Gas fractionation plants

Four main methods can be used to produce gas spirit:

1. Cooling

2. Deep cooling

3. Absorption with denuded oil

4. Hard surface absorption.

In the cooling method gas containing liquid is cooled down to temperatures in the interval from -10°C to -40°C. At such temperature about 90% of propane and all butane (and also heavier compounds) are liquefied and can be separated during fractionation.

In the deep cooling method more complete ethane separation is performed. For that purpose temperature of gas containing liquid is decreased to the interval from -100°C to -140°C. In such conditions 95% of ethane and all propane (and also heavier compounds) are separated from the gas.

Absorption with denuded oil is performed in older gas fractionation plants the same way as it is done in appropriate refinery units. Standard procedure allows producing about 70% of propane and 100% of butane and heavier compounds. Using cooled denuded oil can in addition provide for 50-75% of ethane.

Hard surface absorption is an interesting process, which is used in cases when only dew point must be changed (i.e. remove only the heaviest compounds, which can condense during transportation). Many gas sale contracts include requirements for dew point (temperature at which drops start to settle out) to be not higher than -10°C with gas line pressure about 800 psi. Depending upon specific gas flow this may require complete removal of petroleum gasoline and partial removal of butanes.

Some porous materials, such as absorbent carbon, silica gel and alumina, may make big volumes of vapors condense on their surface. As liquid stays on the surface of hard substance, this process is called “adsorption” but not “absorption” (in the last case liquid gets inside the material). When sufficient volume of liquid is condensed (in this case, gas spirit) the process is stopped or the flow is directed to different tank containing new portion of adsorbent. Liquids are removed from adsorbent surface by treating it with superheated steam, collected and condensed.

Hard surface absorption produces 10-15% of butanes and 50-90% of petroleum gasoline.

The words to be memorized:

1. Gas fractionation plant – газофракционирующая установка (ГФУ)

2. denuded oil – отбензиненное абсорбционное масло

3. gasoline – бензин (газолин)

4. silica gel – силикагель

5. straight-run residue – прямогонный остаток

6. alumina – оксид алюминия

EXERCISE 6 Answer the following questions.

1. How many methods can be used to produce gas spirit?

2. Where is absorption with denuded oil performed?

3. Hard surface absorption is an interesting process, isn`t it?

4. What requirements do many gas sale contracts include?

5. What is dew point?

6. What kind of porous materials may make big volumes of vapors condense on their surface?

7. What is the difference between “adsorption” and “absorption”?

8. What is happening when sufficient volume of liquid is condensed?

9. How are liquids removed from adsorbent surface?

EXERCISE 7 Connect the terms with their definitions.

1. denuded oil	1. the removal of a liquid by the capillary, osmotic, chemical, or solvent reaction in a substance
2. crude distillation	2. a substance that promotes a chemical reaction but is not affected by the reaction
3.rectifier	3. mixing gasoline by adding components increasing octane number
4. absorption	4. naphtha, supplied for gas absorption
5. sour oil	5. a device in the rectifier providing for drainage of condensed hydrocarbons from the plate down to the lower plate
6. catalyst	6. oil containing low concentration of sulfur
7. sweet oil	7. oil containing high concentration of sulfur
8. run	8. separation of crude oil into fractions (fractionation)
9. downcomer	9. a column at the refinery in which crude oil is separated into5-6 fractions
10. compounding	10. a fraction of crude oil

EXERCISE 8 Translate from English into Russian.

1. Rectifier is used for crude distillation but vat residue cannot be cracked there due to insufficient temperature.

2. Effective limits of boiling are temperatures at which fractions are considered relatively separated.

3. Straight-run fractions of heavy gas oil are heated in the cracker under higher pressure with catalyst, which facilitates the process.

4. When catalyst surface is covered with sediments, it is not active no more and must be regenerated.

5. Sponge coke is used for production of electric rods, calcium carbide and graphite.

6. Jet and diesel fuels are produced from heavy gas oil during hydrocracking.

7. Highly aromatic gasoline distillates are used as high-level octane components or for production of aromatic hydrocarbons.

8. Heavy cracked gas oil can be used as an initial product for thermal cracking.

9. Light fractions are delivered to gas fractionation plant and straight-run gasoline is directed for compounding.

10. Crude is pumped into the rectifier with the crude pump, which first delivers the crude to the heater and then – to the rectifier.

EXERCISE 9 Translate the text into English.

Нефтеперерабатывающие заводы

В целом, нефтеперерабатывающие заводы делятся на простые и сложные, но аналитики также часто употребляют термин «очень сложные».

Нефтеперерабатывающий завод, работающий по простой схеме, включает перегонку сырой нефти, гидроочистку средних дистиллятов и каталитический риформинг нафты.

Нефтеперерабатывающий завод, работающий по сложной схеме, включает всё то же самое плюс каталитическую крекинг-установку и установки алкилирования и газофракционирования.

Нефтеперерабатывающий завод, работающий по очень сложной схеме, включает всё то же самое, что при сложной схеме, плюс установки либо по производству олефинов, либо по сокращению количества остатка (например, установка коксования).

В стандартной отраслевой модели могут быть рассчитаны выходы нефтепродуктов из каждого сорта сырой нефти для каждой схемы переработки. Это позволяет выяснить, насколько выгодна переработка конкретного сорта нефти по конкретной схеме.

EXERCISE 10 Make up your own topic “Oil refining” and be ready to retell it and discuss with your group mates.