Energetic Analysis of Hydrogen Production in a Sugar-Ethanol Plant

Abstract: In the present work it is evaluated the possibility of incorporating the production of hydrogen through the steam reforming of ethanol in a sugar-alcohol plant. The analysis is made using as a model an existing plant located in São Paulo, the Pioneros Distillery. An energetic and exergetic analysis is performed. Three operating scenarios were analyzed. In the first configuration the plant only generates electricity to supply its internal needs. In a second scenario the plant uses all the bagasse to generate electricity, targeting to sell electric power. Finally it was considered the possibility to incorporate the hydrogen production by ethanol steam reforming. The capacity of the plant to produce hydrogen is evaluated. The surplus bagasse is used to generate the electricity and thermal energy required for hydrogen production. A part of the anhydrous alcohol is used in the reformer for hydrogen production. An energetic study of the plant is developed based on the first law of thermodynamics. Some important parameters related to the thermal system performance are evaluated like: steam consumption in the process, specific consumption of steam turbines; and those properly related to plants of sugar-ethanol sector as: electrical or mechanical power generated from one ton of sugarcane and power generated from a given amount of bagasse burned in the boiler. It is considered the possibility of generating electricity using bagasse, which could be sold to the local energy concessionaire. Characteristic parameters of a cogeneration system (α and β) are also evaluated, these parameters depend on the characteristics of the thermodynamic system and the operating strategy. The system energy losses, excluding those located in the boiler and the electric generator, are higher in scenario 2 than in scenario 1. The efficiency is 70% in Scenario 1 and 57% in scenario 2. In scenario 3, the plant's potential for hydrogen generation is 4,467,000Nm3/year (951Nm3/h). To achieve this, the new process uses 7 % of the anhydrous ethanol produced in the plant, which implies a surplus of 37 lethanolanhydro/tcane available for sale. In this configuration all the bagasse is used for electricity and heat generation required for the hydrogen production. The hydrogen could be used for fuel cell vehicles. The plant is able to supply 68 buses with autonomy of 200 to 300 km per day. The incorporation of the hydrogen production process by steam reforming represents an attractive alternative to the sugar-alcohol sector.