Experimental Study on the Effects of Declivitous Angle of Secondary Air on the Flow Characteristics and Coal Combustion of a Down-Fired

2011 ◽  
Author(s):  
Jian Shi ◽  
Yuzhong Chen ◽  
Yubo Hou ◽  
Bin Yao
Keyword(s):  
Fly Ash ◽  
Flow Field ◽  
Carbon Content ◽  
Coal Combustion ◽  
Field Experiments ◽  
Combustion Process ◽  
Flow Characteristics ◽  
Cold Flow ◽  
Horizontal Momentum ◽  
Secondary Air

Aiming at Foster Wheeler (FW) technology down-fired boiler with horizontal F layer secondary air, in which the strong horizontal momentum of the secondary air seriously pounds the down flowing coal gas flame, making the problems of short trip of coal flame and low flame fullness of the furnace, and this leads to higher carbon content of fly ash and so on. A designed adjusting device making the declivitous angle of secondary air is erected in the F layer wind box of a FW down-fired furnace, so the declivitous angle of secondary air can be regulated freely. By this means, the declivitous angle of the F layer secondary air is able to be refined depending on the real combustion situation to achieve the best configuration of the momentum radio by downward momentum from the arch and horizontal momentum from the front/rear wall. As a result, it is able to adapt the change of the furnace combustion situation, extending the flame travel, and improving the combustion process and efficiency. This method was applied to a 300MW grade FW down-fired boiler, and the cold flow field results by fireworks showed the down flow depth of the primary air increasing with the declivitous angle. The best flow field was achieved as the declivitous angle was set to 45°. Based on the cold flow field experiments, combustion experiment was accomplished to compare with the coal combustion performance before the declivitous refinement of the F layer secondary air. It was shown that the carbon content of the fly ash was greatly decreased after the refinement, and the combustion efficiency was increased by 3.3%.

scholarly journals Simulation of Thermal Effects on the Flow Field in a Pilot-Scale Kiln

2021 ◽  
Author(s):  
I. A. Sofia Larsson ◽  
Anna-Lena Ljung ◽  
B. Daniel Marjavaara
Keyword(s):  
Flow Field ◽  
Coal Combustion ◽  
Thermal Effects ◽  
Iron Ore ◽  
Combustion Process ◽  
Pilot Scale ◽  
Mixing Properties ◽  
Process Gas ◽  
Mixing Rates ◽  
Computational Fluid Dynamics Cfd

AbstractThe flow field and coal combustion process in a pilot-scale iron ore pelletizing kiln is simulated using a computational fluid dynamics (CFD) model. The objective of the work is to investigate how the thermal effects from the flame affect the flow field. As expected, the combustion process with the resulting temperature rise and volume expansion leads to an increase of the velocity in the kiln. Apart from that, the overall flow field looks similar regardless of whether combustion is present or not. The flow field though affects the combustion process by controlling the mixing rates of fuel and air, governing the flame propagation. This shows the importance of correctly predicting the flow field in this type of kiln, with a large amount of process gas circulating, in order to optimize the combustion process. The results also justify the use of down-scaled, geometrically similar, water models to investigate kiln aerodynamics in general and mixing properties in particular. Even if the heat release from the flame is neglected, valuable conclusions regarding the flow field can still be drawn.

Effect of unburned carbon content in fly ash on the retention of 12 elements out of coal-combustion flue gas

2012 ◽  
Vol 24 (9) ◽  
pp. 1624-1629 ◽  
Author(s):  
Lucie Bartoňová ◽  
Bohumír Čech ◽  
Lucie Ruppenthalová ◽  
Vendula Majvelderova ◽  
Dagmar Juchelková ◽  
...  
Keyword(s):  
Fly Ash ◽  
Carbon Content ◽  
Flue Gas ◽  
Coal Combustion ◽  
Unburned Carbon

scholarly journals Numerical Investigation on Co-firing Characteristics of Semi-Coke and Lean Coal in a 600 MW Supercritical Wall-Fired Boiler

2019 ◽  
Vol 9 (5) ◽  
pp. 889 ◽  
Author(s):  
Chang’an Wang ◽  
Qinqin Feng ◽  
Qiang Lv ◽  
Lin Zhao ◽  
Yongbo Du ◽  
...  
Keyword(s):  
Fly Ash ◽  
Carbon Content ◽  
Combustion Zone ◽  
Combustion Process ◽  
Nox Emission ◽  
Outlet Temperature ◽  
Excess Air ◽  
Furnace Outlet ◽  
Blending Method ◽  
Lean Coal

Semi-coke is one of the principal by-products of coal pyrolysis and gasification, which features the disadvantages of ignition difficulty, low burnout rate, and high nitrogen oxides (NOx) emission during combustion process. Co-firing semi-coke with coal is a potential approach to achieve clean and efficient utilization of such low-volatile fuel. In this paper, the co-firing performance of semi-coke and lean coal in a 600 MW supercritical wall-fired boiler was numerically investigated which has been seldom done previously. The influences of semi-coke blending ratio, injection position of semi-coke, excess air ratio in the main combustion zone, the co-firing method, and over fire air (OFA) arrangement on the combustion efficiency and NOx generation characteristics of the utility boiler were extensively analyzed. The simulation results indicated that as the blending ratio of semi-coke increased, the NOx emission at furnace outlet decreased. The blending methods (in-furnace versus out-furnace) had certain impacts on the NOx emission and carbon content in fly ash, while the in-furnace blending method showed more flexibility in co-firing adjustment. The injection of semi-coke from the upper burners could significantly abate NOx emission at the furnace outlet, but also brought about the rise of carbon content in fly ash and the increase of outlet temperature. Compared with the condition that semi-coke and lean coal were injected from different burners, the burnout ratio of the blend premixed outside the furnace was higher at the same blending ratio of semi-coke. With the excess air ratio in the main combustion zone increased, NOx concentration at the furnace outlet was increased. The excess air ratio of 0.75 in the main combustion zone was recommended for co-firing 45% semi-coke with lean coal. The operational performance of the boiler co-firing semi-coke was greatly affected by the arrangement of OFA as well. The amount of NOx generated from the supercritical wall-fired boiler could be reduced with an increase of the OFA height.

Effect of Permeable Ribs on Thermal-Flow Characteristics in an Internal Cooling Duct

2020 ◽  
Vol 13 (1) ◽  
Author(s):  
Naveen Sharma ◽  
Andallib Tariq ◽  
Manish Mishra
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Field Experiments ◽  
Flow Characteristics ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Energy Budgets ◽  
Internal Cooling ◽  
High Heat Transfer ◽  
Turbulent Statistics

Abstract This study aims to understand the effect of flow structures within the inter-rib regions of a novel permeable rib configuration in vertical and horizontal streamwise planes upon surface heat transfer parameters. In this investigation, the liquid crystal thermography (LCT) and particle image velocimetry (PIV) are used to extract the local heat transfer and flow-field information, respectively. The effect of slit-converging angle (ϕ = 0 deg, 5 deg, 10 deg, and 15 deg) are examined at a typical Reynolds number of 42,500 and relative rib pitch ratio of 10. Surface- and spanwise-average and overall augmentation Nusselt numbers are obtained along with the pressure drop measurements. Flow-field experiments are performed in both vertical and horizontal streamwise planes, and the results are expressed in terms of mean velocities, stream traces, turbulent statistics, coherent structures, and turbulent kinetic energy budgets. Critical points are also identified on the basis of critical point theory, which provides evidences of the different flow phenomena accountable for enhance mixing between the ribs. The secondary flow coming from the slit shows three-dimensionality in the flow resulting to higher turbulence intensity and rotational motion (say higher turbulent mixing), and thereby leading to high heat transfer just behind the permeable rib. The permeable ribs are also helpful in the reduction of friction factor by 32% with a typical ϕ value of 5 deg, compared to solid ribs, while the thermohydraulic performance increases with increasing ϕ from 0 deg to 15 deg up to 21%. The pentagonal ribs with convergent slit provide comparable or better performance among the permeable rib geometries used in the pertinent literature.

The Flow Field in a Virtual Model of a Rotary Kiln as a Function of Inlet Geometry and Momentum Flux Ratio

2015 ◽  
Vol 137 (10) ◽  
Author(s):  
I. A. Sofia Larsson ◽  
T. Staffan Lundström ◽  
B. Daniel Marjavaara
Keyword(s):  
Flow Field ◽  
Rotary Kiln ◽  
Momentum Flux ◽  
Combustion Process ◽  
Flux Ratio ◽  
Middle Part ◽  
Momentum Flux Ratio ◽  
Fuel Jet ◽  
Inlet Geometry ◽  
Secondary Air

The rotary kiln is the middle part of a grate-kiln iron ore pelletizing process and consists of a large, cylindrical rotating oven with a burner in one end. The flame is the heart of the process, delivering the necessary heat. The combustion process is largely controlled by the turbulent diffusion mixing between the primary fuel jet and the combustion air, called the secondary air, which is mostly induced through the kiln hood. The relatively high momentum of the secondary air implies that the resulting flow field has a significant impact on the combustion process, justifying a systematic study of the factors influencing the dynamics of the secondary air flow field, by neglecting the primary fuel jet and the combustion. The objective of this work is thus to investigate how the geometry and the momentum flux ratio of the inlets affect the flow field in the kiln. Down-scaled models of the kiln are investigated numerically. It is found that the resulting flow field is highly affected by both the geometry and momentum flux ratio of the inlet flows, including effects from pressure driven secondary flow occurring in the semicircular inlet ducts. The dynamics of the flow is further investigated using proper orthogonal decomposition (POD) resulting in a deeper understanding of the forming, interaction and convection of the vortical structures.

scholarly journals Electricity Evaluation and Emission Characteristics of Poultry Litter Co-Combustion Process

2019 ◽  
Vol 9 (19) ◽  
pp. 4116 ◽  
Author(s):  
Qian ◽  
Lee ◽  
Chandrasekaran ◽  
Yang ◽  
Caballes ◽  
...  
Keyword(s):  
Fly Ash ◽  
Natural Gas ◽  
Water Flow Rate ◽  
Poultry Litter ◽  
Combustion Process ◽  
Operating Conditions ◽  
Emission Characteristics ◽  
Combustion System ◽  
Fluidized Bed Combustion ◽  
Secondary Air

Electricity generation and emission characteristics during the poultry litter and natural gas co-combustion process has rarely been studied. In this study, a Stirling engine was successfully integrated into the existing lab-scale swirling fluidized bed combustion system in order to further investigate the poultry litter and natural gas co-combustion process. Electricity, gaseous emissions, particulate matter (PM), and fly ash composition were analyzed under various operating conditions. Results indicated that the electricity reached 905 W under a water flow rate of 13.1 L/min and an engine head temperature of 584 °C. It was found that excess air (EA) ratios between 0.79 and 1.08 can relatively produce more electricity with lower emissions. At a secondary air (SA) height of 850 mm, secondary air/total air (SA/TA) ratios between 0.22 and 0.44 may significantly reduce NOx and CO emissions. By increasing the mixing ratio (MR), SO2 was reduced while NOx increased at the beginning of co-combustion process but then decreased again. Additionally, PM results were lower than Maryland emissions standards. The fly ash results showed a higher nutrient content (close to 16%). This study shows the possibility of using poultry litter as a sustainable energy source for energy production while emitting lower emissions in the small decentralized combustion system

Characterization of Catalyzed Devitrification in Quenched Fly Ash Melts

1984 ◽  
Vol 43 ◽  
Author(s):  
Subhash H. Risbud
Keyword(s):  
Fly Ash ◽  
Coal Combustion ◽  
Ceramic Body ◽  
Combustion Process ◽  
Bottom Ash ◽  
Waste Utilization ◽  
Raw Material ◽  
Friable Material ◽  
Air Pollution Control ◽  
Silica Alumina

Coal combustion produces enormous quantities of residual ash often called bottom ash or fly ash. The fly ash component contains lightweight cenospheres giving the ash a fluffy character. Fly ash is captured in the coal combustion process by air pollution control devices as the gases exit the stack. Fly ash compositions are usually highly siliceous consisting mainly of the oxides of silica, alumina, calcia, and iron oxides; minor constituents such as MgO, alkali oxides, TiO2 etc. are also almost invariably present in quantities of ≈0.5 to 3 wt%. Two important aspects of crystallization of fly ash melts and glasses relate to the prevention of boiler slagging [1] and, from a waste utilization point of view, to the development of new products using fly ash as a raw material[2–4]. Ash devitrification on cooling of the melt results in friable material that does not stick to boiler walls as easily as glassy slag [5]. From another standpoint, crystallization of glassy ash slag to a fine grained equiaxed microstructure is considered a desirable glass-ceramic body for thermomechanical reasons [6].

Influence of Air Distribution Modes on Boiler Efficiency

2015 ◽  
Vol 733 ◽  
pp. 517-521
Author(s):  
Xiao Hui Wang ◽  
Hai Ping Xiao ◽  
Xiang Ning ◽  
Yu Kun Dai
Keyword(s):  
Fly Ash ◽  
Carbon Content ◽  
Oxygen Content ◽  
Flame Temperature ◽  
Beam Waist ◽  
Air Distribution ◽  
Boiler Efficiency ◽  
Distribution Mode ◽  
Secondary Air

The influence of air distribution modes on boiler efficiency was researched by combustion adjustment tests. Boiler efficiency variation was studied by changing factors such as oxygen content, upper tertiary air, over fire air and secondary air distribution modes. Boiler efficiency reached maximum under 3.9% design oxygen content. Carbon content in fly ash increased as upper tertiary air ratio, consequently boiler efficiency declined. Average furnace flame temperature decreased inversely as over fire air baffle opening, and boiler efficiency variation was small. Under different conditions, boiler efficiency varied within 1.12%. Beam waist air distribution mode obtained the highest boiler efficiency.

Lightweight Geopolymer Binder with Abaca Fiber in Different Curing

2016 ◽  
Vol 841 ◽  
pp. 140-147 ◽  
Author(s):  
Triwulan ◽  
Luvi Yusepa Dwijayanti ◽  
Januarti Jaya Ekaputri ◽  
Ridho Bayuaji
Keyword(s):  
Fly Ash ◽  
Coal Combustion ◽  
Combustion Process ◽  
Environmental Safety ◽  
Light Weight ◽  
Steam Curing ◽  
Foaming Agent ◽  
Materials Used ◽  
Curing Method ◽  
Geopolymer Binder

Light weight buildings are required in Indonesia to reduce the risk due to the earthquakes. Therefore, the presence of lightweight materials are needed. Moreover, fly ash that is a waste of coal combustion process, has a basic ingredient of geopolymer binder. If the geopolymer binder is mixed with a foaming agent, it will be a lightweight geopolymer binder, in which it can be used as wall elements that have light weight. Furthermore, the utilization of fly ash will reduces the pollution due to the release of CO2 during production of Portland cement. Thus the use of fly ash results in environmental safety. This study investigate about fibrous lightweight geopolymer binder, in which the main materials used was fly ash with the alkali activator such as NaOH and Na2SiO3. Foaming agent was used to form micro-pores. Abaca fiber was used as a reinforcement to avoid cracks. Normal curing and steamed curing were utilized at temperature 60°C for 6 hours. Meanwhile, tests conducted were compressive strength, density and porosity. Steam curing method resulted an increase in strength and gives less density even though the same amount of pores was formed.

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