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Common Causes of Failures in Heat Exchange Stations and Methods to Eliminate Them 【Keywords】Heat exchange station, causes of failure, methods of elimination 【Abstract】Common causes of failures in heat exchange stations and methods to eliminate them. Due to issues in design, installation, operation, etc., certain failures that affect safe and efficient operation often occur in steam-water heat exchange station heating systems. Analyzing the causes of these failures and identifying solutions not only reduces the randomness in work and improves efficiency, but also helps to detect faults before they occur and address them promptly, ensuring the safe operation of heat exchange stations, as well as energy savings, cost reduction, and increased production and revenue. Common faults in steam-water heat exchange stations can be classified into: faults that occur easily during commissioning, faults that arise frequently during operation, and faults caused by unexpected situations. 1 Faults that commonly occur during commissioning The faults that are likely to arise during commissioning include steam-water shock in the steam pipes, damage to pressure relief valves, and blockage of traps. 1.1 Steam-water shock in steam pipes: When steam is first introduced into a steam pipe, heat exchange between the steam and the pipe walls results in the formation of some condensed water. As this condensed water moves along with the steam, it encounters obstacles, which causes fluctuations in its flow and thus leads to shock waves. As long as the condensate is drained in a timely manner, the shock will diminish quickly or not occur at all. Therefore, when steam is supplied for the first time, it is necessary to establish proper procedures for steam supply, strictly control the rate of temperature rise in the pipes, drain condensate in a timely manner, and prevent water hammer from occurring. During the steam supply process, if the condensate drain valve is unable to discharge condensate due to blockage or other reasons, steam supply should be stopped immediately, and it should be resumed only after the issue has been resolved. When a water hammer sound is heard during steam supply, steam supply should also be stopped or the drainage rate should be increased promptly; steam supply can be resumed only after the water hammer sound disappears and all the condensate has been drained. Do not close the drain valve after hearing the water hammer sound, to avoid damaging the system. 1.2 Damage to the pressure reducing valve: The pressure reducing valve is equipped with a bypass valve; this valve should be opened during operation to ensure proper preheating on both sides of the valve. Otherwise, a large temperature difference between these two sides can occur, leading to damage to the pressure reducing valve. Close the bypass valve only after normal operation is achieved. When introducing steam into the heat exchanger, be sure to preheat the pipes first; do not introduce the steam too quickly, and gradually increase the steam flow rate after the pipes have been fully preheated. 1.3 Blockage of traps: Generally, two or three sets of condensate traps are installed for the heat exchangers, along with a bypass line; valves are provided to control flow before and after the traps as well as on the bypass line. At the time of initial operation, close the valves before and after the trap and open the bypass valve to allow the condensate to flow through the bypass; once the temperature of the condensate reaches a certain level, then activate the trap. In this way, the dirt that emerges during initial operation can be drained through a bypass, preventing the water strainer from getting clogged. However, some condensate traps in heat exchangers do not have bypass pipes installed. During the initial operation, dirt such as scale can easily clog the traps, resulting in a reduced flow of condensate and thereby a decrease in the heat exchange capacity of the heat exchanger. In such cases, the traps should be cleaned promptly, and regular cleaning should also be carried out during operation. 2 Frequent faults during operation The common faults that occur during operation include insufficient heat transfer capacity, inadequate circulation flow, water hammer inside the heat exchanger, and leaks in the heat exchanger. 2.1 Insufficient heat transfer capacity of the heat exchanger The insufficient heat transfer capacity of a heat exchanger is generally caused by the following factors: an undersized unit, insufficient steam supply, poor drainage of condensate, blockages in the water circuits, air remaining inside the heat exchanger, and severe scaling within the heat exchanger. 2.1.1 Too small a selection: When there are no issues with either the circulating water system or the heating steam system, it is only possible to meet the heat exchange requirements at high steam inlet pressures, and the temperature of the condensed water discharged is high. Once the steam pressure drops, it becomes impossible to ensure the required level of heat exchange. This situation is usually caused by choosing a radiator that is too small. If the selected size is too small, the condensate discharge temperature is high, resulting in heat waste. Furthermore, normal heating cannot be ensured when the steam pressure is low; the heat exchanger should be replaced or added promptly. 2.1.2 Insufficient steam volume is manifested as an inability to maintain the heat transfer rate when the steam pressure entering the heat exchanger is low. It should be checked whether the pressure relief valve is properly adjusted. If the pressure before the pressure regulator is low and the regulator cannot be activated, the bypass valve of the pressure regulator should be opened. If the pressure in front of the main steam valve is too low, the external steam network and the steam source should be checked; once the steam pressure is resolved, the heat transfer capacity will also be ensured. 2.1.3 Poor condensate drainage: If this is caused by a clogged trap, the problem can be resolved promptly by cleaning the trap. Additionally, if the condensate pipes are designed to be too small, it can lead to poor drainage of condensate, making it difficult to adjust the heat exchange capacity. In this case, increasing the size of the condensate pipes is required to resolve the issue. 2.1.4 Waterway blockage: Characteristics include a large temperature difference between the outlet and inlet water of the heat exchanger, a large pressure difference between the inlet and outlet water, a high temperature of the condensate water, and insufficient heat transfer capacity. Blockages in the water channels result in a reduced water circulation flow rate in the heat exchanger, as well as a decrease in the heat transfer coefficient. Solutions: First, carry out backwashing; second, disassemble the heat exchanger for cleaning. The cause of blockages in the water circuits of the heat exchanger is the presence of many impurities in the outer tubes – especially in newly installed piping systems – as well as the inadequate cleaning capacity of the cleaning devices. The scrubber should be improved in a timely manner to enhance its cleaning performance, and the waste accumulated within it should be removed regularly. In addition, it is necessary to strengthen the construction management of newly built pipeline networks; during installation, any foreign objects inside the pipes must be removed, and the newly built networks should be thoroughly flushed before being connected to the main system. 2.1.5 Steam path blockage: Characteristics include a small temperature difference between the inlet and outlet water, a low temperature of the condensate water (almost equal to the inlet water temperature), but the steam pressure is not low. Solution: First, check whether the trap is clogged and whether the drainage capacity of the drain pipe meets the requirements; second, check the steam filter and the steam inlet valve. If a filter is not installed in the steam pipeline, the possibility of blockage in the heat exchanger’s steam circuit should be considered. Whether the steam circuit of the heat exchanger is blocked is related to the quality of pipe cleaning after the completion of steam pipeline construction. When the steam path of the heat exchanger is severely blocked, it should be disassembled for cleaning. 2.1.6 Air remaining in the heat exchanger – This situation can be avoided by ensuring that the air in the heat exchanger is removed at the time of initial operation, and by checking for any residual air during operation. 2.1.7 Severe scaling inside the heat exchanger: The cause of scaling in the heat exchanger is poor quality of the circulating water. The preventive measures are: first, to control the water quality of the circulating water; second, to reasonably regulate the ranges of quantity adjustment and quality adjustment; third, to strive to reduce water loss in the pipeline network. Scaling in the heat exchanger results in a low outlet water temperature and a high temperature of the condensed water discharged, thereby **reducing the efficiency of the heat exchanger**. Solutions: First, disassemble the heat exchanger for cleaning; second, perform chemical cleaning on the heat exchanger. 2.2 Insufficient circulating water flow: If the number of heating users keeps increasing while the pumps remain the same, it will result in insufficient circulating water flow in the system; in such cases, the circulation pumps should be replaced or more pumps should be used. Insufficient circulating water flow is indicated by a large temperature difference between the supply water and return water. It is primarily necessary to check whether there is air accumulation or blockage inside the pump, as well as whether the impeller is worn or if there are any other issues that affect the pump’s performance. The inlet and outlet valves of the circulation pump, the check valve on the bypass pressure relief pipe of the circulation pump, as well as the strainer, etc., should be inspected. A clogged strainer (excessive pressure difference before and after the strainer) will result in too low pressure at the inlet of the circulation pump, or even a vacuum condition, which affects the flow rate of the circulating water. If the pump inlet pipe remains empty even after the strainer has been cleaned, it is usually due to an insufficient flow capacity of the strainer; in such cases, the strainer should be modified to increase its flow capacity. 2.3 Water hammer in heat exchangers Water hammer in heat exchangers is generally caused by an excessively high level of condensate water inside the heat exchanger. This can generally be resolved by increasing the amount of condensate discharged. The steam can also be paused, the condensate drained, and then steam supplied again. 2.4 Heat exchanger leakage Heat exchanger leakage is divided into external leakage and internal leakage. External leaks are easy to detect; appropriate countermeasures can be taken based on the cause of the leak. If there is an internal leak in the heat exchanger, there is usually a water hammer sound inside the heat exchanger, and the amount of condensate water increases significantly; even after the steam supply is stopped, the condensate continues to flow out. In such cases, the heat exchanger needs to be disassembled for repair. 3 Emergency situations: The main emergency situations include sudden power outages, sudden shutdown of circulation pumps, and sudden loss of pressure in the pipeline network. 3.1 Sudden power outage: The main measure is to close the steam valve promptly to prevent steam from flowing and causing heating. If the steam valve does not close properly, the condensate valve should be closed to prevent heating from occurring on the steam side. And close the inlet and outlet valves of the heat exchanger to prevent vaporization-induced water hammer. Then further measures can be taken to address the issue of poor sealing of the steam valve. 3.2 Sudden shutdown of the circulation pump: In the event of a sudden shutdown of the circulation pump, the backup circulation pump should be started promptly. If it is not ready, the steam supply should be stopped first; once the standby pump is operating properly, then the steam supply can be resumed. The circulation pump that stopped operating suddenly cannot be started immediately without identifying the cause, to avoid damaging the equipment. When multiple circulation pumps operate together, it is not easy to detect if one of them suddenly stops working. Therefore, it is necessary to identify the range of pressure fluctuations, conduct regular inspections, and always pay attention to any changes in system pressure and temperature. Setting high and low water pressure alarms is beneficial for safe operation. 3.3 Sudden loss of pressure in the pipeline network: In the event of a sudden loss of pressure in the heating pipeline network, the steam valve should be closed first, and at the same time the circulation water pump should be stopped. While sending people to check the external network, the method of using supply and return water bags for sectional pressure testing is employed to identify the leaking branch; thereafter, the other branches are put into operation, and the leak location is located and addressed promptly. After a malfunction occurs at the heat exchange station, it is first necessary to observe carefully and analyze the situation in order to determine the cause of the fault. Only after being confident of the diagnosis should measures be taken to resolve the issue. It is important to consider all relevant factors thoroughly in order to identify the key issues, and avoid drawing premature or incorrect conclusions, which could result in wasted resources in terms of manpower, materials, and time.