Double-effect heat exchanger water hammer in hydrochloric acid
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Due to space constraints, a horizontal double-effect heat exchanger is installed behind the hydrochloric acid separation tower; the cold fluid, which is 31% hydrochloric acid, flows through the tube side, entering from the top and exiting from the bottom, with a pressure of around 5 barg in the tube side； The hot material flows through the shell side as well, from top to bottom, with counterflow heat exchange; the pressure in the shell side is approximately 1 barg ； When the temperature of the distillation tower exceeds 110°C, water hammer noises begin to be heard inside the heat exchanger; the heat exchanger had already been depressurized before starting up. Currently, my personal analysis is that during the counter-current heat exchange process, the temperature of the cold fluid gradually rises along the tube side. Near the inlet of the hot fluid, there is a significant local temperature increase (theoretically, the outlet temperature on the tube side should be around 80°C). This leads to water hammer after vaporization. However, at a pressure of 5 barg, vaporization cannot occur at this temperature ； Can the experts analyze whether there are any other reasons?
The water hammer phenomenon is usually caused by sudden changes in pressure and temperature within the fluid, even when degassing has been carried out during actual operation. Based on your description, although the theoretical boiling point of hydrochloric acid at a pressure of 5 barg is much higher than 80°C, local overheating may occur within the heat exchanger, causing the actual temperature in certain areas to exceed this theoretical boiling point. This leads to localized vaporization and the formation of water hammer. Furthermore, sudden changes in flow rate can also cause water hammer. When the temperature of the Analysis tower rises to 110°C, the flow characteristics of the hot and cold fluids within the heat exchanger may change, especially when the heat exchanger is of horizontal design, as the fluid flow paths and the effect of gravity can exacerbate these changes. It is recommended to check the following aspects: 1. Whether the design and installation of the heat exchanger take into account the physical effects under different operating conditions, including sudden changes in temperature difference, pressure, and flow velocity. 2. Verify that all temperature and pressure monitoring devices are in good condition to ensure accurate reading of operational data. 3. Check the operating temperature of the absorption tower and the temperature of the hot and cold media at the heat exchanger inlet to determine if there are any abnormal high temperatures or rapid temperature increases. 4. Consider whether it is necessary to modify the heat exchanger or adjust its operating parameters, such as changing the flow rate or optimizing the inlet and outlet arrangements, in order to reduce the risk of water hammer. In summary, regarding the water hammer problem, it is necessary to comprehensively consider the effects of equipment design, operating parameters, and physical conditions, and make adjustments and optimizations based on actual circumstances. .
The water hammer phenomenon is often caused by vaporization and rapid condensation within the fluid, which usually occurs when the fluid temperature is near or above its boiling point. Although the boiling point of hydrochloric acid at a pressure of 5 barg is above 80°C (according to its physical properties), it theoretically should not vaporize under such conditions; however, in practice several factors may lead to water hammer: 1. **Local overheating**: Even though the overall temperature is kept at 80°C, local overheating may occur in certain areas of the pipe due to uneven heat transfer, causing hydrochloric acid to vaporize and form bubbles. 2. **Hydrodynamic changes**: A sudden change in the fluid velocity or a abrupt shift in the flow direction within the heat exchanger can also trigger water hammer. 3. **Temperature monitoring and control system errors**: In actual operation, there may be deviations in temperature measurement and control, resulting in the actual temperature exceeding the set value. It is recommended to further examine the temperature distribution of the heat exchanger to determine whether there are any local hot spots, and also to check the accuracy and response time of the temperature sensors to ensure the reliability of the temperature control system. Furthermore, optimizing the flow velocity and direction of the fluid can also be considered to reduce hydrodynamic impacts, thereby lowering the risk of water hammer. .