Influence of syngas components and ash particles on the radiative heat transfer in a radiant syngas cooler

Radiant syngas cooler(RSC)is widely used as a waste heat recovery equipment in industrial gasification.In this work,an RSC with radiation screens is established and the impact of gaseous radiative property models,gas components,and ash particles on heat transfer is investigated by the numerical simulation method.Considering the syngas components and the pressure environment of the RSC,a modified weighted-sum-of-gray-gases model was developed.The modified model shows high accuracy in validation.In computational fluid dynamics simulation,the calculated steam production is only 0.63%in error with the industrial data.Compared with Smith's model,the temperature decay along the axial direction calculated by the modified model is faster.Syngas components are of great significance to heat recovery capacity,especially when the absorbing gas fraction is less than 10%.After considering the influence of particles,the outlet temperature and the proportion of radiative heat transfer are less affected,but the difference in steam output reaches 2.7 t·h^(-1).The particle deposition on the wall greatly reduces the heat recovery performance of an RSC.

Exploring influence of MgO/CaO on crystallization characteristics to understand fluidity of synthetic coal slags

The crystallization has significant influence on fluidity of slag and slag discharge of entrained-flow-bed(EFB) gasifier. The crystallization characteristics and fluidity of five synthetic slags with different MgO/CaO ratios prepared on the basis of the range of oxide contents of Zhundong coal ash were investigated in this study. The results show that with the MgO/CaO ratio increase, the initial crystallization temperature increases, and the main temperature range of crystallization ratio growth moves to higher temperature range gradually which causes Tp25(Tp25is the temperature corresponding to the viscosity of 25 Pa·s)to increase. Mg-rich crystals are formed preferentially than Ca-rich crystals when adding the same amount of MgO and CaO during cooling. The effective slagging operating temperature range decrease from 217 ℃ for the slag with a 0:4 MgO/CaO ratio to 44 ℃ for the slag with a 4:0 MgO/CaO ratio with the MgO/CaO ratio increase. The slags with 2:2 and 1:3 MgO/CaO ratios show similar effective slagging operating temperature range, Tp25and the temperature corresponding to the viscosity of 2 Pa·s.However, compared with the slag with a 1:3 MgO/CaO ratio, the crystallization ratio and rate of slag with a 2:2 MgO/CaO ratio are lower within lower temperature range(1300–1200 ℃), causing its lower critical viscosity temperature and wider actual operating temperature range. Of the five slags, the widest effective slagging operating temperature range and the lowest Tp25of the slag with a 0:4 MgO/CaO ratio due to its low crystallization ratio, and wider actual operating temperature range of the slag with a 2:2 MgO/CaO ratio make the two slags suitable for slag discharge of EFB gasifier.

Effect of slag composition on corrosion resistance of high chromia refractory bricks for industrial entrained-flow gasifier

The slag composition corresponding to different coals varies significantly,which directly affects the operation of industrial entrained-flow gasifier and the service life of refractory bricks.In this study,the corrosion resistance of several typical coal slags for gasification on high chromia refractory bricks was comparatively investigated by static laboratory crucible tests and thermodynamic simulations.The results demonstrated that the corrosion degree of high chromia refractory bricks by different coal slags was high-Ca/Na slag>high-Fe slag>high-Si/Al slag.The surface structure of the refractory was relatively flat after corrosion by high-Si/Al slag,and the primary corrosion reaction was the partial dissolution of the matrix by the slag.High-Fe slag was prone to the precipitation of iron phases as well as the formation of(Mg,Fe)(Al,Cr)_(2)O_(4)composite spinel layer at the slag/refractory interface.The high-Ca/Na slag was susceptible to react with the refractory to yield a low melting point phase,which led to the destruction of the matrix structure of the refractory and an isolated distribution of particles.In addition,the monoclinic ZrO_(2) in the refractory reacted with CaO in the slag to formed calcium zirconate,which loosened its phase toughening effect,was the primary factor that aggravated the refractory corrosion.

Effect of carbon dioxide on oxy-fuel combustion of hydrogen sulfide:An experimental and kinetic modeling

CO_(2) is an important component in the acid gas and it is necessary to study the effect of CO_(2) presence on the oxy-fuel combustion of H_(2)S with particular focus on the formation of carbonyl sulfide(COS).The oxyfuel combustion of acid gas was conducted in a coaxial jet double channel burner.The distribution of flame temperature and products under stoichiometric condition along axial(R=0.0)and radial at about 3.0 mm(R=0.75)were analyzed,respectively.The Chemkin-Pro software was used to analyze the rate of production(ROP)for gas products and the reaction pathway of acid gas combustion.Both experimental and simulation results showed that acid gas combustion experienced the H2S chemical decomposition,H_(2)S oxidation and accompanied by H_(2) oxidation.The CO_(2) presence reduced the peak flame temperature and triggered the formation of COS in the flame area.COS formation at R=0.0 was mainly through the reaction of CO_(2) and CO with sulfur species,whereas at R=0.75 it was through the reaction of CO with sulfur species.The ROP results indicated that H_(2) was mainly from H_(2)O decomposition in the H_(2)S oxidation stage,and COS was formed by the reaction of CO_(2) with H_(2)S.ROP and other detailed analysis further revealed the role of H,OH and SH radicals in each stage of H_(2)S conversion.This study revealed the COS formation mechanisms with CO_(2) presence in the oxy-fuel combustion of H_(2)S and could offer important insights for pollutant control.

Structural characterization of char during co-gasification from torrefied sludge and Yangchangwan bituminous coal

The present study aims to investigate the physico-chemical structural evolution characteristics of char structure of CO_(2) atmosphere torrefaction pretreated sludge with Yangchangwan bituminous coal(YC)during co-gasification.The co-gasification reactivity of torrefied sludge and YC was measured using a thermogravimetric analyzer.The co-gasification reactivity of torrefied sludge with YC was thoroughly explored in depth by in situ heating stage microscope coupled with traditional characterization means of char sample(Scanning electron microscope,nitrogen adsorption analyzer,laser Raman spectroscopy).The results show that the gasification reaction rate of sludge treated under CO_(2) atmosphere and coal blended char was better than other char samples at 1100–1200℃.The torrefied sludge under CO_(2) atmosphere promoted its thermal decomposition to the maximum extent,so that it eventually was transformed into a large number of small broken particles.The specific surface area and ID1/IG ratio of blended char of torrefied sludge under CO_(2) atmosphere and YC were 1.70 and 1.07 times higher than that of YC,respectively.The in situ technique revealed that YC char with the addition of torrefied sludge undergo gasification by shrinking core modes and the presence of obvious ash melting flow phenomenon.It was more obvious than that of YC.

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,pilotscale 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 ultralarge-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.

Effect of ash removal on structure and pyrolysis/gasification reactivity of a Chinese bituminous coal

In this study,the effect of ash removal on Shenfu bituminous coal was investigated.The coal was pretreated by hydrofluoric acid(HF)pickling,and the raw/pretreated coal chars were prepared at 900°C in a fixed bed reactor.The structure of coal and char were detected by Fourier transform infrared(FTIR)and Raman spectroscopy.The reactivity was tested in a thermogravimetric analyzer,including coal pyrolysis and char gasification.The reaction kinetics was analyzed through the Coats–Redfern method,master plots,the model-free and model-fitting method.The results show that the HF pickling can remove silicon from coal efficiently,and the macromolecular framework of coal is quite stable according to FTIR.The Raman parameters imply some carbonaceous structure on coal surface changed.For slow pyrolysis of coal,the effect of heating rate is considered.The changes of pyrolysis characteristics and kinetics are insignificant.For char gasification,the reactivity under isothermal and non-isothermal condition are discussed with an emphasis in different residence time of devolatilization process.In kinetic control region(low temperature),the activation energy(Ea)is very close(about 240 kJ/mol)for all chars.With the temperature increases,the reactivity of raw coal char is more easily suffered by diffusion.The random pore model is more suitable for the ash-free coal char,and the char with long residence time has a larger value of structural parameterψand smaller value of pre-exponential factor A.The Ea calculated by model-fitting and model-free method were in good agreement.

Physico-chemical structure evolution characteristics of coal char during gasification in the presence of iron-based waste catalyst

The present study aims to explore the physico-chemical structure evolution characteristic during Yangchangwan bituminous coal(YCW)gasification in the presence of iron-based waste catalyst(IWC).The catalytic gasification reactivity of YCW was measured by thermogravimetric analyzer.Scanning electron microscope–energy dispersive system,nitrogen adsorption analyzer and laser Raman spectroscopy were employed to analyze the char physico-chemical properties.The results show that the optimal IWC loading ratio was 5 wt%at 1000°C.The distribution of IWC on char was uneven and Fe catalyst concentrated on the surface of some chars.The specific surface area of YCW gasified semi-char decreased significantly with the increase of gasification time.i.e.,the specific surface area reduced from 382 m2/g(0 min)to 192 m2/g(3 min),meanwhile,the number of micropores and mesopores decreased sharply at the late gasification stage.The carbon microcrystalline structure of YCW gasified semi-char was gradually destroyed with the increase of gasification time,and the microcrystalline structure with small size was gradually generated,resulting in the decreasing order degree of carbon microcrystalline structure.IWC can catalyze YCW gasification which could provide theoretical guidance for industrial solid waste recycling.

Special issue on coal gasification: science and technology

Coal,one of the fossil fuels which is burned for heat,contributes a quarter of the world’s primary energy and two-fifths of its electricity.According to the World Energy Model(WEM)provided by the International Energy Agency(IEA),the total primary energy demand from coal reached 3750 Mtoe in 2017,and its growth rate will decrease a lot in the future 10–20 years.Nevertheless,coal will remain as the main primary energy in the next few decades.

Experimental and numerical modeling of carbonized biomass gasification: A critical review

Gasification is one of the most significant and well-researched pathways to produce energy from biomass among the different options available.It is a conversion through thermo-chemical process that takes place within a gasifier,with interconnected factors that have an impact on how well the gasifier works.Gasification of carbonized biomass,which has a variety of effects on both the gasification process and the final product,is a significant method of producing energy from raw biomass that contains a lot of moisture or has non-homogeneous morphology.Although carbonized biomass has the potential to eliminate or significantly reduce tar formation,which is the most difficult aspect of biomass gasifier design and operation,it has not received the attention it merits even though gasification of biomass is a well-known conversion process with extensive research and development spanning all sectors of the process.This review gathers and analyzes the growing number of experimental and numerical modeling approaches in gasification of carbonized biomass based on exact conditions such as type of modeling considerations,feedstock,gasifier,and assessed parameters.The study also provides an overview of various models,such as equilibrium and kinetic rate models and numerical simulations of carbonized biomass gasification schemes based on computational fluid dynamics and Aspen Plus,while comparing the modeling approaches and results for each type of models that are described in the literature.Also,this review encompasses a broad variety of technologies,from laboratory reactors to industrial scale.Overall,this review offers a brief overview of the modeling decisions that must be taken at the beginning of a modeling research.

In-situ study on structure evolution and gasification reactivity of biomass char with K and Ca catalysts at carbon dioxide atmosphere

The structural evolution and gasification reactivity of biochar prepared from the pyrolysis of wheat straw were investigated by in-situ Raman spectroscopy and thermogravimetric analysis.The Raman spectra consisted of a combination of four Lorentzian bands(D1,D2,D4,G)and one Gaussian band(D3)in the first-order region.The experimental results showed that the addition of catalysts or the presence of ash could improve the CO_(2) gasification reactivity of biochar and result in a larger ID1/IG ratio and a lower IG/IALL ratio,meaning that the carbon structure was less ordered,and there were also more active sites such as amorphous carbon and cross-linked structures;Ca-based catalysts and K-based catalysts changed the evolution of biochar structure in a different way in CO_(2) atmosphere,the ID3/ID1 of Ca-based biochar was close to the value of non-catalyst biochar and decreased slowly,indicating that the Ca-based catalysts can stabilize the aromatic rings,while the IG/IALL of K-based biochar decreases significantly and the ID3/ID1 increased significantly,indicating the increase of carbon structure defects and the cracking of large aromatic rings in bio-char into small ones;a scheme of K and Ca reaction with biochar in CO_(2) gasification process was proposed.

Residence time distribution and modeling of the liquid phase in an impinging stream reactor

Based on some experimental investigations of liquid phase residence time distribution(RTD)in an impinging stream reactor,a two-dimensional plug-flow dispersion model for predicting the liquid phase RTD in the reactor was proposed.The calculation results of the model can be in good agreement with the experimental RTD under different operating conditions.The axial liquid dispersion coefficient increases monotonously with the increasing liquid flux,but is almost independent of gas flux.As the liquid flux and the gas flux increase,the liquid dispersion coefficient of center-to-wall decreases.The axial liquid dispersion coefficient is much larger than that of center-to-wall,which indicates that the liquid RTD is dominated mainly by axial liquid dispersion in the impinging stream reactor.

Crystallization and viscosity-temperature characteristics during co-gasification of industrial sludge and coal

Co-gasification of industrial sludge(IS)and coal was an effective approach to achieve harmless and sustainable utilization of IS.The long-term and stable operation of a co-gasification largely depends on fluidity of coal-ash slag.Herein,the effects of IS addition on the crystallization and viscosity of Shuangmazao(SMZ)coal were investigated by means of high temperature stage coupled with an optical microscope(HTSOM),a scanning electron microscopy coupled with an energy dispersive Xray spectrometry(SEM-EDS),X-ray diffraction(XRD),a Fourier transform infrared spectrometer(FTIR),and FactSage software.The results showed that when the proportion of IS was less than 60%,with the addition of IS,the slag existed in an amorphous form.This was due to the high content of SiO_(2) and Al_(2)O_(3) in SMZ ash and blended ash,which had a high glass-forming ability(GFA).The slag formed at a high temperature had a higher polymerization degree and viscosity,which led to a decrease in the migration ability between ions,and ultimately made the slag difficult to crystallize during the cooling.When the proportion of IS was higher than 60%,the addition of IS increased the CaO and FeO content in the system.As network modifiers,CaO and FeO could provide O^(2−)at a high temperature,which reacted with silicate network structure and continuously destroyed the complexity of network structure,thus reducing the polymerization degree and viscosity of slag.At this time,the migration ability between ions was enhanced,and needle-shaped/rod-shaped crystals were precipitated during the cooling process.Finally,the viscosity calculated by simulation and Einstein-Roscoe empirical formula demonstrated that the addition of IS could significantly improve the fluidity of coal ash and meet the requirements of the liquid slag-tapping gasifier.The purpose of this work was to provide theoretical support for slag flow mechanisms during the gasifier slagging-tapping process and the resource treatment of industrial solid waste.