Daily use, management, and troubleshooting of shell-and-tube heat exchangers

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Daily use, management, and troubleshooting of shell-and-tube heat exchangers. Daily use, management, and troubleshooting of shell-and-tube heat exchangers. I. Use of shell-and-tube heat exchangers: 1. During the start-up and shutdown of the equipment, the heat exchanger should be heated and cooled gradually to avoid excessive pressure differences and thermal shock. Additionally, when shutting down, the principle of \"heat first, then cold\" should be followed, that is, the hot medium should be removed first, followed by the cold medium； At startup, it follows the principle of \"cool first, then heat\", that is, the cold medium is introduced first, followed by the hot medium. 2. Carefully check the equipment’s operating parameters; overheating and overpressure are strictly prohibited. For heat exchangers with a differential pressure design, the specified pressure difference must not be exceeded during operation. 3. Operators must strictly adhere to safety operating procedures, and conduct regular inspections of the heat exchange equipment to check the stability of the foundation supports as well as for any leaks in the equipment. 4. The temperatures and pressure drops of the fluids in the tube side and shell side should be checked regularly to analyze any leaks or scaling in the heat exchanger. When the pressure drop increases and the heat transfer coefficient decreases beyond a certain value, effective cleaning methods should be selected based on the medium and the structure of the heat exchanger. 5. The vibration of the heat exchanger should be checked regularly. II. Routine inspections 1. The purpose of routine inspections is to identify any problems or potential hazards in the equipment in a timely manner, so that appropriate preventive and corrective actions can be taken to avoid equipment failures. 2. The inspection includes checking for any leaks in the equipment, as well as whether the insulation is in good condition. Check whether there is any obvious deformation in the areas without insulation or cooling equipment, and whether the foundation or supports are in good condition. 3. Check whether parameters such as temperature, flow rate, and pressure of the on-site instruments are normal, and whether the equipment is experiencing overheating or overpressure. 4. Use devices such as listening rods to determine whether there are any abnormal noises from the equipment, and verify whether there is any friction or vibration among the heat exchangers inside it. 5. Routine inspection -- Temperature: ① The changes in the temperature at the inlet and outlet of the heat exchanger directly reflect changes in its heat exchange capacity. The flow rates and temperatures at the inlet and outlet of the heat exchanger should be measured regularly. When the heat transfer capacity becomes too low to meet the process requirements, it is necessary to improve this capacity through mechanical or chemical cleaning in order to satisfy and maintain the needs of the process operation. ②When water is used as the cooling medium, its outlet temperature should ideally be kept at 50°C, as temperatures above 50°C can cause corrosion of the pipes and severe scaling in the heat exchanger, thereby affecting its heat exchange efficiency; therefore, the outlet water temperature should not exceed 65°C. 6. Routine inspections – Circulating cooling water: ① For circulating cooling water, it is necessary to regularly test its quality to ensure that it meets the standards specified in GB/T 50050-2017 \"Quality standards for circulating cooling water\". When the water quality does not meet these standards, it should be treated using the methods outlined in the \"Design specifications for industrial circulating cooling water treatment\" standard. 7. Routine inspection – Pressure: ① By checking the pressure difference, it is possible to determine whether the heat exchanger is fouled, whether there is throttling due to blockages, and whether there are any leaks. ②During operational procedures, if a sudden change in pressure is detected, whether it increases or decreases, in addition to checking the heat exchanger itself, it is also necessary to examine other pipes, flanges within the system, as well as the machinery used for transporting the fluid medium. By considering the influence of various factors on the system, the cause of this change should be identified as quickly as possible. 8. Routine inspections — Heat exchangers whose operating temperature for heat retention or insulation is significantly higher or lower than the ambient temperature require such measures; the integrity of the heat retention or insulation layer directly affects the heat transfer performance of the heat exchanger. If the insulation or heat-insulating layer is damaged, moisture will accumulate on the outside of the casing, causing localized corrosion of it; therefore, any damage detected should be repaired promptly. III. Causes of Failures in Shell-and-Tube Heat Exchangers and Corresponding Solutions
1. Interpenetration of the two media (internal leakage):
Causes:
① Corrosion, perforation, or cracking of the heat exchange tubes.
② Cracking at the joints between the heat exchange tubes and the tube sheet.
③ Leakage in the seal of the floating head flange in floating-head heat exchangers.
Solutions:
① Replace or plug the leaking heat exchange tubes.
② Re-seal the joints by welding or plugging them.
③ Replace the sealing gaskets.

2. Sealing leakage at the flanges:
Causes:
① Insufficient pressure resistance, corrosion, or deterioration of the gaskets.
② Insufficient strength, looseness, or corrosion of the bolts.
③ Insufficient rigidity of the flanges and defects in the sealing surfaces.
④ Misalignment or improper fitting of the flanges.
⑤ Poor quality of the gaskets.
Solutions:
① Tighten the bolts and replace the gaskets.
② Upgrade the material of the bolts, tighten them, or replace them.
③ Replace the flanges or address the existing defects.
④ Realign the flanges or replace them.
⑤ Replace the gaskets.

3. Poor heat transfer efficiency:
Causes:
① Scaling on the heat exchange tubes.
② Poor water quality, excessive oil contamination, and microbial growth.
③ Short circuits in the partition plates.
Solutions:
① Use chemical cleaning or jet cleaning to remove scale.
② Improve filtration, purify the fluid, and better manage water quality.
③ Replace the gaskets in the tube box or replace the partition plates if the resistance increase exceeds acceptable levels.
Causes:
① Failed filters.
② Scaling inside and outside the shell and tubes.
Solutions:
① Clean or replace the filters.
② Use jet cleaning or chemical methods to remove scale.

4. Severe vibration:
Causes:
① Resonance caused by the frequency of the fluid.
② Resonance induced by vibrations in external pipes.
Solutions:
① Change the flow rate or alter the natural frequency of the tube bundle.
② Strengthen the pipes to reduce vibration