Industrial vacuum trucks, also known as industrial vacuum loaders, are used to recover, contain, and carry solids, dry bulk powders, liquids, slurries, and thick sludge from hard-to-reach areas. Guzzler Manufacturing, an industrial vacuum truck manufacturer based in Streator, Illinois, has long-standing expertise in pneumatic conveying—both dilute and dense phase—for all kinds of industrial applications.
Ben Schmitt, product manager at Guzzler Manufacturing, was kind enough to discuss pneumatic conveying with Blower & Vacuum Best Practices Magazine. Topics covered include: the differences between dilute phase and dense phase conveying, ideal applications for dense phase offloaders, and the common challenges involved in dense phase pneumatic conveying.
Please explain the differences between dilute phase and dense phase conveying.
Dilute phase pneumatic conveying typically uses higher conveying velocities in order to keep the material suspended in the air stream and conveyed. When material is pneumatically conveyed through a hose via the dilute phase process, the hose typically has a higher ratio of air to material conveyed. Described as low-pressure/high-velocity systems, entry air pressure is typically under 15 psig at the beginning, and closer to atmospheric pressure at the end. Conveyance velocity ranges from about 2500 fpm at the beginning of the system to 6000 fpm toward the end.
Dense phase, on the other hand, uses lower conveying velocities, but the air stream in the hose has a lower ratio of air to material conveyed. Therefore, a dense phase system conveys more material per amount of airflow, and is a more efficient system for conveying large bulk materials. Pressures for dense phase conveyance range from approximately 15 psig to 50 psig. Guzzler dense phase offloaders use 14.5 psig at up to 700 cfm.
For what applications/materials are dense phase offloaders best suited?
Guzzler dense phase offloading systems are ideal for applications where the cleanup and recovery of valuable raw materials, such as powered cement, lime, carbon black, some types of sand, acetate flake and plastic pellets, are desired. A prime example is the cement industry, where cement powder often accumulates below conveyors. This resource can be vacuumed into the body of the Guzzler truck and dense phase offloaded back into storage silos for reuse.
Dense phase systems can move most any product, including fly ash, dog food and sludge.
How are these systems controlled? Can you describe a typical operation?
When using a dense phase system on a vacuum truck, the first step is to isolate the main collection hopper, where material is stored, from the vacuum system, and raise the debris body to allow the material to flow to the rear discharge cone. The CycloBlower system is then engaged, and pressurization of the debris body begins. Once the desired pressure level has been reached, control valves at the discharge cone are controlled by the operator to allow air and material to mix. The Guzzler dense phase system also features fluidizing valves which continually agitate the material to fluff it into the air stream. This agitates the material into the air stream prior to entering the main air stream.
The Guzzler system uses a positive displacement blower that is commonly found on bulk cement transport trucks. The CycloBlower is ideal for this application because of its efficiency and relatively high airflow and pressure capabilities.
Gardner Denver CycloBlower
Designed to clean and recover solids, dry bulk powders and liquids, industrial vacuum trucks are used for all kinds of applications. Using vacuum to load and positive displacement to unload, these trucks pneumatically convey a wide variety of materials, including sand, cement, liquids, slurries, and kinds of feeds—such as corn, rice, beans, and oats.
When designing a truck for pneumatically conveying valuable product, it is imperative to select the proper blower for the application. Brought to market in the 1960s, Gardner Denver’s CycloBlower has a long-standing reputation for reliability, design versatility, and fast offloading times. In addition, it provides oil-free air to prevent product contamination.
The CycloBlower from Gardner Denver is ideal for providing pulsation-free and oil-free pressurized air.
Addressing Varying Airflow Requirements for Different Materials
Pressure offloading typically requires 10 to 15 psi of air pressure. Airflow requirements change based on the material being conveyed. Powders, such as cement, flour, and fly ash, typically require between 220 to 350 cfm. Food products like corn, rice, and beans generally require 260 to 350 cfm. Larger and denser materials, like pebbles, require additional airflow, ranging between 430 and 610 cfm.
The CycloBlower features a compact helical screw blower. Its two screw-type rotors mesh together to provide pulsation-free and oil-free pressurized air. Connected to the engine power by a PTO driveshaft, the CycloBlower provides 18 psi continuous, and 20 psi at intermittent duty. Up to 17”Hg of vacuum can be achieved, with airflows of up to 1060 cfm. The blower comes in two different sizes, one with a 9-inch rotor profile, and another with a 12-inch rotor profile. The 12-inch rotor model delivers more airflow, and can be leveraged on haulers dedicated to a certain kind of product.
Benefits of Helical Screw Blowers
While bi-lobe blowers are commonly used for the tank and truck markets, the CycloBlower’s helical screw design brings several unique benefits for designing an industrial vacuum truck. Importantly, CycloBlower models weigh an average of 50 pounds less than their bi-lobe blower counterparts. This, in conjunction with its compact design, makes the CycloBlower easier to integrate on mobile platforms.
In addition, the CycloBlower is driven by the gate-end rotor, so it requires less RPMs than bi-lobe products. The lower RPM consumption translates directly to less fuel consumption, and greater savings. Finally, the compression process of a helical screw blower delivers lower discharge temperatures than bi-lobe blowers—an important factor when conveying sensitive materials, such as food products or plastic pellets.
What are common challenges involved in dense phase offloading?
The biggest challenge is becoming familiar with the operation of the system and the fluidizer valves. The goal is to adjust the valves so that the material enters the air stream in a dense phase condition. Too much air from the fluidizer valves will put the material into a dilute phase, which compromises the dense phase conveyance efficiency. There is a visual sight glass that allows the operator to monitor the material conveying in the hose, providing a visual indicator as to proper conveyance. Typically, the vacuum truck operator is also the person responsible for offloading the material back into the storage silo.
The Guzzler NX air mover, as seen here, features the advanced dense phase offloading system.
How do changes in particle size, density and texture impact performance?
When conveying material, it’s important to understand the makeup of the material. The lighter, or less dense, the material, the higher the material can be conveyed. More textured or jagged material has increased surface area, making it easier to be grabbed and carried into the air stream. The larger the particle size of the material being conveyed, the more difficult it is to be conveyed. Irregularly shaped, larger material can become lodged in smaller hose systems. The key to preventing this from happening is to understand the application. The offload system works on a 4-inch discharge hose. Trying to convey material that may be near the 4-inch size can be problematic. Alternative offload options should be evaluated. Some contractors use guards on the end of their vacuum hose to prevent larger material from being recovered. This method would also be another solution to prevent clogging.
How are Guzzler offloaders designed for reliability and economical maintenance?
At Guzzler Manufacturing, our primary design consideration is to ensure our equipment is durable, reliable and easily maintained. We make a point to provide access to the air path to ensure each Guzzler machine operates effectively and efficiently for the life of the equipment. Each air path has an access door to allow cleaning of the airways and paths.
We continually work with Guzzler customers to gather application and product feedback, and we implement product improvements based on that feedback. All Guzzler products undergo a thorough testing process to ensure they exceed customer expectations. New product designs are first tested on our CAD system by using finite element analysis (FEA) to highlight potential high stress areas. We then use our dedicated technology center to perform various levels of testing, which may range from strain gauging of the potential high-stress areas, to filtration and airflow tests. Additionally, we use a local test facility to perform endurance and life-cycle testing.
We also use the test facility’s test track to put our equipment through real-world endurance track testing. Once these tests are completed, select customers participate in real-life field application testing with our equipment. At that point, we move into the production stage. Once in production, each product goes through a multi-point inspection where equipment performance is tested and verified prior to delivery to our customer. Additionally, Guzzler uses high-quality components to ensure long-lasting reliability.
Can you discuss some of the unique attributes of the Guzzler NX?
The Guzzler NX air mover features the advanced dense phase offloading system. This vacuum loader tackles the toughest applications, from solids and dry bulk powders—like fly ash—to liquids, slurries and thick, heavy sludge.
Leveraging Gardner Devner’s CycloBlower, the Guzzler NX air mover is ideal for dense phase offloading applications.
The dense phase offloading system allows the operator to quickly and easily reclaim, recycle and redistribute valuable material. The innovative system combines pressure offloading with vacuum recovery, providing a closed-loop system that eliminates spills. Additionally, the dense phase offloading system allows conveyance of dry material up to 120 feet vertically. This system is ideal for cement or dry bulk powder applications. Material can easily be blown back into storage silos, rail cars or other appropriate containers. Vacuum recovery returns any carryover back to the tank, closing the loop in the loading and unloading process.
Please describe the Guzzler CL as a dense phase offloading option.
A dense phase offloading option for the Guzzler® CL industrial vacuum loader was introduced by Guzzler Manufacturing in early 2015. Designed to increase value by recovering valuable resources for reuse, the optional batch offloading system is ideal for offloading powders, such as cement and lime, into large silos. The truck features a high-pressure (14.5 psi), direct-drive CycloBlower rotary pump with up to 750 cfm of free air displacement. The system pneumatically conveys material through a 4-inch (10.16 cm) hose up to 125 feet (7.62 m) vertically. In addition, the rear of the dense phase offloading configuration features a specially designed transfer cone with six fluidizing nozzles that fluff material into the air stream for improved material conveyance.
The powerful and efficient industrial vacuum system operates effectively in remote or inaccessible locations more than 1000 feet away. Simple to operate and easy to maintain, this Guzzler vacuum truck provides 100-percent accessibility to all internal chambers, and provides the lowest air-to-cloth ratio. Air-to-cloth ratio is the measurement of airflow in cfm to filter cloth area. The lower the number, the more filter air the unit has for the cfm of conveyance. This lower ratio allows the equipment to more easily move air through the system while vacuuming.
The Guzzler CL is also available with a vane pump pressure offload system (high-pressure, low airflow), which is ideal for the vacuum loading of liquids, sludges and thicker materials.
To read more about Pneumatic Conveying, please visit www.blowervacuumbestpractices.com/industries/conveying.