Gas turbines integrated with biomass gasification in a combined cycle power plant (Bio-IGCC) provide a path to power production with very high efficiency. Over 60% fuel-to-power efficiency has been demonstrated with natural gas. The fast ramp and relatively low cost make Bio-IGCC via gas turbines the ideal complement to intermittent power from wind turbines and PV cells. With stricter pollutant regulations and in order to promote the use of renewable fuels there is a great interest in improving fuel flexibility. An important feature of biomass gasification is that its properties vary depending on the feedstock and gasification principle and that the combustion characteristics are significantly different from conventional fuels. This makes it interesting to develop CFD models that can be used to simulate the combustion of syngas in existing gas turbines and for design optimization of new gas turbines. The TECFLAM swirl burner geometry, which is designed to be representative of common gas turbine burners, was selected for an assessment of the differences between a typical hydrocarbon fuel and syngas. A two-stage approach was employed with development and validation of an advanced CFD model. The validated model was used to compare the flame shape and other characteristics of the flow between methane, 40% hydrogen enriched methane and four typical syngas compositions. The syngas compositions used are representative of practical gasification processes and biomass feedstocks. It was found that the syngas fuels experience lower swirl intensity due to high axial velocities that weaken the inner recirculation zone. A strong correlation was found between the laminar flame speed and the flame shape. The simulation of a typical combustion geometry with syngas is quite demanding and requires a long computational time. In order to speed up the parametric analysis and to make it possible to test more configurations a Two-Step, One Way coupled method was assessed. This is a common approximation in CFD that is used to solve complex problems with limited computational resources. The test case used for the assessment was the CeCOST burner that uses strong swirl for flame stabilization. Only isothermal flow was investigated to eliminate the influence from flow – chemistry interactions. This method effectively divides the domain in two parts, one downstream and one upstream. The assumption behind this method is that the downstream part should not have a big influence on the upstream part and hence it could be solved separately. From the comparison it was found that the full solution and the approximations were in good qualitative agreement. However, there were some minor quantitative discrepancies, and it was proposed that the explanation for the differences could be the slightly different solution approaches that were used for the full simulation (URANS) and the two approximate solutions (RANS). The speed-up from using the approximate method was close to one order of magnitude. However, because an artificial steady inlet cannot reproduce all the dynamic phenomena created by a swirler, for the continuation a full CeCOST domain was used. LES modelling was also employed to be able to identify smaller structures that would affect flame stability. Using LES and the Artificially Thickened Flame model, a syngas composition that relates to Black Liquor gasification was modelled. The flame front position using the CH2O mole fraction was estimated and it correlated well with the position estimated by the progress variable. The flame front position found by using the OH mole fraction was different to the two previous ones, predicting the hot part of the flame.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:ltu-90452 |
| Date | January 2022 |
| Creators | Papafilippou, Nikolaos |
| Publisher | Luleå tekniska universitet, Energivetenskap, Luleå |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Licentiate thesis, comprehensive summary, info:eu-repo/semantics/masterThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | Licentiate thesis / Luleå University of Technology, 1402-1757 |
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