2012 – winter Issue

Turn Up the HEAT!

A single frozen line on a cold January night could result in days of lost production. Especially in the case of freeze protection, heat trace is an important element of a plant's process system. A well-designed heat trace system with automated control capability can be expected to function with minimal operator or maintenance efforts.

The intent of heat trace is to provide heat to a pipe, tank, or other equipment using a line of heat transfer fluid (such as steam) or using an electrically heated cable. It is used primarily to prevent freezing or to reduce viscosity of a liquid to allow for effective pumping. Other heat trace uses include compensation for heat loss; eliminating the formation of liquid in gas or powder lines and minimizing the formation of solids in liquid pipe lines.

Heat trace control scenarios range from simple to complex based upon the type of heat trace used and the process requirements. Here are a few heat trace control options for consideration

Self-Regulating "" No Control With self-regulating heat trace, no heat trace control method is required. The heat trace can be left on and will increase or decrease heating based on the temperature. This is the simplest and least costly installation method. However, it results in increased energy consumption and holds the possibility of freezing if operators forget to turn the heat trace on when ambient temperatures begin to fall.

Ambient Thermostat Adding an ambient thermostat for control reduces the chance that operators will forget to turn on heat trace circuits when the ambient temperature falls below freezing. Ambient thermostats are most useful where heat trace is installed primarily for freeze protection.

Field Located Thermostats Field located thermostats allow for control of each process line based on the temperature of the line. As the line temperature drops, the heat trace is energized and heats the line. Field thermostats are a cost effective method for processes that must maintain temperatures greater than freezing. Field thermostats are more energy efficient because the heat trace is turned off when heating is not required.

Full Feature Control Panels Full feature control panels leverage current transmitters, line temperature sensors, and vessel temperature sensors to monitor and control the heat trace. Operator set points energize the heat trace based on line and vessel temperatures. The control panels typically display what heat trace is energized, temperature, and current. Certain control panels can be configured to log this information and display it graphically. Heat trace control panels increase installation costs but can reduce the total cost of ownership of a heat trace system through energy conservation and preventative maintenance processes.

Heat trace is not a "?one-size-fits' all package. Therefore, as you choose the type of heat trace you will use, it's important to understand how the heat trace will function, heat trace monitoring methods, and control scenarios for the trace. Making smart decisions in the design of your heat trace system will minimize installation costs, maximize process performance, and reduce overall cost of ownership.

For more information on the types of heat trace and control options best for your facility, contact Interstates Instrumentation at 712.722.1665.