From: Childress, Jerry [mailto:jchildress@mcgillairclean.com] 

Sent: Wednesday, April 24, 2013 3:12 PM

To: Holloway, Thomas C. (Tom)

Subject: RE: From McGill AirClean Web Site

Tom,

Most of the things that you mentioned below can affect the performance of a DSI/FF emission control 

system. There are some others as well. 

Primary factors affecting acid gas reduction:

1. Temperature - dry injected calcium hydroxide typically reacts best at lower temperatures while 

sodium bi-carb is better at higher temps.

2. Flue gas moisture content - lime usually reacts better in higher moisture content gas streams. Does 

not affect bi-carb that much.

3. Reagent - particle size and surface area of the reagent. Sometimes it is necessary to mill sodium bicarb to get the best utilization. Reagent chemistry is also important although most reputable suppliers 

of either reagent typically have products with good chemistry.

4. Reaction time and mixing - good mixing of the reagent and the flue gas is important for higher 

removal efficiencies. We sometimes provide dry reaction chambers that provide mixing and retention 

time prior to entering the baghouse.

5. Stoichiometric ratio - increasing the reagent feed rate will sometimes improve the removal 

efficiencies although you can reach a point of diminishing returns. DSI is typically not as efficient at acid 

gas reduction or reagent usage when compared to a spray-dry absorber. An SDA still ends up with a dry 

product but the reagents are mixed with water and injected as a slurry or a solution and the flue gas 

heat evaporates the droplets. We put one of these at a Belden Brick plant in Sugarcreek, Ohio. I think it 

is the only SDA on brick kilns anywhere. That facility also has an ESP for particulate control as opposed 

to a fabric filter. It is probably the only facility at a brick plant with an ESP.

6. Fabric filter- with a FF there is a secondary reaction opportunity as the flue gas containing residual 

acid gases passes through the dustcake on the bags. A portion of this dustcake will contain unreacted 

lime or bi-carb because you will be injecting at stoichiometric ratios greater than 1:1. So, there will be 

some additional contact time and reactions at that point. Maintaining a good dustcake can help with 

the overall removal efficiencies. The bags should not be over cleaned which destroys too much of the 

dustcake and decreases the effect of this secondary contact. If the air-to-cloth ratio is too high, the 

baghouse may need to be cleaned too frequently in order to control the system pressure drop. So, the 

baghouse could be undersized. Felted bags typically provide the best dustcake formation. There are 

other factors to consider as well when making the fabric selection.

One or more of the above can affect the system performance. It is usually a combination of things that 

prevent a system from performing properly. If you have a specific site in mind, and could provide me 

with some information regarding the existing conditions, I would be glad to take a look and make some 

suggestions. 
Regards,

Gerald J. Childress, National Sales Manager McGill AirClean LLC

1777 Refugee Road

Columbus, Ohio 43207-2119

614/829-1350, Cell: 614/937-1816

Fax: 614/445-8759

-----Original Message-----

From: Holloway, Thomas C. (Tom) [mailto:tcholloway@rti.org]

Sent: Wednesday, April 24, 2013 1:55 PM

To: Childress, Jerry

Subject: RE: From McGill AirClean Web Site

Jerry,

Thanks for the referral to Norit. I have contacted them for further information about mercury removal 

efficiency for the brick industry.

Another question has come up from the brick industry that I hope you can help with, specifically what, if 

anything, can be done to improve the performance of an existing control system, in this case a dry 

sorbent injection system followed by a baghouse, for the control of acid gases (e.g., hydrogen fluoride, 

hydrogen chloride) and particulate matter. Is it as simple as 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, using larger/more efficient bags, or some other parameter adjustment? Are there 

limitations to what can be done to improve performance? Any assistance you can provide in answering 

these questions would be greatly appreciated. Thanks.

Tom Holloway

RTI International

3040 Cornwallis Rd., P.O. Box 12194

Research Triangle Park, NC 27709

Phone: (919) 316-3733

Fax: (919) 541-7155

E-mail: tcholloway@rti.org