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  1. Answer the questions.

  1. What are fractionators?

  2. What are the natural gas processing plants used to?

  3. Where is the processed natural gas used?

  4. What does raw natural gas typically consist of?

  5. What are the Natural Gas Liquids?

  1. Read formulae and find elements.

1.

CH4

ethane

2.

c2H6

1.

methane

3.

c3H8

isobutane

4.

I1-C4H10

carbon dioxide

5.

i-C4Hio

propane

6.

O

O

ethanethiol

7.

CH3SH

butane

8.

C2H5SH

methanethiol

9.

N2

helium

10.

He

nitrogen

  1. Find in the reference list the derivatives of the words.

Nature - Gas - Process -

Fraction - Use - Pure -

Residence — Commerce - Industry -

Consume —

Natural, consummate, processor, gasification, reside, frac- tionators, commercialese, naturopath, procession, gaseous, processing, useful, processed, consumption, naturalize, used, usage, consumation, purify, consumable, resident, industriuos, gasohol, purification, useless, residency, gasometer, commercia- lize, naturalism, residential, commercial, industrial, consumer.

  1. Translate and recognize the headword or root of the word. Use the following word combinations in the sentences of your own.

  • natural gas, gas alarm, gas bomb, gas bracket, gas burner, gas coke, gas engine, gas chamber, gas coal, gas main, gas lighter, gas meter, gas oven, gas pipe, gas producer, gas shelter, gas torch, gas stove, gas tank, gas station, gas helmet.

  • house plant, plant life, plantain, plantation, power plant.

-raw material, raw data, raw spirit, raw sugar, raw rec- ruits, raw-boned, rawness.

  1. Look through the stages of gas processing and answer the by-questions.

  1. The raw gas is pipelined to a gas processing plant where the initial purification is made for the removal of acid gases (hydrogen sulfide and carbon dioxide).

What acid gases are removed during the initial purification?

  1. In the last ten years, a new process based on the use of polymeric membranes to dehydrate and separate the carbon dioxide and hydrogen sulfide from the natural gas stream is gaining acceptance.

What is used to dehydrate and separate acid gases from natural gas stream?

  1. The removed acid gases are then routed into a sulfur recovery unit which converts the hydrogen sulfide in the acid gas into elemental sulfur.

Where are the removed acid gases routed?

  1. There are a number of processes available for that conversion, but the Claus process is usually selected. The residual gas from the Claus process is commonly called tail gas and that gas is then processed in a tail gas treating unit (TGTU) to recover and recycle residual sulfur-containing compounds back into the Claus unit.

What is tail gas?

  1. The next step in the gas processing plant is to remove water vapor from the gas using either the regenerable absorption in liquid

triethylene glycol (TEG), commonly referred to as glycol dehydration, or a Pressure Swing Adsorption (PSA) unit which is regenerable adsorption using a solid adsorbent. Other newer processes requiring a higher pressure drop like membranes or dehydration at supersonic velocity using, for example, the Twister Supersonic Separator may also be consi- dered.

There are two ways of removing water vapor from the gas, aren’t there?

  1. Mercury is then removed by using adsorption processes such as activated carbon or regenerable molecular sieves.

What element is removed by using adsorption processes?

  1. Nitrogen is next removed and rejected using one of the three processes :

  • Cryogenic process using low temperature distillation. This process can be modified to also recover helium, if desired.

  • Absorption process using lean oil or a special solvent as the absorbent.

  • Adsorption process using activated carbon or molecular sieves as the adsorbent. This process may have limited applica- bility because it is said to incur the loss of butanes and heavier hydrocarbons.

How many processes are used to remove nitrogen?

  1. The next step is to recover of the natural gas liquids (NGL) for which most large, modern gas processing plants use another cryogenic low temperature distillation process invol- ving expansion of the gas through a turbo-expander followed by distillation in a demethanizing fractionating column. Some gas processing plants use lean oil absorption process rather than the cryogenic turbo-expander process.

What does the cryogenic low temperature distillation process involve?

  1. The residue gas from the NGL recovery section is the fi- nal, purified sales gas which is pipelined to the end-user mar- kets.

What is the final stage of gas recovery?

  1. The recovered NGL stream is processed through a fractionation train consisting of three distillation towers in series: a dethanizer, a depropanizer and a debutanizer. The overhead product from the dethanizer is ethane and the bottoms are fed to the depropanizer. The overhead product from the depropanizer is propane and the bottoms are fed to the debutanizer. The overhead product from the debutanizer is a mixture of normal and isobutane, and the bottoms product is a C5+ mixture. The recovered streams of propane, butanes and C5+ are the final NGL by-products from the gas processing plant.

What is the purpose of distillation towers?

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