A steam locomotive clattering along the tracks. A paddle steamer plying the Murray River. A dreadnought battleship powered by a steam engine.
Many of us think the steam era is over. But even though steam engines have been replaced by internal combustion engines and now electric motors, the modern world still relies on steam. Almost all thermal power plants, from coal to nuclear, require steam to operate. (Gas plants generally do not.)
But why? That's because of what we discovered thousands of years ago. In the first century C.E., the ancient Greeks invented the aeolian steam turbine. Heat turns water into steam, and steam has very useful properties. It's an easy gas to make and push.
This simple fact means that even as the dream of fusion power gets closer and closer, we are still stuck in the steam age. The first commercial fusion power plants will rely on cutting-edge technology that can contain plasmas much hotter than the sun's core, but will still be combined with humble steam turbines that convert heat into electricity through motion.
Why are we still dependent on Steam?
It takes a significant amount of energy to boil water, making it the highest energy of any common liquid we know. Water requires approximately 2.5 times more energy to evaporate than ethanol and 60% more energy than liquid ammonia.
Why use steam instead of other gases? Water is inexpensive, non-toxic, and can be easily converted from a liquid into an energy gas that can be condensed back into a liquid for continued use.
The reason the steam has lasted so long is because water is abundant enough to cover 71% of the Earth's surface, and water is a useful way to convert thermal energy (heat) into mechanical energy (motion) and into electrical energy (electricity). The reason we look to electricity is because it can be easily transmitted and can work for us in many fields.
When water turns to steam in a closed container, it expands significantly and increases pressure. High-pressure steam, like other gases, can store enormous amounts of heat. If an outlet is present, the vapor surges through the outlet at a high flow rate. When a turbine is placed in the exit path, the force of the escaping steam causes the turbine's blades to rotate. Electromagnets convert this mechanical movement into electricity. The vapor condenses back into water and the process begins again.
Steam engines used coal to heat water and produce steam to drive the engine. Nuclear fission splits atoms to create heat, which causes water to boil. Nuclear fusion fuses heavier isotopes of hydrogen (deuterium and tritium) into helium-3 atoms, generating much more heat to boil water, create steam, and drive turbines to produce electricity.
If you look at the final process in most thermal power plants, including coal, diesel, nuclear fission, and even nuclear fusion, you can see that the old technology of steam has been used as much as possible.
Steam turbines that drive large alternating current generators that produce 60% of the world's electricity are truly beautiful. Hundreds of years of metallurgical technology, design, and complex manufacturing have brought the steam turbine to near perfection.
Will we continue to use Steam? The new technology produces electricity without using any steam. While solar panels rely on incoming photons hitting electrons in silicon to create an electric charge, wind turbines work like steam turbines, except that wind, rather than steam, blows the turbine. Some forms of energy storage, such as pumped hydro, use turbines but liquid water rather than steam, while batteries do not use steam at all.
These technologies are quickly becoming important sources of energy and storage. But the steam doesn't go away. If we use thermal power plants, we will still use steam.
Why can't heat be converted to electricity?
You may be wondering why so many steps are necessary. Why can't heat be converted directly to electricity?
It is possible. Thermoelectric devices are already being used in satellites and space probes.
Made from special alloys such as lead-tellurium, these devices rely on the temperature difference between the hot and cold junctions between these materials. The greater the temperature difference, the greater the voltage that can be generated.
The reason these devices are not ubiquitous is that they only produce direct current (DC) at low voltages and have an efficiency of converting heat to electricity between 16 and 22 percent. In contrast, the efficiency of state-of-the-art thermal power plants is up to 46%.
Running a society with these heat conversion engines would require a large array of these devices to produce sufficiently high DC currents and then use inverters and transformers to convert them into the alternating currents we are familiar with. So you can avoid steam, but you have to add a new transformation to make electricity useful.
There are other ways to convert heat into electricity. High-temperature solid oxide fuel cells have been under development for decades. The device operates as hot as 500 to 1,000 degrees Celsius and can produce DC electricity by burning hydrogen or methanol (without an actual flame).
These fuel cells can achieve efficiencies of up to 60% and potentially even higher. Although promising, these fuel cells are not yet ready for prime time. Catalysts are expensive and the heat is strong, so their lifespan is short. But progress is being made.
Until these technologies mature, we will have to use steam as a way to convert heat into electricity. It's not that bad. Steam works.
The clattering sound of a steam locomotive might make you think it's an archaic technology from the past. However, our civilization still relies heavily on steam. Once fusion power is achieved, steam could help provide electricity well into the future. The steam era isn't really over.
This article is republished from: conversation Under Creative Commons License. read original article.
Image source: Siemens Pressebild via Wikimedia Commons