Performance evaluation of novel surface flame self-aspirated porous radiant burners for cooking applications

Porous radiant burners (PRBs) are based on the principle of porous media combustion (PMC) in which both combustion and stabilization of the flame take place towards the end of combustion zone (CZ). It has lot of advantages over conventional free flame burners. The porous matrix has high thermal conductivity and high emissivity. Hence, contributions to conduction, convection and radiation in the PMC are significant. This paper presents experimental results on the thermal and emission performance of newly developed, bi-layered, self-aspirated porous radiant surface flame burners used in cooking applications. It comprises firebrick material in the CZ and steel balls in the preheating zone (PZ). Performance of this burner is compared to that of a conventional cooking burner (CB) within the operating range of 0.5–2 kW. The effect of burner geometry (one is circular and the other one is square in cross section) on the thermal performance and emission using liquefied petroleum gas (LPG) as the fuel is also studied and their thermal performances are compared to the conventional ones. The experimental results have revealed that the thermal efficiencies of circular and square PRBs are much higher than those of the conventional burner. The maximum thermal efficiency of the self-aspirated circular porous radiant burner (SCPRB) is found to be 71.78% at the flow rate (V) of 2.0 m/s with a porosity of 85%, whereas the thermal efficiency obtained from self-aspirated square porous radiant burner (SSPRB) is marginally less than that of SCPRB at the corresponding flow rate and porosity. The emission levels are much lower in these novel PRBs as compared with the conventional burner and these values are well below the World Health Organization (WHO) standard. The NO_x emission values corresponding to the optimum velocity of 2.0 m/s are 87 ppm for CB, and 24 and 27 ppm, respectively, for SCPRB and SSPRB. CO emission values are 32, 33 and 155 ppm for SCPRB, SSPRB and CB, respectively, corresponding to the optimum velocity of flow.     

ANN–GA approach for predictive modeling and optimization of NOx emission in a tangentially fired boiler

An artificial neural network (ANN) and genetic algorithm (GA) approach to predict NOx emission of a 210 MW capacity pulverized coal-fired boiler and combustion parameter optimization to reduce NOx emission in flue gas, is proposed. The effects of oxygen concentration in flue gas, coal properties, coal flow, boiler load, air distribution scheme, flue gas outlet temperature, and nozzle tilt were studied. The data collected from parametric field experiments was used to build a feed-forward back-propagation neural net. The coal combustion parameters were used as inputs and NOx emission as outputs of the model. The ANN model was developed for full load conditions and its predicted values were verified with the actual values. The algebraic equation containing weights and biases of the trained net was used as fitness function in GA. The genetic search was used to find the optimum level of input operating conditions corresponding to low NOx emission. The results proved that the proposed approach could be used for generating feasible operating conditions.     

Challenges in dissimilar friction stir welding of aluminum 5052 and 304 stainless steel alloys

In this study, dissimilar friction stir welding of aluminum 5052 and stainless steel 304 has been carried out with different process parameters. This investigation provides a better insight regarding the defect formation of the weld joints with tilt angles ranging from 0 ° to 2.5 °. The experiments were conducted according to Taguchi L9 orthogonal array by changing the tool rotational speed, and welding speed. The tool pin was kept 70 % towards the aluminum with the tool rotational speed ranging from 800 min⁻¹ to 1200 min⁻¹ with a varying traverse speed of 5 mm/min to 15 mm/min. The bottom part of the stir zone was perfectly welded without any defects. Tunnel defect was detected just above the bottom welded surface. Microstructural analysis reveals that the weld between both materials is formed on the retreating side, whereas on the advancing side, the weld was formed with void defects. Mostly, the stir zone is filled with irregular shaped aluminum and steel parts which were detached from the base material. Several other defects such as voids, cracks, and fragmental defects were observed in the stir zone irrespective of the process parameters. It was observed from the experimental investigations that the tunnel defect can be reduced by increasing the tilt angle.     

纯氧点火技术在300MW机组的应用

纯氧点火技术是利用氧气替代空气作为助燃剂,直接送入燃烧器内部参与燃料点燃的点火技术。通过将原有最下层四只燃烧器改造为装有微油枪加氧点火助燃的煤粉燃烧器以及在炉前加装供氧系统来保证纯氧的安全输送和稳定燃烧。纯氧的投入使燃料得到充分燃烧,加强了燃烧初期的稳定性,提高了燃烧效率,直接使机组在启停以及低负荷稳燃过程中的安全性、经济性、环保性得到较好的提升。     

低氮改造后再热汽温偏低的燃烧调整研究

针对某330 MW燃煤锅炉低氮改造后出现的再热汽温偏低问题,从锅炉燃烧调整策略角度进行对策研究,主要分析了燃烧器摆角、配风方式、燃烧器投运层分布、上层煤种、上层煤粉细度、水平烟道吹灰和机组自动调节品质等因素对再热汽温的影响。结果表明,再热汽温偏低的现象主要出现在锅炉中低负荷（250 MW以下）工况,通过增加燃烧器仰角、采用倒宝塔配风方式、提高上层燃烧器利用率、加大上层入炉煤发热量、减小上层入炉煤粉细度、加强水平烟道吹灰和优化机组自动调节品质等手段可改善再热汽温偏低问题。提出的燃烧调整策略对同类锅炉改造问题具有重要借鉴意义。     

Effects of Tilt Angle on the Properties of Dissimilar Friction Stir Welding Copper to Aluminum

In the present investigation, dissimilar materials such as electrolytic tough pitch copper, and aluminum 6061-T651 were welded by friction stir welding technology. Effects of tool tilt angle on the mechanical and metallurgical properties were studied experimentally for dissimilar material systems. In the present study, the tool tilt angle was varied from 0° to 4° with an interval of 1°, while the other parameters such as rotational speed, welding speed, tool pin offset, and workpiece material position were kept constant. Macrostructure analysis, tensile test, macro hardness measurement, scanning electron microscopy, and energy dispersive x-ray spectrographic tests were performed to evaluate the weld properties of dissimilar copper–aluminum joints. The results revealed that a defect free dissimilar copper–aluminum friction stir welding was achieved by tilt angles 2°, 3°, and 4°. The maximum tensile strength was reported to be 117 MPa and the macro hardness was reported to be 181 VH (in the nugget zone) at a tilt angle of 4°. The macro hardness was increased as the tilt angle increases from 0° to 4°. In addition to this, the thermo-mechanically affected zone (at the copper side) was found to be the weakest zone for a dissimilar copper–aluminum friction stir welding system.     

Analysis of heat transfer in the furnace of the P-67 boiler P-67 furnace and improvement of its design

The results of experimental study of heat transfer in the furnace of the P-67 boiler (under the Russian trademark) burning Kansk-Achinsk coal are presented. Means of improving the design of the furnace device are proposed.Notation N energy unit power, MW - _fur furnace air excess coefficient - r gas recirculation degree - q_in incident radiation flux density, kW/m² - a spacing between the combustion chamber walls, m - b_b burner width, m - n number of the burner row, starting from below - and inclination angles of the burners located in front of and behind the combustion chamber axis - d diameter of the conventional circumference, tangential to which the burners are directed, m - q_ch heat-stress of the radiant heat absorbing surface of the active combustion zone, MW/m² - furnace-mean thermal efficiency of deflecting walls Krasnoyarsk Institute of Non-Ferrous Metals, Siberian Branch of the All-Union Heat Engineering Institute, Krasnoyarsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 64, No. 3, pp. 275–278, March, 1993.     

In situ combustion measurements of CO with diode-laser absorption near 2.3 microm

In situ measurements of CO concentration were recorded with tunable diode-laser absorption spectroscopy techniques in both the exhaust and the immediate post-flame regions of an atmospheric-pressure flat-flame burner operating on ethylene air. Two room-temperature cw single-mode InGaAsSb/AlGaAsSb diode lasers operating near 2.3 microm were tuned over individual transitions in the CO first overtone band (v' = 2 <-- v" = 0) to record high-resolution absorption line shapes in the exhaust duct [79 cm above the burner, approximately 470 K; R(15) transition at 4311.96 cm(-1)] and the immediate postflame zone [1.5 cm above the burner, 1820-1975 K; R(30) transition at 4343.81 cm(-1)]. The CO concentration was determined from the measured absorption and the gas temperature, which was monitored with type-S thermocouples. For measurements in the exhaust duct, the noise-equivalent absorbance was approximately 3 x 10(-5) (50-kHz detection bandwidth, 50-sweep average, 0.1-s total measurement time), which corresponds to a CO detection limit of 1.5 ppm m at 470 K. Wavelength modulation spectroscopy techniques were used to improve the detection limit in the exhaust to approximately 0.1 ppm m (approximately 500-Hz detection bandwidth, 20-sweep average, 0.4-s total measurement time). For measurements in the immediate postflame zone, the measured CO concentrations in the fuel-rich flames were in good agreement with chemical equilibrium predictions. These experiments demonstrate the utility of diode-laser absorption sensors operating near 2.3 microm for in situ combustion emission monitoring and combustion diagnostics.     

Ceramic fuel cells to replace metal burners

Global warming is thought to result from emissions largely caused by combustion reactions. Designs of burners and specifications of their materials are therefore of primary importance in restraining the warming phenomena. This paper proposes a new type of ceramic burner which incorporates many of the innovations which are needed to improve burner performance, including catalytic combustion, premixed fuel/air, recuperation of combustion heat, recycling of reaction products, electric-ignition and electron extraction. The key problems of fuel variation and thermal shock resistance of the ceramic are addressed through the concept of 'reaction gradient' in which the rich sequence of oxidation reactions during combustion is spread through three extended catalytic regimes along the isothermal ceramic device. It is evident that ceramic burners are necessary to provide catalytic activity and to promote electron transfer. The conclusion is that ceramic will ultimately replace metal in burners requiring low emissions and high exergy output.     

Simulation of gas-solid combustion characteristics in a 1000 MW CFB boiler for supercritical CO2 cycle

Supercritical CO₂ (S-CO₂) power cycle has become one of the most efficient and low-pollution cycle schemes to improve thermal power generation efficiency and reduce energy consumption around the world. In this study, the 3D physical model of a 1000 MW S-CO₂ circulating fluidized bed (CFB) boiler with annular furnace is established to simulate the gas-solid combustion process based on the MP-PIC method under the Eulerian-Lagrangian framework. By comparing with the conventional water steam CFB boiler, the S-CO₂ CFB boiler has a smooth and stable gas-solid flow pattern with good uniformity of the particle concentration and velocity distribution, indicating that the annular structure and the layout of the heating surfaces is conducive to the gas-solid flow uniformity. The gas-solid phase temperature distributes uniformly basically without sudden rise or sudden drop, and the temperature difference between the solid phase and the gas phase is not large, which reflects the good combustion uniformity of the S-CO₂ CFB boiler. Compared with 300 MW and 600 MW S-CO₂ CFB boilers, the 1000 MW one shows a higher carbon conversion rate, lower desulphurization effect, and lower nitrogen removal performance with the CO, NO, and SO₂ outlet concentration of 0.002%, 5.8 mg/m³, and 125 mg/m³, respectively.     

Simulation on coal-fired supercritical CO2 circulating fluidized bed boiler: Coupled combustion with heat transfer

Using supercritical carbon dioxide (S-CO₂) as the working fluid integrated in a circulating fluidized bed (CFB) boiler is a rising technology used to improve the power generation efficiency and reduce gas pollutant emissions in coal-fired power generation systems. This study established a comprehensive 3-D model based on an Eulerian-Lagrangian frame to simulate the combustion process. A new method was presented using constant heat flux as the boundary obtained from the coupled simulation of heat transfer and combustion. The gas phase was described with large eddy simulation (LES). The solid phase used the multi-phase particle-in-cell (MP-PIC) approach. Simulations were carried out in a 10 MW S-CO₂ CFB boiler (with cross section area of 3.557 × 3 m² and height of 21.01 m). Combustion characteristics obtained in boundary heat flux and excess air ratio were numerically investigated. Results showed that the temperature profile was relatively uniform in the whole boiler and the furnace temperature increased with the increase of boundary heat flux. Emissions of CO₂ and SO₂ declined with the increase of boundary heat flux while CO emission increased. An increased excess air ratio caused a decrease in furnace temperature and the rise of CO and SO₂. The characteristics of combustion and pollutant emissions were optimal with the heat flux at around 25–37 kW/m² and an excess air ratio at 1.18–1.25.     

微油点火燃烧器一级燃烧室点火性能试验研究

试验研究了不同一次风速和煤粉质量分数条件下微油点火燃烧器一级燃烧室的点火性能.研究结果表明,燃烧室中心温度随一次风速和煤粉质量分数的增加,呈先降低后增加的趋势;燃烧室中心线上的CO体积分数随一次风速的增加而增大,但随煤粉质量分数的增加而减小;燃烧室出口中心处的NOx体积分数随一次风速和煤粉浓度的增加则均呈现上升趋势.     

Single- and double-pass FSW lap joining of AA5456 sheets with different thicknesses

Friction stir welding of AA5456 aluminium alloy with different thicknesses was investigated for single- and double-pass lap joint configurations. The influences of tool tilt angle in first and second passes, and rotational and welding speeds in second pass on metallurgical structure and joint strength were studied. The results indicated that tilt angle significantly influences material flow and imperfection formation, and accordingly controls the weld mechanical properties. The best results were achieved by tilt angle of 5° for single pass, and tilt angle, rotational speed and traverse speed of 5°, 250?rev?min^??1 an 50?mm?min^??1 respectively for double-pass. The characteristics of hooking and cold lap defects were used as criteria to recognise the influence of processing conditions on joint performance.     

Tube-in-Basket burner for rice husk. II: Performance of TiB burners

Three working models, TiB MK II, MK IIK and III, capable of continuous combustion, are described. It is shown that these burners can be operated continuously in a stable pseudo-steady-state manner by means of intermittent charging of husk from the top and discharging of ash from the bottom. Mass and heat balance data, flame temperatures, combustion efficiencies and heat transfer efficiencies for heating water in a vessel are included. Combustion efficiency of about 72% was achieved in TiB MK II by making a significant change in the basket design, the lower half being made conical. The efficiency was boosted further to roughly 82% in MK IIK by extending the bottom rim of the cone straight down by an additional 7·5 cm and replacing the upper basket cylinder by a fully enclosed box. A water heating jacket was also incorporated in this model around the upper end of its burner tube. This modification resulted in a highly efficient water heating or steam raising device. Comparison with step-grate furnaces shows that TiB burners have similar or superior performance characteristics with additional advantages of simplicity, compactness and low cost.     

Formulation of new correlations in terms of extraterrestrial radiation by optimization of tilt angle for installation of solar photovoltaic systems for maximum power generation: case study of 26 cities in India

This paper deals with finding of optimum tilt angle for installation of optimized solar photovoltaic system in India. The optimization of tilt angles is performed using measured solar radiation data for 26 cities in India. The tilt angle is changed from 0° to 90° at step of 1° to find out optimum tilt angle for which monthly average solar radiation is maximum. It was found that the optimum tilt angle varies between 0° and 63° throughout the year in India. The monthly optimum tilt angle is maximum in December for all cities in India. It is found that increase in maximum solar radiation at monthly optimum tilt angle in comparison to latitude based tilt angle and annual optimum tilt angle varies from 5.85% to 8.08% and 5.95% to 8.34%, respectively, showing monthly optimum tilt angle is beneficial for maximum power generation for different cities in India. The novelty of this study is new correlations of optimum tilt angle in terms of extraterrestrial radiation are developed for estimating monthly optimum tilt angle for installation of photovoltaic systems at different sites in India. The root mean square error in correlation equations varies from 0.1256 to 0.9771.     

Study on scale-up characteristics of oxy-fuel combustion in circulating fluidized bed boiler by 3D CFD simulation

The oxy-fuel combustion CFB technology as a promising carbon capture technologies needs to study the scale-up process for the commercial diffusion. Numerical simulation would be a rational tool to investigate the gas-solid flow and oxy-fuel combustion process before constructing an expensive and complicated industry-scale plant. A three-dimensional (3D) CFD simulation according to the Eulerian-Lagrangian approach was applied to simulate the hydrodynamics of gas-solid flow and oxy-fuel combustion process in lab-scale, pilot-scale and industry-scale CFB boiler (from 0.1 MW_th to 330 MW_e). Results present the differences of the boiler configuration, the gas-solid flow and the oxy-fuel combustion characteristics between lab-scale, pilot-scale and industry-scale CFB boilers. The cross-section thermal load gradually decreased, while the cross-section area increased with the thermal inputs increased. In the lab-scale and pilot-scale oxy-fuel CFB, the particle velocity field was more uniform than that in the industry-scale CFB. The carbon conversion ratio increased with an increase in the thermal input. The emission of CO, NO and SO₂ in the industry-scale oxy-fuel CFB boilers was lower than those in the lab-scale and pilot-scale. A larger oxy-fuel combustion power plant is beneficial to carbon capture and low pollutant emission. The results would be beneficial to the design and operation of industry-scale oxy-fuel CFB.     

600MW亚临界机组锅炉优化燃烧试验研究

介绍了某电厂600MW亚临界机组锅炉燃烧调整试验。对制粉系统进行了优化调整：分析了不同负荷下氧量的变化对锅炉效率的影响,并给出了最佳氧量值;在600MW负荷下进行了二次风箱压力对锅炉效率影响试验,并做出了二次风箱压力对锅炉效率影响曲线;分析了锅炉NOx排放特性。     

Emission spectroscopy for coal-fired cyclone furnace diagnostics

Using a spectrograph and charge-coupled device (CCD) camera, ultraviolet and visible light emission spectra were obtained from a coal-burning electric utility's cyclone furnaces operating at either fuel-rich or fuel-lean conditions. The aim of this effort is to identify light emission signals that can be related to a cyclone furnace's operating condition in order to adjust its air/fuel ratio to minimize pollutant production. Emission spectra at the burner and outlet ends of cyclone furnaces were obtained. Spectra from all cyclone burners show emission lines for the trace elements Li, Na, K, and Rb, as well as the molecular species OH and CaOH. The Ca emission line is detected at the burner end of both the fuel-rich and fuel-lean cyclone furnaces but is not detected at the outlet ends of either furnace type. Along with the disappearance of Ca is a concomitant increase in the CaOH signal at the outlet end of both types of furnaces. The OH signal strength is in general stronger when viewing at the burner end rather than the exhaust end of both the fuel-rich and fuel-lean cyclone furnaces, probably due to high, non-equilibrium amounts of OH present inside the furnace. Only one molecular species was detected that could be used as a measure of air/fuel ratio: MgOH. It was detected at the burner end of fuel-rich cyclone furnaces but not detected in fuel-lean cyclone furnaces. More direct markers of air/fuel ratio, such as CO and O2 emission, were not detected, probably due to the generally weak nature of molecular emission relative to ambient blackbody emission present in the cyclone furnaces, even at ultraviolet wavelengths.     

Dislocation structures of low-angle boundaries in Nb-doped SrTiO3 bicrystals

Dislocation core structures in low-angle boundaries of Nb-doped SrTiO₃ bicrystals were investigated by high-resolution electron microscopy. Bicrystals with tilt angles of 2°, 4°, 6° and 8° with respect to the [001] zone axis were prepared by joining two single crystals at 1873 K. All of the boundaries consisted of a regular array of dislocations whose spacing gradually decreased with an increase in tilt angle. Except for the 2° tilt-angle boundary, the dislocation cores exhibited a dissociation from a[010] into two partials of a/2[010] on (100). Furthermore, two kinds of dislocation core structures were observed; Sr–Sr atomic columns and Ti–O atomic columns inside the cores. In addition, it was found that the positioning of adjacent cores along the boundary tended to change from a linear form to a zig-zagg shape as the tilt angle was increased from 4° to 8°. In the case of the linear array, dislocation core structures including Sr–Sr columns or Ti–O columns alternately appear. In contrast, only one core structure was observed in the zig-zagged array. On the other hand, the dislocation cores in the 2°-tilt-angle boundary had another type of dissociation with a/2[110] or a/2[111] partials, which included the twist component at a tilt axis of [001].     

Thermoluminescent properties of Mn-doped YAP synthesized by the solution combustion method

The work describes results of Mn-doped YAlO₃ (YAP) nanocrystalline materials synthesized by the solution combustion method using urea as a fuel. The materials were characterized by X-ray powder diffraction, scanning electron microscopy and luminescence techniques. The combustion synthesis method with codoping with Hf⁴⁺ ions allows to obtain highly efficient YAP:Mn²⁺ phosphor with negligible emission from Mn⁴⁺ ions that can be applicable for thermoluminescent dosimetry of ionizing radiation. Namely, the phosphor has a single dominating thermal glow peak at about 200 °C with the green emission near 530 nm related to Mn²⁺(Y) ions.