Optimization of decoupling combustion characteristics of coal briquettes and biomass pellets in household stoves

Burning coal briquettes or biomass pellets in household decoupling stoves is of significance to the reduction of residential pollutant emissions such as NO and CO. In order to make full use of the superiority of decoupling combustion technology, the household stoves should be specially designed and optimized to adapt to fuel types and combustion characteristics. Using numerical simulation and experimental validation, this study quantitatively clarified that the reducibility of devolatilization char plays an important role in the suppression of NO emission in the decoupling combustion of coal, while the reducibility of pyrolysis gases has a dominant effect on the reduction of NO in the decoupling combustion of biomass. An optimal parameter combination of throat height and grate angle was obtained for the simultaneous suppression of NO and CO emissions in the household decoupling stove burning coal briquettes. Two types of decoupling stoves were developed to enable the clean combustion of biomass pellets. The A-type biomass stove with a multi-pass smoke tunnel shows a better comprehensive NO and CO reduction effectiveness than the B-type biomass stove consisting of a two-stage grate structure and an S-shaped pyrolysis chamber. The optimal structural parameters provided references for the design and manufacture of commercial decoupling coal and biomass stoves.

Co-liquefaction of Coal and Used Tire in Supercritical Water

The co-liquefaction of lignite coal and used tire was performed in a 250-ml batch reactor, in supercritical water under a nitrogen atmosphere to investigate the effects of temperature (380-440℃), water/feedstock ratio (4/1-10/1 (wt./wt.)) and the % used tire content in the feedstock (0-100 wt.%) on the conversion efficiency, liquid yield and oil composition attained. The maximum conversion and oil yield were 67 and 50%, respectively, obtained at 400℃ at 1 min, with water/feedstock ratio of 10/1 and 80% used tire content. The distillation characteristics of the oil products, analyzed by simulated distillation gas chromatography, revealed that the oil composition depended significantly on the reaction temperature. The co-liquefaction of coal and used tire yielded a synergistically increased level of oil production. Moreover, the total conversion level obtained with co-liquefaction alone was almost equal to those obtained in the presence of either Fe2O3 or NiMo as catalysts, under the same conditions. Therefore, supercritical water is a good medium for the dissolution of the volatile matter from a coal and used tire matrix.

Thermogravimetric characteristics of corn straw and bituminous coal copyrolysis based the ilmenite oxygen carriers

Herein,the co-pyrolysis reaction characteristics of corn straw(CS)and bituminous coal in the presence of ilmenite oxygen carriers(OCs)are investigated via thermogravimetry coupled with mass spectrometry.The results reveal that the participation of OCs weakens the devolatilization intensity of co-pyrolysis.When the CS blending ratio is<50%,the mixed fuel exhibits positive synergistic effects.The fitting results according to the Coats-Redfern integral method show that the solid-solid interaction between OCs and coke changes the reaction kinetics,enhancing the co-pyrolysis reactivity at the high-temperature zone(750-950C).The synergistic effect is most prominent at a 30%CS blending ratio,with copyrolysis activation energy in the range of 26.35-40.57 kJ·mol^(-1).

Co-pyrolysis of bituminous coal and biomass in a pressured fluidized bed

An experimental study on co-pyrolysis of bituminous coal and biomass was performed in a pressured fluidized bed reactor.The blend ratio of biomass in the mixture was varied between 0 and 100 wt%,and the temperature was over a range of 550–650℃ under 1.0 MPa pressure with different atmospheres.On the basis of the individual pyrolysis behavior of bituminous coal and biomass,the influences of the biomass blending ratio,temperature,pressure and atmosphere on the product distribution were investigated.The results indicated that there existed a synergetic effect in the co-pyrolysis of bituminous coal and biomass in this pressured fluidized bed reactor,especially when the condition of bituminous coal and biomass blend ratio of 70:30(w/w),600℃,and 0.3 MPa was applied.The addition of biomass influenced the tar and char yields and gas and tar composition during co-pyrolysis.The tar yields were higher than the calculated values from individual pyrolysis of each fuel,and consequently the char yields were lower.The experimental results showed that the composition of the gaseous products was not in accordance with those of their individual fuel.The improvement of composition in tar also indicated synergistic effect in the co-pyrolysis.

Comparison of kinetic models for isothermal CO_2 gasification of coal char–biomass char blended char

This study investigated the isothermal gasification reactivity of biomass char （BC） and coal char （CC） blended at mass ratios of 1：3, 1：1, and 3：1 via isothermal thermogravimelric analysis （TGA） at 900, 950, and 1000℃ under CO2. With an increase in BC blending ra- tio, there were an increase in gasification rate and a shortening of gasification time. This could be attributed to the high specific surface area of BC and the high uniformity of carbon structures in CC when compared to those in BC. Three representative gas-solid kinetic models, namely, the volumetric model （VM）, grain model （GM）, and random pore model （RPM）, were applied to describe the reaction behavior of the char. Among them, the RPM model was considered the best model to describe the reactivity of the char gasification reaction. The activa- tion energy of BC and CC isothermal gasification as determined using the RPM model was found to be 126.7 kJ/mol and 210.2 kJ/mol, re- spectively. The activation energy was minimum （123.1 kJ/mol） for the BC blending ratio of 75%. Synergistic effect manifested at all mass ratios of the blended char, which increased with the gasification temperature.

Co-gasification of coal and biomass an emerging clean energy technology: Status and prospects of development in Indian context

Co-gasification of coal and biomass is emerging as potential clean fuel technology to achieve high thermodynamic efficiency with relatively low CO2 emission. The coal and biomass have been exclusively gasified more than a century to obtain gas–liquid fuels and the production of chemicals. Co-gasification has higher efficiency than the solitary coal gasification because the cellulose, hemicellulose and lignin content of biomass help to ignite and enhance the rate of gasification. It is suggested that the extensive research on carbon reactivity pattern, heat release, reaction kinetics, etc. may support to reduce the uncertainties in the co-gasification performance of coal and biomass blends, particularly in India. The prospects of co-gasification technology in Indian context have been discussed considering the abundance of varieties of coal and biomass. The suitability of existing gasifier procedures and their limitations with operating parameters like temperature, residence time, density optimisation, feed rate, agglomeration intensity, the tar formation and techno-economics involved are described. Also, this paper reviews the research highlights of the history of co-gasification and the advancement in upcoming challenges like a design of gasifier, access and preparation of biomass, disposal of residue, environmental concerns and reassurance to the operators for execution of large and small-scale projects.

The mechanism and products for co-thermal extraction of biomass and low-rank coal with NMP

The high-value utilization of low-rank coal would allow for expanding energy sources,improving energy efficiencies,and alleviating environmental issues.In order to use low-rank coal effectively,the hypercoals(HPCs)were co-extracted from two types of low-rank coal and biomass via N-methyl-2-purrolidinone(NMP)under mild conditions.The structures of the HPCs and residues were characterized by proximate and ultimate analysis,Raman spectra,and Fourier transform infrared(FT-IR)spectra.The carbon structure changes within the raw coals and HPCs were discussed.The individual thermal dissolution of Xibu(XB)coal,Guandi(GD)coal,and the biomass demonstrated that the biomass provided the lowest thermal dissolution yield Y1 and the highest thermal soluble yield Y2 at 280℃,and the ash content of three HPCs decreased as the extraction temperature rose.Co-thermal extractions in NMP at various coal/biomass mass ratios were performed,demonstrating a positive synergic effect for Y2 in the whole coal/biomass mass ratios.The maximum value of Y2 was 52.25wt% for XB coal obtained with a XB coal/biomass of 50wt% biomass.The maximum value of Y2 was 50.77wt% for GD coal obtained with a GD coal/biomass of 1:4.The difference for the optimal coal/biomass mass ratios between XB and GD coals could be attributed to the different co-extraction mechanisms for this two type coals.

Co-firing of coal and biomass in oxy-fuel fluidized bed for CO2 capture: A review of recent advances

The co-firing of coal and biomass in oxy-fuel fluidized beds is one of the most promising technologies for capturing CO2.This technology has attracted wide attention from academia and industry in recent years as a negative emission method to capture CO2 produced by carbon contained in biomass.In the past decades,many studies have been carried out regarding experiments and numerical simulations under oxy-fuel combustion conditions.This paper firstly briefly discusses the techno-economic viability of the biomass and coal co-firing with oxycombustion and then presents a review of recent advancements involving experimental research and computational fluid dynamics(CFD)simulations in this field.Experimental studies on mechanism research,such as thermogravimetric analysis and tube furnace experiments,and fluidized bed experiments based on oxy-fuel fluidized beds with different sizes as well as the main findings,are summarized as a part of this review.It has been recognized that CFD is a useful approach for understanding the behaviors of the co-firing of coal and biomass in oxyfuel fluidized beds.We summarize a recent survey of published CFD research on oxy-fuel fluidized bed combustion,which categorized into Eulerian and Lagrangian methods.Finally,we discuss the challenges and interests for future research.

Waste biomass from production process co-firing with coal in a steam boiler to reduce fossil fuel consumption:A case study

Waste biomass is always generated during the production process in industries. The ordinary way to get rid of the waste biomass is to send them to landfill or burn it in the open field. The waste may potentially be used for co-firing with coal to save fossil fuel consumption and also reduce net carbon emissions. In this case study, the bio-waste from a Nicotiana Tahacum （NT） pre-treatment plant is used as the biomass to co-fire with coal. The samples of NT wastes were analysed. It was found that the wastes were of the relatively high energy content which were suitable for co-firing with coal. To investigate the potential and benefits for adding NT wastes to a Fluidised Bed Combustion （FBC） boiler in the plant, detailed modelling and simulation are carried out using the European Coal Liquefaction Process Simulation and Evaluation （ECLIPSE） process simulation package. The feedstock blending ratios of NT waste to coal studied in this work are varied from 0% to 30%. The results show that the addition of NT wastes may decrease the emissions of CO2 and SOx without reducing the boiler performance.

Biomass gasification and Polish coal-fired boilers for process of reburning in small boilers

Reburning was applied to Polish automatic coal-fired retort boiler (25 kW).The use of bio-syngas reduced NOx emissions from the boiler by over 25%,below the significant level of 200 mg/m3 .Reburning was carried out using an integrated system consisting of the boiler and a fixed-bed 60 kW (GazEla) gasification reactor.The process gas was continuously introduced above the coal burner of the boiler.The process parameters of the boiler and the gasifier were also measured and compared with the other units.Characteristic NOx emissions from automatic and manually operated boilers were also presented.

Predictions of elemental composition of coal and biomass from their proximate analyses using ANFIS, ANN and MLR

The elemental composition of coal and biomass provides significant parameters used in the design of almost all energy conversion systems and projects.The laboratory tests to determine the elemental composition of coal and biomass is time-consuming and costly.However,limited research has suggested that there is a correlation between parameters obtained from elemental and proximate analyses of these materials.In this study,some predictive models of the elemental composition of coal and biomass using soft computing and regression analyses have been developed.Thirty-one samples including parameters of elemental and proximate analyses were used during the analyses to develop multiple prediction models.Dependent variables for multiple prediction models were selected as carbon,hydrogen,and oxygen.Using volatile matter,fixed carbon,moisture and ash contents as independent variables,three different prediction models were developed for each dependent parameter using ANFIS,ANN,and MLR.In addition,a routine for selecting the best predictive model was suggested in the study.The reliability of the established models was tested by using various prediction performance indices and the models were found to be satisfactory.Therefore,the developed models can be used to determine the elemental composition of coal and biomass for practical purposes.

Characterization of bio-coal briquettes blended from low quality coal and biomass waste treated by Garant■bio-activator and its application for fuel combustion

Experimental research was carried out on the manufacturing of bio-coal briquettes from a blend of two different types of low-quality coal and biomass waste in the absence of coal carbonization,where the third blend of the material was fermented by adding a bio-activator solution before pressurizing the components into briquettes.The coal samples from Caringin-Garut Regency(BB-Garut)had a low calorific value and a high sulfur content(6.57 wt%),whereas the coal samples from Bayah-Lebak Regency(BB-Bayah)had a higher calorific value and a lower sulfur content(0.51 wt%).The biomass added to the coal blend is in the form of fermented cow dung(Bio-Kohe),and it had a calorific value of 4192 kcal/kg and a total sulfur content of 1.56 wt%.The main objective of this study is to determine the total decrease in the sulfur content in a blend of coal and biomass in which a fennentation process was carried out using a bio-activator for 24 h.The used bio-activator was made from Garant■(1:40)+molasses 1 wt%/vol,and its used amount was 0.2 L/kg.Also,the total sulfur content in the blend was 1.00 wt%-1.14 wt%,which fulfills the necessary quality requirements for non-carbonized bio-coal briquettes.The pyritic and sulfate content in the raw coal was dominant,and the organic sulfur,when fermented with Garant■,was found to be less in the produced bio-coal briquettes by 38%-58%.

Simulation Study on Influence of Steam on Co-gasification of Biomass and Coal in a Fluidized Bed

生物质与煤共气化可解决生物质不易稳定流化以及气化气焦油含量高的问题。文中利用Aspen Plus软件对流化床生物质与煤共气化进行模拟。为了更真实地反映流化床内的实际反应情况，采用嵌入 FORTRAN 气化反应动力学及流体动力学子程序的连续搅拌釜式反应器来代替惯用的Gibbs反应器，结果表明该模型的模拟值与试验值吻合较好。利用灵敏度分析功能研究了水蒸气/物料质量比（S/F）对产气组分、热值和气化效率等参数的影响，结果表明：增大水蒸气与物料质量比有利于氢气产率的提高，当S/F值取0.35~0.45时，气化效率和产气热值较高。

On-line tracking of pulverized coal and biomass fuels through flame spectrum analysis

This paper presents a new approach to the on-line tracking of pulverized coal and biomass fuels through flame spectrum analysis.A flame detector containing four photodiodes is used to derive multiple signals covering a wide spectrum of the flame from visible,near-infrared and mid-infrared spectral bands as well as a part of far-infrared band.Different features are extracted in time and frequency domains to identify the dynamic "fingerprints" of the flame.Fuzzy logic inference techniques are employed to combine typical features together and infer the type of fuel being burnt.Four types of pulverized coal and five types of biomass are burnt on a laboratory-scale combustion test rig.Results obtained demonstrate that this approach is capable of tracking the type of fuel under steady combustion conditions.

Thermal Behavior of Coal and Biomass Blends in Inert and Oxidizing Gaseous Environments

Oxy-fuel combustion and gasification (pre-combustion) may have potential for capturing carbon dioxide at lower costs for power generation. Oxy-co-firing and co-gasifying coal with biomass could further reduce effective CO2 emissions and utilize renewable energy resources. A key feature of these two approaches is that they process fuel in concentrated CO2 or O2/CO2 instead of N2 or O2/N2. Accurate predictive models of these processes using blends of coal and biomass can be used in process simulation and could aid in the development and implementation of these technologies. To develop these accurate predictive models, it is important to understand the conversion routes and thermal behavior of these fuels in appropriate gas environments. The objectives of this study are to investigate the impact of inert and oxidative gaseous environments on thermal behavior and reactivity of coal and biomass blends and to study the effect of biomass percentage on coal/biomass blend co-utilization. Fuel samples included a Powder River Basin (PRB) sub-bituminous coal, yellow pine wood sawdust pellets, and mixtures of 10 and 20 weight percent wood in coal. The samples were tested under N2, CO2, and 10% O2 in CO2 by volume using a non-isothermal thermogravimetric method for temperatures up to 1000℃. Fuel weight losses of both coal and wood are essentially the same in CO2 as in N2 in the low temperature range, but higher in 10% O2 in CO2 compared to N2 and CO2. However, total weight losses at 1000℃ under CO2 and 10% O2 in CO2 are similar and higher than in N2 due to char gasification by the CO2 and combustion by O2. The char combustion in 10% O2 in CO2 takes place at lower temperature than char gasification in CO2. Coal and wood blends have higher reactivity compared to coal alone in the lower temperature range due to the high volatile matter content of wood. Interactions of wood and coal in these gas environments and blend percentage are discussed.

The Properties and Suitability of Various Biomass/Coal Blends for Co-Gasification Purposes

Gasification is a promising technology for the production of gaseous fuels, mainly syngas, which is produced from the hydrocarbon-based materials such as coal and biomass. Currently, coal is the main feedstock that is used for the gasification process due to its large reserves and higher energy per volume. However, the use of coal has been a more concern because of the environmental impacts caused by the emission of toxic gases such as the sulphides, sulphates and nitrates as well as the ash slagging problems forming inside the gasifier. On the other hand, biomass is a renewable energy resource of interest as a replacement for coal to reduce the environmental impacts associated with fossil fuel usage. Much consumption of fossil fuels has caused serious energy crisis and environmental impacts, globally. Co-gasification of coal and biomass is considered as a connection between energy production based on fossil fuels and energy production based on renewable fuels. The utilization of biomass by co-gasification with coal causes reductions of carbon dioxide, nitrogen and sulfur emissions due to the renewable character of biomass and low contamination content in biomass. This study determined the properties of various biomass/coal blends and their suitability for co-gasification in a downdraft biomass gasifier. A bomb calorimeter was used to determine the calorific values of the material. CHNS and XRF analysis were carried out to determine the elemental analysis of the material. Thermogravimetric analysis (TGA) was conducted to investigate the thermal degradation of the material. The kinetic analysis of the various feedstocks allows the prediction of the rate at which co-gasification takes place. The results suggested that blending coal with biomass result in a faster reaction rate at lower temperatures than that of coal alone and lower activation energy due to the high quantity of volatile matter in biomass.

Thermochemical Conversion of Coal and Coal-Biomass Blends in an Autothermal Moving Bed Gasifier: Experimental Investigation

A unique laboratory scale auto-thermal moving bed gasifier was designed for studying the thermochemical conversion of coal-biomass blends. For this purpose, two coals (lignite and sub-bituminous), two biomass materials (corn stover and switchgrass), and their respective blends were used. Gasification characteristics of the fuels were evaluated with an emphasis on improving the producer gas composition. The efficiency and product gas compositions reveal that utilizing the inner stainless-steel tubing better promotes heat transfer upwards in the axial direction when compared to utilizing quartz insulation. The H2/CO ratio at the same operating conditions is much higher due to the increase in bed temperature and heat transfer upwards in the axial direction. This improved the overall efficiency by at least 20%. Using pure oxygen and steam, efficiency greater than 50% was obtained for blends with corn stover at steam to oxygen ratio of 2:1. Also, using air as the gasifying agent greatly improved the H2/CO ratios and overall efficiency in blends with corn stover. In contrast, blends with switchgrass were not very effective with respect to the overall gasification characteristics. Blending switchgrass with coal may not be viable option from the viewpoint of generating high quality producer gas for downstream operations.

System Performance and Pollution Emission of Biomass Gas Co-Firing in a Coal-Fired Boiler

To reduce greenhouse gases emission and increase the renewable energy utilization portion in the world, the biomass gasification coupled with a coal-fired boiler power generation system is studied. It is a challenge to achieve optimum performance for the coupled system. The models of biomass gasification coupled with co-firing of coal in a boiler have been established. A comparative study of three kinds of biomass (Food Rubbish, Straw and Wood Pellets) has been done. The syngas produced in a 10 t/h gasifier is fed to a 330 MWe coal-fired boiler for co-combustion, and the co-firing performances have been compared with pure coal combustion case under the conditions of constant boiler load. Results show that co-firing decreases the furnace combustion temperature and raises the flue gas temperature for Food Rubbish and Straw, while, flue gases temperature decrease in case of Wood Pellets. At the same time NOx and SOx emissions have reduced. The system efficiencies at constant load for Food Rubbish, Straw and Wood Pellets are 83.25%, 83.88% and 82.56% when the optimum conditions of gasification and co-firing process are guaranteed.

露天煤矿排土场边坡植被恢复群落稳定性研究

为了揭示露天煤矿排土场边坡植被恢复群落稳定性的动态特征和变化模式,以内蒙古北电胜利露天煤矿4个排土场为研究对象,选取Shannon-Wiener多样性指数、Margalef丰富度指数、Pielou均匀度指数和Simpson优势度指数、植被盖度、植被高度、地上和地下生物量8个指标,构建了基于群落结构稳定性与群落功能稳定性的排土场边坡植被恢复群落稳定性评价体系,采用综合评价法对处于人工植被恢复中的内排土场和恢复年限分别为4 a、5 a、8 a的沿帮排土场、南排土场和北排土场的南、北方向边坡植被恢复群落稳定性进行综合评估,并对群落稳定性因子与土壤含水量、有机质、全氮、全磷、全钾等环境因子间关系进行分析,探究影响排土场边坡群落稳定性的影响因素。结果表明:(1)随着恢复年限的增加,边坡植被群落稳定性整体呈稳步上升趋势,但与草原站背景值相比,其综合评价指数处于较不稳定或不稳定状态。(2)随着恢复年限的增加,排土场边坡群落稳定性由结构稳定性主导转向功能稳定性主导。恢复初期受人工影响,物种多样性提高,结构稳定性较高,随着时间的推移,结构稳定性波动下降,功能稳定性上升,其中地下生物量增长迅速,生物量向地下转移,进而形成矿区特有的植物群落结构稳定与功能稳定转变特征。(3)从坡向来看,随着恢复年限的增加,边坡群落稳定性逐渐由南坡优于北坡转变为北坡优于南坡。(4)南坡的结构稳定性与环境因子的相关性较高,而北坡的功能稳定性与环境因子相关性较高,表明不同坡向的群落采用了不同的响应策略以适应环境的变化,丰富的有机质和全氮含量对排土场边坡群落功能性稳定性会产生积极影响。

水蒸气辅助煤与生物质回转炉共热解制高热值可燃气特性研究

煤与生物质共热解作为实现这两种含碳资源高效清洁利用的重要技术路径,对实现碳中和目标有重要意义。本文旨在探究水蒸气辅助下,不同条件对煤与生物质共热解制备高值可燃气体(H_(2)、CH_(4)、CO)的影响。在大型回转炉中,探究了褐煤与玉米秸秆共热解及水蒸气辅助共热解温度、掺混比对H_(2)、CH_(4)、CO产气量和热值的影响,并通过Aspen Plus搭建热解模型对其进行验证。实验及仿真结果表明:秸秆与褐煤存在明显的协同效应,无水蒸气时最佳产气条件可燃气热值超过3000 J/L(热解温度600℃,秸秆掺混比80%)。水蒸气条件下,促进了共热解可燃气高热值组分H_(2)、CH_(4)、CO的生成,最佳条件下可燃气热值提升88%达到5639 J/L(热解温度800℃,秸秆掺混比80%)。