Air Staging Technology Research Articles

Insight into the gas pollutants emission of rural solid waste during the gasification-combustion process: Influencing factors and mechanisms

With the rapid development of rural areas, effective disposal of rural solid waste (RSW) has emerged as a critical concern. In this study, the gasification-combustion technology concerning air-staged technology was employed in the treatment of RSW and its main components (rubber, PVC, and food waste(FW)). This study focused on analyzing the emission patterns and total amounts of NOx, SO2, and HCl. For RSW, the gasification-combustion experiment effectively reduced NOx and SO2 emissions compared to the combustion experiment. The amount and patterns of gaseous pollutant emissions were significantly impacted by changes in gasification temperature, combustion temperature, and proportion of air (PA). Besides, due to the interplay of RSW's constituents, the change in gasification temperature and PA resulted in different emission patterns for FW and RSW. Under the combined action of constituents, the trend of RSW SO2 emission amount was distinct from its S sources due to the potential sulfation impact. The RSW's HCl emissions were found to be minimally affected by changes in temperature, PA, and reaction technique. This research manages the miniaturized centralized incinerator disposal of RSW and helps the control of gas pollutants emission.

Numerical study on coal/ammonia co-firing in a 600 MW utility boiler

Co-firing NH3 in coal-fired power plants is an attractive method to accelerate the pace of global decarbonization. However, the contradiction between achieving elevated temperature within the furnace and maintaining low NOx emission constrains the utilization of NH3 as fuel. In this study, 3-dimensional numerical simulations on coal/NH3 co-firing cases were conducted in a full-scale boiler for the first time. The influences of NH3 blending ratio, O2 enrichment combustion and deep air-staging technology were investigated. The results show that the burnout properties of NH3 are excellent in co-firing boiler. Higher NH3 blending ratio leads to lower temperature in the furnace. Enriching O2 concentration to 30% in the secondary air can compensate the temperature decline caused by 50% NH3 co-firing, while it brings an undesired surge in NOx concentrations. The high temperature and strong reducing atmosphere (HT&SRA) could be created by combining the O2 enrichment and deep air-staging combustion. The NO emission drops by 49.6% due to HT&SRA. Then, high flue gas temperature and low NOx emission can be achieved simultaneously. HT&SRA improves the overall exergy efficiency for 50% NH3 co-firing case from 51.65% to 51.78%. The findings open up a promising strategy for utilizing NH3 as a stationary fuel.

Effects of exhaust tube vortex on the in-furnace phenomena in a swirl-stabilized pulverized coal flame

This paper presents an experimental investigation of the effects of the exhaust tube vortex (ETV) on pollutant emissions and carbon burnout performance. The novelty in this study is to improve understanding of combustion behavior with the ETV structure via detailed in-furnace measurements (temperature, gas-phase species concentration, carbon burnout, emissions, and etc.) in a 16-kWth coal-fired furnace. The experiment considered two different swirling flames (co- and counter-swirl) with four air staging positions. A hollow tubular structure such as the ETV structure has been created under the co-swirl condition. The values of NOx emissions are about 430 ppm, but the CO emission is lower and carbon burnout is approximately 2% higher than that of the counter-swirl unstaging condition at the furnace outlet. For the air staging conditions, the air staging position 3 (SL3) maintained the generated ETV structure stronger in the primary combustion zone. The SL3 condition produced the lowest CO emission at about 275 ppm, and a relatively low emission of NOx showed with the highest carbon burnout performance of approximately 94.5% or more. The SL3 condition is the most favorable condition for the synergistic effect of air staging technology on the ETV structure with a low-NOx swirl-stabilized burner.

Enhanced combustion behavior and NOx reduction performance in a CFB combustor by combining flue gas recirculation with air-staging: Effect of injection position

In circulating fluidized bed (CFB) boilers, the flue gas recirculation (FGR) is an important technical means to promote de-NOx combustion. However, the conventional injection position of recycled gas seriously hinders the combustion efficiency and the flexibility of load regulation. To solve this, thermal-state experiments are conducted on a lab-scale CFB combustor to explore the feasibility of adopting novel FGR and air staging technology to achieve low NOx emission and sufficient combustion efficiency. The effects of FGR/supplementary burnout air (SBA) injection positions and operating parameters on temperature profile, combustion efficiency and original NOx emission in the furnace are discussed in detail. The synergistic effect of FGR and SBA on combustion characteristics and NOx reduction is also analyzed. Eventually, a systematic approach to enhance NOx control and combustion efficiency in fluidized bed is proposed. The key results indicate that the NOx reduction rate reaches 46.15% by adopting middle FGR and top SBA, which exceeds the reduction performance of utility boilers with conventional FGR. Also, the furnace outlet temperature and combustion efficiency can be ensured to be over 860 °C and 98.4% respectively, thus to provide new technical basis for enhancing de-NOx combustion in CFB boiler at low load, as well as the prospective guidance for FGR retrofitting of various fluidized bed combustors.

Control of NOx emissions by air staging in small- and medium-scale biomass pellet boilers.

The effect of air staging strategies on NOx control was investigated on a 210-kW small-scale biomass boiler (SBB) and a 1.4-MW medium-scale biomass boiler (MBB). Considering the de-NOx effect, as well as the convenience and economy for future wide use, the structures of the secondary air duct and the fuel feed tube were innovatively designed to solve the problems of the traditional prototype. The preliminary experiment showed that the lowest NOx emission was achieved when the air excess (ε) was equal to 2.04. Then, additional operating modes were conducted on the MBB to further optimize the air staging strategies. The optimal air staging strategy of the MBB (the secondary to primary air flow ratio (λ) and the ε were equal to 0.13 and 0.76, respectively) could decrease the NOx emission from 338.12 to 148.14mg/m3. Furthermore, the SO2 emissions and the lowest NOx emission of the SBB and the MBB could meet most emission standards of China and some developed countries. The thermogravimetric analysis (TG) and combustion characteristics of the wood fuel showed that the air staging was a suitable de-NOx technology for wood combustion, and the slagging was less likely to occur under the selected condition. Hence, the air staging technology was an effective and low-cost method for the emission reduction of biomass boilers. This study provided a practical basis for future research on the gas emission control of biomass boilers.

Impact of multi-hole-wall air coupling with air-staged technology on H2S evolution during pulverized coal combustion

The multi-hole-wall air coupling with air-staged technology (MH&AS) was developed for pulverized coal combustion to affect a simultaneous realization of multiple benefits, including prevention of high-temperature corrosion, highly efficient burning of pulverized coal, and low NOx emissions. In this work, the impact of MH&AS on H2S evolution under different conditions was investigated by applying a laboratory-scale MH&AS furnace to test its feasibility for preventing high-temperature corrosion. Some important inclusions were obtained: (i) the lack of multi-hole-wall air for Daheng (DH) coal combustion resulted in H2S concentration exceeding the critical value (namely, 100 ppm) causing high-temperature corrosion, but H2S near the wall could be completely eliminated with a multi-hole-wall air ratio (αm) of 0.1; (ii) the higher the pyrite content of the coal sample was or the smaller the particle size, the larger the H2S concentration near the wall; (iii) the four reactions leading to H2S formation were validated by Gibbs free energy and chemical equilibrium constant calculations. This study affirms the efficiency of MH&AS in mitigating the high-temperature associated with air-staged combustion.

Impact of the Multihole Wall Air Coupling with Air Staged on NOx Emission during Pulverized Coal Combustion

Air-staged combustion is one of the most sophisticated and effective technologies for reducing NOx emission during pulverized coal combustion. However, it may also result in problems of high-temperature corrosion, slagging, and high-imperfect/incomplete combustion loss. In order to prevent these problems, the multihole wall air coupling with air-staged technology (MH&AS) has been developed. The aim of this work is to investigate the impact of MH&AS on NOx emission by applying a laboratory scale of a MH&AS furnace. The results show that there existed an optimal multihole wall air ratio to significantly reduce the NOx emission. For example, with burner air ratios of 0.6, 0.7, 0.8, and 0.9, the corresponding optimal multihole wall air ratios were 0.100, 0.075, 0.050 and 0.025, respectively. The air distribution mode with a smaller burner air ratio and its optimal multihole wall air ratio were more conducive for NOx reduction. Furthermore, the influence of coal properties on NOx emission was also evaluated. T...

Chemical composition and speciation of particulate organic matter from modern residential small-scale wood combustion appliances

Combustion technologies of small-scale wood combustion appliances are continuously developed decrease emissions of various pollutants and increase energy conversion. One strategy to reduce emissions is the implementation of air staging technology in secondary air supply, which became an established technique for modern wood combustion appliances. On that account, emissions from a modern masonry heater fuelled with three types of common logwood (beech, birch and spruce) and a modern pellet boiler fuelled with commercial softwood pellets were investigated, which refer to representative combustion appliances in northern Europe In particular, emphasis was put on the organic constituents of PM2.5, including polycyclic aromatic hydrocarbons (PAHs), oxygenated PAHs (OPAHs) and phenolic species, by targeted and non-targeted mass spectrometric analysis techniques. Compared to conventional wood stoves and pellet boilers, organic emissions from the modern appliances were reduced by at least one order of magnitude, but to a different extent for single species. Hence, characteristic ratios of emission constituents and emission profiles for wood combustion identification and speciation do not hold for this type of advanced combustion technology. Additionally, an overall substantial reduction of typical wood combustion markers, such as phenolic species and anhydrous sugars, were observed. Finally, it was found that slow ignition of log woods changes the distribution of characteristic resin acids and phytosterols as well as their thermal alteration products, which are used as markers for specific wood types. Our results should be considered for wood combustion identification in positive matrix factorisation or chemical mass balance in northern Europe.

CFD investigation on combustion and NOx emission characteristics in a 600 MW wall-fired boiler under high temperature and strong reducing atmosphere

In this paper, a modified air staging technology for pulverized coal boilers was proposed, to notably reduce NOx emission by creating a zone with high temperature and strong reducing atmosphere (HT&SRA) in furnace. Here, the conventional air staging technology was employed in combination with increasing O2 fraction of feeding gas in primary zone (O2.p). The new technology was numerically verified in a 600MW wall-fired boiler and the temperature distribution, the char burnout and the effectiveness in NOx reduction were mainly examined. The results indicate that a sufficiently low stoichiometric O2 ratio in primary zone (SRp) is essential to reduce NOx emission by increasing O2.p. The effectiveness in NOx reduction by increasing O2.p also depends greatly on the injection position of over fire air (OFA). Under the condition of 0.7 SRp and a relatively high OFA position, the NOx emission could be reduced by 27.6% when O2.p is increased from 21% to 33%, while the incomplete combustion heat loss only shows a slight rise. In addition, the NOx reduction ratio could reach to >60% through the proposed low-NOx combustion technology compared with the current operation condition.

On-line analysis of organic emissions from residential wood combustion with single-photon ionisation time-of-flight mass spectrometry (SPI-TOFMS)

A study about the temporal variation of organic emissions from a modern wood log fired masonry heater was carried out with different gas analysis techniques: single-photon ionisation time-of-flight mass spectrometry (SPI-TOFMS) for real-time analysis of volatile (VOC), intermediate-volatile (IVOC) and semi-volatile organic compounds (SVOC), and a gas analyser system for gaseous components CO2, CO, NOx and organic gaseous carbon (OGC, quantified by flame ionisation detector). The emissions of three in Europe common types of firewood (beech, birch and spruce) were investigated by combustion of six consecutive batches of 2.5kg each over 4h. Batchwise emissions and temporal variations during combustion were discussed. Emission factors over the whole combustion cycle for OGC, VOC and IVOC were right up to one order of magnitude lower than in many previous studies due to latest improvements of air staging technology in wood log fired masonry heaters, whereas CO and NOx remained comparable. Regarding each combustion experiment, more than 50% of the total intensity of the mass spectra occurred during the combustion of the first two batches. Moreover, the molecular signatures of burning phases (‘ignition’, ‘stable combustion’ and ‘ember’) were examined by using non-negative matrix factorisation (NMF) and principal component analysis (PCA) in sequence. Marker substances for wood or biomass combustion, such as phenolic species or furan derivatives, exhibited highest relative abundance during ‘stable combustion’, whereas ‘ember’ is distinctly characterised by polyunsaturated hydrocarbons, such as benzene or naphthalene, through pyrosynthesis; in ‘ignition’, secondary decomposition products dominated. Nevertheless, highest quantitative emissions always occurred during ‘ignition’ at the beginning of each batch, followed by the phases ‘ember’ and ‘stable combustion’.

Effect of inner secondary air cone length of a centrally fuel‐rich swirl burner on combustion characteristics and NOx emissions in a 0.5 MW pulverized coal‐fired furnace with air‐staging

AbstractLow NOx burners and air staging technology are the most economic and effective means of reducing NOx emissions from coal‐fired furnaces. However, it is difficult to significantly reduce NOx emissions through air‐staged combustion in the furnace without reducing the boiler efficiency. The aim of this work was to study the effect of the inner secondary air cone length of a centrally fuel‐rich swirl coal combustion burner on combustion and NOx characteristics using a 0.5 MW laboratory furnace with air‐staging. Gas temperature and concentrations of gaseous species (O2, CO, and NOx) were measured in the primary combustion and burnout zones for different inner secondary air cone lengths. It was found that the inner secondary air cone length had significant effects on NOx emissions, unburned carbon content in the fly ash, and ignition performance of the burner. As the inner secondary air cone length increased, the unburned carbon content in the fly ash level increased, NOx emissions decreased, and pulverized‐coal ignition occurred later. The optimized results provide an important reference for engineering design. © 2015 Curtin University of Technology and John Wiley & Sons, Ltd.

Effect of Preoxidation O2 Concentration on the Reduction Reaction of NO by Char at High Temperature

Preoxidation experiments were carried out to determine the effect of temperature, ranging from 1000 to 1600 °C, on the O2 enhancement of NO reduction by a bituminous coal char. The results showed that there is a critical O2 concentration that gives a maximum amount of NO reduced by char. The effect of O2 on the reduction of NO indicates a balance between the oxidation reaction and the formation of surface complexes on the char. A large number of C(O) surface complexes can form during the gasification process of char but cannot stably exist at high temperature. The presence of active vacant sites in the complexes is an important factor affecting the reduction of NO and char. This analysis provides a theoretical foundation for further reducing NO emissions during coal combustion. In recent work, we found that a four-level air-staged combustion technology realized ultralow NOx emissions of ∼100 mg/Nm3 at 6% O2, which is much lower than that obtained by the current single-level air-staged technology with NOx ...

Research of Low NOx Combustion with Large-Angle Counter Flow of a Fuel-Rich Jet and Its Particle-Dynamics Anemometer (PDA) Experiment

On the basis of counter flow of primary air with fuel rich in company with overall air-staged technology, this paper introduces a new pulverized coal combustion technology that can realize low NO x emission, high combustion efficiency, slagging, and high-temperature corrosion prevention by employing overall air-staged combustion, large-angle counter flow of primary air with a fuel-rich jet and forming a partial area of high-temperature and high pulverized coal concentration in the furnace. To verify technical data, research has been conducted on a 1025 t/h tangential firing boiler adopting this technology and a three-dimensional particle-dynamics anemometer (PDA) is employed on this prototype for measurement of the characteristics of two-phase gas/particle flows in the burner area. The distribution of the particle concentration and size distribution of the primary air, as well as the gas/particle velocity field were obtained. The experiments also measure the flowing characteristics of over-fired air (OFA) and secondary air. The results show that, with counter flow of fuel-rich jet technology, more particles can be injected into the high-temperature side in the furnace, the concentration of the particle is higher at the high-temperature side than that near the water wall, and the particle concentration of large particles is also lower near the water wall. The research shows that the counter-flow technology combined with overall air-staged technology of the tangential firing boiler can realize low NOx emission and high efficiency combustion and can prevent slagging on the surface of the water wall and high-temperature corrosion.

06/00261 Development of an air staging technology to reduce NO x emissions in grate fired boilers : Staiger, B. et al. Energy, 2005, 30, (8), 1429–1438

06/00261 Development of an air staging technology to reduce NO x emissions in grate fired boilers : Staiger, B. et al. Energy, 2005, 30, (8), 1429–1438

Development of an air staging technology to reduce NO x emissions in grate fired boilers

Experiments with a newly designed controlled multiple air staging technology (CMAST) in grate firings show a considerable reduction in NO x emissions. The applicability of the CMAST depends on fuel parameters. Fuels with high moisture content cause a drop in the heat output during full load operation due to the reduced fuel conversion. Due to reduced temperatures in the furnace, the emissions of products of incomplete combustion rise during part-load operation. More primary air is necessary to decrease incomplete combustion products, thus preventing the successful implementation of the multi-air-staging technique. Experiments in the laboratory, and test and commercial firings assist in understanding the influence of different fuel characteristics on the combustion system, and detect practical potentials and limits of air staging. On this basis, concepts have been developed for an optimised operation of grate firings dependent on the fuel characteristics. These results promise a further improvement of combustion technology using wood fuels.