Minimum Environmental Load Reduction in Heavy Duty Gas Turbine by Bleeding Lines

Abstract

The power generation and energy market scenarios are requiring the power generation plants to fulfill more flexible operations respect to the recent past. One of the main concerns of plant operators is the lowering of minimum load at which the machines can be exercised while respecting the pollution limits. A strategy to improve minimum turndown capability by reducing the minimum environmental load of heavy duty axial gas turbines is here presented: it is based on the use of the compressor air bleeding lines (blow-off lines). The described technical development activities are based on the numerical modeling of blow-off lines and bleeding compressor sections; these preliminary tasks have been followed by on-field plant testing. The blow-off lines modeling reserves a particular regard, due to the somehow non-usual fluid dynamics involved. A Fanno flow 1D approach has been adopted to properly model the bleeding lines fluid flow whereas full 3D numerical solutions have been developed to get a better insight of the bleeding plenums and of the line sector including the valve. In addition, the gas turbine components off-design behavior and the overall performances are computed by the Ansaldo modular simulation code. Numerical analysis and performed field tests are here presented and results are compared, showing a good agreement, in accord to the simplified model adopted. Additional comparisons with different alternative strategies are finally presented in terms of gas turbine power and excess air variation. The described technique by blow-off lines opening shows to be able to fulfill the required task by incrementing the plant operative flexibility and guaranteeing safe plant operation. The technique drawbacks are a gas turbine slightly lower efficiency and the lower output flue gas temperature, whose relative importance have to evaluate by the plant operators. At present the long term sustainability of the new operative condition is the object of a deeper and longer field testing phase.

Retrofittable Solutions Capability for a Gas Turbine Compressor

“…In all the presented simulations, mixing planes with non-reflecting boundary conditions (Giles [8,9]) have been adopted to couple consecutive rows. A local matching interface was used between the last stator and the OGV since they share the same blade count [4,3].…”

“…Despite their rapid development expected over the next decades, gas-fired power plants are required to maintain a key role in the energy horizon, in order to ensure grid stability and peak demand, and so to reach extreme off-design conditions. The increasingly restrictive regulations imposed by the European community have led to strong interest in the development and optimization of technologies, that can be retrofitted to an existing combined-cycle power plant to enhance flexibility, as well as increase performance and lower emissions (General Electric [12], Alstom Power [18], Ansaldo Energia [3]).…”

Retrofittable Solutions Capability for Gas Turbine Compressors

“…The increasingly restrictive regulations imposed by the European community have led to strong interest in the development and optimization of technologies that can be retrofitted to an existing combined-cycle power plant to enhance flexibility as well as increase performance and lower emissions (General Electric [4], Alstom Power [5], Ansaldo Energia [6]).…”

Gas turbine minimum environmental load extension with compressed air extraction for storage

“…For GTs, it is desirable to reduce the low load capability without exceeding the CO limits. This can be made possible by some approaches that include Variable Inlet Guide Vane (VIGV) extension [4], use of bleed-off valves (BOV) [5] and through bleed extraction for storage (Compressed Air Energy Storage -CAES) that applies to this study. Pratyush et al [6] in a Siemens study indicated that extended VIGV closure, bypassing compressed air around the combustor, and optimizing rotor cooling can bring about a MEL of 40% and 28% (without and with catalytic CO capturing respectively).…”

“…Similarly, Alstom explored the use of sequential burners in their GT26, currently owned by Ansaldo Energia; Ruchti et al [7] suggest that the engine could achieve a MEL of 20% by switching off one of its burners and still operate satisfactorily in combined cycle operation. More recently, Ansaldo Energia investigated the use of BOV, presented in Coiffi et al [5]. The authors performed a thermodynamic and aerodynamic analysis of a BOV, showing a 29% reduction of MEL.…”