Nitrogen Purging: When, Why and How?
Nitrogen purging is often used to clean pipelines, vessels and plants from potentially hazardous or clogged materials or gasses. The process is followed before commissioning, as part of a petrochemical plant or pipeline shut-down and decommissioning process, and when maintenance must be performed on a pipeline or plant.
Why nitrogen for purging?
It is a inert gas and can thus be safely used to clean and neutralise systems or pipes that are used to transport potentially hazardous gases. Because it is a non-combustible gas, it can be used with potentially hazardous substances without the risk of combustion. It is also a dry gas, making it effective in the displacement of moisture. With it also inert enough to displace oxygen, the gas can be used to create a dry and stable atmosphere as hydrocarbons are removed from the system.
Where and when to use nitrogen purging
The gas is pumped into a system at high pressure. This displaces the presence of oxygen in the system, and subsequent risk of an explosion. With this process it is possible to create the perfect environment for removing volatile substances from a system. It is used for the shutdown processes of systems where the oxygen level is too high for safe operation.
It is used for drying moisture-sensitive pipelines. In these instances, theliquid nitrogen is first vaporised before it is fed into the pipeline to dry the line to a required dew point. The gas is, furthermore, used to displace or dilute content for plant or pipeline maintenance purposes, during the commissioning or turnaround phases, and for shut-down processes.
Most used methods
The method to follow is subject to the application requirement, the equipment size, type and shape, and the location of outlet points.
Use pressure for transferring liquid without a pump
The vessel’s headspace is to transfer of liquid from one space to another. The method is applicable when a pump cannot be used for the liquid transfer process or where materials limit the effectiveness of a pump-based transfer process.
If the system has many complex cross-sections, the dilution method can be used to mix the nitrogen with the gas and purge it through one outlet. With this method it is important that the inlet and outlet points are far enough from each other to ensure safepurging.
Dilution of content through a pressure holding vacuum process
Where a vessel only has one outlet, the conventional sweep process may not be possible. In this instance, the vessel is pressurised withnitrogen. The content mixes with nitrogen, causing acceptable dilution of the content. The content is then vented. The process is repeated until all content is removed from the vessel or until the contamination level is at the required level.
Pigging and displacement
If the vessel, such as a pipeline, doesn’t have complicated cross-sections, the pigging method can be used. With this approach, nitrogen is used to push the scraper piston, known as a pig, to push the contents out. The amount ofnitrogen required depends on factors such as the length of the pipe and the volume of content that must be dispersed.
Where to get professional help with the processes
Do you need to de-commission, maintain or re-commission a pipeline or plant? Need to transfer liquid from one vessel to another without a pump system? We offer an extensive range of services to do so safely. Get in touch for more information about our nitrogen purging services.