Martina Hohloch

Micro Gas Turbine Test Rig for Hybrid Power Plant Application

Within the scope of a hybrid power plant project a micro gas turbine test rig was developed and is actually under construction at the DLR Institute of Combustion Technology. The test rig consists of a Turbec T100PH micro gas turbine and the required piping system for the hybrid application. Instead of a real solid oxide fuel cell (SOFC) stack a fuel cell simulator is used to avoid any risks for the sensitive and expensive real device. This simulator is able to emulate the SOFC interface conditions. The present paper reports the underlying pressurized hybrid power plant cycle, the setup of the test rig and the selection of the subsystems. Initially the micro gas turbine, equipped with a detailed instrumentation, was analyzed separately. First experimental data obtained with the micro gas turbine are presented.Copyright

Validation of a T100 Micro Gas Turbine Steady-State Simulation Tool

Micro gas turbines (MGT) provide a highly efficient, low-pollutant way to generate power and heat on-site. MGTs have also proven to be a versatile technology platform for recent developments like utilization of fuels with low specific heating values and solar thermal electricity generation. Moreover, they are the foundation to build novel cycles like the inverted Brayton cycle or fuel cell hybrid power plants.Numerical simulations of steady operation points are beneficial in various phases of MGT cycle development. They are used to determine and analyze the future potentials of innovative cycles for example by predicting the electrical efficiency and they support the thermodynamic design process (by providing mass flow, pressure and temperature data). Numerical Simulation allows to approximate off-design performance of known cycles e.g. power output at different ambient conditions. Additionally, numerical simulation is used to support cycle optimization efforts by analyzing the sensitivity of component performance on cycle performance. Numerical models of the MGT components have to be tuned and validated based on experimental data from MGT test rigs.At DLR institute of combustion technology a MGT steady-state cycle simulation tool has been used to analyze a variety of cycles and has been revised for several years. In this paper, the validation process is discussed in detail. Comparing simulation data with measurement data from the DLR Turbec T100 test rig has led to extensions of the numeric models, on the one hand, and to modifications of the test rig on the other. Newly implemented numerical models account for the generator heat release to the inlet air and the power electronic limitations. The test rig was modified to improve the temperature measurement at positions with uneven spatial temperature distribution such as the turbine outlet. Analyzing these temperature distributions also yields a possible explanation for the apparent strong recuperator efficiency drop at high load levels, which was also observed by other T100 users before.Copyright

Experimental Characterization of a Micro Gas Turbine Test Rig

For the development of efficient and fuel flexible decentralized power plant concepts a test rig based on the Turbec T100 micro gas turbine is operated at the DLR Institute of Combustion Technology. This paper reports the characterization of the transient operating performance of the micro gas turbine by selected transient maneuvers like start-up, load change and shut-down. The transient maneuvers can be affected by specifying either the electrical power output or the turbine speed. The impact of the two different operation strategies on the behavior of the engine is explained. At selected stationary load points the performance of the gas turbine components is characterized by using the measured thermodynamic and fluid dynamic quantities. In addition the impact of different turbine outlet temperatures on the performance of the gas turbine is worked out. The resulting data set can be used for validation of numerical simulation and as a base for further investigations on micro gas turbines.Copyright

Experimental Investigation of a SOFC/MGT Hybrid Power Plant Test Rig: Impact and Characterization of Coupling Elements

The main topic of the paper is the discussion of the operational behavior of the solid oxide fuel cell (SOFC)/micro gas turbine (MGT) hybrid power plant test rig with the pressure vessels of the SOFC emulator. In the first part a brief introduction to the test rig and its components is given. In the arrangement of the test rig the MGT is connected via an interface to the tubing system. Here, the preheated air after the recuperator can be led either to the emulator or via a bypass tube directly to the MGT. Furthermore, there is a direct connection between the compressor outlet and emulator for the startup and shutdown procedure. The facility is equipped with detailed instrumentation, including mass flow meters, thermocouples and pressure probes. In the second part of the paper the characterization of the hybrid power plant test rig is shown. To analyze the thermodynamic and fluid dynamic impact of the coupling elements various studies were carried out. Hereby, the influence of the coupling elements on the operational behavior, system stability and system performance of the micro gas turbine is shown for stationary load points, as well as during transient maneuvers like startup, load-change and shutdown. To avoid critical operating conditions limitations were defined and emergency maneuvers were developed and tested. Out of these investigations an operating concept for the hybrid power plant test rig can be derived.Copyright

Analysis of Operational Strategies of a SOFC/MGT Hybrid Power Plant

The present work deals with the analysis of operational concepts for a SOFC/MGT hybrid power plant based on a test rig at the DLR, Institute of Combustion Technology. Here, a Turbec T100 micro gas turbine and a fuel cell emulator are used. The emulator is composed of two pressure vessels. The first represents the cathode volume of the fuel cell to simulate the residence time and pressure loss. The second is equipped with a natural gas combustor to emulate the varying heat input of the fuel cell. The MGT and the SOFC are connected via different piping paths. The procedures start-up, load change and shutdown are analyzed in matters of temperature gradients, pressure gradients and fluctuations, as well as the air mass flow provided at the interconnections to the coupling elements. To achieve the required inlet conditions of the SOFC, transient operations, using the different piping paths, are investigated. Concepts for heating-up and cooling the SOFC using hot air from the recuperator and relatively cold air from the compressor outlet are experimentally tested and characterized. Selected critical situations and their effect on the SOFC are investigated. An emergency operation, its impact on both subsystems and limitations are shown. Further operational limits of the MGT control system and power electronic were observed and analyzed. Based on the experimental results, the applicability of the used MGT procedures in a hybrid power plant was reconsidered. Finally, adaptions and strategies for the operational concept are derived and discussed.

Experimental characterization of a swirl stabilized MGT combustor

A swirl stabilized MGT combustor (Turbec T100) was operated with natural gas and was experimentally characterized in two test rigs, a pressurized and optically accessible MGT test rig and an atmospheric combustor test rig. For the detailed characterization of the combustion processes, planar OH-PLIF and simultaneous 3D-stereo PIV measurements were performed in the atmospheric combustor test rig. Flow fields, reaction zones and exhaust gas emissions are reported for a range of pressure scaled MGT load points. Parameter studies on combustor inlet conditions (e.g. air preheating temperature, air and fuel mass flow rates and fuel split) were conducted in the atmospheric combustor test rig. From the parameters studies the fuel split between the pilot and the main stage and the air preheating temperature were found to have the biggest impact on the flame shape, flame stabilization and exhaust gas emissions. The measurements of the ATM test rig are compared with measurements of the pressurized MGT test rig with and without an optically accessible combustion chamber. Opened and closed conical flame and flow pattern were found in both test rigs. Reasons for the two flame and flow pattern are supposed to be the interaction of pilot stage combustion and flow field and the interaction of the dilution air with the combustion and the flow field. The results are discussed and compared with repect to a transferability of combustion characteristics from the ATM test rig to the MGT test rigs.Copyright

OH* Chemiluminescence and OH-PLIF Measurements in a Micro Gas Turbine Combustor

In this work the combustion behavior of the Turbec T100 natural gas/air combustor was analyzed experimentally. For the visualization of the flame structures at various stationary load points OH* chemiluminescence and OH-PLIF measurements were performed in a micro gas turbine test rig equipped with an optically accessible combustion chamber. The OH* chemiluminescence measurements are used to get an impression of the shape and the location of the heat release zones. In addition the OH-PLIF measurements enabled spatially and temporarily resolved information of the reaction zones. Depending on the load point the shape of the flame was seen to vary from cylindrical to conical. With increasing thermal power load the maximum heat release zones shift to a lifted flame. Moreover, the effect of the optically accessible combustion chamber on the performance of the micro gas turbine is evaluated.Copyright