Application of an Energy Efficient Hot Air Recirculation Controlled Closed System Environment for Parchment Coffee Dehydration in Puerto Rico

Abstract

The high and increasing costs associated with propane gas, diesel and electricity used by mechanical dryers have negatively affected the coffee processors in Puerto Rico. In 1991 the cost to process one hundred pounds of parchment coffee was $14.13, while in 2011 was over $35.00. From all the sectors within the coffee industry in Puerto Rico, the processors are the ones that have experience the largest increases in operational cost, over 145% in the past years, mainly due to post harvesting drying. To address this specific challenge, the Department of Agriculture of Puerto Rico (DAPR) assigned funds to research coffee dehydration energy efficient alternatives that would reduce the costs to the coffee processors of the island. As part of this effort, a hot air recirculation controlled closed-system (HARC2S) was designed and constructed at the University of Puerto Rico at Mayagez. The basic concept of the HARC2S is to condition the hot air that has already passed through the coffee bean mass and direct it back to the mechanical dryer. The hot air conditioning consist in removing part of the moisture from the recirculation air with a heat exchanger that uses water at ambient temperature, to increase the moisture absorbing capacity of the air before it re-enters the mechanical dryer. Experimental results of the HARC2S, under various operational configurations, provided substantial drying energy savings ranging from 12% to 59%. The range variation in energy savings is due to the system operational configurations and possible variations of the parchment coffee bean ripeness state from the various batch experiments. Investing in the development and implementation of this technology will provide not only sustainable operation of the coffee processors facilities, but will also sustain close to 20,000 jobs with potential employment growth representing over a $41 million annual income to the local economy.