Supercritical carbon dioxide regenerative Brayton cycle with multiple recuperators and auxiliary compressors

Method for producing energy by means of a supercritical carbon dioxide (sCO2) regenerative Brayton cycle with N recuperators in series and N or N−1 auxiliary compressors, where N≥3, the method comprising a main compression process, and further:

• a. expanding a stream of supercritical CO2 (sCO2) in a turbine to a pressure between 3 MPa and 10 MPa to generate a sCO2 stream RHIN, for generating some mechanical or electrical energy;
• b. cooling the sCO2 stream RHIN in the N recuperators, this cooling step comprising the following steps c to e:
• c. cooling the sCO2 stream RHIN to a stream RHON by heating a stream RCIN to generate a stream RCON in the recuperator number N, stream RHIN-1 corresponds to the stream RHON;
• d. cooling the sCO2 stream RHIN-1 to generate a stream RHON-1 in recuperator number N−1 by heating a stream RCIN-1 to generate a stream RCON-1, wherein the stream RHON-1 is split into two streams:
• a stream RHIN-2 and a stream ACIN-1, compressing the stream ACIN-1 in an auxiliary compressor N−1 to the pressure of the stream RCON-1 thereby generating a stream ACON-1, mixing the stream ACON-1 with the stream RCON-1, thereby obtaining the mixture stream RCIN, and sending the stream RHIN-2 to the recuperator N−2;
• e. If N>3, repeating step d) for the recuperators number N−2 to recuperator number 2;
• f. cooling the sCO2 stream RHI1 to generate a stream RHO1 in recuperator number 1 by heating a stream RCI1 to generate a stream RCO1, wherein the stream RHO1 is split into two streams:
• a stream CI and a stream ACI1, compressing the stream ACI1 in an auxiliary compressor 1 to the pressure of the stream RCO1 thereby generating a stream ACO1, mixing the stream ACO1 with the stream RCO1, thereby obtaining the mixture stream RCI2, and sending the stream CI to the cooler to generate a stream MCI, and sending the stream MCI to the main compression process, performing an intercooling stage within the main compression process, thereby generating the stream RCI1 at the exit of the main compression process;
• wherein N is calculated as i−1, for the value of i corresponding to the number of the iteration for which Tout,i>TRHIN−pinchi is fulfilled, considering in iteration i=1 Tin,1 is defined as the temperature of the main compression process inlet, Pin and Pout are defined as the main compression process inlet pressure and outlet pressure and Tout,1 is defined as the outlet temperature of main compression process, and by using following relations for iterations i>1:
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• and calculating Tin,i=Tout,i-1+pinchi-1 at the beginning of each iteration for i>1, a number i of iterations until Tout,i≥TRHIN−pinchi is fulfilled, where Tin,i stands for the temperature of (i−1)th auxiliary compressor inlet, hin,l stands for the specific enthalpy of (i−1)th auxiliary compressor inlet, sin,i stands for the specific entropy of (i−1)th auxiliary compressor inlet, hout,s,i stands for the specific enthalpy of the outlet of the (i−1)th auxiliary compressor for an adiabatic and isentropic compression, hout,i stands for the specific enthalpy of stream leaving the (i−1)th auxiliary compressor and Tout,i stands for the outlet temperature of (i−1)th auxiliary compressor, i being defined as the number of iterations, starting with i=1 for the main compression process and pinchi being defined as the minimum temperature difference between the cold stream and hot stream of the ith recuperator.