Investigation of the steam-cooled blade in a steam turbine cascade

With the increasing demand for electricity,an efficiency improvement and thereby reduced CO2 emissions of the coal-fired plants are expected in order to reach the goals set in the Kyoto protocol.It can be achieved by a rise of the process parameters.Currently,live steam pressures and temperatures up to 300 bars and 923 K are planned as the next step.Closed circuit steam cooling of blades and vanes in modern steam turbines is a promising technology in order to establish elevated live steam temperatures in future steam turbine cycles.In this paper,a steam-cooled test vane in a cascade with external hot steam flow is analyzed numerically with the in-house code CHTflow.A parametric analysis aiming to improve the cooling effectiveness is carried out by varying the cooling mass flow ratio.The results from two investigated cases show that the steam cooling technique has a good application potential in the steam turbine.The internal part of the vane is cooled homogeneously in both cases.With the increased cooling mass flow rate,there is a significant improvement of cooling efficiency at the leading edge.The results show that the increased cooling mass flow ratio can enhance the cooling effectiveness at the leading edge.With respect to trailing edge,there is no observable improvement of cooling effectiveness with the increased cooling mass flow.This implies that due to the limited dimension at the trailing edge,the thermal stress cannot be decreased by increasing the cooling mass flow rate.Therefore,impingement-cooling configuration at the trailing edge might be a solution to overcome the critical thermal stress there.It is also observed that the performance of the cooling effective differs on pressure side and suction side.It implicates that the equilibrium of the cooling effectiveness on two sides are influenced by a coupled relationship between cooling mass flow ratio and hole geometry.In future work,optimizing the hole geometry and cooling steam supply conditions might be the solutions for an equivalent cooling effectiveness along whole profile.

Hybrid system-a promising way solving future energy problems

With the increasing demand for electricity,an efficiency improvement and thereby reduced CO2 emissions of the power plants are expected in order to reach the goals set in the Kyoto protocol.In comparison to conventional systems,the hybrid-systems with the use of synergetic effects offer the possibility to provide a substantial contribution to spare our natural resources and protect our environment.Combined Cycle Power Plants belongs innately hybrid system in the centralized energy market.They can provide large amounts of power and have a quick start-up time.The MGT/FC hybrid system is quite promising in the decentralized energy market.It is widely used in stand-alone applications.Furthermore,the combination of fossil and renewable power plant technologies contains a large synergy potential to increase the efficiency of processes for power plants.New materials,innovative cooling technology,new combustion concepts and optimized production methods are needed to make the potential of these new technologies accessible for a quantum leap in the efficiency.For this it needs considerable research work and good coordinated research projects between the state,industry,research laboratories and universities.

Designing a power plant with highest efficiency:results from SFB 561

The goal of Collaborative Research Centre(SFB) 561 "thermally highly loaded,porous and cooled multi-layer systems for combined cycle power plants" is to expand the current technological and scientific knowledge on power plants in order to achieve total efficiencies of 65% in a combined cycle power plant in the year 2025.Therefore,the aero-thermomechanical,structural-mechanical,materials' scientific and production fundamentals for the development of steam and gas turbine components that are able to withstand highest thermal loads are being worked out within this SFB.This means for the gas turbine that combustion chamber outlet temperatures of 1520℃ at 1.7MPa are to be attained.In order to control these high temperatures,it is not only required to develop new materials' solutions,including thermal barrier coatings,but also to apply improved cooling techniques,as for example effusion cooling.This novel cooling concept is to be realised through open-porous structures.These structures can consist of drilled open-porous multi-layer systems or open-porous metallic foams.The development of graded multi-layer systems is also extremely important,as the grading will enable the use of coolant in dependence of the requirements.The live steam parameters in the high pressure turbine are expected to be increased up to approximately 700℃ with pressure of 30MPa.These elevated steam parameters can be encountered with Ni-base alloys,but this is a costly alternative,associated with many manufacturing difficulties.Therefore,the SFB proposes cooling the highly loaded turbines instead,as this would necessitate the application of far less Ni-base alloys.To protect the thermally highly loaded casing,a sandwich material consisting of two thin face sheets with a core of a woven wire mesh is used to cover the walls of the steam turbine casing.The current state of the research shows that by utilising innovative cooling technologies a total efficiency of 65% can be reached without exceeding the maximum allowable material temperature,thereby prolonging the life-span.