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 130th 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 Meadow Lane, Durham, NC 27713 

John Cochran 

CERAM Environmental, Inc., 7304 West 130th Street, Suite 140, Overland Park, KS 

66213 

ABSTRACT 

The St. Johns River Power Park is installing SCR systems on two pulverized coal units 

cofiring high arsenic and silica coals with up to 30 percent petroleum coke containing 

high levels of vanadium and sulfur. This fuel combination created significant challenges 

for maintaining low SO2/SO3 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, catalyst design, and equipment life. Additional 

consideration was given to operations and fuel management strategies to minimize fuel 

impacts on SCR operation. This paper discusses the design challenges faced and special 

features incorporated to maintain fuel flexibility and plant availability, including catalyst 

procurement, reactor/ductwork design, and other system features. Additionally, results 

are presented regarding testing various catalyst types after exposure to flue gas from 

cofiring 30 percent petroleum coke (petcoke) and 70 percent coal for up to 6,000 hours 

and from the SCR system performance test. 

10.3155/2008CP175.96
2 

INTRODUCTION 

The St. Johns River Power Park (SJRPP) is located 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 station consists of two 

670 MW (gross) coal fired power plants. Both units are baseloaded with high capacity 

factors. SJRPP was required to install selective catalytic reduction (SCR) systems on both 

units to reduce nitrogen oxide (NOx) 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 and maintenance (O&M) costs and plant 

interruptions. In addition, SJRPP fires a unique variety of fuels (which is discussed in 

detail in this paper), and the SCR systems needed 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 phases. The first phase entailed preliminary 

engineering and consisted of characterization testing, design basis development, 

assessment of balance-of-plant issues, CoPilot®catalyst testing, development of ductwork 

arrangement, ductwork arrangement fatal flaw analysis, and cost estimating. The second 

phase involved project implementation and consisted of detailed engineering, equipment 

procurement, construction, and startup. 

Figure 1 is an arrangement drawing for the SCR layout at the SJRPP units. Flue gas from 

the economizer is split and sent through one of two SCR reactors. 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 ammonia, diluted in air, is injected into the 

flue gas by the AIG. The flue gas then enters the SCR reactor where the ammonia and 

NOx react in the presence of the catalyst to form nitrogen (N2) 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 isolate the SCR for maintenance. The air heaters 

have been retrofitted with ammonium bisulfate-resistant baskets. 

FUELS BACKGROUND 

For the first 10 years of commercial operation (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 substantial 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 bunkering of the two materials; all burners 

fired the same blend of petcoke and coal. This was standard procedure from 1997 until 

burner improvements allowed a preferred 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 result, 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 allowing the petcoke blend to be increased 

to 30 percent. The new standard procedure involved using two pulverizers (8 burners) 

with petcoke, and four pulverizers (16 burners) with coal. The two pulverizers with 

petcoke were biased down to attain the desired 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 petcoke 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 result of the range of 

fuels and direct bunkering operations described above. Localized effects on the catalyst 

could be anticipated from the direct bunkering of individual fuels. The fuels considered 

for the SCR design are listed in Table 1. Particularly 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, and the high silica of the Colombian coal. The 

following briefly describes concerns associated 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 potential for catalyst erosion due to the erosive nature of the 

fly ash. This coal normally contains 10 percent ash (up to 18 percent), with fly ash silica 

contents in the range of 57 to 62 percent, and fly ash alumina contents in the range of 17 

to 22 percent in the ash. 

Domestic Coal 

Eastern Kentucky domestic coal has a high potential for catalyst deactivation due to the 

relatively high level of arsenic in the coal compared to the relatively low amount of 

calcium oxide (CaO) in the fly ash. The arsenic 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 results 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 gaseous arsenic is formed in the burner flame, 

excess CaO from the other fuels will not reduce 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 second is the presence of a high concentration 

of vanadium in the fuel. 

Petcoke 

Firing Petcoke 

Firing 
5 

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 visible emissions from sulfur trioxide (SO3). 

The MOT for an application is established to avoid significant buildup of ammonium 

bisulfate (ABS) on the catalyst. The MOT is determined based on the SO3 and the 

ammonia concentrations in the flue gas. When firing 30 percent petcoke at SJRPP, the 

sulfur dioxide (SO2) and SO3 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 SO2 and SO3 concentrations in the flue gas when 
6 

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 approximately 2,000 ppm of vanadium. Considering 

a 30 percent blend, the combusted fuel blend 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 catalyst 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 SO2 to SO3 conversion rate across the catalyst and will slow the rate of 

catalyst deactivation. The levels of SO3 will increase as a function of time when firing 

petcoke. 

Impact of Direct Bunkering on the SCR Design 

While direct bunkering is more beneficial than 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 bunkering, the fuels are fired separately and their 

individual products of combustion segregate as they exit the furnace. Undisturbed, 

channeling typically occurs as the gas propagates 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 arsenic in the domestic fuel, the 

different levels of uncontrolled NOx produced by the different fuels, the change of the 

NOx profile over the load range, and changes 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 engineer will typically 

utilize the design fuel and guaranteed performance from major equipment suppliers to 

establish the criteria for sizing 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 major air quality control systems, because the 

original criteria are theoretical and actual 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 load and fuel combinations, as defined in 

Table 2. The purpose of the testing was to “bracket” the normal operating 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 appear to be any discernable pattern to NOx

concentrations as a function of fuel or coal mill configuration. The testing also indicated 

that the boiler is oxidizing a relatively high portion of the sulfur in the fuel to SO3 (more 

than 2 percent), resulting in high SO3 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 included the evaluation of 1 year of operating 

data received from the plant information system. Economizer outlet temperature data are 

of particular interest. Outlet temperatures significantly above 850° F can result in 

sintering of the SCR catalyst. A more common concern is the minimum gas temperature 

at low loads. Low flue gas temperatures can result in ABS formation and plugging of 
8 

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, MW

Economizer 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 criteria 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) 

750-800 750-800 750-800 640 
9 

 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 NOx

Emission Rate 

lb/MBtu 0.4 0.4 0.4 0.4 

Maximum NOx

Emission Rate 

lb/MBtu 0.66 0.66 0.66 0.5 

Maximum SO2 

Concentration 

ppmvw 2,050 1,058 1,960 1,865 

Average SO3 

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 invited to participate in a testing program using 

CoPilot® test reactors. This testing program consisted of placing catalyst plate and 

honeycomb elements from the prospective suppliers 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 gas 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 specification 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 bidder’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 evaluation criteria. Each 

item on the list was assigned a rating that indicated the importance of that item. Based on 

this comprehensive technical and commercial 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 all parties gain an understanding of the impacts 

of the individual fuels, but they also gained an understanding of the impacts of direct 

bunkering. In addition, the visits gave SJRPP an understanding of the project 

implementation philosophies of each vendor. Finally, the process gave all parties 

confidence in the ability of the catalyst to meet performance guarantees. 

CO-PILOT® TESTING 

During the initial design phase of the project, 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 direct bunkering scenario. 

The CoPilot® test reactor is an in situ test reactor that allows for catalyst exposure at SCR 

reactor velocities to the actual plant flue gas conditions. The general arrangement of the 

CoPilot® test reactor is depicted on Figures 4 and 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 directly 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 installed and removed from the ductwork while the 

unit was on line. The CoPilot® is equipped with an LPA screen, soot blower, flow 

straightening grid, inlet and outlet temperature 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 Gas
11 

Figure 5. CoPilot® Test Reactor

CoPilot® Catalyst Test Reactor

Air Amplifier/

Eductor

Inlet Temperature, 

Pressure and Test Taps

NH3 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 tested. 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 catalyst in all three CoPilot® test reactors in an effort to 

obtain as much information as possible prior to the catalyst production date. By the 

completion of CoPilot® testing, one catalyst sample had 7,280 hours of flue gas exposure. 

Activity and SO2 to SO3 Conversion Rate Test Results 

Table 4 summarizes the results of the activity and SO2 to SO3 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 

SO2 to SO3

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 provided 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 noticeable initial increase in catalyst activity 

up to 2,000 hours. There are two reasons for this. First, as the catalyst is initially installed 

in a flue gas atmosphere, a “sulphation” process occurs, which causes a slight increase in 
13 

catalyst activity. Second, the initial accumulation of vanadium from the petcoke will 

cause an increase in activity. 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, resulting in catalyst deactivation in the long 

term. 

The SO2 to SO3 conversion rate test results 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 SO2 to SO3

conversion rate over time when firing 30 percent petcoke. 

Figure 7: CoPilot® SO2 to SO3 Conversion Rate Testing Summary

Bulk and Surface Chemical Analysis Results 

The bulk and surface chemical analysis results 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 analysis results is related to the accumulation of 

arsenic on the catalyst surface and in the bulk catalyst 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 exposed 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 fired 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 SO2 to SO3 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 available for testing had only 2,135 hours of flue gas exposure. 

The initial SO2 to SO3 conversion rate was designed very low to account for the expected 

deposition of vanadium on the catalyst and the corresponding 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 m3

Catalyst Deactivation Basis Low (K/Ko=0.88) due to 30% petcoke blend 

Catalyst Wall Thickness 1.0 mm 

Initial Oxidation Rate 0.25% (Ammonia Off/800° F) with three 

catalyst layers installed 

Guarantee NOx Outlet 0.06 lb/MBtu (85% NOx 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, including input from 

SJRPP and Black & Veatch, in order to provide an optimized catalyst for the project. As 

indicated in Table 4, one catalyst sample was able to achieve 7,280 hours of operation in 

the CoPilot®. 

Fuel Changes Late in Project 

In the summer of 2007, the SJRPP Fuels Department 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 costly 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, and 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 since 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 revisited 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, the most difficult aspect was the consideration 

that the original catalyst was designed for very little deactivation. With 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 percent 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 20000

Required Reactor Potential

Operating 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 catalyst design for the 
16 

project while limiting cost impacts. The objective of SJRPP was to not change the 

catalyst volume for the project. Considering that the system was installed to control stack 

SO3 emissions (described subsequently) and that the SO2 to SO3 conversion rate would 

not be time dependent as it would be for petcoke blends, there was sufficient margin to 

accept increased oxidation from the catalyst. 

Consequently, the revised catalyst design resulted 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 commercial 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 High 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 NOx Outlet 0.06 lb/MBtu (85% NOx 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 design. Design features 

included the following. 

High Mechanical Strength 

The catalyst was designed with a 1.0 mm catalyst 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 catalyst supplied for this 

project can be washed and regenerated 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 maintained by using a large pitch catalyst. 
17 

Full Height Catalyst Frames 

The original catalyst design utilized a catalyst height of approximately 1000 to achieve 

the performance guarantees. However, the catalyst was installed into steel frames that 

were large enough to hold the maximum length element of 1,300 mm. In this way, the 

soot blowers could be placed in the proper 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 needed 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 the SCR design to provide SJRPP 

with maximum fuel flexibility. 

System Design for Direct Bunkering 

The characterization tests showed a significant change in the NOx profile over the load 

range. The ratio between the fuels fired changes over the load range, resulting in changes 

to the NOx profile, which cannot be accommodated with the ammonia injection grid only. 

To disrupt natural channeling at SJRPP, a static 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 dynamics (CFD) and experimental modeling 

afforded the project the flexibility to evaluate different mixing technologies to ensure that 

sufficient mixing of gas species would mitigate 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 mixer provides a very high mixing efficiency 

at a low pressure drop. 

System Design for Flue Gas Temperature 

There were two main temperature issues that 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 operating 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 temperatures 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. Figure 10 illustrates the 

temperature distribution from the characterization testing. It shows the variation in 

temperature that occurs at low load at the economizer outlet when the unit is firing a 

combination of 30 percent petcoke/35 percent Colombian coal/35 percent domestic coal. 

As can be seen from the figure, the temperature 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 condensation temperature, even if the average temperature is above the ABS condensation temperature. This temperature stratification is 

corrected through the use of the static mixer, as shown on Figure 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 minimizing 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 NOx and flue gas velocity distribution 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 remain on the floor of the ductwork. Therefore, in 

order to minimize the potential for ash on the 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 and address areas where dust tended to settle 

out of the flue gas. 
19 

Figure 10: Temperature Distribution of Flue Gas Exiting Economizer

Although the ductwork needed to be designed for 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 address these conflicting 

design requirements between the petcoke and Colombian coal, the ductwork was 

designed with minimal internal bracing. The vast 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 unburned carbon and minimizing the potential for 

erosion. 

Reactor Design 

A key requirement for providing fuel 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 the combined use of both CFD and physical 

flow modeling. Through this modeling effort, Flowtack (CERAM’s flow modeler for the 

project) developed a graduated straightening grid (GSG) at the inlet of the reactor in lieu 

of the traditional turning vane/straightening grid configuration. 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 arsenic from the domestic coal. Calcium reacts 

with the gaseous arsenic in the fuel and forms 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 further 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 concentration of calcium in the ash of the 

domestic fuel. 

SO3 Control System 

After SJRPP began firing petcoke, it installed an ammonia injection system downstream 

of the air heater to control SO3 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 percent petcoke and considering the increasing 

SO2 to SO3 conversion rate over time due to the vanadium accumulation, the SO3 control 

system would remain capable of reducing the SO3 concentrations to 5 ppm or less at the 

stack to avoid visible emissions. 

The original system is a conventional anhydrous ammonia flue gas conditioning system, 

built in 1999. This system consisted of an ammonia storage tank, vaporizers, dilution air 

blowers, controls and injection lances. The 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 electrostatic precipitators (ESPs). Each unit has 20 

injection lances. The ammonia reacts with SO3 in the flue gas to form ammonium 
21 

bisulfate, which condenses on the fly ash particles and is collected in the ESP, effectively 

removing the SO3 from the flue gas. 

System modifications to improve overall operability 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 superheated ammonia vapor to 

the dilution air stream. A third dilution air blower was installed in the system to provide 

backup for either existing blower, thus increasing reliability. The injection lances were 

redesigned to ensure better distribution of the ammonia in the flue gas and to improve the 

durability of the lances. The SO3 control system was upgraded to allow better system 

turndown, as well as to ensure adequate control range for higher SO3 concentrations 

leaving the SCR system as a result of the SO2 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 result, the SCR system design was required to 

prevent LPA from reaching the catalyst. 

The LPA capture design was developed through 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 the LPA from the flue gas. 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 gas 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 NoNOx. 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 capability of operating the units on full load with 

only three of the four fans in operation. Increasing 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 effect 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 the 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 flexibility. 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.