Oil free three-stage reciprocating compressor and CO2 system comprising such a compressor

A system for a CO2 regeneration plant comprising a foam trap, a low pressure water scrubber, a stepless three-stage compressor comprising one or more intercoolers or cooling units and water separators, a regenerable dehydrator, a condensing unit comprising a condenser, where the stepless three-stage compressor comprises a three-stage reciprocating compressor, wherein the three-stage reciprocating compressor comprises pistons, suction and compression chambers in which a gas is compressed in a plurality of stages, where each stage of the plurality of stages is connected in series with at least one other stage of the plurality of stages and a first stage is fluidly connected to an inlet configured to receive uncompressed or pre-compressed gas, wherein the three-stage reciprocating compressor comprises three-stage pistons configured to move synchronously along a common axis in one connected unit such that first and second stage suction and compression chambers share a piston as well as a cylinder wall, a top headpiece, and a bottom headpiece on each side of the piston, wherein the three-stage reciprocating compressor comprises a third stage piston extending from a center of the piston through an opening in the top headpiece, the third stage piston comprises a third stage cylinder wall comprising a smaller diameter than a diameter of the cylinder wall for stage one and two, the third stage cylinder wall extends from the top headpiece, wherein each stage is fluidly separated by one or more one way valves, wherein a second stage suction and compression chamber is formed between the cylinder wall and a piston skirt as well as between an underside of the piston and the bottom headpiece placed in a bottom of the cylinder wall.