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Steam Generators vs. Steam Boilers


If you are searching for a steam energy solution for your business, you likely have come across the confusing differentiation between a steam generator and a steam boiler. The most basic understanding of these two systems is that they both produce energy through steam, however, they accomplish this in fundamentally different ways. These differences affect everything about each system, including their size, operation, and most importantly, their application.

Because steam boilers and steam generators are intended to be used in entirely different situations, it’s essential for a business to understand the discrepancies between them. Understanding the design of these two systems will help in choosing which is right for meeting your energy production needs.

What is a Steam Boiler?

Steam boilers are typically larger pressure vessels capable of providing energy to industrial operations. They accomplish this by boiling water at subcritical pressures with intricate fuel systems. In some jurisdictions, the high pressure and high steam output capability of steam boilers requires a fully certified and licensed operator to be on-site in order to be operated. There are two common designs for a steam boiler: firetube and watertube.

In a firetube design, a steam boiler is a pressure vessel comprised of a large shell in which the hot gases of combustion pass through one or more boiler tubes connected to the front and rear boiler sheet. The most common firetube type is the scotch marine firetube boiler, which utilizes a large furnace tube and many smaller boiler tubes. The hot gases from the combustion process pass through the tubes transferring the heat to the surrounding water. This process develops the high temperature required to boil the water and begin the steaming process.

The watertube boiler actually inverts this design. The water flows through the smaller diameter boiler tubes while the combustion gases travel around them to transfer heat to the water. The boiler tubes in the watertube design carry the heated water inside the tubes between the lower drum (mud drum) and upper drums (steam drum), with the generated steam accumulating in the upper drum. Heat is generated in the furnace area and transferred to the water through two main zones, the furnace zone and the convection zone, while the hot gases are moving across the tubes and out the exhaust.

What is a Steam Generator?

Compared to steam boilers, steam generators have less steel built into their design, utilizing a single tube coil instead of many smaller diameter boiler tubes. A specialized feedwater pump is used to continuously pump the feedwater through the coil. A steam generator uses a once through, forced flow, design to convert the incoming water to steam during the single pass through the water coil. As water passes through the coil, the heat is transferred from the hot gases which causes the water to convert to steam. The generator design does not utilize a steam drum where the steam of a boiler has a disengagement area from the water in so the use of a steam/water separator to achieve 99.5% steam quality is required.

Because generators do not utilize a large pressure vessel as in a firetube, they are often smaller and quicker to start up, making them ideal for quick on demand situations. However, this comes at the cost of energy production, as generators have low turn-down rates, and are therefore less capable of providing steam during periods of variable demand.

Advantages of a Steam Boiler

When it comes to deciding which of these systems is right for your business, the key consideration is simple: output and demand. While steam generators are quicker to start up, they are limited in size as their maximum capacity falls short of a typical watertube boiler. Steam boilers, on the other hand, are designed for long-term industrial use. The larger capacities of a steam and hot water boiler are powerful enough to support large-scale, high demand critical operations that see swings in steam demand. The water stored in the steam boilers allows for a much better response to changing steam demand from the plant than the single through design of a steam generator.

It is also worth noting that steam boilers are more adaptable to the needs of a business. Depending on the construction of your building or its energy usage, steam boilers can be packaged and designed to meet any of your demands. If your business is in need of a custom industrial boiler solution, contact Powerhouse today!

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