天然焦_H_2O气化反应Aspen Plus模拟研究

运用Aspen Plus软件平台对天然焦-H2O气化反应进行了热力学模拟计算,研究了反应碳份额、水蒸气流量、反应温度、压力和反应气氛对天然焦气化反应煤气成份、热值的影响。结果表明,RYIELD模块在整个模拟系统中能很好地描述天然焦"热解"过程;水蒸气流量1.16 kg/h是天然焦完全气化的临界点;增大温度和压力能有效促进气化和改善煤气的品质,但并非越大越好,综合考虑下,实际运行的温度和压力宜分别在850～1 000℃和0.1～6.0 MPa范围内选定;不同的反应气氛下,天然焦气化反应特性有很大差异,在水蒸气气氛下能获得更好的煤气品质。     

天然焦的微观结构及催化气化特性

利用X射线衍射(XRD)技术分析了天然焦和烟煤的微观结构特性,在TGA92型热重分析仪上采用非等温热重法进行了天然焦试样的气化反应特性试验,研究了不同添加量的钾、钙基催化荆对气化反应过程的影响,采用Freeman-Carroll方法计算了天然焦的气化动力学参数.结果表明,天然焦的有序化程度要高于烟煤,化学活,性较低,但两者物理性质相似;钾基催化剂对天然焦样品的气化反应有明显的催化作用,随着钾含量的进一步增加,碳转化速率的增长速率逐渐减缓;钙基催化剂亦能有效地促进天然焦的气化,随着钙含量的增大,碳转化率先增后降,存在一最佳Ca含量.     

基于等转化率法的生物焦CO_2气化反应动力学参数研究

利用热重分析仪在800~950℃对稻秆焦和木屑焦CO2等温气化过程进行了研究。分别采用等转化率法和随机孔模型求解了稻秆焦和木屑焦气化反应的动力学参数。通过等转化率法发现,随着碳转化率的增加,反应活化能随着碳转化率的升高而增大,稻秆焦和木屑焦在碳转化率为0.02时刻(即接近初始时刻)的活化能分别为157.2 k J/mol和166.4 k J/mol;采用随机孔模型计算得到稻秆焦和木屑焦的活化能分别为155.1 k J/mol和165.5 k J/mol,与等转化率法求得的碳转化率为0.02时刻的活化能接近,表明随机孔模型可以准确地描述稻秆焦和木屑焦的气化特性。同时发现,同一气化温度下,稻秆焦的结构参数大于木屑焦的结构参数;不同温度下的同一焦炭的结构参数f与对应的气化温度存在良好的指数关系。最后结合结构参数f与气化温度的指数关系表达式,得出稻秆焦和木屑焦的等温气化反应动力学随机孔模型速率表达式。     

锡林浩特褐煤气化特性研究

利用同步热分析仪研究了制焦温度、气化温度以及升温速率等因素对煤焦气化特性的影响。研究结果表明:随着制焦温度的升高,煤焦的气化失重量减少,气化反应的时间延长,气化反应性略有降低。随着气化温度的提高,锡林浩特褐煤煤焦在相同时间内的碳转化率增加,煤焦的气化时间缩短,气化温度对煤焦的气化反应性有较大的影响。随着升温速率的增大,TG曲线、DTG曲线均向高温侧偏移。升温速率越大,相同温度时煤焦的碳转化率越低,气化反应速率达到峰值对应的气化温度随升温速率的增大而升高。随着升温速率的增大,煤焦气化反应活性变好,气化反应进行的更加剧烈。     

生物质半焦CO2气化反应动力学研究

采用热天平研究生物质半焦CO2气化反应动力学特性。考察半焦粒径、热解制焦温度以及热解制焦气氛对气化反应碳转化率的影响。采用随机孔模型、未反应芯缩核模型和混合模型对生物质半焦气化反应速率随碳转化率变化的趋势进行拟合,并求出半焦气化的动力学参数,结果表明随机孔模型的拟合效果最好。     

天然焦-H2O催化气化反应特性

在流化床气化试验装置上进行了天然焦-H2O催化气化反应试验,考察了催化剂种类、混合催化剂配制方式及其添加量对煤气产量、碳转化率和煤气热值等的影响.结果表明,Ca基、Fe基和Cu基硝酸盐均能有效地促进气化反应,但催化效果有所差异,由好到差的顺序为Cu基Fe基Ca基;当Ca基、Fe基和Cu基硝酸盐按10:35:55机械混合时,可实现3种催化剂的最优配制;当最优配置催化剂添加量为3%时能得到最佳的催化效果和经济性.     

煤焦气化反应动力学研究

气流床气化技术是煤炭清洁、高效转化的重要途径和发展方向之一。利用热天平,采用等温热重法对抽样选出的煤种在800℃～1 400℃温度范围内进行了煤焦CO2气化反应动力学特性研究。研究结果表明:高温下煤焦的气化反应特性不同于低温时的反应特性,在900℃～1 000℃时气化反应逐步由化学反应控制过渡到过渡区控制,在1 100℃～1 300℃时气化从反应过渡区控制逐步到扩散区控制;不同粒径的煤粉气化反应,在相同的时间内,1 000℃时的碳转化率、气化反应速率比950℃时的碳转化率、气化反应速率高很多,950℃时的碳转化率、气化反应速率比900℃时的碳转化率、气化反应速率高。     

氧量对天然焦蒸汽气化特性的影响研究

在小型流化床(50mm、高1600mm)实验装置上对沛城煤矿天然焦-蒸汽气化反应进行实验研究,考察蒸汽中掺入氧气,共同作为气化介质对气化反应产气量、碳转化率、煤气热值和煤气组分等因素的影响,同时与ASPENPLUS软件对其气化过程的模拟结果进行了对比。实验中,天然焦试样量0.2kg/h,蒸汽量1.05kg/h,气化温度900℃,实验结果表明:气化介质中氧量明显影响天然焦蒸汽气化特性。随着氧含量的增加,初始阶段(0～0.2L/min)煤气产量提高了1.76倍,碳转化率提高了1.94倍,两者均显著增加;随着氧量的进一步增加(0.2～1.0L/min),其增加幅度趋缓,产气量增加1.16倍,碳转化率增加1.34倍。煤气中有效气体(H2+CO+CH4)的体积分数和煤气热值均持续减少,有效气体份额从76.9%下降到54.3%,煤气热值从9.01MJ/m3减少到6.34MJ/m3,而CO2体积分数增加明显,从23.1%增加到37.3%。Aspen模拟结果与实验结果基本一致,具有实际指导意义。     

天然焦富氢气化初步试验研究

我同天然焦储量丰富.但其应用研究尚不够深入.氢能作为一种清洁理想的二次能源,具有广阔的应用前景.在常压同定床上进行天然焦富氢气化试验研究,考察反应温度、Ca/C摩尔比以及水蒸气流量对气化特性的影响.试验结果表明,反应温度及水蒸气流量一定,Ca/C摩尔比为1.0时,气化效果最好.反应温度750℃,Ca/C摩尔比1.0,天然焦加入总量1.5 g,水蒸气流量4.8 L/min时,产气中H2、CO2、CO及CH,产量体积分数分别为64.2%、28.3%、5.5%和1.9%,碳转化率达36.7%,并与同一产地的烟煤富氢气化进行了对比实验.     

生物质热解参数对焦碳生成特性及产氢率的影响

选取一定量筛分干燥后的松木屑作为实验材料,同时选取煅烧白云石粉及橄榄石粉作为实验反应催化剂.在石英管式炉上650～900℃温度范围内分别完成松木屑、松木屑与催化剂混合物的快速热解过程以及热解焦碳的气化反应过程.木屑低温热解时焦碳产生量多、比表面积大、气化活性好;白云石与木屑混合热解后焦碳产生量显著增多,优于橄榄石,低温热解产物潜在产氢率高.较低温度热解焦碳与水蒸气气化反应产气中氢体积含量可超过70%.     

稻壳变工况反应动力学研究

采用热重分析仪研究了稻壳变工况气化特性,考察了气化反应温度、气化介质流量和操作压力对稻壳气化反应特性的影响,利用反应动力学理论对压力影响反应活化能的变化进行了计算。结果表明:稻壳气化反应过程中,碳转化率随温度的升高而增加,气化剂流量在60 ml/min以上时可以消除气化剂向外扩散的影响,随着气化压力的提高,气化反应速率加快,稻壳试样的碳转化率有所增加,在同一反应时刻,该增加关系并不是线性的,当压力较高时,空气与稻壳的还原反应所受影响较弱,稻壳气化反应活化能随压力增加先降低后上升,该现象说明压力过高对气化反应有抑制作用。     

高温快速加热条件下压力对煤气化反应特性的影响

建立了一套能同时实现高温高压和快速加热的实验设备和研究方法,使煤气化反应动力学基础研究能在与实际气流床煤气化炉相近的条件下进行.研究表明,当CO2体积分数相同时,最大CO生成速度随压力的升高而升高;煤焦的气化反应速度随全压的升高而升高.即使全压和CO2体积分数不同,只要CO2的分压、温度等其他条件相同,煤焦的气化反应速度就基本上一致.说明全压和CO2体积分数对煤焦气化反应速度的影响可以归纳为CO2分压的影响.高温快速加热条件下,除了温度以外,CO2分压是影响煤气化特性的重要因素.     

Study on pulverized coal gasification using waste heat from high temperature blast furnace slag particles

A combined species transport and reaction-discrete phase model was established to numerically study pulverized coal gasification using waste heat from high temperature slag particles. The effects of slag particles temperature, coal/gasification agent mass ratio and water content in gasification agent on the gasification characteristics were discussed. The results indicate that higher particle temperature leads to better gasification reaction efficiency. Compared to the maximum syngas productivity (67.9%) and carbon conversion efficiency (91.7%) at 1500 K, they are respectively reduced to about 45% and 60% when temperature drops to 1000 K. Excessive or insufficient pulverized coal would have a negative effect on the syngas production for a specific flow rate of gasification agent, and the appropriate proportion range is 0.8–0.84. The CO yield declines with the increase of particles diameter, while H₂ firstly increases and then declines attributing to the lower gasification agent temperature and higher flow velocity gained at larger diameter. The raise of water content in gasification agent is beneficial to H₂ production, but CO yield continues to decline after the water content exceeds 5% for the reason that the incomplete combustion of volatiles and the gasification reaction of coke are inhibited. The diameter of slag particles and the water content suitable for coal gasification reaction are 2.0–2.5 mm and 5%–10%, respectively.     

Hydrogen production by partial oxidative gasification of biomass and its model compounds in supercritical water

Partial oxidative gasification in supercritical water is a new technology for hydrogen production from biomass. Firstly in this paper, supercritical water partial oxidative gasification process was analyzed from the perspective of theory and chemical equilibrium gaseous product was calculated using the thermodynamic model. Secondly, the influence of oxidant equivalent ratio on partial oxidative gasification of model compounds (glucose, lignin) and real biomass (corn cob) in supercritical water was investigated in a fluidized bed system. Experimental results show that oxidant can improve the gasification efficiency, and an appropriate addition of oxidant can improve the yield of hydrogen in certain reaction condition. When ER equaled 0.4, the gasification efficiency of lignin was 3.1 times of that without oxidant. When ER equaled 0.1, the yield of hydrogen from lignin increased by 25.8% compared with that without oxidant. Thirdly, the effects of operation parameters including temperature, pressure, concentration, and flow rate of feedstock on the gasification were investigated. The optimal operation parameters for supercritical water partial oxidative gasification were obtained.     

Kinetics of woodchips char gasification with steam and carbon dioxide

Kinetics of woodchips char gasification has been examined. Steam and CO₂ were used as the gasifying agents. Differences and similarities between kinetics of steam gasification and CO₂ gasification have been discussed. Comparison was conducted in terms of gasification duration, evolution of reaction rate with time and/or conversion, and effect of partial pressure on reaction rate. Reactor temperature was maintained at 900 °C. Partial pressure of gasifying agents varied from 1.5 bars to 0.6 bars in intervals of 0.3 bars. Steam and CO₂ flow rates were chosen so that both gasifying agents had equal amount of oxygen content. CO₂ gasification lasted for about 60 min while steam gasification lasted for about 22 min. The average reaction rate for steam gasification was almost twice that of CO₂. Both reaction rate curves showed a peak value at certain degree of conversion. For steam gasification, the reaction rate peak was found to be at a degree of conversion of about 0.3. However, for CO₂ gasification the reaction rate peak was found to be at a conversion degree of about 0.1. Reaction rates have been fitted using the random pore model (RPM). Average structural parameter, ψ for steam gasification and CO₂ gasification was determined to be 9 and 2.1, respectively. Average rate constant at 900 °C was 0.065 min⁻¹ for steam gasification and 0.031 min⁻¹ for CO₂ gasification. Change in partial pressure of gasifying agents did not affect the reaction rate for both steam and CO₂ gasification.     

Hydrogen production from coal gasification in supercritical water with a continuous flowing system

The technology of supercritical water gasification can convert coal to hydrogen-rich gaseous product efficiently and cleanly. A novel continuous-flow system for coal gasification in supercritical water was developed successfully in State Key Laboratory of Multiphase Flow in Power Engineering (SKLMF). The experimental device was designed for the temperature up to 800 °C and the pressure up to 30 MPa. The gasification characteristics of coal were investigated within the experimental condition range of temperature at 650–800 °C, pressure at 23–27 MPa and flow rate from 3 kg h⁻¹ to 7 kg h⁻¹. K₂CO₃ and Raney-Ni were used as catalyst and H₂O₂ as oxidant. The effects of main operation parameters (temperature, pressure, flow rate, catalyst, oxidant, concentration of coal slurry) upon gasification were carried out. The slurry of 16 wt% coal + 1.5 wt% CMC was successfully transported into the reactor and continuously gasified in supercritical water in the system. The hydrogen fraction reached up to 72.85%. The experimental results demonstrate the bright future of efficient and clean conversion of coal.     

A new HYSYS model for underground gasification of hydrocarbons under hydrothermal conditions

A new subsurface process model was developed using the ASPEN HYSYS simulation environment to analyse the process energy and gasification efficiency at steady-state equilibrium conditions. Injection and production wells were simulated using the HYSYS pipe flow utilities which makes use of the Beggs and Brill flow correlation applicable for vertical pipes. The downhole reservoir hydrothermal reactions were assumed to be in equilibrium, and hence, the Gibbs reactor was used. It was found that high W/C ratios and low O/C ratios are required to maximise gasification efficiency at a constant hydrocarbon feed flowrate, while the opposite is true for the energy efficiency. This occurs due to the dependence of process energy efficiency on the gas pressure and temperature at surface, while the gasification efficiency depends on the gas composition which is determined by the reservoir reaction conditions which affects production distribution. Another effect of paramount importance is the increase in reservoir production rate which was found to directly enhance both energy and gasification efficiency showing conditions where the both efficiencies are theoretically maximised. Results open new routes for techno-economic assessment of commercial implementation of underground gasification of hydrocarbons.     

Performance simulation and thermodynamics analysis of hydrogen production based on supercritical water gasification of coal

The heating method of SCWG reactor is critical to system construction, and almost all existing reactors rely on external heat sources. In this article, the thermodynamic equilibrium model is established to predict the distribution of gasification products from supercritical water gasification of coal. The transformation rule of gas components in the SCWG process of coal and oxidation process of gasification products is explored. Especially, the influence of key parameters such as feedstock concentration, gasification temperature and pressure on the hydrogen yield during the gasification and oxidation processes is also discussed. Based on the above research, the autothermal gasification system for hydrogen production integrated supercritical water gasification of coal and oxidation of gasification products is proposed. The flow matching of supercritical water, coal slurry, and oxygen and its effect on the autothermal hydrogen yield are discussed. By optimizing the flow rate of the reactants, 80% of the hydrogen production efficiency is achieved.