1 

## St. Johns River Power Park 2 x 670 MW SCR - Designed to Ensure Fuel Flexibility

Paper # 96

Gerald Smith St. Johns River Power Park, 11201 New Berlin Road, Jacksonville, FL 32226

Noel Rosha CERAM Environmental, Inc., 7304 West 130t h Street, Suite 140, Overland Park, KS 66213
Robert Branning Tackticks, LLC., 1708 Selva Marina Drive, Atlantic Beach, FL 32233

Diane Fischer Black & Veatch, 11401 Lamar, Overland Park, KS 66211
Kathryn Robinson Black & Veatch, 9000 Regency Parkway, Suite 300, Cary, NC 27518

Volker Rummenhohl Tackticks, LLC., 247 Booth Mea dow Lane, Durham, NC 27713

John Cochran CERAM Environmental, Inc., 7304 West 130t h Street, Suite 140, Overland Park, KS 66213


### ABSTRACT
The St. Johns River Power Park is installi ng SCR systems on two pulverized coal units cofiring high arsenic and silica coals with up to 30 percent petrol eum coke containing high levels of vanadium and sulfur. This fu el combination created significant challenges for maintaining low SO 2 /SO 3 conversion rate while accommodating high catalyst deactivation and high erosion potential.
During project design development, attention was paid to the effect of various fuel characteristics on process configuration, cat alyst design, and equipment life. Additional consideration was given to operations and fuel management strategies to minimize fuel impacts on SCR operation. This paper discusse s the design challenges faced and special features incorporated to maintain fuel flexib ility and plant availabi lity, including catalyst procurement, reactor/ductwork design, and ot her system features. Additionally, results are presented regarding testing various catal yst types after exposure to flue gas from cofiring 30 percent petroleum coke (petco ke) and 70 percent coal for up to 6,000 hours and from the SCR system performance test.2 

### INTRODUCTION The St. Johns River Power Park (SJRPP) is loca ted in Jacksonville, Florida, and is owned by Florida Power & Light Company and JEA. JEA operates the units, and the power output for these units is shared equally by the owners. The stati on consists of two 670 MW (gross) coal fired power plants. Both units are baseloaded with high capacity factors. SJRPP was required to install select ive catalytic reduction (SCR) systems on both units to reduce nitrogen oxide (NO x ) emissions. SJRPP established ambitious goals for the SCR systems. Because the units are baseloaded, the SCR systems need to provide a high level of availability and reliability while minimizing future operations a nd maintenance (O&M) costs and plant interruptions. In addition, SJR PP fires a unique variety of fuels (which is discussed in detail in this paper), and the SCR systems n eeded to be able to accommodate the various fuels.

SJRPP contracted with Black & Veatch to perform detailed design of the SCR systems. This effort was broken down into two phase s. The first phase entailed preliminary engineering and consisted of characteriz ation testing, design basis development, assessment of balance-of-plant issues, CoPilot ® catalyst testing, deve lopment of ductwork arrangement, ductwork arrangement fatal flaw analysis, and cost estimating. The second phase involved project implementation and c onsisted of detailed engineering, equipment procurement, construction, and startup. Figure 1 is an arrangement drawing for the SCR layout at the SJR PP units. Flue gas from the economizer is split and sent through one of two SCR reacto rs. Each half of the flue gas passes through a large particle ash (LPA) collection screen, a static mixer, and the ammonia injection grid (AIG). Anhydrous ammoni a, diluted in air, is injected into the flue gas by the AIG. The flue gas then en ters the SCR reactor where the ammonia and NO x react in the presence of the catalyst to form nitrogen (N 2 ) and water. The flue gas then passes through the air heater. The SCR system is equipped with an SCR bypass and isolation dampers to allow SJRPP to isolat e the SCR for maintenance. The air heaters have been retrofitted with ammoni um bisulfate-resistant baskets.


### FUELS BACKGROUND For the first 10 years of commercial opera tion (beginning in 1987), SJRPP primarily burned a domestic source of bituminous coal delivered by rail and a coal source from Colombia, South America. To realize substant ial fuel savings, petcoke was introduced to the fuel mix in 1997. The blend was limited to 20 percent petcoke after testing revealed poor flame stability with higher blends. This blend of 80 percent coal and 20 percent petcoke was achieved through synchronized bunke ring of the two mate rials; all burners fired the same blend of petcoke and coal. This was standard procedure from 1997 until burner improvements allowed a preferre d method of firing beginning in 2005.3 Figure 1: General Arrangement for SCR Systems at SJRPP

Burner improvements made in 2003 and 2004 provided flame stability while firing 100 percent petcoke in a burner. As a resu lt, SJRPP abandoned the synchronized fuel loading and began to directly bunker the two fuels. This meant that the fuels were no longer blended and only one fuel was fired in each burner. This direct bunkering method provided many benefits for SJRPP including a llowing the petcoke blend to be increased to 30 percent. The new standard procedure involved using two pul verizers (8 burners) with petcoke, and four pulverizers (16 burne rs) with coal. The two pulverizers with petcoke were biased down to attain the desi red blend of 30 percent. The preferred firing method places the petcoke in burners low in the furnace, but with direct support from even lower burners. This does not preclude pe tcoke from being fired in any of burners. Figure 2 shows the preferred petcoke firing arrangement.


### SCR DESIGN AND OPERATION CHALLENGES The SCR retrofit for SJRPP involved significant challenges as a resu lt of the range of fuels and direct bunkering operations describe d above. Localized effects on the catalyst could be anticipated from th e direct bunkering of individual fuels. The fuels considered for the SCR design are listed in Table 1. Part icularly troublesome for SCR system design and operation is the high vanadium and sulfur content of the petcoke , the high arsenic and low calcium of the eastern domestic coal, a nd the high silica of the Colombian coal. The following briefly describes concerns a ssociated with each fuel supply.4 Figure 2: SJRPP Boiler Elevation Showing Burner Rows

CL Burners 7 Rows

D
E C
F B G A



### Colombian Coal Colombian coal has a high potenti al for catalyst erosion due to the erosive nature of the fly ash. This coal normally contains 10 percen t ash (up to 18 percent), with fly ash silica contents in the range of 57 to 62 percent, a nd fly ash alumina contents in the range of 17 to 22 percent in the ash.


### Domestic Coal Eastern Kentucky domestic coal has a high pot ential for catalyst deactivation due to the relatively high level of arseni c in the coal compared to the relatively low amount of calcium oxide (CaO) in the fly ash. The arseni c levels can be as high as 30 ppm, while the CaO concentrations in the ash can be as low as 0.5 percent. If this fuel is direct fired, this ratio of arsenic to CaO will result in a high catalyst deactivation rate. A relatively high level of arsenic to CaO result s in problematic levels of gaseous arsenic, which is a severe catalyst poison. A high rate of deactivation might be avoided if the domestic coal were blended prior to the burners. However, direct bunkering does not allow for any dilution of the high arsenic to low CaO ratio with the higher CaO of the other fuels. Since the majority of the gase ous arsenic is formed in the burner flame, excess CaO from the other fuels will not re duce the formation of gaseous arsenic where the eastern domestic coal is direct bunkered.


### Petcoke Blend
There are two main concerns associated with firing up to 30 percent petcoke. The first is the high level of sulfur in the fuel and the s econd is the presence of a high concentration of vanadium in the fuel. Petcoke Firing Petcoke Firing5 Table 1. SJRPP fuel quality.

Fuel Source Domestic Coal Colombian Coal Petcoke Ultimate Fuel Analysis (% by mass) Carbon 68 63.9 79.94 Hydrogen 4.4 4.6 3.22 Sulfur 0.85 (Max 1.8) 0.7 (Max 1.1) 5.79 (Max 6.94) Nitrogen 1.5 1.18 1.56 Oxygen 8.15 7.99 0.72 Chlorine 0.1 0.03 0.17 Ash 11 (Max 15) 9.6 (Max 17.5) 0.6 (Max 5.25) Moisture 6.0 (Max 15) 12.0 (Max 15) 8.0 Higher Heating Value (HHV), Btu/lb 12,000 11,300 14,000 Ash Mineral Analysis (% by mass) Silica (silicon oxide) 53 (Max 58) 60.2 (Max 62) 27.48 Alumina (aluminum oxide) 31.7 (Max 36) 20.2 (Max 23) 8.85 Titania (titanium oxide) 1.4 1.0 0.57 Calcium Oxide 1.2 (Min 0.5%) 2.5 (Min 1.3%) 3.2 (Min 1.5%) Potassium Oxide 2.0 2.3 0.89 Phosphorous Pentoxide 0.4 0.24 0.06 Magnesium Oxide 1.3 2.3 0.98 Sodium Oxide 0.6 0.6 2.43 Iron Oxide 6.0 8.4 4.83 Sulfur Trioxide 0.4 2.1 2.6 Manganese 0.06 Undetermined 2.0 0.10 0.86 Trace Metal Analysis, ppm Vanadium 48.3 55.7 2,042 Lead 16.94 6.2 29.9 Arsenic 28.92 4.17 13.54 ppm = parts per million
Petcoke has an average sulfur content of 5.8 percent, with a range of 3.5 to 6.9 percent. The high amount of sulfur in the petcoke affects the catalyst minimum operating temperature (MOT) and the potential for visi ble emissions from sulfur trioxide (SO 3 ). The MOT for an application is establishe d to avoid significant buildup of ammonium bisulfate (ABS) on the catalyst. The MOT is determined based on the SO 3 and the ammonia concentrations in the flue gas. Wh en firing 30 percent petcoke at SJRPP, the sulfur dioxide (SO 2 ) and SO 3 concentrations in the flue gas are (on average) 1,750 ppm and 51 ppm, respectively, with maximum local concentrations of up to 2,050 ppm and 100 ppm, respectively. Conversely, the SO 2 and SO 3 concentrations in the flue gas when6 no petcoke is fired average 614 ppm and 15 ppm, respectively. When firing 30 percent petcoke, the resulting MOT is 630° F and when firing 100 percent coal, the MOT is reduced to 605° F. The petcoke fired at SJRPP contains appr oximately 2,000 ppm of vanadium. Considering a 30 percent blend, the combusted fuel ble nd has in excess of 600 ppm vanadium. The presence of these high amounts of vanadium in the blended fuel, as discussed herein, leads to vanadium deposition on the SCR catal yst over time. Vanadium is the primary active metal in the SCR catalyst. An increase in vanadium on the catalyst will result in an increase in the SO 2 to SO 3 conversion rate across the catalyst and will slow the rate of catalyst deactivation. The levels of SO 3 will increase as a function of time when firing petcoke. 

### Impact of Direct Bunkeri ng on the SCR Design While direct bunkering is more beneficial th an fuel blending for SJRPP, it presents additional challenges for the SCR design. Because of averaging effects, fuel blending can often mitigate unfavorable properties of a given fuel when it is fired in a blend with a different fuel. However, with direct bunkeri ng, the fuels are fired separately and their individual products of combustion segregat e as they exit the furnace. Undisturbed, channeling typically occurs as the gas propa gates to the SCR unit, which can result in accelerated deactivation within targeted areas of each catalyst layer.

Areas of concern include the high concentration of arseni c in the domestic fuel, the different levels of uncontrolled NO x produced by the different fuels, the change of the NO x profile over the load range, and change s of the profile depending on which burner rows are used for the different fuels.


### DEVELOPMENT OF DESIGN BASIS Plant Characterization Testing When designing an SCR retrofit for a large central generating station, it is critical that the team have a thorough understanding of certain operating parameters for the units. When designing air quality control equipment for a new station, the engi neer will typically utilize the design fuel and gua ranteed performance from ma jor equipment suppliers to establish the criteria for sizi ng air quality systems such as SCR. For existing units that have been operating for an extended period of time, it is not a good practice to utilize the original design criteria for the retrofit of ma jor air quality control systems, because the original criteria are theoretical and actu al operation depends on the fuel, equipment condition, and operating practices. Therefore, when designing major air quality control retrofit projects, it is prudent to conduct a series of baseline or characterization tests to establish the actual operating conditions of the unit at various operating points and, in the case of the SJRPP units, fuel combinations.7 In February 2006, SJRPP contracted with Clean Air Engineering to perform an extensive characterization test program on Unit 1. Units 1 and 2 are assumed to be identical. The general purpose of the test program was to determine the following, under various loads and fuel combinations:

• Flue gas temperature distribution

• Flue gas flow distribution

• Emissions concentrations

• Boiler operating parameters

• Fuel and ash analyses
Testing was performed at nine different lo ad and fuel combina tions, as defined in Table 2. The purpose of the testing was to “bracket” the normal ope rating conditions of the units.

Table 2. Characterization testing loads.

Coal Content Load Identifier Unit Load, MW (gross) Petcoke Domestic Coal Colombian Coal 1 670 30% 35% 35%

2 670 (with different mills) 30% 35% 35%

3 300 Up to 30% 35% 35% 4 300 None None 100% 5 450 30% 35% 35% 6 670 30% 70% None 7 670 30% None 70% 8 670 None 50% 50% 9 670 None 100% None

The test results indicate there does not a ppear to be any discernable pattern to NO x concentrations as a function of fuel or coal mill configuration. The testing also indicated that the boiler is oxidizing a relatively hi gh portion of the sulfur in the fuel to SO 3 (more than 2 percent), resulting in high SO 3 concentrations in the flue gas (51 ppmdv). This information was used in the SCR design and is discussed later in this paper. Part of the characterization testing effort in cluded the evaluation of 1 year of operating data received from the plant information sy stem. Economizer outlet temperature data are of particular interest. Outle t temperatures significantly above 850° F can result in sintering of the SCR catalyst. A more comm on concern is the minimum gas temperature at low loads. Low flue gas temperatures can result in ABS formation and plugging of8 SCR catalyst and air heater surfaces. Figure 3 provides a summary of the economizer outlet temperatures as a function of unit load.

Figure 3: Unit Load Versus Economizer Outlet Temperature

Unit Load Vs. Econ Outlet Temp

400 450 500 550 600 650 700 750 800 850 900

0 100 200 300 400 500 600 700 800 Gross Generator Load, MWEconomizer Outlet Temp, F

Based on the results of the characterization testing and the review of operating data, a design basis was established for the project. Table 3 summarizes the cr iteria utilized to design the SJRPP SCR systems.

Table 3. Design basis for SCR system design (total flow, not per reactor).

Units Design Load with

Petcoke Design Load without Petcoke Maximum Load with

Petcoke Minimum Load with

Petcoke Petcoke Firing Percent 30 0 30 30 Domestic Coal Firing Percent 35 50 35 35

Colombian Coal Firing Percent 35 50 35 35

Unit Load (gross) MW 670 670 670 300 Flue Gas Temperature at SCR Inlet °F (Range) 750-800 750-800 750-800 6409 Units Design Load with

Petcoke Design Load without Petcoke Maximum Load with

Petcoke Minimum Load with

Petcoke Flue Gas Temperature for Material Selection °F 824 824 824 Not Applicable

Typical NO x Emission Rate lb/MBtu 0.4 0.4 0.4 0.4

Maximum NO x Emission Rate lb/MBtu 0.66 0.66 0.66 0.5

Maximum SO 2 Concentration ppmvw 2,050 1,058 1,960 1,865

Average SO 3 Concentration ppmdv 51 14.5 51 52.4



### PROCUREMENT PROCESS FOR SCR CATALYST Because of the fuel challenges on this project, the catalyst procurement followed a unique process. First, three catalyst suppliers were invite d to participate in a testing program using CoPilot ® test reactors. This testing program consisted of placing catalyst plate and honeycomb elements from the prospective supp liers into a test apparatus that allowed each of the elements to be exposed to the flue gas from the SJRPP boilers. (Additional details on this program are provided in the next section of this paper.) The catalyst elements were rotated periodically between all three CoPilot ® reactors to ensure that each element was exposed to the same flue ga s conditions. After 2,100 hours of operation in the CoPilot ® reactors, the catalyst elements were removed from the flue gas and shipped to the respective catalyst suppliers for activity testing and oxidation rate testing.

While the CoPilot ® testing was being performed, Black & Veatch developed the catalyst procurement specification. SJRPP issued the sp ecification for bid to each of the three bidders prior to the completion of the 2,100 hour CoPilot ® test.

SJRPP and Black & Veatch then visited each of the catalyst suppliers to witness the activity testing and to discuss each bi dder’s project execution philosophies and guarantees. After the visits, each bidder submitted its proposal to SJRPP for evaluation. SJRPP and Black & Veatch evaluated the bids using a pre- established list of ev aluation criteria. Each item on the list was assigned a rating that i ndicated the importance of that item. Based on this comprehensive technical and commercia l evaluation, CERAM was selected as the catalyst supplier for the SJRPP project . CERAM manufactures a homogeneous honeycomb catalyst.10 The unique process for procuring catalyst had several benefits. First, the CoPilot ® testing allowed the prospective catalyst suppliers and SJRPP to understand the impact of the various fuels fired at SJRPP. Not only did a ll parties gain an unders tanding of the impacts of the individual fuels, but they also gained an understanding of the impacts of direct bunkering. In addition, the visits gave SJ RPP an understanding of the project implementation philosophies of each vendor. Finally, the process gave all parties confidence in the ability of the catal yst to meet performance guarantees.


### CO-PILOT ® 

### TESTING During the initial design phase of the proj ect, CERAM recommended that the CoPilot ® catalyst test reactor for SJRPP be used as a tool to determine the impact of firing 30 percent petcoke, as well as the abrasive Colombian coal and the high arsenic eastern domestic coal, in a di rect bunkering scenario.

The CoPilot ® test reactor is an in s itu test reactor that allows for catalyst exposure at SCR reactor velocities to the actua l plant flue gas conditions. Th e general arrangement of the CoPilot ® test reactor is depicted on Figures 4 an d 5. Considering the in situ location, the catalyst is directly subject to the gas and fly ash conditions present in the full-scale SCR system. Installing the catalyst test sample di rectly into the ductwork avoids the common problems associated with slip stream test reactors (e.g., representative dust loading, temperatures, etc.). The CoPilot ® was developed with a double-hingeddoor design that allowed the catalyst test element to be inst alled and removed from the ductwork while the unit was on line. The CoPilot ® is equipped with an LPA screen, soot blower, flow straightening grid, in let and outlet temperat ure indication, pressure drop indication, and inlet and outlet ports for flue gas sampling.

Figure 4. CoPilot ® Test Reactor 

### CoPilot ® 

### Door Action



## Air Side Flue Gas Side Allows for Catalyst Test Element Removal Without Unit Outage

Rotated Into

Flue Gas

Rotated Out of Flue Gas11 Figure 5. CoPilot ® Test Reactor



## CoPilot ® 

## Catalyst Test Reactor

Air Amplifier/ Eductor Inlet Temperature, Pressure and Test Taps NH 3 Injection and Sootblower

Straightening Grid

Test Element Outlet Temperature, Pressure and Test Taps

A total of three CoPilot ® test reactors were installed in the ductwork downstream of the SJRPP economizer. Two were installed on Unit 2 (2A and 2B), and the third was installed on Unit 1. As discussed previously, honeycomb and plate catalyst elements from three suppliers (including CERAM) were te sted. The goal of the testing was to assess catalyst oxidation rate increases and to characterize deactivation while burning a 30 percent petcoke blend. It was also intended that the suppliers would obtain information helpful to size the catalyst for the site specifics present at the SJRPP. After CERAM was selected as the catalyst supplier, additional CoPilot ® testing was performed using only a CERAM cat alyst in all three CoPilot ® test reactors in an effort to obtain as much information as possible pr ior to the catalyst production date. By the completion of CoPilot ® testing, one catalyst sample had 7,280 hours of flue gas exposure. Activity and SO 2 to SO 3 Conversion Rate Test Results
Table 4 summarizes the results of the activity and SO 2 to SO 3 conversion rate testing performed on the catalyst samples.12 Table 4. SJRPP CoPilot ® reactor catalyst test results summary.
Fuels Fired (% of heat input) Sample ID Relative Activity,

K/Ko Relative SO 2 to SO 3 Conversion

Rate, % Hours of Operation Colombian Dom Coal Petcoke 4083 1.0 1.0 0 4083 1.11 1.0 956 56 16 27 4084 1.0 1.0 0 4084 1.10 1.09 2,135 27 43 30 4084 0.93 1.47 7,280 37 34 29 5011 1.0 1.0 0 5011 0.85 1.0 4,535 63 35 2 5012 1.0 1.0 0 5012 1.01 1.13 5,145 44 28 28
The catalyst activity testing results provide d confirmation of the expected catalyst deactivation rates when firing both 100 percent coal and also a 70 percent coal/30 percent petcoke blend. The catalyst deactivation rates are illustrated graphically on Figure 6.

Figure 6. CoPilot ® Catalyst Activity Testing Summary

When firing 30 percent petcoke, there is a noti ceable initial increase in catalyst activity up to 2,000 hours. There are two reasons for this. Fi rst, as the catalyst is initially installed in a flue gas atmosphere, a “sulphation” pro cess occurs, which causes a slight increase in13 catalyst activity. Second, the initial accumula tion of vanadium from the petcoke will cause an increase in activit y. Over time, the accumulation of catalyst poisons from the fuels, such as arsenic, will continue to accumulate and overtake the activity benefits associated with the vanadium accumulation, re sulting in catalyst deactivation in the long term.

The SO 2 to SO 3 conversion rate test re sults from the CoPilot ® samples confirm the expected increase in conversion rate over time when firing 30 percent petcoke. Figure 7 graphically illustrates the test results and the predicted increase in the SO 2 to SO 3 conversion rate over time when firing 30 percent petcoke.

Figure 7: CoPilot® SO 2 to SO 3 Conversion Rate Testing Summary

Bulk and Surface Chemical Analysis Results The bulk and surface chemical analysis result s verified the accumulation of vanadium on the catalyst surface and in the bulk material of the CoPilot ® catalyst samples. Another important result of the chemical analys is results is related to the accumulation of arsenic on the catalyst surface and in the bulk ca talyst material. In the instance of Sample 5011 (which was exposed to 100 percent coal), the accumulation rate of arsenic was very high compared to the samples that were expos ed to a 30 percent petcoke blend. Much of the arsenic accumulation in all samples is related to the domestic coal, which has a high arsenic to CaO ratio.14 

### CATALYST DESIGN Original Catalyst Design The original operating conditions specified as the basis for competitive bidding assumed that a 30 percent petcoke blend would be fi red continuously. Based on the results of the CoPilot ® testing performed to date, as well as CERAM’s extensive experience with catalyst applications with high vanadium bearing fuels, CERAM developed a catalyst design that included a full set of guarantees and warrantees, including initial and end of life SO 2 to SO 3 conversion rates. The original catalyst design is summarized in Table 5. It should be noted that at the time of the original bid, the CoPilot ® catalyst samples avail

able for testing had only 2,135 hours of flue gas exposure.

The initial SO 2 to SO 3 conversion rate was designed very low to account for the expected deposition of vanadium on the ca talyst and the corre sponding increase in conversion rate.

Table 5. Original SJRPP catalyst design summary.

Fuel Blend Basis 70% Coal/30% Petcoke Catalyst Pitch 8.2 mm Catalyst Volume 770 m 3 Catalyst Deactivation Basis Low (K/Ko=0.88) due to 30% petcoke blend Catalyst Wall Thickness 1.0 mm Initial Oxidation Rate 0.25% (A mmonia Off/800° F) with three catalyst layers installed Guarantee NO x Outlet 0.06 lb/MBtu (85% NO x reduction) Guarantee Life 18,000 hours



### Continuation of CoPilot ® 

### Testing After CERAM was selected as the catalyst supplier for the SJRPP project, catalyst CoPilot ® testing continued to be performed in an effort to obtain as much information as possible. If further CoPilot ® testing provided differing design information, CERAM agreed to modify the catalyst design in an “open book” manner, in cluding input from SJRPP and Black & Veatch, in order to provid e an optimized catalyst for the project. As indicated in Table 4, one catalyst sample wa s able to achieve 7,280 hours of operation in the CoPilot ®

. 

### Fuel Changes Late in Project In the summer of 2007, the SJRPP Fuels Depart ment issued solicitations for the purpose of procuring the required fuel for the Calendar Years 2008 and 2009. The bids received indicated that foreign coal was now less cost ly than petcoke blends and domestic coal sources. As such, the SJRPP Fuels Department (with approval from the Fuels Committee and Executive Committee) eliminated petcoke from the fuel mix for 2008. Consequently,15 the design basis for the catalyst was significantly affected, a nd a complete redesign of the catalyst was necessary. The shift from a petcoke blend required a complete redesign of the catalyst in order to meet the new operating conditions. This fuel blend modification did not change the other design criteria for the installed system si nce the system is otherwise designed with flexibility to handle the three types of fuel sources: domestic bituminous coal, foreign bituminous coal, and petcoke fuel. The catalyst has also been revis ited in case petcoke prices change to a more favorable rate to be able to handle the varied fuel mixtures with minor life impact. NOTE: During the summer of 2008, bids were received regarding the 2009 fuel suply. A domestic coal source was selected, and in 2009, SJRPP will be burning both domestic and foreign coal supplies and no petcoke product. 

### Revised Catalyst Design In considering the revised fuel conditions, th e most difficult aspect was the consideration that the original catalyst was designed for very little deactivation. W ith the elimination of petcoke from the fuel blend, catalyst deactivation became highly significant. Figure 8 illustrates the effect of this deactivation rate change on the initial sizing. The change to 100 percent coal operation required a 36 per cent increase in reactor potential to accommodate the increased deactivation anticipated.

Figure 8: SJRPP Reactor Potential With and Without Petcoke

0% 20% 40% 60% 80% 100% 120% 140% 160%

0 5000 10000 15000 20000RequiredReactorPotential

O p eratin g Hours 

### SJRPP Reactor Potential (18,000 Hour Sizing Basis)

With Petroleum Coke (low deactivation)

Without Petroleum Coke (high deactivation)

CERAM worked to redesign the SCR catalyst in an open book manner, with direct input from SJRPP and Black & Veatch, in order to provide a suitable ca talyst design for the16 project while limiting cost impacts. The obj ective of SJRPP was to not change the catalyst volume for the project. Considering that the syst em was installed to control stack SO 3 emissions (described subsequently) and that the SO 2 to SO 3 conversion rate would not be time dependent as it would be for pe tcoke blends, there was sufficient margin to accept increased oxidation from the catalyst. Consequently, the revised catalyst design result ed in a change in catalyst chemistry, but the original catalyst volume was maintained without change. As such, CERAM provided the revised catalyst design without any comme rcial impact to the project. The revised catalyst design is summarized in Table 6.

Table 6. Revised SJRPP catalyst design summary.

Fuel Blend Basis 100% Coal Catalyst Pitch 8.2 mm Catalyst Deactivation Basis Hi gh due to high arsenic coal Catalyst Wall Thickness 1.0 mm Initial Oxidation Rate 2.0% (Ammonia Off/800° F) with three catalyst layers installed Guarantee NO x Outlet 0.06 lb/MBtu (85% NO x reduction) Guarantee Life 18,000 hours


### Provisions for Catalyst Management The SCR catalyst was designed with provisions to allow the maximum flexibility in catalyst management planning. The volatility of the fuels market for SJRPP was the main consideration for including such provisions in the catalyst desi gn. Design features included the following. High Mechanical Strength The catalyst was designed with a 1.0 mm cat alyst wall thickness to achieve a high mechanical strength. The accumulation of vanadium on the catalyst (from firing the petcoke blend) or from deactivation due to arsenic (from firing eastern domestic coal) may result in the need for catalyst washing or regeneration. The cataly st supplied for this project can be washed and regenerate d as many as four to five times. Catalyst Pitch The catalyst pitch selected for SJRPP was an 8.2 mm pitch. Considering the ash loading with either 100 percent coal or a 70/30 petcoke blend, this is a conservative catalyst pitch design. Fuel flexibility is maintain ed by using a large pitch catalyst.17 Full Height Catalyst Frames The original catalyst design ut ilized a catalyst height of approximately 1000 to achieve the performance guarantees. However, the cataly st was installed into steel frames that were large enough to hold the maximum lengt h element of 1,300 mm. In this way, the soot blowers could be placed in the prope r location for possible future catalyst installations that had longer catalyst lengths, up to a maximum of 1,300 mm.


### FLEXIBLE SCR SYSTEM DESIGN The catalyst was not the only component of the SCR system that was affected by the fuels burned at SJRPP. In addition to the precautions taken in catalyst design, the SCR ductwork, reactor, and peripherals n eeded to be able to handle the variety of fuels fired at SJRPP without affecting plant reliability or availability. This section of the paper discusses other system features that were included in th e SCR design to provide SJRPP with maximum fuel flexibility. 

### System Design for Direct Bunkering

The characterization tests showed a significant change in the NO x profile over the load range. The ratio between the fuels fired cha nges over the load range, resulting in changes to the NO x profile, which cannot be accommodated with the ammonia injection grid only.
To disrupt natural channeling at SJRPP, a st atic mixer was included in the design. This mixer, upstream from the AIG, was modeled to ensure that the design met specific mixing criteria. Computational fluid dyna mics (CFD) and experimental modeling afforded the project the flexibility to evaluate different mixing technologies to ensure that sufficient mixing of gas species would m itigate the effects of direct bunkering and temperature stratification, as discussed later in this paper.
Figure 9 shows the special design of the HI-TEC® Static Mixer designed by FlowTack, LLC, during the flow modeling efforts. The mi xer provides a very high mixing efficiency at a low pressure drop. 

### System Design for Flue Gas Temperature There were two main temperature issues th at drove SCR system design. First, during operation with petcoke, flue gas temperatures exiting the economizer are high compared to other coal fired boilers. The average opera ting temperatures at full load are between 750° F and 800° F, and excursion temperatures of 824° F have been experienced. During operation on other fuels, the flue gas temp eratures are somewhat lower. However, because of the potential for petcoke firing, materials selection was based on a design temperature of 824° F. This required the use of ASTM A588 material for the ductwork and ASTM A335 P11 material for the AIG.18 Figure 9: Front-to-Back Low Pressure Drop HI-TEC® Static Mixer

Temperature distribution in the ductwork is the second temperature issue that was addressed in the SCR system design. Because of the direct bunkering of fuel, the flue gas temperature leaving the economizer is not well distributed. Figur e 10 illustrates the temperature distribution from the characteri zation testing. It shows the variation in temperature that occurs at low load at th e economizer outlet when the unit is firing a combination of 30 percent petcoke/35 percen t Colombian coal/35 percent domestic coal. As can be seen from the figure, the temper ature varies across the duct by almost 100° F. Stratified temperatures at low load will result in the formation of ABS in localized areas with temperatures below the ABS condensati on temperature, even if the average temperature is above the ABS condensation temper ature. This temperat ure stratification is corrected through the use of the static mixer, as shown on Fi gure 8. As previously stated, the mixer is located just upstream of the AIG to ensure even temperature distribution into the grid. The static mixer is effective in mi nimizing the temperature stratification into the AIG. The temperature stratification is reduced by the static mixer from a worst-case value of ±45° F to a value of ±24° F. It should also be noted that the static mixer provides significant improvement in the NO x and flue gas velocity di stribution entering the AIG. 

### Ductwork Design The ductwork was designed for all three fuels that could be fired in the units. Petcoke firing results in high levels of unburned carbon, which significantly increases the risk of fires in the ductwork. This risk is most prevalent in areas of the ductwork where ash is allowed to settle out of the flue gas and rema in on the floor of the ductwork. Therefore, in order to minimize the potential for ash on th e ductwork floor, the ductwork was designed for a high average flue gas velocity of 60 ft/s. In addition, CFD modeling and physical flow modeling were performed to identify a nd address areas where dust tended to settle out of the flue gas.19 Figure 10: Temperature Distributio n of Flue Gas Exiting Economizer

Although the ductwork needed to be designed fo r a high flue gas velocity to minimize the potential for fires, this high velocity is detrimental when burning Colombian coal. The Colombian coal ash has extremely high silica content (up to 62 percent), making it very erosive. Therefore, if the SCR systems at SJRPP were to be designed for firing only Colombian fuel, Black & Veatch would have designed the ductwork for a much lower velocity to minimize duct erosion from the high silica ash. To addr ess these conflicting design requirements between the petcoke and Colombian coal, the ductwork was designed with minimal internal bracing. The va st majority of the structural support was provided by stiffeners on the outside of the duct. The few internal braces located within the ductwork are protected by erosion shields. The decision to minimize internal bracing allows SJRPP the flexibility of firing both the petcoke and Colombian coals, while still minimizing the potential for fires from unbur ned carbon and minimizing the potential for erosion. 

### Reactor Design A key requirement for providing fu el flexibility is to ensure even flow distribution into the catalyst under all fuel combinations. The internal straightening devices for the SCR systems at SJRPP were designed through th e combined use of both CFD and physical flow modeling. Through this modeling effort, Flowtack (CERAM’s flow modeler for the project) developed a graduated st raightening grid (GSG) at the inlet of the reactor in lieu of the traditional turning vane/s traightening grid configuratio n. Figure 11 is a drawing of the GSG. This device provides excellent flow distribution at the catalyst inlet under all fuel conditions.20 Figure 11: Drawing of Graduating Straightening Grid



### Limestone System Gaseous arsenic is a severe catalyst posion. A limestone addition system was incorporated into the SCR design at SJRPP to increase the calcium level in the domestic coal to aid in mitigating the high gaseous ar senic from the domestic coal. Calcium reacts with the gaseous arsenic in the fuel and form s a solid arsenic that does not deactivate the catalyst. Limestone is metered and deposited directly onto the coal conveyor belt whenever domestic coal is transferred to the unit’s silos. The limestone is then fed into the pulverizers along with the coal, providing fu rther mixing of the limestone and coal to optimize the effects of the additional calcium in the fuel. The limestone addition is controlled to provide a minimum 3 percent c oncentration of calcium in the ash of the domestic fuel.


### SO 3 

### Control System After SJRPP began firing petcoke, it installe d an ammonia injection system downstream of the air heater to control SO 3 emissions. The control of visible stack emissions or “blue plume” was of high importance for SJRPP. As part of the SCR project, the system was evaluated to ensure that, when firing 30 pe rcent petcoke and cons idering the increasing SO 2 to SO 3 conversion rate over time due to the vanadium accumulation, the SO 3 control system would remain capable of reducing the SO 3 concentrations to 5 ppm or less at the stack to avoid visible emissions. The original system is a conventional a nhydrous ammonia flue ga s conditioning system, built in 1999. This system consisted of an ammonia storage tank, vaporizers, dilution air blowers, controls and injection lances. Th e ammonia injection lances, which inject diluted ammonia into the flue gas, are mounted vertically in the duct, downstream of the air heaters and upstream of the electrosta tic precipitators (ESPs ). Each unit has 20 injection lances. The ammonia reacts with SO 3 in the flue gas to form ammonium21 bisulfate, which condenses on the fly ash partic les and is collected in the ESP, effectively removing the SO 3 from the flue gas. System modifications to improve overall operabi lity and reliability were included as part of the SCR project. The system supply was tied in to the new SCR anhydrous ammonia storage tanks, thus providing much greater supply capacity. The vaporizers were replaced with two new 100 percent capacity vaporizers that provide s uperheated ammonia vapor to the dilution air stream. A third dilution air blower was installe d in the system to provide backup for either existing blower, thus increa sing reliability. The injection lances were redesigned to ensure better distribution of th e ammonia in the flue gas and to improve the durability of the lances. The SO 3 control system was upgraded to allow better system turndown, as well as to ensure ad equate control range for higher SO 3 concentrations leaving the SCR system as a result of the SO 2 oxidation across the catalyst. 

### Design for Large Particle Ash
SJRPP has experienced significant problems with LPA, which, if allowed to reach the catalyst, will plug the catalyst. As a resu lt, the SCR system design was required to prevent LPA from reaching the catalyst. The LPA capture design was developed th rough both CFD modeling and physical flow modeling and consists of two elements. First, aerodynamic baffles were added to the economizer outlet to remove the majority of th e LPA from the flue ga s. At this location, the LPA ash drops into the economizer hoppers. The remaining LPA is collected by the LPA screen, which was designed to withstand the high silica Colombian coal ash and was placed in a location in the duct where a flue ga s velocity of 40 ft/s could be maintained through the screen. In addition, the screen is thermal coated with an erosion-resistant material supplied by NoNO x . Wear testing was performed using the Colombian coal ash to confirm that the coated screen could withstand erosion from the high silica ash. 

### Fan Upgrades Adding SCR systems required changes to the induced draft (ID) fan capacity. Additionally, to allow maximum flexibility in operation and fuel variations, SJRPP wanted to return to its original design cap ability of operating the units on full load with only three of the four fans in operation. Incr easing the ID fan capacity was achieved by replacing the rotors and motors, while maintaining the fan housing and foundations. An SCR addition normally has very little e ffect on the combustion air system. However, the increased possibility of air heater pluggage due to ABS formation after the SCR system, along with existing concerns about unit limitations because of forced draft (FD) and primary air (PA) fan margins, prompted SJRPP to modify the FD and PA fans by adding fan tips. The fans were tipped to th e maximum extent possible without requiring new motors.22 

### SUMMARY The SCR systems for Units 1 and 2 at the SJRPP are designed to meet all of the goals for operation while allowing maximum fuel flexib ility. The systems are designed to provide a high level of availability and reliability while minimizing future O&M costs and the risk of plant outages. These goals were met through the careful testing and selection of catalyst and through the incorporation of specific design features to minimize the potential for visible emissions and catalyst deactivation.