Natural gas is something that we all rely on in the modern world. It is a type of fossil fuel that is usually gathered from underground reservoirs by companies that use giant wells. But, what happens after it has been gathered? Before natural gas can be used in our own homes and workplaces, it has to go through a series of rigorous processes inside of a natural gas processing plant.
What is a natural gas processing plant?
The natural gas that you use within your own home, as a consumer, is very different to the natural gas that can be found in its ‘raw’ state in underground reservoirs. A natural gas processing plant is a type of facility that has been specifically designed to perform the process of separating all of the impurities from this ‘raw’ state of natural gas. This process produces ‘pipeline quality’ natural gas.
This is actually really important because the majority of major transportation pipelines will only allow natural gas to flow through their pipelines if the gas has a specific chemical make-up. Meaning that all of the extra hydrocarbons and fluids need to be separated at the natural gas processing plant before the gas can enter the pipelines.
How does natural gas reach the processing plant?
Some of the processing that is involved in ‘cleaning’ the raw natural gas can actually be done at or around the wellhead itself, but all of the steps that are involved in the complete process have to take place at a processing plant. To get to the processing plant, the natural gas has to be transported through a massive system of incredibly small pipes.
If the gathering system of pipes is quite complicated, it could involve thousands of miles of pipes that connect up to a hundred oil wells to the same natural gas processing plant. Given that the pipes are only small in diameter, this means that more and more pipes have to be added.
What has to be removed from the natural gas?
The contaminants that have to be removed from the natural gas at the processing plant could quite easily be separated into two different categories. These would include valuable by-products that should be collected and waste by-products that should be disposed of. For example, the Natural Gas Liquids (NGL) that can be gathered during the purification process all hold their own value.
Some of the main contaminants that have to be removed include:
- Hydrocarbons that are much heavier than methane – Raw natural gas is mainly composed of methane. Other hydrocarbons that have to be separated from the natural gas include ethane, propane, isobutene and other heavy hydrocarbons. These are collectively referred to as Natural Gas Liquids.
- A number of different acid gases –These include carbon dioxide, hydrogen sulphide, ethanethiol and a few other acid gases. Other gases like nitrogen and helium also have to be removed from the natural gas.
- Water –Water can be found as both liquid water and water vapor in raw natural gas. Both have to be removed before the natural gas can enter major pipelines. Liquid hydrocarbons also have to be removed at the natural gas processing plant, including natural-gas condensate and crude oil.
- Potentially dangerous substances – Both mercury and naturally occurring radioactive material (NORM) can be found in raw natural gas. The mercury is usually only found in small amounts, but it still has to be removed. Natural gas can contain radon and the water in the raw natural gas could contain traces of radium. Both of these could have the potential to be dangerous if they were not removed.
Why do the contaminants have to be removed?
Generally speaking, all of the contaminants that can be found in raw natural gas have to be removed. This is to make sure that the natural gas is suitable for transportation via major transportation pipelines. These contaminants are removed at the natural gas processing plant for many reasons. Each major pipeline transmission and distribution company sets standards. The natural gas must meet these standards in order to be transported through their pipelines.
These standards have been put in place for a number of different reasons. However, most of them are in place to ensure that none of the by-products can damage the pipeline. For example:
- The gas has to be delivered at a hydrocarbon dew point temperature that is specified by the distribution company. This is to ensure that no condensation occurs during pipeline transportation. Otherwise, due to the pressure that the gas will be exposed to, condensation would result in liquid slugs that could potentially damage the pipeline.
- The gas must not contain any particulate solids or liquid water. Otherwise, the pipeline could be susceptible to either erosion or corrosion. Both of these would shorten the lifespan of the pipeline and cause an array of problems.
- All of the naturally occurring radioactive material (NORM) must have been removed from the natural gas. Otherwise, it could render both piping and equipment radioactive as time passes.
In order to make sure that all of these contaminants are removed so that the natural gas can flow through major transportation systems, the natural gas has to go through a series of purification processes. These include everything from a cryogenic process that recovers helium to a process that specifically removes and gathers all of the valuable natural gas liquids (NGL).
What happens next?
Once the natural gas has been cleaned and processed in a natural gas processing plant, it is ready to enter major transfer pipes that can take it to where it is needed. If the natural gas still contains contaminants, then it will not be able to enter these pipelines. Upon entering these main channels, the natural gas can finally be distributed and used by consumers.