Abstract

The sCO2 closed-loop Brayton cycle is an alternative to the standard steam-Rankine cycle for generating electrical power from a heat source. The sCO2 Brayton cycle is advantageous because it can be more efficient, use less water, and have smaller turbomachinery than the steam-Rankine cycle. While there are several research groups advancing the technology necessary to utilize the sCO2 Brayton cycle on an industrial scale, none of these groups use solid fuel combustion as the heat source. A Brigham Young University-led project developed and tested a pilot-scale sCO2 Brayton cycle unit (1.6 MWth) using natural gas, pulverized coal, and pulverized biomass as the fuel. This work analyzes the data collected during operation of the unit and introduces a predictive model of the primary heat exchanger (PHX) temperature as a response to changes in operating conditions. The sCO2 Brayton cycle unit was operated for 407 hours, with 248 of those hours being continuous. The unit operated unmanned for 62% of the total operated time. Relevant data collected during operation are analyzed and used to understand the system behavior. The challenge in operating the unit is controlling the PHX temperature. Since there is no phase change in the PHX in the sCO2 Brayton cycle, the PHX tubes can experience rapid sensible heating as the conditions in the furnace change. Rapid changes in PHX temperature cause the PHX tubes to lose structural integrity which could cause the PHX tubes to burst. To ensure long term viability of the PHX, changes in operating conditions must be made in such a way to avoid rapid changes in PHX temperature. The predictive model uses a sCO2 temperature sub-model that calculates the transient temperature change of the working fluid as operating conditions change. The model then uses a 1D finite-difference heat transfer model to predict the temperature response of the PHX at a location near the flame. The finite-difference model uses measured PHX temperature to determine its initial temperature profile and the net radiative heat flux from the flame and refractory walls and the convective heat flux from the flow of sCO2 are used as boundary conditions. Parameters in the model were optimized to minimize error with two different data sets representing different changes in operating conditions. The model was evaluated using another data set and had an error in the rate of temperature change of 5.4% when the firing rate increased and a 62.7% error when the firing rate decreased.

Degree

PhD

College and Department

Ira A. Fulton College of Engineering; Chemical Engineering

Rights

https://lib.byu.edu/about/copyright/

Date Submitted

2025-12-17

Document Type

Dissertation

Keywords

supercritical Brayton cycle, sCO2, temperature modeling, power generation, solid fuels, combustion

Language

english

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Engineering Commons

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