Session: 06-10 Hydrogen for Aviation & Industry

Paper Number: 152903

The Hydrogen-Fueled Allam Cycle: Thermodynamic Evaluation and Optimization After a Fuel Switch to Hydrogen 

The Allam Cycle is one of the most promising concepts in thermal power generation, especially due to its high thermal efficiency (>60%) and power production, zero NO_x and near-zero CO₂ emissions, and high-pressure, high-purity extraction of carbon dioxide for commercial use or storage. This makes it competitive in cost of electricity with traditional thermal power plants that do not capture carbon. As a natural gas fueled prototype has been successfully tested, and an industrial-scale plant (300 MWe) is expected to begin construction in 2024, most recent publications have focused on the fossil-fuel-based Allam Cycle.

In view of a global shift towards renewable energies and the imminent scarcity of fossil energy sources, the transition of both traditional thermal power plants and the Allam Cycle to hydrogen fuel becomes more and more relevant. This raises questions about the performance, required design modifications, and operational challenges associated with switching to hydrogen. Although various combinations of working fluids and fuels have been discussed in the literature, a thorough design and a thermodynamic analysis of the H₂-fired Allam Cycle has yet to be carried out.

This work presents a first thermodynamic analysis of the H₂-fueled Allam Cycle with a simplified Aspen Hysys model. The results allow a first comparison between the CH₄-fired and H₂-fired Allam Cycle and show the infrastructural adjustments required for this fuel switch. Preventing and compensating the unintended but inevitable release of CO₂ within the water condensate is identified as a key challenge. Three different methods to tackle that issue are proposed and evaluated through simulation. For a more detailed analysis, the integration of hydrogen compression to combustor pressure, oxygen preheating and a heat exchanger network for heat recuperation are then added to the process model. The final model will include a simplified model for turbine cooling, to allow a better estimation of the thermal efficiency of the H₂-Allam Cycle.

Assuming the same parameters for both CH₄-fired and H₂-fired Allam Cycle, the thermal efficiency of the latter rises by around 6% based on the lower heating value (LHV). This is mainly due to reduced compression work and higher specific turbine work resulting from the increased specific isobaric heat capacity of the steam-enriched working fluid. Furthermore, less fuel mass is needed to reach the same TIT and net turbine power output, due to the higher LHV of hydrogen. This results in decreased oxygen needs and thus a smaller air separation unit. Also, the newly proposed condensate water treatment reduces the CO₂ losses to 9 g/s and can be implemented in the original Allam Cycle. However, when accounting for the energy required for hydrogen processing and losses due to turbine cooling the thermal efficiency of the new cycle drops significantly but remains competitive with the CH₄-Allam Cycle.

Presenting Author: David Bocandé Helmut Schmidt University of Hamburg

Presenting Author Biography: 2016: German-French Bachelor of Science in mechanical engineering at Université de Loraine and htw Saarbrücken
2020: Master of science in energy technology at the Leibniz Universität Hannover
since 2021:
PHD-Student
- process modelling in Aspen Hysys and Matlab
- building a test rig for H2 combustion in steam

Authors:

David Bocandé Helmut Schmidt University of Hamburg
Julia Rohardt Technische Universität Hamburg
Markus Schatz Helmut Schmidt University of Hamburg