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Recent Operating Results of the Five New Wet FGD Installations

For Ameren Corporation

Bruce C. Studley: VP, After Market Services

Hitachi Power Systems America, Ltd.

Robert Nicolo: AQCS Product Director

Hitachi Power Systems America, Ltd.

Steve Mosch: Director, Air Quality Control Systems Engineering

Hitachi Power Systems America, Ltd.

ABSTRACT

Hitachi Power Systems America, Ltd. has recently completed the Start-Up, Performance 

Testing and several months of operation on the five (5) Wet Limestone Forced Oxidation 

Scrubbers (WFGD) installed in Missouri and Illinois for Ameren. Ameren Corporation is 

the parent of utility companies that serve 2.4 million electric customers and 1 million 

natural gas customers in a 64,000 square-mile area of Missouri and Illinois. 

This paper will discuss the project backgrounds along with the design and operating 

performance of the advanced SO2 reduction technology that was implemented on these 

five units.

The performance of these WFGDs has delivered ultralow SO2 emissions which also 

demonstrates the capability to reliably deliver CO2 capture ready clean flue gas for future 

carbon capture programs where single digit PPM SO2 emissions are required. The paper 

will discuss the advanced design features and performance of these WFGD systems 

including SO2, SO3, PM, and mercury capture efficiencies. These installations are reliably 

achieving over 99% SO2 reductions without the use of additives, internal packing/trays or 

other chemical additions.

With the new Utility MACT requirements expected to be finalized soon, these units will 

have the advantage of their excellent multi-pollutant control aspects. It will be most 

important to achieve lower acid gasses, mercury, and filterable PM emissions in light of the 

new regulations.
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INTRODUCTION

Ameren as part of their continued investments in environmental improvements at their 

operating plants awarded in April 2006 five (5) WFGDs along with the associated wet 

limestone grinding systems, piping, rotating equipment, valves and instrumentation and 

controls to Hitachi Power Systems America, Ltd. (HPSA). The WFGDs are located at 

three of Ameren’s coal fired power plants as shown in Figures 1, 2 and 3 which include;

Sioux Units 1 & 2 (2 x 535 MW) West Alton, MO

Duck Creek Unit 1 (465 MW) Canton, IL

Coffeen Unit 1 (360 MW) & Unit 2 (590 MW) Coffeen, IL

Advanced design features were employed into the WFGDs to accommodate the wide 

range of inlet flue gas sulfur and chlorine concentrations and to maximize SO2 removal 

efficiency. The vessels themselves, or spray towers, are made of carbon steel which was 

flake glass lined to allow continuous operation to chloride levels as high as 50,000 ppm. 

With respect to the scrubber inlet ducts they were made of Hastelloy C276 (UNS N10276). 

With all five wet limestone forced oxidation scrubbers successfully coming online between 

May 2009 and January 2011 performance has been superior with the ability of achieving 

over 99% SO2 reductions without the use of additives or internal packing/trays. The 

performance to date of these WFGDs has consistently delivered ultralow SO2 emissions in 

addition to the removal of other pollutants. Beyond SO2 capture, the WFGDs also 

effectively remove SO3, particulate matter, and oxidized mercury, etc. The design basis for 

the WFGDs included SO2 removal efficiency of 99%, SO3 removal efficiency of 60%, 

mercury (Hg) removal as it pertains to oxidized mercury of 90% and particulate (PM) 

removal to less than 0.015 lb/MMBtu. In addition, the WFGDs have all operated to date 

with an availability of 100%.

 Fig. 1 Sioux Units 1 & 2 Fig. 2 Duck Creek Unit 1

 Fig. 3 Coffeen Units 1 & 2 
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WFGD DESIGN AND EQUIPMENT SELECTION

HPSA’s advanced spray tower streamlined design for high efficiency and low power 

consumption and equipment selection was based on optimizing both the installed and 

overall life cycle costs. Wherever possible the duplication of equipment was maximized to 

simplify operations and maintenance along with stocking of spare parts. Key design 

criteria included an SO2 removal efficiency of 99% while using limestone slurry with up to 

95% passing through a 325 mesh screen with the potential to operate at chloride levels as 

high as 50,000 ppm, while producing gypsum with an oxidation level of greater than or 

equal to 99%. 

Basic design criteria for the WFGDs with respect to incoming flue gas as specified by 

Ameren is presented in Table 1. 

Table 1 – Basic Design Criteria

Sioux 1 & 2 Duck Creek Coffeen 1 Coffeen 2

Absorber MW 535 465 360 590

Coal Type Bituminous/PRB Bituminous Bituminous Bituminous

Sulfur Content (%) 2.15 3.41 3.47 3.47

Inlet S02 Conc (ppmd – 3% O2) 2,048 3,325 3,304 3,304

Inlet SO3 Conc. (ppmd – 3% O2) 14 - 17 15 – 23 49 – 55 46 – 51

Inlet Dust (lb/106Btu) 0.07 0.109 0.071 0.071

Gas Flow Rate (acfm) 1,915,000 1,485,900 1,337,200 2,214,400

Inlet Temp. (deg. F) 340 305 305 305

Process design criteria included having a gas velocity from 13 to 14 feet/second, a liquid to 

gas ratio (L/G) ranging from 140 to 160 gallons/103 ACF, a gas contact time in excess of 

2.0 seconds, a liquid residence time of 6 minutes, and sufficient solids residence time in 

hours to assure guaranteed gypsum production.

With respect to materials of construction, which were selected for the high chloride 

operating condition, Figure 4 below describes both the vessel and its major components.
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 Fig. 4 Materials of Construction

It is worth noting that with respect to the Sioux WFGDs that Ameren Misssouri after 

construction of the absorbers had been initiated elected to line the inside of the vessels 

with Stebbins tiles versus the flake glass lining. This required a structural review of the 

vessels primarily at the transition cones because of the additional loading on the vessel 

walls caused by the tiles, which simply required the installation of additional external 

stiffeners. In order to minimize any differential expansion between the vessel walls and 

the internal tile and grout a high reflectance white paint was used externally.

With respect to absorber island equipment selection the duplication of equipment between 

plants was maximized to simplify overall operations and maintenance along with stocking 

of spare parts. Pertinent details of major support equipment are outlined below:

All Recycle Slurry Pumps are Weir model 800TYGSL with varying motor sizes and 

gear boxes.

All absorber Bleed Pumps are Weir model EEAH with a capacity of 1,600 gpm.

All Oxidation Air Blowers are Siemens – Turblex model KA with varying motor sizes 

and gearboxes.

All Oxidation Air Agitators are Philadelphia Mixing Solutions model 3850 with 75 HP 

motors. 

All Absorber Spray Nozzles are Spraying Systems type 4B-Hollow Cone made of 

silicon carbide. 

All Mist Eliminators are Munters model DV-210 vertical flow 2-stage elements. 
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All Limestone Mills are Metso horizontal wet ball mills rated at 38 tph with Stock 

Equipment weigh belt feeders.

PERFORMANCE RELATED PROCESS DESIGN FEATURES

Incorporation of Hitachi’s key process design criteria was essential in being able to 

guarantee an SO2 removal efficiency of 99% while producing a high quality gypsum 

byproduct. As shown in Figure 5 the spray zone section and configuration of the different 

levels of spray headers and nozzles coupled with the quantity of slurry being recycled is 

critical. A typical spray header and nozzle arrangement design for an individual level is 

shown in Figure 6.

 

 Fig. 5 Absorber Cross Section Fig. 6 Spray Header Design

The overall result of properly incorporating the key process design criteria when coupled 

with a high gas velocity of 13 to 14 feet/second produces the following:

High spray flux which minimizes velocity variation 

High spray flux which maximizes gas to liquid contact

Higher spray density near absorber walls increases spray coverage and eliminates 

sneakage

Progressive flux density moves the gas away from the absorber wall toward the 

center
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Figure 7 shows two spray header levels with nozzles trussed together with direct bonding 

of the SiC spray nozzles. Figure 8 displays the overlapping high density spray patterns 

resulting in the generation of fine droplets.

 Fig. 7 Typical Spray Headers Fig. 8 Overlapping High Density

 Spray Patterns

The design of the absorber reaction tank is also important when coupled with in-situ forced 

oxidation employing side mounted agitators and air lances. The result being a high level of 

solids for enhanced SO2 removal and better dewatering coupled with sufficient residence 

time to ensure good gypsum crystal growth. Figure 9 shows a typical agitator and air 

lance arrangement which are spaced at the appropriate locations around the tank, while 

Figure 10 displays the dispersion of air bubbles.

 Fig. 9 Agitator and Air Lance Fig. 10 Dispersion of Air Bubbles to 

 Allow Forced Oxidation
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Elimination of the maximum amount of mist which is allowed to leave the 

absorber is also a key feature. This was accomplished through the two stage mist 

eliminators installed at the top of the absorber just upstream of the outlet duct. 

Figure 11 displays a typical mist eliminator arrangement which results in a 

maximum entrained moisture carry over at the outlet of less than or equal to 0.070 

grains/scf.

 Fig. 11 Mist Eliminator Arrangement

OPERATING PERFORMANCE OF THE WFGDs

At the conclusion of the construction effort of all five (5) WFGDs, along with other 

modifications and improvements being made by Ameren, tie-in outages of sufficient 

duration were under taken and the units returned to service. Upon reaching continuous full 

load operation of the boilers the scrubbers were fine tuned and all in a position to initiate 

performance testing within four (4) weeks. Actual performance test dates for the individual 

units were:

Duck Creek Unit 1 May 20, 21, 2009

Coffeen Unit 1 February 3, 4, 5, 2010

Coffeen Unit 2 May 11, 2010

Sioux Unit 1 January 18, 19, 20, 2011

Sioux Unit 2 December 16, 17, 2010

It is important to also realize that the type of coal being burned at all three Ameren plants 

had changed significantly from the basic criteria of primarily all bituminous coal to a large 

percentage of Power River Basin (PRB) coal. Specifically, the fuel blend of coal used 

during the tests and currently being consumed is:

Duck Creek 70% PRB/30% Bituminous

Coffeen 95% PRB/5% Bituminous

Sioux 80% PRB/20% Bituminous
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Results of the performance tests undertaken with respect to emissions are shown in the 

following tables, and appreciating the significant changes in the actual coal being burned 

from the design criteria, clearly indicates the ability of all five (5) WFGDs to perform at 

levels well in excess of the guarantee levels. Because of the identical design parameters 

of the units at Coffeen and Sioux their test results have been averaged. 

Table 2 – Duck Creek Performance Test Results

Parameter Guarantee Test Result

Particulate Emissions ≤ 0.015 lb/MMBtu 0.0045 lb/MMBtu

SO2 Removal ≥ 99% Removal 99.83% Removal

SO2 Emissions ≤ 0.064 lb/MMBtu 0.0038 lb/MMBtu

SO3 Removal ≥ 60% Removal 72.1% Removal

Mercury Removal ≥ 90% Removal of Oxidized Mercury 99.0% Removal

Table 3 – Coffeen Performance Test Results

Parameter Guarantee Test Result

Particulate Emissions ≤ 0.015 lb/MMBtu 0.0047 lb/MMBtu

SO2 Removal ≥ 99% Removal 99.95% Removal

SO3 Removal ≥ 60% Removal 67.45% Removal

Mercury Removal (Note) ≥ 90% Removal of Oxidized Mercury 84.35% Removal

Note: The slightly lower % removal of Oxidized Mercury is a result of the test being 

conducted while firing a 95% PRB/5% bituminous blend with very low speciation of 

Mercury into the ionic form. Consequently, one of the outlet results was below the 

quantitative limit. In addition, it should be noted the Hitachi guarantee is based on 

firing an Illinois coal that has an estimated chlorine content of 0.12%, while the 

tested fuel has an estimated chlorine content of less than 0.02%. This chlorine 

content is critical in speciating Mercury into the ionic form.

Table 4 – Sioux Performance Test Results

Parameter Guarantee Test Result

Particulate Emissions ≤ 0.015 lb/MMBtu 0.0062 lb/MMBtu

SO2 Removal ≥ 99% Removal 99.65% Removal

SO2 Emissions ≤ 0.04lb/MMBtu 0.005 lb/MMBtu

SO3 Removal ≥ 60% Removal 72.25% Removal

Mercury Removal ≥ 90% Removal of Oxidized Mercury 98.7% Removal

In addition, the non-emission guarantees associated with a gypsum oxidation level of ≥ 

99%, and the limestone consumption and power consumption levels required were all 

satisfactorily obtained. 
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CONCLUSIONS

The successful installation of all five (5) WFGDs and their ongoing continuous ability 

to consistently deliver ultralow SO2 emissions in addition to the removal of other 

pollutants, has clearly established the ability to maximize the removal of critical 

pollutants from these coal fired electrical plants through the use of Hitachi’s 

advanced spray tower wet scrubbers. 

Ameren’s continued investments in environmental improvements at their operating 

plants is a clear indication of their commitment to providing their customers with 

clean, reliable energy, while preserving, protecting and improving the environment.

Hitachi’s WFGD experience on a worldwide basis with the completion of these five 

units and those currently in design and construction totals at 75 installations. Inlet 

SO2 concentrations range from 500 to 4,000 ppm with absorber capacities to 1,050 

MWs.