•Pyrolysis characteristics of phenol as tar model compounds were investigated.•Distribution of gaseous products in micro fluidized bed reactor were determined.•Apparent activation energies for individual gaseous products were calculated.•Reaction mechanisms for evolution profiles of gas components were evaluated.Thermal cracking characteristic of phenol as the model compound of biomass tar was investigated on a micro fluidized bed reactor. Pyrolysis kinetics for individual gaseous component, including hydrogen, methane, carbon monoxide and carbon dioxide were determined based on the iso-conversional and model-fitting approaches. Results indicated that carbon monoxide accounted for the biggest percentage of the total gas yield during pyrolysis of phenol. The evolution profiles of hydrogen energy and carbon monoxide were more affected by reaction temperature compared to methane and carbon dioxide. In the major conversion fraction from 20% to 80%, the apparent activation energies of methane (49.67 kJ/mol) and carbon dioxide (30.87 kJ/mol) were lower than that of hydrogen (145.2 kJ/mol) and carbon monoxide (53.35 kJ/mol). The most probable reaction mechanism for the formation of hydrogen and methane was three-dimension diffusion while chemical reaction and contracting sphere could describe the generation of carbon monoxide and carbon dioxide, respectively.

This study is devoted to investigate the characteristics and kinetics of biomass tar cracking in a micro fluidized bed reactor for liquids (MFBRL). The carbon balance and conversion were measured to estimate the performance of MFBRL, and the results showed good reproducibility and reliability. H2, CH4 and CO comprised the vast bulk of the producer gas and the total volume fraction of them increased from 69.85% to 93.62% (973–1173 K). Kinetic parameters, including reaction order, pre-exponential factor and apparent activation energy, were studied with the isothermal method. The reaction orders varied greatly with temperature, suggesting that temperature significantly affected the reaction mechanism. The pre-exponential factors for H2, CH4, CO and gas mixtures were in the range of 2.37 × 103 to 2.87 × 105 S−1, while the apparent activation energies ranged from 62.96–100.2 kJ mol−1. Compared to the fixed bed experiments, the derived results were obviously higher, indicating the kinetic parameters were more suitable for describing the intrinsic reactions.

•An innovative gasifier with three air stage was designed to realize uniform air distribution.•The LHV and cold gas efficiency attained a good condition when ER was 0.25–0.27.•The tar yield as low as 0.5 g/Nm3 was achieved by increasing ER.•Temperature and tar yield were improved as the increase of feeding rate.The main objective of this paper is to study the effect of design and operating parameters, mainly reactor geometry, equivalence ratio and biomass feeding rate, on the performance of the gasification process of biomass in a three air stage continuous fixed bed downdraft reactor. The gasification of corn straw was carried out in the gasifier under atmospheric pressure, using air as gasifying agent. The results demonstrated that due to the three stage of air supply, a high and uniform temperature was achieved in the oxidation and reduction zones for better tar cracking. The designing of both the air supply system and rotating grate avoided bridging and channeling. The gas composition and tar yield were affected by the parameters including equivalence ratio (ER) and biomass feeding rate. When biomass feeding rate was 7.5 kg/h and ER was 0.25–0.27, the product gas of the gasifier attained a good condition with lower heating value (LHV) about 5400 kJ/m3 and cold gas efficiency about 65%. An increase in equivalence ratio led to higher temperature which in turn resulted in lower tar yield which was only 0.52 g/Nm3 at ER = 0.32. Increasing biomass feeding rate led to higher biomass consumption rate and process temperature. However, excessively high feeding rate was unbeneficial for biomass gasification cracking and reforming reactions, which led to a decrease in H2 and CO concentrations and an increase in tar yield. When ER was 0.27, with an increase of biomass feeding rate from 5.8 kg/h to 9.3 kg/h, the lower heating value decreased from 5455.5 kJ/Nm3 to 5253.2 kJ/Nm3 and tar yield increased from 0.82 g/Nm3 to 2.78 g/Nm3.

The current paper concerns the process of non-woody biomass gasification, particularly about releasing processes of detrimental elements. The gasification of corn straw was carried out in a downdraft fixed bed gasifier under atmospheric pressure, using air as an oxidizer. The effects of the operating conditions on gasification performance in terms of the temperature profiles of the gasifier, the composition distribution of the producer gas and the release of sulphur and chlorine compounds during gasification of corn straw were investigated. Besides, the gasification characteristics were evaluated in terms of low heating value (LHV), gas yield, gasification efficiency and tar concentration in the raw gas.According to the experimental results, operating conditions have great influence on the temperature profiles of the gasifier and the composition distribution of the product gas. During the gasification of non-woody biomass, the variations of the concentration of sulphur and chlorine compounds in gaseous and ash are not a monotonic tread under different operating conditions. Besides, over the ranges of the equivalence ratio(ER) examined, higher or lower ER both degraded the quality of gas and gasification efficiency. If ER is regarded as a function of the combustible species, the optimum value of ER is 0.28–0.32, and the optimal LHV of 5.39 MJ/Nm3, gas yield of 2.86 Nm3/kg, gasification efficiency of 73.61% and tar concentration of 4617 mg/Nm3 is obtained at different ER.Highlights► Gasification of non-woody biomass in a downdraft fixed bed gasifier. ► Influence of ER on the distribution of sulphur and chlorine compounds. ► Influence of ER on the temperature profiles and gasification characteristics. ► Too high or too low ERs both degrade the quality of gas and gasification efficiency.