A thermogravimetric method under constant temperature replacing the beginning inert gas with burning air was established in this study for determining the combustion kinetics of single char particle. The combustion pr...A thermogravimetric method under constant temperature replacing the beginning inert gas with burning air was established in this study for determining the combustion kinetics of single char particle. The combustion process of three types of coals, Fujian Longyan coal, Fujian Yong’an coal and Shandong coal, with diameter of 3.0—4.5 mm, in thermobalance under 900℃ was discussed using the familiar shrinking-core model.While the combustion of single char approached the end, the outside and the ash layer diffusion resistances tend to be zero as the reaction resistance dominated in the total resistance of combustion.Therefore, at this stage the inherent oxidation reaction constant (k_R) of the above char samples were estimated by analyzing the total resistance of combustion.The good agreement of combustion reaction rate between data determined in this study and calculated values obtained from reference in the drop tube furnace system, implied that the inherent oxidation reaction constant (k_R) determined by the thermogravimetric method under constant temperature was satisfactory and valuable. The gas diffusion through the ash layer of char particle during combustion process was discussed also. At the ash layer thickness half the char radius, the ash layer resistance in the combustion process reached a maximum value, at which the total resistance of combustion,1/K,was less than 25 s·m -1 and would be close to the reaction resistance,1/k_C,approaching the end of combustion. So the effects of gas diffusion resistance through ash layer on char combustion process could be ignored during the whole combustion process.展开更多
Recognizing the nature and formation progress of the ash deposits is essential to resolve the deposition problem hindering the wide application of large-scale biomass-fired boilers.Therefore,the ash deposits in the su...Recognizing the nature and formation progress of the ash deposits is essential to resolve the deposition problem hindering the wide application of large-scale biomass-fired boilers.Therefore,the ash deposits in the superheaters of a 220 t/h biomass-fired CFB boiler were studied,including the platen(PS),the high-temperature(HTS),the upper and the lower low-temperature superheaters(LTS).The results showed that the deposits in the PSs and HTSs were thin(several millimeters)and compact,consisting of a yellow outer layer and snow-white inner layer near the tube surface.The deposits in the upper LTS appeared to be toughly sintered ceramic,while those in the lower LTS were composed of dispersive coarse ash particles with an unsintered surface.Detailed characterization of the cross-section and the initial layers in the deposits revealed that the dominating compositions in both the PSs and the HTSs were Cl and K(approximately 70%)in the form of KCl.Interestingly,the cross-section of the deposition in the upper LTS exhibited a unique lamellar structure with a major composition of Ca and S.The contents of Ca and Si increased from approximately 10%to approximately 60%in the deposits from the high temperature surfaces to the low temperature ones.It was concluded that the vaporized mineral matter such as KCl played the most important role in the deposition progress in the PS and the HTS.In addition,although the condensation of KCl in the LTSs also happened,the deposition of ash particles played a more important role.展开更多
To investigate the relationship between volcanic activity and sediment record on regional and temporal scales,158 surface sediment samples were collected from the East China Sea Shelf to the northern Okinawa Trough (O...To investigate the relationship between volcanic activity and sediment record on regional and temporal scales,158 surface sediment samples were collected from the East China Sea Shelf to the northern Okinawa Trough (OT),and two cores recovered in the northern and southern OT,respectively.Mineralogy,grain-size,and geochemical analyses of those samples show that:1) volcanic glass,volcanic-type pyroxene,hypersthenes,and magnetite increase in sediment influenced by volcanic activity;2) sediment grain sizes (and also silt content) increase in ash layers;and 3) the contents of Na2O and Zr are higher,while terrigenous elements,e.g.,TFe2O3 and K2O,and biogenous compositions,e.g.,CaO and Sr,are relatively lower in ash layers than those of non-ash layers.The distribution of volcanic ash has three distinguishing characteristics:1) volcanic ash is more abundant in the northern and central OT than the southern OT;2) volcanic ash increases from continental shelf to the trough;3) the sediment during the last 12 000 a suggests stronger volcanic events than during 15 000-12 000 a.The eruptive locations,frequency,and volume of calderas are among the most important factors controlling the distributions of volcanic ash.In addition,the main Kuroshio warm current that extends northward probably impeded the diffusion of volcanic ash to the west and south in the OT.However,a southward current probably carried some volcanic ash toward southern OT.展开更多
[Objectives] The aim was to determine the moisture,ash and extract contents in Leontopodium franchetii Beauv. from different localities. [Methods] The contents of moisture,total ash,acid-insoluble ash and extract in L...[Objectives] The aim was to determine the moisture,ash and extract contents in Leontopodium franchetii Beauv. from different localities. [Methods] The contents of moisture,total ash,acid-insoluble ash and extract in L. franchetii from different localities were determined according to the methods described in Chinese Pharmacopoeia( 2015 Edition). [Results] In the 10 samples,the contents of moisture were all less than or equal to 15. 0%; the contents of total ash were all below 12. 0%; and the contents of acid-insoluble ash were all less than 3. 0%. The contents of water-soluble extract( by cold-soaked extraction method) in the samples were all below 12. 0% except those from Hongyuan Prairie of Sichuan Province and Xinglong Mountain in Lanzhou City,Gansu Province. [Conclusions]The contents of the four indicators measured in this experiment varied by small margins,indicating that the quality was relatively stable. This study provides theoretical data for the revision of the quality standards for L. franchetii.展开更多
文摘A thermogravimetric method under constant temperature replacing the beginning inert gas with burning air was established in this study for determining the combustion kinetics of single char particle. The combustion process of three types of coals, Fujian Longyan coal, Fujian Yong’an coal and Shandong coal, with diameter of 3.0—4.5 mm, in thermobalance under 900℃ was discussed using the familiar shrinking-core model.While the combustion of single char approached the end, the outside and the ash layer diffusion resistances tend to be zero as the reaction resistance dominated in the total resistance of combustion.Therefore, at this stage the inherent oxidation reaction constant (k_R) of the above char samples were estimated by analyzing the total resistance of combustion.The good agreement of combustion reaction rate between data determined in this study and calculated values obtained from reference in the drop tube furnace system, implied that the inherent oxidation reaction constant (k_R) determined by the thermogravimetric method under constant temperature was satisfactory and valuable. The gas diffusion through the ash layer of char particle during combustion process was discussed also. At the ash layer thickness half the char radius, the ash layer resistance in the combustion process reached a maximum value, at which the total resistance of combustion,1/K,was less than 25 s·m -1 and would be close to the reaction resistance,1/k_C,approaching the end of combustion. So the effects of gas diffusion resistance through ash layer on char combustion process could be ignored during the whole combustion process.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.51806075 and 51922045),and the Analytical and Testing Center of Huazhong University of Science and Technology.
文摘Recognizing the nature and formation progress of the ash deposits is essential to resolve the deposition problem hindering the wide application of large-scale biomass-fired boilers.Therefore,the ash deposits in the superheaters of a 220 t/h biomass-fired CFB boiler were studied,including the platen(PS),the high-temperature(HTS),the upper and the lower low-temperature superheaters(LTS).The results showed that the deposits in the PSs and HTSs were thin(several millimeters)and compact,consisting of a yellow outer layer and snow-white inner layer near the tube surface.The deposits in the upper LTS appeared to be toughly sintered ceramic,while those in the lower LTS were composed of dispersive coarse ash particles with an unsintered surface.Detailed characterization of the cross-section and the initial layers in the deposits revealed that the dominating compositions in both the PSs and the HTSs were Cl and K(approximately 70%)in the form of KCl.Interestingly,the cross-section of the deposition in the upper LTS exhibited a unique lamellar structure with a major composition of Ca and S.The contents of Ca and Si increased from approximately 10%to approximately 60%in the deposits from the high temperature surfaces to the low temperature ones.It was concluded that the vaporized mineral matter such as KCl played the most important role in the deposition progress in the PS and the HTS.In addition,although the condensation of KCl in the LTSs also happened,the deposition of ash particles played a more important role.
基金Supported by the Pilot Project of the National Knowledge Innovation Program of the Chinese Academy of Science (No. KZCX2-YW-221)the National Natural Science Foundation of China (No. 40506016,90411014 and 40976026)National Basic Research Program of China (No. 2007CB815903)
文摘To investigate the relationship between volcanic activity and sediment record on regional and temporal scales,158 surface sediment samples were collected from the East China Sea Shelf to the northern Okinawa Trough (OT),and two cores recovered in the northern and southern OT,respectively.Mineralogy,grain-size,and geochemical analyses of those samples show that:1) volcanic glass,volcanic-type pyroxene,hypersthenes,and magnetite increase in sediment influenced by volcanic activity;2) sediment grain sizes (and also silt content) increase in ash layers;and 3) the contents of Na2O and Zr are higher,while terrigenous elements,e.g.,TFe2O3 and K2O,and biogenous compositions,e.g.,CaO and Sr,are relatively lower in ash layers than those of non-ash layers.The distribution of volcanic ash has three distinguishing characteristics:1) volcanic ash is more abundant in the northern and central OT than the southern OT;2) volcanic ash increases from continental shelf to the trough;3) the sediment during the last 12 000 a suggests stronger volcanic events than during 15 000-12 000 a.The eruptive locations,frequency,and volume of calderas are among the most important factors controlling the distributions of volcanic ash.In addition,the main Kuroshio warm current that extends northward probably impeded the diffusion of volcanic ash to the west and south in the OT.However,a southward current probably carried some volcanic ash toward southern OT.
基金Supported by National Key Technology Research and Development Program(2015BAC05B02)Fundamental Research Funds for the Central Universities(2018NZD10)
文摘[Objectives] The aim was to determine the moisture,ash and extract contents in Leontopodium franchetii Beauv. from different localities. [Methods] The contents of moisture,total ash,acid-insoluble ash and extract in L. franchetii from different localities were determined according to the methods described in Chinese Pharmacopoeia( 2015 Edition). [Results] In the 10 samples,the contents of moisture were all less than or equal to 15. 0%; the contents of total ash were all below 12. 0%; and the contents of acid-insoluble ash were all less than 3. 0%. The contents of water-soluble extract( by cold-soaked extraction method) in the samples were all below 12. 0% except those from Hongyuan Prairie of Sichuan Province and Xinglong Mountain in Lanzhou City,Gansu Province. [Conclusions]The contents of the four indicators measured in this experiment varied by small margins,indicating that the quality was relatively stable. This study provides theoretical data for the revision of the quality standards for L. franchetii.
