NATURAL GAS PROCESSING:A brief look at the natural gas

industry ByUndergraduates: Robert VanLeeuwen, Matthew

Martinez, Loralie FaulkFaculty: Dr. Carl Murphy, Dr. Ali Pilehvari, Mohsen

Dirbaz (graduate student)

Typical Composition of Natural Gas

Methane – CH4 : 70 – 90% Ethane – C2H6 : 0 – 20% Propane – C3H8 : 0 – 20% Butane – C4H10 : 0 – 20% Carbon Dioxide – CO2 : 0 – 8% Nitrogen – N2 : 0 – 5% Hydrogen Sulfide – H2S : 0 – 5% Oxygen – O2 : 0 – 0.2% Rare Noble Gases – Ar, He, Ne, Xe : traces

Focus of study

While there is much to discuss in the field of processing natural gas, this presentation will focus on three very important steps:

1. Water Removal via Liquid Desiccant (TEG Glycol)

2. Cryogenic Turbo Expansion 3. Fractionation of Natural Gas Liquids

Cost analysis will also be used to display the economical aspect of natural gas processing.

TEG Glycol Dehydration

When taken from the wellhead, natural gas is partially saturated with water.

Water left with natural gas during processing will tend to form solid hydrates, which will build up in pipes and impede the flow of natural gas in the system.

Liquid desiccant known as glycol is dispersed through the top of the tower which absorbs the water and dehydrates the gas.

TEG Glycol Dehydration (Cont.)

The glycol-water solution exits the bottom of the tower and is ‘flashed’ in a flash tank to vaporize any trapped methane or associated gases.

The glycol-water solution is heated to vaporize the water (boiling point: 212o F) from the glycol (boiling point: 400o F). This allows glycol to be recycled in the dehydration process.

Removing water gets rid of solid hydrates and lowers the dew point (the temperature at which condensate first forms) of the natural gas.

Cryogenic Turbo ExpansionDemethanization requires the natural

gas be cooled and then put into an expansion chamber to reduce the gas temperatures to a range of -120 to -150 degrees Fahrenheit.

By reaching these low temperatures, the heavier hydrocarbons condense to a liquid state, while methane remains gaseous, thus separating them.

Energy gained from the expansion process is used to recompress the gaseous methane which can then be shipped off. This process also allows for a high ethane recovery rate of up to 95%.

Fractionation of NGLsIn order to be distributed and

sold to consumers, natural gas liquids must be broken up into their components.

This can be easily done because each component has different boiling points, so starting with the lightest hydrocarbon (and therefore, easiest to boil), each is brought to a vapor while the heavier hydrocarbons remain liquids and continue through the process until all components are separated.

Cost Analysis using Capcost

Using the Capcost program, simulation processing plants can be accurately modeled financially, to find out whether or not building a plant with certain specifications will be profitable.

Modeling requires plant manufacturing costs, raw material costs, maintenance costs and expected profits from processed products.

Project simulation rate of return (over a period of ten years, discounted profitability) – 14.9%

Cash Flow Diagram

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Cash Flow Diagram

Project Life (Years)

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Conclusion

Natural Gas Processing is an exciting and rewarding career choice for promising Chemical Engineers.

The future of Natural Gas Processing looks very bright, as consumer demand grows.