Effect Of Air Staging Research Articles

Effect of air staging on low-NOx combustion performance of regenerative heating furnace for oil shale retort

Effect of air staging on low-NOx combustion performance of regenerative heating furnace for oil shale retort

Effect of air staging and porous inert material on the emission of volatile organic compounds in solid biomass combustion

The present paper delves into experimental data to assess the effects of the inclusion of a zirconium porous medium in the emissions of a laboratory-scale biomass combustor, with a focus on particulate matter and volatile organic compounds. While other studies have focused on the effects of the material on solid particulate matter or gaseous emissions, this research is focused on volatiles, their capture and storage. A novel sampling train for the capture of volatiles has been designed based on active carbon adsorption on a refrigerated environment, and its performance was evaluated through thermogravimetric analysis, showing the affinity of this porous medium towards lighter organic compounds. The retention time of the sample was also studied, and the data revealed that after three to six hours the sample had degraded significantly when stored in airtight plastic bags inside a glass desiccator at 22 °C. An analysis of the particulate matter emitted was also carried out. Volatile organic compounds were also found to follow the behavior of particulate matter, with the scenarios where low solid particles were emitted being also those in which volatiles release was minimized.

The effects of air staging and combustion air control on black carbon and other particulate and gaseous emissions from a sauna stove

The combustion of wood in small-scale appliances emits significant amounts of particulate and gaseous pollutants into the atmosphere, leading to impaired air quality and adverse health and climate effects. Simple and easily implemented reduction techniques are needed to address this issue. In this study, different air staging strategies in a sauna stove were investigated with high temporal resolution, and the relationships between combustion air settings, combustion parameters, and different emission components were examined. Air staging was found to decrease PM1 and BC emissions by 43 and 41 %, and CO and OGC emissions by 23 and 42 %, respectively, when the stove was used in its standard configuration. Reducing and redistributing primary air decreased emissions further. BC emissions were lowest when the sauna stove was operated with an air-to-fuel ratio of 1.5. BC correlated weakly with gaseous emissions, with the exception of acetylene, highlighting the role of C2H2 as a precursor gas in soot formation. High OC/EC ratios during experiments with inefficient combustion conditions led to high average AAE values, which ranged from 1.23 to 1.41. Instantaneous AAE values correlated with concentrations of carbonyl compounds, especially acetaldehyde, suggesting that carbonyls may be indicative of BrC in wood smoke. The results show that significant emission reductions can be achieved in a simple combustion device with small, easily implemented modifications. In addition, the highly time-resolved data revealed relationships between various emission components, combustion conditions and the formation and properties of soot.

Effect of Air Staging on Nox Emissions in Biomass Combustion in a Bubbling Fluidized Bed

Effect of Air Staging on Nox Emissions in Biomass Combustion in a Bubbling Fluidized Bed

Effect of exhaust tube vortex on NOx reduction and combustion characteristics in a swirl-stabilized pulverized coal flame

Experimental investigations were conducted on the effect of the exhaust tube vortex (ETV) and the synergistic effect of the ETV and air staging on nitrogen oxide (NO) concentration and carbon monoxide (CO) concentration, as well as carbon burnout in a swirl-stabilized pulverized coal-fired furnace. To elucidate the aforementioned effects, four different swirl combinations were prepared derived from co-swirl and counter-swirl through five staging air injection positions. The results show that the ETV contributes to unburned carbon (UBC) combustion through its hollow-tube structure in the co-swirling flame. In addition, the temperature is distinguishable in the case of the 60°–60° co-swirl combination (Sco, 1.37/1.50), and 60°–60° counter-swirl combination (Sct, 1.37/1.50) because of the shape of the inner recirculation zone (IRZ) and the occurrence of the ETV. Although the ETV effect follows the swirl intensity, the 50°–50° co-swirl combination (Sco, 0.95/1.03) is the most favorable for the ETV effect under the unstaged condition, considering the behavior of the burner aerodynamics that contains the IRZ and the flame propagation dependent on the swirl vane angle. The result without an ETV is reflected in Sct, 1.37/1.50, meaning incomplete combustion of the coal during the combustion procedure. In terms of the synergistic effect, NO and CO reduction rates, as well as carbon burnout are needed to evaluate the best overall performance. According to evaluation, Sco, 1.37/1.50 at staging level 3 (SL3) has the highest synergistic effect because the effect of air staging is maximized in SL3 given the longest particle residence time in the re-burning zone.

An experimental study into the effect of air staging distribution and position on emissions in a laboratory scale biomass combustor

Air staging strategy is a proven technology to provide efficient biomass combustion with less gaseous and particulate emissions. In this study, two different secondary air distribution modules are employed at two different axial positions from the bed surface in a 15 kW fixed-bed laboratory scale combustion system includes grate and underfeed bed stocker. The effects of air staging on temperature, burning rate, gaseous and particulate emissions have been assessed over a selected primary air flow rate and a range of secondary air flow rates. Secondary air inlet module with uniform distribution of air results in 50% CO reduction by shifting the combustion to a more fuel lean environment and high temperature in the post-combustion zone. Remarkable decrease in particulate matters smaller than 1 μm is achievable through adjusting a uniform secondary air module in an appropriate distance from the bed. The non-uniform secondary air configuration increases the gaseous and particulate emissions than the uniform configuration. These results emphasise the need for further studies to better understand the effect of air staging on particulate and gaseous emissions.

Effects of air staging on emission characteristics in a conical fluidized-bed combustor firing with sunflower shells

This paper presents experimental results investigated from combustion of sunflower shells in a conical fluidized-bed combustor at feed rate 45 kg/h. Effects of operating parameters, such as excess air (EA) and secondary air to total air ratio (S/T) on combustion performance and emission characteristics of CO, CxHy and NO as well as combustion efficiency (ηc) were studied. Temperature and gas concentrations were measured along the combustor and at the outlet. The secondary air was tangential injected to the combustor at 0.5 m above the fuel feeding system and it was supplied at S/T = 0–0.4 for EA of 20–80%. The high combustion rates were found into two different zones of the combustor; in the bed region with the primary air and in freeboard region which were evidenced by two peaks of CxHy and CO concentrations. According to Thailand emission standard, the optimum operating condition to control CO and NO emissions at the quite high combustion efficiency (∼99%) seems to be EA at 40–60% and S/T = 0.3. Compared with conventional combustion, air staged combustion can reduced the NO emission by 27% when the combustor was operated at EA = 40% and S/T = 0.3. However, CO and CxHy emissions were apparently high.

Numerical Study the NOx Emission Characteristics of 600MW Opposed Swirling Coal-Fired Utility Boiler

In this paper, a computational fluid dynamics (CFD) model of a 600 MW opposed swirling coal-fired utility boiler has been established to numerically study the NOx emission characteristics under different ratios of over fire air (OFA) and modes of in-service burner layers. The current CFD model had adopted a chemical percolation devolatilization (CPD) model and been validated by comparing the simulated results with the experimental data. The numerical simulation results show that, with increasing the ratio of OFA, the carbon content in fly-ash increase somewhat linearly and the NOx emission reduce significantly, and the OFA ratio of 30% is optimal with higher burnout of pulverized coal and lower NOx emission. The different in-service burner layer modes have different influences on the residence time of the pulverized-coal particles, effect of air staging in the burner region and flue gas temperature at the exit of the lower furnace. Stopping the upper burner layers can increases the residence time of the pulverized-coal particles, resulting in the reduction of the carbon content in the fly ash and the increase of the pulverized-coal burnout. The flue gas temperature at the exit of the lower furnace can also decrease, which would be helpful to reducing the slagging tendency on the surfaces of the platen superheaters.

Effect of air staging on fine particle, dust and gaseous emissions from masonry heaters

There is a need to decrease the detrimental particle and gaseous emissions from residential wood combustion appliances. One encouraging alternative is to stage the air supply which improves the combustion conditions in small appliances. In this study, two types of combustion technologies were studied in conventional masonry heaters (CMH) and modern masonry heaters (MMH). Air staging in the MMHs considerably reduced the particle and gas emissions. The greatest reduction was observed in gaseous and particulate organic emissions. Methane emissions were reduced by 74%–91% and carbon monoxide by 26%–81%. The reduction of fine particle mass (PM1) was 14%–58%. Elemental carbon (EC, i.e. soot) emission increased in small combustion appliances but declined in large appliances. In addition, dust (TSP, Total Suspended Particulate matter i.e. Dust) emissions from hot flue gas were compared with the fine particle mass emissions from diluted sample. PM1 emissions measured from diluted flue gas were 1.1–4.4-fold as compared to TSP collected from hot flue gas. This may be attributable to the fact that organic vapors partially had penetrated into the TSP filter in a gaseous form whereas when they were diluted, semivolatile species condensed on the particles. It can be concluded that air staging is an effective way to reduce gaseous and organic emissions from batch combustion appliances. Particle emission measured from diluted flue gas represents a more realistic results than TSP (hot sampling), because in dilution, also the organic fraction of the particle emissions is taken into account.

Effect of air staging on a coaxial swirled natural gas flame

In the framework of a research program to investigate air staging applied to swirling flames, an experimental investigation aimed at studying pollutant emissions is reported. Staged combustion is accepted as an effective way to reduce nitrogen oxides in gas turbine combustors and, in the present study, is applied to a swirled flame fueled by natural gas, to analyze the potential for further reducing nitrogen oxides emissions in a coaxial, non-premixed combustor under overall lean conditions. The results indicate that the full benefits of air staged combustion in swirling flames depend mainly on the method of fuel injection. The most common method of axial injection of a premixed jet into a co-axial swirling airflow does not realize the required fast mixing. By radial injection of the premixed first stage in the secondary co-axial airflow, more efficient and faster centrifugal mixing is achieved, and hence shorter residence time and higher combustion intensity. This fuel injection strategy results in a more stable flame and dramatic reduction of NOx emissions when the first stage equivalence ratio is approaching the stoichiometric value. Still photographs of the flame and isothermal flow patterns are also reported to help correlate flame morphology and mixing features with nitrogen oxides emission.

Effects of Air Staging and Load on Fine-Particle and Gaseous Emissions from a Small-Scale Pellet Boiler

Fine-particle and gaseous emissions from a modern small-scale pellet boiler were studied with different air-staging settings and under different load operations. Commercial wood pellets were used in the boiler, which worked with a top-feed fuel input. Partial load operation experiments included half-load 12.5 kW and low-load 7 kW. In air-staging experiments, the amounts of primary air were decreased by 71 and 82% while simultaneously keeping constant total air/fuel ratios. This was found to result in considerably lower emissions than during normal full-load operation with factory settings. The reduction in fine-particle emissions was based on both a decrease in alkali metal emissions and emissions of unburnt carbonaceous particles. However, when the amounts of secondary air were decreased by 17 and 33%, there were higher emissions of both fine particles and gases during full-load operation, especially of emission components originating from incomplete combustion. The primary air/secondary air ratio correlated with CO, PM1, K, EC, and SO4 emissions. Furthermore, correlations were found between the primary air/fuel ratio and particle geometric mean diameter (GMD) and between the secondary air supply and GMD. These correlations were seen with all measured points, which indicates that they apply to all of the operational situations that were studied. The results show that there is significant potential for decreasing particle emissions from automated pellet combustion systems by optimizing combustion air staging in the furnace.

Effects of Hybrid Reburning System with SNCR and Air Staging on NOx Reduction and Thermal Characteristics in Oxygen-Enhanced Combustion

The reburning process has been demonstrated to be a very effective and simple technique for reducing NOx emission and has been successfully applied to many industrial fields. Likewise, the air staging process is one of the most effective techniques for control of NOx emission. Nowadays, selective non-catalytic reduction (SNCR) method has been suggested as the advanced process for NOx reduction. The main goal of this study is to examine the effects of hybrid reburning system with SNCR and air staging on NOx reduction. Experimental study has been done to examine the formation characteristics of NOx in a lab scale combustor (15 kW) with various oxygen-enhanced combustion conditions. This study reports four experimental cases. Experimental case 1 was performed regarding the reburning process. Reburn fuel fraction in the reburning zone and the amount of additional air in the burnout zone have been studied for NOx reduction. Air staging and hybrid reburning with air staging effects were considered in experimental case 2. The effects of air staging on the gas temperature distribution and heat flux rate were studied. For case 3, SNCR process was considered. The effects of various NH3 fraction values and the amount of main air on NOx reduction and CO emission were considered when oxygen enhanced combustion was used. Finally, hybrid reburning system with SNCR and air staging were studied for case 4. Based on the effectiveness of each De-NOx process, the advantage of hybrid reburning system with SNCR and air staging was found and discussed.

Effect of Air-Staging on Mercury Speciation in Pulverized Fuel Co-combustion: Part 2

The concerns regarding global warming and need for new energy resources brought the concept of biomass and waste as secondary fuels to the power industry. Mercury emissions in cases of cofiring of chicken manure, olive residue, and B-wood with a high volatile bituminous coal blend are studied in the first part of this paper. The use of secondary fuels significantly affects NOx emissions due to different types of nitrogen present in the fuel matrix. Air-staging is a proven in-furnace NOx reduction technology. The present work mainly involves bench scale studies to investigate the effect of air-staging on partitioning of mercury in pulverized fuel co-combustion. The combustion experiments are carried out in an entrained flow reactor at 1300 °C with a 20%th share of secondary fuels. Elemental and total gaseous mercury from the reactor is measured on-line, and ash is analyzed for particulate mercury along with elemental and surface properties. Reducing the air stoichiometry in the primary zone of the combustor increases unburnt carbon which in turn reduces mercury emissions in the gas phase. Ash analysis shows the effect of surface area, particle size, and unburnt carbon on mercury capture. Calcium variation in the ash was observed due to formation of different slag in reducing and oxidizing conditions and might have affected the mercury capture in combination with the above parameters. A low iron concentration of ash does not seem to affect the capture of mercury. The results will help in predicting different forms of mercury emitted from the furnace at desired operating conditions which will eventually form the basis for the design of the control strategies for mercury emissions.

Thermal aspects of a circulating fluidized bed with air staging

In this study, effects of air staging on wall-to-bed heat transfer were investigated in a laboratory scale circulating fluidized bed (0.23 m ID, 7.6 m high). The bed was operated under ambient conditions with silica sand particles (dp=89 µm, ρp=2650 kg m−3). Two different designs of secondary air (SA) injectors were used for air staging: radial and tangential. Bed-to-wall heat transfer measurements were carried out at three elevations above the SA injection port. The results indicate that similar to non-SA operation, the heat transfer with air staging depends strongly on the cross-sectional average suspension density. Tangential secondary injection was found to increase the bed-to-wall heat transfer above the SA injection port significantly due to increased suspension density compared with non-SA operation. Copyright © 2005 John Wiley & Sons, Ltd.

SO 2 capture and N 2O reduction in a circulating fluidized-bed boiler: influence of temperature and air staging

The effects of air staging and bed temperature on sulfur capture performance in a circulating fluidized-bed boiler fired with bituminous coal were studied. Normal air staging, no staging and intensified staging were compared at normal (850 °C) and high (930 °C) temperatures. The results clearly show that high temperatures and staged combustion are detrimental to sulfur capture performance. Sulfur capture was reduced by more than half with intensified staging at 850 °C. At the high temperature, sulfur capture was still possible without staging, but at greatly reduced efficiency. In the two cases with staging, the sulfur capture was negative in the period 2–3 h after a temperature increase, as a result of reductive decomposition of calcium sulfate. The temperature-dependence without staging indicates that reducing conditions affect sulfur capture in this case as well. The increase in temperature from 850 to 930 °C halved N 2O emissions, from ~ 100 to 50 ppm (at 6% O 2).