Coal Water Slurry Gasification Research Articles

Magnetization roasting characteristic and mechanism of gasification slag from coal-water slurry gasifier

ABSTRACT Iron content in gasification slag is second only to silicon and aluminum, which is expected to be a new breakthrough in the integrated application of gasification slag. Magnetization roasting is an efficient method to change the form of iron-containing phases as well as to enhance magnetic properties from slags. The magnetic variation of different particle size fractions of gasification slags (GS1, GS2) during roasting was investigated by the yield of magnetic ash particles. The magnetic transformation mechanism of iron-containing phases was revealed by the vibrating sample magnetometer (VSM), X–ray diffractometer (XRD), and scanning electron microscopy with energy-dispersive spectrometry (SEM–EDS). The results showed that the magnetic ash particle yield rose as the roasting temperature increased. When the roasting temperature was 750°C, the magnetic ash particle yield of each particle size fractions increased from 14%–21% (GS1) and 7%–18% (GS2) to 81%–99% and 29%–96%, respectively. Specially, the magnetic ash particle yield of 0.125–0.074 mm fractions increased from 21% (GS1) and 18% (GS2) to 98% and 94%, and the saturation magnetization increased from 1.80 emu/g (GS1) and 5.45 emu/g (GS2) to 10.25 emu/g and 8.23 emu/g, under the conditions of 750°C (roasting temperature), 30 min (roasting time) and 2.5 A (magnetic excitation current) when the gasification slag was roasted in air, a part of iron–containing phases was transformed from Fe(II) to Fe3O4 and γ-Fe2O3, another part of iron-containing phases could be substituted into the feldspar and pyroxene minerals by homogeneous substitution. Furthermore, residue carbon combustion and gas diffusion lead to reduction of ash particle size, rough and porous surface, and increase of magnetization reaction sites, which can strengthen the mass transfer process and promote magnetic transformation of iron-containingphases in slags.

Failure analysis of the end surface of the burner nozzle made of UMCo50 material in long-term high temperature oxygen-enriched sulfur-chlorine environment

As the core device of coal water slurry gasification technology, the failure of the burner nozzle will bring serious technical and safety problems. The purpose of this paper is to determine the mechanism of burner failure based on the characteristics of corrosion products and cracks. The results showed that the Cr2O3 oxide film on the surface of UMCo50 was damaged under the effect of mechanical erosion, high temperature and stress, and the corrosive elements S and Cl in the combustion chamber made it further cracked and peeled off. Therefore, the matrix was corroded and cracks occurred. During the crack propagation process, more M23C6 carbides were precipitated at the grain boundary, it caused Cr-depleted at the grain boundary, which reduced the corrosion resistance of the matrix near the grain boundary. The exfoliation of carbides distributed along the grain boundary also accelerated crack propagation. Through XPS and XRD analysis, it was found that the main corrosion products on the crack surface of the failed parts were: Cr2O3, CoCr2O4, CoO, Fe2O3, FeS. According to the causes of failure analysis, the corresponding improvement measures are put forward.

Simulation research on optimization of a 200 MW IGCC system

The integrated gasification combined cycle (IGCC) has increasingly attracted attention as a promising high-efficiency clean coal technology. The oxygen-to-carbon ratio (O/C), nitrogen reinjection coefficient (Xgn), and integration air separation coefficient (Xas) affect system performance greatly. Based on the selected coal type, this paper establishes a 200 MW IGCC system model with coal–water slurry gasification, matches the three-pressure reheating heat recovery steam generator and syngas coolers, simulates and calculates the system performance of O/C, Xas and Xgn using Thermo-flex software. From the perspective of the whole system, the optimal O/C of the system is obtained as 0.91 considering the syngas composition and gasification temperature. From the perspective of system efficiency, the Xgn is obtained as 60 % with the Xas of 20 %. The overall IGCC system model is optimized using the optimized O/C, Xgn, and Xas to obtain higher system power and efficiency, the system power generation efficiency can improve up to 51.52 %. A thermal balance diagram of the IGCC system is drawn using the calculation results and provides a reference for the future design and operation of IGCC systems.

Problems and Countermeasures in the Oxygen System of GE Coal Water Slurry Gasification Plant

Problems and Countermeasures in the Oxygen System of GE Coal Water Slurry Gasification Plant

Techno-economic feasibility and comparison of coal water slurry concentration on a coal to methanol plant with consideration of carbon capture and storage

ABSTRACT In this study, the effect of slurry concentration and carbon dioxide capture and storage (CCS) equipment on the techno-economic feasibility of a coal-to-methanol (CTM) process with coal water slurry (CWS) gasification are investigated, while the effective means to improve the economic benefit of methanol factory are proposed. The sensitive factors including production scale, coal price, and carbon tax are investigated, especially the CWS concentration is compared at 63% and 68% scenarios. A CTM plant with 180 × 104 t/a production scale shows that the saving cost could reach 29.20 × 106 US$ and the CO2 emission could be reduced by 0.65 × 106 t/a every year as the CWS concentration increases. The investment in CCS equipment would increase the production cost (PC) per methanol raising by 7–8%, while the CCS introduction would effectively alleviate the PC increment caused by the carbon tax. Note that as the carbon tax exceeded 9.42 US$/t, the benefit for CCS on the reduction of PC would be more significant. The outcomes of this study have suggested that increasing the CWS concentration is an effective method to reduce the PC and improve the economic benefit. The CCS technology could effectively reduce CO2 emissions and mitigate the raising of PC caused by carbon tax. The findings have manifested a well feasibility for environment benefit improvement by solid content increasing and CCS introduction in response to energy and environmental challenges for the cleaner production and sustainable development.

Energetic-environmental-economic assessment of utilizing weak black liquor to produce syngas for replacing evaporation based on coal water slurry gasification

As the main pollutant of paper mills, black liquor has brought great pressure to the wastewater treatment process of paper mills. Based on the coal-water slurry gasification (GS-CWS) technology, this paper designed the gasification system of black liquid coal-water slurry (GS-BLCWS) by utilizing weak black liquor of pulp mills, investigated and modeled the energy requirements of the GS-BLCWS. Feasibility assessment of the GS-BLCWS and the traditional alkali recovery systems (TARS) were carried out, including energy efficiency, economic feasibility and environmental impacts. The comparison results showed that the steam demands of two technologies can be self-sufficient. But the total energy efficiency of GS-BLCWS (69.78%) is higher than that of the TARS integrating GS-CWS (63.07%), and the energy output ratio of black liquor increased from 9.9% to 69.78%. From an economic point of view, GS-BLCWS can generate syngas, which can be used for drying in the papermaking workshop and shows better economic efficiency. Meanwhile, GS-BLCWS has lower environmental impacts that there is no emission of sulfur oxides and particulate matter. Considering the short payback period (5.81 years) of GS-BLCWS, the small environmental impact, and the self-sufficiency of steam and electricity, it has broad application prospects.

Problems and Optimization Measures of High Pressure Flash System in GE Coal Water Slurry Gasification Plant

Problems and Optimization Measures of High Pressure Flash System in GE Coal Water Slurry Gasification Plant

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.

Simulation Research on Coal-Water Slurry Gasification of Oil-Based Drill Cuttings Based on Fluent

Simulation Research on Coal-Water Slurry Gasification of Oil-Based Drill Cuttings Based on Fluent

Effect of Coal Water Slurry Gasification Slag on Soil Water Physical Characteristics and Properties in Saline-Alkali Soil Improvement

To explore the effect of coal water slurry (CWS) gasification slag on the soil water physical characteristics of saline-alkali soil in the Yellow River Basin of Inner Mongolia, CWS gasification coarse slag (GCS) and gasification fine slag (GFS) were used as improvement materials and mixed with saline-alkali soil in different proportions. The influence mechanism of GCS and GFS on saline-alkali soil water holding capacity was investigated by measuring particle size composition, water holding capacity, and the change in the soil water characteristic curve after mixing. The results showed that adding gasification slag improved the particle size composition of saline-alkali soil, with sand content increased by -3.79%~217.31% and clay and silt content decreased by 5.77%~56.50% and -0.38%~41.53%, respectively. Soil bulk density decreased significantly ( P < 0.05 ), with a decrease range of 15.17%~45.1%. The soil texture changed from silty loam to sandy loam, and the water retention performance improved, affecting the soil saturated water content, capillary water holding capacity, and field water holding capacity ( P < 0.05 ), with increases ranging from 20.75%~86.15%, 7.84%~27.81%, and -1.89%~34.56%, respectively. After adding GCS and GFS, the VG model fit the soil water characteristic curve of saline-alkali soil well, indicating that the addition of gasification slag enhanced soil water retention significantly. In conclusion, CWS gasification slag effectively improved the water physical properties of saline-alkali soil and significantly enhanced the water retention and water holding capabilities.

Effect of Coal Blending on Ash Fusibility and Slurryability of Xinjiang Low-Rank Coal

This work investigated the effect of coal blending on ash fusibility and slurryability of Xinjiang low-rank coal. The results showed that Xinjiang low-rank coals were characterized by high internal water content, high volatile content, high ash fusing point, and poor slurryability, which can not be directly used in coal water slurry gasification. The blending method not only reduced the ash fusibility but also improved the slurryability of these low-rank coals. When the coals with low calcium and high silicon contents (KG and YK) were blended with coal with high calcium content (SH), the ash fusion temperatures of the blended coal were significantly reduced. Moreover, the SH coal showed the worst slurryability performance with a concentration of 48.56%. The slurryability of HS coal can be dramatically improved by blending with KG. When the mass fraction of KG coal reached 70%, the concentration of coal water slurry increased by 11%. For the blended coal of KG and YK, the concentration and stability of coal water slurry gradually increase with the increasing mass ratio of KG. The coal blending method can effectively improve the concentration of coal water slurry for the low-rank coals, which were difficult-to-prepare slurry.

Numerical Analysis of Fracture Failure Behavior of Refractory Lining in Coal-Water Slurry Gasifier.

Fatigue crack fracture is one of the main reasons for the failure of a refractory lining in a coal-water slurry gasifier. To explore the fracture failure behavior of a refractory lining during the operation of a gasifier, the stress intensity factor (SIF) and J-integral at crack front were calculated by the finite element method, and a crack growth model for the refractory was established. At the same time, the effects of different crack length, depth, and angle on the stress and SIF, as well as J-integral distribution around the crack-tip, were presented. The simulation results demonstrated that very large stresses occurring at the crack tip and the distribution regulation of KI and J-integral along the crack front for surface cracks were similar. The maximum values occurred near the two ends of the crack (θ = 0°, 180°), and the minimum values appeared near the deepest crack front (θ = 90°). KI and J-integral values at the same position increase with increasing crack length and depth and decrease with the angle of crack when the a/c was kept constant. Furthermore, J-integral results indicated that excessive crack depths were likely to cause destabilizing crack growth. These results have provided a reliable theoretical basis for fracture analysis and life prediction of the refractory lining in a gasifier.

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.

Study on the composition and structure characteristics and dry decarbonization separation of coal water slurry gasification fine slag

Efficient separation and high-valued utilization of coal gasification ash or slag limit the clean and green development of coal chemical industry. In this paper, a coal-water slurry gasification fine slag (CWSFS) was studied by wet screening and classification. The relationship between the particle composition with different sizes and the structural characteristics was investigated by means of proximate analysis, XRF, XRD, BET and SEM. A classification method of CWSFS was proposed to guide the high-valued utilization of coal gasification slag. Then, dry separation of a coal-water slurry gasification fine slag was carried out using a combined treatment method of crushing and dissociation and airflow classification. The results show that the CWSFS particles of different sizes have obvious differences in fixed carbon content, ash composition and mineral types. For the CWSFS with the particle size above 74 μm, the fixed carbon content is more than 60%, the calorific value is more than 20 MJ/kg, the specific surface area is relatively high and the main component is the residual carbon that contains magnetite and brookite. For the CWSFS with particle sizes between 13–74 μm, the fixed carbon content is between 20%–60%, the calorific value is between 11–19 MJ/kg, the specific surface area is small and the main mineral types are pyroxene, marcasite and hematite, etc. For the CWSFS with a particle size between 0–13 μm, the fixed carbon content is less than 20% and the calorific value is less than 10 MJ/kg, which mainly includes the amorphous glass phase that was rich in aluminum, iron and calcium, quartz and a small amount of fayalite, muscovite and other minerals. According to the fixed carbon content of CWSFS with different particle sizes, the above three components with varying particle size ranges are defined as high-carbon component, medium-carbon component and low-carbon component, respectively. The dry separation test shows that the air flow crushing and classification process can achieve a higher product yield of 29.60% and a high ignition loss of 93.76%, compared to the traditional disc crushing-classification process. Airflow crushing was proved to be able to effectively increase the dissociation degree of residual carbon and greatly improve the separation and enrichment rate of residual carbon.

Research on a soft-measurement model of gasification temperature based on recurrent neural network

Abstract Gasification temperature measurement is one of the most challenging tasks in an entrained-flow gasifier and often requires indirect calculation using the soft-sensor method, a parameter prediction method using other parameters that are more easily measurable and using correlation equations that are widely accepted in the gasification field for the temperature data. Machine learning is a non-linear prediction method that can adequately act as a soft sensor. Furthermore, the recurrent neural network (RNN) has the function of memorization, which makes it capable of learning how to deal with temporal order. In this paper, the oxygen–coal ratio, CH4 content and CO2 content determined through the process analysis of a 3000-t/d coal-water slurry gasifier are used as input parameters for the soft sensor of the gasification temperature. The RNN model and back propagation (BP) neural network model are then established with training-set data from gasification results. Compared with prediction set data from the gasification results, the RNN model is found to be much better than the BP neural network based on important indexes such as the mean square error (MSE), mean absolute error (MAE) and standard deviation (SD). The results show that the MSE of the prediction set of the RNN model is 6.25°C, the MAE is 10.33°C and the SD is 3.88°C, respectively. The overall accuracy, the average accuracy and the stability effects are well within the accepted ranges for the results as such.

Carbon Resource Recovery and Recycle of Fine Slag from Coal Water Slurry Gasification

Carbon Resource Recovery and Recycle of Fine Slag from Coal Water Slurry Gasification

Measurement and simulation of viscosity characteristics of coal ash slag under water vapor condition in coal gasification

The long term and safe operation of entrained gasifiers strongly depends on smooth and steady removal of the ash slag. Management of slag behavior for safe slag-tapping requires the well understanding of slag viscosity temperature behavior and reliable prediction model for the slag viscosity in presence of water vapor. Based on the ratio of acidic to basic oxides (A/B) in coal ash, the viscosity temperature characteristics were studied under Ar with water vapor, and the optimization model for predicting the slag viscosity as a function of T and slag composition, including the constituent H2O was established. When water vapor is present in Ar, the slag viscosities decreased due to the breaking of Si-O-Si bridge bonds for the slags with A/B < 0.8. As A/B ≥ 0.8, the slag viscosities increased which ascribed to the formation of free hydroxyl. The viscosity prediction model for the fully molten slags and partly crystallized slags was developed under water vapor atmosphere based on the modified viscosity models in Ar. The modified Urbain model has been used to predict the completely molten slag and the remaining liquid phase for partly crystallized slags. The viscosities of heterogeneous slags were predicted by modified Roscoe model. These models can predict well the slag viscosity and Tcv. This work enables the prediction of slag viscosity at high temperature under water vapor condition and will provide a theoretical basis for the operation of entrained flow gasification, especially for the coal water slurry gasification.

Mineralogical examination of the entrained-flow coal gasification residues and the feed coals from northwest China

Minerals are the dominant impurities in coal and their changes in gasifiers could cause many problems such as fouling, slagging, and ash deposition. The mineralogy of the coal gasification residues derived from two commercial entrained-flow coal gasification plants from the Ningdong Energy and Chemical Industry Base were determined. A range of minerals were detected by the analyses of X-ray diffraction and scanning electron microscope with associated energy-dispersive X-ray spectrometer (SEM–EDS). The mineral species formed in General Electric (GE) gasification were more abundant than that in the Gaskombinat Schwarze Pumpe (GSP) gasification. The neoformed minerals such as grossular and hedenbergite detected in the residues indicated that the gasification processes share some similarities with magmatism in geological system. The existence of wustite in the GE coal gasification residues indicated the reductive environment in the GE gasifier. Compared to the GSP feed coals, the higher proportions of calcite, pyrite, and siderite and the higher Na contents in the GE feed coals indicated that the ash problems probably happen in the coal-water slurry gasification. Reducing the proportions of those Na-, Ca-, and Fe-containing mineral from the feed coal is necessary for the improvement of the coal gasification process.

Application of qualitative trend analysis in fault diagnosis of entrained-flow coal-water slurry gasifier

Entrained-flow coal-water slurry (CWS) gasification is a clean and efficient energy utilization technology and it was difficult to avoid misoperation during gasifier operation process. Qualitative trend analysis (QTA) is a data-driven method based on process history, and has been widely used in process monitoring and fault diagnosis. In this study, a suitable on-line basic primitive sequence processing method combining QTA and the extended sliding window trend extraction (SWTE) method is developed for the operation of entrained-flow CWS gasifier. Based on the optimized method, trend extraction and primitive sequence processing on three sets of data, i.e., gasifier temperature, gasifier pressure, and slag discharge hole pressure difference, were performed in this study. The optimized method could be effectively applied to the real-time monitoring and fault diagnosis of entrained-flow gasifier since its output was simple and accurate.

Aggregating structure in coal water slurry studied by eDLVO theory and fractal dimension

Coal water slurry gasification is a main source of hydrogen in the developing hydrogen economy. Moreover, biomass and waste can be added, making gasification process greener. To expand the application of coal water slurry and gasification process, it is necessary to understand the micro-structure in this large particle suspension system. In this paper, the micro-structure in coal water slurry was studied by extended DLVO (eDLVO) theory and fractal dimension, which is used to explain the mechanism of stability in large particle suspension systems. The interaction between two coal particles was characterized from the interparticle potential and energy barrier based on the eDLVO theory. The rheology and stability between different types of coals are measured and explained by the aggregating structure and fractal dimension in coal water slurry. The results indicated that there would be an aggregating structure in high rank coals, due to the interparticle potential caused by the surface properties, but probably not in low rank coals. This aggregating structure can be described and characterized by fractal dimension. The aggregation of particles is the source of the stability for high rank coals, as the close-packed 3D network structure in large particle suspension can support coal particles from settling down. The results have demonstrated that the combination of the eDLVO theory and rheological measurement is an effective way to investigate the stability of large particle suspension systems.