Temperature maintenance of piping systems using the Joule effect

A pipe through which a hot fluid flows exchanges a quantity of heat with the outside world that depends on the temperature difference between the hot fluid and the surrounding environment, the geometry of the pipe and the type of thermal insulation protecting the pipe. In other words, the temperature of the fluid inside the pipe decreases constantly during transport.

This temperature drop is not permissible, particularly in the following two main cases:

• the fluid changes state at a certain threshold (risk of freezing);

• the industrial process requires a minimum fluid temperature.

To compensate for this phenomenon, various devices known as heat tracing systems have been developed. These systems supply a quantity of heat equivalent to the heat lost to the surrounding environment. The temperature of the fluid thus remains identical between the pipe inlet and outlet.

Of course, traditional steam or heat-transfer fluid solutions exist for temperature maintenance:

• tracer tube: a tube in which pressurized steam or a heat-transfer fluid circulates is placed along the pipework to be maintained at temperature. By conduction, it transfers heat to the pipe;

• the double jacket: a second tube, concentric with the first, is placed around the piping to be maintained at temperature. The steam or heat transfer fluid circulates in the annular space thus created, transmitting heat directly to the internal piping.

Both solutions have the advantage of using inexpensive energy. On the other hand, they generally involve a high level of maintenance.

Electric solutions are therefore an interesting alternative. While investment costs are comparable (for technologies offering the same temperature homogeneity), maintenance costs are very low. As the installed power is low (usually just a few dozen kilowatts), energy costs are more than offset by maintenance savings.