The safe removal of residual dust is a critical element when processing solids. It’s also needed throughout production, from active ingredient handling through packaging and shipment of finished product. A central dust collection system removes particulate, increases safety, and reduces maintenance costs. The reality is that these systems are often inadequate. Many were installed quickly over the years, a stopgap measure to accommodate growing production demands. Attempts to link single collection units resulted in a compromise that lacked proper controls and was expensive to operate.
The solution is to incorporate a comprehensive, modern system that better protects personnel and equipment, promotes productivity and keeps operating costs in line. This can often be accomplished optimizing existing equipment.
A Case Study
A major German manufacturer dealing with increased product demand encountered problems with dust control. Its existing collection system consisted of single units in either standalone applications or in a battery of units. None were interconnected. Compounding the problem was the fact that a number of different filter suppliers were involved, making it difficult to efficiently maintain the system. The result was an increased risk of dust contamination during the disposal/discharge and filter changing process. In addition to dealing with dust contamination issues, the company planned to integrate central vacuum points and pneumatic conveying lines with its production operation, each requiring different pressure levels within the system.
Process and System Considerations
The first step was a systematic check of the existing dust collection system. A new system was proposed reusing as many components as possible.
The company developed specifications for the project based on process flow. Some ideas conflicted because of space or equipment limitations, requiring creative solutions. In one instance, a vacuum cleaner connection was engineered to achieve low airflow and high under-pressure. In another, minimal velocities in some of the raw gas ducts had to be considered. Constant, well-defined airflow was necessary to ensure dust was collected without capturing product.
Overall, there were significant amounts of air volume at low under-pressures—such as in the nozzle plate—as well as a pneumatic line that conveys dust from filter units with a high under-pressure to the central dust collector.
An ATEX version of the filter was specified. This system featured explosion suppression in relevant areas, contamination-free dust disposal, and containment within compliance with the required OEL steps.
Once in place, an additional challenge presented itself: how to ensure the safe-change validity of all filter elements. Because the process lines ran constantly, there could be no interference caused by additional air supply or with pressure in the production areas—even with varying amounts of incoming air. Along with these considerations, space limitations and a short installation window had to be addressed.
To meet the challenges posed, discrete engineering and customized equipment were needed. A pilot plant was established and dust samples analyzed in the lab to gauge whether the safe-change of filter elements was validated. The results were positive and a system was installed that used Herding Filtration filter technology and operated on two separate pressure stages.
Putting the Solution To Work
Within the system, dust removal from work areas and machinery is completed through large air volumes to filters working at a typical maximum pressure of 10” WC. The filter units and dust disposal are adjustable to accommodate continuous process operation.
Collected dusts are pneumatically conveyed to a central collector with an adjustable vacuum system with an under-pressure up to 14.75“ Hg. The system generates a maximum extraction capacity of 1,470 ft3/min, a necessity to allow for conveyor lines that run up to 400 ft. The design also features interconnected cleaning hoses and captures both regenerated dust and API, optimizing safe-change. Dust from the containment system is extracted in a CLS (Continuous Linear System) that meets contamination-free dust disposal requirements.
The system operates in two pressure stages. It is integrated with existing components to provide centrally controlled dust collection.
Sinter-plate filters are used in this application because they typically provide high removal efficiency. To meet ATEX requirements, a Herding PharmEx filter was used. Based on its structure, this unit does not require any tertiary measures and can be installed at any point in a production area. At other points, explosion suppression was used. Sinter-plate filters also act as a barrier for Ex Zoning.
Sinter plate filters are engineered for permanent application and require little or no maintenance.
System Proving Itself
The containment system was validated at the critical points—the pipeline routes, collector unit and CLS unit—through an SME - PAC - Lactose test. It has not required maintenance in nearly two years. The collection efficiency of the sinter-plate filters reduces the amount of dust channeled to the downstream safety filter; consequently, the filter rarely requires changing. When a filter needs changing, it is accomplished under contamination-free safe-change conditions with WIP pre-cleaning.
The case study illustrates that existing equipment can be efficiently modernized to optimize the safety of employees and process equipment.
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