Business growth creates new challenges. This is the case for plant engineers and maintenance managers responsible for the efficient operation of the most common form of dust collection equipment — pulse-jet baghouses — used in foundries across the globe. Many baghouses were designed and built to accommodate a certain amount of air flow that was sufficient for past demands. As foundries have increased production, these flow requirements have amplified and the original design of the baghouses are no longer suitable. Their obsolescence is perpetuated by raised scrutiny on emissions and the focus on the business community’s responsiveness as good corporate neighbors and stewards to a sustainable environment.
In this blog, we will explore pleated filter element (PFE) technology and examine how two foundries successfully upgraded their pulse-jet dust collectors by installing PFEs, resulting in:
- Increased air volume.
- Improved filtration efficiency.
- Reduced emissions.
- Lower overall plant maintenance requirements.
EPA and OSHA
The Environmental Protection Agency (EPA) and Occupational Safety & Health Administration (OSHA) regulations have become increasingly more stringent, requiring foundries to upgrade their current operational ventilation systems to comply with regulatory standards. Foundries have evaluated their furnaces, shakeout, pouring and cooling lines, sand handling systems, finishing areas and many other parts of their operations reliant on pulse-jet dust collectors for proper ventilation. Their evaluations have found a multitude of problems, including:
- High air-to-cloth ratios.
- Emissions caused by poor media filtration efficiency.
- Inlet abrasion of filter bags.
- Low air volumes at source due to excessive baghouse differential pressures.
- Loss of production due to filter bag changeout downtimes.
- High upward (interstitial) velocities between filter bags, resulting in ineffective cleaning.
- Pulse cleaning systems consume large volumes of compressed air.
As a result, foundries are looking for ways to upgrade their dust collection. The most economical and preferred option is to modify existing baghouses rather than installing completely new systems, which would require significant capital investment. PFEs provide an effective solution to this challenge.
PFE technology optimizes existing systems
Pleated filter elements, such as those manufactured by Parker Hannifin, are filters that use either a molded polyurethane or metal top and bottom that are used as direct replacement for standard felted filter bag and cage assemblies in pulse-jet baghouses, as well as in new equipment. Spun-bonded polyester fabric is the most common media used in PFEs because of its tight pore structure and rigid physical properties that allow it to hold a self-supported pleat —providing as much as 200 to 300% more filtration area at 99.992% efficiency than a filter bag in the same tubesheet hole.
Successful applications of PFE
A major Midwest foundry used a three-compartment, 882-bag shaker baghouse to ventilate four induction furnaces, a scrap preheater system, and a magnesium inoculation station. The foundry struggled with the following problems in its dust collection system:
- Twelve-month filter bag life.
- High differential pressure due to media binding caused by particulate loading.
- Loss of ventilation air in the furnace area.
- Excessive emissions.
- High labor costs associated with keeping the old system operational.
As a solution, the company converted the original shaker system to an engineered pulse-jet style cleaning system using BHA® PFEs manufactured by Parker Hannifin's Industrial Gas Filtration and Generation Division. The baghouse was retrofitted with a new tubesheet and a walk-in clean air plenum, to allow for a top-load design filter element. The baghouse has been operating consistently since the retrofit.
Since the retrofit, the baghouse has been operating consistently and the following results have been reported:
- Upgraded air volume from 28,000 CFM to the required 55,000 CFM.
- The amount of compressed air required for pulse-jet cleaning has been reduced from 60% to 40%.
- Stack testing has confirmed that performance easily meets new environmental regulations.
A large foundry that manufactures castings for the automotive industry had a top-load design pulse-jet baghouse that contained 650 felted filter bags and cages. The unit ventilated several shot blast cabinets, grinders, and other finishing equipment. The system was originally designed at an air-to-cloth ratio of 6.1:1. The filter bags measured 5.25 in. in diameter by 12 ft. in length, for a total cloth area of 16.5 ft2 per filter bag. The challenges the foundry was experiencing with the current design were:
- Bottom-bag abrasion caused by the filter bags’ bottoms hanging directly above the parting line of the hopper. Abrasive metallic dust created small pinholes in the bottom of 9 inches of the filter bags.
- Unacceptable emissions at the discharge stack.
- Significant production time reduction.
The foundry engineering team determined that installing Parker BHA PFEs in the dust collector was the most cost-effective solution.
Post installation results include:
- Because of the PFEs' compact design, the filter bottoms were positioned five feet above the dirty-air plenum eliminating the bottom bag abrasion.
- Reduction in the air-to-cloth ratio to 3.2:1.
- Air consumption at the collector was reduced by 30% resulting in increased overall system efficiency.
- Unplanned maintenance and shutdowns were eliminated.
- A reduction in average differential pressure across the filter elements to 3.0 to 3.5 inch water gauge.
Pulse-jet dust collectors used in most foundry applications can be successfully upgraded with the installation of pleated filter elements. The case studies show that when aggressively designed to air-to-cloth ratios and demands for increased airflow capacity cause poor dust collector performance, the installation of PFEs can dramatically lower differential pressures, improve filtering efficiencies, reduce emissions and lower overall plant maintenance requirements.
This blog was contributed by the Filtration technology team, Parker Industrial Gas Filtration and Generation Division.