Dry dust collectors and humidity don’t react well together.  Baghouses and cartridge collectors operate by having dirty (dusty) air enter the housing.  Multiple filters (bags or cartridges) are located in the housing.  The air travels through the filter and then exits the dust collector.  The filters are a mesh of fibers that allow air to travel through small holes, while dust is too large to pass.  The dust builds up a layer (dust cake), further limiting the subsequent dust’s ability to pass through while allowing the air to pass.  From time to time the dust collector will clean the filters by shaking them or using compressed air to expand them.  This causes the outer layer of the dust cake to fall off.

Humidity can cause problems in the process described above.  Humidity is a way to express the amount of water in the air, (the higher the humidity, the higher the amount of water in the air).  When high humidity air enters a dust collector with fabric filters, there is a chance that the water vapor will condense and create water droplets or the dust on the filters will absorb the water as the airflow passes through.  Many dusts change their physical properties when the water content increases.  Some become sticky, some become hard like concrete, etc.  When this happens to the dust cake, it affects the ability of the air to pass through and the ability of the dust to fall off during cleaning.

When dust becomes sticky, it will adhere to neighboring dust particles and not want to fall during cleaning.  Dust that becomes hard (like concrete) will prevent air from passing through.  When one of these issues develop in a dust collector the pressure drop across the dust collector will increase.  Over time, an increased pressure drop will lower the airflow being pulled through the system.  This will decrease the airflow being picked up at hoods, therefore lowering dust collection at where operators are located.

Humidity can also be introduced in the dust collector in the compressed air.  When air is compressed, the temperature of the air increases, thereby increasing the water content of the air.  The compressed air is at its saturation point.  As the air moves through the line, it cools, thereby condensing water in the system.  If additional drying technology isn’t installed, the compressed air will have water droplets in it as it is used in the dust collectors.  This will cause the filter cake to wet and cause issues as described above.  This is why it is important to dry compressed air when dealing with dust that is affected by water.

However, sometimes no matter how you treat your compressed air, you continue to have issues.  This could be because the airline travels outside and in winter time it gets very cold. It could be because you are located near a large body of water, and humidity is high.  One way to minimize the effect on your dust collector is to minimize the dust getting to your dust collector.  Cyclone pre-filters are ideal for these applications.  Cyclones collect dust and water droplets using centrifugal motion.  This means they aren’t affected by the changes to the dust as a filter is.  Cyclone pre-filters can often remove up to 80% of the dust before a dust collector with filters.  This means you can lower the number of water droplets going into your dust collector and minimize the cleaning required, thereby not getting as much water from the compressed air system. 

To learn more about the different types of Dust Collection methods,  please contact our experts at 440-543-7400 or click on the button below to get our whitepaper, Top 5 Reasons to Use a Cyclone as a Pre-Filter.

At one time mechanical dust collectors were the industry standard in dust collection and air pollution control. However, with an ever increasing focus on air quality, EPA regulations regarding dust collection have steered the manufacturing world toward the higher efficiency capabilities of fabric filter baghouses, cartridge filters, and other dust collection equipment utilizing filter media. This change has undoubtedly helped to reduce the amount of harmful emissions released into the atmosphere in manufacturing processes. Unfortunately, the use of these fabric filter baghouse collectors is not without cost. The limitations of filter media such as moisture, heat, and high particulate volumes have added to the challenges of successful dust collection. Additionally, the high cost of bag or cartridge replacement, maintenance issues, and expensive pulse-jet controls to clean filter media can add up. The solution to these headaches for many has been the use of mechanical dust collectors before final-stage filtration.

Mechanical dust collectors use a cyclonic air flow to separate particulate from an air stream. The centrifugal force created by the rotary flow throws the dust out of the air stream and toward the walls of the collector. In a typical cyclone, the particulate strikes the wall of the collector and falls to a hopper below for collection. Cleaned air is then vented through the top of the collector. While this form of collection can be highly efficient in dealing with large, dense particulate, extremely fine dust lacks the inertia to escape the air stream and is subsequently carried out with the cleaned air. Some high efficiency cyclones like the Aerodyne 'S' Series, use two air streams, to more efficiently separate the dust. The Aerodyne's powerful secondary air stream intercepts the particulate before it contacts the side wall, reducing wear when handling abrasive materials. This secondary air stream also helps to sustain the cyclonic action inside the collector, thereby increasing its efficiency.

Filter media dust collectors such as baghouses and cartridge filters use a fine filter media to remove dust from an air stream. The dust-laden air is drawn into the collector where it passes through the filter media and particulate is intercepted. Dust builds up on the filter until it is cleaned or replaced. Cleaned air is then vented out of the collector.

Many manufacturing processes involve circumstances that make it very difficult to rely completely on a baghouse. Heavy dust loading can be a maintenance nightmare for a filter media collector. A rock crushing operation based out of Minnesota realized the benefits of placing a cyclonic dust collector before its baghouse. The enormous amount of rock dust generated in the crushing operation was blinding the bags and causing frequent shutdowns. The decision was made to install a cyclonic dust collector to receive the dust before being sent through the bag house. The cyclone captured the vast majority of the rock dust, leaving only a small amount of fine particulate for the bag house to handle. The cost of the additional equipment was quickly recovered through fewer shutdowns and less frequent bag replacement.

Processes involving high temperature exhaust gas also plague filter media collectors. The hot air temperatures exhausted from foundries, glass making plants, and power plants can burn the filter media used by most baghouses. While high temperature filter bags and cartridge filters are available, they can be an expensive addition and are still not completely immune to the heat. Used as a spark arrestor, a cyclonic dust collector can be placed before a bag house to both reduce the temperature of the air stream and the particulate loading before it enters a final stage filter.

While a mechanical dust collector may not be necessary in every application, the benefits that can be gained from this proven technology are evident. As emission standards become more stringent and process costs continue to rise, any advantage that can be taken should be considered. By comparing process costs such as materials, labor, and downtime with the expense of a cyclone, a decision can be made as to the need for such equipment.

To learn more about the different types of Dust Collection methods,  please contact our experts at 440-543-7400 or click on the button below to get our whitepaper, Not Your Grandfather's Cyclone.