The previous work found that the additive kaolin could scavenge not only sodium(Na)but also calcium(Ca)and magnesium(Mg),which is the important ash fluxing agents in low rank coal combustion.Such scavenging effects of...The previous work found that the additive kaolin could scavenge not only sodium(Na)but also calcium(Ca)and magnesium(Mg),which is the important ash fluxing agents in low rank coal combustion.Such scavenging effects of kaolin on fine ash formation were studied in the present work.A typical Zhundong coal and its blends with kaolin at dosages of 1,2 and 4 wt%were combusted in an electrically heated drop tube furnace(DTF)at 1300℃.The fine ashes generated were collected and size segregated by a low pressure impactor(LPI).The morphology and chemical composition of fine ash were analyzed by scanning electron microscopy equipped with an energydispersive spectrometer(SEM-EDS).In addition,char/ash particles were sampled at various positions of DTF to elucidate how kaolin additive affected the fine ash formation process.The results further showed that apart from the scavenging of volatile Na,kaolin additive could also strongly scavenge the refractory Ca,Mg and Fe in the fine ash during Zhundong coal combustion,which transformed the sintered particles with irregular shape into melted spherical particles,and finally resulted in the considerable decrease of these elements in both PM_(0.4)and PM_(0.4-10)by melting and agglomeration.The close contacts between kaolin particles and coal resulted from physically mixing were a key factor responsible for the reaction of kaolin with the refractory Ca,Mg and Fe.展开更多
Coal gasification technology is a prominent technology in the coal chemical industry and serves as the fundamental basis for various process industries,including coal-based chemicals,coal-based liquid fuels,Integrated...Coal gasification technology is a prominent technology in the coal chemical industry and serves as the fundamental basis for various process industries,including coal-based chemicals,coal-based liquid fuels,Integrated Gasification Combined Cycle(IGCC) power generation,multi-generation systems,hydrogen production,and fuel cells.The gasification process generates significant quantities of ash residue,with annual emissions exceeding tens of millions of tons and accumulation reaching hundreds of millions of tons.Accordingly,there is an urgent need to investigate methods for its disposal.The combustion of gasified fine ash(GFA) was conducted in a tube furnace,and the conventional shrinking core model was modified to accurately predict the combustion behaviors at different temperatures(900℃-1500℃).We divided the reaction temperatures into three ranges,which is defined as unmelted combustion(TFT) and mixed combustion(DTFT),the surface ash of GFA grains fell off,and the residual carbon and gas-phase reactants were nearly no longer affected by the diffusion resistance,thus significantly accelerated the reaction of internal residual carbon.In order to predict the melt combustion process more accurately,the time term of the shrinkage core model(SCM) is modified,and the effective diffusion coefficient of T>FT is defined.展开更多
The aim and scope of the present study were to determine the efficacy of UFFA in evaluating the workability,static and dynamic stabilization properties,retention period,and slump loss of SCC systems in their fresh sta...The aim and scope of the present study were to determine the efficacy of UFFA in evaluating the workability,static and dynamic stabilization properties,retention period,and slump loss of SCC systems in their fresh state,as well as their compressive strength at various ages.Microstructure(SEM and XRD)of blended SCC systems were studied.Also,the thermogravimetry behavior of blended SCC specimens were researched.According to the evaluated results,incorporating up to 20%UFFA into fresh concrete improved its performance due to its engineered fine particle size and spherical geometry,both of which contribute to the enhancement of characteristics.Blends of 25%and 30%of UFFA show effect on the water-binder ratio and chemical enhancer dosage,resulting in a loss of homogeneity in fresh SCC systems.The reduced particle size,increased amorphous content,and increased surface area all contribute to the pozzolanic reactivity of the early and later ages,resulting in denser packing and thus an increase in compressive strength.The experimental results indicate that UFFA enhances the properties of SCC in both its fresh and hardened states,which can be attributed to the particles’fineness and their relative effect on SCC.展开更多
The disposal of waste has become an environmental issue due to the limited available landfilling space. This paper aims to compare the characteristics of hydrated lime with fine sewage sludge ash (FSSA) and coal fly a...The disposal of waste has become an environmental issue due to the limited available landfilling space. This paper aims to compare the characteristics of hydrated lime with fine sewage sludge ash (FSSA) and coal fly ash (CFA). Multiple techniques, X-ray fluorescence (XRF), X-ray diffraction (XRD), the Fourier transform infrared (FTIR), compressive strengths, thermophysical properties, and setting time were used to assess the physicochemical characteristics of the lime-based materials. X-ray fluorescence and X-ray diffraction were used to determine the chemical composition and phases of ashes, lime and binders. The results showed that the chemical composition of ashes is similar to that of cement. Besides glass, the main minerals identified in CFA and FSSA are quartz (SiO<sub>2</sub>) and anhydrite (CaSO<sub>4</sub>). Moreover, calcium aluminium oxide (Ca<sub>3</sub>Al<sub>2</sub>O<sub>6</sub>) was detected for CFA and phosphorus calcium silicate (Ca<sub>2</sub>SiO<sub>4</sub>-Ca<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>) for FSSA and minor phases were detected for both. FTIR measurements were carried out to characterize the inorganics components of different samples. Compressive strengths of mortars with different formulations have shown that both have a long-term positive effect which might be related to a pozzolanic activity. For the CFA the L<sub>3</sub> binder consisting of 60% of coal fly ash and 40% lime has a higher compressive strength than the others while for the FSSA the L<sub>4</sub> binder consisting of 80% fine ash and 20% lime has a higher compressive strength than the others. Both binders setting start times are greater than that of cement but shorter than that of lime. The study of the thermophysical properties of binders shows that they have a higher thermal resistance than cement mortar. Moreover, binders heat up less quickly because of their low effusivity compared to cement. Lime-based materials system could be a promising option to both relieve the waste disposal pressure and provide a potential sustainable construction material.展开更多
To decrease the cement and SF content of RPC by using ultra-fine fly ash （UFFA） and steel slag powder （SS）, the effect of these mineral admixtures on compressive strength of RPC were investigated. The experimental...To decrease the cement and SF content of RPC by using ultra-fine fly ash （UFFA） and steel slag powder （SS）, the effect of these mineral admixtures on compressive strength of RPC were investigated. The experimental results indicate that the utilization of UFFA and SS in RPC is feasible and has prominent mechanical performance. The microstructure analysis （SEM and TG-DTG-DSC） demonstrated that the excellent mechanical properties of RPC containing SS and UFFA were mainly attributed to the sequential hydration filling effect of the compound system.展开更多
The effect of grinding on the chemical and physical properties of rice husk ash was studied. Four rice husk ashes with different finenesses, i.e. coarse original rice husk ash （RHA0）, RHA1, RHA2, and RHA3 were used ...The effect of grinding on the chemical and physical properties of rice husk ash was studied. Four rice husk ashes with different finenesses, i.e. coarse original rice husk ash （RHA0）, RHA1, RHA2, and RHA3 were used for the study. Ordinary Portland cement （OPC） was partially replaced with rice husk ash at 20% by weight of binder. The water to binder ratio （W/B） of the mortar was maintained at 110%±5% with flow table test. Specific gravity, fineness, chemical properties, compressive strength, and porosity test of mortars were determined. The differences in chemical composition of the rice husk ashes with different finenesses from the same batch are small. The use of RHA3 produces the mortars with good strength and low porosity. The strength of the mortar improves with partial replacement of RHA3 in comparison with normal coarse rice husk ash. The use of RHA3 results in a strong and dense mortar, which is due to the better dispersion and filling effect, as well as an increase in the pozzolanic reaction.展开更多
The aim of this study was to assess the performance of the combustion process during medical waste incineration by studying physical properties of the ashes produced. Combustion characteristics data including maximum ...The aim of this study was to assess the performance of the combustion process during medical waste incineration by studying physical properties of the ashes produced. Combustion characteristics data including maximum temperatures, total weight of waste loaded, weight of ashes, weight reduction, sieve analysis and particle size distribution were determined experimentally. The test runs were conducted in a newly installed incinerator at Temeke district hospital. The average maximum temperatures achieved in the primary chamber was 397.8℃and 839℃ for secondary chamber with average incineration cycle time of 99 minutes. These temperatures were lower compared to the design temperatures of 650℃ and 950℃ as a result of loading wet waste. The ash samples were collected under the incinerator grate by randomly sampling the ashes for each run after weighing the total ash. The particle size distribution of ashes observed was not uniform due to presence of non-combustible materials in the sharps waste. However, the fineness modulus ranged between 2.0 and 4.0, which is in the acceptable range. From the above results it was concluded that, the incinerator performance was high in terms of the parameters assessed. To improve the incinerator performance further, it was recommended that the medical waste should be stored in a dry place away from rain.展开更多
气流床气化过程产生的煤气化细渣(gasification fine slag,GFS)含碳量较高,已有的资源化利用均包含脱碳处理过程,而循环流化床(circulating fluidized bed,CFB)燃烧技术具有良好的燃料适应性,但业内普遍认为在煤气化细渣(以下简称气化细...气流床气化过程产生的煤气化细渣(gasification fine slag,GFS)含碳量较高,已有的资源化利用均包含脱碳处理过程,而循环流化床(circulating fluidized bed,CFB)燃烧技术具有良好的燃料适应性,但业内普遍认为在煤气化细渣(以下简称气化细渣)形成的过程中,残碳被包裹在熔融玻璃体内,因而在CFB燃烧温度(约900℃)下,很难燃尽。为了探寻CFB锅炉高效燃尽气流床气化细渣的可行性,先后研究了细渣中碳与灰的赋存形态、碳反应活性及其在流化床条件下的燃烧特性。扫描电镜分析结果及细渣破碎前后烧失试验对比结果,揭示了多孔残碳颗粒同灰颗粒分离的微观形貌,且研磨前后细渣失重之差仅为2.86%,进而明确了气化细渣中的残碳主要存在于熔融无机物之外,即“灰炭分离”赋存形态;热重分析(thermogravimetric analysis,TGA)及马弗炉中的燃尽试验证明了在CFB中温燃烧条件下可以实现气化细渣的燃尽。由于气化细渣属于Geldart分类法中的A类粒子,采用传统CFB的常用流化风速无法为其提供足够的系统停留时间,故无法实现细粒度气化细渣在CFB炉中的高效燃烧。根据快速流态化图谱,提出了纯燃气化细渣的低气速细粒子快速流态化(low velocity fine particle fast fluidization,LFFF)‒CFB燃烧技术,选择远低于常规流化风速、稍大于转变速度Utr的流化速度,可显著提高气化细渣在系统内的停留时间;利用一维CFB燃烧模型,对气化细渣在低流化气速下的流动特性及CFB锅炉温度分布进行预测分析。最后,提出了纯燃气化细渣的LFFF燃烧技术,设计了年处理24万t气流床气化细渣的75 t/h CFB锅炉方案。展开更多
基金the National Key Research and Development Program of China(No.2016YFB0600601)National Natural Science Foundation of China(Nos.51676075 and 51520105008).
文摘The previous work found that the additive kaolin could scavenge not only sodium(Na)but also calcium(Ca)and magnesium(Mg),which is the important ash fluxing agents in low rank coal combustion.Such scavenging effects of kaolin on fine ash formation were studied in the present work.A typical Zhundong coal and its blends with kaolin at dosages of 1,2 and 4 wt%were combusted in an electrically heated drop tube furnace(DTF)at 1300℃.The fine ashes generated were collected and size segregated by a low pressure impactor(LPI).The morphology and chemical composition of fine ash were analyzed by scanning electron microscopy equipped with an energydispersive spectrometer(SEM-EDS).In addition,char/ash particles were sampled at various positions of DTF to elucidate how kaolin additive affected the fine ash formation process.The results further showed that apart from the scavenging of volatile Na,kaolin additive could also strongly scavenge the refractory Ca,Mg and Fe in the fine ash during Zhundong coal combustion,which transformed the sintered particles with irregular shape into melted spherical particles,and finally resulted in the considerable decrease of these elements in both PM_(0.4)and PM_(0.4-10)by melting and agglomeration.The close contacts between kaolin particles and coal resulted from physically mixing were a key factor responsible for the reaction of kaolin with the refractory Ca,Mg and Fe.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No.XDA21040602)Youth Innovation Promotion Association,Chinese Academy of Sciences (Grant No.2020150)。
文摘Coal gasification technology is a prominent technology in the coal chemical industry and serves as the fundamental basis for various process industries,including coal-based chemicals,coal-based liquid fuels,Integrated Gasification Combined Cycle(IGCC) power generation,multi-generation systems,hydrogen production,and fuel cells.The gasification process generates significant quantities of ash residue,with annual emissions exceeding tens of millions of tons and accumulation reaching hundreds of millions of tons.Accordingly,there is an urgent need to investigate methods for its disposal.The combustion of gasified fine ash(GFA) was conducted in a tube furnace,and the conventional shrinking core model was modified to accurately predict the combustion behaviors at different temperatures(900℃-1500℃).We divided the reaction temperatures into three ranges,which is defined as unmelted combustion(TFT) and mixed combustion(DTFT),the surface ash of GFA grains fell off,and the residual carbon and gas-phase reactants were nearly no longer affected by the diffusion resistance,thus significantly accelerated the reaction of internal residual carbon.In order to predict the melt combustion process more accurately,the time term of the shrinkage core model(SCM) is modified,and the effective diffusion coefficient of T>FT is defined.
文摘The aim and scope of the present study were to determine the efficacy of UFFA in evaluating the workability,static and dynamic stabilization properties,retention period,and slump loss of SCC systems in their fresh state,as well as their compressive strength at various ages.Microstructure(SEM and XRD)of blended SCC systems were studied.Also,the thermogravimetry behavior of blended SCC specimens were researched.According to the evaluated results,incorporating up to 20%UFFA into fresh concrete improved its performance due to its engineered fine particle size and spherical geometry,both of which contribute to the enhancement of characteristics.Blends of 25%and 30%of UFFA show effect on the water-binder ratio and chemical enhancer dosage,resulting in a loss of homogeneity in fresh SCC systems.The reduced particle size,increased amorphous content,and increased surface area all contribute to the pozzolanic reactivity of the early and later ages,resulting in denser packing and thus an increase in compressive strength.The experimental results indicate that UFFA enhances the properties of SCC in both its fresh and hardened states,which can be attributed to the particles’fineness and their relative effect on SCC.
文摘The disposal of waste has become an environmental issue due to the limited available landfilling space. This paper aims to compare the characteristics of hydrated lime with fine sewage sludge ash (FSSA) and coal fly ash (CFA). Multiple techniques, X-ray fluorescence (XRF), X-ray diffraction (XRD), the Fourier transform infrared (FTIR), compressive strengths, thermophysical properties, and setting time were used to assess the physicochemical characteristics of the lime-based materials. X-ray fluorescence and X-ray diffraction were used to determine the chemical composition and phases of ashes, lime and binders. The results showed that the chemical composition of ashes is similar to that of cement. Besides glass, the main minerals identified in CFA and FSSA are quartz (SiO<sub>2</sub>) and anhydrite (CaSO<sub>4</sub>). Moreover, calcium aluminium oxide (Ca<sub>3</sub>Al<sub>2</sub>O<sub>6</sub>) was detected for CFA and phosphorus calcium silicate (Ca<sub>2</sub>SiO<sub>4</sub>-Ca<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>) for FSSA and minor phases were detected for both. FTIR measurements were carried out to characterize the inorganics components of different samples. Compressive strengths of mortars with different formulations have shown that both have a long-term positive effect which might be related to a pozzolanic activity. For the CFA the L<sub>3</sub> binder consisting of 60% of coal fly ash and 40% lime has a higher compressive strength than the others while for the FSSA the L<sub>4</sub> binder consisting of 80% fine ash and 20% lime has a higher compressive strength than the others. Both binders setting start times are greater than that of cement but shorter than that of lime. The study of the thermophysical properties of binders shows that they have a higher thermal resistance than cement mortar. Moreover, binders heat up less quickly because of their low effusivity compared to cement. Lime-based materials system could be a promising option to both relieve the waste disposal pressure and provide a potential sustainable construction material.
基金Funded by the Guide Project in National Science & Technology Pillar Program during the 10th Five-Year Plan Period (2003BA652C)
文摘To decrease the cement and SF content of RPC by using ultra-fine fly ash （UFFA） and steel slag powder （SS）, the effect of these mineral admixtures on compressive strength of RPC were investigated. The experimental results indicate that the utilization of UFFA and SS in RPC is feasible and has prominent mechanical performance. The microstructure analysis （SEM and TG-DTG-DSC） demonstrated that the excellent mechanical properties of RPC containing SS and UFFA were mainly attributed to the sequential hydration filling effect of the compound system.
基金the Commission on Higher Education (MUA) of Thailandthe Sustainable Infrastructure Research and Development Center of Khon Kaen University (SIRDC)Department of Civil Engineering of Rajamangala University of Technology Phra Nakhon (RMUTP)
文摘The effect of grinding on the chemical and physical properties of rice husk ash was studied. Four rice husk ashes with different finenesses, i.e. coarse original rice husk ash （RHA0）, RHA1, RHA2, and RHA3 were used for the study. Ordinary Portland cement （OPC） was partially replaced with rice husk ash at 20% by weight of binder. The water to binder ratio （W/B） of the mortar was maintained at 110%±5% with flow table test. Specific gravity, fineness, chemical properties, compressive strength, and porosity test of mortars were determined. The differences in chemical composition of the rice husk ashes with different finenesses from the same batch are small. The use of RHA3 produces the mortars with good strength and low porosity. The strength of the mortar improves with partial replacement of RHA3 in comparison with normal coarse rice husk ash. The use of RHA3 results in a strong and dense mortar, which is due to the better dispersion and filling effect, as well as an increase in the pozzolanic reaction.
文摘The aim of this study was to assess the performance of the combustion process during medical waste incineration by studying physical properties of the ashes produced. Combustion characteristics data including maximum temperatures, total weight of waste loaded, weight of ashes, weight reduction, sieve analysis and particle size distribution were determined experimentally. The test runs were conducted in a newly installed incinerator at Temeke district hospital. The average maximum temperatures achieved in the primary chamber was 397.8℃and 839℃ for secondary chamber with average incineration cycle time of 99 minutes. These temperatures were lower compared to the design temperatures of 650℃ and 950℃ as a result of loading wet waste. The ash samples were collected under the incinerator grate by randomly sampling the ashes for each run after weighing the total ash. The particle size distribution of ashes observed was not uniform due to presence of non-combustible materials in the sharps waste. However, the fineness modulus ranged between 2.0 and 4.0, which is in the acceptable range. From the above results it was concluded that, the incinerator performance was high in terms of the parameters assessed. To improve the incinerator performance further, it was recommended that the medical waste should be stored in a dry place away from rain.
文摘气流床气化过程产生的煤气化细渣(gasification fine slag,GFS)含碳量较高,已有的资源化利用均包含脱碳处理过程,而循环流化床(circulating fluidized bed,CFB)燃烧技术具有良好的燃料适应性,但业内普遍认为在煤气化细渣(以下简称气化细渣)形成的过程中,残碳被包裹在熔融玻璃体内,因而在CFB燃烧温度(约900℃)下,很难燃尽。为了探寻CFB锅炉高效燃尽气流床气化细渣的可行性,先后研究了细渣中碳与灰的赋存形态、碳反应活性及其在流化床条件下的燃烧特性。扫描电镜分析结果及细渣破碎前后烧失试验对比结果,揭示了多孔残碳颗粒同灰颗粒分离的微观形貌,且研磨前后细渣失重之差仅为2.86%,进而明确了气化细渣中的残碳主要存在于熔融无机物之外,即“灰炭分离”赋存形态;热重分析(thermogravimetric analysis,TGA)及马弗炉中的燃尽试验证明了在CFB中温燃烧条件下可以实现气化细渣的燃尽。由于气化细渣属于Geldart分类法中的A类粒子,采用传统CFB的常用流化风速无法为其提供足够的系统停留时间,故无法实现细粒度气化细渣在CFB炉中的高效燃烧。根据快速流态化图谱,提出了纯燃气化细渣的低气速细粒子快速流态化(low velocity fine particle fast fluidization,LFFF)‒CFB燃烧技术,选择远低于常规流化风速、稍大于转变速度Utr的流化速度,可显著提高气化细渣在系统内的停留时间;利用一维CFB燃烧模型,对气化细渣在低流化气速下的流动特性及CFB锅炉温度分布进行预测分析。最后,提出了纯燃气化细渣的LFFF燃烧技术,设计了年处理24万t气流床气化细渣的75 t/h CFB锅炉方案。
