Pressurized Entrained Flow Reactor Research Articles

A hybrid particle model with advanced conversion parameters and dynamic drag model applied for the CFD modeling of an entrained-flow gasifier

The main focus of the current work is to establish a hybrid particle model to depict the char conversion process, taking into account the influence of pore diffusion on the carbon consumption rate. Compared to existing char conversion models, the new hybrid model uses advanced correlations for conversion parameters such as the density and diameter exponents α and β and the Random Pore Model correction factor γ, which are functions of char conversion and effectiveness factor. CFD simulation results for a Pressurized Entrained-Flow Reactor (PEFR) using the hybrid particle model are in good agreement with experimental data. In addition, the current work also introduces dynamic drag models based on the development of the shape of spherical and non-spherical particles during the char conversion process. The dynamic drag models, which up to now has been missed in calculation of particle trajectories, are examined to evaluate their influences on the total carbon conversion of the PEFR. Furthermore, the performance of ideal particle sub-models such as the Uniform Conversion Model and Shrinking Unreacted Particle Model are also studied and compared with that of the hybrid particle model. PEFR CFD simulation results illustrate considerable differences between the carbon conversion profiles obtained with these sub-models and those profiles obtained using the hybrid particle model.

Morphology of char particles from coal pyrolysis in a pressurized entrained flow reactor: Effects of pressure and atmosphere

A pressurized drop tube furnace was used to study the pyrolysis behavior of bituminous and lignite coal at elevated pressure. Experiments were conducted at the pressure range from 1 to 10 atm in 100% N2 or 100% CO2 atmosphere. The volatile yields, char morphology, swelling ratio, and pore structure were discussed in detail. The results show that the pressure, atmosphere and coal rank could effect on the volatile releasing and char evolution significantly. In N2 atmosphere, the total volatile yields of YL and NM coal decrease as the pressure elevated, while in CO2 atmosphere, the mass release of NM coal increases at high pressure contributed by the reaction of CO2 with organic macromolecule inside the particles; different with bituminous coal, no significant swelling behavior is found with the increase of pressure; the BET surface area of YL char decreases as the pressure increases, while for lignite coal, in N2 atmosphere and at high pressure, less macro pores are formed, which could contribute to the BET surface area. While in CO2 atmosphere, the CO2-macromocular organic reaction would promote the volatile releasing, and the BET surface area decreases significantly at high pressure.

Computational fluid dynamics analysis of char conversion in Sandia's pressurized entrained flow reactor.

Design and analysis of practical reactors utilizing solid feedstocks rely on reaction rate parameters that are typically generated in lab-scale reactors. Evaluation of the reaction rate information often relies on assumptions of uniform temperature, velocity, and species distributions in the reactor, in lieu of detailed measurements that provide local information. This assumption might be a source of substantial error, since reactor designs can impose significant inhomogeneities, leading to data misinterpretation. Spatially resolved reactor simulations help understand the key processes within the reactor and support the identification of severe variations of temperature, velocity, and species distributions. In this work, Sandia's pressurized entrained flow reactor is modeled to identify inhomogeneities in the reaction zone. Tracer particles are tracked through the reactor to estimate the residence times and burnout ratio of introduced coal char particles in gasifying environments. The results reveal a complex mixing environment for the cool gas and particles entering the reactor along the centerline and the main high-speed hot gas reactor flow. Furthermore, the computational fluid dynamics (CFD) results show that flow asymmetries are introduced through the use of a horizontal gas pre-heating section that connects to the vertical reactor tube. Computed particle temperatures and residence times in the reactor differ substantially from the idealized plug flow conditions typically evoked in interpreting experimental measurements. Furthermore, experimental measurements and CFD analysis of heat flow through porous refractory insulation suggest that for the investigated conditions (1350 °C, <20 atm), the thermal conductivity of the insulation does not increase substantially with increasing pressure.

Impact of pressure on the carbon structure of char during pyrolysis of bituminous coal in pressurized entrained-flow reactor

The impact of pressure on the carbon structure of a Chinese bituminous coal was investigated using a pressurized entrained-flow reactor in the temperature and pressure ranges of 700-900 °C and 0.1-4.0MPa, respectively. Pyrolysis pressure had a significant influence on the physiochemical and carbon structure of chars. The specific surface area and the swelling ratio of chars reached their highest values at 1.0MPa. Fourier transform infrared spectroscopy (FTIR) analysis showed that higher pressures enhanced the decomposition of functional groups in chars. Raman spectroscopy analysis results revealed that at elevated pressures, the organic matrix and functional groups were removed from the char structure, leading to higher ordering of the carbon structure. During X-ray diffraction (XRD) analysis, parameters such as the stacking height (Lc), interlayer spacing (d002) and lateral size of the graphite structures (La) were used to evaluate the graphitic structures in chars. The results showed an increase in Lc, La, and the average number of graphene sheets with pyrolysis pressure, indicating a more ordered carbon structure at elevated pressures. The d-spacing of char was in the range of 3.34-3.37 A, similar to typical graphitic structures.

Advanced Concepts in Modular Coal and Biomass Gasifiers

The program involves the application of a novel gasification concept, termed a modular allothermal gasifier (MAG) to produce syngas from coal, biomass, and waste slurries. The MAG employs a steam-driven gasification process using a pressurized entrained flow reactor wherein the external wall surfaces are catalytically heated to 1000 °C via heterogeneous combustion of a portion of the produced syngas. The MAG can be fed by a hydrothermal treatment reactor for biomass and waste feedstocks, which employs well-developed hydrothermal processing technology using the addition of heat and water to provide a uniform slurry product. The hydrothermal treatment reactor requires no preprocessing and a clean syngas is produced at high cold gas efficiency (80%). Importantly, the MAG can operate over a wide range of positive pressures up to 3 MPa (30 bar) which provides process control to vary the output to match end-use needs or feedstock rate. The system produces minimal emissions and operates at significantly higher efficiency and lower energy requirements than pyrolysis, plasma gasification, and carbonization systems. The system is compact and modular, making it easily transportable, for example, to a variety of sites, including those where remoteness, inaccessibility, and space limitations would preclude competing systems. The system can be applied to small gasification systems without the increase in heat losses that plague conventional small scale gasifiers. Test results and model simulations are presented on a single tube system and analyses of a variety of configurations presented.

Numerical and experimental study of heavy oil gasification in an entrained-flow reactor and the impact of the burner concept

This work studies the heavy oil gasification experimentally and numerically. The experimental investigations use the semi-industrial test facility HP POX (High Pressure Partial Oxidation gasifier), operated at the Institute of Energy Process Engineering and Chemical Engineering, TU Bergakademie Freiberg. The HP-POX facility with a capacity of 5 MW operates under industrial conditions and features comprehensive instrumentation. The numerical model considers state-of-the-art model approaches and a detailed determination of the droplet size distribution, applying breakup models to the liquid heavy oil phase. The optical system of the HP-POX allows the heavy oil injection to be observed; these observations are then used to evaluate the droplet size distribution. The numerical model approach is validated against two lab-scale experiments from the literature, which also provide data on high pressure and temperature conditions. Validation A is the pressurized entrained-flow reactor of the Commonwealth Scientific and Industrial Research Organisation applying coal gasification at 20bar. Validation B is the research gasifier for liquid fuel, of the Central Research Institute of Electric Power Industry that gasifies Orimusion® at 19bar. The numerical model shows good agreement for both experiments, and for the heavy oil gasification experiment in the HP-POX plant. The validated model is used to study the impact of two different burner concepts on gasification characteristics. Burner 1 has a central fuel injection and an annular gasification agent injection, while Burner 2 has a central gasification agent injection and an annular fuel injection. The results show that Burner 1 achieves a higher syngas yield (H2+CO) but with higher soot production in comparison to the simulation results for Burner 2.

Gasification kinetics of a bituminous coal at elevated pressures: Entrained flow experiments and numerical simulations

Predicting conversion rates of solid fuels in entrained flow gasifiers, operating at increased temperatures and pressures, and better understanding the underlying reaction kinetics are of major interest for all industrial gasification applications. Numerical simulations in combination with experiments in lab- and pilot-scale entrained flow reactors help to understand the occuring reaction processes and can be used for gasifier optimization. The presented model is based on the software Ansys Fluent 16.0 and is validated for a bituminous coal with focus on the impact of total pressure. An nth order effectiveness factor approach with measured intrinsic reaction kinetics is applied in order to take diffusion limitations into account, and a thermal annealing model is included in order to account for the influence of decreased reactivities of the char surface due to deactivation, both being relevant at increased operating temperatures. The required model input parameters are derived from pyrolysis experiments and laboratory analyses. The simulation results are in good agreement with experimental data obtained from a pressurized entrained flow reactor operated at the Technische Universität München. The validation experiments are carried out at an operating temperature of 1200°C, at total pressures of 0.5MPa, 1.0MPa and 2.0MPa, and with a constant molar O/C ratio of one.

Numerical simulation of entrained flow gasification: Reaction kinetics and char structure evolution

Numerical simulations can help to improve the design of entrained flow gasifiers. The presented 3D-CFD model, developed using the software ANSYS Fluent 15.0, is validated against experimental data obtained from a pilot-scale pressurized entrained flow reactor. The comparison of the model with experiments shows a good correlation for the investigated Rhenish lignite. It is established that the modeling approach is suitable for predicting pressure- and temperature-dependent conversion rates in entrained flow gasifiers. This work focuses on the comprehensive modeling of char particle reactions. Pore diffusion and boundary layer diffusion become relevant at high temperatures. An nth order effectiveness factor approach with intrinsic reaction kinetics is applied in order to account for these diffusion limitations. Furthermore, the influence of thermal deactivation on the reactivity of the char surface is included. Several submodels are introduced, with focus on the structural evolution of char particles. A new pore structure model for high temperatures is developed that describes the surface area, the diameter, the density, the porosity and the mean pore diameter of the particles as a function of reaction regime and char conversion. User defined functions (UDF) include all submodels as well as the aforementioned effectiveness factor approach for the reactions of char with O2, CO2 and H2O. The computational effort is comparable to combustion simulations performed with standard models available in the software used.

From laboratory-scale experiments to industrial-scale CFD simulations of entrained flow coal gasification

In this work advanced gasification models of four Australian coals were calibrated using laboratory-scale experiments with the aim of extrapolating these information for simulating large-scale gasification processes using CFD. In particular, the four studied coals, ranging from semi-anthracite to sub-bituminous, were extensively characterized using high-pressure bench and laboratory scale techniques.Coal devolatilization is modeled using the empirical competing two-step models, whose parameters are calibrated in a pre-processing step by means of the advanced CPD, FG-DVC and FLASHCHAIN®pyrolysis models. The results of the advanced pyrolysis models are at first validated against true volatile yield data obtained at high pressures and heating rates from wire-mesh reactor experiments.Char gasification is modeled using a nth-order intrinsic kinetics model. At first, intrinsic char kinetics was measured in kinetic regime from experiments in pressurized thermogravimetric analysis. Then, gasification experiments in a laboratory-scale pressurized entrained flow reactor have been used for estimating the reactivity in pore-diffusion regime, defining the diffusivity inside the particle pores.Finally, the calibration of the same coals have also been tested in a 5MW pilot-scale gasifier, offering a unique opportunity to apply our model over the continuum of laboratory and pilot scales. The model results again show good agreement with the experimental data of syngas composition and carbon conversion evaluated at the exit of the gasifier. The simulations of the pilot-scale gasifier demonstrates that industrial-scale gasification processes can be accurately predicted using advanced coal conversion models, adequately calibrated through laboratory-scale experiments.

CO2 Char Gasification Rates of Sawdust, Switchgrass, and Corn Stover in a Pressurized Entrained-Flow Reactor

An entrained-flow flat-flame burner reactor was used to measure apparent CO2 gasification rates of near-spherical biomass chars of poplar sawdust, switchgrass, and corn stover using particle residence times <270 ms at total pressures of 10 and 15 atm. The gas temperature and bulk CO2 partial pressure ranges in these gasification experiments were 1258–1891 K and 6.1–13.5 atm, respectively. A new method was developed to produce near-spherical particles from nonspherical biomass chars. The apparent CO2 gasification rates for the three biomass chars with mean diameters near 100 μm were fit to a global first-order model, and the optimal kinetic parameters are reported. The measured gasification rate of poplar sawdust was about 3.9 times faster than that of switchgrass char, but only about 20% faster than that of the corn stover char.

Effect of Pressure on Char Formation during Pyrolysis of Pulverized Coal

Char samples prepared in a pressurized entrained flow reactor (PEFR) at a pressure of 2.0 MPa and in a drop tube furnace (DTF) at atmospheric pressure have been examined. Chars generated in the PEF...

Effects of Pressure and Oxygen Concentration on the Combustion of Different Coals

A pyrometric method was used for simultaneous in situ measurement of the temperature and size of individual coal particles in a pressurized entrained flow reactor. Several series of measurements we...

Characterization of burning char particles under pressurized conditions by simultaneous in situ measurement of surface temperature and size

Surface temperature and size of individual burning char particles were measured at elevated temperature and pressure using a two-color pyrometric technique. Experimental results obtained in a pilot-scale pressurized entrained flow reactor are presented. The studies concern two German coals: the Göttelborn high volatile bituminous (hvb) coal and Rhenish brown coal from the opencast mine Garzweiler. The obtained results show considerably different particle behavior due to different coal properties. In the case of the Göttelborn hard coal, typical excess temperatures at oxygen concentration of 12 vol % are about 350 K. in comparison to about 550 K in the case of the Garzweiler brown coal. The obtained number size distributions of the brown coal show a narrow fraction that is almost equal to the fed particle fraction. The hard coal char particles are much more scattered and shifted toward large particle sizes. This is found to be due to the tendency of particle swelling. For Garzweiler brown coal, a clear T p − D p dependence was found for the subset of burning char particles in all measurements, whereas the dependence was weaker, if any, for Göttelborn coal. The T p − D p dependence was approximated, by a regression line, and its slope was used for the characterization of the char burnout behavior. The found T p − D p dependence is assumed to be due to transient heat conduction from the particle surface toward the center. A qualitative heat balance at the particle surface is given that shows the main parameters that impact the particle surface temperature.

Formation of NO, NO2, and N2O from Gardanne Lignite and Its Char under Pressurized Conditions

The purpose of this investigation was to distinguish reactor-independent trends in the formation of N2O, NO, and NO2 from trends depending on the mode of combustion. The same char powder was studied with two different devices: a pressurized thermobalance (PTGA) where the particles are in contact and the gas flows through the char bed, and a pressurized entrained flow reactor (PEFR) where the particles are far from each other, moving in the gas flow. In addition, the proportions of nitrogen oxides formed from volatile-N and char-N were investigated with the PEFR and a modified thermobalance (MTGA), where the sample was burned as single pellets. A French (Gardanne) lignite or its char was used in the experiments. An increase in total pressure decreased the emissions of NO and increased the emissions of NO2 in both the PEFR and the PTGA. However, the effect of oxygen partial pressure was different. In PTGA, carbon monoxide emission was high, increased with PO2, and participated in NO and N2O reduction. Cons...

Pyrometric measurement of the temperature and size of individual combusting fuel particles

A two-color pyrometric technique was developed for the in situ simultaneous measurement of individual fuel-particle temperatures and sizes in a pressurized entrained flow reactor (PEFR). A method that requires only a single optical port was developed, and a specially designed optical probe was manufactured for the measurements at the PEFR. The fuel-particle temperature was obtained by applying two-color pyrometry. The particle size was determined from the same pyrometric signals. A discrimination method was developed to confirm that the detected particle was valid for particle sizing. Several series of measurements were made at a PEFR at different process conditions, and some typical results are shown.

Conversion of fuel nitrogen through HCN and NH 3 to nitrogen oxides at elevated pressure

Reactions of fuel nitrogen during pyrolysis and combustion of pulverized HVb coal, two peats and fir back were studied experimentally in a pressurized entrained flow reactor at T = 1123 and 1273 K, p = 0.2, 0.4 and 0.8 MPa. Mass loss of fuel, release of C, N, H and O, and formation of NH 3 and HCN were measured during pyrolysis (in N 2 containing O 2 < 20 ppmv). Mass loss, and formation of NO, N 2O and NO 2 through HCN and NH 3 were measured during combustion at 4–5 vol.% O 2. The rate of pyrolysis of high-volatile fuels (fir bark and peat) increased with pressure. The reverse trend was found with HVb coal. The order of release of the elements studied from the fuel (O > H > C > N) was found to be independent of pressure. The HCN NH 3 ratio in the flame was dependent on the fuel-O fuel-N ratio and independent of pressure. Pressure did however increase the N 2O NO ratio, because the concentrations of the key radicals in NO formation are decreased by pressure. With peats, the formation of N 2O increased slightly with pressure. The emission of N 2O however doubled with wood bark when the pressure increased from 0.2 to 0.8 MPa. Formation of NO 2 increased distinctly with pressure, and was fuel-dependent. One peat sample produced three times as much NO 2 as the other under identical conditions.

Pyrolysis and Combustion of Pulverized Wheat Straw in a Pressurized Entrained Flow Reactor

Within the past decade, there has been an interest for pressurized combustion and gasification of solid fuels in power plants due to the potential for high efficiency. The utilization of new types of solid fuels for pressurized combustion and gasification depends on char yield and char reactivity at relevant conditions. The pressurized entrained flow reactor designed at Riso is introduced. Pyrolysis and combustion at 10 and 20 bar pressure have been studied using pulverized wheat straw. Samples of partly reacted particles are collected, and the conversion is calculated using the ash tracer technique. The pyrolysis experiments show a yield larger than the yield from the proximate analysis. The pyrolysis is completed in about 1s, and the yield is the same for 10 and 20 bar pressure. The combustion experiments show a high reactivity with oxygen, and the effects of pressure on combustion are discussed using the 10 and 20 bar experiments.

Pressurized Pulverized Fuel Combustion in Different Concentrations of Oxygen and Carbon Dioxide

Theoretical and experimental studies showed that increasing gas pressure at constant gas composition most strongly increases the combustion rate of less reactive coals, which are difficult to burn completely in atmospheric pulverized fuel boilers. The effect of pressure increase is greatest near 0.1 MPa and less at higher pressures. The limit at which increase in pressure has an effect varies from coal to coal, depending on the particle size. With less reactive coals and small particles, the effect can be seen at pressures greater than 1 MPa. The relative effect of pressure increases when the gas oxygen content is low, improving the burnout in furnaces. The effect of pressure is small for large particles and reactive fuels. At high pressures the rates of homogeneous and heterogeneous reactions increase raising the maximum particle temperature; the higher temperature may increase the extent of devolatilization and further decrease the total combustion time. Combustion rate and the temperature of burning coal particles were measured in experiments with a pressurized entrained flow reactor under the following conditions: gas temperature 1073−1473 K, pressure 0.2−0.8 MPa, oxygen partial pressure 0.025−0.1 MPa, and partial pressure of CO2 0.05−0.2 MPa. Measured and calculated results showed increased carbon dioxide concentration in the combustion environment to have an insignificant effect on the combustion rate in the studied temperature region, but it lowered the particle temperature to some extent, suggesting that the gasification reaction CO2−C takes place as well. Calculations indicated that in pressurized combustion the rate of gasification reaction is greater at higher temperatures.

Effects of pressure, gas temperature and CO 2 and O 2 partial pressures on the conversion of coal-nitrogen to NO, N 2O and NO 2

The effects of pressure (2–16 bar), gas temperature (800–1100°C) and the partial pressures of carbon dioxide (0.01–4 bar) and oxygen (0.2–2 bar) on the formation of N 2O, NO and NO 2 from coal-N were studied. Bituminous coal, 75–125 μm, was burned as a dilute pressurized suspension in an electrically heated pressurized entrained-flow reactor. Nitrogen oxides were analysed by an on-line FT-i.r. The experimental conditions differed from those of an earlier study in that high concentrations of CO 2 (up to 80 vol.%) and higher oxygen partial pressures and especially concentrations (up to 50 vol.%) were used. The results were analysed by a partial-least-squares method. Increase of pressure decreased the conversion of fuel-nitrogen to NO, and had a weak effect on its conversion to N 2O. Increase of P CO 2 increased slightly the conversion of fuel-N to N 2O. The effect of P CO 2 on NO formation was too weak to be clearly detected, although a weak decrease in conversion may occur when P CO 2 is increased from 1 bar to 4 bar. The conversion of fuel-N to NO 2 was weak, but increased clearly when P CO 2 was increased from 1.5 bar to 2.0 bar.