Biomass pyrolysis kinetics: A comparative critical review with relevant agricultural residue case studies

Biomass is currently seen as a promising renewable energy source, which can be sustainably utilized in the production of fuels and electric energy adding no carbon dioxide to the environment. Co-gasification has unveiled its potential amongst thermal techniques, as a result of the valuable products obtained, strengthening a solid position in the conversion of residues. Thus, the prevention of a complete depletion of non-renewable sources is supported and the effects of their utilization alleviated. Extensive literature review was conducted and, few reports on co-gasification of biomass and wastes were found. In this context, this review addresses their thermal conversion, highlighting issues related to the equipment, operating conditions and physicochemical phenomena involved in such a complex process. Among other conclusions, the most important finding of this work was the synergy often encountered between the two feedstocks, proving co-gasification can overcome several of the individual gasification issues enhancing products quality and yields over biomass or wastes alone, and attesting its environmental-friendly character, with lower greenhouse gas emissions. It was also possible to depict some trends on the effect of biomass and waste blending ratios, as well as elucidating some of the mechanisms involved in their interaction. These are majorly explained by the response of molecules during pyrolysis and by hydrogen transfer from waste polymers to biomass derivatives. Experimental conditions were also assessed, fluidized beds being reported as the most suitable reactors for biomass and wastes, under several different possible combinations of operational parameters. A critical discussion is presented, aiming to contribute to a more profound understanding of this matter, its key points and noteworthy potential.

Co-gasification and recent developments on waste-to-energy conversion: A review

The product gas produced from gasification of solid fuel contains various impurities such as particulates, toxin gases, tar, vapours of heavy metals, etc. Presence of tar is a major issue which requires to be addressed before the use of gas product in the downstream process. Tar causes problems in the process equipment like flow channels, power generating units, etc. Generally gasification technology is adapted for the utilization of low grade coal, municipal solid waste, agro-waste, bio-waste, etc., which generates toxic and emits various hazardous compounds of chlorine, sulphur, nitrogen and heavy metals like Mn, Cd and Hg. Various alkali metals like Na, K, etc., generated through the gasification of wastes also create problem in the downstream processes when condensed at low temperature. The key challenge to commercializing gasification technology is to generate a clean fuel gas which meets the global emission standards. This paper provides a comprehensive overview of the fuel gas cleaning methods those are used to remove the contaminants and gas impurities generated from various types of reactor for gasification of coal or biomass.

A review on the fuel gas cleaning technologies in gasification process

The gasification of biomass produces a syngas that can be used for electricity generation and fuels/chemicals production. However, tar is generated along with the syngas as a by-product which causes problematic issues in the end-use of the syngas, such as blockages, plugging and corrosion. Catalytic steam reforming is a suitable option to convert tar into more syngas in the presence of nickel-based catalysts, as the preferred catalyst, mainly due to their activity and low cost. There has been considerable research reported in the literature on modified nickel-based catalysts for steam tar reforming. These modifications have been carried out in order to improve the performance of the Ni-based catalysts for tar reforming, mainly in terms of catalyst stability and activity. Such improvements are achieved by manipulating the properties of the catalyst. This paper therefore presents a critical assessment of these modifications on Ni-based catalysts available in the literature for improved tar reforming. The modifications considered in this review were categorised as: the addition of secondary metal (Fe, Co, Cu, Cr), the addition of noble metals (Pt, Pd, Rh, Au, Rh, Ir), addition of rare earth metals as promoters (Ce, La), alkali and alkaline earth metals (Sr, Ba, Ca, Mg,Ba) and modification of the support material. The paper aims at understanding the properties responsible for the improved performance of the modified Ni-based catalysts in comparison with unmodified Ni-based catalysts. The review paper will serve as a guide for further improvement of Ni-based catalysts for biomass tar reforming.

Modified nickel-based catalysts for improved steam reforming of biomass tar: A critical review

This chapter will describe how heating of a solid fuel leads to flaming ignition. The discussion will be centred on flaming ignition of solid fuels but will not address smouldering or spontaneous ignition since these subjects will be covered in Chaps. 19 and 20 respectively. Thus, the presence of a source of heat decoupled from the solid and fuel gasification will be assumed throughout the chapter.

Flaming Ignition of Solid Fuels

An enthalpy-based pyrolysis model for charring and non-charring materials in case of fire

A new, simple pyrolysis model for charring materials is applied to several numerical and experimental test cases with variable externally imposed heat fluxes. The model is based on enthalpy. A piecewise linear temperature field representation is adopted, in combination with an estimate for the pyrolysis front position. Chemical kinetics are not accounted for: the pyrolysis process takes place in an infinitely thin front, at the ‘pyrolysis temperature’. The evolution in time of pyrolysis gases mass flow rates and surface temperatures is discussed. The presented model is able to reproduce numerical reference results, which were obtained with the more complex moving mesh model. It performs better than the integral model. We illustrate good agreement with numerical reference results for variable thickness and boundary conditions. This reveals that the model provides good results for the entire range of thermally thin and thermally thick materials. It also shows that possible interruption of the pyrolysis process, due to excessive heat losses, is automatically predicted with the present approach. Finally, an experimental test case is considered. Copyright © 2009 John Wiley & Sons, Ltd.

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Application of a simple enthalpy-based pyrolysis model in numerical simulations of pyrolysis of charring materials

In this paper, we describe the results from an experimental campaign, focused on vertical upward flame spread over a charring material. First, for validation purposes of simulation tools, we report on cone calorimeter results for square (9.8 cm x 9.8 cm), 1.65 cm thick, medium density fibre samples, mounted horizontally. Temperature is shown at the surface and at different depths. The mass of the sample is continuously measured. From the raw data, we derive the temporal evolution of the mass loss rate due to pyrolysis. Different externally imposed heat fluxes are investigated (20, 30 and 50 kW/m(2)), onto dry and wet material. Afterwards, for the configuration of two particle board plates (0.025 m thick, 0.4 m wide and 2.5 m high), vertically mounted face to face is considered. Two different horizontal spacing distances between the two plates are studied (30.5 and 10.5 cm). The purpose of this set-up is to investigate the vertical upward flame spread with strong radiative heat feedback. To that purpose, the temporal evolution of surface temperature is measured over the height of the plates. The measurement data are used to test a pyrolysis model in numerical simulations. Copyright (C) 2010 John Wiley & Sons, Ltd.

Study of pyrolysis and upward flame spread on charring materials-Part I: Experimental study

Simulation results, obtained by means of application of an enthalpy-based pyrolysis model, are presented. The ultimate focus concerns the potential of the model to be used in flame spread simulations. As an example we discuss vertically upward flame spread over a charring material in a parallel plate configuration. First, the quality of the pyrolysis model is illustrated by means of cone calorimeter results for square (9.8 cm × 9.8 cm exposed area), 1.65 cm thick, horizontally mounted MDF samples. Temperatures are compared at the front surface and inside the material, for different externally imposed heat fluxes (20, 30 and 50 kW/m2), for dry and wet samples. The mass loss rate is also considered. Afterwards, vertically upward flame spread results are reported for large particle board plates (0.025 m thick, 0.4 m wide and 2.5 m high), vertically mounted face-to-face, for different horizontal spacings between the two plates. The simulation results are compared to experimental data, indicating that, provided that a correct flame height and corresponding heat flux are applied as boundary conditions, flame spread can be predicted accordingly, using the present pyrolysis model. Copyright © 2010 John Wiley & Sons, Ltd.

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Study of vertical upward flame spread on charring materials—Part II: Numerical simulations

Syngas from gasification of carbon-rich feedstock is used for power generation as well as for the production of synthetic fuels and commodity chemicals. Tar removal forms a major challenge in the effort to make these syngas valorisation technologies technically and commercially feasible. Tar removal methods can be divided into two categories: (1) primary methods or treatments inside the gasifier, and (2) secondary methods or hot gas cleaning after the gasifier. The most important features of the primary and secondary tar removal methods, as well as the most recent developments in this field, are reviewed and discussed in this paper. For advanced syngas applications (e.g. gas engines), primary measures are generally not sufficient. In that case, primary methods can be used as a tool to optimise the gas composition for the secondary cleaning step. Corona plasma for tar removal is discussed in more detail. This promising technology will be used in future research on the cracking of real tars obtained from refuse derived fuel (RDF) pyrolysis.

https://lirias.kuleuven.be/bitstream/123456789/417096/2/ABosmans_ELFM2013_final.pdf

Shivanand Wasan

Papers

An enthalpy-based pyrolysis model for charring and non-charring materials in case of fire

Application of a simple enthalpy-based pyrolysis model in numerical simulations of pyrolysis of charring materials

Study of pyrolysis and upward flame spread on charring materials-Part I: Experimental study

Study of vertical upward flame spread on charring materials—Part II: Numerical simulations

Waste-to-clean syngas: avoiding tar problems