BASIN ELECTRIC 

POWER COOPERATIVE 

171 7 EAST INTERSTATE AVENUE 

BISMARCK. NORTH DAKOTA 58503-0564 

PHONE 701 -223-0441 

FAX: 7011224-5336 

February 25,2009 

Mr. David Finley, Administrator 

Air Quality Division 

WY Department of Environmental Quality 

122 West 25th Street 

Herschler Building 

Cheyenne, WY 82002 

Dear Mr. Finley, 

The Department of Environmental Quality (DEQ) notified Basin Electric in June 2006 that the 

Laramie River Station (LRS) was a Best Available Retrofit Technology (BART) applicable source, 

which required a BART engineering and modeling analysis for reducing visibility impacts in 

accordance with the Environmental Protection Agency's Guidelines for BART Determinations under 

the Regional Haze Rules (40 CFR Part 51). Visibility impacts for LRS were evaluated at two 

Federal Class I areas -- Badlands National Park and Wind Cave National Park. 

A BART review was required to identify the best retrofit technology for the reduction of nitrogen 

oxides (NOx), sulfur dioxide (SO2), and particulate matter (PM) emissions from Laramie River 

Station Units 1, 2 and 3. Basin Electric contracted Black & Veatch to conduct a BART analysis to 

identify technically feasible and cost-effective technologies following the BART Guidelines. A 

modeling analysis was completed to evaluate the impact on visibility in the two identified Class I 

areas. Reports and subsequent revisions of the BART analyses were submitted to your office on 

February 28, 2007; September 25, 2007; February 14, 2008; and July 24, 2008. 

As a result of several discussions between Basin Electric and DEQ, Basin Electric proposes a 

BART limitation for NOx emissions on a plant-wide 30-day rolling average based on a pound-perhour limitation of 4,082 pounds per hour for the station. 

We are proceeding with our plans to install over-fire air (OFA) on Unit 1 this spring, Unit 2 in the 

spring of 2010, and on Unit 3 in the spring of 201 1. In addition, we plan to upgrade to Low-NOx 

Burners (LNB) on Units 1, 2, and 3 in 2012, 2013, and 2014, respectively. While we anticipate 

emissions of 0.18 IbImmBtu under ideal operating conditions, normal emissions are likely to be 

higher. Please see the attached letter from our OFA contractor, Burns & McDonnell. A letter is also 

attached from Black & Veatch, who performed our BART analysis, with their company's perspective 

on NOx emission rates with LNBIOFA. 

After Basin Electric and DEQ agree on a plan, we will present it to the Missouri Basin Power Project 

(MBPP) management and ask approval from the project owners. 

A Touchstone Energym Cooperative 63 - 

Equal 

Employment 

opporruniiy 

Employer 
February 25, 2009 

Page 2 

If you have any questions, please contact me at 701-557-5654 or Lyle Witham at 701-557-5652. 

Sincerely, 

Robert L. Eriksen, P.E. 

Sr. Environmental Compliance Administrator 

/g mj 

Enclosures 

cc: Chad Schlichtemeier, DEQ 

Mike Fluharty 

David Cummings 

Lyle Witham 
BLACK & VEATCH 

MEMORANDUM 

Basin Electric Power Cooperative B&V Project 145423 

Laramie River Station B&V File 30.0000 

LNB and OFA Control Effectiveness February 24, 2009 

On September 27, 2007, Basin Electric Power Cooperative (BEPC) submitted the Best 

Available Retrofit Technology (BART) report for Laramie River Station (LRS), which 

identifies the control effectiveness for NOx after the retrofit of low NOx burners (LNB) 

and over-fire air (OFA) at the three LRS units. The BART analysis was prepared by 

Black & Veatch (B&V) for BEPC. 

LRS Units 1, 2, and 3 each have a 550 MW (net) capacity and are equipped with 

Babcock & Wilcox (B&W) sub-critical boiler and opposed-wall fired burners. In the 

BART report, LNB with OFA have been identified as a technically available and 

applicable control technology for the reduction of NOx emissions from the LRS units. 

The baseline NOx emission rate from the LRS units based on continuous emissions 

monitoring (CEM) annual emissions averages from 2001 to 2003 is 0.27 lb/MBtu. 

In the BART report, the control effectiveness for LNB with OFA of 0.15 lb/MBtu was 

determined based on the results of a computational fluid dynamics (CFD) modeling study 

commissioned by BEPC and completed by a third party combustion modeling expert in 

2004. The CFD model study simulated the effects of adding and optimizing OFA ports 

specifically for the LRS units. 

Wall fired units are typically fitted with numerous burners mounted on the front and/or 

rear wall of the furnace. Each burner is fed coal, primary air and secondary air to safely 

and efficiently burn the pulverized coal fed to that burner. Primary air is the carrier for 

the pulverized coal fed to that individual burner and secondary air is typically fed to the 

periphery of the coal and primary air stream to provide sufficient oxygen for complete 

combustion of the coal. 
BLACK & VEATCH 

MEMORANDUM Page 2 

Basin Electric Power Cooperative B&V Project 145423 

Laramie River Station February 24, 2009 

LNB and OFA Control Effectiveness 

To reduce the production of unintended byproducts of combustion such as NOx, the 

temperature of combustion at the burner as well as the timing and mixing rate of the 

secondary air with the primary combustion products are controlled to limit NOx

production. In addition to reducing the peak burner flame temperatures, the general 

philosophy for reducing the NOx generated from a wall fired burner is to reduce the 

oxygen and nitrogen that is available in the highest temperature region of the burner 

flame to limit the rate the fuel bound nitrogen as well as the atmospheric nitrogen is 

oxidized to form NOx. Once this initial combustion has taken place at the burners, the 

balance of the combustion air is provided by over-fire air ports to enable complete 

combustion of the vaporized fuel components prior to being cooled by the radiant and 

convective heat transfer surfaces of the boiler. NOx production can be minimized in the 

lower furnace area around the burners by limiting the total combustion air and 

maintaining a reducing atmosphere. This reducing atmosphere especially in the presence 

of sulfur in the flue gas stream can cause significant corrosive attack of the furnace heat 

transfer surfaces. This potential for rapid corrosion of the furnace walls, limits the 

staging of combustion in the lower furnace area and the effectiveness of LNB to limit 

NOx production. 

As well as the increased potential for fire-side corrosion of the furnace walls in the case 

of insufficient oxygen in the lower furnace, in a typical coal-fired boiler, there may be as 

many as 49 individual burners that must operate in concert to provide for the combustion 

of coal in this manner. To minimize NOx formation, the quantities of coal, primary air 

and secondary air must be supplied in a uniform quantity to each burner. The 

performance of each individual burner must be maintained to minimize NOx production 

to the lowest level. Due to the physical difficulty of continuously providing this equal 

balance of air and fuel as well as fuel fineness to each burner, this theoretical peak 

BLACK & VEATCH 

MEMORANDUM Page 4 

Basin Electric Power Cooperative B&V Project 145423 

Laramie River Station February 24, 2009 

LNB and OFA Control Effectiveness 

Wall Fired

Figure 2 - Controlled and Uncontrolled NOx Emissions from PC Wall-Fired Boilers 

In addition to optimizing the LNB-OFA to ensure complete burn-out of char, evaluation 

of NOx control effectiveness resulting from LNB-OFA system installed in an opposedwall system needs to take into account several key boiler and combustion characteristics: 

• Composition of fuel combusted 

• Ability of unit to monitor air and fuel flow (for combustion optimization) 

• Boiler physical design and arrangement 

• Burner fuel and air balance 

• Mill fineness 

• Boiler management system (e.g. neural networks) 

• Boiler cleaning technologies. 
BLACK & VEATCH 

MEMORANDUM Page 5 

Basin Electric Power Cooperative B&V Project 145423 

Laramie River Station February 24, 2009 

LNB and OFA Control Effectiveness 

While the CFD model study of the burner with OFA at LRS units considered the items 

listed above, it assumes a steady-state condition with all these process variables that 

might impact the production of NOx from the LRS units. At steady-state operation, and 

with operation to optimize all boiler and combustion characteristics to minimize the 

production of NOx, an outlet NOx of 0.15 lb/MBtu was determined to be achievable 

based on the design of the optimized OFA ports. 

Therefore, this outlet NOx value is dependent on the LRS boilers/combustion process 

operating at a steady-state condition, while maintaining an even/optimum combustion air 

and fuel distribution, with little variation in the composition of the fuel and the fineness 

out of the coal mills. However, in actual operating conditions, this optimized, steadystate condition can seldom be maintained. Therefore, the controlled outlet NOx of 0.15 

lb/MBtu should be classified as a theoretical, lowest achievable outlet NOx when the 

operating conditions approach the optimum conditions used for the modeling inputs. 

In addition to that, a review of the CFD model study recently identified an error with the 

use of sea-level conditions (for combustion air barometric pressure), when the LRS units 

are located in an area with an elevation much higher than sea-level. This resulted in the 

CFD model study based on combustion air that is denser than actual. This impacts the 

modeled NOx outlet of 0.15 lb/MBtu since denser combustion air is more favorable to 

minimize the production of NOx during combustion. The correction to the lower flue gas 

density also reduces the furnace residence time so will increase the potential for 

excessive unburned char from combustion. To reduce the char and associated slagging, 

fouling and corrosion, the level of staging in the lower furnace will be reduced as well as 

the quantity of over fire air flow. This will reduce the performance of the LNB system. 
BLACK & VEATCH 

MEMORANDUM Page 6 

Basin Electric Power Cooperative B&V Project 145423 

Laramie River Station February 24, 2009 

LNB and OFA Control Effectiveness 

The CFD model expert estimated that a 5% error was introduced into the CFD model 

study results. 

Since the assumptions used to develop the CFD model study was based on optimum and 

steady-state conditions, which cannot be maintained during normal operations of the LRS 

boilers, with the impacts of the error introduced by the use of a wrong basis on the 

density of combustion air, the controlled NOx outlet after the retrofit of LNB-OFA is 

expected to be higher than the result of the original CFD model study of 0.15 lb/MBtu. 

For BART, the control effectiveness for NOx should be based on a demonstrated and 

achievable level. Since BEPC is currently considering LNB with OFA retrofits at the 

LRS units, the most recent CFD combustion model study performed in 2008 will be more 

representative than the values reported in the BART analysis report submitted in 2007. It 

was identified that the controlled outlet NOx from this recent model is 0.18 lb/MBtu with 

an accuracy of 20%. This range of accuracy is consistent with predicted model 

information when verified by an actual test from our experience. In addition to the 

results of this recent combustion model, an evaluation of reported CEM data from 2005 

to 2006 indicated that several wall-fired boilers combusting subbituminous coal equipped 

with LNB-OFA demonstrated a 30-day rolling average NOx ranging from 0.18 to 0.21 

lb/MBtu.