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## Emissions Control: Cost-Effective Layered Technolog y for Ultra-Low N... http://www.coalpowermag.com/ops_and_maintenance/Emi ssions-Contro...

1 of 6 9/8/2010 11:49 AMFull Issue Text January 1, 2007 

# Emissions Control: Cost-Effective Layered Technolog y for Ultra-Low NOx Control
Charles E. Trippel, PE, is a vice president with Ad vanced Combustion Technology Inc. He can be reached at ctrippel@advancedcombustion.net. Layering NO x

control technologies can reduce a coal-fired unit’ s NO x emissions to levels achievable by selective cataly tic reduction alone. Advanced Combustion Technology Inc. (ACT) ( www.advancedcombustion.net ) has demonstrated that using several in combinatio n can cut emissions from boilers firing eastern bituminous co al or No. 6 oil to less than 0.15 lb/mmBtu. The following two case studies prove the effectiven ess of a three-step process that combines implement ations of low-NO x burners, separated overfire air (SOFA), and high-energy reagent techno logy (HERT). The first two steps should be familiar , but the third may require explanation. The HERT system can be characterized by five design s/goals that work with low-NO x burners and SOFA to minimize emissions: Injecting urea into a portion of the SOFA stream, e nabling the chemical to interact with NO x in flue gas. Improving load-following capability from 30% to 100 % of the unit’s rating. Using a mechanical atomizer to form small-diameter urea droplets. Using the hot SOFA stream to vaporize the fine ureadroplets, which increases their coverage. The opti mum reaction temperature range has been determined to be 1,600F to 2,100F. Minimizing the number of urea injectors required. 

### Paper Tiger The first case study reports the results of testing the three-step process on a tangentially fired boi ler owned and operated by Blue Ridge Paper Products Inc. The boiler (Figure 1) burns eastern b ituminous coal to produce 400,000 lb/hr of superhea ted steam at 730F. Its balanced-draft furnace has 12 burners, four at each of three eleva tions. Layering the three technologies reduced NO x from the uncontrolled baseline of 0.70 lb/mmBtu to less than 0.15 lb/mmBtu. Baseline flyas h loss-on-ignition (LOI) was <9% with opacity below15%. ACT designed and supplied the low-NO x burners and the SOFA and HERT systems.

1. Tangentially fired boilers use furnace dynamics to enhance combustion. Burner upgrades can achieve only limited NO x reduction. Source: Advanced Combustion Technology Inc. During the design phase, computational fluid dynami cs (CFD) modeling was used to simulate the performa nce of each system before installation. The modeling was staged to validate t he model as work progressed; the first model was of the baseline burner and furnace region. The simulations then projected the impact on NO x emissions and combustion performance of each syste m addition. The field performance of the HERT system also was simulated prior to completing the final system design. In each instance, the CFD model correctly predicted the final performance of the various NO x control technologies, working alone and in concert

. To summarize the results of activating each of the three systems in sequence: Using the low-NO x

burners alone reduced emissions of the pollutant f rom 0.70 lb/mmBtu to 0.48 lb/mmBtu while maintainin g flyash LOI below 10% and CO emissions below 50 ppm. Adding the SOFA system further reduced the NO x level to 0.28 lb/mmBtu. Adding the HERT system brought NO x emissions down to 0.15 lb/mmBtu — representing a 7 8% reduction from the baseline level. How were these exemplary results achieved? The low- NO x burners stage combustion at their outlets, inhibit ing the formation of the pollutant. The SOFA system (Figures 2 and 3), which is designe d for 15% combustion air flow, diverts air from theburner zone to the upper furnace, enhancing combustion staging. As mentioned earlier, the HERT system injects a urea mist in a portion o f the SOFA stream, enabling the urea to mix with combustion gases in the upper furnace. The heat of the SOFA steam vaporizes the mist on conta ct, improving its range over that produced by a conventional selective noncatalytic reduction system (Figure 4). 

## Emissions Control: Cost-Effective Layered Technolog y for Ultra-Low N... http://www.coalpowermag.com/ops_and_maintenance/Emi ssions-Contro...

2 of 6 9/8/2010 11:49 AM2. Adding secondary (separated) overfire air can fu rther reduce NO x emissions from a tangentially fired boiler equippe d with low-NO x burners. Source: Combustion Technology Inc.

3. Here's how the device shown in Figure 2 was inst alled on the boiler of a paper plant. Courtesy: Advanced Combustion Technology Inc.

4. This CFD model predicts the velocity contours of the urea and SOFA streams. Values shown are in ft/ sec. Courtesy: Advanced Combustion Technology Inc. 

## Emissions Control: Cost-Effective Layered Technolog y for Ultra-Low N... http://www.coalpowermag.com/ops_and_maintenance/Emi ssions-Contro...

3 of 6 9/8/2010 11:49 AMOnly four HERT injectors (Figure 5), one in each SO FA port, were needed to achieve average NO x reduction of 50% over the boiler’s load range. No additional pressure part penetrations wer e required to install the HERT system. With the sys tem operating, the ammonia slip across the load range was less than 1 ppm at the air heate r inlet.

5. The high-energy reagent technology (HERT) inject or is visible at the lower right of the image. Courtesy: Advanced Combustion Technology Inc. The HERT system’s capital and operating costs were pegged at $1,100 per ton of NO x removed. Working together, the three technologies reduced NO x

levels to those achievable by a selective catalyti c reduction system at a fraction of its cost. All t hree technologies were supplied and installed for the equivalent cost of $25/kW. 

### Works on Oil Burners, Too The second case study demonstrated the effectivenes s of the layered approach to NO x reduction on a wall-fired boiler firing No. 6 oil. The boiler powers the 125-MW Unit 2 of NRG Energy Inc.’s 770-M W Middletown (Conn.) power station. Unit 2 was orig inally designed to burn eastern bituminous coal. It was uprated from 110 MW to 125 MW when the 12 circular-register burners were conve rted to fire No. 6 oil or natural gas only at four elevations. To test the three-step approach, ACT first upgraded those burners with low-NO x models of its own design (Figure 6) and modified t he boiler’s existing SOFA system to improve combustion dynamics and optimize CO burnout in the upper furnace. Withthe new burners and the enhanced SOFA system in operation, the boiler’s NO x emissions fell from the full-load baseline value o f 0.39 lb/mmBtu to 0.22 lb/mmBtu. That wasn’t enough of a reduction, because the goal of the laye red approach — applied to oil-burning boilers — is aNO x level of less than 0.15 lb/mmBtu.

6. A close-up of one of the low-NO x burners that ACT designed and installed on Unit 2 of NRG Energy's Middletown (Conn.) power station. Courtesy: Advanced Combustion Technology Inc. The next step was to install the HERT system and de monstrate its ability to further reduce NO x. Before doing so, ACT took the opportunity to use its portable test system to verify the HERT sys tem’s performance. The portable test system (Figure7) contains a urea-metering module, a dilution water-and-mixing module, and high-energy i njectors designed for the specific application. Theinjectors make use of a carrier air stream as well as SOFA carrier air. 

## Emissions Control: Cost-Effective Layered Technolog y for Ultra-Low N... http://www.coalpowermag.com/ops_and_maintenance/Emi ssions-Contro...

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7. These are the three components of the portable t est sytem that ACT uses to test the effect of injecting a reagent into a separated overfire air stream. Courtesy: Advanced Combustion Engineering I nc. The injectors were tested in the SOFA ports and at one level of observation ports. Activating the HERTsystem and two injectors reduced full-load NO x

from 0.22 lb/mmBtu to 0.118 lb/mmBtu (exceeding th e design goal), with an ammonia slip of 6.2 ppm. Op erating all three systems — the low-NO x

burners, SOFA, and HERT — produced an overall NO x reduction of 67%. All three systems can be supplie d and installed on a boiler of this type for a cost between $7/kW and $1 0/kW. Based on the success of the demonstration, NR G permanently installed the HERT system on Unit 2 and has operated with the NO x less than 0.12 lb/mmBtu across the load range and with ammonia slip of less than 4.6 ppm. This article is based on the author’s presentation at the U.S. DOE-NETL 2006 Environmental Controls Conference.

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## Emissions Control: Cost-Effective Layered Technolog y for Ultra-Low N... http://www.coalpowermag.com/ops_and_maintenance/Emi ssions-Contro...

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