July 31, 2014

Where Do NGLs Come From?

Good question!

Below is a slide that summarizes the supply in the US:

NGLs from Gas Production and Gas Plants

Gas plants are responsible for most of the volume and virtually all of the ethane.  One thing to note is that Canada has significant gas plant capabilities and produces significant NGLs to the markets.  These fields vary in the amount of NGLs they produce.  The amount of NGLs in the gas is commonly referred to as “Gallons per Thousand Cubic Feet” or GPM, where “M” means 1000 cubic feet.

Here is where the major plays are located and the GPMs associated with each:

Gas Fields and GPMs

 

NGLs from Refineries

Crude oil refineries create NGLs as a byproduct of the refining processes.  However, since many of these NGLs created in a refinery are consumed in the refinery to build other products, they do not produce a great deal of the NGL volumes.

The NGL that is the primary product for a refinery is propane.  Propane is really a byproduct of several processes.  As most people are aware, refineries are really geared to manufacture gasoline and diesel, which are also known as finished fuels.  Propane could be considered a “finished fuel”, but it is really a lighter byproduct of the fractionation processes.

Crude refineries are much more complex than gas plants.  In fact, a “gas plant” actually resembles the Saturated Gas Unit ( SGU ) on a crude unit, or the Vapor Recovery Unit (VRU) on a cat cracker.  Crude oil is really a mixture of many hydrocarbons that range from methane the light end to vaccumn tar / petroleum coke at the other.  When fractionation occurs, all of the components are separated out by boiling point.  Additionally,  some of the fractionated products undergo cracking and reforming, which make more of fuel products that can be fractionated again.

It is a big circle.  Once hydrocarbons enter a refinery, one of 2 things happen to it:

  1. It is refined into a product of some sort, whether it is a finished product or an intermediate product that is sold to someone else.
  2. It is used as fuel.

Back to NGLs!

Ok….so what happens is that each of these processing units will have a fractionator that will yield different products that are similar to the gas plant products.  Since a refinery is geared toward gasoline production, all of the components that are heavier than propane ( C3) will be used for gasoline production.

If the refinery is close to a chemical plant, the ethane may be sold as chem plant feed.  Additionally, they might combine some of the propane with the ethane to produce a mix product for the chem plants.  If they do not sell the ethane to the chems, it will wind up in the fuel gas system with the methane and spare hydrogen.

So….what we have left for NGL production from a refinery is propane.  Here is a partial list of the units that can make propane in a refinery.

  1. Crude Units – Actually, it is the saturated gas unit attached to the crude unit.  The overhead ( light stuff ) from the atmospheric tower in a crude unit gets sent to the Sat Gas Unit, which produces propane.
  2. Cat Crackers – ( excuse me … Fluid Catalytic Cracking Units, also know as FCCUs).  These units run the heavy gas oil from the crude units as feed, crack it, then fractionate the cracked molecules.  The overhead from the main fractionator goes over to the Vapor Recovery Unit ( VRU ).  Sound similar to the Crude Unit fractionation?    That is because it is.
  3. Cokers – There are various kinds of these units.  They run the bottoms from the Crude Unit.  They heat their feed up to the point that it will form petroleum coke.  This gets deposited in big drums with the tall dereks on them.  What is not deposited is the lighter vapors, which go to the coker fractionator.  The propane falls goes out with the vapor.
  4. Alkylation Units – Most people don’t realize this is a byproduct of the process.  Most alky units combine isobutane and butylene to make alkylate.  Propane is a byproduct.
  5. Several Other Units – It really depends on the configuration of the refinery.  Propane is created as a byproduct in the catalytic polymerization units and probably several more.  Many of these units may not produce propane directly, but produce it in the offgas product.  It may or may not be separated later, depending on the refinery configuration.

 

 

About ssk

Stan Keller is ssk. I have worked in and around the energy industry all of my life. Information Technology is now my primary focus and I work with companies that need assistance with all kinds of automation for their transactions systems. Check out my full profile at Linked in .