Ships are now the eighth largest source of CO2 emissions in the world and the goal of the International Maritime Organization (IMO) is to reduce these emissions by at least 50% by 2050 compared to 2008. a researcher at the Polytechnic School of the University of São Paulo (Poli-USP) sought alternatives to improve the energy efficiency of vessels in the oil and gas industry. One of them achieved a reduction of about 10% in both CO2 and fuel. The study has just been published in the prestigious Energies, an international scientific journal dedicated to the area of electrical energy.
"The proposed scheme considers the adaptation of the ship. The main generators, original to the vessel, are maintained, but, in addition, we make use of complementary sources of energy: auxiliary generators, batteries and fuel cell", explains electrical engineer Giovani from São Paulo. Giulio Tristão Thibes Vieira, first author of the article. "The main objective of the work was to analyze the ideal configuration of a ship's energy system, taking into account the use of three types of batteries and fuel cells with hydrogen tanks of different sizes. the possibilities of combination between them".
Best combination – The best result presented was the combination that brings together main and auxiliary generators, as well as a lithium, oxide, nickel, manganese and cobalt battery with a capacity of 3,119 kilowatt-hours (kWh), in addition to a fuel cell unit of the proton exchange membrane (PEMFC) type and a tank capable of storing 581 kilograms of hydrogen. As you know, in the fuel cell, hydrogen reacts with oxygen that comes from the environment. The energy released is transformed into electrical current that powers the vessel and the process generates only heat and pure water as waste. "This combination provided the most significant result we obtained in the research: it reduced CO2 emissions by 10.69%", celebrates Vieira. "Furthermore, the decrease in emissions also represents a similar reduction in fuel consumption."
The article is the result of the doctorate that Vieira has been carrying out since 2018 at Poli-USP. In turn, the doctorate is an offshoot of his master's (Analysis of hybrid power for ship propulsion using energy storage systems), defended by the researcher that year, at the same institution. The study was carried out within the scope of the Hybrid Energy System for Ships project, which was underway between 2016 and 2020 in the first phase of the programs of the Research Center for Innovation in Greenhouse Gases (RCGI), financed by Shell do Brasil and the Research Support Foundation of the State of São Paulo (Fapesp).
"The time at the RCGI was essential to support my research. My master's degree dealt with the electrical part of the ship. In the doctorate, I migrated to the energy part. Now, the members of the group formed at RCGI continue their studies in the area, but independently of the research center", says Vieira.
The study was carried out using Homer software and was focused on the analysis of the performance of a platform supply vessel (or PSV, for Platform Supply Vessel). It is a type of vessel used to support offshore oil and gas platforms. In this case, these vessels usually transport goods and equipment to the high seas. "In the research, we established the following path: the ship leaves the port loaded and heads towards the platform. There it unloads the cargo in an operation called DP and returns to the lighter port. Thus, we were able to analyze the different energy demands throughout the operation" , reports.
The time curve that the ship needs to complete this route was based on data from another master's thesis (A methodology to select the electric propulsion system for platform support vessels), carried out by Cristian Andrés Morales Vásquez, also at Poli -USP. "We made this curve based on the number of hours per operating time that the ship remains in each stage of the mission", continues the researcher.
Hot topic – Ways to reduce CO2 emissions from ships is a hot topic around the world, as the researcher, who is currently studying at Aalborg University, in Denmark, points out. The invitation came thanks to an article he wrote in 2019 for the RCGI Hybrid Energy System for Ships project, coordinated by Professor Bruno Souza Carmo, from Poli-USP.
"Interest in this topic has been growing worldwide since the late 2000s. In 2008, the IMO took the decision to reduce the global limit on sulfur oxide emissions, resulting from fuel combustion, by the world's merchant fleet. Later, the IMO 2020 regulation established that the sulfur limit in ships' fuel was dropped from 3.5% to 0.5%. .1%", says Vieira.
A short-term solution for ships to adapt to low CO2 emissions is to use retrofit. According to the researcher, there are already companies in the world that produce a type of container that houses battery packs with their management and protection system, as well as converters. "In addition, this container has its internal temperature controlled. It is a solution ready to be installed on ships", says Vieira. Also according to the scholar, research indicates that 50% of the ships in activity in the world today will continue to operate until 2030. "We, researchers, need to think of short-term solutions so that these vessels adapt to a new reality and reduce emissions of CO2. This study illuminates some possibilities", says Vieira.
The researcher estimates that the use of batteries may be a short-term solution, as the fuel cell, being relatively new, is a technology that is not very accessible from an economic point of view. Therefore, in addition to the issue of emission, the study also focused on battery life. "Batteries help to reduce emissions in two moments. They discharge when demand is low and replace the main generators when they would operate at a point of lower efficiency. Then, these batteries are charged to work as a load and raise the generator load factor, which generally leads to a better efficiency point", explains Vieira. However, the process of charging and discharging causes wear on the battery. "A battery with more charge and discharge cycles has a shorter lifespan, and this has a financial impact that needs to be evaluated", he concludes.