Boiler water redness treatment

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Dealing with redness of boiler water In late May this year, the person in charge of equipment management of a pharmaceutical factory came to me and asked me a question and asked for a solution.: Figure 1▲The discharged water of boiler No. 2 is sometimes red and sometimes reddish brown. Our pharmaceutical factory has two 2-ton steam boilers of model WNS2-1.25-Q to provide heat for production. Boiler No. 1 uses resin softened water as feed water, and boiler No. 2 uses reused steam condensate as the main water supply, and softened water as supplement. The color of the boiler water in No. 1 boiler using softened water is normal. When blowing down the sewage in the No. 2 boiler using steam condensate water, the boiler water sometimes turns red and sometimes reddish brown. After increasing the sewage blowdown, there is still no improvement. The color of the boiler water becomes red and muddy. After the boiler water is left to stand, there is a red precipitate at the bottom. The steam condensate reused by No. 2 boiler occasionally turned slightly red in color, and the pH value of the condensate water was 5.5. Measures were taken to increase the pH value by adding sodium carbonate, sodium hydroxide, and ammonia in the steam condensate recovery tank. However, the red color of the boiler water in No. 2 boiler was not significantly improved. I would like to know what is the problem and how to solve it. Figure 2▲The water in boiler No. 2 is red (middle), the condensed water is slightly red (left), and the water in boiler No. 1 is normal in color. 1. The reason why the boiler water is red I reply: The color of the boiler water in No. 2 boiler is red. The red water in the boiler is the reason for the high concentration of iron ions in the boiler water. Iron ions are the product of corrosion of the boiler system. The presence of red water in the boiler for a long time means that the boiler is suffering from continuous corrosion. The cause of corrosion of the steam boiler system is usually the combined action of oxygen corrosion and acidic corrosion caused by carbon dioxide. Oxygen corrosion comes from the lack of deaeration measures in the boiler system or the inefficiency of the deaeration equipment. ； The acidic corrosion caused by carbon dioxide originates from the thermal decomposition of carbonate or bicarbonate into carbon dioxide in the replenishing water, or the steam condensed water is dissolved in the air through open recycling. The steam condensed water is very pure as distilled water. Tests have shown that when 1 milligram of carbon dioxide is dissolved in 1 liter of pure water, the pH value of the pure water drops from 7 to 5. The pH value of the steam condensed water in No. 2 boiler is 5.5, which is carbon dioxide acidic water. The corrosion rate cannot be underestimated. The corrosion of the boiler steam system produces iron ions. When the iron ion concentration in the steam condensation water is below 600 micrograms per liter, it usually does not show color. The color of the steam condensation water reused by the No. 2 boiler occasionally turns slightly red. At this time, the iron ion content in the steam condensation water is about 700 micrograms per liter or more (the national standard requires that the iron ions in the boiler feed water should be less than 700 micrograms per liter). (less than 300 micrograms), the steam condensate water with excessive iron ions directly enters the boiler. As the pot water continues to evaporate and concentrate, the colorless divalent iron ions are heated and oxidized into colored trivalent iron ions. The color of the boiler water begins to turn red. As the saying goes, pot water turns red, boiler water turns red, and boiler wastewater turns red. This is the case with boiler red water. 2. The dangers of red boiler water. If the boiler has red water for a long time, it means that the boiler is suffering from continuous corrosion. The iron ions in the steam condensate water exceed the standard and the boiler water turns red. The iron ions in the boiler water will adhere to the heating surface of the boiler and form iron oxide scale. Iron oxide scale can cause three types of harm to boilers. 2.1 The hazards of red boiler water 1 are that the average thermal conductivity of iron oxide scale is 0.1-0.2kcal/mh·℃, which is about 1/370 of steel. Iron rust scale has poor thermal conductivity. Iron oxide scale adheres to the heating surface of the boiler, which will reduce the boiler output, reduce the thermal efficiency of the boiler, increase natural gas fuel energy consumption, and increase the boiler operating cost. 2.2 The second hazard of boiler water turning red is that if the iron oxide scale or rust scale reaches a certain thickness, the boiler tube will overheat for a long time and cause creep, and it will only be a matter of time before the boiler tube bursts. 2.3 The third hazard of boiler water redness is that iron oxide scale adheres to the heating surface of the boiler. Due to the electrochemical corrosion effect, corrosion under the scale, that is, pit corrosion, occurs. As time goes by, the corrosion pit deepens, and it is only a matter of time that the corrosion pit perforates and leaks on the heating surface of the boiler, posing a hidden danger to production safety. 3. How to deal with the redness of boiler water. To solve the problem of redness of boiler water, it is necessary to reduce the content of iron ions in the boiler water. There are usually two ways.: 3.1 The first way to solve the problem of redness of boiler water and reduce the content of iron ions in the boiler water is to install physical iron removal filtering equipment at the end of steam condensate water recovery. The iron removal equipment filters out the iron ions in the steam condensation water, allowing the color of the steam condensation water to return to normal. If the iron ions in the steam condensation water meet the standard, it can be directly and safely reused in the boiler. Disadvantages of high temperature steam condensate iron removal equipment: High-temperature steam condensate water iron removal equipment requires a large one-time investment ； High-temperature steam condensate water iron removal equipment occupies a large area, and the operation and maintenance costs of high-temperature steam condensate water iron removal equipment are not low. ； The filter material of high-temperature steam condensate iron removal equipment needs to be replaced once every 2-3 years, and the cost of replacing the filter material accounts for about one-third of the equipment cost. ； High temperature steam condensate water iron removal equipment cannot increase the PH value of steam condensate water ； High-temperature steam condensate iron removal equipment can neither solve the corrosion of acidic steam and condensate water on boiler steam system and condensate recovery system equipment and pipelines, nor can it solve the system oxygen corrosion. System corrosion has always existed, and the source of iron ions has always existed. High-temperature steam condensate iron removal equipment can filter and remove iron. * * * * * . 3.2 The second way to solve the problem of redness of boiler water and reduce the content of iron ions in the boiler water is to add chemicals to the boiler feed water or steam condensate water to solve the acid corrosion caused by oxygen corrosion and carbon dioxide in the system. Commonly used chemicals include sodium carbonate, sodium hydroxide, ammonia, and BF-31T. 3.2.1 Advantages and Disadvantages of Adding Sodium Carbonate to Solve the Redness Problem of Boiler Water Adding sodium carbonate to the boiler steam condensate water can increase the PH value of the condensate and boiler water. It can only solve the acid corrosion of the condensate water and the boiler body. It cannot solve the problem of oxygen corrosion and can only partially alleviate the problem of boiler red water. The disadvantage of adding sodium carbonate to the boiler steam condensate is that it increases the salt content of the boiler water. After the sodium carbonate is dissolved and ionized, the carbonate is heated and decomposes into carbon dioxide, which is one of the reasons for the decrease in the pH value of the condensate. 3.2.2 Advantages and Disadvantages of Adding Sodium Hydroxide to Solve the Redness Problem of Boiler Water Adding sodium hydroxide to the boiler steam condensate water can increase the PH value of the condensate and boiler water. It can only solve the acid corrosion of the condensate water and the boiler body. It cannot solve the oxygen corrosion problem and can only partially alleviate the red water problem. The disadvantage of adding sodium hydroxide to boiler steam condensate water is that sodium hydroxide is a strong base and a strong electrolyte. The pH value of sodium hydroxide is highly volatile. After sodium hydroxide is added, the pH of the water will easily rise. Adjusting the pH value is faster and more direct. It is also easy to overdo it and do not add too much. Adding too much sodium hydroxide will cause the pot water to be too alkaline, causing steam and water to evaporate. ； The amount of sodium hydroxide added is difficult to control. Excessive free NaOH will cause high relative alkalinity, and alkali embrittlement will also cause corrosion to the equipment. 3.2.3 Advantages and Disadvantages of Adding Ammonia to Solve the Redness Problem of Boiler Water Ammonia is a common pH regulator and has many advantages. The most important thing is that ammonia is weakly alkaline. The concentration of ammonia added is generally not large, and the cost is low. When the pH value is greater than 8, ammonia can completely neutralize carbon dioxide in the water to generate NH4HCO3. Adding ammonia to the boiler feed water can increase the PH value of the feed water, boiler water, and condensate water. It can only solve the acid corrosion of the boiler system, but cannot solve the oxygen corrosion problem. It can partially alleviate the red water problem. There are four issues that need to be paid attention to when adding ammonia to adjust the pH value of furnace water and steam to alleviate corrosion. 1. Ammonia has a certain corrosive effect and is easy to volatilize ammonia gas. The storage and use of liquid ammonia is a source of danger. ； 2. The ammonia gas-liquid ratio is not good, with more gas phase side and less liquid phase side. The pH value of ammonia water cannot be maintained for a long time, and the dosage is large. ； 3. When too much ammonia is added to the feed water, the corrosion of copper is relatively strong with the participation of dissolved oxygen, and copper metal heat exchangers and instrument accessories are prone to corrosion. ； 4. Adding ammonia to adjust and increase the pH can prevent carbon dioxide from corroding pipelines during transportation, but it cannot effectively control oxygen corrosion. Oxygen corrosion in steam and condensate systems is still ongoing, and can only partially solve the problem of boiler water redness. 3.2.4 Advantages and disadvantages of adding BF-31T condensate protective agent to solve the problem of boiler water redness. BF-31T condensate system protective agent is an exclusive product of Beijing University of Chemical Technology. The main components of BF-31T condensate protective agent are neutralizing agents, film-forming agents and other additives. It has a film-forming neutralizing function, good stability, and a reasonable gas-liquid phase distribution ratio, which can quickly control the overall system corrosion of the boiler. The neutralizing agent plays the role of increasing the pH value of boiler feed water, boiler water, steam and condensate, and neutralizing the weak acid corrosion caused by carbon dioxide in the water. ； The film-forming agent forms a monomolecular layer of hydrophobic protective film on the metal surface. The gaps between the film molecules are smaller than the cross-sections of carbon dioxide and oxygen, preventing the corrosive gas molecules O2 and CO2 from contacting the metal, thereby preventing corrosion of the metal. ； A reasonable gas-liquid phase distribution ratio can effectively distribute the agent into the gas-liquid phase in the metal pipeline, which can effectively solve the metal corrosion of the gas-liquid two-phase system. It is especially suitable for the protection and anti-corrosion of intermittent steam equipment. BF-31T condensate system protective agent has simple on-site working conditions and no requirements for condensate temperature and iron content. Some equipment for iron removal has requirements for condensate temperature and iron content. BF-31T condensate system protective agent is not affected by production load fluctuations and has good buffering performance, and will not affect the performance of water quality treatment indicators. The cost of the BF-31T condensate system protective agent will decrease with the cumulative use of the agent in the system, and there will be no wastewater discharge problems like backwashing of other equipment. The coating speed of BF-31T condensate system protective agent is fast, and the condensate water quality iron ion (full iron index) quickly reaches the standard within 72 hours, which provides convenience for pharmaceutical experiments. It can completely replace the deaerator and deoxidizer. Compared with common equipment iron removal processes and other measures on the market, BF-31T condensate system protective agent does not require huge investment in fixed equipment, and does not require expensive filter material replacement (use period is about 3 years, total cost 20-30%). It not only protects system equipment and pipelines, extends the service life of the boiler system, but also completely cuts off the source of iron ions, allowing the condensate water to be recycled and reused. The boiler can be used safely, and the condensate iron removal can be achieved. Dear colleagues, does your unit's steam boiler have "red water" phenomenon? Has the pH value of steam condensation water been low and acidic? Has the color of the steam condensation water turned red or yellow, or has the iron content of the steam condensation water exceeded the standard? How did you solve it? What methods are you using for boiler scale inhibition, descaling, and corrosion inhibition? Regarding the adjustment of PH value of boiler feed water, redness of boiler water, hardness of return water, boiler corrosion and scaling, tube explosion, steam system corrosion, steam condensate water iron exceeding the standard, acidic steam condensate water turning red, boiler water quality testing and other issues, Yan Hui of Beijing University of Chemical Technology, I86OO475386, is always welcome to communicate with students about new technologies related to boilers. Colleagues are always welcome to share their experience in boiler equipment management and use, and learn from each other. * . Treatment of boiler water turning red. 4. Boiler water redness treatment test case After in-depth communication with the person in charge of the equipment management of the pharmaceutical factory, they understood the actual working conditions of the pharmaceutical factory's boiler. It was recommended to purchase a 10-day supply of chemicals to conduct an efficacy test of anti-corrosion red water treatment chemicals for the boiler system. Figure 3 ▲ Water sample of No. 2 boiler. Since the gas production of the pharmaceutical factory's boiler is not large, 4 barrels of 100 liters of BF-31T condensate system protective agent were purchased for a 10-day "Effectiveness Test of Anti-corrosion Red Water Treatment Agent for the Boiler System of a Pharmaceutical Co., Ltd.". During the test, the amount of chemical added was gradually reduced. Samples of boiler water and steam condensate water from No. 2 Boiler were taken every day for appearance comparison and third-party testing data as a basis for judging the effectiveness of the agent. Figure 4▲No. 2 Boiler Steam Condensate Water Sample Pharmaceutical Factory Boiler System Anti-corrosion Red Water Treatment Agent Effectiveness Test On the second day, the slightly reddish color appearance of the No. 2 Boiler Steam Condensate Water Sample returned to normal (see Figure 3 of the No. 2 Boiler Condensate Water Sample) ； The water color of No. 2 boiler is red, and the red color does not change much (see Figure 4 of the water sample of No. 2 boiler). On the third day of the effectiveness test of the anti-corrosion red water treatment agent in the boiler system of the pharmaceutical factory, the boiler discharge volume was increased and the boiler water replacement was accelerated. The color and appearance of the steam condensate water sample of No. 2 Boiler was completely transparent (see Figure 3 of the condensate water sample of No. 2 Boiler). ； The water color of No. 2 boiler is red, and the red color becomes lighter (see Figure 4 of the water sample of No. 2 boiler). On the 4th day of the efficacy test of the anti-corrosion red water treatment agent in the boiler system of the pharmaceutical factory, the boiler discharge volume was increased and the boiler water replacement was accelerated. The color and appearance of the steam condensate water sample of No. 2 Boiler was completely transparent (see Figure 3 of the condensate water sample of No. 2 Boiler). ； The water color of No. 2 boiler is red, and the red color continues to become lighter (see Figure 4 of the water sample of No. 2 boiler). On the 5th day of the efficacy test of the anti-corrosion red water treatment agent in the boiler system of the pharmaceutical factory, the boiler discharge volume was increased and the boiler water replacement was accelerated. The color and appearance of the steam condensate water sample of No. 2 Boiler was completely transparent (see Figure 3 of the condensate water sample of No. 2 Boiler). ； The water color of No. 2 boiler turns light red (see picture 4 of the water sample of No. 2 boiler). On the 6th day of the efficacy test of the anti-corrosion red water treatment agent for the boiler system of the pharmaceutical factory, the boiler discharge volume was increased and the boiler water replacement was accelerated. The color and appearance of the steam condensate water sample of No. 2 Boiler is completely transparent (see Figure 3 of the condensate water sample of No. 2 Boiler) ； The red color of the water in the No. 2 boiler disappeared (see Figure 4 of the water sample of the No. 2 boiler). On the 7th day of the efficacy test of the anti-corrosion red water treatment agent for the boiler system of the pharmaceutical factory, the boiler discharge volume was increased and the boiler water replacement was accelerated. The color and appearance of the steam condensate water sample of No. 2 Boiler is completely transparent (see Figure 3 of the condensate water sample of No. 2 Boiler) ； The red color of the water in the No. 2 boiler disappeared and the color returned to normal (see Figure 4 of the water sample of the No. 2 boiler). On the 8th day of the efficacy test of the anti-corrosion red water treatment agent for the boiler system of the pharmaceutical factory, based on experience, judging from the color of the steam condensate water sample and boiler water sample of No. 2 boiler, the overall corrosion of the boiler system has been completely controlled. The iron ions in the condensate water reached the standard, the color of the boiler water was normal, and the boiler discharge volume returned to normal. The boiler water sample and condensate water sample of the No. 2 boiler were tested by a third party. The effectiveness test of the anti-corrosion red water treatment agent of the boiler system ended ahead of schedule. 5. Postscript It has been 14 months since the boiler of this pharmaceutical factory officially adopted the anti-corrosion treatment plan of BF-31T condensate water protectant. The boiler has been operating safely and stably, and there have been no problems such as corrosion of boiler system equipment and pipelines, redness of boiler water, redness of sewage, yellow color of steam condensation return water, and excess iron ions in boiler red water. Due to the stable operation of the boiler and good boiler water quality, the boiler sewage discharge volume has dropped significantly compared with before the treatment, reducing pollution and emissions, and saving a lot of energy and water resources. Treatment of boiler water reddening (Yan Hui)