Pyrolysis of ramie residue: kinetic study and fuel gas produced in a cyclone furnace

The thermal decomposition behavior of ramie residue (RR) and the characteristics of fuel gas produced in a cyclone furnace were studied. The pyrolysis kinetics was investigated using thermogravimetric analysis (TGA) at heating rates of 5-20°C/min. The results showed that RR mainly decomposed between 250 and 390°C, and the apparent activation energy ranged from 200 to 258 kJ/mol. In the cyclone furnace, fast pyrolysis, partial combustion and gasification occurred almost simultaneously, and the thermal energy was supplied by partial combustion of RR powder at the hypo stoichiometric amount of air. Higher effect of equivalence ratio (ER) led to higher reaction temperature and fewer contents of tar and char, but too high ER lowered fuel gas content and degraded fuel gas quality. Over the ranges of the experimental conditions, the gas yield varied between 1.07 and 2.08 N m(3)/kg and the LHV was between 3350 and 4798 kJ/Nm(3).     

Experimental study on air-stream gasification of biomass micron fuel (BMF) in a cyclone gasifier

Based on biomass micron fuel (BMF) with particle size of less than 250 microm, a cyclone gasifier concept has been considered in our laboratory for biomass gasification. The concept combines and integrates partial oxidation, fast pyrolysis, gasification, and tar cracking, as well as a shift reaction, with the purpose of producing a high quality of gas. In this paper, experiments of BMF air-stream gasification were carried out by the gasifier, with energy for BMF gasification produced by partial combustion of BMF within the gasifier using a hypostoichiometric amount of air. The effects of ER (0.22-0.37) and S/B (0.15-0.59) and biomass particle size on the performances of BMF gasification and the gasification temperature were studied. Under the experimental conditions, the temperature, gas yields, LHV of the gas fuel, carbon conversion efficiency, stream decomposition and gasification efficiency varied in the range of 586-845 degrees C, 1.42-2.21 N m(3)/kg biomass, 3806-4921 kJ/m(3), 54.44%-85.45%, 37.98%-70.72%, and 36.35%-56.55%, respectively. The experimental results showed that the gasification performance was best with ER being 3.7 and S/B being 0.31 and smaller particle, as well as H(2)-content. And the BMF gasification by air and low temperature stream in the cyclone gasifier with the energy self-sufficiency is reliable.     

Biomass as an energy source: thermodynamic constraints on the performance of the conversion process

In the present work an equilibrium model (gas-solid), based on the minimization of the Gibbs energy, has been used in order to estimate the theoretical yield and the equilibrium composition of the reaction products (syngas and char) of biomass thermochemical conversion processes (pyrolysis and gasification). The data obtained from this model have also been used to calculate the heating value of the fuel gas, in order to evaluate the overall energy efficiency of the thermal conversion stage. The proposed model has been applied both to partial oxidation and steam gasification processes with varying air to biomass (ER) and steam to carbon (SC) ratio values and using different feedstocks; the obtained results have been compared with experimental data and with other model predictions obtaining a satisfactory agreement.     

Operational characteristics of a 1.2-MW biomass gasification and power generation plant

In this study, we analyzed the operational characteristics of a 1.2-MW rice husk gasification and power generation plant located in Changxing, Zhejiang province, China. The influences of gasification temperature, equivalence ratio (ER), feeding rate and rice husk water content on the gasification characteristics in a fluidized bed gasifier were investigated. The axial temperature profile in the dense phase of the gasifier showed that inadequate fluidization occurred inside the bed, and that the temperature was closely related to changes in ER and feeding rate. The bed temperature increased linearly with increasing ER when the feeding rate was kept constant, while a higher feeding rate corresponded to a lower bed temperature at fixed ER. The gas heating value decreased with increasing temperature, while the feeding rate had little effect. When the gasification temperature was 700–800 °C, the gas heating value ranged from 5450–6400 kJ/Nm³. The water content of the rice husk had an obvious influence on the operation of the gasifier: increases in water content up to 15% resulted in increasing ER and gas yield, while water contents above 15% caused aberrant temperature fluctuations. The problems in this plant are discussed in the light of operational experience of MW-scale biomass gasification and power generation plants.     

Gasification of palm empty fruit bunch in a bubbling fluidized bed: a performance and agglomeration study

Gasification of palm empty fruit bunch (EFB) was investigated in a pilot-scale air-blown fluidized bed. The effect of bed temperature (650-1050 °C) on gasification performance was studied. To explore the potential of EFB, the gasification results were compared to that of sawdust. Results showed that maximum heating values (HHV) of 5.37 and 5.88 (MJ/Nm3), dry gas yield of 2.04 and 2.0 (Nm3/kg), carbon conversion of 93% and 85 % and cold gas efficiency of 72% and 71 % were obtained for EFB and sawdust at the temperature of 1050 °C and ER of 0.25. However, it was realized that agglomeration was the major issue in EFB gasification at high temperatures. To prevent the bed agglomeration, EFB gasification was performed at temperature of 770±20 °C while the ER was varied from 0.17 to 0.32. Maximum HHV of 4.53 was obtained at ER of 0.21 where no agglomeration was observed.     

生物质气化制取代用天然气的模拟

介绍了生物质气化制取代用天然气的技术,并利用Aspen Plus软件建立了串行流化床生物质气化制取代用天然气的模型,并对整个流程进行模拟。着重研究了气化过程中操作参数(气化温度Tg、S/B)对甲烷化反应过程主要指标(包括甲烷产率、碳转化率等)的影响。研究结果表明提高气化温度和S/B有利于提高气化产物中生物质合成气的浓度,并得到较高氢碳比的合成气,从而可以提高甲烷的产率和整个系统的碳转化率;为获得较高的甲烷产率和碳转化率,适宜的气化温度为700～750℃,S/B值在0.4左右。     

Experimental study on cyclone air gasification of wood powder

In this paper, effects of the equivalence ratio (ER) and the secondary air on the gasification system were studied. The results indicate that as the ER varies in the range of 0.20–0.26, the low heating value (LHV) of the producer gas is in the range of 3.64–5.76 MJ/Nm³, the carbon conversion is 55%–67% and the cold gas efficiency of the gasification system is 33%–47%. In contrast to the gasification without the secondary air, air staged process is a gasification method capable of increasing the LHV of the producer gas from 4.63 to 5.67 MJ/Nm³, the carbon conversion from 65.5% to 81.2%, and the cold gas efficiency of the gasifier from 42.5% to 56.87%, while the tar content of the producer gas decreases from 13.96 to 5.6 g/Nm³. There exists an optimum ratio of the secondary air.     

Biomass steam gasification--an extensive parametric modeling study

A model for steam gasification of biomass was developed by applying thermodynamic equilibrium calculations. With this model, the simulation of a decentralized combined heat and power station based on a dual fluidized-bed steam gasifier was carried out. Fuel composition (ultimate analysis and moisture content) and the operating parameters, temperature and amount of gasification agent, were varied over a wide range. Their influences on amount, composition, and heating value of product gas and process efficiencies were evaluated. It was shown that the accuracy of an equilibrium model for the gas composition is sufficient for thermodynamic considerations. Net electric efficiency of about 20% can be expected with a rather simple process. Sensitivity analysis showed that gasification temperature and fuel oxygen content were the most significant parameters determining the chemical efficiency of the gasification.     

Biomass–oxygen gasification in a high-temperature entrained-flow gasifier

The technology associated with indirect biomass liquefaction is currently arousing increased attention, as it could ensure a supply of transportation fuels and reduce the use of petroleum. The characteristics of biomass–oxygen gasification in a bench-scale laminar entrained-flow gasifier were studied in the paper. Experiments were carried out to investigate the influence of some key factors, including reaction temperature, residence time and oxygen/biomass ratio, on the gasification. The results indicated that higher temperature favored H₂ and CO production. Cold gas efficiency was improved by > 10% when the temperature was increased from 1000 to 1400 °C. The carbon conversion increased and the syngas quality was improved with increasing residence time. A shorter residence resulted in incomplete gasification. An optimal residence time of 1.6 s was identified in this study. The introduction of oxygen to the gasifier strengthened the gasification and improved the carbon conversion, but lowered the lower heating value and the H₂/CO ratio of the syngas. The optimal oxygen/biomass ratio in this study was 0.4. The results of this study will help to improve our understanding of syngas production by biomass high-temperature gasification.     

Characteristics of rice husk gasification in an entrained flow reactor

Experiments were performed in an entrained flow reactor to better understand the characteristics of biomass gasification. Rice husk was used in this study. Effects of the gasification temperature (700, 800, 900 and 1000 °C) and the equivalence ratio in the range of 0.220.34 on the biomass gasification and the axial gas distribution in the reactor were studied. The results showed that reactions of CnHm were less important in the gasification process except cracking reactions which occurred at higher temperature. In the oxidization zone, reactions between char and oxygen had a more prevailing role. The optimal gasification temperature of the rice husk could be above 900 °C, and the optimal value of ER was 0.25. The gasification process was finished in 1.42 s when the gasification temperature was above 800 °C. A first order kinetic model was developed for describing rice husk air gasification characteristics and the relevant kinetic parameters were determined.     

Two-stage steam gasification of waste biomass in fluidized bed at low temperature: parametric investigations and performance optimization

Steam gasification of waste biomass has been studied in a two-stage fluidized bed reactor, which has the primary pyrolysis fluidized bed using silica sand as bed material and the secondary reforming fixed bed with catalyst. The main objectives are parametric investigation and performance improvement especially at low temperature of around 600 °C using the wood chip and the pig manure compost as feedstock. Main operating variables studied are pyrolysis temperature, catalytic temperature, steam/biomass-C ratio, space velocity and different catalyst. Reaction temperatures and steam/C ratio have important role on the gasification process. About 60 vol.% H2 (dry and N2 free) and about 2.0 Nm3/kg biomass (dry and ash free basis) can be obtained under good conditions. Compared to Ni/Al2O3, Ni/BCC (Ni-loaded brown coal char) has a better ability and a hopeful prospect for the stability with coking resistance.     

Effects of gasifying conditions and bed materials on fluidized bed steam gasification of wood biomass

The effect of steam gasification conditions on products properties was investigated in a bubbling fluidized bed reactor, using larch wood as the starting material. For bed material effect, calcined limestone and calcined waste concrete gave high content of H(2) and CO(2), while silica sand provided the high content of CO. At 650 degrees C, calcined limestone proved to be most effective for tar adsorption and showed high ability to adsorb CO(2) in bed. At 750 degrees C it could not capture CO(2) but still gave the highest cold gas efficiency (% LHV) of 79.61%. Steam gasification gave higher amount of gas product and higher H(2)/CO ratio than those obtained with N(2) pyrolysis. The combined use of calcined limestone and calcined waste concrete with equal proportion contributed relatively the same gas composition, gas yield and cold gas efficiency as those of calcined limestone, but showed less attrition, sintering, and agglomeration propensities similar to the use of calcined waste concrete alone.     

A novel reforming method for hydrogen production from biomass steam gasification

In this work, an experimental study of biomass gasification in different operation conditions has been carried out in an updraft gasifier combined with a porous ceramic reformer. The effects of gasifier temperature, steam to biomass ratio (S/B), and reforming temperature on the gas characteristic parameters were investigated with and without porous ceramic filled in reformer. The results indicated that considerable synergistics effects were observed as the porous ceramic was filled in reformer leading to an increase in the hydrogen production. With the increasing gasifier temperature varying from 800 to 950 °C, hydrogen yield increased from 49.97 to 79.91 g H₂/kg biomass. Steam/biomass ratio of 2.05 seemed to be optimal in all steam-gasification runs. The effect of reforming temperature for water-soluble tar produced in porous ceramic reforming was also investigated, and it was found that the conversion ratio of total organic carbon (TOC) contents is between 71.08% and 75.74%.     

Study on biomass circulation and gasification performance in a clapboard-type internal circulating fluidized bed gasifier

We investigated the solid particle flow characteristics and biomass gasification in a clapboard-type internal circulating fluidized bed reactor. The effect of fluidization velocity on particle circulation rate and pressure distribution in the bed showed that fluidization velocities in the high and low velocity zones were the main operational parameters controlling particle circulation. The maximum internal circulation rates in the low velocity zone came almost within the range of velocities in the high velocity zone, when u_H/u_mf = 2.2–2.4 for rice husk and u_H/u_mf = 3.5–4.5 for quartz sand. In the gasification experiment, the air equvalence ratio (ER) was the main controlling parameter. Rice husk gasification gas had a maximum heating value of around 5000 kJ/m³ when ER = 0.22–0.26, and sawdust gasification gas reached around 6000–6500 kJ/m³ when ER = 0.175–0.24. The gasification efficiency of rice husk reached a maximum of 77% at ER = 0.28, while the gasification efficiency of sawdust reached a maximum of 81% at ER = 0.25.     

Steam–air fluidized bed gasification of distillers grains: Effects of steam to biomass ratio,equivalence ratio and gasification temperature

In this study, thermochemical biomass gasification was performed on a bench-scale fluidized-bed gasifier with steam and air as fluidizing and oxidizing agents. Distillers grains, a non-fermentable byproduct of ethanol production, were used as the biomass feedstock for the gasification. The goal was to investigate the effects of furnace temperature, steam to biomass ratio and equivalence ratio on gas composition, carbon conversion efficiency and energy conversion efficiency of the product gas. The experiments were conducted using a 3 × 3 × 3 full factorial design with temperatures of 650, 750 and 850 °C, steam to biomass ratios of 0, 7.30 and 14.29 and equivalence ratios of 0.07, 0.15 and 0.29. Gasification temperature was found to be the most influential factor. Increasing the temperature resulted in increases in hydrogen and methane contents, carbon conversion and energy efficiencies. Increasing equivalence ratio decreased the hydrogen content but increased carbon conversion and energy efficiencies. The steam to biomass ratio was optimal in the intermediate levels for maximal carbon conversion and energy efficiencies.     

Experimental studies on producer gas generation from wood waste in a downdraft biomass gasifier

A process of conversion of solid carbonaceous fuel into combustible gas by partial combustion is known as gasification. The resulting gas, known as producer gas, is more versatile in its use than the original solid biomass. In the present study, a downdraft biomass gasifier is used to carry out the gasification experiments with the waste generated while making furniture in the carpentry section of the institute’s workshop. Dalbergia sisoo, generally known as sesame wood or rose wood is mainly used in the furniture and wastage of the same is used as a biomass material in the present gasification studies. The effects of air flow rate and moisture content on biomass consumption rate and quality of the producer gas generated are studied by performing experiments. The performance of the biomass gasifier system is evaluated in terms of equivalence ratio, producer gas composition, calorific value of the producer gas, gas production rate, zone temperatures and cold gas efficiency. Material balance is carried out to examine the reliability of the results generated. The experimental results are compared with those reported in the literature.     

Process simulation of single-step dimethyl ether production via biomass gasification

In this study, we simulated the single-step process of dimethyl ether (DME) synthesis via biomass gasification using ASPEN Plus™. The whole process comprised four parts: gasification, water gas shift reaction, gas purification, and single-step DME synthesis. We analyzed the influence of the oxygen/biomass and steam/biomass ratios on biomass gasification and synthesis performance. The syngas H₂/CO ratio after water gas shift process was modulated to 1, and the syngas was then purified to remove H₂S and CO₂, using the Rectisol process. Syngas still contained trace amounts of H₂S and about 3% CO₂ after purification, which satisfied the synthesis demands. However, the high level of cold energy consumption was a problem during the purification process. The DME yield in this study was 0.37, assuming that the DME selectivity was 0.91 and that CO was totally converted. We performed environmental and economic analyses, and propose the development of a poly-generation process based on economic considerations.     

Effects of the reforming reagents and fuel species on tar reforming reaction

In this study, using wood chips and polyethylene (PE) as fuels, the effects of air and/or steam as reagents on the tar reforming were clarified quantitatively with a simulated gasifier/reformer apparatus of a two-staged gasification process. The results show that when only steam or air was supplied into the reformer, the tar residual rate (defined as the ratio of the tar amount in the reformed gas to the tar amount in the pyrolysis gas) and the carbon particulate concentration in both reformed gases produced from pyrolysis gases of wood chips and PE decreased with the increase of the steam ratio (H₂O/C, 0–1.0) or the air ratio (ER, 0–0.30). Supplying steam into the reformer to suppress carbon particulate formation for PE pyrolysis gas is more effective than for wood chips pyrolysis gas. Comparing with the results of steam only reforming, the effect of air supply on reduction of the tar residual rate was more significant, while that on suppression of carbon particulate formation was smaller.     

Unconverted chars obtained during biomass gasification on a pilot-scale gasifier as a source of activated carbon production

Biomass gasification was used to produce activated carbon on a pilot-scale fluidised-bed gasifier. The feedstock included both biomass alone and biomass mixed with coal and coal/granulated plastic wastes. This paper reports the results obtained from four different runs undertaken under various conditions of fuel supply, different ratios of steam/air for the gasification and temperature. These conditions were selected because they led to a significant amount of unconverted chars produced during gasification (from 0.72 to 1.4 kg) which then served as raw material for the production of activated carbon whilst the amount of gas obtained was also high enough for its potential use for different end-use applications. From the analysis of the results obtained, it can be concluded that a reasonable porosity development (mainly in the area of narrow micropores) was obtained by gasifying unblended pine wastes with steam for 4 h, producing about 1.4 kg of good-quality activated carbon (micropore volume of 0.263 cm(3)/g). In other runs, chars with a reduced microporosity development (i.e. 0.180 cm(3)/g) were obtained, however, they could be used as a proper starting material for the chemically activated carbon production.     

Assessment of black liquor gasification in supercritical water

Supercritical water gasification of black liquor (waste pulping chemicals) has been examined. The aim was to evaluate the feasibility of using this technique to convert such bio-based waste to value added fuel products, as well as recovery of pulping materials. Supercritical gasification may improve overall process efficiency by eliminating the energy intensive evaporation step necessary in conventional process and product gas obtained at high pressure may be ready for utilization without any compression requirement. Appropriate operating parameters, including pressure, temperature, feed concentration, and reaction time, which would yield the highest conversion and energy efficiency were determined. Reaction was performed in a quartz capillary heated in a fluidized bed reactor. Results indicated that pressure between 220 and 400 atm has insignificant influence on the gas products and extent of carbon conversion. Increasing temperature and residence time between 375-650 degrees C and 5-120 s resulted in greater gas production, overall carbon conversion, and energy efficiency. Maximum conversion to H(2), CO, CH(4), and C(2)H(X) was achieved at the highest temperature and longest residence time tested showing an overall carbon conversion of 84.8%, gas energy content of 9.4 MJ/m(3) and energy conversion ratio of 1.2. Though higher carbon conversion and energy conversion ratio were obtained with more dilute liquor, energy content was lower than for those with higher solid contents. Due to anticipated complex design and high initial investment cost of this operation, further studies on overall feasibility should be carried out in order to identify the optimum operating window for this novel process.