The Energy Platform is an initiative of the Institute for Energy and the Environment which aims the disclosure of systematized information regarding electricity generation in Brazil. While you browse through its features, it is possible to locate in an interactive map each one of these power plants, along with information about their technical details, water usage indicators, Brazillian Development Bank (BNDES) financing, energy auctions, water resources management, environmental permitting and annual electricity generation. Moreover, it is also possible to access the main documents related to the processes of environmental permitting and water usage permitting. The database is also available for download, containing all the information used in order to develop this platform and can contribute to de development of studies regarding the electricity and environment interface. Thus, this platform aims to intensify the discussion about the environmental impacts of Brazil’s electricity sector and provide the access to detailed information, aiding the natural resources management across the power sector.
How the platform was developed?
The Energy Platform presents, throughout this present version, every fossil fueled thermoelectric power plant, over 100 MW, which is operating, under construction or hired through the energy auctions but still haven't started their construction process. In order to develop this platform, many information sources were consulted, systematizing the data as follows:
Where does our electricity come from?
The centralized wind, thermoelectric, hydroelectric and solar power plants, combined with the transmission structure, make up Brazil's Interconnected System (SIN). Almost Brazil's entire territory (96,6%) is covered by this system, which is composed by four subsystems - Southern, Midwestern/Southeastern, Northeastern and Northern -, which enable the interconnection of different generation facilities, electricity distributors and final consumers. Mainly composed by hydroelectric and thermoelectric power plants (hydrothermal system), Brazil's SIN is controlled by the National System Operator (ONS), which is responsible for planning and controlling the operation of the generating facilities. At this point, the decision of operating the power plants is centralized, changing daily the composition of the sources responsible for electricity supply in Brazil.
National Interconnected System (SIN)
Since 2012, according to the resolution nº482 of the National Agency of Electric Energy (ANEEL), is now possible to generate decentralized electricity in places such as houses, shops and rural constructions, bringing the electricity generation to the consumer. For more information, click here.
How does the thermoelectricity conversion works?
Thermoelectricity is the conversion of thermal energy into electricity through the operation of a thermodynamic cycle. Conventionally, thermoelectricity conversion technologies are divided into four routes: Rankine Cycle, Brayton Cycle (open cycle), Combined Cycle and Combustion Engine. The following image combines these technologies and the possibilities of using different fuel. There is also below a brief explanation of the working principles of each cycle.
Fuel and thermodynamic cycle combination
Find below a simplified diagram of each thermodynamic cycle by clicking on the boxes:
Thermoelectric power plants operating Rankine and Combined cycles require cooling systems in order to reduce the temperature of the combustion products. On the other hand, Brayton cycles reject heat directly to the environment and combustion engines need low amount of water on their auxiliary cooling systems. The power plant’s chosen cooling system, since it is the main water consumption source, exerts great influence on the water consumption from the basin where the power plant is located. These power plants, most of the times, can use alternatives to the water cooling systems like air cooling, reducing dramatically the water consumption. On the other hand, air cooling presents a higher need for initial investments and can cause losses in efficiency, mainly in regions that presents higher temperatures.
Each power plant presented by this platform includes data regarding its water consumption profile (indicators). These indicators present volumes of water catchment, consumption, evaporation and discharge, presented by time (m³/hour) and produced electricity (m³/MWh) units. Moreover, it is possible to visualize, when presented by the entrepreneur, these indicators related to the power plant’s operation profile (average yearly operation and maximum yearly operation).
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Rankine cycle: Steam turbine
The Rankine Cycle operates by using steam produced in a boiler, which passes through a turbine and rotates its blades (conversion into kinetic energy), losing pressure. The necessary heat to convert the water (high purity fluid, usually demineralized to avoid encrustations and corrosion) into steam is supplied by a fuel which feeds the boiler. The turbine blades rotation is then transmitted by a shaft to the electric generator. The steam, after losing its pressure passing by the turbine, goes through a condenser, aiming the conversion into liquid water to reenter the cycle. Finally, the water (now in a liquid form), is pumped, raising its pressure to return to the boiler.
Brayton Cycle: Gas turbine
This cycle uses a gas turbine in which the heat is added under constant pressure. The system is simple, requires low investment and its assembly is compact which permits its complete installation in a reduced area. The working principle is simple: natural gas is injected in a combustion chamber in a presence of compressed air and, after burning this mixture, the products of the combustion are then directed to a turbine, triggering the movement of the blades. Like the Rankine Cycle, the turbine is connected to an electric generator by a shaft, producing electricity. The cycle completes into the atmosphere, from where the initial mass of air is extracted and the products of the combustion after passing by the turbine, are released. These gases, after the process, are still under high temperatures (over 500ºC / 932 ºF).
Combined Cycle: Gas turbine + steam turbine
The combined cycle results from the combination of the Brayton Cycle and the Rankine Cycle. This joint is very advantageous because the temperature of the exhaust gases from the first cycle (Brayton) presents the same order of magnitude of the beginning of the second cycle (Rankine – about 500ºC). In order to combine both cycles, it is necessary a heat recovery boiler, that will utilize the energy of the exhaust gases after the gas turbine and generate the necessary steam for the Rankine Cycle. In this boiler, more fuel can be added, called afterburning, aiming the provision of even more heat to the steam formation process.
Engines are machines responsible for the conversion of energy into mechanical work. Internal combustion engines are the ones in which the fuel is burned inside the equipment, a mechanism which comprises a piston, connecting rod and crankshaft. The alternate movement (up and down) of the piston inside the cylinder is transformed into a spinning movement by means of the connecting rod and the crankshaft. This spinning movement is connected to generator’s shaft, producing electricity. Power plants operating combustion engines are usually smaller considering installed capacity. Engines are more indicated to operate decentralized systems since they are easy to operate and present low maintenance costs.
Water cooling - Once-through
Water passes through the power plant’s condenser, cooling directly the products of the combustion and returns to the waterbody. This technology presents huge water catchment but low water consumption.
Water cooling system - semi closed loop - natural draft
Water is used to reduce the temperature of the combustion products. Later, this water is conducted to a tower in order to be also cooled by natural air convection, and return to the cooling cycle. Moderate water catchment and high water consumption due to the evaporation process within the towers.
Water cooling system - semi closed loop - forced draft
Working similarly to the natural draft systems, water is used to reduce the temperature of the combustion products. Later, this water is conducted to a tower in order to be also cooled but, at this point, there are air ventilators helping the process. Moderate water catchment and high water consumption due to the evaporation process within the towers.
Indirect air cooling
Air is used to chill the water, which is responsible for cooling the products from the combustion and is running in a closed loop. Low water usage but it is responsible for an overall efficiency loss.
Direct air cooling
The products of the combustion process are cooled using only air through finned surfaces. There is no water involved in the process but there is an efficiency loss of the process.
The hybrid cooling cycle operates using elements from both water and air cooling. These elements can be used separate or at the same time, aiming a better performance. Therefore, it is possible to utilize the efficiency of the wet system during warm days and save water during the rest of the year. The hybrid system can save up 50% of the water used by the wet systems. The main disadvantage from the hybrid system is the cost which is more elevated than building a wet system itself. Moreover, it is also necessary to consider that there is still a significant water consumption, mainly during summer months, and that these systems need to consider the costs of maintenance of both wet and dry cooling systems.