Kinetics and mechanism of CO2 gasification of coal catalyzed by Na2CO3, FeCO3 and Na2CO3–FeCO3

The purpose is to develop a mild catalytic CO₂-gasification technology that can promote CO₂ utilization and reduce cost in air separation systems with improving system efficiency and obtaining desirable gaseous products. In this study, the influence of Na, Fe and their composite catalysts on the structure and gasification reactivity of chars derived from pyrolysis of Powder River Basin (PRB) coal was investigated. The results showed that a strong positive synergistic effect between Na and Fe catalyst in the gasification process was observed, the catalytic activity of the added catalysts was in order of: 4% Na > 3% Na–1%Fe > 2% Na-2% Fe > 1% Na-3% Fe > 1% Na-2% Fe > 4% Fe > raw coal. The catalysts inhibited the growth of the aromatic ring structure and enriched the generation of O-containing functional groups. Compared to Fe, the Na-based catalyst could easily diffuse into inner pores of coal char, forming C–O–Na structure and thus increasing the gasification reactivity of chars. In addition, due to the formation of inert material between SiO₂ and Na, the catalytic activity of Na catalysts was significantly decrease at the late stage of char conversion. Comparatively, the Fe-based catalysts showed better stability life. Moreover, it was found that the activation energy for CO₂-gasification of PRB coal can be decreased by 50% due to the addition of Na catalyst.     

CO2 gasification of dairy and swine manure: A life cycle assessment approach

CO₂ gasification of three different chars obtained from the pyrolysis of two dairy manure samples and a swine manure sample was evaluated. Dairy samples were firstly pretreated by anaerobic digestion process and swine sample by bio-drying process. Subsequently, manure samples were pyrolyzed between 30 °C and 980 °C obtaining a solid fuel (biochar), which was later gasified using different vol.% CO₂ (15–90%) which was the gasifying agent. Gasification was conducted at 900 °C. Thermal behavior and gasification characteristics were studied by means of the thermogravimetric-mass spectrometric analysis. In this sense, the reactivity of the samples was influenced by the catalytic activity of the mineral matter contained in the remaining biomass ashes. On the other hand, the viability of the manure gasification process vs the traditional use of manure as fertilizer was studied by means of the life cycle assessment (LCA) methodology. Two different scenarios were analyzed: gasification of manure sample before anaerobic digestion (Pre) and gasification of manure after anaerobic digestion (Dig R). According to the results obtained, the gasification of char Pre was the most viable scenario from the economic and environmental viewpoints whereas the gasification of char Dig R was the best energetic option.     

Coal char gasification for co-production of fuel gas and methane decomposition catalysts

Partial gasification of coal char was conducted with addition of metal oxides for co-production of fuel gas and methane decomposition catalysts. Effect of the metal composition (Ni, Co and Fe based mono- or bi-metals) was investigated on the fuel gas production and the resultant catalyst surface and textural properties, morphology and performance in catalytic methane decomposition (CMD). Besides H₂-rich fuel gas production (the combustion energy up to 11.03–23.42 MJ/kg_char) from the gasification, the gasification residue can directly serve as the effective and efficient catalyst for CMD. The Fe and Fe–Co composite oxides were found to be better among the mono- and bi-metallic oxides for the fuel gas production during the gasification, respectively. The Ni-based mono-/bi-metallic catalysts could display high and stable methane conversion (up to 80%) during the 600-min CMD test at 850 °C. Promotional role of the second metal in CMD was discussed on the carbon diffusion, metal mobility and reducibility, formation and growth of the deposited carbons. The formed carbon morphology after CMD was analyzed based on the Kirkendall effect and Tammann temperature and further correlated to the potential catalyst deactivation.     

Detailed kinetic analysis and modelling of the dry gasification reaction of olive kernel and lignite coal chars

The dry gasification process of solid fuels is a promising pathway to mitigate and utilize captured CO₂ emissions toward syngas generation with tailored composition for several downstream energy conversion and chemical production processes. In the present work, comprehensive kinetic analysis and reaction modelling studies were carried out for olive kernel and lignite coal chars gasification reaction using pure CO₂ as gasifying agent. Chars reactivity and kinetics of the gasification reactions were thoroughly examined by thermogravimetric analysis at three different heating rates and correlated with their physicochemical properties. The reactivity of olive kernel char, as determined by the mean gasification reactivity and the comprehensive gasification characteristic index, S, was almost three times higher compared to that of the lignite coal char. It was disclosed that the fixed carbon content and alkali index (AI) have a major impact on the reactivity of chars. The activation energy, E_a, estimated by three different model-free kinetic methods was ranged between 140 and 170 kJ/mol and 250–350 kJ/mol for the olive kernel and lignite coal chars, respectively. The activation energy values for the lignite coal char significantly varied with carbon conversion degree, whereas this was not the case for olive kernel char, where the activation energy remained essentially unmodified throughout the whole carbon conversion range. Finally, the combined Malek and Coats-Rendfrem method was applied to unravel the mechanism of chars-CO₂ gasification reaction. It was found that the olive kernel char-CO₂ gasification can be described with a 2D-diffusion mechanism function (D2) whereas the lignite coal char-CO₂ gasification follows a second order chemical reaction mechanism function (F2).     

Experimental study on the key factors affecting the gasification performance between different biomass: Compare citrus peel with pine sawdust

This work aims to reveal the advantages of citrus peel gasification and investigate the key factors affecting gasification performance. The gasification performance of citrus peel and pine sawdust are compared in a fixed bed reactor, and the reactivity and properties of biochar were investigated. The results showed that the H₂ yield and carbon conversion efficiency of citrus peel gasification were 34.35 mol/kg_biomass and 66.30%, respectively, which were higher than those of pine sawdust. Due to the high reactivity of citrus peel char, it only takes 100 min for the citrus peel to complete the gasification reaction, which is significantly faster than pine sawdust. Although the specific surface area of citrus peel char is lower than that of pine sawdust char, both the low degree of graphitization and the high catalytic index (2426.96) are favorable for the conversion of char, which ultimately lead to the high reactivity of citrus peel char.     

Steam gasification of Greek lignite and its chars by co-feeding CO2 toward syngas production with an adjustable H2/CO ratio

Low-rank lignite is among the most abundant and cheap fossil fuels, linked, however, to serious environmental implications when employed as feedstock in conventional thermoelectric power plants. Hence, toward a low-carbon energy transition, the role of coal in world's energy mix should be reconsidered. In this regard, coal gasification for synthesis gas generation and consequently through its upgrade to a variety of value-added chemicals and fuels constitutes a promising alternative. Herein, we thoroughly explored for a first time the steam gasification reactivity of Greek Lignite (LG) and its derived chars obtained by raw LG thermal treatment at 300, 500 and 800 °C. Moreover, the impact of CO₂ addition on H₂O gasifying agent mixtures was also investigated. Both the pristine and char samples were fully characterized by various physicochemical techniques to gain insight into possible structure-gasification relationships. The highest syngas yield was obtained for chars derived after LG thermal treatment at 800 °C, due mainly to their high content in fixed carbon, improved textural properties and high alkali index. Steam gasification of lignite and char samples led to H₂-rich syngas mixtures with a H₂/CO ratio of approximately 3.8. However, upon co-feeding CO₂ and H₂O, the H₂/CO ratio can be suitably adjusted for several potential downstream processes.     

Steam gasification of energy crops of high cultivation potential in Poland to hydrogen-rich gas

In the paper energy crops of considerable cultivation potential in Poland, namely: Salix viminalis, Helianthus tuberosus, Sida hermaphrodita, Spartina pectinata, Andropogon gerardi and Miscanthus X giganteus were tested in terms of steam gasification reactivity of biomass chars, as well as yields and composition of product gas in steam gasification and lime-enhanced steam gasification in a laboratory scale fixed bed reactor at 650 °, 700 ° and 800 °C.The highest value of reactivity for 50% of carbon conversion, R₅₀, was observed for Sida hermaphrodita, regardless the process temperature.Application of CaO for in-situ CO₂ capture in steam gasification of biomass chars resulted in hydrogen content increase at 650 °C to the levels comparable with the ones reached at 800 °C without carbonation reaction. Also hydrogen and total gas yields increased in tests of lime-enhanced gasification.     

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.     

Modelling and experimental investigations on gasification of coarse sized coal char particle with steam

The steam gasification characteristics of coal char produced two sub-bituminous coals of different origin have been investigated through modelling and experiments. The gasification experiments are carried out in an Isothermal mass loss apparatus over the temperature range of 800–900 °C using a gas mixture of 65% steam and 35% N₂. A fully transient single particle gasification model, based on the random pore model, is developed incorporating reaction kinetics, heat and mass transport inside the porous char particle and the gas film. Stefan-Maxwell equation and Knudson diffusion are incorporated in the multi-component diffusion of species and pore diffusion. The model is validated with the experimental data of the present authors as well as that reported in the literature. The particle centre temperature is found to increase, then decrease and increase again to reach the reactor temperature finally, and the trend is more prominent for the larger particles. The pore opening phenomenon is more evident in SBC2 char, leading to a final char porosity of 0.65 vis-à-vis 0.52 in SBC1 and making it more reactive. Temporal evolution of contours of carbon conversion and concentration of other gaseous species like steam, H₂O, H₂, CO and CO₂ in the particle are computed to investigate the gasification process. A higher temperature is found to favour both the rate peak and the total production of H₂ for both the chars. The total H₂ production from SBC2 char is found to be 0.0189 mol and 0.0236 mol at 800 and 850 °C, while the same for SBC1 char is0.0232 mol and 0.0290 mol respectively. The reaction follows the shrinking core model at the outset, shifting to the shrinking reactive core model subsequently.     

Conversion of cassava rhizome using an in-situ catalytic drop tube reactor for fuel gas generation

The air-gasification of cassava rhizome mixed with Ni/α-Al₂O₃ catalyst in a drop tube reactor for production of fuel gas was carried out in this work. The conversion was performed at different temperatures from 873 to 1073 K, equivalence ratio (ER) of 0.2–0.6, and semi-continuous feeding of raw material for 30 min. Gas yields, cold gas efficiency (CGE) and lower heating value of fuel gas (LHV) were compared with non-catalytic cases. Generally, higher temperature and ER significantly improved the performance of cassava rhizome gasification. Similar for both of non-catalytic and catalytic cases, at optimum temperature of 1073 K and ER of 0.6, the maximum gas yields were closed to 80% while yields of char and tar were kept minimal at 4% and 11%, respectively. Addition of prepared catalysts resulted in greater CGE and LHV of 92% and 8.6 MJ/N m³, respectively, comparing to the non-catalytic case of 61% and 6.36 MJ/N m³, respectively. Moreover, the measured gas distribution data were comparable with the result obtained from thermodynamics conversion model based on minimization of Gibbs free energy of product gases using elemental composition of cassava rhizome (C_3.13H_5.2O_3.52N_0.03S_0.04.) constrained by mass and energy balances for the system. As a result, the gas product distribution and characteristics obtained from this experimental implied its suitability for heat and power applications.     

Gasification reactivity and synergistic effect of conventional and microwave pyrolysis derived algae chars in CO2 atmosphere

This research focuses on the isothermal and non-isothermal CO₂ gasification of an algal (Chlorella) char prepared via two different thermal processing systems, i.e. conventional and microwave-assisted pyrolysis. It was found that chars prepared via microwave irradiation showed higher CO₂ gasification reactivity than that of chars prepared via the conventional method. Meanwhile, the activation energy of microwave char was found to be 127.89 kJ/mol, which was 46.3 kJ/mol lower than that of conventional char, indicating improved reactivity of microwave char. The systematic characterisation of both conventional and microwave chars shows that the higher reactivity of microwave char could be attributed to its large BET surface area, low crystalline index and high active sites. In addition, it was found that microwave heating contributed to high reactivity of chars through generating large amount of primary char, the formation of hot spot and high specific surface area and pore volume. Results of co-gasification under isothermal conditions revealed the existence of greater synergistic effects between coal char and microwave algae char than those of coal char and conventional algae char. Furthermore, based on the relative Rs (average gasification rate), a novel index proposed to quantify the interactions in co-gasification process, Australian coal char/microwave assisted char blend experienced 10% higher interactions compared to Australian coal char/conventional assisted char blend.     

Impacts of char structure evolution and inherent alkali and alkaline earth metallic species catalysis on reactivity during the coal char gasification with CO2/H2O

In this work, we studied the effects of char structural evolution and alkali and alkaline earth metallic species (AAEMs) catalysis on the reactivity during the char gasification with CO₂, H₂O, and their mixture. The gasified chars with different carbon conversion levels were prepared, and their physicochemical structures were characterized via nitrogen adsorption and FT‐Raman techniques. The concentrations of AAEMs in different modes were obtained by the sequential chemical extraction method. The reactivities of the raw and gasified chars were analyzed by the thermogravimetric analysis. The gasification atmospheres had varied effects on the physicochemical structure of coal char. The gasified char obtained in the CO₂ atmosphere had a lower aromatic condensation degree compared with that obtained in the H₂O atmosphere, irrespective of the temperature. The impact of the atmospheres on the specific surface area of the char varied with the temperature because H₂O and CO₂ have different routes of development of pore structure with coal char. A large specific surface area facilitates the exposure and dispersion of more AAEMs on the surface of the channel, which is conducive to their contact with the gasification agent to play the catalytic role. Thus, the reactivity of the gasified char is well correlated with its specific surface area at different gasification temperatures. In the absence of AAEMs, the chemical structure of coal char becomes the dominant factor affecting the reactivity.     

Rapid pyrolysis and CO2 gasification of anthracite at high temperature

Anthracite could be burnt efficiently at high temperature utilizing oxy-coal technology. To clarify the effects of temperature and atmosphere on char porosity characteristics, char morphology, fuel-N conversion, and reducing products release, rapid pyrolysis and CO₂ gasification of anthracite was carried out in a high temperature entrained-flow reactor to simulate the condition in a pulverized coal furnace. Developed pore structure was formed in the gasification chars, which could be contributed to charCO₂ reaction at high temperatures. More mesopores were formed in internal carbon skeleton and retained against collapse and coalescent for gasification chars than pyrolysis chars. Compared with pyrolysis char, smoother and denser surface was observed in gasification char with the irregular bulges disappeared due to the destruction of external carbon skeleton. Char-N could be oxidized to NO in CO₂ atmosphere and then reduced to N₂ by (CN) on the char surface. Char-N release was greatly promoted due to gasification reaction along with poly-condensation at high temperature; and the preact release of char-N would result in a larger portion of NO_x reduction in the following reduction zone with the oxygen-staging combustion technology compared with that in air-staging combustion. Complementally, homogeneous reduction in NO_x emission would play a minor effect for anthracite in oxy-coal combustion because of the deficiency of CH₄ and HCN, especially at high temperature.     

Syngas production by gasification of aquatic biomass with CO2/O2 and simultaneous removal of H2S and COS using char obtained in the gasification

Applicability of gulfweed as feedstock for a biomass-to-liquid (BTL) process was studied for both production of gas with high syngas (CO + H₂) content via gasification of gulfweed and removal of gaseous impurities using char obtained in the gasification. Gulfweed as aqueous biomass was gasified with He/CO₂/O₂ using a downdraft fixed-bed gasifier at ambient pressure and 900 °C at equivalence ratios (ER) of 0.1–0.3. The syngas content increased while the conversion to gas on a carbon basis decreased with decreasing ER. At an ER of 0.1 and He/CO₂/O₂ = 0/85/15%, the syngas content was maximized at 67.6% and conversion to gas on a carbon basis was 94.2%. The behavior of the desulfurization using char obtained during the gasification process at ER = 0.1 and He/CO₂/O₂ = 0/85/15% was investigated using a downdraft fixed-bed reactor at 250–550 °C under 3 atmospheres (H₂S/N₂, COS/N₂, and a mixture of gases composed of CO, CO₂, H₂, N₂, CH₄, H₂S, COS, and steam). The char had a higher COS removal capacity at 350 °C than commercial activated carbon because (Ca,Mg)S crystals were formed during desulfurization. The char simultaneously removed H₂S and COS from the mixture of gases at 450 °C more efficiently than did activated carbon. These results support this novel BTL process consisting of gasification of gulfweed with CO₂/O₂ and dry gas cleaning using self-supplied bed material.     

Solar-driven steam-based gasification of sugarcane bagasse in a combined drop-tube and fixed-bed reactor – Thermodynamic,kinetic, and experimental analyses

Syngas production via steam-based thermochemical gasification of Brazilian sugarcane bagasse, using concentrated solar energy for process heat, was thermodynamically and experimentally investigated. Energy and exergy analyses revealed the potential benefits of solar-driven over conventional autothermal gasification that included superior quality of syngas composition and higher yield per unit of feedstock. Reaction rates for the gasification of fast pyrolyzed bagasse char were measured by thermogravimetric analysis and a rate law based on the oxygen exchange mechanism was formulated. In order to provide residence times long enough for adequate char conversion, a laboratory-scale entrained flow reactor that combines drop-tube and fixed-bed concepts was developed. Testing was performed in an electric furnace with the final aim to supply heat by concentrated solar radiation. Experimental runs at reactor temperatures of 1073–1573 K and a biomass feed rate of 0.48 g/min yielded high-quality syngas of molar ratios H₂/CO = 1.6 and CO₂/CO = 0.31, and with heating values of 15.3–16.9 MJ/kg, resulting in an upgrade factor (ratio of heating value of syngas produced over that of the feedstock) of 112%. Theoretical upgrade factors of up to 126%, along with the treatment of wet feedstock and elimination of the air separation unit, support the potential benefits of solar-driven over autothermal gasification.     

Co–gasification of coal/biomass blends in 50 kWe circulating fluidized bed gasifier

This paper reports gasification of coal/biomass blends in a pilot scale (50 kWe) air-blown circulating fluidized bed gasifier. Yardsticks for gasification performance are net yield, LHV and composition and tar content of producer gas, cold gas efficiency (CGE) and carbon conversion efficiency (CCE). Net LHV decreased with increasing equivalence ratio (ER) whereas CCE and CGE increased. Max gas yield (1.91 Nm³/kg) and least tar yield (5.61 g/kg of dry fuel) was obtained for coal biomass composition of 60:40 wt% at 800 °C. Catalytic effect of alkali and alkaline earth metals in biomass enhanced char and tar conversion for coal/biomass blend of 60:40 wt% at ER = 0.29, with CGE and CCE of 44% and 84%, respectively. Gasification of 60:40 wt% coal/biomass blend with dolomite (10 wt%, in-bed) gave higher gas yield (2.11 Nm³/kg) and H₂ content (12.63 vol%) of producer gas with reduced tar content (4.3 g/kg dry fuel).     

Evolution of pore structure and fractal characteristics of coal char during coal gasification

This study classifies the evolutionary properties of coal char pore structure which occur during coal gasification. CO₂ gasification of various coal samples was carried out in a fixed bed reactor. The resulting chars were analysed using N₂ isothermal adsorption/desorption and scanning electron microscopy (SEM), coupled with fractal theory. Analytical results indicate that the pore structure of coal char underwent micropore evolving, enlarging and overlapping, while more mesopores and macropores developed with continued gasification. The surface area of coal char increased to its maximum value when carbon conversion reached approximately 50%. Fractal calculation results showed that two types of fractal structures associated with the coal char surface and pore structure underwent stereome development and elapsing. However, the evolutionary properties were unique for different coal samples. High rank coal had a complex spatial structure with more micro-pores, whereas lower rank coal had a much flatter spatial structure.     

Direct production of hydrogen-enriched syngas by calcium-catalyzed steam gasification of Shengli lignite/chars: Structural evolution

Calcium has been proved to be efficient for the catalytic steam gasification of lignite. In this study, we studied the steam gasification of lignite with Ca(OH)₂ added by wet impregnation for to produce hydrogen. The effect of calcium on the microstructural evolution and char gasification behavior in the presence of steam were studied. The distribution of the gaseous products was examined by using fixed-bed micro reactor equipment for steam gasification. Partially gasified chars obtained at different temperatures (400, 500, 600, and 700 °C) in the gasification process were characterized by scanning electron microscopy coupled with energy dispersive spectroscopy, ¹³C nuclear magnetic resonance, Fourier-transform infrared spectroscopy, and Raman spectroscopy. The results suggested that a “Ca-carboxylate-like structure” was formed due to the addition of calcium to lignite. This Ca-carboxylate-like structure increased the thermal stability of the original carboxylic structure in lignite. As a result, the calcium-added coal retained more oxygen-containing structures, formed more defects, and possessed significantly lower aromatic structures due to the formed Ca-complexes during steam gasification. Therefore, it can be inferred that the Ca-complexes in the lignite char increased the gasification reactivity of char.     

炭化气氛对黑液煤浆及不同煤种气化反应特性的影响

煤气化前阶段的炭化气氛(温度、时间)影响到煤焦的气化反应特性.采用不同的炭化温度和炭化时间制备了黑液水煤浆、普通水煤浆以及其他5种煤的焦样,得到了各种煤焦气化反应的碳转化率;同时,通过扫描电子显微镜分析手段鉴别焦炭表面孔隙分布情况.试验结果表明,相同炭化气氛下得到的7种不同煤焦中,黄陵煤焦的气化活性最高,说明煤化程度越高反应性越低;由于黑液中有机物和无机物钠盐的影响,黑液水煤浆焦的气化特性高于普通水煤浆焦和新汶煤焦.煤焦的气化反应性,不仅与煤阶有关,还和煤焦中含氧官能团和无机化合物的含量有关,同时煤浆中外在添加的无机物组分也影响到煤焦的气化活性.     

Improving the performance of fluidized bed biomass/waste gasifiers for distributed electricity: A new three-stage gasification system

Methods to increase the conversion of char and tar in fluidized bed gasifiers (FBG) are discussed, with the focus on small to medium-size biomass/waste gasifiers for power production (from 0.5 to 10 MW_e). Optimization of such systems aims at (i) maximizing energy utilization of the fuel (maximizing char conversion), (ii) minimizing secondary treatment of the gas (by avoiding complex tar cleaning), and (iii) application in small biomass-to-electricity gasification plants. The efficiency of various measures to increase tar and char conversion within a gasification reactor (primary methods) is discussed. The optimization of FBG by using in-bed catalysts, by addition of steam and enriched air as gasification agent, and by secondary-air injection, although improving the process, is shown to be insufficient to attain the gas purity required for burning the gas in an engine to produce electricity. Staged gasification is identified as the only method capable of reaching the targets mentioned above with reasonable simplicity and cost, so it is ideal for power production. A promising new stage gasification process is presented. It is based on three stages: FB devolatilization, non-catalytic air/steam reforming of the gas coming from the devolatilizer, and chemical filtering of the gas and gasification of the char in a moving bed supplied with the char generated in the devolatilizer. Design considerations and comparison with one-stage FBG are discussed.