气流量和煤样粒度对煤焦-CO2气化反应的影响

研究了反应气流量和煤样粒度如何影响热天平杯状坩埚内进行的煤焦－CO2气化反应。实验结果表明：反应气流量和煤样粒度对于煤焦－CO2气固相反应有影响；随反应气流量增加，煤焦反应速率增大；恒温和恒升温速率条件下，煤样粒度对气化反应影响不同，原因是恒升温速率下煤焦气化反应还受到气化温度的影响。热天平反应单元进口气体由氮气切换为CO2后，其反应炉内CO2浓度变化是一个逐渐增加的过程，进口气流量越大，反应炉内CO2浓度增加速度越快。     

锯木屑在超临界水中气化制氢过程的主要影响因素

以锯木屑混合羧甲基纤维素钠（CMC）为反应原料,利用连续管流反应器,在反应器外壁面温度稳定在650 ℃条件下,对反应压力在17.5～30 MPa,反应停留时间在14.4～50 s,浓度范围为4%～9%（质量分数）的湿生物质浆液进行了超临界水气化制氢实验研究,讨论了气化过程的主要参数压力、温度、反应停留时间以及物料浓度对气化结果的影响.锯木屑在超临界水中接近完全气化,生成气体产物的主要成分是H₂、CH₄、CO、CO₂以及少量的C₂H₄和C₂H₆,气化产物中的H2含量可以超过40%.同时,实现了气化反应液体产物的循环利用.     

不同影响因素对煤焦气化特性的影响

为了消除内、外扩散对煤焦气化反应的影响,通过热重分析仪进行了3种煤焦的气化反应实验,气化剂为CO2.研究了焦样粒径大小、焦样质量和气化剂流量对气化反应的影响,最终确定消除内、外扩散时的实验条件.此外还研究了气化温度对煤焦气化过程的影响.根据实验结果选取了3种动力学模型进行拟合,选取最适合描述气化反应的模型.结果表明:煤焦粒径对气化反应没有影响;随着煤焦质量减少,煤焦气化活性增加,但煤焦质量降低至一定值后气化活性不再变化;随着CO2流量增加,煤焦气化活性增加,但CO2流量增加至一定值后气化活性不再变化.混合反应模型最适合描述煤焦的气化反应过程.     

煤焦加压化学链气化反应特性和机理

采用机械混合法制备的Fe₂O₃/膨润土为载氧体,在加压固定床中进行煤焦化学链气化试验和动力学研究,借助拉曼和N₂吸附等温线表征手段,分析压力对煤焦反应活性及煤焦碳结构和孔结构的影响,讨论煤焦加压化学链气化反应机理。结果表明：系统总压从0.46MPa增加至0.80MPa时,煤焦化学链气化反应速率从0.0159min^-1提高至0.0309min^-1;水蒸气分压增加75%,H₂/CO摩尔比值增加74%。煤焦加压化学链气化过程可以用随机孔模型（RPM）描述,系统总压增加有利于内部扩散。系统总压增大煤焦的比表面积增加,水蒸气分压增大煤焦的反应活性提高,因而提高了煤焦化学链气化反应速率。     

高温煤焦气化反应的Langmuir-Hinshelwood动力学模型

应用基于吸附和脱附原理的Langmuir-Hinshelwood （L-H） 动力学模型来描述煤焦在H₂O和CO₂混合气氛下的气化反应时,存在单独活性位和相同活性位两个相互矛盾的假设。在管式炉实验装置内考察了在不同气化温度和气化剂分压的条件下,内蒙煤焦（NMJ）与H₂O和CO₂的气化反应特性,获得了NMJ-H₂O 和NMJ-CO₂反应的L-H动力学模型,同时考察了H₂、CO对煤焦气化反应的抑制作用,并探究了NMJ在H₂O和CO₂混合气氛下的气化反应机理。研究结果表明：NMJ-H₂O以及NMJ-CO₂反应的活化能分别为214.78 kJ·mol^-1和145.96 kJ·mol^-1。H₂对NMJ-H₂O以及CO对NMJ-CO₂的反应存在明显的抑制作用,且CO的抑制作用随反应温度的降低而愈加明显。基于L-H动力学模型计算得到的反应速率曲线与实验结果十分吻合。对于NMJ在H₂O和CO₂混合气氛下的气化反应,基于相同活性位假设的L-H模型的反应速率预测值与实验结果吻合,更加适用于NMJ在混合气氛下的气化反应机理。     

煤焦在气化合成气中高温气化反应特性

在固定床管式炉反应器中进行了煤焦在H₂O、CO₂、H₂和CO混合气氛中气化特性的实验研究,考察了反应温度、原料气组成和加煤量对产物气组成以及碳转化率的影响。实验结果表明,在各实验条件下,合成气与煤焦反应后CO流量均增加最多,H₂少量增加。煤焦与CO₂的反应受到明显抑制。混合气体通过与煤焦反应可以提高有效气（CO+H₂）的含量,实验条件下反应出口气体中有效气浓度比反应结束时最多提高3.3个百分点。反应速率受气化剂之间的竞争和气化产物的抑制作用较为明显,在1100℃和1300℃时,煤焦在相同气化剂流量的合成气中的最高反应速率分别只有在纯气化剂（水蒸气或CO₂）中最高反应速率的49%和69%。受到多种气体组分之间的相互影响,气体在孔道里的扩散和吸附对反应影响更加显著,随机孔模型可以较好地拟合此类反应,而不考虑孔结构的均相模型和缩芯模型拟合度较差。     

高温烟气中煤焦气化行为

针对高温烟气中煤焦的气化行为,本文采用FactSage 6.1计算了煤焦在高温烟气下的高温反应特性,并利用热重分析仪分析了煤焦气化行为。通过沉降炉实验进一步研究了不同温度、气体配比、粒径条件下气体产物的动态析出特性,同时计算了评价指标α、β、LHV值。结果表明：随着温度的升高,气体产物H₂和CO的含量增加,β、α、LHV值增大,CH₄和CO₂的含量下降。在温度为1200℃时,β、α值分别由CO₂/CO比为10∶70时的10.80%、5.21%增加到CO₂/CO比为50∶30时的24.71%、41.06%。同时,随着CO₂/CO比值的增大,高温烟气对煤焦气化反应抑制减弱。通过对比反应温度和粒径对煤焦气化反应的影响,得出反应温度远大于粒径对煤焦气化反应的影响。通过实验验证了向高温烟气中喷吹煤焦制备高品质可燃气体方法的可行性。     

滴管炉内不同煤阶煤焦水蒸气气化反应特性

在滴管炉内对煤焦与水蒸气气化反应进行了实验研究,考察了煤阶、气化温度、水蒸气与进料煤焦质量比（气焦比）对气化气体产物释放特性以及煤焦转化率的影响。实验温度为1100、1200、1300和1400℃,气焦比分别为0.4：1、0.6：1和1：1。研究发现：滴管炉内不同煤焦的水蒸气气化气体产物以H₂含量最高,CH₄含量最低。不同煤阶热解焦、气化温度以及气焦比的变化影响滴管炉内水蒸气气化产物气体组成和转化率的高低。随气化温度的升高,神府煤焦和北宿煤焦气化气体产物中H₂和CO产率不断增大,H₂/CO的比值则逐渐减小,碳转化率有不断增加的趋势。在气化温度大于1200℃的条件下,当气焦比从0.4：1增至0.6：1,神府煤焦和北宿煤焦的碳转化率变化幅度不大（5%以内）;当气焦比从0.6：1增至1：1,北宿煤焦的碳转化率略微降低,而神府煤焦的碳转化率增幅则在15%以上。     

超临界水中氨基乙酸的气化产氢特性

鉴于湿生物质如食品加工工业残余物和城市污泥中含有大量蛋白质的情况,以氨基乙酸作为蛋白质的模型化合物进行超临界水气化实验,研究了反应温度和反应时间耦合条件下Na₂CO₃的催化特性以及氨基乙酸气化产物特性。结果表明：添加Na₂CO₃会增大氨基乙酸的气化效率、氢气的体积分数和产率以及反应后液体化学需氧量（COD）的去除率,且添加质量分数为0.1%时的催化效果优于0.2%;Na₂CO₃主要是对H₂产率产生影响,其催化机理与已有碱性化合物的催化机理不同,可能是通过促进氨基乙酸的水解产物（甲酸）的脱羧反应来提高H₂的产率;氨基乙酸气化效率可达99.4%,生成物包括H₂、CO₂、N₂、CH₄和C₂～C₃气体,其中H₂的体积分数可超过50%,产率可达1.8 L·g^-1,且超过一半的份额来源于水,反应后液体清澈透明,COD和pH值指标均可以达到《生活杂用水水质标准》,可以进行回收利用。     

高温煤焦/CO2气化反应的动力学研究

对煤气化随机孔模型的动力学控制区的假设进行了改进,建立了高温煤焦/CO2气化反应碳转化率(X)与反应时间(t)的修正随机孔模型:X=1-exp[-kt(a+bkt+k2t2)],并在950℃～1 400℃气化温度范围内,用修正随机孔模型模拟淮南慢速热解煤焦和淮南快速热解煤焦/CO2气化反应,所得表观活化能范围分别为121.99kJ/mol～153.75kJ/mol和88.57kJ/mol～121.39kJ/mol.结果表明,修正随机孔模型的拟合效果优于随机孔模型和收缩未反应芯模型的拟合效果,能很好地体现煤焦气化反应的动力学特征,且该模型适用于不同煤焦的气化反应模拟.     

微型流化床反应分析及其对煤焦气化动力学的应用

在概述最新研发的微型流化床反应分析(micro-fluidized bed reaction analysis,MFBRA)方法与应用的基础上,应用该方法进一步研究了半焦-CO₂、半焦-水蒸气等温气化反应动力学,并与热重分析(thermogravimetric analyzer,TGA)求取的气化反应动力学数据比较。在最小化气体扩散的实验条件下,利用MFBRA和TGA测定求算的半焦-CO₂、半焦-水蒸气气化反应在受反应动力学控制的低温段的活化能非常接近,说明了MFBRA对等温气化反应分析的适用性和可靠性。实验研究还发现:半焦-CO₂、半焦-水蒸气气化反应在MFBRA中受反应动力学控制的温度范围较在TGA中明显宽,且在具有明显扩散影响的高温段通过MFBRA测定的半焦-CO₂气化反应表观活化能明显大于利用TGA测定的值,表明在MFBRA中受到的气体扩散抑制效应较小。     

Reaction-diffusion model of TGA gasification experiments for estimating diffusional effects

A 2D non-isothermal and non-equimolar reaction-diffusion model is developed in order to assess the diffusional effects that may take place during the CO₂ gasification of a biomass char contained in the cylindrical crucible of a horizontal-arm thermogravimetric apparatus (TGA). The model takes into account the chemical reaction rate and the effective transport properties as a function of the local conversion and therefore as a function of time and position within the char bed. Intraparticle diffusion and structural changes of the char bed during the gasification are also included. The model results showed good agreement with the experimental ones obtained at different temperatures and CO₂ partial pressures, and points out the relevant role of diffusional effects in TGA experiments. The effectiveness factor defined as the ratio of the measured to the intrinsic reaction rates at the same gas conditions stronglly depends on temperature and CO₂ partial pressure and may be as low as 0.2 at 950 °C and 50% char conversion. The marked variation found for the effectiveness factor at different conversions suggests the necessity of a complementary analysis of the variation of the diffusional effects with conversion when TGA experiments for kinetic determination are carried out.     

CO2 gasification kinetics of two alberta coal chars

CO₂ gasification kinetics of chars from two Alberta coals (Obed Mountain, high volatile bituminous and Highvale, subbituminous) have been studied using a thermogravimetric analyzer (TGA) and a fixed bed reactor. Charification and gasification reactions were performed sequentially in both the TGA instrument and in the fixed bed reactor to simulate real gasifier operating conditions. TGA and fixed bed data were processed numerically to evaluate the kinetic rate of CO₂ gasification of the chars. Calculated gasification kinetics could be correlated using both the volume reaction and the grain models. Activation energies of the kinetic rate constants were near 200 kJ/mol for both Highvale and Obed Mountain coal chars using the TGA data. The activation energies calculated for the Obed Mountain coal char using the fixed bed reactor were about 250 kJ/mol. For all the cases studied the calculated activation energies were nearly the same for both the volume and grain reaction models.     

Diffusional effects in TGA gasification experiments for kinetic determination

Wood matter from pressed oil-stone char gasification rates were measured in a thermogravimetric apparatus to assess the importance of diffusion limitations. Three sets of experiments were conducted at various temperatures, CO₂ and CO partial pressures and crucible geometries. The set carried out with a monolayer bed of very fine particles well-exposed to the gas flow was used to evaluate the intrinsic gasification reactivity of the char and to obtain two kinetic equations: an nth-order equation and a Langmuir-Hinshelwood type equation. The other two sets of tests were used to evaluate the external (through a stagnant gas layer) and the internal (through a bed of char particles) diffusion resistances. The results showed that the internal diffusion resistance in a 3 mm deep char bed is quite significant and should not be disregarded in these kinetics determinations. Observed to intrinsic reactivity ratios (i.e. effectiveness factors) as low as 0.2 were calculated based on gasification tests at 950 °C. Furthermore, this study points towards a significant CO inhibition effect due to its accumulation inside the bed.     

Gasification kinetics of five coal chars with CO<Subscript>2</Subscript> at elevated pressure

For five coals, the reactivity of char-CO₂ gasification was investigated with a pressurized thermogravimetric analyzer (PTGA) in the temperature range 850-1,000 C and the total pressure range 0.5-2.0 MPa. The effect of coal rank, initial char characteristics and pressure on the reaction rate were evaluated for five coal chars. The reactivity of low lank coal char was better than that of high rank coal char. It was found that Meso/macro-pores of char markedly affect char reactivity by way of providing channels for diffusion of reactant gas into the reactive surface area. Over the range of tested pressure, the reaction rate is proportional to CO₂ partial pressure and the reaction order ranges from about 0.4 to 0.7 for five chars. Kinetic parameters, based on the shrinking particle model, were obtained for five chars.     

铁基复合载氧体煤化学链气化反应特性及机理

以水蒸气作为气化/流化介质,在流化床中研究了两种铁基复合载氧体的化学链气化反应特性及循环特性,并对气化过程中的反应机理、动力学方程进行了推断。结果表明:温度为920℃时,添加不同修饰物的铁基复合载氧体与煤焦气化的反应活性依次为Fe4Al6K1>Fe4Al6>Fe4Al6Ni1。在多次循环实验过程中,合成气成分保持稳定,表明Fe4Al6K1复合载氧体循环特性良好。XRD谱图分析表明,六次氧化还原实验后的铁基载氧体氧化态仍为Fe₂O₃。K⁺主要以铁酸钾形态存在,该结构有利于促进化学链气化反应。利用高斯函数对气化反应速率进行了峰拟合,拟合结果表明化学链气化主要分为3个阶段:化学链作用阶段、煤气化阶段以及Fe₃O₄向FeO转变的气化阶段。     

高变质程度无烟煤热天平水蒸气催化气化动力学(Ⅰ)碳酸钠催化剂

以碳酸钠为催化剂,用热天平的等温热重法研究了4种高变质程度无烟煤（挥发分含量V_ad=2.69%～4.35%）常压下纯水蒸气催化气化反应动力学.在加和不加Na₂CO₃条件下,测定了温度为750～950℃无烟煤的化学反应控制条件下的转化率与时间的关系.加Na₂CO₃的转化率与时间的关系用缩芯模型和修正体积模型进行了良好的拟合关联,得出这4种高变质程度无烟煤水蒸气催化气化反应的反应速率常数、活化能和指前因子,按反应速率常数表示的反应活性大小顺序为：永安丰筛>永安加筛>上京煤>永定煤,活化能范围：147.70～199.79 kJ·mol^-1.与不加催化剂的结果相比,加Na₂CO₃的具有更小的活化能和指前因子,低温（750～850℃）时催化效果更明显.     

Intrinsic char reactivity of plastic waste (PET) during CO2 gasification

Char reactivity has a strong influence on the gasification process, since char gasification is the slowest step in the process. A sample of waste PET was devolatilised in a vertical quartz reactor and the resulting char was partially gasified under a CO₂ atmosphere at 925 °C in order to obtain samples with different degrees of conversion. The reactivity of the char in CO₂ was determined by isothermal thermogravimetric analysis at different temperatures in a kinetically controlled regime and its reactive behaviour was evaluated by means of the random pore model (RPM). The texture of the char was characterised by means of N₂ and CO₂ adsorption isotherms. The results did not reveal any variation in char reactivity during conversion, whereas the micropore surface area was affected during the gasification process. It was found that the intrinsic reaction rate of the char can be satisfactorily calculated by normalizing the reaction rate by the narrow micropore surface area calculated from the CO₂ adsorption isotherms. It can be concluded therefore that the surface area available for the gasification process is the area corresponding to the narrow microporosity.     

Effect of pressure on gasification reactivity of three Chinese coals with different ranks

The gasification reactivities of three kinds of different coal ranks (Huolinhe lignite, Shenmu bituminous coal, and Jincheng anthracite) with CO₂ and H₂O was carried out on a self-made pressurized fixed-bed reactor at increased pressures (up to 1.0 MPa). The physicochemical characteristics of the chars at various levels of carbon conversion were studied via scanning electron microscopy (SEM), X-ray diffraction (XRD), and BET surface area. Results show that the char gasification reactivity increases with increasing partial pressure. The gasification reaction is controlled by pore diffusion, the rate decreases with increasing total system pressure, and under chemical kinetic control there is no pressure dependence. In general, gasification rates decrease for coals of progressively higher rank. The experimental results could be well described by the shrinking core model for three chars during steam and CO₂ gasification. The values of reaction order n with steam were 0.49, 0.46, 0.43, respectively. Meanwhile, the values of reaction order n with CO₂ were 0.31, 0.28, 0.26, respectively. With the coal rank increasing, the pressure order m is higher, the activation energies increase slightly with steam, and the activation energy with CO₂ increases noticeably. As the carbon conversion increases, the degree of graphitization is enhanced. The surface area of the gasified char increases rapidly with the progress of gasification and peaks at about 40% of char gasification.     

基于NiO载氧体的煤化学链燃烧实验

采用流化床反应器并以水蒸气作为气化-流化介质,研究了以NiO为载氧体在800～960℃内的煤化学链燃烧反应特性。实验结果表明,载氧体与煤气化产物在反应器温度高于900℃体现了高的反应活性。随着流化床反应器温度的提高,气体产物中CO₂的体积浓度(干基)呈单调递增;CO、H₂、CH₄的体积浓度(干基)呈单调递减;煤中碳转化为CO₂的比率逐渐递增,碳的残余率逐渐递减。反应器出口气体CO₂、CO、H₂、CH₄的生成率随反应时间呈单峰特性,H₂生成率的峰值远小于CO的峰值;且随反应器温度升高,CO₂生成率升高,CO、H₂、CH₄的生成率降低。反应温度高于900℃时,流化床反应器NiO载氧体煤化学链燃烧在9 min之内就基本完成,CO₂含量高于92%。