Entrained Flow Gasification Process Research Articles

Thermal radiation at high-temperature and high-pressure conditions: Comparison of models for design and scale-up of entrained flow gasification processes

Thermal radiation is an important sub-process in high-pressure entrained flow gasification. However, it was seldom investigated in previous CFD studies and was usually accounted for by common radiation and simplified gas radiation property models. Therefore, this study performed comparative one-dimensional radiation and two-dimensional CFD simulations with respect to the bioliq Entrained Flow Gasifier (bioliq EFG). The one-dimensional radiation simulations were applied to compare the effects of advanced and simplified gas radiation property models for atmospheric and high-pressure entrained flow gasification conditions, while the CFD simulations were carried out to investigate the performance of simplified gas radiation property models incorporated within the CFD model of the bioliq EFG. The segmental heat removal from the cooling screen of the bioliq EFG was applied as experimental basis for comparison with the numerical predictions. Based on the comparisons, this study provides recommendations for the selection of gas radiation property models for CFD simulations with the discrete ordinates model and with focus on entrained flow gasification. In case of largely isothermal and homogeneous conditions with exemption of the flame zone, weighted-sum-of-grey-gas models can be used with the discrete ordinates model if user-defined weighted-sum-of-grey-gas models (i) are obtained from accurate line-by-line calculations, (ii) are based on conditions prevailing in the reactor and (iii) are incorporated using the band approach. In absence of such weighted-sum-of-grey-gas models, full-spectrum correlated-k distribution models based on the latest tabulations can be used instead for CFD simulations of entrained flow gasification processes. In addition to that, sensitivity analyses showed that a coarse discretisation of the radiative transfer equation within the boundary layer, inaccurate gas species concentrations in the boundary layer (within a ±5% margin) and the P-1 approximation can be accepted for high-pressure conditions while soot radiation becomes important at soot volume fractions above 10−6 and should be accounted for if such conditions are expected.

Effect of powder column height on the compression behavior of rice husk powder under gas pressurization

The pressurized pneumatic conveying of biomass powder was a key technical challenge to be solved urgently for the entrained-flow gasification process. The dynamic compression characteristics of rice husk powder with different heights under gas pressurization were experimentally studied. The rice husk powder column was highly compressible and the gas was easy to permeate. The agglomeration effect of rice husk powder increased the void fraction and reduced the packing density. Furthermore, the compressibility of the powder column increased with height. The mechanism was probably mainly related to the movement distance of particles and the pressure drop of the gas through the powder column. Based on the Sone model, we proposed a model for the relationship between the pressure and the variation of relative height with an error of ± 1 %.

Entrained flow gasification: Impact of fuel spray distribution on reaction zone structure

Entrained flow gasification (EFG) is an important process for generating syngas from biogenic and anthropogenic waste based feedstocks for a future circular economy. The EFG process is characterized by complex interactions between different physical and thermo-chemical sub processes which determine syngas quality and process efficiency. The understanding of these sub processes is essential for the development of validated models, and therefore for design and scale up of EFG reactors. EFG processes using a central jet burner configuration feature flames that can be described as inverse diffusion flames superimposed by a fuel spray. The flames are characterized by (i) the conversion of liquid and slurry droplets and (ii) the oxidation of recirculating synthesis gas with the gasification medium. This work studies the interactions between fuel and oxidizer in the near-flame region of an atmospheric EFG process. The model fuel ethylene glycol was gasified using oxygen-enriched air for two different burner nozzle configurations. Spray imaging, OH-LIF and Fuel Tracer-LIF measurements were carried out in addition to gas temperature measurements to characterize the fuel distribution and the flame structure. The experimental results show that narrower fuel spray distributions result in shorter flames and changes in flame shape from a compact to a hollow cone shape in the downstream flame region. The experiments were accompanied by 2-phase free-jet modeling and RANS based CFD modeling. The models were improved to reflect the experimental findings including the fuel spray distributions. The simulation results predict the observed flame structures well using both models and for both burner nozzle configurations. The changes in flame structure for different spray distributions can be explained by local stoichiometry using the results of the 2-phase free-jet model.

Numerical simulation of entrained flow gasification based on properties and kinetic characteristics of pulverized coal particles

Gasification kinetic parameters of coal char based on the random pore (RPM) model are obtained with CO2 and H2O using a high-pressure thermogravimetry analysis (TGA) under atmospheric pressure and 4.0 MPa pressure, considering the influence of internal diffusion and particle structure varying with carbon conversion. The Chemical Percolation Devolatilization (CPD) model is used to modify the actual volatile content. Through the coupling of the gasification kinetic reaction model, a comprehensive numerical simulation method of the entrained flow gasification process is established. This method is used to simulate the typical gasifier of HTL (a gasification technology of Changzheng Engineering Co.) in an industrial plant. The research shows that the intrinsic reaction parameters obtained by TGA under high pressure can give a more reasonable reaction state of coal char particles in the gasifier than that measured under atmospheric pressure, and the simulation results are in good agreement with the industrial data. In addition, HTL adopts a single top-fired burner and multi-channel swirling feed type. The particles are entrained and mixed with swirling oxygen, and the combustion reaction is completed quickly in the upper part of the gasifier. In contrast, the gasification reactions are relatively slow and mostly dominate in the recirculation zone and pipe flow zone, leading to high carbon conversion.

Comparison of physicochemical properties and gasification reactivity of soot from entrained flow gasification processes

Soot formation has been a hurdle to the development of entrained flow gasification (EFG) technology, as it damages the apparatus and remains a pollutant. Soot has a poor gasification reactivity in the multiphase flow in furnace. In this study, differences in physicochemical properties and their relationship with gasification reactivity were revealed for natural gas-derived soot (NGS), coal-derived soot (CS), and biomass-derived soot (BS) from EFG process. A comparative study was also conducted between the gasifier soot and a commercial carbon black (CB), N330. The thermogravimetric analyzer (TGA) results showed the descending order of the activation energy (Ea) of gasifier soot was NGS > BS > CS, in both CO2 and H2O gasification process. Transmission electron microscopes (TEM) and Raman spectrum further determined that the gasification reactivity was highly dependent on the carbon content, carbon type, and graphitization degree but less dependent on soot microstructure. This study also investigated the potential replacement of commercial N330 as a rubber reinforcement additive with soot as a pollutant. This replacement was based on the microstructure similarities between soot and CB, as determined using fractal dimension (Dp) as an indicator on a statistical level from TEM. The Dp of NGS was 1.35, 1.06 times larger than that of CS, and 1.22 times larger than of BS. It was highly feasible that NGS would have the close physical property of N330 and could potentially replace the expensive N330 as a rubber reinforcement material.

Oxidation characteristics of soot in different entrained flow gasification processes

The morphological structure of six samples including the rapid pyrolysis soot of solid fuels (coal, biomass), the soot from non-catalytic partial oxidation(NCPOX) of natural gas in a laboratory pilot plant and an industrial plant, the commercial carbon black in natural gas furnace/coal tar furnace, were characterized by using a transmission electron microscope. Based on atmospheric thermogravimetric analyzer, the non-isothermal method (50–800 °C) was adopted to study the ignition point and the oxidation reaction rate of soot, and the oxidation reaction kinetic parameters of soot was obtained. Studies showed that the physical and chemical properties of various soot were quite different. The soot from the rapid pyrolysis of coal and biomass presented a higher sphericity and a larger particle size. The Lab-NCPOX-soot was formed at a lower temperature which caused the particle being wrapped by a carbon capsule. The Ind-NCPOX-soothad a hollow structure and a small particle size. The reactivity of the Lab-NCPOX-soot is close to that of the Ind-NCPOX-soot, which is 3.1 times that of the commercial natural gas furnace carbon black and 3.2 times that of the commercial coal tar furnace carbon black; the reactivity of NCPOX-soot is 9.0 times of the rapid pyrolysis soot of coal, and 26.6 times of the rapid pyrolysis soot of biomass. The activation energy of 2 kinds of NCPOX-soot and 2 kinds of commercial carbon blacks present staged forms with increasing temperature. The activation energy of the 2 rapid pyrolysis soot was basically unchanged with increasing the temperature.

Comparison of Physicochemical Properties and Gasification Reactivity of Soot From Entrained Flow Gasification Processes

Comparison of Physicochemical Properties and Gasification Reactivity of Soot From Entrained Flow Gasification Processes

A deep insight on the coal ash-to-slag transformation behavior during the entrained flow gasification process

Recent research provided deep insight on the coal ash-to-slag transformation characterization during the entrained flow gasification process, with experimentation on a 40 kg/hr (dry basis) coal-fed opposed multi-burner (OMB) entrained flow gasifier and simulation via FactSage™ software. A general mechanism is presented to relate the gasifier design temperature, ash fluid temperature, and operating temperature with the degree of the slag polymerization. The change of the high temperature zone, the corresponding particle residence time in the high temperature zone, and syngas composition have obvious effects on the slag mineral transformation behavior. Mineral types formed on the wall of the gasifier chamber were mainly anorthite (CaAl2Si2O8), aluminum oxide (Al2O3), and calcium sulfide (CaS). These minerals transformed to anorthite and diopside (CaMgSi2O6) at the slag hole zone, while the minerals at the lock hopper were anorthite, orthoclase (KAlSi3O8), quartz (SiO2), gypsum (CaSO4), calcite (CaCO3), and halite (NaCl). FactSage™ predicted minerals as anorthite, diopside, orthoclase, and albite (NaAlSi3O8), etc., where the slag temperature was below the ash fluid temperature and when the ratios of CO/CO2 and (CO + H2)/CO2 were lower than 1.0 and 2.0, respectively. By simulation, residual carbon was found to be the dominant factor over syngas composition to cause mineral transformation, and this was verified experimentally. The Ca-based crystals, typically anorthite, was shifted to diopside, near the slag hole zone, and a linear relationship was found between the content ratios of diopside/(anorthite + diopside), CaO/SiO2, and (CaO + MgO)/SiO2. A dimensionless number, θ, was defined to characterize the changing chemical composition and the degree of slag polymerization, with temperature deviation from the design condition. Three zones of θ were identified and related to the deviation between the actual gasification condition from the design condition. A low slag polymerization degree corresponded with a higher temperature deviation between the actual condition and design condition, and this proved that increased residual carbon content and changing iron valence state increased the mineral types when the slag temperature was below the ash fluid temperature.

Impact of Chemistry–Turbulence Interaction Modeling Approach on the CFD Simulations of Entrained Flow Coal Gasification

This paper examines the impact of different chemistry–turbulence interaction approaches on the accuracy of simulations of coal gasification in entrained flow reactors. Infinitely fast chemistry is compared with the eddy dissipation concept considering the influence of turbulence on chemical reactions. Additionally, ideal plug flow reactor study and perfectly stirred reactor study are carried out to estimate the accuracy of chosen simplified chemical kinetic schemes in comparison with two detailed mechanisms. The most accurate global approach and the detailed one are further implemented in the computational fluid dynamics (CFD) code. Special attention is paid to the water–gas shift reaction, which is found to have the key impact on the final gas composition. Three different reactors are examined: a pilot-scale Mitsubishi Heavy Industries reactor, a laboratory-scale reactor at Brigham Young University and a Conoco-Philips E-gas reactor. The aim of this research was to assess the impact of gas phase reaction model accuracy on simulations of the entrained flow gasification process. The investigation covers the following issues: impact of the choice of gas phase kinetic reactions mechanism as well as influence of the turbulence–chemistry interaction model. The advanced turbulence–chemistry models with the complex kinetic mechanisms showed the best agreement with the experimental data.

Effect of elevated pressure on air-assisted primary atomization of coaxial liquid jets: Basic research for entrained flow gasification

Highly resolved numerical simulations have been conducted for a generic, coaxial air-blast atomizer designed for fundamental research of entrained flow gasification processes. Objective of the work is to gain a detailed knowledge of the influence of elevated reactor pressure on the primary atomization behaviour of high-viscous liquid jets. In agreement with measured breakup morphology and breakup regimes proposed in literature, the simulations yield a pulsating mode instability of liquid jet, along with disintegrations of fibre-type liquid fragments for different pressures. From the mechanism point of view, the breakup process has been shown to be triggered by concentric, axisymmetric ring vortices, which disturb the liquid jet surface in a first stage and penetrate further into the intact core, leading to interfacial instabilities and pinch-off of liquid ligaments. The liquid jet breaks up faster at elevated pressure, leading to a shorter core length LC. The calculated exponent (b≈−0.5) of the power law for fitting the decrease of LC with p agrees well with measured correlations from literature in terms of varied momentum flux ratio M and Weber number WeG, although water jets, atmospheric pressure and different air-assisted, external mixing nozzles were used in these works. Therefore, the effect of elevated pressure is equivalent to that of increased M or WeG, which scale linearly with p or the gas density for the current setup. The specific kinetic energy of liquid kL has been found to be increased with p, which is particularly pronounced in the high frequency range. A first-order estimate has been proposed, which can be used for the evaluation of liquid kinetic energy or droplet velocity within the spray. The results have been validated by simulations with twice-refined resolution, yielding a grid-independence behaviour with respect to the primary breakup characteristics. However, the follow-up processes with secondary breakup and spray dispersion are reproduced better by using the finer grid.

Evaluation of carbon forms and elements composition in coal gasification solid residues and their potential utilization from a view of coal geology

As the development of coal gasification technology expands in China, the resulting solid by-products can become environmental and economic concerns. Evaluation of carbon forms and elemental composition in coal gasification solid residues from three advanced commercial-scale entrained-flow gasification plants in China related to feedstock coal properties are studied and their potential utilization is discussed in the present study. The properties of the residues of the three entrained-flow gasification processes differed as a result of the type of process applied, even though the properties of their feedstocks are similar. Eight types of carbon forms were identified. The high-inertinite feedstock resulted in a fusinite-like carbon being the primary carbon form of the residues, except for the General Electric fine residue (GE-FR) sample. The carbon contents of the coarse residues (CRs) produced from the Opposed Multi-Burner (OMB) coal-water slurry gasifier and the Gaskombiant Schwarze Pumpe (GSP) pulverized coal gasifier are comparable, lower than 2% (Cd), but a high content of carbon present as “black particles” (79.90%, Cd) was concentrated from the OMB-CR sample. Fourier transform infrared spectroscopy (FTIR) analyses indicate that the main functional group of the fusinite-like material in OMB-CR is methyl (CH3–). From the chemical composition point of view, the high proportions of F2O3 and CaO in the GE residues make them potential sources of high-Fe or high-Ca material. The relatively high concentrations of In, Ga, Sb, Cs, Cr, Ba, and rare earth elements in the residues make them potential raw materials for extracting critical trace elements, especially the OMB-FR and GSP-FR samples for extracting Ga.

Study on Char-Ash-Slag-Liquid Transition and Its Effect on Char Reactivity

In the entrained flow gasification process, char-ash-slag-liquid transition affected the gasification reactivity. Meihuajing bituminous coal (MB) and Xiaolongtan lignite (XL) were chosen to prepare...

The application of fly ash gasification for purifying the raw syngas in an industrial-scale entrained flow gasifier

A fly ash entrained flow gasification process was developed to simultaneously remove and utilize fly ash in the raw syngas coming directly from fluidized and fixed bed gasifiers. The present in situ experiments at a full load of 80,000 Nm3/h showed that, compared to the raw syngas, the effective syngas (CO + H2) concentration in the purified syngas was slightly decreased, from 72.98% to 72.63%. In contrast, the average mass fraction of carbon in the fly ash was greatly reduced, from 29.5% to below 2%. This gasification process was determined to rapidly heat the entirety of the raw syngas to more than 1285 °C based on fast combustion of a small quantity of the raw syngas and all of the gasifying agent. Thermal analysis showed that the initial gasification temperature of the raw syngas was 1985 °C. Heat loss from the purified syngas was 20.6% of the fuel heat quantity, while the heat loss from unburned combustible gas accounted for 75.1%. Laboratory-scale airflow experiments were also conducted to determine the volume concentration distribution of the gasifying agent at the outlet of a single burner.

Techno-economic assessment of process integration models for boosting hydrogen production potential from coal and natural gas feedstocks

The elevated energy demands from past decades has created the energy gaps which can mainly be fulfilled through the consumption of natural fossil fuels but at the expense of increased greenhouse gas emissions. Therefore, the need of clean and sustainable options to meet energy gaps have increased significantly. Gasification and steam methane reforming are the efficient technologies which resourcefully produce the syngas and hydrogen from coal and natural gas, respectively. The syngas and hydrogen can be further utilized to generate power or other Fischer Tropsch chemicals. In this study, two process models are developed and technically compared to analyze the production capacity of syngas and hydrogen. First model is developed based on conventional entrained flow gasification process which is validated with data provided by DOE followed by its integration with the reforming process that leads to the second model. The integrated gasification and reforming process model is developed to maximize the hydrogen production while reducing the overall carbon dioxide emissions. Furthermore, the integrated model eradicates the possibility of reformer’s catalyst deactivation due to significant amount of H2S present in the coal derived syngas. It has been seen from results that updated model offers 37% increase in H2/CO ratio, 10% increase in cold gas efficiency (CGE), 25% increase in overall H2 production, and 13% reduction in CO2 emission per unit amount of hydrogen production compared to base case model. Furthermore, economic analysis indicated 8% reduction in cost for case 2 while presenting 7% enhanced hydrogen contents.

Simulation and optimization of rice husk gasification using intrinsic reaction rate based CFD model

Entrained flow gasification processes of rice husk were simulated and optimized in this study using an intrinsic reaction rate based CFD model. A detailed sensitivity analysis was conducted to characterize the effects of operation parameters on the gas composition, gas production and cold gas efficiency. Gasification temperature, average particle diameter, ER (equivalence ratio) and CO2/biomass (mass ratio of carbon dioxide to biomass) are important operation parameters affecting the gasification process, and they were investigated in this study. Three-objective optimization of rice husk gasification was performed base on the response surface methodology (RSM) to maximize CO content, gas production, and cold gas efficiency, and the Pareto optimal solutions were obtained from NSGA-II (non-dominated sorting genetic algorithm) to instruct gasification operation. With standard TOPSIS (technique for order preference by similarity to ideal situation), the optimal solutions with CO concentration of 25.15%, gas production of 1.96 Nm3/kg and cold gas efficiency of 65.34% were obtained.

Simulation of Coal Gasification in a Low-Temperature, High-Pressure Entrained-Bed Reactor with a Volatiles Condensation and Re-Evaporation Model

The objective of this study is to implement a tar condensation and re-vaporization sub-model in a previously established Computational Fluid Dynamics (CFD) model for the Entrained Slagging Transport Reactor (E-STR) gasifier, modified from the existing E-Gasifier simulation models in previous studies. The major modifications in E-STR, compared to the existing E-GasTM design, include higher operating pressure and lower temperature, with the aim of achieving a higher H2/CO ratio of syngas, which is more favorable for synthetic natural gas (SNG) production. In this study, the aforementioned sub-model is described by the UDF (User-Defined Function) and incorporated in a previously developed computational model for entrained-flow gasification process, to study the syngas composition without implementing a tars-cracking catalyst in the E-STR gasifier. The results show that incorporating the tar condensation model leads to a formation of approximately 6.47% liquid volatiles and an exit temperature increase about 135 K, due to the release of latent heat. These sub-models have been successfully implemented and will be useful in the condition that the gasifier temperature is intentionally kept low, just as the E-STR gasifier. The results indicate that high pressure and less oxygen feed produce a higher H2/CO ratio, more favorable for SNG production.

Parameter analysis of an entrained flow gasification process

This work presents primary results of a parameter study for entrained flow gasification using a steady-flow reactor model. The influences of important parameters such as coal types, gasifier pressure, gas/coal feeding rate, and coal particle size were studied based on coal conversion and gas product species. The prediction results were compared and validated against those published previously. In particular, a relative importance of reaction stoichiometry, temperature, reaction time (kinetics), or residence time considered in this simulation work was evaluated to affect the gas composition produced from different coals. The optimal carbon monoxide concentration was observed at an oxygen-to-fuel ratio of 0.8, while a greatest carbon conversion was found at a steam-to-fuel ratio of 0.4. Coal particle size has a strong influence on carbon conversion. However, the coal feeding rate has no effect on carbon conversion despite differences in residence time.

Effect of water vapor on coal ash slag viscosity under gasification condition

The entrained flow gasification process employs a high temperature, high pressure slagging gasifier, in which the viscosity of the slag plays a key role in determining operating conditions. Many studies have focused on the viscosity of slag under the reducing atmosphere, especially CO + CO2 and CO + H2. As an important component in the gasification syngas, the effect of water vapor on the slag viscosity temperature properties is not yet clear. In order to keep the stable operation of the gasifier, the effect of water vapor on the viscosity temperature properties of the slag were studied in this work. Ash fusion temperatures (AFTs) decrease with the increasing water vapor proportion. Although mineral species do not change obviously, the content of SiO2 in the ash decreases, and more amorphous substances forms when water vapor is added. The slag viscosity and temperature of critical viscosity (TCV) also decrease with the introduction of water vapor, while the effect is not obvious due to the low solubility at ambient pressure. It is confirmed that water vapor weakens the melts network structure by breaking [Si–O–Si] bonds. Meanwhile, the network modifier, [AlO6]9−, increases with the increasing water vapor proportion. Besides, water vapor inhibits the growth of the crystal. As its proportion increases, the average particle size of crystals decreases, leading to the decrease of the slag viscosity and TCV. The results provide a theoretical basis for the effect of water vapor on the slag viscosity and will be benefit for the operation of entrained flow gasification, especially for the coal water slurry gasification.

Effect of moisture on flowability of pulverized coal

Reliable feeding of pulverized coal into the gasifier is of great importance for the pressurized entrained-flow gasification process. Moisture and corresponding interparticle force can strongly affect the flowability of pulverized coal. In this paper, flow properties of pulverized coal were measured using a PT-X powder flow tester and a FT-4 powder flow rheometer. With respect to several flow indicators including angle of repose (AOR), Hausner ratio (HR), Carr’s flowability index (CFI), basic flow energy (BFE), cohesion (C), angle of internal friction (ϕ) and flow index (ffc), pulverized coal with different moisture contents was classified into different categories and the flow properties of each category were analyzed and compared. Secondly, a combination of a continuum approach and a particle–particle approach to describe the multi-scale nature of the mechanical properties of pulverized coal were carried out. The interparticle forces of pulverized coal with different moisture contents were predicted using a microscale approach with the Rumpf equation combined with the experimental results from the shear tester. The results were further compared with those calculated using a theoretical approach with the combination of the Kelvin equation and the Laplace–Young equation. Finally, the mechanism of moisture’s effect on flow was described by the relation between the bulk structure of wet particle systems and moisture. The results indicated that moisture had different effects before and after critical values, according to which four regimes including the “dry regime”, the “dispersed moisture regime”, the “consolidated moisture regime” and the “slurry regime” were defined with increasing moisture content.

Petrological Characteristics and Trace Element Partitioning of Gasification Residues from Slagging Entrained-Flow Gasifiers in Ningdong, China

In order to better understand the petrological characteristics of gasification residues and trace element partitioning during entrained-flow gasification processes, oil-immersion microscopy, X-ray diffraction, scanning electron microscopy combined with an energy dispersive detector, inductively coupled plasma mass spectrometry, a Milestone DMA-80 Hg analyzer, and pyrohydrolysis in conjunction with a fluorine ion-selective electrode were employed to study samples collected from three commercial-scale slagging entrained-flow gasifiers in Ningdong, China. Petrological analysis indicated that dominant organic components in the residues were inertiods, fusinoids, tenuinetworks, and crassisnetworks. In addition, vitroplast and cenosphere were observed in coarse residues produced from water–slurry coal gasification. The main inorganic components were quartz, calcite, spinel, and a large amount of Al–Si glass. After gasification, most trace elements were significantly enriched in the residues. Critical trace elem...