Question

What does natural gas processing include (at the field level)?

Answer 1

Processing of natural gas mainly include 4 steps

1. Oil and Condensate Removal from natural gas

Natural gas is dissolved in oil underground the well primarily due to the formation of pressure. Outside the well, there is an atmospheric pressure which is quite low as compared to underground pressure so when this natural gas and oil is produced, it will separate on its own, simply due to decreased pressure. In such cases, separation of oil and gas is relatively easy, and the oil and gas are sent separate ways for further processing.

But in certain instances, the separation is not the easy one and specialized pieces of equipment are installed to separate oil and natural gas. An example of this type of equipment is the Low-Temperature Separator (LTX). When our conventional separator doesn't work, these kinds of separator most often used for wells producing high-pressure gas along with light crude oil or condensate. These separators use pressure difference principle and cool the wet natural gas and separate the oil and condensate.

2. Dehydration or water removal

This process usually involves one of two processes: either absorption or adsorption

• Absorption: An example of absorption dehydration is known as Glycol Dehydration. In this process, wet gas enters at the bottom and glycol enters at the top. Countercurrent operation takes place. Glycol has a chemical affinity for water. when glycol is in contact with a stream of natural gas that contains water, glycol absorbs the water out of the gas stream.
• Adsorption: In adsorption, the water vapour is condensed and collected on the surface. Solid-desiccant dehydration is one of the examples of adsorption. It usually consists of two or more adsorption towers, which are filled with a solid desiccant. Desiccants generally include activated alumina or a granular silica gel material. Wet natural gas is allowed passed through these towers, from top to bottom. As the wet gas passes around the particles of desiccant material, water is retained on the surface of these desiccant particles.

3. Separation of Natural Gas Liquids

The removal of natural gas liquids usually takes place in a relatively centralized processing plant and uses techniques similar to those used to dehydrate natural gas.There are two basic steps to the treatment of natural gas liquids in the natural gas stream. First, the liquids must be extracted from the natural gas. Second, these natural gas liquids must be separated themselves, down to their base components.

In this process, dehydrated Gas leaving the high-pressure separator is cooled by the heat exchanger. The gas is first cooled to a constant temperature and pressure. An external refrigeration cycle then lowers the temperature. Gas is then cooled by isenthalpic expansion. Then liquid fractions recovered from the bottom of the separator.

4. Sweetening

Natural gas from some wells contains significant amounts of sulfur and carbon dioxide. Sulfur causes the rotten egg smell and commonly known as ‘sour gas’. Sour gas is undesirable because the sulfur compounds it contains can be extremely harmful, even lethal, to breathe.

For sweetening process, primary pieces of equipment are – Absorber, Stripper, & together with associated piping, heat exchanger & exchanger equipment. Sour Gas enters through the bottom of the scrubber.Countercurrent operation takes place with Amine as a solvent. Sweetened gas leaves to the top of the absorber. Similarly, the carbon dioxide and other acid gases are also separated by the same process.