Electric process heaters and decarbonisation in hydrocarbon processing

Processing and refining hydrocarbons ultimately requires the use of high heat for a number of critical steps, and heaters based on fossil fuels have traditionally filled those roles. But with mounting pressure to mitigate carbon dioxide emissions and advance long-term decarbonisation goals, engineers have been exploring the potential for electric process heaters. This would allow several heating steps to be completed using “clean” electricity from renewable sources.

Dennis Long

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Article Summary

Importantly, replacing fossil fuel heaters with electric heaters would allow for a reduction in “Scope 1” carbon dioxide emissions. As defined by Buehler (see the May 2022 issue of this publication), Scope 1 emissions are the direct result of burning fuels like natural gas or fuel oil for process heating. Scope 2 emissions result from the need to import energy, while Scope 3 emissions are produced while using a product (for example, emissions from car and truck tailpipe emissions). All three types of emissions must be reduced in order to hit decarbonisation targets.

What is holding back Scope 1 emission reduction?

An informal survey of Watlow customers and prospects has revealed that a full 90% of oil and gas leaders are already actively engaged in decarbonisation efforts. Hydrocarbon processors are no longer focused on if they should decarbonise, but how they will decarbonise.

So why aren’t electric process heaters more ubiquitous in the energy sector today? Surprisingly, familiarity might be the main reason. Until now, such heaters have played only very narrow roles in hydrocarbon processing and have tended to be smaller, operating at lower voltages. Although larger heaters are easily imaginable, engineers recognise that a number of questions then arise when it comes to their control and maintenance.
In short, no one wants to be first into the water when it comes to running larger medium-voltage thermal systems.

What engineers might not know is that medium-voltage process heaters have been developed and used, and their operation is already well understood. Implementing such heaters simply requires having the right technical experience – experience made possible by contracting with the right partners. The good news for industry is that modern electric heaters can provide the same – or improved – performance that hydrocarbon engineers have come to expect from fossil fuel powered heaters, and thus can play a key role in decarbonisation efforts.

Rethinking the size and scope of electric heaters
To even consider replacing fossil fuel-burning heaters, we need to have a clear understanding of the current capabilities of electric process heaters. Replacement does not make sense to begin with if electric heaters do not come with the needed size and power required to heat processes that currently depend on fossil fuels. Many of those processes would require larger electric heaters well above the well-known one megawatt (MW) variety; for example:
•    Feed/Product Exchanger, 2 MW (or larger)
•    Dehydration Inlet Preheater, 3 MW (or larger)
•    Heater Treater, 4 MW (or larger)
•    Molecular Sieve Regen, 6 MW (or larger)
•    Waste Gas Heater, 6 MW (or larger)
•    Once-Thru Steam Generator, 20 MW (or larger)
•    Crude Heater, 28 to 200 MW (or larger)
•    Hot Oil Heater, 32 MW (or larger)
•    LNG Vaporiser, 34 MW (or larger)
•    Thermal Oxidiser, 54 MW (or larger)
•    Hot Water Heater, 56 MW (or larger)
•    FCC Heaters, 150 to 200 MW (or larger)

Fortunately, heaters do exist that can handle these power requirements. In terms of physical size, 60-inch NPS tubesheets are highly attainable. Nothing prevents even greater size; the technology exists to produce electric heat exchangers of physical size comparable to a shell and tube heat exchanger. An electric heat exchanger of the same physical size (as a shell and tube) will have a larger available heating duty, due to the constant heat flux technology.

With equipment of this size, a single vessel can have two heat exchanger bundles; such a setup can produce a single process vessel with a 15 MW duty rating or more. The few suppliers providing electric heaters at this scale can raise or lower the duty rating as technical requirements dictate. This kind of size and power presents a viable alternative for operations currently fired by fossil fuels.

What about control?
Some of the most common questions about larger process heaters have to do with control:
•    What additional elements are needed to ramp up the heater?
•    How does turn-on/ramp-up affect the existing electrical system?
•    How is temperature monitored and controlled?
•    What additional safety precautions are needed?

Just because larger electric heaters have not traditionally been used to heat all processes in the petrochemical industry does not mean that the technology is theoretical or untested. Far from it: Field-proven power switching devices have been in use for low voltage electric process heaters and electric medium voltage motors in a number of industries for years, and the ability to control voltage is well established.

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