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 re‐phrase 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