Colorado Department of Public Health and Environment - Air Pollution Control Division

Reasonable Progress Evaluation for RICE Source Category Page 1

RECIPROCATING INTERNAL COMBUSTION ENGINE (RICE) SOURCE 

CATEGORY

NOx Emission 4-Factor Analysis for Reasonable Progress (RP)

I. Source Description

The review of potential RP sources involved an evaluation all Colorado stationary sources with

actual SO2, NOx or PM10 emissions over 100 tons per year based on Air Pollution Emissions 

Notice (APEN) reports from 2007. There were one-hundred-thirteen (113) sources identified as 

exceeding the 100 tons/year threshold for any of the three pollutants which were further 

analyzed, using ArcGIS mapping, to determine the exact distance from the centroid of the source 

to the nearest Class I Area (CIA) boundary. The Q/d was calculated for each source, where “Q” 

is the sum of the SO2, NOx and PM10 emissions in tons per year and “d” is the source distance 

from the nearest CIA in kilometers; which resulted in the identification of seventeen (17) point 

sources with a Q/d 20. The Q/d threshold was determined based on conducting a sensitivity 

analysis of previous subject-to-BART CALPUFF modeling of BART eligible sources that 

indicated a value of 20 represented about 0.3 deciview of change in visibility impairment.

An evaluation of the 17 RP sources identified only one source directly associated with RICE 

equipment, a compressor station (Ignacio B Plant) that uses natural gas-fired RICE. The Ignacio 

B compressor station is located southeast of Durango on Southern Ute Indian Tribal land which 

is outside the jurisdiction of the State of Colorado; consequently the Division is unable to 

provide a 4-factor NOx control evaluation and associated determination for this particular RP

source.

In addition to individual point sources with a Q/d 20, the Division evaluated categories of 

sources that were determined to be significant and subject to evaluation under RP. The Colorado 

point source emission inventory indicates that stationary internal combustion engines (see below 

table), particularly large industrial natural gas fired reciprocating internal combustion engines

(RICE), are a significant source category of NOx emissions that represents about 16% of 

statewide point source NOx emission inventory1. 

Colorado Internal Combustion Engine NOx Emissions from the PRP 2018b Emission Inventory

Category Subcategory 2018 NOx Emissions (tpy)

Industrial

Natural Gas Fired 16,199

Large Bore Engine 256

Distillate Oil (Diesel) 225

Liquefied Petroleum Gas 27

Gasoline 24

Electric Generation All 4,323

Commercial/Institutional All 1,152

Engine Testing All 5

Total: 22,210

 

1 Total 2018 Statewide Point Source NOx is projected at 101,818 tons per year based on the WRAP PRP2018b 

emission inventory.
Colorado Department of Public Health and Environment - Air Pollution Control Division

Reasonable Progress Evaluation for RICE Source Category Page 2

The majority of the RICE operating in Colorado are associated with the oil and gas industry. 

The power generated by these RICE is generally used to compress natural gas for line 

transmission or to generate electricity in remote locations. The designation “large” refers to 

RICE that have an engine rating of at least 100 horsepower (hp) for the purpose of this 

document.

Stationary RICE produce power by combustion of fuel and are operated at various air-to-fuel 

ratios (AFR). If the stoichiometric ratio is used, the air and fuel are present at exactly the ratio to 

have complete combustion. An air-to-fuel ratio controller uses exhaust O2 to control the 

combustion ratio. RICE that are operated with fuel-rich ratios (exhaust O2 < 0.05%) at or near 

stoichiometric, are called rich-burn engines (RB), or alternatively RICE that operate with air-rich 

ratios (exhaust O2 > 7 to 8%) above stoichiometric, are called lean-burn engines (LB). The 

undesirable combustion emissions from natural gas fired RICE are primarily nitrogen oxides 

(NOx, consisting of primarily nitric oxide and nitrogen dioxide), carbon monoxide (CO), and 

volatile organic compounds (VOCs). Oxides of nitrogen are formed by thermal oxidation of 

nitrogen from the air. CO and VOCs are byproducts of incomplete combustion.

There are site specific considerations for using either type of engine, depending on the

parameters that are most important for the operator. RB engines have lower oxygen levels and 

higher temperatures in the engine exhaust, which allows for the use of a 3-way catalyst (nonselective catalyst) which is effective at reducing NOx, CO, and VOCs in the exhaust. Because 

the air-to-fuel ratio is rich with fuel, more fuel is used, which results in increased combustion

temperatures, increased engine power, and decreased engine efficiency. Higher temperatures 

result in more NOx being formed during the combustion process. Conversely, LB engines have 

higher oxygen levels in the combustion chamber, which decreases the combustion temperature

thereby reducing how much NOx is formed. Because the air-to-fuel ratio is lean with fuel, less 

fuel is used, which results in decreased combustion temperatures, decreased engine power, and 

increased engine efficiency. The use of an oxidation catalyst on a lean burn engine similarly 

results in decreases in CO and VOC emissions but the performance for controlling NOx
Colorado Department of Public Health and Environment - Air Pollution Control Division

Reasonable Progress Evaluation for RICE Source Category Page 3

emissions is very low because LB engine exhaust temperatures are below the optimum 

temperature range for effective NOx control due to reduced catalyst reactivity. The above chart 

provides the relative change in NOx emissions and engine exhaust temperature as a function of 

air-to-fuel ratio.

II. Natural Gas-Fired RICE Source Category Emissions - Statewide

Since natural gas-fired RICE comprise over 73% of the NOx emissions in statewide RICE source 

category, the analysis will focus exclusively on NG-fired RICE. In 2018, the statewide NG-fired 

RICE source category is projected to contribute the following emissions:

Statewide Natural Gas Fired RICE Source Category Emissions*

Total Number of 

Sources with 

NG-fired RICE

Pollutant

Number 

Sources with 

RICE

> 100 tpy

Number 

Sources with 

RICE

> 40 tpy

Number 

Sources 

with RICE

< 2 tpy

2018 

Emissions 

(tpy)

497

NOx 40 85 82 16,199

SO2 0 0 486 115

* Point Source Natural Gas Fired RICE Emissions based on APEN report data supplied to the WRAP for the 

PRP2018b Emission Inventory.

Based on the PRP 2018b emission inventory, statewide there are about 497 sources using NGfired RICE and about 40 sources that emit NOx emissions greater than 100 tons per year. During 

a recent 2008 rulemaking, the Division conducted a detailed analysis of RICE outside the 9-

county metro area (referenced as “statewide”) and determined that there are about 1,340 NGfired RICE statewide2

, which includes about 593 NG-fired RICE over 500 hp as indicated in the 

below table.

Statewide Natural Gas-Fired RICE Over 500 Horsepower Outside the 9-County Metro Area

SCC Description Number of RICE

2-CYCLE LEAN BURN (NG) 84

4-CYCLE LEAN BURN (NG) 204

4-CYCLE RICH BURN (NG) 305

Total: 593

In addition to the 593 RICE listed above, the 2004 Denver Early Action Compact rulemaking 

identified 139 NG-fired RICE3over 500 hp that were subject to control requirements of nonselective catalytic reduction on 79 RB RICE and oxidation catalyst on 60 LB RICE in the 9-

county metro area. Consequently, there are a total of 732 NG-fired RICE over 500 hp in 

Colorado.

It is difficult to readily determine the exact number of NG-fired RICE below 500 hp but over 100 

hp because engines were sometimes grouped together in a single permit. However, a preliminary 

review of APEN data indicates that there are approximately 234 NG-fired RICE below 500 hp 

but over 100 hp. The remaining 513 NG-fired RICE have design capacities under 100 hp.

 

2 The Statewide RICE count does not include RICE in the 9-county metro area which was subject to an earlier 

rulemaking, thus the actual number of total RICE in the State of Colorado is higher.

3 Reference Final Economic Impact Analysis – Revisions to Regulation No. 7, February 11, 2004.
Colorado Department of Public Health and Environment - Air Pollution Control Division

Reasonable Progress Evaluation for RICE Source Category Page 4

III. NOx Control Technology Evaluation

Step 1: Identify All Available Technologies

Generally in retrofit applications, NOx emissions from engines can be reduced either through 

combustion controls or adding post combustion emission controls (e.g., catalysts) to the engine 

exhaust. Catalysts are designed to speed up desired reactions. The rate of chemical reaction is a 

function of several parameters, including air-to-fuel ratio, engine load and exhaust temperature. 

Catalysts have specific temperature ranges that must be achieved for optimum NOx reduction. 

The below diagram roughly depicts the catalyst performance for conversion of NOx emissions 

using a NSCR and SCR on rich and lean burn engines.

Six retrofit technologies have been identified to lower NOx emissions from rich/lean burn 

natural gas-fired internal combustion engines.

1. Lean Burn – Air/Fuel Ratio Adjustment

2. Lean Burn – Ignition or Spark Timing Retard

3. Rich Burn – Non Selective Catalytic Reduction (NSCR) Catalyst (3-way)

4. Rich/Lean Burn – Selective Non-Catalytic Reduction (SNCR)

5. Lean Burn – Selective Catalytic Reduction (SCR)

6. Replacement with electric motors

Colorado requires that emissions from rich burn RICE (applicable statewide4) be controlled 

using a 3-way catalyst (NSCR) with air/fuel controller if control costs are below $5,000 per ton. 

Few of the statewide rich burn RICE demonstrated control costs exceeding the $5,000 cost offramp. Consequently, the state concludes that such NSCR controls are installed on the majority 

of rich burn RICE over 500 HP statewide. Therefore, the following analysis does not evaluate 

lower benefit NOx controls such as air/fuel adjustment or ignition/spark timing adjustment for 

rich burn RICE despite the technical feasibility of such controls.

 

4 Reference Colorado Regulation Number 7, see section XVII.E.3.a
Colorado Department of Public Health and Environment - Air Pollution Control Division

Reasonable Progress Evaluation for RICE Source Category Page 5

It is important to clarify that lean burn RICE are not subject to NOx retrofit controls because

Regulation 7 requires statewide lean burn RICE over 500 HP to install retrofit oxidation catalyst 

control, which is only effective for control of VOC and CO, if the VOC control cost is under 

$5,000 per ton. This Regulation was effective as of July 1, 2010.

Step 2: Eliminate Technically Infeasible Options

Technology #1 - LB (Air/Fuel Ratio Adjustment): This technology is technically feasible.

Technology #2 - LB (Ignition/Spark Timing Retard): This technology is technically feasible.

Technology #3 – RB (3-way NSCR Catalyst): This technology is technically feasible.

Technology #4 – RB/LB (SNCR): This technology is technically feasible.

Technology #5 – LB (SCR): This technology is technically feasible.

Technology #6 – Replace RICE with electric motors: This technology is technically feasible.

Step 3: Evaluate Control Effectiveness of Each Remaining Control Technology

Technology #1 - Lean Burn (Air/Fuel Ratio Adjustment): In lean burn engines, increasing the air 

to fuel ratio decreases the NOx emissions. Extra air dilutes the combustion gases, thus lowering 

peak flame temperature and reducing thermal NOx formation. In order to avoid de-rating, 

combustion air to the engine must be increased at constant fuel flow, requiring a turbocharger. 

An automatic air-to-fuel ratio controller also will be required. This control method is most 

effective on fuel-injected engines. Typically, for lean burn engines the air/fuel ratios are 

increased from normal levels of 50% excess air up to excess air levels of 240%. The upper limit 

is constrained by the onset of misfiring at the lean limit. This condition also increases CO and 

VOC emissions. Naturally aspirated engines and engines with fuel injected into the intake 

manifold plenum do not have identical air-to-fuel ratios in each cylinder, this results in limited 

ability to vary the A/F ratio. To maintain acceptable engine performance at lean conditions, high 

energy ignition systems (HEIS) have been developed that promote flame stability at very lean 

conditions. On lean burn RICE, air/fuel ratio adjustment generally achieves about 5-30% 

reduction5in NOx emissions but is very specific to each engine and typical loading.

Technology #2 - Lean Burn (Ignition/Spark Timing Retard): This adjustment lowers NOx 

emissions by moving the ignition event to later in the power stroke. Because the combustion 

chamber volume is not at its minimum, the peak flame temperature will be reduced, thus 

reducing thermal NOx formation. Ignition timing retard is applicable to all engines. It is 

implemented in spark ignition engines by changing the timing of the spark, and in compression 

ignition engines by changing the timing of the fuel injection. For variable loads, an electronic 

ignition/injection control system is required. On lean burn RICE, ignition/spark timing retard 

generally achieves about 20% reduction in NOx emissions.

Technology #3 - Rich Burn NSCR: This technology uses three-way catalysts to promote the 

reduction of NOx to nitrogen and water. CO and hydrocarbons are simultaneously oxidized to 

carbon dioxide and water. NSCR is applicable only to rich burn engines (i.e. those with exhaust 

oxygen concentration below about one percent). NSCR, in addition to the catalysts and catalyst 

 

5 Reference – State of the Art (SOTA) Manual for Reciprocating Internal Combustion Engines, State of New Jersey 

Department of Environmental Protection, 2003.
Colorado Department of Public Health and Environment - Air Pollution Control Division

Reasonable Progress Evaluation for RICE Source Category Page 6

housing, require an oxygen sensor and automatic air to fuel ratio controller to maintain an 

appropriate air to fuel ratio. Some ammonia can be produced particularly as the catalyst ages. 

The simplified reactions governing NSCR are as follows:

NOx + CO  CO2 + N2

NOx + HC  CO2 + H2O + N2

The exhaust passes over a catalyst, usually a noble metal (platinum, rhodium or palladium) 

which reduces the reactants to N2, CO2 and H20. Typical exhaust temperatures for effective 

removal of NOx are 800-1200 degrees Fahrenheit. An oxidation catalyst using additional air can 

be installed downstream of the NSCR catalyst for additional CO and VOC control. This includes 

4-cycle naturally aspirated engines and some 4-cycle turbocharged engines. Engines operating 

with NSCR require air/fuel control to maintain high reduction effectiveness typically around 80 

to 90 percent NOx control. Extremely tight control of the air to fuel ratio operating range is 

accomplished with an electronic air to fuel ratio controller.

Technology #4 - Rich/Lean Burn SNCR: SNCR is applicable to both lean burn natural gas and 

diesel engines. SNCR involves injecting ammonia or urea into regions of the exhaust with 

temperatures greater than 1200 – 2000 degrees Fahrenheit. The nitrogen oxides in the exhaust 

are reduced to nitrogen and water vapor. Additional fuel is required to heat the engine exhaust to 

the correct operating temperature. Heat recovery from the engine exhaust can limit the 

additional fuel requirement and concurrent additional emissions from heating exhaust gases. Ten 

parts per million of ammonia (slip) is considered reasonable for SNCR. Temperature is the 

operational parameter affecting the reaction - as well as degree of contaminant mixing with 

reagent and residence time. Additional control of particulate matter (up to 85% diesel particulate 

matter), volatile organic compounds (up to 90 percent) and carbon monoxide (up to 70 percent) 

may be realized by the afterburning effect of this technology. On both rich burn and lean burn 

RICE, SNCR generally achieves about 50 to 95% reduction in NOx emissions.

Technology #5 – Lean Burn SCR: SCR uses catalyzed reduction of NOx with injected ammonia 

or urea solution. This technology is applicable to lean burn engines only (i.e., those with greater 

than about one percent exhaust oxygen, as oxygen is a reagent in the selective reduction 

reaction.) SCR may be used with lean burn (SI), dual fuel or diesel engines (CI). SCR produces 

unreacted ammonia (slip) and monitors are necessary to provide correct control of ammonia 

injection rates to minimize slip. When used with diesel engines, it is important to use a low 

sulfur fuel and sulfur resistant catalyst. Sulfur dioxide in the exhaust can be oxidized over the 

SCR catalyst to sulfuric acid mist, and when combined with unreacted ammonia, produces 

sulfate particulate.

For an SCR system using urea, the first stage of the catalyst bed is the hydrolysis catalyst, which 

converts the urea to ammonia. In the second stage of the catalyst, the ammonia and NOx react to 

form nitrogen gas and water with some unreacted ammonia passing through. Base metal 

catalysts, typically vanadium and titanium, are used for exhaust gas temperatures between 450oF 

and 800 oF. For higher temperatures (675 oF to 1100 oF), zeolite catalysts may be used. Both the 

base metal and zeolite catalysts are sulfur tolerant for diesel engine exhaust. Precious metal SCR 

catalysts are useful for low temperatures (350 oF to 550 oF). When using precious metal SCR 

catalysts, attention should be paid to the fuel sulfur content and the appropriate formulation 

selected. This is not a concern with RICE fired with natural gas.
Colorado Department of Public Health and Environment - Air Pollution Control Division

Reasonable Progress Evaluation for RICE Source Category Page 7

Reactions of NOx over SCR catalyst:

6NO2 + 8NH3  7N2 + 12H2O

6NO + 4NH3  5N2 + 6H2O

4NO + 4NH3 + O2  4N2 + 6H2O

2NO + 4NH3 + 2O2  3N2 + 6H2O

An SCR system consists of reagent storage, feed and injection system, and a catalyst and catalyst 

housing. Predictive mapping of engine operating parameters can be used to monitor and control 

the SCR reaction. Precious metal catalysts can reduce NOx by 80%. Zeolite catalysts can 

reduce NOx by 90% with minimal sulfur dioxide to sulfur trioxide conversion. Exhaust gas 

temperatures greater than the upper limit (850 F) will pass the NOx and ammonia unreacted 

through the catalyst.

Technology #6 – Replace RICE with electric motors: This control technology results in 

complete reduction of NOx emissions at the RICE location, although the electric power provided 

to the motor must be supplied by a power plant located at some distant location. There is a net 

reduction in NOx emissions from consolidating operations although the amount of reduction 

depends on the distance from the power plant as transmission line losses reduce the effectiveness 

of this control. Another consideration is the proximity to high voltage lines which may limit the 

practically of this control option in rural areas.

The below table summarizes each available technology and the technical feasibility for NOx 

Control.

NG-Fired RICE – NOx Technology Options and Technical Feasibility

Technology Emission Reduction 

Potential (%)

Technically Feasible?

(Y = yes, N = no)

Lean Burn (Air/Fuel Ratio Adjustment) 5-30% Y

Lean Burn (Ignition/Spark Timing Retard) 20% Y

Rich Burn NSCR 80-90% Y

Rich/Lean Burn SNCR 50-95% Y

Lean Burn SCR 80-90% Y

Replace RICE with electric motors 60-100% Y

Step 4: Evaluate Impacts and Document Results

Factor 1: Cost of Compliance

Technology #1 - Lean Burn (Air/Fuel Ratio Adjustment): In naturally aspirated LB engines and 

LB engines where fuel is injected into the intake manifold plenum, each cylinder does not have 

an identical air-to-fuel ratio, thus changes in the A/F ratio are very limited and therefore of little 

benefit, although the cost of such adjustment is minimal. Additional NOx emission reduction 

benefit is gained through the addition of a turbocharger and an automatic air-to-fuel ratio 

controller. The cost of adding these controls is very specific to the engine size and design but 

generally ranges between $320 to $8,300 per ton6of NOx reduced.

 

6 Reference – Supplementary Information for Four Factor Analysis by WRAP States, EC/R Incorporated, May 4, 

2009, see table 3-3.
Colorado Department of Public Health and Environment - Air Pollution Control Division

Reasonable Progress Evaluation for RICE Source Category Page 8

Technology #2 - Lean Burn (Ignition/Spark Timing Retard): Based on a general analysis of NG 

fired RICE for the WRAP states4, the cost of this control ranges between $310 to $2,000 per ton 

of NOx depending on engine size and firing design.

Technology #3 - Rich Burn NSCR: Regulation Number 7 requires rich burn RICE over 500 HP 

to install retrofit NSCR controls if the cost of control is under $5,000 per combined ton (NOx 

and VOC) statewide. This Regulation was effective as of July 1, 2010. None of the operators of

rich burn RICE outside the metro-area ozone non-attainment area submitted information 

demonstrating control costs in excess of $5,000 per ton cost threshold, consequently, the 

majority of natural-gas fired RB RICE over 500 HP must operate an NSCR with an AFR

controller.

Emission Reduction from NSCR Retrofit of RICE > 500 hp

Statewide RICE Category* Count** NOx Reduction (tpy)

Lean Burn 500 HP 288 minimal***

Rich Burn 500 HP 305 5,800

Notes:

* This data represents statewide RICE, excluding the 9-county metro area (ozone non-attainment area) which 

was addressed in an earlier rulemaking for the Early Action Compact.

** Data obtained from 2008 APENs

*** Retrofit NSCR for lean burn RICE was not required because of minimal NOx reduction

Annualized Costs for Rich Burn RICE Control Device

Item Capital Costs 

(one time)

O&M 

(recurring)

Total Annualized 

Cost

(15 yrs)

NSCR with AFR Controller* $35,000 -

$10,851

Operating - $6,000

Subtotal Costs: $35,000 $6,000

Annualized Costs: $4,851 $6,000

Notes:

* Cost estimates obtained from "Denver Early Action Compact Analysis of Stationary Sources" Nov. 3, 2003

Costs Associated with Statewide Retrofit of Natural Gas-fired RB RICE ≥ 500 HP

Category Number of 

Devices

Annualized 

Cost per Device

Total Device 

Cost

NOx Reduction 

[tpy] $/ton

NSCR & AFR 

Controller 305 $10,851 $3,309,555 5,800 $571

Technology #4 - Rich/Lean Burn SNCR: SNCR usually requires reheating of the exhaust to 

achieve the proper temperature range for effective NOx conversion; this is particularly true for 

lean burn RICE where excess oxygen results in exhaust temperatures well below the required 

levels. The Division was unable to acquire cost information for this control option, thus no cost 

estimates have been provided. The scarcity of SNCR data on NG-fired RICE may suggest other 

post combustion NOx controls are preferred, particularly SCR which has more reliable control 

effectiveness under a variety of load conditions.
Colorado Department of Public Health and Environment - Air Pollution Control Division

Reasonable Progress Evaluation for RICE Source Category Page 9

Technology #5 – Lean Burn SCR: Depending on the engine size, catalyst used and the level of 

sophistication of the control system, SCR costs generally range about $430 to $4,900 per ton of 

NOx reduced.

Technology #6 – Replace RICE with electric motors: Depending on the engine size, length and 

capacity of the power line required, the costs generally range from $100 to $4,700 per ton of 

NOx reduced7. These costs do not include any potential impact from increases in electrical load 

at the power plant. The true cost of replacing RICE with electric motors is dependent on the 

distance from the power plant and the amount of compression power required. In actuality, 

larger compressor stations with multiple large engines would produce significant increased 

demands at a nearby power plant and possibly significant demands on the line transmission 

system that would escalate the costs to levels much higher than the $4,700 control cost. 

Colorado has about 40 large compressor stations, thus the estimation of costs would require a 

case-by-case analysis which was not done for this RP evaluation. Although, if all statewide 

RICE (above 500 horsepower) were converted to electric motor compression, then a minimum of 

approximately 600 MW of extra generating capacity would be required. Realistically, the actual 

generating capacity required is probably much higher when transmission losses and peak demand 

cycles are factored into the load demands.

Factor 2: Time Necessary for Compliance

Technology #1, 2, 4, 5 and 6: If Colorado was to decide to adopt a particular control strategy, up 

to 2 years will be needed to develop the necessary rules and undergo Legislative review. Subject 

sources may then require up to a year to procure the necessary capital to purchase control 

equipment. The Institute of Clean Air Companies (ICAC) has estimated that approximately 13 

months is required to design, fabricate, and install SCR or SNCR technology for NOX control8.

However, the time necessary will depend on the type and size of the unit being controlled. For 

instance, in past rulemakings, typically 18 months may be required to install a particular control 

technology on hundreds of engines. Additional time, up to 12 months may be required for 

staging the installation process if multiple sources are to be controlled at a single facility. Based 

on these figures, the total time required achieve the NOx emission reductions for reciprocating 

engines is estimated at about 5 years.

Technology #3: This control option is implemented and was effective on July 1, 2010.

Factor 3: Energy Impacts and Non Air-Quality Impacts

In general, air-to-fuel-ratio adjustments and ignition retarding technologies have been found to 

increase fuel consumption by up to 5%, with a typical value9of about 2.5%. This increased fuel 

consumption would result in increased CO2 emissions. Installation of SCR on any type of engine 

would cause a small increase in fuel consumption, about 0.5%, in order to force the exhaust gas 

through the catalyst bed. This would produce an increase in CO2 emissions. In addition, spent 

 

7 Bar-Ilan, Amnon, Ron Friesen, Alison Pollack, and Abigail Hoats (2007), WRAP Area Source Emissions Inventory 

Protection and Control Strategy Evaluation - Phase II, Western Governors Association, Denver, Colorado, Chpt 4.

8

Institute of Clean Air Companies (2006), Typical Installation Timelines for NOx Emissions Control Technologies 

on Industrial Sources.

9 Center for Alternative Fuels, Engines & Emissions (2005), Alice Austen Ferry Emissions Tests, M.J. Bradley & 

Associates, Manchester, NH, Page 13.
Colorado Department of Public Health and Environment - Air Pollution Control Division

Reasonable Progress Evaluation for RICE Source Category Page 10

catalyst would have to be changed periodically, producing an increase in solid waste disposal10. 

Replacing RICE with electric motors may require construction of additional power plants to 

accommodate increased power demands.

Factor 4: Remaining Useful Life:

Generally the operational life of a catalyst is approximately 5 to 15 years, depending upon 

factors such as how it is maintained and the particular duty cycle of the engine.

Step 5: Select Reasonable Progress Control

The state has determined that control technology #3, rich burn NSCR w/air-fuel controller, 

represents reasonable progress for the natural gas-fired RICE source category in this planning 

period. The estimated reduction of 5,800 tons/year represents about 36% of the NG RICE total 

NOx emissions.

The State of Colorado regulates RICE under Colorado Air Quality Control Commission 

Regulation No. 7 (Reg. 7) Section XVII. Further NOx emission reduction benefits are 

anticipated in the future because of tighter NOx emission standards in Regulation 7 that require 

emissions from RICE shall not exceed the following emission performance standards:

Colorado Emission Standards Natural Gas-Fired RICE

RICE 

Horsepower Construction or Relocation Date

Emission Standards (grams/hp-hr)

NOx CO VOC

< 100 Any NA NA NA

≥ 100 and ≤ 500

On or after 1/1/08 2.0 4.0 1.0

On or after 1/1/11 1.0 2.0 0.7

> 500

On or after 7/1/07 2.0 4.0 1.0

On or after 7/1/10 1.0 2.0 0.7

RICE that are subject to an emissions control requirement in a federal Maximum Achievable 

Control Technology (MACT) standard under 40 CFR Part 63, a Best Achievable Control 

Technology (BACT) limit, or a New Source Performance Standard under 40 CFR Part 60 are not 

subject to Reg. 7 Section XVII.

 

10 EPA (2002), EPA Air Pollution Control Cost Manual, 6th ed., EPA/452/B-02-001, U.S. EPA, Office of Air 

Quality Planning and Standards, RTP.