Why Refinery Decarbonisation Cannot Ignore FCC Units
Why refinery decarbonisation is entering a more complex phase
Refinery decarbonisation is moving into a more demanding stage.
For much of the past decade, the direction of travel has been relatively clear. Improve energy efficiency, reduce fuel intensity, introduce lower-carbon hydrogen and, where possible, electrify supporting systems. These approaches remain important and are already contributing to measurable reductions in emissions across refining operations.
However, as these measures begin to take effect, the remaining challenge becomes more visible. Not all emissions within a refinery can be addressed through changes in energy supply or efficiency improvements. A significant proportion is embedded in the process itself.
This distinction matters because it changes the type of solution required. Where emissions are process-driven rather than energy-driven, they cannot be eliminated through substitution alone. They require intervention at the point of release.
This is the point at which carbon capture becomes less of a theoretical option and more of a practical requirement.
Why FCC units sit at the centre of this challenge
Fluid Catalytic Cracking (FCC) units are one of the clearest examples of this shift.
FCC is a core refining process used to convert heavy hydrocarbons into lighter, higher-value products such as gasoline and petrochemical feedstocks. It is a well-established and essential part of modern refining operations.
During the process, carbon deposits form on the catalyst surface. These deposits, commonly referred to as coke, are periodically burned off in a regenerator. This combustion process produces a flue gas stream with a relatively high concentration of carbon dioxide, typically in the range of 10 to 18 percent.
The key point is that these emissions are not primarily linked to the fuel used to power the process. They arise from the chemistry of the refining operation itself.
As a result, FCC units often represent one of the largest single sources of carbon dioxide emissions within a refinery, frequently accounting for between 20 and 35 percent of total Scope 1 emissions.
This places them in a unique position. They are both highly significant in terms of emissions and structurally resistant to the decarbonisation approaches currently receiving the most attention.
Why conventional transition strategies do not fully address FCC emissions
Much of the current transition strategy in refining is built around hydrogen.
Low-carbon hydrogen is being deployed to replace conventional hydrogen production from steam methane reformers, reducing emissions associated with fuel processing and hydrotreating. This represents an important and necessary step forward.
However, hydrogen substitution addresses only a specific subset of emissions. It does not extend to process emissions generated within FCC units.
This creates a structural gap.
A refinery may successfully decarbonise its hydrogen supply and improve its overall energy efficiency, yet still retain a substantial emissions profile due to FCC operations. The more progress is made elsewhere, the more visible this gap becomes.
This is not a failure of strategy. It is a reflection of the underlying complexity of industrial systems.
But it does mean that achieving meaningful emissions reduction at site level requires additional solutions that operate beyond fuel substitution.
Why timing is changing the conversation
For many years, this gap could be acknowledged without immediate action.
That is becoming increasingly difficult.
Across Northwest Europe, carbon dioxide transport and storage infrastructure is moving into operation. Projects such as Northern Lights in Norway, Porthos in the Netherlands and Antwerp@C in Belgium are creating viable pathways for captured carbon dioxide to be permanently stored.
This development changes the context for capture.
When storage is not available, capture remains a constrained or theoretical exercise. When storage becomes accessible, the focus shifts toward the sources of emissions that can realistically be captured and connected into that infrastructure.
At the same time, regulatory pressure and corporate targets are tightening. The 2030 horizon is no longer a distant ambition but a near-term operational constraint.
Together, these factors are moving FCC emissions from a recognised issue to an actionable priority.
Why FCC units represent a practical capture opportunity
From a technical perspective, FCC units are not the most challenging capture environment.
The relatively high carbon dioxide concentration in the regenerator flue gas makes them more favourable than many dilute industrial streams. The emissions are continuous, centralised and well characterised.
These characteristics align with the requirements for effective post-combustion capture.
What has been missing historically is not technical feasibility, but alignment between technology readiness, infrastructure availability and commercial drivers.
That alignment is now beginning to form.
As a result, FCC units are moving from being an overlooked part of the emissions profile to a logical focus for deployment.
Where Tree Associates fits into this shift
At Tree Associates, this is an area we are now engaging with directly.
Our recent feasibility work on FCC emissions within a European refinery has focused on the regenerator flue gas stream as a capture target. This work builds on our broader approach to carbon capture, which centres on producing high-purity liquid carbon dioxide ready for transport, storage or utilisation.
What this work has highlighted is the scale and consistency of the opportunity. FCC units are not isolated edge cases. They are present across the majority of large refining assets and represent a repeatable application for capture technology.
This is strategically important.
As the market moves toward deployment, repeatability becomes as important as performance. Solutions that can be applied across multiple sites with similar characteristics have a significantly higher likelihood of adoption.
FCC units provide that kind of opportunity.
Why this subject matters for Tree’s wider thought leadership
For Tree Associates, FCC units are not only a technical opportunity. They are also a useful lens through which to explain the broader direction of industrial decarbonisation.
They highlight the distinction between energy-related emissions and process emissions.
They demonstrate the limits of relying solely on substitution-based strategies.
They reinforce the growing importance of carbon capture as a complementary solution rather than an optional one.
This makes FCC a valuable subject for engaging with industry, policy and investment audiences. It connects directly to real-world constraints and helps frame the transition in practical rather than theoretical terms.
As the market continues to evolve, these kinds of grounded, asset-level discussions are likely to become increasingly important.
Closing thought
Refinery decarbonisation will not be defined by the areas that are easiest to address.
It will be defined by how effectively the industry responds to the emissions that remain once the initial gains have been made.
FCC units sit firmly in that category.
They are not new, but they are becoming more important.
And in many cases, they may prove to be one of the clearest indicators of whether decarbonisation in refining can move from strategy into delivery.
At Tree Associates, that is exactly the point at which the conversation becomes most meaningful.
