Why Isn't Using Differential Pressure Acceptable For My Air Permit CAM?

Posted by Earl Parker on Apr 21, 2017 11:00:00 AM

Rolling averages, pounds per hour vs. grains per standard dry cubic foot, PM 10 vs. PM 2.5…the complexities of emissions control, monitoring and compliance can make facility personnel feel overwhelmed at times. Trying to navigate the murky combination of environmental regulations from Federal, State and Local authorities while also striving to hit production targets can pose a challenge. At times, this is further complicated by the fact that many plants do not possess state of the art pollution control equipment and must rely on legacy systems in order to achieve compliance. 

In light of this, one question/complaint we hear at times from dust collector operators involves the use of dust collector differential pressure in their air permit’s Compliance Assurance Monitoring (CAM) plan. After each plant receives finalized emissions limits from the regulating authorities as part of its air permit it must then submit a CAM plan that outlines how the facility will monitor the performance of its control devices. This plan then needs to be approved by the regulatory body as part of the plant’s air permit. 

Many engineers want to use dust collector differential pressure as the compliance indicator as opposed to other indicators, such as particle concentration as read by a triboelectric detection device. Since many plants have used DP in their CAM plans - it must be a viable option, right? Let’s consider why  this approach no longer works and other reasons why plants should consider using triboelectric monitoring for their air permit CAM plans. 

Why Dust Collector Differential Pressure Was Used as Part of Air Permit CAM Plans in the PastGraphic Comparison of PM 2.5 and PM 10

In the early days of pollution control regulations finding an accurate way to measure particulate matter emissions was easier said than done. Since the small particles measure only several microns in diameter (too small to see with the naked eye until concentrations reach critical levels) accurately measuring them in the field across many different applications proved quite a challenge. However, it was well established that fabric filter dust collection systems could reliably collect upwards of 99.99% of these particles when operated correctly within a certain differential pressure range. Therefore, for many years authorities approved CAM plans that used dust collector DP as a proxy for absolute particle emissions levels. The theory went that as long as plants kept their collectors running within a specified DP range where collection efficiency was highest (usually between 3” - 6” w.g.) that indicated that the system was functioning at peak efficiency and was thus capturing the required percentage of emissions. 

Why Differential Pressure is No Longer Used for CAM PlansTRIBO_dsp_U3600.jpg

While the above system worked well in the past given the technology available at the time, it no longer meets the demands of modern applications. First, stricter emissions regulations now mandate lower permissible emissions and requiring the capture of even finer particles (PM 2.5) compared to only coarse PM 10 of older regulations. Second, monitoring technology has advanced greatly in the last 40 years to where accurate monitoring of particle emissions no longer proves difficult for nearly all applications. Additionally, DP, while an indicator of performance, does not always correlate directly to emissions levels coming from a fabric filter collector. Any number of other issues can occur that would result in higher emissions while not necessarily impacting the DP of the unit. (Interesting deeper look at this topic at baghouse.com if interested.)

For these reasons, newer CAM plans and Air permits use DP monitoring as an indicator of collector operation for proper cleaning  - not for emissions monitoring. You will still find older air permits where plants do not fall under NESHAPS that will still list DP monitoring as the required method, or on legacy systems grandfathered into the older requirements. But the trend today, in place of DP, many plants make use of particle concentration from triboelectric systems for their air permit CAM plans. While many plants also make use of opacity measurements, this too faces challenges within regards to the latest emissions standards, such as EPA MACT regulations. For these reasons, many plants have decided that triboelectric monitoring provides significant advantages over other monitoring methods.  

Leave Differential Pressure for Dust Collector Control - not Monitoring

Compelling reasons exist to move away from collector differential pressure for your plant’s CAM plan. As we have seen, it was never an optimal solution for emissions monitoring to begin with, always lacking consistent correlation and reliability. Additionally, as emissions regulations have progressively tightened over the years the industry has developed more advanced PM monitoring technologies such as triboelectric devices (as is outlined in this graphic) to assist plants in attaining compliance.

Would you like to learn more about why triboelectric technology is the best option for your facility’s CAM plan? Click here to receive a free consultation from one of Auburn’s experience emissions experts today!

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Topics: Air Permits, Particulate Monitoring