Baghouses don't make gypsum products, but they certainly have the power to shut down production lines. Here, Luis Castano outlines the latest ways that gypsum plant operators can optimise baghouse performance to minimise maintenance and avoid costly unplanned downtime.
The basic principle of the baghouse is child's play. Contaminated air passes through a filter media. The dust collects on the filter, allowing clean gas to be released to the atmosphere. So far, so simple. But how do we remove the dust that builds up on the outside of the filter media? The efficiency of cleaning affects baghouse availability and performance - and hence plant performance as a whole. Throughout history engineers have presented a range of options:
Shakers: The first baghouses, installed from the 1930s onwards, were cleaned by shaking the filter bags back and forth to remove the dust. This had to take place when a section of the baghouse was not in operation, reducing availability. The presence of many moving parts also made them prone to mechanical failure and bag damage. While this technology should be obsolete, there are still shaker baghouses in operation. You know who you are!
Reverse Air: Fast-forward to the 1950s, baghouses were cleaned by blowing air in the opposite direction to the normal flow. This advancement did away with the complexity of the shaker baghouses and offered very gentle cleaning. However, the cleaning was almost too gentle, bordering on ineffective, meaning that it took a long time to clean bags. As with the shaker technology, a section of the baghouse would have to be offline during cleaning, restricting availability. This technology is now obsolete, but there are retrofit options to upgrade to the latest technology.
Pulse-Jets: This is the state-of-the art technology for baghouse cleaning. Individual bags are cleaned using short, high-intensity pulses of compressed air, sending a shock-wave that removes the dust far more effectively and enables much more rapid and effective cleaning. This means that the baghouse can also be smaller, reducing its footprint and the need for repairs. The only moving parts are a spring and a rubber diaphragm, meaning high reliability. On top of this, it is possible to clean specific sections of bags separately. This means that the baghouse - and the plant it supports - can stay in continuous operation.
More recent developments
However, pulse-jet technology is also not particularly new, dating from 1959 and only widely used since the 1970s. While the basic principle has endured for more than 50 years, there have been numerous developments that have further enhanced baghouse performance:
Synthetic fibres: The first filter media were made from natural materials like cotton. These did not stand up well to the demands of pulse-jet technology. Considerably stronger synthetic materials, including polyester, are much more suited and exhibit far greater expected lifetimes. Indeed they were essential to pulse-jet technology becoming the dominant approach. They take one hell of a beating!
Better Valves: Double-diaphragm pulse valves, which started to come online in the 1980s provided stronger and shorter pulses of compressed air, leading to more rapid and efficient cleaning.
PTFE Membranes: Also in the 1980s, bag manufacturers started use PTFE membrane laminated filter media. This meant that the PTFE membrane became the filter, allowing improved filtration efficiency and dust release. Initially, the cost of PTFE membrane coated bags was 3-4 times greater than uncoated regular ones, but this has since reduced to 1.3 to 1.5 times the regular bag cost. If you are still not using PTFE membranes in 2024, this is low-hanging fruit for better efficiency in your baghouse.
Pleated Filters: From the 1990s onwards, pleated filters offered enhanced efficiency and cleaning thanks to their increased surface area. Pleated filers work very well for dry powders but should not be used for moist processes.
Beyond the innovation plateau
Since the 1990s, new innovations have become much more thin on the ground. We have reached an innovation plateau. And there are new challenges too. I have spent more than 30 years visiting industrial plants to correct issues with baghouses, pneumatic systems, fans and much besides. In the past there was always a baghouse expert - let's call them 'Baghouse Joe.' This individual was responsible for maintaining the smooth running of the baghouses at a given plant and knew them extremely well. However, at some point in the past couple of decades, this position was generally eliminated, with the justification that this role can be carried out by general maintenance. This is a decision that served well only in the short term. Baghouses are no longer being given the attention they deserve and there is a near universal lack of baghouse expertise at the plant level. This is detrimental to their effective use and, with it, the performance of the plant. Plants no longer pay attention to the baghouse until it breaks. I routinely board planes to visit plants and remedy the resulting situations.
Latest developments
Smart Pulse Valve: New IAC Smart Pulse Jet Valves replace the spring and rubber diaphragm with a single moving part made of a hard-wearing elastomer. The new design moves in a similar way to the spring and diaphragm, but, by removing the weakest mechanical part in the valve, greatly enhances reliability. IAC estimates that the Smart Pulse Valve can withstand 10 million pulses, the same as being used once every 30 seconds for 10 years. In addition, the Smart Pulse Valve packs a bigger punch that is audibly different from a conventional pulse jet valve. It makes a huge noise, like a rock concert. You can hear the power!
While it might seem that this would shorten bag life, the opposite is the case. Bag lifespan is more a function of the pulse frequency than it is of pulse pressure. The higher pulse pressure enables the Smart Pulse Valve to do the same cleaning with fewer pulses, extending bag life. It is an in-kind replacement. Just replace the valves and your baghouse performance will be immediately enhanced.
IAC Smart Plant: The IAC Smart Plant is a baghouse monitoring system that acts like a virtual Baghouse Joe. It highlights potential issues to the maintenance team or plant manager before they become a disaster. The Smart Plant combines a range of data obtained from third-party sensors, including: differential pressures, pulse pressures, temperature, discharge valve condition, fan vibrations, leaks, fan motor power, hopper levels and more. The plant can access insights that were simply not possible before, greatly enhancing equipment monitoring among staff. This leads to more informed and more effective operation.
The overall investment is now minimal thanks to modern technology. At less than US$5000, the return on investment would be the moment that the first disaster was avoided. If the system stops an engineer getting on a plane to attend an emergency, it has paid for itself.
Concluding remarks
The humble baghouse has come a long way over the past 80 years, but now holds an increasingly marginal position in the minds of plant operators. Gypsum plants that want to avoid major downtime should pay this often-neglected piece of equipment the full attention it deserves.
About Luis Castano
Luis Castano is Applications Engineering Manager at Industrial Accessories Company (IAC), an original equipment manufacturer of baghouse installations, spare parts and solutions. He has more than 30 years of experience in troubleshooting baghouse issues at wallboard plants and other industrial facilities around the US and elsewhere.
