Estudo de viabilidade para a produção de gás de síntese em uma usina de etanol

Abstract

One of Brazil's main industries is the sugarcane industry, which has great potential for growth over the years. In this industry, there are several byproducts and wastes generated that are currently not widely used, such as sugarcane bagasse, sugarcane straw, CO 2 produced in fermentation, and vinasse. Over time, the use of these byproducts, especially sugarcane bagasse and vinasse, has been studied to produce different products such as second-generation ethanol, other biofuels, and electricity. Another potential product that can be made in a sugarcane refinery is syngas, a mixture of carbon monoxide and hydrogen used for fuel synthesis, such as methanol. Syngas can be produced directly or indirectly. An indirect route to the production of syngas in the sugarcane industry would be the capture of carbon dioxide after fermentation and the production of hydrogen through water electrolysis using excess plant energy generated by bagasse burning. These gases would react in a reactor to form syngas, which is part of the concept known as Power-to-Liquids (PtL). The direct route would be from the gasification of sugarcane bagasse, a thermochemical process that converts carbon-rich materials into a gaseous mixture, which is part of the concept Biomass-to-Liquids (BtL). This study compared the BtL and PtL concepts but only up to the production of syngas, an intermediate product for the production of liquid hydrocarbons. The comparison was based on four main criteria: 1) yield of each route using a common calculation base, 2) capital expenditure (CAPEX) estimate to build a plant coupled to a medium-sized ethanol plant in Brazil, 3) annual operating cost estimate (OPEX) to find the production cost, and 4) technological maturity of each route. To conduct this study, literature was consulted to define the battery limit of each route (all unit operations involved), to consult equipment and utilities values, and to calculate the energy demand involved in each route. At the end of the study, it was found that in a medium-sized sugarcane plant in Brazil, processing 3.5 million tons of sugarcane per year, it would be possible to build a coupled plant that produces about 6.36 t/h of syngas by the gasification route (BtL) or one that produces about 2.52 t/h of the same gas, using electricity and carbon dioxide from fermentation (PtL). Additionally, it was found that the minimum cost of the product for the BtL concept route is 60% of the value found by the PtL concept route, but the CAPEX for the PtL route is lower than for the BtL route, due to a lower production of syngas.