Heat Exchanger Problem Analysis and Solution

The frequent operation troubles of water-to-water heat exchanger include the following

Phenomenon
The temperature of hot fluid outlet is 1.1 or more times as high as the temperature of cold fluid outlet.
Reason
Because of the scale deposit, the thermal resistance is increasing. The way to solve the problem is to wash out the deposit.
Case
A 10 years old heat supply system covers 4×10 m, and has the heat supply capability of 2.8 MW. In 2005, the system bumped into the problem that the primary side liquid valve is completely opened, and the speed control is invalid. This moment, the system had the related operational parameters include the liquid inlet temperature of 70℃, liquid outlet temperature of 65 oC, secondary liquid inlet temperature of 42℃, secondary liquid outlet temperature of 45℃.

For contrast, at the same time, another system in the same district in normal operation had the related parameters, including the liquid inlet temperature of 70℃, liquid outlet temperature of 44 oC, secondary liquid inlet temperature of 41℃, secondary liquid outlet temperature of 48℃. Its side liquid valve is not fully opened.

The maintenance worker disassembled the problem heater, and washed out the 1mm thick mud or scale deposit upon the plate to get the problem solved. The operation parameters of the recovered system are as follows, the primary liquid inlet temperature is 70℃,and outlet temperature is 45 oC, the secondary side liquid inlet temperature is 41℃, and the outlet temperature is 49℃。

Phenomenon
The temperature of hot fluid outlet is approaching to the temperature of cold fluid outlet, and both them are too low.
Reason
The problem is caused by the blockage inside the heat transfer device or the gas blockage in water inlet pipe. The way to solve is to check the device regularly, and discharge the gas regularly by using the air evacuation valve.
Case
The heat exchange station of one government office building in normal operation has the working parameters including primary inlet temperature of 70℃, outlet temperature of 45℃, secondary inlet temperature of 41℃, and outlet temperature of 49℃.It bumped into the problem described above, and showed the working parameters of primary inlet temperature of 70℃, outlet temperature of 32℃, secondary inlet temperature of 28℃ and outlet temperature of 33℃.

When the attendants disassembled the equipment, they found the flow channels are blocked by foreign matters. After they cleaned the equipment, the system got back to normal operation again, and all the parameters returned to normal.

The Guangchuan heat exchange station also bumped into the problem like above. After cleaning the heat exchanger and dirt separator, the system did not get back to normal operation. Till the maintainers found a “ r ” type curve during the path of liquid flow, they take measures to discharge the gas inside the fluid channels. After the air discharging for 15 minutes, the water temperature got back to the required level.

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