December 18, 2015

EPA Docket Center 

WJC West Building

Environmental Protection Agency

Mailcode 28221T

1200 Pennsylvania Ave., NW

Washington, DC 20460 

RE: Docket ID No. EPA–HQ–OAR–2015-0341, Notice of Availability of the 

Environmental Protection Agency’s Update of Two Chapters in the 

EPA Air Pollution Control Cost Manual (80 Fed. Reg. 33515 (June 12, 

2015))

The Institute of Clean Air Companies (ICAC) is submitting comments in response to the 

October 21, 2015 letter from Mr. Larry Sorrels. The questions from the October 21 

letter are restated along with the ICAC responses for each item.

Section 1.2.4 SNCR System: ICAC noted that this section was out of date and could 

provide input for making revisions. We invite you to offer material suitable for a 

rewritten draft of the revised section, or a written statement of what the SNCR 

background section should include.

ICAC Response: In general the section provides a good general description of an 

SNCR System. However, there are different configurations provided by individual

SNCR providers that may utilize different approaches. There are several paragraphs 

noted below that have been redlined to show the suggested changes to this section.

A. The first paragraph of Section 1.2.4 on Page 1-20 should be modified as follows:

There are were two original basic designs for the application of SNCR. The first is was

an ammonia based system known as Thermal DeNOx that was developed and patented 

by Exxon Research and Engineering Company in 1975. The second system was 

developed and patented by the Electric Power Research Institute (EPRI) in 1980. It is a 

urea-based process known by the trade name NOx OUT. The technology was originally 

licensed to Fuel Tech, which holds held several additional patents that claimed

improvements and enhancements to the basic process. Since that time, there have 

been a number of variations and improvements to the urea SNCR process, which are 

noted earlier in Section 1.2. Fuel Tech has several sub-licensees authorized to 

supply and install SNCR technology in several industrial sectors. 

An SNCR system has four basic steps to accomplish: 
2

 Receiving and storing the reagent; 

 Diluting, metering, and mixing the reagent; 

 Injecting diluted reagent at appropriate locations in the boiler; and 

 Mixing the reagent with flue gas. 

These steps are common to both urea and ammonia SNCR; however, the design and 

equipment specifications for the two systems are different, because anhydrous 

ammonia based systems use the injection of is injected as a vapor while urea is injected 

as an aqueous solution. Aqueous ammonia based SNCR systems are very similar to 

aqueous urea systems in terms of the overall system approach of injecting a solution, 

and therefore are similar in terms of equipment. Anhydrous and aqueous ammonia 

based systems can be effective on units where the injection temperatures are in the 

range of 1600-1800F. However, Uurea is typically used in large boiler applications of 

SNCR because it is safer to store, and has better dispersion properties, and can use

urea droplet evaporation for effective injection at much higher temperatures found in 

utility furnace applications. Ammonia based systems have been effective on industrial 

boilers and some fluidized bed utility boilers, but urea is the dominant reagent for utility 

furnace applications. . A discussion of the SNCR equipment is given below. Figure 1.9 

presents a simplified system flow schematic and Table 1.5 lists the equipment 

requirements for urea-based SNCR.

B. Second bullet on Page 1-24 under the heading of Injectors

 Wall injectors are attached to the inner wall of the boiler at specified locations. 

There is generally one nozzle for each injector location. Wall injectors are used in 

smaller boilers and urea based systems, where short-range injection is sufficient 

to mix the reagent with the flue gas. They have a longer operating life than lance 

injectors because they are not directly exposed to hot flue gas. Wall injectors 

can either be use air or mechanical atomization prior to injection.

C. Last paragraph of Section 1.2.4, Page 1-25

The reagent injection systems used for anhydrous ammonia-based systems are 

generally more complicated and expensive than those used in urea-based systems [29]. 

These systems inject gas-phase ammonia rather than an aqueous solution. For this 

reason, anhydrous ammonia-based systems often use high-energy lance systems with 

multiple injectors. The lances are placed in a grid formation across the width and height 

of the boiler passes.
3

Figure 1.10, Approximate NSR Estimation for Urea: ICAC noted it could share more 

recent data related to the relationship between NSR and desired NOx reduction, 

particularly for inlet NOx concentrations below 0.5 lb/MMBtu. We are interested in 

receiving the data that is referred to in this comment.

ICAC Response: After reviewing Figure 1.10, ICAC would recommend using the urea 

utilization calculation from Page 4 of the final version of the IPM Model – Updates to 

Cost and Performance for APC Technologies SNCR Cost Development Methodology, 

dated March 2013, which was prepared by Sargent and Lundy with funding from EPA, a 

copy of which is attached for convenience. We believe that this general calculation 

provides a good estimating tool for urea utilization. There are a number of parameters 

which affect actual utilization including boiler geometry, furnace temperatures, 

residence time, and combustion conditions. An estimate on a case by case basis by an 

experienced technology provider is suggested beyond the basic tool used in the IPM 

model, which is based on more recent information than Figure 1.10.

Thank you for your consideration of these comments. Please feel free to contact Haley 

Armstrong, ICAC, at (202) 478-6188 if you have questions or need more information. 

Sincerely,

Betsy Natz

ICAC Executive Director

cc: L. Sorrels, EPA