Why Vertical Shaft Kilns Are Still in Use

Mention an industrial kiln today, and most people will assume you’re talking about modern rotary kilns. However, there’s an older type of kiln that – surprisingly – still sees plenty of use around the world: the vertical shaft kiln.

At the Kiln Technology Company Company, we specialize in supporting all types of kilns, including these older types. How do they work, and why are they still preferred in some fields? Let’s take a look.

The Basics of Vertical Shaft Kilns

As the name suggests, a vertical shaft kiln is effectively a huge heated vertical tube that is filled from the top, with final products coming out the bottom. Unlike a rotary kiln, there is no mechanical motion outside of automated systems feeding the top and removing material from the bottom. All heating, calcination, and product movement happens entirely through the forces of gravity and airflow.

At the top, the raw materials are turned into damp pellets by adding around 12-14% water weight. Then they’re fed into the kiln which, ideally, is kept constantly topped up with materials making their way through.

The kiln’s interior is divided into three zones, from top to bottom: preheating, calcining, and cooling.

In the preheating zone, the water in the pellets evaporates, while allowing the pellets to keep their semi-solid form. As the pellets sink, their temperature continues to rise until the temperature approaches 1000℃.

As they sink, they enter the calcining zone, typically defined by the rise in temperature above 1000℃. The materials typically combust at this point, burning off the coal, and causing the materials’ temperatures to rise to 1300℃ or higher. The pellets become calcined clinkers during this process.

Finally, they drop into the cooling zone, which features cold air being blown in from the bottom. The clinker cools and drops out the bottom to be carried away.

The Pros and Cons of Vertical Shaft Kilns

In most situations, rotary kilns are superior to vertical shaft kilns. They typically have better-controlled combustion, and produce more reliable materials. In addition, vertical shaft kilns can send huge amounts of CO2 into the atmosphere, as well as a lot of heat, whereas rotary kilns are better at capturing waste materials and heat.

However, they are traditionally considered better at calcining limestone and quick lime, and the relative lack of moving parts makes them easier to maintain over time. Still, these benefits are not considered compelling in most fields. The main reason vertical shaft kilns are still in use is simple inertia, especially in less-developed areas which lack the resources to upgrade, or whose governments lack stricter pollution regulations.

For The Best In Kilns And Services, Call In The Kiln Technology Company Company

We are widely regarded as one of the top kiln service companies in the United States and have assisted production facilities across the country. From installation to repairs to decommissioning, we provide a full suite of services to support operations that rely on kilns for materials production.

To learn more about the Kiln Technology Company Company or request a consultation, just contact us.