[Red Badger]

I have a question.

I thought a barrel of crude oil contained X gallons of gasoline, Y gallons of Diesel, Z gallons of heating oil and numerous other hydrocarbons like motor oil, heavy fuel oil, asphalt, etc.

Why does the season make any difference? If a refiner distills the crude in summer or winter doesn’t the oil produce the same amounts of each chemical?

What am I missing?.................

[thackney]

US refineries add additional processing to maximize the gasoline production. It changes a few percentage points of the amount of gasoline produced, typically after spend nearly a billion dollars at a larger refinery.

The EPA then mandates changes to the mixture creating gasoline and diesel from summer to winter, so the product the refinery makes has to change each swing season.

[SAJ]

It is easy for the refiner to 'bias' the refining of a given shipment of crude by changing the operation of the refinery. This is a regularly-done process, typically once in the spring and once in the fall.

Speaking VERY broadly, if the refiners sets the refinery to utilise more 'cracking', he obtains somewhat more gasoline. Equally, if he sets the refinery to more distillation, he obtains more #2 oil (essentially heating oil/diesel).

There are other variables in play, of course, regarding aromatics, bunker fuel, and so forth. And, quite naturally, the characteristics of the crude that is input into the refinery control to a great degree just how much of 'whatever' product can be produced.

Hack, I know this is wildly oversimplified. If there are any obvious errors, I apologise (and pls correct them). If you have a link to a site "Basics of Crude Refining" or some such, pls post it.

Thanks, and FReegards!

[taxcontrol]

It is not as “fixed” as a hard ratio. Refineries can alter how they crack the crude to achieve different ratios. Further, some seasons (winter in particular) require oxygenated fuels in some states. Thus, a custom blend has to be created to meet that market.

The justification for this legislative requirement is reduction in emissions.

[Eva]

There is a supply and demand element to everything in a free market. We pay at least a dime more for gasoline in my county ecsuse of the Canadian market even though there we two refineries here and our gasoline is delivered to stations by trucks, it never enters the pipeline.

Prices are somewhat controlled by the company that controls the pipeline, usually the largest company in the region.

[conservatism_IS_compassion]

Basically home heating fuel oil and diesel are the same stuff, to a first approximation at least. That alone should make diesel more scarce and expensive in the winter than in the summer.

[thackney]

If a refiner distills the crude in summer or winter doesn’t the oil produce the same amounts of each chemical?

I came across a good overview that better explains the why to your question from yesterday. I suspect you were only thinking of the separation portion. This is probably more than you wanted to know.

All refineries perform three basic steps:

Separation
Conversion
Treatment

http://www.eia.gov/energyexplained/index.cfm?page=oil_refining#tab2

Separation

Heavy petroleum components or fractions are on the bottom; light fractions are on the top. This difference in weights allows for the separation of the various petrochemicals. Modern separation involves piping oil through hot furnaces. The resulting liquids and vapors are discharged into distillation units.

Inside the distillation units, the liquids and vapors separate into fractions according to their weight and boiling point.

The lightest fractions, including gasoline and liquid petroleum gas (LPG), vaporize and rise to the top of the tower, where they condense back to liquids.

Medium weight liquids, including kerosene and diesel oil distillates, stay in the middle of the tower.

Heavier liquids, called gas oils, separate lower down, while the heaviest fractions with the highest boiling points settle at the bottom of the tower.

Conversion

Cracking and rearranging molecules takes a heavy, low-valued feedstock and changes it into a lighter, higher-valued output such as gasoline. This is where fractions from the distillation units are transformed into streams (intermediate components) that eventually become finished products.

The most widely used conversion method is called cracking because it uses heat and pressure to crack heavy hydrocarbon molecules into lighter ones. A cracking unit consists of one or more tall, thick-walled, bullet-shaped reactors and a network of furnaces, heat exchangers, and other vessels.

Cracking is not the only form of crude oil conversion. Other refinery processes rearrange molecules to add value rather than splitting molecules.

Alkylation, for example, makes gasoline components by combining some of the gaseous byproducts of cracking. The process, which essentially is cracking in reverse, takes place in a series of large, horizontal vessels and tall, skinny towers.

Reforming uses heat, moderate pressure, and catalysts to turn naphtha, a light, relatively low-value fraction, into high-octane gasoline components.

Treatment

The finishing touches occur during the final treatment. To make gasoline, refinery technicians carefully combine a variety of streams from the processing units. Octane level, vapor pressure ratings, and other special considerations, determine the blend.

It is the reason the simplified flow diagram of a refinery looks like:

Keep in mind each one of those boxes above represents many different pieces equipment used together in a process unit. For example:

Fluid Catalytic Cracking unit

Delayed coker