Alloy-based Rotary Dryers

Alloy-based Rotary Dryers

When prospective customers engage us to provide them with a customized material processing solution, they inquire, “With what materials are your rotary dryer shells manufactured?”

Our Sr. Application Engineers indicate to them that we have built thousands of rotary dryer shells using select metals from the full spectrum of carbon steels, stainless steels and alloys. Yet our recommended dryer shell design for your specific application will be primarily informed by your material’s specifications, your processing criteria, and your production goals. Each Louisville Dryer is custom-engineered and fabricated for your specific purpose.

For industries that process materials with exacting requirements (including distilleries, corn wet milling, wood processing, activated carbon and petrochemical), many common elements of our dryer design recommendations relate to temperature tolerance, pressure resistance, oxidation and corrosion resistance. For these extreme environments of high pressures, temperature and/or corrosivity, rotary dryers fabricated using alloy materials are well-suited for such tough service.

Rotary dryers fabricated with the wrong materials for your specific application can result in excessive wear, damaging corrosion and premature failure – all resulting in very expensive operational downtime.

Watch the following three video segments to learn more from our Application Engineering Team about our alloy-based rotary dryers:

What are your rotary dryers made of?
Which industries need rotary dryers built with alloys?

Learn which alloys Louisville Dryer Co. uses in their custom-built dryers and components, and which industries use them– including distilleries, corn wet milling, wood processing, activated carbon, petrochemical, pharmaceutical, food and others. See some examples of steam tube dryers that we have fabricated using various alloys.

Why would a customer need an alloy-built rotary dryer?
Which materials and processes would benefit from them?

In this segment, Louisville Dryer Co. identifies various applications requiring alloy-based rotary dryers – including considerations of chemical reactiveness (corrosion and wear from acidic or basic environments), potential contamination of the processing material by the dryer, and high-temperature tolerance.

What are some of the challenges when manufacturing rotary dryers with alloys?
And what production protocols and quality control measures do you employ to ensure the integrity of these alloys?


Hear from Louisville Dryer Co. about some of the challenges and QC protocols implemented when building rotary dryers with alloy materials – including our positive material identification tests, specific welding procedures to maintain alloy integrity, and diligent segregation of the alloy from carbon steel.

As you can see, Louisville Dryer Co. application engineers and dryer craftsmen have the industry knowledge, technical expertise, and proven experience to fashion a custom solution with The Lowest Cost per Revolution for your team.

Call or email us today to get one step closer to solving your processing challenges and achieving your production and business goals.
Hemp Activation/Decarboxylation in Steam Tube Dryers

Hemp Activation/Decarboxylation in Steam Tube Dryers

As part of our lifelong learning, Louisville Dryer Co. engineers regularly interact directly with processing industry customers and continue to make discoveries. Most recently, with changes in legislation for the burgeoning hemp industry and as the quantity of hemp to be processed has skyrocketed, entrepreneurs have reached out to technical experts in drying sciences and technology to help them explore their options for cost-effective solutions.

Hemp processors who were wanting to reduce their drying times by accurately controlling the drying environment consulted with Louisville Dryer Co. applications engineers.

As part of this endeavor, using our production-worthy scaled-down dryers in our Research & Development/Testing laboratory, we have engaged in leading-edge testing to determine which of their methods of processing and drying would perform the best for handling hemp.

In our Research & Development/Testing Laboratory, we use production-worthy scaled-down dryers to assist companies in developing new products such as wood composites, airbag propellants, rocket fuel, algae-derived oils, and more.

For an organic material such as hemp, a steam tube dryer is typically the ideal choice for the process since it allows for slow, even heating to remove internal moisture without scorching. Historically, a separate necessary step is the activation of the CBD-A as it exists in the hemp plant so that it is converted into the usable form CBD. This process is called activation or decarboxylation and makes the hemp’s chemical properties accessible for human bodies to process. The original understanding was that drying and decarboxylation were two separate steps and that they would need to take place in separate pieces of equipment to optimize each process.

Through hemp R&D experiments in our own testing laboratory, Louisville Dryer Co. engineers discovered that hemp dried in their Steam Tube Dryer went through the decarboxylation process: which is the necessary reaction where the organically present THCA or CBDA (from the cannabinoid-rich oil extracts) is converted into THC or CBD, which provides the consumer with the desired medicinal effects of the product.

What Louisville Dryer engineers observed in their laboratory and confirmed through independent testing was that decarboxylation can take place inside the steam tube dryer and is dependent upon the temperature and residence/dwell time of the material. In one of the tests, material was hand-harvested from a small local hemp farm and immediately taken to Louisville Dryer’s facility for processing.

Upon arrival, one of the first goals was to get the material to a manageable size that would make it through the steam tube dryer. Although a commercial unit can handle larger particles than the lab dryers, it is still valuable to know successful techniques for particle size reduction for instances when entire plants are being harvested.
Using a woodchipper, hemp flowers with some stems were chopped and collected. The resulting feed material was manually weighed and fed into the pilot steam tube dryer by hand. Through product material evaluation and testing, it was discovered that dryer material indicated a higher level of decarboxylation since lower product discharge moisture indicates higher material temperature. One of the major benefits is that the material can be activated and ready for use without it needing to be burned or further processed for decarboxylation to occur.
As hemp production needs increase, the next logical step for processors is to minimize the manual labor historically involved in smaller scale operations. For example, we have spoken with customers who still hang hemp in barns to dry in a similar manner to tobacco. This may work sufficiently for very small farms and acreage, but very quickly the costs and headaches of manually harvesting and hanging material become apparent on a larger scale.
In addition, there have been reports of improper ventilation that has led to product loss through molding. Another issue is the large footprint required for barns or similar buildings to hang hemp especially as the quantity to process increases. The steam tube dryer allows for material drying to take place in minutes and hours instead of days and weeks as with more traditional methods and naturally helps to prevent contamination of the hemp because of this and through less time spent handling/re-handling.

With decades of experience in the agricultural processing industry, Louisville Dryer Co. manufactures direct heat dryers for processing hemp and steam tube dryers with a range of capacities to dry wet hemp biomass with an output moisture content between 10-12%.

To learn which processing technologies would be optimal for your material and application, contact our team of Applications Engineers at (800) 735-3163 or fill out our online contact form.

Drying Distillers Grains: Steam Tube Dryer vs. Direct Heat Dryer

Drying Distillers Grains: Steam Tube Dryer vs. Direct Heat Dryer

Consider a drying system to process 20 tons per hour of combined wet cake and syrup produced in an ethanol plant or distillery. At 66% combined feed moisture dried to 10% moisture content, the mass balance would be as follows:

Feed MaterialDischarge Material
Dry Solids13,600 LB per Hour13,600 LB per Hour
Moisture26,400 LB per Hour 1,511 LB per Hour
Total40,000 LB per Hour15,111 LB per Hour

Evaporation:                     24,889 LB per Hour

The heat requirement for drying is approximately 27.2 MMBTU.

Direct Heat Dryer

Using a direct heat dryer system for the process above, the system schematic would be similar to the one shown in Figure 1. Note that the dry material recycle loop is not shown since it would be identical for either dryer.

Drying Distillers Grains Direct Heat Dryer

The direct heat dryer in the example is equipped with a combustion system having a dryer inlet gas temperature of 1,000 F. Based on this system, the dryer exhaust gas discharge volume would be 53,000 ACFM. The system is provided with a flue gas recirculation system. This is included for two reasons:

  • Since the gas is laden with water vapor and combustion products (from having passed through the burner), it lowers the amount of oxygen present in the drum in order to prevent combustion from occurring inside the dryer.
  • It reduces the amount of gas having to go to the thermal oxidizer for destruction of VOC.

    This operating cost of the system is not just the drying but also the cost to operate a thermal oxidizer. This type of system also requires two additional fans, which cause increased horsepower requirements and exponential complexity of process control.

    Steam Tube Dryer

    Using a steam tube dryer system for the process above, the dryer system schematic would be similar to the one shown in Figure 2.

    Drying Distillers Grains Steam Tube Dryer

    Because the steam tube dryer employs steam to do the work, very little air is required. Typically, the dryer is run under slight negative pressure and a small amount of air is vented into the dryer to offset dust from puffing out. Thus, the primary content in the exhaust stream is water vapor instead of air.

    Since water is condensable, the exhaust gas goes through a condensing scrubber where a great deal of the water is collapsed back to liquid phase and removed. The remaining saturated air stream is taken back to the boiler and used as combustion air. The boiler acts as the VOC combustor – potentially negating the need for an RTO.


    Employing a steam tube dryer for processing DDGS may initially appear to be a more costly system (because the dryer itself is more expensive, and a boiler is required).

    Yet, for true comparison, the following factors of the overall system also need to be considered:

      • Steam tube dryers do not require heated air to operate.
      • Steam tube dryers do not require recycle gas stream for fire prevention.
      • Steam tube dryers are easily controlled by simple modulation of a steam valve.
      • Steam tube dryers do not require a thermal oxidizer system for most biomass systems. If an RTO is required, it is 75% smaller than with direct heat.
      • Steam tube dryers have an atmospheric environmental impact a fraction of direct heat dryers.
      • Considering the cost of an RTO verses a boiler, the steam tube dryer system may have a smaller initial cost.
      • Since the boiler for a steam tube dryer system may act as a thermal oxidizer, the operating cost is much lower.

    Learn more about When you would need a Steam Tube Dryer vs. a Direct Heat Dryer.

    Contact our Application Engineers to discuss your operation’s specific needs and how we can help you achieve The Lowest Cost per Revolution.

    How Steam Tube Dryers Process Materials

    How Steam Tube Dryers Process 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/500F 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 tube dryer parts

    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.

    steam tube dryer standard steam chest

    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

    pipe manifold

    For certain applications, an alternative to the fabricated Steam Chest design is needed. For example, the Louisville Dryer Pipe Manifold design is a available based on customer preference. The Pipe Manifold 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 saturated 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).
    Steam Tube Dryers Process


    Steam Tube Dryer Videos

    To view how our Steam Tube Dryers process temperature-sensitive, volatile or corrosive materials, watch this video.

    This segment is one in our new video series on Steam Tube Dryers:

    • WHY choose our custom Steam Tube Dryers for processing Distillers Dried Grains (DDGS) and other temperature-sensitive materials?
    • HOW do our Steam Tube Dryers process materials?
    • WHAT components comprise our Steam Tube Dryers?
    • WHERE in a Steam Tube Dryer is the material processed?
    • HOW LONG do our Steam Tube Dryers operate efficiently, safely and profitably?
    • WHO is Louisville Dryer Company?

    Green Drying

    Using clean steam rather than products of combustion, Louisville Steam Tube Dryers are one of the most ecologically friendly drying technologies. As indirect heat dryers, they use the latent heat from clean low-temperature saturated steam rather than hot gases from fossil fuel-fired combustion systems. This highly efficient heat-transfer design also makes Louisville Steam Tube Dryers one of the most thermally efficient drying technologies.

    The residual non-condensable gases left inside of the steam tubes once the steam has condensed are vented through a flexible connection attached to a common Vent Header that is mounted at the feed end of the dryer. This Vent Header has thermostatically controlled vent valves which allow the cooler non-condensable gases to be efficiently vented as they accumulate while containing valuable steam energy inside the steam tubes.

    Since the Steam Tube Dryer utilizes the latent heat of steam to drive the drying process, only a small amount of sweep air is required to remove the water vapor driven off the product generated in the drying process. This is usually less than about 30% of the exhaust gas required for a direct heat dryer for the same process parameters.

    Central Discharge CS Seal Steam Tube Dryers

    The gap between the stationary Feed and Discharge housings at either end of the Steam Tube Dryer is sealed to keep ambient air from leaking into the dryer. Various sealing technologies are used depending on the process parameters. These seals may be as simple as tensioned woven fabric belts and as sophisticated as machined packed and inert gas purged seals (e.g. solvent extraction and other vapor capture applications).

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

    Our 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. Materials of construction range from carbon steel to various nickel alloys and duplex stainless steels.

    Steam Tube Dryer Louisville Dryer

    We 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.

    Contact our Applications Engineers today to begin finding your custom solution.