A plant operating at high temperature for prolonged periods of time will see thermal degradation of its heat transfer fluids. One common byproduct of this process is the formation of “heavy” or long-chain hydrocarbons, which are detected by measuring the carbon content of a fluid. The accumulation of carbon in a heat transfer fluid, and thus a thermal plant, can potentially reduce a plant’s production output. A number of interventions can be used to maintain or reduce the presence of carbon in a fluid; these approaches are outlined here.
A heat transfer fluid (HTF) is central to many processes requiring heat to manufacture or produce, for example, processed foods, chemicals, or energy. All HTFs degrade over time and form a mixture of “light” and “heavy” chain hydrocarbons. In Plant Services’ May issue (“Don’t light my fire: Keep flammable vapors at bay”), I wrote about how light chain hydrocarbons can be effectively managed using a light-ends removal kit (LERK) or batch venting. We now turn our attention to managing their heavy-chain counterparts (i.e., carbon).
Carbon accumulates in a HTF as it thermally degrades at high temperature or oxidizes at high temperature in the presence of oxygen or upon exposure to air. Hence, there is a need for a thermal plant’s maintenance team to routinely measure the level of carbon in a HTF. This is critical for the health of the HTF and the plant, as the carbon formed and suspended in the HTF is “sticky” and will adhere to internal surfaces of the thermal system, including both the pipework and the heater.