Improving Health and Safety with Pneumatic Conveying Systems
The very nature of enclosed pneumatic conveying systems to efficiently transport dry bulk materials lends itself to improved safety and higher quality products.
The principal motivation for a ceramic manufacturer to automate material handling is generally to streamline production, improve quality and/or reduce safety and hygiene risks. However, the use of pneumatic conveyors to improve one of those areas frequently causes improvement in another—and those improvements always lead to a healthier bottom line.
Understanding Pneumatic Conveying
Pneumatic conveying systems use vacuum and positive pressure to gently and quickly move materials from point to point with nothing in the way to impede the efficiency of the materials’ movement. Used to convey, batch, and weigh dry materials from fine powders to plastic pellets and caps, pneumatic conveyors consist of five basic pieces of equipment that come together to work as one: a pickup point where material is introduced into the system, convey tubing where material is transferred, a vacuum receiver that collects transferred material, a vacuum producer that powers the system, and a control module that regulates conveying cycles and integrates with other machinery.
These fully enclosed systems protect materials from air, dirt and waste. In addition, because product does not escape the system, particulates that can endanger workers’ respiratory health or settle on equipment and surfaces to pose an explosion hazard are prevented from entering the environment.
Some of the more common health and safety issues in the ceramic industry include: repetitive strain injuries, often associated with manual material handling (especially when dealing with higher bulk density materials like silicon carbide); worker exposure to respirable dusts, such as crystalline silica, that cause respiratory disease; and explosive fugitive dusts like metallic powders that can lead to dust explosions.
Any time powders or bulk dry materials are open-dumped into any process, whether into a blender, a hopper, packaging machine, etc., a puff of dust is created, launching particulates into the air and creating fugitive dust. Fugitive dust, or particulate matter (PM), is basically any solid or liquid suspended in the air through wind or human interaction. While half of all fugitive dusts are greater than 10 microns (a human hair is 70 microns) and settle on surfaces rather quickly, the other half are smaller than 10 microns (not visible to the naked eye) and can remain suspended in the air for days or weeks.
When ceramic and glass manufacturers incorporate pneumatic conveying systems into their production process to transfer bulk solids, the foremost improvement is eliminating the dust control problem and the subsequent operator exposure issues. Secondary benefits include the production enhancements inherent with pneumatic conveyors that shave time off a process, either through increased throughput or reduced housekeeping.
According to the American Society of Safety Engineers (ASSE), reducing seconds from a single process can have a huge impact. An example from a document on ASSE’s website, “ROI of Ergonomic Improvements: Demonstrating Value to the Business,” validates how shaving 3.2 seconds from a task can reduce direct labor costs by $29,000 per year.
Such was the case when a ceramic manufacturer in North America wanted to change the manner in which it was loading its blenders at one of its specialty powders facilities. The company produces advanced ceramics for a wide range of markets, including those in extreme-duty environments to those that require ultra-pure cleanrooms. The manufacturer had previously used a drum dumper and hopper to load its V-blender, which created an undesirable amount of dust in the blender-loading cell.
The ceramic manufacturer had heard about Vac-U-Max’s adaptation of vacuum transfer called direct charge blender loading, which had been designed specifically for the direct charge loading of blenders, mixers, reactors and any vessel capable of withstanding a vacuum. With this blender loading system, a facility’s blender or mixer is the primary receiver, and the conveyor manufacturer configures systems specific to each application while providing the power source, filters, controls, and adapters.
Power options include vacuum pump packages from 3 hp and higher, as well as a venturi power unit that is available in single to quadruple venturi versions. Direct charge blender loading systems standardly convey up to 7,000 lbs per hour; when they exceed that rate, the systems are equipped with increased levels of automation.
Since systems are configured specifically for each application with standard equipment, direct charge blender loading systems come with the option of either floor-standing or suspended blender loaders, designed to significantly reduce the amount of carryover and eliminate product loss. With floor-standing units, once the blender is loaded and equalized, carryover releases into an airtight vessel that preserves product integrity, allowing for reuse or safe disposal. The advantage of floor-standing units is that they are readily accessible for cleaning and can be equipped with casters, allowing them to service more than one blender. The advantage of suspended units is that once the blender is loaded and equalized, material automatically discharges back into the blender, eliminating carryover and the need to handle product manually.
Based on the ceramic manufacturer’s requirements, a 10-hp blender loading system with a floor-standing filter separator enabled the transfer of 25,000-lb batches from drums, via a pick-up wand, through a 2.5-in. convey line to the blender. The system increased throughput to 450 lbs every 6-8 minutes, with only 60 lbs of carryover into the floor-standing filter separator, equating to a quarter of 1% (0.0024) of the batch size.
Because the blender loading system pulls, or vacuums, material into the blender (as opposed to the previous open dumping cycle), no dust is generated during blender loading. This improved the ceramic manufacturer’s process cleanup by 90%.
Improving the bottom line through a reduction in work hours for process cleanup and increased uptime isn’t the only way to boost profits with vacuum conveying systems. When practical, systems can also reclaim product.
Manufacturers reclaim product for a number of reasons, including reductions in primary material costs and the amount of waste product sent to disposal, adding environmental benefits. In the ceramic industry, a common reclamation application is recovering dry mixes from bagging operations. When Featherlite, a manufacturer of concrete blocks, masonry materials and dry mix products, wanted a way to reclaim Portland cement from its bagging operation in El Paso, Texas, vacuum technology was used to reduce the amount of manual labor needed to preserve the heavy material.
“There is a lot of spillage where we package Portland cement from bags tearing,” says Ysai Pineda, plant manager. “We use the Vac-U-Max equipment to clean it up and put it back into the cement holding tank where it is being dispensed.”
The plant operates one 10-hr shift four days per week and fills between 5,000 and 10,000 bags of cement each week. An industrial vacuum cleaner was adapted to do the work of a pneumatic conveyor in order to deliver reclaimed Portland cement back into the hopper that feeds that bagging machine. This cost-effective, dual-purpose machine also serves as a breakaway vacuum. The unit has the ability to disconnect from the bagging unit and be connected to a 55-gal intercept drum, with typical housekeeping hoses and tools, to clean the outside of the bagging area as needed for spills and general housekeeping.
Breakaway systems use powerful portable vacuum units, which can move 10,000 lbs per hour, in concert with several small tubing networks. Individual tubing networks are created in work areas throughout the facility, and the portable unit is rolled from one tubing network to the next, and so on, providing the convenience of a multi-inlet central vac (or in this case, a pneumatic conveyor) with the energy efficiency and flexibility of a portable vacuum.
For the bagging operation at Featherlite, a tubing network was set up to accommodate reclamation. A pickup adaptor was placed below the bagging head, and a 12 x 22-in. receiver was located above the bagging machine to discharge collected cement back into the machine, eliminating product loss and improving working conditions by eliminating manual cleanup of heavy materials.
“The original Vac-U-Max unit we purchased in 1997 is still performing,” Pineda says. “If we are running Portland, it is on the whole time. We are constantly using it to recycle product from around the machine back to the hopper. I’ve been here for 14 of the 19 years that we’ve had it and I don’t remember it being down, except maybe a handful of times for general maintenance.”
Additional areas in the brick industry where vacuum technology is used include cleaning kiln cars that transfer product in and out of kilns, and conveying special ingredients and additives like pigments, glazes, and minerals to the brick making process.
Using pneumatic conveyors to transfer ingredients in the ceramic industry has become the standard, particularly as manufacturers continue to seek sophisticated production processes to minimize particle contamination. Particle contamination can wreak havoc in many industries, rendering products defective, wasting resources and reducing throughput. In the ceramic and glass industries, particulate contamination that causes defects is often the result of fugitive airborne dust. Even when isolated in blending rooms, fugitive dust moves through the plant by convection currents that naturally move from hot to cold areas.
As advances in materials and processes for ceramics continue (e.g., 3-D printers), pneumatic conveyors will continue to be part of the industry’s landscape and the first defense against particle contamination and safety issues, all while increasing efficiency and precision. Reduced downtime, product reclamation, fugitive dust mitigation, greater product quality, improved ergonomics and healthier respiratory environment are some of the most common benefits realized by ceramic manufacturers when incorporating pneumatic conveyors in the processing environment.