Project Cluster / 2010-09-14

Turbine combustion that produces lower amounts of harmful substances

Research approach

Burners for partially pre-mixed flames that are specific to gas turbines ©DLR

Gas and steam turbine power plants require additional research in the areas of innovative gas turbine technology (compressor, combustion chamber, turbine) and improved system integration. The turbine inlet temperature must be increased significantly in order to achieve higher efficiencies. To this end, new burner systems have to be developed that will achieve particularly low emissions and comply with broader stability limits even in the case of higher fuel flexibility or of exhaust gas recirculation. The combustion engineering challenges here include changed fuel specifications, higher flame temperatures and the minimisation of harmful substances. In addition, optimal combustion in partial-load operation is required in order to supply balancing energy.

Research goals

  • Increasing fuel flexibility (burner systems for a large spectrum of fuels: natural gas / hydrogen-rich synthesis gases / alternative fuels, data and models for reaction kinetics)
  • Broadening of stability limits (buzzing, ignition and extinguishing behaviour, active and passive damping)

Outlook

The overall goal is to develop reliable, low-emission gas turbine burners that are flexible with regard to fuels for a wide range of gas and liquid fuels containing hydrocarbons. Pioneering new burner concepts are to be investigated with regard to their flexibility by using partially or fully decarbonised fuels and fuel mixtures of various compositions, for example. This type of flexible burner concept offers very great potential for achieving energy supply that reduces or even fully eliminates CO2 emissions. In order to increase power plant efficiency, gas turbine burners are to be modified so that they can be used with even higher turbine inlet temperatures in the future. To achieve this goal, burner performance data, thermodynamic data, design principles and operating parameters have to be determined and combined for a new concept so that they can be adjusted in a coordinated manner in the development of new combustion chamber concepts.

In addition, combustion systems need to be developed for natural gas that has significant fractions of higher hydrocarbons, and certification of these systems for temperatures of up to 1,700 °C and for high pressures needs to be completed. Innovative design approaches are also necessary in order to minimise both NOx emissions and combustion chamber buzzing, which significantly increases at higher temperatures.

 

The heat release during the combustion process is not homogenous, which leads to pressure changes in the combustion zone. At certain frequencies, these pressure changes can combine to result in dangerous pressure pulses that damage the equipment. This topic is covered by the broader subject of thermoacoustics. These undesirable, thermoacoustically induced combustion vibrations make it particularly difficult to develop improved combustion systems that operate at higher pressures and temperatures. In addition, they also limit the fuel flexibility. For this reason, improvements to thermoacoustic design processes and test methods are critical to the development of low-CO2 gas turbine combustion chambers that offer fuel flexibility.

It is known that lean and low-emission combustion systems are particularly susceptible to combustion instabilities. Reliable knowledge concerning thermoacoustic stability is necessary for these systems. Only then can a high degree of flame stability be achieved in future high-power gas turbines. This particularly applies to partial-load operation. Among the parameters to be investigated are the thermoacoustic stability limits and the amplitudes of the acoustic pressure in high-temperature combustion systems over a large range of pressures.

Background

The specification of nitrogen oxide (NOx) limit values is an important constraint in the conceptual design of a gas turbine combustion system. The current limit values in Germany are 25 ppm (15% O2). The values in other countries are even lower. This means that, in addition to a low temperature difference between the combustion temperature and the turbine inlet temperature, the goal of a low residence time must also be achieved in order to prevent the formation of thermal NOx. Compact combustion systems have been developed for this purpose that are characterised by a low cooling air requirement. Increasingly demanding requirements in the past have led to silo combustion chambers being replaced by the annular combustion chambers that can be found in almost all large-scale gas turbines nowadays.

 

In order to further increase turbine inlet temperatures and reduce NOx limit values, it is necessary to develop new burner concepts and further develop new combustion chamber concepts – particularly with the constraint that thermoacoustically induced combustion chamber vibrations should be avoided. High combustion temperatures correlate with the increased formation of thermal nitrogen oxides. Compliance with nitrogen oxide limit values has become an important constraint in the conceptual design of combustion chambers. For many years now, catalytic combustion has been regarded as an alternative to conventional burner-specific or other measures (e.g. water injection) and processes, as catalytic combustion produces almost no nitrogen oxides.

10 current research projects

Combustion investigations for a gas turbine process with exhaust gas recirculation for efficient CO2 capture
Organisation carrying out research: ALSTOM Power Systems GmbH
Project number: 0327810A

 

Interaction between combustion chamber and turbine
Organisation carrying out research: Technische Universität Darmstadt - Fachbereich Maschinenbau - FG Gasturbinen, Luft- und Raumfahrtantriebe
Project number: 0327725D

 

Aerodynamic interaction between combustion chamber and turbine
Organisation carrying out research: Technische Universität Darmstadt - Fachbereich Maschinenbau - FG Gasturbinen, Luft- und Raumfahrtantriebe
Project number: 0327719F

 

Aerodynamic interaction between combustion chamber and turbine; CFD-aided simulation of the overall gas turbine system (computational fluid dynamics)
Organisation carrying out research: Technische Universität Darmstadt - Fachbereich Maschinenbau - FG Energie- und Kraftwerkstechnik

Project number: 0327719G

 

Aerodynamic interaction between combustion chamber and turbine
Organisation carrying out research: Rolls-Royce Deutschland Ltd & Co KG
Project number: 0327718R


Description of turbulent flow behaviour in combustion chambers with lean, partially pre-mixed combustion
Organisation carrying out research: Helmut-Schmidt-Universität - Universität der Bundeswehr Hamburg - Fachbereich Maschinenbau - Professur für Energietechnik - Laboratorium für Strömungsmaschinen
Project number: 0327716L

 

High-temperature burners with reduced emissions
Organisation carrying out research: Siemens Aktiengesellschaft - Power Generation - Dep. PE324
Project number: 0327716N

 

Prediction of combustion noise and thermoacoustic instabilities using a coupling of LES and CAA
Organisation carrying out research: Technische Universität Darmstadt - Fachbereich Maschinenbau - FG Energie- und Kraftwerkstechnik
Project number: 0327725B

 

Integrated passive damping systems to reduce thermoacoustic instabilities in gas turbine combustion chambers
Organisation carrying out research: Rolls-Royce Deutschland Ltd & Co KG
Project number: 0327717K

 

High-temperature combustion system for a flexible operating range
Organisation carrying out research: Siemens AG - Energy Sector - Dep. E F PR GT EN 412
Project number: 0327718N

 

High-temperature combustion system for a flexible operating range - HTV flex Op
Organisation carrying out research: German Aerospace Center (DLR) - Institute of Combustion Technology (EN-VT)
Project number: 0327718O