Rotary Kilns
Many kilns, by definition, are refractory lined – using materials which are resistant to decomposition by heat, pressure or chemical attack. The refractory retains its strength and form at high temperatures.

Basically, rotary kilns are rotary shells that are insulated on the inside – which must be done with precise engineering, design and installation of the refractory bricks or other interior lining. Special focus must be placed on the critical relationship between the dryer shell and its rolling components.

Refractory used in rotary kilns prevent premature shell degradation from heat, pressure and chemical attack.

Refractory-lined kilns are designed to operate 24/7 because the primary factor which shortens their operating life is the thermal changes experienced from ambient temperature ramping up to 1000°F or 2000°F or more. Rotary kilns must be designed and operated carefully to gradually elevate their temperature and then stabilize it at a given rate for its production.

Louisville Dryer Rotary Kilns
Louisville Dryer Company provides both refractory lined Direct-Fired Kilns and Indirect Heat Kilns – often for incineration and gasification of petroleum sludges, biomass, or municipal solid waste. The process material is heated in the rotary unit and in a semi-inert gas stream. The complex organic molecules are converted to synthesis gas. This syngas is withdrawn to a secondary combustion system – ultimately converting waste to energy.

This Louisville Dryer rotary dryer kiln shell was recently custom designed to incinerate industrial process waste and convert it into energy.

For this custom application, the biosolids will be gasified from complex organic compounds into simple hydrocarbons – which will be extracted and then routed back into the burn chamber.

Dimensions and weight of this Rotary Dryer Kiln Shell custom engineered and manufactured by Louisville Dryer craftsmen are approximately:
• 14.5 ft. in diameter x 40 ft. in length
• 9” thick refractory lining
• 50,000 lb. tires (riding rings)
• 250,000 lb. dryer shell + 250,000 lb. refractory = approx. 500,000 lbs. total unit weight.

Once the refractory has been installed (on the inside of this kiln), approximately half a million pounds of steel and brick will rotate to the customer’s specifications with high accuracy and longevity.

To learn how Louisville Dryer applications engineers can custom-design, fabricate and install a long-lasting rotary kiln for your application, contact us today.

The Answer is a Definite – Maybe.

For Starters
A number of people in the process industry have highly recommended and promoted the idea of insulating dryers and kilns, even some that are already operating in the field. There is absolutely no simple answer as to whether dryers and kilns should be insulated. As with most industrial equipment, a well-founded and accurate answer for your specific component in your specific application would require a professional study of the metallurgical and thermal transfer aspects of operating your dryer/kiln while processing its full range of materials at its full spectrum of operating temperatures.

Optimizing Results for each Customer
Louisville Dryer Company and our affiliates have built over 5,000 dryers for all types of industries processing a wide array of materials, temperatures, and production rates. Most every dryer/kiln is custom-designed and evaluated in our own fabrication facilities even though many of them are going to be commissioned within the same industry – as some will be operating in slightly different conditions.

Based on Louisville Dryer’s 120+ years of corporate legacy and solution-providing experience, we have honed best practices and procedures for calculating and projecting each unit’s performance longevity. We take pride in earning and continually maintaining the industry designation as providing rotary dryers and drums with The Lowest Cost per Revolution.

Precision Dryer Testing Laboratory
Our applications engineers indicate that the best way to confirm optimal results for a unit is through material testing. We have in own test laboratories multiple scale models and designs of test dryers, and operator-engineers with experience in precision testing.

To facilitate accurate test runs, we request that the processor or end-user send samples of their actual material(s) to be processed, which will be precisely measured and run under careful controls in the Louisville Dryer test lab unit. The test dryers are of the same design as full-scale in-production unit; they are just scaled-down versions.

Precision Dryer Testing Laboratory
Our applications engineers indicate that the best way to confirm optimal results for a unit is through material testing. We have in own test laboratories multiple scale models and designs of test dryers, and operator-engineers with experience in precision testing.

To facilitate accurate test runs, we request that the processor or end-user send samples of their actual material(s) to be processed, which will be precisely measured and run under careful controls in the Louisville Dryer test lab unit. The test dryers are of the same design as full-scale in-production unit; they are just scaled-down versions.

Louisville Dryer testing units include both direct-fired dryers (both in co-current and counter-current airflow patterns) and direct-heat dryers (where the source of hot gases is generated external to the units). Our lab also houses scaled rotary steam tube dryers – which can operate under a variety of steam temperatures and pressures and adjusted to very precisely remove moisture down to one-tenth of one percent.

Our test lab also operates indirect heat models where the heat is supplied on the external shell from multiple burner-firing positions. Having scale models of the full range of dryers is an important contribution toward our custom-design, fabrication and maintenance of full-scale units for very specific and demanding applications – considering all requirements of the material to be produced, moisture to be removed, temperature needed to effectively yet safely process the customer’s materials, and more.

Over the decades Louisville Dryer Company has precision-tested numerous various materials and have catalogued the results, amassing a valuable source of performance information. And we still regularly test new combinations of materials and operating conditions since some processors want to do more than dry their materials, but also change the state or phase of material and/or combine ingredients to create a new product.

Custom Design of Every Dryer/Kiln
As our engineers step through the custom design process, they consider multiple operating factors including the angle of repose of the material, the amount of lifting material and if there is degradation by the veiling, the length of time in-process needed to remove either external or internal moisture of material, production rate, the amount and type of emissions (both particulate and products of combustion which may exit the rotary drying unit).

To Insulate or Not to Insulate

Rotary Kilns
Toward answering this frequently posed question, an initial differentiation is made between rotary dryers and rotary kilns. In general, many kilns, by definition, are refractory lined. Basically, the unit is insulated on the inside of the rotary shell, which must be done with a great deal of precise engineering, design and installation of the refractory brick or interior lining of the kiln.

Additional considerations must be made for kilns which need to be fabricated with less common materials or for those which will be processing end-user materials that require a high-heat input in at least a portion of the unit and, perhaps, cooling in the longer shell section.

Most of the refractory-lined kilns are designed to operate 24 hours a day/7 days a week because the factor which shortens their operating life more than anything is the thermal changes experienced from ambient temperature ramping up to 1000°F or 2000°F or more. Thus, they have to be designed and operated carefully to gradually elevate their temperature and then stabilize it at a given rate for its production materials.

Rotary Dryers
Generally speaking, rotary drying units which process materials at a lower temperature and at a constant 24/7 production are often better candidates for insulation. Of course, the insulating of rotary dryers yields lower savings than with rotary kilns because, with rotary dryers, there is less loss of shell heat from drying operations at lower temperatures.

The insulation decision become more complex when evaluating drying units with operating temperatures between those of the typical rotary kiln and rotary dryer. The drying units in this medial range are the ones which, perhaps, need to elevate material up to several hundred degrees Fahrenheit and then operate in a start-and-stop mode.

Such units which operate at these higher temperature ranges tend to affect the performance of the internal flighting, dams or baffling as the entire rotary cylinder heats and expands during processing. The rate of expansion of this rotary cylinder is very critical and will dramatically impact the entire life of the drying unit.

Furthermore, if the process is subject to stops and starts daily, or even multiple times a day, those operations also can create internal corrosion in the internal shell and dramatic corrosion between the external shell and any layer of insulating materials.

Again, perhaps there are some BTU savings of energy loss from the external of the shell, but this cost-wise is more than compensated for based on shortening the life and vastly increasing the chances for frequent maintenance of the entire shell, supporting tires, circumferential tires, support rollers and trunnions, the drive gear, the support pads and structures for the tires and gear, seal systems and many other factors.

If the calculations are not made precisely, the gap between the dryer/kiln when it’s heated up will have a lot of slack, what’s known as ‘creep’, and the unit will tend to wear in an irregular pattern and shorten the life of the tire-mounting and can also affect the carrier rolls/trunnions and the drive system.
Likewise, if the unit is not engineered correctly and the thermal expansion of the rotating shell presses into the tires too much, the result can crush the shell and then cause cracking, dents, and many other problems in the process.

With these real concerns in mind, one of the functions which our Louisville Dyer engineers perform in many heavy-duty design rotary units is an FEA (Finite Element Analysis) to measure and evaluate many of those factors. This process will then help them determine if insulation should be used on the shell or some portion of the unit.

Insulation of New Custom-Designed Dryers vs. Existing Rotary Dryers/Kilns vs. Used/Repurposed Rotary Dryers/Kilns:
Our engineers report that, once they have done the relevant testing and evaluation of new custom-designed dryers and considering the production and temperature ranges and other relevant factors, it is sometimes appropriate to insulate certain rotary dryer unit. While, on the other hand, it is often at great peril to plant/production facility when operator-owners choose to insulate an existing dryer or used/repurposed units without first employing proper testing.

One relevant example shown here is a rotary drying unit which is a very efficient rotary aggregate dryer. The input of its ambient material may be as low as 40°F, while the unit commonly processes and elevates the exit temperature of the material to over 850°F. What is remarkable is that the exit gas temperature going to the air pollution equipment is only around 280°F.

This case is a very efficient heat transfer rotary process. And it would absolutely be the worst candidate for insulating the rotary shell. The operation starts and stops multiple times every day. Since the shell frequently expands and contracts, were it to be insulated there would be great potential for corrosion and more rapid wear.

What would be even more severe for this case would be the cracking of the shell or compression of the shell by the tires if there was not ample design in the process for shell expansion. Another issue would be that the temperature on the shell on the burner end would be hundreds of degrees more than the shell on the intake material feed end.

So, the quandary would be trying to insulate its various sections differently: first a 20 ft, section with a certain amount/type, then a 27 ft. section with a different amount/type, and then none. This approach to shell insulation could not provide dependable nor desirable results.

Then, of course, there are several fly-by-night brokers or even scam artists who claim that virtually any rotary unit can be used to process most any material. They claim that a nominal rotary drying unit can be purposed for six or eight different types of material, at all temperatures, for all production rates – which is certainly misleading and, in many cases, fraudulent.

The Bottom Line
Insulation of a rotary drying unit can be acceptable when all the design and operation factors are tested and evaluated before custom-building the unit.

To learn more details about dryer/kiln insulation, or to request information on our custom dryer designs, contact us at 800-396-6365 and
louisvilledryer.com.

When a customer requested our advice on the most effective long-lasting seal technology for steam tube dryers in petrochemical applications, our application engineers designed and ran a Seal Test Assembly to generate live test data to inform and confirm their recommendations.

To gather relevant data in a controlled environment, our engineers and fabricators built a scale-model steam tube dryer seal assembly in our own test lab.

For this test seal, we decided to use chevron V-packing in lieu of the traditional square packing. Whereas square-packing is made from woven PTFE and integrated graphite, the chevron V-packing is made of extruded polymer – which is optimally suited for maximal segregation of external oxygen from entering the internal dryer’s closed inert atmosphere. The V-packing is housed within a machined, cooling-jacketed, stuffing box.

To simulate a real processing environment, we mounted the test unit on a slew bearing, and allowed to float with the rotating seal surface using adjustable die springs.

Electrodes were attached to induce heat and ports were used to pressurize the system up to 1 PSIG, and gauges were installed and monitored.

The test unit operated continuously over the course of three years with only minimal tweaking such as bearing lubrication. The test data confirmed the effectiveness of using the longer life chevron V-packing on both the feed and discharge end of central discharge dryers in petrochemical applications. They significantly limit the leakage of ambient atmosphere or vapors and prevent the intake of external oxygen.

Why Central Discharge?

The Louisville Dryer “CS” Central Discharge Steam Tube Dryer design was developed for solvent extraction, and processing materials wetted with liquids other than water, which must be processed in an inert atmosphere and where the vapors must be captured and not allowed to escape to atmosphere.

Many materials at some point in their manufacture are volatile and reactive with O2 which can degrade the product, ignite, or explode. Some materials are processed with acids or volatile liquids where if leaked to atmosphere can cause injury to personnel, or damage to surrounding equipment or facilities.

The Louisville Dryer “CS” Central Discharge Steam Tube Dryer reduces the required sealing area by conveying the dried product through the center of the steam chest with helical discharge flights, into a very efficiently sealed discharge housing. The “CS” sealing mechanism is comprised of a machined mechanical seal and packing assembly which allows for static and dynamic purging with a variety of process gases and/or steam. Cooling water can be used in applications where required, as well as grease purge glands.

The Louisville Dryer “CS” seal design can be designed for process side pressures up to 1.5 PSIG, and in a number of carbon steel alloys and nickel alloys for highly corrosive applications. They are most effective when installed on both the feed end of the dryer and the discharge end.

Test Your Product in Louisville Dryer Company’s Test Lab

Curious how testing your product in our production-worthy scaled dryers in our own leading-edge research and development lab can benefit your company? We have manufactured coolers to help companies develop new products such as wood composite, airbag propellant, rocket fuel, algae-derived oils and others. Our test engineers can help determine best processes and equipment for your team. Call us today at 800-735-3163.