Influence of the HTC treatment on fast pyrolysis of agricultural biomass

XXIV International Symposium on Combustion Processes, September 23-25, 2019, Wroclaw, Poland

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Influence of the HTC treatment on fast pyrolysis of agricultural biomass

Eddy Bramer1_, Paweł Owczarek1_{, Anton Bijl}1_{, Lukasz Niedzwiecki}2, *_{, Artur Pozarlik}1, Krzysztof Mościcki2_{, Mateusz} Wnukowski2_{, Halina Pawlak-Kruczek} 2_{, Gerrit Brem}1

1 _{Faculty of Engineering Technology, Thermal Engineering Group, University of Twente, Drienerlolaan 5,7522 NB Enschede} 2 Department of Boilers, Combustion and Energy System, Wrocław University of Science and Technology,

Wyb.Wyspiańskiego 27 50-370 Wrocław

* corresponding author: lukasz.niedzwiecki@pwr.edu.pl

Keywords: hydrothermal carbonization, wet torrefaction, fast pyrolysis, kinetics, cyclonic TGA

Biomass is one of the renewable energy sources of increasing importance. Biomass is believed to be CO2

neutral. The reason for that is the fact that CO2 emitted from combustion of biomass can be reabsorbed by the

next generation of plants, and used for their growth.

Hydrothermal carbonization (HTC), also called wet torrefaction, is a thermal valorization process, typically performed at 200 °C up to 260 °C, in subcritical water under saturation pressure [1]. Hydrothermal carbonization is also capable of removing a part of inorganic fraction of the biomass [1]–[3]. In general, there are some indications, that thermal valorization of biomass could enhance its properties, with respect to its subsequent pyrolysis [4].

Fast pyrolysis is a process of thermal decomposition of solid fuel that aims to achieve high yield of liquid products. Pyrolysis generally speaking is a thermochemical conversion process with use of heat, which causes decomposition of solid fuel into non-condensable and condensable gases as well as solids (char). Fast pyrolysis is designed to maximize yield of condensable products (Bio Oil, also known as pyrolysis oil) [5]. Typically fast pyrolysis employs high heating rates (order of magnitude of 100 °C/s) and temperatures between 450 °C and 550 °C [5], and residence time in the order of magnitude of 1 s [6].

PyRos is a fast pyrolysis installation developed by Thermal Engineering group at University of Twente in Netherlands. Reactor is patented (patent number WO0134725) and located at the premises of the university. Pilot plant can process 30 kg of biomass per hour. PyRos is a cyclonic shaped reactor and biomass is being injected into the cyclone with preheated inert material (sand) and gases. Centrifugal forces separate solids and from condensable vapours and gases. Solids slide down the reactor walls. Biomass is in direct contact with hot inert sand which allows to achieve high heat transfer reaching 500 up to 700 W/m2_{K. This also allows easy}

introduction of catalyst. Produced char is used in Fluidised Bed combustor to obtain heat necessary for the process [7]. Moreover, Thermal Engineering group at University of Twente developed a bespoke TGA, that allows achieving heating rates comparable to PyRos [8]. Key element of Cyclonic TGA is a cyclonic reactor chamber. Inside this chamber devolatization of sample takes place, when sample is injected into the reactor, using specially designed feeding system. Injected particles are entrained by carrying gas (N2) delivered into the reactor

via N2 inlet. Nitrogen is preheated inside of the preheater, before injection into the reactor chamber. Gas is being

injected into the chamber in tangential direction. Whole rig is placed on a very sensitive balance, with a high speed damped load cell.

Within the scope of the performed work was characterisation of the process with special respect to the first phase of the process, namely devolatization of solid feedstock. The main goal of the work was the determination of the fast pyrolysis kinetics of pretreated and unpretreated biomass, with respect to particle size, severity of the HTC pretreatment (process temperature and residence time) and addition of catalyst. Additionally, Biot number was used to determine if obtained kinetic data can be considered as apparent or intrinsic, for the investigated ranges of particle sizes and temperatures. The range was chosen, based on actual process conditions, typical for the fast pyrolysis reactor.

XXIV International Symposium on Combustion Processes, September 23-25, 2019, Wroclaw, Poland

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Fig. 1. Arrhenius plot for fast pyrolysis of raw and wet torrefied Miscanthus

It can be concluded, based on the results (Fig.1), that using wet torrefaction, as a pretreatment before fast pyrolysis, influences the kinetics of the fast pyrolysis of Miscanthus, increasing the rate of the process.

Acknowledgements

The authors would like to thank the European Commission, the National Centre for Research and Development (Poland), Nederlandse Organisatie Voor Wetenschappelijk Onderzoek (Netherlands) and Swedish Research Council Formas for funding in the frame of the collaborative international consortium (RECOWATDIG) financed under the 2018 Joint call of the WaterWorks2017 ERANET Cofund. This ERA-NET is an integral part of the activities developed by the Water JPI. The corresponding author would like to thank also Erasmus + program for the possibility to perform part of the research at the University of Twente.

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