Low-grade fly ash (rejected fly ash,rFA),a significant portion of the pulverized fuel ash (PFA) produced from coal-fired power plants and rejected from the ash classifying process,remains unused due to its high carbon...Low-grade fly ash (rejected fly ash,rFA),a significant portion of the pulverized fuel ash (PFA) produced from coal-fired power plants and rejected from the ash classifying process,remains unused due to its high carbon content and large particle size (>45μm).But it is thought that the rejected ash may have potential uses in chemical stabilization/solidification (S/S) processes which need relatively lower strengths and a lower chemical reactivity.Flue Gas Desulphurisation (FGD) sludge is a by-product of air pollution control equipment in coal fired power plants whose chemical composition is mainly gypsum.As there is no effective usage of both of these two materials,it is of interest to research on the possible activation of rFA using FGD.This paper presents experimental results of a study on the properties of rFA activated by the FGD in rFA-cement pastes.Different percentages of FGD were added into the mix to study the effects of the FGD on the reaction of the rFA blended cement pastes.The results show that FGD takes effect as an activator only at late curing ages.Adding Ca(OH) 2 enhances the effect of FGD on activating the hydration of rFA.Also,10% FGD by weight of rFA is the optimal addition in the rFA-cement pastes.The results of the compressive strength measurements correlate well with the porosity results.展开更多
The feasibility of utilization of flue gas desulfurization （FGD） gypsum and Class-C fly ash （CFA） to prepare CFA-based geopolymer were studied. The results showed that geopolymer made from 90% CFA and 10% FGD gyps...The feasibility of utilization of flue gas desulfurization （FGD） gypsum and Class-C fly ash （CFA） to prepare CFA-based geopolymer were studied. The results showed that geopolymer made from 90% CFA and 10% FGD gypsum （FGDG） which was thermally treated at 800 ℃ for 1 h obtained the better compressive strength of 37.0 MPa. The micro characteristics and structures of the geopolymer samples of CFA and CFA-FGDG were tested by XRD, FT-IR, and SEM-EDXA after these samples cured at 75 ℃ for 8 h followed by 23 ℃ for 28 d. Both the geopolymer samples of CFA and CFA-FGDG have significant asymmetric stretching of A1-O/Si-O bonds and Si-O-Si / Si-O-A1 bending band. In geopolymer sample of CFA-FGDG, a small quantity of lathy products probably being the ettringite wrapped over the spherical fly ash particle, and the concentration of sulfur is much more than that in geopolymer sample of CFA. It is indicated that FGD gypsum may react during alkali-activated and geopolymeric process.展开更多
Among the technologies to control SO2 emission from coal-fired boilers, the dry flue gas desulphurization (FGD) method, with appropriate modifications, has been identified as a candidate for realizing high SO2 removal...Among the technologies to control SO2 emission from coal-fired boilers, the dry flue gas desulphurization (FGD) method, with appropriate modifications, has been identified as a candidate for realizing high SO2 removal efficiency to meet both technical and economic requirements, and for making the best quality byproduct gypsum as a useful additive for improving alkali soil. Among the possible modifications two major factors have been selected for study: (1) favorable chemical reaction kinetics at elevated temperatures and the sorbent characteristics; (2) enhanced diffusion of SO2 to the surface and within the pores of sorbent particles that are closely related to gas-solid two-phase flow patterns caused by flue gas and sorbent particles in the reactor. To achieve an ideal pore structure, a sorbent was prepared through hydration reaction by mixing lime and fly ash collected from bag house of power plants to form a slurry, which was first dewatered and then dried. The dry sorbent was found capable of rapid conversion of 70% of its calcium content at 700℃, reaching a desulphurization efficiency of over 90% at a Ca/S ratio of 1.3. Experiments confirmed that the diffusion effect of SO2 is an important factor and that gas-solid two-phase flow plays a key role to mixing and contact between SO2 and sorbent particles. For designing the FDG reactor, a new theoretical drag model was developed by combination of CFD with the Energy Minimization Multi-Scale (EMMS) theory for dense fluidi-zation systems. This new drag model was first verified by comparing calculated and measured drag values, and was then implemented in simulation of gas-solid two-phase flow in two circulating fluidized beds with different sizes and flow parameters. One riser has diameter and height of 0.15 m×3m and another one 0.2m×14.2m. Their superficial gas velocities are 4 and 5.2 m·s-1, respectively, and the circulating rate 53 and 489 kg·(m-2·s-1). FCC particles were used in both cases. The results show that not only the static pressure drop along the riser height, but also radial distributions of particle volume fraction have been very well predicted in comparison with experiments. The new drag model is expected to shed more light on the further improvement of SO2 diffusion to solid sorbent and optimization of reactor structure.展开更多
文摘Low-grade fly ash (rejected fly ash,rFA),a significant portion of the pulverized fuel ash (PFA) produced from coal-fired power plants and rejected from the ash classifying process,remains unused due to its high carbon content and large particle size (>45μm).But it is thought that the rejected ash may have potential uses in chemical stabilization/solidification (S/S) processes which need relatively lower strengths and a lower chemical reactivity.Flue Gas Desulphurisation (FGD) sludge is a by-product of air pollution control equipment in coal fired power plants whose chemical composition is mainly gypsum.As there is no effective usage of both of these two materials,it is of interest to research on the possible activation of rFA using FGD.This paper presents experimental results of a study on the properties of rFA activated by the FGD in rFA-cement pastes.Different percentages of FGD were added into the mix to study the effects of the FGD on the reaction of the rFA blended cement pastes.The results show that FGD takes effect as an activator only at late curing ages.Adding Ca(OH) 2 enhances the effect of FGD on activating the hydration of rFA.Also,10% FGD by weight of rFA is the optimal addition in the rFA-cement pastes.The results of the compressive strength measurements correlate well with the porosity results.
基金Funded by the National Natural Science Foundation of China(Nos.51208370,51172164)the Specialized Research Fund for the Doctoral Program of Higher Education(Nos.20110072120046,20090072110010)of China
文摘The feasibility of utilization of flue gas desulfurization （FGD） gypsum and Class-C fly ash （CFA） to prepare CFA-based geopolymer were studied. The results showed that geopolymer made from 90% CFA and 10% FGD gypsum （FGDG） which was thermally treated at 800 ℃ for 1 h obtained the better compressive strength of 37.0 MPa. The micro characteristics and structures of the geopolymer samples of CFA and CFA-FGDG were tested by XRD, FT-IR, and SEM-EDXA after these samples cured at 75 ℃ for 8 h followed by 23 ℃ for 28 d. Both the geopolymer samples of CFA and CFA-FGDG have significant asymmetric stretching of A1-O/Si-O bonds and Si-O-Si / Si-O-A1 bending band. In geopolymer sample of CFA-FGDG, a small quantity of lathy products probably being the ettringite wrapped over the spherical fly ash particle, and the concentration of sulfur is much more than that in geopolymer sample of CFA. It is indicated that FGD gypsum may react during alkali-activated and geopolymeric process.
文摘Among the technologies to control SO2 emission from coal-fired boilers, the dry flue gas desulphurization (FGD) method, with appropriate modifications, has been identified as a candidate for realizing high SO2 removal efficiency to meet both technical and economic requirements, and for making the best quality byproduct gypsum as a useful additive for improving alkali soil. Among the possible modifications two major factors have been selected for study: (1) favorable chemical reaction kinetics at elevated temperatures and the sorbent characteristics; (2) enhanced diffusion of SO2 to the surface and within the pores of sorbent particles that are closely related to gas-solid two-phase flow patterns caused by flue gas and sorbent particles in the reactor. To achieve an ideal pore structure, a sorbent was prepared through hydration reaction by mixing lime and fly ash collected from bag house of power plants to form a slurry, which was first dewatered and then dried. The dry sorbent was found capable of rapid conversion of 70% of its calcium content at 700℃, reaching a desulphurization efficiency of over 90% at a Ca/S ratio of 1.3. Experiments confirmed that the diffusion effect of SO2 is an important factor and that gas-solid two-phase flow plays a key role to mixing and contact between SO2 and sorbent particles. For designing the FDG reactor, a new theoretical drag model was developed by combination of CFD with the Energy Minimization Multi-Scale (EMMS) theory for dense fluidi-zation systems. This new drag model was first verified by comparing calculated and measured drag values, and was then implemented in simulation of gas-solid two-phase flow in two circulating fluidized beds with different sizes and flow parameters. One riser has diameter and height of 0.15 m×3m and another one 0.2m×14.2m. Their superficial gas velocities are 4 and 5.2 m·s-1, respectively, and the circulating rate 53 and 489 kg·(m-2·s-1). FCC particles were used in both cases. The results show that not only the static pressure drop along the riser height, but also radial distributions of particle volume fraction have been very well predicted in comparison with experiments. The new drag model is expected to shed more light on the further improvement of SO2 diffusion to solid sorbent and optimization of reactor structure.
