Common Faults of Heat Exchanger and A Complete Collection of Fault Clearance Methods
The temperature difference and differential pressure between water outlet and water inlet of the heat exchanger are large, the condensate temperature is high and the heat exchange amount is insufficient. Water line block will lead to reduced water circulation flow of the heat exchanger, decreased coefficient of heat transfer, etc.. How to settle these faults? Let’s learn together today.
I. Faults easily occurred in commissioning
1. Steam and water impact in the steam pipeline
In the initial stage of steam delivery of the steam pipeline, the steam conducts heat transfer with the pipeline shell to generate some condensed water, which will meet resistance when moving ahead with the steam, generate fluctuation and form impact. As long as the condensed water is discharged in time, the impact will decrease soon or not be formed. Therefore, the steam delivery regulations should be carefully formulated in the initial stage of the delivery, the temperature rise speed of the pipeline should be strictly controlled, the condensed water should be discharged in time, and water hammer should be completely eradicated. In the process of steam delivery, if the condensate drain valve cannot discharge condensed water due to blockage or other factors, steam delivery should be immediately stopped and only restarted until the problem is settled. When the water hammer sound is heard in the process of steam delivery, steam delivery should also be stopped, or water discharge should be quickly increased, and steam delivery can only be restarted until the water hammer sound is eliminated and the condensed water is completely discharged. Be sure not to shut down the drain valve after the water hammer sound is heard, so as not to cause system damage.
2. Damage of pressure reducing valve
The pressure reducing valve is equipped with a by-pass, and the by-pass valve should be opened in commissioning, so that the reducing valve can be fully preheated, otherwise, the reducing valve will have overly large temperature difference and be damaged. The by-pass valve should be closed until the commissioning is normal. Be sure to remember that the pipeline should be preheated at first when steam is delivered to the heat exchanger, the steaming can not be excessively fast, and the steam flow should be gradually increased after sufficient preheating.
3.Blockage of steam traps
Generally, two or three sets of heat exchanger condensate steam traps will be deployed, and a bypass will be installed. Valve control will be set in front and back of the traps and in the bypass. In initial commissioning, the valves in front and back of the traps should be closed, and the bypass valve be opened, so that the condensed water passes through the bypass. The traps should be put into operation after the condensate temperature reaches a certain value, in this way, the dirts washed out in initial commissioning can be drained away through the bypass, so as to prevent blockage of the traps. However, the condensate traps of some heat exchangers are not equipped with bypass pipes, thus blockage of steam traps is easily caused by dirts such as incrustation in initial commissioning, resulting in the reduction of condensate water flux and the decrease of heat exchange amount of the heat exchanger, in such a case, the traps should be cleaned in time, and cleaned regularly in operation.
II. Faults easily occurred in operation
1. Insufficient heat exchange amount of the heat exchanger
Insufficient heat exchange amount is generally caused by the following factors: undersize model selection, insufficient steam quantity, obstructed drainage of condensate water, waterway blockage, unexhausted air and severe scaling in the heat exchanger, etc..
1) Undersize model selection
If the circulating water process and the heating steam process operate normally, the requirement of heat exchange amount can only be met when the initial steam pressure is high, the discharge temperature of the condensate water is high, and once the steam pressure lowers, the heat exchange amount cannot be guaranteed, then generally the model selection of the heat exchanger is undersize. Undersize model selection will lead to high condensate discharge temperature and waste of heat, besides, normal heat supply cannot be guaranteed when steam pressure is low, hence, in this case, the heat exchanger should be replaced or supplemented.
2)Insufficient steam quantity
Insufficient steam quantity is manifested as the heat exchange amount can not be guaranteed when the initial steam pressure of the heat exchanger is low. Whether the reducing valve is correctly adjusted should be checked. If the upstream pressure of the reducing valve is low, and the valve can not start, the by-pass valve of the reducing valve should be opened. If the upstream pressure of the main steam valve is excessive low, the outer steam network and the steam source should be checked. As long as the steam pressure is kept normal, the heat exchange amount can be guaranteed.
3)Obstructed drainage of condensate water
If the obstructed drainage is caused by blockage of the traps, then the problem can be solved timely as long as the traps are cleaned. In addition, obstructed drainage can also occur if the condensate pipeline is designed undersize, thus causing difficulties in the adjustment of the heat exchange amount. In this case, the condensate pipeline should be enlarged.
4)Waterway blockage
Waterway blockage has the following characteristics: the temperature difference between water inlet and water outlet of the heat exchanger is large, the condensed water temperature is high, and the heat exchange amount is insufficient. Waterway blockage will lead to reduced water circulating flow of the heat exchanger and decreased heat transfer coefficient. The treatment methods include back washing and cleaning in the case of disassembled heat exchanger. Waterway blockage is caused by excessive impurities in the outer pipeline network especially the newly built pipeline network as well as the poor removing ability of the dirt separator. The solution is that the dirt separator should be modified in time to improve the decontamination performance, and dirts in the dirt separator should be discharged regularly. In addition, the construction management of the new pipe network should be strengthened, foreign bodies in the pipeline should be cleaned up during installation, and the new pipe network should be rinsed thoroughly and then combined for installation.
5)Steam way blockage
Steam way blockage has the following characteristics: the temperature difference between water inlet and water outlet is small, the condensate temperature is low (almost the same with water inlet temperature), but the steam pressure is not low. The treatment methods are as follows: firstly check whether the traps are blocked and whether the water drainage amount of the drain pipeline meets requirement; secondly check the steam filter and the steam inlet valve. If no filter is set in the steam pipeline, consider the possibility of steam way blockage of the heat exchanger. Steam way blockage of the heat exchanger may be related to the quality of pipeline cleaning after the construction of the steam pipeline. The heat exchanger should be disassembled for cleaning in the case of severe steam way blockage.
6)Unexhausted air in the heat exchanger
Such case can be avoided as long as air in the heat exchanger is exhausted during initial commissioning, and air exhaust is checked in operation.
7)Severe scaling in the heat exchanger
The reason for scaling in the heat exchanger is bad quality of the circulating water.
The precautionary measures are as follows: first, control the quality of circulating water; second, reasonably control the range of quantity regulation and qualitative regulation; third, try to reduce water loss in the pipeline network. Scaling in the heat exchanger will lead to low outlet water temperature, high condensate discharge temperature and greatly decreased efficiency of the heat exchanger. The treatment methods are as follows: first, disassemble the heat exchanger for cleaning; second, carry out chemical cleaning on the heat exchanger.
2. Insufficient circulating water flow
If the number of heating users continues to increase, and the water pumps remain unchanged, the circulating water flow in the system will be insufficient, in this case, the circulating pumps should be replaced or the number of circulating pumps in operation should be increased. Insufficient circulating water flow is manifested as overly large temperature difference between water supply and backwater. Primarily, whether air accumulating or blockage occurs in the pump, whether the impeller is worn or whether there are other faults that affect the pump performance should be checked. Besides, the inlet and outlet valves of the circulating pumps, the check valve of the bypass relief vent and the dirt separator should be checked. Dirt separator blockage (excessive pressure difference between front and back of the dirt separator) will cause excessive low inlet pressure of the circulating pump and even pumping out, thus affecting the circulating water flow. If the inlet pipe of the pump still pumps out after the dirt separator is cleaned up, generally the excess flow of the dirt separator is designed insufficient. In this case, the dirt separator should be modified and the excess flow be increased.
3. Water hammer in the heat exchanger
Water hammer in the heat exchanger is generally caused by overly high level of condensed water in the heat exchanger, which in most cases can be solved by increasing the discharge of condensed water, besides, steam can be stopped until the condensed water is discharged.
4. Leakage of the heat exchanger
Leakage of the heat exchanger can be divided into outside leakage and inner leakage. Outside leakage can be easily detected and handled by taking corresponding countermeasures according to the cause of leakage. If the heat exchanger has an inner leakage, generally there will be the sound of water hammer in the heat exchanger, the condensed water volume will sharply increase, and the condensate water discharge will not stop after the steam is stopped. In this case, the heat exchanger should be disassembled for repair.
Ⅲ Emergencies
1.Sudden power failure
The main treatment measure is to close the steam valve timely, so that the steam cannot be circulated or heated. If the steam valve is not closed tightly, the condensate valve should be closed to prevent circulating and heating of the steam side, besides, the inlet and outlet valves of the heat exchanger should be closed to prevent vaporization and water hammer. Further on, other measures should be taken to solve the problem of not tightly closed steam valve.
2.Sudden outage of the circulating pump
The stand-by circulating pump should be started in time in the case of sudden outage of the circulating pump. If preparation has not yet been made, the steam should be stopped first and restarted until the stand-by pump is brought into normal operation. The suddenly outaged circulating pump can not be started immediately before the cause is identified, so as not to cause equipment damage. In the combination operation of multiple circulating pumps, sudden outage of one of the pumps can not be easily detected. Therefore, the range of pressure fluctuation should be marked, inspection and examination should be made diligently, and attention should be paid to the fluctuation of system pressure and temperature at any time. In addition, the setting of high and low water pressure alarm is beneficial to safe operation.
3.Sudden pressure loss of the pipeline network
In the case of sudden pressure loss of the pipeline network, the steam valve should be closed first and meanwhile the circulating water pump should be stopped. Besides, personnel concerned should be designated to check the outer network, meanwhile, the branch with water leakage should be determined by the method of branch pressure test via water supply and backwater bags. Then other branches should be put into operation, and the water leakage points should be detected out and processed in time. After the failure of the heat exchange station, first the fault cause should be found out by careful observation and analytical judgment, and then the troubleshooting measures should be taken with confidence in success. Various influencing factors should be turned over to find out where the shoe pinches. Don’t make specious conclusion untimely, so as not to cause the waste of manpower, material resources and time.
