A: John B. Johnson, FLSmidth, says:
Companies spend unnecessarily on their baghouses every year because of unexpected process problems and poor preventive maintenance planning. A plant might decide to prioritize current operations over preventive maintenance planning, lack resources and workers to properly maintain and manage equipment, or not know how to maintain a baghouse.
The fact is, however, that simple preventive measures and planning can actually reduce expenses, improve safety, and reduce worker stress levels at your plant. Companies with no plan in place, faced with an emergency, need-it-now situation, might say, “The expense is no object because we have to have it.” But no company has that kind of budget or flexibility. You’ll likely pay 20 to 50 percent more in an emergency situation than if you’d planned ahead. To avoid this kind of emergency situation:
Plan for outages. Many companies don’t properly plan for outages (or scheduled plant downtime). Typically, outage times vary by industry. Cement and lime plants tend to schedule outages from January to April, steel plants from June to July or November to December, and chemical plants before the summer months since baghouse work is labor-intensive and cooler temps provide better working conditions. Generally, though, outage times are fall to winter and winter to spring, so demand for filter bags, cages, accessories, parts, related equipment, and service personnel is high during those periods. Cut expenses by buying ahead so products are made ahead of your outage and ensure service personnel are scheduled well in advance.
Use a checklist. Use a checklist so you don’t forget anything. List all your baghouse equipment on a spreadsheet with specific details — number of filter bags, number of compartments, bag descriptions, baghouse location and process, vendor part numbers, plant designation SKU, and typical filter bag life.
Utilize an inventory support plan. One challenge companies face is that they aren’t allowed to keep the required inventory on hand to maintain their baghouses. If that’s the case for you, work with your supplier to develop a “make and hold” plan. This is where the supplier agrees to make and hold a specific quantity of filter bags until the customer releases the order for delivery. Reliable suppliers should be willing to keep your spare and outage parts on the shelf until you need them. An inventory support plan typically has a time limit of 6 to 12 months. Since the manufacturing lead time for a filter bag is mainly due to waiting on the raw materials, the inventory support plan also can be a blanket agreement for the supplier to keep raw materials on hand, further minimizing customer wait time. This is called a “release and make” program.
Use the dye test. Test filter bags before startup — even if you think they’re problem-free. Companies make the mistake of ignoring the baghouse during an outage if there are no plans to remove old filter bags and install new ones. Any time an outage occurs, you should plan on inspecting the baghouse to confirm that the equipment, structure, and filter bags are in good condition. Sending fluorescent dye powder through the baghouse via the induced-draft fan is one way to confirm that existing bags are in good condition and that the tubesheets (or plate into which the filter bags are seated), walls, and other metal-to-metal contact points are free of holes or small cracks. Dye powder travels through the system as dust would. If there’s a breach, the fluorescent powder goes through it and enters the clean side of the baghouse (above the tubesheet). Inspecting with a black light under dark conditions will show you exactly where the leak occurred and taking this simple step will ensure that baghouse startup will go smoothly once the outage is complete.
Adopt startup best practices. Startup procedures are critical to baghouse and filter bag performance and service life. Startup is unique to each application, but generally you should:
- Visually inspect to ensure all parts are properly installed and ready.
- Make sure differential pressure gauges and other monitoring devices are operational.
- Take steps to not exceed baghouse design airflow or velocities.
- Preheat the baghouse prior to startup with clean, hot air before introducing dust into the baghouse.
- Season filter bags by letting a dust cake build up prior to the initial cleaning.
Precoat filter bags. Precoat new filter bags during the startup process for protection and durability. Several types of precoat material exist, but the most effective is a perlite-based powder that provides consistent surface coverage. Precoating a new filter bag will minimize dust impingement of fine particles into the filter media, allowing bags to operate at an optimum level after initial startup. Other precoat benefits include protection against excessive moisture that could be introduced during startup and protection against hydrocarbon buildup, which is oily and hard to remove and can quickly blind filter bag material.
FLSmidth, Bethlehem, PA, is a global engineering company and supplier of one-source plants, systems, and services to the cement and minerals industries. The company’s dust collection brand, AFT (Advanced Filtration Technologies), is produced in Evans, GA.