Tertiary Air Research Articles

The Performance and Emission Parameters Based on the Redistribution of the Amount of Combustion Air of the Wood Stove

Several factors affect how particulate matter and gaseous emissions are formed during the combustion processes of biomass. The amount of combustion air, as well as its redistribution, is one of these factors. This article deals with the performance and emission parameters determined using different distributions of the amount of combustion air of the wood stove with beech wood as a fuel. Eighteen different settings of primary, secondary and tertiary air supplies were realized, while heat output, efficiency, particulate matter, carbon monoxide and nitrogen oxides were measured or determined. The aim of this article is to identify the optimal air distribution between primary, secondary, and tertiary air supplies focused on the mentioned parameters. Based on the results, two settings (25/50/25 and 0/100/0) could be the optimal variant. However, the concentration of particulate matter reached a higher value during the setting with a ratio of 25/50/25, similar to a ratio of 50/25/25. The measurement during the setting with a ratio of 0/100/0 could be influenced by the existing embers on the grid before the start of the measurement. However, it is important to supply all three types of combustion air with the main emphasis on the secondary air supply due to the completely use of the combustible gases.

Damage assessment of a cement plant partially collapsed depending on various causes

This study aims at examining the possible causes of the brittle collapse of a tertiary air duct system under vertical loads. Problems related to the design and construction stages were examined. The entire process was illustrated using a tertiary air duct case study in a cement plant. In the plant, the tertiary air duct collapsed without any earthquake, blast, or impact effects. The current study includes a field study, examination of an original/revised design project, and numerical simulation. In the first stage of the study, the existing state of the collapsed system and its compliance with static and mechanical projects were examined. Secondly, a two-dimensional finite element analysis was performed to determine project eligibility. The causes of the system were determined based on the data obtained in the former stages. The results showed that the causes of partial collapse included project errors, construction faults, and project incompatibilities.

Experimental study on effects of multistage reactant and air jet velocities on self-preheating characteristics and NOx emission of burning pulverized coal

To explore the NOx control strategies deeply, this study investigated the effects of multistage reactant and air jet velocities, including preheated fuel jet velocity (vpf), ratio of internal secondary air jet velocity to external secondary air jet velocity (R12) and ratio of first-staged tertiary air jet velocity to second-staged tertiary air jet velocity (M12), on combustion characteristics and NOx emission of pulverized coal on a 30 kW self-preheating combustion test rig. During preheating, as vpf increased, the temperature at different locations increased. And the concentrations of the main combustible gases (CO and H2) in the coal gas and the conversion rate of each component in the pulverized coal increased first and then decreased at the outlet. Moreover, vpf also influenced the particle characteristics greatly. The particle size of preheated coal char decreased first and then increased, while its specific surface area and reacting activity increased first and then decreased. The good self-preheating characteristics had a positive impact on the subsequent combustion and NOx emission. During combustion, vpf, R12 and M12 had different effects on the temperature distribution in the down-fired combustor (DFC). Under different vpf, the temperature distribution was relatively complex, and it was mainly regulated by the self-preheating characteristics, combustion share and jet velocity of the preheated fuel. As R12 increased, the temperature increased gradually in the upper part of the DFC, meaning the upper combustion was promoted. M12 mainly affected the position of the main combustion region, which shifted down as M12 increased. Moreover, increasing M12 could also reinforce the combustion in the main combustion region. vpf, R12 and M12 also influenced combustion efficiency and NOx emission obviously with certain change regularities. As vpf and R12 increased, the combustion efficiency increased first and then decreased, while NOx emission decreased first and then increased. As M12 increased, the combustion efficiency decreased first and then increased, while NOx emission increased first and then decreased. Moreover, compared to lower M12, it was more favorable to improve the combustion when M12 was higher.

Effect of low-nitrogen combustion system with flue gas circulation technology on the performance of NOx emission in waste-to-energy power plant

NOx as a major gaseous contaminant, reducing NOx emissions has become a pressing concerns. At present, the SNCR process is preferred for waste-to-energy power plants. In this paper, a method of low-nitrogen combustion system with flue gas circulation combined with SNCR was proposed to reduce NOx emissions. A portion of the hot flue gas at the tail of the furnace is extracted as circulation flue gas, and the circulation flue gas is sprayed into the SNCR as tertiary air. The experimental research was conducted in a 500 t/d waste-to-energy power plant. Firstly, the air distribution of the incinerator with the low-nitrogen combustion system is discussed, the circulation flue gas can completely replace the secondary air to reach the boiler rated evaporating capacity and reduce NOx emissions. Next, the supply position of the tertiary air was studied, and the supply position worked best in the upper of SNCR. Finally, the usage of the low-nitrogen combustion system can reduce urea consumption by around 35%. The circulation flue gas extracted in the incinerator contains a small amount of particulate matter. It is a problem to be considered for further industrial application.

A methodology for sectoral analysis of the economy

Subject. The article analyzes sectors of the Russian economy, based on the Harvard Paradigm. Objectives. The purpose is to develop a sectoral analysis technique and test it on the Russian enterprises data. Methods. I employ general scientific principles and research methods, like abstraction, generalization of approaches of domestic and foreign authors on identification, development and analysis of sectors, and the industry analysis. Results. The presented technique for analyzing economic sectors includes three stages. At the first stage, I investigate basic conditions, namely factors (forces) of competition in the sector under study, profitability and risk, and special aspects of State regulation. At the second stage, I analyze the behavior of companies in the sector and assess the operational efficiency, investment and financial activity of enterprises. At the third stage, the indicators of value creation and dynamics of sector development are analyzed. The methodology was tested on data from enterprises in four sectors of the economy: primary (extraction of coal, oil, natural gas, etc.), secondary (production of chemicals, iron and steel production, etc.), tertiary (water, air, and space transport, etc.), and quaternary (development of computer software, activities in the field of information technology, R&D). Conclusions. I tested the hypothesis about the dynamics of economic sectors’ development based on calculations, and identified positive trends in the Russian economy, i.e. the faster growth of tertiary and quaternary sectors and their relatively high efficiency. As for negative trends, they include low investment activity of enterprises, posing a threat to economic growth.

Numerical and Experimental Investigation of a Non-Premixed Double Swirl Combustor

This paper focuses on a detailed numerical investigation combined with experimental research for a non-premixed swirl combustor, which aims to analyze the effects of the blade angle of the outer swirler and equivalence ratio on flow and combustion characteristics. In the experiment, the temperature in the furnace was obtained with a thermocouple, while a realizable k-ε turbulence model and two-step reaction mechanism of methane and air are used in the numerical method. The calculation results are in good agreement with the experimental data. The results reveal that the air flow rate through the swirler accounts for a small amount of the total air due to the influence of the draft fan, and there is no central recirculation zone (CRZ) despite the presence of the swirler. It was also found that NO emissions gradually decrease as the blade angle of the outer swirler increases. It was also indicated that the average temperature is 100 K higher than the general combustor with a 58° blade angle in the furnace by increasing the equivalent ratio of the tertiary air area, and the NO emissions reduced by approximately 25%. This study can provide guidance for the operation and structural design of non-premixed swirl combustors.

Investigation of the direct-flow jets vortex motion in the M-shaped boiler invert furnace

For advanced ultra-supercritical parameters (A-USC) of steam, the design of an M-shaped boiler is proposed, designed to operate in a 500 MW unit on a lean coal (grade TR). The boiler profile is selected from the condition of minimizing the length of the main steamlines made of expensive nickel-alloy steel. With regard to this boiler, a scheme has been developed for pulverized coal combustion in an invert furnace using direct-flow burners and nozzles. Research has been carried out on the physical model of the furnace in the implementation of this combustion scheme: a qualitative study of the trajectories of the burner jets, jets of secondary and tertiary air obtained by their hot spark visualization; quantitative determination of the main characteristics of burner jets and their weight gain. The studies have shown the high efficiency of the recommended scheme of the furnace-burner device: a staged supply of the oxidizer along the flame length and along the furnace height is organized; the dynamic pressure of jets on the furnace wall tubes is excluded; vortex furnace aerodynamics should provide a high degree of burnout of coal dust particles; air jets evenly fill the horizontal section of the furnace; the ejection capacity of turbulent jets is much higher than for a flat submerged jet.

The Effect of the Ratio of the Secondary and Tertiary Air on the Outlet Velocity Field of the New Swirling Pulverized Coal Burner

ABSTRACT The outlet velocity field of the pulverized coal burner is one of the important factors affecting its operating characteristics. In this article, cold tests were carried out for a new swirl burner with a pre-combustion chamber, and the influence of the air ratio on the outlet velocity field of the burner was studied. Through the cold single-phase test on the 1:3 model test bench, the burner outlet cold air velocities were obtained. The results shown that the formation of the central recirculation zone was mainly affected by the secondary air, a stable central recirculation zone could not be formed when the velocity of secondary air was too low. When the total air of the burner was fixed, the secondary air increased, the length of the central recirculation zone increased, and the mixing speed between different flows increased. When the ratio of the mass flow of the secondary air to tertiary air increased from 26:74 to 85:15, the reflux rate increases 5.5 times, which helped to keep the combustion stable.

Experimental study on NOx emissions of pulverized coal combustion preheated by a 2 MW novel self-sustained preheating combustor

In the study, a potentially feasible low-NOx combustion technology, based on self-sustained preheating combustion of pulverized coal, is proposed. A 2 MW novel self-sustained preheating combustion test rig was employed, and bituminous coal was used in the experiment. A novel internal fluidized bed combustor (IFBC) was used as the preheating chamber for pulverized coal, followed by air staging in the combustion chamber. Preheating characteristics of the IFBC and the temperature distribution in the primary combustion zone were discussed. Next, the effects of the air staging ratio of the preheated fuel burner and the positions of tertiary air on the combustion characteristics and NOx emissions of bituminous coal were investigated. The results demonstrated that pulverized coal led to a clean and efficient operation, producing a minimum NOx emission of 72 mg/Nm3 (@ 6% O2). The fuel could be preheated to above 900 °C stably, and the obtained conversion rate of fuel-bound N (fuel-N) was up to 80.2% in the IFBC. Moreover, the temperature profile in the primary combustion zone exhibited a symmetrical distribution along the central axis of the preheated fuel burner. The high-temperature primary combustion zone moved upward with increasing air staging ratio of the preheated fuel burner, and a region with low oxygen and strong reducibility was formed, inhibiting NOx generation. To maximally reduce NOx emission, a large retention time in the reducing zone and uniform mixing of reactants were crucial. The multi-layer arrangement and delayed supply of tertiary air were found to be conducive to significantly reducing NOx emissions.

NOX reduction in calciner using air staging and raw meal split technology

The manufacture of cement is highly energy-intensive and emission-intensive due to the large heat needed for plant. Nitrus Oxide (N2O) is one of the major greenhouse gas emitted into the atmosphere through it. The purpose of this work is to reduce NOX emissions inside calciner by using air staging and raw meal split technology. Tertiary air staging enables the fuel to be combusted in two different areas. Three cases are simulated using three different flow rate of tertiary air inside calciner using CFD software. The raw meal also split and passed into two zones. In order to gain confidence in the model used, non-premixed coal combustion is modeled and validated using the experimental data presented in the literature. Based on the results predicted, the calciner performance is analysed in depth. When the quantity of air through upper tertiary air inlet is increasing NOX formation decreasing. By comparing three cases it is found that case 70%–30% air-flow through the upper inlet and lower inlet respectively 362 ppm NOX produced, which is less than the other two cases.

Characteristics of Preheating Combustion of Power Coal with High Coking Properties

Yankuang coal with the high coking property is difficult to use through direct combustion. The main purpose of this paper is to study the combustion characteristics and NOx emissions of this type of coal using preheating combustion technology. The experimental results show that after the pulverized coal is preheated, the char residue characteristic is significantly reduced from 5 to 1. During the preheating process, the preheating temperature is stable at about 910°C, and the particle size of char after preheating is reduced, and the pore structure and specific surface areas are increased. The combustion temperature of preheated fuel is stable at around 1100°C, and the combustion efficiency can reach more than 99% under different conditions. Changing the structure of the secondary air nozzles during the preheating combustion process can influence the characteristics of emissions. The NOx emission of the central nozzle is about 112 mg/Nm3 lower than that of the annular nozzle. Changing the tertiary air distribution modes can reduce the final NOx emissions to 215 mg/Nm3 (@6%O2), and the corresponding conversion ratio of fuel N to the final NOx is 4.2%. The results of this experiment prove that the Yankuang coal can achieve stable combustion by preheating combustion technology, and this proposed a new way for the utilization of Yankuang coal.

Investigations on combustion optimization and NOX reduction of a 600-MWe down-fired boiler: Influence of rearrangement of tertiary air and jet angle of secondary air and separated over-fire air

Low-NOX combustion is the main technology for reducing NOX emission in coal-fired plants. In this work, numerical simulation was conducted on a 600-MWe down-fired lean coal boiler to study the effects of important factors on NOX reduction, namely, the arrangements of tertiary air (TA), the jet angle of secondary air (SA), the separated over-fire air (SOFA) ratio, and the SOFA jet angle. The optimal arrangement was obtained with the original TA moved down; the jet angle of SA (A layer) at 20° (downdip); the SA (F layer) and the TA at 20° and 30° (downdip), respectively; and the SOFA set in the upper furnace, with a 20% ratio and a 30° jet angle. The NOX emissions were reduced from 1527 mg/m3 to 773 mg/m3 in the optimized system. Meanwhile, the exhaust gas temperature decreased from 1387 K to 1369 K, and the unburned carbon content increased slightly by 0.24%, with the overall boiler efficiency kept nearly constant. The in situ measurement results are consistent with the simulation predictions.

Influence of mass air flow ratio on gas-particle flow characteristics of a swirl burner in a 29 MW pulverized coal boiler

In a gas/particle two-phase test facility, a three-component particle-dynamics anemometer was used to measure the characteristics of gas/particle two-phase flows in a 29 megawatt (MW) pulverized coal industrial boiler equipped with a new type of swirling pulverized coal burner. The distributions of three-dimensional gas/particle velocity, particle volume flux, and particle size distribution were measured under different working conditions. The mean axial velocity and the particle volume flux in the central region of the burner outlet were found to be negative. This indicated that a central recirculation zone was formed in the center of the burner. In the central recirculation zone, the absolute value of the mean axial velocity and the particle volume flux increased when the external secondary air volume increased. The size of the central reflux zone remained stable when the air volume ratio changed. Along the direction of the jet, the peak value formed by the tertiary air gradually moved toward the center of the burner. This tertiary air was mixed with the peak value formed by the air in the adiabatic combustion chamber after the cross-section of x/d = 0.7. Large particles were concentrated near the wall area, and the particle size in the recirculation zone was small.

Experimental research on cement grate cooler system and numerical simulation of its clinker cooling process

The grate cooler is of considerable importance in cement production and its heat distribution plays an important role in evaluating the energy utilization efficiency. In this study, we analyze the heat distribution in the entire grate cooler system of a 5000 t/d cement plant through experiments, and acquire the mass flow rates, inlet temperatures, and outlet temperatures of the cooling air and clinker. The experimental results show that the sensible heats of secondary and tertiary air, air discharged, clinker discharged, and the surface dissipation heat account for 50%, 40%, 9%, and 1% of the total heat flowing in the system, respectively; this indicates the necessity of recovering the exhaust air. Therefore, based on the experimental results, an improved model of the clinker cooling process of the grate cooler system is proposed. The simulation of the two schemes of cyclic air technique, using the numerical model, to induce the exhaust air in the chimney to the first grate plate and second grate plate, indicates that inducing the exhaust air to the first grate plate is more effective for recovering the waste heat.

Experiment study on NOx emission characteristics of the ultra-low volatile fuel in a 2 MW novel pulverized fuel self-sustained preheating combustor

The pyrolysis semi-coke, with ultra-low volatile content, is difficult to burn effectively with conventional combustion technology. In this research, a 2 MW novel self-sustained preheating combustion test rig was constructed. Efforts were made to investigate the effects of secondary air ratio, the air staging degree of preheated fuel burner, and the position of tertiary air on the combustion characteristics and NOx emissions of semi-coke. The results showed that NOx emission was reduced to 67 mg/Nm3 (@6% O2) with a combustion efficiency of 99.2%. The internal fluidized bed combustor (IFBC) could provide high-temperature preheated fuel for the combustion chamber steadily. Also, 69.3% of the fuel-bound nitrogen was released in the IFBC. The temperature distribution in the combustion chamber became uniform under the multi-layer arrangement of tertiary air. As the secondary air ratio decreased from 0.50 to 0.40, NOx emissions decreased due to the enhancement of reducing atmosphere in the reducing zone. Besides, the deeper air staging of the preheated fuel burner contributed to forming a region of low oxygen and strong reducibility at the early staged combustion, which could inhibit the generation of NOx. The strong mixing and long dwell time in the reducing zone were essential for the reduction of NOx emissions. The multi-layer and delayed arrangement of tertiary air could reduce NOx emissions significantly.

Numerical simulation of low nitrogen oxides emissions through cement precalciner structure and parameter optimization

To reduce nitrogen oxides (NOx) emissions in the combustion process, the structure and parameters of a 4500 t d−1 precalciner were optimized. The precalciner model was established using ANSYS FLUENT software (version 14.5). The effects of raw material angle, tertiary air velocity, and tertiary air temperature on NO concentration were studied. A Box-Behnken design (BBD) with three factors was employed to establish a two-order response model based on response surface methodology. The results showed that the simulated total NO concentration at outlet was 526 ppm. Compared to the monitoring data of 496 ppm, the error was within an acceptable range. The raw material angle primarily affected the generated location and rate of NO. The NO concentration at the precalciner outlet increased from 124 ppm to 220 ppm, when the tertiary air velocity increased from 22 m s−1 to 38 m s−1. When the temperature was 1123 K, the NO concentration rose to the highest value of 211 ppm. The interaction between the tertiary air velocity and tertiary air temperature was insignificant, while the other interactions were significant (P < 0.05). Finally, a new response surface model was obtained through optimization, which can accurately predict NO concentration. The optimum conditions for low NOx combustion were a raw material angle of 70°, tertiary air velocity of 26 m s−1, and tertiary air temperature of 1280 K.

The impacts of different profiles of the grate inlet conditions on freeboard CFD in a waste wood-fired grate boiler

The common combustion disturbances in the fuel bed in a grate-fired boiler pose a great challenge to accurate modelling of the fuel bed conversion. Therefore, it is difficult to describe the lengthwise profiles of the combustibles leaving the fuel bed into the freeboard accurately. This paper investigates how different fuel bed models or grate inlet profiles will affect the Computational Fluid Dynamics simulation of combustion in the freeboard in industrial grate boilers. Two grate inlet conditions, which are very different in the profiles along the grate but yield the same total mass, momentum, species and energy fluxes into the freeboard, are used in the freeboard simulation of a 13 MWth grate boiler, respectively. The key findings from the comparison between the simulation results and measurement data are as follows. Firstly, the fuel bed model or grate inlet condition accounting for the realistic lengthwise biomass conversion pattern can be used reliably for the simulation of a grate boiler and simulation-based boiler optimisation. Secondly, the impacts of different fuel bed models or different profiles of the grate inlet conditions are virtually restricted only to the vicinity of the fuel bed or in the primary combustion chamber. After the secondary combustion chamber in which up-flowing gas is mixed well with the secondary and tertiary air jets, the simulation results are close to each other. For more general and reliable applications, a comprehensive bed model resolving the mixing, reactions, heat and mass transfer in the fuel bed, is needed and under development.

Industrial-scale investigations on effects of tertiary-air declination angle on combustion and steam temperature characteristics in a 350-MW supercritical down-fired boiler

Industrial-scale experiments were conducted to study the effects of tertiary air declination angle (TDA) on the coal combustion and steam temperature characteristics in the first 350-MW supercritical down-fired boiler in China with the multiple-injection and multiple-staging combustion (MIMSC) technology at medium and high loads. The experimental results indicated that as the TDA increased from 0° to 15°, the overall gas temperature in the lower furnace rose and the symmetry of temperature field was enhanced. The ignition distance of the fuel-rich coal/air flow decreased. In near-burner region, the concentration of O2 decreased while the concentrations of CO and NO increased. The concentration of NO decreased in near-tertiary-air region. The carbon in fly ash decreased significantly from 8.40% to 6.45% at a load of 260 MW. At a TDA of 15°, the ignition distances were the shortest (2.07 m and 1.73 m) at a load of 210 MW and 260 MW, respectively. The main and reheat steam temperatures were the highest (557.2°C and 559.4°C at a load of 210 MW, 558.4°C and 560.3°C at a load of 260 MW). The carbon in fly ash was the lowest (4.83%) at a load of 210 MW. On changing the TDA from 15° to 25°, the flame kernel was found to move downward and the main and reheat steam temperatures dropped obviously. The change of TDA has little effect on NOx emissions(660–681 mg/m3 at 6% O2). In comprehensive consideration of the pulverized coal combustion characteristics and the unit economic performance, an optimal TDA of 15° is recommended.

Effects of the tertiary air injection port on semi-coke flameless combustion with coal self-preheating technology

A novel coal self-preheating combustion technology was adopted to generate high temperature gas-solid two-phase fuel. Experiments on flameless combustion of the two-phase fuel were conducted in a 30-kW coal self-preheating combustion test rig. In flameless mode, effects of the single and the multi levels tertiary air injection ports were discussed, and the flue gas compositions (NOx and CO) and temperatures along the axis of the down-fired combustor were analyzed. To visualize the combustion process, the flame images were captured. It is confirmed that flameless combustion of high temperature gas-solid two-phase fuel can be easily established, and (1) the temperature profile is uniform and it is transparent in the combustor; (2) NOx emission can be reduced about a half compared to other combustion modes; (3) for a single level tertiary air, NOx emission can be minimized by the proper injection port while NOx emission and CO emission might be increased by an inappropriate port; (4) for the multi levels tertiary air, NOx emission can be reduced further by moderate tertiary air injected in the reducing zone, and NOx might be increased while some tertiary air is injected in the burnout zone. It is clear that NOx and CO emissions can be controlled in a low level by rationally arranging two level tertiary air injection ports under flameless combustion.

Rotary kilns in current cement industry

Short rotary kilns with cyclone heat exchangers are commonly used in current cement industry. The principle is the installation of precalciner, even in the case of kilns with low capacity, not exceeding 3000 tons per day. The best method of tertiary air introducing is the usage of separate duct from grate cooler, which justifi es widespread use of these coolers. Alternative fuels, as whole tires, can be burned in precalciners, on special furnaces.