Cyclone Gasifier Research Articles

Numerical simulation of a biomass cyclone gasifier: Effects of operating conditions on gasifier performance

In Nordic countries, biomass gasification in a cyclone gasifier combined with a gas engine has been employed to generate small scale heat and power. Numerical simulations were carried out to analyze the effect of different operating conditions on the functioning of the gasifier. Reynolds-Averaged Navier-Stokes equations are solved together with the eddy-break up combustion model in conjunction with a modified k − ϵ model to predict the temperature and the flow field inside the gasifier. Results were compared with the experimental measurements in a 4.4 MW cyclone gasifier constructed by Meva Energy AB at Hortlax, Piteå, Sweden. The predicted results were in good agreement with the experimental data and the model provides detailed information about the gas compositions, cold gas efficiency and temperature field. Furthermore, the model allows different operating scenarios to be examined in an efficient manner such as the number of inlets, fuel to air velocity difference (slip-velocity) and moisture content in the fuel feedstock. The cold gas efficiency, composition of product gases and outlet temperature were monitored for each test case. These findings help to understand the importance of geometry modification, feedstock contents and make it possible to scale-up the gasifier for future applications.

Influence of Different Materials on the Mechanical Aspects in the Design of Cyclone Gasifier

Cyclone gasifier is used as the energy conversion system for the biomass. The design and material selection for the cyclone gasifier is important, which affect the strength of the gasifier during the operation. This research aims to investigate the effect of the various materials to the mechanical aspects (i.e., stress, strain and displacement) of the cyclone gasifier. The mechanical aspects analysis is carried out by using the finite element (FE) based software. The stress, strain and displacement of the cyclone gasifier’s structure was analyzed for various stainless steel materials (i.e., ferritic (FSS), AISI 316, 1023 CSS, 201 ASS and AISI 4130). The finite element analysis revealed the use of 201 ASS experienced highest stress (221 MPa). Lowest strain and displacement were found on 201 ASS and 1023 CSS, respectively. These research findings are expected to be used as the reference for the engineer in the material selection process for the design and fabrication of cyclone gasifier.

Numerical Simulation of Biomass Gasification in an Entrained Flow Cyclone Gasifier

A transient, two-way coupled Eulerian–Lagrangian computational fluid dynamics model has been developed for numerically investigating the gasification process of wood powder inside a cyclone-shaped reactor. The suggested model has considered heat and mass transfer, drying, devolatilization, and homogeneous and heterogeneous reactions. The model is validated using the experimental data from a commercial entrained-flow cyclone gasifier. The changes in gas composition as a function of equivalence ratio and the behavior of gasification process agreed well with the experimental measurement. Trajectories of individual particles were captured, and the behavior, mass fraction, and temperature distribution of several representative particles in different sizes were studied. Moreover, the model was successful in prediction of produced gas lower heating value, cold gas efficiency, and carbon conversion.

Effect of process parameters on the performance of an air-blown entrained flow cyclone gasifier

ABSTRACTEntrained flow gasification of biomass in a cyclone reactor combined by a gas engine has been applied in Nordic countries as one of the preferred methods for generating combined heat and power in small scales. The purpose of the current study was to optimise the gasification plant efficiency and understanding the influence of operating conditions. The experiments were carried out in a 2.4 MW(th) commercial gasification power plant. The gasifier was operated in optimum at a rather low lambda around 0.27 and a temperature of 950°C. The lower heating value of the clean product gas at this lambda was 5.95 MJ/Nm3. The experimental results also were compared with the predicted values from thermodynamic equilibrium calculations by Factsage 7.0. The performance of five different types of biofuels including torrefied spruce, peat, rice husk, bark and stemwood were assessed and compared with each other using thermodynamic equilibrium and available experimental data.

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.

Modeling of Particle-Laden Cold Flow in a Cyclone Gasifier

Isothermal transient Eulerian–Lagrangian simulation of the turbulent gas–solid flow in a cyclone gasifier with two inlet tubes at 890 °C has been performed. The single-phase gas flow is modeled using SSG Reynolds stress turbulence model. Ten thousand representative solid particles of different sizes are injected from each inlet continuously at every second of simulation time. Particles are finally stopped as soon as they arrive at the outlet or reach the bottom plate of the gasifier. The effect of particle-to-gas coupling on the pressure and velocity of the flow and particles motion inside the gasifier is studied. The numerical approach can reasonably predict the impact of particle load on the gas flow as presented in the experimental results. Single particles are traveled throughout the transient gas flow field by using Lagrangian approach. High temperature of the gas flow inside the gasifier has significant effects on the swirl intensity reduction, damping the turbulence in the core region, pressure, and particle behaviors. However, the presence of solid particles does not have a notable influence on the swirl intensity and turbulence.

Gasification of Furniture Waste Sawdust in a Cyclone Gasifier

Sawdust is one of the major biomass that was produced over 1 million ton per year in Thailand. A large amount of sawdust can be used as renewable energy. Gasification is one of the high-efficiency processes to convert biomass to the gaseous product. Sawdust is suitable to be converted to the gaseous product due to its high proportion of volatile (73%). In this work, sawdust thermal conversion was investigated by using a stairmand type cyclone gasifier with 100 mm diameter. The operation of the cyclone with short residence time and high efficiency of particulate separation from the gaseous product is suitable for a small particle like sawdust. The influences of equivalence ratio (0.15-0.60) and reactor temperature (700°C, 800°C and 900°C) on the waste conversion performance were determined. The gas composition (CO, CO2, CH4, H2, and CnHm), carbon and hydrogen conversions, lower heating value and cold gasification efficiency were reported. The data analysis indicated the optimum equivalence ratio is 0.45. Excessively lower or higher equivalence ratio negatively affected the gas composition and heating value of gaseous product. The optimum of reactor temperature is 900°C. The lower temperature also adversely affected the gaseous product, conversion of carbon and hydrogen. The lower heating value of product gas is range from 0.95-3.45 MJ/m3 and the cold gasification efficiency is range from 28-68%. The optimal condition of sawdust gasification in cyclone gasifier is equivalence ratio of 0.45 and temperature of 900°C at which total carbon and hydrogen conversionsare 90% and 60%, respectively.

Characteristics of rice husk gasification in cyclone pyrolysis-suspended combustion system

The cyclonic gasification technology could realize self-separation of syngas and residual carbon, simplifying the purification system. In cyclone pyrolysis-suspension combustion system, bottom air was fed into carbon-rich area of gasifier. Due to the high height/diameter ratio and uneven temperature distribution in cyclone gasifier, the primary/secondary/bottom air rates were 30%, 20%, and 50%, respectively. Effects of gasification intensity and air equivalent ratio on rice husk gasification performance were explored. The results show that for cyclone pyrolysis-suspension combustion, the optimum gasification intensity is 885.24 kg/m2h. Strengthening the subregion of air supplement could cause a gradual increasing of temperature along the axis of gasifier. The syngas yield was independent of gasification intensity, but increased from 0.98 Nm3/kg at ER = 0.23 to 1.38 Nm3/kg at ER = 0.32. At ER = 0.26~0.29, the gasification performance is best, with gas heat value of 4.99~5.37 MJ/Nm3, cold gasification efficiency of 48.25~49.67% and tar content of 5.38~5.75 g/Nm3.

Experimental Study on Autothermal Cyclone Air Gasification of Biomass

Cyclone gasification technology is commonly used for biomass fuels with small particle sizes, such as rice husks and wood chips. This paper explored the effects of gasification intensity and equivalence ratio on the performance characteristics of an autothermal cyclone gasifier. Increasing the gasification intensity caused the syngas' heating value, the cold gasification efficiency and the carbon conversion rate to increase to a maximum for an intensity of 885.24 kg/(m2 h) before then decreasing as the gasification intensity was further increased. Increasing the equivalence ratio from 0.23 to 0.32 increased the overall temperature of gasifier, decreased the tar content (from 6.84 to 4.96 g/N·m3), and increased the carbon conversion rate (from 47.2% to 62.3%). Increasing the equivalence ratio to 0.26 also increased the syngas' heating value to its maximum of 4.25 MJ/N·m3, which then decreased with further increases in equivalence ratio. A similar trend was observed for the gasification efficiency, which ranged from 30% to 37%. From these tests, a gasification intensity of 885.24 kg/(m2 h) and an equivalence ratio of 0.26 appeared optimal for the autothermal cyclone air gasification of biomass process studied here.

Experimental study of cyclone pyrolysis – Suspended combustion air gasification of biomass

Based on the original biomass cyclone gasifier, the cyclone pyrolysis-suspension combustion gasification technology was constituted with a bottom wind ring to build the biochar suspension combustion zone. This technology decouples the biomass pyrolysis, gasification (reduction reaction) and combustion (oxidation reaction) within the same device. With the feed amount and total air fixed, the effect of air rate arrangement on temperature distribution of the gasifier, syngas components and gasification parameters was studied. With the secondary air rate (0.20) and bottom air rate (0.50), the gasification efficiency was best, with gas heating value of 5.15MJ/Nm3, carbon conversion rate of 71.50%, gasification efficiency of 50.80% and syngas yield of 1.29Nm3/kg. The device with biochar for the tar catalytic cracking was installed at the gasifier outlet, effectively reducing the tar content in syngas, with a minimum value of 1.02g/Nm3.

Turbulence Modelling of a Single-Phase Flow Cyclone Gasifier

The current work aims to make a foundation for an engineering design of a cyclone gasifier to be able not only to predict its flow field with a suitable accuracy but also to investigate a large number of design alternatives with limited computer resources. A good single-phase flow model that can form the basis in an Euler-Lagrange model for multi-phase flow is also necessary for modelling the reacting flow inside a cyclone gasifier. The present paper provides an objective comparison between several popular turbulence modelling options including standard k-e and SST with curvature corrections, SSG-RSM and LES Smagorinsky models, for the single-phase flow inside cyclone separators/gasifiers that can serve as a guide for further work on the reacting multi-phase flow inside cyclone gasifiers and similar devices. A detailed comparison between the models and experimental data for the mean velocity and fluctuating parts of the velocity profiles are presented. Furthermore, the capabilities of the turbulence models to capture the physical phenomena present in a cyclone gasifier that affects the design process are investigated.

Numerical modeling of a 500 kW air-blown cyclone gasifier

Cyclone gasification of biomass in combination with a gas engine has been considered as a process for combined heat and power production. In this work a numerical model of the cyclone gasification process of wood powder was developed intended to be used as a tool for future engineering design of cyclone gasifiers. The model is based on an Euler–Lagrange formulation for the multiphase flow where the biomass powder was treated as a dispersed phase and the gas as a continuous phase. The results from the simulation are compared with experimental measurement in a 500 kWth cyclone gasifier that uses wood powder as fuel. The model was able to predict the gas composition change with increasing equivalence ratio. The relative error for the main gas component was between 2.5 and 4.4%, 2.8 and 5.4%, and 2.6 and 17.3% for CO2, CO and H2. CH4 was predicted with a relative error of between 3.8 and 19.2%. Also the model was able to predict the char amount out from the gasifier with reasonable accuracy. The obtained lower heating value from the model was between 3.5 and 5.2 MJ/Nm3 whereas the calculated based on measurement was 4.0–5.3 MJ/Nm3.

Simulation of a Gas-Solid Flow Field in a Two-Stage Rice Husk High-Temperature Pyrolysis and Gasification Cyclone Gasifier

A scheme for using a two-stage cyclone gasifier for high-temperature rice husk pyrolysis and gasification to reduce the tar content in biogas is presented in this study. The two-stage cyclone gasifier consisted of an upper cyclone high-temperature pyrolysis chamber and a lower steam spray gasifier. The staging pyrolysis and gasification process used in this study can increase the carbon conversion efficiency and reduce tar content by increasing the pyrolysis temperature. This process uses part of the produced gas for combustion in an external burner to generate high-temperature (1600 °C) anaerobic flue gas and to provide heat for pyrolysis and gasification. This study simulates the isothermal gas phase and the gas-solid flow field for the upper cyclone chamber, as well as the gas-solid flow field, with steam (heat transfer between the steam and the gas is considered), for the entire gasifier by varying the structural and operational parameters. The optimal parameters for the cyclone gasifier for good mixing and lengthy residence (2.3 to 4.8 s) of the rice husk particles were found to be inlet angles of 20° and 30° with inlet velocities between 40 and 80 m/s.

Influence from fuel type on the performance of an air-blown cyclone gasifier

Entrained flow gasification of biomass using the cyclone principle has been proposed in combination with a gas engine as a method for combined heat and power production in small to medium scale (<20MW). This type of gasifier also has the potential to operate using ash rich fuels since the reactor temperature is lower than the ash melting temperature and the ash can be separated after being collected at the bottom of the cyclone. The purpose of this work was to assess the fuel flexibility of cyclone gasification by performing tests with five different types of fuels; torrefied spruce, peat, rice husk, bark and wood. All of the fuels were dried to below 15% moisture content and milled to a powder with a maximum particle size of around 1mm. The experiments were carried out in a 500kWth pilot gasifier with a 3-step gas cleaning process consisting of a multi-cyclone for removal of coarse particles, a bio-scrubber for tar removal and a wet electrostatic precipitator for removal of fine particles and droplets from the oil scrubber (aerosols). The lower heating value (LHV) of the clean producer gas was 4.09, 4.54, 4.84 and 4.57 MJ/Nm3 for peat, rice husk, bark and wood, respectively, at a fuel load of 400kW and an equivalence ratio of 0.27. Torrefied fuel was gasified at an equivalence ratio of 0.2 which resulted in a LHV of 5.75 MJ/Nm3 which can be compared to 5.50 MJ/Nm3 for wood powder that was gasified at the same equivalence ratio. A particle sampling system was designed in order to collect ultrafine particles upstream and downstream the gasifier cleaning device. The results revealed that the gas cleaning successfully removed >99.9% of the particulate matter smaller than 1μm.

Experiments and numerical simulation of sawdust gasification in an air cyclone gasifier

In this paper the gasification of sawdust in an air cyclone gasifier was investigated to produce a high quality fuel gas with less tar. The effect of air to fuel ratio on the gasification characteristics was studied. The results indicate that as the air to fuel ratio varying from 0.23 to 0.35, the lower heating value of the produced gas is 4.5–5.7MJ/Nm3, the carbon conversion is 77.0–94.2%, the cold gas efficiency of the gasification system is 53.6–63.0%, while the tar content is 4.4–8.4g/Nm3. A detailed CFD model of a cyclone gasifier has been developed, based on the Fluent package. Models of sawdust pyrolysis and combustion of volatiles and char have been added to the standard model. The model provides information on the gas temperature in the gasifier and the composition of the outlet gas.

Characteristics of cyclone gasification of rice husk

Abstract The gasification characteristics of the rice husk were studied in a cyclone gasifier using air as the gasifying medium to generate the fuel gas with available heating value and less tar content. The influence of equivalence ratio on temperature profiles, composition and low heating value of the produced gas, tar content, carbon conversion and cold gas efficiency was investigated. The equivalence ratios considered in this study were 0.20–0.32. The results show that the optimal equivalence ratio is 0.29 and the maximum temperature of gasification should be lower than 1000 °C. In order to optimize the performance of the cyclone gasifier, the main body of the gasifier was lengthened and air staged gasification was carried out. The low heating value of the produced gas, carbon conversion, cold gas efficiency and tar content are 4.72 MJ/Nm 3 , 57.5%, 37.3% and 1.85 g/Nm 3 , respectively.

Experimental research on fuel staging cyclone gasification of wood powder

Fuel staging cyclone gasification of wood powder was studied in a cyclone gasifier using air as the gasifying medium. A part of fuel was fed into the upper part of the gasifier, where main part of oxidation reactions took place. Another part of fuel was fed into the lower part of the gasifier. The high temperature flue gas and particles in the upper part of the gasifier were forwarded into the lower part of the gasifier to provide endothermic heat for fuel pyrolysis and reduction reactions. The influences of fuel staging, the equivalence ratio and fuel distribution on temperature profiles, composition, lower heating value and tar content of the produced gas, energy transformation including carbon conversion and cold gasification efficiency, were investigated in this study. The optimum range of equivalence ratio is 0.26–0.29 and the staged fuel ratio is not more than 20%. The lower heating value of the produced gas, the fuel gas production and the tar content are 5.36–5.77MJ/Nm3, 1.70–1.84Nm3/kg and 2.15–2.39g/Nm3, respectively. While the cold gas efficiency is about 61%.

Experimental research on air staged cyclone gasification of rice husk

A novel air cyclone gasifier of rice husk has been used to obtain experimental data for air staged gasification. Three positions and five ratios of secondary air were selected to study effect of the secondary air on the temperature profile in the gasifier and quality of syngas. Temperature profile and the syngas component are found to be strongly influenced by the injection position and ratio of the secondary air. Generally, gas temperature in all conditions increased at the early stage of reaction, and then decreased in the reduction zone where reactions were endothermic. The peak temperature in the gasifier changed with the injection positions and ratios of the secondary air, which could be as high as 1056 °C. The concentration of CO 2, CO, H 2 and CH 4 increased with the secondary air while the O 2 concentration remained constant. The syngas component exhibited different laws when the secondary air ratio was changed. It was also shown that the optimum condition was that the secondary air was injected in the oxidization zone at a secondary air ratio of about 31%. Under that condition, the fuel gas production was 1.30 Nm 3/kg, the low heating value of the syngas was 6.7 MJ/Nm 3, the carbon conversion rate was 92.2% and the cold gas efficiency of the gasifier was 63.2%. The tar content of the syngas was also studied in this paper. It decreased from 4.4 g/m 3 for gasification without the secondary air to 1.6 g/m 3 for gasification with the secondary air injected in the oxidization zone.

Gasification of rice husk in a cyclone gasifier

The experimental results of air gasification of rice husk in the cyclone gasifier were presented at the fuel rate of 20.1 kg/h. With the equivalence ratios varied in the range of 0.21–0.32, the heating value of the producer gas decreases from 6.98 MJ/Nm3 to 3.11 MJ/Nm3 and the cold gas efficiency decreases from 64% to 31%. However, the tar content in the prouder gas decreases with the increase of the equivalence ratio. The rice husk and ash were examined under a scanning electron microscope (SEM) and energy dispersive X-ray (EDX) elemental analysis. The outer surface of the fuel particle which is of scale structure does not change basically during the gasification. The pyrolyzed gas is mainly released from the inner surface of the fuel particle.

An experimental study on air gasification of biomass micron fuel (BMF) in a cyclone gasifier

Biomass micron fuel (BMF) produced from feedstock (energy crops, agricultural wastes, forestry residues and so on) through an efficient crushing process is a kind of powdery biomass fuel with particle size of less than 250 μm. Based on the properties of BMF, 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, characteristics of BMF air gasification were studied in the gasifier. Without outer heat energy input, the whole process is supplied with energy produced by partial combustion of BMF in the gasifier using a hypostoichiometric amount of air. The effects of equivalence ratio (ER) and biomass particle size on gasification temperature, gas composition, gas yield, low-heating value (LHV), carbon conversion and gasification efficiency were studied. The results showed that higher ER led to higher gasification temperature and contributed to high H 2-content, but too high ER lowered fuel gas content and degraded fuel gas quality. A smaller particle was more favorable for higher gas yield, LHV, carbon conversion and gasification efficiency. And the BMF air gasification in the cyclone gasifier with the energy self-sufficiency is reliable.