Influence of the Heat Loss on the Performance of a Two-stage Gasification Reactor

This paper investigates the gasification efficiency of a two stage gasifier, described in all detail in previous works, as a function of the heat loss across the reactor walls. The behaviour of the reactor was simulated using a simple mathematical model already reported in previous papers. The examined heat loss ranges from 0% of the heat produced by the exothermic reactions into the reactor, up to 20%. Calculations have been performed by keeping constant both the injected total oxygen and its partition between the two stages, while different feedstocks have been used, such as landfill gas, municipal solid waste (MWS), willow and rice straw. The results of calculation show that the gasification efficiency at fixed oxygen injection is greatly influenced by the feedstock. The elaboration of the obtained data indicates also that the trend of the gasification efficiency vs. heat loss is a function of the high heating value of the feedstock and of the ratio between the oxygen present into the reactor (injected + the one of the feedstock) and the stoichiometric oxygen necessary to transform the feeding into carbon dioxide and steam.

SYNGAS DERIVED FROM CATALYTIC GASIFICATION OF FINE COAL WASTE USING INDONESIAN POTENTIAL CATALYST

Fine coal waste from the coal mining process has not been used as clean energy even though the amount is very abundant in the world. The conversion of fine coal to syngas is a new way to increase the value of fine coal. Syngas composition, gas ratio, gasification efficiency, and heating value of syngas have been determined under various conditions of temperature (550-750 °C) and bentonite catalyst ratio (0-0.25). The results indicate that fine coal is the suitable raw material for the gasification process. At the highest temperature (750 °C), the gas composition consists of 42.6 vol% H2, 19.1vol% CO, 19.5 vol% CH4, and 7.9vol% CO2. The best performance was achieved when the catalyst/feed ratio is 0.25 with the gas composition of 54.3vol% H2, 26.2vol% CO, 23.8 vol% CH4, and 3.5vol% CO2, heating value and gasification efficiency were 19.72 MJ/Nm3 and 72.27% at 750 °C.

Gasification of spent pot-lining from the aluminum industry

Aluminum production generates enormous spent pot lining (SPL) waste of around one million tons yearly, and these wastes are usually disposed in landfills. Hence, the technical feasibility of SPL gasification using both equilibrium and reactive high-fidelity modeling was evaluated in this study. Three SPL with different washing treatment, i.e., water (WWSPL), acid treated (ATSPL), and full treated (FTSPL, a combination of both water and acid washing) were used for the modeling. The equilibrium model considered twelve species, while the high-fidelity simulation was modeled with multiple species. Moreover, the high fidelity model is governed by the steady non-isothermal Navier–Stokes equation coupled with the discrete phase in Eulerian–Lagrangian scheme. The process metrics were assessed via the produced syngas fraction (CO/H2) and gasification efficiency (GE). The equilibrium analysis of WWSPL, ATSPL, FTSPL, respectively, resulted in GE of 40, 65, and 75%. The corresponding syngas molar fractions for CO and H2 were 0.804 and 0.178 at 1450 °C; 0.769 and 0.159 at 1100 °C; and 0.730 and 0.218 at 1150 °C. These results suggest the potentiality and feasibility of gasifying the treated SPL, which was considered in the high-fidelity. Although the results show different trend from equilibrium for the FTSPL gasification (i.e., small molar fraction of CO2 and H2O and high syngas fraction dominated by CO at 0.75 and 0.1 H2 at best GE of 70%), it re-emphasizes the potential of the gasification of FTSPL as recyclable/renewable energy source. Graphical abstract

Thermodynamic Analysis of Biomass Gasification Using Aspen Plus: Comparison of Stoichiometric and Non-Stoichiometric Models

The gasification process involves several reactions that occur simultaneously and are interrelated by several independent variables. Simulation tools can help us to understand the process behaviour and predict the efficiency and final composition of the products. In this work, two thermodynamic equilibrium models developed in Aspen Plus® software were assessed: a non-stoichiometric model based on the feedstock composition and on the most probable compounds expected from the results of the gasification process using minimisation of Gibbs free energy and a stoichiometric model based on a set of chemical reactions considered as the most relevant to describe the gasification process. Both models were validated with experimental data from a bubbling fluidised bed semi-pilot scale gasifier using pine kernel shells (PKS) as feedstock. The influence of temperature, stoichiometric ratio (SR) and steam to biomass ratio (SBR) were analysed. Overall, predictions of the gas composition and gasification efficiency parameters by the stoichiometric model showed better agreement to the experimental results. Our results point out the significance of an accurate description of the equilibrium composition of producer gas with the stoichiometric model for the gasification of biomass.

Mathematical modeling of thermal decomposition of resins in the process of reversed gasification of plant biomass

THE PURPOSE. Of this work is to estimate parameters for a sufficiently comlete thermal decomposition of tarry products of the fixed-bed gasification of wood fuel. METHODS. To this end, mathematical models are used in different statements: the decomposition of the tar is considered in the approximations of one- and two-reaction kinetic scheme; to assess the influence of the bed height and temperature, the convection-diffusionreaction equation with a given temperature distribution along the length of the reaction zone is used; the temperature of the gasification process is estimated from experimental data and thermodynamic calculations. Along with the numerical model of the decomposition of the tar, a simplified analytical expression (for large Peclet numbers) is applied, the limits of its applicability are determined. RESULTS. Of calculations show that the efficiency of the airblown gasification of wood is determined by the temperature level of the oxidation stage: in the range of modes in which the optimal values of efficiency are achieved, the conversion of tarry products does not proceed sufficiently completely due to kinetic limitations; an increase in the specific consumption of the oxidizer leads to a decrease in efficiency due to stoichiometric reasons. CONCLUSION. Physicochemical limitations do not allow reaching the limiting values of gasification efficiency, shifting the optimal modes towards increasing the specific air consumption; a decrease in the yield of tar requires, first of all, changes in the thermal modes of gasification (for example, external heating or an increase in the oxygen concentration).

Thermodynamic Analysis of Hydrogen Production From Coal Char Gasification in Triple-Bed Circulating Fluidized Bed

The triple-bed circulating fluidized bed gasifier is a new type of the gasification process in which the combustion process, pyrolysis process, and gasification process of the fuel are carried out in different reactors. The inert heat carrier is used to transfer heat between the reactors. In this way, the gasification efficiency of char is improved since the tar and pyrolysis gas generated in the pyrolysis process will no longer hinder the gasification of the char. The thermodynamic equilibrium model is used to simulate the gasification process of the triple-bed circulating fluidized bed, and the sub-models are established to simulate combustion, pyrolysis, and gasification processes. The simulation results agree well with the experimental values. Besides, the model studies the effects of key parameters such as the gasification reaction temperature and the ratio of steam to C (S/C) on gasification performance. Results showed that higher gasification reaction temperature has a positive effect on gasification performance, S/C may not be too high, and excessive water vapor will directly affect the gasification reaction.

EXPERIMENTAL STUDIES ON GASIFICATION PERFORMANCE OF SAWDUST AND SAWDUST PELLET IN A DOWNDRAFT BIOMASS GASIFIER

In this work, a comparative analysis of the gasification process of sawdust (SW) and sawdust pellet (SWP) utilizing a downdraft gasifier was performed. The gasification was conducted in a research-scale fixed-bed gasifier applying air as an oxidizing agent. The comparison between the raw (sawdust, SW) and treated biomass (sawdust pellet, SWP) was investigated for the syngas composition and gasification performance at the fixed condition of gasification temperature at 750 °C and equivalence ratio of 0.25. The gasification performance was tabulated in the form of heating value of the syngas (HHVsyngas), gasification efficiency (ηGE) and carbon conversion efficiency (ηCCE). It was found out that SWP produced the highest H2 and the lowest CO2. Furthermore, SWP also present the better gasification performance than SW. SWP achieved the high HHVsyngas, ηGE, and ηCCE at 4.2152 MJ/Nm3, 24% and 37%, respectively.