The effects of the secondary air excess ratio(λ_(2))on the self-preheating combustion characteristics and NO_(x)emission of semi-coke have been experimentally studied on a bench-scale test rig.Flameless combustion of...The effects of the secondary air excess ratio(λ_(2))on the self-preheating combustion characteristics and NO_(x)emission of semi-coke have been experimentally studied on a bench-scale test rig.Flameless combustion of the high-temperature preheated fuel(coal gas&coal char)has been achieved in all experimental cases.Through fire-observation windows,the combustion zone was transparent and no flame fronts were seen.Additionally,differentλ_(2)in this study were basically within the common range of self-preheating combustion technology.The results manifested that the rapid ignition of coal gas and the recirculation of high-temperature flue gas resulted in relatively high combustion temperatures close to the secondary air nozzle exit.With the increase of.12,the unburned carbon content of fly ash increased slightly and combustion efficiencies of all experiments exceeded98%.Moreover,the exit NO_(x)emission was not reduced linearly,which was dissimilar from conventional air staging combustion.The main reason was that the volatile-N was released in the self-preheating device,and the air staging method could not effectively reduce the char-NO_(x).In the course of the experiments,the lowest NO_(x)emission was 64.35 mg/m3(@6%O2)whenλ_(2)was 0.40.展开更多
As the major primary energy source in China,coal has been proved to be capable to improve its physical and chemical characteristics by the pretreatment of the self-preheating burner.In this study,the effects of alteri...As the major primary energy source in China,coal has been proved to be capable to improve its physical and chemical characteristics by the pretreatment of the self-preheating burner.In this study,the effects of altering operating conditions including preheating temperature(T_(p))and primary air equivalence ratio(λ_(p))on preheating characteristics of three typical pulverized coal were investigated on a bench-scale test rig.The high-temperature coal gas compositions along the axis of the riser and at the outlet of the self-preheating burner were measured,and the coal char and coal tar produced in the preheating process were collected and analyzed separately.The results indicated that with the significant release of volatile and the occurrence of chemical reactions,cracks and micropores emerged on the surface of the particles,making the pore structure on the surface more developed,and T_(p)had the most significant effect on the structure of coal particles.Additionally,there were evident differences in the corresponding operating conditions when the preheating characteristics of the three typical coal reached optimally.And preheating had the strongest influence on the degree of anthracite modification.With respect to coal tar,the increase of T_(p)andλ_(p)further promoted its secondary cracking and oxidation,resulting in a decrease in production yield.In this study,for bituminous coal and lignite,a large amount of coal tar were produced during preheating and the highest production yields could reach 5.74%and 6.15%,respectively.While for anthracite,the production yield was intensely low due to its own coal properties,all below 1.02%.展开更多
The study focused on the effects of the interaction between axial and radial secondary air and the reductive intensity in reduction region on combustion characteristics and NO_(x) emission in a 30 kW preheating combus...The study focused on the effects of the interaction between axial and radial secondary air and the reductive intensity in reduction region on combustion characteristics and NO_(x) emission in a 30 kW preheating combustion system.The results revealed that the interaction and reductive intensity influenced the combustion in the down-fired combustor(DFC) and NO_(x) emission greatly.For the temperature distribution,the interaction caused the position of the main combustion region to shift down as R_(2-12)(ratio of axial secondary air flow to radial secondary air flow) decreased or λ_(2)(total secondary air ratio) increased,and there was the interplay between both of their effects.As R_(3-12)(ratio of first-staged tertiary air flow to second-staged tertiary air flow)increased,the decrease in the reductive intensity also caused the above phenomenon,and the peak temperature increased in this region.For the NO_(x) emission,the interaction affected the NO_(x) reduction adversely when λ_(2) or R_(2-12) was higher,and the range of this effect was larger,so that the NO_x emission increased obviously as they increased.The decrease in the reductive intensity caused the NO_(x) emission increased under the homogeneous reduction mechanism,while was unchanged at a high level under the heterogeneous reduction mechanism.For the combustion efficiency,the interaction improved the combustion efficiency as λ_(2) increased when R_(2-12) was lower,while reduced it as λ_(2) increased excessively when R_(2-12) was higher.The proper decrease in the reductive intensity caused the combustion efficiency increased obviously,while was hardly improved further when the intensity decreased excessively.In this study,the lowest NO_(x) emission was only 41.75 mg/m^(3) without sacrificing the combustion efficiency by optimizing the interaction and reductive intensity.展开更多
基金supported by Strategic Priority Research Program of the CAS(XDA29010200)CAS Project for Young Scientists in Basic Research(YSBR-028)Youth Innovation Promotion Association of the CAS(2019148)。
文摘The effects of the secondary air excess ratio(λ_(2))on the self-preheating combustion characteristics and NO_(x)emission of semi-coke have been experimentally studied on a bench-scale test rig.Flameless combustion of the high-temperature preheated fuel(coal gas&coal char)has been achieved in all experimental cases.Through fire-observation windows,the combustion zone was transparent and no flame fronts were seen.Additionally,differentλ_(2)in this study were basically within the common range of self-preheating combustion technology.The results manifested that the rapid ignition of coal gas and the recirculation of high-temperature flue gas resulted in relatively high combustion temperatures close to the secondary air nozzle exit.With the increase of.12,the unburned carbon content of fly ash increased slightly and combustion efficiencies of all experiments exceeded98%.Moreover,the exit NO_(x)emission was not reduced linearly,which was dissimilar from conventional air staging combustion.The main reason was that the volatile-N was released in the self-preheating device,and the air staging method could not effectively reduce the char-NO_(x).In the course of the experiments,the lowest NO_(x)emission was 64.35 mg/m3(@6%O2)whenλ_(2)was 0.40.
基金supported by CAS Project for Young Scientists in Basic Research(YSBR-028)Strategic Priority Research Program of the Chinese Academy of Sciences(XDA21040100)Youth InnovationPromotion Association of the Chinese Academy of Sciences(2019148)。
文摘As the major primary energy source in China,coal has been proved to be capable to improve its physical and chemical characteristics by the pretreatment of the self-preheating burner.In this study,the effects of altering operating conditions including preheating temperature(T_(p))and primary air equivalence ratio(λ_(p))on preheating characteristics of three typical pulverized coal were investigated on a bench-scale test rig.The high-temperature coal gas compositions along the axis of the riser and at the outlet of the self-preheating burner were measured,and the coal char and coal tar produced in the preheating process were collected and analyzed separately.The results indicated that with the significant release of volatile and the occurrence of chemical reactions,cracks and micropores emerged on the surface of the particles,making the pore structure on the surface more developed,and T_(p)had the most significant effect on the structure of coal particles.Additionally,there were evident differences in the corresponding operating conditions when the preheating characteristics of the three typical coal reached optimally.And preheating had the strongest influence on the degree of anthracite modification.With respect to coal tar,the increase of T_(p)andλ_(p)further promoted its secondary cracking and oxidation,resulting in a decrease in production yield.In this study,for bituminous coal and lignite,a large amount of coal tar were produced during preheating and the highest production yields could reach 5.74%and 6.15%,respectively.While for anthracite,the production yield was intensely low due to its own coal properties,all below 1.02%.
基金Youth Innovation Promotion Association,CAS (2019148)CAS Project for Young Scientists in Basic Research (YSBR-028)the National Natural Science Foundation of China (No.52006233) are gratefully acknowledged。
文摘The study focused on the effects of the interaction between axial and radial secondary air and the reductive intensity in reduction region on combustion characteristics and NO_(x) emission in a 30 kW preheating combustion system.The results revealed that the interaction and reductive intensity influenced the combustion in the down-fired combustor(DFC) and NO_(x) emission greatly.For the temperature distribution,the interaction caused the position of the main combustion region to shift down as R_(2-12)(ratio of axial secondary air flow to radial secondary air flow) decreased or λ_(2)(total secondary air ratio) increased,and there was the interplay between both of their effects.As R_(3-12)(ratio of first-staged tertiary air flow to second-staged tertiary air flow)increased,the decrease in the reductive intensity also caused the above phenomenon,and the peak temperature increased in this region.For the NO_(x) emission,the interaction affected the NO_(x) reduction adversely when λ_(2) or R_(2-12) was higher,and the range of this effect was larger,so that the NO_x emission increased obviously as they increased.The decrease in the reductive intensity caused the NO_(x) emission increased under the homogeneous reduction mechanism,while was unchanged at a high level under the heterogeneous reduction mechanism.For the combustion efficiency,the interaction improved the combustion efficiency as λ_(2) increased when R_(2-12) was lower,while reduced it as λ_(2) increased excessively when R_(2-12) was higher.The proper decrease in the reductive intensity caused the combustion efficiency increased obviously,while was hardly improved further when the intensity decreased excessively.In this study,the lowest NO_(x) emission was only 41.75 mg/m^(3) without sacrificing the combustion efficiency by optimizing the interaction and reductive intensity.
