How to prevent scaling in acid coolers?

Control the quality of the cooling circulating water; there are professionals who specialize in treating the quality of circulating water!

An electronic descaling device can be installed at the outlet of the circulating water pump.

Keep the concentrations of calcium and magnesium ions within acceptable limits; in other words, it is necessary to manage the relationship between alkalinity and hardness, as well as control the temperature of the circulating water at the outlet

Reply 3# cordone: What is the actual effectiveness of electronic scale removers?

First, ensure the quality of the raw water; during operation, apply chemical treatments such as scale inhibitors and biocides, while also enhancing the accountability of operators and improving the inspection system.

This post was last edited and replied to by Purple Sky on 2010-6-11 10:53. Reply 1# qhjhne: When the acid cooler is in operation, the following phenomena may occur: a. A decrease in the efficiency of the heat exchanger; b. A significant increase in the temperature of the acid at the outlet of the acid cooler; c. Poor flow of water within the cooler. The occurrence of the above phenomena indicates that scaling has already formed inside the acid cooler. If not addressed promptly, the scaling and blockages will gradually worsen, narrowing the flow channels within the heat exchange tubes. In severe cases, some or all of the heat exchange tubes may become completely blocked by hard layers of scale. Scaling has a significant impact on the safe operation and service life of acid coolers. When scaling is severe, it raises the temperature of the tube walls in the heat exchanger, increases the anode protection current required in the shell side, accelerates the consumption of the main cathode, and shortens the cathode’s lifespan ； On the other hand, under-scale corrosion may occur inside the tubes; the concentration of CL- in the water beneath the scale keeps increasing, and CL- is highly detrimental to stainless steel. In severe cases, corrosion and perforation of the inner surface of the tubes can lead to leaks in the acid cooler. To handle it properly and in a timely manner, it is necessary to understand its causes and take appropriate measures. 1. Scaling refers to the solid substances that gradually accumulate on the inner surface of stainless steel pipes as a result of contact with unclean fluids. Based on the mechanism of fouling layer deposition, fouling can be classified into particulate fouling, crystalline fouling, chemical reaction fouling, corrosion fouling, biological fouling, and solidified fouling. The fouling of acid coolers mainly consists of crystalline fouling and biological fouling; crystalline fouling includes carbonate scale, sulfate scale, and silica scale layers that form inside the tubes ； Biofouling refers to microbial fouling, which produces sludge; this sludge in turn provides conditions for the growth of biofouling. Under suitable temperature conditions, biofouling can form a layer of fouling of a certain thickness. Scale forms when the tube wall temperature is high, the concentration of calcium and magnesium ions in the water is high, and the flow velocity of water inside the tubes is low. 2. There are two methods for removing scale: physical and chemical methods. Currently, the physical cleaning method used in China involves high-pressure water flushing; however, since it requires specialized equipment and results in high cleaning costs, it is not very suitable for use in sulfuric acid plants. The chemical methods mainly include non-stop cleaning and stop-start chemical cleaning. A dedicated \"operational scale inhibitor and remover\" can effectively remove scale and prevent its formation without shutting down the system. During parking for maintenance, pickling can be used to remove scale; for acid coolers, nitric acid pickling is the recommended method. Since the acid cooler is made of stainless steel, CL- can cause pitting on the surface of austenitic stainless steel; therefore, cleaning with HCL is strictly prohibited ； H2SO4 reacts with Ca2+ and Mg2+ in water to form CaSO4 and MgSO4, which are extremely difficult to dissolve; therefore, using sulfuric acid for cleaning is not recommended either. Nitric acid for cleaning is readily available, specialized acid cleaning corrosion inhibitors are well-developed, and the costs are not high. For thin layers of scale, the scale inside the pipes can be removed within a few hours by using a cleaning fluid circulation method ； When the scale accumulation on the inner wall of the pipe exceeds 1 mm, it is considered severe scaling; in such cases, a combined cleaning method involving soaking and circulation can be used, and the cleaning time must also be increased accordingly. 3. Some users use river water directly as the coolant for their coolers; as seasons change, solid particles in the water can sometimes clog the heat exchange tubes. The ideal solutions are to install a simple filtering device at the water inlet, or to allow the water to settle in a simple tank before it enters the acid cooler. 4. Algal clogging of heat exchange tubes often occurs in southern regions, especially during the hot summer months. When the temperature of the circulating water in coolers, motor coolers, and fiberglass cooling towers is above 30°C, it creates conditions favorable for the growth of various types of algae. Greenish deposits appear on the inner walls of the tank; sometimes they grow very rapidly. If not dealt with promptly, these algae will attach themselves to the water tanks of the heat exchangers, reducing the amount of water flowing through the coolers and thereby lowering the efficiency of heat exchange in those coolers. There are already \"biocides and algaecides\" designed specifically for acid chillers, which can quickly eliminate various types of algae within a few days at low cost. Additionally, acid coolers often suffer from leakage problems; here is an analysis of the underlying causes along with corresponding solutions: The main reasons for leakage in acid coolers are as follows: 1. Metallurgical defects in the raw materials: issues such as minor inclusions, micro-cracks in the heat exchange tubes, or defective welds in the pipes. Therefore, it is particularly important to select and inspect the raw materials carefully. Acid coolers with metallurgical defects will develop problems at these weak points after operating for a period of time. 2. Manufacturing defects in acid coolers: Issues such as insufficient weld material or slag inclusion during the welding of heat exchange tubes to the tube sheet, along with failures to detect these problems during inspections or improper handling, can all lead to leaks. 3. The operating conditions do not match the design parameters: For example, if the amount of circulating acid increases and causes the flow velocity on the acid side to exceed 1.2 m/s, it becomes difficult to maintain the passivation film; the corrosion rate of the heat exchange tubes will increase significantly, and the cooler is prone to damage. 4. Operation parameters were not adjusted in a timely manner after changes in process conditions: for example, the acid temperature exceeded the designed value, or the temperature of the water entering the acid cooler was too high. 5. The startup and shutdown of the equipment are not carried out in strict accordance with the operating procedures: factors such as high-temperature sulfuric acid being introduced directly into an acid cooler that has not been pre-passivated, or the cooling water not being turned on during operation, can all lead to a shortened lifespan of the equipment or even its damage. Inspection and repair of acid cooler leaks: Acid cooler leaks are relatively easy to detect. When the pressure on the acid side is greater than that on the water side (which is the case in most field applications where pumps are used after the treatment unit), sulfuric acid can be detected using pH test strips. In daily operations, it is necessary to regularly measure the pH value on the water side, especially during the initial operation phase, when tests should be conducted at the end of each shift. When the pressure on the water side is greater than that on the acid side (as in systems where pumps are used before the treatment unit), water from the cooler will flow into the sulfuric acid at the point of leakage; if the leakage is severe, the temperature of the sulfuric acid will rise significantly and its concentration will decrease. At this time, since the tube surface at the leakage site remains in an activated state, a large current is required. The method for repairing leaks in acid coolers is essentially the same as that used for ordinary shell-and-tube heat exchangers; the usual emergency repair approach involves blocking the tubes from both sides of the tube sheet, thereby disrupting the circulation of the engine coolant within the cooler. For the pipe plugging operation, the sulfuric acid in the acid cooler should first be drained, and then the tube sheet should be washed thoroughly with large amounts of clean water; no residual acid must remain at the welding sites. The material to be used for plugging the pipes should be 316L plugs, and 316L electrodes should be used as well. The heat exchange tubes surrounding the leaky tube should also be partially welded shut. After welding is complete, start the acid pump to circulate the acid and check for any leaks at the welded areas; if leaks are present, repeat the above procedure until all leaks are eliminated. Typical acid coolers are designed with a margin of about 10%; in devices where blockages are rare, the loss in heat exchange area is not significant, and this does not have a major impact during actual use. For acid coolers with many blocked tubes, it is recommended to send them to the original supplier during the major repair period for necessary inspections and tube replacement. In summary, as a commonly used sulfuric acid cooler today, the acid chiller boasts advantages that other sulfuric acid cooling devices cannot match. It offers great operational flexibility; by understanding its characteristics, following the operating procedures strictly in daily use, and enhancing monitoring, it is entirely possible to avoid malfunctions. If faults are dealt with promptly and in an appropriate manner, production can be restored quickly, minimizing losses. :loveliness: