How Steam Tube Dryers Process Materials

Including Temperature-Sensitive, Volatile & Corrosive Materials

How Materials are Dried and Processed Using Steam Heat Transferred Through Tubes

A steam tube dryer is like a rotating shell-and-tube heat exchanger in which medium pressure, saturated steam is charged through a rotary steam joint, into the manifold and then into several heat transfer tubes – typically at a nominal 100-150 psig (and up to 450 psig/500° F service for reacting granular solids). Concentric rows of these tubes run the length of the dryer; one to six rows depending on the dryer size and duty requirements.

Steam Chest Design

A steam and condensate manifold chamber, referred to as a Steam Chest, is mounted on the product discharge end of the dryer. This Steam Chest distributes steam to each of the steam tubes and collects the condensate formed as the steam transfers its latent heat to the material being processed. The steam condenses and the condensate is removed from the dryer and taken back to the boiler. The dryer utilizes only the latent heat of condensation, making the dryer one of the more efficient drying systems in the world.

The process material is fed into the drum through a screw conveyor and then tumbles over the outside of the tubes. As indirect heat, the thermal load of the saturated steam in the tubes is not in direct contact with the material. The steam remains inside the tubes while the material lies outside of them. The material cascades on the outside of the tubes and condenses the steam on the inside of the tubes, and that conductive and radiant heat is used to dry the material.

The latent heat is efficiently drawn from the steam (about 850 BTUs per pound) and transferred through the tube wall and into the material – which drives off its moisture. Our dryers execute this process at a consistent temperature – providing a very uniform heating of the material particles.

The water condensed out of the steam is continuously removed from the steam chest through a stationary siphon and cycled back to the boiler for regeneration. And the dried product discharges through ports in the shell at the steam chest end of the dryer.

Pipe Manifold Design

For certain applications, an alternative to the fabricated Steam Chest design is needed. For example, the Pipe Manifold design is comprised of concentric rings of pipe, one for each row of steam tube in the dryer, set on different planes, which are connected to a center steam and condensate distribution chamber with steam supply pipes, and condensate return pipes. Each row of steam tubes extends through the dryer and is welded to its corresponding manifold ring.

The Steam Advantage

Steam Tube Drying is thermally very efficient and friendly as heat loss through the cylinder wall is minimal since the steam tubes are fully enclosed by the dryer.
This indirect heat system is also much safer for processing temperature-sensitive organics and volatile chemicals, which could catch fire even at low temperatures.
The exhaust gas from the dryer is about 80% less than what is required for direct heat dryers, which significantly reduces the size and cost of the air pollution control equipment.
Using steam enables us to maintain an inert environment, which is safer for your materials and production/maintenance team.
Since Steam Tube Dryers process under lower temperatures and without gases present in a direct-fired dryer, your material will not get scorched or burnt as much as they might from using Direct Heat Dryers.
Thus, your material will maintain or receive better coloring, and its bypass proteins will be protected by not being overheated (which is important for digestion of Distillers Dried Grains by livestock).

A Video on Steam Tube Dryers

To view how Louisville Dryer Steam Tube Dryers process temperature-sensitive materials, watch the following one-minute video:

You can view other concise videos about steam tube dryers by Louisville Dryer here – including how steam tube dryers process dried distillers grains (DDG/DDGS), dryer longevity, steam tubes and components, and dryer processing zones.

Louisville Dryer Company is an ASME Division I Design and Manufacturing Center

Louisville Dryer indicates that their Steam Tube Dryers are custom engineered for each specific application. The steam side component is a pressure vessel, designed and manufactured in conformance with the latest edition of ASME Section VIII, Division I. They are stamped and registered with the National Board. Their materials of construction range from carbon steel to various nickel alloys and duplex stainless steels.

Louisville Dryer reports that they have completed thousands of installations processing hundreds of materials around the world and pioneered many of the technologies applied to today’s Direct Heat Dryers and coolers, Indirect Heat Dryers and calciners, Steam Tube Dryers and Water Tube Coolers.

Materials processed include organic and inorganic chemicals, petrochemicals, grains, metals, aggregates, and waste byproducts. If the material is granular solid, it probably has been processed in a Louisville Dryer. The Applications Engineers at Louisville Dryer Company can help you find your custom solution.