Nov-2023

Conversion to a green refinery configuration: Assessing options, risks, and viability (ERTC 2023)

In order to meet the mandates of the Paris Agreement, as well as carbon intensity and greenhouse gas emission reductions, fossil fuel-based transportation fuels will be substituted by a combination of electric vehicles, bio-derived and renewable fuels.

Scott Sayles and Robert Ohmes
Becht

Article Summary

Existing refining and petrochemical assets are key elements in this equation, and there is a need to examine processing and configuration options to align to the new feedstock and product profiles as well as energy input options. Those entities that are able to meet the changes in this dynamic market while remaining profitable will continue as viable enterprises.

Framing Renewable Fuels Challenge
The regulatory environment provides the economic structure for the viable conversion of fossil fuel refineries into biorefineries (see Figure 1). The first step in the conversion is removing carbon from fired sources, while the reduction of fossil feedstocks and replacement with bio-feeds and renewable sources will occur over a longer duration.

The power requirements of the refinery will be satisfied from green sources or highly integrated systems. Electricity will increasingly be generated from low-carbon sources such as wind turbines, solar panels, and nuclear energy. The co-processed steam from gasification or steam methane reforming (SMR) and/or auto thermal reforming (ATR) operations will supplant the steam from on-demand boilers, thereby reducing fired duty. At the same time, hydrogen will replace fossil fuel combustion in higher-temperature furnaces.

Reducing pre-combustion emissions entails the removal of carbon from the fuel gas system. Pre-combustion configurations are summarised in Figure 2. Post-combustion removal uses either chemical or physical separation technologies to remove the CO₂ from the flue gases.     

Refining Schemes
Biorefinery schemes start with the available technologies and are feed-dependent, as shown in Figure 3. The renewable challenge is to get feedstock to the processing facilities on a scalable basis, along with associated costs and a sustainability basis. Seed oils are the easiest of the potential feeds but are in competition with the food supply and are not a long-term viable option. The third-generation feeds, such as wood waste or municipal waste, require further upgrading, and the current challenge is to create a sufficient supply of those feedstocks.

Feed and Product Possibilities
A refinery effectively takes low H/C fossil crudes or biomass and converts them into high H/C ratio products using hydrogen addition and/or carbon rejection processes:
υ    Triglycerides: A reasonable scale biofeed facility would be in the 250 tkpa to 3 mtpa range. The best possible economic outcome is to leverage existing fossil fuel refineries and supply chains. The feedstocks are different enough in composition that the feedstock storage considerations need modification.
ϖ    Advanced renewables: Feeds not readily processed using current technology are considered advanced renewable feeds, such as:
•  Cashew nut oil
•  High oleic sunflower oil extract
•  Animal fat
•  Brown grease
•  Tall oil pitch
•  Wastewater oil collections (fats, oil, and grease, or FOG).
ω     Lignocelluloses: Lignocellulosic materials like woody biomass and waste are the most difficult to convert and require pretreating to remove contaminants prior to entering the refinery.
•    Fast pyrolysis:  The use of fast pyrolysis converts biomass into a liquid that is high in water content and oxygen compounds. The pyrolysis oil and fossil fuel are not compatible and, when mixed, produce a sediment that fouls equipment. As such, this is not a recommended option.
•    Gasification: Gasification converts all carbon-containing molecules into hydrogen, CO (syngas), and CO₂. The products are further converted to additional hydrogen or, via Fischer-Tropsch reactions, into many different molecular combinations.
•    Hydrothermal liquefaction: Hydro-processing thermal liquefaction (HTL) is an upgrading option to convert biomass at moderate temperatures and high pressure via depolymerisation and deoxygenation to simpler molecules.
•    Refinery feeds: In general, fossil feeds and renewable feeds are not compatible, thereby requiring separate processing until the renewable oxygen content is reduced to nearly zero.

Options
The conceptual configuration for the biorefinery depends on the viewpoint and risk profile of the operator. Table 1 gives examples of biorefineries and the progression to the scale required to meet the current transportation fuel demand.
υ    Renewable process train: The renewable feeds from triglycerides are processed in a pretreatment unit (PTU) and then directly into the hydroprocessing units.
ϖ    Hydrogen demand increase and hydrogen supply options: Hydrogen demand and generation are anticipated to increase from the current capacity of 2.5 mtpa to 9 mtpa, with a drive to shift to lower emission technologies via the now commonly named blue, green or pink/yellow hydrogen.
ω Electrical supply: The ability to provide green electricity enables the refinery to maximise electricity usage, especially for power requirements, thereby reducing the fired fuel requirements for power generation. The use of electric heaters and boilers is an emerging technology to ‘electrify’ process heat and steam generation sources.
ξ Logistics: Renewable feeds are much more reactive than fractions generated from crude oil. These new feeds contain oxygenate species and reactive olefins/diolefins that can be biologically degraded /oxidised and can lead to both gum/coke or stable emulsion formation. These species can also have greater corrosion potential. Volatile biological breakdown products can result in objectionable odours if they are vented from the tank. Various mitigation measures exist for each of those threats.

Scenarios and Emissions
The different future refinery will operate with clean fuels utilities and limited carbon-fired sources. The feeds to the biorefineries will be from non-food sources and require upgrading in the liquid scenarios. The final scenario utilises gasification of the biomass and Fischer-Tropsch (FT) to convert the syngas into liquid fuels or other products.
υ    Separate trains: This scenario utilises existing refinery assets and augments them with a new biomass train fed by raw biomass or partially upgraded biomass via pyrolysis or HTL processes (wood waste and algae). The upgrading systems may be located near the source of the biomass (see Figure 4).
ϖ Integrated system: The integration of the biofuels into the fossil train allows utilisation of the existing refining equipment. In this configuration, the first unit saturates and produces feeds for processing in existing units.
ω Fossil train with gasification: The use of a gasifier that can potentially charge solids, liquids or gas opens up the facility to process a wide array of biomass. Gasification produces the syngas feed for the commercially proven FT section. An option not explored in this article is the capability of the syngas to be converted into a wide array of chemicals and lube oils.
ξ Yield comparison: Each configuration has a unique yield and quality. All three options are about the same in terms of the yield structure. Yields for the three configurations yields are shown in Table 2.

Conclusions
The biorefinery of the future will have a zero carbon emission operation with the potential to produce a yield slate considerably higher in renewable feed-sourced materials. The application of pre- or post-combustion technologies will allow for significant decarbonisation of Scope 1 and 2 emissions. Further decarbonisation will occur via the application of renewable electricity sources to offset fossil-generated power. The combination of renewable feedstock and hydrogen generated from renewable power or with captured CO₂ allows for significant decarbonisation of the product slate, thereby meeting Scope 3 emission reduction targets. Proper handling of the feed materials as well as the supply chain and logistics elements will allow the industry to benefit from existing refining infrastructure and achieve economies of scale.

This short article originally appeared in the 2023 ERTC Newspaper, which you can VIEW HERE