Higher Gas Turbine Operation Flexibility by Improved Diffuser Vanes of a Radial Compressor

Transcription

1 Higher Gas Turbine Operation Flexibility by Improved Diffuser Vanes of a Radial Compressor STAR EUROPEAN CONFERENCE March 2011 Amsterdam, The Netherlands Dipl.-Ing. Anis Haj Ayed GmbH, Aachen, Germany

2 B&B AGEMA GmbH is an independent engineering Contact: service company providing consultancy, expertise, design and calculation for turbo machinery and power plants. Established in 1995 and located in Aachen (Germany), GmbH operates worldwide and independently for the benefits of its customers. GmbH Juelicher Strasse Aachen, Germany Phone: +49 (0) Fax: +49 (0) info@bub-agema.de Web: GmbH

3 Background Motivation & Task Compressor Geometry Operation Range Improvement Full Model Verification Conclusion Content

4 Advanced gas turbine process: high efficiency, complex process: Experiments showed need for operation range extension. uses STAR-CCM+ to investigate and improve single components with respect to operation range. High pressure compressor improvement case is presented. Background

5 Complex gas turbine control due to large number of components Repeated gas turbine trips due to stall of HP compressor Limited operating range of HP compressor: Limited gas turbine operation and control range Limited experimental flexibility Limited components life time due to increased vibrations levels and gas turbine trips (sudden shut down) Enlarge compressor operation range as much as possible by modifying as less parts as possible!! Motivation & Task

6 compressor inlet outlet scroll impeller inlet case vaned diffusor Compressor Geometry: Overview

7 outlet scroll impeller 17 vanes vaned diffusor 20 blades Compressor Geometry: Diffusor

8 Simplified segment model (rotational periodicity) One blade passage and one vane passage Simplified inlet case to include the bend in front of the impeller Coarse Calculation Grid - Fast calculation of full speed lines for different Vane configurations: operation range - Comparative evaluation of different vane designs Modeling Strategy

9 Turbulence Model: Realizable k,ε two layer, all y+ wall treatment Upstream Boundary: stagnation inlet Downstream Boundary: pressure outlet Interface type: Mixing plane diffusor outlet diffusor vane air inlet impeller blade coarse calculation grid (approx cells) cyclic boundaries Calculation Model

10 surge at m = 4.38 kg/s surge point choke at m = 5.41 kg/s Calculation Result: original vane

11 velocity [m/s] original vane acceleration negative incidence mixing plane m = 4.39 kg/s (near surge) compressor blade Calculation Result: original vane

12 Mach Number [-] original vane acceleration negative incidence mixing plane m = 4.39 kg/s (near surge) compressor blade Calculation Result: original vane

13 Mach Number [-] modified vane original vane acceleration negative incidence mixing plane m = 4.39 kg/s (near surge) compressor blade Vane Modification

14 velocity [m/s] modified vane improved incidence mixing plane m = 4.39 kg/s compressor blade Calculation Result: Modified vane

15 Mach Number [-] modified vane improved incidence mixing plane m = 4.39 kg/s compressor blade Calculation Result: Modified vane

16 m = 0.4 kg/s (~ 9%) m = 0.22 kg/s (~ 4%) Calculation Results: Speed Lines

17 Full 360 degree Model including detailed inlet case, impeller, vaned diffuser and outlet scroll Unsteady simulation for: - original compressor - modified compressor Verification of Design performance Full Model Verification

18 Inlet pipe Unsteady calculation of original compressor Unsteady calculation of modified compressor impeller mass flow = 4.2 kg/s Turbulence Model: Realizable k,ε two layer, all y+ wall treatment Upstream Boundary: mass flow inlet Downstream Boundary: pressure outlet Outlet scroll Implicit unsteady solver, time step approx polyhedral cells Modeling Strategy

19 original compressor: reversed flow velocity [m/s] impeller Outlet scroll Calculation Results

20 modified compressor original compressor homogenous flow reversed flow impeller Outlet scroll velocity [m/s] Calculation Results

21 Modification implemented within two days at very low cost Surge/stall margin even larger than predicted - More stability during gas turbine start up - More operation flexibility of the complex gas turbine process - Possibility to identify behaviour of other components STAR-CCM+ as reliable and efficient Tool for Engineering Success Experimental Validation & Conclusion