Research on coal staged conversion poly-generation system based on fluidized bed

A new coal staged conversion poly-generation system combined coal combustion and pyrolysis has been developed for clean and high efficient utilization of coal.Coal is the first pyrolysed in a fluidized pyrolyzer.The pyrolysis gas is then purified and used for chemical product or liquid fuel production.Tar is collected during purification and can be processed to extract high value product and to make liquid fuels by hydro-refining.Semi-coke from the pyrolysis reactor is burned in a circulating fluidized bed(CFB)combustor for heat or power generation.The system can realize coal multiproduct generation and has a great potential to increase coal utilization value.A 1 MW poly-generation system pilot plant and a 12 MW CFB gas,tar,heat and power poly-generation system was erected.The experimental study focused on the two fluidized bed operation and characterization of gas,tar and char yields and compositions.The results showed that the system could operate stable,and produce about 0.12 m^(3)/kg gas with 22 MJ/m^(3)heating value and about 10 wt%tar when using Huainan bituminous coal under pyrolysis temperature between 500 and 600℃.The produced gases were mainly H_(2),CH_(4),CO,CO_(2),C_(2)H_(4),C_(2)H_(6),C_(3)H_(6)and C_(3)H_(8).The CFB combustor can burn semi-coke steadily.The application prospect of the new system was discussed.

Graphene Array-Based Anti-fouling Solar Vapour Gap Membrane Distillation with High Energy Efficiency

Photothermal membrane distillation(MD)is a promising technology for desalination and water purification.However,solar-thermal conversion suffers from low energy efficiency(a typical solar-water efficiency of ~50%),while complex modifications are needed to reduce membrane fouling.Here,we demonstrate a new concept of solar vapour gap membrane distillation(SVGMD)synergistically combining self-guided water transport,localized heating,and separation of membrane from feed solution.A free-standing,multifunctional light absorber based on graphene array is custom-designed to locally heat the thin water layer transporting through graphene nanochannels.The as-generated vapour passes through a gap and condenses,while salt/contaminants are rejected before reaching the membrane.The high solar-water efficiency(73.4% at 1 sun),clean water collection ratio(82.3%),excellent anti-fouling performance,and stable permeate flux in continuous operation over 72 h are simultaneously achieved.Meanwhile,SVGMD inherits the advantage of MD in microorganism removal and water collection,enabling the solar-water efficiency 3.5 times higher compared to state-of-the-art solar vapour systems.A scaled system to treat oil/seawater mixtures under natural sunlight is developed with a purified water yield of 92.8 kg m-2 day-1.Our results can be applied for diverse mixed-phase feeds,leading to the next-generation solar-driven MD technology.

The catalytic effect of the Na and Ca-rich industrial wastes on the thermal ignition of coal combustion

The catalytic effects of four industrial wastes,namely,the soap residue(SR),brine sludge(BS),calcium carbide residue(CCR),and white lime mud(WLM),on coal thermal ignition were investigated.The acidity of palmitate anion associated with Na+in SR was lower than that of chloride anion combined with Na+in BS,which resulted in an improved the combustion of SR.The acidity of OH-anion combined with Ca2+in CCR was lower than that of CO32-anion combined with Ca2+in WLM,resulting in CCR exhibiting a better catalytic effect on coal ignition.The alkaline metal Na had lower initial ionisation energy than the alkaline earth metal Ca.Therefore,the Na-rich SR exhibited higher catalytic activity on coal ignition than Ca-rich CCR.The ignition temperature of coal with 0.5%SR decreased from 544 to 503°C.

Design of Supercapacitor Electrodes Using Molecular Dynamics Simulations

Electric double-layer capacitors(EDLCs) are advanced electrochemical devices for energy storage and have attracted strong interest due to their outstanding properties. Rational optimization of electrode–electrolyte interactions is of vital importance to enhance device performance for practical applications. Molecular dynamics(MD) simulations could provide theoretical guidelines for the optimal design of electrodes and the improvement of capacitive performances, e.g., energy density and power density. Here we discuss recent MD simulation studies on energy storage performance of electrode materials containing porous to nanostructures. The energy storage properties are related to the electrode structures, including electrode geometry and electrode modifications. Altering electrode geometry, i.e., pore size and surface topography,can influence EDL capacitance. We critically examine different types of electrode modifications, such as altering the arrangement of carbon atoms, doping heteroatoms and defects, which can change the quantum capacitance. The enhancement of power density can be achieved by the intensified ion dynamics and shortened ion pathway.Rational control of the electrode morphology helps improve the ion dynamics by decreasing the ion diffusion pathway. Tuning the surface properties(e.g., the affinity between the electrode and the ions) can affect the ionpacking phenomena. Our critical analysis helps enhance the energy and power densities of EDLCs by modulating the corresponding electrode structures and surface properties.

Highly Thermo-Conductive Three-Dimensional Graphene Aqueous Medium

Highly thermo-conductive aqueous medium is a crucial premise to demonstrate high-performance thermal-related applications.Graphene has the diamond comparable thermal conductivity,while the intrinsic two-dimensional reality will result in strong anisotropic thermal conductivity and wrinkles or even crumples that significantly sacrifices its inherent properties in practical applications.One strategy to overcome this is to use three-dimensional(3D)architecture of graphene.Herein,3D graphene structure with covalent-bonding nanofins(3D-GS-CBF)is proposed,which is then used as the filler to demonstrate effective aqueous medium.The thermal conductivity and thermal conductivity enhancement efficiency of 3D-GS-CBF(0.26 vol%)aqueous medium can be as high as 2.61 W m-1 K-1 and 1300%,respectively,around six times larger than highest value of the existed aqueous mediums.Meanwhile,3D-GS-CBF can be stable in the solution even after 6 months,addressing the instability issues of conventional graphene networks.A multiscale modeling including non-equilibrium molecular dynamics simulations and heat conduction model is applied to interpret experimental results.3D-GS-CBF aqueous medium can largely improve the solar vapor evaporation rate(by 1.5 times)that are even comparable to the interfacial heating system;meanwhile,its cooling performance is also superior to commercial coolant in thermal management applications.

Influence of temperature and Ca(OH)2 on releasing tar and coal gas during lignite coal pyrolysis and char gasification

The yield of tar and syngas has been investigated by catalytic pyrolysis of Pingzhuang lignite(PZL)over Ca(OH)2 catalyst in temperature range of 600℃-1000℃in a tube furnace.The results show that the yield of volatile pyrolysis increases and char decreases with rising temperature for both raw and catalyzed Pingzhuang lignite.The hydrogen fraction(H2)increased from 20%to 40%for the PZL sample;but,for the PZL-Ca(OH)2 sample,H2 fraction fluctuated randomly between 35%to 42%,with the maximum H2 fraction found at 1000℃.The Gaschromatography mass-spectroscopic(GC-MS)analysis revealed that the maximum tar yield at 800℃and 700℃was obtained for PZL and PZL-Ca(OH)2,respectively.The surface morphology of PZL and PZL-Ca(OH)2 chars underwent different transformation in the presence of catalyst as illustrated by SEM/EDX,FTIR,and BET analysis.Furthermore,char sample was investigated for the carbon conversion and reactivity index using TGA analysis under N2 and CO atmosphere.

Conversions of fuel-N, volatile-N, and char-N to NO and N_2O during combustion of a single coal particle in O_2/N_2 and O_2/H_2O at low temperature

Oxy-steam combustion is a promising next-generation combustion technology.Conversions of fuel-N,volatile-N,and char-N to NO and N_2O during combustion of a single coal particle in O_2/N_2and O_2/H_2O were studied in a tube reactor at low temperature.In O_2/N_2,NO reaches the maximum value in the devolatilization stage and N_2O reaches the maximum value in the char combustion stage.In O_2/H_2O,both NO and N_2O reach the maximum values in the char combustion stage.The total conversion ratios of fuel-N to NO and N_2O in O_2/N_2are obviously higher than those in O_2/H_2O,due to the reduction of H_2O on NO and N_2O.Temperature changes the trade-off between NO and N_2O.In O_2/N_2and O_2/H_2O,the conversion ratios of fuel-N,volatile-N,and char-N to NO increase with increasing temperature,and those to N_2O show the opposite trends.The conversion ratios of fuel-N,volatile-N,and char-N to NO reach the maximum values at b O_2N=30 vol%in O_2/N_2.In O_2/H_2O,the conversion ratios of fuel-N and char-N to NO reach the maximum values at b O_2N=30 vol%,and the conversion ratio of volatile-N to NO shows a slightly increasing trend with increasing oxygen concentration.The conversion ratios of fuel-N,volatile-N,and char-N to N_2O decrease with increasing oxygen concentration in both atmospheres.A higher coal rank has higher conversion ratios of fuel-N to NO and N_2O.Anthracite coal exhibits the highest conversion ratios of fuel-N,volatile-N,and char-N to NO and N_2O in both atmospheres.This work is to develop efficient ways to understand and control NO and N_2O emissions for a clean and sustainable atmosphere.

The effects of gas flow pattern on the generation of ozone in surface dielectric barrier discharge

Ozone production utilizing surface dielectric barrier discharge(SDBD)was experimental studied for different flow patterns considering the influences of transversal flow,lateral flow and different lateral flow positions.Results show that the flow patterns have a remarkable impact on the ozone yield by affecting the uniformity and turbulenee of gas flow.Meanwhile,distributing the O2 flow rate according to the intensity of the plasma reaction would also increase the generation efficiency of SDBD for ozone production.By improving the uniformity and introducing the lateral flow to the transversal flow,the highest ozone yield was obtained in flow pattern'F‘.In this case,the ozone yield increased by 28.4%to 131 g kWh^-1 from 102.8 g kWh^-1 in flow pattern‘A’.

Influence of coke rate on thermal treatment of waste selective catalytic reduction(SCR)catalyst during iron ore sintering

Waste selective catalytic reduction(SCR)catalyst as a hazardous waste has a significant impact on the environment and human health.In present study,a novel technology for thermal treatment of waste SCR catalyst was proposed by adding it to sinter mix for iron ore sintering.The influences of coke rate on the flame front propagation,sinter microstructure,and sinter quality during sintering co-processing the waste SCR catalyst process were studied.In situ tests results indicated the maximum sintering bed temperature increased at higher coke rate,indicating more liquid phase generated and higher airflow resistance.The sintering time was longer and the calculated flame front speed dropped at higher coke rate.Sinter microstructure results found the coalescence and reshaping of bubbles were more fully with increasing coke rate.The porosity dropped from 35.28%to 25.66%,the pore average diameter of large pores decreased from 383.76μm to 311.43μm.With increasing coke rate,the sinter indexes of tumbler index,productivity,and yield,increased from 33.2%,9.2 t·m^(-2)·d^(-1),28.9%to 58.0%,36.0 t·m^(-2)·d^(-1),68.9%,respectively.Finally,a comprehensive index was introduced to systematically assess the influence of coke rate on sinter quality,which rose from 100 to 200 when coke rate was increased from 3.5%(mass)to 5.5%(mass).

Oxygen-vacancy-anchoring Ni_(x)O_(y) loading towards efficient hydrogen evolution via photo-thermal coupling reaction

Oxygen vacancy(Vo)is a significant component in defect engineering.The present work reports the anchoring effects of initial Vo for further loading modifications and the reducing capacity of photoinduced Vo for pure water splitting.Herein,we propose Ni-loaded Cu-doped TiO_(2)(NCT)materials by successive doping and loading.The continuously added Ni ions should accumulate around the Vos and gradually grow into complete nickel oxide crystals,achieving a higher average valence state of the Ni species.NiO crystals can be detected on a 0.5%NCT sample,while the structure of Ni_(2)O_(3) has been confirmed with a higher nickel mass ratio.Moreover,the introduction of nickel oxide effectively improves the photochemical and electrochemical performance by the interface charge separation,finally reaching an H2 yield of 30.6 pmol/g-cat on 0.5%NCT for Vo-based photo-thermal coupling reaction,which consists of Vo generation in photo and Vo consumption in thermal environment.In situ infrared spectroscopy further indicated that the presence of high valence state nickel oxide hindered the H2 formation but effectively promoted the conventional oxidizing reaction,with an H2 yield of 20.6 mmol/g-cat in a methanol-water reaction on the 2.0%NCT material.In summary,Vo controls the morphological structure of Ni loading and produces diverse effects for reactions with dissimilar mechanisms,which provides a novel way to design modifications for promoting various chemical reactions.

Pore-structure regulation and heteroatom doping of activated carbon for supercapacitors with excellent rate performance and power density

Activated carbon(AC)has attracted tremendous research interest as an electrode material for supercapacitors owing to its high specific surface area,high porosity,and low cost.However,AC-based supercapacitors suffer from limited rate performance and low power density,which mainly arise from their inherently low electrical conductivity and sluggish ion dynamics in the micropores.Here,we propose a simple yet effective strategy to address the aforementioned issue by nitrogen/fluorine doping and enlarging the micropore size.During the treatment,the decomposition products of NH4F react with the carbon atoms to dope the AC with nitrogen/fluorine and simultaneously enlarge the pores by etching.The treated AC shows a higher specific surface area of 1826 m2 g^(−1)(by~15%),more micropores with a diameter around 0.93 nm(by~33%),better wettability(contact angle decreased from 120°to 45°),and excellent electrical conductivity(96 S m^(−1))compared with untreated AC(39 S m^(−1)).The as-fabricated supercapacitors demonstrate excellent specific capacitance(26 F g^(−1)at 1 A g^(−1)),significantly reduced electrical resistance(by~50%),and improved rate performance(from 46.21 to 64.39%at current densities of 1 to 20 A g^(−1)).Moreover,the treated AC-based supercapacitor achieves a maximum energy density of 25 Wh kg^(−1)at 1000 W kg^(−1)and a maximum power density of 10,875 W kg^(−1)at 15 Wh kg^(−1),which clearly outperforms pristine AC-based supercapacitors.This synergistic treatment strategy provides an effective way to improve the rate performance and power density of AC-based supercapacitors.

Frequency comparative study of coal-fired fly ash acoustic agglomeration

Particulate pollution is main kind of atmospheric pollution.The fine particles are seriously harmful to human health and environment.Acoustic agglomeration is considered as a promising pretreatment technology for fine particle agglomeration.The mechanisms of acoustic agglomeration are very complex and the agglomeration efficiency is affected by many factors.The most important and controversial factor is frequency.Comparative studies between high-frequency and low-frequency sound source to agglomerate coal- fired fly ash were carried out to investigate the influence of frequency on agglomeration efficiency.Acoustic agglomeration theoretical analysis,experimental particle size distributions （PSDs） and orthogonal design were examined.The results showed that the 20 kHz high-frequency sound source was not suitable to agglomerate coal-fired fly ash.Only within the size ranging from 0.2 to 0.25 μm the particles agglomerated to adhere together,and the agglomerated particles were smaller than 2.5 μm.The application of low-frequency （1000–1800 Hz） sound source was proved as an advisable pretreatment with the highest agglomeration efficiency of 75.3%,and all the number concentrations within the measuring range decreased.Orthogonal design L16 （4） 3 was introduced to determine the optimum frequency and optimize acoustic agglomeration condition.According to the results of orthogonal analysis,frequency was the dominant factor of coal-fired fly ash acoustic agglomeration and the optimum frequency was 1400 Hz.

Release characteristic of different classes of sodium during combustion of Zhun-Dong coal investigated by laser-induced breakdown spectroscopy

Serious fouling and slagging problems are associated with the combustion of Chinese Zhun-Dong coal due to its high content of sodium(Na). Understanding the release characteristic of Na during the combustion is essential to viable utilization of this coal. In this work, coal samples were treated with a sequence of solvents: water(H2O), ammonium acetate(NH4Ac), hydrochloric acid(HCl), and the release characteristics of various classes of Na during coal combustion were investigated using the technique of laser-induced breakdown spectroscopy. The relative contribution of various Na classes to the Na release during each combustion stage was found to be similar, in the order of H2O-soluble Na [ NH4 Acsoluble Na [ HCl-soluble Na [ insoluble Na. Sodium released during the devolatilization stage can be attributed to each of the sodium classes. After the devolatilization stage,H2O-soluble Na and NH4Ac-soluble Na dominated the Na release during both char and ash stages. Over 64 % of the total Na released during combustion comes from the H2O-soluble Na, which suggests that the Na release during the combustion of Zhun-Dong coal can be reduced effectively after treatment by H2 O washing.

Moisture distribution in sludges based on different testing methods

Moisture distributions in municipal sewage sludge, printing and dyeing sludge and paper mill sludge were experimentally studied based on four different methods, i.e., drying test, thermogravimetric-differential thermal analysis （TG-DTA） test, thermogravimetric- differential scanning calorimetry （TG-DSC） test and water activity test. The results indicated that the moistures in the mechanically dewatered sludges were interstitial water, surface water and bound water. The interstitial water accounted for more than 50% wet basis （wb） of the total moisture content. The bond strength of sludge moisture increased with decreasing moisture content, especially when the moisture content was lower than 50% wb. Furthermore, the comparison among the four different testing methods was presented. The drying test was advantaged by its ability to quantify free water, interstitial water, surface water and bound water; while TG-DSC test, TG-DTA test and water activity test were capable of determining the bond strength of moisture in sludge. It was found that the results from TG-DSC and TG-DTA test are more persuasive than water activity test.

LES investigation of swirl intensity effect on unconfined turbulent swirling premixed flame

A finite reaction rate model is presented as a closure of large eddy simulation(LES) to numerically study an open premixed methane/air swirling flame. The resultant model is firstly validated by comparing with reported data and then employed to investigate the effect of swirling intensity on flow field, flame characteristics and combustion instability of the swirling flame. Three different swirl numbers are considered. The LES results show that as swirling intensity increases, the vortex entrainment and micro-mixing are enhanced, leading to more lean equivalent ratios at flame front; consequently, higher swirling number causes lower flame temperatures and slower CO oxidization; for all simulated swirl numbers,flame fronts are completely located out of the recirculation zones and anchored at the inner surface of the annular swirling steams; swirl number has a crucial effect on swirling flame extension toward radial and tangential dimensions and then significantly affects streamwise flame length, which is a great influencing factor on combustion instability; vortex-induced disturbance on flame in streamwise plays a critical role in combustion instability.

SO2 Emission Characteristics and BP Neural Networks Prediction in MSW/Coal Co-Fired Fluidized Beds

The SO_2 emission characteristics of typical MSW components and their mixtures have been investigated in aΦ150mm fluidized bed.Some influencing factors of SO_2 emission in MSW fluidized bed incinerator were foundout in this study.The SO2 emission is increasing with the growth of the bed temperature,and it is rising with theincreasing oxygen concentration at furnace exit.When the weight percentage of auxiliary coal is being raised,theconversion rate of S to SO_2 is largely going up.The SO_2 emission decreases if the desulfurizing agent (CaCO_3) isadded during the incineration process,but the desulfurizing efficiency is weakened with the enhancement of thebed temperature.The fuel moisture content has a slight effect on the SO_2 emission. Based on these experimentalresults, a 12×6×1 three-layer 13P neural networks prediction model of SOR emission in MSW/coal co-firedfluidized bed incinerator was built.The prediction results of this model give good agreement with theexperimental results,which indicates that the model has relatively high accuracy and good generalization ability.It was found that BP neural network is an effectual method used to predict the SO_2 emission of MSW/coalco-fired fluidized bed incinerator.

Atmospheric emission characterization of a novel sludge drying and co-combustion system

A novel system combining sludge drying and co-combustion with coal was applied in disposing sludge and its atmospheric emission characteristics were tested. The system was composed of a hollow blade paddle dryer, a thermal drying exhaust gas control system, a 75 tons/hr circulating fluidized bed and a flue gas cleaning system. The emissions of NH3, SO2, CH4 and some other pollutants released from thermal drying, and pollutants such as NOx, SO2 etc. discharged by the incinerator, were all tested. Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans （PCDD/Fs） in the flue gas from the incinerator were investigated as well. The results indicated that the concentrations of NOx and SO2 in the flue gas from the incinerator were 145 and 16 mg/m^3, respectively, and the I-TEQ concentration of 2,3,7,8-substitued PCDD/Fs was 0.023 ng I-TEQ/Nm^3. All these values were greatly lower than the emission standards of China. In addition, there was no obvious odor in the air around the sludge dryer. The results demonstrated that this drying and co-combustion system is efficient in controlling pollutants and is a feasible way for large-scale treatment of industrial sludge and sewage sludge.

Non-uniform distribution of gas-solid flow through six parallel cyclones in a CFB system: An experimental study

In large-scale circulating fluidized bed （CFB） boilers, it is common to use multiple cyclones in parallel for the capture of solids, assuming that gas-solid flow to be the same in the cyclones. This article presents a study investigating gas-solid flow through six parallel cyclones in a CFB cold test rig. The six cyclones were located asymmetrically on the left and right walls of the riser. Solid volume fraction and particle velocity profiles at the riser outlets and in the horizontal ducts were measured using a fiber optical probe. Cyclone pressure drop and solid circulating rate were measured for each individual cyclone. Measure- ments showed good agreement as to the non-uniform distribution of the gas-solid flow, which occurred mainly across the three cyclones on one side： the middle cyclones on both sides had higher particle veloc- ities. Conversely, the solid volume fractions, solid fluxes and solid circulating rates of the middle cyclones were lower than those of the other four cyclones. The apparent reason for the flow non-uniformity among the cyclones is the significant flow non-uniformity at the riser outlets. Under typical operating conditions, the solid volume fractions at the riser outlets had a deviation of up to 26% whereas the solid circulating rates at the stand pipes, 7%. These results are consistent with most other studies in the literature.

Direct Numerical Simulation of Particle Dispersion in the Flow Around a Circular Cylinder

The major objective of the paper is to use direct numerical simulation method to get the dispersion patterns of different Stokes number particles in cylinder wake at low Reynolds numbers. The gas fluid structure is simulated by a spectral-element method with third-order accuracy. Non-reflecting boundary condition is specified for the outlet downstream boundary. Lagrangian approach is used to trace particle trajectory. The simulation results show factors to be considered to characterize the particle dispersion and find different particle dispersion pattern in a circular cylinder wake and in a plane wake.

Effects of CO_(2)atmosphere on slow pyrolysis of high-ash lignite

Slow pyrolysis of a typical high-ash lignite in China was carried out in atmospheres of N_(2),20%CO_(2)/N_(2),40%CO_(2)/N_(2),and 60%CO_(2)/N_(2)in a fixed bed reactor.The evolution of char,tar,and gases in yield and characteristics,and the physico-chemical characteristics of chars in different atmospheres were compared.Results revealed that CO_(2)almost behaves as an inert gas in the evolution of char and CO before 600℃.The decrease in char and CO_(2)yields and the increase in CO yield at temperatures higher than 600℃are ascribed to the occurrence of char-CO_(2)gasification.The higher the CO_(2)level present in the atmosphere,the higher the severity of the gasification becomes.Introducing CO_(2)into the atmosphere raises tar and water yields but cuts down H_(2),CH_(4),and C_(2)H_(6)yields.The promotion of tar yield results from the higher phenols and aliphatics yields in the presence of CO_(2).The reduction of H_(2)yield is associated with the increase in water yield,while the decline of light hydrocarbon gases is connected with the suppression effects of CO_(2)on methyl decomposition.The role of inherent minerals was also investigated by comparing product yields from raw coal and demineralized coal.The comparison indicated that the char-CO_(2)gasification rate is sharply reduced to nearly zero without the catalytic effects of calcium,iron,and magnesium minerals.The evolution of tar and light hydrocarbon gases in the CO_(2)-containing atmosphere greatly depends on inherent minerals.Without minerals,tar yield is inhibited in the presence of CO_(2).In the absence of minerals,CO_(2)hardly has influences on CH_(4)and C_(2)H_(6)yields.