Effect of hydrogen combustion reaction on the dehydrogenation of ethane in a fixed-bed catalytic membrane reactor

A two-dimensional non-isothermal mathematical model has been developed for the ethane dehydrogenation reaction in a fixed-bed catalytic membrane reactor. Since ethane dehydrogenation is an equilibrium reaction,removal of produced hydrogen by the membrane shifts the thermodynamic equilibrium to ethylene production.For further displacement of the dehydrogenation reaction, oxidative dehydrogenation method has been used.Since ethane dehydrogenation is an endothermic reaction, the energy produced by the oxidative dehydrogenation method is consumed by the dehydrogenation reaction. The results show that the oxidative dehydrogenation method generated a substantial improvement in the reactor performance in terms of high conversions and signi ficant energy saving. It was also established that the sweep gas velocity in the shell side of the reactor is one of the most important factors in the effectiveness of the reactor.

Single-step chemistry model and transport coefficient model for hydrogen combustion

To satisfy the needs of large-scale hydrogen combustion and explosion simulation,a method is presented to establish single-step chemistry model and transport model for fuel-air mixture.If the reaction formula for hydrogen-air mixture is H2+0.5O2→H2O,the reaction rate model is ?? =1.13×10?5[H2][O2]exp(?46.37T0/T) mol(cm3 s)?1,and the transport coefficient model is ?=K/CP=ρD=7.0×10?5T 0.7 g(cm s)?1.By using current models and the reference model to simulate steady Zeldovich-von Neumann-Doering(ZND) wave and free-propagating laminar flame,it is found that the results are well agreeable.Additionally,deflagration-to-detonation transition in an obstructed channel was also simulated.The numerical results are also well consistent with the experimental results.These provide a reasonable proof for current method and new models.

Modeling of propane dehydrogenation combined with chemical looping combustion of hydrogen in a fixed bed reactor

A redox process combining propane dehydrogenation(PDH)with selective hydrogen combustion(SHC)is proposed,modeled,simulated,and optimized.In this process,PDH and SHC catalysts are physically mixed in a fixed-bed reactor,so that the two reactions proceed simultaneously.The redox process can be up to 177.0%higher in propylene yield than the conventional process where only PDH catalysts are packed in the reactor.The reason is twofold:firstly,SHC reaction consumes hydrogen and then shifts PDH reaction equilibrium towards propylene;secondly,SHC reaction provides much heat to drive the highly endothermic PDH reaction.Considering propylene yield,operating time,and other factors,the preferable operating conditions for the redox process are a feed temperature of 973 K,a feed pressure of 0.1 MPa,and a mole ratio of H_(2) to C_(3)H_(8) of 0.15,and the optimal mass fraction of PDH catalyst is 0.5.This work should provide some useful guidance for the development of redox processes for propane dehydrogenation.

NO_x emission characteristics of hydrogen internal combustion engine

To study the economic advantages of hydrogen internal combustion engine, an experimen- tal study was carried out using a 2.0 L port fuel-injected （PFI） hydrogen internal combustion engine. Influences of fuel-air equivalence ratio φ, speed, and ignition advance angle on heat efficiency were determined. Test results showed that indicated thermal efficiency （ ITE ） firstly increased with fuel- air equivalence ratio, achieved the maximum value of 40. 4% （ φ = 0.3 ）, and then decreased when was more than 0. 3. ITE increased as speed rises. Mechanical efficiency increased as fuel-air equiva- lence ratio increased, whereas mechanical efficiency decreased as speed increased, with maximum mechanical efficiency reaching 90%. Brake thermal efficiency （BTE） was influenced by ITE and me- chanical efficiency, at the maximum value of 35% （φ =0.5, 2 000 r/min）. The optimal ignition ad- vance angle of each condition resulting in the maximum BTE was also studied. With increasing fuel- air equivalence ratio, the optimal ignition angle became closer to the top dead center （ TDC ）. The test results and the conclusions exhibited a guiding role on hydrogen internal combustion engine opti- mization.

CFD based exploration of the dry-low-NO_(x) hydrogen micromix combustion technology at increased energy densities

Combined with the use of renewable energy sources for its production,hydrogen represents a possible alternative gas tuibine 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 tuibine combustion systems cannot be directly applied for dry-low-NO_(x)(DLN)hydrogen combustion.Thus,the development of DLN combustion technologies is an essential and challenging task for the future of hydrogen fuelled gas turbines.The DLN micromix combustion principle for hydrogen fuel has been developed to significantly reduce NO_(x)-emlssions.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 flash-back and the low NO_(x)-emlssions due to a very short residence time of reactants in the flame region of the micro-flames.The micromix combustion technology has been already proven experimentally and numerically for pure hydrogen fuel operation at different energy density levels.The aim of the present study is to analyze the influence of different geometry parameter variations on the flame structure and the NO_(x)emission and to identify the most relevant design parameters,aiming to provide a physical understanding of the micromix flame sensitivity to the burner design and identify further optimization potential of this innovative combustion technology while increasing its energy density and making it mature enough for real gas turbine application.The study reveals great optimization potential of the micromix combustion technology with respect to the DLN characteristics and gives insight into the impact of geometry modifications on flame structure and NO_(x)emission.This allows to further increase the energy density of the micromix burners and to integrate this technology in industrial gas turbines.

Experimental and numerical investigations of the dry-low-NO_(x) hydrogen micromix combustion chamber of an industrial gas turbine

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-NO_(x)(DLN)hydrogen combustion.Thus,the development of DLN combustion technologies is an essential and challenging task for the future of hydrogen fuelled gas turbines.The DLN micromix combustion principle for hydrogen fuel has been developed to significantly reduce NO_(x) 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 flash-back and the low NO_(x) emissions due to a very short residence time of reactants in the flame region of the micro-flames.The micromix combustion technology has been already proven experimentally and numerically for pure hydrogen fuel operation at different energy density levels.The aim of the present study is to apply and compare different combustion models for the characterization of the micromix flame structure,its interaction with the flow field and its NO_(x) emissions.The study reveals great potential for the successful application of numerical flow simulation to predict flame structure and NO_(x) emission level of micromix hydrogen combustion,help understanding the flow phenomena related with the micromixing,reaction zone and NO_(x) formation and support further optimization of the burner performance.

Numerical Simulation of Tip Leakage Vortex Effect on Hydrogen-Combustion Flow around 3D Turbine Blade

In these years, a lot of environmental problems such as air pollution and exhaustion of fossil fuels have been discussed intensively. In our laboratory, a hydrogen-fueled propulsion system has been researched as an alternative to conventional systems. A hydrogen-fueled propulsion system is expected to have higher power, lighter weight and lower emissions. However, for the practical use, there exist many problems that must be overcome. Considering these backgrounds, jet engines with hydrogen-fueled combustion within a turbine blade passage have been studied. Although some studies have been made on injecting and burning hydrogen fuel from a stator surface, little is known about the interaction between a tip leakage vortex near the suction side of a rotor tip and hydrogen-fueled combustion. The purpose of this study is to clarify the influence of the tip leakage vortex on the characteristics of the 3-dimensional flow field with hydrogen-fueled combustion within a turbine blade passage. Reynolds-averaged compressible Navier-Stokes equations are solved with incorporating a k-ε turbulence and a reduced chemical mechanism models. Using the computational results, the 3-dimensional turbulent flow field with chemical reactions is numerically visualized, and the three-dimensional turbulent flow fields with hydrogen combustion and the structure of the tip leakage vortex are investigated.

3D Computation of Hydrogen-Fueled Combustion around Turbine Blade-Effect of Arrangement of Injector Holes

Recently, a number of environmental problems caused from fossil fuel combustion have been focused on. In addition, with the eventual depletion of fossil energy resources, hydrogen gas is expected to be an alternative energy resource in the near future. It is characterized by high energy per unit weight, high reaction rate, wide range of flammability and the low emission property. On the other hand, many researches have been underway in several countries to improve a propulsion system for an advanced aircraft. The system is required to have higher power, lighter weight and lower emissions than existing ones. In such a future propulsion system, hydrogen gas would be one of the promising fuels for realizing the requirements. Considering these backgrounds, our group has proposed a new cycle concept for hydrogen-fueled aircraft propulsion system. In the present study, we perform 3 dimensional computations of turbulent flow fields with hydrogen-fueled combustion around a turbine blade. The main objective is to clarify the influence of arrangement of hydrogen injector holes. Changing the chordwise and spanwise spacings of the holes, the 3 dimensional nature of the flow and thermal fields is numerically studied.

Progress in hydrogen enriched hydrocarbons combustion and engine applications

The paper summarized the work on hydrogen enriched hydrocarbons combustion and its application in engines. The progress and understanding on laminar burning velocity, flame instability, flame structure flame and chemical kinetics were presented. Based on funda- mental combustion, both homogeneous spark-ignition engine and direct-injection spark-ignition engine fueled with natural gas-hydrogen blends were conducted and the technical route of natural gas-hydrogen combined with exhaust gas recirculation was proposed which experimen- tally demonstrated benefits on both thermal efficiency improvement and emissions reduction.