What Pig Launchers and Receivers Do
All hygienic, sanitary and process pigging systems need a method of introducing the pig (or pigs) safely in to the line and propelling the pig to and from source and destination. They also need somewhere to store the pigs when they’re not actually ‘pigging’. These are the key functions of pig launchers and pig receivers.
How PIG LAUNCHERS AND PIG RECEIVERS Work
Depending on the application, pigs can be propelled by gases such as nitrogen, compressed air or carbon dioxide, or sometimes by water, cleaning fluid or even the next batch of product.
Also known as pig stations, pig launchers and pig receivers consist of specialist valves which control the pig propellant, and hence the pig.
The pigging system sequence is usually semi or fully automated. Pig detectors close to the pig launchers and receivers send a proximity signal to the software or control system so that the location of the pig is always known.
The pigging sequence itself is extremely quick. Opening and closing of the valves in the launch and receive stations is carefully controlled and ensures the pig is safely propelled along the line without risk of contaminating the product. It also ensures clean in place (CIP) or normal processing can resume as soon as the pigging sequence has finished.
Usually, the pig launcher stores the pig when not in use, and includes a housing to contain the pig. This housing is slightly larger than the pig to enable flow of water or cleaning fluids around the pig for CIP. The housing design also enables safe removal of the pig, for example for inspection or replacement. In HPS systems, the housings are designed so that it is possible to access the pig safely while normal processing is taking place. This means there’s no interruption or disruption to production if, for example, the pig needs changing.
HPS pigging systems include robust safety features and interlocks that ensure the pig and housing can only be accessed when safe to do so.
Returning the Pig
While the pig launcher introduces the pig into the process line, the basic role of the pig receiver is to send it back again when it has reached its destination. All HPS pigs are bi-directional, so can travel either way along the pipe (some manufacturers produce pigs that can only travel in one direction, which severely limits pigging system design and efficiency, particularly regarding automation).
Set up specifically to quickly, safely and efficiently return the pig with minimal disruption to the line, pig receivers are usually simpler in design than pig launchers. Because they don’t store the pig, there’s no pig housing. However, there are exceptions and some pigging systems, for example, multi destination and double-pig systems, may include housings in both the launch and receive stations, in which case both types of station are nearly identical.
Good quality pigging system design is one of the most important factors of pigging system implementation. This is because nearly all pigging systems are bespoke; designed specifically around a particular process and application. Pig launchers and receivers within these systems are similarly bespoke: their design depends on the propellant used, liquid being processed, length and diameter of pipeline, pigging sequence, type of pig and so on. There are also specialist designs of pig launcher and receiver, for example, to eliminate ‘dead space’ and recover absolute maximum amount of product. Therefore, there’s a wide variety of these pigging system components available – please contact HPS for further information.
To see how different pigging systems operate, please take a look at these pigging system demonstration videos.
For more information about pigging system design, pig launchers, pig receivers or any other aspect of liquid product recovery, then please get in touch.