Abstract:

This Master’s Thesis is divided in the respective two parts: ‘Energy balance in a Thermal
Assisted Mechanical Dewatering (TAMD) process’ and ‘Pinch analysis for Alfalfa TAMD dewatering’.
The TAMD procedure is a solid/liquid separation process investigate at the RAPSODEE research
center of ‘l’École des Mines d’AlbíCarmaux’. It consists in a hybrid process in which a temperature is
applied at the same time as the mechanical dewatering process. In this way a bigger quantity of final
dry solid content is obtained.
The objective of the first and the most important Master’s Thesis part is to determinate if there is
an energy saving with the use, as a separation process, of the TAMD process, instead of the habitual
mechanical dewatering plus dryer. In this order, the necessary thermal energy in the TAMD process is
calculated from the integration of its heat flow density. This heat flow density is obtained, from
laboratory measured temperatures, by the Inverse Conduction Methodology that allows solving the
direct problem by an iterative algorism. The MATLAB software is used to implement the algorism. To
justify the use of the Inverse Methodology, the heat flow density is also calculated by the direct form
and the results, obtained by each process, are compared. It can be seen that only the inverse
methodology allows a good approximation in the thermal diffusion unstable period. The error standard
deviation of measured temperatures, spread on the heat flux, is calculated to verify the goodness of the
methodology. The optimal processing conditions are founded. Finally, the two necessary energies in
mechanical dewatering plus drying and the TAMD process, to achieve the same final dry solid content,
are calculated and compared. In this order, the ‘RD’ ratio, ratio between the energy required for drying
and the latent heat of vaporization, is used. Energy savings can be seen using the process of TAMD
(RD=1.25 for the normal dewatering process and RD= 0.109 for the TAMD).
The TAMD process can also be applied to Alfalfa dewatering. It must be followed by a thermal
dryer to obtain the needed final dry solid content to use the product as animal feed. The application of
the TAMD process to Alfalfa dewatering has the advantage, respect the usual procedure (thermal
drying), that a green juice with great proprieties for the humans is obtained. Energy savings using the
TAMD process, rather than the usual dewatering process, has also been determined using the inverse
model in the first part of this Master's Thesis. We want to see if it’s possible to utilise the exhaust gases
from the thermal dryer to give the necessary thermal energy at TAMD process through a heat
exchanger. In this way, Pinch analysis is used. The Pinch bases are established, a mass and energy
balance to obtain the necessary Pinch values is done, the hot and cold system streams are identified and
a first Heat Interchange Network is determinate. 