The fire-retarding effect of inorganic phosphorus compounds on the combustion of cellulosic materials

The pyrolysis and combustion of cellulosic substances treated with MAP and DAP have been studied using thermal analysis, flame spread tests and a specifically designed apparatus for smoldering combustion test. The samples used were: cotton string, cotton fabric and pure cellulose powder. Diammonium Phosphate (DAP) and Monoammonium Phosphate (MAP) can reduce the combustion and pyrolysis maximum mass loss temperature, decrease the initial pyrolysis temperature and considerably increase mass residue. Moreover, MAP and DAP reduce the flaming combustion rate of cellulosic materials and completely inhibit smoldering combustion. This study can facilitate a better understanding of the mechanism of pyrolysis and combustion of fire-retarded cellulosic materials.     

生物质焦制备条件对其燃烧反应特性的影响

在热重分析仪上,研究了生物质焦的制备条件对其燃烧反应特性的影响。生物质焦由闪速裂解技术制得,裂解温度为 748 K、773 K和823 K;原料含水质量分数为0、7.0%和11.3%。研究发现,生物质焦中挥发性物质的质量分数和H/C质量比随裂解温度的增加而降低,其燃烧反应性随裂解温度的增加而降低;与高裂解温度条件下制得的生物质焦相比,低裂解温度条件下制得的生物质焦具有较高的反应活化能和对燃烧温度更敏感。原料含水量对生物质焦的燃烧反应特性影响很小;但对高裂解温度条件下制得的生物质焦中的挥发性组分含量有较大的影响。简化的生物质焦本征燃烧反应幂函数动力学模型可以很好地描述其燃烧行为。     

Mechanism and kinetics for the initial steps of pyrolysis and combustion of 1,6-dicyclopropane-2,4-hexyne from ReaxFF reactive dynamics

We report the kinetic analysis and mechanism for the initial steps of pyrolysis and combustion of a new fuel material, 1,6-dicyclopropane-2,4-hexyne, that has enormous heats of pyrolysis and combustion, making it a potential high-energy fuel or fuel additive. These studies employ the ReaxFF force field for reactive dynamics (RD) simulations of both pyrolysis and combustion processes for both unimolecular and multimolecular systems. We find that both pyrolysis and combustion initiate from unimolecular reactions, with entropy-driven reactions being most important in both processes. Pyrolysis initiates with extrusion of an ethylene molecule from the fuel molecule and is followed quickly by isomerization of the fuel molecule, which induces additional radicals that accelerate the pyrolysis process. In the combustion process, we find three distinct mechanisms for the O(2) attack on the fuel molecule: (1) attack on the cyclopropane, ring expanding to form the cyclic peroxide which then decomposes; (2) attack onto the central single bond of the diyne which then fissions to form two C(5)H(5)O radicals; (3) attack on the alkyne-cyclopropane moiety to form a seven-membered ring peroxide which then decomposes. Each of these unimolecular combustion processes releases energy that induces additional radicals to accelerate the combustion process. Here oxygen has major effects both as the radical acceptor and as the radical producer. We extract both the effective activation energy and the effective pre-exponential factor by kinetic analysis of pyrolysis and combustion from these ReaxFF simulations. The low value of the derived effective activation energy (26.18 kcal/mol for pyrolysis and 16.40 kcal/mol for combustion) reveals the high activity of this fuel molecule.     

垃圾衍生燃料等温快速热解和燃烧反应特性

利用热天平和管式炉对RDF(Refuse Derived Fuel)等温快速热解和燃烧反应特性进行了研究。实验发现，在等温快速升温的条件下，RDF热解和燃烧的反应速率都非常快，从受热开始到反应结束需60 s～80 s;从开始失重到完成反应为20 s。RDF热解和燃烧热重反应曲线非常类似，都只有一个反应失重区;RDF组成对其燃烧和热解反应性有重要影响，含有橡胶的RDF的热解和燃烧反应速率较小。在650 ℃～800 ℃RDF快速热解产物中气、液产物的产率可达80%～90%，而固体产物的产率只有10%～20%，热解气体的热值为20kJ/m3，RDF较适合进行热解处理。     

The pyrolysis of cigarette paper under the conditions that simulate cigarette smouldering and puffing

The combustion properties and pyrolysis behavior of cigarette paper under the pyrolysis conditions of cigarette smouldering were investigated by micro-scale combustion calorimetry (MCC), thermogravimetric analysis coupled to Fourier transform infrared spectrometer (TG-FTIR), respectively. MCC results demonstrated that the combustion and pyrolysis behavior are influenced by heating rate obviously. TG-FTIR results illustrated that the composition of the gaseous products were mainly composed of CO₂, H₂O carbonyl compounds, CO, and methanol. Flash pyrolysis experiment in combination with high performance liquid chromatography (FPy-HPLC) was used to study the pyrolytic formation of eight carbonyl compounds (i.e., formaldehyde, acetaldehyde, acetone, acrolein, propionaldehyde, crotonaldehyde, methyl ethyl ketone, and butyraldehyde) during the pyrolysis of cigarette paper under the pyrolysis conditions of cigarette puffing. Moreover, the solid char formed after the flash pyrolysis experiments were studied by X-ray photoelectron spectroscopy (XPS). It had been found that the pyrolysis temperature influenced the formation of carbonyl compounds and the composition of char greatly.     

不同烟草生物质热解释放致香物质的研究

采用烟叶和烟梗为原料,使用热裂解气相色谱法对烟草的燃烧时间、燃烧温度进行控制,精确模拟实际烟草致香物质释放环境,精确捕获、并半定量物质,从而在实验室模拟、分析、研究烟草燃烧物中致香物质的组成和特点。研究分别考察了两种生物质在500℃、550℃下释放的致香物质组成。结果表明,烟梗、烟叶中元素组成中硫、氮两种元素含量低,而C/H比值两种烟草生物质均较高。两个热解温度下烟叶的热解产物中致香物质的含量均明显高于烟梗。升高热解温度均有利于获得更高相对含量的热解成分。烟叶热解产物中烯烃类物质相对含量比烟梗中多,而烟梗热解产物中酚类物质含量比烟叶中多。提高热解温度有利于酮类致香物质含量产生。     

Experimental investigation and numerical simulation of the combustion of flexible polyurethane foam with larger geometries

Numerical modelling of the combustion of flexible polyurethane foam (FPUF) is challenging, as the structural collapse and shrinkage of the foam complicate its pyrolysis, and two fuel items are involved in the combustion. Two-layer pyrolysis models were established based on the bench-scale tests over the past decade, but the accuracy was limited when simulating the combustion of FPUF with larger geometries. To improve the accuracy of the numerical simulation, small-scale experiments were conducted to investigate the combustion of FPUF with a larger geometry. Firstly, numerical simulations using a two-layer pyrolysis model proposed in the most recent research were performed to simulate the combustion of FPUF in the small-scale experiments. It was found that the heat release rate (HRR) was over-predicted in the initial combustion stage. Subsequently, based on the analysis of the visual and measured data obtained from the small-scale experiments, a three-layer model was proposed to describe the pyrolysis of FPUF in flaming combustion. The three-layer model was validated with the comparison of the predicted and experimental data. The results indicate that the numerical simulation using the three-layer model has a better performance in replicating the combustion of FPUF under well-ventilated conditions. While, the capability of the three-layer model was limited when it was used to simulate the combustion of FPUF in under-ventilated conditions, as it is found that ventilation influences the HRR of FPUF to a significant extent.     

Pyrolysis behavior of pectin under the conditions that simulate cigarette smoking

In this paper, the formation mechanism of pyrolysis gases released during the pyrolysis of pectin under the conditions that simulate cigarette smouldering was investigated by thermogravimetric analysis coupled to Fourier transform infrared spectrometer (TG-FTIR). Moreover, the combustion behavior of pyrolysis gases was studied by micro-scale combustion calorimetry (MCC). TG-FTIR results illustrated that the composition of the gaseous products was mainly composed of CO₂, H₂O, CO, methanol, methane and carbonyl compounds. MCC results demonstrated that the combustion of pectin was mainly determined by the prolysis gases formed in the temperature range of 200-300 °C. Flash pyrolysis experiment in combination with high performance liquid chromatography (FPy-HPLC) was used to study the pyrolytic formation of eight carbonyl compounds (i.e. formaldehyde, acetaldehyde, acetone, acrolein, propionaldehyde, crotonaldehyde, methyl ethyl ketone and butyraldehyde) during the pyrolysis of pectin under the pyrolysis conditions of cigarette puffing. Results demonstrated that pyrolysis temperature influenced the formation of acetaldehyde, acrolein, propionaldehyde and butyraldehyde greatly, while nitrogen flow affected the generation of formaldehyde, acetone, crotonaldehyde and methyl ethyl ketone deeply.     

煤与混合废塑料共热解固体产物中氯的赋存形态及在燃烧时的释放特性

通过红外光谱、热重 质谱及燃烧 水解实验，研究了煤与废塑料共热解固体产物中氯的赋存形态及在燃烧过程中氯的释放特性。结果表明，温度低于600℃热解的半焦中存在有机氯化合物；600℃以上热解的半焦（或焦炭）中氯主要以无机盐类存在。燃烧过程中氯的释放率与燃烧温度，煤与废塑料共热解的温度以及共热解时废塑料的加入量有关。燃烧温度越高，氯的释放率越大，900℃燃烧时，氯的释放率都在94%以上；在同一温度燃烧时，热解温度越高，氯的释放率越低。400℃热解的半焦最高释放率达99.86%，而1000℃热解的焦炭的最高释放率为94.35%。     

Study of the combustion mechanism of oil shale semicoke in a thermogravimetric analyzer

Oil shale semicoke, formed in retort furnaces, is a source of severe environmental pollution and is classified as a dangerous solid waste. For the industrial application of oil shale semicoke in combustion, this present work focused on the thermal analysis of its combustion characteristics. The pyrolysis and combustion experiments of semicoke were conducted in a Pyris thermogravimetric analyzer. From the comparison of pyrolysis curves with combustion curves, the ignition mechanism of semicoke samples prepared at different carbonization temperatures was deduced, and was found to be homogeneous for semicoke samples obtained at lower carbonization temperature, shifting to heterogeneous with an increase in the carbonization temperature. The effect of carbonization temperatures and heating rates on the combustion process was studied as well. At last, combustion kinetic parameters of semicoke were calculated with the binary linear regression method, showing that activation energy will increase with increasing the heating rate.     

A comparative study on the pyrolysis of metal- and ash-enriched wood and the combustion properties of the gained char

This study aims to investigate the pyrolysis behaviour of metal-contaminated wood and the combustion properties of char derived from wood pyrolysis. Seven metals (Na, Mg, Ca, Zn, Cd, Pb and Fe(III)) were introduced to willow in cation form by ion-exchange and the thermal behaviour of demineralised samples and samples with additional ash were also investigated.The results show that the char yield increased from 21% to 24–28% and levoglucosan yield in vapour phase decreased from 88% to 62–29% after the addition of inorganic compounds, even though the metal binding capacity of wood varied from one metal ion to another. While char yield seems to be effected mainly by the concentration of the metal ions, levoglucosan yield was more dependent on the ionic species especially when sodium ions were present. When combustion experiments were carried out with char made of the metal enriched wood, two consecutive steps were observed, both effected by the presence of inorganic compounds. The first step was identified as the release and combustion of volatiles, while the second peak of the burning profile is the actual combustion of the fixed carbon. The burnout temperatures, estimated ignition indices and the conversion indicate that the type and not the amount of metal ions were the determining factors during the second step of combustion.     

The relation between dioxin concentration from exhaust gas of diesel engine and chlorine content

In this paper, an experiment has been used to study the effect of pyrolysis stage (from injection to combustion) to dioxin exhaust from diesel engine. The characteristics of diesel fuel pyrolysis have been applied in order to calculate the mean molecular weight in varied temperatures and measure the concentration of inorganic chlorine (HCl). On the other hand, measuring the chlorine content of these particles after diesel pyrolysis enables researchers to find out the pyrolysis temperature that has the lowest possibility to produce dioxin. Additionally, the post-pyrolysis carbon particle diameter has been observed through electronic microscope so as to evaluate the combustion condition of the combustion stage. Result from this study would be helpful for researchers to understand the probability of dioxin formation.     

炉前煤低温干馏工艺中脱硫行为的模拟研究

为了提供燃煤炉前低温干馏系统中硫的脱除和转化的工业设计依据，采用自制的程序升温固定床反应器，在模拟燃煤炉前低温干馏的工况下考察了热解温度及Ca/S原子比对热解产物中硫分布的影响。结果表明，由于CaO的存在，循环流化床（CFB）锅炉的循环灰具有明显的固硫作用，在480℃~640℃、煤热解气、液产物中60％～70％的硫以CaS的形式固定在灰中。相同热解温度下，固硫作用随着Ca/S原子比的提高而增加，焦油收率和焦油中硫含量均有所下降。     

The influence of fine structure on the pyrolysis of cellulose. II. Pyrolysis in air

The pyrolysis of purified celluloses in air at 251°C was studied. The pyrolysis was found to obey first-order kinetics, and the rate constants correlated with the crystallinities, orientations and accessibilities of the samples. The results are interpreted in terms of an oxygen-catalyzed decomposition, with the accessibility of oxygen to the cellulose determining the rate of pyrolysis. The production of levoglucosan under conditions approaching combustion was shown to be a function of the crystallinity and orientation of cellulose. Some levoglucosan appears to be produced from the less ordered regions.     

蔗渣的热解与燃烧动力学特性研究

利用热重分析仪对蔗渣在不同升温速率下的热解、燃烧失重特性进行了研究。采用Friedman法对反应过程中可能存在的反应机理进行初步判断，蔗渣热解过程由其主要组分半纤维素、纤维素和木质素热解的三个独立的平行反应来描述，相应的反应活化能分别为203.92 kJ·mol-1、238.50 kJ·mol-1和77.11 kJ·mol-1； 蔗渣燃烧过程分为两段，第一段类似于其热解过程，第二段由木质素热解和残焦燃烧共同组成的连续反应，反应活化能为255.57 kJ·mol-1和159.11 kJ·mol-1。通过非线性回归法拟合获得的曲线与实验曲线基本一致，证实了蔗渣的热解、燃烧过程中存在着上述假定的反应机理。     

Thermal degradation and evolved gas analysis of thiourea-formaldehyde resin (TFR) during pyrolysis and combustion

Thiourea formaldehyde resin (TFR) has been synthesized by condensation of thiourea and formaldehyde in acidic medium and its thermal degradation has been investigated using TG-FTIR-MS technique during pyrolysis and combustion. The results revealed that the thermal decomposition of TFR occurs in three steps assigned to drying of the sample, fast thermal decomposition of polymers, and further cracking. The similar TG and DTG characteristics were found for the first two stages during pyrolysis and combustion. The combustion process was almost finished at 680?°C, while during pyrolysis a total mass loss of 93 wt% is found at 950?°C. The release of volatile products during pyrolysis are NH₃, CS₂, CO, HCN, HNCS, and NH₂CN. The main products in the second stage are NH₃ CO₂, CS₂, SO₂, and H₂O during combustion. In the next stage, the combustion products mentioned above keep on increasing, but some new volatiles such as HCN, COS etc., are identified. Among the above volatiles, CO₂ is the dominant gaseous product in the whole combustion process. It is found that the thermal degradation during pyrolysis of TFR produced more hazardous gases like HCN, NH₃, and CO when compared with combustion in similar conditions.     

Physicochemical properties evolution of chars from palm kernel shell pyrolysis

To clarify the effect of the pyrolysis operating conditions of the biomass on the physicochemical properties of the char and its combustion reactivity, palm kernel shell was pyrolyzed at different temperatures (400–700 °C). Analyses such as proximate and ultimate analysis, XRD, FTIR, N₂ adsorption, and SEM were used to investigate the physicochemical properties of biochar samples. The results show that an increase in pyrolysis temperature led to a development of pore structure and specific surface area of the produced biochar, which was beneficial for improving the biochar combustion reactivity. Besides, with increase in pyrolysis temperature, the carbon content exhibits a raise trend, but the oxygen and hydrogen contents exhibit the opposite behavior, and the aromaticity and graphitization degree of biochar produced at high temperature also increase. The combustion reactivity of biochar was found to be highly dependent on the pyrolysis temperature, and the aromatic structure and graphitization degree have greater effects on biochar combustion reactivity than those of the specific surface area and pore structure.     

应用TGA-FTIR研究不同来源污泥的燃烧和热解特性

在空气气氛下，利用热重分析方法研究了三种不同来源的污泥燃烧特性。探讨水处理工艺和污泥处理工艺对污泥中有机物的分布影响和燃烧特性影响。研究发现，污水厌氧工艺和污泥厌氧工艺均导致结构复杂、燃烧温度高的有机物生成。在氮气气氛下利用热重红外联用技术，对比研究了同种污泥的热解和燃烧特性，污泥热解主要发生有机物裂解成小分子和小分子的挥发，氧气的存在加速了污泥的裂解。污泥热解温度200℃～500℃，主要气体H2O、CO2、CO以及甲烷等烃类，CO2在高温750℃还存在一个析出峰，由于无机碳酸盐的分解。     

城市污水污泥燃烧特性和动力学特性分析

采用热重分析仪对城市污水污泥进行热重实验,通过TG(热重)、DTG(微分热重)和DSC(差示扫描量热)曲线的分析对比,获得污水污泥热解和燃烧不同阶段的特性。低于250℃,燃烧与热解的热重曲线基本吻合,说明在此之前,失重速率主要受控于有机物的分解以及析出,燃烧过程对失重影响不明显。燃烧DTG曲线呈现“W”峰型,第一个失重速率峰与热解DTG曲线基本对应,高于410℃,燃烧DTG曲线出现显著的加速。采用Coats-Redfern 积分法,假设不同的反应模型进行拟合,推断出污泥燃烧过程中两个DTG峰体现出不同的反应机理。借鉴煤燃烧机理分析认为,污泥燃烧反应初期挥发分的燃烧受控于化学反应速率,随着温度的不断提高,剩余挥发分的燃尽和固定碳的燃烧总反应速率逐渐受扩散因素控制。基于分析所得污泥燃烧机理,采用四个独立的平行反应模型模拟污泥的燃烧过程,拟合曲线与实验数据吻合良好。     

不同煤燃烧方式降低NOx排放比较及解耦燃烧应用

采用两段反应器研究了三种煤在不同燃烧方式下抑制NO_x生成的效果。结果表明,煤的热解气和部分气化生成气再燃均能较好的抑制NO_x生成,抑制效果优于空气分级燃烧,解耦燃烧方式抑制NO_x生成的效果最显著,相对于传统燃烧其NO_x排放降低了32%以上。煤种对各种燃烧方式降低NO_x的程度有明显影响,煤中单位氮含量的燃料比(固定碳/挥发分)越小,煤的热解气和部分气化生成气再燃以及解耦燃烧方式下NO_x的排放量越低。在煤部分气化生成气再燃烧方式中,部分氧化气化段通氧量不同,降低NO_x排放的效果也不同,在氧气体积分数为8%~10%时的NO_x生成量最低。基于解耦燃烧技术原理,研制了1.4 MW解耦燃烧工业锅炉,在燃烧同一煤种时,解耦燃烧锅炉和传统立式锅炉相比,烟气中NO_x排放量降低了32.9%。