I was wondering about where all the refineries are. Wasn't quite aware that there aren't any refineries from Georgia to Maryland. I was thinking maybe some might only go a short distance, but there's basically nothing between certain points. I keep on hearing that Colonial has 5500 miles of pipes, but it's only about 1600 miles between Texas and New Jersey. Maybe some of it is pipes going in different directions, although I understand that some of their pipes are bidirectional.
However, as an electrical engineer, I'm familiar with "pipelining" in electronics. The idea is that things can be split up into stages where each stage can be simultaneously operated with another piece of data in the previous stage. It's roughly akin to how a physical pipeline might transport 87 octane, 92 octane, and diesel one after the other. It's my understanding that the transmix of different gasoline grades isn't that bad because it can still be sold as the lower octane rating fuel. But mixing diesel with gasoline is another matter.
The one thing I'm not sure about is what happens if they have to do an emergency halt. They say the turbulent flow minimizes mixing. But what happens if there's no turbulent flow. Maybe with pigs they don't mix, but this pipeline stopped for several days.
How are different products and grades kept separate in the pipeline?
Different product batches are pushed through the system next to each other. The stream is always in a “turbulent flow” condition which minimizes mixing. Products are sequenced in the pipeline according to their characteristics. For example, regular unleaded gasoline may be shipped next to a batch of premium unleaded gasoline. When the flow of product is “cut” or diverted for delivery or into a storage tanks, the “cut” is made to protect the entire premium gasoline batch, thus allowing some premium to be added to the regular, unleaded gasoline. Similar steps are taken to protect distillate products such as jet fuel, Ultra Low Sulfur Diesel (ULSD), and home heating oil. When products with incompatible characteristics come into contact with each other, the resulting interface is defined as transmix. Transmix is stored separately and re-processed into a useful product.