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Steam Generators Vs. Steam Boilers

The inside of a steam boiler has many more tubes than the inside of a steam generator.
The inside of a steam boiler has many more tubes than the inside of a steam generator. | Source

The nomenclature of industrial boiler and energy generation can be a little confusing, even when you know the territory! For example, look at the difference between "steam generators" and ”steam boilers." A steam boiler generates energy by generating steam, and a steam generator generates energy by generating steam, so...wait, what? I know, I know—it almost sounds like a bad tongue twister. A simple explanation doesn't do these machines justice, so if you really want to know what makes them different, you have to take a look at their guts and come to understand how they do what they do. It's like Zen: You have to look inside to find the answers!

How Steam Boilers Work

There are two main types of steam boiler systems: fire-tube and water-tube boilers. They're similar, but it's definitely worth explaining their differences before we get into the more complicated stuff. First, we'll look at the fire-tube boiler. Inside the boiler is a massive tank of water, and coursing through the water are pipes, or "tubes." A fire in the boiler burns fuel, and the fuel gases surge through the pipes. There are so many pipes and the gases are so hot that they heat up the water from inside, causing steam to rise off the top to be used as energy.

A water-tube boiler is very similar, but fundamentally opposite—the gas and the water essentially switch places. Now, the inside of the boiler is filled with a large number of tubes, and inside each tube is water that feeds in from a reservoir near the bottom. Once again, fuel burns and creates hot gas, but this time, the gas heats the water from outside the tube. Water in the tubes heats up and steam filters out of the tops of the tubes, while the water not yet hot enough to convert cycles back down to the reservoir before going through the tubes again. This technology is newer than fire-tube boilers.

These boilers are generally used in industrial applications, because they are oftentimes very large, very powerful machines. These aren't necessarily like the boiler in your basement—these are pieces of equipment that can take up entire warehouses, or more, generating enough steam-based energy to power factories!

Compared to Steam Generators

Now that you understand a water-tube boiler, it's much easier to understand how steam generators are different from your typical industrial boiler. Remember, a typical steam boiler has a whole bunch of tubes inside, right? Well, a steam generator only has one. Yes, one. But don't let that make you think that it's simple! In fact, it's quite the opposite. That one tube coils around and around in tight curls, like a spring. While these machines can be structured vertically or horizontally, we'll stick to vertical ones right now.

In one of these, the coils go down one side of the steam generator and up the other. At the top of the generator, water feeds in with a reservoir much smaller than you would see in a fire-tube or water-tube boiler. That water is heated at the top and circulates down through the windy tube, and by the time it's hot enough to turn into steam, a single exit point at the bottom of the tube allows the steam to escape in a concentrated stream. If there's any residual water left, it trickles out of the same exit point and is caught in a filter that lets only steam through. Any excess gases produced during the process travel up the other side of the tube and are eventually released.

Advantages of a Steam Generator

You can see now how steam generators are similar in principle to other steam boiler systems while remaining fundamentally different. These fundamental differences change the entire operation of the system, which is generally less powerful than a full boiler, but features several advantages. For example, a steam generator sports a simpler construction that makes is easier to operate than a full-scale industrial boiler. These generators are also smaller, making them more versatile when you're working with limited space—you often see them utilized as auxiliary boilers.

Another reason they are often used as auxiliary boilers is that they start up very quickly. Because of their compact design, single water tube and relatively lower water content, these machines can be up and running at full power in a much shorter amount of time than full-scale boilers, making them useful in emergency situations. It's like comparing a racing motorcycle to a military tank -- the former accelerates faster and works quickly, but isn't very strong, while the latter chugs along but is ultimately more powerful. And because they generally cost less than full-scale boilers as well, they may be more cost-appropriate for applications that don't necessarily require such high levels of steam.

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