AC operation for circulating water

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This post was last edited by eyen on 2012-2-23 at 16:45. Treatment of water in oil refining cycles: There are many issues, so please discuss them. Introduction: The origin of circulating water treatment. In industrial circulating cooling water systems, the water becomes increasingly concentrated over time due to water evaporation and wind-induced losses; as a result, the levels of salts in the water increase, the amounts of cations and anions rise, and the pH value changes significantly, leading to deteriorated water quality. Moreover, the temperature, pH value, and chemical composition of the circulating water facilitate the growth of microorganisms, while the ample sunlight available in cooling towers creates ideal conditions for algae growth. And for scale control, corrosion control, microbial control, and so on, circulating water treatment is essential. 　　Main problems that arise during the operation of circulating water: * (1) Scale: As the circulating water evaporates continuously during the cooling process, the salt concentration in the water increases, and when it exceeds the solubility of certain salts, they precipitate out. Common types of scale include calcium carbonate, calcium phosphate, magnesium silicate, etc. Scale has a relatively dense texture, which **reduces the heat transfer efficiency; a scale thickness of 0.6 millimeters can reduce the heat transfer coefficient by 20%. 　　(2) Scale: Scale is primarily composed of organic substances in water, microbial colonies and their secretions, sediment, dust, etc. It has a soft texture; not only does it reduce heat transfer efficiency, but it also causes corrosion beneath the scale, thereby shortening the service life of the equipment. 　　(3) Corrosion: The corrosion of heat exchange equipment caused by circulating water is primarily electrochemical corrosion. Its causes include manufacturing defects in the equipment, sufficient oxygen in the water, corrosive ions in the water (such as Cl-, Fe2+, Cu2+), as well as dirt formed by mucus secreted by microorganisms. The consequences of corrosion are severe; without control, heat exchangers and water pipeline equipment can be rendered unusable in a very short time. 　　(4) Microbial sludge: Due to the sufficient oxygen, appropriate temperature, and favorable nutrient conditions present in the circulating water, it is highly suitable for the growth and reproduction of microorganisms. If not controlled in a timely manner, this will rapidly lead to deteriorating water quality, odor formation, and discoloration. A large amount of sludge will accumulate in the cooling tower, even causing blockages, which significantly reduces its cooling efficiency and accelerates equipment corrosion. Therefore, microbial growth must be controlled in circulating water treatment. Microbial hazards: Microorganisms in circulating cooling water originate from two sources. First, cooling towers require a large amount of air to be introduced during the evaporation of water, and microorganisms are brought into the cooling water along with this air. Second, the water used to replenish the cooling water system contains microorganisms to some extent, and these microorganisms also enter the cooling water system via the replenishment water. 　　Under sunlight, algae carry out photosynthesis using carbon sources such as carbon dioxide and bicarbonate in water; they absorb carbon as nutrients and release oxygen. As a result, when algae proliferate in large numbers, the dissolved oxygen level in water increases, which facilitates oxygen depolarization and thus accelerates the corrosion process. The excessive growth of microorganisms in circulating water systems causes the water to turn black, produces an unpleasant odor, and pollutes the environment. At the same time, a large amount of sludge is formed, which reduces the cooling efficiency of the cooling tower, and the wood deteriorates and rots. Sludge deposits inside the heat exchanger, reducing heat transfer efficiency and increasing head loss. The sludge that accumulates on the metal surface can cause severe under-scale corrosion; moreover, it prevents corrosion and scale-inhibiting agents from acting on the metal, preventing these agents from exerting their intended protective effects. In addition to accelerating corrosion beneath scale, microbial sludge also causes certain bacteria to produce secretions that directly corrode metals during their metabolic processes. All these problems prevent the circulating water system from operating safely over the long term, affecting production and resulting in severe economic losses. Therefore, the threat posed by microorganisms is just as serious as that caused by scale and corrosion to cooling water systems; in fact, it can be said that controlling the threat of microorganisms is the top priority among these three issues. 　　The activity of microorganisms in circulating water can be measured through the following chemical analysis tests: (1) Residual chlorine (free chlorine). When using chlorination for disinfection, it is important to pay attention to the timing of the appearance of residual chlorine as well as its level, because severe microbial growth leads to a significant increase in the amount of chlorine consumed in the circulating water. 　　(2) Ammonia: Circulating water generally does not contain ammonia, but ammonia may appear in the water due to leaks in the process fluids or the absorption of ammonia from the air. This situation should not be taken lightly; in addition to actively identifying the source of the ammonia leak, it is also necessary to check whether nitrite is present in the water. The ammonia content in the water should ideally be kept below 10 mg/l. 　　(3) NO2‑: When ammonia and nitrite are present in water, it indicates that nitrite bacteria have already converted ammonia into nitrite. In such cases, chlorination in the recirculating water system becomes very difficult; more chlorine is required, and it is hard to achieve the desired residual chlorine level. The concentration of NO2‑ in water should preferably be kept below 1 mg/l. 　　(4) Chemical oxygen demand: When microorganisms multiply extensively in water, the COD level increases, as the mucus secreted by bacteria raises the concentration of organic matter in the water. By analyzing chemical oxygen demand, it is possible to observe the trends in microbial activity in the water. Under normal conditions, the COD level in water should be less than 5 mg/l (using the KMnO4 method). (h) The damage caused by microorganisms in circulating water is extremely serious; taking measures after such damage has occurred often proves to be inefficient, and it requires a large amount of biocides and money. Therefore, it is essential to conduct comprehensive monitoring of the microbial conditions in circulating cooling water in advance. The concentration ratio of circulating water refers to the degree to which the circulating water becomes more concentrated over time due to factors such as water evaporation and wind-induced losses, as measured relative to the amount of make-up water used; it is an important comprehensive indicator for assessing the quality of water control. The concentration ratio is low, resulting in high water consumption and wastewater discharge, as well as inadequate utilization of the water treatment chemicals ； A high concentration ratio can reduce water usage and save on water treatment costs ； However, if the concentration ratio is too high, the tendency of water to form scale increases, which makes it more difficult to control scaling and corrosion. Water treatment chemicals become less effective, and it becomes harder to control microorganisms; therefore, there needs to be a reasonable limit for the concentration ratio of circulating water. Formation of scale: In closed-loop water systems, scale is formed from supersaturated water-soluble components. Water contains various salts such as bicarbonates, carbonates, chlorides, and silicates. Among these, the dissolved bicarbonates like Ca(HCO3)2 and MgHCO3)2 are the most unstable and tend to decompose easily into carbonates. Therefore, when there is a high concentration of dissolved bicarbonates in the cooling water, as the water flows over the surface of the heat exchanger, especially the areas with higher temperatures, it decomposes due to the heat ； When phosphate and calcium ions are present in water, calcium phosphate precipitate will also form ； Calcium carbonate and Ca3(PO4)2 belong to compounds with low solubility; their solubility does not increase as temperature rises, but rather decreases with rising temperature. Therefore, on the heat transfer surface of the heat exchanger, these insoluble salts can easily reach a supersaturated state and crystallize in the water. Especially when the flow rate of water is low or the heat transfer surface is rough, these crystalline deposits accumulate on the surface, forming what is commonly known as scale. Due to their dense and hard structure, these scale deposits are also referred to as hard scale. Common components of scale include calcium carbonate, calcium sulfate, calcium phosphate, magnesium salts, and silicates. Circulating water treatment technology: Based on the characteristics of the enterprise’s circulating water system and its operational conditions, as well as the local water quality characteristics, a water treatment solution suitable for those conditions is selected. Measures such as the addition of chemicals are used to keep the parameters of the circulating water within specified ranges, thereby ensuring the long-term operation of production equipment while also improving the efficiency of water reuse. The use of circulating water treatment technology can bring significant economic benefits to enterprises, as well as positive social benefits to society. Therefore, the application of circulating water treatment technology is highly necessary