Rice Straw Gasification Research Articles

Parametric study of pyrolysis and steam gasification of rice straw in presence of K2CO3

A parametric study of pyrolysis and steam gasification of rice straw (RS) was performed to investigate the effect of the presence of K2CO3 on the behavior of gas evolution, gas component distribution, pyrolysis/gasification reactivity, the quality and volume of synthetic gas. During pyrolysis, with the increase in K2CO3 content in RS (i) the instantaneous CO2 concentration was increased while CO concentration was relatively stable; (ii) the yield of CO2 and H2 increased on the cost of CH4. During steam gasification of RS, with the increase in K2CO3 content in RS (i) the instantaneous concentration of CO2 and H2 increased while instantaneous concentration of CO and CH4 decreased; (ii) the yield of CO2 and H2 production and total yield increased; and (iii) yield of CO and CH4 production followed the order: 9% K2CO3 RS<6% K2CO3 RS<raw RS<3% K2CO3 RS<water-leached RS. Water-leached RS showed the highest pyrolysis reactivity, while stream gasification reactivity was proportional to K2CO3 content in RS. The results of this study reveal that the presence of K2CO3 during pyrolysis and steam gasification of RS effectively improves production of H2 rich gas.

Synthesis of Bio‐Dimethyl Ether Based on Carbon Dioxide‐Enhanced Gasification of Biomass: Process Simulation Using Aspen Plus

AbstractProcess simulation for a single‐step synthesis of dimethyl ether (DME) based on the CO2‐enhanced gasification of rice straw was conducted using Aspen Plus. The process consists of a gasification unit, a heat recovery unit, a gas purification unit, a single‐step DME synthesis unit, and a DME separation unit. In the simulation, highly pure DME was produced by the control of CO2 concentration in syngas to a very low level prior to synthesis. A gasification system efficiency of 36.7 % and CO2 emission of 1.31 kg kgDME−1 were achieved. This bio‐DME production based on the CO2‐enhanced gasification of biomass was cost‐effective as it required 19.6 % less biomass than that of DME production based on conventional biomass gasification. The performance and environmental benefits of the proposed process could be further improved by the utilization of unreacted gases and the managing of CO2 generated by the incorporation of a polygeneration concept or carbon storage.

Energy, exergy and environmental analyses of conventional, steam and CO2-enhanced rice straw gasification

In this study, air, steam and CO2-enhanced gasification of rice straw was simulated using Aspen Plus™ and compared in terms of their energy, exergy and environmental impacts. It was found that the addition of CO2 had less impact on syngas yield compared with gasification temperature. At lower CO2/Biomass mass ratios (<0.25), CO2-enhanced gasification showed a lower GSE (gasification system efficiency) than conventional gasification, which was below 22.1%. However at higher CO2/Biomass ratios, CO2-enhanced gasification demonstrated higher GSE than conventional gasification. The GSE of CO2-enhanced gasification continued to increase to 58.8% when CO2/Biomass ratio was raised to 0.87. It was also found that chemical exergy was 2.05–4.85 times higher than physical exergy. The syngas exergy increased with CO2 addition, which was mainly due to the increase in physical exergy. The maximum exergy efficiency occurred in the temperature range of 800 °C–900 °C. For CO2-enhanced gasification, exergy efficiency was found to be more sensitive to temperature than CO2/Biomass ratios. In addition, the preliminary environmental analysis showed that CO2-enhanced gasification resulted in significant environmental benefits compared with steam gasification. However novel assessment methodologies are still needed to better evaluate the advantages of CO2 utilization.

Analysis of synthesis gas production with a flexible H2/CO ratio from rice straw gasification

A parametric analysis of two gasification processes (i.e., steam–air and steam–CO2) of rice straw feedstock is performed using a thermodynamic model-based approach developed in Aspen plus. The possibility of one step H2/CO ratio adjustment in a gasifier at thermal self-sufficient condition is observed. The effects of changes in the ratio of gasifying agent on the syngas yield, H2/CO ratio, total energy consumption and cold gas efficiency of the system at different gasifying temperatures in the range of 500–1000°C are investigated. The syngas yield of both gasification processes significantly increases at low temperature until it reaches a maximum value and is stable at temperatures higher than 700°C. However, the steam–CO2 system offers higher syngas productivity and a lower H2/CO ratio. The total energy consumption of the system is also investigated, and the steam–air system consumes less energy and the thermal self-sufficient conditions are revealed, whereas the steam–CO2 system shows the inverse effect. Based on the thermal self-sufficient condition for syngas production, the operating conditions offering the highest syngas yield of 42% of with Fischer–Tropsch specification can be obtained at a gasifying temperature of 700°C and steam- and air-to-biomass ratios of 0.57 and 1.17, respectively. At these conditions, the cold gas efficiency of 38% is achieved.

Improving the Synthesis Gas Quality in Catalytic Gasification of Rice Straw by an Integrated Hot-Gas Cleaning System

This research investigates an enhanced removal rate of tar and trace pollutants (e.g. hydrogen chloride and hydrogen sulfide, H2S) in the gasification of rice straw, using an integrated in situ tar reduction and hot-gas cleaning technique. The gasification temperature was set at 900°C and equilibrium ratio (ER) was 0.30 in the gasifier. In the in situ tar reduction method, the catalyst, dolomite with an amended ratio of 0–15% was introduced to the gasifier. The integrated hot-gas cleaning system applied a multi-packed tower to remove the tar, sulfur and/or chlorine byproduct in syngas at 250°C. The packed materials composed of zeolite, calcined dolomite and activated carbon. The experimental results indicated that the tar concentration of syngas was approximately 20 g/kg. However, in catalytic gasification with 5% dolomite addition, the tar concentration reduced to 17 g/kg. The tar reduction efficiency was approximately 15% by an in situ dolomite addition. When applying the integrated hot-gas cleanup system, the tar was virtually eliminated. The total tar elimination rate was almost 100% and the cleaned syngas could be applied in other energy utilization equipment. On the other hand, the H2S and HCl concentration were 101 ppmv and 991 ppmv, respectively. After the integrated syngas cleaning system, the H2S and HCl were decreased to 7.9 ppmv and 410 ppmv with a removal efficiency of 92.1% and 58.6%, respectively. It can be concluded that combining the in situ method with the integrated syngas cleaning system can effectively reduce the amount of byproduct and enhance the syngas quality in the gasification of rice straw.

CO2–steam mixture for direct and indirect gasification of rice straw in a downdraft gasifier: Laboratory-scale experiments and performance prediction

This paper explored the feasibility of CO2 as alternative gasifying agent of steam to obtain higher thermal efficiency in biomass gasification. The effect of the gasifying agent on gas evolution and thermal efficiency was examined by using a lab scale downdraft gasifier. The results were also compared with the output of pyrolysis with N2. The reaction atmosphere in indirect and direct gasification was simulated by carrying out the experiments without and with O2 presence. The reaction conditions were varied in the temperature range from 750°C to 950°C by changing the CO2 molar fraction in gasifying agent to the ratio of 0, 30 and 60vol.% in balance with steam. 40vol.% of N2 fraction was kept during O2 free experiments, while 31.7vol.% of N2 and 8.3vol.% O2 were kept during the experiments with the presence of O2. At all examined condition, gasification yielded more combustible gas than pyrolysis. Furthermore, high CO2 fraction in gasifying agent generally resulted in low H2 yield and high CO yield. These substitutions mostly lowered the energy yield of the producer gas, but in the other hand also reduced the preheating energy of gasifying agent. Thus, optimizations of these changes were investigated for gaining highest thermal efficiency of the gasification process. Highest thermal efficiency of the process without O2 was 52% under N2 (40vol.%)–CO2 (60vol.%) atmosphere at the temperature of 850°C. For the process with O2, where the part of gasifying agent preheating energy supplied by the biomass partial combustion, the highest thermal efficiency was 60% under the CO2 (60vol.%)–O2 (8.3vol.%)–N2 (31.7vol.%) atmosphere at the temperature of 950°C. CO2 utilization as a gasifying agent potentially increases the thermal efficiency of biomass conversion process compared with pyrolysis or conventional indirect and direct gasification, i.e. pure-steam gasification and O2–steam gasification.

Gasification of rice straw in an updraft gasifier using water purification sludge containing Fe/Mn as a catalyst

This study investigated the feasibility of gasification of rice straw using an Fe/Mn sludge as a catalyst. The Fe/Mn sludge contained iron and manganese compounds produced from a water purification plant. The gasification temperature and equivalent ratio (ER) was set at 900 °C and 0.30, respectively, with an amended catalyst ratio of 0%–15%. Experimental results indicated that the combustible gas production was increased from 0.61 m3/kg to 0.72 m3/kg with the Fe/Mn sludge addition. The lower heating value (LHV) of combustible gas and energy density (ED) were also increased with an increase in Fe/Mn sludge addition. The LHV and ED increased from 14.76 MJ/Nm3 to 15.82 MJ/Nm3 and from 1.37 MJ/MJ to 1.47 MJ/MJ, respectively. In conclusion, the catalytic gasification of rice straw was more efficient on an energy yield basis with the Fe/Mn sludge addition. The Fe/Mn sludge used in this research has been developed as a potential catalyst for the application of rice straw gasification.

L’ostéosynthèse par plaque Lambda des fractures de l’extrémité distale de l’humérus. Résultats d’une série continue de 75 fractures

The feasibility and operation performance of the gasification of rice straw in an atmospheric fluidized-bed gasifier was studied. The gasification was carried out between 700 and 850 °C. The stoichiometric air–fuel ratio (A/F) for rice straw was 4.28 and air supplied was 7–25% of that necessary for stoichiometric combustion. Mass and power balances, tar concentration, produced gas composition, gas phase ammonia, chloride and potassium concentrations, agglomeration tendencies and gas efficiencies were assessed. Agglomeration was avoided by replacing the normal alumina-silicate bed by a mixture of alumina-silicate sand and MgO. It was shown that it is possible to produce high quality syngas from the gasification of rice straw. Under the experimental conditions used, the higher heating value (HHV) of the produced gas reached 5.1 MJ Nm−3, the hot gas efficiency 61% and the cold gas efficiency 52%. The obtained results prove that rice straw may be used as fuel for close-coupled boiler-gasifier systems.

Hydrogen Production from Rice Straw Gasification over Modified-Limestone Catalyst

Malaysian limestone modified with and additions of transition metal promoters (Ni, Fe, and Co) were used for gasification of biomass. The effects of selected metal oxide loading and the addition of sodium carbonate, Na2CO3 as additive and its influence on limestone catalytic activity during gasification for hydrogen conversion were investigated. The catalysts were synthesized through deposition-precipitation (DP) method and characterized by using X-ray diffraction (XRD), Brunauer-Emmet-Teller (BET) surface area, thermal gravimetric analysis (TGA) and scanning electron microscopy (SEM). Temperature programmed gasification (TPG) was conducted to investigated the gasification reaction of rice straw and the product gases were analysed using online mass spectrometer. The gasification process was carried out in partial oxygen (5% O2/Helium) environment heating from 50 to 900 °C with mass ratio biomass to catalyst of 2:1. From the results, Ni promoter was found to give the highest H2 conversion followed by Co and Fe. The calcined limestone had shown to act as a catalyst and CO2 sorbent thus enhancing the production of hydrogen. Moreover, additional of Na2CO3 during gasification process had shown a further increment of H2 production.

Gasification of rice straw in a fluidized-bed gasifier for syngas application in close-coupled boiler-gasifier systems

The feasibility and operation performance of the gasification of rice straw in an atmospheric fluidized-bed gasifier was studied. The gasification was carried out between 700 and 850°C. The stoichiometric air–fuel ratio (A/F) for rice straw was 4.28 and air supplied was 7–25% of that necessary for stoichiometric combustion. Mass and power balances, tar concentration, produced gas composition, gas phase ammonia, chloride and potassium concentrations, agglomeration tendencies and gas efficiencies were assessed. Agglomeration was avoided by replacing the normal alumina-silicate bed by a mixture of alumina-silicate sand and MgO. It was shown that it is possible to produce high quality syngas from the gasification of rice straw. Under the experimental conditions used, the higher heating value (HHV) of the produced gas reached 5.1MJNm−3, the hot gas efficiency 61% and the cold gas efficiency 52%. The obtained results prove that rice straw may be used as fuel for close-coupled boiler-gasifier systems.

The effect of steam on pyrolysis and char reactions behavior during rice straw gasification

Steam gasification of biomass can generate hydrogen-rich, medium heating value gas. We investigated pyrolysis and char reaction behavior during biomass gasification in detail to clarify the effect of steam presence. Rice straw was gasified in a laboratory scale, batch-type gasification reactor. Time-series data for the yields and compositions of gas, tar and char were examined under inert and steam atmosphere at the temperature range of 873–1173 K. Obtained experimental results were categorized into those of pyrolysis stage and char reaction stage. At the pyrolysis stage, low H 2, CO and aromatic tar yields were observed under steam atmosphere while total tar yield increased by steam. This result can be interpreted as the dominant, but incomplete steam reforming reactions of primary tar under steam atmosphere. During the char reaction stage, only H 2 and CO 2 were detected, which were originated from carbonization of char and char gasification with steam (C + H 2O→CO + H 2). It implies the catalytic effect of char on the water–gas shift reaction. Acceleration of char carbonization by steam was implied by faster hydrogen loss from solid residue.

Simulation of Rice Straw Oxygen-Steam Gasification in an Entrained-Flow Gasifier Using ASPEN PLUS

Biomass oxygen-steam gasification associated with synthesis technology known as indirect biomass liquefaction is regarded as one of the most promising technologies of biomass utilization. In this paper, a comprehensive gasification model was developed for the simulation of rice straw oxygen-steam gasification using ASPEN PLUS. The gasification process was divided into two parts: pyrolysis and gasification. The RYield module was used to simulate the pyrolysis process with an external FORTURN program to calculate the pyrolysis products while the gasification process was calculated by the RCSTR module. With the help of the model, the gasification of rice straw was simulated under different residence time, different temperature and different amount of steam. The results showed that the proper residence time and temperature is 1.5s and 1300°C, respectively. The optimum amount of steam is steam/biomass=0.12 while the addition of oxygen is oxygen/biomass=0.2.

No.56 稲わらの水蒸気ガス化におけるニッケル触媒の影響(重質油・バイオマス・コプロセッシング(2))

No.56 稲わらの水蒸気ガス化におけるニッケル触媒の影響(重質油・バイオマス・コプロセッシング(2))

Gasification of different biomasses in a dual-bed gasifier system combined with novel catalysts with high energy efficiency

Syngas has been produced from the gasification of various biomasses such as jute stick, bagasse, rice straw, and saw dust of cedar wood using a dual-bed gasifier combined with a novel catalyst. The gasification conditions were 150 mg/min of biomass feeding, ER=0.25, catalyst (3 g) at temperature range of 823–923 K. The carbon conversion to gas and yield of useful gases such as CO, H2, and CH4 were dependent on the properties of biomass. In terms of the formation rate of useful gases, the biomass quality was in the order of cedar wood > jute stick > bagasse > rice straw. Although the rice straw gasification is comparatively difficult in a single-bed gasifier due to its high ash content (22.6%), it becomes possible in a dual-bed reactor system. The dual-bed gasifier using Rh/CeO2/SiO2 catalyst that has been developed gave higher conversion to gas and higher yield of CO+H2+CH4 than did the single-bed gasifier. In the case of cedar wood gasification, although a small amount of coke was formed on the catalyst surface, the tar was not formed at all even at 823 K. However, in the case of other biomass, especially for rice straw, a significant amount of coke on the catalyst surface and tar was formed even at the high temperature (923 K).

Syngas production by biomass gasification using Rh/CeO 2/SiO 2 catalysts and fluidized bed reactor

We have been developed novel catalysts for gasification of biomass with much higher energy efficiency than conventional methods (non-catalyst, dolomite, commercial steam reforming Ni catalyst). From the result of the gasification of cellulose over novel Rh/CeO 2/SiO 2 catalysts, it is found that the gasification process consists of the reforming of tar and the combustion of solid carbon. We also tested novel Rh/CeO 2/SiO 2 in the gasification with air, pyrogasification, and steam reforming of cedar wood. As a result, Rh/CeO 2/SiO 2 gave higher yield of syngas than the conventional steam reforming Ni catalyst. Furthermore, we compared the performance between single and dual bed reactors. Single bed reactor was effective in the gasification of cedar, however, it was not suitable for the gasification of rice straw since a rapid deactivation was observed. Gasification of rice straw, jute stick, baggase using the fluidized dual-bed reactor and Rh/CeO 2/SiO 2 was also investigated. Especially, the catalyst stability in the gasification of rice straw clearly was enhanced by using the fluidized dual bed reactor.

Gasification of different biomasses in a dual-bed gasifier system combined with novel catalysts with high energy efficiency

Syngas has been produced from the gasification of various biomasses such as jute stick, bagasse, rice straw, and saw dust of cedar wood using a dual-bed gasifier combined with a novel catalyst. The gasification conditions were 150mg/min of biomass feeding, ER=0.25, catalyst (3g) at temperature range of 823–923K. The carbon conversion to gas and yield of useful gases such as CO, H2, and CH4 were dependent on the properties of biomass. In terms of the formation rate of useful gases, the biomass quality was in the order of cedar wood > jute stick > bagasse > rice straw. Although the rice straw gasification is comparatively difficult in a single-bed gasifier due to its high ash content (22.6%), it becomes possible in a dual-bed reactor system. The dual-bed gasifier using Rh/CeO2/SiO2 catalyst that has been developed gave higher conversion to gas and higher yield of CO+H2+CH4 than did the single-bed gasifier. In the case of cedar wood gasification, although a small amount of coke was formed on the catalyst surface, the tar was not formed at all even at 823K. However, in the case of other biomass, especially for rice straw, a significant amount of coke on the catalyst surface and tar was formed even at the high temperature (923K).

The effect of Na2CO3 on the catalytic gasification of rice straw over nickel catalysts supported on kieselguhr

Rice straw was catalytically gasified over nickel catalysts supported on kieselguhr. Ni catalyst activated the gasification step from the formed oil. The effect of sodium carbonate on the formation of carbonized solid, oil and gas composition was also investigated. With the addition of sodium carbonate, the gas yield was largely increased and the formation of oil through liquefaction also increased. A reaction pathway on the gasification of rice straw was discussed.

97/01029 Calcined dolomite, magnesite, and calcite for cleaning hot gas from a fluidized bed biomass gasifier with steam: life and usefulness

We have been developed novel catalysts for gasification of biomass with much higher energy efficiency than conventional methods (non-catalyst, dolomite, commercial steam reforming Ni catalyst). From the result of the gasification of cellulose over novel Rh/CeO2/SiO2 catalysts, it is found that the gasification process consists of the reforming of tar and the combustion of solid carbon. We also tested novel Rh/CeO2/SiO2 in the gasification with air, pyrogasification, and steam reforming of cedar wood. As a result, Rh/CeO2/SiO2 gave higher yield of syngas than the conventional steam reforming Ni catalyst. Furthermore, we compared the performance between single and dual bed reactors. Single bed reactor was effective in the gasification of cedar, however, it was not suitable for the gasification of rice straw since a rapid deactivation was observed. Gasification of rice straw, jute stick, baggase using the fluidized dual-bed reactor and Rh/CeO2/SiO2 was also investigated. Especially, the catalyst stability in the gasification of rice straw clearly was enhanced by using the fluidized dual bed reactor.