Biochar for horticultural and agricultural applications using high temperature torrefaction technology Pradeep Ravi Supervisors: Prof Dr. D.J.E.M Roekaerts, ir.Bart de Vries, Dr. Luis Cutz, Dr.Lorenzo Botto & Dr.Ralph Lindeboom Biomass currently accounts for less than 10 percentage of the world’s renewable energy production. Currently the major global sustainability issue stems from the sourcing of virgin wood chips from dense forests for pellet production. An alternative is to use residual biomass from agriculture or forestry, which is produced in large volumes, to produce different products that range from biofuels to chemicals via thermochemical conversion technologies. Among thermochemical technologies, torrefaction is a promising route to produce solid biofuel known as biochar. With an increasing potential for biomass production coupled with an increased scrutiny on the use of biomass as a green fuel, the need for alternative clean applications for the biochar is critical. The aim of this study is to investigate new and novel agricultural residues or other waste streams to produce biochar using high temperature (350 °C) torrefaction technology. The obtained biochar is evaluated experimentally to determine the best feedstocks out of the ones that are selected from a performance and cost point of view for horticultural applications. . This research aims to provide a clear and useful analytical tool which will benefit the scientific community to select suitable biomass materials based on material properties and end applications. The efficacy for the various torrefied biomass feedstocks on the soil and its stability are tested. Overall, about 50 different biomass feedstocks were identified and evaluated based on past performances from literature. The top 10 best performing feedstocks were sourced and subjected to various physical and chemical characterization tests with a specific focus on soil remediation. The selected materials were torrefied in a fixed bed pilot reactor Scanning Electron Microscopy with Energy Dispersive X-Ray Spectroscopy (SEM-EDS), Brunauer–Emmett–Teller (BET) and pH measurements. Ultimately the feedstocks were scored and ranked from best to worst performing biochar for soil remediation and sequestration-based applications. The results of this project indicate potential for biochar production from woody, grassy and other processed materials that could help to remove the dependence on evergreen forests and wood chips. The system proposed in this work could also yield negative emissions since the feedstocks are residual flows and the biochar is going to be used in the soil.

Emission of fine and ultrafine particles from wood fired cook stoves are a major concern worldwide especially in the many countries where biomass cookstove are used on daily basis. Due to their small size these particles can reach deep within the lungs and cause various health issues. The effect of insertion of a turbulent agglomerator in the cookstove chimney on the number of small particles emitted has been investigated. This device consists of a number of properly designed obstacles in the flow increasing the turbulence level and enhancing collisions and agglomeration of particles. The device is suitable because it requires little extra investment and does not require an external energy source. First an analytical model of the flow through a Plancha type cookstove was made in MATLAB, in order to obtain estimates for the flow properties at the chimney inlet. Next, CFD simulations were performed using Ansys Fluent R3 and the grid generator program CFMesh+ software. Eulerian-Lagrangian (EL) simulations of dispersed multiphase flow were made to determine the particle dynamics within the flow domain. Particle agglomeration was studied using Eulerian-Eulerian (EE) simulations in combination with the population balance equation (PBE) for particle size. Appropriate agglomeration kernels were implemented via user-defined functions. A key feature taken into account is that agglomeration of particles for particles smaller than the Kolmogorov scale is determined by Brownian motion whereas turbulence takes over as driver for agglomeration for particles larger than the Kolmogorov scale. The turbulence properties were obtained using the standard k-ϵ model with standard wall functions. To check the operation of the CFD model, a first application of the EE approach was made to a turbulent agglomerator with extra air injection via a jet in the side wall. This was studied in a simplified 2D geometry. In the investigated case it was observed that the turbulence caused by the jet has larger effect than the turbulence of the obstacles. Next, the EL and EE CFD models were applied to a agglomerator type for which experimental data are available. These simulations concern a 3D domain representing chimney with obstacles creating turbulence. To be relevant for the cookstove chimney case operation at a lower flow rate than the experiment had to be studied. Wakes behind obstacles play an important role. Large particles have higher probability to bypass the wakes. The wakes provide zones with larger mean residence time where the agglomeration process can have more effect. The simulations using the PBE provided quantitative results for the evolution of the volume fraction of different size classes of particles. It was found that for the considered chimney (lower velocity, hence lower turbulence level) the turbulent agglomeration effect is too weak to obtain a sufficient removal efficiency of submicron particles (under 1%). In case of higher particle load higher removal efficiency can be achieved.