Nov-2022

Decarbonising fired process heaters with zero-emission electric heat

Replacing conventional fossil fuel-based combustion systems with electric resistance heating systems can result in significant decarbonisation gains.

James Lewis
Chromalox

Article Summary

As global greenhouse gas emissions continue to rise steadily, governments are implementing more aggressive carbon policies to promote the decarbonisation of critical sectors, like energy, which continues to be one of the largest single sources of carbon emissions due to heavy reliance on emission-intensive processes for steam generation and process heating. While it is understood which sectors are the largest contributors, achieving pollution reductions is an ongoing challenge. Carbon policies are a good foundation to drive change but require cooperation, collaboration, and time to reach their full potential and prevent carbon drift. In addition, these policies alone cannot drive the change needed to meet global emission targets, as they only promote the incentive and push the penalties associated with emissions but do not offer the solution for decarbonising. Instead, finding viable alternatives to the combustion equipment deeply ingrained in the industry is critical towards the long-term success of energy sustainability.

Among the solutions on the market today, some companies have looked to waste heat recovery (WHR) systems as a method of reducing their emissions. WHR systems capture lost heat from process outputs and recirculate it to other parts of the plant to reuse energy that has already been created. These systems provide improvements over stand-alone fuel-fired equipment by improving operational efficiency, reducing emissions, and reducing necessary equipment sizes, but they are not perfect. WHR systems are typically expensive and should be evaluated to see if the benefits outweigh the cost to implement. In addition, the captured heat is at a lower quality and temperature and may not always be suitable for all plant processes, particularly those that run at higher temperatures. This often requires large, oversized exchangers to capitalise on the heat recovery. In the end, WHR provides value over conventional fossil fuel-based systems but does not allow for true carbon neutrality when paired with combustion sources.

Electric resistance heating
A more practical solution is the use of electric resistance heating to avoid direct Scope 1 emissions from facilities altogether. While the elimination of Scope 1 emissions is generally the primary focus of any given facility, negating Scope 2 emissions is equally as important.

Although very few countries are fully powered by renewable energy sources, the share of renewable energy in the energy mix is steadily increasing. More options are also becoming available that include the development of more advanced micro-grids, localised generation of renewable power, and more advantageous Power Purchase Agreement (PPA) plans from power providers who offer renewables as part of their mix. The increased implementation of renewable energy sources allows for the avoidance of Scope 2 emissions to provide a zero-emission solution from generation to process.

Electric resistance heating technologies are not a new concept and have been on the market for over 100 years, particularly in the hydrocarbon processing industry, which is a major contributor to global greenhouse gas emissions. With the development of medium voltage electric resistance technology, even more opportunity exists to replace conventional fossil fuel systems in the energy sector, specifically within the oil and gas industry. Medium voltage heaters operate at higher voltage potentials, from 1000V up to 7200V. This increase in voltage means a significant reduction in amp draw (current), which in turn drastically downsizes and simplifies the necessary infrastructure to support the installation. Fewer amps mean fewer wires, contactors, fuses, and overall fewer connection points, simplifying maintenance and improving uptime. In addition, electric resistance heaters are 100% efficient at taking applied energy and converting it into heat. Losses do occur by means of heat dissipation in the power switching components and I2R losses in the power wiring. However, through the reduction of these core components, the losses are further mitigated, leading to operational efficiencies upwards of 99% with Direct Connect MV heating technology.

Another asset of electric resistance heating is its versatility. Electric heating elements can be banked together and installed in flanges, fittings, pipes, vessels, and more. With the metal protective sheath being an inherent feature of the electric tubular element, various grades of high-temperature and corrosion-resistance alloys can be chosen, such that electric heating elements can be used across numerous thermal processes. This is especially valuable when considering the variance in applications across refining and petrochemical processes. Electric heating can even come in the form of heat tracing, which is a valuable technology that can effectively replace old steam tracing lines. There are numerous benefits when considering you are eliminating the combustion steam generator in addition to all the complex steam tracing lines and providing a simpler technology that is easier to install and maintain.

Separation and conversion
When looking at how electric heating technology can be used in refinery and petrochemical facilities, it is important to consider the types of applications that currently exist. There are many different types of processing units, each playing an important role in the overall process of converting feedstock oil into finished petroleum products and sustainable fuels.

A typical refinery will have a dozen or more of these processing units, which primarily fall into two categories: separation and conversion. Traditionally heat used in refineries for oil feedstock and other hydroprocessing systems, which require large amounts of energy, is generated using API 560 fossil fuel-fired heaters. API 560 heaters make up the majority of a refinery and petrochemical facility’s CO2 emissions out of the heater stack. For example, a 34 MMBTU/hr fired heater can emit up to 15,900 tons/year of CO2. This is equivalent to emissions of 3,245 cars on the road per year.

To improve the efficiency of the API 560 heater, heat from the stack is often captured and recirculated to the combustion section of the system to improve the efficiency of the fossil fuel-fired heater. However, the aforementioned drawbacks of WHR are still present, and the emissions are still significant.

There are numerous process technologies and refinery/petrochemical designs throughout the industry that are currently serviced by API 560 fossil fuel-fired heaters that are good candidates for electrification using electric resistance technology. A closer look at these processes can reveal how electric heating technology can displace conventional combustion heat sources.

For separation units, the most common found in refineries are atmospheric and vacuum distillation. Atmospheric distillation for crude and bio-crude begins with feedstock oils comprised of a mixture of hydrocarbons. This feedstock oil is first heated and then put into a distillation column, also known as a still, where different products boil off and are recovered at different temperatures. The distillation process separates this crude oil into broad categories of its component hydrocarbons, or ‘fractions’. The temperatures required for the process can extend upwards of 1000ºF, well within the ranges for electric process heaters.