Secondary Air Research Articles

Development of a Hydrogen Micro Gas Turbine Combustor: Atmospheric Pressure Testing

Abstract The vision of a carbon-neutral world implies the shift from fossil to clean fuels for combustion-driven processes and machines like gas turbines. Green hydrogen is a promising alternative to substitute natural gas and other fossil fuels. In the H2mGT project, funded by the German BMWK, a microgas turbine (mGT) burner with 100% hydrogen firing is developed and validated. The project is collaboration between Technische Universität Berlin (TUB) and the manufacturer Euro-K GmbH. The project consists of three phases: (1). Atmospheric pressure tests with a fused silica combustion chamber; (2). Atmospheric pressure tests with counterflow-cooled steel combustion chamber and secondary air injection; (3). Validation of the burner in the micro gas turbine at elevated pressure levels. This paper will present the results of Phase 1. The hydrogen burner is based on a swirl-stabilized burner of TUB and was scaled to match the requirements of the mGT with its 130 kW thermal power. The burner design features multiple geometrical parameters to enable the optimization of the flame towards low NOx emissions. Therefore, a variable swirl intensity, additional axial momentum of air in the mixing tube, a movable center-body and different fuel injection locations are implemented. Phase 1 investigates the parameter space in terms of flame stability, operational range, and parameter impact on flame shape and emissions. Therefore, temperature, pressure, and emission measurements as well as OH* imaging are carried out. It is found that the flame can be operated over a large range of equivalence ratios and preheating temperatures up to 500 ∘C for many parameter settings. However, at some configurations, flashback into the mixing tube is triggered. As expected, the NOx emissions are mainly influenced by the equivalence ratio, the fuel distribution, and the swirl intensity. Single-digit emissions are reached up to an equivalence ratio of 0.4 at atmospheric pressure conditions. Furthermore, at low air mass flow, the burner can be operated at 100% natural gas or 100% hydrogen without any geometry changes. The fuel switch, thereby, does not change the NOx emissions significantly if reasonable normalization is used.

LES of a pressurized sooting aero-engine model burner using a computationally efficient discrete sectional method coupled to tabulated chemistry

This work is focused on the modeling and analysis of soot formation and oxidation in the pressurized ethylene-based model burner investigated at DLR. This burner features a dual swirler configuration for the primary air supply and includes secondary dilution jets inside the combustion chamber, showing reacting flow characteristics representative of the RQL combustor technology. Large-eddy simulations (LES) of the DLR burner are conduced here to assess a coupling approach between flamelet generated manifold (FGM) chemistry and discrete sectional method (DSM) based soot model with clustering method. First, a validation of the numerical results is conducted for the gas velocity and temperature fields, and good agreement is obtained for both mean and fluctuating quantities. The Soot Volume Fraction (SVF) computed from LES shows a satisfactory agreement with the experimental data in both SVF distribution and magnitude. The analysis also includes a numerical investigation of the soot production and the Particle Size Distributions (PSD). Finally, the configuration without secondary air is evaluated and an accurate prediction of the SVF field is also obtained. In this case, the absence of dilution air strongly influences the central region of the combustion chamber, and soot distribution and PSD are mainly affected by transport and dilution, not oxidation. It is finally concluded the proposed modeling framework is capable of predicting the soot field and particle size distributions inside the combustor for both operating conditions.

Improvement of syngas quality from two-stage downdraft wood gasification through steam and oxygen injection

The transition from fossil fuels to clean energy sources requires the supply of gaseous fuels from renewable origin for a number of applications. Such applications include in particular high-temperature heat for industries, and Combined Heat and Power (CHP) for flexible, decentralized power production. Gasification of lignocellulosic biomass is a good candidate to this end, converting solid biomass such as wood residues into a more versatile and CO2-neutral gaseous fuel. Today, the use of syngas remains limited due to its relatively low energy density and challenges related to its residual tar content.To improve the quality of syngas on these two aspects, we have studied the injection of steam and oxygen in a pilot two-stage downdraft gasifier. Replacing secondary air by oxygen enhances the Lower Heating Value (LHV) by 65%, while steam injection boosts the H2/CO ratio and damps the temperature rise due to oxygen. The gasification efficiency is enhanced by both oxygen and steam. As a drawback, oxy-steam conditions yield more Class III and IV tars in the syngas. The combined use of oxygen and steam can enhance the volumetric power of syngas-based CHP engines, and provide a sustainable fuel for high-temperature industrial applications.In future research, longer runs should be done to confirm the effects of steam and oxygen on conversion efficiency. The injection of steam and oxygen at the primary stage should also be studied. The presented results will help choosing whether to use oxygen and steam in downdraft gasification applications, and support the validation of numerical models.

Evaluation of different machine learning approaches for predicting high concentration episodes of ground-level ozone: A case study in Catalonia, Spain

Ground-level ozone (O3) is a pollutant with a great impact on human health and the environment. As a secondary air contaminant of photochemical origin, those areas with greater exposure to solar radiation, such as Spain and other Mediterranean countries, are considerably affected. With the aggravation of O3 pollution, it is important to provide reliable forecasting tools to help stakeholders implement more effective policies to mitigate the negative impact associated with this problem. In this regard, Machine Learning-based models have emerged in recent years, since they are able to identify complex relationships between ozone levels and relevant variables. However, their application to capture the most extreme events remains difficult. In this work, different ML approaches for predicting daily maximum 8-h average ozone (O3,MDA8) were compared, investigating their ability to forecast the highest concentration levels recorded. Two variants of the Random Forest algorithm (regression and classification) were applied to a specific area of Catalonia, Spain, with a special interest due to the high number of episodes of exceedance of O3 concentration levels. The predictive models were built with a 1 day time horizon, using datasets from 2002 to 2020. The variables used as inputs were other air pollutants concentrations and meteorological processes, monitored the day before to the target day to be predicted, and time information. Although results showed reasonable overall performances, low accuracy was achieved when forecasting the highest episodes of O3,MDA8. To improve the capacity of the models in predicting high-O3,MDA8 concentration levels, a methodology was proposed to fine-tuning the original predictions of the ML models according to a classification metric, G-Mean, which allows adjusting the balance between the correct predictions of different classes. Using the Sensitivity and Specificity metrics, the classical approaches were compared with the original ones proposed in the present study. The results obtained, for all the cases analysed, showed a mean increase in Sensitivity of 0.28, associated with a greater number of True Positives (correct predictions of high O3-episodes). On the other hand, the average Specificity value decreased, due to the appearance of a greater number of False Positives, although this reduction was only 0.05. The proposed criteria showed promising results, better balancing classification metrics and increasing the ratio of correct predictions linked to the higher ranges of O3.

Summertime response of ozone and fine particulate matter to mixing layer meteorology over the North China Plain

Abstract. Measurements of surface ozone (O3), PM2.5 and its major secondary components (SO42-, NO3-, NH4+, and organic carbon (OC)), mixing layer height (MLH), and other meteorological parameters were made in the North China Plain (NCP) during the warm season (June–July) in 2021. The observation results showed that the summertime regional maximum daily 8 h average ozone (MDA8 O3) initially increased and reached the maximum value (195.88 µg m−3) when the MLH ranged from approximately 900 to 1800 m, after which the concentration of O3 decreased with further increase in MLH. Interestingly, synchronous increases in PM2.5 concentration along with the development of the mixing layer (MLH <1200 m) were observed, and the positive response of PM2.5 to MLH was significantly associated with the increase in SO42- and OC. It was found that this increasing trend of PM2.5 with elevated MLH was driven not only by the wet deposition process but also by the enhanced secondary chemical formation, which was related to appropriate meteorological conditions (50 % < RH <70 %) and increased availability of atmospheric oxidants. Air temperature played a minor role in the change characteristics of PM2.5 concentration, but it greatly controlled the different change characteristics of SO42- and NO3-. The concentrations of PM2.5, its major secondary components, and the oxidation ratios of sulfate (SOR) and nitrate (NOR) increased synchronously with elevated MDA8 O3 concentrations, and the initial increase in PM2.5 along with increased MLH corresponded well with that of MDA8 O3. We highlight that the correlation between MLH and secondary air pollutants should be treated with care in hot weather, and the superposition-composite effects of PM2.5 and O3 along with the evolution of mixing layer should be considered when developing PM2.5–O3 coordinated control strategies.

The effects of key parameters on the gas/particle flows characteristics in the furnace of a Foster Wheeler down-fired boiler retrofitted with novel low-load stable combustion technology

Through a gas-particle cold-modeling experiment, the particle dynamic analyzer (PDA) is used to investigate the effects of fuel-lean coal/airflow angle and ratio of oil secondary air to F-layer secondary air on the gas/particle flows characteristics in the furnace of a Foster Wheeler (FW) down-fired boiler with enhanced stable combustion technology. As the fuel-lean coal/airflow angle increases from 10° to 45°, the peak value of the vertical dimensionless velocity of the gas/particle flows gradually increases, and the peak position gradually moves to the near wall region. As the ratio of oil secondary air to F-layer secondary air (the secondary air ratio for short) increased, the peak value of the vertical dimensionless velocity of the gas/particle flows gradually increased and the peak value position of the dimensionless velocity gradually moved towards the near-wall region. In actual operation, for the perspective of performance and safety, the recommended fuel-lean coal/airflow angle and secondary air ratio is 30°and 1:2 respectively. The enhanced stable combustion technology had been applied to two 600 MW FW down-fired boilers, and these boilers can achieve stable operation when burning a wide range of coal quality under the load section from 200 MW to 600 MW.

Significant Impact of Reactive Chlorine on Complex Air Pollution Over the Yangtze River Delta Region, China

AbstractThe chlorine radical (Cl) plays a crucial role in the formation of secondary air pollutants by determining the total atmospheric oxidative capacity (AOC). However, there are still large discrepancies among studies on chlorine chemistry, mainly due to uncertainties from three aspects: (a) Anthropogenic emissions of reactive chlorine species from disinfectant usage are typically overlooked. (b) The heterogeneous reaction uptake coefficients used in air quality models resulted in certain differences. (c) The co‐effect of anthropogenic and natural emissions is rarely investigated. In this study, the Weather Research and Forecasting (WRF)‐Community Multiscale Air Quality (CMAQ) modeling system (updated with 21 new reactions and a comprehensive emissions inventory) was used to simulate the combined impact of chlorine emissions on the air quality of a coastal city cluster in the Yangtze River Delta (YRD) region. The results indicate that the new emissions of reactive chlorine and the updated gas‐phase and heterogeneous chlorine chemistry can significantly enhance the AOC by 21.3%, 8.7%, 43.3%, and 58.7% in spring, summer, autumn, and winter, respectively. This is more evident in inland areas with high Cl concentrations. Our updates to the chlorine chemistry also increases the monthly mean maximum daily 8‐hr average (MDA 8) O3 mixing ratio by 4.1–7.0 ppbv in different seasons. Additionally, chlorine chemistry promotes the formation of fine particulate matter (PM2.5), with maximum monthly average enhancements of 4.7–13.3 μg/m3 in different seasons. This study underlines the significance of adding full chlorine emissions and updating chlorine chemistry in air quality models, and demonstrates that chlorine chemistry may significantly impact air quality over coastal regions.

Electrochemical testing of zeolite-based gas-diffusion electrodes for secondary metal air batteries—in memory of Prof. A. Milchev

Electrochemical testing of zeolite-based gas-diffusion electrodes for secondary metal air batteries—in memory of Prof. A. Milchev

Analysis of Combustion of a Steam Boiler with Chips and Bark as Fuel

PT. Medco is a business entity engaged in managing industrial plantation forests and one of the company’s branches is in South Papua—Merauke. This company manages wood to be processed into raw materials for paper and other purposes. Timber production activities that produce waste in very large volumes, these wastes still have a high calorific value which their utilization will produce fuels that can be used, one of which is as fuel for boilers for power generation. This study uses a qualitative method where research is conducted to obtain the necessary data to then be analyzed again by calculating combustion using the British Thermal Unit (BTU) analysis method. Preliminary data required for qualitative analysis include operational and technical steam boiler data. The fuel used in the combustion process is wood chips and bark obtained from production residue or what can be called waste. The results of the calculation of the combustion process in the 1 × 7 MW steam boiler (PLTU) PT. Medco shows Carbon (C) 34.47%, Hydrogen (H2) 4.22%, Sulfur (S) 0.06%, Oxygen (O2) 30.75%, Nitrogen (N2) 0.22%, Water (H2O) 27.80%, Ash 2.48% and a calorific value of Hight Heating Value (HHV) 9160.8 Btu/lb, Excess water 30% and fuel consumption of 16784 kg/h. The mass flow rate of steam is 35 tons or 66150 lb/h with a combustion gas temperature of 1490 °C and an adiabatic temperature formed in the furnace of 1075 °C. Primary air requirement is 43594.91 kg of air and the secondary air requirement is 18727.24 kg of air. The heat energy that is put into the steam boiler from the results of the combustion process is 98.24 × 106 BTU/h or 28.77204 MW, the heat that is utilized for the process of changing the fluid phase of the liquid in the water pipes along the boiler wall is only 83.038 × 106 BTU/h or 24.31975425 MW. So, it can be concluded that there is an energy loss of 15.2020 × 106 BTU/h or 4.452286 MW.

Industrial Rotary Kiln Burner Performance with 3D CFD Modeling

As the need to minimize environmental impacts continues to rise, it is essential to incorporate, advance, and adopt renewable energy sources and materials to attain climate neutrality in industrial operations. It is established that economic growth is built upon infrastructure, where the cement industry plays a crucial role. However, it is also known that this industry is actively looking for ways to transition toward low-carbon practices to encourage sustainable and environmentally conscious practices. To this end, the use of refuse-derived fuels to substitute fossil fuels is very appealing, as these have the potential to lower clinker production costs and CO2 emissions. Bearing this in mind, the primary objective of this work is to gain insights into the combustion behavior in an industrial rotary kiln by studying real-life scenarios and to assess the potential of substituting alternative fuels for fossil fuels to reduce CO2 emissions. A 3D CFD turbulent combustion model was formulated in Ansys® considering a Pillard NOVAFLAM® burner, where refuse-derived and petcoke fuels were used, and different secondary air mass flows were considered. From the obtained results, it was possible to conclude that the outcome of the combustion process is greatly influenced by the fuel-to-air ratio. Increasing the secondary air mass flow promotes the occurrence of a complete and efficient combustion process, leading to enhanced fuel conversion and the decreased formation of pollutants such as CO, soot, and unburned hydrocarbons. An increase in combustion efficiency from 93% to 96% was observed, coupled with a slight decrease in the pollutant mass fraction in the flue gas.

Characteristics of multi-cycle two-phase pulse detonation waves traveling near the lean combustion limit

The need for high combustion efficiency in two-phase pulse detonation engines necessitates the implementation of a lean combustion concept. However, there have been no research initiatives attempting to conduct two-phase pulse detonation in a lean combustion environment due to the highly sensitive nature of the deflagration-to-detonation transition toward the reactivity of the reactant composition. The present study explores methods to realize lean combustion organization in two-phase pulse detonation through the incorporation of secondary air injection. Valveless pulse detonation operation based on gasoline was carried out, while the frequency varies from 20 to 100 Hz. The initiation and propagation characteristics of the pulse detonation wave are influenced first by the equivalence ratio of the detonation initiation section and then by the equivalence ratio of the detonation propagation section. Furthermore, secondary air injection enabled a reduction in the minimum global equivalence ratio for the stable operation of multi-cycle two-phase pulse detonation waves to 0.38, while maintaining an 80% detonation rate.

Design of a Novel α-Shaped Flue Gas Route Flame Incinerator for the Treatment of Municipal Waste Materials

In order to improve the combustion characteristics of municipal waste materials and reduce excess pollutants generated during the incineration process, this study develops a novel waste incinerator with an α-shaped flue gas route. This has been achieved through the application of momentum vector synthesis theory in order to modify the secondary air structure in a conventional incinerator, resulting in enhanced combustion efficiency of the incinerator. Computational Fluid Dynamics (CFD) based cold state test results demonstrate that with appropriate modifications to the design of the incinerator, the flue gas propagates through a longer α-shaped route rather than conventional L-shaped route. Hot state tests have been carried out on a full scale 750 tons/day waste incinerator. Test rests show that the temperature of the flue gas increases by 138% under the front arch when secondary air supply is being incorporated into the design of the incinerator, resulting in better combustion of the municipal waste materials, lower emissions and higher thermal efficiency of the incinerator. The results obtained in this study confirm the rationality and feasibility of momentum flow rate method for better design of waste incinerators.Graphical

Investigation of aerodynamics in combustion of vegetative waste on isothermal models

Modern agricultural vehicles contain a large number of components, which include micro Abstract. Conventional furnaces using alternative fuels, such as vegetable waste (VW), are widely used instead of furnaces operating on conventional fuels. The furnaces aggregated with dryers of SZT and SP type are widely used in agriculture and food industry. Two models with a suspended bed were investigated: with flare-vortex and cyclone-vortex modes. The first model assumes the presence of an inclined grate in a rectangular chamber with a concentrated supply of secondary blast, primary blast with material is supplied above the grate in its lower part, and the second model assumes a cylindrical-shaped chamber with primary air inlet in the center and cyclonic secondary blast inlet at a certain height. This scheme is close to the first, only in the lower part of the model concentrated input of primary blast with material. The methodology of aerodynamics studies included: feeding of material from the hopper; material cutoff after steady-state mode; collection and weighing of fallen particles from the model; determination of the time of material presence in the model by labeled particles. Modeling of aerodynamics for different schemes of furnace process organization showed the possibility of creating two-span or single-span furnace blocks depending on the required operating mode. The results of comparative studies of aerodynamics of flare-vortex and cyclone-vortex modes are given. The results of comparative studies of aerodynamics of flare-vortex and cyclone-vortex modes are given. Optimal blowing parameters, secondary and primary air ratio, furnace design parameters contributing to the maximum specific volume heat stress are determined.

Observations of ozone, acyl peroxy nitrates, and their precursors during summer 2019 at Carlsbad Caverns National Park, New Mexico

ABSTRACT Carlsbad Caverns National Park (CAVE) is located in southeastern New Mexico and is adjacent to the Permian Basin, one of the most productive oil and natural gas (O&G) production regions in the United States. Since 2018, ozone (O3) at CAVE has frequently exceeded the 70 ppbv 8-hour National Ambient Air Quality Standard. We examine the influence of regional emissions on O3 formation using observations of O3, nitrogen oxides (NOx = NO + NO2), a suite of volatile organic compounds (VOCs), peroxyacetyl nitrate (PAN), and peroxypropionyl nitrate (PPN). Elevated O3 and its precursors are observed when the wind is from the southeast, the direction of the Permian Basin. We identify 13 days during the July 25 to September 5, 2019 study period when the maximum daily 8-hour average (MDA8) O3 exceeded 65 ppbv; MDA8 O3 exceeded 70 ppbv on 5 of these days. The results of a positive matrix factorization (PMF) analysis are used to identify and attribute source contributions of VOCs and NOx. On days when the winds are from the southeast, there are larger contributions from factors associated with primary O&G emissions; and, on high O3 days, there is more contribution from factors associated with secondary photochemical processing of O&G emissions. The observed ratio of VOCs to NOx is consistently high throughout the study period, consistent with NOx-limited O3 production. Finally, all high O3 days coincide with elevated acyl peroxy nitrate abundances with PPN to PAN ratios > 0.15 ppbv ppbv−1 indicating that anthropogenic VOC precursors, and often alkanes specifically, dominate the photochemistry. Implications: The results above strongly indicate NOx-sensitive photochemistry at Carlsbad Caverns National Park indicating that reductions in NOx emissions should drive reductions in O3. However, the NOx-sensitivity is largely driven by emissions of NOx into a VOC-rich environment, and a high PPN:PAN ratio and its relationship to O3 indicate substantial influence from alkanes in the regional photochemistry. Thus, simultaneous reductions in emissions of NOx and non-methane VOCs from the oil and gas sector should be considered for reducing O3 at Carlsbad Caverns National Park. Reductions in non-methane VOCs will have the added benefit of reducing formation of other secondary pollutants and air toxics.

Nitric oxide removal by synergistic photooxidation and adsorption using Pd1/g-C3N4-UiO-66-NH2 P-A heterojunction

Simultaneous avoidance of secondary air pollution and catalyst deactivation remains a challenge for existing photocatalytic removal of nitric oxide (NO). Herein, a photocatalysis-adsorption (P-A) heterojunction is synthesized for eco-friendly NO removal by facilely grinding Pd single atoms (Pd1) anchored g-C3N4 (48CN/Pd) with UiO-66-NH2 (UION). Under visible-light irradiation, the 40UION-CN/Pd composite shows 93.91 % of NO removal efficiency with only 2.73 % of NO2 emissions and negligible catalyst deactivation. The DeNOx index increases remarkably from −0.66 for 48CN/Pd to 0.86 for 40UION-CN/Pd. Furthermore, the synthesized P-A heterojunction efficiently removes NO from real flue gases produced by a domestic coal-fired stove and from SO2-rich flue gases. The mechanism exploration based on experimental investigations and density functional theory (DFT) calculations reveals that UION captures the NO2 selectively produced by 48CN/Pd, simultaneously suppressing NO2 emissions and refreshing active sites for NO photooxidation. Moreover, the results of X-ray photoelectron spectroscopy (XPS), charge density difference calculation, energy-resolved distribution of electron traps (ERDT) and in-situ Kelvin probe force microscopy (KPFM) reveal that the built-in electric field and Type-II heterojunction formed between 48CN/Pd and UION promote the separation of photogenerated carriers, enhancing the catalytic activity of the composite. This work provides an innovative strategy to avoid NO2 emission and catalyst deactivation during photocatalytic NO removal.

Flow characteristics of radial inflow in impeller rear cavity with baffle plate

The research purpose of this paper is to explore the influence of the baffle plate on the airflow in the rear cavity of the centrifugal impeller and optimize the performance of the secondary air system's air bleed section. In this paper, a comprehensive experimental study was carried out on the flow characteristics in the impeller rear cavity with baffle plate. The windage torque, flow structure and pressure drop between inlet and outlet were measured respectively. The experiment was carried out with the condition that the range of rotational Reynolds number was from 8.33 × 105 to 22.2 × 105 and the range of mass flow rate coefficient was from 0.92 × 104 to 2.92 × 104. The results show that the static cavity and the narrow stator-rotor cavity formed by the baffle plate effectively suppress the overall swirl coefficient in the cavity. Thus, the static pressure and total pressure drop in the rotor–stator cavity were reduced. The influence of the baffle plate on the windage torque of the rotary disk is related to the turbulence parameters. Under large turbulence parameters, the windage torque would be reduced with baffle plate, while under small turbulence parameters, the baffle plate would increase with baffle plate. In general, the baffle plate can improve the flow capacity and optimize the bleed air performance with proper structure and operation conditions.

Volatile organic compound fluxes in the agricultural San Joaquin Valley – spatial distribution, source attribution, and inventory comparison

Abstract. The San Joaquin Valley is an agricultural region in California that suffers from poor air quality. Since traffic emissions are decreasing, other sources of volatile organic compounds (VOCs) are gaining importance in the formation of secondary air pollutants. Using airborne eddy covariance, we conducted direct, spatially resolved flux observations of a wide range of VOCs in the San Joaquin Valley during June 2021 at 23–36 ∘C. Through land-cover-informed footprint disaggregation, we were able to attribute emissions to sources and identify tracers for distinct source types. VOC mass fluxes were dominated by alcohols, mainly from dairy farms, while oak isoprene and citrus monoterpenes were important sources of reactivity. Comparisons with two commonly used inventories showed that isoprene emissions in the croplands were overestimated, while dairy and highway VOC emissions were generally underestimated in the inventories, and important citrus and biofuel VOC point sources were missing from the inventories. This study thus presents unprecedented insights into the VOC sources in an intensive agricultural region and provides much needed information for the improvement of inventories, air quality predictions, and regulations.

Optimization of secondary air operation parameters of waste incineration boiler based on response surface methodology

To reduce the NOx emission concentration of waste incineration boilers and improve the thermal efficiency of incinerators, the combustion process of a 600 t/d incineration boiler was numerically investigated. First, the influences of the secondary air injection angle, velocity and temperature on the NOx concentration at the waste incineration boiler outlet and the thermal efficiency of the incinerator were analyzed through a single factor simulation test. Then, coupling optimization of key operating parameters, including the secondary air injection angle, velocity and temperature, was conducted via the response surface design method to obtain the specific functional relationships between outlet NOx concentration, incinerator thermal efficiency, front wall secondary air injection angle, rear wall secondary air velocity and secondary air temperature, as well as the optimal operating parameters for the boiler. The results showed that when the secondary air injection angle of the front wall ranges from 68°∼80° and the secondary air injection angle of the back wall is 67°, the minimum NOx concentration is 142.23 mg/m3, and the maximum thermal efficiency of the incinerator reaches 85.51 %. When the secondary air velocity at the front wall is 42 m/s and the secondary air velocity at the back wall ranges from 42 ∼ 66 m/s, the NOx concentration at the outlet is the lowest at 140.05 mg/m3, and the thermal efficiency of the incinerator is the highest at 85.63 %. When the secondary air temperature ranges from 297.16 ∼ 309.16 K, the NOx concentration at the outlet is the lowest at 155.45 mg/m3, and the thermal efficiency of the incinerator is the highest at 84.64 %. The secondary air injection angle, velocity and temperature impose significant effects on the NOx concentration at the outlet and thermal efficiency of the incinerator. The optimal parameters, as determined in the multifactor simulation test, include a 77° secondary air injection angle of the front wall, 69 m/s secondary air velocity at the back wall, and 297.15 K secondary air temperature. Under these conditions, the NOx concentration at the outlet is 134.98 mg/m3, and the thermal efficiency of the incinerator reaches 86.11 %. This study has important guiding significance for reducing pollution and improving the efficiency of waste incineration boilers.

Numerical Study of the Effect of Imaginary Circle Diameter on the Combustion in a Corner-tangentially-fired Boiler

The key factor affecting the combustion and operation of corner tangentially fired boilers (CTFBs) is the diameter of the imaginary circle. In this paper, the temperature and reducing gas distribution in a 350 MW supercritical CTFB were studied numerically, and the influence of imaginary circle diameter on combustion characteristics was analyzed. The results show that: 1) When the diameters of the imaginary circles of the primary and secondary air are decreased, there will be a delay in combustion. This is not profit to the steady-state burning of coal powder. In addition, the temperature near the water wall decreases, and the volume fraction of CO and H2S decreases on the rear side of the main combustion area, but increases significantly on the side of the fire. 2) By reducing only the diameter of the imaginary circle of primary air, the ignition distance of pulverized coal in the lower burner can be advanced, which is profit to improving combustion stability at low loads. Besides, the temperature, CO and H2S volume fraction near the water wall all decrease. 3) When the imaginary circle diameters of primary and secondary air in the upper part of the furnace are reduced, the temperature, volume fraction of CO and H2S in the adjacent layer near the water wall are increased.

Numerical study on optimization of secondary air box in a 600 MW opposed wall-fired boiler

The opposed wall-fired boiler has been widely employed in power plants in China due to its adaptability. However, the airflow in the same layer burners from the large air box is uneven, affecting the combustion characteristics of pulverized coal and causing the corrosion and slagging of the water-cooled wall. In this study, the numerical simulation is performed on a 600 MW wall-fired boiler to investigate the air distribution and flow characteristics of each burner and the secondary air duct under variable boiler loads (100%, 75%, 50%, and 30%), which would provide the basis for optimization of the secondary air box. The effectiveness of the modified burner, over-fire air (OFA) nozzle, and secondary air duct is demonstrated through the numerical simulation. The results indicate that the burner and OFA nozzle exhibit distinct flow deviation characteristics within the original air box. Specifically, the burner demonstrates a flow deviation ranging from 2% to 4%, whereas the OFA nozzle exhibits a flow deviation ranging from 10% to 35%. Integrating poly air rings into the burners and OFA nozzles on the sidewall separately addresses the issue of non-uniform flow distribution of the OFA nozzle while concurrently improving the air flow rate on both sides of the burners and OFA nozzles. The main air duct could be divided into three smaller air ducts by installing two deflectors at the corner of the secondary air duct. This scheme effectively decreases the pressure drops at the corner interface from 337.4 to 254.3 Pa. The findings of this study could have the potential to offer scientific insights into and recommendations for the optimal functioning of the boiler system.