Effect of Fe_(2)O_(3) on the Formation of Micro Glass Beads under Air Staged Combustion

The effect of Fe_(2)O_(3) on the formation of micro glass beads(MGBs)under air staged combustion was studied.The experimental temperature was 1450℃,and Hegang bituminous coal was used as the experimental object.X⁃ray diffractometer(XRD),ash fusion tester,viscosity formula and scanning electron microscopy(SEM)were used to analyze the fly ash.Nano Measurer 1.2 software was used to measure the diameter of MGBs.The results showed that with the increase of Fe_(2)O_(3) in Hegang coal,the glass phase in fly ash first increased and then decreased.When the amount of Fe_(2)O_(3) was 15%,the content of the glass phase was the highest,which was 51.26%.The ash melting point first decreased and then increased,while the viscosity gradually decreased and the particles gradually became spherical.With the increase of Fe_(2)O_(3),the proportion of MGBs with particle size less than 10μm increased gradually.From the above results,it can be concluded that the addition of Fe_(2)O_(3) is conducive to the formation of MGBs and the reduction of particle size.

Role of Air Staging in a Batch-Type Fixed Bed Biomass Combustor under Constant Primary Air

Staged combustion of biomass is the most suitable thermo-chemical conversion for achieving lower gaseous emissions and higher fuel conversion rates.In a staged fixed bed combustion of biomass,combustion air is supplied in two stages.In the first stage,primary air is provided below the fuel,whereas in the later stage,secondary air is supplied in the freeboard region.The available literature on the effects of air staging(secondary air location) at a constant primary air flow rate on combustion characteristics in a batch-type fixed bed combustor is limited and hence warrants further investigations.This study resolves the effect of air staging,by varying the location of secondary air in the freeboard at five secondary to total air ratios in a batch-type fixed bed combustor.Results are reported for the effects of these controlled parameters on fuel conversion rate,overall gaseous emissions(CO_(2),CO and NO_x) and temperature distributions.The fuel used throughout was densified hardwood pellets.Results show that a primary freeboard length(distance between fuel bed top and secondary air injection) of200 mm has higher fuel conversion rates and temperatures as well as lower CO emissions,at a secondary to total air ratio of 0.75 as compared to primary freeboard length of 300 mm.However,NO_x emissions were found to be lower for a primary freeboard length of 300 mm as compared to 200 mm.An increase in secondary to total air ratio from 0.33 to 0.75 resulted in higher freeboard temperatures and lower CO as well as NO_x emissions.The outcomes of this study will be helpful in the effective design of commercial scale biomass combustors for more efficient and environmentally friendly combustion.

NO_(x) and H_(2)S formation in the reductive zone of air-staged combustion of pulverized blended coals

Low NO_(x) combustion of blended coals is widely used in coal-fired boilers in China to control NO_(x) emission;thus,it is necessary to understand the formation mechanism of NO_(x) and H2S during the combustion of blended coals.This paper focused on the investigation of reductive gases in the formation of NO_(x) and H2S in the reductive zone of blended coals during combustion.Experiments with Zhundong(ZD)and Commercial(GE)coal and their blends with different mixing ratios were conducted in a drop tube furnace at 1200℃–1400℃with an excessive air ratio of 0.6–1.2.The coal conversion and formation characteristics of CO,H_(2)S,and NO_(x) in the fuelrich zone were carefully studied under different experimental conditions for different blend ratios.Blending ZD into GE was found to increase not only the coal conversion but also the concentrations of CO and H2S as NO reduction accelerated.Both the CO and H2S concentrations inblended coal combustion increase with an increase in the combustion temperature and a decrease in the excessive air ratio.Based on accumulated experimental data,one interesting finding was that NO and H2S from blended coal combustion were almost directly dependent on the CO concentration,and the CO concentration of the blended coal combustion depended on the single char gasification conversion.Thus,CO,NO_(x),and H2S formation characteristics from blended coal combustion can be well predicted by single char gasification kinetics.

Influence of Air Staging on the Operation Characteristics of the CFB System

To guide the application of gasification agent staging in circulating fluidized bed(CFB)gasifiers,a cold model test was implemented to study the effects of air staging on the operation of the CFB system.The results show that the re-entrainment of the solid in the downward solid flow by the secondary air jet reduces the back-mixing of solid into the dense phase zone and increases the total entrainment rate.The uniformity of axial solid holdup profile in the riser is improved by air staging.With increasing secondary air ratio,the solid concentration in the dense and dilute phase zones increases because the solid in the standpipe is transferred into the riser.After air staging,the pressure drop of the cyclone significantly increases,which results from the disturbance of the inside flow field and the increase in inlet solid concentration.Within the experimental range,the failure of the system appears as gas leakage in the standpipe.This failure can be understood as the mismatch of the mass balance and pressure balance of the system after air staging.Therefore,the results also provide guidance for the matching design of key components for the implementation of gasification agent staging.

Investigation of the segregation of a binary particle mixture in a square circulating fluidized bed with air staging

To further understand the segregation characteristics of a binary particle mixture in a riser,the flow behaviors of particles with different sizes were experimentally and numerically investigated in a cold square circulating fluidized bed.The impact of the gas velocity,solid circulation rate,initial coarse particle fraction,and air staging on the coarse particle fraction and axial pressure drop were examined.The experimental results show that air staging can significantly promote the pressure drop of a binary mixture at the bottom of the bed compared with that of monosized particles.Meanwhile,the segregation of the binary mixture at the bottom is hindered.It was also found that there was clear radial segregation owing to a higher coarse particle fraction near the wall compared with the bed's center and its corner.

Fluidized bed combustion of high water content alcohol extracted herb residue and the impacts of blending wasted activated coke

Combustion of herb residues(HRs)for heat recovery is a good way for their utilization,but there exists such a problem as high concentration NOx emission in flue gas.The alcohol extracted herb residue(AEHR),one special type of HRs,was chosen as the object and was subjected to immediate combustion in a fluidized bed reactor to investigate the characteristics of its resulting NOx emission.The results showed that,most of the NOx in the flue gas was produced from the char nitrogen(C-N);as the fuel water content increased,the NOx emission concentration exhibited a trend of first decreasing and then increasing;and a properly low combustion temperature inhibited the NOx emission upon the premise of ensuring full combustion.Air staging combustion was adopted to effectively control NOx:the NOx emission concentration in the flue gas was reduced to 296 mg⋅m􀀀3 and the NOx emission reduction rate reached 46.51%compared to conventional combustion.Co-combustion by blending wasted activated coke(WAC)into the AEHR helped both stabilize the combustion state and reduce further the NOx emission.When the blending ratio of WAC fell within a proper range of 20-30%,the NOx emission concentration in the flue gas was as low as 231.4 mg⋅m􀀀3.In addition to the dilution effect of the combustion flue gas of the blended WAC,the local reducing atmosphere caused by its incomplete combustion as well as its strong absorbability and catalytical effect was accountable for the further decrease of the NOx emission concentration.