Hydrocarbon pyrolysis with less exhaust emission

A process for performing pyrolysis, comprising:

• separating from air at least an oxygen-containing stream, the oxygen-containing stream comprising 90 vol. % or more O2;
• combusting a first fuel with a first portion of the oxygen-containing stream in the presence of at least a portion of a recycle stream at a pressure of 10 MPa-a or more to produce a heated working fluid, the recycle stream comprising 80 vol. % or more CO2;
• operating a turbine using the heated working fluid to produce power and an intermediate working fluid comprising at least CO2 and H2O;
• combusting a second fuel with a second portion of the oxygen-containing stream in the presence of the intermediate working fluid to form a heated intermediate working fluid;
• exposing the heated intermediate working fluid to a plurality of furnace tubes in a pressurized pyrolysis environment to transfer heat to the plurality of furnace tubes and produce a depressurized working fluid comprising a pressure of 800 kPa-a to 3000 kPa-a;
• pyrolyzing at least a portion of a hydrocarbon-containing feed in the plurality of furnace tubes to form a pyrolysis effluent comprising at least a process gas comprising ethylene;
• transferring at least part of the produced power a) to a process gas compressor to compress the process gas, b) to a refrigeration compressor to cool the process gas, c) to a refrigeration compressor to cool the depressurized working fluid in a cooling step in a series of cooling and compressing steps, or d) a combination of two or more of a), b) and c);
• performing the series of cooling and compressing steps on the depressurized working fluid to form a water stream and a CO2-containing stream, the CO2 in the depressurized working fluid and the CO2-containing stream being in a single phase during the series of cooling and compressing steps;
• and
• compressing at least a portion of the CO2-containing stream to form a compressed CO2-containing stream, the recycle stream comprising at least a first portion of the compressed CO2-containing stream.