Applies Dilution to Lower Combustion Temperature and Emissions, Allowing Engines to Operate on Pure Hydrogen while Minimizing the Generation of Nitrous Oxides
Retrofitting gas turbine engines with inlet air dilution enables hydrogen gas combustion for power generation without excessive nitrous oxide emissions. Hydrogen utilization in gas turbine engines is an intense focus in the energy industry. Efforts are underway by global original equipment manufacturers of terrestrial gas turbines to meet the mandates for decarbonization goals set by the European Union and other countries. While the industry has made progress in allowing increased percentages of hydrogen in fuel blends, the use of 100% hydrogen in practical, flexible systems remains rare, preventing the achievement of zero-carbon generation. There is a need to replace hydrocarbon fuels with hydrogen in legacy systems to reduce greenhouse gas emissions.
The primary challenge associated with hydrogen combustion is the production of large amounts of nitrous oxides (NOx), which plays a significant role in atmospheric pollution. When hydrogen reacts with pure air, it causes excessively high local temperatures, rapidly creating nitrous oxide unless it is premixed or diluted. However, premixing hydrogen increases the likelihood of dangerous flame flashback due to its rapid ignition time, still generating nitrous oxide and damaging equipment. Meanwhile, dilution requires a diluent gas, such as a steam of nitrogen, burdening the system and decreasing plant efficiency. A different strategy is necessary to suppress nitrous oxide production using hydrogen fuel.
A researcher at the University of Florida has developed a design methodology for retrofitting natural gas turbines to burn hydrogen with minimal nitrous oxide (NOx) emissions. The retrofitted system recirculates its own exhaust to lower emissions, especially applicable to gas turbines with simple diffusion burners.
Application
Retrofits natural gas turbines for diffusion burning of hydrogen and diluted air with minimal nitrous oxide emissions
Advantages
- Requires only external modifications to conventional natural gas turbines, streamlining the retrofitting process
- Dilute air combustion prevents hot spots and other sources of nitrous oxide production as well as damage to the hardware
- Produces power without any hydrocarbon combustion, lowering greenhouse gas emissions when using green hydrogen
Technology
This system for retrofitting gas turbine engines enables them to run on pure hydrogen without exceeding the regulated nitrous oxide limits. Dilution of combustion air with an inert gas reduces nitrous oxide emissions in gas turbines. The turbine exhaust gas is a natural source of the inert gas. Dilution with exhaust, also known as exhaust gas recirculation (EGR), occurs by cooling some of the turbine outflow to mix with incoming air, providing efficiency benefits and external heat.
The turbine design approach straightforwardly retrofits conventional natural gas turbines to utilize EGR and reduce nitrous oxide pollution without requiring a fully redesigned combustor. The retrofit modifies the external ductwork to capture a part of the exhaust gas and pass it through a heat exchanger or absorption refrigeration system. After cooling, the captured exhaust mixes with fresh air before re-entering the engine. This accomplishes the dilution of the fresh air necessary for reduced nitrogen oxide formation and the prevention of hot regions when the diluted air combusts with hydrogen fuel. The overall process requires no fuel premixing, avoids dangerous flashback, and operates as a simple diffusion burner.
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