Technical issue of long heating time in heat exchangers

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Dear experts in this industry, I’ve run into a problem with heat exchangers recently and would like to share it with you all for discussion. I hope you can help identify the cause and offer some suggestions. Thank you! The heat exchanger is a spiral-wound tube heat exchanger (brand: Shandong Nuowei, NERVE), used to heat circulating water with steam; this circulating water is then used for cleaning containers. Specific operating parameters: Heat source: 0.6 MPa saturated steam; Cooling medium: pure water at 25°C, heated to 88°C. Requirements: The total amount of water is 30 t, with a circulation rate of 100 t/h; the heating process is designed to reach the specified temperature within 1.5 hours. Problem description: It can be heated to over 70 degrees in about 1 hour, while it takes 2–3 hours to raise the temperature from over 70 degrees to 88°C. The heating time at higher temperatures is too long – 2 hours longer than designed – and the actual maximum heating temperature reaches 86°C. Problem troubleshooting: 1. The technologies of both parties have been used to thoroughly review the initial design, and both the heat exchange area and flow rate meet the requirements of the operating conditions ； 2. During normal production, the requirements can be fully met, and the overall heat load is no problem ； 3. The installation method has been verified to be correct: steam enters from above and exits from below, while circulating water enters from below and exits from above; vertical installation ； 4. The heat source and interface pipe sizes are satisfactory and meet the requirements ； 5. The total water volume should be added at 30t, so that the circulation volume meets the requirements ； 6. The circulating water is fresh water ； Empty the pipeline before heating ； 7. The circulating water is purified water, so there is no issue of scale formation that could reduce heat exchange efficiency; moreover, it is cleaned after each use, which eliminates the risks of scale formation and blockages. 8. During normal production, the bypass valve of the steam trap is in a slightly open state. 9. The heating time required the first time to reach the specified temperature is 3.5 hours, while it takes a little over two hours for the second heating cycle to reach the same temperature; this basically rules out any issues with the equipment. An overview shows that steam traps play a role in preventing steam from entering and draining water in steam heating systems; by selecting the appropriate steam trap, steam heating equipment can achieve its highest efficiency. To achieve the most optimal results, it is necessary to have a comprehensive understanding of the operating performance and characteristics of various types of steam traps. For a steam trap to function as a vapor barrier and water drain, it must be able to “identify” steam from condensed water. “The detection of steam and condensate is based on three principles: density difference, temperature difference, and phase change. Thus, three types of steam traps were manufactured based on three principles: they are classified as mechanical, thermostatic, and thermodynamic types. Working principle: The steam trap is installed between the steam heating equipment and the condensate return header. When turned on, the barrel is at the bottom and the valve is fully open. After entering the steam trap, the condensate flows to the bottom of the tank, filling the valve body and submerging it entirely; thereafter, the condensate is discharged to the return water header through the fully open valve. Steam also enters the steam trap from the bottom of the tank, occupying the upper part of the tank and creating buoyancy. The barrel slowly rises, moving the lever gradually toward the valve seat until the valve is completely closed. Air and carbon dioxide gas gather at the top of the steam trap through the exhaust holes in the barrel. The steam discharged from the vent holes condenses due to the heat dissipation by the steam trap. When the incoming condensed water begins to fill the tank, the tank starts to exert a pulling force on the lever. As the condensation level continues to rise, the force generated increases until it is sufficient to overcome the pressure difference and open the valve. As the steam trap valve begins to open, the pressure difference acting on the valve disc decreases. The tank body will drop rapidly, causing the valve to open fully. The non-condensable gases accumulated at the top of the steam trap are discharged first, followed by the condensed water. As the water flows out of the tank, it carries the dirt with it and exits through the drain valve. As the condensate is discharged, steam begins to flow back into the steam trap, and a new cycle starts. Devices that use and utilize steam only require steam. Condensate water is inevitably generated within such equipment; this condensate becomes a harmful fluid, and it also contains air and other non-condensable gases, which are responsible for causing malfunctions and reducing the performance of the equipment. Under such circumstances, the most important functions of a steam trap are as follows: (1) it can quickly remove the condensed water that is generated. (2) Prevent steam leakage. (3) Remove air and other non-condensable gases. After discussing it with the client, almost all aspects have been taken into account. Fortunately, there is no impact during operation now; it was just that the heating time at the beginning was too long. However, out of a sense of responsibility towards our customers and to avoid such situations in the future, I would appreciate it if someone could offer some advice. Thank you!