What a refinery does

A refinery separates, converts, treats and blends crude oil into useful products. The skyline is complicated because each part of that job needs different equipment.

Everyone in Baytown has looked at the towers. Fewer people have been told, in plain words, what happens inside them. This is that telling — from the government's own manuals and the Energy Information Administration, translated.

Start with the barrel

Crude oil is not a thing; it's a crowd. Pull a barrel out of the ground and you're holding thousands of different molecules — some so light they'd boil on a warm afternoon, some so heavy they'd sit in your hand like tar — plus a little sulfur, nitrogen, oxygen and a trace of metal. None of it is useful as it comes. A refinery exists to sort the crowd by weight, break the heavy ones into lighter ones, clean out the sulfur, and mix what's left into things a truck, a jet or a lawnmower can burn. The Energy Information Administration says every refinery does the same three things in the same order: separate, convert, treat.

One number to keep: in a recent year, the average U.S. refinery got about forty-five gallons of product out of every forty-two-gallon barrel. Not magic — lighter molecules take up more room than the heavy ones they came from. The plant sells more volume than it buys.

Separate: the tower

Crude comes off the ship or the pipeline, gets its salt washed out, and is heated in a furnace to somewhere around 650 to 700 degrees — hot enough that most of it is vapor by the time it enters the bottom of a steel column about 120 feet tall. That column is the tower you can see from the ferry. Inside it are trays, one above another, and the physics is simple enough to explain to a child: light things rise. The lightest molecules — gases, propane, butane — climb all the way to the top. Gasoline-range naphtha condenses a little lower. Kerosene and jet fuel lower still. Diesel and gas oil below that. And the heaviest fraction, which never turns to vapor at all, drains out the bottom as a black residue the plant calls "resid." OSHA's technical manual lists the cuts in exactly that order, top to bottom.

The resid isn't waste — it still has good molecules in it — but you can't just heat it harder, because at those temperatures it would start cracking apart on its own, uncontrolled. So it goes to a second, fatter tower run under a vacuum, where lower pressure lets the heavy stuff boil at a temperature it can survive. Out of the vacuum tower come more gas oils, the base stocks for lubricating oil, and a bottom so heavy it becomes asphalt or feed for the coker.

Convert: the heavy work

Straight distillation would give the country far too much heavy oil and far too little gasoline, so the middle of every big refinery is a set of units that rearrange molecules. OSHA's manual describes each; here they are in one line apiece.

The cat cracker takes heavy gas oil and breaks it into gasoline-range pieces over a catalyst so fine it flows like a liquid, at 900 to 1,000 degrees. The catalyst gets coated in coke and is burned clean in a regenerator, over and over, all day. This is the unit that makes most of America's gasoline.
The hydrocracker does the same breaking, but under hydrogen at a thousand pounds of pressure or more, which makes cleaner diesel and jet fuel.
The coker is where the very bottom of the barrel goes: heated to about 900 degrees and held in huge drums for a day while it cracks into lighter oil and a solid, coal-like leftover — petroleum coke — that gets cut out of the drum with water jets. About a twentieth of every barrel ends up as coke.
The alky unit takes the small gas molecules the crackers throw off and, with a strong acid as matchmaker, builds them into alkylate — the cleanest, highest-octane thing that goes into gasoline.
The reformer takes low-octane naphtha and reshapes it over a platinum catalyst into high-octane reformate, and gives off hydrogen as a by-product — hydrogen the plant then uses everywhere else.

Treat: taking the sulfur out

Sulfur poisons the platinum, corrodes the pipe, and — when the fuel is burned — becomes the acid in acid rain and the soot in the air. So nearly every stream passes through a hydrotreater: heated, mixed with hydrogen, pushed through a catalyst bed under pressure, until the sulfur and nitrogen come off as hydrogen sulfide and ammonia and are stripped away. OSHA says the step removes about ninety percent of the contaminants. It's the reason the diesel at the pump is "ultra-low sulfur": federal rule since 2010, fifteen parts per million, down from as much as five thousand a generation ago. The EPA credits that change with cutting harmful emissions from trucks and equipment by more than ninety percent. Every time you don't smell a diesel bus, thank a hydrotreater.

Blend: the last table

Nothing that comes out of a single unit is sold as it is. Blending is the final, quiet step where streams from a dozen units are mixed in exact ratios with additives to hit a specification: regular at 87 octane, premium at 91 to 94, diesel, jet, and the specialty lines — lube base stock, wax, asphalt. The pump number on Garth Road is the average of two laboratory tests, and it was decided in a blending room a few miles from where you fill up.

The things you can see from outside

The flare. A flare is a safety valve with a flame on it. The EPA describes it as a device that burns waste gas at a high, remote point rather than letting it escape unburned, and says its main job at a refinery is to handle emergencies — a unit trips, pressure has to go somewhere fast, and the flare burns it at ninety-eight percent efficiency instead of letting an explosive cloud form at ground level. A big flare is usually the safety system doing its job, not the plant breaking — and it is also an emissions source in its own right, which is why flaring is regulated and the plant has to report the large events. Both things are true at once. The plant-alerts page explains how to read one.
Steam. Plumes off cooling towers and vents are mostly water. Refineries use steam by the ton — to strip light molecules out of heavy ones, to lower pressure in towers, to drive equipment.
The furnace stacks. The heaters that bring crude to temperature; the tallest chimneys on the skyline.
The tank farm. Crude waiting to go in, product waiting to go out, and the one thing a refinery can't run without: room.

Baytown's own

The complex on the Ship Channel is three plants on one site, per the company's fact sheet: a refinery with a crude capacity around 588,000 barrels a day, among the largest in the country; a chemical plant; and an olefins plant. What the refinery makes is the list above — gasoline grades, ultra-low-sulfur diesel, jet, lube oils, waxes, specialty hydrocarbons. What the chemical plant does is the next page.

How to read the skyline from the bridge

Cross the Fred Hartman at dusk and you can name what you're looking at, once. The tall, thin ones with platforms every twenty feet are the towers — distillation columns, the separators. The tall ones with no platforms and a plume are heater stacks, the chimneys of the furnaces. The single stack with a flame is the flare, usually off to one edge where the wind takes it. The pairs of fat, squat cylinders with a tall derrick between them are coker drums, the derrick holding the drill that cuts the coke out. The long low rows of squares are exchanger banks and the pipe rack running between everything. The spheres are pressurized gas — propane, butane. The flat round tanks in the distance are crude and product, and the biggest of them hold more than a neighborhood uses in a year. The blocky windowless building near the middle is the control room. Learn those seven shapes and the whole Ship Channel becomes legible; the refinery, the olefins plant and the chemical units are the same alphabet in different words.

One barrel, one house

Follow a single barrel through the unit and out to a Baytown kitchen. Nearly half of it becomes gasoline, in the truck in the driveway. A bit more than a quarter becomes diesel — the school bus, the delivery van, the tractor at the rice farm up 146. A tenth becomes jet fuel, which is how the grandparents get here from Ohio. A twentieth becomes coke, which fires cement kilns and steel mills. A few gallons become propane for the grill, asphalt for the street out front, the base of the oil in the engine and the wax on the cheese. The Energy Information Administration keeps the exact split; the plain version is that the barrel that came off the ship at the dock on Tuesday is, by Friday, in every room of the house. The refinery doesn't make one product. It makes the ordinary day.

The people in it

Two thousand employees on the company's own count and about as many contractors on an average day, at the big one alone — operators, mechanics, instrument techs, lab techs, inspectors, engineers, the office, the security at the gate, the medical station. The town's surname list is on those badges. Most of them will never see the whole plant; a unit is a career. What they share is the thing this page is trying to give you: they know what the shapes are for. The control room is where that knowing sits; the operator's day is what it looks like on a Tuesday.

Why it matters that you know

Because the people who run it are your neighbors, because the thing you're looking at from the bridge is one of the largest machines on earth, and because a town that lives next to a refinery deserves to understand it in the same plain words its operators use. The unit names on this page are the ones on the badges at Lee College. Now you can read them.

Read it plainly

Crude oil is a mixture.
Heat starts the separation.
Pressure changes some reactions.
Catalysts change reaction pathways.
Hydrogen helps remove contaminants.
Sulfur must be controlled.
Blending finishes many products.
Storage connects units to markets.
Pipes connect the process together.
Operators keep conditions inside limits.
Maintenance keeps equipment trustworthy.
The skyline is a process map.

Sources

U.S. Energy Information Administration, "Energy Explained": oil and petroleum products; refining crude oil — the refining process; refining inputs and outputs; octane in depth; use of oil. OSHA Technical Manual, Section IV, Chapter 2, "Petroleum Refining Processes." U.S. EPA, diesel fuel standards (40 CFR 80 Subpart I) and the Air Pollution Control Technology Fact Sheet on flares. ExxonMobil Baytown Complex fact sheet.

En español

Lo que hace una refinería: el crudo no es una cosa sino una multitud de moléculas de distintos pesos, con azufre, nitrógeno y trazas de metales. Toda refinería hace tres cosas en orden — separar, convertir, tratar — según la Administración de Información Energética. Separar: el crudo se calienta a unos 650–700 grados y entra a una torre de unos 120 pies; lo ligero sube (gases, propano, butano), luego la nafta de gasolina, el queroseno y el combustible de avión, el diésel, y el residuo pesado sale por el fondo; ese residuo va a una torre al vacío que produce gasóleos, bases lubricantes y asfalto. Convertir: el craqueador catalítico rompe el gasóleo pesado en gasolina a 900–1,000 grados; el hidrocraqueador hace lo mismo con hidrógeno a alta presión para diésel y combustible de avión más limpios; el coquizador cocina el fondo del barril en tambores enormes y deja coque de petróleo; la unidad de alquilación arma alquilato de alto octanaje con un ácido como catalizador; el reformador reconvierte nafta sobre platino y produce hidrógeno. Tratar: el hidrotratador quita cerca del noventa por ciento del azufre y el nitrógeno; por eso el diésel es de ultra bajo azufre — quince partes por millón desde 2010, según la EPA. Mezclar: nada se vende tal como sale de una unidad; la gasolina regular de 87 octanos se decide en una sala de mezclas. Lo que se ve desde afuera: la antorcha es una válvula de seguridad con llama — quema el gas de emergencia al noventa y ocho por ciento en vez de dejar que forme una nube explosiva; el vapor de las torres de enfriamiento es agua; las chimeneas son los hornos; el parque de tanques es espacio. El complejo de Baytown: refinería (unos 588,000 barriles diarios, entre las más grandes del país), planta química y planta de olefinas, según la hoja de datos de la empresa.

Cómo leer el horizonte desde el puente. Las altas y delgadas con plataformas cada seis metros son las torres de destilación; las altas sin plataformas y con pluma son las chimeneas de los hornos; la sola con llama es la antorcha; los pares de cilindros gordos con una torre de perforación en medio son los tambores del coquizador; las filas largas y bajas son los intercambiadores y el rack de tubería; las esferas son gas a presión; los tanques planos a lo lejos son crudo y producto; el edificio sin ventanas en medio es la sala de control. Siete formas y todo el Canal se vuelve legible. Un barril, una casa. Casi la mitad se vuelve gasolina; poco más de un cuarto, diésel; una décima, combustible de avión; una vigésima, coque; unos galones, propano para la parrilla, asfalto para la calle, la base del aceite del motor y la cera del queso. El barril que bajó del barco el martes está, el viernes, en cada cuarto de la casa. La gente que está adentro. Unos dos mil empleados y otros tantos contratistas en un día promedio, solo en la grande; la lista de apellidos del pueblo está en esas credenciales; una unidad es una carrera.