In part due to sustainability initiatives, the process industry is considering electric heaters for more applications. HTRI launched electric heater service types in Xist® 9.1. Since that release, we have received numerous inquiries from members about the technology and how to perform a reliable thermal design.
Although no industry standard has yet been generally accepted to guide designers, an API standard for electric heaters is under development. HTRI has prepared a guidebook to help members successfully implement this technology.
HTRI’s Guidebook for Electric Process Heaters provides general background information on immersion electric process heaters (EPHs) and assists members in using the EPH option in Xist 9.1 and later. The guidebook explains the basics of electric process heaters, including a description of the heating elements, bundle configuration, power supply, instruments and controls. In addition to a design checklist, the guidebook also discusses thermal design for topics such as
- maximum watt density
- radiation and convection
- design margin
- avoiding hot spots and other safety considerations
The guidebook introduces the types of electric heaters that Xist can model, with specific notes on the software capabilities and limitations, as well as recommendations to help users more effectively evaluate electric heaters in Xist.
HTRI will revise this guidebook based on improvements in the technology, changes in best practices, and results of new research.
1.1 Advantages of electric heaters
1.2 Disadvantages of electric heaters
2 Basics of electric process heaters (EPHs)
2.1 Components of an EPH
2.1.1 Heating elements
2.1.2 Element bundle
2.1.3 Element supports
2.1.4 Cold end
2.1.5 Power supply
2.1.6 Instrumentation and methods of measurement
2.2 Electric heater industry standards
2.2.1 Pressure vessel/assembly
2.2.2 Electrical components
3 Thermal design of electric heaters
3.1 Maximum duty or heat flux
3.1.1 Duty
3.1.2 Heat flux
3.2 Design margin
3.2.1 Heat duty uncertainty
3.2.2 Spare elements
3.2.3 Other uncertainties in design
3.2.4 Overall margin
3.3 Shellside design
3.3.1 Baffle/support choice
3.3.2 Laminar flow
3.4 Design to avoid hot spots
3.4.1 Sheath temperature limits
3.5 General design
3.6 Design information required by vendors and users
3.7 Instrumentation and controls (I&C) design
3.7.1 Controls for reboilers
3.7.2 Shutdown matrix
3.8 Design checklist
3.8.1 Design algorithm
3.8.2 Constraints
3.9 Reliability and safety considerations
3.9.1 Reliability
4 Modeling electric heaters in Xist
4.1 Model implementation
4.1.1 Constant heat flux method
4.1.2 HTRI shellside methods
4.1.3 Radiation
4.1.4 Default electric heater settings
4.1.5 Available service types/configurations
4.1.6 Rating case mode behavior
4.1.7 Vibration analysis
4.2 Model limitations
4.2.1 Identifying hot spots
4.2.2 Predicting low velocity regions
4.3 Creating a case in Xist
4.3.1 Heat flux specification
4.3.2 Shell style
4.3.3 Element geometry
4.3.4 Unheated length
4.3.5 Maximum sheath temperature
4.3.6 Tube layout
4.3.7 Baffles
4.3.8 Nozzle position
4.3.9 Fluid property specification
4.4 Interpretation of Xist results
4.4.1Marg in on maximum sheath temperature
4.4.2 Output examination
4.4.3 Determination of maximum sheath temperature
Nomenclature
References
Appendix A Additional information
Appendix B Calculation examples