(73d) Electric Heaters: Fouling, Feeders, Vaporization, PSVs, and More

There is a large increase in effort and funding for process electric heaters throughout the world because of new renewable energy sources of electric power. Chemical Engineers are often not familiar with either the simple or sophisticated issues associated with electric heaters. This presentation will introduce engineers to some of these issues.

Eight of the different available electric heater technologies will be briefly listed. The advantages of electric heaters will be described and the challenges regarding very high temperature electric heaters will be summarized. The fundamental issues surrounding constant temperature heat transfer and constant flux heat transfer as it relates to turbulent convection and fluid eddies will be explained.

Design calculations unique to electric heat applications will be presented:

(1) The results of a numerical study will be provided to demonstrate the problem of fouling with electric heater heat transfer and how a radiation-based design can reduce this problem.

(2) The importance and challenges of penetrating a pressure boundary with electric power feeds will be explained. The results of an additional numerical heat transfer study for one common feeder design will be presented.

(3) As an example of how direct electric heat differs from a steam heated exchanger, a comparison using vaporization will be given.

(4) The pressure relief calculation for a blocked pressure vessel with electric heat cannot be found in codes and common manuals. A method will be provided and explained for a blocked electric heater with a single-phase fluid.

Important ohmic resistor materials will be listed with some characteristics important for their suitability in various applications. Changes and opportunities in the industry include improved radiant heat transfer software, improved fouling tolerance, ultra-high temperature materials, and electric steam heaters and superheaters.