Copper slag assisted coke reduction of phosphogypsum for sulphur dioxide preparation

The reduction of phosphogypsum(PG)to lime slag and SO_(2)using coke can effectively alleviate the environmental problems caused by PG.However,the PG decomposition temperature remains high and the product yield remains poor.By adding additives,the decomposition temperature can be further reduced and PG decomposition rate and product yield can be improved.However,the use of current additives such as Fe_(2)O_(3)and SiO_(2)brings the problem of increasing economic cost.Therefore,it is proposed to use solid waste copper slag(CS)as a new additive to reduce PG to prepare SO2,which can reduce the cost and meet the environmental benefits at the same time.The effects of proportion,temperature and thermostatic time on PG decomposition are investigated by experimental and kinetic analysis combined with FactSage thermodynamic calculations to optimize the roasting conditions.Finally,the reaction mechanism is proposed.It is found that adding CS to the coke and PG system can increase the rate of PG decomposition and SO_(2)yield while lowering the PG decomposition temperature.For example,when the CS/PG mass ratio increases from 0 to 1,PG decomposition rate increases from 83.38%to 99.35%,SO_(2)yield increases from 78.62%to 96.81%,and PG decomposition temperature decreases from 992.4℃to 949.6℃.The optimal reaction parameters are CS/PG mass ratio of 1,Coke/PG mass ratio of 0.06 at 1100℃for 20 min with 99.35%PG decomposition rate and 96.81%SO_(2) yield.The process proceeds according to the following reactions:2CaSO_(4)+ 0.7C + 0.8Fe_(2)SiO_(4)→0.8Ca_(2)SiO_(4)+ 0.2Ca_(2)Fe_(2)O_(5)+ 0.4Fe_(3)O_(4)+2SO_(2)+ 0.7CO_(2)Finally,a process for decomposing PG with coke and CS is proposed.

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.

Preparation of biomass-derived carbon loaded with MnO_(2) as lithium-ion battery anode for improving its reversible capacity and cycling performance

Biomass-derived carbon materials for lithiumion batteries emerge as one of the most promising anodes from sustainable perspective.However,improving the reversible capacity and cycling performance remains a long-standing challenge.By combining the benefits of K2CO_(3) activation and KMnO_(4) hydrothermal treatment,this work proposes a two-step activation method to load MnO_(2) charge transfer onto biomass-derived carbon(KAC@MnO_(2)).Comprehensive analysis reveals that KAC@MnO_(2) has a micro-mesoporous coexistence structure and uniform surface distribution of MnO_(2),thus providing an improved electrochemical performance.Specifically,KAC@MnO_(2) exhibits an initial chargedischarge capacity of 847.3/1813.2 mAh·g^(-1) at 0.2 A·g^(-1),which is significantly higher than that of direct pyrolysis carbon and K2CO_(3) activated carbon,respectively.Furthermore,the KAC@MnO_(2) maintains a reversible capacity of 652.6 mAh·g^(-1) after 100 cycles.Even at a high current density of 1.0 A·g^(-1),KAC@MnO_(2) still exhibits excellent long-term cycling stability and maintains a stable reversible capacity of 306.7 mAh·g^(-1) after 500 cycles.Compared with reported biochar anode materials,the KAC@MnO_(2) prepared in this work shows superior reversible capacity and cycling performance.Additionally,the Li+insertion and de-insertion mechanisms are verified by ex situ X-ray diffraction analysis during the chargedischarge process,helping us better understand the energy storage mechanism of KAC@MnO_(2).

A comprehensive CFD combustion model for supercritical CFB boilers

A combustion model of a large-scale supercritical circulati ng fluidized bed (CFB) boiler was developed for comprehensive computational-fluid-dynamics analysis. The model incorporates gas-solid hydrodynamics, coal combustion, heat transfer on heat exchange surfaces in the furnace, and heat transfer between fumace and working medium in the heat transfer tubes. In simulating the dense and dilute phases in the fumace, the gas-solid hydrodynamics is based on the Euler-Euler model and energy-minimization multiscale drag model. Coal combustion entails evaporation, devolatilization, char combustion, gas homoge neous reaction, and pollutant emission. The coefficient ofheat transfer between gas-solid and the waterwall is estimated using the cluster renewal model, and for radiation, the discrete ordinate model is used. Moreover, thermohydraulic processes in the membrane wall are also in eluded in the heat transfer process. The model was successfully applied in simulations of a 350-MW supercritical CFB boiler. Detailed distributions of solids concentration, oxygen, heat flux, and working medium temperature in the boiler furnace are presented.

Predictions of NOx/N2O emissions from an ultra-supercritical CFB boiler using a 2-D comprehensive CFD combustion model

NOx and N2O emissions from an ultra-supercritical circulating fluidized bed(CFB)boiler were predicted using a two dimensional(2-D)comprehensive computational fluid dynamics(CFD)combustion model.This model was developed from a three dimensional model for a supercritical CFB boiler previously constructed by our group.Based on an analysis of the NOx and N2O conversion processes in a CFB boiler,the primary formation and destruction reactions were introduced into the 2-D model and coupled.The resulting model was validated using data from the Baima 600 MW supercritical CFB boiler,and then applied to a 660 MW ultra-supercritical CFB boiler.The effects of excess air,the secondary air(SA)to(primary air(PA)plus SA)ratio and the SA injection height on NOx and N2O emissions were investigated.The results show that a higher excess air volume increases both NOx and N2O emissions,while increasing the SA/(PA+SA)ratio somewhat reduces both the NOx and N2O concentrations.On the basis of the results of this work,optimal locations for SA injection ports so as to lower NOx and N2O emissions are recommended.

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.

Anti-wear beam effects on gas-solid hydrodynamics in a circulating fluidized bed

Anti-wear beams installed on water walls of circulating fluidized bed （CFB） boilers are one of the most effective ways to protect against water-wall erosion. Beam effects from, for example, beam size and superficial gas velocity were investigated on gas-solid hydrodynamics in a CFB test rig using CFD simulations and experimental methods. The downward flow of the wall layer solids is observed to be disrupted by the beam but is then restored some distance further downstream. When falling solids from the wall layer hit the anti-wear beam, the velocity of the falling solids decreases rapidly. A fraction of the solids accumulates on the beam. Below the beams, the falling solids have reduced velocities but upward-moving solids were observed on the wall. The effect of the beam increases with width and superficial gas velocity. Wear occurs mainly above the beam and its variation with width is different above to below the beam. There is an optimum width that, when combined with beam height, results in less erosion.

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.

Experiments on the effect of the pressure on the mineral transformation of coal ash under the different reaction atmosphere

This paper investigated the effect of the pressures,reaction atmospheres and coal ash species on the ash fusibility with high-pressure thermogravimetric analysis(PTGA)apparatus and X-ray diffraction(XRD)analysis.Each specimen analyzed by XRD was observed for the mineral conversion and formation of new minerals with the pressures under different atmospheres.These results indicate that the pressure restrains the transformation and decomposition of minerals.Many low-temperature minerals are still present under the elevated pressure.The different reaction atmospheres have different effects on the formation of coal ash minerals.Under the N_(2)atmosphere,the present microcline may decrease the melting temperature of coal ash.And later,it transforms into sanidine at high pressure;thus,the melting temperature of coal ash may increase.Under the CO_(2)atmosphere,the minerals such as microcline,lomonitite,geothite and illite are still present with the increase in pressure;this may reduce the melting temperature.While under the H_(2)O atmosphere,there are magnetite and anorthoclase,which may produce the low-temperature eutectics decreasing the melting temperature.The coal ash abundance in basic oxides or higher SiO_(2),Fe_(2)O_(3),K_(2)O and Na_(2)O has lower melting temperature.While the ash sample with more SiO_(2)and Al_(2)O_(3)and less Fe_(2)O_(3)and basic oxides may lead to higher melting temperature.