Abstract:
In Mozambique, the attraction toward biomass briquette production is highly enhanced due to the
increment of energy demand in the country and the high cost of charcoal and firewood with their
high environmental, health, and economic impact. Among briquette production processes, drying
is the most energy-intensive, where moisture content is reduced from 50% up to 10%. In the
country, briquette producers use the open sun drying technique which takes 5 to 7 days depending
on the weather condition. Accordingly, the proposed system intended to answer these drying
problems through the Design and Performance Analysis of Solar Tunnel Dryer for Charcoal Dust
Briquette of Verde Africa Lda factory.
The proposed model includes a solar tunnel greenhouse dryer (STD) as a drying chamber and a
solar air heater (SAH) as an additional heat source. The design and size optimization of the
chamber was done based on the total amount of daily production, the quantity of water to be
removed, drying period, the thermal energy required, available solar radiation, and operating
temperature. SAH was selected based on the analysis of numerical modeling, to observe
temperature variation of the air at the collector exit, which was used as an input parameter for the
chamber. A 3D Computational Fluid Dynamics (CFD) analysis of unloaded and 2 loaded models
of STD had been performed based on heat transfer analysis and radiation model to study the
uniform distribution of temperature inside the chamber.
It was found that the overall size of the drying chamber is 17.5 𝑚 Γ 4 𝑚 Γ 2 𝑚 and the surface
area of the SAH collector is 10𝑚2
. Hot air flowing through the outlet of SAH at 1.3572 𝐾𝑔/𝑠 and
an average of 58.8β had been provided at the inlet of STD to heat the air stream and briquette in
the chamber. The daily average thermal efficiency of the drying system is 47.54%. The average
temperature of the air inside the chamber is above 50β around 6 hours of the day and uniformly
distributed except June and July which are below 50β throughout the day. The value of daily total
useful energy received from the drying air is greater than the amount of thermal energy required
for the drying process, from this it can be concluded that one batch of briquette can dry within one
day. Compared to the open sun drying method the drying period will reduce from 5 to 1 day using
the proposed solar tunnel dryer
