Design of a steam boiler for cashew nut processing

Details

Supervisors

Jeanmart, Hervé

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil mécanicien, à finalité spécialisée

Abstract

This work is part of the Biostar project that targets small and medium-sized companies in West Africa to help them through the energetic transition, by implementing bioenergy production units from their organic waste. One of these companies is ANASAM, a cashew nut processing company located in Burkina Faso. To generate the steam needed to process the cashew nuts, ANASAM uses a steam boiler heated by a furnace in which empty cashew nut shells are pyrolyzed. The NITIDAE company that produces the boiler of the ANASAM company would like to reduce the pressure inside the boiler for safety (less risks when empty heating of the boiler), economic (less and/or cheaper material) as well as environmental (shorter heating time) reasons. Therefore the aim of this thesis is to design a steam boiler for cashew nut processing. In the current work, we first modeled the thermodynamic behaviour of the content of the boiler throughout the operational steps of the actual boiler, by using a Python code that we developed to obtain an estimation of the outgoing mass flow rate of the generated steam. Next, we simulated the influence of several parameters of the boiler (quality of the heat exchange, height of the boiler, volume of the boiler, initial water volume inside the boiler) on the maximal pressure that is needed to obtain the same mean outgoing mass flow rate. Improving the heat exchange between the hot source and the inside of the boiler will decrease the maximal pressure needed to obtain the same outputs and at the same time reduce the material needed as well as the heating time. While increasing the volume of the boiler decreases the maximal pressure needed and thereby the risks when empty heating, it requires more material to build the boiler and increases the heating time. Increasing the height of the boiler has a positive impact on all aspects. Yet, the impact is smaller than the impact of improving the heat exchanger and more difficult to implement as it requires the replacement of the boiler. The initial water volume can be optimized for every boiler design to minimize the maximal pressure needed to obtain the same outputs. Its effect is minimal, but, as it does not present any disadvantage, it is always interesting to ensure that the optimal water volume is used. We can conclude that, to meet all three concerns raised by NITIDAE, the most interesting parameters of the actual boiler to adapt are the heat exchanger and the initial water volume pumped inside it. In case the boiler has to be replaced or the effects of the improvement of the heat exchange are insufficient, changing the height could add benefit.