Streamlined unloading/transfer of carbon black.
The McCook plant receives and processes large quanties of carbon black The plant uses three grades of carbon black pellets, all of which were being delivered by railcar. By 2002, Parker engineers wanted to change the pneumatic conveying equipment installed for rail unload at the McCook plant because of frequent downtime caused by the vacuum conveyor's internal filter, which repeatedly ruptured or became plugged. The plugging and need for filter replacement occureed with what the engineers considered unacceptable frequency.
Another problem centered on the transfer of carbon black to the main black storage silos directly adjacent to the primary processing building. The carbon black was being fed pneumatically from the railcars into the infeed hopper of an enclosed bucket elevator. The elevator buckets scooped the material from the hopper and moved it up to a horizontal drag conveyor that was set up to distribute the material to the appropriate silos. While bucket elevators are widely used in many industries, they are not always the ideal choice. In this application, carbon black can stick to buckets and build up in the drag conveyor. When switching between grades, cross-contamination can be difficult to control. Consequently, additional maintenance is needed between deliveries of different grades of carbon black to ensure complete segregation of the different materials. Mechanical systems cannot compensate for exposure to atmospheric humidity, potentially causing additional handling problems. Moist carbon black does not mix easily with clay and whiting, which are other rubber compound consituents. Bucket elevators also require frequent maintenance and adjustment, which translates into more downtime.
Mechanical systems can also be hard on conveyed materials, and when pellets of carbon black are broken up by rough handling, their flow and mixing characteristics are adversely affected so that they tend to plug in hoppers and require longer mixing times with the other rubber constituents. On top of all this, Parker was pushing plant output to a level that the existing bucket system could not reliably support.
By January 2002, some bearings and other components of the bucket elevator were worn and needed to be fixed. Managers decided instead to replace the entire aging bucket elevator with a pneumatic system. They felt that pneumatic conveying would offer the McCook plant several immediate and significant advantages. Pneumatic systems easily adapt to automation and completely contain the product, eliminating many housekeeping and environmental issues. Pneumatic lines can easily be blown clean with convey air when various graded materials, such as the plant's carbon black, must be handled separately without cross-contamination. When retrofitting an existing plant, pneumatic convey line routing offers installation flexibility: Lines can easily be routed to multiple destinations around obstacles, other equipment and through walls. In addition, pneumatic conveyors are compact, require much less installation work and maintenance than mechanical units, and can conveniently fit inside a plant layout and be moved when necessary.
Management at McCook called Cyclonaire in York, NE, for its recommendations. Cyclonaire designs and manufactures bulk material handling systems, components and controls.
Cyclonaire's engineers requested application information, such as required convey rates and distances, along with carbon black samples for testing. At the company's CycloTech System proving facility, pneumatic conveying equipment can be evaluated to measure conveying rates in setups designed to simulate the actual system that clients will have installed in their plants, right down to line dimensions and elbows. Full-scale simulations of customers' applications enable Cyclonaire engineers to verify that systems and components under consideration will meet target convey rates and other design parameters. During testing, captured data include average and instantaneous material rates, airflow, cycle times, conveyed weights and system pressure, along with material degradation and other physical property changes.
For Parker, material integrity and purity received special attention. Tests focused on simulating transfers from railcars through pneumatic lines to bulk storage. Avoiding product degradation was very important, so engineers ran the tests with a dense phase convey system, which has low convey line velocities for gentle handling. Dense phase conveyors use high-pressure air to move materials at higher material-to-air ratios than other phases of pneumatic conveying. This combination minimizes degradation, yet allows for high conveying rates to meet process demands.
Test results supported the selection of a new dense phase conveyor as a replacement for the entire existing dilute phase vacuum-pneumatic-mechanical rail unloading system. Specifically, project engineers recommended using Cyclonaire's patented DPV-B Series dense-phase conveyor. DPV-B conveyors feature dense phase vacuum loading and pressure conveying. They can be installed indoors or outdoors and fit where low headroom makes other types of conveyors impractical. Because they are vacuum loaded, no pit is required for these bottom discharge units, and Cyclonaire DPV conveyors can be customized for almost any dense-phase conveying application, including bulk unloading from rail to truck delivery, in-plant transfer, and scaling and batching. In the McCook application, the DPV conveyor's pneumatic conveying lines would replace both the bucket elevator and the belted drag conveyor located above the silos, and Cyclonaire ball-type diverter valves would replace and simplify the silo distribution equipment, ensuring minimal cross-contamination.
DPV-B conveyors are specifically designed for moving large quantities of friable pelletized materials like carbon black, as well as powdered, granular and abrasive materials. The high-pressure air required to operate the conveyor was available from a standard industrial air compressor already in the plant. The compressor had a desiccant dryer capable of reducing the air moisture content to a dew point well below a level of concern, even for outdoor conditions during winter months. When Cyclonair air injectors are installed at specified intervals along the conveying lines, the DPV can move material over virtually any distance.
These desirable characteristics were capped by capital investment and operating costs significantly below the cost of constructing and maintaining a new mechanical system using a bucket elevator and horizontal distribution conveyors.
To balance capacity and budget targets, Cyclonaire designed the McCook system around a DPV-B with 25 cubic foot capacity. This unit meets Parker's desired conveying rates and has a cycling frequency that lends itself to prolonged component sevice life. This solution also enabled Parker to unload hopper-bottom railcars and trucks without the need for a pit of any kind, saving further expense. Cyclonaire custom built a simple, lightweight aluminum pan that clamps to the railcar hopper outlet flange for unloading. A 5" vacuum hose connects the hopper pan to the DPV conveyor.
As part of the conversion, four Cyclonaire bin vent dust collectors were installed atop the four carbon black storage silos. These high-efficiency units provide product and air separation and dust control for the various grades of carbon black. They feature pulse jet cleaning to maintain filter media effectiveness, ready access to filter bags and differential pressure gauges to indicate when service is needed.
Before the conversion, the four carbon black storage silos shared a single dust collector. By replacing the single unit with four bin vent dust collectors, engineers eliminated a source of potential cross-contamination and improved overall dust collection efficiency. The four dust collectors remove carbon black dust from the air exhausted from the silos and discharge this useable material back into the silos.
To handle the distribution in place of the drag conveyor, company engineers supplied air-actuated Cyclonaire ball-style diverter valves for installation in the convey line. These stainless steel diverters are designed for rugged, high-pressure service, offer unobstructed flow to minimize product degradation and allow conveying to multiple destinations. Valve bearings are protected by an o-ring seal to permit indoor/outdoor installation, and the valve seat design prevents material migration into the cast body.
Cyclonaire vacuum-loaded dense phase conveyors use only positive air pressure for both vacuum loading and pressurized conveying. The heart of the system is a high-pressure venturi of proprietary design. The venturi generates a vacuum that draws carbon black in dense phase mode from the railcars into the DPV conveyor's 25 cubic foot transfer vessel. A high-level control senses when the transfer vessel is full. The system controller then automatically switches to discharge mode and pressurizes the vessel for conveying material to the storage silos. Cycling between vacuum loading and pressure discharge is completely automatic. Cyclonaire's proprietary venturi eliminates the extra filtration, the vacuum pump and other equipment that would be required by a conventionally designed vacuum/pressure pneumatic system. This results in substantial savings and a simpler, more compact design. For Parker Hannifin, the DPV controls were integrated with existing plant controls so that the system requires minimal operator supervision and can be remotely operated and monitored. Working with a single source manufacturer for all the major conversion components offered Parker Hannifin a significant advantage over sourcing from multiple suppliers. Cyclonaire accepted complete system responsibility and was able to take the conversion project from concept engineering and project management through start-up supervision. This allowed the McCook staff to remain focused on its core responsibilities during planning and construction. In addition, Cyclonaire provided factory-trained service technicians to assist with equipment start-up and offer formal classroom and in-plant operator training. The topics covered system theory and operation, adjustment procedures, preventive maintenance, troubleshooting and repair techniques.
According to McCook plant engineer Bruce Bair, "The conversion reduced our unload times, downtime and ongoing costs. The Cyclonaire DPV cuts about 30% from our unload cycle time, so it allows us to increase throughput. The new setup also eliminated real and potential problems with particle degradation and cross-contamination that we were fighting. The DPV-based system met all our objectives and proved to be a good investment from every angle. In addition, the training provided was thorough and complete, and Cyclonaire service was outstanding. Their people supervised installation of the equipment, fired it up and showed us how to run it on our own."
Adapting to change
In 2003, less than a year after the Cyclonaire equipment was placed in service, Parker changed suppliers of McCook's carbon black. Shipments by rail required 16 days of lead time. Parker identified a supplier that could deliver carbon black at competitive rates by truck with only an eight-hour lead time. Bruce Bair noted, "Thanks to the versatility of the pneumatic equipment, all that was required to change from a rail unload to a truck unload system was relocating the DPV to an enclosure we built for truck receiving." The only system change was a new Cyclonaire-supplied pick-up pan to fit the hopper-bottom trucks. For the rest of the pneumatic system, no modifications were necessary. Cyclonaire provided two options for connecting to the trucks, including the new pick-up pan sized and shaped to clamp directly to the round truck hop-per gates and a QuadLift receiver dolly on castors fitted with vacuum hose and a boot to mate with the truck gates, designed to reduce the time required for hookups.
Using Cyclonaire's QuakLift dolly became the preferred docking method. An operator would simply guide the low-height dolly into position under a truck and align its pick-up pan with each of the truck's hopper gates in turn as each hopper was ready to be unloaded. Four pneumatically actuated lifters at the corners of the QuadLift dolly elevate the pan to press it firmly against the hopper gate to form a complete seal, then the gate is opened. As the truck empties, it rises, so during unloading, the pneumatic lifters expand to maintain a tight seal that eliminates carbon black leakage.
In early 2004, Cyclonaire was called on to solve a second set of problems at McCook. The plant's original pull-push pneumatic conveyors, built by another pneumatic conveyor manufacturer, were still being used to move carbon black from the four exterior storage silos to the compound mixing area. However, this sub-system was plugging on a weekly basis, causing costly and unacceptable downtime and major housekeeping issues. Sometimes the main problem appeared to be erratic overflow control in the pneumatic lines. At other times, the plugging occurred in an aging rotary diverter.
"The manufacturer of the original conveyors had installed pneumatic boosters at regular intervals in the lines to augment the line pressure, but the results were not adequate," Bair explained. Cyclonaire changed out the existing boosters and replaced them with its patented Convey Line Injectors. As a matter of standard procedure, these small, simple units had been used in the earlier unloading conversion project to control material transit in the high-pressure lines for smooth dense phase conveying. They connect to the control air supply by flexible hoses and are designed to improve the airflow distribution and the size of material slugs in dense phase applications. As an added benefit, the injectors lowered the source tank pressure, resulting in lower line velocities to further minimize material degradation. The injectors Cyclonaire used for the McCook retrofit were 304 stainless steel units for the ultimate in durability. Cyclonaire makes injectors with glass-filled nylon, aluminum or stainless steel construction, and supplies them based on system and customer requirements. They come with integral check valves to prevent back flow of material into the control air, and have a patented locking needle valve for regulating flow. They not only help minimize degradation and plugging, but have the added benefit of facilitating a restart of dense phase flow after unexpected shut down, without having to manually clean out the lines. After a simple installation and setup procedure, the line injectors are essentially maintenance-free.
Distribution of the carbon black for compounding within the plant was another problem. The way the plant was set up, the three grades of carbon black would be separately conveyed from the four main exterior silos to a receiving hopper fitted with a rotary diverter. The rotary diverter would be pneumatically rotated and positioned to flow the material from the hopper into one of four day bins above the four line mixers. This arrangement created the potential for cross-contamination of the material grades caused by residue in the receiving hopper and in the diverter. In addition, the diverter frequently became plugged and had to be manually cleared.
Parker and Cyclonaire engineers worked out a series of modifications to simplify handling by eliminating the receiving hopper, its dust collector and the rotary diverter so that the three grades of carbon black could be delivered directly to day bins above the mixers. To accomplish this, they installed ball-type diverter valves like those used in the initial work at McCook. Bair added, "The diverter valves operate reliably and completely eliminate the risk of mixing grades." Since only three grades of carbon black were in use and there were four bins, Parker engineers turned a split bin into one common bin to have added reserve of the primary grade of carbon black on hand in the event of a deliver disruption.
Now, instead of a single shared dust collector, each of the three grade-specific day bins has its own Cyclonaire bin vent. The new setup simplifies the material routing, eliminates the downtime problem and the sources of potential contamination. In addition to offering more direct routing and cutting costs, this arrangement is also more robust and provides improved dust collection and material segregation.
Bair summarized, "We have been pleased with the results of these two projects, and we have other work planned for Cyclonaire. The new Cyclonaire pneumatic conveyor in effect gives us about a 30% jump in capacity, and the other improvements save the time we previously spent maintaining and cleaning the bucket elevator, belt conveyor and rotary diverter.
by Joe Morris, Cyclonaire