Premixer Design for High Hydrogen Fuels (2005)

This 21-month project translated DLN technology to the unique properties of high hydrogen content IGCC fuels, and yielded designs in preparation for a future testing and validation phase. Fundamental flame characterization, mixing, and flame property measurement experiments were conducted to tailor computational design tools and criteria to create a framework for predicting nozzle operability (e.g., flame stabilization, emissions, resistance to flashback/flame-holding and auto-ignition). This framework was then used to establish, rank, and evaluate potential solutions to the operability challenges of IGCC combustion. The leading contenders were studied and developed with the most promising concepts evaluated via computational fluid dynamics (CFD) modeling and using the design rules generated by the fundamental experiments, as well as using GE's combustion design tools and practices. Finally, the project scoped the necessary steps required to carry the design through mechanical and durability review, testing, and validation, towards full demonstration of this revolutionary technology. This project was carried out in three linked tasks with the following results. (1) Develop conceptual designs of premixer and down-select the promising options. This task defined the ''gap'' between existing design capabilities and the targeted range of IGCC fuel compositions and evaluated the current capability of DLN pre-mixer designs when operated at similar conditions. Two concepts (1) swirl based and (2) multiple point lean direct injection based premixers were selected via a QFD from 13 potential design concepts. (2) Carry out CFD on chosen options (1 or 2) to evaluate operability risks. This task developed the leading options down-selected in Task 1. Both a GE15 swozzle based premixer and a lean direct injection concept were examined by performing a detailed CFD study wherein the aerodynamics of the design, together with the chemical kinetics of the combustion process, were analyzed to evaluate the performance of the different concepts. Detailed 1-D analysis was performed to provide 1-step NOx and 1-step combustion models that could be utilized in CFD to provide more accurate estimates of NOx for more complicated combustion designs. The swozzle results identified potential problems with flame holding, flashback and with adequate mixing. Flame holding issues were further evaluated with laboratory testing to determine under what conditions a jet in cross flow would flame hold. Additional CFD analysis was also performed on fuel injection from a peg to simulate fuel injection off a vane's trailing edge. This task was concluded with a Conceptual Design Review of the two selected design concepts. (3) Optimize design and re-evaluate operability risks. This task extended the analysis of LDI concepts and increased understanding of the optimal design configuration. Designs were selected for subscale combustion laboratory testing and then modeled using CFD to validate CFD methodology. CFD provided a good qualitative match and reasonable quantitative match with the test results. Tests and CFD modeling indicated a path to low NOx combustion with no diluent addition. Different swirler designs were also evaluated and the most promising, a counter rotating swirler, was selected for further evaluation. CFD modeling was performed and the design was optimized to improve mixing. CFD modeling indicated the potential for low NOx combustion without diluent addition. CFD was validated against cold flow testing on a swirler using helium injection in place of hydrogen. Further validation work is still needed to ensure the ability to accurately model the mixing of swirling flows. Entitlement testing was performed on a perfectly premixed H2/N2/air mixture. Results showed that low NOx could be obtained at the temperatures of interest (7FB conditions) with no diluent addition. Results also showed that further NOx reductions might be possible by taking advantage of the very rapid H2 reaction to reduce combustor length and hence residence time. These results also indicate that there is a high probability that a combustor can be built that will meet DOE emissions goals. Based on these results and the promising results for the optimized swirler, the swirler will be the primary concept and the LDI will be maintained in reserve if flameholding issues cannot be resolved.