What is Pressure Drop?
In a baghouse, pressure drop refers to the difference in pressure between the dirty air entering the baghouse and the clean air exiting the baghouse. This difference in pressure is caused by the resistance to airflow through the filter bags, which are used to capture the particles. The pressure drop trend can be used to determine the condition of the filter bags and the overall efficiency of the baghouse. If the pressure drop becomes too high, it can indicate that the filter bags are becoming clogged with particles and the bags need to be replaced.
There are a few ways to control pressure drop in a baghouse:
Regular check on the DP Trend: The DP will trend upwards with time on a scale of a 2-year time chart in normal non-membrane bags or with poor-quality membrane bags. If the membrane quality is good, it will have high filtration efficiency, in that case, the DP trend will be very horizontal & straight for a long period, say 4 to 6 years. Only when the membrane starts to wear off, the DP will start to rise.
Maintenance: Regularly scheduled maintenance on the pulse valves, checking on pulse pressure, air quality, etc. is important in order to ensure the bags are clean and to achieve a steady DP trend.
Proper Bag Selection: Selecting the right filter bag with the appropriate material and filtration efficiency can help to control the pressure drop.
Pulsing Frequency: Increase the frequency of pulse jet cleaning to remove dust from the filter bags, this can help to reduce the pressure drop at the expense of bag life.
Pulsing Pressure: Increase the pressure of pulse jet cleaning to remove dust from the filter bags, this can help to reduce the pressure drop again at the expense of bag life. Fiberglass bags are very susceptible to damage at high pressures.
For RABH: Reverse Air Flow Rate: Adjusting the air flow rate & cleaning frequency can help to reduce the pressure drop.
Adjusting the Air-to-cloth ratio: The air-to-cloth ratio is the ratio of the amount of air that is flowing through the baghouse to the total surface area of the filter bags. Lowering the air-to-cloth ratio can help to reduce the pressure drop. This can be achieved by reducing the false air in the system.
It's important to keep an eye on the pressure drop trend regularly because it can be an indicator of a problem or an opportunity to improve the performance & productivity of the plant.
In the end, if you want really low-pressure drops, you are going to clean more frequently and more vigorously. This will lead to faster wear and tear of the filter bag and then you will see a premature failure.
It is important for plant managers to manage their expectations when purchasing a standard product, as it may not perform at the same level as a high-efficiency product such as those from W.L. Gore. While standard products may be less expensive and more readily available, they may not have the same level of durability, filtration efficiency, or longevity as a premium product like those from W.L. Gore.
Standard bags should be operated at pressure drops which are on the higher side (i.e., 150 mmwg). This way, the cleaning frequency is reduced. Otherwise, if you try to operate standard bags at low DP, the bag will wear and tear faster and have lower bag life.