Entrained Flow Gasifier Research Articles

Corrosion and degradation mechanisms of high chromia refractory bricks in an entrained-flow gasifier: experimental and numerical analysis

As a crucial component of an opposed multi-burner (OMB) coal-water slurry gasifier, severe degradation of the refractory lining frequently results in costly operation delays. In this work, the morphology and damage evolution of the used high chromia refractory bricks in a gasifier were evaluated by experimental tests and numerical analysis to gain insight into the corrosion and degradation behavior of the refractory lining. The results indicated that the degradation of high chromia refractory bricks were mainly owing to the structural spalling caused by slag corrosion and thermal stress induced by temperature gradient. The stress cracks developed at the corroded interface provided a penetration pathway for slag and served as a sub-surface for further corrosion, resulting in additional corrosion and spalling. Furthermore, the formation of the composite spinel phase with a high thermal expansion coefficient also contributed to significant thermomechanical stress. The degradation behavior of high chromia refractory brick followed the “penetration-dissolution/reaction-spalling” mechanism. Based on experimental and numerical results, a conceptual model was developed to describe the progressive degradation mechanism of refractory, and several possible solutions were also suggested.

Three-dimensional Numerical Simulation of Entrained-Flow Gasifier and Influence of Coal Distribution at the Inlet

The research object in this paper is an industrial HTL gasifier in a plant. A three-dimensional model is built. The chemical percolation devolatilization (CPD) model is used to calculate the pyrolysis reaction. Considering the gas diffusion in the inner pores of the particle and the evolution of pore structure, the random pore model (RPM) was used to simulate the chemical reaction on the particle surface, and the gasification reaction kinetic parameter of char was measured by high-pressure thermogravimetry analysis. The slag model was constructed to describe the formation process and distribution of slag. Through the coupling of the above models, a simulation method that combines several submodels for the entrained flow gasifier is built, and the results from simulation are in good agreement with the industrial data. Furthermore, the effect of the uniformity of pulverized coal injection was analyzed by this method. The simulation results reflect that the asymmetric feed of coal will affect gas-solid mixing and reduce carbon conversion, and it leads to a higher local wall temperature and a lower ratio of crude slag to fine slag.

Effects of sludge on the ash fusion behaviors of high ash-fusion-temperature coal and its ash viscosity predication

The co-gasification of sludge and coal is a promising way to regulate coal ash fusion characteristics and recover energy from sludge simultaneously. In this paper, the ash fusion behaviors of high ash-fusion-temperature (AFT) Datong coal, textile dyeing sludge (TDS), their mixtures, and the corresponding AFT modification mechanisms on laboratory scale were investigated by an AFT tester, X-ray diffractometer, Raman spectrometer, and FactSage software. The AFTs of Datong coal mixtures decreased slowly when TDS share was in the range of 0–6%, quickly (6–9%), and then nearly stable (>9%) because of its corresponding increasing basic oxide values (the total content of SO3, CaO, MgO, Fe2O3, Na2O, and K2O). The generations of low melting-point minerals of hercynite and anorthite with TDS additions resulted in the AFT decrease. The decreasing intensity of Si–O–Si peak and the increasing ratio bond of bridging oxygen and non-bridging oxygen led to the AFT decrease. Both the decreases in the temperature at which all minerals change into liquid-phase and the continuously increasing liquid-phase content (at the same relative high temperature) in Datong coal mixed ashes with increasing TDS mass ratio were contributed to the variations of AFT. The viscosity-temperature characteristics variation was also predicted using FactSage calculation. The 9.0–12.0% mass ratio of TDS might be suitable for Datong coal entrained-flow bed gasification.

Analysis of the Effect of Dimensional Variation and Number of Air Inlets on the Efficiency of Gasification Stoves using Computational Fluid Dynamic (CFD) Simulation

Nowadays, the consumption of non-renewable energy is high. As a result, the availability of this energy is decreasing. Because of this, other energy alternatives are needed. One example of another option is the use of biomass. An example of using biomass is the gasification process. This process was carried out in a device called a gasification stove, namely a gasifier. A gasifier has been developed to produce an optimal combustion system. The constraints in this development are costs for manufacture and the potential for failure. Therefore, simulations using Ansys Computational Fluid Dynamics (CFD) software student versions were carried out to reduce the costs for manufacture and the potential for failure of the gasifier. The simulation contains dimensional variations and the number of air inlets of gasifier of downdraft gasifier, updraft gasifier, and entrained flow gasifier. Further, the influence of the dimensions and quantity of inlet that affect each design’s efficiency and the temperature was examined. The simulation results show that the best dimensions for the downdraft gasifier, updraft gasifier, and entrained flow gasifier are height and diameter of 50cm; 14.5cm (A1), 144cm; 70cm (C1), and 900cm; 300cm (B3), respectively. The best number of air inlets of A1, C1, and B3 gasifiers is 6, 1, and 6, respectively. Thus, the efficiency of each gasifier A1, C1, and B3 are 11.393%, 9.354%, and 50.885%, respectively. Furthermore, the A1, C1, and B3 gasifiers temperatures were 1055.25 K, 1383.44 K, and 3580.15 K, respectively. Therefore, this study suggested that the gasifier development could be optimized using simulation to reduce manufacturing costs and failures.

Biomass Entrained Flow Gasification Technology and CFD Numerical Simulation

Aiming at the dry pulverized biochar fuel refined by thermochemical conversion technology, its properties were obtained through experiment. By blending 5% additives to improve the ash fusion characteristics of biomass particles and considering the viscosity-temperature characteristics and the matching principle of CO2 reaction activity, the entrained flow gasification technology scheme of biomass particles was formulated. Based on the gasification reaction kinetics of dry pulverized biochar, a numerical simulation model was established to predict the flow characteristics, syngas composition, and particle conversion process in the gasifier. The results show that under the swirling entrainment and centrifugal force, the oxidizing reaction of particles is completed in the upper part of the gasifier quickly after mixing with oxygen. And the gasification reduction reaction occurs in the recirculating area and the pipe flow area. These effectively complete the conversion of char. The simulation results are in good agreement with the equilibrium calculation values, which proves the feasibility and rationality of the biomass particle entrained flow gasification technology scheme based on the HT-L.

Application study of Dynamic Mode Decomposition coupled with a high-speed imaging system in jet zone oscillation behavior diagnosis of impinging flames

Dynamic Mode Decomposition (DMD) is a data-driven analysis method for plenty of snapshots, which has good application prospects in the combustion diagnostics base on optical methods. In this study, the self-pulsation combustion instability of four-burner impinging diesel flame was explored based on a bench-scale opposed multi-burner entrained-flow gasifier. The spatiotemporal evolution of the flame structure in the jet zone was studied by DMD analysis. The vortex evolution of the central reaction stream was divided into four stages, and the period of each stage was determined. The boundary streams also have periodic oscillations in the reaction intensity. The modes with high growth factor can accurately identify the oscillation components in different structures of the flame. The corresponding feature DMD modes were in good agreement with the flame structure obtained from the grayscale image, but the local components in the DMD mode may belong to different time scales.

Experimental study on a small-scale oxygen-enriched entrained flow biomass gasifier assisted by non-thermal arc plasma

A small-scale oxygen-enriched entrained flow biomass gasifier consisting of a non-thermal arc plasma torch and a stainless steel bellows was developed. The characteristics of the non-thermal arc plasma were diagnosed. The effects of oxygen concentration and bellows length on the gasification process using rice husk powder as feedstock at a feed rate of 27.1 g/min were studied. The results show that increasing the oxygen concentration of gasifying agent and using longer bellows both lead to the improvement of cold gas efficiency, carbon conversion efficiency, and yields of H2 and CO. The cold gas efficiency of the gasifier at a bellows length of 500 mm and oxygen concentration of 34.7% is 65.8%. And benefiting from low auxiliary energy consumption, the gasifier’s energy efficiency reaches 60.5%. The non-thermal arc plasma assists the entrained flow gasification by converting part of the feedstock into activated reactants.

Numerical study on reaction-induced force of a coal particle: Effect of temperature gradient in entrained-flow gasifier

The ambient temperature in entrained-flow gasifier varies in the large range, and temperature gradient can reach 60,000 ∼ 80,000 K/m in the flame zone. This work numerically studies the effect of temperature gradient on the conversion characteristic and reaction-induced force of a single carbon particle during the gasification process. The single carbon particle is placed in the H2O/CO2 mixture atmosphere with a temperature gradient. The particle size and the average ambient temperature around the particle are considered. The temperature gradient leads to the difference of conversion rate on the particle surface. The net reaction-induced force is formed. The reaction-induced force (Fr) is proportional to d2 (d is the particle diameter). For small particles (d < 30 μm), the Fr can reach the same magnitude as the particle gravity. Additionally, Fr increases linearly with the increase of temperature gradient. With the increase of ambient temperature around the particle, the Fr rapidly increases.

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.

Simulation Study on the Interaction between Chemically Reacting Double Coal Char Particles.

Due to the complex atmosphere of the entrained flow gasifier, it is difficult to obtain reactivity properties of coal char particles under high-temperature conditions by experiment. The computational fluid dynamics simulation method is a key way to simulate the reactivity of coal char particles. In this article, the gasification characteristics of double coal char particles under H2O/O2/CO2 atmosphere are studied. The results show that the particle distance (L) has an influence on the reaction with particles. With the gradual increase of L, the temperature first rises and then falls among the double particles due to the migration of the reaction area, and the characteristics of double coal char particles gradually approach that of single coal char particles. The particle size also has an influence on the gasification characteristics of coal char particles. As the particle size varies from 0.1 to 1 mm, the reaction area of particles becomes smaller at high temperature and finally attaches to the surface of the particles. The reaction rate and carbon consumption rate increase with increasing particle size. As the size of double particles is changed, the reaction rate trend of double coal char particles at the same particle distance is basically the same, but the change degree of reaction rate is different. With the increase of the distance between coal char particles, the change of the carbon consumption rate is larger for the small particle size.

Model Development and Numerical Investigation of the Slag Formation in an Entrained-Flow Gasifier

Understanding the formation and the flow of molten slag in the water-cooled membrane wall pulverized coal entrained flow gasifier was very important to determine the wall heat transfer and the reactor operation. In the standard model’s CFD simulation, the wall boundary condition was only able to be set as a fixed heat flow, which was not accurate in describing the influence of the temperature distribution and slag distribution on heat transfer under the actual situation. In this work, an extensive and detailed slag model was established and validated. The complete slag model included a particle capture model, wall heat transfer model, and slag thickness model through real-time coupling with CFD. Particle capture criteria were discussed and used to decide the particle behavior if particles collide on the reactor wall. The slag flow model was established from this criterion to calculate the mass flow rate and the thickness of the liquid slag. The slag thickness model calculated the heat transfer at each wall location, and the coupled temperature, slag thickness, and heat transfer curves were finally obtained through iteration. The models were proved reliable by comparing the simulation with industrial results. The model predicted the slag thickness of liquid and solid slags, the wall temperature, and the heat flux through the wall. The model’s establishment further understood the slag formation, slag thickness distribution, and wall temperature distribution. It also played a guiding function in industrial operations.

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 %.

Determination of running temperature in entrained flow gasifier in regard to coal ash melting thermal kinetic effects

The operating temperature of entrained flow gasifier is one of the important parameters to determine its gasification efficiency, which is empirically estimated by ash fusion temperatures (AFTs) in the industry. However, the measurements of AFTs in labs are conducted at a very low heating rate (5–10 °C/min) compared to industrial entrained flow gasifiers (several hundred °C/s). The melting behaviors of coal ash under such huge varied conditions are different due to thermo-kinetic effects. Here, the factors concerning coal ash melting thermo-kinetics including heating rate, particle size, and retention time are explored by AFTs analyzer, thermal mechanical analysis, in-situ hot stage microscope and differential scanning calorimetry. The results of the investigation demonstrated that ash particle size and retention time showed limited influence on ash fusion behavior, while the influence of heating rates can not be ignored. Furthermore, an Arrhenian-based regression model covering major thermo-kinetics was developed to quantitatively predict the running temperature. The developed model suggested using the temperature that shrinkage corresponds to 75% to extrapolate the running temperature. The model can help to determine the operating temperature of slagging gasifiers.

Numerical Study and Experimental Verification of Biomass Conversion and Potassium Release in a 140 kW Entrained Flow Gasifier.

In this study, a Eulerian-Lagrangian model is used to study biomass gasification and release of potassium species in a 140 kW atmospheric entrained flow gasifier (EFG). Experimental measurements of water concentration and temperature inside the reactor, together with the gas composition at the gasifier outlet, are used to validate the model. For the first time, a detailed K-release model is used to predict the concentrations of gas-phase K species inside the gasifier, and the results are compared with experimental measurements from an optical port in the EFG. The prediction errors for atomic potassium (K), potassium chloride (KCl), potassium hydroxide (KOH), and total potassium are 1.4%, 9.8%, 5.5%, and 5.7%, respectively, which are within the uncertainty limits of the measurements. The numerical model is used to identify and study the main phenomena that occur in different zones of the gasifier. Five zones are identified in which drying, pyrolysis, combustion, recirculation, and gasification are active. The model was then used to study the transformation and release of different K species from biomass particles. It was found that, for the forest residue fuel that was used in the present study, the organic part of K is released at the shortest residence time, followed by the release of inorganic K at higher residence times. The release of inorganic salts starts by evaporation of KCl and continues by dissociation of K2CO3 and K2SO4, which forms gas-phase KOH. The major fraction of K is released around the combustion zone (around 0.7-1.3 m downstream of the inlet) due to the high H2O concentration and temperature. These conditions lead to rapid dissociation of K2CO3 and K2SO4, which increases the total K concentration from 336 to 510 ppm in the combustion zone. The dissociation of the inorganic salts and KOH formation continues in the gasification zone at a lower rate; hence, the total K concentration slowly increases from 510 ppm at 1.3 m to 561 ppm at the outlet.

The influence of torrefaction temperature and reaction time on the properties of torrefied sun‐dried millet and sorghum straws from the arid and semi‐arid zones of western Africa

AbstractThere are increasing demands for syngas production. Fossil‐based fuels are expensive and environmentally unfriendly. Affordable, sustainable, and environmentally healthy alternatives and sustainable fuel sources are needed. This study focused on producing tor‐chars from two different tropical biomasses (from Nigeria, West Africa), which were torrefied and characterized to improve their properties for potential use as sustainable feedstocks in an entrained flow gasifier for syngas production. Torrefaction temperatures of 230, 240, 250, and 270 °C and residence times of 30 and 60 min were used to torrefy sundried sorghum straw (SS) and millet straw (MS) at particle size ≤5 mm. The properties of torrefied MS and SS improved significantly due to torrefaction. The optimum conditions for pretreatment of sundried MS and SS were 240 °C and 60 min, at which increased energy density significantly compensated for the severe mass loss and significant degradation of hemicellulose and cellulose. Under these conditions, the respective mass and energy yields were 53 wt% and 75% for millet straw and 49 wt% and 75% for sorghum straw. The O:C atomic ratio decreased to 0.3 in MS tor‐chars and 0.2 in SS tor‐chars resulting in higher heating values of 25 MJ kg−1 and 27 MJ kg−1, respectively. Under optimum conditions, the ash content increased by 107% to be approximately 7 wt% in MS tor‐char, and by 118% to about 7 wt% in SS tor‐char. These properties are promising for potential feedstocks in co‐firing plants or gasification systems. © 2022 The Authors. Biofuels, Bioproducts and Biorefining published by Society of Industrial Chemistry and John Wiley &amp; Sons Ltd.

Computational Investigation on the Impact of Coal Feed Size in a Tangentially Fired Gasifier

ABSTRACT Using a validated comprehensive model, the effect of coal particle size on two-phase flow inside a tangentially fired, Mitsubishi Heavy Industry entrained-flow coal gasifier is investigated. It is observed that the length of the central recirculation zone (CRZ) formed in the gasifier flow increases with an increase in the mean size of the injected coal particles. The CRZ lengths are 5.6, 4.5 & 2.1 m, respectively, for the cases with particle size distributions (PSDs) having mass mean diameters of 80, 40 & 20 µm. The generic swirl number, , captures this impact of particle size on the CRZ length, whereas the conventional swirl number, , is unable to do so. The value of does not vary significantly over most of the gasifier’s constant diameter zone in each case simulated in the present work, thereby underlining the utility of this swirl number to characterize similarity in swirl dynamics. Further, the analysis of the impact of coal particle size on char conversion yields that the PSD with finer particles leads to higher conversion due to the better combustibility of finer particles.

Experimental investigation on entrainment in two-phase free jets

In the present research, the influence of atomization on the mixing ratio, representing entrainment in the gas phase of a two-phase free jet, is investigated at ambient conditions. The local mixing ratio is determined from the tracer gas (helium) concentration in the gas phase. Radial profiles of the mixing ratio are measured at several axial distances for 3 different nozzles applying 5 different gas-to-liquid ratios (GLR) for the two-phase free jet as well as a single-phase free jet. Common characteristics between the two-phase free jet and the single-phase free jet have been found. The mixing ratio of the two-phase free jet can be modeled using a semi-empirical approach for single-phase free jets from literature. The experimental data is used to determine the empirical parameters of the two-phase free jet model for the simulation of the flame structure in an entrained flow gasifier from Hotz et al., 2021 (https://doi.org/10.1016/j.fuel.2021.121392) (Hotz et al., 2021). The experimental data of the mixing ratio is available on Mendeley data as supplementary material of the present research (https://doi.org/10.17632/t66f8swg6w.1) (Hotz, 2022).

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.

Investigation on variation mechanisms of ash fusion and viscosity of high calcium-iron coal by coal blending

In this work, the ash fusion temperature (AFT) and viscosity modification behaviors of high calcium-iron coal ash (MO) were investigated by blending coal with high silicon-aluminum coal ash (P4). X-ray powder diffractometer (XRD), Fourier transform infrared spectrometer (FT-IR), Raman, and FactSage thermodynamic software were selected to investigate the AFT and viscosity change mechanisms. With the increase of P4 mass ratio, the AFT of MO mixtures increased from slowly (0–20 %) to rapidly (20 %–30 %), and then to slowly (30 %–50 %), and the ash viscosity also increased correspondingly. When the amount of P4 was in the range of 30–40 %, the flow temperature (FT) and viscosity of ash samples were 1368–1395 °C and 4.28–5.02 Pa·s, respectively, which met the requirements of entrained-flow bed gasification slag tapping. The XRD results showed that the disappearance of hauyne and the formation of anorthite were the main reasons for the mixed MO AFT increase. With the increasing P4 mass ratio, Si-O and Si-O-Al in ash samples moved to the high-frequency region in FT-IR, indicating the formations of more stable silicate network structures; the R-value (R = (Q3 + Q2)/(Q1 + Q0)) gradually increased indicating the increases in polymerization degree. The both led to the increases in viscosity. The decreasing ratio of non-bridged oxygen bond to bridged oxygen bond with increasing P4 percentage also explained the AFT and viscosity variation.

Performance of minerals and crystallization properties of synthetic slags with various CaO/MgO in slagging gasifiers

AbstractThe fluidity of coal ash slag at high temperatures is an important factor that determines its applicability and operating conditions in entrained flow gasification. In this study, six synthetic slags with different CaO/MgO rations were prepared to study their effect on slag fluidity. The results showed that the flow temperature of slags decreased first and then increased with the decrease of CaO/MgO ratio. When the slag had a high or low CaO/MgO ratio, or when the contents of CaO and MgO in the slag were similar, the homogeneous slag showed a lower viscosity. The crystallization tendency of Ca was stronger than that of Mg. During cooling, slags with high or low CaO/MgO ratio showed obvious crystallization tendency, and formation of crystals would lead to a sharp increase in slag viscosity, so that the temperature of critical viscosity of slags decreased first and then increased with the decrease of CaO/MgO ratio.