Completely weathered phyllite(CWP)soil is a kind of special soil with high swell potential,while red clay is a special soil with high shrinkage.This means that these two kinds of special soils are usually not suitable...Completely weathered phyllite(CWP)soil is a kind of special soil with high swell potential,while red clay is a special soil with high shrinkage.This means that these two kinds of special soils are usually not suitable for direct use as subgrade fill.To reduce the swell index of the CWP soil and the shrinkage of red clay at the same time,it was proposed to blend the CWP soil with red clay to improve their basic characteristics.A series of swell index tests and dry-wet cycle tests of the blended soils have been carried out at varying blending ratios,compaction coefficients and moisture contents.The test results show that the free swell index of the blended soil decreases with the increase of red clay,moisture content and compaction coefficient,respectively.The fissure density of the blended soil first decreases and then increases with the blending ratio,with the lowest being zero when the blending ratio is ranging from 20%to 40%.Through particle microscopic analysis and elemental composition analysis,it is found that the neutralization effect,the dilution effect of swell minerals,and the partition effect of coarse particles play an important role in restraining expansion and shrinkage deformation of the blended soil.Based on the liquid limit requirement of Chinese Railway Design Code(TB 10001-2016),the optimal blending ratio of red clay has been proposed to be 50%.Compared with the CWP soil,the free load swell index of the blended soil is reduced by 45.0%and the fissure density is reduced by 99.3%compared with that of red clay.Therefore,it is feasible to improve the CWP soil by blending it with red clay at an optimal ratio of 50%by using the neutralization effect of the expansion of CWP and shrinkage of red clay.展开更多
The utilization of powdery semi-coke as a power fuel in pulverized coal-fired power plants has become a new and potential technique to consume the excess powdery semi-coke.The characteristic of low volatile results in...The utilization of powdery semi-coke as a power fuel in pulverized coal-fired power plants has become a new and potential technique to consume the excess powdery semi-coke.The characteristic of low volatile results in poor combustion performance and high NO_(x) emission,and to co-fire with bituminous coal is a practical strategy to address this problem.However,the co-combustion characteristics and the inherent interaction between semi-coke and coal remain insufficiently understood.In addition,the influences of secondary air arrangement,the boiler operation load,and the fuel type on co-combustion process are still unclear,which is urgent to be further explored.In the present study,experiments and numerical simulations were jointly utilized to inquire into the co-combustion behaviors and NO_(x) emission features of semi-coke and coal.The results demonstrated that the"out-furnace method"was a suitable choice for small-capacity boiler when the proportion of semi-coke was 33%,due to the limited combinations of the semi-coke injection position.It was recommended that semi-coke was preferred to be injected from the middle layers of the furnace under the"in-furnace method"to improve the overall co-combustion performance.The critical value of the separated over fire air ratio in this study was 27.5%,over which a slight drop of carbon content in fly ash could come about.Moreover,the elevation in the proportion of separated over fire air gave rise to the significant decline of NO_(x) concentration.The constricted secondary air arrangement was preferred to be employed due to the high boiler efficiency.The separated over fire air and the surrounding air needed to maintain a wide-open degree to prevent the increase of NO_(x) emissions and the coking of nozzles.For the load reduction regulation method adopted in this study,the NO_(x) concentration first rose and then dropped,while the burnout ratio decreased obviously as the operation load was reduced.Different combinations of coal and semi-coke generated significant influences on co-combustion behaviors within the furnace.The NO_(x )generated by high-volatile fuel (bituminous coal) combustion was mainly affected by volatile-N,while the NO_(x )generated by low-volatile fuel (semi-coke) was mainly impacted by char-N.This study is of guiding significance for the efficient and clean utilization and beneficial to the large-scale application of powder semi-coke in power plants.展开更多
基金This work is supported by the National Natural Science Foundation of China(Grant Nos.52068027,51668018,51768021).
文摘Completely weathered phyllite(CWP)soil is a kind of special soil with high swell potential,while red clay is a special soil with high shrinkage.This means that these two kinds of special soils are usually not suitable for direct use as subgrade fill.To reduce the swell index of the CWP soil and the shrinkage of red clay at the same time,it was proposed to blend the CWP soil with red clay to improve their basic characteristics.A series of swell index tests and dry-wet cycle tests of the blended soils have been carried out at varying blending ratios,compaction coefficients and moisture contents.The test results show that the free swell index of the blended soil decreases with the increase of red clay,moisture content and compaction coefficient,respectively.The fissure density of the blended soil first decreases and then increases with the blending ratio,with the lowest being zero when the blending ratio is ranging from 20%to 40%.Through particle microscopic analysis and elemental composition analysis,it is found that the neutralization effect,the dilution effect of swell minerals,and the partition effect of coarse particles play an important role in restraining expansion and shrinkage deformation of the blended soil.Based on the liquid limit requirement of Chinese Railway Design Code(TB 10001-2016),the optimal blending ratio of red clay has been proposed to be 50%.Compared with the CWP soil,the free load swell index of the blended soil is reduced by 45.0%and the fissure density is reduced by 99.3%compared with that of red clay.Therefore,it is feasible to improve the CWP soil by blending it with red clay at an optimal ratio of 50%by using the neutralization effect of the expansion of CWP and shrinkage of red clay.
基金financial support from the National Key R&D Program of China (2017YFB0602003)。
文摘The utilization of powdery semi-coke as a power fuel in pulverized coal-fired power plants has become a new and potential technique to consume the excess powdery semi-coke.The characteristic of low volatile results in poor combustion performance and high NO_(x) emission,and to co-fire with bituminous coal is a practical strategy to address this problem.However,the co-combustion characteristics and the inherent interaction between semi-coke and coal remain insufficiently understood.In addition,the influences of secondary air arrangement,the boiler operation load,and the fuel type on co-combustion process are still unclear,which is urgent to be further explored.In the present study,experiments and numerical simulations were jointly utilized to inquire into the co-combustion behaviors and NO_(x) emission features of semi-coke and coal.The results demonstrated that the"out-furnace method"was a suitable choice for small-capacity boiler when the proportion of semi-coke was 33%,due to the limited combinations of the semi-coke injection position.It was recommended that semi-coke was preferred to be injected from the middle layers of the furnace under the"in-furnace method"to improve the overall co-combustion performance.The critical value of the separated over fire air ratio in this study was 27.5%,over which a slight drop of carbon content in fly ash could come about.Moreover,the elevation in the proportion of separated over fire air gave rise to the significant decline of NO_(x) concentration.The constricted secondary air arrangement was preferred to be employed due to the high boiler efficiency.The separated over fire air and the surrounding air needed to maintain a wide-open degree to prevent the increase of NO_(x) emissions and the coking of nozzles.For the load reduction regulation method adopted in this study,the NO_(x) concentration first rose and then dropped,while the burnout ratio decreased obviously as the operation load was reduced.Different combinations of coal and semi-coke generated significant influences on co-combustion behaviors within the furnace.The NO_(x )generated by high-volatile fuel (bituminous coal) combustion was mainly affected by volatile-N,while the NO_(x )generated by low-volatile fuel (semi-coke) was mainly impacted by char-N.This study is of guiding significance for the efficient and clean utilization and beneficial to the large-scale application of powder semi-coke in power plants.
