optimum placement of the outlet temperature sensor on a stepper/SCR application. As the operation was not at 100%, some of the circuits were in the off position. The inlet gas was not heated evenly, resulting in a much lower outlet gas temperature. This was easily solved by moving the temperature sensor further down from the outlet to ensure sufficient gas mixing before measuring the overall temperature. EPHs specifications include an extra power rating in case the operating voltage is less than specified and allowances are made for operating versus design flow conditions. Sizing the EPH for the minimum voltage as well as the design flow case thus combining the two specifications (one electrical and one process) results in an exponentially over-sized heater, as Watts=Volt2/Resistance. Electrical design considerations The electrical choices affect the process and mechanical aspects of the EPH and should be taken into consideration. Common EPH controls include on/off, stepper, stepper/SCR, and full SCR. Stepper/SCR works using multiple circuits, for example, an EPH with eight circuits will have seven circuits with on/off switching and one with full SCR control. Modern SCRs and their controllers are made specifically for electric heating applications, including zero cross, burst firing, single cycle delayed triggering, and phase angle. SCRs with zero voltage switching (zero- cross SCRs) reduce harmonic distortion caused by phase angle control. Terminal connections can expand and contract with usage. Today’s heaters have electrical terminals with constant torque spring-loaded washers to prevent losing electrical terminals and buss bar. Ceramic insulation should be used as they do not expand nor compress over time. Over-temperature sensing of the heater bundle is mandatory for industrial applications. RTDs should always be used as they cannot be miswired, and the controller will detect any loss of signal. Both the over-temperature controller and the associated magnetic contactors should be wired in a fail-safe mode. Any interruption of the control will disconnect power to the EPH.
This should never occur, and if it does, an operator must visit the control panel to reset the loop. Most process engineers are unaware of the electrical engineering aspects of a control panel, and most electrical engineers are unaware of the heat transfer requirements of a heat exchanger. Typically, EPHs are categorised in the heat exchanger category as ‘electric heater’, which encompasses a whole array of electric heating technologies. ‘Electric process heater’ should be a distinct category separate from others such as drum heaters, and heat trace. Conclusion Decarbonisation significantly expands the addressable markets for EPHs, and as industry transitions towards carbon net zero, it should embrace the benefits EPH technology offers. High energy-consuming manufacturing processes should consider replacing gas or fired heating systems with ‘clean’ EPHs. As heater technology has advanced over the years, inherent problems have been systematically removed, yet other considerations remain. These considerations become more important as the scale of the EPH technology increases. Standard specifications have been developed for heat exchangers and pumps, and an EPH industrial specification, which doesn’t hamper EPH potential and will be a guide to its growth, must be properly created for all industries to follow. In developing this standard, it will be important to balance setting the specifications as tightly as possible whilst allowing for continual improvement and recognising the need to tune and customise the EPH design to extend application areas. A third-party organisation must either take up the challenge or be created to arbitrate a specification with input from all EPH technology leaders. This organisation will regulate the growth of EPH technology as it enhances decarbonisation efforts in all industries.
Craig Tiras firstname.lastname@example.org
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