There is an economy of scale involved in the refining of oil, and larger facilities are already tied into existing pipeline networks--both incoming and outgoing. Permitting a new facility would be tougher than expanding existing ones, as the past few years of refinery development have shown (refiners opted for the latter).
Guarding myriad facilities is perhaps more difficult than guarding one or two, even though larger facilities might be more of a terror target.
Refineries are surrounded by chemical plants for a reason: ship the feedstocks for the chemical plants next door, rather than ship them longer distances. Shipping those same multiple and more specialized feedstocks to chemical plants would negate some of the economic advantage of the more localized refineries. (Think ethylene, tolulene, etc.), especially when the costs of environmental compliance are factored in.
Where modular facilities might pay off is for the production of fertilizer or electricity from otherwise flared wellhead gas, especially if those facilities could be moved in a few truckloads. Some separation of heavier gasses, water, etc. might have to occur onsite for the process to be efficient, and the units would have to be able to be tuned to differing gas mixtures inherent in different wells and over the well's production history. Plus, all that would have to get EPA approval, which could be a real bugaboo (along with allocation of extraction taxes and royalty issues--something for the lawyers to sort out).
Still, something only flared at the production site could conceivably be turned into a viable resource.
-——Where modular facilities might pay off is for the production of fertilizer or electricity from otherwise flared wellhead gas-——
On Monday I visited a very large American company building equipment for an electric generating plant in Abu Dhabi. It was like the tower of Babel........ engineers of many national origins with two common languages. Those were English and American engineering project management methods. (but I digress)
The electricity generated by the flare gas is used to smelt aluminum. When complete, it will be the largest capacity aluminum smelter in the world
A simple topping plant is very unlikely to meet current EPA requirements of ULSD.
Cost of Diesel climbed because cost of making ULSD climbed. It isn’t made with simple topping.