Viabilidade técnica e econômica da secagem natural e por ar desumidificado em unidade de secagem elétrica de grãos de café arábica

Abstract

Coffee drying has been enhanced by the constant search for specialty coffees, to reduce costs and losses, to increase the coffee beverage quality and to mitigate the financial impacts of the productive oscillations of the coffee market. Traditional drying includes the patio or the mechanical dryers that complement pre-drying, but both have factors that, when uncontrolled, degrade the quality of the coffee. This scenario leads to the emergence of new drying technologies, such as the partial dehydration of the drying air before sending it to the grain mass. The objective of this study was to analyze the technical and economic feasibility of drying coffee (Coffea arabica L.) with dehydrated air by means of evaporator coils and preheated with condensing coils consisting of an electric drying system. The coffee quality evaluation methodology consisted in gathering twelve coffee triplicate samples obtained from four distinct regions in the states of São Paulo and Minas Gerais, comparing them to control samples (obtained from concrete terrariums). The quality was given by the sensorial test of beverage and followed the methodology proposed by the Specialty Coffee Association of America (SCAA). The technical feasibility considered the multiple comparison of the means of grains retained in the sieve n. 17, of the baffle and sieve bottom n. 13, the number of defects and the drink test. Defining a range of values for the sale price of coffee, electricity acquisition cost, monthly interest rate, and maintenance time whose expenses are equivalent to the depreciation of the patio, the Rotational Central Compound Design (DCCR) was constructed with 28 tests for the analysis of cash flow and net investment of commercial scale dryings. These parameters were used to determine the Discounted Payback (PBD), Internal Rate of Return (IRR), Net Present Value (NPV) and Percent Return on Investment (ROI) indicators used to define the feasibility of machine deployment. The use of these machines presented advantages on drying in concrete patio, greater quantity of grains retained in the sieve n. 17 (346%) and higher score in the test of drink (5.36%) and the coffee dried with dehydrated air presented fewer broken and defective grains (72.41% less). The parameters used in the optimization of the DCCR showed the project's desirability of 98.98% for coffee marketing conditions of R$ 599.00 sc-1 (or higher), acquisition of electric energy not exceeding R$ 0.63 kWh-1, monthly interest rates lower than 0.39% and maintenance time, whose expenses are equivalent to the depreciation of the yard of less than 11.63 years. The statistical design showed optimized responses of PBD of 2.27 years, NPV of R$ 10.05 million, IRR of 52.53% and ROI of 8.66. It was observed a directly proportional relationship between the investment feasibility and the sale price of the coffee bag and the inverse relation with the other variables, while the annual amount spent on the maintenance of the patio was the variable that had the least influence on the desirability of the investment. It was concluded that these drying units, as they were designed, do not require pre-drying in the yard and that there was an increase in the average price of coffee (12.11%), and the use of dehydrated airfor drying coffee is technically and economically viable. It was also observed that the optimization of these air dehydration units occurs in properties with an area of not less than 104.7 ha and mean productivity of 24.84 sc ha-1. Other systems with different cooling capacities should be tested for properties with cultivated planted. Also, it was verified that the drying time in the patio is dependent on the climate and that the increase in the height of the stationary cover of grains implies the reduction of the area of the patio.