Development of continuous mixer for homogeneization and feeding of bagasse and sugarcane straw in boiler

Abstract

Mechanized sugarcane harvesting has grown strongly in recent years, from 33% in 2007/2008 crop to 96.5% in the 2019/2020 crop, which represents a harvested area of 4,244.7 million hectares, nd it is estimated that there are between 10 and 20 ton ha-1 in the year of straw, which means around 30 million tons of straw considering the removal of only 50% of the total available in the field (CONAB, 2020). The boilers of the sugarcane mills traditionally generate steam from burning of sugarcane bagasse from the ethanol and sugar production process, however, due to the great availability of straw in the field with attractive energy value, has been growing interest in the use and analysis of the operation of the boilers using the sugarcane straw as fuel in to increase the cogeneration of thermal and electric energy (Bizzo et al., 2014).The Straw use as fuel in the boilers, requires its processing and its addition in mixtures with sugarcane bagasse. The straw available at the mill, before processing, has larger fibers and low density in relation to bagasse. The conventional boiler feed system is designed and operates according to the standards and physical characteristics of the sugarcane bagasse obtained after industrial processing. The bagasse has a granulometric regularity of 99% <12.5mm, an average humidity of 50% and a density of 145.0 kg / m3 of bagasse, allowing adequate compaction and continuous flow in the feeding system, maintaining the firing stability in the furnace, condition essential to guarantee the nominal steam and energy generation capacity in the boiler. Straw has a larger and irregular granulometry, with less humidity varying between 10% and 40%, therefore, its use in mixtures with bagasse in the boilers, requires an adequate process of homogenization and humidity control to maintain continuity in the boiler feeders. However, currently adding straw to bagasse in the boiler conveyor system is not able to produce an effective mixture between the materials. Due to the lack of agitation and adequate distribution of materials, agglomerates of different densities are formed in the supply ducts, resulting in blockages and interruptions in the boiler feeders, and thus in reducing the amount of fuel burned and in the steam generation capacity. The current boiler feed system can have a significant increase in the capacity and efficiency in the use of straw, through a mixer of straw and sugarcane bagasse that promotes greater homogenization between the quantities fed. This process would allow mixing of defined quantities, ensuring control of the fuel conditions, continuity in the supply and stability in the furnace burning, maintaining the nominal steam generation capacity of the boiler. (AU)