# Optimization of Exergy Output Rate in a Supercritical CO2 Brayton Cogeneration System

## TL;DR

This paper introduces a supercritical CO2 Brayton system to improve energy efficiency by recovering waste heat, increasing exergy output by 16% through optimized parameters.

## Contribution

A novel supercritical CO2 Brayton cogeneration system with optimized parameters for enhanced exergy output rate is proposed.

## Key findings

- Exergy output rate increased by 16.06% with optimized mass flow rate and pressure ratio.
- Optimal thermal conductance allocation favors regenerator and cooler over heater.
- The system offers improved energy efficiency and sustainability for industrial waste heat recovery.

## Abstract

To address low energy utilization efficiency and severe exergy destruction from direct discharge of high-temperature turbine exhaust, this study proposes a supercritical CO2 Brayton cogeneration system with a series-connected hot water heat exchanger for stepwise waste heat recovery. Based on finite-time thermodynamics, a physical model that provides a more realistic framework by incorporating finite temperature difference heat transfer, irreversible compression, and expansion losses is established. Aiming to maximize exergy output rate under the constraint of fixed total thermal conductance, the decision variables, including working fluid mass flow rate, pressure ratio, and thermal conductance distribution ratio, are optimized. Optimization yields a 16.06% increase in exergy output rate compared with the baseline design. The optimal parameter combination is a mass flow rate of 79 kg/s and a pressure ratio of 5.64, with thermal conductance allocation increased for the regenerator and cooler, while decreased for the heater. The obtained results could provide theoretical guidance for enhancing energy efficiency and sustainability in S-CO2 cogeneration systems, with potential applications in industrial waste heat recovery and power generation.