Session: 05-01: GT Performance

Paper Number: 153495

Transient Analysis of Hydrogen Co-Fired Gas Turbines During Load-Following Operation 

Efforts are being made to use hydrogen as a fuel in gas turbines instead of fossil fuels in order to reduce carbon dioxide emissions in the power generation sector. When hydrogen is co-fired in gas turbines using natural gas as fuel, the main issues addressed include flash back and an increase in NOx emissions, and many studies are being conducted on the combustion side to solve these problems. Assuming a scenario where hydrogen co-firing is possible, the composition and properties of the combustion gases change, which shifts the operating point of the gas turbine and leads to changes in performance. Therefore, predicting how the operating points and performance of gas turbines change is important, but research in this area is still insufficient. Thus, this study analyzed hydrogen co-firing gas turbines from a performance perspective, particularly considering the shift in operating points and changes in fuel composition during load-following operations with transient analysis.

To apply hydrogen co-firing to gas turbines, additional variables beyond the co-firing ratio must be controlled, and it can be implemented in various scenarios. In previous studies by our group, hydrogen co-firing was applied in two scenarios to analyze changes in operating points and performance in the full-load area. The first scenario involved maintaining the turbine inlet temperature (TIT) at the design point, and the second involved maintaining the gas turbine output at the design point. This work aims to analyze the transient behavior of the hydrogen-cofired gas turbine subject to the two operating scenarios (maintaining TIT or output) in comparison to the natural gas fired cases.

To conduct an analysis for load-following operations, partial load control curves for the gas turbine are needed. While these curves can vary among engine manufacturers, a typical logic was adopted. A constant TIT control was first applied as the load decreased from full load. After the turbine exhaust temperature (TET) reached a set limit, a constant TET control was applied. The extent to which the operating points shift varies depending on the co-firing ratio and scenario applied, resulting in different control curves with this control logic. Therefore, partial load control curves applicable to each condition were first derived.

During load-following operations, PID control was applied to match the load, adjusting the fuel flow to maintain shaft speed, and the angle of the inlet guide vane (IGV) was adjusted to move along the control curve appropriate for the ratio of compressor discharge pressure (CDP) to turbine exhaust temperature (TET). The same PID gains as when using only natural gas as fuel were applied, and the dynamic characteristics such as overshoot and undershoot were analyzed. For example, when using the same PID gains for 10% power reduction from the reference full load, the 50% co-firing ratio exhibited a 0.54%p greater TIT overshoot in comparison to the natural gas fired case. This could have a critical impact on the lifespan of turbine blades operating at high temperatures. This indicates the control logic needs to be revised (i.e. PID gains should be reset), the research focus of this study was given to optimize the control logic through setting the right PID gains so that similar dynamic characteristics could be achieved even when hydrogen is co-fired. Additionally, changes in dynamic characteristics according to the ramp rate during load control, as well as changes according to the magnitude of the load change, were also analyzed. This study allows for the understanding of the dynamic characteristics of hydrogen co-fired gas turbines in different operating scenarios, and the result can be utilized for actual engine control logics in consideration of critical operation factors such lifespan management of high-temperature components.

Presenting Author: Ji Hun Jeong Inha University

Presenting Author Biography: Ji Hun Jeong received his Master’s degree from the Department of Mechanical Engineering, Inha University in 2019 and is currently working on doctoral degree in the same department. His research interests include performance analysis and simulation of gas turbine operation and hydrogen co-firing.

Authors:

Ji Hun Jeong Inha University
Tong Seop Kim Inha-University