Abstract
Coffee bean (Coffea arabica) processing generates high amount of residues that are sources of environmental pollution. Therefore, an appropriate solution is needed. The objective of this study was to determine the potential of coffee pulp to produce briquettes and pellets. The study included pulp drying (using air, solar and hot air methods); the production of briquettes and pellets; the evaluation of their energy, physical and mechanical properties; and the evaluation of pellet quality using X-ray densitometry. The results showed that the pulp presented an initial moisture content of 90%, resulting in drying times of 699, 308 and 55 hours for air, solar and hot air drying, respectively, and the calorific values of the pellets and briquettes were 12,501 kJ kg-1 and 11,591 kJ kg-1, respectively. The ash content was 8.68% for the briquettes and 6.74% for the pellets. The density of the briquettes was 1,110 kg m-3, compared with 1,300 kg m-3 for the pellets. The apparent densities were 1,000 kg m-3 and 600 kg m-3 for the briquettes and pellets, respectively, and the water absorptions by the briquettes were 7.90% and 8.10% by the pellets. The maximum horizontal compression effort was 26.86 kg cm-2, measured in the pellets, compared with 4.52 kg cm-2 in the briquettes. The maximum horizontal load was 93.24 kg, measured in the briquettes, compared with 33.50 kg in the pellets. The value of the pellet durability test was 75.54%. X-ray densitometry showed that the pellet was uniform and a few cracks were observed on the pellet surface.
Highlights
More than 98 000 ha are dedicated to coffee production in Costa Rica (Alfaro; Rodriguez, 1994)
The objective of this study is to present a proposal for drying coffee pulp based on three drying systems: air, sun and high temperature chamber
The wet material was dried using three different methods that are commonly used in Costa Rica. These drying systems are: (i) Air drying: performed in Cartago, Costa Rica, from October through December (Figure1a). This site is located at 1,380 m asl; the temperature ranges from 17.6 to 19.3 oC, the relative moisture content ranges from 87.5 to 89.5%, the precipitation ranges from 0 to 50 mm month-1 and the wind speed from 12.5 to 13.4 m h-1. (ii) Solar drying: studies and tests were performed in a solar dryer with a 6 m3 capacity (Figure 1c)
Summary
More than 98 000 ha are dedicated to coffee production in Costa Rica (Alfaro; Rodriguez, 1994). 20% of the volume of ripe coffee cherries, i.e., the seed or bean, is used. 80% of the fruit becomes waste during processing (Alfaro; Rodriguez, 1994). Coffee residues comprise the husk, pulp and wastewater, all of which pollute the environment (Alfaro; Rodriguez, 1994). 11,764 tons of coffee are produced per day during harvesting, which are associated with ecological damage (Alfaro; Rodriguez, 1994). The use of residues in Costa Rica and other developing countries is limited because of a lack of technology and inadequate knowledge of agricultural waste (Ulloa et al, 2004; Tenorio; Moya, 2012).
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