Characteristics of cardboard and paper gasification with CO2

Evolutionary behavior of syngas chemical composition and yield have been examined for paper and cardboard at three different temperatures of 800, 900 and 1000 °C using CO₂ as the gasifying agent at constant flow rate. Specifically the evolution of syngas chemical composition with time has been investigated. Pyrolysis of the sample was dominant at the beginning of the gasification process as observed from the high initial devolatilization of the sample followed by char gasification of material to form syngas for a long period of time. Results provided the role of gasification temperature on kinetics of the CO₂ gasification process. Increase in gasification temperature provided increased conversion of the sample material to syngas. Thus the sample conversion to syngas was low at the low temperature of 800 °C while at elevated temperatures of 900 and 1000 °C substantial enhancement of the kinetics process occurred. The evolution of extensive reaction rate of carbon-monoxide was calculated. Results show that increase in temperature increased the extensive reaction rate of carbon-monoxide. The global behavior of syngas chemical composition examined at three different temperatures revealed a peak in concentration of H₂ to exhibit after few minutes into the gasification that changed with gasification temperature. At 800 °C gasification temperature peak in H₂ was displayed at 3 min into gasification while it decreased to only 2 min, approximately, at gasification temperatures of 900 and 1000 °C. The effect of reactor temperature on CO mole fraction has also been examined. Increase in the gasification temperature enhances the mole fraction of CO yields. This is attributed to the increase in forward reaction rate of the Boudouard reaction (C+CO₂2CO). The results show important role of CO₂ gas for the gasification of wastes and low grade fuels to clean syngas.     

联合CO2捕集的生物质化学链气化制备合成气系统分析

本文提出以Fe₂O₃为载氧体、以CaO捕集CO₂的生物质化学链气化系统,利用Aspen Plus软件对该系统进行了模拟,以合成气组成（干基）、合成气氢碳比、含碳产物的碳摩尔分布、冷气效率及收率等为系统性能评价指标,重点分析了燃料反应器温度（T_FR）、载氧体Fe₂O₃与生物质碳摩尔比（Fe₂O₃/C）、水蒸气与生物质碳摩尔比（Steam/C）、CaO与生物质碳摩尔比（CaO/C）等系统参数对固体生物质化学链气化系统的影响。结果表明,在T_FR = 825℃、Fe₂O₃/C = 0.5、Steam/C = 0.71和CaO/C = 0.26条件下,合成气制备系统性能较优,合成气中H₂和CO₂含量分别为55.2%和15.4%,氢碳比为1.93,冷气效率为78.2%,被CaCO₃捕集的生物质碳为18.2%,收率（湿气基）为1.95 Nm³/kg_biomass,其中合成气中H₂和CO收率为1.24 Nm³/kg_biomass。     

烟煤煤焦等温CO2气化动力学模型研究

在建立的化学反应动力学控制实验条件下利用自建固定床实验台研究了烟煤煤焦等温CO2气化反应特性。采用均相模型、未反应收缩核模型和修正体积模型计算得到气化反应活化能分别为147.7kJ/mol、102.9kJ/mol和155.5kJ/mol。利用等转化率法避开反应机理函数的选择,计算得到反应活化能为144.1～166.0kJ/mol。通过比对不同模型相关系数大小以及与等转化率法计算所得活化能范围符合程度相结合的方法,确定均相模型和修正体积模型为最佳动力学模型;根据修正体积模型中经验常数b≈1,可认为修正体积模型与均相模型为同一模型。因此确定烟煤煤焦CO2气化反应最佳动力学模型为均相反应模型。     

High quality syngas production from pressurized K2CO3 catalytic coal gasification with in-situ CO2 capture

The enhanced K-catalytic coal gasification by CO₂ sorption reaction (EKcSG) was proposed to produce syngas with high content of H₂ and CH₄ and perform in-situ CO₂ capture. CO₂ is reduced dramatically with the introduction of the CaO into the reactor under typical K-catalytic coal gasification condition (3.5 MPa, 700 °C). The carbonation reaction of CaO can promote the syngas production by improving the equilibrium of the water-gas shift reaction and supplying heat for coal gasification reaction. In the presence of the CaO sorbent (Ca/C = 0.5), the CO₂ concentration in the product gas decreased from 25.61% to 12.80% compared with that without CaO. Correspondingly, the total concentration of H₂ and CH₄ is improved from 65.61% to 82.99% and the carbon conversion reached above 95%. The effect of Ca/C ratio and reaction temperature was investigated during the EKcSG process. It is considered that Ca/C ratio of 0.5 is the best proportion in terms of carbon conversion and CO₂ absorption in our experimental conditions.     

Modeling of fixed bed downdraft biomass gasification: Application on lab‐scale and industrial reactors

This study aimed at presenting a model to simulate downdraft biomass gasification under steady‐state or unsteady‐state conditions. The model takes into account several processes that are relevant to the transformation of solid biomass into fuel gas, such as drying; devolatilization; oxidation; CO₂, H₂O, and H₂ reduction with char, pressure losses, solid and gas temperature, particle diameter, and bed void fraction evolution; and heat transfer by several mechanisms such as solid–gas convection, bed–wall convection, and radiation in the solid phase. Model validation is carried out by performing experiments in two lab‐scale downdraft fixed bed reactors (unsteady‐state conditions) and in a novel industrial pilot plant of 400 kW_th–100 kW_e (steady‐state conditions). The capability of the model to predict the effect of several factors (reactor diameter, air superficial velocity, and particle size and biomass moisture) on key response variables (temperature field, maximum temperature inside the bed, flame front velocity, biomass consumption rate, and composition and calorific value of the producer gas) is evaluated. For most response variables, a good agreement between experimental and estimated values is attained, and the model is able to reproduce the trend of variation of the experimental results. In general terms, the process performance improves with higher reactor diameter and lesser air superficial velocity, particle size, and moisture content of biomass. The steady‐state simulation appears to be a versatile tool for simulating different reactor configurations (preheating systems, variable geometry, and different materials). Copyright © 2013 John Wiley & Sons, Ltd.     

Sorbent enhanced hydrogen production from steam gasification of coal integrated with CO2 capture

In this work, CO₂ capture and H₂ production during the steam gasification of coal integrated with CO₂ capture sorbent were investigated using a horizontal fixed bed reactor at atmospheric pressure. Four different temperatures (650, 675, 700, and 750 °C) and three sorbent-to-carbon ratios ([Ca]/[C] = 0, 1, 2) were studied. In the absence of sorbent, the maximum molar fraction of H₂ (64.6%) and conversion of coal (71.3%) were exhibited at the highest temperature (750 °C). The experimental results verified that the presence of sorbent in the steam gasification of coal enhanced the molar fraction of H₂ to more than 80%, with almost all CO₂ was fixed into the sorbent structure, and carbon monoxide (CO) was converted to H₂ and CO₂ through the water gas shift reaction. The steam gasification of coal integrated with CO₂ capture largely depended on the reaction temperature and exhibited optimal conditions at 675 °C. The maximum molar fraction of H₂ (81.7%) and minimum CO₂ concentration (almost 0%) were obtained at 675 °C and a sorbent-to-carbon ratio of 2.     

Hydrogen production from coal gasification for effective downstream CO2 capture

The coal gasification process is used in commercial production of synthetic gas as a means toward clean use of coal. The conversion of solid coal into a gaseous phase creates opportunities to produce more energy forms than electricity (which is the case in coal combustion systems) and to separate CO₂ in an effective manner for sequestration. The current work compares the energy and exergy efficiencies of an integrated coal-gasification combined-cycle power generation system with that of coal gasification-based hydrogen production system which uses water-gas shift and membrane reactors. Results suggest that the syngas-to-hydrogen (H₂) system offers 35% higher energy and 17% higher exergy efficiencies than the syngas-to-electricity (IGCC) system. The specific CO₂ emission from the hydrogen system was 5% lower than IGCC system. The Brayton cycle in the IGCC system draws much nitrogen after combustion along with CO₂. Thus CO₂ capture and compression become difficult due to the large volume of gases involved, unlike the hydrogen system which has 80% less nitrogen in its exhaust stream. The extra electrical power consumption for compressing the exhaust gases to store CO₂ is above 70% for the IGCC system but is only 4.5% for the H₂ system. Overall the syngas-to-hydrogen system appears advantageous to the IGCC system based on the current analysis.     

Photocatalytic effect of ZnO on carbon gasification with CO2 for high temperature solar thermochemistry

A photocatalytic effect of ZnO on carbon gasification with CO₂ was studied using a concentrated Xe beam to enhance the gasification rate in solar/chemical energy conversion process. The sample, activated carbon impregnated with ZnO (5 wt%), was heated at 873 K by a Xe beam irradiation with UV (<400 nm). The gasification rate at 873 K increased 2 folds in comparison with the Xe irradiation without UV, but, the difference of the rate of CO evolution decreased with the increasing temperature from 873 to 1073 K. The carbothermal reduction of ZnO (ZnO+C→Zn+CO) proceeded at above 950 K, which was demonstrated by XRD analysis and thermodynamic calculation. These results indicate that the photocatalytic effect of ZnO with the UV irradiation enhance the gasification rate of carbon at low temperature (873 K).     

单位电量CO_2排放强度与单位产值CO_2排放强度关系初探

电力单位产值CO2排放强度是全国单位产值CO2排放强度的重要组成部分,其既与电力行业排放绩效即单位发电量CO2排放强度有关,也与全社会能源效率、电气化水平、资源与市场情况等因素相关。本文系统分析了有关指标的统计特征、国际对比、影响因素及趋势预测,指出"十二五"及"十三五"期间,不论是单位电量CO2排放强度,还是电力单位产值CO2排放强度,其下降幅度都是有限的,需要理性看待并科学设置规划指标。     

农村生物质气化集中供气站的建设及其运营管理

结合生物质气化实际工作经验,系统地介绍了农村生物质气化集中供气站建设中经常出现的问题,以及与之相对应的有效解决方案,初步分析并提出了农村生物质气化集中供气站经济科学的运营管理手段和方法.     

下吸式固定床的生物质H2O/CO2气化数值模拟研究

利用Aspen Plus 软件建立干桦木屑在下吸式固定床气化炉中的气化模型,模拟值与文献实验值吻合良好。利用Aspen Plus的灵敏度分析模块模拟分别以水蒸气（H₂O）和二氧化碳（CO₂）为气化剂时气化剂/生物质碳比（GC值）对气化结果的影响,并结合H₂O、CO₂各自的特点研究其复合气化。结果表明,H₂O气化时可获得富氢煤气,但其净CO₂排放量较高;CO₂气化时碳转化率及冷煤气效率较低,但净CO₂排放量较低;H₂O、CO₂复合气化使碳转化率及冷煤气效率略有降低,但可有效减少气化系统中的净CO₂排放量。     

Co-production system of hydrogen and electricity based on coal partial gasification with CO2 capture

To solve the problems of high cost and low efficiency of conventional co-production system of hydrogen and electricity with low hydrogen-to-electricity ratio, a novel co-production system based on coal partial gasification with CO₂ capture is proposed and thermodynamically analyzed. The new system integrates the conceptions of cascade conversion of coal and cascade utilization of syngas to realize the system with high efficiency, low cost, environmental friendliness and flexible hydrogen-to-electricity ratio. The performance of the new system is evaluated by an Aspen Plus model and effects of the operating conditions are also studied. It is found that the system with capturing CO₂ of 59.7% and hydrogen-to-electricity ratio of 4.76 holds a high exergy efficiency of 54.3% when the carbon conversion ratio of the pressurized fluidized bed (PFB) gasifier is equal to 0.7. The carbon conversion ratio of the PFB gasifier is a dominant factor to decide the performance of system. In comparison with the series-type co-production system, the parallel-type co-production system and separate production system, the new system proposed in this study has exergy-saving efficiency of 17.7%, 15.1% and 8.9%, respectively.     

Kinetics of CO2 gasification of biomass char in granulated blast furnace slag

The CO₂ gasification reactions of biomass char in granulated BFS (blast furnace slag) were isothermally investigated using a thermogravimetric analyzer with the temperature ranging from 1173 K to 1323 K. The effects of temperature, biomass type and granulated BFS on the kinetic characterizations of CO₂ gasification of biomass char were illuminated. The kinetic mechanism models and parameters were obtained through a novel two-step calculation method. The results indicated that the CO₂ gasification reactivity of biomass char as conversion and gasification index increased with the increase of temperature and it could be promoted through granulated BFS. The CO₂ gasification reactivity of CS (cornstalk) char with lower alkali index was lower than that of PS (peanut shell) char. The A₄ model (Avrami-Erofeev (m = 4) model) and A₃ model (Avrami-Erofeev (m = 3) model) were demonstrated as the best appropriate models for CO₂ gasification of CS char and PS char, respectively. The gasification activation energy of CS char ranging from 155.08 to 160.48 kJ/mol was higher than that of PS char whether with or without granulated BFS. Granulated BFS could decrease the activation energy of CO₂ gasification of char at any biomass type.     

An oxy-fuel mass-recirculating process for H2 production with CO2 capture by autothermal catalytic oxyforming of methane

A new oxy-fuel H₂ generation process with CO₂ avoidance is provided. The process utilizes mass recirculation of CO and H₂O to the oxyforming reactor. A comparison between non-recirculating and mass-recirculating oxyforming reactor operation is given. Main benefits of mass recirculation are emphasized. The oxyforming reactor is integrated with the H₂ and CO₂ separators, fuel cell and O₂ generator. In the process C/O is equal to 0.5 while C/H determines the temperature level in the reactor. The reaction system includes combustion, steam reforming and water–gas shift reactions. The oxyforming process is found to be mass transport controlled with O₂ as the limiting reactant. It is emphasized that under MR conditions the decomposition of H₂/CO₂ by water–gas shift reaction is suppressed by means of CO/H₂O-enrichment and hence MR conditions allow for higher temperatures beneficial to endothermic steam reforming reaction. Under MR conditions the thermodynamic equilibrium limits are overcome and all reactions are forced to proceed to the completion which enables 100% selectivities to H₂ and CO₂. The effects of operation parameters such as temperature, flow rate, pressure and composition are examined. The derived S-terms enable for the concise interpretation of the effect of pressure on the concentration gradients transverse to the flow. The consistent control algorithm of the oxyforming reactor is provided.     

Metal-organic frameworks for CO2 photoreduction

Metal-organic frameworks (MOFs) have attracted much attention because of their large surface areas, tunable structures, and potential applications in many areas. In recent years, MOFs have shown much promise in CO₂ photoreduction. This review summarized recent research progresses in MOF-based photocatalysts for photocatalytic reduction of CO₂. Besides, it discussed strategies in rational design of MOF-based photocatalysts (functionalized pristine MOFs, MOF-photosensitizer, MOF-semiconductor, MOF-metal, and MOF-carbon materials composites) with enhanced performance on CO₂ reduction. Moreover, it explored challenges and outlook on using MOF-based photocatalysts for CO₂ reduction.     

Natural gas fired combined cycle power plant with CO2 capture

A natural gas (NG) fired power plant is designed with virtually zero emissions of pollutants, including CO₂. The plant operates in a gas turbine-steam turbine combined cycle mode. NG is fired in highly enriched oxygen (99.7%) and recycled CO₂ from the flue gas. Liquid oxygen (LOX) is supplied by an on-site air separation unit (ASU). By cross-integrating the ASU with the CO₂ capture unit, the energy consumption for CO₂ capture is significantly reduced. The exergy of LOX is used to liquefy CO₂ from the flue gas, thereby saving compression energy and also delivering product CO₂ in a saleable form. By applying a new technique, the gas turbine efficiency is increased by about 2.9%. The net thermal efficiency (electricity out/heat input) is estimated at 45%, compared to a plant without CO₂ capture of 54%. However, the relatively modest efficiency loss is amply compensated by producing saleable byproducts, and by the virtue that the plant is pollution free, including NO_x, SO₂ and particulate matter. In fact, the plant needs no smokestack. Besides electricity, the byproducts of the plant are condensed CO₂, NO₂ and Ar, and if operated in cogeneration mode, steam.     

Modelling of a downdraft biomass gasifier with finite rate kinetics in the reduction zone

A model of a downdraft gasifier has been developed based on chemical equilibrium in the pyro‐oxidation zone and finite rate kinetic‐controlled chemical reactions in the reduction zone. The char reactivity factor (C_RF) in the reduction zone, representing the number of active sites on the char and its degree of burn out, has been optimized by comparing the model predictions against the experimental results from the literature. The model predictions agree well with the temperature distribution and exit gas composition obtained from the experiments at C_RF=100. A detailed parametric study has been performed at different equivalence ratios (between 2 and 3.4) and moisture content (in the range of 0–40%) in the fuel to obtain the composition of the producer gas as well as its heating value. It is observed that the heating value of the producer gas increases with the increase in the equivalence ratio and decrease in the biomass moisture content. The effect of divergence angle of the reduction zone geometry (in the range of 30–150°) on the temperature and species concentration distributions in the gasifier has been studied. An optimum divergence angle, giving the best quality of the producer gas, has been identified for a particular height of the reduction zone. Copyright © 2009 John Wiley & Sons, Ltd.     

神华煤粉在CO2和N2高温气氛下SOx生成释放规律的研究

通过在固定反应床实验系统上,进行了不同燃烧气氛、不同氧气体积浓度、不同燃烧环境温度及不同颗粒粒径下神华煤粉的燃烧实验,在实验过程中对气体污染物SOx生成释放规律进行了研究。发现了CO2气氛下SOx呈现双峰现象,即在煤粉燃烧过程中,S元素转化成SOx的过程分为挥发分释放阶段和焦炭燃烧阶段。SOx释放过程中第一个峰的积分值占总积分值的百分比随着燃烧环境温度的升高而降低,即在较高的燃烧环境温度下SOx主要来源于无机硫化合物。在煤粉燃烧过程中,SOx生成释放曲线的2个峰值随着氧气浓度的升高而增加,SOx总生成量也略为增加;单位氧气消耗量生成的SOx(记为YSOx)随着燃烧环境温度的升高而升高;煤粉颗粒粒径对YSOx的影响规律不明显。高温1 600℃下,煤粉自固硫特性的作用下SOx的生成量与1 000℃时相当。     

The impact of CHP generation on CO2 emissions

The combined generation of heat and power (cogeneration) is praised by many as a technique for reducing the emissions of CO₂ in industrialized nations. This is generally true but not always. In this article we discuss the impact of some major variables on the CO₂ emission reduction capacity of cogeneration. Two sets of variables are predominant: the characteristics of the CHP process and the composition of the electricity generation sector. We highlight the interaction between the two sets of variables with the help of diagrams.