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25
2018
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06
Instructions for Using Tube Coolers
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Summary:
1. Overview: Tube coolers are heat exchange devices widely used in industrial sectors such as metallurgy, chemical engineering, machinery, energy, transportation, light industry, and food. They are suitable for various conditions including cooling, condensing, heating, evaporating, and waste heat recovery. Due to their robust structure, high elasticity, and strong adaptability, significant improvements have been made in terms of structure, process, and materials in recent years, making their technical performance more reasonable and advanced. Therefore, among the many types of heat exchangers, tube heat exchangers still hold a significant position.
1. Overview
The tube-type cooler is a heat exchange device widely used in industrial sectors such as metallurgy, chemical engineering, machinery, energy, transportation, light industry, and food. It is suitable for various conditions such as cooling, condensing, heating, evaporation, and waste heat recovery. Due to its robust structure, high elasticity, and strong adaptability, significant improvements have been made in its structure, process, and materials in recent years, making its technical performance more reasonable and advanced. Therefore, among the many types of heat exchangers, tube heat exchangers still hold an important position.
2. Structure and Working Principle
The tube-type cooler consists of two main parts: the external shell and the internal cooling body. Due to different structural forms, it can be classified into threaded and flanged types based on external connection forms; horizontal and vertical types based on installation forms; floating plate and floating head types based on floating forms; coiled and finned tube types based on cooling tube structures; and various structural forms such as arc baffle plates, rectangular baffle plates, double weir baffle plates, and circular baffle plates based on flow diversion structures, all selected according to specific conditions.
The external shell includes: the cylinder, water distribution cover, and return water cover. It is equipped with oil inlet and outlet pipes, water inlet and outlet pipes, and additional features such as oil, water, and air discharge plugs, zinc rod installation holes, and thermometer interfaces.
The cooling body consists of cooling tubes, fixed hole plates, movable hole plates, and baffle plates. The two ends of the cooling tubes are connected to the fixed and movable hole plates; the fixed hole plate is connected to the external flange, and the movable hole plate can freely expand and contract within the external body to eliminate the impact of temperature changes on the cooling tubes due to thermal expansion and contraction. The baffle plates enhance heat transfer and support the cooling tubes.
The heat medium in the tube-type cooler enters through the inlet on the cylinder, flowing sequentially through various flow diversion channels to the outlet. The cooling medium flows in a double-pipe arrangement, meaning the cooling medium enters half of the cooling tubes from the water inlet through the water distribution cover, then flows into the other half of the cooling tubes from the return water cover to the other side's water distribution cover and outlet. During the double-pipe flow process, the cooling medium absorbs the residual heat released by the heat medium and discharges it from the outlet, maintaining the working medium at the rated working temperature.
3. Use and Operation
1. The foundation of the cooler must be sufficient to prevent the equipment from sinking. There should be enough space at the end of the fixed hole plate cover to allow for the extraction of the tube bundle from the shell. When positioning the equipment, it should be done according to hoisting specifications, and after leveling, the anchor bolts should be tightened, and the inlet and outlet pipes for hot and cold media should be connected.
2. Before starting the cooler, all air in the chamber should be released to improve heat transfer efficiency. The steps are as follows:
(1) Loosen the air release plugs at the hot and cold media ends and close the media discharge valve;
(2) Slowly open the water inlet valves for the hot and cold media until the hot and cold media overflow from the air release holes, then tighten the air release plugs and close the water inlet valves.
3. When the water temperature rises by 5 to 10°C, open the water inlet valve for the cooling medium (Note: Do not open the water inlet valve quickly, as a large flow of cooling water through the cooler can cause a poorly conductive 'subcooled layer' to form on the heat exchanger surface over time), then open the inlet and outlet valves for the heat medium to allow it to flow, and adjust the flow rate of the cooling medium to maintain the heat medium at the optimal operating temperature.
4. If electrochemical corrosion occurs on the cooling water side, zinc rods can be installed at designated locations.
5. A filtration device should be installed before the cooler for relatively dirty media.
6. The pressure of the medium being cooled should be greater than that of the cooling medium.
4. Maintenance and Repair
1. After long-term operation, the surface of the cooling tubes may accumulate scale, increasing thermal resistance and flow resistance, gradually reducing heat exchange performance and failing to meet cooling requirements. Clearly, the focus of maintenance should be on cleaning the dirt. Here are several cleaning methods:
(1) Mechanical Method
a. Use an electric pipe cleaning tool. This involves a motor driving a flexible shaft to rotate, with a nylon or steel wire brush attached to the end for cleaning, while water is injected around the shaft through a waterproof cover to wash away loose dirt in a timely manner.
b. Use a round pipe with a steel wire brush welded to one end, similar in diameter to the inner diameter of the pipe, rotating and pushing it forward. Dirt can accumulate in the inner cavity of the pipe without thickening, making it easier to push through. This method is commonly used but requires significant labor.
(2) Use a high-pressure pump (pressure 10-20 MPa) to spray high-pressure water for flushing, which is effective and mainly used for cleaning between pipes.
(3) Use sponge balls for automatic cleaning inside the heat exchange tubes. Different hardness sponge balls can be used depending on the type of scale. For special hard scale, a 'strip' type diamond sand sponge ball can be used. The sponge ball, being soft and elastic, enters the heat exchange tube, compresses against the inner wall, and creates relative motion with the tube wall, continuously rubbing against it to remove deposits.
(4) Chemical Cleaning Method:
a. For cleaning the oil side, trichloroethylene solution can be used for reverse circulation cleaning, with the solution pressure not exceeding the rated working pressure. The cleaning time depends on the dirt condition, followed by flushing with clean water until the outflowing water is clean.
b. Soak in carbon tetrachloride. Fill the cooler with the solution and observe the color after 15-20 minutes. If it is severely corroded, replace it with new liquid and soak again until the outflowing solution is similar in color to clean water, then rinse repeatedly with clean water. This cleaning should be done in a well-ventilated environment to avoid poisoning. This method is suitable for oil cleaning.
2. Most failures of the cooler are caused by the cooling tubes. Due to corrosion, cavitation, and wear, the tube walls may thin and perforate, and due to thermal expansion and contraction, vibrations during fluid movement can cause mechanical damage at connections and elsewhere. When the cooling tubes are damaged, the two media will intermix, and timely repairs should be made. The methods include:
(1) Identify the damaged cooling pipes and seal both ends with pipe plugs. The taper of the pipe plug should be between 3 to 5 degrees, and the hardness of the pipe plug material should be less than or equal to the hardness of the pipe. The total number of sealed pipes must not exceed 10% of the total number.
(2) Remove the damaged pipe and replace it with a new one, then re-expand it.
(3) If there is leakage at the connection between the pipe end and the tube sheet, it should be re-expanded. If corrosion is severe, the tube bundle should be replaced.
3. The cooler that is not in use during winter should have all internal media drained to prevent freezing and cracking of the equipment.
4. The disassembly and reassembly of the cooler should be carried out according to the following steps:
(1) Close the oil and water valves, drain the retained media, and then remove the cooler from the system.
(2) Remove the return water cover and the water distribution cover, and check the sealing rings, damage to the cooling pipes, and accumulation of dirt. If only pipe plugging or replacement of cooling pipes is needed, it can be done immediately. If the cooling tube bundle needs to be removed, it must be pulled out from the direction of the fixed tube sheet (for large coolers, it can be done vertically with the fixed tube sheet facing down, and then use lifting equipment to lift the shell to expose the tube bundle).
(3) During assembly, follow the reverse process of disassembly, and the sealing rings should generally be replaced with new ones.
(4) After installation, separate air-tightness tests should be conducted on the oil side and then the water side, with the test pressure being greater than 1.2 times the actual working pressure.
5. Faults and Troubleshooting
Decreased heat exchange performance
1. Faults and Causes
(1) Insufficient cooling water flow;
(2) Accumulation of gas in the chamber;
(3) Accumulation of dirt on the heat exchange tube wall increases flow resistance and thermal resistance;
(4) Oil floating in the machine oil or a mixture of oil and cooling water;
(5) Leakage at the flange connection between the return water cover and the water distribution cover;
(6) Corrosion at the connection between the dynamic and static hole plates and the heat exchange tube, leading to loss of sealing.
2. Troubleshooting Methods
(1) Faults and Causes
① Open the inlet valve wider;
② Clear blocked pipelines, valves, filters, or heat exchange tubes;
(2) Unscrew the plug to release air;
(3) Use appropriate methods to clean the dirt on the inner and outer surfaces of the heat exchange tube;
(4) ① Replace the heat exchange tube;
② Use pipe plugs to seal damaged pipes (not exceeding 10%);
(5) ① Tighten the screws on both end caps;
② Replace the sealing gasket;
(6) Replace the tube bundle.
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Specializing in the research, development, production and sales, equipment consulting, maintenance, and accessory services of heat exchange technology, equipment, and systems, and undertaking the design and installation of thermal system engineering, energy conservation and emission reduction, and energy conservation and emission reduction system engineering.
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