THE USE OF BIOMASS RESIDUES IN THE BRAZILIAN SOLUBLE COFFEE INDUSTRY M. A. SILVA*},S. A. NEBRA$,M. J. MACHADO SILVA$ and C. G. SANCHEZ% *DTFD, FEQ, UNICAMP, P.O. Box 6122, 13083-970, Campinas, S.P., Brazil $DE, FEM, UNICAMP, P.O. Box 6122, 13083-970, Campinas, S.P., Brazil %DETF, FEM, UNICAMP, P.O. Box 6122, 13083-970, Campinas, S.P., Brazil (Received 3 January 1997; revised 17 October 1997; accepted 21 October 1997) AbstractÐThe objective of this paper is to discuss the use of coee grounds in the Brazilian soluble cof- fee industry. This residue is used as a fuel in the boilers of the same industry; so, data about their utiliz- ation are presented and analysed, discussing the actual technology and the advantages of improving the drying of the biomass with the exhaust combustion gases. After that, an experimental study is reported on the characteristics of this material, which are important for the combustion process, including the transport, storage and drying, the mean diameter of the particles, talus angle, apparent and real density, sphericity, surface area, terminal velocity, spontaneous ignition temperature and heat of combustion. # 1998 Published by Elsevier Science Ltd. All rights reserved KeywordsÐResidues; burning; coee grounds; terminal velocity; spontaneous ignition; combustion heat. 1. INTRODUCTION The necessity of conserving nature and the increasing consumption of energy resources have led researchers to the study of renewable sources of energy. Among these renewable sources, the combustion of the following agri- cultural residues are some of the most import- ant: ears of corn, rice husks, cotton twigs, coconut ®bres, jute stems and wheat straw. 1,2 There are also agricultural industrial residues such as sugar cane bagasse 1 and coee grounds (Dutra, personal communication). 3,4 All of these residues can have other uses, and opting for one utilization over another depends on a global analysis which takes into account the economic, social and environmen- tal aspects. The coee grounds, which are the subject of this paper, are the residues of the soluble cof- fee industry. Soluble coee, without the ad- dition of carbohydrates, was ®rst produced in about 1950 in the U.S.A., 5 and its consump- tion has increased since then, reaching 19% of the total coee consumed in the world in 1980. 6 As a consequence, the production of coee grounds has increased, and their dispo- sal has become a matter of increasing con- cern. Brazil began to produce soluble coee in 1962, and it has been a major world producer since 1970, when production reached 36 million kilograms per year. 7 In 1989, there were 11 plants (ABICS, personal communi- cation), with 85% of the production going to the external market. In 1988, only 11.8% of the coee exported was in the form of soluble coee, which totalled 120 million kilograms with a value of 213 million dollars. 5 Initially, 1.86 kg of spent coee grounds were produced for each kilogram of soluble coee. 5 With improvements to the industry, this ®gure dropped to 1.27 kg in 1967, 7 and it is now 0.91 kg. 8 The daily volume of coee grounds production is therefore high, consid- ering that after the extraction of the soluble coee, it has a humidity of 75±80% (w.b.), which is reduced to 50% after pressing (Dutra, personal communication). 1,3,5,9 Coee grounds are highly pollutant due to the presence of organic material that demands a great quantity of oxygen in order to degrade. Simply piled up, they can ferment and produce spontaneous combustion, as has occurred in some storage sites (Dutra, per- Biomass and Bioenergy Vol. 14, Nos. 5/6, pp. 457±467, 1998 # 1998 Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain 0961-9534/98 $19.00 + 0.00 PII: S0961-9534(97)10034-4 }Corresponding author. 457