Compression system, method for starting up compression system, and method for stopping compression system

A compression system comprising:

• a supply line to which raw material gas is supplied;
• a first compression part that compresses the raw material gas flowing through the supply line;
• an impurity removal part that removes an impurity from the raw material gas compressed by the first compression part;
• a second compression part that further compresses the raw material gas that has passed through the impurity removal part;
• a discharge line that guides the raw material gas compressed by the second compression part to the outside;
• an upstream side shutoff valve and a downstream side shutoff valve that are respectively provided at a front stage and a rear stage of the impurity removal part to sandwich the impurity removal part therebetween, and of which a flow rate of at least one is adjustable;
• a gas addition line capable of guiding compressed gas between the downstream side shutoff valve and the second compression part;
• and
• an open/close valve provided in the discharge line.