Burning Loss Research Articles

Numerical research of gas-related defects for gray cast iron during sand casting

A novel simulation route included Arrhenius formula, mass conservation and Darcy’s law has been established, which can predict gas-related defects of gray cast iron. The effect of casting and solidification process on the thermal history, burning loss and pressure profile of the sand core was evaluated. Results showed that the pressure in surface region of the sand core was increased gradually, the binder in the sand core reached the decomposition temperature and sand core became thinner. The formation of these defects are highly dependent on the decomposition behavior inside the solidification system.

Combustion Characteristics and Visualization Analysis of a Biomass Pellet Oriented in Different Positions in a Fixed-Bed Reactor at Different Operating Conditions

For all real-world applications, such as fluidized-bed and packed-bed combustion, it is essential to understand the combustion characteristics of an individual solid biomass particle. Under a variety of operating circumstances, investigations on the combustion and mass loss of single pellets of sugarcane (SC) and guava leaves (GL) were conducted. A visualization technique was used to capture the combustion processes of volatile and char. Both homogeneous ignition and hetero–homogeneous simultaneous ignition of both volatiles and char were found. When compared to the material composition and particle-size distribution of the pellet, the brightness of the pellet changed differently with increasing air mass flow rate and hot air temperature. By increasing the hot air temperature and air mass flow rate, the volatile flame of biomass pellets was made shorter and brighter, which lowered the volatile burnout duration. The majority of the entire conversion time is spent on char burning. Compared to other angles, the pellet orientation angle of 30° has a shorter ignition time, a lower surface temperature, and a lower burnout temperature.

Effects of nano-CaCO3 and nano-iron phosphate on microstructure and properties of SiO2 porous ceramics prepared by direct foaming

SiO2 porous ceramics are often used in industrial kilns for thermal insulation. Burning loss method is the main method for preparing SiO2 porous ceramics at present, but there are problems of environmental pollution and uneven pore distribution. Meanwhile, SiO2 is prone to cracking due to crystal-to-crystal transformations. In order to overcome above problems, in this study, nano-CaCO3 and nano-iron phosphate with high activity have been used to stabilize the crystal-to-crystal transformations of SiO2, and SiO2 porous ceramics have been prepared by simple and environmental direct foaming method. Results show that the addition of nano-CaCO3 and nano-iron phosphate can promote the formation of tridymite and densification of SiO2 porous ceramics, which can also increase their pore wall thickness and improve compressive strength. In addition, the compressive strength of SiO2 porous ceramics is proportional to their relative density, which is consistent with the Ashby’s theory. And their thermal conductivity is well matched with the universal model, indicating that SiO2 porous ceramics have complex pore structures. Comparing the effects of nano-CaCO3 and nano-iron phosphate on SiO2 porous ceramics, it is concluded that nano-CaCO3 as the mineralizer is better than nano-iron phosphate. This study enriches the fabrication technology of energy-saving and environmentally friendly SiO2 porous ceramics, which is of great significance to the practical production and application of SiO2 porous ceramics.

Combustion and mass loss behavior and characteristics of a single biomass pellet positioning at different orientations in a fixed bed reactor

This study aims to investigate the combustion characteristics and mass loss behaviors of rice straw and wheat straw biomass pellets experimentally in a laboratory fixed bed combustor under various operating conditions. High-speed photography was used to record images of the combustion process, and a sensitive balance was utilized for recording the particle mass history during the combustion process in addition to K-type thermocouples for temperature measurements. For both materials, the single pellet was exposed to various air temperatures and different flow rates of air. The orientation of the biomass pellet was positioned at various angles from 0 (horizontal), 30°, 45°, 60° (inclined), and 90° (parallel) to the hot air stream at different flow rates. Both glowing reactions and flameless ignition have been noticed in all experiments at all pellet orientations. All pellets experienced low and high luminosity volatiles without flames, followed by a bright radish color and short-lived combustion of the chars. Although the volatile contents of the two materials are identical, the volatile combustion duration of wheat straw (17–258 s) is less than that of rice straw (20–300 s), which could be due to differences in particle sizes, shapes, and structural compositions. The results also show that increased air temperatures lessen the time it takes for volatile and char to ignite and burn off. It also raises the temperature of surface ignition. Starting from the horizontal position and increasing the orientation angle of the pellet, the volatile and char ignition times increase up to 30° and then drop up to 90°, with angle 45° giving the lowest value. The same pattern was also noticed for volatile and char burnout times. The pellet horizontal position (0°) exhibits reduced combustion and mass loss (%) time intervals. The order of increasing the maximum temperature at the pellet surface was 30° > 60° > 90° angles. Increasing the air temperature reduces the times of char combustion, devolatilization, volatile burnout, and char burnout. As the air flow rate increases, the effect on the combustion parameters alternates between increasing and decreasing values.

Effect of microstructure and stress ratio on fatigue crack propagation behavior of A7N01 aluminum alloy fiber laser-VPTIG hybrid butt welded

In this paper, the fatigue crack growth rates of A7N01 aluminum alloy welded joint in weld zone (WZ) and heat affected zone (HAZ) are compared under the stress ratio of 0.1. At the same time, the fatigue crack growth rate of WZ under different stress ratios is studied. The results show that the difference of microstructure leads to different fatigue crack growth rates in different areas of welded joints. The HAZ shows better fatigue crack growth resistance and slower fatigue crack growth rate. However, due to the burning loss of Zn element in the WZ, the precipitation of strengthening phase after solidification in the molten pool is less, and the fatigue crack propagation resistance is weak. After 60 days of natural aging, the number of precipitated phases in the WZ and HAZ increased, and the fatigue crack propagation resistance is improved compared with that in the welded condition. Compared with grain boundary strengthening, precipitation strengthening is more important. With the increase of stress ratio, the fatigue crack closure effect in WZ gradually weakens, and the fatigue crack propagation rate increases.

Effects of fuel injection strategy and ammonia energy ratio on combustion and emissions of ammonia-diesel dual-fuel engine

As the greenhouse effect continues to intensify, ammonia, a carbon-free fuel, is gradually gaining attention. The ammonia-diesel dual-fuel (ADDF) engine can effectively overcome the disadvantages of high auto-ignition temperature and slow flame speed of ammonia, which is an effective way to reduce greenhouse gas (GHG). Aiming at achieving high thermal efficiency and low emissions of ADDF engine, the effects of ammonia energy ratio (AER) and injection strategy on combustion and emission characteristics were studied by combining experimental and simulation results. It was found that as the AER increased from 0 % to 90 %, the gross indicated thermal efficiency (ITEg) decreased continuously. Due to the slow flame speed of ammonia and the inhibition of the dehydrogenation process during the low temperature reaction of diesel, the emission of unburned ammonia increased significantly, reaching 31 g/kwh under the condition of 50 % AER. Improving the combustion efficiency of ammonia and reducing the emission of unburned ammonia were the keys to improving the ITEg of ADDF engine. Amino groups have a denitrification effect, and nitric oxide (NO) can be reduced to more stable nitrogen (N2). Therefore, NO emissions decreased when the AER increased. The production and consumption of nitrous oxide (N2O) were influenced by temperature, and its production region was mainly the low temperature region where the reaction of ammonia occurred, while N2O was reduced to N2 at high temperature conditions. As the AER increased, the deterioration of N2O emissions was not conducive to reducing GHG. The double injection strategy can significantly improve the activity of the mixture, accelerate combustion, reduce unburned ammonia emissions and incomplete combustion losses. By optimizing the injection strategy and regulating the combustion process, an ITEg of 49.18 % can be achieved when the AER was 50 %, and GHG can be reduced by 14.2 %.

High-dimensional multi-objective optimization algorithm for combustion chamber of aero-engine based on artificial neural network-multi-objective particle swarm optimization

This paper considers optimizing the performance of high-temperature combustion chamber of an aero-engine based on a concentric and hierarchical model. First, sample data for the design variables are obtained based on Latin hypercube sampling method, and a one-dimensional program is used to obtain the true values of combustion efficiency and total pressure loss corresponding to each group of variables. The obtained data are then pre-processed to establish a dataset. Second, a multi-layer artificial neural network (ANN) architecture is designed and a surrogate model of the combustion-related performance of the combustor is established using a data-driven method. The results of global sensitivity analysis based on variance show that ratio of fuel flow to air flow (fuel–air ratio) and the total inlet pressure are the most important factors influencing the two objective functions. Finally, we optimize the multi-objective combustion-related performance of the surrogate model by applying the particle swarm optimization algorithm to it. The results of experiments show that the ANN-based model could accurately predict the efficiency of combustion and total pressure loss of the chamber, yielding root mean-squared errors of 0.0107 and 0.3032%, respectively. It also had better generalization ability than the cubic polynomial surrogate model. Compared with the cubic polynomial model, it generated an optimal Pareto solution set as prediction that had higher values in both objective functions. The proposed model might require better data that can be obtained using intelligent sampling methods so that deeper neural networks can be designed to reduce error and improve its optimization design.

Simulation and Experimental Study on the Low NOx Combustion of 35 Kw Biomass Boiler with Air Staging

In the present research, numerical simulations and combustion experiments were carried out using a 35 kW biomass low nitrogen combustion furnace. For this purpose, the boiler structure and fluid area in the furnace were modeled. Subsequently, the grid was divided and the parameters such as speed and pressure were set using Gambit. Then, the model was introduced into Fluent in order to simulate the combustion process and for flow field output and analysis. By analyzing the distribution and changes in temperature field, velocity field, and NOx concentration field under different air supply schemes, and performing low nitrogen combustion experiments, the influence of different air supply schemes on fuel combustion and NOx emission was determined. Through the mutual verification of simulation and experimental research, the optimal air distribution scheme was obtained. The results showed that: without the air staged combustion, combustible gas and air were not properly mixed. As a result, the loss of mechanical incomplete combustion occurred. Under air-staged combustion, the addition of the secondary air reduced the “chimney flow” phenomenon in the furnace to a certain extent. The combustible gas and air were mixed more adequately and the reaction rate and efficiency significantly increased. In addition, with the introduction of the secondary air, the air and the flue gas in the furnace were more efficiently mixed. Moreover, the temperature in the upper combustion area of the furnace decreased by 300–500 K, which slowed down the rate of nitrogen oxides production. This effect was intensified when the proportion of the secondary air increased. The status of the combustion process and changes in the concentration of NOx in the flue gas were compared and analyzed under various working conditions. Data indicated that the optimal air distribution scheme was that with 70% of the primary air and 30% of the secondary air. In this case, the NOx emissions were 27% lower than those without the air staged combustion.

Energy and exergy characteristics of an ethanol-fueled heavy-duty SI engine at high-load operation using lean-burn combustion

Ethanol, as the most produced renewable biofuel, is considered a promising low-carbon alternative to petroleum-based fuels in the transport sector due to its high energy density and auto-ignition resistance. The lean-burn combustion in spark-ignition (SI) engines has the potential to further improve thermal efficiency in regard to knock mitigation and the reduction of combustion temperature. However, the characteristics of lean-burn combustion in an ethanol-fueled engine in relation to the combustion losses and the gas-exchange process remain unclear, especially for high-load operation. This study contributes with a deeper understanding of the high-load performance of an ethanol-fueled heavy-duty SI engine using lean-burn combustion. Based on the experimental results from a single-cylinder engine test, a 6-cylinder engine model is built by integrating a validated predictive combustion model to characterize the lean-burn combustion process. The engine’s thermal efficiency and combustion phasing are evaluated for knock limited operation and then compared to the theoretical optimum which is regardless of knock. The energy and exergy balances are applied to evaluate the effect of dilution with excess air ratios up to 1.8. Losses through heat transfer, exhaust flow, and incomplete combustion are quantified. In addition, entropy generated through combustion is discussed to identify the relationship between exergy destruction and different operating conditions. In the context of lean-burn combustion, the thermal efficiency at high-load operation incrementally increases from 40.4% at stoichiometric condition to 47.3% at an excess air ratio of 1.8. At the same time, the exergy destruction through combustion increases by 3.3 percentage points across the selected dilution range. Furthermore, the challenging requirements to realize lean-burn combustion with lower exhaust gas temperatures and higher intake boost pressures is assessed through an exergy analysis of the turbocharging system.

Mathematical Model of Hot Water Boiler and its Experimental Validation

Low efficiency of isolated heat supply systems based on coal-fired hot water boilers requires the search of feasible control systems reducing incomplete combustion and exhaust heat losses. The paper considers a mathematical model enabling to calculate burned coal weight and boiler efficiency by a measurement set of various parameters. The proposed model is successfully validated on an experimental unit simulating a heat supply system and can be used to develop various control systems for hot water boilers, including adaptive ones.

The effects of unburned-gas temperature and pressure on the unstable behavior of cellular-flame fronts generated by intrinsic instability in hydrogen-air lean premixed flames under adiabatic and non-adiabatic conditions: numerical simulation based on the detailed chemical reaction model

ABSTRACT The effects of unburned-gas temperature and pressure on the unstable behavior of cellular-flame fronts in hydrogen-air lean premixed flames are elucidated by numerical simulations. The detailed chemical reaction mechanism with seventeen reversible reactions of eight reactive species and a diluent is adopted for hydrogen-air combustion and heat loss is taken into account. The burning velocity of a planar flame increases as the unburned-gas temperature increases, and it decreases as the unburned-gas pressure and heat loss increase. In the dispersion relation, the growth rate increases and the unstable range widens when the unburned-gas temperature increases. The former decreases and the later narrows when the heat loss becomes larger. The normalized growth rates become large under the non-adiabatic conditions. The normalized burning velocity of a cellular flame is large when the pressure is high and heat loss is large, and it decreases as the temperature increases at high pressure. This shows that the high unburned-gas temperature at high pressure weakens the instability in hydrogen-air lean premixed flames. With increasing the domain size, the burning velocity of a cellular flame increases, and the cellular-flame front becomes more unbalance. This is an aspect of the long-wavelength disturbance to the unstable behavior of cellular-flame front.

Research Progress of Coating Preparation on Light Alloys in Aviation Field: A Review

This paper systematically introduces the application status of coating-preparation technology on light alloys in the field of aviation parts repair. Included are the advantages and disadvantages of thermal spraying technology and laser cladding technology in the application process, as well as the research status and application prospects of the emerging cold spray (CS) technology and supersonic laser deposition (SLD) technology. Compared with traditional thermal-spraying technology, CS has many advantages, such as low spraying temperature, low oxygen content of the coating, and low porosity, which can effectively avoid oxidation, burning loss, phase change, and grain length during thermal spraying. CS can prepare oxygen-sensitive, heat-sensitive, amorphous, and nanomaterial coatings that are difficult to prepare by traditional thermal-spraying technology. However, in the preparation of high-strength super-hard alloys, CS has shortcomings such as low deposition efficiency and bonding strength. SLD overcomes the shortcomings of CS while inheriting the advantages of CS. In the future, both technologies will be widely used in repairing and remanufacturing in the field of aviation. Based on the principles of CS and SLD, this paper introduces, in detail, the deposition mechanism of the coating, and the specific application examples of CS in the aviation field at the present stage are described. The research and application status of the two technologies in the fields of anti-corrosion coating, wear-resistant coating, functional coating, repair, and remanufacturing in recent years are reviewed. Finally, the application and development prospects of CS and SLD are discussed.

Analysis of energy cascade utilization in the chemically precooled engine cycle from a perspective of indirect combustion

Chemically precooled engine has the potential to raise the flight speed and reduce fuel consumption for next generation hypersonic vehicle. Revealing the mechanism of chemical energy cascade utilization of fuel is the key to guide the design of chemical precooling process and ensure high engine performance, for which the studies about the cascade release of fuel energy level in the indirect combustion process have been performed to evaluate the performance level that can be achieved. The results indicate that there is an optimum relative performance gain of indirect combustion with each fuel, where the ammonia has the highest relative gain of 35%. Further, considering both the heat absorption capacity and calorific value of fuel, a dual fuel solution with ammonia and n-decane is the best precooling method. Besides, increasing the fuel cracking rate is helpful to reduce the energy level loss in the whole energy release process. Moreover, the exergy loss of indirect combustion is 36.13% lower than that of direct combustion. Finally, except for combustors, the exergy losses of nozzle and pre-cooler are larger than other engine components, reaching 8.21% and 5.99% respectively. Overall, the results in this paper are beneficial for developing high performance hypersonic engines.

Preparation of Ti-coated diamond/WC-Co-based cemented carbide composites by microwave-evaporation titanium-plating of diamond particles and microwave hot-press sintering

Diamonds are considered ideal additives for improving the wear resistance of cemented carbide materials and thus for extending their service life. However, the poor wettability and thermal stability of diamonds limit their effectiveness. To solve this problem, in this study, microwave-evaporation technology, a low-cost and simple approach, was used to prepare a uniform titanium coating on diamond surface with an optimized diamond-to-titanium-hydride ratio of 5:3 and an optimized holding time of 1 h at 760 °C. The TiC interlayer with needle-rod microstructure was observed. The coating could increase the oxidation weight-loss temperature by 152.7 °C. The different steps of the high-temperature ablation process of Ti-coated diamond were also revealed. Then, Ti-coated diamond/WC-Co-based cemented carbide composites with uniform microstructure, good interfacial bonding, and no thermal burning loss of diamond were prepared using microwave hot-press sintering with a temperature of 1050 °C only and a pressure of 40 MPa, leading to good wear resistance. The wear rate of the composites prepared with Ti-coated diamond was 25.7% lower at room temperature and 50.7% lower at 400 °C than that of the uncoated diamond. This approach minimized the thermal damage to diamond since both Ti-coated diamond and the composites were prepared at low temperatures.

Effects of piston shape and nozzle specifications on part-load operation of natural gas–diesel dual-fuel RCCI engine and its application to high load extension

• Effects of piston shape and multi-angle nozzle were evaluated for DF RCCI operation. • Enhanced air utilization w/multi-angle nozzle reduced combustion and HT losses. • The highest GIE of RCCI improved as 51.8 % by hardware modifications. • Intake air amount could be increased by lowering CR (from 17 to 15) at the maximum load. • The maximum load of RCCI could be extended from 81 (reference) to 101 kW of BP. In this study, the effects of modifications of both the piston shape and injector nozzle are experimentally investigated for high load extension of a natural gas–diesel dual-fuel reactivity-controlled compression ignition (RCCI) engine. First, a bathtub shape with a reduced compression ratio is applied to the modified piston which was reported to improve the flame propagation in squish volume, the cooling loss, and the air induction rate under the same limit of in-cylinder pressure from previous studies. In addition, a multiangle two-layer injector is used to extend the maximum load, which has been proven to be effective for unburned hydrocarbon emissions and gross indicated efficiency in part-load operation in our previous study. The experiments are conducted under both 1200 rpm part-load operation (approximately 1950 J/cylinder per cycle of fuel input energy) and 1800 rpm maximum load operation. The objectives are to comprehensively evaluate the effects of the modifications on natural gas–diesel RCCI operation and verify the effects of all load conditions. The experimental results reveal that the changes in the piston—reduction in the compression ratio and a bathtub piston shape—are effective for both NOx and smoke emissions as the diesel injection timing is advanced. Although the multi-hole double layer (combined narrow and wide injection) has less effect on emissions compared to that of the change in piston, it affects the mixing process inside the cylinder, thus retarding the combustion phasing, prolonging the combustion duration, and eventually reducing the cooling loss. Both modifications are highly effective for advanced diesel injection timing corresponding to RCCI operation, which extends high-load operation from 80.9 to 101 kW of brake power, relatively 24.8 % increase, by adopting both the piston and injector modifications. Based on the modifications, the mass fraction of natural gas is suggested to be approximately 80 %. A higher fraction causes the variation in the maximum in-cylinder pressure to be extremely sensitive to allow robust operation. In contrast, if it is lower, the amounts of both NOx and smoke emissions exceed the emission standard levels (0.4 g/kWh and 15 mg/kWh for NOx and smoke emissions, respectively, corresponding to Stage-V of non-road engine operation).

Quantifying Lidar Elevation Accuracy: Parameterization and Wavelength Selection for Optimal Ground Classifications Based on Time since Fire/Disturbance

Pre- and post-fire airborne lidar data provide an opportunity to determine peat combustion/loss across broad spatial extents. However, lidar measurements of ground surface elevation are prone to uncertainties. Errors may be introduced in several ways, particularly associated with the timing of data collection and the classification of ground points. Ground elevation data must be accurate and precise when estimating relatively small elevation changes due to combustion and subsequent carbon losses. This study identifies the impact of post-fire vegetation regeneration on ground classification parameterizations for optimal accuracy using TerraScan and LAStools with airborne lidar data collected in three wavelengths: 532 nm, 1064 nm, and 1550 nm in low relief boreal peatland environments. While the focus of the study is on elevation accuracy and losses from fire, the research is also highly pertinent to hydrological modelling, forestry, geomorphological change, etc. The study area includes burned and unburned boreal peatlands south of Fort McMurray, Alberta. Lidar and field validation data were collected in July 2018, following the 2016 Horse River Wildfire. An iterative ground classification analysis was conducted whereby validation points were compared with lidar ground-classified data in five environments: road, unburned, burned with shorter vegetative regeneration (SR), burned with taller vegetative regeneration (TR), and cumulative burned (both SR and TR areas) in each of the three laser emission wavelengths individually, as well as combinations of 1550 nm and 1064 nm and 1550 nm, 1064 nm, and 532 nm. We find an optimal average elevational offset of ~0.00 m in SR areas with a range (RMSE) of ~0.09 m using 532 nm data. Average accuracy remains the same in cumulative burned and TR areas, but RMSE increased to ~0.13 m and ~0.16 m, respectively, using 1550 nm and 1064 nm combined data. Finally, data averages ~0.01 m above the field-measured ground surface in unburned boreal peatland and transition areas (RMSE of ~0.19 m) using all wavelengths combined. We conclude that the ‘best’ offset for depth of burn within boreal peatlands is expected to be ~0.01 m, with single point measurement uncertainties upwards of ~0.25 m (RMSE) in areas of tall, dense vegetation regeneration. The importance of classification parameterization identified in this study also highlights the need for more intelligent adaptative classification routines, which can be used in other environments.

Influence of TIG welding process parameters on microstructure and mechanical properties of as-cast Mg–8Li–3Al–2Zn-0.5Y alloy

In this study, the feasibility of TIG welding of as-cast Mg–8Li–3Al–2Zn-0.5Y alloys was investigated, and the quality of welded joints using different welding currents was evaluated in terms of microstructural evolution and mechanical properties. The results showed that the welding position of plates was successfully welded with good formability and no obvious welding defects at the investigated processing parameters. Significant refinement of phase size was beneficial to improve the mechanical properties of the welded joints. Under the influence of heat input, the AlLi phase in the heat-affected zone dissolved into the matrix, which improved the mechanical properties of the welded joint. The ultimate tensile strength, yield strength and elongation of the welded joint at 100 A were 224.8 MPa, 177.4 MPa and 9.9%, respectively, which is 159.5%, 159% and 43.8% of the corresponding values of the base alloy in the as-cast state. The burning loss of Li element in the welded joint was effectively controlled, which confirmed the feasibility of this welding process for welding Mg–Li alloys.

Performance analysis of biomass driven thermophotovoltaic system from energy and exergy perspectives

• Propose a thermo-physical model of biomass-TPV and conduct a parametric analysis. • Present biomass-TPV/T concept for photo-thermal energy cascade conversion. • Effect of fuel and combustion design is analyzed from energy and exergy perspectives. • Increasing the TPV area and the regenerator design improves efficiency by more than 10%. • Provide reference for the design of TPV power device driven by fuel combustion. The new thermophotovoltaic (TPV) technology driven by biomass fuel is an important way of solar indirect use, it can directly convert thermal energy into electrical energy through thermal radiation; and it is more suitable for the cascade utilization of energy when compared to direct solar-TPV. Therefore, to identify the principles of energy conversion within the biomass-TPV, this study conducted a thermodynamic analysis of a biomass-TPV power device from energy and exergy perspectives. A thermo-physical model of TPV verified by experimental data was established. The concept of biomass-thermophotovoltaic/thermal (TPV/T) combined conversion was summarized to achieve cascade utilization. Particular consideration is given to the effects of biomass fuels, combustion chamber designs and selective filters on the thermodynamic performance of biomass-TPV device and biomass-TPV/T conversion. The results show that the largest exergy loss of biomass combustion accounts for 40%. The biomass fuel moisture increases the exergy losses in combustion and flue gas and thus reduces TPV efficiency by more than 3 percent points. Increasing the TPV area and the regenerator design are beneficial for reducing the exergy loss of flue gas and improving TPV efficiency by more than 10 percent points. Narrow-band filters decrease the exergy losses of TPV emitter and cell, while increasing the loss in flue gas. The narrow-band filter is more suitable for TPV/T combined conversion. This study provides a reference for the design and optimization of biomass-driven TPV conversion system.

Effect of nitriding treatment on char reducing nitric oxide at high temperature

To reduce nitric oxide (NO) emissions from coal-fired industrial boilers, char waste could be collected from the tail flue and fed into the furnace to reduce NO, which would also decrease the incomplete combustion loss. Nitriding treatment could be used to enhance the NO reducibility of char waste. In this paper, char with nitriding treatment (nitriding char) was prepared from Shenhua char and urea. The effect of nitriding treatment on char reducing NO at high temperatures (700 °C–900 °C) was studied using a fixed-bed experimental system and various urea masses and pretreatment times. Increasing the urea mass and decreasing the pretreatment time resulted in more urea residue being present in the char, which increased the nitrogen complex which existed in the form of C(N) and caused the surface enrichment of nitrogen element, but blocked the pore structure. In an inert atmosphere, the NO reduction rates of all the nitriding chars were higher than that of the raw char, but there was an optimal limit parameter for the urea mass and pretreatment time. The presence of 2 vol% O2 was not conducive to the NO reduction by nitriding char because of the higher char-nitrogen (char-N) content resulting from the nitriding treatment, which generated more NO and offset the benefit of the nitriding treatment. This paper provides a useful NO control strategy in coal-fired industrial boilers, and the relevant process route has achieved a 20%–35% decrease in NO emissions in engineering applications.

Preparation of calcium hexaluminate porous ceramics by gel-casting method with polymethyl methacrylate as pore-forming agent

Calcium hexaluminate (CA6) porous ceramics were prepared by gel-casting method, with α-Al2O3 and CaCO3 as raw materials and polymethyl methacrylate (PMMA) microspheres as pore-forming agent. The effects of the amount of pore-forming agent PMMA microspheres on the phase composition, bulk density, apparent porosity, flexural strength, microstructure, thermal shock stability and thermal conductivity of CA6 porous ceramics were systematically studied. The pores of CA6 porous ceramics are mainly formed by the burning loss of PMMA microspheres and the decomposition of organic matter. Adding an appropriate amount of PMMA microspheres as pore-forming agent has a positive effect on the thermal shock stability of CA6 porous ceramics. When the amount of pore-forming agent is 15 wt%, the volume density of CA6 porous ceramics is 1.33 g/cm3, the porosity is 63%, the flexural strength is 13.9 MPa, the thermal shock times can reach 9 times, and the thermal conductivity is 0.293 W/(m·K), which can meet the application in refractory, ceramics or high temperature cement industries.