Avaliação do aproveitamento energético dos resíduos da indústria de óleo de rícino por meio da cogeração

Abstract

The castor bean plant (Ricinus communis L.) is an oilseed crop from which castor oil is extracted, that has various applications, such as a bio lubricant, raw material for bioplastics and biodiesel, additive in coatings, cosmetic and pharmaceutical. In the processing of castor beans, in addition to the oil, several by-products are produced, including straw, husk (in the agricultural phase), and seed cake (industrial stage). The demand for renewable energy sources and products with a reduced environmental impact continues to grow. In this context, agro-industries have been studied according to the biorefinery approach, which seeks to utilize all parts of the plant to produce value-added products, minimizing waste disposal. Currently, the application of castor bean by-product is concentrated only on the use of seed cake as a biofertilizer or additive in animal feed. However, this and the other residues have energy potential that could be exploited. In this work, their use as sources for cogeneration was studied, seeking to evaluate the generation capacity of this industry, optimization factors of thermal cycles, as well as technical and environmental limitations involved. For this purpose, three systems were proposed and simulated in Aspen Plus software. They differ in terms of heat source: direct burning of straw and husk (in System 1) or anaerobic digestion of seed cake for biogas production which is then burned (in Systems 2 and 3); and in terms of the thermodynamic cycle used for cogeneration: Rankine (in Systems 1 and 2) and Brayton (in System 3). Based on an industry with a processing capacity of 100 thousand tons of seeds/year, the useful energy (work + recovered heat) obtained in Systems 1-A (husk and a portion of the straw obtained through manual harvesting), 2 and 3 was 24.5, 6.9 and 7.0 MW, respectively. And in case 1-B, which considers that all agricultural residue would be available for burning, the rate reached 91 MW. System 3 had low work output due to the limitation of combustion temperature to avoid NOx and CO emissions. In all evaluated scenarios, the castor bean industry would be self-sufficient in terms of its electrical and thermal energy usage.