Simulation model to improve the fuel distribution of furnaces combusting herbaceous biomass

Project Number 418

Based on the political developments of recent years, which provide for a significant reduction in CO₂ emissions, increased use of herbaceous biomass is becoming increasingly important. As a renewable energy source, this can help reduce CO₂ emissions and, in the case of straw, is an agricultural by-product, meaning that there is no competition to food production. With the increasing spread of energetic straw use, the optimization of the transport of herbaceous biomass becomes more and more relevant.

A well-suited method for transport is the pneumatic conveying, which is already used in some straw burning units. A sub-optimal operation of pneumatic conveying can lead to malfunction and increased operating costs. Due to their length, the particles can become entangled with one another and thus lead to blockages in the pneumatic conveying or to fluctuations in the mass flow. Pressure losses are also influenced by the particle shape.

Currently available design diagrams, calculation approaches and recommendations are insufficiently suitable for herbaceous biomass. The focus of the project is therefore on the experimental and numerical investigation of the pneumatic transport of herbaceous biomass with the aim to be able to describe it more reliably and thus to make a concrete contribution to the optimization of its transport. For the numerical investigations, the discrete element method (DEM), which is able to reproduce particle systems with a large number of particles in detail, is coupled with a numerical flow simulation (CFD).

By extending the method with a bending model, deformations of stalks can be simulated. The simulation methodology makes it possible, in close connection to experimental investigations, to map a multiplicity of different operating states with relatively little effort and allows direct access to numerous particle- and fluid-related variables. On the basis of the data thus obtained those for the design and the operation important diagrams and correlations are derived. These concern, for example, the prevailing conveying conditions, the strand length, the pressure drop, and the forces acting on the particles or the deceleration or acceleration in manifolds.

The research project is funded by the German Federal Ministry for Economic Affairs and Energy via the AiF under the funding number 19995 N. It will be conducted from 2018 to 2020 by the Department of Mechanical Process Engineering and Processing at the Technical University of Berlin.