Numerical calculation on combustion process and NO transformation behavior in a coal-fired boiler blended ammonia: Effects of the injection position and blending ratio

Ammonia (NH₃), as a potential carbon-free alternative fuel, can be blended into coal-fired boiler to achieve significant pollution reduction and carbon reduction, but there are concerns about high NOx emissions due to high nitrogen content. According to the characteristics of coal/NH₃ co-combustion, a dual-fuel co-combustion model with strong adaptability and high accuracy was established in this study through Chemkin software to study the influence of different injection positions and blending ratios on combustion characteristics and NOx generation process. Then, the co-combustion model was applied to the three-dimensional CFD calculation process of a 330 MWe front-fired boiler, and the combustion characteristics, NOx distribution and reaction process were calculated when cal. 20% NH₃ was blended in the primary air. The results show that when cal. 20% NH₃ is blended, the change of NO content mainly occurs in ignition zone and flame zone, and the transformation behavior of N in NH₃ is optimized to a 15-step elementary reaction; The temperature distribution in the furnace is similar, and the average temperature at the furnace outlet decreases from 1033 °C to 988 °C, while NH₃ have a preferential combustion reaction with air than coal, resulting in a decrease in the burnout rate of coal; The NOx concentration at the furnace outlet decreases from 355 mg/Nm³ to 281 mg/Nm³, which is 20.85% lower than that under the pure coal burning condition, and the variation range of O₂ concentration and unburned NH₃ concentration is small.     

Fe doped Ni–Co alloy by electroplating as protective coating for solid oxide fuel cell interconnect application

To obtain higher electrical conductivity and lower area specific resistance (ASR), the 10% Fe doped Ni–Co (NCF) alloy was prepared on SUS 430 steel substrate by electroplating for solid oxide fuel cells (SOFCs) interconnects application. Then, the SUS 430 steels and NCF coated steels were oxidized at 800 °C. The microstructure and oxide phase of samples were tested by scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). These results proved that the NCF coated steel achieved the lower oxidation rate of 9.28 × 10⁻¹⁴ g²cm⁻⁴s⁻¹ and ASR of 14.72 mΩ cm².     

燃煤机组耦合固废焚烧关键技术研究进展

[目的]燃煤与固体废弃物混合掺烧不仅可以实现固废的能量回收利用,也是实现燃煤发电的碳减排的路径之一。[方法]文章综述讨论了燃煤电站掺混固废的研究工作,主要介绍了基于目前主流的电站锅炉为反应器开展燃煤与不同固废掺混的燃烧应用与技术发展;从燃料经济性、混合燃料的飞灰特征、污染物排放以及碳税角度评价燃煤掺混固废的燃烧技术发展;最后讨论了直接掺混和间接掺混的技术的特点。[结果]燃煤直接掺混固废燃烧时需要尽可能减少对锅炉运行的影响,特别是气体污染物的排放以及飞灰对换热面的影响和飞灰无害化处置。间接掺混可以避免混合燃料燃烧对炉膛的影响,但是需要较高的硬件成本投资且耦合技术较为复杂。富氧燃烧技术依旧需要对现有锅炉结构优化来提高该技术的适用性。[结论]直接掺混可实现性与成本优于间接掺混,且循环流化床燃料适应广的特点有利于燃煤直接掺混固废燃烧技术的应用,随着基于循环流化床的富氧燃烧技术的发展将更有利于实现火电厂的碳减排。     

Test results from sugar cane bagasse and high fiber cane co-fired with fossil fuels

Cofiring tests were conducted in a boiler at the Hawaiian Commercial & Sugar factory at Puunene, Hawaii. Three tests were conducted; a baseline test firing coal and fuel oil (Test 1) and two cofiring tests utilizing coal, fuel oil, and biomass. In the latter two tests, bagasse (Test 2) and a blend of bagasse and fiber cane (Test 3) were used as the biomass fuel. Biomass accounted for 62% and 50% of the total energy inputs for Tests 2 and 3, respectively. All three tests were conducted in a spreader stoker-type boiler operating at a steam flow rate of 46.5 tonne h⁻¹ at 63.2 bar and 400 °C. Fuel properties, boiler efficiency, solids removed in the pollution control devices, and stack emissions of criteria pollutants were monitored during the test campaign and results are reported herein. In addition, a laser induced breakdown spectroscopy probe and a deposition probe were installed near the superheaters to characterize fire-side ash behavior under each of the test conditions.     

污泥与煤在流化床内混燃特性的试验研究

在一个内径为100 mm的循环流化床燃烧试验台上对煤与污泥的混合燃烧特性进行了试验研究.污泥来自重庆某污水处理厂.试验研究了煤与污泥的混合比、燃料量对燃烧特性的影响,得到了床温变化、床压变化、污染物排放等试验结果,并分析了其影响冈素.结果表明:污泥只能与煤按一定比例混合后,才能够稳定燃烧;燃烧过程中的床压变化,与常规的燃煤循环流化床有较大的差异.     

Characteristics of co-combustion and kinetic study on hydrothermally treated municipal solid waste with different rank coals: A thermogravimetric analysis

This study presents an investigation on the influence of hydrothermally treated municipal solid waste (MSW) on the co-combustion characteristics with different rank coals, i.e. Indian, Indonesian and Australian coals. MSW blends of 10%, 20%, 30% and 50% (wt.%) with different rank coals were tested in a thermogravimetric analyser (TGA) in the temperature range from ambient to 700 °C under the heating rate of 10 °C/min. Combustion characteristics such as volatile release, ignition and burnout were studied for the blend fuel. Different ignition behavior was observed depending on the blends composition and the coal rank. The result of this work indicates that the blending of MSW improves devolatization properties of coal. But it was found that the co-combustion characteristics of MSW and coal blend cannot be predicted only from the pyrolytic and or devolatization phenomena as the other factors such as the coal quality also plays a vital role in deciding the blends co-combustion characteristics. The TGA combustion profiles showed that the combustion characteristics of blends followed those of parent fuels in both an additive and non-additive manners. These experimental results help to understand and predict the behavior of coal and MSW blends in practical applications.     

The shock tube pyrolysis of pyridine

Fossil fuels such as coal and heavy fuel oils contain up to about 2 per cent by weight of fuel nitrogen, most of this being present in pyridine or pyrolic aromatic structures. Under pyrolytic conditions these ring structures decompose to give HCN and CH₃CN. For present day computer modelling of NO_x formation in flames it is necessary to know the mechanism and rates of reaction. A number of previous studies of pyridine pyrolysis have been undertaken using shock tubes or flow reactors. In this present study a shock tube was used to obtain the kinetics of pyridine decomposition in the range 1590–2335 K and with pressures between 2.2 and 3.4 atm. Two independent sets of data were obtained. One set of results was found to be represented by an Arrhenius rate constant k=10^9.7±0.5 exp (−220.0 kJ mol⁻¹ RT⁻¹)s⁻¹. For the other work k= 10^9.8±0.5 exp (−228.191±18.42 kJ mol⁻¹ RT⁻¹)s⁻¹. In addition, the pyrolysis mixtures of pyridine plus toluene have also been studied to understand the synergistic effects. The results indicated the strong involvement initiated by fission of the pyridine ring system. Copyright © 2000 John Wiley & Sons, Ltd.     

Experimental and Numerical Study on Co-combustion Behaviors and NO_x Emission Characteristics of Semi-coke and Coal in a Tangentially Fired Utility Boiler

The utilization of powdery semi-coke as a power fuel in pulverized coal-fired power plants has become a new and potential technique to consume the excess powdery semi-coke.The characteristic of low volatile results in poor combustion performance and high NO_x emission,and to co-fire with bituminous coal is a practical strategy to address this problem.However,the co-combustion characteristics and the inherent interaction between semi-coke and coal remain insufficiently understood.In addition,the influences of secondary air arrangement,the boiler operation load,and the fuel type on co-combustion process are still unclear,which is urgent to be further explored.In the present study,experiments and numerical simulations were jointly utilized to inquire into the co-combustion behaviors and NO_x emission features of semi-coke and coal.The results demonstrated that the"out-furnace method"was a suitable choice for small-capacity boiler when the proportion of semi-coke was 33%,due to the limited combinations of the semi-coke injection position.It was recommended that semi-coke was preferred to be injected from the middle layers of the furnace under the"in-furnace method"to improve the overall co-combustion performance.The critical value of the separated over fire air ratio in this study was 27.5%,over which a slight drop of carbon content in fly ash could come about.Moreover,the elevation in the proportion of separated over fire air gave rise to the significant decline of NO_x concentration.The constricted secondary air arrangement was preferred to be employed due to the high boiler efficiency.The separated over fire air and the surrounding air needed to maintain a wide-open degree to prevent the increase of NO_x emissions and the coking of nozzles.For the load reduction regulation method adopted in this study,the NO_x concentration first rose and then dropped,while the burnout ratio decreased obviously as the operation load was reduced.Different combinations of coal and semi-coke generated significant influences on co-combustion behaviors within the furnace.The NO_(x )generated by high-volatile fuel (bituminous coal) combustion was mainly affected by volatile-N,while the NO_(x )generated by low-volatile fuel (semi-coke) was mainly impacted by char-N.This study is of guiding significance for the efficient and clean utilization and beneficial to the large-scale application of powder semi-coke in power plants.     

Experimental investigation on ignition and burnout characteristics of semi-coke and bituminous coal blends

Ignition and burnout characteristics of semi-coke and bituminous coal blends were investigated by thermogravimetric analyzer and drop tube furnace. The results showed that the ignitability index and the comprehensive combustion characteristic index of the blends decrease as the blending proportion of semi-coke increases, but the average activation energy of the blends increases gradually. Ignition mode of bituminous coal is changed from homogeneous to hetero-homogeneous ignition with the increasing of semi-coke content in the blends. When the mixing proportion of semi-coke is lower than 45%, the burnout rate is lower than the weighted value in the early stage of combustion and gradually higher than the weighted value with the development of combustion process. However, the burnout is always lower than the weighted value to mix with 67% semi-coke. Increasing furnace temperature from 850 °C to 1050 °C can improve the mid-term reaction process, alleviate the negative effects of semi-coke on the co-combustion process and increase the burnout rate. So less than 45% semi-coke blending ratio and increasing furnace temperature are recommended for semi-coke and bituminous coal co-combustion.     

煤粉切圆燃烧П型布置锅炉屏式过热器热力不均匀分析与优化布置

基于对煤粉切圆燃烧П型布置锅炉屏式过热器烟气侧热力不均匀特性举例分析,以及对现有减轻屏式过热器热偏差技术措施的总结,给出了解决煤粉切圆燃烧П型布置锅炉前屏过热器与后屏过热器各屏间热偏差的方法,利用结构不均、水力不均和热力不均相互匹配的方法给出了前屏过热器与后屏过热器的优化布置方案,对减轻煤粉切圆燃烧П型布置锅炉屏式过热器热偏差有参考价值。     

Assessment of key parameters in tannery sludge management: A prerequisite for energy recovery

Environmental regulations are getting more restricted related to landfilling of biodegradable waste. The solution to these problems is using the biodegradable portion of sludge waste for agricultural or thermal utilization. This paper is based on the physico-chemical analysis of different proportions of sludge with coal and rice husk for co-combustion to optimize the parameters like sulfur, ash, and gross heating value (GHV). A significant increase in GHV of secondary sludge with different combinations of coal and rice husk was observed as compared to primary sludge combinations representing 13.55–21.80 Mj/kg and 11.52–19.12 Mj/kg, respectively. The combination RSSC-1 (50% sludge and 50% coal) is highly significant with p < 0.01 and can be utilized as fuel because of the high GHV and low sulfur content. This study concludes that co-combustion of sludge in an eco-friendly manner, using modified thermal methods, may turn into a valuable fuel like traditional biomass.     

Impact of miscanthus yield on harvesting cost and fuel consumption

Miscanthus is emerging as a potential bioenergy crop because of its high yield and ability to reduce greenhouse gas emissions. However, there is a lack of data on harvesting machinery performance for the USA conditions, and influence of yield on harvesting cost and fuel consumption. This study quantified performance of a mower-conditioner and a large square baler for Illinois conditions, and investigated influence of yield on fuel consumption and harvesting costs. To calculate performance parameters, a field area was segmented from which a bale was formed. Then in the segmented field area, yield and machine performance parameters were determined. The mower-conditioner's field capacity was 1.8 ha h⁻¹, and diesel consumption was 19.2 L ha⁻¹. The baler's field capacity was 1.4 ha h⁻¹, and diesel consumption was 19.7 L ha⁻¹. The mowing cost was 4.8 $ Mg⁻¹, and baling cost was 6.8 $ Mg⁻¹. An inverse correlation (R² = 0.62) was found between miscanthus yield and harvesting cost ($ Mg⁻¹), and a direct correlation (R² = 0.67) was found between miscanthus yield and fuel consumption (L ha⁻¹). It is expected that this study would help in more accurate assessment of environmental impact and economic feasibility of miscanthus, and may lead to further studies for quantifying crop yield and machine performance interactions.     

The effect of increased extraction of forest harvest residues on soil organic carbon accumulation in Sweden

The demand and potential for increasing the use of bioenergy from harvest residues in Sweden are large. However, harvest residue (branches and tops) and stump extraction negatively affect soil organic carbon (SOC) accumulation. The main objective of this study was to assess the effects of increased harvest residue extraction on soil organic carbon (SOC) accumulation at national level. Further, the reduction in CO2 by substituting coal with biofuel from harvest residues and stumps was assessed. Several scenarios with increased harvest residue extraction were simulated with the forest management system HUGIN and the SOC decomposition model Q and the effects on SOC accumulation in Swedish coniferous forest soils were assessed. All scenarios resulted in decreased SOC accumulation. The decrease in SOC accumulation was largest for stump extraction, with 0.15 Mg C ha⁻¹ y⁻¹ loss on average over a 100-year simulation period. In all scenarios, the short-term effects on SOC accumulation were greater than the long-term effects. The effect of substituting coal with bioenergy was an immediate reduction of net CO₂ emissions. An increase in the use of forest residues leads to CO₂ mitigation in the atmosphere, even when SOC losses are accounted for.     

Investigation of the effect of detergent–dispersant additives on the oxidation stability of biodiesel,diesel fuel and their blends

Basic materials of biodiesels and molecular structure of different biodiesels were discussed with special focus on their oxidation stability and post-additization. Commercial biodiesels produced from rapeseed oil and used cooking oil were blended to diesel fuel in 5%, 7%, and 10% mass fraction. The samples were stored at ambient temperature for one year to simulate the effects of strategic storage and/or long stock turnover rate. Following the one year storage period the samples were treated with BHT antioxidant and/or succinic type detergent–dispersant additives in 300 mg kg⁻¹, 600 mg kg⁻¹ and 900 mg kg⁻¹ concentrations. BHT was applied as antioxidant additive, while the detergent–dispersant additives were either newly developed additives (polyisobutylene succinic anhydride derivatives containing fatty acid methyl ester in their molecular structure) or commercial ones. Structure of the developed additives and their mechanism is described in detail. Rancimat and Seta TOST devices were applied to evaluate the effect of the additives on the oxidation stability of the samples. It was found that the decrease of oxidation stability during storage can be partially compensated with post-additization by suitable detergent–dispersant additives. Oxidation of biodiesels during Rancimat measurement was investigated with infrared spectroscopy. The results showed that during the thermal oxidation fatty acid methyl esters decompose to carbonyl, carboxyl and hydroxyl compounds, while cis-trans isomerization also occurs.     

Heat transfer characteristics in a small-scale fluidized bed boiler

Heat transfer characteristics in a small-scale fluidized bed boiler (2MW_th) were studied using lignite and corn cob as fuels. Depending on air velocity, the heat transfer rates from bed to water membrane wall and from hot flue gas to convective tube bank were in the ranges 75–55% and 25–45% of the total heat absorbed by the boiler, respectively. At designed capacity, the heat transfer flux based on bed cross sectional area and on water membrane wall area were about 0·45 and 0·15 MWm⁻², respectively. Under the conditions studied, it was found that the overall heat transfer coefficient between bed and water membrane wall was 100–300 W m⁻² K⁻¹, whereas that between flue gas and convective tube bank was 10–30 Wm⁻² K⁻¹. The study of heat transfer to a horizontal tube immersed in the bed as well as placed in the freeboard region were also studied. The effective heat transfer coefficients were found to be 300–800 W m⁻² K⁻¹ for in-bed tube and 30–150 W m⁻² K⁻¹ for the freeboard region, depending on air velocity. Comparison of these data with those predicted by both modelling and correlation reported in the literature was also made. For the immersed tube, good agreement was observed for low air velocity, while at high air velocity the experiment produced results twice those estimated from modelling and correlation. For the freeboard region, the model gave a fair prediction.     

Fabrication of a double-layered Co-Mn-O spinel coating on stainless steel via the double glow plasma alloying process and preoxidation treatment as SOFC interconnect

To improve oxidation resistance, prevent Cr evaporation and maintain appropriate electrical conductivity of AISI 430 stainless steel (430 SS) as the solid oxide fuel cells' (SOFCs) interconnect, a double-layered Co-Mn-O spinel coating is fabricated successfully on 430 SS via a simple double glow plasma alloying process (DGPA) followed by heating in the air (preoxidation treatment). The double-layered Co-Mn-O spinel coating is composed of a thick MnCo₂O₄ spinel outlayer and a thin mutual-diffused (MnCoFe)₃O₄ oxide innerlayer. The isothermal and cyclic oxidation measurements are used to investigate the oxidation resistance, and the ASR test is performed to evaluate the conductivity for the coated and uncoated specimens. The coated specimen has a lower oxidation kinetics rate constant (9.0929 × 10⁻⁴ mg² cm⁻⁴ h⁻¹) than the uncoated one (1.900 × 10⁻³ mg² cm⁻⁴ h⁻¹) and the weight gain of the coated specimen (0.84 mg cm⁻²) is less than that of bare steel (1.29 mg cm⁻²) after 750 h oxidation. Meanwhile, the coated specimen holds a lower area specific resistance (0.029 Ω cm²) compared to the uncoated one (2.28 Ω cm²) after 408 h oxidation. Furthermore, the compact Co-Mn-O spinel coating can effectively impede Cr-volatilization. Additionally, the probable mechanism of the Co-Mn alloy conversion into spinel and the electronic conduction behavior in the spinel are discussed. The effects of mutual-diffused oxide innerlayer on oxidation behavior and conductivity are investigated.     

Autothermal reforming study of diesel for fuel cell application

Diesel is one of the best hydrogen storage systems, because of its very high hydrogen volumetric density (100 kg H₂ m⁻²) and gravimetric density (15% H₂). In this study, several catalysts were selected for diesel reforming. Three experimental catalysts (Pt on gadolinium-doped ceria, Rh and Ru on the same support) and two commercial catalysts (FCR-HC14 and FCR-HC35, Süd-Chemie, Inc.) were used to reform diesel. The effects of operating conditions, such as temperature, O₂/C16 and H₂O/C16 on autothermal reforming (ATR) were investigated. In addition, by analyzing the concentrations of products and the temperature profiles along the catalyst bed, we studied the reaction characteristics for a better understanding of the ATR reaction. The fuel delivery and heat transfer between the front exothermic part and the rear endothermic part of the catalyst bed were found to be significant. In this study, the characteristic differences between a surrogate fuel (C₁₆H₃₄) and commercial grade diesel for the ATR were also examined.     

Anthracite pretreatment for high-performance direct carbon solid oxide fuel cell — A green pathway for power generation

Coal-fueled direct carbon solid oxide fuel cell (DC-SOFC) is a very attractive electrochemical conversion device. However, coal contains a certain amount of ash, such as Al, Si, S, etc., which are toxicants for SOFC components. To solve the above problem, anthracite is pyrolyzed at 600 °C to obtain semi-coking coal results in better cell performance. The results show that the higher carbon gasification oxidation activity of semi-coking coal is due to the higher amount of fixed carbon and catalyst. Therefore, more fuel gas (CO) is available in the anode chamber for the Boudouard reaction. Also, the electrochemical performance of both coals as DC-SOFC fuel was compared using La_0·4Sr_0·6Co_0·2Fe_0·7Nb_0·1O_3-δ (LSCFN) as anode. The maximum power density (MPD) of the DC-SOFC with semi-coking coal is 596 mW cm⁻² at 850 °C, much higher than that of the SOFC using anthracite (396 mW cm⁻²) as the fuel. Furthermore, at the same fuel content, the cell fueled with semi-coking coal has a longer discharge time (30 h), which shows a better stability.     

Measures of the environmental footprint of the front end of the nuclear fuel cycle

Previous estimates of environmental impacts associated with the front end of the nuclear fuel cycle (FEFC) have focused primarily on energy consumption and CO₂ emissions. Results have varied widely. This work builds upon reports from operating facilities and other primary data sources to build a database of front end environmental impacts. This work also addresses land transformation and water withdrawals associated with the processes of the FEFC. These processes include uranium extraction, conversion, enrichment, fuel fabrication, depleted uranium disposition, and transportation.To allow summing the impacts across processes, all impacts were normalized per tonne of natural uranium mined as well as per MWh(e) of electricity produced, a more conventional unit for measuring environmental impacts that facilitates comparison with other studies. This conversion was based on mass balances and process efficiencies associated with the current once-through LWR fuel cycle.Total energy input is calculated at 8.7 × 10^− 3 GJ(e)/MWh(e) of electricity and 5.9 × 10^− 3 GJ(t)/MWh(e) of thermal energy. It is dominated by the energy required for uranium extraction, conversion to fluoride compound for subsequent enrichment, and enrichment. An estimate of the carbon footprint is made from the direct energy consumption at 1.7 kg CO₂/MWh(e). Water use is likewise dominated by requirements of uranium extraction, totaling 154 L/MWh(e). Land use is calculated at 8 × 10^− 3 m²/MWh(e), over 90% of which is due to uranium extraction. Quantified impacts are limited to those resulting from activities performed within the FEFC process facilities (i.e. within the plant gates). Energy embodied in material inputs such as process chemicals and fuel cladding is identified but not explicitly quantified in this study. Inclusion of indirect energy associated with embodied energy as well as construction and decommissioning of facilities could increase the FEFC energy intensity estimate by a factor of up to 2.     

Probabilistic single box approach for modeling PAHs associated with combustion aerosols in a typical indoor environment

Firewood, coal, dung cake, kerosene and Liquefied Petroleum Gas (LPG) are the most commonly used fuels for cooking and heating purposes in developing countries. Combustion of such fuels leads to high concentrations of pollutants in the indoor environment. Polycyclic aromatic hydrocarbons (PAHs) are emitted during residential combustion, and have carcinogenic and genotoxic properties. In this study, data from an experimental setup for estimation of emission rate of particulate-bound PAHs generated during combustion of such fuels are used. PAHs emission rates were used in a probabilistic single box model for prediction of time average particle associated indoor B(a)P equivalent (B(a)P_eq) concentrations of PAHs resulting from typical Indian cooking. Model parameters such as fuel consumption rate, stove power and cooking time were also evaluated experimentally. Particle bound B(a)P_eq PAH emission factor was found to be highest (0.96 mg kg⁻¹) for dung cake, and lowest for LPG (0.48 mg kg⁻¹) among tested fuels. The time averaged B(a)P equivalent concentrations in indoor environment were found to be 0.82, 0.45, 0.87, 0.30, and 0.14 μg m⁻³ for firewood, coal, dung cake, kerosene and LPG respectively. Results reveal that there was higher B(a)P equivalent concentration during combustion of biomass (dung cake, fire wood) as compared to fossil fuels (coal) and non-solid fuels (kerosene, LPG). Predicted time averaged indoor air B(a)P_eq concentrations of PAHs were found to be much higher than the WHO indoor air guideline values for all tested fuels.