Power Stations
The Energy Groove is a website about renewable energy. However, in the context of renewable energy it is important to understand conventional power generation, which includes most of the world’s current energy creation. To put this into context, virtually all of the power we use still comes from these conventional sources, and it is these sources that have created the modern world we live in. All of our technology has been driven by this including the current development of renewable energy.
However, it is now widely accepted that, as important as these conventional sources are today, many are reaching their limit in terms of availability as non-renewable resources and are also responsible for negatively impacting on the natural world.
Power stations include:
- Fossil fueled power plants
- Coal
- Oil
- Natural gas
- Nuclear fueled power plants
- Hydroelectric dams
- Geothermal power plants (see article this website)
- Waste incineration plants
Power plants that create electricity from fossil fuels use these fuels for combustion to create heat that is converted to steam that then drives an electrical generator. The process begins with a fuel that is fed into a furnace. The heat from the furnace boils a liquid, usually water, to create steam which is then fed to a turbine. The turbine rotates a shaft that is connected to an electrical generator. The generator creates electricity which is then sent to a power grid.
The exception to this system is natural gas, because it can be used to power either a steam or gas turbine.
Power stations that use fossil fuels can be between 33% to 48% efficient. The remaining energy is lost in the form of heat, although with certain power plant designs, known as cogeneration power plants, the waste heat can be used for district heating.
Byproducts of this process are waste heat and flue gas emissions that include CO2. However, there are a number of solutions to capture flue gases, and in particular the technologies designed for carbon capture processes (see article this website).
Like fossil fuel plants, the mechanism of nuclear power plants is designed to create steam that drives a turbine. This process involves creating a controlled nuclear fission reaction that releases heat. The heat is transported via a coolant to a boiler where steam is created to drive a steam generator.
Nuclear reactors have gone through three generations of design and a fourth generation is being developed, with further generations, i.e., fifth and beyond, also under research. These are termed generation I, II, III and IV nuclear reactors. The objective of pursuing new reactor designs is based on safety and efficiency. Reactor designs currently in use are generation II and III. Generation IV reactors are being developed, but probably won’t be in commercial use before 2030. Generation IV reactors will include “significant advances in sustainability, safety and reliability, economics, proliferation resistance and physical protection” 1.
With current nuclear reactor technology nuclear waste is created when raw materials are converted to nuclear fuel, as well as after the fuel has been used. Dealing with nuclear waste requires a sophisticated waste management process. It is an important factor when considering developing and using nuclear power plants due to the implied hazards, which include negative affects for human health, the environment, and nuclear weapons proliferation.
Because controlling a nuclear reactor is an extremely complex process the potential for failure is present throughout the mechanism as well as from human input. For mechanism failure this includes nuclear meltdowns and steam explosions. Regarding human input failure, studies have revealed that the strict procedures technicians must follow can be so demanding that unsanctioned alternatives can develop. Also, failures can be so complex that technicians don’t have the experience to solve them in time.
Beyond operational issues, safety related to nuclear power plants includes the risks of politically motivated attacks and nuclear weapons proliferation.
- Because nuclear power plants are important as energy resources as well as safety risks, they are good targets for terrorists or hostile powers.
- Nuclear waste storage creates a condition where weapons grade nuclear material is present, and this creates the risk that it can be obtained and used in the form of hostile nuclear weapons.
Converting waste to energy involves:
- Burning waste to boil water to drive a steam generator
- Producing a combustible gas, e.g., methane, that can be used as a fuel
Burning waste has an electric efficiency of 14 – 28%, the rest is lost to heat, but much of this can be used to heat buildings. Burning waste creates pollutants that include gases with high acidic levels as well as CO2, but with smoke stack scrubbers the release of these gases into the atmosphere can be minimized.
When waste is dumped in landfills it produces methane gas in amounts that have more than twice the global warming potential of the CO2 created when the same amount of waste is burned.
Beyond incineration, converting waste to energy includes: (from Wikipedia)
- Gasification (produces combustible gas, hydrogen, synthetic fuels)
- Thermal depolymerization (produces synthetic crude oil, which can be further refined)
- Pyrolysis (produces combustible tar/biooil and chars)
- Plasma arc gasificationPGP or plasma gasification process (produces rich syngas including hydrogen and carbon monoxide usable for fuel cells or generating electricity to drive the plasma arch, usable vitrified silicate and metal ingots, salt and sulphur)
Non-thermal technologies:
- Anaerobic digestion (Biogas rich in methane)
- Fermentation production (examples are ethanol, lactic acid, hydrogen)
- Mechanical biological treatment (MBT)
- MBT + Anaerobic digestion
- MBT to Refuse derived fuel
Even though when properly managed converting waste to energy can be a relatively clean and efficient form of energy creation, it does raise issues when compared to the benefits of waste recycling (see the below article).
http://www.nytimes.com/2008/07/04/business/worldbusiness/04iht-rbogwaste.html?_r=1
Links
http://en.wikipedia.org/wiki/Power_station