperature drop? That’s amazing. Are there any test reports from authoritative institutions? Take a look and broaden your horizons.