Liqiao Jiang

Study on thermodynamic characteristic and optimization of steam cycle system in IGCC

Abstract In order to increase the overall efficiency of IGCC, integration of the steam-side subsystem in IGCC is attracting more and more attention with the development of technology and experience achievement. The existing design methods are generally the simulation and analysis of their performance under the conditions of the given steam subsystem configuration. This usually results in only partial optimization. In this paper, a new idea is presented and a new method––simultaneous optimization of configuration and parameters––is investigated and used for IGCC steam subsystem. These are expected to overcome the shortcomings of the previous ones, adapt to various IGCC technological demand for steam subsystem and realize better cascade utilization of exhaust heat from gas turbine. The optimization model for steam subsystem is established, based on modular modeling idea of general system integration. Case study shows that the synthesis optimization method and model presented in this paper are valuable for steam subsystem performance analysis and optimization design of IGCC.

The Deposition and Burning Characteristics During Slagging Co-Firing Coal and Wood: Modeling and Numerical Simulation

Numerical analysis was used to study the deposition and burning characteristics of combining co-combustion with slagging combustion technologies in this paper. The pyrolysis and burning kinetic models of different fuels were implanted into the WBSF-PCC2 (wall burning and slag flow in pulverized co-combustion) computation code, and then the slagging and co-combustion characteristics—especially the wall burning mechanism of different solid fuels and their effects on the whole burning behavior in the cylindrical combustor at different mixing ratios under the condition of keeping the heat input same—were simulated numerically. The results showed that adding wood powder at 25% mass fraction can increase the temperature at the initial stage of combustion, which is helpful to utilize the front space of the combustor. Adding wood powder at a 25% mass fraction can increase the reaction rate at the initial combustion stage; also, the coal ignitability is improved, and the burnout efficiency is enhanced by about 5% of suspension and deposition particles, which is helpful for coal particles to burn entirely and for combustion devices to minimize their dimensions or sizes. The results also showed that adding wood powder at a proper ratio is helpful to keep the combustion stability, not only because of the enhancement for the burning characteristics, but also because the running slag layer structure can be changed more continuously, which is very important for avoiding the abnormal slag accumulation in the slagging combustor. The theoretic analysis in this paper proves that unification of co-combustion and slagging combustion technologies is feasible, though more comprehensive and rigorous research is needed.

A Surface Analysis-Based Investigation of the Effect of Wall Materials on Flame Quenching

An investigation of a premixed methane-air flame was conducted with a slit burner between two parallel walls to examine the effects of wall material and temperature on flame quenching. Three different materials (i.e., zirconia ceramics, stainless steel 304, and Si) were tested at wall temperatures of 100–700°C. The quenching distances for the three wall materials at the same temperature decrease in the order stainless steel 304 > Si > zirconia ceramics. For all materials, the quenching distance shortens with increasing wall temperature. To clarify the differences among the materials, the surface structure and composition of the raw and used walls were characterized by X-ray diffraction and X-ray photoelectron spectroscopy. The results show that the percentages of chemisorbed oxygen on the surfaces decrease in the order zirconia ceramics > Si > stainless steel 304—a behavior that can be correlated with the order of quenching distances of the three wall materials, which moves from small to large. In short, the higher the percentage of chemisorbed oxygen, the shorter the quenching distances.

Study on a Lower Heat Loss Micro Gas Turbine Combustor with Porous Inlet

A micro gas turbine combustor with a sintered porous chamber wall as inlet was tested and simulated. When burning methane in the 2.14 cm3 chamber volume combustor, its maximum power density reached 336 M W/m3. The combustion efficiency was above 90% when producing 850–1100 K exit gas. The pressure drop ratio of the porous inlet was below 5 kPa with 6 L/min premixed gas flow rate at hot condition. Compared with a conventional solid-wall micro combustor with heat recovery channel, the outside wall temperature of the porous-wall micro combustor decreased 150–200 K, and the heat loss ratio reduced from 40–80% to 20–40%. Direct numerical simulation based on the skeletal chemical kinetics model was used to elucidate the flame structure and heat loss reducing mechanism of the porous-wall micro combustor.

Effect of surface reactions on ignition delay of methanol/air mixture

A surface reaction kinetic model for the combustion of methanol/air mixture was developed in order to investigate the ignition inhibitory mechanism of wall on the premixed gas in a micro closed volume. In this model, except for H, O, OH and CH3 radicals, the absorption of hydrogen peroxide and hydroperoxyl on the surface were also considered. By applying CHEMKIN-Pro software, the model was integrated into the calculation of homogeneous combustion process of gas mixture. Surface reactions were found resulting in the increase of ignition delay time. The sensitivity analysis showed that the loss of hydrogen peroxide on the wall was the main reason, due to the direct suppression effect on the generation and accumulation of OH in the radical pool. However, the loss of hydroperoxyl would take the place of hydrogen peroxide as the main inhibitory factor when the sticking coefficient became as large as the order of 10−3. In addition, the ignition delay time increased with sticking coefficient or surface-area-to-volume ratio. Enhancing the initial temperature of premixed gas was able to reduce the inhibitory effect of surface reactions.

Numerical Study on the Propagation of Premixed Flames in Confined Narrow Disc-Shape Chambers

ABSTRACT The laminar flame propagation in narrow confined disc-shape chambers of millimeter scale is investigated, concerning the flame front displacement speed and the influences from the changes of the gap width and radius. An asymptotic analysis treating the flame front as a discontinuity successfully predicts the velocity profiles of the flame front and illustrates the importance of heat release parameter and laminar flame speed of the fuel. The unsteady flame propagation process is simulated by a full numerical computation which employs the n-butane/air mixture as the reactant. The numerical simulation emphasizes the sensitivity of spatial scale to the flame propagation in narrow spaces, indicating that the acceleration rate and the maximum speed of the flame have a non-monotonic relation with the gap width, of which the optimal value is about 0.8 mm. Faster flame propagation is favored for larger gap radius due to stronger flame straining, but it is restricted by the gap width.

Quantitative gaseous temperature and mole concentration measurements in spray generated mixture by p-xylene-PLIF imaging

ABSTRACT The current study originally presents a detailed approach to implement the p-xylene based two-color PLIF for measuring gaseous mixture temperature and mole concentration field simultaneously. An 80 * 0.8 mm2 laser sheet at 266 nm is employed to excite homogenous p-xylene/nitrogen steady mixture flow in a calibration cell, where the known p-xylene mole concentration and temperature are adjustable. Doing so, the full band/spectral (centered at 289 nm) fluorescence intensity are respectively captured by ICCD camera that allows establishments of temperature–fluorescence ratio database. Concomitantly, the full band fluorescence intensity correlation with temperature and mole concentration is rightly created as well. Utilizing the identical laser sheet and detection channel, the quantitative temperature and mole concentration field in a far-field developed-spray region could be inferred by terms of full band/spectral fluorescence imaging through previous calibration database. The error propagation issue of temperature and mole concentration measurement by this approach are discussed. As a result, it is found that the relative temperature and mole concentration uncertainties are in the range of 5.4 ~ 7.3% and 8 ~ 9.3% (or 12.3 ~ 18.7% by bottom-up approach), respectively, within studied temperature range of 423 ~ 573K. Therefore, the suitability and capability of p-xylene as the tracer for spatio-temporal temperature and mole concentration measurements are preliminarily validated, which offers an alternative tracer option for gasoline/its surrogate spray studies. It is noted that replacing the p-xylene by other suitable fluorescence tracer, i.e.,1-methylnaphthalene, this approach could be rightly performed for studies of Diesel engine, or even gas turbine.

Numerical Study On Combustion Characteristics Of Partially Premixed Tubular Flame Burner For DME

ABSTRACT The combustion characteristics of dimethyl ether (DME) in a partially premixed tubular flame burner have been investigated numerically. The species distribution, stability limit of tubular flame, wall temperature and burn-off rate have been studied at different equivalence ratios and inlet velocities. Meanwhile, the corresponding combustion characteristics in the rapidly mixed tubular flame burner have been simulated and compared. The results show that the partially premixed burner forms a unique species distribution and the fuel and the oxidant are not mixed uniformly. This unique species distribution will promote the chemical enthalpy supply to the flame front by recirculation reverse flow in the center, and thus strengthen the combustion process. Based on this unique species distribution, the partially premixed burner has larger tubular flame stability limit, lower heat loss, and higher burn-off rate, especially for lean operating conditions. Comparing the formation mechanisms of the tubular flames in two types of burners, it is found that the partially premixed burner forms partially premixed tubular flame, which is no need to create a uniform premixed gas zone, thereby suppressing the influence of velocity difference between fuel and oxidant present in the rapidly mixed burner.

Experimental Study on Propane/Air Flame Propagation Characteristics in a Disc-Like Gap Chamber

ABSTRACT A disc-like gap chamber was developed to investigate the microscale effects on flame propagation characteristics in closed chamber, which is very important to understand the combustion process in micro internal combustion engines. Under initially normal pressure and temperature, the morphology and evolution of outwardly propagating flame, the flammable limit, flame speed and flame instability of propane-air flames influenced by gap width and equivalence ratio were experimentally studied. The results show that, as the gap width nearly equals to the quenching distance, the sustained propagation was possible only with rich flames. The smooth flames and wrinkled flames were observed. It clearly shows that the flame wrinkles developed gradually instead of instantaneously. The flame speed was slower in the 2.0 mm gap chamber than in a conventional combustion bomb, and the flame speed decreased with the increase of flame radius. As a result, the flame acceleration was not observed in present experiments. With the smaller gap width, the wrinkled flame occurred early, and the flame speed was slower. Due to the geometry of disc-like gap chamber, simple theoretical analysis indicates that the heat loss and elevated pressure play important roles in reducing flame speed.

Ignition Characteristics of Premixed Methane/air in Micro Chamber

The ignition process of premixed methane/air in a micro-scale chamber is simulated with the combination of surface chemistry and gas-phase reactions. The effect of different parameters on the ignition characteristics are analyzed in detail and the sensitive analysis is performed on main elementary reactions. It is found that the ignition of the mixture is inhibited by surface reaction, which mainly depends on the sticking ability of the surface on CH3 radical. The ignition inhibition can be reduced by increasing the initial temperature and pressure. The increase of equivalence ratio has small impact on ignition delay time when it is larger than stoichiometric ratio. The ignition delay time would increase significantly with surface-area-to- volume ratio. The product of sticking coefficient and surface-area-to-volume ratio can be used to measure the intensity of surface reaction. The larger the product is, the stronger the inhibition of the surface reaction on ignition has.