I am a bit late posting my first real topic on why US refiners cannot use all the USL TO. Last night my first attempt disappeared when I pressed the publish button and I lost all my work. I have also had to sanitize the images to take out the logos

To set the stage one first has to understand a how a refinery works and what it produces. To keep things simple I am going to use a simple refinery that produces transport fuels and some co products. I have colour coded the main processes in the refinery under 4 headings which are:

Separation – usually distillation

Molecular re-arrangement – upgrading as in isomerisation, reforming, alkylation

Conversion – fluid catalytic cracking, hydrocracking, coking

Treating- usually hydrotreating

The first stage of refining is the distillation though the crude distillation (CDU) and the vacuum distillation (VDU) units

The products are:

1. LPG

2.  naphtha- BP <80 deg C

3. Jet Kerosine BP 175- 230 deg C

4. Diesel- Gas Oil BP 230-375 deg C

5. Atmospheric Residue BP>375 degC

The atmospheric residue is further process I the VDU to produce:

6. Vacuum Gas Oil – BP 375-550 deg C

7. Vacuum Residue BP > 550 deg C

These seven primary products are further processed in the downstream processes.

The naphtha stream is split into light and heavy naphtha. The light naphtha is processed in an isomeriser to produce isomerate which increase the octane number to about 82 RON and the heavy naphtha is processed in the reformer which produces reformate with an RON of about 95-98.

The jet fuel and diesel/ gas oil stream are processed with hydrogen in their respective hydrotreaters( aka hydrodesulphurisation) which reduces the sulphur content and stabilises the products.

The atmospheric residue is sent to the vacuum distillation unit (VDU) which separate the stream into vacuum gas oil (VGO) and vacuum residue.

The vacuum gas oil is process in the fluid catalytic cracker which cracks the VGO in LPG, FCC gasoline, light cycle oil (LCO), and a heavy fuel oil.

The C4 LPG is processed in an alkylation unit which produces a high quality gasoline stream called alkylate. The LCO stream is a low quality diesel stream that is mixed with the CDU diesel/ gas oil streamthe low quality FCC fuel oil (sometimes called slurry oil) is blended into the vacuum gas oil stream as fuel oil. I hated handling slurry oil.

To make finished gasoline all the gasoline components need to be blended together in the gasoline pool to produce finished gasoline with a boing range of about 0 – 200 deg C:

1. Reformate  RON 95 <40%

2. FCC gasoline  RON 91 35-40%

3. Isomerate  - RON 82 <10%

4. Alkylate  RON 95

5. Ethanol RON 130

RON = research octane number – this is the number posed on the pump in the EU.

MON = motor octane number which is a more severe test and is always less than the RON

In the US the pump octane number is known as the Octane Index and is (RON+MON)/2

An EU 95 RON gasoline is about 91Octane Index in the US.

As can be seen the production of gasoline is quite complex and requires multiple components to meet the specification. Gasoline is also the most expensive fuel to produce both financially  and energy wise.

Moving onto the US LTO conundrum we need to understand how crude oil differs from source to source. See the second  image which depicts the different product yields for 4 different crude types. As can be seen the Brent crude of 38 API and Arab Heavy of 28 API produces very different yields of the primary products, especially the atmospheric residue  31% Brent and 53% Arab Heavy.

When a refinery is designed it is based on specific API gravity. In the 1970’s when many refineries were built the typical refinery was designed around medium type crude such as Russian Urals and Arab Light. The crude yield in the CDU were limited by the hydraulic capacity throughout the various product draw off in the CDU. This set the refinery capacity. Thus if the refinery was charged with a lower or higher API gravity crude oil there would be a limitation in one of more draw off’s. In the third image there is a comparison of refinery running Urals crude being charged with lighter Brent. The naphtha/LPG capacity is about 23 kbd with a charge of 100 kbd. If Brent is then processed the naphtha capacity would limit the crude charge to 69 kbd- a 31kbd(%) in crude processing capacity. Not only does this reduce the processing capacity but the other streams will also be reduced . In this case the atmospheric residue would be limited to 21.5 kbd- 50% less than the Urals crude residue.

The lower residue yield would reduce the feed to the FCC, to such an extent it may not be able to operate successfully and as a result gasoline production would be cut back . FCC gasoline is a major part of the gasoline pool and this would make the refinery imbalanced. Excess reformate would have to be sold off, probably at a loss. Notwithstanding, the energy balance across the CDU and other units would be out of balance increasing operating costs.

In the 1980’s when gasoline was the main fuel (still is in the US) the advent of unleaded gasoline required many changes and upgrades to the global refinery fleet. FCC gasoline became almost mandatory and deeper processing units were installed. The US Gulf Coast refineries invested heavily in processes to run heavy crude from Mexico and Venezuala along with heavy Canadian crude. This involved installing coker units, residue hydrocrackers, solvent de-asphalters and more hydrotreating capacity to process the heavy sour(high sulphur) crude oils.

The advent of large volumes of US LTO presented another problem. How would the LTO be processed as the refinery configurations could only handle  small inputs of LTO. This resulted in most of the LTO being exported, much of it going to places which wanted lighter crude for naphtha production. Some refineries have a special type of CDU (condensate splitter) that is specially designed for such streams. The LTO naphtha is very desirable for petrochemical production, specifically for steam crackers which produce olefine building blocks (ethylene, propylene, butadiene , benzene). The main LTO export markets include China, Korea, Japan and Europe.

The US no longer possesses naphtha steam crackers. It does have a very significant fleet of steam crackers but these consume mainly ethane and propane, and cannot crack naphtha. If all goes to plan you should be able to open a file Basic Refining which includes more detail on refining. In the slides you will see a crude assay for Brent crude. This is a very useful  document for people like me as it not only provides yield data but also other important parameters which influence how the crude can be processed. Many crude assays are available on-line from Exxon, BP, Total, Equinor and a few others. Most crude assays are behind a paywall. The are literally thousands of crude assays and as the reservoir depletes the crude assay will change over time.

I will give a few details about my experience. I started work in 1978 as a mud logger working on a drill ship called the Sedco 445. I realised that this was not for me an quickly moved on and started working for an ICI company  which provided water treatment services. After a few years I moved to Saudia Arabia and worked in Juabail and moved form water treating to refining and petrochemicals. This role taught me a lot and I was involved in the commissioning of 3 steam crackers and 1 refinery. When you work in Saudi Arbia you go with two buckets- one for shit and one for money. When one if full you go home. (advice form Stan Filipis who worked for Shell). I then worked as a contractor in most of the UK refineries, which in the 1980’s were numerous ( 14 and now 4). I then spent some time as a product manager for hydrocarbons’ in London for almost 9 years before moving to my last employer Evonik for 25 years. My job role in Evonik was Head of Feedstocks and Petrochemical Technologies. The feedstocks I looked for came from refineries and steam crackers, and I have worked on projects in the US, EU, Middle East, China, Malaysia and a few others. I still work full time for Evonik but now I am self employed as a result of some company re-organisations. I am well past my reinterment date but like to keep my brain active. For 30 years I had a pilots licence and during this time I owned both a fixed wing Rutan Long Eze and a Hughes 269 helicopter. These days my main hobby is clay pigeon shooting.