Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

TOXECONTM Retrofit for Multi-Pollutant Control on 

Three 90-MW Coal-Fired Boilers 

Topical Report: Performance and Economic 

Assessment of Trona-Based SO2/NOx Removal at the 

Presque Isle Power Plant 

Prepared for: 

We Energies 

DOE/NETL 

Prepared by: 

ADA-ES, Inc. 

8100 SouthPark Way, Unit B 

Littleton, CO 80120 

(303) 734-1727 

August 25, 2008 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

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Table of Contents 

Summary.................................................................................................................................. 1

Introduction............................................................................................................................. 1

Background ............................................................................................................................. 2

Test and Equipment Description........................................................................................... 3

Trona Background Information...................................................................................... 4

Trona Injection Equipment ............................................................................................. 4

Trona/Ash Unloading Issues............................................................................................ 7

SO2, NOx and Opacity Measurement.............................................................................. 7

Test Results.............................................................................................................................. 8

Baseline Testing ................................................................................................................ 8

Parametric Testing ......................................................................................................... 10

Schedule and Materials Handling........................................................................ 10

SO2 and NOx Removal .......................................................................................... 11

Baghouse Pressure Drop and Cleaning Frequency............................................ 15

Economic Assessment of Full-Scale Trona Injection......................................................... 17

Introduction..................................................................................................................... 17

Process Design................................................................................................................. 17

Trona Injection System......................................................................................... 17

Ash Handling System ............................................................................................ 19

Cost Estimates and Results............................................................................................ 20

Capital Costs.......................................................................................................... 20

Operating and Maintenance Costs ...................................................................... 22

Levelized Costs ...................................................................................................... 25

Removal Cost per Ton of SO2 Removed ............................................................. 28

Conclusions............................................................................................................................ 30

References.............................................................................................................................. 31

APPENDIX A – Cost Estimates and Results – Details...................................................... 32

Capital Costs.......................................................................................................... 32

Operating and Maintenance Costs ...................................................................... 34

Levelized Costs ...................................................................................................... 39

Removal Cost per Ton of SO2 Removed ............................................................. 46
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

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List of Tables 

Table 1. Schedule of Activities for SO2/NOx Control Testing................................................. 3

Table 2. Trona Injection Results. ............................................................................................ 11

Table 3. System Design Criteria for SO2 Control System at Presque Isle (6000 lb/hr 

injection, >70% SO2 control). ........................................................................................... 18

Table 4: Summary of Equipment, Balance-of-Plant, and Engineering Costs...................... 21

Table 5. Total First-Year Fixed Operating & Maintenance Costs....................................... 23

Table 6. Variable First-Year Operating & Maintenance Costs for Power ......................... 24

Table 7. First-Year Variable Operating & Maintenance Costs for Sorbent Delivered by 

Rail and by Rail/Truck Combination to the Plant.......................................................... 24

Table 8. First-Year Variable Operating & Maintenance Costs for Landfill Waste Disposal

.............................................................................................................................................. 25

Table 9. First-Year Total Variable Operating & Maintenance Costs ................................. 25

Table 10. Economic Factors and Parameters......................................................................... 26

Table 11. Levelized Capital Costs............................................................................................ 26

Table 12. Total Levelized Fixed Operating & Maintenance Costs ...................................... 27

Table 13. Levelized Total Variable Operating & Maintenance Costs ................................. 27

Table 14. Total Levelized Costs (Capital and Fixed & Variable O&M Costs) ................... 28

Table 15. Removal Cost per Ton of SO2 ................................................................................. 29

Table 16. Summary of Equipment, Balance-of-Plant, and Engineering Costs ................... 33

Table 17. Fixed O & M Costs – Ash Handling Labor Cost Parameters............................. 34

Table 18. Fixed O & M Costs – Ash Handling Labor Costs for Three SO2 Removal Rates

.............................................................................................................................................. 35

Table 19. Fixed Operating & Maintenance Costs for Equipment Operating, Maintenance 

and Support Labor ............................................................................................................ 35

Table 20. Total First Year Fixed Operating & Maintenance Costs ...................................... 36

Table 21. Power Requirements to Run Trona Injection System .......................................... 37

Table 22. Variable Operating & Maintenance Costs for Power .......................................... 37

Table 23. Variable Operating & Maintenance Costs for Sorbent Delivered by Rail to the 

Plant .................................................................................................................................... 38

Table 24. Variable Operating & Maintenance Costs for Sorbent Delivered by a 

Combination of Rail and Truck to the Plant................................................................... 38

Table 25. Variable Operating & Maintenance Costs for Disposing the Waste to the 

Landfill................................................................................................................................ 39

Table 26. Total Variable Operating & Maintenance Costs .................................................. 39

Table 27. Levelized Capital Costs............................................................................................ 40

Table 28. Levelized Fixed Operating & Maintenance Costs for Ash Handling Labor ...... 41

Table 29. Levelized Fixed Operating & Maintenance Costs for Equipment Operating, 

Maintenance, and Support Labor .................................................................................... 41

Table 30. Levelized Total Operating & Maintenance Costs ................................................. 42

Table 31. Levelized Variable Operating & Maintenance Costs for Power ......................... 42

Table 32. Levelized Variable Operating & Maintenance Costs for Sorbent Delivered by 

Rail to the Plant.................................................................................................................. 43

Table 33. Levelized Variable Operating & Maintenance Costs for Sorbent Delivered by a 

Combination of Rail and Truck to the Plant................................................................... 43
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Table 34. Levelized Variable Operating & Maintenance Costs for Waste Disposal.......... 44

Table 35. Levelized Total Variable Operating & Maintenance Costs ................................. 44

Table 36. Levelized Costs (Capital, Fixed, and Variable Levelized Costs) .......................... 45

Table 37. Removal Costs per Ton SO2 Removed .................................................................... 46

List of Figures 

Figure 1. Staging Area for Trona Injection Equipment.......................................................... 5

Figure 2. Trona Injection Trailer Blowers and Controls........................................................ 6

Figure 3. Injection Ports............................................................................................................. 7

Figure 4. Baseline SO2 and NOx Data ....................................................................................... 9

Figure 5. Unloading Reacted Trona/PAC/Ash Mixture........................................................ 10

Figure 6. SO2 Removal vs. Trona Injection Rate................................................................... 12

Figure 7. SO2 Removal Profiles. .............................................................................................. 12

Figure 8. NOx Removal During Trona Injection................................................................... 13

Figure 9. Effect of 5926 lb/hr Trona Injection on SO2, NOx, and Opacity.......................... 14

Figure 10. Effect of 5926 lb/hr Trona Injection without PAC Injection.............................. 14

Figure 11. Baghouse Operation During Trona Injection Testing. ....................................... 16

Figure 12: Schematic of the Trona Injection Equipment at Presque Isle Units 7, 8 and 9. 19

List of Acronyms 

DOE Department of Energy 

PAC Powdered Activated Carbon 

NSR Normalized Stoichiometric Ratio 

MMacf Million actual cubic feet of flue gas 

O&M Operating & Maintenance 

EPRI Electric Power Research Institute 

CEM Continuous Emissions Monitor 

RATA Relative Accuracy Test Audit 

TCR Total Capital Requirement 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

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Summary 

Under a DOE Clean Coal Program, activated carbon injection has been used to demonstrate 

continuous mercury removal at We Energies’ Presque Isle Power Plant (PIPP). Trona injection 

tests were also performed at PIPP from July 31 through August 10, 2007. The purpose of these 

tests was to determine if dry trona injection prior to the TOXECONTM baghouse would result in 

at least 70% sulfur dioxide (SO2) reduction, and to assess any related change in mercury 

removal. Some minor nitrogen oxide (NOx) reduction was also anticipated from these tests. 

Balance of plant issues associated with trona injection and subsequent ash handling were also 

evaluated. 

A temporary injection system was set up near the Units 7-9 stack with individual hoses and 

lances feeding each of the Unit ducts. The injection point was near the existing PAC injection 

ports in each duct and downstream of the plant NOx analyzers used for boiler feedback. SO2 and 

NOx analyzers were temporarily installed upstream of the trona injection point on each of the 

three ducts for monitoring during the tests. Existing analyzers were used at the stack to measure 

SO2, NOx, and opacity. 

During the test period, the trona injection rate was varied, which provided the data necessary to 

complete an SO2 removal curve. Powdered Activated Carbon (PAC) injection continued at pretrona injection test levels with trim control on, which allowed some variability (+/- 20%) in 

injection rate. PAC injection was turned off one day to determine if there was an effect from 

PAC on SO2 removal. Due to a negative effect from trona injection on mercury removal, PAC 

injection was increased on one day to try to regain a >90% removal rate. 

The goal of 70% SO2 removal was achieved during this two week test period when using 5926 

lb/hr of trona. This corresponds to an average Normalized Stiochiometric Ratio (NSR) of 1.02. 

The NSR is the molar ratio of the sorbent injected to that theoretically required for complete 

reaction with SO2. The inlet concentration of SO2 varied from 0.48-0.64 lb/MBtu. The highest 

removal was 74.1% with PAC injection at 3.8 lb/MMacf. There was very little reduction in total 

NOx during the test period, although the presence of the side reaction with NO producing NO2

was observed during when PAC injection was turned off. Injection of trona for SO2 control 

resulted in a decrease in mercury removal using activated carbon. The mercury removal slowly 

recovered overnight to the pre-trona injection levels of >90%. 

An economic assessment of a full-scale trona injection system included equipment and other 

capital costs along with sorbent cost (trona and increased amount of PAC to maintain 90% 

removal) and O&M costs. The cost to remove SO2 varied from $1,448/ton at 45% removal and 

one silo to $2,231/ton SO2 at 70% removal with 3 silos. 

Introduction 

We Energies’ Presque Isle Power Plant is the site of a DOE Clean Coal demonstration project 

being conducted under a cooperative agreement with Wisconsin Energy Corporation and the 

Department of Energy (DOE). The primary goal of this project is to reduce mercury emissions 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

2 

using a TOXECONTM system designed to clean the combined flue gases of Units 7, 8, and 9 at 

the Presque Isle Plant. An additional goal is to reduce NOx and SO2 emissions. 

TOXECONTM is an Electric Power Research Institute (EPRI) patented process in which a fabric 

filter system (baghouse) installed downstream of an existing particulate control device is used in 

conjunction with sorbent injection for removal of pollutants from combustion flue gas. The flue 

gas emissions are controlled from the three units using a single baghouse. Mercury is controlled 

by injection of activated carbon, while NOx and SO2 reduction was tested by injection of 

sodium-based sorbents. Both the mercury and SO2/NOx control sorbents were removed from the 

gas stream by the baghouse. 

The overall objectives of this project are to demonstrate the operation of the TOXECONTM 

multi-pollutant control system and: 

1. Achieve 90% mercury removal from flue gas through activated carbon injection 

(achieved). 

2. Reduce particulate emissions through collection by the TOXECONTM baghouse 

(achieved). 

3. Maintain 100% utilization of fly ash collected in the existing electrostatic precipitator 

(achieved). 

4. Demonstrate reliable, accurate mercury CEM suitable for use in the power plant 

environment (achieved). 

5. Evaluate the potential for 70% SO2 control and trim control of NOx from flue gas through 

sodium-based or other novel sorbent injection, while maintaining 90% mercury removal. 

6. Recover 90% of the mercury captured in the sorbent. 

Objective #5 was the focus of the test program described in this report. 

Background 

Testing of SO2/NOx control sorbents to date in the TOXECONTM/COHPAC® configuration 

included: 

• Full-scale tests injecting sodium bicarbonate and sodium sesquicarbonate (trona) 

upstream of the Big Brown COHPAC® baghouse for SO2 control.1

• Pilot tests of sodium and lime sorbents injected upstream of COHPAC® for SO2 control 

at Southern California Edison’s Mohave Station.2

• Slipstream tests of sodium-based materials, lime, activated carbon, and a proprietary 

catalyst for NOx, SO2, SO3, HCl, HF, and Hg at the PSEG Hudson Generating Station.3

Test results indicate that sodium-based products can achieve from 30% to 70% SO2 reduction. 

At normal flue gas temperatures, lime/calcium products are not effective for SO2 control. 

Sodium-based sorbents also reduced NOx by 10% to 20%. HCl removal was as high as 50% at 

Hudson using sodium sesquicarbonate. 
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Test and Equipment Description 

This test effort was designed to support the overall objectives of the TOXECONTM retrofit at 

Presque Isle as well as to further the technical understanding of the TOXECONTM technology for 

both We Energies and the greater industry. Parametric and continuous tests were planned to 

assess the capability of trona injection upstream of the TOXECONTM baghouse to control SO2

and NOx. Injection equipment and measurement instrumentation were installed specifically for 

these tests. The following were the objectives of the testing program: 

1. Quantify the trona injection rate versus SO2/NOx removal. 

2. Record baghouse performance over the test period, showing how pressure drop, 

cleaning frequency and mercury removal change. 

3. Determine if there is any negative effect of trona injection on emissions (NO2

production). 

4. Evaluate the technical and economic performance of trona as an option for full-scale 

SO2 control. 

The tests for SO2/NOx control were conducted in two phases, baseline and parametric testing, as 

shown in Table 1. Measurements were taken during July to determine baseline conditions. 

Parametric testing data was used to characterize the performance of trona across a range of 

injection concentrations and at different PAC injection concentrations. Originally, a 5 day 

continuous test was scheduled but due to shipping and material handling issues this phase was 

cancelled. 

Table 1. Schedule of Activities for SO2/NOx Control Testing. 

SO2-NOx Control Activity Duration (Days) Start Date Boiler Load 

Baseline Testing 21 07/09/2007 Normal Operation 

Equipment Installation and Shakedown 2 07/30/2007 Normal Operation 

Parametric Testing 10 08/1/2007 Full Load 6AM–6PM 

The final test plan for injecting trona to control SO2 and NOx was distributed to the project team 

in July. The plant completed the installation of SO2 and NOx analyzers at each of the three ducts 

upstream of the sorbent injection point in early July. These analyzers provided data on untreated 

SO2 and NOx levels for both baseline and injection testing. 

Plant operators kept the three units at full, steady load during the two week test period. The 

boiler soot blowers were used every hour on a staggered schedule with the three units to keep the 

flue gas temperature from fluctuating during testing. PAC injection was left unchanged initially. 

The logic allowed for the injection rate to vary +/- 20% to keep 91% mercury removal. 
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Trona Background Information 

Trona is a sodium-based, naturally occurring mineral (sodium sesquicarbonate). The trona used 

during this test program was obtained from Solvay Chemicals, Inc. and was mined in Green 

River, Wyoming. The purified SOLVAir Select 200 trona was shipped by rail to Chicago then 

loaded into hopper trucks for delivery to Marquette, Michigan. The hopper trucks typically 

carried 45,000 – 48,000 lb of trona depending on the test schedule. The particle size of the trona 

averaged 26 μm according to the Certificate of Analysis accompanying the material. 

The formula for sodium sesquicarbonate is: 

Na2CO3 .

 NaHCO3 . 2H2O 

sodium carbonate .

 sodium bicarbonate . water 

When heated to 257-482oF in a duct or a calciner, the sodium trona decomposes to sodium 

carbonate according to the formula: 

2(Na2CO3 .

 NaHCO3

.

 2H2O) → 3Na2CO3 + CO2 + 5H2O 

When injecting trona into a coal fired power plant flue gas, it reacts with hydrochloric acid and 

SO2 according to the following: 

Na2CO3

.

 NaHCO3 . 2H2O + 3HCl → 3NaCl + 4H2O +2CO2

2(Na2CO3 .

 NaHCO3 . 2H2O) + 3SO2 → 3Na2SO3 + 4CO2 + 5H2O 

3Na2SO3 + 1.5O2 → 3Na2SO4 

Review of industry literature emphasizes the benefit of injecting trona in a hot-side (greater than 

700 °F) location. Trona experiences what is referred to as a “popcorn effect” where at high 

temperature the thermal decomposition reaction results in an expanded particle with a high 

surface area to mass ratio, improving the chemical availability of the sodium compound. This 

change improves the effectiveness by a factor of between 5 and 10. Trona will still react with 

SO2 if injected at lower temperatures (typical cold-side temperature around 300 to 350 °F) but 

loses the reactivity otherwise gained by the particle expansion. Consequently, for lower 

temperature applications more trona is required to achieve the same SO2 removal efficiency. 

During the first 10 days of August, the flue gas entering the baghouse at Presque Isle varied from 

333 – 372 o

F. 

Trona Injection Equipment 

The injection equipment for this test program was obtained from Bulk Conveyor Specialist, Inc. 

and staged near the Units 7-9 stack as shown in Figure 1. This equipment consisted of a trailer 

holding approximately 40 tons of trona and a separate trailer housing the blowers and controls 

(Figure 2). This system injected sorbent at the shipped particle size. Feed rate for the trona was 

from 2,200 lb/hr up to 5,900 lb/hr at full load to cover a wide range of stoichiometric ratios. 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

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Figure 1. Staging Area for Trona Injection Equipment 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

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Figure 2. Trona Injection Trailer Blowers and Controls. 

The trona was fed to three injection lances which were located downstream of the ID fan 

discharges, but upstream of the point where the ducts combine. Each lance discharged sorbent 

into the center of its duct, where turbulent flow provided gas/sorbent mixing. The lances were 

located below the current PAC injection lances (white hose in Figure 3). This is downstream of 

the NOx analyzer probe used for boiler feedback. 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

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Figure 3. Injection Ports 

Trona/Ash Unloading Issues 

Prior to field testing, there was some concern that the reacted trona/ash/PAC from the baghouse 

would be difficult to unload and transport using the existing ash-handling equipment. The 

reacted trona hardens when wetted, and Presque Isle typically uses a wet unloader for the 

PAC/ash mixture. This mixture is then hauled by truck to the landfill. 

Benetech, Inc. performed a series of laboratory tests on the anticipated final product from the 

baghouse and developed a chemical to prevent hardening of the mixture. A tanker truck of the 

chemical along with injection equipment was prepared and shipped to Presque Isle for the 

testing. Provisions were made to add this chemical to the water spray used in the wet unloader. 

SO2, NOx and Opacity Measurement 

SO2 and NOx monitors were installed on a temporary basis by We Energies near the exit of the 

ID fan on each duct to establish baseline levels coming from each boiler. At the stack, the plant 

continued to utilize the installed SO2 and NOx monitors to establish native removal across the 

TOXECONTM system and provide removal rates during trona injection. 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

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Data from the inlet and stack monitors was collected continuously by the plant data acquisition 

system (EDS) and saved on the historian computer. The data was downloaded every week 

during baseline and every day during trona injection. 

Prior to the trona injection testing, three Relative Accuracy Test Audits (RATAs) were 

performed on the SO2 and NOx monitors in the Units 7, 8, and 9 flues. The Unit 7 RATA was 

performed on June 13, 27, and 28, 2007. The Unit 8 RATA was performed on June 5 and 6, 

2007. The Unit 9 RATA was performed on June 5 and 6, 2007. 

The results of the RATAs reported by the testing company were: 

“The test results from this test program indicate that each CEM system meets 

the United States Environmental Protection Agency (USEPA) annual 

performance specification for relative accuracy as published in 40 CFR Part 60 

and/or 40 CFR Part 75.” 

Test Results 

Baseline Testing 

The purpose of the baseline test was to establish the concentrations of pollutants leaving the air 

preheater and to determine if there was any native capture across the TOXECONTM fabric filter 

without sorbent injection. Figure 4 shows inlet and outlet data for SO2 and NOx for the three 

ducts and flues during July. As expected, none of the three graphs show any removal across the 

baghouse prior to trona injection. In addition to the flue gas measurements for SO2/NOx, ash 

samples were taken from the baghouse hoppers. A composite sample of ash from four hoppers 

was used to characterize the ash during this time. 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

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Unit 7 Baseline SO2 and NOx

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

7/2/07 7/7/07 7/12/07 7/17/07 7/22/07 7/27/07 8/1/07

Time

Rate (lb/MMBtu) 

SO2 Inlet

SO2 Outlet

NOx Inlet

NOx Outlet

Unit 8 Baseline SO2 and NOx

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

7/2/07 7/7/07 7/12/07 7/17/07 7/22/07 7/27/07 8/1/07

Time

Rate (lb/MMBtu) 

SO2 Inlet

SO2 Outlet

NOx Inlet

NOx Outlet

Unit 9 Baseline SO2 and NOx

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

7/2/07 7/7/07 7/12/07 7/17/07 7/22/07 7/27/07 8/1/07

Time

Rate (lb/MMBtu) 

SO2 Inlet

SO2 Outlet

NOx Inlet

NOx Outlet

Figure 4. Baseline SO2 and NOx Data 
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Parametric Testing 

Schedule and Materials Handling 

The trona injection equipment was set up at Presque Isle on Monday, July 30, 2007. All of the 

injection hoses and lances were installed by late afternoon. Electricity was connected to the 

blower trailer by 3:30 pm. 

The first truckload of trona arrived on site Tuesday morning. This truck carried 48,000 lbs, 

which partially filled the hopper truck. In order to test the wet unloader and the effect of the 

anti-setup chemical supplied by Benetech, four hours of injection at 2,200 lb/hr was performed 

on Tuesday, July 31. At the end of the four hours, the ash silo was unloaded using the chemical 

in the water feed to the pin mixer. The ash silo had been unloaded earlier in the day so the 

majority of the ash in the silo contained reacted trona. 

There were no problems with hardening or setting up of the reacted trona/ash/PAC in the wet 

unloader or in the ash truck. Benetech also provided 10 gallons of a “trona release chemical” for 

spraying on the inside of the ash truck bed and the inside of the pin mixer. Bottom ash from 

Units 5 and 6 (bituminous coal) was used to line the bottom of the ash truck also since the 

efficacy of the release chemical or anti-setup chemical had not been tested at full scale yet. 

Figure 5 shows the material being unloaded at the landfill. The consistency was similar to wet 

sand. The next day the material still had not changed in consistency. 

Figure 5. Unloading Reacted Trona/PAC/Ash Mixture 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

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On Wednesday morning, August 1, the ash silo was unloaded to remove the accumulated 

material from overnight. This material contained significant amounts of reacted trona that had 

been cleaned from the bags over the course of several hours after injection had stopped. This 

unloading process was inadvertently performed without the anti-setup chemical, and there were 

no problems with the material setting up in either the mixer or the truck. Over the course of the 

next few days, unloading at the end of injection was done with the chemical, and in the morning 

without. There were no issues with setup either with or without the chemical. The wetted 

material showed a significant heat of reaction and was still steaming when unloaded at the 

landfill. 

During the second week of testing, the ash silo was unloaded after injection using water only (no 

anti-setup chemical). Although there was a noticeable heat associated with the mixing, the 

material didn’t set up in the pin mixer or in the truck. A sample was taken at the landfill and the 

next day it still hadn’t set up. The reaction with water to form a solid hydrate may have occurred 

in the pin mixer but the action of the mixer may have kept the material from solidifying. The 

main risk of wetting the trona/ash/PAC without the anti-setup chemical is that if the mixer stops, 

the wet material in the mixer would likely solidify and would be very difficult to remove. 

Parametric testing began August 1, 2007. During this test phase all three units were at full load. 

The original plan was to vary the sorbent injection rate from approximately 2,200 lb/hr up to 

5,400 lb/hr. There was some concern that the ash system could not handle a sorbent injection 

rate above 5,400 lb/hr. The vacuum system used to pull ash from the hoppers and transport it to 

the silo was rated for 5,000 lb/hr. Adding the ash and PAC (110 lb/hr and 130 lb/hr 

approximately) put the highest injection rate well above the rating for the vacuum system. 

SO2 and NOx Removal 

Table 2 shows the injection rate and SO2 removal for the test period. The maximum removal 

achieved during the testing was 74.1% when co-injecting 3.8 lb/MMacf PAC. 

Table 2. Trona Injection Results. 

Date Trona 

Injection 

Rate (lb/hr) 

Average 

NSR* 

SO2 Inlet 

(lb/MBtu) 

SO2

Removal 

(%) 

Comments 

8/1/07 2223 0.37 0.50-0.66 46.6 

8/2/07 2223 0.41 0.48-0.63 47.6 

8/3/07 4446 0.81 0.48-0.59 65.4 

8/4/07 4446 0.79 0.50-0.58 65.5 

8/5/07 5432 0.97 0.49-0.57 69.8 

8/6/07 5926 - - - Difficulty feeding trona – test stopped 

8/7/07 5926 1.02 0.52-0.60 70.7 

8/8/07 5926 1.02 0.52-0.66 68.5 PAC injection turned off during am 

8/9/07 5926 1.03 0.49-0.62 72.1 PAC injection ramped up to 3.8 lb/MMacf 

8/10/07 5926 1.02 0.51-0.64 74.1 Started PAC injection at 3.8 lb/MMacf at 

start of trona injection 

* Normalized Stoichiometric Ratio 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

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As seen in Table 2 and Figure 6 below, the best SO2 removal was observed when PAC was 

being injected at an unusually high level for this site (3.8 lb/MMacf). This was done to try to 

recover the >90% mercury removal. This PAC injection rate was at the end of a test day, and the 

mercury removal was at 89%. During all trona injection tests, mercury removal degraded, and 

then slowly recovered overnight when no trona was injected (discussed below). 

SO2 Removal Using Trona

40

45

50

55

60

65

70

75

80

0 1000 2000 3000 4000 5000 6000 7000

Trona Injection Rate (lb/hr)

SO2 Removal (%)

PAC Injection Off

PAC Injection at 3.8 lb/Mmacf

Figure 6. SO2 Removal vs. Trona Injection Rate. 

Figure 7 shows typical SO2 removal profiles at varying trona injection rates. There was an initial 

rapid increase in removal but it took 3-4 hours before removal became somewhat steady. Most 

test periods were 8 hours, but one day was only 6 hours. When trona injection was turned off, 

there was an initial rapid decrease in SO2 removal, but it didn’t come back to baseline levels for 

5-6 hours, which was the time required to perform a full cleaning cycle on the baghouse. 

SO2 Removal Using Trona

0

20

40

60

80

100

0 2 4 6 8 10 12 14 16

Time (hr)

Removal (%)

2223 lb/hr 4446 lb/hr 5432 lb/hr 5926 lb/hr 5926 lb/hr high PAC

Figure 7. SO2 Removal Profiles. 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

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In addition to the impacts on SO2, a small reduction in NOx emissions was expected based upon 

work at other test sites. As shown in Figure 8, there was no noticeable reduction in NOx. 

NOx Removal Using Trona

5926 lb/hr

-10

-5

0

5

10

15

20

0 2 4 6 8 10 12 14

Time (hr)

Removal (%)

Trona Injection Began

Trona Injection Stopped

Figure 8. NOx Removal During Trona Injection. 

At other test sites, a side reaction from using trona is the creation of small amounts of NO2, 

which results in a brownish plume and an increase in opacity. Figure 9 shows an increase of 

about 0.75% in the three opacity monitors during the highest injection rate used. There was no 

visible brown plume during this test. 

At the end of the trona injection period on August 7, PAC injection was also turned off and kept 

off overnight and through the start of trona injection on August 8. At mid-day on August 8 a 

brownish plume was seen coming from the stack. This is the first time this had occurred. The 

opacity levels on all three monitors increased by almost 3% (Figure 10). PAC injection was 

resumed at 1:00 pm and within 30 minutes the plume had been visibly reduced and the opacity 

decreased. 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

14 

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

9:00 12:00 15:00 18:00 21:00 0:00 3:00

SO2 and NOx (lb/MMBTU)

0

10

20

30

40

50

60

70

80

Removal (%)

Unit 9 Inlet (SO2)

Unit 9 Outlet (SO2)

Unit 9 Inlet (NOx)

Unit 9 Outlet (NOx)

SO2 Removal

NOx Removal

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

9:00 12:00 15:00 18:00 21:00 0:00 3:00

Opacity (%)

Flue 7 Opacity

Flue 8 Opacity

Flue 9 Opacity

Figure 9. Effect of 5926 lb/hr Trona Injection on SO2, NOx, and Opacity. 

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

3:00 6:00 9:00 12:00 15:00 18:00 21:00

SO2 and NOx (lb/MMBTU)

0

10

20

30

40

50

60

70

80

Removal (%)

Unit 9 Inlet (SO2)

Unit 9 Outlet (SO2)

Unit 9 Inlet (NOx)

Unit 9 Outlet (NOx)

SO2 Removal

NOx Removal

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

3:00 6:00 9:00 12:00 15:00 18:00 21:00

Opacity (%)

Flue 7 Opacity

Flue 8 Opacity

Flue 9 Opacity

Figure 10. Effect of 5926 lb/hr Trona Injection without PAC Injection 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

15 

Baghouse Pressure Drop and Cleaning Frequency 

Any impacts on the cleaning cycle and pressure drop were closely monitored. The fabric filter 

was cleaned in an online mode for all parametric tests. Figure 11 shows the effect of trona 

injection on baghouse operation during the entire injection period. As mentioned earlier, 

mercury removal was negatively affected during trona injection, but recovered overnight. The 

air-to-cloth ratio didn’t change during testing. The cleaning frequency increased slightly during 

testing. 

One unexpected side effect due to trona injection into the baghouse was degradation in mercury 

removal. On August 9, the PAC injection was increased throughout the trona injection period to 

try to recover 90% mercury removal. By the end of the injection period, PAC injection was at 

3.8 lb/MMacf and mercury removal was at 89%. On August 10, PAC injection was increased to 

3.8 lb/MMacf at the start of trona injection and there was still a reduction in removal initially. 

PAC injection reached 4.6 lb/MMacf without regaining 90% mercury removal. Previous tests 

show an initial drop in removal, then a partial recovery after several hours. 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

16 

0

1

2

3

4

5

6

7

8

9

10

7/27/07 8/1/07 8/6/07 8/11/07

Hg (ug/m3)

0

25

50

75

100

125

150

175

200

225

250

275

300

325

350

375

7/27/07 8/1/07 8/6/07 8/11/07

Total Boiler Load (MW)

Temperature (F)

0.0

0.5

1.0

1.5

2.0

2.5

Gas Flow Rate (MMacfm)

0

1

2

3

4

5

6

7

7/27/07 8/1/07 8/6/07 8/11/07

Pressure Drop (inches H2O)

0

1

2

3

4

5

6

7/27/07 8/1/07 8/6/07 8/11/07

A/C Ratio (ft/min)

Trona Injection Rate (k#/hr)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0 Clean Frequency

(pulses/bag/hr)

Trona Injection

0

10

20

30

40

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60

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90

100

7/27/07 8/1/07 8/6/07 8/11/07

Hg Removal (%)

0

0.5

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1.5

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2.5

3

3.5

4

4.5

5

PAC Injection Conc. 

(lb/MMacf)

Hg Outlet

Hg Inlet

PAC Injection 

Baghouse Inlet Temp

Hg Removal

Fl-Fl Pressure Drop

Compartment 1-5 

Pressure Drop

Cleaning Frequency 

Compartments 1-5 

Flue Gas Volume

Total Boiler Load

A/C Ratio

Figure 11. Baghouse Operation During Trona Injection Testing. 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

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Economic Assessment of Full-Scale Trona Injection 

Introduction 

An economic assessment was performed to determine the cost for the installation and operation 

of a full-scale, commercial trona injection system at We Energies’ Presque Isle Power Plant 

Units 7, 8 and 9. Based on the results from the tests described above, cost and design estimates 

were made for a permanent trona injection system. The design premises and the results of the 

economic analysis are presented here. A detailed description of the economic analysis is 

presented in Appendix A. 

Estimates were made for sorbent usage and costs were estimated for three injection rates of 2223 

lb/hr, 4446 lb/hr, and 5926 lb/hr, which include treatment for the flue gas from all three units. 

From the tests completed in August 2007, these injection rates correlate to SO2 removal rates of 

approximately 45%, 64%, and 70%. The cost and design of process equipment has been 

estimated based on the test results for up to 70% SO2 control and on the plant-specific 

requirements such as sorbent storage capacity, plant arrangement, sorbent transportation and 

delivery options, retrofit issues, controls interface, etc. 

A consequence of simultaneously injecting trona for SO2 control and injecting PAC for mercury 

control was significant degradation in mercury removal. August 2007 tests showed an initial 

drop in mercury removal, then a partial recovery after several hours. This economic assessment 

includes cost estimates for the increase of PAC usage required when injecting trona. Normal 

average injection rates at Presque Isle of PAC for 90% mercury removal were 1.5 lb/MMacf for 

DARCO® Hg-LH and 2.5 lb/MMacf for DARCO® Hg. To achieve 90% mercury removal while 

injecting trona at a rate required for 70% SO2 removal, DARCO® Hg-LH would need to be 

injected at approximately 4.5 lb/MMacf and the injection rate for DARCO® Hg was assumed to 

be at 7.5 lb/MMacf, based on the required increase in DARCO® Hg-LH usage.. The increased 

requirement for PAC was not measured at the lower trona injection rates. The PAC increase was 

calculated based on a linear increase from baseline to the highest injection rate. PAC injection 

rates costs for the SO2 removal rates are summarized below in the section regarding variable 

operating costs in Appendix A. 

Process Design 

Trona Injection System 

Costs were estimated for two different equipment setups. The first setup consists of one bulk 

storage silo with three pneumatic conveying systems. The second setup consists of three bulk 

storage silos, each dedicated to a single unit with one pneumatic conveying system on each silo. 

Note that the silo size is the same (150,000 lbs trona/silo) for the one- and three-silo systems. 

The three-silo setup is the type that is installed at Mirant’s Potomac Station. 

The conveying distances and the storage site were assumed to be the same as the test in August 

2007. The silo was sized based on the capacity to hold approximately one day worth of trona at 

the maximum design injection rate of 6,000 lb/hr. This would be approximately 4 truckloads 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

18 

(40,000 lb) or one rail car load (200,000 lb) for the combined 3 units. The issue of material 

packing in the silo and inhibiting the flow-ability of the material was considered in the sizing of 

the silo. The 3-silo option outlined in the tables below would provide the plant with a 3-day 

supply of trona. Table 3 displays the design criteria for an SO2 control system. 

Table 3. System Design Criteria for SO2 Control System at Presque Isle (6000 lb/hr 

injection, >70% SO2 control). 

Parameter 3-Silo System 1-Silo System 

Number of silos 3 1 

Number of injection trains 3 3 

Design feed capacity/train (lb/hr) 2000 2000 

Total trona storage capacity (lbs) 450,000 150,000 

Conveying distance (ft) 300 300 

Sorbent Trona Trona 

 Aerated density (lb/ft3) 49 49 

 Settled density (lb/ft3) 69 69 

 Particle MMD (microns) 26 26 

The trona can be delivered by two methods. One option is to have the trona railed to nearby 

Ishpeming in 200,000-lb capacity rail cars and then transferred to self-unloading pneumatic bulk 

tanker trucks and delivered in 40,000-lb batches. Another option is have a rail spur installed to 

the plant and have rail cars directly unload to the storage silo(s). Both options have been cost 

estimated; however, the cost for a rail spur was not included. 

The silo is equipped with a bin vent filter to contain dust during the unloading process. The 

silo is a shop-built, dry-welded tank with level indicators and load cells to monitor sorbent 

level and inventory. If only one silo is used, then that silo will have three hopper cones with 

a blower for each cone. If three silos are used, then each silo will have one hopper and 

blower. 

The sorbent is fed from the hopper(s) by rotary valves into the conveying lines. The conveying 

air is supplied by blowers. The air provides suction to draw the sorbent into the conveyer piping 

and carries it to the injection lances where it is dispersed into the duct. There are three injection 

lances, which are located downstream of the ID fan discharges, but upstream of the point where 

the ducts combine. Each lance discharges sorbent into the center of its duct, where turbulent 

flow will provide gas/sorbent mixing. The lances will be located below the current PAC 

injection lances. This is downstream of the NOx analyzer probe used for boiler feedback. Figure 

12 shows the schematic of the plant and includes the two options for the trona silo(s). 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

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ESP APH

TOXECON 

BAGHOUSE

ESP APH

ESP APH

PAC SILO

THREE

TRONA 

SILOS

Unit 9

Unit 8

Unit 7

SINGLE 

TRONA 

SILO

-ORFigure 12: Schematic of the Trona Injection Equipment at Presque Isle Units 7, 8 and 9 

Ash Handling System 

Some modifications and upgrades to the existing plant equipment would be required to 

accommodate a full-scale trona injection system. These include upgrades to the electrical supply 

to provide new service to the injection system as well as intercom phones and area lighting. 

The spent trona/ash/PAC mixture will be collected in the baghouse, conveyed to the ash silo and 

unloaded into ash trucks that dispose of the material in the landfill as is the current operating 

procedure. The ash handling capacity will need to be increased to accommodate the higher 

loading of material. The existing 4 in. conveyor piping system is adequate although a new 

mechanical exhauster capable of up to 15 in Hg will need to be installed. The new mechanical 

exhauster motor size would need to be increased from 10 HP to 20-25 HP. 

The increased vacuum level produced by a new mechanical exhauster increases the gas flow rate 

in the ash system and therefore creates a larger air-to-cloth ratio in the filter separator. An air-tocloth ratio of 4:1 is desirable so an increased filter area would be required with trona injection. 

To achieve this ratio the existing filter/separators could be operated in parallel, however this 

leaves the system without a redundant filter/separator. Another option is to replace the existing 

filter/separator with two larger capacity, continuous operating, filter/separators. Modifications to 

the ash silo building would be necessary, such as extending the bin roof and modifying the bin 

structure to support the higher loadings of the bigger filter/separators. An alternative would be 

to install pleated bags in the existing system. 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

20 

Cost Estimates and Results 

Costs for capital equipment, operations, maintenance, and power were provided by vendors as 

well as estimated using the economic basis provided in EPRI’s Economic Evaluation of DryInjection Flue Gas Desulfurization Technology6

. The capital and fixed and variable O&M costs 

were then converted into and combined as 20-year levelized costs using the traditional EPRI 

Levelized Cost or Uniform Annual Cost analysis typical of historical EPRI studies and as used in 

Reference 6. This methodology provides a suitable first-cut approximation and comparison of 

the time-value of money over the 20-year estimated life of the trona injection system options 

considered. 

Different scenarios of equipment set-up and injection rates were priced and compared. These 

scenarios and the economic analysis results are summarized below. A more-detailed description 

of the analysis is presented in Appendix A. 

Capital Costs 

The costs of equipment and installation for the trona injection system and balance-of-plant 

systems are shown in Table 4. This table compares the capital cost elements for the one-silo vs. 

three-silo systems. Capital costs for a permanent trona injection system include the storage 

silo(s), blowers, conveyor piping, dehumidifiers, and modifications to the ash handling system. 

Bulk Conveyor Specialist, Inc provided the cost estimates for the trona storage and injection 

equipment and installation. The required capital equipment is summarized below. A moredetailed description of these capital cost elements is presented in Appendix A. 

• Storage Silo: Skirted, carbon steel shell with cone. Storage capacity of 75 tons. Includes bin vent 

collector, bin discharger, discharge valve, bin indicators, weigh hopper, rotary valves, control panel, 

blowers, dehumidifiers. 

• Blowers. 

• Conveyor Piping. 

• Lances. 

• Housing for Redundant Blowers and Dehumidifiers. 

• Mechanical Exhauster Package

• Larger Capacity Filter/Separator
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

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Table 4: Summary of Equipment, Balance-of-Plant, and Engineering Costs 

Trona Injection System and Balance-of-Plant Equipment and Installation Costs 

Presque Isle Power Plant Units 7, 8, and 9 

COST CAPITAL COST ELEMENT DESCRIPTION 

1 Silo 3 Silos 

Trona Storage/Injection System (Equipment Cost) 

• Silo (s) - Including: $ 595,000 $ 1,785,000 

75 ton Capacity Storage Silo, 1 Hopper Below Silo, 1 

Blower, 1 Dehumidifier Pkg, Conveyor Piping (300 ft) 

• Lances (*Injection lances from test can be used in 

permanent system; additional lances are optional at 

$5,000 per lance) 

 $ 5,000* $ 5,000* 

• Redundancy (equipment added for 3 injection lines per 

1 silo), Including: 

 $ 98,500 $ - 

Splitter Valve, 2 Hoppers, 2 Rotary Valves, 2 Blowers, 

2 Dehumidifier Packages, Housing for Blowers and 

dehumidifiers 

Installation of Trona Storage/Injection Equipment $ 580,000 $ 580,000 

Includes civil, electrical, mechanical and piping 

TOTAL PROCESS EQUIPMENT $ 1,273,500 $ 2,365,000 

 

Increase In Ash Handling Capabilities 

• 2 Mechanical Exhauster Packages $ 15,000 $ 15,000 

• Larger Capacity Filter/Separator (Design and Supply) $ 200,000 $ 200,000 

TOTAL ASH HANDLING EQUIPMENT UPGRADES $ 215,000 $ 215,000 

TOTAL EQUIPMENT COSTS (Installed Cost, TEC) $ 1,488,500 $ 2,580,000 

General Facilities (10% of TEC) $148,850 $258,000

Engineering and Home office Fees (12.5% of TEC) $186,062 $322,500 

Project Contingency (25% of Process Equip. + 20% of Ash Handling Equip.) $361,375 $634,250

Process Contingency (7.5% of Process Equip. + 5% of Ash Handling Equip.) $106,262 $188,125

TOTAL PLANT COST (TPC) $2,291,050 $3,982,875

Preproduction Costs (=(1/12)*(Fixed O&M + Var O&M)+.02*TPC) $397,921 $431,757

TOTAL CAPITAL REQUIREMENT (TCR) $2,688,971 $4,414,632

As shown in Table 4, the total capital requirement (TCR) for a project includes not only the 

capital cost estimates provided by the vendor, but also such factored estimates as funds for 

general facilities, engineering and home office fees, project and process contingencies, and 

preproduction costs. These factored estimates were calculated in accordance with EPRI 

guidelines and are consistent with those factors used in the analysis in Reference 6 as shown in 

the table. The TCR for a three-silo system is about 1.6 times that for a one-silo system. 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

22 

Operating and Maintenance Costs 

The operating and maintenance (O&M) costs associated with trona injection for SO2 control 

include fixed and variable costs. Fixed O&M costs include labor, maintenance materials, and 

administrative and support labor. The variable O&M costs vary depending on unit and other 

capacity factors and include sorbent, power, and waste disposal. 

Fixed O&M Costs 

The fixed O&M costs include: 

• labor costs for ash handling 

• operating and maintenance labor costs for the silo and injection equipment 

• maintenance materials 

• administrative and support labor 

The maintenance labor, materials and support labor are estimated using known costs for the 

TOXECON system installed and operating at Presque Isle. 

Applicable labor rates, maintenance, and operating materials costs were determined for three 

SO2 removal rates (45%, 64%, and 70%). For example, the ash handling system labor costs 

increase as SO2 removal rates increase due to the need for more frequent ash unloading and 

disposal because of the increased sorbent injection rates. Operating labor costs also vary slightly 

depending on the type of PAC used due to slight differences in injection rate. 

The operating labor costs for the silo and injection equipment are constant for different SO2 

removal rates as well as constant with either one-silo or three-silo systems. The operating, 

maintenance and project overhead costs are estimated from the annual costs associated with the 

TOXECON system currently at Presque Isle. The maintenance materials are estimated in the 

same manner. 

Table 5 summarizes the first-year fixed O&M costs calculated for this analysis. As seen, the 

Fixed O&M costs do not vary depending on whether a one- or three-silo system is used. 

However, costs do vary depending upon the type of sorbent used and on the SO2 removal rate. 

Table 5 shows the total first year fixed O&M costs comparing costs at different SO2 removal 

rates. 

Note that these first-year O&M costs in Table 5 can also be expressed in terms of $/yr, although 

such numbers do not reflect the application of levelization factors to reflect the time-value of 

money. Levelized O&M and capital costs are discussed below. The development of these fixed 

O&M costs and the assumptions made are described in more detail in Appendix A. 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

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Table 5. Total First-Year Fixed Operating & Maintenance Costs 

Total First Year Fixed O&M Cost 

1 or 3 Silos SO2 Removal Rate 

O&M Labor & Material Costs* 45% 64% 70% 

• Labor Costs for Ash Handling 

Trona + DARCO® Hg + Ash $132,740 $265,880 $357,860 

Trona + DARCO® Hg-LH + Ash $126,470 $256,800 $345,500 

 

• O&M Labor & Materials & Support 

Labor for Silo & Injection Equipment 

O&M Labor Costs $360,000 $360,000 $360,000

Maintenance Materials $108,000 $108,000 $108,000

Total First Year Operating, Maintenance, 

& Support Costs (Silo & Injection) $468,000 $468,000 $468,000 

TOTAL O&M COSTS, 1 or 3 SILOS 

(Trona + DARCO®

 Hg + Ash) $600,740 $733,880 $825,860 

TOTAL O&M COSTS, 1 or 3 SILOS 

(Trona + DARCO®

 Hg-LH + Ash) $594,470 $724,800 $813,500 

*PAC injection rate varied for each SO2 removal rate. 

Variable O&M Costs 

The variable O&M costs vary depending on unit and other capacity factors and include estimates 

for: 

• Power Costs 

• Sorbent Costs 

• Landfill Costs 

The sorbent costs include trona as well as the increased PAC needed to keep the mercury 

removal at 90%. Power costs were estimated from the equipment power requirements and the 

current busbar cost of power production as obtained from the utility. 

Power Costs 

The electrical requirements for the trona injection system include power for blowers, rotary 

valve motors, bin discharger, and dehumidifiers. Each injection system requires power for one 

blower, one dehumidifier, and one rotary valve. There is one bin discharger per silo. Therefore, 

for a one-silo system with one large silo, power for one discharger is needed. For a three-silo 

system, power for 3 dischargers is needed. The long-term running power required is roughly 

half of the power required for start-up (connected load). The system power in kW is calculated 

knowing the amperage and voltage needed for the different components, along with a power 

factor and knowledge of the estimated time that each component operates. 

Table 6 summarizes the estimated variable first-year operating cost for power estimated for oneand three-silo injection systems by summing the power usage requirements for each component 

and using an assumed busbar cost to produce power of $0.03/kWh as estimated by the utility. 

The calculations and intermediate steps used to determine the power cost estimate are presented 

in more detail in Appendix A. 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

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Table 6. Variable First-Year Operating & Maintenance Costs for Power 

Variable O&M Costs: Power 

 1 –Silo System 3-Silo System 

Power Usage, in kW 42.35 127.05

Unit Power Cost, in $/kWh $0.03 $0.03 

Power Cost, in $/yr $11,125 $33,375 

Sorbent Costs 

Sorbent costs vary depending on the desired SO2 removal percentage and on the delivery 

method. Costs for trona and PAC increase as SO2 removal levels increase due to the need for 

higher sorbent injection rates; this includes the increased trona injection rate as well as the 

increased PAC injection rate to maintain mercury removal levels. The cost for trona to be railed 

directly to the plant is $140/ton assuming the costs to install a rail spur is picked up under 

another project. If a rail spur is not installed to the plant, the trona can be railed to Ishpeming, 

then loaded into a truck from there and delivered to the plant by truck. Using a combination of 

rail and truck would cost $155/ton. 

The amount of PAC needed to maintain 90% mercury control increases as trona injection 

increases due to the interference of trona injection with the PAC’s ability to capture mercury. 

Table 7 summarizes the sorbent costs for the two delivery methods for the three SO2 removal 

rates of 45, 64 and 70%. Also reflected in the table are the effects on first-year sorbent costs of 

different unit costs, and injection rates for trona and the PAC mercury sorbent, whether 

DARCO® Hg or DARCO® Hg-LH. The unit costs and injection rates assumed for each sorbent, 

delivery method and for each SO2 removal rate as well as the steps taken to arrive at the total 

values summarized in Table 7. Additional details are provided in Appendix A. 

Table 7. First-Year Variable Operating & Maintenance Costs for Sorbent Delivered by 

Rail and by Rail/Truck Combination to the Plant 

Variable O&M Costs: Sorbent Delivered By Rail* or Combination to Plant 

SO2 Removal Rate Sorbent Costs in $/yr** 45% 64% 70% 

Delivered by Rail* to Plant 

Trona + DARCO® Hg $1,405,651 $2,836,597 $3,887,797 

Trona + DARCO® Hg-LH $1,460,182 $2,934,162 $3,920,647 

Delivered by Rail† and Truck† 

Trona + DARCO® Hg $1,514,056 $3,053,407 $4,178,520

Trona + DARCO® Hg-LH $1,568,587 $3,150,972 $4,211,370 

* Trona rail spur assumed to be installed under separate project 

** Minus PAC that would already be injected 

† Trona railed to Ishpeming and trucked to plant 

Waste Disposal Costs 

The variable O&M costs for waste disposal are the costs required to landfill the spent sorbent 

captured in the baghouse. The 2007 unit cost to landfill material was $44.40. The unit cost for 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

25 

landfill along with the waste production rates for each sorbent was used to calculate the total cost 

to landfill the waste for both PAC sorbents for each of the three SO2 reduction rates as 

summarized in Table 8. Since this is a differential cost estimate that considers only the effect of 

adding a trona injection system, the costs do not reflect the ash and PAC waste that is disposed 

of while running at full load with no trona injection. The waste production rates and steps used 

in calculating the waste disposal costs summarized in Table 8 are shown in more detail in 

Appendix A. 

Table 8. First-Year Variable Operating & Maintenance Costs for Landfill Waste Disposal 

Variable O&M Costs: Waste Disposal 

SO2 Removal Rate Waste Disposal Costs, in $/yr** 45% 64% 70% 

Trona + DARCO® Hg $336,780 $674,575 $907,940

Trona + DARCO® Hg-LH $330,360 $661,010 $886,060 

**minus PAC/Ash waste that would already be disposed of 

 

Total Variable O&M Costs 

Table 9 shows the total variable O&M costs at the three different SO2 removal rates and for the 

different delivery methods. The total O&M costs include costs for power, sorbent usage, and 

disposal costs. 

Table 9. First-Year Total Variable Operating & Maintenance Costs 

Total Variable O&M Costs 

SO2 Removal Rate Total Variable O&M Costs, $/yr 45% 64% 70% 

Trona Delivered by Rail to 

Plant 

Trona + DARCO® Hg $1,775,800 $3,544,550 $4,829,115 

Trona + DARCO® Hg-LH $1,823,915 $3,628,550 $4,840,085 

Trona Delivered by 

Rail/Truck 

Trona + DARCO® Hg $1,884,210 $3,761,360 $5,119,840 

Trona + DARCO® Hg-LH $1,932,320 $3,845,360 $5,130,810 

Levelized Costs 

Levelized costs were computed to represent a constant cost value for the operating and capital 

costs over the lifetime of the equipment and project. In other words, the levelized costs take the 

present value of the net costs and spread them evenly over a period of time. This makes it 

possible to compare costs looking into the future. For this assessment levelized costs are 

presented in units of mills/kWh, where a mill is 1/1000 of a dollar. 

The key economic parameters and factors used in this analysis are summarized in Table 10. The 

calculations to determine levelized costs assumed a discount rate of 7.5% and a 20-year 

levelization factor was used. The capital costs are converted using a fixed charge rate of 15.0% 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

26 

and the O&M costs are converted using levelization factors of 1.29 for all costs including power 

and consumables. 

Table 10. Economic Factors and Parameters 

Economic Factors & Parameters 

Year of Estimate 2007 

Plant Life 20 Years 

Capital Recovery Factor 0.15 

Fixed Charge Rate 15% 

O&M Levelization Factor 1.29 

Normal Capacity Factor 0.75 

Power Capacity Factor 0.85 

This methodology is consistent with typical historical EPRI studies, and in particular, the factors 

used here reflect those used in Reference 6. The use of a 15% Fixed Charge Rate is consistent 

with using a Capital Recovery Factor of 0.15, a typical approximation currently used by EPRI 

and utilities today for levelizing capital costs. Although the factors used here are 

generalizations, their use is a reasonable approximation for a first-cut economic evaluation for 

the rough comparison of these similar options. Should any utility desire to pursue these options 

more seriously for a given plant, a detailed economic analysis using economic factors and a 

methodology specific to the utility’s current normal practice would be advised to confirm the 

economic viability of each option. 

Levelized Capital Costs 

The calculations used to determine levelized capital costs are shown in detail in Appendix A. 

Table 11 summarizes the levelized total capital requirement for the one- and three-silo options. 

The total capital requirement for three silos is less than double the requirement for one silo. 

Table 11. Levelized Capital Costs 

Levelized Capital Costs (20 yr, Current $ Basis) 

LEVELIZED TOTAL CAPITAL REQUIREMENT 1-Silo System 3-Silo System 

Levelized $/yr $403,345 $662,195 

Levelized $/kW $1.49 $2.45

mills/kWh 0.23 0.37 

By comparison, the total capital requirement for a green-field installation of a pulse-jet baghouse 

on a 250 MW unit might cost approximately 50 $/kW as suggested by an EPRI study published 

in 1992.7 

Levelized O&M Costs 

The detailed steps in calculating levelized fixed and variable O&M costs are discussed in 

Appendix A. Tables 12 and 13 summarize the levelized fixed and variable O&M costs, 

respectively, resulting from this analysis. These tables summarize the levelized costs for the two 

PAC sorbents versus the three SO2 removal rates. 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

27 

Table 12. Total Levelized Fixed Operating & Maintenance Costs 

Levelized Total Fixed O&M Cost 

SO2 Removal Rates Levelized Total Fixed O&M Costs 

45% 64% 70% 

Trona + DARCO® Hg + Ash 

Levelized $/yr $774,950 $946,705 $1,065,360 

Levelized mills/kWh 0.44 0.53 0.60

Trona + DARCO® Hg-LH + Ash 

Levelized $/yr $766,870 $934,990 $1,049,415 

Levelized mills/kWh 0.43 0.53 0.59 

Recall that the variable O&M costs are dependent not only on the SO2 removal rate and type of 

PAC sorbent used, but also on the transportation mode to the plant; i.e., whether the sorbent is 

taken to the plant directly by rail or whether the Rail/Truck combination is used. This is 

reflected in the levelized total variable O&M costs given in Table 13. 

Table 13. Levelized Total Variable Operating & Maintenance Costs 

Levelized Total Variable O&M Costs 

SO2 Removal Rate Levelized Total Variable O&M Cost 

45% 64% 70% 

Trona Delivered by Rail to Plant 

Trona + DARCO® Hg 

Levelized $/yr $2,290,786 $4,572,466 $6,229,557 

Levelized mills/kWh 1.29 2.58 3.51

Trona + DARCO® Hg-LH 

Levelized $/yr $2,352,853 $4,680,826 $6,243,710 

Levelized mills/kWh 1.33 2.64 3.52

Trona Delivered by Rail/Truck 

Trona + DARCO® Hg 

Levelized $/yr $2,430,629 $4,852,150 $6,604,588 

Levelized mills/kWh 1.37 2.74 3.72

Trona + DARCO® Hg-LH 

Levelized $/yr $2,492,695 $4,960,510 $6,618,742 

Levelized mills/kWh 1.41 2.80 3.72

Total Levelized Costs 

Table 14 shows the total levelized costs, which includes the total variable O&M costs, total fixed 

O&M costs and total capital costs at three removal rates and for the two PAC sorbents for the 

two sorbent delivery methods. This is presented for the both the one- and three-silo systems. 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

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Table 14. Total Levelized Costs (Capital and Fixed & Variable O&M Costs) 

TOTAL Levelized Costs 

Total Levelized Cost (Capital and SO2 Removal Rate 

Fixed & Variable O&M Costs) 45% 64% 70% 

1-SILO SYSTEM 

Trona Delivered by Rail to Plant 

Trona + DARCO® Hg 

mills/kWh 1.96 3.34 4.34

Trona + DARCO® Hg-LH 

mills/kWh 1.99 3.39 4.34

 

Trona Delivered by Rail/Truck 

Trona + DARCO® Hg 

mills/kWh 2.03 3.50 4.55

Trona + DARCO® Hg-LH 

mills/kWh 2.06 3.55 4.55

 

3-SILO SYSTEM 

Trona Delivered by Rail to Plant 

Trona + DARCO® Hg 

mills/kWh 2.10 3.48 4.49

Trona + DARCO® Hg-LH 

mills/kWh 2.13 3.54 4.48

 

Trona Delivered by Rail/Truck 

mills/kWh 2.18 3.64 4.70

Trona + DARCO® Hg-LH 

mills/kWh 2.21 3.70 4.70

Removal Cost per Ton of SO2 Removed 

The best way to compare SO2 removal technologies is on the basis of $/ton of SO2 removed. 

Table 15 shows the cost per ton of SO2 removed using trona at full scale for the three SO2

removal rates considered as compared for the two PAC sorbent options and the two sorbent 

delivery options. These values are levelized over 20 years. 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

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Table 15. Removal Cost per Ton of SO2

Levelized Total Cost per Ton of SO2 Removed ($/ton) 

No. of Silos, Delivery Method, and SO2 Removal Rate 

Sorbent 45% 64% 70% 

1 SILO 

Trona Delivered by Rail to Plant 

Trona + DARCO® Hg $1,483 $1,780 $2,116

Trona + DARCO® Hg-LH $1,506 $1,809 $2,115

 

Trona Delivered by Rail/Truck 

Trona + DARCO® Hg $1,543 $1,864 $2,219

Trona + DARCO® Hg-LH $1,566 $1,893 $2,218

 

3 SILOS 

Trona Delivered by Rail to Plant 

Trona + DARCO® Hg $1,594 $1,858 $2,187

Trona + DARCO® Hg-LH $1,617 $1,887 $2,186

 

Trona Delivered by Rail/Truck 

Trona + DARCO® Hg $1,654 $1,942 $2,290

Trona + DARCO® Hg-LH $1,677 $1,971 $2,290

Inspection of Table 15 reveals that the greatest impact on the cost per ton of SO2 removal is 

primarily due to the rate of sorbent injection. Note that in a one-silo system for both sorbents 

and both delivery methods, the cost typically increases by a factor of about 1.4 to increase SO2

removal from 45% to 70%. For a three-silo system, the capital required for the larger system 

becomes a more significant in total cost. However, the sorbent cost still dominates and the total 

cost per ton of SO2 removed increases by a factor of about 1.35. 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

30 

Conclusions 

The goal of 70% SO2 removal was achieved during this two week test period when injecting 

5926 lb/hr of trona. This corresponds to an average NSR of 1.02. The inlet concentration of 

SO2 varied from 0.48-0.64 lb/MBtu. The highest removal was 74.1% with PAC injection at 3.8 

lb/MMacf. 

There was very little reduction in NOx during the test period. In addition, the effect of a side 

reaction, where NO is oxidized to produce NO2, was observed on one test day when PAC 

injection was turned off. This indicates that there is some conversion of NO to NO2, but not 

enough to measure on the stack NOx CEMs and considerably below the target of 30% reduction. 

The NO2 level was high enough to be visible and cause an increase in opacity of almost 3%. On 

days when PAC injection was occurring, the opacity increased by a maximum of 0.75% but 

there was no visible plume. 

Injection of trona for SO2 control resulted in a decrease in mercury removal using activated 

carbon. This effect was seen every day that trona was injected. The mercury removal slowly 

recovered overnight to the pre-test level of >90%. On the last two days of testing, PAC injection 

was increased to regain the >90% removal rate. Test conditions did not allow sufficient time to 

achieve this target rate while injecting trona. An estimate of the required PAC is 3X the pretrona test rate. 

Baghouse and tube sheet pressure drop increased during trona injection, causing an increase in 

cleaning frequency from 0.18 p/b/hr to 0.22 p/b/hr. 

Plant operators kept the three units at full, steady load during testing. The boiler soot blowers 

were used every hour on a staggered schedule to keep the flue gas temperature from fluctuating 

during testing. Trona was injected near the PAC injection port, which should have resulted in 

excellent mixing with the flue gas before reaching the baghouse. The trona injection had no 

effect on boiler operations. 

The reacted trona, PAC, and ash were unloaded from the ash silo using a wet unloading system. 

Because sodium carbonate will react with water to form solid hydrates, an anti-setup chemical 

was initially used with the water during unloading. No setup of the baghouse mixture was seen 

either in the mixer or in the transport truck. During the first week, an unloading during the 

morning occurred without the chemical, also resulting in no setup in the mixer or truck. The 

material may have been forming hydrates during mixing, preventing a hard setup. The use of the 

anti-setup chemical should be considered in future tests unless it can be shown that the mixing 

system prevents a solid setup in the mixer or truck. 

An economic assessment of a full-scale trona injection system included equipment and other 

capital costs along with sorbent cost (trona and increased amount of PAC to maintain 90% 

removal) and O&M costs. The cost to remove SO2 varied from $1,483/ton at 45% removal and 

one silo to $2,290/ton SO2 at 70% removal with 3 silos. 
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31 

References 

1. EPRI Project Report number ADA4352002F01, March 1994. 

2. EPRI Project RP 3083-05 Final Report (Mohave Pilot Tests), April 1996. 

3. EPRI Project #TR-110867, “Assessing Air Pollution Control Options at the Hudson 

Station of Public Service Electric and Gas,” August 1998. 

4. Standards of Performance for New Stationary Sources National Emission Standards for 

Hazardous Air Pollutants Addition of Method 29 to Appendix A of Part 60 and 

Amendments to Method 101A of Appendix B of Part 61 | Federal Register | USEPA03-

08-2007 

a. Federal Register document 

b. URL:http://www.epa.gov/EPA-AIR/1996/April/Day-25/pr-23270.html

5. Mirant Corporation, “Trona Injection Tests Mirant Potomac River Station Unit 1 

November 12 to December 23, 2005”, January 16, 2006. 

6. Economic Evaluation of Dry-Injection Flue gas Desulfurization Technology, EPRI CS4373, EPRI Project 1682-1, January 1986. 

7. Economic Evaluation of Particulate Control Technologies, Volume 1: New Units, EPRI 

TR-100748, EPRI Project 3083-04-1, September 1992. 
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32 

APPENDIX A – Cost Estimates and Results – Details 

Costs for capital equipment, operations, maintenance, and power were provided by vendors as 

well as estimated using the economic basis provided in EPRI’s “Economic Evaluation of DryInjection Flue Gas Desulfurization Technology.” The costs are broken into sections of capital 

costs, operating and maintenance costs, and all are converted to 20-year levelized costs. 

Different scenarios of equipment set-up and injection rates were priced and compared. 

The capital costs assumed an availability of 100% until these costs were levelized where a 

capacity factor of 75% was used. The fixed and variable operating and maintenance costs used a 

capacity factor of 75% throughout both the first year and levelized estimations with an exception 

of power which used an 85% capacity factor. 

Capital Costs 

The costs of equipment and installation for the trona injection system and balance-of-plant 

systems are shown in Table 16. This table compares the cost for one-silo and three-silo systems. 

Capital costs for a permanent trona injection system include the storage silo(s), blowers, 

conveyor piping, dehumidifiers, and modifications to the ash handling system. Cost estimates 

for the trona storage and injection equipment and installation costs were provided by Bulk 

Conveyor Specialist, Inc. A description of capital equipment is shown below. 

• Storage Silo: Skirted, carbon steel shell with cone. Storage capacity of 75 tons. Includes bin vent 

collector, bin discharger, discharge valve, bin indicators, weigh hopper, rotary valves, control panel, 

blowers, dehumidifiers. Bin Vent Collector: Shaker type, 280 sq. ft. cloth, air-to-cloth ratio of 3:1. 

• Bin Discharger: 8 in. diameter, 1 Hp motor. 

• Discharge Valve: pneumatic knife gate. 

• Bin Indicators: (3) paddle type. 

• Weigh Hopper: 2000 lb capacity with load cells, 1.5 Hp rotary valve feeders, and one level 

indicator. 

• Control Panel: Allen Bradley, PLC Logic. 

• Blowers: 350 CFM, 8-10 psi with in-and-out silencers. 

• Conveyor Piping: 3” schedule 80, estimated length of 300’. 

• Lances: 2” schedule 80 pipe, 304 stainless steel, 5’2” in length from flange to tip with 45 degree 

beveled tip. 

• Housing for Redundant Blowers and Dehumidifiers: Skirted silo does not have sufficient space 

available for redundant blowers and dehumidifiers, a small building would be required. 

• Mechanical Exhauster Package: Exhauster motor size increased from 10 Hp to 20-25 Hp, capable 

of pulling 15 inHg (14 inHg at full load). 

• Larger Capacity Filter/Separator: Two larger, continuous operating filter/separators. 

Modifications to bin roof by extending 14’ and bin structure by modifying support steel frame 

across bin roof to accept higher loads. 
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Table 16. Summary of Equipment, Balance-of-Plant, and Engineering Costs 

Trona Injection System and Balance-of-Plant Equipment and Installation Costs 

Presque Isle Power Plant Units 7, 8, and 9 

Budget Item Description Cost 

 1 SILO 3 SILOS 

Trona Storage/Injection System 

Silo $ 595,000 $ 1,785,000 

Equipment Included 

75 ton Capacity Storage Silo 

1 Hopper Below Silo 

1 Blower 

1 Dehumidifier Package 

Conveyor Piping (300 ft) 

Lances (*Injection lances from test can be used in permanent 

system; additional lances are optional at $5,000 per lance) $ 5,000* $ 5,000* 

Redundancy (equipment added for 3 injection lines per 1 silo) $ 98,500 $ - 

Splitter Valve 

2 Hoppers 

2 Rotary Valves 

2 Blowers 

2 Dehumidifier Packages 

Housing for Blowers and dehumidifiers 

Installation of Trona Storage/Injection Equipment $ 580,000 $ 580,000 

Includes civil, electrical, mechanical and piping 

TOTAL PROCESS EQUIPMENT $ 1,273,500 $ 2,365,000 

Increase In Ash Handling Capabilities 

2 Mechanical Exhauster Packages $ 15,000 $ 15,000 

Exhauster motor size increase (10 Hp to 20-25 Hp) 

Larger Capacity Filter/Separator $ 200,000 $ 200,000 

Design and Supply 

TOTAL ASH HANDLING EQUIPMENT UPGRADES $ 215,000 $ 215,000 

TOTAL EQUIPMENT COSTS (TEC) $ 1,488,500 $ 2,580,000 

General Facilities (10% of TEC) $148,850 $258,000

Engineering and Home office Fees (12.5% of TEC) $186,062 $322,500 

Project Contingency (25% of Process Equip. + 20% of Ash Handling Equip.) $361,375 $634,250

Process Contingency (7.5% of Process Equip. + 5% of Ash Handling Equip.) $106,262 $188,125

TOTAL PLANT COST (TPC) $2,291,050 $3,982,875

Preproduction Costs (=(1/12)*(Fixed O&M + Var O&M)+.02*TPC) $397,921 $431,757

TOTAL CAPITAL REQUIREMENT (TCR) $2,688,971 $4,414,632
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Operating and Maintenance Costs 

The operating and maintenance (O&M) costs associated with trona injection for SO2 control 

include fixed and variable costs. Fixed O&M costs include labor, maintenance materials, and 

administrative and support labor. The variable O&M costs vary depending on unit and other 

capacity factors and include sorbent, power, and waste disposal. 

Fixed O&M Costs 

The fixed O&M costs include estimates of labor costs for ash handling and costs for operating 

and maintenance of the silo and injection equipment. It also includes estimates for maintenance 

materials and for administrative and support labor. The maintenance labor, materials and support 

labor are estimated using known costs for the TOXECON system installed and operating at 

Presque Isle. 

Table 17 shows the operating labor cost parameters assumed for this cost analysis. 

Table 17. Fixed O & M Costs – Ash Handling Labor Cost Parameters 

Ash Handling Operating Labor Cost Parameters

Operating Labor Cost Parameter 

Ash Handling 

rate $/hr (truck+ driver) $70 

ton/load (tons) 20 

time/load (hrs) 5 

Normal Capacity Factor 0.75 

Table 18 indicates how the Ash Handling Labor cost estimates were determined using the labor 

parameters indicated in Table 17 along with the number of loads of trona/ash/PAC required for 

the three SO2 removal rates of 45%, 64% and 70%. The labor costs increase as SO2 removal 

rates increase due to the need for more frequent ash unloading and disposal. The 2007 rate for 

an ash truck and driver is about $70/hr with each truck-load capable of hauling 40,000 lbs or 20 

tons. It takes roughly 5 hours to unload the ash and dispose of it in the landfill. 

The number of loads of trona/ash/PAC to be disposed of assumes 100% material injected will be 

captured and disposed of and also incorporates a capacity factor of 75%. The equation below 

was used to determine the number of loads per year: 

# Loads/Year = (((WPRtrona + WPRPAC)*NCF)–((WPRPAC,no trona inj.)*NCF)) / (Tons per load) 

 WPR: Waste Production Rate (tons/hour) 

 NCF: Normal Capacity Factor 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

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Table 18. Fixed O & M Costs – Ash Handling Labor Costs for Three SO2 Removal Rates 

Fixed O&M Cost: Ash Handling Operating Labor 

 SO2 Removal Rate 

 45% 64% 70% 

# of Loads Per Year 

Trona + DARCO® Hg + Ash 379 760 1022

Trona + DARCO® Hg-LH + Ash 361 734 987

Man-hours Per Year 

Trona + DARCO® Hg + Ash 1896 3798 5112

Trona + DARCO® Hg-LH + Ash 1807 3669 4936

Labor Costs for Ash Handling 

($/yr) 

Trona + DARCO® Hg + Ash $132,739 $265,880 $357,860

Trona + DARCO® Hg-LH + Ash $126,473 $256,797 $345,500

The operating labor costs for the silo and injection equipment are constant for different SO2 

removal rates as well as constant with either one-silo or three-silo systems. The operating, 

maintenance and project overhead costs are estimated from the annual costs associated with the 

TOXECON system currently at Presque Isle. The maintenance materials are estimated in the 

same manner. The first year labor costs on projects such as this are usually higher than the 

following years due to the first year start-up issues and optimization of long-term operation. 

Table 19 shows the fixed costs of equipment operating, maintenance and support labor. 

Table 19. Fixed Operating & Maintenance Costs for Equipment Operating, Maintenance 

and Support Labor 

Fixed O&M Cost: Equipment Operating, Maintenance, and Support Labor 

1st Year 

Operating Labor Costs 1 SILO 3 SILOS 

Operating & Maintenance Labor Costs, in $/yr* $360,000 $360,000 

*Includes operating labor, maintenance labor, project overhead costs 

Maintenance Materials, in $/yr $108,000 $108,000 

 

TOTAL FIRST YEAR OPERATING, MAINTENANCE, AND 

SUPPORT COSTS $468,000 $468,000 

. 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

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Table 20. Total First Year Fixed Operating & Maintenance Costs 

Total First Year Fixed O&M Cost 

1 or 3 Silos SO2 Removal Rate 

O&M Labor & Material Costs* 45% 64% 70% 

Labor Costs for Ash Handling 

Trona + DARCO® Hg + Ash $132,740 $265,880 $357,860 

Trona + DARCO® Hg-LH + Ash $126,470 $256,800 $345,500 

Labor Costs for Silo and Injection 

Equipment 

Total First Year Operating, 

Maintenance, & Support Costs $468,000 $468,000 $468,000 

TOTAL O&M COSTS, 1 or 3 SILOS 

(Trona + DARCO®

 Hg + Ash) $600,740 $733,880 $825,860 

TOTAL O&M COSTS, 1 or 3 SILOS 

(Trona + DARCO® Hg-LH + Ash) $594,470 $724,800 $813,500 

Variable O&M Costs 

The variable O&M costs include estimates for sorbent costs, landfill costs and power costs. The 

sorbent costs include trona as well as the increased PAC needed to keep the mercury removal at 

90%. Power costs were estimated from the equipment’s power requirements and the current cost 

of power production. 

Power Costs 

The electrical requirements for the trona injection system include power for blowers, rotary 

valve motors, bin discharger, and dehumidifiers. Each injection system requires power for one 

blower, one dehumidifier, and one rotary valve. There is one bin discharger per silo, therefore, if 

there is one large silo power for one discharger is needed, but with 3 silos power for 3 

dischargers is needed. The long-term running power required is roughly half of the power 

required for start-up. Table 21 shows the amperage needed for the different components and the 

conversion to kilowatts. Table 22 shows the estimated costs required for long-term running of 

the injection system using an assumed cost to produce power of $0.03/kWh. The power cost 

estimations use a Power Capacity Factor of 85%. 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

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Table 21. Power Requirements to Run Trona Injection System 

Power Requirements, 1 Injection System (Amps) 

Item Motor Description Amps Required 

Blowers: 30 Hp, 480 Vac, 3 phase 40 amps at full load 

Rotary Valve: 1 Hp each (2) 1.6 amps each (2) 

Bin Discharger: 1.5 Hp 3.0 amps 

TOTAL AMPS AT FULL LOAD 46.2 amps 

TOTAL AMPS WHILE RUNNING (~1/2 

Full Load) 20 amps 

 

Dehumidifiers: 40 amps 

TOTAL (amps) 60 amps 

Power Requirements, 1 Injection System (kW) 

TOTAL in kW, 3 phase (kW=(1.73*Volts*Current*Power Factor)/1000) 42.35

Power Capacity Factor 0.85

Volts 480

Power Requirements, 3 Injection Systems (kW) 

TOTAL in kW, 3 phase 127.05

Table 22. Variable Operating & Maintenance Costs for Power 

Variable O&M Costs: Power 

 1 Injection System 3 Injection Systems 

Power Usage, in kW 42.35 127.05

Unit Power Cost, in $/kWh $0.03 $0.03 

Power Cost, in $/yr $11,125 $33,375 

Sorbent Costs 

Sorbent costs vary depending on the SO2 removal percentage desired and on the delivery 

method. Cost for both trona and PAC increase as SO2 removal percentages increase. The cost 

for trona to be railed directly to the plant is $140/ton assuming the costs to install a rail spur is 

picked up under another project. If a rail spur is not installed to the plant the trona can be railed 

to Ishpeming then loaded into a truck from there and delivered to the plant by truck. Using a 

combination of rail and truck would cost $155/ton. 

The amount of PAC needed to maintain 90% mercury control increases as trona injection 

increases due to trona interfering with the PAC’s ability to capture mercury. Table 23 shows the 

sorbent costs for trona being delivered directly to the plant by rail and Table 24 shows the 

sorbent costs for trona being delivered by a combination of rail and truck. Both tables have unit 

costs for trona, DARCO® Hg, and DARCO® Hg-LH and display the injection rates required for 

different SO2 removals. The sorbent cost estimations use a capacity factor of 75% 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

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Table 23. Variable Operating & Maintenance Costs for Sorbent Delivered by Rail to the 

Plant 

Variable O&M Costs: Sorbent Delivered By Rail to Plant 

Sorbent Unit Cost, FOB PIPP , in 

$/ton Rail* 

Trona $140 

DARCO® Hg $1,100 

DARCO® Hg-LH $2,100 

 *Trona rail spur assumed to be installed under separate project 

 Injection Rates (ton/hr) 

Sorbent 

SO2 Removal 

of 45% 

SO2 Removal 

of 64% 

SO2 Removal 

of 70% 

Trona 1.1 2.2 2.95

DARCO® Hg 0.142 0.20 0.25

DARCO® Hg-LH 0.085 0.1185 0.14

Sorbent Costs, in $/yr** 

Trona + DARCO® Hg $1,405,651 $2,836,597 $3,887,797 

Trona + DARCO® Hg-LH $1,460,182 $2,934,162 $3,920,647 

 **minus PAC that would already be injected 

Table 24. Variable Operating & Maintenance Costs for Sorbent Delivered by a 

Combination of Rail and Truck to the Plant 

Variable O&M Costs: Sorbent Delivered By Rail and Trucked To Plant 

Sorbent Unit Cost, FOB PIPP , in 

$/ton Rail + Truck* 

Trona $155 

DARCO® Hg $1,100 

DARCO® Hg-LH $2,100 

 *Trona railed to Ishpeming and trucked to plant 

 Injection Rates (ton/hr) 

Sorbent 

SO2 Removal 

of 45% 

SO2 Removal 

of 64% 

SO2 Removal 

of 70% 

Trona 1.1 2.2 2.95

DARCO® Hg 0.142 0.20 0.25

DARCO® Hg-LH 0.085 0.1185 0.14 

Sorbent Costs, in $/yr** 

Trona + DARCO® Hg $1,514,056 $3,053,407 $4,178,520

Trona + DARCO® Hg-LH $1,568,587 $3,150,972 $4,211,370 

 **minus PAC that would already be injected 

Waste Disposal Costs 

The variable O&M costs for waste disposal are the costs required to landfill the spent sorbent 

captured in the baghouse. The 2007 unit cost to landfill material was $44.40. Table 25 shows 

the waste produced for the different SO2 removal rates and the costs required to landfill the 

waste. The costs do not include the ash and PAC waste that is disposed of while running at full 

load with no trona injected. The waste disposal cost estimations use a capacity factor of 75%. 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

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Table 25. Variable Operating & Maintenance Costs for Disposing the Waste to the 

Landfill 

Variable O&M Costs: Waste Disposal 

Landfill Cost, in $/ton $ 44.40 

Waste Production Rates (ton/hr) 

Waste Product SO2 Removal 

of 45% 

SO2 Removal 

of 64% 

SO2 Removal 

of 70% 

Trona 1.1 2.2 2.95

Hg 0.142 0.20 0.25

Hg-LH 0.085 0.1185 0.14

Ash (110 lb/hr) 0.055 0.055 0.055

Waste Disposal Costs, in $/yr** 

Trona + DARCO® Hg $336,777 $674,575 $907,941

Trona + DARCO® Hg-LH $330,560 $661,010 $886,063

**minus PAC/Ash waste that would already be disposed of 

 

Table 26 shows the total variable O&M costs at different SO2 removal rates and at different 

delivery methods. The total O&M costs include costs for power, sorbent usage, and disposal 

costs. 

Table 26. Total Variable Operating & Maintenance Costs 

Total Variable O&M Costs 

Removal Rates 

Total Variable O&M Costs, in $/yr

SO2 Removal 

of 45% 

SO2 Removal 

of 64% 

SO2 Removal 

of 70% 

Trona Delivered by Rail to 

Plant 

Trona + DARCO® Hg $1,775,803 $3,544,547 $4,829,114

Trona + DARCO® Hg-LH $1,823,917 $3,628,547 $4,840,085

Trona Delivered by 

Rail/Truck 

Trona + DARCO® Hg $1,884,208 $3,761,357 $5,119,836

Trona + DARCO® Hg-LH $1,932,322 $3,845,357 $5,130,808

Levelized Costs 

Levelized costs were computed to represent a constant cost value for the operating and capital 

costs over the lifetime of the equipment and project. In other words, the levelized costs take the 

present value of the net costs and spread them evenly over a period of time. This makes it 

possible to compare costs looking into the future. For this assessment levelized costs are 

presented in units of mills/kWh, where a mill is 1/1000 of a dollar. 

The calculations to determine levelized costs assumed a discount rate of 7.5% and a 20-year 

levelization factor was used. The capital costs are converted using a fixed charge rate of 15.0% 

and the O&M costs are converted using levelization factors of 1.29 for all costs including power 

and consumables. 
Topical Report: Trona-Based SO2/NOx Removal at Presque Isle 

 

40 

Levelized Capital Costs 

The capital costs are converted to levelized capital costs using a fixed charge rate of 15.0%. The 

levelized capital costs for $/year are calculated by multiplying the capital costs by the fixed 

charge rate of 15.0%. The levelized capital costs in $/kW are calculated by dividing the $/year 

amount by the nominal kilowatts produced by the plant, 270000kW for Presque Isle Power Plant. 

The levelized costs represented by mills/kWh are calculated using the following formula and a 

capacity factor (NCF) of 75%. 

LCC (mills/kWh) = ((1000) * (CC) * (LFCR)) / ((NCF) * (8760 hr/yr)) 

 LCC: Levelized Capital Costs 

CC: Capital Costs ($/kW) 

LFCR: Levelized Fixed Charge Rate 

NCF: Normalized Capacity Factor 

Table 27 shows the levelized capital costs and compares costs for a one-silo system versus a 

three-silo system. The total capital requirement for three silos is less than double the 

requirement for one silo. 

Table 27. Levelized Capital Costs 

Levelized Capital Costs (20 yr, Current $ Basis) 

Levelized Fixed Charge Rate 15% 

 1 SILO 3 SILOS 

TOTAL LEVELIZED EQUIPMENT COST (Installed) 

Levelized $/yr (TEC * LFCR) $223,275 $387,000 

Levelized $/kW (TEC * LFCR / 270000 kW) $0.83 $1.43 

mills/kWh (1000* TEC*LFCR)/(270000kW*(8760 hrs/yr)*NCF)) 0.13 0.22 

TOTAL LEVELIZED PLANT COST 

Levelized $/yr (TPC * LFCR) $343,657 $597,431 

Levelized $/kW (TPC * LFCR / 270000 kW) $1.27 $2.21 

mills/kWh (1000* TPC*LFCR)/(270000kW*(8760 hrs/yr)*NCF)) 0.19 0.34 

TOTAL LEVELIZED CAPITAL REQUIREMENT 

Levelized $/yr (TCR * LFCR) $403,345 $662,195

Levelized $/kW (TCR * LFCR / 270000 kW) $1.49 $2.45 

mills/kWh (1000* TCR*LFCR)/(270000kW*(8760 hrs/yr)*NCF)) 0.23 0.37 

Levelized Fixed O&M Costs 

Tables 28 and 29 show the fixed operating and maintenance levelized costs for ash handling 

labor and equipment operating, maintenance, and support labor. These tables are summarized in 

Table 30. The calculations for the levelized fixed O&M costs are done in the same manner as 

the levelized capital costs but use a levelization factor of 1.29 in accordance with the EPRI 

Economic Analysis rather than the 15% fixed charge rate. 
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Table 28. Levelized Fixed Operating & Maintenance Costs for Ash Handling Labor 

Levelized Fixed O&M Cost: Ash Handling Operating Labor 

Operating Labor Levelization Factors 

Ash Handling 

Capacity Factor 75% 

O&M Levelization Factor 1.29 

 Removal Rates 

 

SO2 Removal 

of 45% 

SO2 Removal 

of 64% 

SO2 Removal 

of 70% 

Levelized Labor Costs for Ash 

Handling 

Trona + DARCO® Hg + Ash 

$/yr $171,233 $342,985 $461,639

$/kW $0.63 $1.27 $1.71

mills/kWh 0.10 0.19 0.26

Trona + DARCO® Hg-LH + Ash 

$/yr $163,150 $331,268 $445,695

$/kW $0.60 $1.23 $1.65

mills/kWh 0.09 0.19 0.25

Table 29. Levelized Fixed Operating & Maintenance Costs for Equipment Operating, 

Maintenance, and Support Labor 

Levelized Fixed O&M COST: Equipment Operating, Maintenance, and Support Labor

Operating Labor Levelization Factors 

Equipment Operating, Maintenance, and Support Labor 

Capacity Factor 75%

O&M Levelization Factor 1.29 

 1 or 3 Silo(s) 

Levelized Operating & Maintenance Labor Costs * 

$/yr $464,400 

$/kW $1.72 

mills/kWh 0.26 

*Includes operating labor, maintenance labor, project overhead costs 

Levelized Maintenance Materials 

$/yr $139,320 

$/kW $0.52 

mills/kWh 0.08 

TOTAL LEVELIZED OPERATING, MAINTENANCE, AND 

SUPPORT COSTS 

$/yr $603,720 

$/kW $2.24 

mills/kWh 0.34 
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Table 30. Levelized Total Operating & Maintenance Costs 

Levelized Total Fixed O&M Cost 

Operating Labor Levelization Factors 

Capacity Factor 75% 

O&M Levelization Factor 1.29 

 Removal Rates 

 

SO2 Removal 

of 45% 

SO2 Removal 

of 64% 

SO2 Removal 

of 70% 

Levelized Total Fixed O&M Costs 

Trona + DARCO® Hg + Ash 

$/yr $774,953 $946,705 $1,065,360

$/kW $2.87 $3.51 $3.95

mills/kWh 0.44 0.53 0.60 

Trona + DARCO® Hg-LH + Ash 

$/yr $766,870 $934,990 $1,049,415 

$/kW $2.84 $3.46 $3.89 

mills/kWh 0.43 0.53 0.59 

Levelized Fixed O&M Costs 

Tables 31 through 34 show the variable operating and maintenance levelized costs for power, 

sorbents, and waste disposal. These tables are summarized in Table 35. The calculations for the 

levelized variable O&M costs are done in the same manner as the levelized fixed O&M costs 

and use a levelization factor of 1.29 in accordance with the EPRI Economic Analysis. 

Levelized Power Costs 

Table 31 shows the levelized power costs. A capacity factor of 75% is assumed and a 

levelization factor of 1.29 is used for power in accordance with the EPRI Economic Analysis. 

Table 31. Levelized Variable Operating & Maintenance Costs for Power 

Levelized Variable O&M Costs: Power 

Capacity Factor 0.75 

Levelization Factor 1.29 

 

 1 Injection System 3 Injection Systems 

Power Usage, in kW 42.35 127.05 

Levelized Power Cost 

$/yr $14,351 $43,054 

$/kW 0.05 0.16 

mills/kWh 0.008 0.024 

Levelized Sorbent Costs 

Table 32 shows the levelized costs for sorbent delivered to the plant by rail. Table 33 shows the 

levelized costs for sorbent delivered to the plant by rail/truck. The levelized costs for trona and 

DARCO® Hg are compared to the levelized costs of trona and DARCO® Hg-LH at three 
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different SO2 removal rates. A capacity factor of 75% is assumed and a levelization factor of 

1.29 was used in accordance with the EPRI Economic Analysis. 

Table 32. Levelized Variable Operating & Maintenance Costs for Sorbent Delivered by 

Rail to the Plant 

Levelized Variable O&M Costs: Sorbent Delivered By Rail to Plant 

Capacity Factor 75% 

Levelization Factor 1.29 

 Removal Rates 

Levelized Sorbent Costs 

SO2 Removal 

of 45% 

SO2 Removal 

of 64% 

SO2 Removal 

of 70% 

 

Trona + DARCO® Hg* 

$/yr $1,813,290 $3,659,211 $5,015,259 

$/kW $6.72 $13.55 $18.58

mills/kWh 1.02 2.06 2.83 

Trona + DARCO® Hg-LH* 

$/yr $1,883,635 $3,785,069 $5,057,635 

$/kW $6.98 $14.02 $18.73

mills/kWh 1.06 2.13 2.85

 *minus PAC that would already be injected 

Table 33. Levelized Variable Operating & Maintenance Costs for Sorbent Delivered by a 

Combination of Rail and Truck to the Plant 

Levelized Variable O&M Costs: Sorbent Delivered By Rail and Trucked to Plant 

Capacity Factor 75% 

Levelization Factor 1.29 

 Removal Rates 

Levelized Sorbent Costs 

SO2 Removal 

of 45% 

SO2 Removal 

of 64% 

SO2 Removal 

of 70% 

 

Trona + DARCO® Hg* 

$/yr $1,953,133 $3,938,896 $5,390,291 

$/kW $7.23 $14.59 $19.96

mills/kWh 1.10 2.22 3.04 

Trona + DARCO® Hg-LH* 

$/yr $2,023,478 $4,064,754 $5,432,667 

$/kW $7.49 $15.05 $20.12

mills/kWh 1.14 2.29 3.06

 *minus PAC that would already be injected 

Levelized Waste Disposal Costs 

Table 34 shows the levelized waste disposal costs. The levelized costs for landfilling a 

combination of trona, DARCO® Hg and ash are compared to levelized costs for landfilling trona, 

DARCO® Hg-LH and ash at three different SO2 removal rates. A capacity factor of 75% was 

assumed and a levelization factor of 1.29 was used in accordance with the EPRI Economic 

Analysis. 
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Table 34. Levelized Variable Operating & Maintenance Costs for Waste Disposal 

Levelized Variable O&M Costs: Waste Disposal 

Capacity Factor 75% 

Levelization Factor 1.29 

 Removal Rates 

Levelized Waste Disposal Costs 

SO2 Removal 

of 45% 

SO2 Removal 

of 64% 

SO2 Removal 

of 70% 

 

Trona + DARCO® Hg* 

$/yr $434,422 $870,200 $1,171,244

$/kW $1.61 $3.22 $4.34

mills/kWh 0.24 0.49 0.66

Trona + DARCO® Hg-LH* 

 $/yr $426,164 $852,703 $1,143,021

$/kW $1.58 $3.16 $4.23

mills/kWh 0.24 0.48 0.64

 *minus PAC that would already be injected 

Total Levelized Variable O&M Costs 

Table 35 shows the total levelized variable operating and maintenance costs. The levelized costs 

for power, sorbent, and waste disposal are added up and can be compared as one silo versus 

three silos at three different SO2 removal rates. 

Table 35. Levelized Total Variable Operating & Maintenance Costs 

Levelized Total Variable O&M Costs 

Removal Rates 

Levelized Total Variable O&M Cost 

SO2 Removal 

of 45% 

SO2 Removal 

of 64% 

SO2 Removal 

of 70% 

Trona Delivered by Rail to Plant 

Trona + DARCO® Hg 

$/yr $2,290,786 $4,572,466 $6,229,557

$/kW $8.48 $16.94 $23.07 

mills/kWh 1.29 2.58 3.51

Trona + DARCO® Hg-LH 

$/yr $2,352,853 $4,680,826 $6,243,710 

$/kW $8.71 $17.34 $23.12 

mills/kWh 1.33 2.64 3.52 

Trona Delivered by Rail/Truck 

Trona + DARCO® Hg 

$/yr $2,430,629 $4,852,150 $6,604,588 

$/kW $9.00 $17.97 $24.46 

mills/kWh 1.37 2.74 3.72

Trona + DARCO® Hg-LH 

$/yr $2,492,695 $4,960,510 $6,618,742 

$/kW $9.23 $18.37 $24.51 

mills/kWh 1.41 2.80 3.72 
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Total Levelized Costs 

Table 36 shows the total levelized costs, which includes the total variable O&M costs, total fixed 

O&M costs and total capital costs at three removal rates. 

Table 36. Levelized Costs (Capital, Fixed, and Variable Levelized Costs) 

Levelized Total Costs 

Removal Rates 

Total Levelized Cost (Capital, Fixed, 

and Variable Costs) 

SO2 Removal 

of 45% 

SO2 Removal 

of 64% 

SO2 Removal 

of 70% 

1 SILO 

Trona Delivered by Rail to Plant 

Trona + DARCO® Hg 

$/yr $3,469,084.86 $5,922,516.40 $7,698,261.25

$/kW $12.85 $21.94 $28.51

mills/kWh 1.96 3.34 4.34

Trona + DARCO® Hg -LH 

$/yr $3,523,067.86 $6,019,159.39 $7,696,470.85

$/kW $13.05 $22.29 $28.51

mills/kWh 1.99 3.39 4.34 

Trona Delivered by Rail/Truck 

Trona + DARCO® Hg 

$/yr $3,608,927.31 $6,202,201.30 $8,073,293.28

$/kW $13.37 $22.97 $29.90

mills/kWh 2.03 3.50 4.55

Trona + DARCO® Hg -LH 

$/yr $3,662,910.31 $6,298,844.29 $8,071,502.87

$/kW $13.57 $23.33 $29.89

mills/kWh 2.06 3.55 4.55 

3 SILOS 

Trona Delivered by Rail to Plant 

Trona + DARCO® Hg 

$/yr $3,727,934.08 $6,181,365.62 $7,957,110.48

$/kW $13.81 $22.89 $29.47

mills/kWh 2.10 3.48 4.49

Trona + DARCO® Hg -LH 

$/yr $3,781,917.08 $6,278,008.62 $7,955,320.07

$/kW $14.01 $23.25 $29.46

mills/kWh 2.13 3.54 4.48 

Trona Delivered by Rail/Truck 

Trona + DARCO® Hg 

$/yr $3,867,776.53 $6,461,050.52 $8,332,142.50

$/kW $14.33 $23.93 $30.86

mills/kWh 2.18 3.64 4.70

Trona + DARCO® Hg -LH 

$/yr $3,921,759.53 $6,557,693.52 $8,330,352.10

$/kW $14.53 $24.29 $30.85

mills/kWh 2.21 3.70 4.70
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Removal Cost per Ton of SO2 Removed 

Table 37 shows the cost per ton of SO2 removed using trona at full scale. These values are 

levelized over 20 years. The amount of SO2 removed is based on the baseline emission rate of 

5,200 tons per year for all three units combined. The cost per ton of SO2 removed is calculated 

by dividing the levelized total costs ($/yr) given in table 36 by the amount removed from the 

baseline for each removal rate. The cost per ton of SO2 removed varied from $1,483 to $2,290. 

Table 37. Removal Costs per Ton SO2 Removed 

Levelized Total Cost per Ton of SO2 Removed ($/ton) 

No. of Silos, Delivery Method, and 

Sorbent SO2 Removal Rate 

* 45% 64% 70% 

1 SILO 

Trona Delivered by Rail to Plant 

Trona + DARCO® Hg $1,483 $1,780 $2,116

Trona + DARCO® Hg-LH $1,506 $1,809 $2,115

 

Trona Delivered by Rail/Truck 

Trona + DARCO® Hg $1,543 $1,864 $2,219

Trona + DARCO® Hg-LH $1,566 $1,893 $2,218

 

3 SILOS 

Trona Delivered by Rail to Plant 

Trona + DARCO® Hg $1,594 $1,858 $2,187

Trona + DARCO® Hg-LH $1,617 $1,887 $2,186

 

Trona Delivered by Rail/Truck 

Trona + DARCO® Hg $1,654 $1,942 $2,290

Trona + DARCO® Hg-LH $1,677 $1,971 $2,290