Parametric studies on corn combustion characteristics in a fixed bed: Primary air flow rate and different corn lengths (original) (raw)
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Energy, 2018
This experiment was conducted on fixed bed combustion in a one-dimensional bench. The effects of ash and moisture content on the combustion characteristics of corn straw were determined. The two parameters directly relate to the burning rate and affect combustion efficiency and the release of gas. The bed temperature distribution, mass loss rate and gas composition were measured in the bed. The results show that the optimum char combustion efficiency was achieved at 10% moisture content of corn combustion. A slight increasing the moisture content to 10% can obtain a higher bed temperature and accelerate the ignition rate in the char oxidation stage, while there is also a slight decrease in the conversion ratio of C to CO. The conversion rate of S to SO 2 for 10% moisture content was higher with the temperature zone above 1000 C. With the increased ash content, there was a slight increase in the average ignition rate; the bottom bed temperature increased with a serious ash slagging. C was converted to CO and presented a slightly increasing trend for higher ash content and the conversion of N to HCN. This work provides an overall understanding of corn combustion for large boiler system.
Assessment of chopped corn straw lengths for combustion in a fixed bed using a numerical model
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In this paper, both a numerical model and an experimental study were developed to determine the important parameters of corn length for combustion behavior in a fixed-bed reactor. As an important factor impacting thermal conversion, changes in the burning rate follow variations in corn length, which then affect gas emissions. As a result of insufficient knowledge concerning the mechanisms of complex combustion, the development of a combustion system has been restricted. Modeling of this combustion system will complement experimental data; however, improving such a model is challenging as a result of the unique characteristics of corn, such as its moisture content and porosity. The results show that corn straw with a shorter length has a shorter ignition time, increased bed temperature, and reduced amounts of unburned carbon in the ash residues. Furthermore, the burning of shorter corn straw causes high emission concentrations from pyrolysis products, such as CH4 , CO, and most prevalently NO, near the grate, which indicates the beginning of the char oxidation stage. Corn straw with longer lengths increases the difficulty of accurately modeling the irregular shape of corn straw particles for theoretical calculations. In addition, in an actual bed, local bed structures that have not been uniformly mixed result in uncertainties in the flame propagation as well as the time at which the fuel is ignited. The application of numerical modeling allows for a more detailed description of the corn combustion process and can be used as a reference to develop biomass combustion in a large system.
Experimental analysis of the influence of air-flow rate on wheat straw combustion in a fixed bed
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Biomass in the form of crop residues represents a significant energy source in regions whose development is based on agricultural production. Among many possibilities of utilizing biomass for energy generation, combustion is the most common. With the aim of improving and optimizing the combustion process of crop residues, an experimental rig for straw combustion in a fixed bed was constructed. This paper gives a brief review of working characteristics of the experimental rig, as well as the results for three different measuring regimes, with the purpose to investigate the effect of air-flow rate on the wheat straw combustion in a fixed bed. For all three regimes analysed in this paper bulk density of the bed was the same, 60 kg/m3, combustion air was without preheating and air-flow rates were: 1152, 1872, and 2124 kg/m2h. The effect of air-flow rate on the ignition rate, burning rate, temperature profile of the bed and flue gas composition were analysed. It was concluded that in the...
Assessment of primary air on corn straw in a fixed bed combustion using Eulerian-Eulerian approach
Energy, 2018
In this paper, mathematical modelling is conducted on the combustion of corn straw in a one-dimensional bench combustion test rig, and the effects of the primary air flow rate are assessed over a wide range. Due to complex solid combustion mechanisms and inadequate knowledge of the process, the development of such combustion system is limited. Numerical modelling of this combustion system has some advantages over experimental analysis, although the development of a complete model for this type of combustion system remains a challenge. Due to its characteristic properties, modelling of biomass combustion has to overcome many difficulties. One such problem is displaying the process of initiating the combustion in numerical modelling. This study finds that the volatile release and combustion of char increases, thus increasing the amount of primary air up to a critical point, where the starting time of ignition becomes shorter as the primary air flow rate increases. The peak concentration of NO decreases with the increase of primary air, whereas with the increase in the amount of air, there is a reduction in the release of SO2 as well as a reduction in CO emissions in the bed.
Effects of air flowrate on the combustion and emissions of blended corn straw and pinewood wastes
Journal of Energy Resources Technology, 2019
This research investigated the effects of the specific primary (under-fire) air flowrate on the combustion behavior of a 50–50 wt % blend of raw corn straw (CS) and raw pinewood wastes in a fixed-bed reactor. This parameter was varied in the range of 0.079–0.226 kg m−2 s−1, which changed the overall combustion stoichiometry from air-lean (excess air coefficient λ = 0.73) to air-rich (excess air coefficient λ = 1.25) and affected the combustion efficiency and stability as well as the emissions of hazardous pollutants. It was observed that by increasing m˙m˙air, the ignition delay time first increased and then decreased, the average bed temperatures increased, both the average flame propagation rates and the fuel burning rates increased, and the combustion efficiencies also increased. The emissions of CO as well as those of cumulative gas phase nitrogen compounds increased, the latter mostly because of increasing HCN, while those of NO were rather constant. The emissions of HCl decreased but those of other chlorine-containing species increased. The effect of m˙m˙air on the conversion of sulfur to SO2 was minor. By considering all of the aforesaid factors, a mildly overall air-rich (fuel-lean) (λ = 1.04) operating condition can be suggested for corn-straw/pinewood burning fixed-bed grate-fired reactors.
Effects of corn ratio with pine on biomass co-combustion characteristics in a fixed bed
Applied Thermal Engineering, 2018
In this study, the effect of corn ratio on pine chip and corn straw (high alkali metals and chlorine) co-combustion in a fixed bed were investigated. The combustion efficiency, gas emissions, and problems of corrosion and deposits were analyzed by detecting bed temperatures, gas compositions (CO2, CO, O2, CH4, C2H6, NOx, HCN, NH3, SO2, and HCl), and alkali metal emissions. The appropriate increase in the corn ratio improved flame propagation speed and shortened ignition time. Pure pine combustion caused some amount of thermal NO emissions, and the high content of N resulted to a relatively high emission of NH3 and HCN, whereas its relationship with the release of NO in the main burning stage was slight. A 30% corn ratio aided in the reduction of NO emission, and the amount of alkali metals in the corn fixed the effect of SO2. The release of KCl and HCl can be considered as the prevalent emission formation of Cl in the blended biomass co-combustion process; the additional corn straw increased the release ratio of metal chloride. The optimum corn ratio (30–50%) provide a certain reference value for the selection of fuel mixture ratio in the operation of real large-scale systems.
Fuel, 2021
The effect of preheating primary air on the co-combustion characteristics of a 50-50% blend of pinewood and corn straw in a fixed bed. The primary air temperatures were assessed from 20 to 130 • C. The co-combustion characteristics were included the co-combustion behaviors and emissions. In order to reveal the features of the combustion process in the porous bed, a two-dimensional unsteady state model was employed to investigate the combustion process in a fixed bed of blended biomass on the combustion process in a fixed bed reactor. Conservation equations of the bed were implemented to describe the combustion process. The gas phase turbulence was modeled using the k-ε turbulent model and the particle phase was modeled using the kinetic theory of granular flow. Results showed that by increasing primary air temperature the residual mass on bed decreased, while the average burning rates and ignition front propagation velocity increased At the primary air temperature of 85 • C the smallest unburned carbon was left in the ash, and the emissions of nitrogen-compounds were relatively small. In contrast, the primary air temperature of 85 • C was found to be well-operating condition, which can be suggested for industrial boiler during blend co-combustion. The simulation results were then compared with experimental data for different temperature, which shows that the combustion process in the fixed bed is reasonably simulated. The simulation results of solid temperature, gas species and process rate in the bed are accordant with experimental data.