System and method for high efficiency power generation using a nitrogen gas working fluid

A method for producing power, comprising:

• combusting a first fuel stream and a first air stream in a first combustor in the presence of a first recycle stream to produce a first combustion stream;
• expanding the first combustion stream in a first turbine to rotate the first turbine and produce power;
• directing at least a portion of a first discharge stream from the first turbine to a first heat exchanger;
• employing the portion of the first discharge stream to heat the first air stream and at least a portion of the first recycle stream that is produced from the first discharge stream with the first heat exchanger;
• combusting a second fuel stream and a second air stream in a second combustor in the presence of a second recycle stream that is produced from the first discharge stream to produce a second combustion stream;
• expanding the second combustion stream in a second turbine to rotate the second turbine to produce power;
• directing the second air stream and the second recycle stream to a second heat exchanger;
• and
• heating the second air stream and the second recycle stream with the second heat exchanger.

A power production system, comprising:

• an air supply configured to supply an air stream;
• a fuel supply configured to supply a fuel stream,
• a combustor configured to combust the fuel stream and the air stream in the presence of a recycle stream to produce a combustion stream that is greater than 50% N2 on a molar basis,
• wherein the air supply and the fuel supply are configured to supply the air stream and the fuel stream in a ratio configured to result in substantially stoichiometric combustion in the combustor with up to about 5% excess O2;
• a turbine configured to expand the combustion stream;
• and
• a heat exchanger configured to receive at least a portion of a discharge stream from the turbine,
• wherein the heat exchanger is configured to employ the portion of the discharge stream to heat the air stream and at least a portion of the recycle stream that is produced from the discharge stream.

A method for producing power, comprising:

• combusting a fuel stream and an air stream in a combustor in the presence of a recycle stream to produce a combustion stream that is greater than 50% N2 on a molar basis,
• wherein the ratio of the fuel stream to the air stream is controlled to result in substantially stoichiometric combustion with up to about 5% excess 02;
• expanding the combustion stream in a turbine to rotate the turbine and produce power;
• directing at least a portion of a discharge stream from the turbine to a heat exchanger;
• and
• employing the portion of the discharge stream to heat the air stream and at least a portion of the recycle stream that is produced from the discharge stream with the heat exchanger.