What color is the circulating water in your factory?
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The color of the desulfurization circulating water is somewhat similar to that of lime water. What’s going on, and what are the possible causes?
Sometimes ours is related to chocolate, haha. The national standard \"Design Code for Industrial Circulating Cooling Water Treatment\" GB50050-2007 states as follows: 1. The background, significance, and characteristics of the revision of the new version of this national standard, GB50050-2007. 1.1 China’s \"Regulations on the Implementation of the Standardization Law\" stipulate that \"after a standard comes into effect, the department responsible for formulating it shall review it in a timely manner in light of the development of science and technology and the needs of economic construction; the review cycle for standards generally should not exceed five years.\" The first edition of our \"Code for Industrial Circulating Cooling Water Treatment\" was GBJ80-83; the second edition, which is the current version GGB50050-95, has been in use for 12 years now, far exceeding the time limit specified for standards, hence it needs to be revised. 1.2 Development of circulating cooling water treatment technologies In China, although the development of chemicals and technologies for circulating cooling water treatment started relatively late, it has kept up with international trends while also conducting research, development, and application efforts tailored to national conditions, resulting in a high starting point and rapid development. Based on digestion and absorption, HEDP, ATMP, EDTMP, PAA, DDM (G4), poly Horse, ma-bing, and polyquaternary ammonium salts were successively developed. Research and development were carried out on \"phosphorus-based composite formulations\" for the treatment of circulating cooling water using polyphosphates/phosphonates/polymers/heterocyclic compounds at the 1970s level, filling a gap in domestic technology and meeting the need for domestically produced chemicals for treating circulating cooling water in large fertilizer plants. In the 1980s, with the introduction of oil processing facilities and large-scale metallurgical plants, efforts were made to adopt the circulating water treatment chemicals and cooling water treatment technologies from renowned foreign companies such as Kurita, Nalco Drew, and Katayama. A large number of new formulations for circulating water treatment agents have been successfully developed, bringing further significant progress to China’s technology for treating circulating cooling water. Based on phosphorus-based composite formulations, \"phosphorus-based alkaline water treatment formulations\", \"fully organic water treatment formulations\", \"molybdenum-based water treatment formulations\", and \"silicon-based water treatment formulations\" have been created. It enables the circulation cooling water to operate under alkaline conditions at a naturally balanced pH level. Such water treatment formulations not only possess the advantages of \"phosphorus-based composite formulations\" but also avoid the mistakes that can occur when acid is added, which makes them very popular among users. Since the 1990s, with further advancements in water treatment technology, domestic water treatment agents and technologies have begun to be exported. At the same time, with the continuous successful development of new phosphonates and new water treatment biocides, the cutting-edge research in water treatment chemicals is now on par with international standards. “The use of \"fully organic water treatment formulations\" is on the rise, while low-phosphorus, phosphorus-free, and metal-free water treatment formulations are increasingly being introduced to the market. The treatment of circulating cooling water in our country began in the late 1970s with the introduction of phosphate-based formulations from abroad, and significant progress has been made since then, indicating that the level of use of water treatment chemicals in our country is quite high. Table 1 shows the development process of circulating cooling water treatment formulations in our country. Table 1 Development of formulations for circulating cooling water treatment in China
Year | Formulation
1975–1979 | Polyphosphate/phosphonate/polyacrylic acid (pH adjusted with acid)
Polyphosphate/phosphonate/zinc/polyacrylic acid (pH adjusted with acid)
1980–1985 | Polyol phosphate/zinc/sulfonated lignin (pH adjusted with acid)
Phosphonate/polymers or copolymers (alkaline treatment)
Silicate or molybdate formulations
1986–1992 | Phosphate/binary or ternary copolymers – fully organic formulations; systems could operate continuously for 1–2 years
1993 | New types of phosphonates and new copolymers entered the market; alkaline treatment became more common
1998 | Development of phosphorus- and metal-free formulations began
Currently, circulating cooling water treatment is being used in the circulating water systems of various industries in China. Whether it is domestic or imported equipment, the chemicals used in circulating cooling water are mostly of domestic production; we now have the capability to address issues such as corrosion, scaling, and biological sludge that occur in cooling water systems under harsh conditions. Since the 1990s, China has also carried out some work on the development of monitoring technologies for circulating cooling water treatment; initial results have been achieved in areas such as tracing and remote control technologies, and an expert system for the scaling process in cooling water systems has been developed successfully. However, we also have significant gaps in these areas; not enough effort has been invested in the computer control and automated management of circulating cooling water systems, which has hindered the improvement of the level of water treatment technologies. China’s technology for treating circulating cooling water is at a high level in certain aspects; for instance, the quality of phosphonate-based water treatment agents in China has improved significantly, reaching or approaching international advanced standards, which has led to their large-scale export. However, overall, the gap compared to international advanced levels remains significant: the focus lies on water treatment management and control levels. The current \"Code for Treatment of Industrial Circulating Cooling Water\" GB50050-95 is based on certain data derived from phosphorus-based and polymer-based water treatment formulations. In fact, by the year 2000, water treatment formulations had evolved to include fully organic ones: new types of phosphonates and copolymers. Phosphorus-free and metal-free water treatment formulations also began to appear. The combination of these new formulations with more scientific approaches to management and automated control has led to significantly improved water treatment results and a wider range of applicable water quality standards. All these advancements in water treatment technology are not reflected in the existing code; therefore, the development of circulating water treatment technologies necessitates an revision of the current \"Code for Treatment of Industrial Circulating Cooling Water\". 1.3 The current situation of water supply in our country also calls for revisions to the existing \"Specifications for Industrial Circulating Cooling Water Treatment\". a Current status of water use in China: China is a country facing water scarcity; the per capita water availability is approximately 2,200 m3, which is less than one-fourth of the world average. With the rapid development of economic activities in China, the problem of water shortage has become increasingly apparent. In normal years, China experiences a water deficit of around 40 billion m3, which severely hinders the progress of its economic development. Water scarcity not only affects economic development but also threatens people’s livelihoods and even their lives; for example, regions such as Sichuan and Inner Mongolia have experienced water shortages for both humans and livestock due to drought. Faced with such a serious situation, water conservation is not only the task of water treatment professionals but also an urgent task for the entire society. The shortage of water resources and low water use efficiency are the main reasons for the current water supply shortages. Natural conditions cannot be changed, but there is still a significant gap between China and developed countries in terms of water use efficiency. China’s water consumption per 10,000 yuan of GDP is about four times the world average, while the water used per 10,000 yuan of industrial output value is 5 to 10 times that of developed countries. China’s irrigation water utilization rate is only 43%, which is half of the level seen in advanced countries. It is clear, then, that there is great potential for water conservation both in industry and agriculture. b Water conservation for all – Saving water is an obligation for everyone. There is no one who does not use water, and no industry that does not require it. Therefore, water conservation is not just the responsibility of the water industry; it is a task shared by all industries and all citizens. By 2003, China’s total water consumption was approximately 530 billion cubic meters, of which 343 billion cubic meters were used for agriculture (about 64.5%), 117 billion cubic meters for industry (about 22%), and 63 billion cubic meters for domestic use (about 12%). Water conservation in agriculture: sprinkler irrigation, drip irrigation ； Water conservation in daily life: water-saving faucets, toilet tanks. Industrial water conservation: First and foremost, it involves reforming production processes, making full use of the waste heat generated during production, and adopting water-free processes such as air cooling. Take this phenomenon as an example: manufacturing plants in industries such as steel, petrochemicals, electricity, petroleum, textiles, and chemicals are all equipped with numerous cooling towers, through which a large amount of heat is released into the atmosphere. This is not only a waste of energy but also a significant waste of water resources. The enormous energy contained in cooling towers is well worth studying and tapping into. Based on a national circulating water volume of 400 million m3/h and a cooling temperature drop of Δt=10 ℃, the heat loss is 4×1012 kilocalories/h; this corresponds to 0.57×106 tons of coal per hour in terms of standard coal, or 0.47×106 cubic meters of natural gas per hour. This represents the heat loss for just one hour. Based on 8,000 hours per year, this amounts to 4.56 billion tons of coal and approximately 4 billion cubic meters of natural gas – which is 19 times the annual coal production in China, which is 240 million tons. What a huge waste of energy. It is evident that there is great potential in energy and water conservation. Next is water conservation in the water industry; 70–80% of industrial water use is for replenishing recycled water, which highlights the important role of recycled water in industrial water conservation. The current production processes are not yet capable of making full use of thermal energy; in other words, cooling towers will continue to be necessary, and recycled water will still have to be used. So, what is the actual water-saving benefit of using recycled water? The water-saving effect of circulating cooling water is extremely significant compared to direct-current cooling water. In the 1950s and 1960s of the last century, **industrial development was just in its infancy; the demand for industrial water was low, and water resources were relatively abundant. As a result, many factories and enterprises used direct-current cooling water, as it was both simple and cost-effective. However, with the development of industrial construction, water resources have become increasingly scarce, forcing factories and enterprises to adopt recycled cooling water. How much water can be saved by adopting this measure? Taking 10,000 m3/h of direct-flow cooling water as an example, by switching to circulating cooling water with a temperature drop of 10°C and a concentration factor N of 3, only 240 m3/h is required; if N is 5, then 200 m3/h is needed. This shows the significant water-saving effect. At the same time, the data above also allow us to conclude that the water-saving effect of the circulating cooling water system itself depends on the level of concentration ratio. Therefore, the most effective measure for water conservation in industrial water use is to employ recycled water with a high concentration ratio. Initially, people’s ideas were quite simple: they thought that by circulating the water and adjusting its temperature, the problem could be solved. But the issue is far from that simple; a series of problems arise during the operation of the circulating water, and if these problems are not properly addressed, the circulating water system simply cannot function. There are many examples, such as the Beijing Chemical Plant (scaling) and the Qixia Mountain Fertilizer Plant (biological overgrowth). In summary, the main problems that arise during the operation of circulating water are as follows: a) Scale formation, which occurs because the circulating cooling water evaporates continuously during the cooling process, increasing the salt concentration in the water; when this concentration exceeds the solubility limit 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 helps to prevent corrosion of the metal surface; however, it **reduces heat transfer efficiency. A scale thickness of 0.6 millimeters results in a 17.9% decrease in the heat transfer coefficient. Burdge is primarily composed of organic substances in water, microbial colonies and their secretions, sediment, dust, etc. Its soft texture not only reduces heat transfer efficiency but also causes corrosion beneath the burdge. The corrosion of heat exchange equipment caused by circulating cooling water is primarily electrochemical corrosion. The factors contributing to this include manufacturing defects in the equipment, sufficient oxygen in the water, corrosive ions in the water (such as Cl-, Fe2+, Cu2+), as well as fouling resulting from mucus secreted by microorganisms. The consequences of such corrosion are severe; without control, the equipment can be rendered unusable in a very short period of time. The growth of microorganisms: Since circulating cooling water contains ample oxygen, an appropriate temperature, and abundant nutrients, it is highly suitable for the growth and reproduction of microorganisms. If not controlled in a timely manner, this will rapidly lead to deterioration of water quality, bad odors, discoloration, the accumulation of large amounts of scale, and increased corrosion of equipment. Therefore, the key to treating circulating cooling water is to control the growth of microorganisms. In the face of these problems, people have, through practical production experiences, continuously summarized, explored, and researched, thereby mastering the methods and techniques to address these hazards. This has ensured the stable operation of the circulating cooling water system, as well as the safe, efficient, and sustainable progress of the enterprise’s production activities. “The \"Design Code for Industrial Circulating Cooling Water Treatment\" presents, in a standardized form, the practical experience and research findings accumulated over time, after being highly summarized and condensed. Its purpose is to serve production, construction, research, design, and construction activities by providing a basis for them. 1.4 Features of the 2007 version of the \"Code for Treatment of Industrial Circulating Cooling Water\" GB50050-2007: The main feature of this revised version, as well as the previous two versions, is its focus on water conservation. With the development of economic construction, the water-saving measures outlined in this revised version go beyond the limitations of earlier versions by including the use of recycled water (treated wastewater) as a supplementary water source. This creates new conditions for water conservation, emission reduction, and environmental protection. Additionally, the revised version covers direct-cooling open-loop circulating cooling water systems, commonly known as turbulent flow cooling water systems, thereby expanding the scope of the code. It covers all circulating cooling water systems that use fresh water as make-up water. Circulating water systems that use seawater as make-up water have not been included this time due to the current level of technological maturity; however, as technology continues to improve, they will gradually be incorporated into the standards. This revision of the \"Specifications for Industrial Circulating Cooling Water Treatment\" represents a comprehensive update with many changes, which will be detailed later. 2. Current status, existing problems, and solutions in the design of industrial circulating cooling water treatment 2.1 Current status of circulating cooling water treatment design In the past, the design played a central role in circulating cooling water systems; from collecting data on such systems to the actual design of the water systems, ordering of equipment, on-site construction, and commissioning, design firms were involved in all stages. However, with the introduction of reform and opening up and the establishment of a socialist market economy, this model of design taking full responsibility has changed significantly. The current approach is a tripartite construction model involving the owner, the designer, and the water treatment company: the owner selects the water treatment company through bidding, after which the design firm carries out the design based on the water treatment plan provided by that company. Since water treatment companies are specialized firms that possess advanced technologies for circulating cooling water treatment and have extensive experience in this field, they are better able to ensure effective water treatment results. 2.2 Existing Problems Since the design of circulating cooling water treatment involves three parties, differences in their positions and viewpoints inevitably lead to disagreements regarding how to address various issues. As a result, design parameters are frequently revised, and problems remain unresolved, which severely impacts the project schedule and the quality of the engineering design. Below, I will briefly introduce some of the technical issues involved in the revision of the \"Specifications for Industrial Circulating Cooling Water Treatment\": a. Quality requirements for water used to replenish circulating water. Typically, the design firm checks the accuracy of the water quality data provided by the client by examining the balance of cations and anions in milliequivalents; the data is considered acceptable if the analysis error is ≤2%. In the current international units, the unit of milliequivalent does not exist; instead, moles are used as the unit. What is a mole? A mole (mol) represents the amount of substance in a system, where the number of units it contains is equal to the number of atoms in 0.012 kg of carbon-12 (12C). When using moles, it is necessary to specify the elementary unit, which can be a molecule, atom, ion, or other elementary units, or specific combinations of these units. It is known that the mass of 1 carbon atom is 1.993×10-26 kg; therefore, the number of carbon atoms in 1 mole of 12C is: Since each gram atom, molecule, ion, or electron contains 6.02×1023 such basic units, this number is known as Avogadro’s constant. In other words, the number of basic units contained in a substance is equal to a certain multiple of Avogadro’s constant; that is, it corresponds to a certain number of moles, n. n can be calculated using the following formula. A detailed explanation of this topic is necessary because there are many misconceptions regarding this unit. Some of the water quality analysis data provided by the owner are balanced based on the molar amount of substances (ions), which is incorrect; it should be balanced based on the charge carried by the substances (cations and anions). b Treatment of phosphorus-containing wastewater: Since the formulations used for treating circulating cooling water generally contain a certain amount of phosphorus, the wastewater discharged from such systems has an excessive phosphorus content. This leads to eutrophication of rivers, lakes, and seas, as well as the proliferation of red tides and blue algae, thereby severely damaging the ecological environment – with very serious consequences. Although the current \"Specifications for Industrial Circulating Cooling Water Treatment\" set strict requirements for discharge water quality parameters, none of the existing circulating cooling water systems are treated for this purpose; the main issue is economic, as there are no technical obstacles. So, as to how to calculate the economic costs, this requires us to take a higher perspective – not just focusing on the economic situation of our own organization, but considering things from the perspective of the entire society. By thinking about the needs of the whole nation and future generations, this issue becomes much easier to address. c Pretreatment water treatment: The level of pollutants in the pretreatment water is even more **above the allowed limits. Since the discharge of pre-coating water is intermittent, with operations starting up and maintenance work being carried out roughly once a year, this further increases the difficulty of treating it; in practice, it is discharged directly without any treatment. d. Sidewashing facilities: The current and revised standards specify that the sidewashing rate should be between 1% and 5%. However, considering the feedback from enterprises in areas with high dust levels regarding insufficient sidewashing, it is allowed to increase this rate appropriately in such areas or those with a high dust index. Currently, bypass filtration systems mostly use valveless filters or mechanical filters; however, some manufacturers report that the filtration efficiency is not satisfactory. The reason for this can be attributed to the fact that, under conditions of low turbidity, the particles of suspended colloids are very small, making it difficult to remove them through simple screening and filtration; the guidelines recommend the use of coagulants. The type of filter can vary; some companies (such as Jinan Refinery) replaced valveless filters with Israeli cartridge filters, but the results were not satisfactory, so they switched to floating disk fiber filters that are operated electrically. The turbidity of the inlet water is 7–8°, while that of the outlet water is 3–5°. e Regarding the net positive suction head of water pumps, this is outside the scope of these specifications, but it has been a problem in water treatment design in the past. In the past, when selecting pumps, it was sufficient to ensure that the water level was 20 cm above the top of the pump for it to operate; this concept is not accurate enough. For small centrifugal pumps in normal-temperature water, this is generally no problem, but for large vertical centrifugal pumps and axial flow pumps, especially hot water pumps, it is necessary to calculate the net positive suction head, and this value must be greater than the cavitation head specified in the pump’s specifications. 2.3 How to address the existing problems: a) Standards or regulations regarding the responsibilities of all parties involved in project construction should be established as soon as possible to clarify the relationships among them. b Accelerate the development of phosphorus-free and metal-free water treatment formulations. Currently, some manufacturers claim to have phosphorus-free water treatment formulas, but when such formulas are recommended in water treatment designs, they fail to provide specific data, which indicates that these phosphorus-free formulas are not yet mature. As far as we know, even the well-known international water treatment companies’ phosphorus-free formulas are only suitable for certain types of water quality. If a phosphorus-free water treatment formula is successfully developed, the aforementioned two major pollution problems can be easily resolved, bringing about tremendous benefits. It is suggested that the Water Treatment Association should organize manufacturers of water treatment chemicals, end-users, and research institutions to work together to overcome these technical challenges. I believe this problem is much simpler than exploring the moon; by pooling societal efforts and taking advantage of the strengths of the socialist system with Chinese characteristics, it will surely be resolved quickly. For wastewater with excessive levels of pollutants in reality, as well as pre-film water, it is recommended to send it to a wastewater treatment plant for treatment. With this revision of the \"Specifications for Industrial Circulating Cooling Water Treatment,\" specific technical solutions for the treatment of phosphorus-containing wastewater have also been provided. 3. Scope of application and terms of the design codes for industrial circulating cooling water treatment 3.1 The scope of application of the \"Codes for Industrial Circulating Cooling Water Treatment\" is clearly specified in Article 1.0.2 of the revised general provisions: \"These Codes for Industrial Circulating Cooling Water Treatment apply to the design of circulating cooling water treatment for new, expanded, and renovated projects that use surface water, groundwater, and reclaimed water as make-up water.\" In other words, all cooling water treatment designs except for seawater circulation are applicable. It should be noted here that the flow rate of circulating cooling water varies; some systems have a flow rate of hundreds of thousands of tons per hour, while others have rates of several hundred tons per hour, or even just dozens or a few tons per hour. Is this standard still applicable in such cases? It can be said with certainty that this standard is applicable regardless of the scale. However, when it comes to treating small-scale circulating cooling water systems using this standard, it may be overkill. Questions such as whether bypass filtration or pre-film formation is necessary for systems with a flow rate of just dozens of tons per hour need to be reconsidered. Currently, efforts are underway to develop a standard specifically for the treatment of small and medium-sized circulating cooling water systems in order to address these issues. 3.2 Noun Terms Everyone here is an expert in circulating cooling water treatment and is well familiar with many of the terms. I will merely explain some of the new terms that have been proposed in this revision of the \"Specifications for Industrial Circulating Cooling Water Treatment\", so as to avoid misunderstandings when encountering these terms in the specifications. a Recirculating Cooling Water System: A water-based cooling medium system that operates in a cyclic manner; it consists of heat exchange equipment, cooling equipment, treatment facilities, pumps, pipelines, and other related components. b Indirect Open Recirculating Cooling Water System (Indirect Open System): A recirculating cooling water system in which heat is transferred to the substance to be cooled indirectly, and the recirculating cooling water loses heat by being in direct contact with the atmosphere. c Indirect closed recirculating cooling water system (closed system): An indirect closed recirculating cooling water system is one in which the circulating cooling water exchanges heat with the substance to be cooled indirectly, and there is also an indirect heat exchange between the circulating cooling water and the cooling medium. d Totally Closed System: A closed-cycle cooling water system in which the circulating cooling water does not come into contact with the atmosphere. e Semi Closed System: A closed circulating cooling water system in which part of the cooling water is in contact with the atmosphere. f Direct Open Recirculating Cooling Water System (Direct Cooling System): A recirculating cooling water system in which the cooling water is in direct contact with the substance to be cooled for heat exchange, and it is also in direct contact with the atmosphere to dissipate heat. g Open System: A general term for intercooled open systems and direct-cooling systems. 4. Main revisions to the \"Design Code for Industrial Circulating Cooling Water Treatment\" This revision is a comprehensive one, with modifications of varying degrees made to each chapter, section, and even most of the provisions. It is not necessary for me to explain each item in detail here; I will only outline the important revisions and the reasons behind them. First, let’s explain how various data values are determined. As we all know, water treatment is an experimental science, and many of the data related to water treatment are derived from practical applications or experiments, rather than through calculations. For example, the Cl- value is determined by taking into account the operational data of circulating cooling water from numerous companies in China, and by selecting the most appropriate indicators – it is not calculated. It cannot be calculated at the moment either. The determination of other water treatment parameters is similar as well. 4.1 Revision of water quality parameters and water treatment control parameters for circulating cooling water. Water quality parameters and control parameters serve as a reflection of water treatment technologies; over the years, the progress in circulating cooling water treatment technologies in China has inevitably led to adjustments in various water quality parameter values. a Turbidity: The term used in current standards is suspended solids; the numerical values for this parameter remain unchanged. The revised version of the \"Specifications for Industrial Circulating Cooling Water Treatment\" simply changes the name of this parameter to turbidity. Why is this modification made? Although both terms refer to the content of suspended solids in water, the diameters of the suspended particles they represent are different. The particle size indicated by the term \"suspended solids\" is 1 μm or larger, while the particle size indicated by \"turbidity\" ranges from 1 nm to 1 μm – that is, what is commonly referred to as colloidal substances. Moreover, the testing methods for these two parameters are also different; the former is determined using filtration, while the latter is determined based on optical principles. There is no conversion relationship between the two. Since colloidal substances play a crucial role in causing fouling and the growth of microorganisms and algae in circulating cooling water, it is more accurate to use turbidity as an indicator for suspended solids, and this value should be kept as low as possible. The turbidity of circulating cooling water has a significant impact on the fouling thermal resistance and corrosion rate of heat exchange equipment; therefore, the lower the value, the better. Practical experience from factory operations shows that when a side filter is installed in the circulating cooling water system, the turbidity of the make-up water can be kept below 5 NTU. In most areas of China, the turbidity of circulating cooling water can be maintained below 10 NTU. Therefore, Table 3.1.1-6 stipulates that for plate, spiral-plate, and finned-tube heat exchangers, the turbidity should not exceed 10 NTU; for other types of heat exchangers, it should generally not exceed 20 NTU. Factory operation data demonstrate that this requirement fully meets the criteria regarding fouling thermal resistance specified in these standards. For power plant condensers, since the flow rate of the circulating cooling water inside their heat transfer tubes is generally greater than 1.5 m/s, and moreover these condensers are equipped with rubber ball cleaning systems, the turbidity requirement for the circulating cooling water in power plant condensers can be relaxed to some extent. b pH value: The range of pH in the new version is wider than that in the current version, reflecting an improvement in the corrosion and scale-inhibition performance of the chemical. c Calcium hardness + methyl orange alkalinity: Current standards for this parameter require the measurement of Ca2+ and alkalinity separately; using a composite index is more scientific. The solubility product of CaCO3: As can be seen from the above equation, the concentration of CO32- changes with the concentration of H+. When the H+ concentration is high, CO32- is converted to HCO3-, which increases the solubility. Therefore, the precipitation of CaCO3 is determined by two factors: the H+ concentration (alkalinity) and the Ca2+ concentration. The calcium carbonate stability index RSI is ≥3.3; this is also an indicator for controlling the precipitation of calcium carbonate, and it is calculated based on the calcium carbonate saturation index. There are multiple formulas for calculation; the recommended formula is: pHs = 9.70 + A + B – C – D. Where A is the coefficient for total dissolved solids, B is the temperature coefficient, C is the calcium hardness coefficient, and D is the alkalinity coefficient. To determine water quality stability: (1) Langlier Index = pH – pHs; if Is > 0, calcium carbonate is supersaturated; if Is < 0, it is unsaturated; if Is = 0, it is in a saturated state. However, due to the metastable zone during calcium carbonate crystallization, this judgment may be inaccurate. Practical experience suggests that Is should range from 0.5 to 2.5 for stable conditions, Is < 0.5 indicates corrosion, and Is > 0.5 indicates scaling. (2) Stability index: S = 2pHs – pH; if S ≈ 6.0, the condition is stable; if S < 3.7, severe scaling occurs; if 3.7 < S < 6.0, scaling still occurs; if 6.0 < S < 7.5, corrosion takes place; if S > 7.5, there is severe corrosion. (3) There are also indices related to scaling, critical pH values, and maximum carbonate hardness. d Total iron: Iron ions are trace ions present in natural water, while the concentration of manganese ions is even lower, at about one-tenth that of iron ions. Generally, the two coexist and are difficult to separate; therefore, the iron content is often used to represent the total amount of iron and manganese ions. The total iron content in water consists of colloidal iron and ferrous ions. Colloidal iron is trivalent iron, usually suspended in water in a colloidal state as hydroxide of iron or hydrates of iron oxides. In closed-loop water systems, it deposits on the surface of water coolers, forming sticky and difficult-to-remove scale that can lead to under-scale corrosion. A portion of colloidal iron can be removed during the pretreatment processes of coagulation and sedimentation. Ferrous ions are soluble ions; in closed-loop water systems, they can promote the crystallization and deposition of calcium carbonate. When phosphorus-based water stabilizers are used, ferrous phosphate deposits with strong adhesiveness may form, and they also serve as a nutrient source for the growth of iron bacteria. Generally, the total iron content in make-up water is required to be <0.2–0.5 mg/L. The total iron level in circulating water should be ≤0.5 mg/L. In the past, total iron in circulating water was either not controlled at all, or it was controlled at levels of <0.5 mg/L, 1.5 mg/L, or 2.0 mg/L. According to statistics from various systems, it is entirely possible to keep the total iron level below 0.5 mg/L; water with such a level has a very low corrosion rate. When the total iron level reaches 1.5 mg/L or 2.0 mg/L, the corrosion rate is actually already above the acceptable limit. Controlling the total iron content in circulating water requires not only regulating the total iron content in the make-up water but also primarily improving the water’s corrosion inhibition properties. For many domestic plants, the total iron level is below 1 mg/L, while in foreign plants it can reach 2.0 mg/L. Regarding the chloride ion level in circulating cooling water, there are various opinions and different standards both domestically and internationally, which poses many difficulties for design work and can even leave one at a loss. The chloride ion level has a significant impact on the treatment of circulating cooling water; unrealistic levels can lead to corrosion and damage of equipment or increased costs for water treatment. Therefore, it is essential to establish a reasonable threshold value. What is the basis for the chloride ion specification in this revision of the \"Specifications for Industrial Circulating Cooling Water Treatment\"? Is it scientific and reasonable? The following explanation is provided regarding this issue. The corrosive effect of chloride ions and the conditions affecting it: Chloride ions are corrosive anions commonly found in natural water. Chloride ions – having extremely high polarity that promotes corrosion reactions – are also highly penetrating; they can easily penetrate the protective layer on the metal surface, leading to crevice corrosion and pitting. In particular, they cause corrosive cracking in austenitic stainless steels, posing a serious threat that can render water coolers unusable in a short period of time. Many austenitic stainless steel equipment used in industries such as chemicals, refining, and metallurgy has poor resistance to chloride corrosion; therefore, this revision is specifically aimed at austenitic stainless steel and carbon steel heat exchange equipment. The main factors affecting corrosion cracking in stainless steel are as follows: (1) Internal stress in the equipment, which is generated during the heating process of the equipment. Although reputable manufacturers carry out heat treatment to eliminate stress after equipment fabrication, some residual stress remains. Additionally, factors such as temperature and mechanical stresses during installation and operation can also cause internal stress in the equipment; chloride ions tend to accumulate in these stressed areas, leading to corrosion. (2) The catalytic effect of chloride ions occurs when internal stresses are present in the equipment. Due to this catalytic effect, stress corrosion cracking occurs in stainless steel equipment, starting first at points of pitting, cracks, or corrosion grooves. The damaged passivation layer cannot be repaired, so the corrosion progresses further until the metal develops branch-like cracks and is destroyed. Some sources indicate that corrosion and cracking can occur as long as there are a few milligrams of chloride ions per liter, or even 0.2 mg/L of chloride ions; the case of stainless steel spherical tanks at Shanghai Jinshan Chemical Plant suffering from corrosion and cracking due to chloride ions also confirms this conclusion. Furthermore, chloride ions tend to accumulate in gaps or under dirt, resulting in high concentrations of these ions. For example, the chloride ion concentration in the circulating cooling water of a certain plant is around 200 mg/L; however, at the gaps where the tube sheet of the shell-side water cooler is connected to the tubes, the chloride ion concentration can reach 20,000–30,000 mg/L. Stress corrosion cracking did not occur in the on-site tube-side water coolers, and this was because the shell-side water cooler had gaps and a low flow rate, which created conditions for the accumulation of chloride ions. In another plant, just two months after it began operation, a large number of heat exchangers started leaking due to corrosion and cracking, even though the chloride ion concentration in the circulating cooling water was only 20–50 mg/L. This shows that the level of chloride ions is not the only factor that causes corrosion and cracking. (3) The inducing effect of temperature: It is well known that temperature is an important factor in chemical reactions, and corrosion cracking is no exception. In the presence of both tensile stress and chloride ions, corrosion is not significant at lower temperatures; however, as the temperature rises, corrosion cracking intensifies. Some sources suggest that austenitic stainless steel begins to corrode at 70°C. On-site inspections revealed that stress corrosion cracking occurred only at the hot end of the water cooler, namely at the inlet side where the process fluid entered; no corrosion was observed at the cold end. Nor was any stress corrosion cracking found in water coolers whose fluid temperature was below 150°C. (4) Dirt and water flow rate are also important factors affecting corrosion; these two factors are interrelated – low flow rates prevent dispersion, which facilitates the accumulation of chloride ions. At the same time, it also promotes the deposition of dirt, further increasing the concentration of chloride ions and thus corrosion. This is also the reason why the shell-side equipment is more prone to corrosion under the same conditions. The chloride ion specifications set by national standards and various manufacturers worldwide: At present, there is no unified standard for the quality of circulating cooling water internationally; therefore, the standards adopted by different manufacturers are determined based on their own experience. Therefore, the standards vary widely in terms of severity; some companies impose strict limits, requiring levels to be below 100 mg/L, or even below 50 mg/L, while other companies are less stringent and set their limits at
Year | Formulation
1975–1979 | Polyphosphate/phosphonate/polyacrylic acid (pH adjusted with acid)
Polyphosphate/phosphonate/zinc/polyacrylic acid (pH adjusted with acid)
1980–1985 | Polyol phosphate/zinc/sulfonated lignin (pH adjusted with acid)
Phosphonate/polymers or copolymers (alkaline treatment)
Silicate or molybdate formulations
1986–1992 | Phosphate/binary or ternary copolymers – fully organic formulations; systems could operate continuously for 1–2 years
1993 | New types of phosphonates and new copolymers entered the market; alkaline treatment became more common
1998 | Development of phosphorus- and metal-free formulations began
Currently, circulating cooling water treatment is being used in the circulating water systems of various industries in China. Whether it is domestic or imported equipment, the chemicals used in circulating cooling water are mostly of domestic production; we now have the capability to address issues such as corrosion, scaling, and biological sludge that occur in cooling water systems under harsh conditions. Since the 1990s, China has also carried out some work on the development of monitoring technologies for circulating cooling water treatment; initial results have been achieved in areas such as tracing and remote control technologies, and an expert system for the scaling process in cooling water systems has been developed successfully. However, we also have significant gaps in these areas; not enough effort has been invested in the computer control and automated management of circulating cooling water systems, which has hindered the improvement of the level of water treatment technologies. China’s technology for treating circulating cooling water is at a high level in certain aspects; for instance, the quality of phosphonate-based water treatment agents in China has improved significantly, reaching or approaching international advanced standards, which has led to their large-scale export. However, overall, the gap compared to international advanced levels remains significant: the focus lies on water treatment management and control levels. The current \"Code for Treatment of Industrial Circulating Cooling Water\" GB50050-95 is based on certain data derived from phosphorus-based and polymer-based water treatment formulations. In fact, by the year 2000, water treatment formulations had evolved to include fully organic ones: new types of phosphonates and copolymers. Phosphorus-free and metal-free water treatment formulations also began to appear. The combination of these new formulations with more scientific approaches to management and automated control has led to significantly improved water treatment results and a wider range of applicable water quality standards. All these advancements in water treatment technology are not reflected in the existing code; therefore, the development of circulating water treatment technologies necessitates an revision of the current \"Code for Treatment of Industrial Circulating Cooling Water\". 1.3 The current situation of water supply in our country also calls for revisions to the existing \"Specifications for Industrial Circulating Cooling Water Treatment\". a Current status of water use in China: China is a country facing water scarcity; the per capita water availability is approximately 2,200 m3, which is less than one-fourth of the world average. With the rapid development of economic activities in China, the problem of water shortage has become increasingly apparent. In normal years, China experiences a water deficit of around 40 billion m3, which severely hinders the progress of its economic development. Water scarcity not only affects economic development but also threatens people’s livelihoods and even their lives; for example, regions such as Sichuan and Inner Mongolia have experienced water shortages for both humans and livestock due to drought. Faced with such a serious situation, water conservation is not only the task of water treatment professionals but also an urgent task for the entire society. The shortage of water resources and low water use efficiency are the main reasons for the current water supply shortages. Natural conditions cannot be changed, but there is still a significant gap between China and developed countries in terms of water use efficiency. China’s water consumption per 10,000 yuan of GDP is about four times the world average, while the water used per 10,000 yuan of industrial output value is 5 to 10 times that of developed countries. China’s irrigation water utilization rate is only 43%, which is half of the level seen in advanced countries. It is clear, then, that there is great potential for water conservation both in industry and agriculture. b Water conservation for all – Saving water is an obligation for everyone. There is no one who does not use water, and no industry that does not require it. Therefore, water conservation is not just the responsibility of the water industry; it is a task shared by all industries and all citizens. By 2003, China’s total water consumption was approximately 530 billion cubic meters, of which 343 billion cubic meters were used for agriculture (about 64.5%), 117 billion cubic meters for industry (about 22%), and 63 billion cubic meters for domestic use (about 12%). Water conservation in agriculture: sprinkler irrigation, drip irrigation ； Water conservation in daily life: water-saving faucets, toilet tanks. Industrial water conservation: First and foremost, it involves reforming production processes, making full use of the waste heat generated during production, and adopting water-free processes such as air cooling. Take this phenomenon as an example: manufacturing plants in industries such as steel, petrochemicals, electricity, petroleum, textiles, and chemicals are all equipped with numerous cooling towers, through which a large amount of heat is released into the atmosphere. This is not only a waste of energy but also a significant waste of water resources. The enormous energy contained in cooling towers is well worth studying and tapping into. Based on a national circulating water volume of 400 million m3/h and a cooling temperature drop of Δt=10 ℃, the heat loss is 4×1012 kilocalories/h; this corresponds to 0.57×106 tons of coal per hour in terms of standard coal, or 0.47×106 cubic meters of natural gas per hour. This represents the heat loss for just one hour. Based on 8,000 hours per year, this amounts to 4.56 billion tons of coal and approximately 4 billion cubic meters of natural gas – which is 19 times the annual coal production in China, which is 240 million tons. What a huge waste of energy. It is evident that there is great potential in energy and water conservation. Next is water conservation in the water industry; 70–80% of industrial water use is for replenishing recycled water, which highlights the important role of recycled water in industrial water conservation. The current production processes are not yet capable of making full use of thermal energy; in other words, cooling towers will continue to be necessary, and recycled water will still have to be used. So, what is the actual water-saving benefit of using recycled water? The water-saving effect of circulating cooling water is extremely significant compared to direct-current cooling water. In the 1950s and 1960s of the last century, **industrial development was just in its infancy; the demand for industrial water was low, and water resources were relatively abundant. As a result, many factories and enterprises used direct-current cooling water, as it was both simple and cost-effective. However, with the development of industrial construction, water resources have become increasingly scarce, forcing factories and enterprises to adopt recycled cooling water. How much water can be saved by adopting this measure? Taking 10,000 m3/h of direct-flow cooling water as an example, by switching to circulating cooling water with a temperature drop of 10°C and a concentration factor N of 3, only 240 m3/h is required; if N is 5, then 200 m3/h is needed. This shows the significant water-saving effect. At the same time, the data above also allow us to conclude that the water-saving effect of the circulating cooling water system itself depends on the level of concentration ratio. Therefore, the most effective measure for water conservation in industrial water use is to employ recycled water with a high concentration ratio. Initially, people’s ideas were quite simple: they thought that by circulating the water and adjusting its temperature, the problem could be solved. But the issue is far from that simple; a series of problems arise during the operation of the circulating water, and if these problems are not properly addressed, the circulating water system simply cannot function. There are many examples, such as the Beijing Chemical Plant (scaling) and the Qixia Mountain Fertilizer Plant (biological overgrowth). In summary, the main problems that arise during the operation of circulating water are as follows: a) Scale formation, which occurs because the circulating cooling water evaporates continuously during the cooling process, increasing the salt concentration in the water; when this concentration exceeds the solubility limit 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 helps to prevent corrosion of the metal surface; however, it **reduces heat transfer efficiency. A scale thickness of 0.6 millimeters results in a 17.9% decrease in the heat transfer coefficient. Burdge is primarily composed of organic substances in water, microbial colonies and their secretions, sediment, dust, etc. Its soft texture not only reduces heat transfer efficiency but also causes corrosion beneath the burdge. The corrosion of heat exchange equipment caused by circulating cooling water is primarily electrochemical corrosion. The factors contributing to this include manufacturing defects in the equipment, sufficient oxygen in the water, corrosive ions in the water (such as Cl-, Fe2+, Cu2+), as well as fouling resulting from mucus secreted by microorganisms. The consequences of such corrosion are severe; without control, the equipment can be rendered unusable in a very short period of time. The growth of microorganisms: Since circulating cooling water contains ample oxygen, an appropriate temperature, and abundant nutrients, it is highly suitable for the growth and reproduction of microorganisms. If not controlled in a timely manner, this will rapidly lead to deterioration of water quality, bad odors, discoloration, the accumulation of large amounts of scale, and increased corrosion of equipment. Therefore, the key to treating circulating cooling water is to control the growth of microorganisms. In the face of these problems, people have, through practical production experiences, continuously summarized, explored, and researched, thereby mastering the methods and techniques to address these hazards. This has ensured the stable operation of the circulating cooling water system, as well as the safe, efficient, and sustainable progress of the enterprise’s production activities. “The \"Design Code for Industrial Circulating Cooling Water Treatment\" presents, in a standardized form, the practical experience and research findings accumulated over time, after being highly summarized and condensed. Its purpose is to serve production, construction, research, design, and construction activities by providing a basis for them. 1.4 Features of the 2007 version of the \"Code for Treatment of Industrial Circulating Cooling Water\" GB50050-2007: The main feature of this revised version, as well as the previous two versions, is its focus on water conservation. With the development of economic construction, the water-saving measures outlined in this revised version go beyond the limitations of earlier versions by including the use of recycled water (treated wastewater) as a supplementary water source. This creates new conditions for water conservation, emission reduction, and environmental protection. Additionally, the revised version covers direct-cooling open-loop circulating cooling water systems, commonly known as turbulent flow cooling water systems, thereby expanding the scope of the code. It covers all circulating cooling water systems that use fresh water as make-up water. Circulating water systems that use seawater as make-up water have not been included this time due to the current level of technological maturity; however, as technology continues to improve, they will gradually be incorporated into the standards. This revision of the \"Specifications for Industrial Circulating Cooling Water Treatment\" represents a comprehensive update with many changes, which will be detailed later. 2. Current status, existing problems, and solutions in the design of industrial circulating cooling water treatment 2.1 Current status of circulating cooling water treatment design In the past, the design played a central role in circulating cooling water systems; from collecting data on such systems to the actual design of the water systems, ordering of equipment, on-site construction, and commissioning, design firms were involved in all stages. However, with the introduction of reform and opening up and the establishment of a socialist market economy, this model of design taking full responsibility has changed significantly. The current approach is a tripartite construction model involving the owner, the designer, and the water treatment company: the owner selects the water treatment company through bidding, after which the design firm carries out the design based on the water treatment plan provided by that company. Since water treatment companies are specialized firms that possess advanced technologies for circulating cooling water treatment and have extensive experience in this field, they are better able to ensure effective water treatment results. 2.2 Existing Problems Since the design of circulating cooling water treatment involves three parties, differences in their positions and viewpoints inevitably lead to disagreements regarding how to address various issues. As a result, design parameters are frequently revised, and problems remain unresolved, which severely impacts the project schedule and the quality of the engineering design. Below, I will briefly introduce some of the technical issues involved in the revision of the \"Specifications for Industrial Circulating Cooling Water Treatment\": a. Quality requirements for water used to replenish circulating water. Typically, the design firm checks the accuracy of the water quality data provided by the client by examining the balance of cations and anions in milliequivalents; the data is considered acceptable if the analysis error is ≤2%. In the current international units, the unit of milliequivalent does not exist; instead, moles are used as the unit. What is a mole? A mole (mol) represents the amount of substance in a system, where the number of units it contains is equal to the number of atoms in 0.012 kg of carbon-12 (12C). When using moles, it is necessary to specify the elementary unit, which can be a molecule, atom, ion, or other elementary units, or specific combinations of these units. It is known that the mass of 1 carbon atom is 1.993×10-26 kg; therefore, the number of carbon atoms in 1 mole of 12C is: Since each gram atom, molecule, ion, or electron contains 6.02×1023 such basic units, this number is known as Avogadro’s constant. In other words, the number of basic units contained in a substance is equal to a certain multiple of Avogadro’s constant; that is, it corresponds to a certain number of moles, n. n can be calculated using the following formula. A detailed explanation of this topic is necessary because there are many misconceptions regarding this unit. Some of the water quality analysis data provided by the owner are balanced based on the molar amount of substances (ions), which is incorrect; it should be balanced based on the charge carried by the substances (cations and anions). b Treatment of phosphorus-containing wastewater: Since the formulations used for treating circulating cooling water generally contain a certain amount of phosphorus, the wastewater discharged from such systems has an excessive phosphorus content. This leads to eutrophication of rivers, lakes, and seas, as well as the proliferation of red tides and blue algae, thereby severely damaging the ecological environment – with very serious consequences. Although the current \"Specifications for Industrial Circulating Cooling Water Treatment\" set strict requirements for discharge water quality parameters, none of the existing circulating cooling water systems are treated for this purpose; the main issue is economic, as there are no technical obstacles. So, as to how to calculate the economic costs, this requires us to take a higher perspective – not just focusing on the economic situation of our own organization, but considering things from the perspective of the entire society. By thinking about the needs of the whole nation and future generations, this issue becomes much easier to address. c Pretreatment water treatment: The level of pollutants in the pretreatment water is even more **above the allowed limits. Since the discharge of pre-coating water is intermittent, with operations starting up and maintenance work being carried out roughly once a year, this further increases the difficulty of treating it; in practice, it is discharged directly without any treatment. d. Sidewashing facilities: The current and revised standards specify that the sidewashing rate should be between 1% and 5%. However, considering the feedback from enterprises in areas with high dust levels regarding insufficient sidewashing, it is allowed to increase this rate appropriately in such areas or those with a high dust index. Currently, bypass filtration systems mostly use valveless filters or mechanical filters; however, some manufacturers report that the filtration efficiency is not satisfactory. The reason for this can be attributed to the fact that, under conditions of low turbidity, the particles of suspended colloids are very small, making it difficult to remove them through simple screening and filtration; the guidelines recommend the use of coagulants. The type of filter can vary; some companies (such as Jinan Refinery) replaced valveless filters with Israeli cartridge filters, but the results were not satisfactory, so they switched to floating disk fiber filters that are operated electrically. The turbidity of the inlet water is 7–8°, while that of the outlet water is 3–5°. e Regarding the net positive suction head of water pumps, this is outside the scope of these specifications, but it has been a problem in water treatment design in the past. In the past, when selecting pumps, it was sufficient to ensure that the water level was 20 cm above the top of the pump for it to operate; this concept is not accurate enough. For small centrifugal pumps in normal-temperature water, this is generally no problem, but for large vertical centrifugal pumps and axial flow pumps, especially hot water pumps, it is necessary to calculate the net positive suction head, and this value must be greater than the cavitation head specified in the pump’s specifications. 2.3 How to address the existing problems: a) Standards or regulations regarding the responsibilities of all parties involved in project construction should be established as soon as possible to clarify the relationships among them. b Accelerate the development of phosphorus-free and metal-free water treatment formulations. Currently, some manufacturers claim to have phosphorus-free water treatment formulas, but when such formulas are recommended in water treatment designs, they fail to provide specific data, which indicates that these phosphorus-free formulas are not yet mature. As far as we know, even the well-known international water treatment companies’ phosphorus-free formulas are only suitable for certain types of water quality. If a phosphorus-free water treatment formula is successfully developed, the aforementioned two major pollution problems can be easily resolved, bringing about tremendous benefits. It is suggested that the Water Treatment Association should organize manufacturers of water treatment chemicals, end-users, and research institutions to work together to overcome these technical challenges. I believe this problem is much simpler than exploring the moon; by pooling societal efforts and taking advantage of the strengths of the socialist system with Chinese characteristics, it will surely be resolved quickly. For wastewater with excessive levels of pollutants in reality, as well as pre-film water, it is recommended to send it to a wastewater treatment plant for treatment. With this revision of the \"Specifications for Industrial Circulating Cooling Water Treatment,\" specific technical solutions for the treatment of phosphorus-containing wastewater have also been provided. 3. Scope of application and terms of the design codes for industrial circulating cooling water treatment 3.1 The scope of application of the \"Codes for Industrial Circulating Cooling Water Treatment\" is clearly specified in Article 1.0.2 of the revised general provisions: \"These Codes for Industrial Circulating Cooling Water Treatment apply to the design of circulating cooling water treatment for new, expanded, and renovated projects that use surface water, groundwater, and reclaimed water as make-up water.\" In other words, all cooling water treatment designs except for seawater circulation are applicable. It should be noted here that the flow rate of circulating cooling water varies; some systems have a flow rate of hundreds of thousands of tons per hour, while others have rates of several hundred tons per hour, or even just dozens or a few tons per hour. Is this standard still applicable in such cases? It can be said with certainty that this standard is applicable regardless of the scale. However, when it comes to treating small-scale circulating cooling water systems using this standard, it may be overkill. Questions such as whether bypass filtration or pre-film formation is necessary for systems with a flow rate of just dozens of tons per hour need to be reconsidered. Currently, efforts are underway to develop a standard specifically for the treatment of small and medium-sized circulating cooling water systems in order to address these issues. 3.2 Noun Terms Everyone here is an expert in circulating cooling water treatment and is well familiar with many of the terms. I will merely explain some of the new terms that have been proposed in this revision of the \"Specifications for Industrial Circulating Cooling Water Treatment\", so as to avoid misunderstandings when encountering these terms in the specifications. a Recirculating Cooling Water System: A water-based cooling medium system that operates in a cyclic manner; it consists of heat exchange equipment, cooling equipment, treatment facilities, pumps, pipelines, and other related components. b Indirect Open Recirculating Cooling Water System (Indirect Open System): A recirculating cooling water system in which heat is transferred to the substance to be cooled indirectly, and the recirculating cooling water loses heat by being in direct contact with the atmosphere. c Indirect closed recirculating cooling water system (closed system): An indirect closed recirculating cooling water system is one in which the circulating cooling water exchanges heat with the substance to be cooled indirectly, and there is also an indirect heat exchange between the circulating cooling water and the cooling medium. d Totally Closed System: A closed-cycle cooling water system in which the circulating cooling water does not come into contact with the atmosphere. e Semi Closed System: A closed circulating cooling water system in which part of the cooling water is in contact with the atmosphere. f Direct Open Recirculating Cooling Water System (Direct Cooling System): A recirculating cooling water system in which the cooling water is in direct contact with the substance to be cooled for heat exchange, and it is also in direct contact with the atmosphere to dissipate heat. g Open System: A general term for intercooled open systems and direct-cooling systems. 4. Main revisions to the \"Design Code for Industrial Circulating Cooling Water Treatment\" This revision is a comprehensive one, with modifications of varying degrees made to each chapter, section, and even most of the provisions. It is not necessary for me to explain each item in detail here; I will only outline the important revisions and the reasons behind them. First, let’s explain how various data values are determined. As we all know, water treatment is an experimental science, and many of the data related to water treatment are derived from practical applications or experiments, rather than through calculations. For example, the Cl- value is determined by taking into account the operational data of circulating cooling water from numerous companies in China, and by selecting the most appropriate indicators – it is not calculated. It cannot be calculated at the moment either. The determination of other water treatment parameters is similar as well. 4.1 Revision of water quality parameters and water treatment control parameters for circulating cooling water. Water quality parameters and control parameters serve as a reflection of water treatment technologies; over the years, the progress in circulating cooling water treatment technologies in China has inevitably led to adjustments in various water quality parameter values. a Turbidity: The term used in current standards is suspended solids; the numerical values for this parameter remain unchanged. The revised version of the \"Specifications for Industrial Circulating Cooling Water Treatment\" simply changes the name of this parameter to turbidity. Why is this modification made? Although both terms refer to the content of suspended solids in water, the diameters of the suspended particles they represent are different. The particle size indicated by the term \"suspended solids\" is 1 μm or larger, while the particle size indicated by \"turbidity\" ranges from 1 nm to 1 μm – that is, what is commonly referred to as colloidal substances. Moreover, the testing methods for these two parameters are also different; the former is determined using filtration, while the latter is determined based on optical principles. There is no conversion relationship between the two. Since colloidal substances play a crucial role in causing fouling and the growth of microorganisms and algae in circulating cooling water, it is more accurate to use turbidity as an indicator for suspended solids, and this value should be kept as low as possible. The turbidity of circulating cooling water has a significant impact on the fouling thermal resistance and corrosion rate of heat exchange equipment; therefore, the lower the value, the better. Practical experience from factory operations shows that when a side filter is installed in the circulating cooling water system, the turbidity of the make-up water can be kept below 5 NTU. In most areas of China, the turbidity of circulating cooling water can be maintained below 10 NTU. Therefore, Table 3.1.1-6 stipulates that for plate, spiral-plate, and finned-tube heat exchangers, the turbidity should not exceed 10 NTU; for other types of heat exchangers, it should generally not exceed 20 NTU. Factory operation data demonstrate that this requirement fully meets the criteria regarding fouling thermal resistance specified in these standards. For power plant condensers, since the flow rate of the circulating cooling water inside their heat transfer tubes is generally greater than 1.5 m/s, and moreover these condensers are equipped with rubber ball cleaning systems, the turbidity requirement for the circulating cooling water in power plant condensers can be relaxed to some extent. b pH value: The range of pH in the new version is wider than that in the current version, reflecting an improvement in the corrosion and scale-inhibition performance of the chemical. c Calcium hardness + methyl orange alkalinity: Current standards for this parameter require the measurement of Ca2+ and alkalinity separately; using a composite index is more scientific. The solubility product of CaCO3: As can be seen from the above equation, the concentration of CO32- changes with the concentration of H+. When the H+ concentration is high, CO32- is converted to HCO3-, which increases the solubility. Therefore, the precipitation of CaCO3 is determined by two factors: the H+ concentration (alkalinity) and the Ca2+ concentration. The calcium carbonate stability index RSI is ≥3.3; this is also an indicator for controlling the precipitation of calcium carbonate, and it is calculated based on the calcium carbonate saturation index. There are multiple formulas for calculation; the recommended formula is: pHs = 9.70 + A + B – C – D. Where A is the coefficient for total dissolved solids, B is the temperature coefficient, C is the calcium hardness coefficient, and D is the alkalinity coefficient. To determine water quality stability: (1) Langlier Index = pH – pHs; if Is > 0, calcium carbonate is supersaturated; if Is < 0, it is unsaturated; if Is = 0, it is in a saturated state. However, due to the metastable zone during calcium carbonate crystallization, this judgment may be inaccurate. Practical experience suggests that Is should range from 0.5 to 2.5 for stable conditions, Is < 0.5 indicates corrosion, and Is > 0.5 indicates scaling. (2) Stability index: S = 2pHs – pH; if S ≈ 6.0, the condition is stable; if S < 3.7, severe scaling occurs; if 3.7 < S < 6.0, scaling still occurs; if 6.0 < S < 7.5, corrosion takes place; if S > 7.5, there is severe corrosion. (3) There are also indices related to scaling, critical pH values, and maximum carbonate hardness. d Total iron: Iron ions are trace ions present in natural water, while the concentration of manganese ions is even lower, at about one-tenth that of iron ions. Generally, the two coexist and are difficult to separate; therefore, the iron content is often used to represent the total amount of iron and manganese ions. The total iron content in water consists of colloidal iron and ferrous ions. Colloidal iron is trivalent iron, usually suspended in water in a colloidal state as hydroxide of iron or hydrates of iron oxides. In closed-loop water systems, it deposits on the surface of water coolers, forming sticky and difficult-to-remove scale that can lead to under-scale corrosion. A portion of colloidal iron can be removed during the pretreatment processes of coagulation and sedimentation. Ferrous ions are soluble ions; in closed-loop water systems, they can promote the crystallization and deposition of calcium carbonate. When phosphorus-based water stabilizers are used, ferrous phosphate deposits with strong adhesiveness may form, and they also serve as a nutrient source for the growth of iron bacteria. Generally, the total iron content in make-up water is required to be <0.2–0.5 mg/L. The total iron level in circulating water should be ≤0.5 mg/L. In the past, total iron in circulating water was either not controlled at all, or it was controlled at levels of <0.5 mg/L, 1.5 mg/L, or 2.0 mg/L. According to statistics from various systems, it is entirely possible to keep the total iron level below 0.5 mg/L; water with such a level has a very low corrosion rate. When the total iron level reaches 1.5 mg/L or 2.0 mg/L, the corrosion rate is actually already above the acceptable limit. Controlling the total iron content in circulating water requires not only regulating the total iron content in the make-up water but also primarily improving the water’s corrosion inhibition properties. For many domestic plants, the total iron level is below 1 mg/L, while in foreign plants it can reach 2.0 mg/L. Regarding the chloride ion level in circulating cooling water, there are various opinions and different standards both domestically and internationally, which poses many difficulties for design work and can even leave one at a loss. The chloride ion level has a significant impact on the treatment of circulating cooling water; unrealistic levels can lead to corrosion and damage of equipment or increased costs for water treatment. Therefore, it is essential to establish a reasonable threshold value. What is the basis for the chloride ion specification in this revision of the \"Specifications for Industrial Circulating Cooling Water Treatment\"? Is it scientific and reasonable? The following explanation is provided regarding this issue. The corrosive effect of chloride ions and the conditions affecting it: Chloride ions are corrosive anions commonly found in natural water. Chloride ions – having extremely high polarity that promotes corrosion reactions – are also highly penetrating; they can easily penetrate the protective layer on the metal surface, leading to crevice corrosion and pitting. In particular, they cause corrosive cracking in austenitic stainless steels, posing a serious threat that can render water coolers unusable in a short period of time. Many austenitic stainless steel equipment used in industries such as chemicals, refining, and metallurgy has poor resistance to chloride corrosion; therefore, this revision is specifically aimed at austenitic stainless steel and carbon steel heat exchange equipment. The main factors affecting corrosion cracking in stainless steel are as follows: (1) Internal stress in the equipment, which is generated during the heating process of the equipment. Although reputable manufacturers carry out heat treatment to eliminate stress after equipment fabrication, some residual stress remains. Additionally, factors such as temperature and mechanical stresses during installation and operation can also cause internal stress in the equipment; chloride ions tend to accumulate in these stressed areas, leading to corrosion. (2) The catalytic effect of chloride ions occurs when internal stresses are present in the equipment. Due to this catalytic effect, stress corrosion cracking occurs in stainless steel equipment, starting first at points of pitting, cracks, or corrosion grooves. The damaged passivation layer cannot be repaired, so the corrosion progresses further until the metal develops branch-like cracks and is destroyed. Some sources indicate that corrosion and cracking can occur as long as there are a few milligrams of chloride ions per liter, or even 0.2 mg/L of chloride ions; the case of stainless steel spherical tanks at Shanghai Jinshan Chemical Plant suffering from corrosion and cracking due to chloride ions also confirms this conclusion. Furthermore, chloride ions tend to accumulate in gaps or under dirt, resulting in high concentrations of these ions. For example, the chloride ion concentration in the circulating cooling water of a certain plant is around 200 mg/L; however, at the gaps where the tube sheet of the shell-side water cooler is connected to the tubes, the chloride ion concentration can reach 20,000–30,000 mg/L. Stress corrosion cracking did not occur in the on-site tube-side water coolers, and this was because the shell-side water cooler had gaps and a low flow rate, which created conditions for the accumulation of chloride ions. In another plant, just two months after it began operation, a large number of heat exchangers started leaking due to corrosion and cracking, even though the chloride ion concentration in the circulating cooling water was only 20–50 mg/L. This shows that the level of chloride ions is not the only factor that causes corrosion and cracking. (3) The inducing effect of temperature: It is well known that temperature is an important factor in chemical reactions, and corrosion cracking is no exception. In the presence of both tensile stress and chloride ions, corrosion is not significant at lower temperatures; however, as the temperature rises, corrosion cracking intensifies. Some sources suggest that austenitic stainless steel begins to corrode at 70°C. On-site inspections revealed that stress corrosion cracking occurred only at the hot end of the water cooler, namely at the inlet side where the process fluid entered; no corrosion was observed at the cold end. Nor was any stress corrosion cracking found in water coolers whose fluid temperature was below 150°C. (4) Dirt and water flow rate are also important factors affecting corrosion; these two factors are interrelated – low flow rates prevent dispersion, which facilitates the accumulation of chloride ions. At the same time, it also promotes the deposition of dirt, further increasing the concentration of chloride ions and thus corrosion. This is also the reason why the shell-side equipment is more prone to corrosion under the same conditions. The chloride ion specifications set by national standards and various manufacturers worldwide: At present, there is no unified standard for the quality of circulating cooling water internationally; therefore, the standards adopted by different manufacturers are determined based on their own experience. Therefore, the standards vary widely in terms of severity; some companies impose strict limits, requiring levels to be below 100 mg/L, or even below 50 mg/L, while other companies are less stringent and set their limits at
Ours is blue, which is strange; it might also be green. In any case, it has a color
Ours are a bit green and blue; haha, they definitely aren’t colorless and tasteless, right?
The color change is mainly caused by ammonia in the water, which leads to the massive proliferation of nitrosifying and nitrifying bacteria. Recommendation: Strengthen the control of microorganisms and improve the chemicals and treatment plans used.
The normal color is similar to that of tap water
The circulating water used in our gas production process is dark brown in color; the circulating water used for desulfurization has a slightly yellowish tint, while the other types of circulating water are clear and colorless. Of course, it’s not tasteless, but when it circulates in the tanks, it appears to have a slight greenish hue.
Our circulating water is slightly turbid yellow-green in color
Our company’s color is yellow-green; after adding the dye, it turns chocolate brown
The circulating water in our company undergoes pretreatment (addition of coagulants and coagulant aids, followed by reaction, sedimentation, and filtration). When an excessive amount of microorganisms is detected in the circulating water, bactericides such as calcium chloride are added. Therefore, the circulating water system in our company ensures high quality, with water that is relatively clear in color.