From: Don Denison [mailto:don.denison@encertec.com] 

Sent: Friday, May 03, 2013 8:13 AM

To: Sroka, Kristin

Subject: Questions regarding DLAs and DIFFs

Dear Kristen,

My answers to your questions are below. I hope this helps explain the situation and your work with 

EPA. If you have any additional questions just let me know.

Sincerely yours,

Don

From: Sroka, Kristin [mailto:ksroka@rti.org] 

Sent: Tuesday, April 30, 2013 4:51 PM

To: don.denison@encertec.com

Subject: Questions regarding DLAs and DIFFs

Mr. Denison,

Thank you for speaking with me earlier today. As I noted on the phone, I work for RTI International, and 

we are providing technical support to the U.S. Environmental Protection Agency to develop new 

regulations for the brick manufacturing industry. Rick Marinshaw from RTI spoke with you in March 

2009 about DLA capabilities, and I have a couple of follow-up questions about both DLAs and DIFFs that I 

am hoping you can help answer.

For DLA:

1. DLA are not specifically designed to reduce particulate matter (PM) emissions, but based on 

your experience, can any nominal PM emissions reductions be achieved with a DLA? If not, 

would it be feasible to add a fabric filter after a DLA to achieve PM emissions reductions? In 

Europe some DLA’s were built specifically for particulate reductions. I was at one installation in 

Germany where a DLA was used to reduce particulate emissions in a coop grass dryer using a 

rotary dryer. In Europe they gave guarantees of less than 50 mg per m3 with DLAs. The 50 

mg/m3 was, I believe, part of their regulations. In many cases the particulate matter from a DLA 

comes from the limestone used as the reagent. The type of limestone has a significant effect on 

the amount of dust produced and the reactivity of the limestone. Softer limestone, having more 

surface area, tend to be more reactive but produce more dust. Hard limestone can be, almost,

unreactive with acid gases but emit almost no dust. In the 1990’s we tested many limestones 

from various parts of the US. There were significant differences in the reactivity of various 

limestones and the majority of those tested had almost no reactivity with the acid gases. I know 

one plant that added an old fabric filter after the DLA but it was installed to reduce or eliminate 

visual emissions which were from the limestone (reagent). This fabric filter was not added to 

reduce particulate from the firing process.

2. Are there ways to enhance/improve the HF emissions reductions performance of an existing DLA, and 

if so, approximately how much would those actions/improvements improve performance? (For this 

question, I’m interested in minor to modest improvements that might be achieved by something like 
increasing the amount of lime used, not necessarily significant improvements, which are addressed 

in Question 3.) My first answer to this question relates to all the remaining questions! The brick 

industry is UNIQUE, and I use all capital letters with intent. Every plant uses a different raw material 

most of which comes directly from a local quarry. Not only does each plant have a unique material 

but many plants use different mixes of local clay and non-clay materials every day and sometimes 

with a small amount of purchased additives. Even the local materials change over time since these 

companies are simply digging the material from a large area and geology changes both in length and 

depth of the quarry. And these are not “high-tech” materials. Basically the materials used in the 

brick industry are those of little value to more costly products. My point is the material being 

process and, therefore logically, the emissions from the process change significantly from plant to 

plant and even from day to day in the same plant. I don’t know of any other industry with these 

significant variables. In actuality, one plant without any type of controls could have a lower 

emission rate of an acid gas or particulate level than a plant with a good DIFF. For a supplier of 

emission control devices all you can do is use the data from one emission test and try to obtain 

acceptable results with any materials or changes in materials the company may experience. For the 

same reasons I assume it’s very difficult to impossible to set realistic limits on an industry basis for 

the brick industry. Now back to the question at hand: In some cases increasing the limestone, 

remember DLA’s use limestone, not lime, would improve the performance. This would be specific to 

plants with higher emissions after the DLA because they had very high emissions before the 

DLA. The only way to specifically answer this question would be by trial and error at each plant and 

knowledge of the emissions before and after the DLA. There are, or at least were, manufactured 

reagents available in Europe. These reagent were pelletized from various materials such as 

limestone, lime, sodium bicarbonate and, I believe in some cases, activated carbon. Years ago we 

checked on availability here in the US or having similar products pelletized in the US but the 

manufacturers said the market was too small.

3. During your discussion with Rick Marinshaw in 2009, you said that if the new HF, HCl, and PM 

standards are significantly more stringent than the vacated limits, most DLAs would need to be 

replaced with DIFFs. Have there been any technology advancements since that time that would 

change that answer, or would a change in control device still be needed? The interesting part of this 

question is “you said..”. Quite frankly I have not recollection of a discussion with Rick Marinshaw in 

2009. That’s not to say it didn’t occur but it must not have seemed important to me at the 

time. Since you all but quote me in this question, do you have a written copy of my comments. I 

would think if I was being recorded or deposed I would recall the conversation. To your 

question: Other than a possible change in reagent, such as a pelletized material, I don’t know of any 

way to significantly improve the efficiency of a DLA. A few months ago I heard a presentation on the 

emission levels being discussed for the brick industry and with that in mind I would need to rephrase my answer from 2009. I am sure no DLA’s will meet all the levels being discussed and I doubt 

DIFFS will be able to meet those levels at many plants. Some plants have such small levels of certain 

pollutants that measuring the remainder after a 95% removal is below reasonably detectable 

limits. I have actually seen stack tests where the HCl was higher after the control device than before 

the control device and there’s no HCl generation in the control device. It’s just a fact; in many cases 

we are dealing in very small numbers. 

For DIFF:

4. Are there ways to enhance/improve the HF, HCl, and PM emissions reductions performance of an 

existing DIFF, and if so, approximately how much would those actions/improvements improve 

performance? (Examples of improvements might include increasing the amount of sorbent injected 
(e.g., lime or sodium bicarbonate) for a given airflow, using a more efficient sorbent formulation, 

replacing the bags, or using larger/more efficient bags.) Conversely, are there things to improve 

performance that might be designed into a new DIFF but cannot be retrofitted to an existing 

DIFF? Again my answer would depend on the specific plant because every plant uses different raw 

materials. Specifically to your examples, the waste reagent from most DIFFs in only about 50% 

reacted. The reagent is in the DIFF and able to remove more acid gas if the acid gas “could be 

found” by the reagent. In this case I doubt adding more reagent would gain much benefit; there’s 

already more reagent than needed. Sodium bicarbonate is specifically used where higher reductions 

of SOx are needed. You must be careful with trying to mix sorbents. You can not combine lime and 

sodium bicarbonate in a tank but if added separately the bicarb will react quicker with the HF so the 

results don’t necessarily benefit the SOx removal. We had one scrubber where we used 3 different 

reagents but found straight lime was best for high HF and straight bicarb was best for SOx 

removal. The brick industry doesn’t have a lot of choice in bag materials. The temperatures of the 

exhaust gases are higher than the operating levels of most bags so replacing the bags with another 

material has limited options. And the highest temperature bags tend to have a lower efficiency for 

acid gas removal. Using larger bags would require a new baghouse. Baghouses, or fabric filter 

systems, need a certain amount of free space for air flow so larger bags in a given system is not 

realistic. If there are more efficient bags available for the temperatures and acid gas levels in the 

brick industry I don’t know of them.

5. The DIFF test data from across the industry does not consistently show good PM control from the 

baghouse section of the DIFF. I know it is difficult to speculate on reasons without knowing any of 

the specifics of the designs or operation of these devices, but do you have any general thoughts on 

why some DIFFs might achieve better PM control than others? PM emissions from a brick plant are 

like emission levels of acid gases. They can vary greatly from plant to plant and even from plant 

product to plant product. In my opinion most particulate emissions from the furnace of a brick 

manufacturing plant come from coatings on the brick, sand required to be placed between brick 

layers to eliminate sticking and the process of “flashing”. Some plants actually have none of these, 

some have all of them and some have none some days and all of them on other days. It would be 

difficult to even guess why one plant would have more particulate emissions than another without 

knowing the loading of PM before the DIFF and specifically what PM is being removed or 

emitted. Similar to my statement on acid gas removal; one plant with no DIFF may have lower PM 

emissions than another plant with a DIFF. That doesn’t mean the DIFF isn’t doing its job. By the 

same token, a DLA may actually produce PM. 

From my experience supplying pollution control devices to the brick industry I doubt I am willing to put 

my company on the line to meet the new control limits being discussed. It’s simply a fact in this 

industry, the emissions, both for acid gas and particulate, vary too much from plant to plant and 

even day to day and the emission levels are so low that simply “finding” the remaining atoms and 

compounds will be difficult to impossible.

Sincerely yours,

ENCERTEC, INC.

Don Denison

President
I know these are somewhat general questions based on hypothetical situations, but any information you 

could provide would be very helpful. I can be reached at 919-316-3838 or ksroka@rti.org. 

Thank you for your help,

Kristin Sroka

RTI International

3040 Cornwallis Road

P.O. Box 12194

Research Triangle Park, NC 27709

Phone: (919) 316-3838

Fax: (919) 541-7155