A study on the discharge rate of biomass briquettes stored in hoppers: Discrete element analysis Carlos González-Montellano*, Álvaro Ramírez Gómez, José M. Fuentes, Eutiquio Gallego, Francisco Ayuga BIPREE Research Group, Universidad Politécnica de Madrid, ETSI Agrónomos, Avda Complutense s/n, 28040 Madrid, Spain *Corresponding author. e-mail: carlos.gonzalez.montellano@upm.es Abstract Silos and hoppers are structures designed for storing and handling very different granular materials in the industry. The discharge rate produced during the discharge processes must be perfectly known in many cases. There exist some classical analytical procedures for estimating the discharge rate and their validity has been checked for many granular materials usually handled in the industry. However, this is not the case of new materials, such us biomass pellets and briquettes. In this work, different discrete element models have been used to predict the discharge rate of biomass pellets from a hopper under different conditions The preliminary results of these models were compared with those obtained using analytical procedures and a good level of agreement has been found. Key words: biomass pellets, discrete element method, hopper, discharge rate 1. Introduction Silos and hoppers are structures designed for the storage and handling of very different granular materials in the industry. Their correct design is essential to ensure an adequate functioning of the industrial process where they are included. One of the design factors to be accounted for is the achievement of a reliable and continuous discharge rate during emptying. For many typical materials, discharge rate issues are well known and analytical procedures exists to describe this process. However, this is still an unknown issue for new materials – such us biomass – which are nowadays being stored and handled in silos and hoppers. The Discrete Element Method (DEM) (Cundal and Strack, 1979) is a numerical technique specifically designed for the simulation of the mechanical behaviour of granular materials and nowadays is becoming increasingly popular. It has proven to be a good prediction tool in many different scenarios involving granular materials (Gonzalez-Montellano et al, 2011). In this work, DEM has been used for simulating the discharge process of biomass briquettes stored in a hopper under different scenarios. The aim of this work is to compare the numerical predictions given by the DEM models with those obtained using analytical procedures. This comparison will allow assessing whether the analytical procedures are valid for biomass materials under different working conditions. 2. Materials and Methods 2.1. Numerical models The DEM models developed in this work aim at describing the filling and discharge of biomass briquettes (made up of crushed vine shots) from a 3D pyramidal hopper with a square outlet. The generic geometry of this hopper can be seen in Fig. 1a. Twelve different DEM models were defined in this paper by particularising the generic dimensions shown in Fig. 1 in order to produce a wide range of different hopper configurations. Each configuration is characterised by particular values of the hopper angle of inclination (θ) and the side of the