How to deal with red discoloration in steam boiler condensed water recovery

First, determine whether the red color of the boiler water is caused by corrosion in the water supply pipes. Second, determine whether it is caused by corrosion within the boiler itself. To put it simply, a red color indicates corrosion, with an increase in iron ions. As for specific solutions: for temporary treatment, improving the water quality by adding chemicals and carrying out continuous blowdown can yield results. For long-term use, it is recommended to carry out a comprehensive cleaning and pre-coating treatment.

Is any chemical added to the furnace, and what is it? Is the feed water deoxygenated? How to recover condensate water – into an advanced water tank or? The condensate water is red in color; what about the boiler water? Try turning on the rows first

It indicates that there is rust inside the pipe; have the line inspection team perform segmented drainage to identify which section of the pipe is rusted.

It is obvious that steam becomes contaminated during use; perhaps the transfer of steam through pipes causes corrosion in those pipes or in the equipment that uses the steam. As a result, the concentration of Fe2+ in the condensate water increases. When this condensate water reaches the water tank in the boiler room, Fe2+ is converted into Fe3+. Therefore, Fe2+ in the condensate needs to be treated before it enters the boiler.

Steam condensate is acidic and appears red; 3 treatment measures. The source of acidity in steam condensate: Steam condensate is similar to distilled water, and its pH value is generally close to 7, indicating neutrality. In boilers that use desalinated water for water supply, ammonia is added to raise the pH value of the desalinated water. Ammonia enters the boiler along with the water supply, vaporizes when heated, and then enters the heat exchanger as steam. There, it condenses and dissolves into the condensed water, allowing the pH value of this condensed water to be raised to 8 or higher. Under normal circumstances, however, the pH value of steam condensed water is around 5.5–6.5, and it is usually acidic with a value below 7. ▲On July 2, 2022, the acidic steam condensate water from a certain facility turned red in color, resulting in a low pH value and an acidic nature of the condensate. The main reason for this was the presence of dissolved CO2 in the water; when CO2 dissolves in water, it forms weak carbonic acid. Moreover, since steam condensate water is very pure, it has poor buffering capacity. Tests have shown that at 25°C, when 1 milligram of carbon dioxide dissolves in 1 liter of pure water, the pH value of that water drops from 7.0 to 5.5. ▲On July 2, 2022, the color of the acidic steam condensate water from a certain facility was red, with a pH value of 6. There are two sources of carbon dioxide in this steam condensate water: one is its dissolution from the air. Air contains 0.03% carbon dioxide, which dissolves into the steam condensate water through the raw water or open steam condensate recovery systems, resulting in a lower pH value and an acidic nature of the steam condensate water. The second source of carbon dioxide in steam condensate comes from the high levels of carbonate or bicarbonate ions in the boiler feed water; after sodium ion exchange softening of this feed water, carbonates and bicarbonates (such as sodium carbonate and sodium bicarbonate) remain in the water. Carbonates and bicarbonates enter the boiler along with the make-up water and are heated to concentrate; the carbonate and bicarbonate ions in the make-up water decompose when heated, with CO2 escaping and entering the steam system. At this point, sodium hydroxide is formed in the boiler water, giving it an alkaline nature. As temperature and pressure decrease, CO2 dissolves into the condensed water to form carbonic acid, causing the pH value in both the steam and the condensed water to drop and making them acidic. NSO3- → CO2↑ + H2O + SO32-; SO32- + H2O → CO2↑ + ON-. The hazards of acidic steam condensate and the reason for its red color: CO2 dissolves in the condensate to form carbonic acid, which lowers the pH of the steam condensate and makes it acidic, thereby generating H+. If the boiler system lacks deoxidization measures or if the efficiency of the deoxidizer is low, or if the steam condensate recovery system is open, oxygen present in the air at 21% concentration can dissolve into the condensate. Both H+ and dissolved oxygen act as cathode depolarizers in corrosion cells, which **accelerates the corrosion of the anodic metals in the equipment and pipelines of the steam and condensate systems**. High-temperature acidic steam condensate can rapidly corrode the equipment and piping in steam and condensate systems; therefore, it cannot be reused in boilers without treatment. Corrosion causes the iron ion level in steam condensate to exceed acceptable limits; colorless ferrous ions are oxidized to ferric ions, and as the concentration of ferric ions increases, the steam condensate takes on colors such as yellow, pink, orange-red, red, dark red, and soy sauce-colored. This is also the reason why some newly installed boiler steam and condensate piping systems become corroded, punctured, or leaky after 4–5 years. In accordance with the national standard GB1576-200 \"Water Quality for Industrial Boilers,\" water with an iron ion content exceeding 0.3 mg/L shall not be used in boilers. Visually, the steam condensate appears pure and transparent; however, when the level of ferrous ions is excessive, it is reused in the boiler without any treatment. As the ferrous ions enter the boiler along with the steam condensate, they are heated, concentrated, and oxidized to form colored ferric ions, which cause the color of the boiler water to turn red. In the cases of red-colored boiler water encountered by the author among steam boiler users, over 85% of them were due to excessive levels of iron in the steam condensate, which was reused in the boiler without proper treatment. Trivalent iron ions act as catalysts for oxygen corrosion inside boilers; they not only accelerate the occurrence of such corrosion but also lead to the formation of iron oxide scale. This scale causes under-scale corrosion as well. Iron oxide scale significantly reduces the heat transfer efficiency of the boiler tubes, and this reduced efficiency results in substantial waste of fuel energy, along with higher exhaust temperatures ； Iron oxide scale not only shortens the service life of boilers, but also, when it accumulates in large quantities within the boiler tubes, it can cause the tubes to expand due to overheating, thereby posing a risk of tube rupture and creating significant hazards to the safe operation of the boiler. ▲On July 11, 2022, the color and appearance of the acidic steam condensate wastewater from a certain facility were improved, making it clear and pure. ▲ On July 11, 2022, the pH value of the acidic steam condensate wastewater from that same facility was adjusted to 8; originally, such wastewater had an acidic color and was red in hue. Three treatment methods were employed to address the red color of the acidic steam condensate. One of the solutions involved adding ammonia to the boiler feed water. Ammonia is weakly alkaline; when heated in the boiler, it escapes along with the steam into the steam system. The steam containing ammonia then passes through heat exchangers or other cooling devices, where, as the temperature and pressure decrease, it condenses into water. Ammonia dissolves in this condensed water, raising its pH value and giving it an alkaline nature. When the pH value exceeds 8, ammonia can completely neutralize carbon dioxide present in the water, resulting in the formation of NH4HCO3. NH3 + H2O → NH4OH (reversible); NH4OH + CO2 → NH4HCO3 (reversible); NH4OH + NH4HCO3 → (NH4)2CO3 + H2O (reversible). Adding ammonia to boiler feed water helps to prevent the red color of acidic steam condensate. Ammonia is inexpensive and is a common pH regulator; when added to boiler feed water, it dissolves in water to form a weakly alkaline solution that raises the pH level of the boiler water. When heated in the boiler water, ammonia evaporates and enters the heat exchange equipment as steam. As temperature and pressure drop, ammonia dissolves back into the condensate. Adding ammonia to boiler feed water increases the pH levels of the boiler water, steam, and condensate, thereby neutralizing the corrosive effect of CO2 in acidic steam and condensate on the system’s equipment and pipelines, and reducing the amount of iron ions in the condensate. Adding ammonia to boiler feed water helps to address the problem of red-colored condensate from acidic steam. Issues to be considered when using ammonia in this manner: 1. Adding ammonia can only control the weakly acidic corrosion caused by CO2; it cannot prevent oxygen-induced corrosion. In water-ammonia fed boiler systems, corrosion of steam pipelines, corrosion of heat exchangers, corrosion of steam condensate pipelines, and excessive iron ions leading to a red color in the steam condensate are common problems ； Issues to be noted when adding ammonia to boiler feed water to address the red color of acidic steam condensate: 2. Ammonia has a certain corrosive effect, and it is also prone to releasing ammonia vapor; the storage and use of liquid ammonia represent a source of danger ； Issues to be noted when adding ammonia to boiler feed water to address the red color of acidic steam condensate: 3. The pH value cannot be maintained for long using ammonia, and a relatively large amount of ammonia is required. Ammonia is volatile and unstable when heated; in the vapor-liquid phase of steam boilers, there is more gas phase and less liquid phase. To maintain the pH level of the steam condensate return water and prevent corrosion in the return pipelines as well as excessive iron content, a large amount of ammonia must be added. This is also why an ammonia smell can sometimes be detected when collecting or discharging steam condensate return water ； Issues to be noted when adding ammonia to boiler feed water to address the red color of acidic steam condensate: 4. When an excessive amount of ammonia is added to the feed water, corrosion of copper occurs more severely in the presence of dissolved oxygen; copper-based heat exchangers, copper pipes, and related instrumentation are prone to corrosion ； Issues to be noted when adding ammonia to boiler feed water to address the red color of acidic steam condensate: 5. Long-term use of high doses of ammonia is detrimental to boiler operation, as excessive amounts of ammonia can cause corrosion. Ammonia is alkaline and accelerates the precipitation of calcium, magnesium, and other substances, leading to scaling in boilers as well as corrosion beneath the scale ； Prolonged use may cause corrosion in valves, pipes, and other components; therefore, its dosage must be strictly controlled, and it should be adjusted appropriately while being added continuously ； Issues to be noted when adding ammonia to boiler feed water to address the red color of acidic steam condensate: 6. The claim that adding ammonia helps control excessive iron ions in steam condensate return water is a fallacy. Adding ammonia can only control the weakly acidic corrosion caused by CO2; it cannot prevent oxygen-induced corrosion. Moreover, since ammonia is volatile and unstable when heated, there is more of it in the gas phase and less in the liquid phase. Additionally, it cannot be added in high doses over a long period of time. Therefore, adding ammonia can only partially alleviate corrosion in steam systems, and it can only reduce the iron ion content in the wastewater resulting from steam condensation to a limited extent. Colleagues, have you experienced situations in your facilities where the pH level of the steam condensate from the steam boilers was low, indicating an acidic condition? Has there ever been a situation where the color of the steam condensate was red or yellow, or where the iron content in the steam condensate was above the acceptable level? How did you solve it? What methods do you use for scale prevention and removal, as well as corrosion protection in boilers? Regarding issues such as adjusting the pH value of boiler feed water, redness of boiler water, hardness in return water, corrosion, scaling, and tube failure in boilers, corrosion in steam systems, excessive iron content in steam condensate, red color of acidic steam condensate, as well as testing and treatment of boiler water quality, Yan Hui from Beijing University of Chemical Technology at 18600475386 is always available for industry colleagues to discuss these problems and exchange experiences. Students are also welcome to share information on new technologies related to boilers, while colleagues can share their experience in managing and using boiler equipment. Everyone involved in boiler operations is encouraged to learn from one another in order to solve various practical problems related to boilers. Three treatment measures for the acidic, red-colored steam condensate. Solution 2 for the red color of acidic steam condensate – Equipment for removing iron from high-temperature steam condensate. This type of equipment filters out the excess iron ions in the condensate, allowing the color of the steam condensate to return to normal levels; as a result, the iron ion content is within acceptable limits, enabling the steam condensate to be reused in boilers safely. Disadvantages of equipment for removing iron from high-temperature steam condensate: High initial investment for such equipment ； Equipment for removing iron from high-temperature steam condensate occupies a large amount of space, and the operation and maintenance costs of such equipment are not low ； The filter media for high-temperature steam condensate iron removal equipment needs to be replaced every 2–3 years, and the cost of replacing this media accounts for about one-third of the total cost of the equipment ； Equipment for removing iron from high-temperature steam condensate cannot increase the pH value of steam condensate ； Equipment for removing iron from high-temperature steam condensate cannot address the corrosion caused by acidic steam and condensate on the equipment and pipelines in the boiler steam system and condensate recovery system; since corrosion in these systems persists, there will always be a source of iron ions. The iron removal through filtration by such equipment is only a temporary solution, not a permanent one. ▲In July 2022, a unit encountered a red color in the acidic steam condensate water; Solution No. 3 for addressing this issue was to add the BF-31T steam condensate water protector. To counteract the oxygen corrosion and weak carbonic acid corrosion caused by acidic steam and condensate on the equipment and pipelines in boiler steam systems and condensate recovery systems, the BF-31T condensate system protector, a product owned exclusively by Beijing University of Chemical Technology, is typically used to prevent such corrosion from occurring. The BF-31T condensate water system protector is a core technology in the Science and Technology Ministry Innovation Fund project “Zero-Waste Steam Generation Technology” undertaken by our unit. The BF-31T condensate system protector product passed the \"Registration by the China Boiler Water Treatment Association\" program in 2003. Technical advantages of BF-31T steam condensate protector in addressing the red color of acidic steam condensate: BF-31T is an alkaline emulsive liquid agent that is volatile. When added to boiler feed water, BF-31T becomes weakly alkaline when dissolved in water. When heated in the boiler water, it evaporates and enters the heat exchange equipment along with the steam; as temperature and pressure drop, BF-31T dissolves back into the condensate. The mechanism by which the BF-31T steam condensate protector works is to form a protective film throughout the boiler system to isolate O2 and CO2, while also raising the pH level of the boiler water, steam, and return water. This approach effectively addresses the problems of oxygen corrosion and weak acid corrosion that are common in steam condensate. It eliminates the source of iron ions in the steam condensate at its root, thereby solving the issue of red-colored condensate. This corrosion-inhibiting mechanism provides both temporary and permanent solutions to the problem of excessive iron levels in condensate; it not only ensures that iron levels are within acceptable limits but also fully protects all equipment and pipelines in the boiler system from further corrosion, perforation, or leakage, **thus extending the service life of the system’s equipment. The technical advantages of BF-31T steam condensate protector in addressing the red color of acidic steam condensate: 2. The BF-31T condensate system protector requires simple operating conditions in practice; there are no requirements regarding condensate temperature or iron content. However, some equipment designed for iron removal does have requirements concerning condensate temperature and iron levels. The BF-31T steam condensate protector addresses the issue of red-colored acidic steam condensate; its technical advantages include the fact that the 3BF-31T condensate system protector maintains good buffering capacity despite fluctuations in production load, without affecting the performance parameters related to water treatment. The technical advantages of BF-31T steam condensate protector in addressing the red color of acidic steam condensate: 4. The cost of BF-31T steam condensate protector decreases as more of it is used within the system, and there are no issues related to wastewater discharge from backwashing or flushing processes like those associated with other types of equipment. Technical advantages of BF-31T steam condensate protector in addressing the red color of acidic steam condensate: 5. Compared to the use of ammonia, BF-31T offers better performance; ammonia can raise the pH level of boiler water and steam, thereby preventing mild acidic corrosion. Ammonia is volatile, with more in the gas phase and less in the liquid phase; it requires large amounts to be used, and it cannot prevent oxygen corrosion. The technology of using BF-31T steam condensate protector to control the pH value in boiler feed water possesses all the advantages of the ammonia addition process: it is reasonably priced ； It will not increase the salt content in the boiler water ； It is volatile and can protect the entire equipment and pipelines of the boiler’s steam and water system. The main components of the BF-31T condensate protector are neutralizing agents, film-forming agents, and other additives; it possesses film-forming and neutralizing functions, good stability, and a suitable vapor-liquid phase distribution ratio, enabling it to rapidly control system corrosion. Neutralizing amines serve to raise the pH of boiler feedwater, furnace water, steam, and condensate, thereby preventing corrosion caused by the weak acids formed by carbon dioxide in water ； The film-forming agent creates a hydrophobic protective film in the form of a monolayer on the metal surface; the gaps between the molecules in this film are smaller than the cross-sectional sizes of carbon dioxide and oxygen, which prevents corrosion-causing gas molecules such as O2 and CO2 from coming into contact with the metal, thus avoiding corrosion of the metal ； A reasonable vapor-liquid phase distribution ratio can effectively distribute the treatment agent between the vapor and liquid phases in metal pipes, thereby effectively addressing metal corrosion in systems with both vapor and liquid phases; it is particularly suitable for the protection and anti-corrosion of equipment that uses steam intermittently. The technical advantages of BF-31T steam condensate protector in addressing the red color of acidic steam condensate: BF-31T allows for rapid coating of the condensate; the iron ion level (total iron content) in the condensate water reaches the specified standards within 72 hours. Acidic steam condensate with a red color also returns to a pure and transparent state within 72 hours, which facilitates experiments using this chemical. It can completely replace deaerators and deoxidizers. Compared to the iron removal processes and other measures used in common equipment on the market, the BF-31T condensate system protector requires no substantial investment in fixed equipment, no operational maintenance costs, and eliminates the need for expensive filter media replacements (with a service life of around 3 years and total costs accounting for 20-30% of the overall cost). It not only protects the system’s equipment and pipelines, thereby extending the lifespan of the boiler system, but also completely eliminates the source of iron ions, thus resolving the problem of red-colored acidic steam condensate. This allows high-temperature, pure steam condensate to be recycled back into the boiler for safe use, achieving an effective solution to iron removal in condensate. Steam condensate is acidic in color and red: 3 treatment methods (Yan Hui)