http://digital.csic.es/bitstream/10261/78793/1/Progress%20in%20chemical-looping%20combustion%20and%20ref....2012.pdf

Progress in chemical-looping combustion and reforming technologies

In recent years, Carbon Capture and Storage (Sequestration) (CCS) has been proposed as a potential method to allow the continued use of fossil-fuelled power stations whilst preventing emissions of CO2 from reaching the atmosphere. Gas, coal (and biomass)-fired power stations can respond to changes in demand more readily than many other sources of electricity production, hence the importance of retaining them as an option in the energy mix. Here, we review the leading CO2 capture technologies, available in the short and long term, and their technological maturity, before discussing CO2 transport and storage. Current pilot plants and demonstrations are highlighted, as is the importance of optimising the CCS system as a whole. Other topics briefly discussed include the viability of both the capture of CO2 from the air and CO2 reutilisation as climate change mitigation strategies. Finally, we discuss the economic and legal aspects of CCS.

Carbon capture and storage update

Lignocellulosic biomass pyrolysis mechanism: A state-of-the-art review

Pyrolysis is one of the thermochemical technologies for converting biomass into energy and chemical products consisting of liquid bio-oil, solid biochar, and pyrolytic gas. Depending on the heating rate and residence time, biomass pyrolysis can be divided into three main categories slow (conventional), fast and flash pyrolysis mainly aiming at maximising either the bio-oil or biochar yields. Synthesis gas or hydrogen-rich gas can also be the target of biomass pyrolysis. Maximised gas rates can be achieved through the catalytic pyrolysis process, which is now increasingly being developed. Biomass pyrolysis generally follows a three-step mechanism comprising of dehydration, primary and secondary reactions. Dehydrogenation, depolymerisation, and fragmentation are the main competitive reactions during the primary decomposition of biomass. A number of parameters affect the biomass pyrolysis process, yields and properties of products. These include the biomass type, biomass pretreatment (physical, chemical, and biological), reaction atmosphere, temperature, heating rate and vapour residence time. This manuscript gives a general summary of the properties of the pyrolytic products and their analysis methods. Also provided are a review of the parameters that affect biomass pyrolysis and a summary of the state of industrial pyrolysis technologies.

Lignocellulosic biomass pyrolysis: A review of product properties and effects of pyrolysis parameters

The conversion of biomass by thermochemical means is very promising for the substitution of fossil materials in many energy applications. Given the complexity of biomass the main challenge in its use is to obtain products with high yield and purity. For a better understanding of biomass thermochemical conversion, many authors have studied in TG analyzer or at bed scale the individual pyrolysis of its main constituents (i.e. cellulose, hemicelluloses and lignin). Based on these studies, this original work synthesizes the main steps of conversion and the composition of the products obtained from each constituent. Pyrolysis conversion can be described as the superposition of three main pathways (char formation, depolymerization and fragmentation) and secondary reactions. Lignin, which is composed of many benzene rings, gives the highest char yield and its depolymerization leads to various phenols. The depolymerization of the polysaccharides is a source of anhydro-saccharides and furan compounds. The fragmentation of the different constituents and the secondary reactions produce CO, CO2 and small chain compounds. For temperature higher than 500 °C, the residues obtained from the different constituents present a similar structure, which evolves towards a more condensed polyaromatic form by releasing CH4, CO and H2. As the aromatic rings and their substituent composition have a critical influence on the reactivity of pyrolysis products, a particular attention has been given to their formation. Some mechanisms are proposed to explain the formation of the main products. From the results of this study it is possible to predict the reactivity and energy content of the pyrolysis products and evaluate their potential use as biofuels in renewable applications.

A review on pyrolysis of biomass constituents: Mechanisms and composition of the products obtained from the conversion of cellulose, hemicelluloses and lignin

Fast pyrolysis of cellulose, xylan, and lignin was experimentally conducted between 350 and 650 °C in a tube furnace, and the effect of temperature on pyrolysis products (char, noncondensable gas, and bio-oil) was investigated. The yields of char, noncondensable gas, and bio-oil were quantified using gas chromatography and gas chromatography with mass spectrometry. The noncondensable gas mainly consists of CO, CO2, CH4, and H2. The bio-oil includes acids, ketones, aldehydes, esters, benzenes, alcohols, alkenes, phenols, alkanels, carbohydrates, etc. The results show that cellulose is the principal source of carbohydrates and phenols are the basis of the bio-oil from lignin, while the bio-oil from xylan mainly consists of acids, ketones, aldehydes, and phenols. The char yields for the three components decrease with an increase in temperature, and the gas yields and bio-oil yields increase with an increase in temperature, reach a maximum at a certain temperature, and then decrease after that temperature. Th...

Experimental Study of Biomass Pyrolysis Based on Three Major Components: Hemicellulose, Cellulose, and Lignin

Chemical-looping combustion of biomass was carried out in a 10 kWth reactor with iron oxide as an oxygen carrier A total 30 h of test was achieved with the same batch of iron oxide oxygen carrier The effect of the fuel reactor temperature on gas composition of the fuel reactor and the air reactor, the proportion of biomass carbon reacting in the fuel reactor, and the conversion of biomass carbon to CO2 in the fuel reactor was experimentally investigated The results showed that the CO production from biomass gasification with CO2 was more temperature dependent than the CO oxidation with iron oxide in the fuel reactor, and an increase in the fuel reactor temperature produced a higher increase for the CO production from biomass gasification than for the oxidation of CO by iron oxide Although the conversion of biomass carbon to CO2 in the fuel reactor decreased with the increase of the fuel reactor temperature, there was a substantial increase in the proportion of biomass carbon reacting in the fuel react

Chemical-Looping Combustion of Biomass in a 10 kWth Reactor with Iron Oxide As an Oxygen Carrier

Hydrogen production from biomass gasification in interconnected fluidized beds is proposed in this paper. It resembles a circulating fluidized bed with the extra bubbling fluidized bed after the cyclone. The circulating fluidized bed is designed for combustion fed with air, the bubbling fluidized bed for biomass gasification fed with steam. Direct contact between the gasification and combustion processes is avoided; the gasification-required heat is achieved by means of the circulation of bed particles. Hydrogen-rich gas is produced free of N2 dilution. The paper intends to provide some process fundamentals about hydrogen production from biomass gasification in interconnected fluidized beds. Simulation of the processes, including chemical reactions and heat/mass balance, is carried out with Aspen Plus software. The effects of gasifier temperature and steam/biomass ratio on the composition of fuel gas, hydrogen yield, carbon conversion of biomass, recirculation of bed particles, etc., are discussed. Some useful results are achieved. The results indicate that both a high hydrogen content and a relatively great hydrogen yield are obtained from biomass gasification in interconnected fluidized beds. The favorable temperature of the gasifier should be between 750 and 800 °C, the combustor temperature should be 920 °C, and the ratio of the steam/biomass should be between 0.6 and 0.7. The increment of hydrogen yield is distinct with the increase of steam/biomass ratio at the lower gasifier temperatures (below 750 °C). The steam/biomass ratio corresponding to maximal hydrogen yield declines with the increase of gasifier temperature. To maintain the gasifier temperature, the recirculation of bed particles increased exponentially with an increase in the gasifier temperature.

Simulation of hydrogen production from biomass gasification in interconnected fluidized beds

Experiments on chemical looping combustion of coal with a NiO based oxygen carrier

Chemical looping combustion (CLC) is a new innovative technology with inherent separation of CO2 without energy penalty. Experiments on chemical looping combustion of biomass/coal were conducted in a 1 kWth continuous reactor, and an Australia iron ore was selected as oxygen carrier. Both biomass/coal mixture and biomass were used as fuels. The effect of temperature on gas composition of both the fuel reactor and the air reactor, conversion efficiency of carbonaceous gases, carbon capture efficiency, and oxide oxygen fraction was investigated. An increase in the fuel reactor temperature produced a higher CO2 concentration in the fuel reactor for biomass/coal mixture, whereas it produced a lower one for pure biomass. CO concentration in the fuel reactor increased in both fuel conditions. Due to the poor oxygen transport capacity and the thermodynamic constraint of the iron ore conversion from Fe2O3 to Fe3O4, a higher temperature would contribute to decreasing the conversion efficiency of carbonaceous gases...

Jun Xiao

Papers

Experimental Study of Biomass Pyrolysis Based on Three Major Components: Hemicellulose, Cellulose, and Lignin

Chemical-Looping Combustion of Biomass in a 10 kWth Reactor with Iron Oxide As an Oxygen Carrier

Simulation of hydrogen production from biomass gasification in interconnected fluidized beds

Experiments on chemical looping combustion of coal with a NiO based oxygen carrier

Chemical Looping Combustion of Biomass/Coal with Natural Iron Ore as Oxygen Carrier in a Continuous Reactor