Coating machine
The coating machine plays a vital role in the fertilizer production line. Its main function is to coat the fertilizer particles to improve the stability and durability of the fertilizer. The coating machine coats a protective film on the surface of the fertilizer particles to prevent the fertilizer from getting damp, caking or nutrient loss during storage and transportation, thereby maintaining the effectiveness of the fertilizer. The coating treatment can also adjust the release rate of the fertilizer so that the nutrients are released more evenly into the soil to meet the long-term needs of plants. The coating machine is usually composed of a conveyor belt, a coating device, and a drying system. It can adapt to the production needs of fertilizers of different types and specifications and is an indispensable and important equipment in modern fertilizer production lines.
WE NOT ONLY PROVIDE RELIABLE PRODUCTS, BUT MORE IMPORTANTLY WE PROVIDE RELIABLE PROCESS DESIGN AND EXPERIMENTATION
working principle
Strip-shaped shovelling plates are welded inside the middle shell of the coating machine, and the strip-shaped shovelling plates can make the particles flip inside the machine.
If liquid coating agent needs to be sprayed, EMCC can equip corresponding tanks and pumps. And the liquid nozzle extends into the cylinder from the end of the drum for spraying.
If powder coating agents need to applied, such as diatomite, kaolin, lime, etc., they will be fed into the coating machine by a screw feeder. When the coating machine rotates, the fertilizer particles surface will be wrapped with a hard shell. The finished particles produced in this way have a good appearance and do not break when transported, making them more suitable for storage.
The appearance of the coating machine is the same as that of the dryer and cooler. It is an inclined horizontal rotary cylinder with a supporting device and a transmission device.
WE NOT ONLY PROVIDE RELIABLE PRODUCTS, BUT MORE IMPORTANTLY WE PROVIDE RELIABLE PROCESS DESIGN AND EXPERIMENTATION
Improving Agglomerates through Coating
Coating, typically carried out in a coating drum, is a finishing process used prolifically throughout industries working with agglomerates to meet a wide variety of objectives.
A surface treatment for particles, coating can enhance specific characteristics of a pellet, granule, or other agglomerate, be it a mineral, chemical, or otherwise. Coatings are frequently applied in order to maintain product integrity, mitigate issues such as dust and/or attrition, or even to improve product performance.
This article will cover the benefits of coating, how the coating process works, and factors to consider in selecting the proper coating for your application.
REASONS FOR COATING
Coatings can offer a variety of benefits depending on the material and application. The diverse market of available coatings has created an opportunity to meet a variety of goals concerning the performance and handling of agglomerates. Some of the most common reasons for coating a material are listed below.
REDUCED DUST & ATTRITION
Dust is not only a nuisance, but depending on the material, may be hazardous as an air pollutant. Additionally, the creation of dust and fines can affect the bottom line; dust can become windblown in some applications, yielding unpredictable and undesirable results, and often resulting in product loss. For these reasons, the control of dust is one of the most common reasons why agglomerates are coated.
Dust is an especially common issue with granules that were created via roll compaction, due to the jagged edges of the granules that can rub together and break down into fines (a phenomenon referred to as attrition).
Coatings can be used to reduce the opportunity for the creation of dust and fines by creating a barrier on the exterior of the granules that helps to prevent product breakdown. A common example of this can be seen in the fertilizer industry, where granules and pellets are often coated with anti-dusting agents to mitigate issues associated with dust. This ultimately improves handling and transportation, as well as application.
Similarly, products that are “soft” can benefit from coating; coating can prevent the breakdown of product during transportation.
MITIGATION OF CAKING & MOISTURE ABSORPTION
The undesirable clumping of particles, referred to as caking, is often a challenge when working with bulk materials and also accounts for one of the primary reasons for which agglomerates are coated.
Caking often occurs during transportation and storage, or while on product shelves, and can occur with many types of materials.
Anti-caking agents can be used as a coating on granules to prevent crystalline structures from forming between agglomerates, ultimately reducing caking and maintaining the integrity of the product.
Similarly, various oils, waxes, clays, polymers, latex’s, and more can all be used to prevent moisture absorption. This is commonly seen in fertilizers such as urea, KCl, ammonium sulfate, and more, which become very soft and have the potential to cause caking if they absorb moisture.
IMPROVED FLOWABILITY
The flowability of a product can sometimes be a challenge when working with bulk materials. Flowability refers to the flow and handling properties of a material in bulk. This affects how material will move through a processing facility, including discharge from rail cars, moving from one conveyor to another, from a hopper to process equipment, and more.
As a surface treatment, coatings can help to improve the flow properties of a material by adjusting the surface characteristics. Granules with a rougher surface quality will have a higher angle of repose (the angle at which a material can be piled before it begins to slide against itself). A high angle of repose can cause issues in terms of flowability.
Conversely, a material with a smooth surface quality will have a lower angle of repose, meaning that it will slip against itself at a lower angle. This helps to ensure that granules move more freely through bins and hoppers and between transfer points and the like.
Various coating types can be used to improve the surface characteristics of a granule, ultimately improving the flowability and handling qualities of the material.
ENHANCED APPEARANCE
Coating is also frequently used for aesthetic purposes; a coating can lend a smooth, shiny surface to otherwise dull granules. This can take a product from average to premium, increasing its marketability.
Coatings can also be used to color particles. This is frequently seen in the roofing industry, where granules are coated in a variety of pigments to create specific colors for use on asphalt shingles.
IMPROVED PRODUCT PERFORMANCE
Coatings can also be used to influence the way a product performs. A coating can affect the solubility of a product, or be used to control its release properties, such as in the fertilizer industry. Coatings can also be used to add another ingredient to the product formulation. For example, cat litters are frequently coated with a clay material to promote the clumping action cat owners desire.
In other cases, “coatings” are used as the carrier themselves in order to improve product performance. This is seen in the fertilizer industry where clay pellets are coated with materials such as herbicides, pesticides, or fungicides. The clay pellets are highly absorbent and can effectively absorb the applied materials. The resulting pellets are similar in size and weight to fertilizers, allowing them to be spread easily with the same equipment.
MAINTAINING PRODUCT INTEGRITY
As has been shown, coatings can be used to ensure product integrity is maintained in a way that allows granules to arrive at their end use in the form in which they were intended. Maintaining the integrity of some products may also serve as a safety measurement. For example, coal dust and sulfur pellets can be a risk of explosion; coatings can be used to reduce this dangerous potential.
COATING SELECTION
There are many types of coatings available, from mineral oils, clays, and waxes, to polymers, latex’s, silica, and just about everything in between. In some cases, multiple coatings, or a combination of coatings, may be required to achieve the desired results.
In selecting a coating(s) for a particular application, many factors need to be taken into consideration. Some of the most critical factors to consider in coating selection are explained here.
INDUSTRY AND APPLICATION
Much like binder selection, the industry and/or end use of a product may dictate which coating(s) are most appropriate. For example, coatings that may pose toxicity risks to soil would not be an appropriate coating for a fertilizer product, while a vegetable derivative would provide an effective coating and could also possibly add value to the product.
COST
As with any other project considerations, cost is often a major factor in coating selection. Some coatings may offer a high-performance solution, but be too costly to be practical. This is especially a concern in industries where margins are already slim.
EASE OF APPLICATION
Ease of application is also an important consideration. Some materials are easily applied and distributed throughout a bed of material (such as oils, waxes, some polymers, and latex’s). The contact action of rolling and tumbling between the pellets aids in transferring the coating uniformly across all the pellets.
Conversely, other coatings might be good in theory, but are challenging and costly to apply. This is often the case with materials such as hot melts, dyes, and acids, because the material does not readily spread on contact. These difficult coating materials may require a specially designed spraying system to assure uniform coating distribution.
COATING: THE IMPORTANCE OF TESTING
Because there are so many variables (base material, coating type, equipment and process variables), it is often desirable to test coatings to determine which type will offer the best results, both in terms of processing and performance, as well as the process and equipment variables needed to produce the desired results.
Testing in a facility such as the EMCC Innovation Center can help to work out these variables and fine-tune the process parameters to meet the unique objectives of the project. Variables might include:
- Coating type and concentration
- Material and coating flow rates
- Retention time
- Nozzle type
- Spray locations
- And more…
CONCLUSION
Coating provides a valuable avenue to maintaining product integrity, improving product handling and performance, and even enhancing appearance when working with agglomerates. There are many factors to consider in selecting a proper coating, as well as what type of equipment should be used to apply the coating. As an industry ripe with variability, testing is often a critical component to achieving the desired results.
EMCC offers custom coating drums designed to meet your process objectives. We can help you to test your material to evaluate various coatings and process parameters and manufacture the equipment needed. For more information, contact us today!
WE NOT ONLY PROVIDE RELIABLE PRODUCTS, BUT MORE IMPORTANTLY WE PROVIDE RELIABLE PROCESS DESIGN AND EXPERIMENTATION
Improving the Fertilizer Coating Process with a Coating Drum
Fertilizer coating continues to be a vital tool in helping fertilizer producers meet market demands. With buyers becoming more discerning, producing a high-quality product according to the required specification has become a necessity in today’s ultra-competitive market, particularly when it comes to specialty fertilizer and soil amendment products.
This evolution of products has prompted an increased demand for better particle coatings. The performance of a coating, however, hinges on its proper application to the product. And while conveyors have long provided a seemingly low-cost option, when a premium product is the goal, the use of a coating drum creates a uniform coating distribution, increases production, reduces downtime, and can even lower production costs.
THE ESSENTIAL ROLE OF FERTILIZER COATING
The need to coat a material is pervasive throughout many industries. A sophisticated finishing process, coating allows producers to control the handling, storage, and performance properties of a granular fertilizer product.
The primary ways in which coating is used in this effort are summarized here.
DUST SUPPRESSION/DE-DUSTING
Coating is an essential method of controlling dust when working with granular products. Dust results in product lost as waste and often creates a hazardous work area, both in terms of an inhalant and in some cases, even as a combustion risk. Furthermore, regulators are increasingly cracking down on fugitive dust at industrial sites.
De-dusting agents are used to create a protective coating around each granule to prevent the generation of dust. This is especially useful with granules that have angular edges, which are more likely to degrade into fines and dust (a phenomenon referred to as attrition).
Fertilizer products that are frequently coated to mitigate dust issues include MAP, DAP, sulfur, and potash.
ANTI-CAKING
Caking prevention is another way in which coating improves fertilizer products (and a variety of industrial materials as well). Caking can occur as a result of many factors, including chemical reaction, moisture absorption, and inadequate cooling. Caking is highly undesirable as it creates handling and storage issues, and often, yields spoiled product.
Like de-dusting agents, anti-caking agents are used to create a protective barrier around each granule. This coating prevents the exchange of moisture between the granule and the external atmosphere, helping producers to maintain product integrity throughout its lifecycle.
As a hygroscopic material, urea is frequently coated to prevent moisture absorption and subsequent caking. Hygroscopic materials may also be coated to prevent absorbed moisture from activating ingredients in the granule.
Urea coated with a dyed wax (right) in the EMCC Innovation Center
CREATING A PREMIUM PRODUCT
Coatings can also be used to modify how a material looks and performs as an end product. This is frequently seen with slow-release or controlled-release fertilizers, where coatings are used to control the rate at which the nutrients or active ingredients are delivered. Similarly, coatings also frequently serve to incorporate beneficial additives into a product, such as a microbial blend.
Coatings can also be used to improve the appearance of granules, be it through color or surface quality. They can also help to enhance flowability. Ultimately, fertilizer coating allows producers to create a premium product in both performance and appearance.
HOW COATING DRUMS WORK
The coating drum consists of a rotary drum which rotates at a defined speed while material is continuously fed into the inlet end.
Set on a slight angle, gravity helps to move material through the drum according to a predetermined retention time. As material moves through the drum, a spray system sprays the coating agent onto the material bed. In some cases, tumbling flights may be used to promote greater bed turning for improved coating-to-granule exposure. Spray systems must be designed for optimal distribution of the coating agent, taking into account factors such as spray locations, nozzle type, bed depth, rotational speed, and more.
Interior of coating drum during testing in the EMCC Innovation Center
Coating drums are typically smaller than a traditional granulation drum, but can range in size from 36” to 15’ in diameter (1 – 4.6m) and handle capacities between 500 lb/hr – 50 TPH.
COATING CAPABILITIES
Coating drums are highly diverse and can accommodate a wide array of both liquid and solid coating types, making them beneficial in nearly any bulk solids coating application. Common coatings include powders, oils, waxes, polymers, or other coating types.
ADVANTAGES OF A COATING DRUM
Producers can spend years developing the perfect coating formulation for their product, but that does not mean it will work; the coating needs to be expertly applied to achieve optimal performance. This is where coating drums offer significant advantages over conveyors:
UNIFORM COATING DISTRIBUTION
When coating with a conveyor, material moves under the coating spray, but is stationary on the belt. This results in a liberal application to the top-most surface area of the material on the belt, while the granules underneath remain untouched. Similarly, if the feed rate of the coating is increased in an effort to improve coating distribution, the top layer will simply become more saturated with only a minimal improvement in distribution.
As material is stationary on the belt, coating with a conveyor results in uneven distribution of coating agent.
Conversely, coating drums tumble granules in a material “bed” as the drum rotates. This motion promotes greater granule-to-granule contact, which thoroughly distributes the coating throughout the bed. The result is a uniform distribution of coating on the entire surface area of each granule.
The tumbling action in a coating drum increases granule-to-granule transfer of the coating, resulting in an even distribution.
A uniform coating on the entirety of each granule’s surface is especially critical when blocking moisture absorption, such as with urea, as any uncoated spot can allow moisture penetration.
It’s important to recognize that with any coating equipment, the product feed rate must be consistent to achieve uniform results. For example, if the feed rate of solids to a coating drum was reduced while the amount of coating agent remained the same, the end product would have a higher quantity of coating than desired and could potentially change the final analysis, depending on the product.
INCREASED PRODUCTION & REDUCED MAINTENANCE
When using a conveyor to coat material, overspray is a common problem; since material typically lies in the center of the belt, coating may be inadvertently sprayed onto the adjacent belt surface. Overspray may also occur as a result of the coating agent spraying through the material, due to a high spray rate, or because material feed rate has been reduced, as shown below.
When material feed rate to the conveyor is reduced or when flowability changes, a significant amount of overspray can occur.
This not only wastes coating agent, but depending on the coating, could cause a number of issues, from pooling to build up. In severe cases, it can require that the operation be stopped for cleaning on a frequent basis.
Conversely, coating carried out in a drum contains the coating process to the drum’s interior and when properly designed, prevents regular disruptions due to buildup, mitigating the need for frequent cleaning to maintain operational uptime.
REDUCED COATING AGENT REQUIREMENT
As mentioned, uncontrolled overspray can result in a significant amount of wasted coating agent.
This problem is alleviated when using a coating drum, as the coating agent is used much more efficiently. This means that the same amount of coating agent provides better results, and in some cases, allows for a reduction in the amount of coating agent required.
TESTING THE FERTILIZER COATING PROCESS
Achieving the perfect coating distribution often requires testing in a facility such as the EMCC Innovation Center.
Testing allows a number of variables to be tested and fine-tuned to reach optimal product coating. Data points may include:
- Rotational speed
- Coating feed rate
- Material feed rate
- Spray locations
- Tumbling flight design
The EMCC Innovation Center is capable of testing all of the variables above (and more) in order to gather the data necessary for the design of a commercial-scale coating drum.
CONCLUSION
Coating is an indispensable tool in producing high-quality granular fertilizer products that meet precise specifications. From improving product performance and appearance, to enhancing handling and application qualities and maintaining a safe production environment, coatings provide an array of benefits that could not be achieved at such a high level otherwise.
Coating performance is largely dependent on its proper application. As a result, when a premium fertilizer product is desired, the use of a coating drum over a conveyor provides significantly more uniform results, while also often increasing production and reducing downtime, and in some cases, even lowering production costs.
EMCC is a leader in custom agglomeration equipment, systems, and testing. Our coating drums and spray systems are designed around the material to be processed for an optimal coating solution. For more information on our testing capabilities or our coating drums, contact us today!
WE NOT ONLY PROVIDE RELIABLE PRODUCTS, BUT MORE IMPORTANTLY WE PROVIDE RELIABLE PROCESS DESIGN AND EXPERIMENTATION
Considerations in Adding a Coating Drum to an Existing Granulation Line
The addition of a coating drum to a granulation line has gained popularity in recent years as producers look to further specialize their products and control quality and performance metrics. Whether producing a fertilizer product or roofing granules, the addition of a coating drum gives producers the opportunity to offer more specialized, premium products with a relatively low barrier to entry.
As producers across industries consider the addition of a coating drum to their production line, they often have a number of questions relating to infrastructure requirements, process and maintenance considerations, and even the coating drum itself.
With extensive experience in retrofitting plants with coating drums, EMCC offers the following guidance.
INFRASTRUCTURE REQUIREMENTS
While much of the infrastructure required to support a coating drum is already in place thanks to the existing granulation line, the addition of a coating drum will require a few further considerations.
SPATIAL FOOTPRINT
The most important consideration is incorporating the coating drum into the existing infrastructure with the allotted space.
Depending on the size of the coating drum, a unit may require anywhere from four to ten feet, up to 14 to 30 feet, and will need to be located after the dryer (or cooler, if applicable).
This may require relocating or modifying the downstream equipment configuration for packaging and loadout, adding on to the building, or the addition of a new floor in order to make room.
FEEDING SYSTEM
The production line will require a feeding system for transporting material from the dryer or cooler discharge to the coating drum. Depending on facility layout, this may be handled with a troughed belt conveyor, steep incline conveyor, bucket elevator, or combination thereof.
COATING HANDLING & INTRODUCTION
The coating itself will require a system for storing, preparing, and feeding the coating into the coating drum. Depending on the type of coating, this might include some type of liquid storage area, heater, filtration system, compressed air and pumps, as well as the drum internals and nozzles for distributing the coating onto the material bed.
CONTROLS
A coating drum can be easily incorporated into the existing controls system. However, producers will need to implement a way to measure the raw material throughput. This is typically done with the use of a volumetric or gravimetric feeder. The coating must also be added in a controlled way to achieve the proper coating-to-product ratio.
PROCESS REQUIREMENTS
The addition of a coating drum is fairly simple in most aspects, due to the fact that it is implemented toward the end of the production line. However, there is one important consideration that cannot be overlooked: product screening must be located before the coating drum.
The ability to achieve a uniform coating depends largely on the uniformity of the incoming product; a wide particle size distribution or the inclusion of fines would be problematic and result in poor coating uniformity.
MAINTENANCE REQUIREMENTS
Coating drums have much the same maintenance requirements as other rotary drum equipment. However, the introduction of the coating component can increase the opportunity for buildup to occur in and around the drum, making buildup prevention and management an essential aspect of preventive maintenance.
MINIMIZING BUILDUP
Additional maintenance and more frequent inspections may be required to minimize any buildup that might occur before it has a chance to escalate into a more serious problem.
Buildup can occur in the drum, at the discharge chute, and at the nozzles. The coating filtration system may also require regular cleaning to prevent buildup.
Various types of liners can be incorporated into the drum to prevent material from sticking to the shell and causing buildup.
TRAINING OPERATORS
While operators and maintenance personnel are likely already familiar with the basic aspects of operating and maintaining rotary drum equipment, they may require additional training on the coating drum and its supporting equipment.
COATING DRUM CONSIDERATIONS
The incorporation of a coating drum into an existing line requires significant attention, but it’s important to note that the design of the coating drum itself requires equal attention to ensure a solution that meets process and product goals.
COATING DRUM TESTING: PROCESS DEVELOPMENT
While coating is simple in theory, in practice it can quickly become complicated, as a number of variables must be carefully balanced to consistently achieve the desired results. For this reason, EMCC recommends testing in the Innovation Center in order to develop a working familiarity with the product and coating, as well as establishing data for scaleup.
The Innovation Center utilizes a pilot-scale coating drum to test and confirm process parameters such as:
- Coating and product feed rates
- Drum speed and slope
- Particle size distribution (PSD)
- Material pretreatment
- Coating and product temperatures
- Retention time
- Material bed action
- Spray nozzle type, location, and angle
Testing is particularly valuable in developing an optimized internal spray system, as well as evaluating drum liners and tumbling/agitation flights.
VARIABLE FREQUENCY DRIVE (VFD)
EMCC also recommends coating drums be equipped with a VFD, or variable frequency drive. A VFD not only gives the operator enhanced control over drum speed during start-up and shutdown, but it also helps in responding to fluctuations in the process. This often translates to lower energy costs, reduced wear on the drum, and decreased loss of product.
CONCLUSION
As more producers look to integrate a coating drum into their existing production line, they must consider various infrastructure, process, and maintenance requirements, as well as the design of the coating drum itself.
As the leading supplier of custom coating drums to various industries, EMCC offers plant managers a comprehensive solution to incorporating coating drums into existing granulation lines. This includes site audits and engineering support, process development testing, custom equipment manufacturing, and parts and service support. For more information, contact us today!
WHY CHOOSE EMCC AS YOUR PARTNER?
Shanghai Exceed Industry Co., Ltd (China EMCC) is a manufacturing enterprise specializing in high-tech fertilizer machinery. For many years, we have devoted to producing inorganic and organic fertilizers granulator equipments. By consistently creating values for our customers around the world, we have become one of the leading suppliers in global agricultural fertilizers industry. With China EMCC, you may get comprehensive services of consulting, design, equipment, installation, training, emergency assistance, field assistance, spare parts and routine maintenance to save fertilizer plants cost.
