Cogeneration unit modifications to maximize the electricity generation in Cuban sugar mills

Abstract: The electricity usage in the world is constantly increasing and it is therefore of high importance to improve the utilization of renewable energy sources. The electricity in Cuba is mainly generated from imported fossil fuels which have a negative environmental effect by a large contribution of carbon dioxide emissions. In the cogeneration unit of sugar factories electricity is generated in turbines from the steam produced in boilers by burning bagasse, a residual from the sugar production. This biomass is a renewable energy source and has a high energy content. In 2009 several parts were upgraded in a sugar factory in Cuba named Carlos Baliño with the aim to improve the efficiency of several production processes. The upgrades resulted in an increased amount of steam that can be used to generate electricity for export to the national grid and an increased amount of excess bagasse. Despite of the upgrades the factory is not able to increase the generation of electricity due to the technical restrictions of the current power turbines. The aim of this study is to further improve the efficiency of the cogeneration unit and maximize the electricity generation in order to increase the revenues for the factory owner by exporting excess electricity to the national grid. This will be performed by investigating an implementation of an extraction condensing turbine and drying the bagasse to the lowest possible moisture content. The modelling consists of four scenarios where different combinations of factors that influence the electricity generation are implemented. The first scenario which is an evaluation of the current situation is used as a reference base for the others. The second scenario determines if it is possible to burn all of the bagasse and continue using the current backpressure turbines. For the third and fourth scenario a change into a condensing extracting turbine is evaluated. Additionally, drying of bagasse to different moisture contents in the fourth scenario is investigated. The results show that the implementation of an extraction condensing turbine and drying of bagasse generated the most electricity. The amount of generated excess electricity that can be sold to the grid was established to 2,8- 3,9MW. The implementations would result in a payback time of 1,4-1,7 years and a yearly profit of 2,6-3,7 million USD. This indicates that implementing an extracting condensing turbine and a dryer is a good investment for Carlos Baliño. The impact of the assumptions and simplifications on the result in this study should be further investigated in order to justify the investment. Future work recommendations to increase the electricity generation include investigation of utilizing SCAR in addition to bagasse and an implementation of a boiler that generated steam with higher temperature and pressure.