Structural properties of residual carbon in coal gasification fine slag and their influence on flotation separation and resource utilization:A review

Coal gasification fine slag(FS)is a typical solid waste generated in coal gasification.Its current disposal methods of stockpil-ing and landfilling have caused serious soil and ecological hazards.Separation recovery and the high-value utilization of residual carbon(RC)in FS are the keys to realizing the win-win situation of the coal chemical industry in terms of economic and environmental benefits.The structural properties,such as pore,surface functional group,and microcrystalline structures,of RC in FS(FS-RC)not only affect the flotation recovery efficiency of FS-RC but also form the basis for the high-value utilization of FS-RC.In this paper,the characteristics of FS-RC in terms of pore structure,surface functional groups,and microcrystalline structure are sorted out in accordance with gasification type and FS particle size.The reasons for the formation of the special structural properties of FS-RC are analyzed,and their influence on the flotation separation and high-value utilization of FS-RC is summarized.Separation methods based on the pore structural characterist-ics of FS-RC,such as ultrasonic pretreatment-pore-blocking flotation and pore breaking-flocculation flotation,are proposed to be the key development technologies for improving FS-RC recovery in the future.The design of low-cost,low-dose collectors containing polar bonds based on the surface and microcrystalline structures of FS-RC is proposed to be an important breakthrough point for strengthening the flotation efficiency of FS-RC in the future.The high-value utilization of FS should be based on the physicochemical structural proper-ties of FS-RC and should focus on the environmental impact of hazardous elements and the recyclability of chemical waste liquid to es-tablish an environmentally friendly utilization method.This review is of great theoretical importance for the comprehensive understand-ing of the unique structural properties of FS-RC,the breakthrough of the technological bottleneck in the efficient flotation separation of FS,and the expansion of the field of the high value-added utilization of FS-RC.

Experimental study on the activation of coal gasification fly ash from industrial CFB gasifiers

Coal gasification fly ash(CGFA)is an industrial solid waste from the coal circulating fluidized bed(CFB)gasification process,and it needs to be effectively disposed to achieve sustainable development of the environment.To realize the application of CGFA as a precursor of porous carbon materials,the physicochemical properties of three kinds of CGFA from industrial CFB gasifiers are analyzed.Then,the activation potential of CGFA is acquired via steam activation experiments in a tube furnace reactor.Finally,the fluidization activation technology of CGFA is practiced in a bench-scale CFB test rig,and its advantages are highlighted.The results show that CGFA is characterized by a high carbon content in the range of 54.06%–74.09%,an ultrafine particle size(d50:16.3–26.1 μm),and a relatively developed pore structure(specific surface area SSA:139.29–551.97 m^(2)·g^(-1)).The proportion of micropores in CGFA increases gradually with the coal rank.Steam activation experiments show that the pore development of CGFA mainly includes three stages:initial pore development,dynamic equilibrium between micropores and mesopores and pore collapse.The SSA of lignite fly ash(LFA),subbituminous fly ash(SBFA)and anthracite fly ash(AFA)is maximally increased by 105%,13%and 72%after steam activation;the order of the largest carbon reaction rate and decomposition ratio of steam among the three kinds of CGFA is SBFA>LFA>AFA.As the ratio of oxygen to carbon during the fluidization activation of LFA is from 0.09 to 0.19,the carbon conversion ratio increases from 14.4%to 26.8%and the cold gas efficiency increases from 6.8%to 10.2%.The SSA of LFA increases by up to 53.9%during the fluidization activation process,which is mainly due to the mesoporous development.Relative to steam activation in a tube furnace reactor,fluidization activation takes an extremely short time(seconds)to achieve the same activation effect.It is expected to further improve the activation effect of LFA by regulating the carbon conversion ratio range of 27%–35%to create pores in the initial development stage.

Mechanism of K/Ni Etching for Biochar-H_(2)O Gasification

Biomass-H_(2)O gasification is a complex thermochemical reaction,including three processes of volatile removal:homogeneous/heterogeneous reforming,biochar gasification and etching.The rate-determining step is biochar-H_(2)O gasification and etching so the DFT is carried out to see the catalytic role of different metal elements(K/Ni)in the zigzag biochar model.The calculation results show that the gasification of biochar-H_(2)O needs to go through four processes:dissociative adsorption of water,hydrogen transfer(hydrogen desorption,hydrogen atom transfer),carbon dissolution and CO desorption.The energy barrier indicated that the most significant step in reducing the activation energy of K is reflected in the hydrogen transfer step,which is reduced from 374.14 kJ/mol to 152.41 kJ/mol;the catalytic effect of Ni is mainly reflected in the carbon dissolution step,which is reduced from 122.34 kJ/mol to 84.8 kJ/mol.The existence of K causes the edge to have a stronger attraction to H and does not destroy theπbonds of biochar molecules.The destruction ofπbonds is mainly due to the role of H free radicals,while the destruction ofπbonds will lead to easier C-C bond rupture.Ni shows a strong attraction to O in OH,which forms strong Ni-O chemical bonds.Ni can also destroy the aromatic structure directly,making the gasification easier to happen.This study explored the catalytic mechanism of K/Ni on the biochar-H_(2)O gasification at the molecular level and looked forward to the potential synergy of K/Ni,laying a foundation for experimental research and catalyst design.

Occurrence,leaching behavior,and detoxification of heavy metal Cr in coal gasification slag

Coal gasification slag(CGS)is a type of solid waste produced during coal gasification,in which heavy metals severely restrict its resource utilization.In this work,the mineral occurrence and distribution of typical heavy metal Cr in CGS is investigated.The leaching behavior of Cr under different conditions is studied in detail.Acid leaching-selective oxidation-coprecipitation method is proposed based on the characteristics of Cr in CGS.The detoxification of Cr in CGS is realized,and the detoxification mechanism is clarified.Results show that Cr is highly enriched in CGS.The speciation of Cr is mainly residual fraction(74.47%-86.12%),which is combined with amorphous aluminosilicate.Cr^(3+)and Cr^(6+)account for 90.93%-94.82%and 5.18%-9.07%of total Cr,respectively.High acid concentration and high liquid-solid ratio are beneficial to destroy the lattice structure of amorphous aluminosilicate,thus improving the leaching efficiency of Cr,which can reach 97.93%under the optimal conditions.Acid leaching-selective oxidation-coprecipitation method can realize the detoxification of Cr in CGS.Under the optimal conditions,the removal rates of Fe^(3+)and Cr^(3+)in the leaching solution are 80.99%-84.79%and 70.58%-71.69%,respectively,while the loss rate of Al^(3+)is only 1.10%-3.35%.Detoxification slag exists in the form of Fe-Cr coprecipitation(Fe_(1-x)Cr_xOOH),which can be used for smelting.The detoxification acid leaching solution can be used to prepare inorganic polymer composite coagulant poly-aluminum chloride(PAC).This study can provide theoretical and data guidance for detoxification of heavy metal Cr in CGS and achieve resource utilization of coal gasification solid waste.

Microscopic mechanism study and process optimization of dimethyl carbonate production coupled biomass chemical looping gasification system

Biomass chemical looping gasification technology is one of the essential ways to utilize abundant biomass resources.At the same time,dimethyl carbonate can replace phosgene as an environmentfriendly organic material for the synthesis of polycarbonate.In this paper,a novel system coupling biomass chemical looping gasification with dimethyl carbonate synthesis with methanol as an intermediate is designed through microscopic mechanism analysis and process optimization.Firstly,reactive force field molecular dynamics simulation is performed to explore the reaction mechanism of biomass chemical looping gasification to determine the optimal gasification temperature range.Secondly,steady-state simulations of the process based on molecular dynamics simulation results are carried out to investigate the effects of temperature,steam to biomass ratio,and oxygen carrier to biomass ratio on the syngas yield and compositions.In addition,the main energy indicators of biomass chemical looping gasification process including lower heating value and cold gas efficiency are analyzed based on the above optimum parameters.Then,two synthesis stages are simulated and optimized with the following results obtained:the optimal temperature and pressure of methanol synthesis stage are 150℃ and 4 MPa;the optimal temperature and pressure of dimethyl carbonate synthesis stage are 140℃ and 0.3 MPa.Finally,the pre-separation-extraction-decantation process separates the mixture of dimethyl carbonate and methanol generated in the synthesis stage with 99.11%purity of dimethyl carbonate.Above results verify the feasibility of producing dimethyl carbonate from the perspective of multi-scale simulation and realize the multi-level utilization of biomass resources.

Integrated vacuum pressure swing adsorption and Rectisol process for CO_(2) capture from underground coal gasification syngas

An integrated vacuum pressure swing adsorption(VPSA) and Rectisol process is proposed for CO_(2) capture from underground coal gasification(UCG) syngas. A ten-bed VPSA process with silica gel adsorbent is firstly designed to pre-separate and capture 74.57% CO_(2) with a CO_(2) purity of 98.35% from UCG syngas(CH_(4)/CO/CO_(2)/H_(2)/N_(2)= 30.77%/6.15%/44.10%/18.46%/0.52%, mole fraction, from Shaar Lake Mine Field,Xinjiang Province, China) with a feed pressure of 3.5 MPa. Subsequently, the Rectisol process is constructed to furtherly remove and capture the residual CO_(2)remained in light product gas from the VPSA process using cryogenic methanol(233.15 K, 100%(mass)) as absorbent. A final purified gas with CO_(2) concentration lower than 3% and a regenerated CO_(2) product with CO_(2) purity higher than 95% were achieved by using the Rectisol process. Comparisons indicate that the energy consumption is deceased from 2.143 MJ·kg^(-1) of the single Rectisol process to 1.008 MJ·kg^(-1) of the integrated VPSA & Rectisol process, which demonstrated that the deployed VPSA was an energy conservation process for CO_(2) capture from UCG syngas. Additionally, the high-value gas(e.g., CH_(4)) loss can be decreased and the effects of key operating parameters on the process performances were detailed.

Recycling and utilization of coal gasification residues for fabricating Fe/C composites as novel microwave absorbents

Under the background of a transformation of the global energy structure,coal gasification technology has a wide application prospect,but its by-product,the coal gasification residue(CGR),is still not being efficiently utilized for recycling.The CGR contains abundant carbon components,which could be applied to the microwave absorption field as the carbon matrix.In this study,Fe/CGR composites are fabricated via a two-step method,including the impregnation of Fe^(3+)and the reduction process.The influence of the different loading capacities of the Fe component on the morphology and electromagnetic properties is studied.Moreover,the loading content of Fe and the surface morphology of the Fe/CGR can be reasonably controlled by adjusting the concentration of the ferric nitrate solution.Meanwhile,Fe particles are evenly inserted on the CGR framework,which expands the Fe/CGR interfaces to enhance interfacial polarization,thus further improving the microwave-absorbing(MA)properties of composites.Particularly,as the Fe^(3+)concentration is 1.0 mol/L,the Fe/CGR composite exhibits outstanding performance.The reflection loss reaches-39.3 dB at 2.5 mm,and the absorption bandwidth covers 4.1 GHz at 1.5 mm.In this study,facile processability,resource recycling,appropriately matched impedance,and excellent MA performance are achieved.Finally,the Fe/CGR composites not only enhance the recycling of the CGR but also pioneer a new path for the synthesis of excellent absorbents.

Effects of Different Calcining Temperatures on the Properties of Ceramsite Prepared by High-carbon Gasification Slag

The structure and characteristics of high-performance lightweight aggregates produced by high-carbon gasification slag were investigated by X-ray diffraction,scanning electron microscopy,thermogravimetry/differential thermogravimetr,differential scanning calorimetry-Fourier transform infrared,and mercury intrusion porosimetry,respectively.The experimental results show that the ceramsite undergoes two weightless stages in the calcining process.With the increase in the calcining temperature,a large number of pores are formed inside the ceramsite,its structure becomes denser,but the calcining temperature band of the ceramsite becomes narrow.The crystalline phase of the ceramsite changes at different calcining temperatures and the mineral phase changes from the earlieralbite,quartz,oligoclase,hematite,etc,to a silica-aluminum-rich glass phase.The 1130℃ is a more suitable calcining temperature,and the cylinder compressive strength of ceramics is 11.59 MPa,the packing density,apparent density,porosity,and water absorption are 939.11 kg/m^(3),1643.75 kg/m^(3),28.11%,and 10.35%,respectively,which can meet the standards for high-strength lightweight aggregates.

Gasification kinetic studies of low volatile weakly caking coal

Present investigation focuses on the fractional conversion of low volatile weakly caking coal(LVWC)under the standard set of operating conditions for gasification.For this purpose,samples of LVWC of different ash content have been collected from Kusunda Area of Bharat Coking Coal Ltd.Gasification results were validated using Homogenous and Shrinking Core kinetic models and the suitability of selected samples for gasification was assessed by estimating the activation energy.The values of activation energy for LVWC samples were obtained in the range of 25.17-44.09 kJ/mol.Further,empirical models were developed to correlate the response of interest with the input variables(temperature,residence time and CO_(2) flow rate).The significance of these developed empirical models was checked using analysis of variance(ANOVA).

Gasification of Organic Waste:Parameters,Mechanism and Prediction with the Machine Learning Approach

Gasification of organic waste represents one of the most effective valorization pathways for renewable energy and resources recovery,while this process can be affected by multi-factors like temperature,feedstock,and steam content,making the product’s prediction problematic.With the popularization and promotion of artificial intelligence such as machine learning(ML),traditional artificial neural networks have been paid more attention by researchers from the data science field,which provides scientific and engineering communities with flexible and rapid prediction frameworks in the field of organic waste gasification.In this work,critical parameters including temperature,steam ratio,and feedstock during gasification of organic waste were reviewed in three scenarios including steam gasification,air gasification,and oxygen-riched gasification,and the product distribution and involved mechanism were elaborated.Moreover,we presented the details of ML methods like regression analysis,artificial neural networks,decision trees,and related methods,which are expected to revolutionize data analysis and modeling of the gasification of organic waste.Typical outputs including the syngas yield,composition,and HHVs were discussed with a better understanding of the gasification process and ML application.This review focused on the combination of gasification and ML,and it is of immediate significance for the resource and energy utilization of organic waste.

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

In this paper,based on Fluent software,a five-nozzle gasifier reactor was established to simulate the gasification process of oil-based drill cuttings coal-water slurry.The influence of concentration and oxygen/carbon atomic ratio on the gasification process of oil-based drill cuttings coal-water slurry was investigated.The results show that when the oxygen flow is constant,the outlet temperature of gasifier decreases,the content of effective gas increases,and the carbon conversion rate decreases with the increase of concentration;When the ratio of oxygen to carbon atoms is constant,the effective gas content rises and the temperature rises with the increase of the concentration,and the carbon conversion rate reaches the maximum value when the concentration of oil-based drill cuttings coal-water slurry is 65%;When the concentration is constant,the effective gas content decreases and the outlet temperature rises with the increase of the oxygen/carbon atom ratio,and the carbon conversion rate reaches 99.80%when the oxygen/carbon atom ratio is 1.03.It shows that this method can effectively decompose the organic matter in oilbased drill cuttings and realize the efficient and cooperative treatment of oil-based drill cuttings.

Cost-Effective Monitoring of the Fuel Air Equivalence-Ratio with a Lambda Sensor and a Microcontroller in a Downdraft Biomass Gasifier

The operation of biomass treatment devices such as gasifiers is based on the control of key parameters that play an important role in product formation. These include: temperature, excess oxygen, relative humidity and biomass composition. This work focuses on excess oxygen and temperature. Unfortunately, flue gas oxygen analyzers are expensive and not accessible to small industries. However, the equivalence ratio is linked to excess oxygen and has the advantage of not depending on biomass composition. This study therefore focuses on the design and development of a device for controlling this equivalence ratio by measuring oxygen concentration using a self-propelled Lambda probe, and a system for monitoring this equivalence ratio using an Arduino Uno 3 microcontroller. The temperature is recorded with an accuracy of ±1.5°C. For a heating time of 10 minutes, the response time to temperature change is around 3 seconds, which is sufficient for the device to function properly. This simple device is an efficient and cost-effective means of checking the equivalence ratio.

U-GAS气化炉高碳飞灰燃烧特性

采用热天平研究了U-GAS气化炉高碳飞灰燃烧特性,考察了灰分以及不同升温速率对飞灰燃烧特性的影响,探讨了飞灰造粒后应用于流化床锅炉燃烧的可行性.结果表明:与入炉煤粉相比,飞灰着火温度高、燃尽时间长、反应性较差;飞灰中灰分对飞灰燃烧性能和反应性能产生不利影响;随着升温速率增大,飞灰着火温度及燃尽温度升高,燃尽时间缩短,反应性增强;造粒后飞灰颗粒着火温度、燃尽温度均与煤粉接近,且它们的燃烧温度区域基本重合,颗粒可用于流化床锅炉燃烧.

Fe_3Al金属滤芯特性及在U-gas煤气化装置中的应用

为了解决U-gas粉煤气化工艺飞灰过滤器装置中陶瓷滤芯的断裂问题,分析了陶瓷滤芯和金属滤芯的性能差异,在装置中安装了国产改进2050型Fe_3Al金属滤芯并投运试验,研究了投运后合成气及飞灰特性、滤芯的微观形貌、过滤效率、流量-压差曲线、滤饼渗透性等特性。结果表明,在与陶瓷滤芯相同过滤精度条件下,Fe_3Al金属滤芯具有孔隙率高、渗透性高、压溃强度大等优势。投运结果表明,Fe_3Al滤芯投运3个月以来无断裂故障,在相近工况条件下,Fe_3Al滤芯运行平衡压差相比陶瓷滤芯下降了50%,且水洗塔悬浮物固含量由1 000~2 000 mg/L下降至100~500 mg/L。

U-GAS粉煤流化床煤气化废水设计及运行实例

针对某化工厂排放的U-GAS粉煤流化床煤气化废水成分复杂、有机物浓度高的特点,采用了预处理-IMC生化处理-臭氧氧化-曝气生物滤池组合工艺。给出了主要构筑物及设计参数,阐述了工程设计技术特点。该工程运行结果表明,在进水CODCr、BOD5、NH3-N的质量浓度分别为500、280、180 mg/L的条件下,出水水质可稳定达到GB 8978—1996《污水综合排放标准》一级标准的要求。

Gasification kinetics of bulk coke in the CO2/CO/H2/H2O/N2 system simulating the atmosphere in the industrial blast furnace

The gasification characteristics and gasification kinetics of coke in complex CO2/CO/H2/H2O/N2 systems similar to the gas system of industrial blast furnace (BF) were studied by the method of isothermal thermogravimetric analysis. The experimental gas compositions and the corresponding temperature were chosen according to data reported for industrial BFs. The gasification behavior of coke was described by the Random Pore Model (RPM), Volumetric Model (VM), and Grain Model (GM). Results showed that the gas composition of the coke gasification zone in BF changes slightly and that the temperature is the most important factor affecting coke gasification. The lower activation energy of coke samples (Coke Reaction Index (CRI)>50) is due to the high Fe2O3 in the ash, lower degree of graphitization, and larger pore structure. In addition, the choice of kinetic model does not differ substantially in describing the gasification mechanism of coke in a BF.

Hydrogen generation from polyvinyl alcohol-contaminated wastewater by a process of supercritical water gasification

Gasification of polyvinyl alcohol （PVA）-contaminated wastewater in supercritical water （SCW） was investigated in a continuous flow reactor at 723-873 K, 20-36 MPa and residence time of 20-450 s. The gas and liquid products were analyzed by GC/TCD, and TOC analyzer. The main gas products were H2, CH4, CO and CO2. Pressure change had no significant influence on gasification efficiency. Higher temperature and longer residence time enhanced gasification efficiency, and lower temperature favored the production of H2. The effects of KOH catalyst on gas product composition were studied, and gasification efficiency were analyzed. The TOC removal efficiency （RTOC）, carbon gasification ratio （RCG） and hydrogen gasification ratio （RHG） were up to 96.00%, 95.92% and 126.40% at 873 K and 60 s, respectively, which suggests PVA can be completely gasified in SCW. The results indicate supercritical water gasification for hydrogen generation is a promising process for the treatment ofPVA wastewater.

Effect of CO_2 and H_2O on gasification dissolution and deep reaction of coke

To more comprehensively analyze the effect of CO_2 and H_2O on the gasification dissolution reaction and deep reaction of coke, the reactions of coke with CO_2 and H_2O using high temperature gas–solid reaction apparatus over the range of 950–1250°C were studied, and the thermodynamic and kinetic analyses were also performed. The results show that the average reaction rate of coke with H_2O is about 1.3–6.5 times that with CO_2 in the experimental temperature range. At the same temperature, the endothermic effect of coke with H_2O is less than that with CO_2. As the pressure increases, the gasification dissolution reaction of coke shifts to the high-temperature zone. The use of hydrogen-rich fuels is conducive to decreasing the energy consumed inside the blast furnace, and a corresponding high-pressure operation will help to suppress the gasification dissolution reaction of coke and reduce its deterioration. The interfacial chemical reaction is the main rate-limiting step over the experimental temperature range. The activation energies of the reaction of coke with CO_2 and H_2O are 169.23 kJ ·mol-1 and 87.13 kJ·mol^(-1), respectively. Additionally, water vapor is more likely to diffuse into the coke interior at a lower temperature and thus aggravates the deterioration of coke in the middle upper part of blast furnace.

Biomass gasification technology:The state of the art overview

In the last decades the interest in the biomass gasification process has increased due to the growing attention to the use of sustainable energy. Biomass is a renewable energy source and represents a valid alternative to fossil fuels. Gasification is the thermochemical conversion of an organic material into a valuable gaseous product, called syngas, and a solid product, called char. The biomass gasification represents an efficient process for the production of power and heat and the production of hydrogen and second-generation biofuels.This paper deals with the state of the art biomass gasification technologies, evaluating advantages and disadvantages, the potential use of the syngas and the application of the biomass gasification. Syngas cleaning though fundamental to evaluate any gasification technology is not included in this paper since; in the authors＇ opinion, a dedicated review is necessary.

U-GAS气化炉加煤系统故障分析与处理

对U-GAS气化炉在劣质煤转化过程中其加煤系统易出现的故障进行了深入分析和研究,提出了相应的改造方案;对充压、泄压系统管路,有关控制程序及阀门等进行改造后,取得了较好的效果。