Dual Bed Gasifier Research Articles

Techno-Economic Study and Environmental Analysis for the Production of Bio-methanol Using a Solar-Aided Dual-bed Gasifier

Techno-Economic Study and Environmental Analysis for the Production of Bio-methanol Using a Solar-Aided Dual-bed Gasifier

Experiment and computational fluid dynamics simulation of in-depth system hydrodynamics in dual-bed gasifier

Dual-bed gasifier is a new gasifier system with separated combustion and gasification zones. The two-zone separation makes it possible to increase calorific value of the producer gas. In order to develop and improve the process operation, understanding of system dynamics and parameters that describe the in-depth hydrodynamics are essential. Computational fluid dynamics is a tool that can be used to explain the complex multiphase system behavior. The considered dual-bed gasifier had 3.00 m height and the maximum width diameters of riser and downcomer were 0.14 and 0.40 m, respectively. Conservation equations of mass, momentum, energy and species for each phase were solved coupling with the kinetic theory of granular flow using ANSYS FLUENT version 12.1. Here, two-dimensional simulation had been successfully determined the flow pattern and chemical reaction corresponding with actual experimental and theoretical data. The calculated results of the solid volume fraction in the riser section showed the bubbling and slugging flow patterns. The product gas composition and gas temperature inside dual-bed gasifer reflected the advantages for this type of reactor over the other conventional gasifiers. The system turbulences were firstly explored in dual-bed system which were normal Reynolds stresses and granular temperatures. For the effect of interphase exchange coefficient model, the pressure-loop using drag force model proposed by Gidaspow was in good agreement with the experiment than the ones proposed by Wen-Yu and Syamlal-O'Brien.

Effect of Steam on Syngas Production in New-Designed Dual-Bed Gasifier

In this research, the effect of steam on synthetic fuel production from sawdust in new-designed dual-bed gasification was studied. The dual-bed gasification reactor composed of bubbling/fast fluidized bed combustor and fixed bed gasifier (pyrolysis included) was designed to produce syngas (CO + H2 + CO2 and CH4). The results showed that syngas produced by the dual-bed gasifier with higher steam/carbon ratio also had higher H2 content. In theory, the various reactions expected to occur in the gasification process were boudouard, water-gas and water-gas shift, methanation and steam reforming. Since the operating temperature was only 500-600°C that the steam reformation of methane was desperately to occur due to its endothermic, then CH4 formation still were found. Producer gas from the new gasifier had relatively high quality in terms of heating value per a unit volume compared to other conventional gasifiers. This can be used directly as good gaseous fuel. However, the product gas was not likely served as precursor in chemical industries due to its still low H2/CO ratio and high CH4 concentration.

Combined gasification of coal and biomass in internal circulating fluidized bed

The paper addresses the combined gasification of biomass and brown coal in an internal circulating fluidized bed (ICFB) for generating a valuable producer gas.A primary method for tar abatement and gas improving was adopted, consisting in a Ni-based catalyst in the bed together with sand. The hydrogen concentration in the producer gas was high (up to 35% in the best case, >20% typically) demonstrating the validity of the ICFB process for co-gasification of coal with biomass. Higher H2 and CO contents and lower tar yields were obtained with greater coal loadings. The tar was reduced by up to three times when changing from inert to a partly catalytic bed, under steam gasification conditions. However, this good figure is contrasted by a rather fast decay in catalytic activity, and a rather low carbon conversion even in presence of the catalyst.A mathematical model based on thermodynamic computations predicts the trend and values of the measured gas concentrations at different steam/fuel ratios, providing useful indications for its optimal choice. The findings of the research reinforce the idea that dual bed gasification is suitable even when a relatively low reactivity fuel is used, such as the brown coal in this study.

Production of Middle Caloric Fuel Gas from Coal by Dual-Bed Gasification Technology

A coal gasification technology for producing middle caloric fuel gas using granular coal is urgently required in China considering the huge energy demand required for project development. This work demonstrated the dual-bed gasification technology on a pilot plant (1000 tons of coal/a) mainly consisting of a fluidized-bed gasifier and a pneumatic combustor using the coal with a particle size of less than 20 mm. Simulation was performed with Aspen Plus to investigate the feasibility of producing a middle caloric fuel gas. It was found that, with a bituminite powdered coal as fuel and air as the gasifying reagent, the pilot plant could operate steadily within a given duration of 16 h. At a gasifier temperature of 900 °C and combustor temperature of 980 °C, a fuel gas with 1680 kcal N−1 m−3 of high heating value (HHV) was produced at an equivalence ratio (ER) of 0.089 (defined as the ratio of the oxygen mole in air supplied in the gasifier to the oxygen mole needed for burning the fed coal completely). The heating value of fuel gas could be enhanced by introducing steam as a supplementary reagent to the gasifier while reducing the air required. Gasification simulation of 10 tons of coal/h indicated that a fuel gas with above 2000 kcal N−1 m−3 of HHV could be obtained with an ER of less than 0.10 and a steam/coal ratio larger than 0.48. The study suggested that dual-bed gasification technology could be employed for producing a middle caloric fuel gas using granular coal with a size of less than 20 mm.

Dual-Bed Gasification of Petcoke: Model Development and Validation

In this work, the problem of modeling a previously proposed dual-bed gasification scheme [Sudiro et al., Energy Fuels 2008, 22, 3894−3901] is addressed. The process consists of a combustor and a gasifier, which are thermally coupled by the circulation of an inert solid, to use air instead of pure oxygen in the combustor. The coal gasification reactor is modeled, taking into account both chemical kinetics and mass transfer between gas phase and char particles. First, the model is developed and validated with reference literature and experimental data for conventional coal gasification using oxygen in both entrained-flow and fluid-bed gasifiers. A series of sensitivity analyses is performed with regard to a conventional gasifier fed by petcoke, and the effects of residence time and oxygen/carbon mass ratio in the feed are investigated over three process variables: char conversion at the gasifier exit, temperature at the gasifier exit, and amount of useful syngas (H2 and CO) produced, in terms of N m3 per ton of petcoke. Finally, the model is extended for application to the dual-bed process. Results from this simulation are compared to those obtained under equilibrium conditions, with an energetically equivalent syngas throughput.

SYNTHETIC NATURAL GAS (SNG) FROM PETCOKE: MODEL DEVELOPMENT AND SIMULATION

In this work the issue of producing SNG from petcoke was addressed by developing a complete process. First, a model for coal gasification, taking into account kinetics and mass transfer was developed; the simulation model was applied to a conceptual dual bed gasification (Sudiro et al., 2008). Then, a process to produce synthetic natural gas (SNG) from syngas was developed, facing the main issue of this process: the temperature control of the methanator. Performances of the global process simulated with Aspen PlusTM have been evaluated, with respect to product yield, CO2 emissions and overall energy efficiency.

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).

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).

Catalyst development for the gasification of biomass in the dual-bed gasifier

A dual-bed gasifier system combined with catalysts was evaluated in the catalytic gasification of cedar wood at low temperatures (823–973 K). The dual-bed gasifier consisted of a primary-bed section for pyrolysis of biomass and separation of pyrolyzed gas and tar from solid products and a secondary-catalytic tar reformer. Catalyst development was carried out on the basis of Rh/CeO 2/SiO 2, which has been developed for the higher conversion of carbon to gas and higher yield of CO+H 2+CH 4. We have also carried out the optimization of reaction conditions. Especially, the tar derived from maximum of 250 mg biomass/min can be totally converted to the gas product by 3 g catalyst in this system using ER=0.25 of total carbon present in the biomass. This performance was much higher than that over commercial steam reforming catalyst. In addition, the amount of coke deposited on Rh/CeO 2/SiO 2 was much smaller. In the dual-bed system combined with excellent catalysts, almost all the tar can be converted to syngas at lower temperature than that needed by the conventional method with high energy efficiency.

Nickel catalyst deactivation in the steam-carbon reaction

Nickel deactivation during steam gasification of carbon is shown to be two types which depend upon the chemical nature of the carbon. For graphite, deactivation is moderate and may be attributed either to catalyst clustering or to effects of the carburization of the nickel. With less-ordered carbons, like Spherocarb, deactivation is severe and rapid. The catalyst particles apparently lose surface area due to encapsulation by a graphite overlayer. Dual-bed gasification indicates that the carbon substrate releases hydrocarbon species which subsequently decompose on the nickel. Analogous results are obtained during the CO 2 and H 2 gasification reactions.