What value would you assign to a properly designed aggregate processing plant?

What value would you assign to a properly designed aggregate processing plant?

Proper engineering design and equipment reliability are essential to a profitable aggregate processing operation; without which significant downtime and other financial losses are inevitable.

Proper engineering design and equipment reliability are essential to a profitable aggregate processing operation. Just a small interruption in production can affect a company’s bottom line. If your plant is not operational then you are not making money. A primary purpose of your equipment provider and servicer is to get you up and running no matter what brand(s) you are using – a team who are not only experts on their components but also on their competitors’ components. A team who can resolve your problems, alleviate pains, and reduce your company’s operating and maintenance expenses – increasing your R.O.I. Here is an excellent example of how our conscientious solutions team did just that.

Within one month of operation, the company observed the rotary counterflow drum mixer drifting and lunging uphill and downhill. The great force of a unit that is 11 ft. in diameter x 50 ft. long rotating with 250 HP did not just run hard against the thrust rollers (which holds the unit in either the uphill or downhill position), but impacted them hard enough to tear them loose from their hard mounts and even breaking the idlers themselves at times. Within their first 30 days of operation, this failed design caused four of the thrust rollers to rip loose – causing their entire plant to shut down.

In 2005 a major U.S. aggregate processor wanted to consolidate some of their production facilities in the Midwest and decided to go with a large 600 TPH plant. They contracted for a ‘super plant’ with a major manufacturer, who assured the customer that they could supply the plant without any major problems. Yet, appearing to only upsize one of the OEM’s existing models – without executing a thorough engineering study and comprehensive structural design analysis, a string of costly major problems began unfurling.

crew loading a silo onto a barge

Operational damage to thrust rollers, tires and trunnions can often be avoided through proper plant design and precise alignment.

Since the thrust rollers sat at an elevation of 11 ft. in the air, it was very difficult, cumbersome, and concerning safety-wise to get access to them to perform damage repair and component replacement. Plant breakdowns became so predictable that the company was forced to purchase an $80,000 man-lift to provide them with sufficient access to safely change out the broken thrust rollers. Without a better solution on hand, the designated change-out crew had to work hard to reduce the change-out time down from a few days to between four to seven hours that were required to do the removals and replacements.

crew loading a silo onto a barge

An $80,000 manlift had to be purchased to minimize downtime every time the thrust rollers had to be replaced. Although nice to have onsite for maintenance, that was a painful and avoidable expense.

The repetitive scenario for their multiple emergency breakdowns required calling the mobile changeout team, positioning the tools and equipment, and waiting for plant components to cool down to a safe temperature. Meanwhile, as the plant remained idle and the silos stood empty, a queue of hauling trucks would line up for blocks – waiting for their orders to be filled. Imagine the disappointment, frustration, stress and dread this repeated scenario caused the plant operators and owners!

crew loading a silo onto a barge

Unscheduled plant downtime from breakdowns is expensive for plant owners and negatively impact their customers, including material haulers lined up, waiting, and delayed from performing their jobs.

Within the first two years of operation, the company called on the OEM to provide support and some warranty consideration to help lessen their financial losses. The OEM did not honor the request and indicated they would consider looking into the equipment problems as a paid service. Upon looking into the problems, they were unable to fix the root cause of the issues. The operating company was simply told they needed to learn how to operate the plant in a better manner per the written guidelines and ensure that the tires and trunnions were aligned properly. The OEM themselves could not do what they were asking the customer to do.

Throughout the next 10 years, the company experienced nothing but trouble from the OEM’s 11’ x 50’ dryer. During that time, 28 thrust rollers were sheared off, multiple tire-rigging bolts broke, numerous discharge sweep end-rings wore or broke off, and they never truly had operational control of the drum.

Hoping to remedy the situation, the company purchased new heavier duty trunnions, bearing assemblies and trunnion bases from another source, but that didn’t solve their problems. In fact, the problem became more severe. Their next step was to bring in an independent company to diagnose and resolved the issues. But that company failed to get the drum under control. Meanwhile damaged thrust rollers continued to pile up in the scrap yard behind the plant.

crew loading a silo onto a barge

Unbelievable damage to thrust rollers, trunnions and tires can result from improper design. In the poorly designed system revealed in this article, 28 thrust rollers had been torn off from the uphill and downhill thrust of its dryer.

After several attempts to remedy the situation, enduring breakdowns for nine years, the company engaged us at Louisville Dryer Company (LDC) to assess and resolve their drum control problems. Following our initial onsite inspection and measurements of the relevant components, we dispatched a field team of engineers and technicians to observe the problematic dryer in operation. Following several days of inspecting, measuring, and testing, our team came to some dramatic conclusions.

Our solutions team observed that when the rotary dryer heated up and expanded, the supporting base and unitary frame heated up at a different rate. Sean Kyser, LDC Project Engineer, reports that “there was a significant difference between static non-loaded conditions vs. dynamic loaded conditions. This system had a built-in problem of deflection because it allowed movement of the trunnion and base. Thus, the dryer did not have a solid operational base of carrier roll trunnions, framework and thrust rollers.”

It was revealed that the OEM had not had this 600TPH design aggregate dryer system back when they had originally agreed to supply it. They basically had only upscaled the motor horsepower and trunnion size – without upgrading the frame, base support and thrust rollers. Such a quick manufacturing approach ignored fundamental engineering practices. Our team further determined that the OEM’s drum frame had no gusset support or enough trunnion cross-beaming to support the weight of the drum – especially when loaded.

We engineered optimal solutions and submitted our recommendations to the customer. The suggested remedy was to stabilize the dryer by constructing a monolithic concrete pier under both trunnion base assemblies. By building a foundation directly under the load-bearing of the trunnions, this method would eliminate all deflection and vibration in both the trunnion base supports and the dryer main axle beam. The customer agreed with the solution and the project was set into motion.

crew loading a silo onto a barge

To stabilize the dryer, the Louisville Dryer field service team constructed monolithic concrete piers beneath the trunnions.

The customer also engaged us to build a completely new replacement rotary dryer and separate bases to be isolated on concrete foundations. The foundations were installed and adjusted to the thousandths for stability and parallel alignment with the tires.

crew loading a silo onto a barge

Louisville Dryer Company provided the new replacement rotary dryer.

Ed Stump, Sr. Installer with Louisville Dryer, oversaw the change-out and commissioning of the new replacement shell while Steve Smith, LDC Sr. Field Technician, was on-site to optically align and record the elevations and slope. They oversaw the concrete pouring and inspected the grout for new piers on which to mount the trunnion bases. By transferring all the load from the drum directly into the pier, the defection and vibration was eliminated. Further accelerated trunnion and tire wear was avoided, and the recurring thrust roller/idler damage and expensive replacement problems were solved.

After everything was aligned and the trunnions set, start-up was a success. Ever since the repair/replacement solution was provided in early 2017, the drum has produced mix flawlessly and under control. The trunnion drive motor amps dropped, and stack temps are the best they have ever been. Major pains were alleviated, the owner/operator’s investment was recovered.

The Louisville Dryer replacement drum has processed over 3 million tons – with virtually no maintenance needed (other than replacing worn flight clips, which cost less than $3,000 for parts and labor). And, they’ve never had to adjust the trunnions once since our solution was implemented over five years ago. The plant superintendent reported that, “No one touches the adjustment of that dryer except Ed from Louisville Dryer.”

crew loading a silo onto a barge

The aggregate processor is very pleased with the complete solution provided by Louisville Dryer Co.

To say that this customer is pleased is an understatement. Of course, the plant personnel are happy that the sound they hear now is the repetitive reliable rotation of our custom-engineering rotary drum vs. the dreaded impacts from breakdowns including the honking of truck horns, the ringing of cellphones, and the complaints from bosses.

Now the customer has two related decisions:
1. What do they do with the 28 thrust rollers which were ripped loose?
2. Should they sell the man-lift? (Operators like having it for other maintenances.)

While their return on investment cannot be calculated accurately, imagine breaking off a thrust roller with five empty silos, trucks and paving crews standing by on a 6,000-ton day – 28 times!

That situation should never have happened. We at Louisville Dryer Company will do whatever it takes to get you up and running for the long term – at the Lowest Cost Per Revolution.

Furthermore, our pleased customer reports incredibly positive results from their chain supplied by Hotmix Parts & Service. To date, the plant has processed over 4.5 million tons using that same chain!

Louisville Dryer Delivers The Lowest Cost per Revolution

Louisville Dryer Delivers The Lowest Cost per Revolution

5 Proven Ways + 3 Examples

As defined by our customers (global manufacturing companies, process and reliability engineers and maintenance teams), successful outcomes of our custom engineering process are system installations that are:

      • On-Time
      • On-Budget
      • For Decades of Reliable and Precise Performance with Minimal Maintenance.

Over 5,000 rotary drying system installations and hundreds of repeat customers have used Louisville Dryer equipment as a core to their business operations. With that proven experience, following are:

Examples of Outstanding Dryer Longevity

1. Your Process Dictates our Technology:

Whether your application requires New Rotary Dryers, Replacement Drums/Shells, or other Rotary Products, our engineering teams expertly design, build and install entire solutions – including dryers surpassing 140 feet in length, 20 feet in diameter, and 200 tons in weight.
crew loading a silo onto a barge

2. Your Service Requirements Drive our Mechanical Design:

We routinely bring operational needs from concepts to design to production – considering your production requirements and process parameters, material characteristics, site and environmental conditions, and so much more.

steam tube dryer standard steam chest

3. Your Products are Thoroughly Tested in our Testing Lab:

When our customers request our advice on the most effective processing solutions for their specific application, we implement pilot scale testing in our own in-house lab to assess their material performances and outcomes with live test data and analysis.

man performing a quality check on a piece of fabrication

4. Your Equipment is Custom Manufactured in our own ASME-accredited Facilities:

Louisville Dryers are fabricated by our expert craftsmen who build dryers every day. Each dryer has a highly specific written inspection and test plan and quality control assessments. What makes a very large piece of rotating equipment reliable is not only the structural integrity of its design, but the precision with which it is fabricated and assembled.

louisville dryer company crew standing in front of an industrial dryer

5. We provide Professional Field Installation and Commissioning Support:

Our professional rotary equipment installation technicians ensure that each Louisville Dryer is properly delivered, assembled, aligned, and secured on its foundations. The service and maintenance life of any piece of rotary equipment is not based solely on the design and quality of the equipment – but also on the precision in which each component is installed, aligned and performance-tested, and on the thoroughness of the operational and preventative maintenance training provided to your team.

industrial dryer installation in progress
engineers inspecting an industrial dryer

Examples of Outstanding Dryer Longevity

As you can see, it is no surprise that the individuals and companies operating these units are extremely pleased with the results from our dryer systems which operate campaigns, often for months and even years with minimal maintenance or issues.

Success Stories about the dryer longevity our clients have enjoyed:

1. One owner-operator processed highly abrasive materials. We reengineered their system’s components to extend the life from a few months up to years. As one measure, we installed abrasion-resistant cast flighting and chrome carbide liners inside their unit to achieve exceptional performance and longevity.

flighting inside an industrial dryer component

2. As another demonstration of success, a large chemical processing company requested that we perform an extensive FEA (finite element analysis) of a rotary unit which they needed to operate under full load for a five-year period without shut down for maintenance.

tubes running into an industrial steam tube dryer

3. As another example, in recent years a company asked Louisville Dryer to evaluate the potential replacement of rotary dryer units in their processing plant. Their units had been operating dependably for decades and decades. Yet this was a complex project as their building had been constructed around the units, plus there was a river on one side of the building.

replacement dryer being installed by louisville dryer company crew

Louisville Dryer was pleased to assist the customer change-out their units with new shells, drives and bases. And it was not surprising that they selected new Louisville Dryer units since their original/legacy units had also been manufactured and installed by Louisville Dryer – in 1943 – providing over 70 years of reliable operation!

Longevity in Motion

Louisville Dryer custom engineered systems routinely deliver what our customers need and expect:

On-Time, On-Budget, for Decades of Reliable Precision Performance with minimal maintenance.

We provide The Lowest Cost per Revolution for Your Team. Contact us today to learn how.

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.

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

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

Choosing the right drying system is a significant investment and critical to your process. It is essential to know the variations between the different dryer options. The heat source is one of the most common differences. Read on and consider the following reasons why we often recommend a steam tube dryer over a direct heat dryer.

 

Steam Tube Drying vs. Direct Heat Drying: What’s the Difference? 

 

Steam Tube Drying  

Steam tube dryers perform as if it were a rotating tube with a shell heat exchanger. The drum is fitted with a high-pressure chamber that distributes steam into tubes running the length of the drum. Because its applications are for low-temperature processes, the equipment required for thermal destruction is reduced or eliminated. 

 

Steam Tube Dryers Are the Most Efficient Industrial Dryer

The most efficient of all the dryers, the steam tube dryer has very little air being exhausted – making the stack loss significantly reduced. The air pollution control system is also much smaller in a steam tube dyer and, since only a minor amount of air is used to sweep out the water vapors, the exhaust volume is a fraction compared to that of a direct heat dryer.

Steam Tube Dryers are also one of the easiest dryer types to operate. Once the steam pressure is set, the unit will take what it needs to do the job. Think of it as having a set-it-and-forget-it technology.

A steam tube dryer is used extensively in processing high-moisture organic materials such as distiller’s grain, gluten feed from the wet milling industry, oilseeds, and a variety of sludges.

steam tube dryer

 

How Does an Industrial Steam Tube Dryer Work?

Material is fed into the drum and tumbles over the outside of the inner tubes. Inside those tubes, steam is collapsing to condensate. The latent heat from the steam—about 850 BTUs per pound—provides the heat energy for drying. The condensate from the steam is removed through a rotary joint. It is then taken back to the boiler for regeneration.

 

Direct Heat Drying

 

How Does A Direct Heat Rotary Dryer Work?

A direct heat rotary dryer uses a hot gas which is induced into a rotary drum. Its heat source may be as simple as a steam coil in low-temperature applications, or it can have a burner for higher temperatures. The burner may combust into a chamber or it may fire directly into the dryer drum. We use the term direct-fired when there is no combustion chamber.

direct heat dryer

 

Direct heat dryers typically work best when the burner system can operate with a minimal amount of excess air or near stoichiometric balance of the gas and air. This allows the dryer to minimize the air required to carry the thermal energy.

 

 

frac sand dryer

 

Wet material is fed into the same end of the drum (parallel flow) or the opposite end of the drum (counterflow) and is picked up and showered (or veiled) into the hot gas stream. The thermal energy is transferred from the hot gas to the material, which heats the solids and the water, ultimately evaporating the water. The primary heat transfer is by convection.

 

frac sand dryer

If your product is not affected by heat from the burner flame or the products of combustion, then a direct-fired unit will provide an efficient drying solution through the full utilization of all three heat transfer methods: radiation, convection, and conduction.

Heat-sensitive materials such as biomass and organic products could be processed with either a direct heat dryer (with an air heater to control the temperature) or a steam tube dryer.

 

 

Why Choose a Steam Tube Dryer over a Direct Heat Dryer? 

 

Developed more than 100 years ago, the Louisville Steam Tube Dryer has always been a quality choice for drying high moisture organic by-products such as brewers’ and distillers’ spent grain. Today, this same dryer technology serves thousands of applications. 

 

What Materials Does an Industrial Steam Tube Dryer Process?

A steam tube drying system is our recommended choice for drying and processing inorganic and organic chemicals and other bulk solid materials including, but not limited to: 

  • Hemp
  • Dried distillers grains (DDG, DDGS)
  • Wet corn (fiber, grits, meal)
  • Wood chips
  • Soda ash
  • Paper mill sludge
  • Oil Seed (soy, sunflower, canola)
  • Soy meal
  • Chemical products
  • Petrochemical products (TA, PTA)
  • Lithium processing
  • Copper concentrate

All our dryers, including the steam tube system, are built in our state-of-the-art factory using proven technologies. Our in-house design team of engineers have vast experience in every type of process and industry; thus, our customers always receive a drying system that is custom fit for their operation. 

 

5 Benefits of A Steam Tube Drying System  

 

#1: More Cost-Effective

Louisville Steam Tube Dryers have been proven superior to other types of indirect-heat dryer installations in which hot gas, rather than steam, is used as the heat source. We provide solutions with the Lowest Cost per Revolution throughout our industries. Maintenance savings alone have often prompted the replacement of other dryer systems with the steam tube dryer.

 

 

#2: Better Quality

A steam tube dryer is classified as an ASME vessel. Thus, the requirements for its construction are more stringent than for other dryers. 

 

 

 

#3: More Efficient 

The steam tube dryer generally operates at a lower temperature than other dryers and rotates at a slower speed. Material tumbles gently around tubes that rotate with the shell, eliminating the friction forces that other types of dryers require.

 

 

 

#4: Easier Maintenance

Louisville Steam Tube Dryers enjoy a longer lifespan than most other dryers and require very little maintenance.

 

#5: Environmentally Friendly

Steam Tube Dryers are environmentally friendly. 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. Typically, the method uses less than about 30% of the exhaust gas required for a direct heat dryer

 

Purchasing A Steam Tube Dryer 

 

Because choosing the right drying system is a major investment and critical to your process, you should be sure you are getting the best equipment available. The Louisville Dryer Company manufacturing facilities hold esteemed accreditation by the American Society of Mechanical Engineers (ASME) and The National Board of Boiler and Pressure Vessel Inspectors

We extend personal attention and service to each customer, ensuring that their rotary processing equipment needs are efficiently met. If you are interested in learning more about the Louisville Dryer Company Steam Tube Drying System and its applications, please reach out directly to Hank Lawson, our Senior Process Engineer. He would be happy to listen and discuss the best options available for your application.

 

Call (800) 735-3163 or fill out our online contact form to get started.

 

Can a Rotary Dryer Operate Under Positive Pressure?

Can a Rotary Dryer Operate Under Positive Pressure?

Our process engineers were recently asked if a rotary dryer could operate under positive pressure. We thought it would be helpful to share the answer and provide a concise review of the distinct roles of positive and negative pressure within a Rotary Dryer system.

Atmospheric pressure is the downward force from the weight of air

Air Pressure, How Does It Work?

First, let’s consider a non-industrial description of air pressure. In the context of barometric pressure as reported by a weather forecaster, we essentially live at the bottom of a sea of air. That air is pushing down on our bodies at a force of about 14.7 pounds per square inch (atmospheric pressure at sea level).

In a closed system such as one with an attached pressure gauge that is set to zero, when suction is applied to the attached line in that system, air would be withdrawn from the system, and the gauge would then read less than zero.  Pressure that is lower than barometric pressure is negative pressure. Whereas if air was blown into the system, the gauge would read positive.

There are positive and negative air pressures

Similarly, in terms of pressure within a building, when you have a fan blowing air out of your house, you can open a window and then fresh air will enter the house – because the pressure in your house would be negative (lower than atmospheric pressure).

If you were to turn that same fan around – and blow air into your house, then the air already in the house would exhaust through the open window because the building is being positively pressurized.

 

How Air Pressure Effects the Drying Process

As it applies to a rotary drying vessel, a positive pressure is created at the burner from the combustion blower system while the rotary dryer is kept at a slight negative pressure to maintain burner flame envelope and to facilitate evacuation of evaporated moisture and dust particles in a controlled manner.

Dryer Pressures effect burner flame shape and efficiency

That negative pressure is controlled by the induced draft fan which can be adjusted to increase the air velocity through the dryer to allow more of the material dust particles to be directed out of the product stream to the Dust Collection system which reduces fines in the finished product. Conversely, the air velocity through the dryer can be reduced to allow more of the finer particles to drop out of the air stream prior to leaving the dryer.

A Switchgrass Dryer and Dust Collection System by Louisville Dryer Company

With each of those factors in mind, the system’s fan should be properly configured so that the dryer is always operating under a slight negative pressure. Under this condition, combustion gases and noxious vapors can be directed to the air pollution control system and not escape through the seams.

A thorough understanding of how pressure dynamics relate to heat management, moisture control and dust flow is integral to the proper design and efficient operation of industrial drying equipment. So, rotary dryer owners and operators should wonder – and confirm – how well their dryers operate under pressure.

A three-stage classification system by Louisville Dryer Company. The knockout boxes and baghouse integrated with the rotary dryer effectively evacuate dust, fines and moisture from the drying process.

Louisville Dryer Company engineers have extensive knowledge and proven experience providing air/exhaust-handling solutions and complete dryer systems for customers throughout the U.S. and the world – from material assessment/product testing to the custom design, fabrication, installation, commissioning and servicing of all components – all of which helps you accomplish your business goals and our professional commitment to your Lowest Cost per Revolution.

To Learn More

Learn about our high-pressure steam tube dryers and other steam tube dryers, and then to request help designing your industrial drying solution, contact our team today.