Gas Turbine Reheat Using In-Situ Combustion
Gas turbine reheat is a well-known technique for increasing the power output of gas turbine, as well as the efficiency in combined cycle operation with higher heat recovery inlet temperatures. The technique also could allow development of an advanced high efficiency turbine with an additional stage, but without a higher inlet temperature. A novel reheat approach, with fuel added via internal passages in turbine airfoils, has been proposed [1]. This avoids the bulky and possible high-NOx discrete reheat combustors used in traditional approaches. The key questions regarding this approach are whether there is sufficient residence time at high temperature for fuel burnout, and whether increased emissions of NOx and CO result. This project examines the chemical kinetics basis of these questions. In the present task detailed chemical kinetics models were used to evaluate injection reheat combustion. Models used included a Siemens Westinghouse diffusion flame model, the set of CHEMKIN gas-phase kinetics equation solvers, and the GRI 3.0 detailed kinetics data base. These modules are called by a reheat-specific main program, which also provides them with data, including gas path conditions that change with distance through the turbine. Conceptually, injection could occur in either of two ways: (1) direct injection via holes in airfoil trailing edges; or (2) injection at the downstream faces of small bluff bodies placed at these edges. In the former case, combustion could occur as a diffusion flame at the hole, as a plume or streak following this zone, or as a substantially mixed out homogeneous region downstream. In the latter case, combustion could occur as a lower temperature, well-mixed, recirculating flame in the wake of the bluff body, followed by burnout in the same sequence of diffusion flame, streak, and mixed out. The results were as follows. In the case of a conventional four-stage engine, vane 1 trailing edge injection can be achieved with complete burnout without a flameholder. However, there are projected NOx and CO penalties of about 10 ppmv each. For vane 2 injection a flameholder is necessary, although the CO survival is expected to be larger, on the order of 50 ppmv. In the case of an advanced five-stage engine, injection at vane 2 (same size and conditions, except temperature, as vane 1 of a 4-stage engine) should be with a flameholder to minimize CO, keeping NOx and CO increases at about 20 and 10 ppmv respectively.
- Research Organization:
- Siemens Westinghouse
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FC26-00NT40913
- OSTI ID:
- 993808
- Country of Publication:
- United States
- Language:
- English
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