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Ecological and Exergetic Analysis of Hydrogen Production in a Sugar-Ethanol Plant

This work aims an ecological and exergetic analysis of the hydrogen production by steam reforming of part of the ethanol produced in a sugar-ethanol plant. The Pioneiros Distillery, located in São Paulo, is used as model for this study.

Three cases are described. In case 1 the plant produces energy only for domestic needs. A part of bagasse is not burned and it is stored. In Case 2, all available bagasse is used for production of steam.

Part of the steam is used in the production process meeting the demand of the plant and the rest of steam is converted into electrical energy that can be sold at concessionaires. In Case 2 it is produced more energy than in Case 1. Case 3 includes the production of hydrogen by steam reforming of a part of the produced ethanol. Steam and energy for steam reforming is generated from combustion of bagasse.

An exergetic analysis is performed. The exergy flows associated with the sugar-ethanol plant are calculated locating and quantifying the losses and irreversibility. The ecological impact of use of the bagasse as fuel to generate thermal and electrical energy for the ethanol reformer was studied. The main pollutants that damage the atmosphere, namely: CO, CO2, NOx and PM have been taking into account.

Carbon Dioxide emissions were calculated taking into account the carbon cycle (considering the absorption of carbon dioxide by the sugarcane during its growth), resulting in negative balance emissions, i.e., carbon dioxide was absorbed in higher amounts than emitted.

The thermodynamics (ηsystem) and ecological (ε) efficiencies of Steam reforming of ethanol were calculated. The thermodynamic efficiency was 56% and the ecological efficiency was 80%. When the carbon cycle is taking into account the ecological efficiency is 90%.

The incorporation of an ethanol reformer in a sugar-ethanol plant for hydrogen production is a very interesting option where environmental benefits are obtained. Problems related with the storage of bagasse are avoided because all the bagasse is burned for the production of steam and energy to the reformer. The amount of hydrogen that can be produced in Pioneiros Distillery could supply fuel for 68 buses with a range from 200 to 300 km per day.
Source: KTH
Author: Colombaroli, Tulio

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