Opposed Multi-burner Research Articles

In-situ study on flow and rotation behaviors of coal particles near the burner plane in an impinging entrained-flow gasifier

The flow behaviors of the coal particles during coal gasification in the entrained-flow gasifier are closely related to the stable operation of the gasifier, while it is difficult to observe the particles during the operation of the gasifier due to the influence of high-temperature environment and complex atmosphere. In this study, based on a bench-scale opposed multi-burner (OMB) coal-water slurry (CWS) entrained-flow gasifier and an advanced visualization system composed of a high-temperature endoscope and a high-speed camera, the flow and rotation behaviors of the coal particles near the burner plane are investigated. The region near the burner plane is divided into jet zone and impinging core. The particle trajectories in the two zones are tracked. The particle velocity distribution and velocity fluctuation index are calculated. The particle rotation and flame oscillation behaviors are quantified. The results show that the proportion of total particle trajectories in the impinging core is higher than that of the jet zone. The velocity of the particles is mostly distributed in the range of 0–4 m/s. The particle fluctuation index in the impinging core is greater than that in the jet zone, indicating that the impinging flow is more unstable in comparison with the jet flow. The particle rotation angular velocity fluctuates within a certain range, while the fluctuation range of flame oscillation angular velocity is extremely great and can be easily disturbed by the flow field. For a single particle undergoing volatile oxidation, flame oscillation and particle rotation are isotropic. The flow field near the burner plane is reconstructed based on particle flow behaviors. The reconstruction results can be applied to verify the simulation of flow field.

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.

Particle motion and evolution characteristics in the impinging-flow zone of an impinging entrained-flow gasifier

The characteristics of the coal particles in the entrained-flow gasifier are closely related to the stable operation of the gasifier. In this study, the particle motion and evolution characteristics in the impinging-flow zone were studied based on the bench-scale coal-water slurry (CWS) opposed multi-burner (OMB) impinging entrained-flow gasification platform and the radial imaging system below the burner plane. The visualization system was applied to obtain particle image sequences under different operating conditions. Image processing algorithms and statistical methods were used to calculate the particle parameters. The results show that the number of particles with small size increases with the rise of O/C ratio (elemental oxygen to elemental carbon). Particle movement is closely influenced by aerodynamic force and gravity, and there are velocity and direction fluctuations during the movement. The different types of particle ignition/oxidation behaviors based on size were described in detail and statistically distributed. The larger particle size and higher O/C ratio contribute to the larger maximum volatile flame area. A time-scale particle evolution model including heating-up, volatile oxidation and char oxidation was established. During particle evolution, the latter part of the volatile oxidation and the early part of the char oxidation overlap in a period of time.

Visualization of Combustion Behavior of a Single Particle in an Entrained-Flow Gasifier

ABSTRACT Based on the opposed multi-burner (OMB) coal-water slurry (CWS) gasification experimental platform, the image visualization technology was used to systematically study the combustion behavior of coal particles in the jet zone and non-jet zone during the high temperature atomization process of CWS in the gasifier. The image processing algorithm and particle tracking algorithm were used to analyze the trajectory of coal particles, the change of volatile flame area during particle movement, and the deflection angle of volatile flame. The combustion behavior of the volatile components of coal particles in the jet zone and non-jet zone indicates that the deflection angle of the flame wake depends on the space position of the coal particles due to the entrainment of the airflow at the boundary of the jet zone and the non-jet zone. The average particle volatile flame area in the jet zone and the non-jet zone decreases with the increase of the oxygen-to-carbon (O/C) ratio. Under the same O/C ratio, the average area of the volatile flame of coal particles in the non-jet zone is larger than that in the jet zone. The deflection angle of the volatile flame of coal particles in the jet zone and the non-jet zone presents positive and negative oscillations, and the deflection angle of the volatile flame varies the most at the boundary between the jet zone and the non-jet zone.

Experimental study of particle evolution characteristics below the burner plane in an impinging entrained-flow gasifier

Based on the bench-scale opposed multi-burner (OMB) coal-water slurry (CWS) impinging entrained-flow gasifier and the visualization imaging systems, the evolution characteristics of particles below the burner plane of gasifier are studied. Image post-processing algorithms and statistical methods are used to analyze and discuss the particle velocity, particle size distribution and particle spatial distribution of the particle group, as well as the volatile flame area and shape of the single particle. The average velocity of particles in the impinging-flow zone is slightly greater than that in the recirculation-flow zone. Compared with the particles in the recirculation-flow zone, the SMD of particles and the particle concentration in the impinging-flow zone are smaller. As the particles move downward along the axial direction of the gasifier, the occurrence frequency of particles in the impinging-flow zone increases.

Post-mortem analysis of Cr2O3-Al2O3-ZrO2 refractory bricks used in an industrial opposed multi-burner gasifier

Periodical relining of the gasifier due to refractory corrosion and failure is a major cost driver in the coal gasification industry. In the present work, the failure mechanisms of Cr2O3-Al2O3-ZrO2 refractory bricks taken from different areas of an industrial opposed multi-burner (OMB) gasifier were investigated by post-mortem analysis. The results demonstrated that a densified (Mg, Fe)O-n(Al, Cr)2O3 complex spinel layer was attained on surface of refractory, which inhibited the further infiltration of slag. The SiO2 and CaO in slag were the main corrosive components and infiltrated into the refractory through pores and cracks. Damage of used bricks was mainly due to crack growth as well as structural spalling caused by different thermal expansion coefficient of de-zirconium layer, infiltration layer and original brick layer. In addition, the failure mechanisms of refractory bricks in different areas were also different owing to unique flow field and structure of OMB gasifier. The dome brick has the smallest wear, which was mainly destroyed by thermal corrosion, the strong scouring of upward flow unit and folded back flow unit. The sidewall brick was damaged by the scouring of high-speed airflow, chemical corrosion and high temperature creep. The damage of lower cone brick was mainly caused by strong mechanical scouring and structural spalling, which has the shortest service life.

Interactions of Cr2O3–Al2O3–ZrO2 refractory with slags in an entrained-flow coal-water slurry gasifier

The corroded microstructures of the Cr 2 O 3 –Al 2 O 3 –ZrO 2 refractory brick in an industrial opposed multi-burner (OMB) coal water slurry gasifier were investigated. It was found that the chromite spinel isolation layer rich in iron and magnesium was formed on the surface of the corroded brick body. By comparing and analyzing the corrosion of different zones in the gasifier, the results indicated that the molten slag entered the brick through the gaps and generated the spinel layer along the edge of the gaps, causing the dense structures of the refractory surface destroyed. In addition, in the high chrome brick corrosion experiment conducted by HTSM, 3 μm sized spinel were observed covering on the surface. The FactSage calculation results showed that the amount of spinel produced would drop significantly as the slag penetrated.

Influence of burner geometry on atomization of coal water slurry in an entrained-flow gasifier

Based on the bench-scale opposed multi-burner (OMB) coal-water slurry (CWS) entrained-flow gasification platform, the influence of burner geometry on atomization characteristics of the CWS in gasifier is investigated. The visualization imaging system is used to obtain image sequences that record the dynamic process of the CWS atomization. The effective image processing algorithms and particle tracking algorithms are applied to analyze and discuss the atomization, particle motion and particle fluctuation characteristics. The primary atomization mode of the CWS jets with different burner structures is the superpulsating atomization. With the increase of A1/A2, the Sauter mean diameter (SMD) of the CWS droplets in the statistical region first increases and then decreases. Along the radial distance, the SMD of the CWS droplets generally increases first and then decreases. As the burner outlet area ratio increases, the particle size fluctuates more intensely, and the particle velocity turbulence first decreases and then increases.

Opposed multi-burner gasification technology: Recent process of fundamental research and industrial application

Opposed multi-burner (OMB) gasification technology is the first large-scale gasification technology developed in China with completely independent intellectual property rights. It has been widely used around the world, involving synthetic ammonia, methanol, ethylene glycol, coal liquefaction, hydrogen production and other fields. This paper summarizes the research and development process of OMB gasification technology from the perspective of the cold model experiment and process simulation, pilot-scale study and industrial demonstration. The latest progress of fundamental research in nozzle atomization and dispersion, mixing enhancement of impinging flow, multiscale reaction of different carbonaceous feedstocks, spectral characteristic of impinging flame and particle characteristics inside gasifier, and comprehensive gasification model are reviewed. The latest industrial application progress of ultra-large-scale OMB gasifier and radiant syngas cooler (RSC) combined with quenching chamber OMB gasifier are introduced, and the prospects for the future technical development are proposed as well.

Distribution and modes of occurrence of heavy metals in opposed multi-burner coal-water-slurry gasification plants

To understand the migration and modes of occurrence of heavy metals in the opposed multi-burner (OMB) coal-water-slurry (CWS) gasification process, samples of coal, coarse and fine slags were obtained from two plants with different capacities. Concentrations of nine hazardous heavy metals (HMs) in these samples, i.e., Ba, Co, Cr, Cu, Mn, Ni, Pb, V, and Zn, were determined to show their migration and enrichment behaviours. A four-step sequential extraction method was implemented to reveal the modes of occurrence of these HMs. Results demonstrated that fine slags were mainly fragmentized spheres and were covered by fine floccules, whilst coarse slags were vitreous, angular and less porous than fine slags. Majority of the heavy metals were more concentrated in fine slags. Chromium was enriched in coarse slags, while Pb and Zn were accumulated in fine slags as indicated by the relative enrichment index. The sequential extraction demonstrated that for the coals, Cr, Cu, Ni, V and Zn were primarily associated with residual fractions (48.8–82.6 wt%), while Co, Mn and Pb were dominant in oxidizable (78.1 wt%), acid soluble (60.0 wt%) and reducible fractions (99.2 wt%), respectively. In fine slags, except for Zn, the other HMs were mainly distributed in residual fraction with 42.3 to 94.8 wt% in fine and coarse slags, respectively. Mobile fraction of HMs was the highest in coals (19.4–93.6 wt%), followed by fine slags (11.6–73.1 wt%) and coarse slags (5.1–41.0 wt%). Based on the leaching ability, except Cu, the HMs content in all slags were above the standard for direct landfill disposal.

Numerical simulation for size optimization of refractory support frame in OMB gasifier

The refractory support frame in opposed multi-burner (OMB) gasifier is used to support the refractory bricks. However, excessive thermal stress in OMB gasifier at high temperature will damage it and cause refractory bricks to collapse. The effect of size and structure on the thermal stress of refractory support frame has remained unclear. A three-dimensional physical structure model of industrial refractory support frame was established. The numerical simulation of temperature distribution and thermal behavior with different thickness and length of the support plate was detailedly investigated by the analysis modules of steady-state thermal and static structural through ANSYS. When the temperature of end face of hot-face brick was 1300°C, the outer surface temperature of steel shell was 210.4°C, which matched well with the measured temperature. As the thickness of support plate increased, the equivalent stress at the center of support plate gradually decreased. With increasing the length of support plate, the value and whole saltation of stress were both the smallest at the length of 230 mm. The optimal size of support plate which was beneficial to decrease the stress and prolong the service life of the refractory support frame was obtained. It could be a better guidance for the size optimization of the refractory support frame.

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.

On-line reset control of a commercial-scale opposed multi-burner coal-water slurry gasification system using dynamic reduced-order model

The entrained flows from four opposed burners enhance the mixing in a coal-water slurry (CWS) gasifier, which increases the extent of carbon conversion. Moreover, the operation of the opposed multi-burner (OMB) gasifier is more flexible because one couple of the opposed burners is allowed to be shut off for a certain period as long as the other couple is still running. Thus, the operation lifetime of the gasification system is determined by the ability to return the shut-off burners to operation, referred to as online reset control (ORC). However, the ORC is manual, which increases the operation uncertainty. In this study, we demonstrate an automatic control strategy using a dynamic reduced-order model (ROM). A reactor network model (RNM) of the gasifier, which considers several sub-models, is developed based on a flow field analysis and particle and gas residence time distributions (RTDs). The dynamic ROM and simulated manual ORC are verified using industrial data (5.8 MPa, 1500 metric tons per day (TPD)). An automatic control scheme for the ORC is proposed. The dynamic ROM is validated to be reliable when operating with the commercial-scale OMB CWS gasification system, as well as with its manual ORC process. The automatic ORC is promising for industrial gasification because the fluctuation ranges of the operation temperature and pressure of the gasifier are acceptable, which indicates that the reliable dynamic ROM can simulate a closed-loop control for a complex reactor.

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.

Visualization study on particle flow behaviors during atomization in an impinging entrained-flow gasifier

Based on the bench-scale opposed multi-burner (OMB) coal water slurry (CWS) entrained-flow gasifier, the particle flow behaviors during atomization in the jet zone and non-jet zone of the gasifier were investigated with advanced visualization apparatus. The particle trajectories and particle size distribution were analyzed with particle tracking algorithm and statistical analysis. The particle trajectories in the jet zone indicate that the motions of particles are simple straight lines. And particle flow behaviors in the jet zone can be divided into three types: rotation, deformation, and fragmentation. However, the particle trajectories in the non-jet zone indicate that the particle motion directions present irregular and are unevenly distributed. Statistical analysis of the particle trajectories shows the proportion of particle trajectories in the non-jet zone is larger than that in the jet zone. And with the increase of O/C ratio, the proportion of particle trajectories distributed in jet zone decreases.

Sensitivity and safety boundary Analysis of Opposed Multi‐Burner Coal Water Slurry Gasification System

Taking the opposed multi-burner (OMB) coal water slurry (CWS) gasification system as the simulation object, based on the gasification process flow-path and the flow field distribution characteristics in the gasifier, the model of CWS gasification system is established by using the chemical simulation software UniSim Design, the simulation results are in good agreement with the industrial data. On this basis, the Morris method is used to analyze the sensitivity of gasification parameters, and the response surface between coal gasification performance index and sensitive parameters is constructed by using the response surface method. The sensitivity of different gasification parameters and the impact of key sensitive parameter interactions on gasification performance indicators is investigated. The results show that the gasification parameters have different sensitivities for different responses. When the operating temperature range of the gasifier is limited to 1212°C to 1400°C and the syngas water-gas ratio is in the range of 1.0 to 1.4, there is a safe boundary for oxygen-coal ratio and CWS concentration. In actual production, the relevant parameters should be avoided to deviate from the safety region. This article provides a reference for the safe and stable operation of actual industrial production.

Refractory failure in entrained-flow gasifier: Investigation of partitioned erosion characteristics in an industrial opposed multi-burner gasifier

Based on an industrial opposed multi-burner (OMB) gasification plant, a complete review of spent refractory materials inside a gasifier, including a study of the macrostructure and partitioned erosion characteristics, is reported based on systemic industrial data. The results are compared with those from a bench-scale gasification platform as well as numerical simulation. Five heavily eroded regions of the refractory were observed in the industrial OMB gasifier: two in the impinging up-flow zone, one in the burner plane, one in the impinging down-flow zone, and one in the cone zone. The erosion of the refractory material in the dome zone and the plug-flow zone is mild. The spalling on the lower side wall is uneven; therefore, the bricks below the region between two adjacent burners are more eroded in the longitudinal direction. Herein, the results can be used for the development of new refractory structure and the optimization of ultra-large-scale gasifiers.

Experimental study on the atomization and particle evolution characteristics in an impinging entrained-flow gasifier

Based on the bench-scale opposed multi-burner (OMB) impinging entrained-flow gasifier and advanced visualization apparatus, studies on the coal water slurry (CWS) atomization process in gasifier were carried out. Morphological classification of the CWS atomization was discussed in detail. The particle size distribution of CWS after atomization was obtained by image processing algorithm and statistical method. The primary atomization modes in gasifier can be divided into: Rayleigh-type breakup and superpulsating breakup. Besides, the spray angle and breakup length are negatively correlated with the oxygen-CWS relative velocity. The secondary atomization modes can be divided into: no breakup, tensile breakup, shear breakup and synergistic breakup. The statistical analysis shows that the particle size of the CWS after atomization show a negative correlation with the oxygen-CWS relative velocity. The greater the difference in relative velocity between oxygen and CWS, the better the atomization effect, but excessive oxygen velocity results in reduced gasification efficiency.

Alkalis atomic emission spectroscopy and flame temperature measurement of diesel impinging flames in an opposed multi-burner gasifier

Atomic emission spectroscopy can well characterize atom release properties and flame temperature. This work aims to investigate the spectroscopic characteristics of alkalis atoms and measurement method of flame temperature in diesel impinging flames, based on a bench-scale opposed multi-burner (OMB) gasifier. A fiber-optic spectrometer and a CCD camera coupled with multiple bandpass filters are used to obtain the spectral emission lines and two-dimensional emission distributions of Na∗ and K∗, respectively. The results indicate that alkalis atoms can be released and excited in impinging region and four jet regions. The emission intensities of Na∗ and K∗ under different O/C are the strongest in the impinging region, suggesting that the atom release concentration and flame temperature are the highest. Moreover, the thermal excitation degree is related to the type of atom, and Na atom is much easier to be excited than K atom. It is confirmed that alkalis atom content and flame temperature were the two main influence factors on the emission intensity, and emission intensity can be used to qualitatively characterize flame temperature under the same O/C. In addition, atomic emission spectroscopy (AES) was given to quantitatively calculate the flame temperature. It is verified that the AES method is and feasible to derive diesel flame temperature and monitor the temperature changes of OMB gasifiers in real time.

Coal char particle secondary fragmentation in an entrained-flow coal-water slurry gasifier

Coal char particle size in the gasifier has an influence on the carbon conversion, gasifier slagging as well as the particle matter content in raw syngas. The particle size distribution in a bench-scale opposed multi-burner (OMB) gasifier illustrated that the secondary fragmentation behavior exists in the entrained-flow gasifier after the particles moving from high temperature impinging flame region to the gasification chamber outlet region. Particles larger than 200 μm in the impinging flame region have porosity structures with fragile shapes. Particle size distributions under different oxygen to carbon ratios (O/C) also indicate that there is an obvious fragmentation while the particle size is larger than 200 μm. As long as the coal char particles move from the impinging flame region towards the gasification chamber outlet region, the secondary fragmentation is probably taken place as a result of percolative fragmentation, undergoing gasification reactions and thermal stress. However, thermal stress fragmentation only has an influence on the particle sizes larger than 350 μm according to the calculation by a simplified mathematical model.