Crude Unit

The Crude Unit separates crude oil into propane, naphtha, kerosene, diesel, gas oils and residuum. Here’s how:

First our crude oil is "washed" with water in a desalter. This removes salts that are a natural part of crude oil. (No one wants salt in their fuel!) Then we heat the crude to about 650° and pipe it to the Atmospheric Distillation Tower.

The tower "boils off" the lightest crude components like propane, naphtha, kerosene and diesel. These four fuels continue on in different directions for more processing.

What’s not boiled off is heated again in the Vacuum Pipe Still and piped to the Gas Oil Distillation Tower. That’s where we remove gas oils for more processing in the Fluid Catalytic Cracking Unit. (Read about that unit further on.)

At the end of this process, the remaining crude is quite heavy. We call it vacuum residuum, and it looks a lot like the asphalt that’s used to make roads. But it’s still useful when we process it in the Delayed Coking Unit.

Delayed Coking Unit

We can still pull more useful products from the residuum! The Delayed Coking Unit (DCU) converts heavy vacuum residuum and asphalt from the Crude Unit into fuel gas, gasoline, diesel, gas oil and petroleum coke. But it takes time and heat for the chemical reaction, called "cracking," to happen.

First we fill a large drum with the heated vacuum residuum. In this drum some of the residuum is "cracked" into products like gasoline and diesel fuel. The product left over in the drum is petroleum coke, and it looks like a cross between a chunk of coal and a sponge. When a drum is filled with coke we use high pressure water to "cut" the coke into small chunks that can fall out of the drum. We use two drums so we can keep one full of oil while we’re cutting the coke from the other.

Fluid Catalytic Cracking Unit

Remember the Gas Oil Distillation Tower? Here’s the next step for the oil from that tower. The Fluid Catalytic Cracking Unit (FCCU or "Cat") upgrades gas oils from the Crude Unit into propane, gasoline, diesel fuel and other products. Remember, lighter products are generally more valuable. And this is where almost half of the plant’s gasoline is produced.

In the Cat reactor a reusable silica-alumina catalyst helps break down (crack) large oil molecules into more valuable, lighter products. We call this unit a Fluid Catalytic Cracking Unit because the catalyst flows like a liquid as it mixes with the oil and circulates through the unit.

But there’s more. A "fractionator" separates gasoline and lighter products from diesel fuel. Then three more distillation towers divide the lighter mixture into gasoline, fuel gas and propane/butanes. Propane- and butane-like products feed the Alkylation and Polymerization Units. That’s up next.

Polymerization

We haven’t yet mentioned propylene; it’s a by-product of the cracking reactions in the FCCU and DCU. What’s it good for? We pass it through beds of phosphoric acid-impregnated catalyst pellets. Polymerization happens. (That’s a scientific name for the process of linking small molecules to make larger molecules.) The end result is "polymer gasoline," used to help blend gasoline. The unit can also produce nonene, a feedstock for making petrochemicals.

Alkylation Units

Here’s another clever way to squeeze more out of crude oil. In the Alkylation (Alky) Units we combine olefins (propylene and butylene) from the FCCU with isobutane and a sulfuric acid catalyst. It’s mixed vigorously before the sulfuric acid is again removed. What’s left is pumped to distillation towers, where it’s separated into liquefied petroleum gas (LPG), mixed butanes and alkylate. Alkylate is a high-octane blending component used in lead-free premium gasolines.

Hydrotreaters

Once kerosene or low octane naphtha is distilled from the Crude Unit, it’s fed directly to the Hydrotreating Unit 1 (HTU-1) to remove sulfur and nitrogen contaminants. In the same way, naphtha and diesel that have been cracked from the FCCU and DCU are pumped to Hydrotreating Unit 2 (HTU-2) for contaminant removal.

Here’s how it works: The fuels are combined with a catalyst in a high pressure, hydrogen-rich atmosphere. The results include hydrogen sulfide, ammonia and desulfurized hydrocarbon. Hydrocarbons are then distilled to produce low octane naphtha and jet fuel.

 

Catalytic Reforming Units

Catalytic Reforming Units 1 and 2 provide a high-octane blending component needed to produce gasoline. First these units are fed low-octane, desulfurized naphtha from the HTU. Heat and a platinum catalyst help rearrange the hydrocarbon molecules. The result: a high-octane hydrocarbon material called reformate, or re-formed gasoline.

An interesting by-product: Chemical reactions in these units produce hydrogen, which is used in the adjacent HTU.

Sulfur Recovery Unit

The Sulfur Complex converts "sour" gases to pure liquid sulfur. This reduces emissions and allows the refinery to process crude oil with a higher sulfur content. First, incoming hydrogen sulfide is converted through controlled combustion. The reaction produces sulfur and water vapor. More hydrogen sulfide is converted to sulfur by passing the gaseous mixture over a catalyst. The resulting liquid sulfur is sold as a fertilizer ingredient.

 

Cogeneration Facility

The plant produces electricity as a by-product of the refining process. About 350,000 pounds per hour in steam produce 140 megawatts of electricity— enough power for 70,000 Northwest homes. Pretty efficient!

Besides that, the Boiler House (which is part of the cogeneration facility) provides our operations with steam, instrument and plant air, boiler feedwater, and fire and service water.

Waste Water Treatment Plant

The Treatment Plant treats waste water through the Process Water Sewer and Clean Water Sewer systems. In fact, all sewage and water must flow through the Treatment Plant before going into the bay. And to ensure that any discharge remains within allowable ranges permitted by the state Department of Ecology, we carefully test for oil, phenols, total suspended solids, ammonia, sulfide, chemical or biological oxygen demand, hydrogen sulfide, mercaptan, chlorine, chloroform, pH and chromate. 

The bottom line?  Treated water is free of contamination in accordance with National Pollution Discharge Elimination System guidelines, and in no way adversely affects the life or flavor of shellfish or other marine life.

The Treatment Plant also handles ballast water from ships and recovers oil for recycling to the refining process.