Junichi Kitajima

Numerical and Experimental Characterization of Low NOx Micromix Combustion Principle for Industrial Hydrogen Gas Turbine Applications

The international effort to reduce the environmental impact of electricity generation, especially CO2-emissions requires considerations about alternative energy supply systems. An effective step towards low pollution power generation is the application of hydrogen as a possible alternative gas turbine fuel, if the hydrogen is produced by renewable energy sources, such as wind energy or biomass. The use of hydrogen and hydrogen rich gases as a fuel for industrial applications and power generation combined with the control of polluted emissions, especially NOx, is a major key driver in the design of future gas turbine combustors.The micromix combustion principle allows a secure and low NOx combustion of hydrogen and air and achieves a significant reduction of NOx-emissions. The combustion principle is based on cross-flow mixing of air and gaseous pure hydrogen and burns in multiple miniaturized diffusion-type flames. For the characterization of the jet in cross-flow mixing process, the momentum flux ratio is used.The paper presents an experimental analysis of the momentum flux ratio’s impact on flame anchoring and on the resultant formation of the NOx-emissions. Therefore several prototype test burner with different momentum flux ratios are tested under preheated atmospheric conditions. The investigation shows that the resultant positioning and anchoring of the micro flames highly influences the NOx-formation.Besides the experimental investigations, numerical simulations have been performed by the application of a commercial CFD code. The cold flow simulation results show the mixing of the air and hydrogen after the injection, in particular in the Counter Rotating Vortices (CRV). Furthermore, the hydrogen jet interacts also with another vortex system resulting from a wake flow area behind the combustor geometry. Furthermore, reacting flow simulations have been performed by the application of a Hybrid Eddy Break-Up (EBU) combustion model. The combustion pressure has been varied from atmospheric conditions up to a pressure of 16 bar.The experimental and numerical results highlight further potential of the micromix combustion principle for low NOx-combustion of hydrogen in industrial gas turbine applications.Copyright

Evaluation of a Catalytic Combustor in a Gas Turbine-Generator Unit

As a final step of the Catalytic Combustor Development Program, a catalytic combustor developed was tested in a 150-kW gas turbine-generator unit. A digital control system was developed to improve its controllability for a transient operation, and a 200-hr continuous operation test was performed to asses the durability of the catalyst. During the test, an excellent performance of the control system was verified, and a very high combustion efficiency of more than 99% and a ultra-low NOx level of less than 5.6 ppm (at 15% O2) were achieved at a 150-kW generator output. In addition, the combustion efficiency has been maintained at over 98% for 200 hours of operation. However, the catalyst exposed to 200 hours of operation showed signs of deactivation.Copyright

Experimental and Numerical Study on Optimizing the DLN Micromix Hydrogen Combustion Principle for Industrial Gas Turbine Applications

Combined with the use of renewable energy sources for its production, hydrogen represents a possible alternative gas turbine fuel for future low emission power generation. Due to the difference in the physical properties of hydrogen compared to other fuels such as natural gas, well-established gas turbine combustion systems cannot be directly applied to Dry Low NOx (DLN) hydrogen combustion.The DLN Micromix combustion of hydrogen has been under development for many years, since it has the promise to significantly reduce NOx emissions. This combustion principle for air-breathing engines is based on cross-flow mixing of air and gaseous hydrogen. Air and hydrogen react in multiple miniaturized diffusion-type flames with an inherent safety against flash-back and with low NOx-emissions due to a very short residence time of the reactants in the flame region.The paper presents an advanced DLN Micromix hydrogen application. The experimental and numerical study shows a combustor configuration with a significantly reduced number of enlarged fuel injectors with high thermal power output at constant energy density. Larger fuel injectors reduce manufacturing costs, are more robust and less sensitive to fuel contamination and blockage in industrial environments.The experimental and numerical results confirm the successful application of high energy injectors, while the DLN Micromix characteristics of the design point, under part load conditions and under off-design operation are maintained. Atmospheric test rig data on NOx emissions, optical flame structure and combustor material temperatures are compared to numerical simulations and show good agreement.The impact of the applied scaling and design laws on the miniaturized Micromix flamelets is particularly investigated numerically for the resulting flow field, the flame structure and NOx formation.© 2015 ASME

The Development of 50kW Output Power Atmospheric Pressure Turbine (APT)

This research seeks to report the development of a 50kW output power atmospheric pressure turbine (APT), based on the Inverted Brayton Cycle, which puts new, distributed power generation technology to practical use by using as energy source gases at normal pressures and high temperature, from industrial furnaces, waste gasification furnaces, gas turbines, and fuel cells which work at high temperatures, (ex. MCFC: Molten Carbonate Fuel Cell, SOFC: Solid Oxide Fuel Cell) and attempts to save energy and reduce CO2. At the last conference (ASME Turbo Expo 2006 in Barcelona), we had presented a paper about the proposal of APT and the results of operation of a 3–5kw APT prototype. This paper describes the designing of a new 50kW output power APT, and shows performance analysis and a review of the effectiveness of its application to industrial furnaces and biomass gasification furnaces. This development is based on a 3–5 kW APT prototype we had built and operated, and evaluated results. The performance simulation results using a general process simulator “HYSYS” show that a new 50kW APT (with recuperating heat exchanger) has a net electric efficiency (LHV) of about 20%. Based on this simulation result, we calculated the power and economical performance of application to industrial furnaces and biomass boilers. The results of these calculations clarify the basic characteristics of a new APT, which can be used as a new system for distributed power generation using waste heat.Copyright

Preliminary Study on Reheat Combustors for Advanced Gas Turbines

Feasibility studies carried out by the Engineering Research Association for Advanced Gas Turbines under the sponsorship of the Agency of Industrial Science and Technology of Japan have indicated that the thermal efficiency of the combined cycle plant incorporating a high temperature reheat gas turbine and a steam turbine can exceed 50 percent. Effects of air vitiation on inflammability limits, combustion efficiency, NOx and wall temperatures of gas turbine combustors are discussed. 13 refs.

Numerical Study on Increased Energy Density for the DLN Micromix Hydrogen Combustion Principle

Combined with the use of renewable energy sources for its production, hydrogen represents a possible alternative gas turbine fuel within future low emission power generation. Due to the large difference in the physical properties of hydrogen compared to other fuels such as natural gas, well established gas turbine combustion systems cannot be directly applied for Dry Low NOx (DLN) hydrogen combustion. Thus, the development of DLN hydrogen combustion technologies is an essential and challenging task for the future of hydrogen fuelled gas turbines.The DLN Micromix combustion principle for hydrogen fuel is being developed since years to significantly reduce NOx-emissions. This combustion principle is based on cross-flow mixing of air and gaseous hydrogen which reacts in multiple miniaturized diffusion-type flames. The major advantages of this combustion principle are the inherent safety against flashback and the low NOx-emissions due to a very short residence time of reactants in the flame region of the micro-flames.For the low NOx Micromix hydrogen application the paper presents a numerical study showing the further potential to reduce the number of hydrogen injectors by increasing the hydrogen injector diameter significantly by more than 350% resulting in an enlarged diffusion-type flame size. Experimental data is compared to numerical results for one configuration with increased hydrogen injector size and two different aerodynamic flame stabilization design laws.The applied design law for aerodynamic stabilization of the miniaturized flamelets is scaled according to the hydrogen injector size while maintaining equal thermal energy output and significantly low NOx emissions. Based on this parameter variation study the impact of different geometric parameters on flow field, flame structure and NOx formation is investigated by the numerical study.The numerical results show that the low NOx emission characteristics and the Micromix flame structure are maintained at larger hydrogen injector size and reveal even further potential for energy density increase and a reduction of combustor complexity and production costs.© 2014 ASME

Experimental and Numerical Characterization of the Dry Low NOx Micromix Hydrogen Combustion Principle at Increased Energy Density for Industrial Hydrogen Gas Turbine Applications

In the future low pollution power generation can be achieved by application of hydrogen as a possible alternative gas turbine fuel if the hydrogen is produced by renewable energy sources such as wind energy or biomass. The utilization of existing IGCC power plant technology with the combination of low cost coal as a bridge to renewable energy sources such as biomass can support the international effort to reduce the environmental impact of electricity generation. Against this background the dry low NOx Micromix combustion principle for hydrogen is developed for years to significantly reduce NOx emissions. This combustion principle is based on cross-flow mixing of air and gaseous hydrogen and burns in multiple miniaturized diffusion-type flames. The two advantages of this principle are the inherent safety against flash-back and the low NOx concentrations due to a very short residence time of reactants in the flame region of the micro-flames.The paper presents experimental results showing the significant reduction of NOx emissions at high equivalence ratios and at simultaneously increased energy density under preheated atmospheric conditions. Furthermore the paper presents the feasibility of enlarged Micromix hydrogen injectors reducing the number of required injectors of a full-scale Micromix combustion chamber while maintaining the thermal energy output with significantly low NOx formation.The experimental investigations are accompanied by 3D numerical reacting flow simulations based on a simplified hydrogen combustion model. Comparison with experimental results shows good agreement with respect to flame structure, shape and anchoring position. Thus, the experimental and numerical results highlight further potential of the Micromix combustion principle for low NOx combustion of hydrogen in industrial gas turbine applications.Copyright

Construction and Performance Evaluation of Prototype Atmospheric Pressure Turbine (APT)

This research seeks to propose an atmospheric pressure turbine (ATP), based on the Inverted Brayton Cycle, which puts new, distributed power generation technology to practical use by using various gases at normal pressures and high temperature, from industrial furnaces, waste gasification furnaces, gas turbines, and fuel cells which work at high temperatures, (ex. MCFC: Molten Carbonate Fuel Cell, SOFC: Solid Oxide Fuel Cell) and attempts to save energy and reduce CO2. However, no research has been presented about the operation of a real APT. This paper describes a review of the effectiveness of APT, and shows an outline for the results of a trial run, as well as the production of an APT prototype. The simulation results using a process simulator “HYSYS” show that a 30 kW system has a generator end efficiency (LHV) of about 32%, which is comparable to the performance of other equipment of a similar power rating, such as micro gas turbines. Based on this simulation result we build a 3–5 kW APT prototype and operate. The result of this operation clarifies the basic characteristics of an APT including a performance of 8.7% thermal efficiency. An APT has a smaller specific power than a gas turbine. Accordingly, since its mechanical and dissipative heat losses are larger by comparison, it is important to reduce these losses to attain higher efficiency. Our APT was operated stably and the possibility can be used as a new system for distributed power generation using waste heat was confirmed.Copyright

Low NOx Combustor Research for a Mach 3 Turbojet Concept Validation Test Results

A unique idea of premixture jet swirl combustor (PJSC) was proposed for the ultra low NOx combustor of a Mach 3 turbojet. The combustor installed six simple premixing chambers which were arranged at certain angles to the center axis also to the circumference axis on the combustor dome. This arrangement formed large and strong recirculating flows necessary to stabilize flame at lean fuel air ratio conditions. The fuel mixing study revealed that the radial fuel injectors inserted in a premixing chamber exhibited a high degree of uniformity. Single can combustors of PJSC with three types of main fuel injectors were manufactured for the high temperature and high pressure combustion test program. All combustors performed stable combustion for a wide range of FAR and obtained combustion efficiency of 99.9 % at Mach 3 cruise conditions, namely inlet temperature of 1008 K, inlet pressure of 830 kPa and fuel air ratio of 0.0223. HTHPC-01 combustor, which installed the radial fuel injectors and had long mixing length, presented the best NOx emissions and achieved emission index of 2 g/kg fuel at that design condition. PJSC met the emission goal of HYPR project, and concept validation test was completed in success.Copyright

Development of a Catalytic Combustor for Small Gas Turbines

To reduce NO/sub x/ emissions significantly, a catalytic combustor was developed. Full scale tests of catalytic combustors designed for application in Kawasaki S1A-02 type gas turbines were conducted. The combustor consisted of a pre-combustion zone, a premixing zone, a catalytic combustion zone, and a variable geometry dilution zone. Liquefied Natural Gas (LNG) was burned in combustor rig tests and results indicated low NO/sub x/ emissions and high combustion efficiencies over a wide range of air/fuel ratios and that the catalytic combustor can be applied to the engine tests.