During the cold of winter when you are running your furnace to heat your home, would it be HVAC-efficient, environmentally helpful or financially wise to leave some of your windows open? Of course not.
Yet for closed controlled systems on a much grander scale, hundreds of industrial direct heat dryers are operated every day without being effectively sealed. Drum Seals which are either absent, poorly designed or damaged often contribute to excessive gas flow through the drum due to air leaking in. Such exhaust gas leaks in the rotary drying process increase fuel consumption (to heat the excess air), increase material carry-out (due to higher gas velocity), place a heavier burden on air pollution equipment and increase operating expenses.
Furthermore, these leaks reduce product quality, fuel efficiency and even production capacity. (Common causes for seal failures are abrasion/contamination, shell expansion/contraction, excessive shell run-out, poor maintenance and product overflow.)
The Problem with Air Leaks
Rotary drums, dryers and kilns serve a crucial role in the processing of hundreds of various consumer products including bulk solids and chemicals. Since dryers utilizing heat transfer in these controlled systems operate with internal temperatures much higher than ambient air, any outside air allowed to leak into* the vessel will reduce the operating temperature and cool the gas stream, thus reducing the overall effectiveness and cost-efficiency of the system.
Furthermore, unintended changes in the processing temperature alter the intended chemical reactions – which negatively affects the state and quality of the end-product.
Specific Examples of How Air Leakage Affects Dryer Efficiency
The 1” gap around the end circumference of this drum shell can cause an air leakage of approx. 5,400 ACFM, which places an unnecessary/avoidable significant burden on the baghouse and fan, resulting in loss of 10-15% of production capacity.
The air leakage allowed by the 1 ½” gap (from missing seals) on this 8 ft. diameter drum is equivalent to a 1’ 9” square hole (= 3.1 sq. ft.) in an exhaust duct!
Poorly maintained (or absent) seals contribute to poor performance and loss of efficiency
The Louisville Dryer Solution
We button up your plant with high-quality durable seals
To close the gap between our rotating vessels and their stationary discharge housing, we custom-design and install seal systems. Our application engineers emphasize that properly designed and maintained seals are a significant contributor to the system’s overall efficiency and can thus provide a relatively prompt ROI for plant owners/managers who invest in them.
If your direct heat dryer does not have a seal system – or is missing leaves/sections of its existing seal, contact us soon to request a diagnostic inspection and solution recommendation from our engineers.
Benefits which your plant could realize from installing/maintaining a proper seal system for your rotary drum/dryer:
Decreased production expenses
Lower maintenance costs (from reduced gas volume/velocity and fan wear)
Saved MBTUs
Raised flame temperature
Increased production capacity
Types of Dryer Seals
When it comes to seals, clearly one size does not fit all. Louisville Dryer Company can offer many different types of drum sealing devices specifically designed to meet the needs of the application process – considering factors including operating temperatures, material in process, dryer size and rotational speed.
Cracking in a dryer shell can cause alarm and anxiety. How will the cracking affect the life of the dryer? Just like a small chip in a car’s windshield, there is concern that high stress on a weakness in a rotary dryer shell could grow into a bigger crack.
With the technical experience of the Louisville Dryer’s field engineers on your side, there is no need for stress. Dryer shell cracks do not always mean that the shell is on the verge of catastrophic failure. We can assess the status of your existing equipment and take the necessary steps to keep you operating efficiently.
Why Do Dryer Shell Cracks Occur?
Cracking generally occurs at high-stress locations and surfaces slowly. They are typically caused by the cyclic loading and unloading at these high-stress locations.
There are four common shell crackings, which we have outlined for you. The causes and concerns vary, as do the repair solutions. We are providing a broad overview of these common cracks to help you assess your needs. Please keep in mind that this is not inclusive of all shell cracks, and we always recommend a professional assessment by a knowledgeable rotary dryer specialist.
Four Common Dryer Shell Cracks | Causes & Solutions
# 1. Shell cracking that moves away from support points.
Identification: Cracks forming lengthwise near the middle of the shell.
Common Cause: Continual overloading or an abrasive or corrosive product that has worn away the thickness of the shell plate.
Common Concern: In this scenario, the shell has started to exceed the limit of its bending stress due to a reduction of shell plate thickness, or excessive weight. At this point, the cracks will continue to get worse, and sometimes at an alarming rate.
Typical Solutions: Wrapping or lining the shell can provide a temporary fix, but it does not add full rigidity back to the unit. A longer-term solution might require cutting that section of the dryer out and installing a new section. If the contributing factor is abrasion or corrosion, then the next step is to identify and mitigate that cause.
# 2. Cracking near the support pads of the riding tires.
Identification: Cracks forming near the tires.
Common Cause: Continuously overloading the unit by running material loads considerably past design.
Common Concern: All components of the rotary are designed with a certain amount of service factors, but those factors can be exceeded. When higher throughput is introduced, the excess stress causes the tires and support pads to transfer that pressure to the shell which can cause a small weakness to increase in size and vulnerability.
Typical Solutions: If you notice this type of cracking, act quickly. Start by reducing the amount of material passing through the unit. Cracks that are not excessive can typically be ground out and rewelded for a cost-effective and simple fix.
# 3. Cracking emanating from the corners of support pads.
Identification: Cracking of this nature typically occurs at support pads with sharp corners.
Common Cause: If the tire pads have sharp terminating corners, then the stress at these locations are exponentially higher than when the pads have rounded ends. It’s like the difference between pressing against something with a knife versus with the back of a spoon.
Typical Solutions: Stress riser induced cracks can be ground out and rewelded. In addition, the sharp corners of the support pads should be removed or the pads should be replaced entirely.
# 4. Cracks around steam tube support bundles.
Identification: Cracks between the supports and shell.
Common Cause: Steam tube supports should be designed to flex with the shell, and not act as a rigid, unforgiving inside stiffener. When supports are stiff, cracking can occur at the welded connections between the supports and shell.
Typical Solutions: Cracks can be ground and welded. U-style support stiffeners should also be installed on the shell externally to reduce stress from the tube support to the shell.
Protect Your Investment
Your dryer is a key piece of your operation and requires the best service from reputable experts.Louisville Dryer has been synonymous with rotary drying equipment for over a century. Our in-house team of engineers has the expertise to respond to any of your needs.
Over our extensive history, we have built, installed, and serviced rotary equipment that processes nearly every imaginable kind of material. No problem is too big or too small for you to contact us. We can help you assess any cause or concern, from small cracks and weaknesses to larger malfunctions and threats to your productivity. You can rest assured you will receive effective solutions that keep your production moving on time and on budget.
The Louisville Dryer team is open and willing to share our knowledge with you. It starts with making a phone call to us at (800) 735-3163 or by taking a moment to fill out our online contact form.
