Letters to the Editor

This letter is a response to the article by W. Quin, M. Dekermenjian, and R.J. Martin (QDM), entitled “Prediction of Particulate Loading in Exhaust from Fabric Filter Baghouses with One or More Failed Bags” (J. Air & Waste Manage. Assoc. 2006, 56, 1177-1183). I need to provide some background before proceeding to the comments on the QDM paper. In the late 1970s, it became apparent that: 1. fabric filter baghouses (FF) were for the first time being seriously considered as an alternative/option to electrostatic precipitators (ESPs) for particulate control of emissions from large coal-fired utilities; and 2. operation and maintenance problems with the FF and ESP had emerged as a major concern, a concern that would significantly impact on the choice of particulate control. The above concerns lead to three articles1–3 that addressed these issues because bag failure is a reality of life. The Theodore and Reynolds1 (TAR) article specifically addressed the area of “the effect of bag failure or baghouse outlet loading. ” In that paper, I developed a unique but simple model that provided a quantitative answer to this effect. There were three major assumptions in my model: (1) the flow rate through the baghouse was constant during and after bag failure(s); (2) bags were assumed to fail catastrophically; and (3) the pressure drop was essentially constant following bag failure(s). These assumptions produced conservative estimates on outlet loading and particle penetration, with lower values resulting if the bag failure was something less than catastrophic. Therefore, any calculated result would have to be viewed as a rough estimate. Assumption number 3, a key assumption, was verified at that time by calculation using a procedure similar to that provided by QDM. Assumption number 3, based on sound engineering judgment, was important to both the model and subsequent analysis. My earlier calculations indicated that this assumption was valid for baghouses with more than 1500 bags. Furthermore, for smaller baghouses (as shown in the example in the TAR1 paper), my calculations also clearly indicated that any detailed analysis would be useless because most baghouses containing less than 1500 bags or (more meaningfully) 150,000 actual cubic feet per minute—depending on design and operating conditions—would be out of compliance after one bag failure. Regarding the QDM paper, I have several problems with the article. 1. QDM did not properly acknowledge in a clear, straightforward manner that they employed my derivation of this unique model (that was based on the constant pressure drop assumption). 2. The comparison of the QDM model with the TAR model was based on a 200 ( 1500) baghouse. As indicated above, this analysis was valueless because the unit would be “catastrophically” out of compliance after the first failed bag. 3. Their graphs depicting performance for 1, 2,. 199, 200 bags were likewise valueless for the reason listed as number 2 above. 4. The authors apparently chose not to provide a meaningful comparison between the two models for larger baghouses where the calculated results are of practical and industrial value. 5. My comparison of the two models for those larger baghouses, where the models’ usefulness tests or significance produced essentially identical results.4 In conclusion, QDM’s repeated negative implications and comments regarding our original work are simply not justified. The technical community would have been better served if the authors just presented their modified model that was based on my original assumption. The authors also used poor engineering judgment in attempting to justify the usefulness of the model with a 200-bag unit example.