Introduction

Conclusions

Hydrogen Combustion

 

 

 

 

 

 

 

 

Hydrogen can be combusted to produce energy, however, because of its high burning temperature, hydrogen combustion in a conventional engine would produce very high levels of NOx. There are some ways to decrease NOx emissions already available. For instance, catalytic burners can reduce the burning temperature and some burners use diffusion for low NOx burning of hydrogen.

One study used a Stirling engine to study internal hydrogen combustion. In this engine, the working gas was heated by initial hydrogen and oxygen combustion followed by water removal. It claimed that the only emission from the engine was water, however, the paper made no mention of NOx elimination and did not have details on safe, stable, and optimized operation of the process or engine components.

 

Another approach uses turbines in hydrogen fueled combustion. Jin and Ishida compared two such cycles, one with chemical looping combustion, and one without. In the turbine without chemical looping, hydrogen fuel, pure oxygen, and water are fed into a combustor. The only product of this combustion is steam because there are no nitrogen sources to produce NOx. The resulting steam is then used to power a gas turbine. However, there is a great deal of energy loss in the combustion, even if steam and not an inert cooling gas is used as a cooling agent. The energy degradation from extremely high temperature hydrogen combustion to very low temperature for water evaporation is, in fact, much worse than that of a standard heat recovery steam generator from middle temperature to low temperature. This energy loss is in addition to the losses to pure oxygen production, which drops efficiency by another 11.5%.

The approach that used chemical looping was more promising. It used two successive reactions, metal oxide reduction with hydrogen, and then the resulting metal’s oxidation with pressurized air, yielding the metal oxide and a high-temperature flue gas. The resultant gases can then be used to power turbines. According to Jin and Ishida, pure hydrogen is the ideal fuel, and because there is no flame to produce NOx, pure oxygen is not necessary to reduce emissions. A schematic of the engine is below.

 

 

 

 

 

 

 

 

 

 

 

Source: Jin H. & Ishida M. A novel gas turbine cycle with hydrogen-fueled chemical-looping combustion. International Journal of Hydrogen Energy 25 (2000) 1209-1215.

Hydrogen combustion could be an effective way to utilize hydrogen energy, however, many developments need to be made before it can be implemented to ensure that it does not cause more environmental problems than it solves. The chemical looping engine shows some promise, but the design is far from fully developed.

Source: www.nature.com

Sources:

Jin H. & Ishida M. A novel gas turbine cycle with hydrogen-fueled chemical- looping combustion. International Journal of Hydrogen Energy 25 (2000) 1209-1215.

Takahashi S. et al. Hydrogen internal combustion sterling engine. JSME International Journal Series B, Vol. 46, No. 4 (2003) 633-642.