Design and Performance Analysis of Solar Tunnel Dryer for Charcoal Dust Briquette of Verde Africa Lda in Mozambique

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 × 4 𝑚 × 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 58.8℃ 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 50℃ around 6 hours of the day and uniformly distributed except June and July which are below 50℃ 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