Modelling and Simulation of the HDPE Pyrolysis Process

Pyrolysis is a thermochemical decomposition of organic compounds such as High-density polyethylene (HDPE) plastics. The product of the HDPE pyrolysis is usually diesel with other wastes (such as carbon black, etc.). A pyrolysis reaction is essentially a decomposition reaction performed at elevated temperatures in the absence of oxygen. This work aims to describe some of the primary driving reactions in pyrolysis and to model and simulate the process. In pyrolysis, on a molecular level, there are many complex reactions taking place. To define all the reactions and include them in a model is a very expensive and time-consuming. In this work, the reactions considered are limited to: Beta−scission, hydrogen abstraction and chain fission. To be able to simulate a chemical reaction, reaction equations are needed. These set of equations are available in the literature. We have solved them in MATLAB® using the in-built ordinary differential equation (ODE) solver. The solution represents the rate of the reaction and the product yield. The key to the solution are the reaction constants

Numerical investigation of microwave-assisted pyrolysis of lignin

A comprehensive three-dimensional mathematical model is developed for studying the microwave-assisted pyrolysis of biomass. Kraft Lignin is considered as biomass feedstock in the model, and a mixture of lignin and char, is used as the sample for pyrolysis. A lumped kinetic model which considers three lumped pyrolysis products (gas, liquid and remaining solid fractions) is coupled with the governing equations for the microwave field, heat transfer, mass transfer, Darcy fluid flow and a transient numerical analysis is performed. The distribution of electric field in the microwave cavity, and the distribution of electric field, temperature, and pyrolysis products within the lignin sample are presented. The lignin sample is predicted to undergo volumetric heating when subjected to microwave heating. Accordingly the reaction zone extends from the center of the biomass sample bed towards the outer surface. Preliminary evaluation of the applicability of the model for assessing the effect of different parameters on the microwave pyrolysis of lignin is also carried out

Experiments and modeling of fixed-bed debarking residue pyrolysis: The effect of fuel bed properties on product yields

This paper presents a study on the fixed-bed pyrolysis of debarking residue obtained from Norway spruce. Analysis is based on the dynamic model of packed bed pyrolysis which was calibrated by determining appropriate reaction rates and enthalpies to match the model predictions with the experimental data. The model comprises mass, energy and momentum equations coupled with a rate equation that describes both the primary and secondary pyrolysis reactions. The experiments used for the model calibration determined the yields of solid, liquid and gaseous pyrolysis products as well as their compositions at three distinct holding temperatures. Subsequently, the dynamic model was used to predict the product yields and to analyze the underlying phenomena controlling the overall pyrolysis reaction in a fixed-bed reactor.Peer reviewe

Effects of intraparticle heat and mass transfer during devolatilization of a single coal particle

The objective of the present work is to elucidate the influence of intraparticle mass and heat transfer phenomena on the overall rate and product yields during devolatilization of a single coal particle in an inert atmosphere. To this end a mathematical model has been formulated which covers transient devolatilization kinetics and intraparticle mass and heat transport. Secondary deposition reactions of tarry volatiles also are included. These specific features of the model allow a quantitative assessment to be made of the impact of major process conditions such as the coal particle size, the ambient pressure and the heating rate on the tar, gas and total volatile yield during devolatilization. Model predictions are compared to a limited number of experimental results, both from the present work and from various literature sources

A review of wildland fire spread modelling, 1990-present, 1: Physical and quasi-physical models

In recent years, advances in computational power and spatial data analysis (GIS, remote sensing, etc) have led to an increase in attempts to model the spread and behaviour of wildland fires across the landscape. This series of review papers endeavours to critically and comprehensively review all types of surface fire spread models developed since 1990. This paper reviews models of a physical or quasi-physical nature. These models are based on the fundamental chemistry and/or physics of combustion and fire spread. Other papers in the series review models of an empirical or quasi-empirical nature, and mathematical analogues and simulation models. Many models are extensions or refinements of models developed before 1990. Where this is the case, these models are also discussed but much less comprehensively.Comment: 31 pages + 8 pages references + 2 figures + 5 tables. Submitted to International Journal of Wildland Fir

Development, modelling and evaluation of a (laminar) entrained flow reactor for the determination of the pyrolysis kinetics of polymers.

Laminar Entrained Flow Reactors were examined to determine whether this type of reactor can be used to measure the kinetic parameters of the pyrolysis reaction of polymers. In case the EFR was operated in the turbulent regime or the diameter of the reactor was to small, sticking of polymer to the reactor wall, became a major problem. In the laminar flow regime this problem did not occur and this operation regime was determined as a function of the Reynolds number. Due to the necessity of operation in the laminar regime significant temperature and velocity gradients exist in the EFR. To correct for these gradients a model was developedincorporating the Navier - Stokes equations to describe the gas phase velocity and temperature distributions and a single particle model to describe the conversion of the individual particles. While correction of the experimental data for the axial gradients proved to be possible, it was not possible to correct this data for radial gradients in the reactor due to the uncertainty in the radial position of the particle. Experiments were performed and corrected for the aforementioned gradients to obtain the first order kinetic parameters for the pyrolysis of LDPE. However, these parameters are inaccurate and therefore a LEFR is preferably not to be used to determine kinetics of particles, if operation of the EFR in the laminar regime is necessary (sticking particles). If possible (non-sticking particles) the EFR should be operated in the turbulent regime. Finally our pyrolysis experiments of LDPE showed that intermediate wax - like products are produced during the pyrolysis reaction, which are pyrolysed further in the gas phase

Biomass gasification for syngas and biochar co-production: Energy application and economic evaluation

Syngas and biochar are two main products from biomass gasification. To facilitate the optimization of the energy efficiency and economic viability of gasification systems, a comprehensive fixed-bed gasification model has been developed to predict the product rate and quality of both biochar and syngas. A coupled transient representative particle and fix-bed model was developed to describe the entire fixed-bed in the flow direction of primary air. A three-region approach has been incorporated into the model, which divided the reactor into three regions in terms of different fluid velocity profiles, i.e. natural convection region, mixed convection region, and forced convection region, respectively. The model could provide accurate predictions against experimental data with a deviation generally smaller than 10%. The model is applicable for efficient analysis of fixed-bed biomass gasification under variable operating conditions, such as equivalence ratio, moisture content of feedstock, and air inlet location. The optimal equivalence ratio was found to be 0.25 for maximizing the economic benefits of the gasification process

Modeling on-grate MSW incineration with experimental validation in a batch incinerator

This Article presents a 2-D steady-state model developed for simulating on-grate municipal solid waste incineration, termed GARBED-ss. Gas-solid reactions, gas flow through the porous waste particle bed, conductive, convective, and radiative heat transfer, drying and pyrolysis of the feed, the emission of volatile species, combustion of the pyrolysis gases, the formation and oxidation of char and its gasification by water vapor and carbon dioxide, and the consequent reduction of the bed volume are described in the bed model. The kinetics of the pyrolysis of cellulosic and noncellulosic materials were experimentally derived from experimental measurements. The simulation results provide a deep insight into the various phenomena involved in incineration, for example, the complete consumption of oxygen in a large zone of the bed and a consequent char-gasification zone. The model was successfully validated against experimental measurements in a laboratory batch reactor, using an adapted sister version in a transient regime. © 2010 American Chemical Society