Mathematical modelling and optimization of biomass-plastic fixed-bed downdraft co-gasification process

Co-gasification of woody biomass and polyethylene is studied using mathematical modeling. The gasification process is downdraft fixed-bed. Comparison of modeling results with some experimental data is made. Influence of biomass/plastic ratio and air equivalence ratio on gasification efficiency is investigated

Numerical estimation of the thermal stability boundaries for the process of thermochemical conversion processes of biomass in quasi-equilibrium approximation

The stationary process of pyrolysis and gasification of plant biomass in a wide range of conditions is considered. The reaction rate in a multicomponent system is a complex function of composition and temperature. To simplify the calculations, we use the approximation of the brutto-reaction: it is supposed that a slow reaction of thermal decomposition of biomass proceeds in the reaction zone with first order kinetics and Arrhenius dependence on temperature. Gas phase reactions rates are considered to be high enough to apply the quasi-equilibrium approximation. Calculations make it possible to estimate the temperature values at the boundary of thermal stability and the position of this boundary for different residence times of biofuel in the reaction zone

Particle Agglomeration of Biomass and Plastic Waste during Their Thermochemical Fixed-Bed Conversion

The article provides state-of-the-art research on agglomeration processes during fixed-bed combustion and gasification of low-grade fuels such as biomass and waste (primarily plastic-containing waste). Such fuels demonstrate complex thermal behaviour: their decomposition and combustion are multistage, accompanied by phase transitions, and may lead to fixed-bed mechanical instability and the non-uniformity of air distribution over the cross-section. To clarify the role of physicochemical factors (fuel composition and properties, reactor conditions), data from different sources are compared. The review shows that the fixed-bed agglomeration regimes can, in a rough approximation, be classified by the sintering mechanism (due to the melting of the mineral part or the organic part), with the following search for each mechanism realisation conditions by comparing the fuel properties and characteristic temperatures. Attempts to theoretically describe and numerically simulate the agglomeration phenomenon as a change in the structure of a reacting dispersed medium are also considered: the main directions in which such approaches can be developed are indicated

Mathematical modelling and optimization of biomass-plastic fixed-bed downdraft co-gasification process

Co-gasification of woody biomass and polyethylene is studied using mathematical modeling. The gasification process is downdraft fixed-bed. Comparison of modeling results with some experimental data is made. Influence of biomass/plastic ratio and air equivalence ratio on gasification efficiency is investigated

On the Existence and Applicability of Extremal Principles in the Theory of Irreversible Processes: A Critical Review

A brief review of the development of ideas on extremal principles in the theory of heat and mass transfer processes (including those in reacting media) is given. The extremal principles of non-equilibrium thermodynamics are critically examined. Examples are shown in which the mechanical use of entropy production-based principles turns out to be inefficient and even contradictory. The main problem of extremal principles in the theory of irreversible processes is the impossibility of their generalization, often even within the framework of a class of problems. Alternative extremal formulations are considered: variational principles for heat and mass transfer equations and other dissipative systems. Several extremal principles are singled out, which make it possible to simplify the numerical solution of the initial equations. Criteria are proposed that allow one to classify extremal principles according to their areas of applicability. Possible directions for further research in the search for extremal principles in the theory of irreversible processes are given

Mathematical modelling of the oxyfuel gasification of pulverized coal fuel

In this work, we studied the efficiency of the coal gasification process under oxyfuel conditions. Using mathematical modelling one-dimensional stationary statement, the optimal parameters of coal processing were determined, air and oxyfuel conditions are compared. The calculated dependences of the characteristics of the gasification process on the stoichiometric ratio at different initial temperatures are constructed. The optimal values of oxygen stoichiometric ratio and the maximum values of cold gas efficiency in the selected range of parameters are determined. The contribution of the thermophysical and reactive properties of the gasification agent to the change in the cold gas efficiency is estimated

Mathematical Modelling of the Fixed-Bed Biomass-Coal Co-Gasification Process

The paper considers mathematical modelling of downdraft fixed-bed gasification process of the mixtures of woody biomass and coal. Biomass/coal ratio, biomass moisture content and air equivalence ratio are varying parameters. Boundaries of the efficient gasification regimes are estimated

Numerical Study on the Efficiency of Biomass and Municipal Waste Fixed-Bed Co-Gasification

The utilization of combustible waste, such as sewage sludge, can be combined with energy production for small-scale consumers. One of the ways of such utilization can be gasification, which makes it possible to obtain a combustible gas suitable for thermal and electric energy production. The aim of this study is to estimate the efficiency of sewage sludge co-conversion with woody biomass using mathematical model that allows to investigate process characteristics under different process conditions (air stoichiometric ratio, fuel mixture composition, initial moisture of sewage sludge). Dependencies of gasification process characteristics are evaluated and compared with published experimental data. Fixed-bed downdraft process is investigated related to using of wood and sewage sludge mixtures. New results are obtained considering process efficiency dependence on input fuel composition, method is proposed to estimate acceptable fuel mixtures based on agglomeration and efficiency requirements

Influence of volatiles oxidation processes on kinetics of sawdust combustion

The paper considers influence of the devolatilization on the combustion of a small woody particle at TGA conditions. Differences between woody char and raw sawdust combustion kinetics are evaluated. Gas formation kinetic parameters are estimated