白酒糟双床解耦燃烧模拟实验研究

采用实验与Aspen Plus模拟相结合的方法,以白酒糟作为富氮高含水生物质残渣的典型代表,研究了生物质残渣双床解耦燃烧的必要性与可行性. 结果表明,高水分白酒糟在普通流化床中存在点火时间长、燃烧稳定性差及NO浓度排放高(>800 mg/m3)的缺点,而采用双床解耦燃烧可减少点火时间,提高燃烧稳定性并降低NO排放浓度50%以上. 模拟结果显示,55%含水率的白酒糟可在双床系统中实现自热燃烧. 以石英砂为床料,在500~900℃的流化床燃烧实验中证实了经工业发酵的纤维素更易燃烧,且未发现白酒糟灰的烧结现象.     

Modeling the temperature in coal char particle during fluidized bed combustion

The temperatures of a coal char particle in hot bubbling fluidized bed (FB) were analyzed by a model of combustion. The unsteady model includes phenomena of heat and mass transfer through a porous char particle, as well as heterogeneous reaction at the interior char surface and homogeneous reaction in the pores. The parametric analysis of the model has shown that above 550 °C combustion occurs under the regime limited by diffusion. The experimental results of temperature measurements by thermocouple in the particle center during FB combustion at temperatures in the range 590-710 °C were compared with the model predictions. Two coals of different rank were used: lignite and brown coal, with particle size in the range 5-10 mm. The comparisons have shown that the model can adequately predict the histories of temperatures in char particles during combustion in FB. In the first order, the model predicts the influence of the particle size, coal rank (via porosity), and oxygen concentration in its surroundings.     

沉降炉中生物质热解产物的脱硝特性

利用连续沉降炉模拟白酒糟循环流化床解耦燃烧再燃区的反应气氛,研究各因素对半焦、焦油和热解气脱硝效率(比脱硝效率)的影响. 结果表明,反应温度由800℃升至1050℃,热解产物比脱硝效率均增大;半焦和焦油达到最佳比脱硝效率所需的停留时间为3.4 s;随反应气中NO浓度由400′10-6(j)增加到1000′10-6(j),热解产物比脱硝效率均呈降低趋势,但NO绝对还原量却呈增加趋势;随反应气中O2浓度增加,半焦比脱硝效率增大,热解气比脱硝效率降低,焦油比脱硝效率呈先增加后减少的趋势,在O2浓度为1.6%(j)时达最大,为60.1%. 在本研究的反应条件下,焦油比脱硝效率最好,热解气次之,半焦效果较差.     

Chemical kinetic modelling of the effect of NO on the oxidation of CH4 under fluidized bed combustor conditions

The ignition and burnout of the volatiles in fluidized bed combustor are essential for its performance and emissions. NO_x are known to sensitize the oxidation of hydrocarbons, CO, and H₂. This effect is relevant especially for fluidized bed combustors, which are operated at relatively low temperatures (i.e. about 850 °C). Different reaction mechanisms and modifications to existing mechanisms have been proposed in the literature to account for these low temperature interactions of NO_x and hydrocarbons. In this work, an existing widely used reaction mechanism is adapted and tested for its capability to describe the NO sensitized oxidation of CH₄ under conditions relevant to fluidized bed combustion. NO lowers the ignition temperature to about 300 °C under the conditions investigated. Three different oxidation paths for the oxidation of CH₄ have been identified and discussed. Their relative importance strongly depends on combustion temperature, indicating that the presence of NO_x significantly affects the oxidation of the volatiles in fluidized bed combustion.     

糠醛渣热解特性及热解挥发产物对其燃烧烟气原位控氮作用

通常,具有高含氮资源禀赋生物质在能源化利用过程中需控制NO_x排放。解耦燃烧是可适用于高含水、高含氮燃料的低NO_x燃烧技术,其对NO_x生成的抑制效果优于其他燃烧技术。为揭示解耦燃烧中热解挥发产物的原位控氮潜力、发展双流化床解耦燃烧技术,以糠醛渣为原料,借助固定床装置和双流化床装置,分别开展其热解特性和双流化床解耦燃烧近实际工况模拟研究。具体地,首先在固定床反应器中考察糠醛渣在不同温度下的热解产物分布,继而借助双流化床反应器考察了热解在线挥发产物对热解半焦同步燃烧烟气中NO_x的还原效果。结果表明：在500~700℃热解温度区间内,随温度的升高,半焦产率逐渐减少,从45.2%下降到39.8%;气体产率呈明显上升趋势,从12.4%上升到22.5%,CO、CH₄、H₂等还原性组分产率增加显著;焦油产率略有降低,从15.9%降低到12.9%;水分产率变化不大。双流化床解耦燃烧实验中,糠醛渣热解挥发产物对热解半焦同步燃烧所产烟气控氮效果良好,热解挥发产物对半焦燃烧烟气NO_x减排效果主要受热解温度、二次风占比影响,总过量空气系数ER=1.3,热解温度600℃、二次风过量空气系数ER₂=0.5时,糠醛渣热解挥发产物对相同热解条件下生成的半焦燃烧（900℃,过量空气系数ER₁=0.8）所产烟气原位控氮效果达到最优,NO_x减排率为54.80%。这表明,可通过控制热解挥发分产物产率、氧化程度,充分发挥挥发分的NO_x还原能力,从而明显改善解耦燃烧原位控氮效果。     

Combustion of single char particles in a turbulent fluidized bed

The combustion of single bituminous char particles (4-12 mm diameter) was studied in a turbulent fluidized bed operated at 1098 K using air as the fluidising medium. Results indicated that particles burn with constant density following a shrinking sphere model. Burning rates are much higher than those observed in a bubbling fluidized bed. The rate of transfer of oxygen to the particle surface is also higher than that observed in bubbling beds. A model is proposed to calculate the Sherwood numbers of the burning carbon particles. Experimental values of the Sherwood numbers agree well with those predicted from the model.     

Pyrolysis characteristics of Oriental white oak: Kinetic study and fast pyrolysis in a fluidized bed with an improved reaction system

The kinetic parameters for the pyrolysis of Oriental white oak were evaluated by thermogravimetric analysis (TGA). The white oak was pyrolyzed in a fluidized bed reactor with a two-staged char separation system under a variety of operating conditions. The influence of the pyrolysis conditions on the chemical and physical characteristics of the bio-oil was also examined. TGA showed that the Oriental white oak decomposed at temperatures ranging from 250 to 400 °C. The apparent activation energy ranged from 160 to 777 kJ mol^− 1. The optimal pyrolysis temperature for the production of bio-oil in the fluidized bed unit was between 400 and 450 °C. A much smaller and larger feed size adversely affected the production of bio-oil. A higher fluidizing gas flow and higher biomass feeding rate were more effective in the production of bio-oil but the above flow rates did not affect the bio-oil yields significantly. Recycling a part of the product gas as a fluidizing medium resulted the highest bio-oil yield of 60 wt.%. In addition, high-quality bio-oil with a low solid content was produced using a hot filter as well as a cyclone. With exception of the pyrolysis temperature, the other pyrolysis conditions did not significantly affect the chemical and physical characteristics of the resulting bio-oil.     

白酒糟循环流化床燃烧灰直接肥料化利用

研究了白酒糟循环流化床燃烧灰直接作为肥料的可能性和效果,以其为肥料种植油菜,考察了油菜在5种土壤中发芽和生长情况. 结果表明,白酒糟燃烧灰对不同生长阶段的油菜有不同影响,对壤质土中的油菜发芽有抑制作用,但能明显改善粘性土壤中油菜的生长环境,油菜的净增量和产量都有明显增加. 白酒糟燃烧灰还能提高酸性土壤pH值,使土壤环境向中性(pH 6.97~7.74)转变,有利于腐殖酸分解和植物生长. 土壤与白酒糟燃烧灰质量比为5:1时,与原土相比,泸州国窖红土壤、泸州青稞土壤及富阳土壤中油菜净增量分别为80.1%, 80.9%, 163.6%,表明利用白酒糟燃烧灰作为植物生长肥料是可行的.     

Combustion of liquid petroleum gas in a fluidized bed furnace with a jetting-mixing distributor

Liquid petroleum gas (LPG) fluidized beds have potential applications in metal heating or workpiece heat treatments. The combustion of LPG and the controls of the atmosphere inside the bed and the bed temperature are very concerned. The combustion of LPG has been investigated in a pilot-scale bubbling fluidized bed with a jetting-mixing nozzle distributor and hollow corundum sphere particles of 0.867-1.212 mm in diameter and 386-870 kg/m³ in bulk density at 800-1100°C. Experiments were carried out for fuel-rich mixtures to explore the possibility to obtain mild oxidizing, non-oxidizing or reducing atmosphere in the bed. Air factor (the ratio of the volume of air actually fed into the bed to that in a stoichiometric mixture) is in between 0.3 and 1.0 and U/U_mf 1.3-3.0. The distributor brings LPG and air into an intense contact sufficient to permit in-bed combustion without backfire problems. The experimental results show that the fluidized bed furnace offers excellent thermal uniformity and temperature control. The size of the combustion zone is usually larger than that of the temperature variation zone. Particle properties, initial bed height, air factor and U/U_mf all affect the bed temperature profile, whereas only the air factor and U/U_mf have significant effects on the combustion in the bed. The bed temperature can be adjusted by separate or combined adjusting of air factor and U/U_mf.     

流化床中燃烧高水高氮酒糟的NO排放特性

采用流化床反应器,研究富水蒸气条件下酒糟燃烧的NO排放特性。结果表明,增加过量空气系数和升高燃烧温度,NO排放浓度升高;对送入燃烧反应器的气体中添加水蒸气模拟高水分燃料燃烧有效地降低了酒糟燃烧的NO排放浓度及总排放量,且在适当条件下可减少NO排放约46%(质量)。酒糟灰分中的金属氧化物对NO的还原有催化作用,且随着温度的升高变强。在含H₂或CO的N₂气氛中,灰分对NO催化还原作用更明显。水蒸气本身对NO没有明显还原作用,说明水蒸气是通过与碳氢化合物反应生成还原性气体,如H₂和CO,从而在酒糟灰催化作用下强化NO的还原。     

Effect of bed depth on characterisation of slow pyrolysis products

The trend towards separation of waste for material recovery could assist with the implementation of waste pyrolysis and gasification processes. Following the previous work on slow pyrolysis of segregated waste materials, this study investigated the effect of bed depth on the yields and properties of pyrolysis products in a fixed bed pyrolyser. The results showed that the bed depth had a strong influence on the properties of pyrolysis products but a small effect on the yield of products. Differences in the liquid yield between the two cases of bed depth (17-57 vol% of the reactor) were observed at temperatures above 500 °C while the difference in the char yield was negligible. The aqueous fraction was 5-15% higher for the bed depth of 57 vol% than for the bed depth of 17 vol%. Increase in the bed depth increased the H/C ratio by a factor of 2-6 in the char product and the CO/CO₂ ratio by a factor of 1.74 in the gas product but slightly decreased in the H/C ratio in the liquid product.     

Pyrolysis of scrap printed circuit board plastic particles in a fluidized bed

Pyrolysis behavior and corresponding pyrolysis products of printed circuit board plastic particles (PCBP particles) were investigated in a fluidized bed using TG-FTIR analysis system. PCBP particles were separated from crashed printed circuit boards using fluidized beds, 354 μm crashed plastic particles were pyrolyzed at the temperature ranging from 20 to 900 °C by a thermogravimetric analyzer. Two stages of decomposition were identified for PCBP particles under nitrogen conditions. The activation energy was 90.49 kJ/mol for the first-stage reaction and 137.80 kJ/mol for the second-stage reaction. Further, gas products, liquid products, and solid residues yielded in the fluidized bed were analyzed using an elemental analyzer and FTIR. It has been found that the liquid yields increased with an increase in pyrolysis temperature, and with an increase in superficial gas velocity. The main compositions of liquid products were aromatic compounds including substituted benzenes. Whereas, the solid products mainly contained char and fiberglass.     

海藻生物质颗粒流化床燃烧试验研究

在小型流化床试验台上研究了海藻颗粒(条浒苔与马尾藻)的流化床燃烧。海藻在流化床内的挥发分析出燃烧时间都在1 min左右。条浒苔颗粒在流化床中燃烧先进行脱水和挥发分的燃烧,接着发生焦炭燃烧,其燃烧过程符合缩核模型,炭核由外向内逐层燃烧,而灰层半径几乎不变。但马尾藻颗粒由于挥发分的大量快速释放而迅速膨胀破碎成屑。另外通过对条浒苔颗粒及不同燃烧时间后收集的焦炭颗粒剖面的SEM扫描电镜观察,发现随着燃烧的进行,颗粒内孔隙增大,微孔表面粗糙。进一步详细研究了两种海藻颗粒(条浒苔与马尾藻)在流化床内单次投料下的燃烧。随着床温的升高,条浒苔释放NO_x相对浓度增加,CO相对浓度减少。而马尾藻释放气体中SO₂与NO_x含量相对条浒苔有所增加;随着床温的升高,CO相对浓度减少。床温的升高使得床内传热速率加快,两种海藻挥发分的析出提前,燃尽时间缩短。风速、床高的升高使得两种海藻燃烧容易,燃尽时间缩短。     

Some process fundamentals of biomass gasification in dual fluidized bed

The dual fluidised bed gasification technology is prospective because it produces high caloric product gas free of N₂ dilution even when air is used to generate the gasification-required endothermic heat via in situ combustion. This study is devoted to providing the necessary process fundamentals for development of a bubbling fluidized bed (BFB) biomass gasifier coupled to a pneumatic transported riser (PTR) char combustor. In a steam-blown fluidized bed of silica sand, gasification of 1.0 g biomass, a kind of dried coffee grounds containing about 10 wt.% water, in batch format clarified first the characteristics of fuel pyrolysis (at 1073 K) under the conditions simulating that prevailing in the gasifier intended to develop. The result shown that via pyrolysis more than 60% of fuel carbon and up to 75% of fuel mass could be converted into product gas, while the simultaneously formed char was about 22% of fuel mass. With all of these data as the known input, a process simulation using the software package ASPEN then revealed that the considered dual bed gasification plant, i.e. a BFB gasifier + a PTR combustor, is able to sustain its independent heat and mass balances to allow cold gas efficiencies higher than 75%, given that the fuel has suitable water contents and the heat carried with the product gas from the gasifier and with the flue gas from the char combustor is efficiently recovered inside the plant. In a dual fluidized bed pilot gasification facility simulating the gasification plant for development, the article finally demonstrated experimentally that the necessary reaction time for fuel, i.e. the explicit residence time of fuel particles inside the BFB gasifier computed according to a plug granular flow assumption, can be lower than 160 s. The results shown that varying the residence time from 160 to 1200 s only slightly increased the gasification efficiency, but the reaction time available in the PTR, say, about 3 s in our case, was too short to assure the finish even of fuel pyrolysis.     

Devolatilization of wood and wastes in fluidized bed

Experiments were carried out in a laboratory fluidized bed (FB) to characterize the devolatilization behavior of wood and various wastes at temperatures applicable to FB gasification and combustion, i.e. 750-900 °C. The fuels tested were pellets made of wood, meat and bone meal, and compost (from municipal solid wastes), as well as dried granulates of sewage sludge (DSS). Determination of yields of char, condensate and light gas, as well as the composition of the gas and the time of devolatilization during the pyrolysis of single fuel batches was made. A simple model was developed to analyze the mode of conversion of a single wood pellet and DSS granulate, giving insight on the controlling mechanisms during devolatilization. The devolatilization kinetics of DSS was determined by tests using fine granulates. The model was successfully applied to simulate the conversion of large DSS granulates and wood pellets under the whole range of temperatures analyzed.     

Model development and validation: Co-combustion of residual char, gases and volatile fuels in the fast fluidized combustion chamber of a dual fluidized bed biomass gasifier

A one-dimensional steady state model has been developed for the combustion reactor of a dual fluidized bed biomass steam gasification system. The combustion reactor is operated as fast fluidized bed (riser) with staged air introduction (bottom, primary and secondary air). The main fuel i.e., residual biomass char (from the gasifier), is introduced together with the circulating bed material at the bottom of the riser. The riser is divided into two zones: bottom zone (modelled according to modified two phase theory) and upper zone (modelled with core-annulus approach). The model consists of sub-model for bed hydrodynamic, conversion and conservation. Biomass char is assumed to be a homogeneous matrix of C, H and O and is modelled as partially volatile fuel. The exit gas composition and the temperature profile predicted by the model are in good agreement with the measured value.     

Numerical modeling of a jetting fluidized bed gasifier and the comparison with the experimental data

A model for a jetting fluidized bed gasifier is developed, treating the grid, bubble and freeboard zones in series. Reactions including char combustion, steam gasification, CO₂ gasification and water–gas shift reaction are taken into account. The effects on model predictions of assumptions regarding the primary products of char combustion and char reactivity factor are analyzed by comparing the predictions with experimental data from a bench-scale jetting fluidized bed gasifier using different kinds of chars. Contributions of various reactions and different zones and phases to carbon conversion are analyzed.     

Modelling of circulating fluidized bed combustion of a char

The combustion of a char in the 41 mm ID riser of a laboratory circulating fluidized bed combustor has been investigated at different air excesses and rates of solids (char and sand) circulating in the loop. Riser performance was characterized by an axial oxygen concentration profile as well as by the overall carbon content and particle size distribution. The proposed model accounts for carbon surface reaction, intraparticle and external diffusion, and attrition. External diffusion effects were relevant in the riser dense region where char was potentially entrapped in large clusters of inert solids. Experimental data and results of the model calculations are in satisfactory agreement.     

低阶煤低温热解半焦在模拟高炉喷吹条件下的燃烧性能

采用自制固定床热解装置在隔绝空气的条件下制备神木长焰煤热解终温分别为400℃、450℃、500℃及550℃的热解半焦,利用管式沉降炉模拟高炉喷吹条件研究神木长焰煤低温热解半焦的燃烧性能,并考察了热解终温、半焦喷吹粒径以及燃烧反应温度对半焦燃烧性能的影响。研究表明：低温热解半焦的燃烧性能优于实验所选用无烟煤的燃烧性能,半焦的燃烧性能与其燃料比之间存在负相关关系,即燃料比越高,燃烧性能越差;降低热解终温、减小半焦喷吹粒径以及提高燃烧反应温度均能改善半焦的燃烧性能,当热解终温为400℃、喷吹粒径100～200目、燃烧反应温度为1100℃时半焦的燃尽度最佳为96%。本实验半焦制备及燃烧条件与现有低温热解和高炉喷吹工艺相符,且热解半焦各项性能均符合喷吹用煤指标。     

Catalytic pyrolysis of woody biomass in a fluidized bed reactor: Influence of the zeolite structure

Catalytic pyrolysis of biomass from pine wood was carried out in a fluidized bed reactor at 450 °C. Different structures of acidic zeolite catalysts were used as bed material in the reactor. Proton forms of Beta, Y, ZSM-5, and Mordenite were tested as catalysts in the pyrolysis of pine, while quartz sand was used as a reference material in the non-catalytic pyrolysis experiments. The yield of the pyrolysis product phases was only slightly influenced by the structures, at the same time the chemical composition of the bio-oil was dependent on the structure of acidic zeolite catalysts. Ketones and phenols were the dominating groups of compounds in the bio-oil. The formation of ketones was higher over ZSM-5 and the amount of acids and alcohols lower than over the other bed materials tested. Mordenite and quartz sand produced smaller quantities of polyaromatic hydrocarbons than the other materials tested. It was possible to successfully regenerate the spent zeolites without changing the structure of the zeolite.