Conversion: cracking and rearranging molecules to add value

This is where refining fanciest footwork takes place—where fractions from the dis­tillation towers are transformed into streams (intermediate components) that eventually become finished products. This also is where a refinery makes money, because only through conversion can most low-value fractions become gasoline.

The most widely used conversion method is called cracking because it uses heat and pressure to "crack" heavy hydrocarbon molecules into lighter ones. A cracking unit consists of one or more tall, thick-walled, bullet-shaped reactors and a network of fur­naces, heat exchangers and other vessels.

Fluid catalytic cracking, or "cat cracking," is the basic gasoline-making process. Using intense heat (about 1,000 degrees Fahrenheit), low pressure and a powdered cata­lyst (a substance that accelerates chemical reactions), the cat cracker can convert most relatively heavy fractions into smaller gasoline molecules.

Hydrocrackingapplies the same principles but uses a different catalyst, slightly lower temperatures, much greater pressure and hydrogen to obtain chemical reactions. Although not all refineries employ hydrocracking, Chevron is an industry leader in us­ing this technology to cost-effectively convert medium- to heavyweight gas oils into high-value streams. The company's patented hydrocracking process, which takes place in the Isocracker unit, produces mostly gasoline and jet fuel.

Some Chevron refineries also have cokers, which use heat and moderate pressure to turn residuum into lighter products and a hard, coallike substance that is used as an industrial fuel. Cokers are among the more peculiar-looking refinery structures. They resemble a series of giant drums with metal derricks on top.

Cracking and coking are not the only forms of conversion. Other refinery process­es, instead of splitting molecules, rearrange them to add value. Alkylation, for example, makes gasoline components by combining some of the gaseous byproducts of cracking. The process, which essentially is cracking in reverse, takes place in a series of large, horizontal vessels and tall, skinny towers that loom above other refinery structures.

Reforminguses heat, moderate pressure and catalysts to turn naphtha, a light, rela­tively low-value fraction, into high-octane gasoline components. Chevron's patented reforming process is called Rheniforming for the rheniumplatmum catalyst used.

Treatment: the finishing touch

Back when Chevron's founders boiled crude oil to get kerosene, they didn't have to worry about customer specifications or government standards. Today, however, a major portion of refining involves blending, purifying, fine-tuning and otherwise improving products to meet these requirements.

To make Chevron gasoline, refinery technicians carefully combine a variety of streams from the processing units. Among the variables that determine the blend are octane level, vapor pressure ratings and special considerations, such as whether the gas­oline will be used at high altitudes. Technicians also add Techron, Chevron's patented performance additive, and dyes that distinguish the various grades of fuel.

Refining has come a long way since the oil boiling days of Pico Canyon, By the time a gallon of gasoline is pumped into a car's tank, it contains more than 200 hydro­carbons and additives. All (hat changing of molecules pays off in a product that ensures smooth, high-performance driving.

WORDLIST

Oil refinery -Нефтеперегонный завод

crude oil, petroleum -сырая нефть

glassworks -стеклянная посуда, изделия

stemware -cтоловое стекло

still -перегонный куб, дистиллятор

separation - сепарация; отделение, очистка

conversion - переработка (конверсия газов)

treatment -технологическая обработка; очистка

distillation tower -ректификационная или

дистилляционная колонна

liquid petroleum gas -сжиженный нефтяной газ

(LPG) gas oil - газовое масло, газойль

distillate -дистиллят, нефтепродукт, отстой;

residuum -тяжелые остатки прямой перегонки

plant -(зд.)установка; завод

stream -(зд)промежуточный нефтепродукт

fluid catalytic cracking -жидко-каталитический крекинг

cat cracker - установка каталитического крекинга

reforming - реформинг (т.е. повторная переработка)

coker -установка для коксования, коксовик

derrick - подъёмник (вышка)

naphtha -лигроин (керосин)

blending -смешивание (с добавлением присадок)

additive - присадка

fine-tuning -доведение до...; доводка

jet fuel - реактивное топливо

afkyfation - алкилирование; алкикатализатор

gas bag -газовая пробка (мешок)

hydrogen chloride -хлорид водорода(соляная кислота)

hydrogen sulfide -сероводород

naphthenic acids - нафтеновые кислоты

demulsifies -антиэмульгаторы

diatomaceous earth -инфузорная (диатомитовая) земля

GLOSSORY:

1. Antiknock compound. A chemical added to gasoline to reduce its tendency to knock. This additive makes it more difficult to ignite the gasoline and air mixture and thus raises its octane number.

2. Cracking. The separation of a large hydrocarbon molecule into two or more smaller hydrocarbon molecules.

3. Reforming. Removal of hydrogen atoms from a cycloparaffin to create an aromatichydrocarbon.

4. Octane number. A measure of a gasoline's resistance to knocking. The high­er the octane number, the harder it is to ignite the fuel and air mixture and the less likely it is to knock.

5. Residual liquid. The liquid that falls to the bottom of a disullation tower because it contains molecules that rarely become gaseous at the temperatures of the tower.

6. Volatile. A material that easily becomes gaseous because its molecules are not strongly attached to one another.

7. Separator (P-tank, surge tank) a device in the form of a tank designed for separation of oil from gas and water. Separators may be vertical or horizon­tal, two-phase or three phase. Some of them are also capable of separating oil from solids due to special filters. The gravity and centrifugal forces are used for the separation process.

EXERCISES