Rice Straw Gasification Research Articles

Thermodynamic Model for Hydrogen Production from Rice Straw Supercritical Water Gasification.

Supercritical water gasification (SCWG) technology is highly promising for its ability to cleanly and efficiently convert biomass to hydrogen. This paper developed a model for the gasification of rice straw in supercritical water (SCW) to predict the direction and limit of the reaction based on the Gibbs free energy minimization principle. The equilibrium distribution of rice straw gasification products was analyzed under a wide range of parameters including temperatures of 400-1200 °C, pressures of 20-50 MPa, and rice straw concentrations of 5-40 wt%. Coke may not be produced due to the excellent properties of supercritical water under thermodynamic constraints. Higher temperatures, lower pressures, and biomass concentrations facilitated the movement of the chemical equilibrium towards hydrogen production. The hydrogen yield was 47.17 mol/kg at a temperature of 650 °C, a pressure of 25 MPa, and a rice straw concentration of 5 wt%. Meanwhile, there is an absorptive process in the rice straw SCWG process for high-calorific value hydrogen production. Energy self-sufficiency of the SCWG process can be maintained by adding small amounts of oxygen (ER < 0.2). This work would be of great value in guiding rice straw SCWG experiments.

Preliminary characterization of residual char after gasification of rice straw

Preliminary characterization of residual char after gasification of rice straw

Biomass gasification technology for a distinct renewable electricity/heat production scheme; Developed regression models based on machine learning algorithms for power/hot water/efficiency/emission data analysis

Rice straw is a promising feedstock for gasification, and using it in combined heat and power systems allows us to generate renewable electricity and heat while reducing reliance on fossil fuels and combatting climate change. As the demand for clean energy grows, machine learning will become even more crucial for managing our energy systems. A combined heat and power system was integrated based on rice straw gasification and the applications of linear and quadratic regression machine learning algorithms were evaluated using the residual analysis and the analysis of variance. The results show that quadratic models outperform linear models in all cases. Specifically, for efficiency modeling, the quadratic model scores 98.2 %, surpassing the linear model's 89.6 %. In emission modeling, the quadratic model outperforms the linear model with an R-sq score of 97 % versus 88.1 %. The results show that equivalence ratio of gasifier has the greatest impact, accounting for 65 % of the observed variation on emission linear model. In the quadratic emission model, linear factors contribute 58 % and quadratic factors contribute 42 %. Among the linear factors, pressure ratio has a significant influence with a contribution rate of 89 %. In terms of quadratic factors, pressure ratio has the highest influence, with a remarkable contribution rate of 92 %. This research emphasizes the significance of enhancing the precision of regression machine learning algorithms by conducting residual analysis and variance analysis.

Hydrogen sulfide removal from simulated synthesis gas using a hot gas cleaning system

This study investigated the removal, adsorption, and regeneration performances of simulated H2S produced from rice straw gasification in a hot gas cleaning system with combination of three types of adsorbents including zeolite, calcined dolomite and activated carbon. These experiments were conducted at 250 ℃ hot gas cleaning system and simulated synthesis gas containing hydrogen sulfide (H2S) concentration at 200 ppm. The experimental results indicated that the tested H2S removal efficiency and adsorbed capacity were observed to be adsorbed in decreasing order: activated carbon > calcined dolomite > zeolite. The adsorption capacities of zeolite, calcined dolomite, and activated carbon are 2.22, 3.16, 5.88 mg S/g adsorbents, respectively. In this research, the calcined dolomite shows poor adsorption-regeneration ability due to its deactivation by H2S. However, the tested zeolite and activated carbon could be fully regenerated at 350 °C with a stable sulfur adsorption capacity during four adsorption-regeneration cycles. These results gained from this study could significantly support researchers obtaining more information about the synthesis gas contaminants removal during hot gas temperature operation process.

Study on chemical kinetics and catalytic cracking of tar from gasification of rice straw using various catalysts

Study on chemical kinetics and catalytic cracking of tar from gasification of rice straw using various catalysts

Mitigating bed agglomeration in a fluidized bed gasifier operating on rice straw

Fluidized bed gasifier is a promising technology with respect to converting biomass to useful energy. Bed agglomeration is an operational challenge that arises during fluidized bed gasification with rice straw as raw materials. Rice straw contains high amounts of potassium and other components that may lower the melting point of ash, causing bed agglomeration. Using alternative bed materials such as alumina, in the place of silica, can mitigate this problem. In Thailand, rice straw is an agricultural by-product of the rice milling processes, produced in large quantities every year. Usually, rice straw management comprises open field burning, which releases greenhouse gases, particulate matter, and other pollutants. In this paper, the behaviors of bed agglomeration and defluidization were investigated during the fluidized bed gasification of rice straw, using silica and alumina as bed materials. The effect of the percentage ratio of silica and alumina (0:100; 25:75; 50:50; 75:25; 100:0) was examined. The operating parameters were as follows: rice straw particle size of 425–850μm, reaction temperature of 700–900 °C, and equivalence ratios (ER) of 0.2 and 0.4. The results showed that the percentage ratio of silica and alumina, 0:100 at 700 °C, had extended the defluidization time of 60 min. The effect of equivalence ratio on bed agglomeration was found to be apparently heightened at a high temperature. The result of SEM/EDX analysis showed that the major elements at the linkage point of the agglomerated particle were Si, K, and Ca, with regard to any proportion of the alumina bed and temperature. In conclusion, low temperature agglomerate formation can be explained by a K2O-CaO-Si2O phase diagram. The results from this investigation can be applied to biomass-fluidized bed gasification, where bed agglomeration entails a plant shutdown and is expensive in terms of maintenance.

Hydrogen production enhancement using hot gas cleaning system combined with prepared Ni-based catalyst in biomass gasification

This paper investigates the hot gas temperature effect on enhancing hydrogen generation and minimizing tar yield using zeolite and prepared Ni-based catalysts in rice straw gasification. Results obtained from this work have shown that increasing hot gas temperature and applying catalysts can enhance energy yield efficiency. When zeolite catalyst and hot gas temperature were adjusted from 250 °C to 400 °C, H2 and CO increased slightly from 7.31% to 14.57%–8.03% and 17.34%, respectively. The tar removal efficiency varies in the 70%–90% range. When the zeolite was replaced with prepared Ni-based catalysts and hot gas cleaning (HGC) operated at 250 °C, H2 contents were significantly increased from 6.63% to 12.24% resulting in decreasing the hydrocarbon (tar), and methane content. This implied that NiO could promote the water-gas shift reaction and CH4 reforming reaction. Under other conditions in which the hot gas temperature was 400 °C, deactivated effects on prepared Ni-based catalyst were observed for inhibiting syngas and tar reduction in the HGC system. The prepared Ni-based catalyst worked at 250 °C demonstrate higher stability, catalyst activity, and less coke decomposition in dry reforming. In summary, the optimum catalytic performance in syngas production and tar elimination was achieved when the catalytic temperature was 250 °C in the presence of prepared Ni-based catalysts, producing 5.92 MJ/kg of lower heating value (LHV) and 73.9% tar removal efficiency.

Quantitative analysis of mass and energy flow in rice straw gasification based on mass and carbon balance

There have been some pilot-scale trials of the fluidized bed and its derivatives for rice and wheat straw gasification in China. Before the industrial promotion, the quantitative data is imperative in preliminary engineering and optimization. A series of experiments were performed on a bench-scale fluidized bed gasifier to obtain data in process in different heat exchange situations. The uncertainty was evaluated and the balance of carbon and mass was performed to verify the quantitative data. Based on the experimental results, the mass and energy flows were established and illustrated in Sankey diagrams. The results show that, as temperature improves from 650 °C to 800 °C, the energy proportion of gas climbs from 27.2 to 64%. When the equivalence ratio decreases, although the calorific value of gas increases from 2.7 to 4.2 MJ/Nm3, the energy proportion of gas does not change much because the gas yield decreases. Finally, the heat exchange, temperature and ER were coupled by interpolation and illustrated in a contour map.

The migration, transformation and control of trace metals during the gasification of rice straw

This research investigates the trace metals speciation, partitioning and removal in rice straw gasification equipped with an integrated hot gas cleaning (HGC) system. The experiments were conducted by fluidized bed gasifier and controlled at 800 °C with equivalence ratio (ER) varied between 0.2 and 0.4. The experimental results indicated that the concerned trace metals Zn, Cr, Cd, and Pb partitioning in the gas phase were increased significantly with an increase in ER. This is because the exothermic reaction could enhance the trace metals reacted with chlorine and/or sulfur as well as correspondingly formed highly volatile metals compounds. However, other tested metals Cu, Na, K, Ca, Mg partitioning was obviously decreased in the gas phase with ER increasing. These tested metals tend to form oxides speciation leading the variation in their partitioning characteristics. The XRD identification and thermodynamic equilibrium simulation results were also confirmed the tested metals speciation and partitioning characteristics. The dominant gaseous species produced from rice straw gasification, such as KCl(g), NaCl(g), KO(g), K2O(g), ZnCl2(g), CrO2Cl2(g), CuCl2(g), PbCl2(g), PbO(g), and Cd(g), were predicted by thermodynamic equilibrium model. The tested metals removal by adsorbents of hot gas cleaning system was found to be adsorbed in decreasing order as: K > Cr > Ca > Pb > Mg > Cd > Na > Zn > Cu. Activated carbon was used in hot gas cleaning system and showed a good performance for adsorbing tested metals, especially for Pb, Cd, Cr, Ca, K, and Mg. In summary, HGC system is proposed as an effective way for improving the syngas quality and reducing trace contaminants emission in rice straw gasification.

Subcritical water gasification of lignocellulosic wastes for hydrogen production with Co modified Ni/Al2O3 catalysts

Nickel-based catalysts with different supports and cobalt loadings were synthesized for hydrothermal gasification of cellulose at 350 °C. The activity of Ni catalysts was found in the order of Al2O3 > spent bleaching clay ash > SiO2 with H2 yield of 80.6%, 69.0% and 57.0%. When 6 wt. % Co was added, 10Ni-6Co/Al2O3 showed the highest H2 yield of 88.4% i.e., 1.44 times that without Co addition. Catalysts were characterized by NH3-TPD, TPR, XRD, BET and XPS, showing that Ni-Co alloy formation promoted H2 production. Single-factor experiments were conducted to study variables in the presence of 10Ni-6Co/Al2O3 with the selected conditions of 0.5 g biomass and 20 min at 350 °C (achieving 94.9% H2 yield from cellulose) for gasification of rice straw, peanut shell and cotton straw with the increase in H2 yield by 51.4, 76.0 and 67.8 times. Ni-Co/Al2O3 catalysts enhanced hydrothermal gasification of actual agricultural residues.

Effects of modified bauxite on the pyrolysis and gasification of rice straw

Effects of modified bauxite on the pyrolysis and gasification of rice straw

Chemical looping gasification of biomass with Fe2O3/CaO as the oxygen carrier for hydrogen-enriched syngas production

Biomass-derived chemical looping gasification is a novel technology to convert biomass into renewable hydrogen-enriched syngas. In this study, bimetallic Fe-Ca oxides were synthesized to be used as oxygen carriers to promote the hydrogen production from the chemical looping gasification of rice straw. The effects of Fe/Ca ratio, temperature together with the cyclic performance of oxygen carrier were studies in terms of produced syngas distribution, solid structure evolution and the durability of oxygen carrier. Results found that two types of calcium ferrites (Ca2Fe2O5 and CaFe2O4) were formed with different Fe/Ca ratios, and Fe and Ca were uniformly distributed within oxygen carriers by wet impregnation method. Compared with pyrolysis or steam gasification, the hydrogen production was largely promoted during the steam chemical looping gasification process due to the iron re-oxidation by steam. When the ratio of Fe:Ca was1:1, the formed oxygen carrier (Ca2Fe2O5) produced the highest hydrogen yield (23.07 mmol/g biomass) at 800 °C, which benefited from one step reduction and oxidation properties of Ca2Fe2O5. A temperature of no less than 800 °C was needed for the completed redox of Ca2Fe2O5 during chemical looping gasification with steam. The cyclic stability test for Ca2Fe2O5 showed that the continuously accumulated Si from biomass ash would destroy the bimetallic Fe-Ca structure to generate CaSiO3 and Fe2O3 after 3 times of cycle, and this led to the decreased hydrogen production during chemical looping gasification cycle. The great hydrogen selectivity of Fe:Ca = 1:1 (Ca2Fe2O5) makes it a suitable candidate of oxygen carrier, but the cyclic durability should be enhanced to enable a better application for chemical looping gasification conversion of biomass.

Experimental Study on Catalytic Biomass Gasification in a Bubbling Fluidized Bed

AbstractA bubbling fluidized‐bed gasification system was selected for catalytic steam gasification of rice straw with four Ni‐based catalysts, i.e., Ni/Al2O3, Ni/CeO2, Ni/MnO2, and Ni/MgO. The effect of temperature, steam/biomass ratio (S/B), and catalyst/biomass ratio (C/B) on the gas composition, char conversion, and hydrogen yield was evaluated. It was found that higher temperature and S/B promote hydrogen production and char conversion. The results also demonstrated that the catalytic activity of Ni/Al2O3 under different S/B values is better than those of the other catalysts. Regarding the catalyst activity, all four catalysts exhibited good performance in terms of tar removal and carbon conversion. However, the performance of Ni/Al2O3 was superior to that of the other three catalysts.

A Prototype Downdraft Gasifier Design with Mechanical Stirrer for Rice Straw Gasification and Comparative Performance Evaluation for Two Different Airflow Paths

In this research, a prototype downdraft throatless gasifier was designed with a mechanical stirrer. The gasifier was designed for gasification of rice straw pellets. The diameter of the reactor was 350 mm and a nominal value for the heat power of biomass input was 70 kW. Rice straws which were collected from Thrace Region of Turkey gasified for determination of the designed gasifier performance in Namik Kemal University Biosystem Engineering Laboratories. The effects of airflow path and stirring process on the gasification efficiency during the gasification process were investigated. Temperatures and airflow rates observed and adjusted by controlling the air flow rate in the automation system constantly. Pellets were gasified using two different airflow paths with the same equivalence ratio of 0.2 and these were compared. Air inlet from the top showed better results than air inlet from tuyeres. For the air inlet from the top, the higher heating value of producer gas was determined as 5.047 MJ Nm-3 and cold gas efficiency was calculated as 65.4%. H2/CO ratio was found as 1.385 which was higher than the air inlet from tuyeres.

Experimental Investigation on Rice Straw Gasification in a Cyclone Gasifier

A cyclone gasifier is an effective technology for the gasification of low-density biomass containing a high ash content. The ash removal performance was improved in the gasifier due to being similar to a cyclone dust collector. The cyclone reactor is relatively simple, easy to use, and has low construction costs compared with a traditional fluidized bed gasifier. In this study, the air gasification characteristics of rice straw were investigated in a cyclone gasifier. The results showed that by increasing the equivalence ratio (ER), the gasifier temperature also increased. This, in turn, led to a higher gas quality (higher heating value (HHV) and lower tar content) and enhanced the gasification performance (gas yield, carbon conversion efficiency, cold gas efficiency, and hot gas efficiency). A high ER reduced the amount of the combustible gas component (CO and H2) and caused the HHV of the producer gas to decrease. The optimum value range of ER was observed to be about 0.29 to 0.34. A smaller feedstock size was more favorable for higher producer gas quality and gasification performance. Biomass moisture content parameters played an important role in the cyclone gasification process. Higher moisture content decreased the gasifier temperature, leading to low gas quality (lower HHV and higher tar content), and resulted in lower gasification performance.

Enhanced trace pollutants removal efficiency and hydrogen production in rice straw gasification using hot gas cleaning system

This study investigates the enhancement of tar and trace gaseous pollutants (e.g. hydrogen sulfide (H2S) and hydrogen chloride (HCl) removal efficiency derived from rice straw gasification using an integrated hot-gas cleaning system. A bubbling fluidized bed gasifier was used by controlling the temperature at 800 °C and equivalence ratio (ER) ranging 0.2 to 0.4. The hot gas cleaning system was operated at 250 °C and designed to combine three types of absorbents including zeolite, calcined dolomite, and activated carbon. Tar, H2S, and HCl removal efficiency and enhanced hydrogen production were also discussed. The experimental results indicated that light fraction tar removal efficiency was higher than 90% and the overall tar removal efficiency was approximately 70%. In the case of ER 0.4, the syngas tar content was decreased from 71.88 g/Nm3 (without hot gas cleaning system) to 16.53 g/Nm3 (with hot gas cleaning system). The tar removal efficiency is nearly 77% using the hot gas cleaning system. The HCl and H2S removal efficiency ranged from 94% to 98% and from 80.7% to 83.92%, respectively. In the case of ER 0.3 and with the hot gas cleaning system, the HCl and H2S concentrations in cleaned syngas gas were less than 40 ppm and 100 ppm, respectively. Meanwhile, the hydrogen concentration of produced gas was also increased from 6.82% to 9.83% with hot gas cleaning system used. It means that the hot gas cleaning system can effectively remove HCl and H2S from produced gas in gasification, but also it has good potential for improving syngas quality and enhancing gas turbine application in the future.

Using chemical looping gasification with Fe2O3/Al2O3 oxygen carrier to produce syngas (H2+CO) from rice straw

The chemical looping gasification of rice straw using Fe2O3/Al2O3 as oxygen carrier was studied at reaction time of 5–25 min, steam-to-biomass (S/B) ratio of 2.0–4.8, reaction temperature of 750–950 °C, and oxygen carrier-to-biomass of 1.0. The gasification can be regarded completed in 20-min reaction. There exist an optimal S/B ratio of 2.8 and reaction temperature of 900 °C leading to maximum performances yielded are 1.22 Nm3/kg gas yield at 54.6% H2+24.2% CO. The studied Fe2O3 oxygen carrier/rice straw is a feasible platform for syngas production from an agricultural waste.

The Effect of Rice Straw Gasification Temperature on the Release and Occurrence Modes of Na and K in a Fluidized Bed

Rice straw gasification was carried out in a laboratory fluidized bed reactor system from 600 to 800 °C in order to well-understand the release and occurrence mode of alkali metals as a function of temperature during the gasification process. Inductively coupled plasma atomic emission spectrometry (ICP-AES) was applied to analyze the original rice straw and obtained fly ash at different temperatures. The results show that the Water-Soluble, Ammonium acetate-Soluble, Hydrochloric acid-Soluble, and Aluminosilicate Combination-Soluble modes of the Na and K contents in rice straw decreased in sequence. The content of Water-Soluble salts of Na and K accounts for more than 50%, while the content of the Aluminosilicate Combination-Soluble mode is the lowest: less than 5%. The release rate of Na appears to be consistent but nonlinear, increasing with gasification conversion ranges between 50.2% and 70.8%, from which we can deduce that temperature is not the only factor that impacts Na emission. The release of K can be divided into two stages at 700 °C. At the first stage, the release rate of K is almost invariable, ranging from 23.3% to 26%. At the second stage, the release rate increases sharply: up to 55.9%. The concentration and the proportion of the Water-Soluble, Ammonium acetate-Soluble, and Hydrochloric acid-Soluble modes of Na in fly ash decrease with a temperature increase. The release of K can be explained as follows: one path is an organic form of K converted into its gaseous phase; the other path is a soluble inorganic form of K that is volatile at a high temperature. With a temperature increase, the Aluminosilicate Combination-Soluble mode of both Na and K increases.

Characterisation of the morphological changes and interactions in char, slag and ash during CO2 gasification of rice straw and lignite

In this work, a heating stage microscope and a thermogravimetric analyzer were adopted to explore behaviors of char-slag/ash transition during CO2 gasification of rice straw (RS) and Neimeng lignite (NM). Effects of demineralized treatment and various gasification temperatures on the char-slag/ash evolution process were studied. Both RS and NM particles exhibited shrinkage particle form at a moderate reaction temperature (1000°C). The variation of the existential state of K with char-slag/ash transition could well explain the reactivity differences between RS raw char and demineralized char. Compared to RS raw char, NM raw char showed a more significant flow of molten slag at 1350°C, which accounted for the high inhibitory effects at the late stage of NM raw char gasification. There is a threshold conversion (x=0.9) during the evolution processes of NM char samples to NM slag/ash at 1200°C and 1350°C, while this threshold value is only existing at 1000°C for RS char gasification.

The effects of prepared iron-based catalyst on the energy yield in gasification of rice straw

This research investigated the feasibility of enhanced energy yield in gasification of rice straw by using a prepared iron-based catalyst. The prepared iron-based catalyst containing 2% (wt%) Fe2O3 was produced by wet impregnation process. Based on the results of produced gas yield, the yield amounts of combustible gases increased with an increase in the prepared iron-based catalyst addition. In the case of gasification temperature 800 °C and below, the yield amount of combustible gas increased by using the prepared iron-based catalyst. Besides, the energy yield efficiency was approximately enhanced from 8% to 74% with the iron-based catalyst addition. In the case of gasification temperature 800 °C and iron-based catalyst addition, the energy yield efficiency of combustible gases is similar with that of gasification temperature 900 °C and without catalyst addition. That is, prepared iron-based catalyst has the good potential for converting rice straw into bio-energy and for reducing the energy requirement in gasification.