Kinetics,thermodynamics and synergistic effects analyses of petroleum coke and biomass wastes during H2O co-gasification

In this study, the H₂O co-gasification of petroleum coke (PC) with low (sulfur and V₂O₅ contents) and different five kinds of biomass wastes were conducted using a thermogravimetric analyzer (TGA). The biomass used were the agricultural wastes (rice husk (RH), rice stalk (RS), and cotton straw (CS)) and by-product wastes (sawdust (SD) and sugar cane bagasse (SCB)). Their reactivities, kinetics and thermodynamics parameters were investigated and compared in detail as well as a synergistic effect during co-gasification of the blends. The kinetics and thermodynamics parameters were estimated by using the homogeneous model (HM) or the first-order chemical reaction (O1) and shrinking core models (SCM) or Phase boundary controlled reactions (R2 and R3). It was found that the biomass wastes was significantly improved the blends gasification reactivity. The obvious significant synergistic effect was observed in the char gasification stage of the blends compared with the pyrolysis stage. Compared to other models the phase boundary controlled reaction (R2) was found to be the best model to predict the experimental data of the co-gasification process. For both reaction stages of single fuels, SD showed the lowest values of activation energy and thermodynamics parameters. The blends of PC: SD and PC: CS provided the lowest activation energy and thermodynamics parameters for the pyrolysis stage and the char gasification stage, respectively. The co-gasification of PC and biomass wastes are a promising technique for the efficient utilization of PC and biomass wastes.     

Thermodynamics research on hydrogen production from biomass and coal co-gasification with catalyst

A model comprises two sub-models, i.e. combustion and gasification models, is developed to simulate a single fluidized bed two-step gasification process and to predict H₂ production under different conditions. The combustion sub-model which consists of volatile precipitation and char combustion sub-models. The combustion sub-model is used to forecast residual char. The gasification sub-model, based on the mass and energy balance, is used to examine thermodynamically the effect on the hydrogen production of calcium oxide as the catalyst. Moreover, the effects of the operational conditions on the hydrogen production such as biomass/coal (mass ratio), temperature, steam/coke, and calcium/coke, are simulated. The results indicate that the addition of calcium oxide at certain conditions can significantly improve hydrogen production and lower the required temperature for gasification. The model predicts that the maximum hydrogen production of 60% can be achieved under the conditions of temperature in the range of 800-850 °C, calcium/coke, steam/coke, and coal/biomass (mass ratio) are 0.5, 1.8, and 1/4, respectively. The model predictions are in good agreement with the experimental data.     

Experimental simulate on hydrogen production of different coals in underground coal gasification

Research on hydrogen production from coal gasification is mainly focused on the formation of CO and H₂ from coal and water vapor in high-temperature environments. However, in the process of underground coal gasification, the water gas shift reaction of low-temperature steam will absorb a lot of heat, which makes it difficult to maintain the combustion of coal seams in the process of underground coal gasification. In order to obtain high-quality hydrogen, a pure oxygen-steam gasification process is used to improve the gasification efficiency. And as the gasification surface continues to recede, the drying, pyrolysis, gasification and combustion reactions of underground coal seams gradually occur. Direct coal gasification can't truly reflect the process of underground coal gasification. In order to simulate the hydrogen production laws of different coal types in the underground gasification process realistically, a two-step gasification process (pyrolysis of coal followed by gasification of the char) was proposed to process coal to produce hydrogen-rich gas. First, the effects of temperature and coal rank on product distribution were studied in the pyrolysis process. Then, the coal char at the final pyrolysis temperature of 900 °C was gasified with pure oxygen-steam. The results showed that, the hydrogen production of the three coal chars increased with the increase of temperature during the pyrolysis process, the hydrogen release from Inner Mongolia lignite and Xinjiang long flame coal have the same trend, and the bimodality is obvious. The hydrogen release in the first stage mainly comes from the dehydrogenation of the fat side chain, and the hydrogen release in the second stage mainly comes from the polycondensation reaction in the later stage of pyrolysis, and the pyrolysis process of coal contributes 15.81%–43.33% of hydrogen, as the coal rank increases, the hydrogen production rate gradually decreases. In the gasification process, the release of hydrogen mainly comes from the water gas shift reaction, the hydrogen output is mainly affected by the quality and carbon content of coal char. With the increase of coal rank, the hydrogen output gradually increases, mainly due to the increasing of coal coke yield and carbon content, The gasification process of coal char contributes 56.67–84.19% of hydrogen, in contrast, coal char gasification provides more hydrogen. The total effective gas output of the three coal chars is 0.53–0.81 m³/kg, the hydrogen output is 0.3–0.43 m³/kg, and the percentage of hydrogen is 53.08–56.60%. This study shows that two-step gasification under the condition of pure oxygen-steam gasification agent is an efficient energy process for hydrogen production from underground coal gasification.     

Catalytic steam co-gasification of biomass and coal in a dual loop gasification system with olivine catalysts

A dual loop gasification system (DLG) has been previously proposed to facilitate tar destruction and H₂-rich gas production in steam gasification of biomass. To sustain the process auto-thermal, however, additional fuel with higher carbon content has to be supplied. Co-gasification of biomass in conjunction with coal is a preferred option. Herein, the heat balance of the steam co-gasification of pine sawdust and Shenmu bituminous coal in the DLG has been analyzed to verify the feasibility of the process with the help of Aspen Plus. Upon which, the co-gasification experiments in the DLG have been investigated with olivine as both solid heat carriers and in-situ tar destruction catalysts. The simulation results show that the self-heating of the DLG in the co-gasification is achieved at the coal blending ratio of 28%, gasification circulation ratio of 19 and reforming circulation ratio of 20 when the gasifier temperature 800 °C, reforming temperature 850 °C, combustor temperature 920 °C and S/C 1.1. The co-gasification experiments indicate that the tar is efficiently destructed in the DLG at the optimized reformer temperature and with olivine catalysts.     

Steam co-gasification of coal and biomass derived chars with synergy effect as an innovative way of hydrogen-rich gas production

The main results of the experimental work on steam co-gasification of Polish hard coal and Salix Viminalis blends in a fixed bed reactor under atmospheric pressure and at the temperature of 700, 800 and 900 °C are presented in the paper. The effectiveness of co-gasification of coal/biomass blends of 20, 40, 60 and 80% w/w biomass content was tested in terms of gas flows, composition, carbon conversion and chars reactivity. A synergy effect in the co-gasification tests, consisting in increase in the volume of hydrogen produced, when compared to the tests of coal and biomass gasification, was observed at all tested temperatures. The observed synergy effect was attributed to the catalytic effect of K₂O present in blend ash (6-10% wt). Moreover, in co-gasification of blends of 20 and 40% w/w biomass content, increase in the total gas yield was observed, when compared to the tests of coal and biomass gasification at all tested temperatures. In tests of co-gasification of blends of higher biomass content (i.e. 60 and 80% w/w), a slight decrease in the total volume of product gas was observed, when compared to the tests of coal and biomass gasification. Nevertheless, higher ratio of biomass in co-gasification makes it still an attractive option in terms of CO₂ emission reduction and increase in hydrogen production.     

Modeling biomass gasification in circulating fluidized beds

Detailed review of existing models resulted in the development of a new mathematical model to study biomass gasification in a circulating fluidized bed. Hydrodynamics as well as chemical reaction kinetics were considered to predict the overall performance of a biomass gasification process. The fluidized bed was divided into two distinct sections: a) a dense region at the bottom of the bed where biomass undergoes mainly heterogeneous reactions and b) a dilute region at the top where most of homogeneous reactions occur in gas phase. Each section was divided into a number of small cells, over which mass and energy balances were applied. A number of homogeneous and heterogeneous reactions were considered in the model. Mass transfer resistance was considered negligible since the reactions were under kinetic control due to good gas–solid mixing. The model is capable of predicting the bed temperature distribution along the gasifier, the concentration and distribution of each species in the vertical direction of the bed, the composition and heating value of produced gas, the gasification efficiency, the overall carbon conversion and the produced gas production rate. The modeling and simulation results were in good agreement with published data.     

Co-pyrolysis and co-gasification of biomass and polyethylene: Thermal behaviors,volatile products and characteristics of their residues

Co-pyrolysis and co-gasification of biomass and plastics could be a promising method to alleviate environmental pollution and provide renewable energy. In this paper, co-pyrolysis and co-gasification of eucalyptus wood (EW) or rice straw (RS) with polyethylene (PE) were investigated by a thermogravimetric analyzer coupled with a Fourier transform infrared spectrometer (TG-FTIR) and a scanning electron microscope coupled with energy-dispersive spectroscopy (SEM/EDS). Results showed that the pyrolysis behaviors were characterized by two stages. The first stage was the decomposition of EW and RS, and the second stage primarily consisted of the degradation of PE. The gasification exhibited a third stage for the reaction of products with CO₂. A synergistic effect was presented in the pyrolysis and gasification of biomass with PE, and it could have a positive effect on the decomposition of biomass. Compared to individual pyrolysis and gasification, co-pyrolysis and co-gasification generated no new substances, but the yield of some products was changed in these processes. In co-pyrolysis, the decomposition of biomass was promoted. In co-gasification, the production of CH₄, CO and oxygenated compounds was inhibited, while the reaction to generate H₂O was promoted. Gasification and the addition of PE both increased the carbon content and reduced the oxygen content of volatile products. Additionally, more metal elements could be deposited in residues when PE was added.     

A review on reactivity characteristics and synergy behavior of biomass and coal Co-gasification

Co-gasification is a promising approach to the clean and high-efficiency co-utilization of biomass and coal with syngas (H₂+CO) production. Gasification reactivity is an important factor influencing the operation conditions choice, carbon conversion efficiency and syngas production performance. Coal-biomass interaction during co-gasification will directly result in the synergy behavior of different forms and intensities on co-gasification reactivity. Due to the fuel origin diversity, structural property difference and reaction process complexity of biomass and coal, a clear understanding of reactivity characteristics and synergy behavior of co-gasification is very essential for revealing co-gasification reaction mechanism and providing theoretical support for actual application. In this paper, the influences factors (such as feedstock type, blended ratio, gasification temperature, co-pyrolysis process, gasification reactor and biomass pretreatment) for co-gasification reactivity and the synergy behavior on co-gasification reactivity are summarized in details, and non-catalytic/catalytic synergy mechanisms for co-gasification are discussed. Previous researchers have acquired a plenty of meaning data, providing important reference for industrial application of co-gasification technology. However, volatile matter-char interaction mechanism during co-pyrolysis was still unclear, AAEM migration and transformation route during co-gasification are lack of in-situ analysis, transfer route and interaction of free radicals during co-gasification process were unknown, and co-gasification kinetics model containing dynamic synergistic/inhibition factors hasn't been established.     

Steam co-gasification of coal and biomass – Synergy in reactivity of fuel blends chars

Development of clean coal technologies is the answer to increasing energy demand and environmental concerns related to conventional coal processing technologies. The technologies of fossil fuel gasification are technically proven and commercially available. Attempts of utilization of waste materials and renewable energy resources in gasification-based energy generation systems has been made, but wide application of such systems is still hindered by issues inherently combined with the characteristics of the materials. These include discontinuous supplies of a fuel of limited resources and varying composition resulting in poor economy of small-scale systems and operating problems related to tars formation and corrosion, especially when biomass utilization is considered. In the light of the above co-gasification seems to offer several advantages through mitigation of undesired effects of both carbon-intensive utilization of coal and low efficient and troublesome operation of biomass/waste-fed gasification systems. The experimental results presented in the paper address the issues of determination of potential synergy effects resulting from the utilization of fuel blends composed of materials of various physical and chemical characteristics, which are still insufficiently discussed in the literature, especially when hydrogen-rich gas production in co-gasification is concerned. The results of reactivity tests of fuel blends of coal and energy crops biomass in the process of steam co-gasification in a laboratory scale fixed bed reactor at 700, 800 and 900 °C are given proving the synergy effect in co-gasification reflected in increased reactivity of fuel blends when compared to coal and biomass chars reactivity under similar process conditions.     

Effect of the blend ratio on the co-gasification of biomass and coal in a bubbling fluidized bed with CFD-DEM

Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) is employed to describe the co-gasification of biomass and coal in bubbling fluidized bed coupled with chemical reaction kinetic model. Six sets of simulations are set up to study the effect of blend ratio on the amount of gasification products compared with experiments. The calorific value of syngas, carbon conversion efficiency, hydrogen conversion efficiency and cold gas efficiency are calculated. Compared with the separate gasification, the hydrogen efficiency and cold gas efficiency in the co-gasification are enhanced. When biomass accounts for 75%, the contents of CO gas and CO₂ gas are the lowest, while the contents of H₂ gas and CH₄ gas are the highest. The high calorific value, carbon conversion efficiency and hydrogen conversion efficiency reach the maximum under this blend ratio. The cold gas efficiency is not obviously affected by the blend ratio, and reaches the maximum when the biomass content is 50%.     

加压喷动流化床煤气化数值模拟

建立了基于CFD的三维非稳态喷动流化床煤气化动力学模型.此模型包含气固流动模型,煤的挥发分析出模型,焦炭气化反应模型和气相间的均相反应模型等子模型.焦炭的非均相反应速率由气体扩散和化学反应动力学共同控制.气体均相反应可以作为二级反应来处理.将试验结果和模拟的计算结果进行了对比,结果表明,入口中心喷动区的温度最高,温度场沿床高方向逐渐降低.煤气质量在加压后有了明显提高.验证的结果表明此CFD模型可以用来预测煤气化的反应过程.     

Mechanisms of Thermochemical Biomass Conversion Processes. Part 2: Reactions of Gasification

Abstract

Gasification as a thermochemical process is defined and limited to combustion and pyrolysis. The gasification of biomass is a thermal treatment which results in a high proportion of gaseous products and small quantities of char (solid product) and ash. Biomass gasification technologies have historically been based upon partial oxidation or partial combustion principles, resulting in the production of a hot, dirty, low Btu gas that must be directly ducted into boilers or dryers. In addition to limiting applications and often compounding environmental problems, these technologies are an inefficient source of usable energy. The main objective of the present study is to investigate gasification mechanisms of biomass structural constituents. Complete gasification of biomass involves several sequential and parallel reactions. Most of these reactions are endothermic and must be balanced by partial combustion of gas or an external heat source.     

温度对喷动流化床煤气化影响的数值模拟

建立了基于CFD的三维非稳态的喷动流化床煤气化动力学模型,考察了温度对喷动流化床煤气化影响。此模型包含了以下子模型：气固流动模型,煤的挥发分析出模型,焦炭气化反应模型,气相间的均相反应模型。焦炭的非均相反应的速率由气体的扩散和化学反应动力学共同控制,气体的均相反应可以作为二级反应来处理。试验结果和模拟的计算结果进行了对比,验证的结果表明了此CFD模型可以用来预测煤气化的反应过程。     

10 MW生物质气化耦合超临界燃煤锅炉系统火用平衡分析

为有效评价生物质气化耦合燃煤锅炉系统能量转换过程,分析该系统的节能潜力,以某10 MW循环流化床生物质气化炉耦合大型超临界燃煤机组为例,建立了该耦合系统的火用分析控制体模型,利用Aspen plus平台对该系统实际运行过程进行火用平衡分析。结果表明：当前运行工况下,生物质气化过程火用损失是耦合系统最大的火用损失,达到42.28%,其次是可燃气体在燃煤锅炉内的燃烧及传热过程,为25.32%。因此系统运行过程中应采取优化运行措施,减小气化过程火用损失,同时气化炉应尽量与高参数的大型机组耦合运行,可燃气体选取在燃煤锅炉合适位置输入,以保证充分燃烧。     

The use of biomass syngas in IC engines and CCGT plants: A comparative analysis

This paper studies the use of biomass syngas, obtained from pyrolysis or gasification, in traditional energy-production systems, specifically internal combustion (IC) engines and combined cycle gas turbine (CCGT) plants. The biomass conversion stage has been simulated by means of a gas–solid thermodynamic model. The IC and CCGT plant configurations were optimised to maximise heat and power production. Several types of biomass feedstock were studied to assess their potential for energy production and their effect on the environment. This system was also compared with the coupling between biomass gasification and fuel cells.     

棉秆与煤混合热解的特性研究

煤与生物质的混和燃烧是生物质利用的重要途径,两者的共热解是其中最重要的反应之一。为了研究煤与棉秆混合热解的影响因素,利用热重分析仪（Thermo Gravimetric Analyzer,简称TGA）,对煤与棉秆以1：1的比例掺混的混合物进行热解过程特性研究。通过对比煤和棉秆共热解过程的差异发现：煤与棉秆混合共热解过程中两者存在一定相互影响,棉秆对煤热解在温度较低的时候有一定促进作用,但随着温度的升高逐渐表现出较明显的相互抑制作用,对于生物质与煤混烧锅炉的设计和运行具有理论指导意义。     

水蒸气气氛下生物质与聚丙烯共气化产气特性数值分析

搭建生物质与废塑料共气化动力学模型,并用实验数据对其进行验证。选用6种生物质和聚丙烯作为共气化反应物,以水蒸气为气化剂,计算气化温度在300～1000℃之间、气化压强在0.1～0.8 MPa之间、聚丙烯和松木锯末质量比例在0.5～2.5之间,以及不同生物质类型等对生物质和聚丙烯共气化产气特性的影响。结果表明：松木锯末气化中添加聚丙烯后,最高产气量和最大产气速率增加,最高产气总流量提高21.46%,最高产气速率提高4.64%,H₂和CO最高产量分别提高54.27%和79.51%;压强增加不利于提高共气化产气的H₂和CO含量,有利于提高CH₄含量;6种常见生物质和聚丙烯共气化产氢量大小顺序为：果皮>棉花秆≈玉米秸秆>杨树木屑>稻秆>条浒苔;聚丙烯掺混比率增加有利于提高H₂、CO和CH₄等组分产量。     

Co-gasification of biomass and coal for methanol synthesis

In recent years, a growing interest has been observed in the application of methanol as an alternative liquid fuel, which can be used directly for powering Otto engines or fuel cells achieving high thermodynamic efficiencies and relatively low environmental impacts. Biomass and coal can be considered as a potential fuel for gasification and further syn-gas production and methanol synthesis. In the near future, the economy of methanol production through coal and biomass gasifications can be achieved by their linking with modern gas-steam power systems. The essence of linking is the full utilisation of the capacity of coal/biomass gasification installations. The up-to-date experience of coal and biomass gasification, including gas processing towards syn-gas and methanol production, is described and discussed. A conceptual flow diagram of pressurized and oxygen feeded co-gasification of biomass and coal integrated with combined cycle and parallel methanol production is evaluated. The effect of methanol production rate on the economy of power production is assessed.     

New concepts in biomass gasification

Gasification is considered as a key technology for the use of biomass. In order to promote this technology in the future, advanced, cost-effective, and highly efficient gasification processes and systems are required. This paper provides a detailed review on new concepts in biomass gasification.Concepts for process integration and combination aim to enable higher process efficiencies, better gas quality and purity, and lower investment costs. The recently developed UNIQUE gasifier which integrates gasification, gas cleaning and conditioning in one reactor unit is an example for a promising process integration. Other interesting concepts combine pyrolysis and gasification or gasification and combustion in single controlled stages. An approach to improve the economic viability and sustainability of the utilization of biomass via gasification is the combined production of more than one product. Polygeneration strategies for the production of multiple energy products from biomass gasification syngas offer high efficiency and flexibility.     

Main routes for the thermo-conversion of biomass into fuels and chemicals. Part 1: Pyrolysis systems

Since the energy crises of the 1970s, many countries have become interest in biomass as a fuel source to expand the development of domestic and renewable energy sources and reduce the environmental impacts of energy production. Biomass is used to meet a variety of energy needs, including generating electricity, heating homes, fueling vehicles and providing process heat for industrial facilities. The methods available for energy production from biomass can be divided into two main categories: thermo-chemical and biological conversion routes. There are several thermo-chemical routes for biomass-based energy production, such as direct combustion, liquefaction, pyrolysis, supercritical water extraction, gasification, air–steam gasification and so on. The pyrolysis is thermal degradation of biomass by heat in the absence of oxygen, which results in the production of charcoal (solid), bio-oil (liquid), and fuel gas products. Pyrolysis liquid is referred to in the literature by terms such as pyrolysis oil, bio-oil, bio-crude oil, bio-fuel oil, wood liquid, wood oil, liquid smoke, wood distillates, pyroligneous tar, and pyroligneous acid. Bio-oil can be used as a fuel in boilers, diesel engines or gas turbines for heat and electricity generation.