1 innovative environmental solutions, inc

. **MEMORANDUM** Date: July

2 7 , 2011 To: Lisa Beal, INGAA From: Jim McCarthy and Jeff Panek , IES Inc. Re: Concentration versus distance profiles from reciprocating internal combustion engines

– Dispersion modeling re sults for two example engines from previous INGAA modeling. Emission impacts from reciprocating internal combustion engines (RICE) have been discussed in conjunction with ongoing negotiations regarding the RI CE NESHAP, 40 CFR 63, Subpart ZZZZ. In a recen t conference call, it was noted that RI CE dispersion modeling could be used to show concentration degradation versus distance plots for example RI CE

. In the call, it was noted t hat previously completed modeling may

be available to demonstrate how modeled ground

- level impacts decrease with distance from the stack. The concentration versus distance plots could thus support approaches being discussed for establishing a distance criterion for RI CE located in sparsel y populated areas

. IES completed dispersi on modeling for INGAA in 2002 and early 2003 during development of the original RICE NESHAP . That rule was proposed in December 2002 and promulgated in June 2004

. Although th e rule was a technology

- based standard, modeling was conducted to understand the range of modeled impacts from example engines to support comments on the proposed rule and discussion associated with the Industrial Combustion Coordinated Rulemaking process. Modeling was completed for two example reciprocating engines , and the effect o f stack height on modeled impact s was assessed

. Dispersion m odeling was completed using IS C3, the preferred EPA model at that time. A ssumptions associated with the two example s are : Example engine #1

– Natural gas

- fired lean burn engine

 800 hp capacity (modeling based on full load operation)

 30% efficiency

(i.e., 8 , 4 70 Btu/hp

- hr heat rate based on lower heating value)

 8% ox ygen in the exhaust (i.e., commensurate with 4

- stroke lean burn engine)

 700 o F exhaust temperature

 15 inch stack diameter

 18 ft stack height (“baseline”

– a range of stack heights were investigated)

 E xhaust velocity

based on the above parameters of 51.1 ft /sec Example engine # 2

– Natural gas

- fired rich burn engine

 1,0 00 hp capacity

(modeling based on full load operation)

 27 % efficiency (i.e., 9 , 400 Btu/hp

- hr heat rate based on lower heating value)

 0.5 % ox ygen in the exhaust (i.e., commensurate with 4

- stroke rich burn engine)

 1,0 00 o F exhaust temperature

 1 2 inch stack diameter

 1 2 ft stack height (“baseline”

– a range of stack heights were investigated)

 Associated exhaust velocity based on the above parameters of 9 1. 5 ft / sec2

The concentration versus distance plots for the two example engines are presented in two figures below. The concentration plotted is the maximum modeled 1

- hour averag e concentration associated with RI CE emissions. These graphs were developed in the 2002

– 2003 timeframe and were not created for this memo (e.g., not updated using AERMOD, the current ly preferred model) . The range of stack heights shown were modeled to assess the effect of stack height , and the taller heights modeled are not indicative of actual installation s or stacks that could actuall y be installed. Flat terrain was assumed for the modeling runs. Modeling was conducted using a “unitized” emission r ate of one gram per second. Pollutant

- specific impacts can easily be scaled based on proportionality to the unitized emission rate. Thus, the modeled impact (shown on the y - axis) is **not** based on any particular exhaust pollutant

. This is a standard approa ch for dispersion modeling when pollutant in

- plume reactions are not assumed

– i.e., the exhaust species does not change from the stack to the point of impact

– because it eliminates the need for multi ple, pollutant specific model runs

. In contrast, t his approach would not be appropriate for modeling NOx impacts when NO to NO 2 conversion reactions are assumed as the plume disperses downwind. When apply ing a unitized emission rates for modeling , impacts for an array of pollutants can be assessed b y scaling the modeled impact based on the actual emission rate for the pollutant(s) of interest , as compared to the unitized rate

. Actual RI CE hazardous air pollutant emission rates are much lower than 1 g/s. Th us, th e scale on the y - axis is not shown in the figu res below because it is not relevant

– i.e., the plots are intended to demonstrate how emission impacts degrade with distance rather than assess the impact for comparison to a threshold level

. The first figure shows con centration versus distance plot s f or the example lean burn engine . The second figure presents the rich burn engine results

. The RICE NESHAP discussions have considered different distances. When interpreting downwind impacts with distance on the x

- axis in the figures below, 402 meters is e quivalent to a quarter mile (i.e., the impact at 400 meters is indicative of a 1⁄4 mile radius). As expected, both figures show that increasing the stack height can significantly reduce the maximum modeled impact by

minimizing or eliminating the effects of structure
- related downwash . More import antly , for the recent RI CE NESHAP discussions, the distance plots show that higher modeled impacts (associated with shorter stacks) decrease rapidly with distance and the results converge over a relative ly short dist ance. For the example lean burn engine, maximum model predicted impacts from all stack heights investigated occurred at a distance of less than 50 meters (equivalent to 164 feet, 55 y ards and 1/32 nd of a mile). At a distance of 100 meters (equivalent to 328 feet, 109 ya rds and 1/16 th of a mile), higher impacts (from shorter stacks) are greatly diminished and at a distance of 150 meters (492 feet, 164 ya rds, just under 1/10 th of a mile) the impacts are minimal and indistinguishable for the broad range o f stack heights modeled. For the example rich burn engine, the maximum impacts from all stack heights investigated are predicted to occur at a distance less than 130 meters (equivalent to 427 feet, 142 y ards and 1/12 th of a mile) primarily

attributable to building “downwash”. At 200 meters (656 feet, 219 0 yards and 1/8 th of a mile), the higher impacts from shorter stacks are greatl y diminished and modeled impacts for various stack heights converge. At 400 meters (1312 feet, 437 y ards, 1⁄4 mile) the impac ts are minimal and indistinguishable for the broad range of stack heights modeled. The figures demonstrate the dispersion and rapid decrease in concentration with distance from “t ypi cal” engine s , and support the use of a distance criterion on the order of 1⁄4 mile or less

.3 **Lean Burn RICE: Concentration vs Distance for different stack heights**

**("unitized" emission rate used for modeling)**

**0 50**  **100 150**  **200 250**  **Distance (m) N** **o r** **m a** **l i** **z e** **d C** **o n** **c e** **n t** **r a** **t i** **o n** **( m** **g /** **m 3** **p e** **r g** **/ s** **) 15 foot**  **20 foot 25 foot**  **35 foot 50 foot**  **55 foot 70 foot**  **80 foot 115 foot**  **150 foot 180 foot** 

**Rich Burn RICE: Concentration vs Distance for different stack heights**

**("unitized" emission rate used for modeling)**

**0 50**  **100 150**  **200 250**  **300 350**  **400 450**  **Distance (m) N** **o r** **m a** **l i** **z e** **d C** **o n** **c e** **n t** **r a** **t i** **o n** **( m** **g /** **m 3** **p e** **r g** **/ s** **) 10 foot**  **15 foot 22 foot**  **35 foot 60 foot**  **80 foot**