## NEW MAGNESIUM – ENHANCED LIME FGD PROCESS

Bob Roden, Lew Benson, and Kevin Smith Carmeuse North America - Technology Center Pittsburgh, PA 15225



### ABSTRACT
Dravo Lime Inc. has developed a new ma gnesium-enhanced lime (MEL) based wet FGD process. This new process is an improve ment upon the older magnesium-enhanced lime based FGD process, which has been in us e for the past 25 year s and serves 15,700 MW of generating capacity. In the year 2 000, 4300 MW of the older magnesium-enhanced lime FGD capacity was converted to improved versions of that produce gypsum rather than calcium sulfite.

This paper describes the new process, the in stallations using this process and discusses performance data. This new process can obtain the high SO 2 removal efficiency of 99% which is the major hallmark of the older process while scrubb ing flue gas with high inlet SO 2 . In addition, this process can produce gyps um of purity close to 98% and obtain a reagent utilization of 99.9%. The new process can also produce byproduct Mg(OH) 2 (magnesium hydroxide) if desired.



### INTRODUCTION

The Thiosorbic ® or the old conventional natural oxid ation MEL FGD process has been in commercial use in the US since the early 1970’ s and has served the needs of the coal fired utility industry extremely well and conti nues to do so now. It served a base of 15,700 MW of generation capacity till recently. The significance of the MEL FGD has always been its capability for very high SO 2 removals due primarily to the highly alkaline scrubbing liquor resultin g from the presence of soluble magnesium sulfite and smaller scrubber sizes. Since the scrubber liquor typically cont ains less than 100 ppm of dissolved calcium ions and thus precludes pot ential for gypsum scaling when the soluble magnesium concentration is maintained at the desired level, the system also has a high availability. The byproduct of this well know n process is principally calcium sulfite solids with some natural oxidation (10-20% mole percent) present. Table 1 shows the list of utilities currently using the MEL FGD. Those units utilizing the new process to produce gypsum are noted with an asterisk.Table 1. List of Utilities with MEL FGD

COMPANY UNIT MW Alabama Electric Cooperative Lowman 2 * 258 Lowman 3 * 258 Allegheny Energy Supply Harrison 1 680 Harrison 2 680 Harrison 3 680 Mitchell 3 300 Pleasants 1 * 684 Pleasants 2 * 684 American Electric Power Conesville 5 444 Conesville 6 444 Gavin 1 1,397 Gavin 3 1,397 Applied Energy Services Beaver Valley * 140 Arizona Public Service Four Corners 1 170 Four Corners 2 170 Four Corners 3 220 WKE Green 1 231 Green 2 223 Henderson 1 175 Henderson 2 175 CINergy East Bend 2 640 Zimmer 1 * 1,397 Orion Power Elrama 1 80 Elrama 2 80 Elrama 3 100 Elrama 4 165 First Energy Mansfield 1 917 Mansfield 2 917 Mansfield 3 * 917 * These units have the new MEL oxidized process

In the year 2000 four of the major utility plants converted to improved versions of the MEL oxidized FGD process. Some of these la rger plants and other smaller conversions were covered in detail in earlier presentations . 1, 2, 3 Three of the four larger plants produces gypsum to supply feed material to new modern high-speed wallboard plants. Prior to this conversion the plants were land-filling the FGD so lids via a fixated land based disposal method following primary (and in one case a secondary) dewatering followed by mixing with fly ash and stabilizi ng with lime. It is well known in this industry that dewatering primarily sulfite solids from the unoxidized MEL FGD system produces at best a filter cak e of 40-50% solids which needs a large amount of fly ash (usually all that is avai lable in the plant) to fixate the we t material. This continues to beone of the drawbacks of the unoxidized MEL FG D process. The new process enables the utility customer to consider alternate uses for the fly ash since it is not needed for stabilization.

Figure 1 depicts the highly porous crysta lline structure of the typical MEL FGD byproduct calcium sulfite.

Figure 1. SEM Image and Analysis for T ypical Calcium Sulfite Feed Material

ANALYSIS TYPICAL VALUES

Filter Cake Solids, wt % 40-50
CaO, wt % 30-35 MgO, wt % 3.0-4.0 Particle Size D50 6-10 micron

Dravo Lime Inc., working together with a utility customer (in one instan ce) and on its own spent a lot of its resources over the past several y ears developing the MEL oxi dation process options.

The incentives for the utilities to consider swit ching to the new oxidized MEL process relate to, among others, a perceived window of demand fo r synthetic gypsum for the new efficient wallboard plants and avoidance of investment to prepare more landfill area needed for extended periods into the future. The environmentally aes thetic desire to produce a usable product from an otherwise waste is also a significant factor. The new wallboard plants are capable of using 100% synthetic gypsum thus minimizing the ne ed for dependence on mined natural rock.

The recently converted major oxidized MEL operations are:

• Unit #3 of First Energy’s Mansfield stati on in Shippingport, PA. (917 MW). The gypsum is supplied to a new Nati onal Gypsum wallboard plant.

• Pleasants Units 1 and 2 of Allegheny Ener gy on Willow Island, WVA. (2 x 684 MW). The gypsum is supplied to a new US Gypsum wallboard plant.

• Zimmer station of CINergy, Moscow, OH. ( 1,397 MW). The gypsum is supplied to a new Lafarge Gypsum wallboard plant.

• Lowman Station Units 2 and 3 of Alabama Electric, Leroy, AL. (2 x 258 MW). The gypsum is sold to a cement produc er and agricultural interests.Two of the converted stations listed in Tabl e 1 also make a byproduct magnesium hydroxide [Mg(OH) 2 ]. The byproduct Mg(OH) 2 is a desirable acid neutraliz ation reagent and can be used in the utility plant for a numb er of beneficial purposes.



### BLEED STREAM OXIDATION (BSO) Process Chemistry

Dravo’s conventional Thiosorbic ® FGD process takes advantage of the relative high solubility of magnesium to increase the alkalinity of the scru bbing liquor. Magnesium enhanced quicklime contains 3-7% MgO and 90-95% CaO that when sl aked, produces a reagent slurry comprised of magnesium hydroxide, Mg(OH) 2 , and calcium hydroxide, Ca(OH) 2 , that is added to the recycle tank for pH control of the scrubbing liquor.

When SO 2 from the flue gas is absorbed in an aqueous solution it forms sulfurous acid, H 2 SO 3
.

SO 2 + H 2 O ➜ H 2 SO 3
The capacity for SO 2 absorption is limited unless an alkaline species is available to react with the sulfurous acid present. The magnesium hydroxide [Mg(OH) 2 ] from the lime slurry reacts with dissolved sulfur dioxide (as H 2 SO 3 ) in either the recycle tank or absorber to form the soluble alkaline salt, magnesium sulfite (MgSO 3 ).

Mg(OH) 2 + H 2 SO 3 ➜ MgSO 3 + 2H 2 O

This species rapidly neutralizes additional absorbed SO 2 forming magnesium bisulfite [Mg(HSO 3 ) 2 ], providing additional SO 2 scrubbing capacity as compared to systems where magnesium sulfite is not present.

MgSO 3 + H 2 SO 3 ➜ Mg(HSO 3 ) 2
Sulfites reacting with Ca(OH) 2 produces calcium sulfite hemihydrate [(CaSO 3 • 1/2H 2 O)] that immediately precipitates in the recycle tank. One mole of calcium hydroxide [Ca(OH) 2 ] from the blend of magnesium hydroxide and lime sl urries reacts with one mole of Mg(HSO 3 ) 2 to form one mole of calcium sulfite solids [CaSO 3 (s) ] and regenerate one mole of MgSO 3 to sustain the cycle of absorption of SO 2 in the absorber.

Ca(OH) 2 + Mg(HSO 3 ) 2 ➜ CaSO 3 •1⁄2H 2 O È + MgSO 3 + 3 / 2 H 2 O

Typical soluble magnesium levels in this process range from 4,000-8,000 ppm.

What is different in the BSO process is that soluble magnesi um levels are elevated to concentrations of 10,000 to 20,000 ppm by one or both of the following means:

1. Recycled liquor from the gypsum producti on portion of the pro cess contains soluble magnesium, sulfates, and chlorides ranging as high as 20,000, 60,000, and 3,500 ppm respectively. The low alkalin ity return liquor co ntributes toward enhancing scrubberchemistry through an exchange of solid phase sulfite and liquid phase sulfate. Only a small amount of ions need exchange to have a beneficial effect on sc rubber chemistry.

MgSO 4 + CaSO 3 ➜ MgSO 3 + CaSO 4
2. Magnesium hydroxide can be generated from the back end of the gypsum process and blended with lime slurry in any desired ra tio of volumes lime slurry to magnesium hydroxide slurry. The blended reagent slurry is used in the scrubber circuit to control pH in the range around 6.0.

By either mechanism, more magnesium sulfite is present than is typical in the traditional Thiosorbic ® FGD process, raising alkalinity of the sc rubbing liquor to higher levels. If high SO 2 removal efficiency is desired to meet or exceed Phase II emission requirements, scrubber alkalinity can be boosted through increasing th e relative amount of recovered magnesium hydroxide to lime slurry. Soluble magnesium and sulfites increase ac cordingly to produce greater liquor alkalinity. As alkalinity increases, scrubber pH can be allowed to drop lower, making more of the soluble sulfites form bisulfite, a mild acid.

Oxidation and gypsum crystallizat ion is performed external to the scrubber circuit thus maintaining high SO 2 removal conditions in the scrubber wi thout the addition of additives other than lime and recovered magnesium hydroxide. The oxidation reactions are shown below.

CaSO 3 •1⁄2H 2 O + 1⁄2O 2 + 3 / 2 H 2 O ➜ CaSO 4 •2H 2 O MgSO 3 + 1⁄2O 2 ➜ MgSO 4

This ex-situ oxidation allows SO 2 scrubbing with lower power cost s associated with lower L/G, less recycle pumps, and physically smaller size of sc rubbers. This feature also makes retrofit of existing first and second generation FGD system s possible without much complication. The presence of bisulfite in slurry bled from the scrubber circuit is taken advantage of in the oxidation step, immediately downstream. Through oxidation of magnesium bisulfite, acid is produced and oxidizer pH drops to belo w 6, which is conducive to oxidation.

Mg(HSO 3 ) 2 + O 2 ➜ MgSO 4 + H 2 SO 4

The gypsum produced from the BSO process has very consistent physical and chemical properties that make it quite su itable for modern high-speed wall board production processes.

Note in Figure 2 the highly crystalline structure of the M EL FGD gypsum product compared to the calcium sulfite feed material of Figure 1.

Figure 2

. SEM Image and Analysis for Typical Gypsum ProductANALYSIS TYPICAL VALUES
Moisture, wt % 10-12 pH 5-8 Purity, wt % 95-98 CaO, wt % 30-35 MgO 80-170 ppm Chloride 20-40 ppm Particle Size D50 80-140 micron



### Options for Magnesium Hydroxide Recovery and Benefits
As mentioned earlier, MEL FGD using the BSO pr ocess can be implemented with or without magnesium hydroxide recovery A utility might choose to include magnesium hydroxide recovery for the following reasons:

• In-plant uses of magnesium hydroxide might in clude neutralization of coal pile run-off water and enrichment of the SO 2 reagent lime slurry to achieve SO 2 removals approaching +99% in the scrubber circuit.

• Raw synthetic magnesium hydroxide slurry wa s recently tested during two campaigns as a boiler injection additive to control SO 3 emissions 4 at First Energy's Bruce Mansfield Plant, Unit 3.

• Mg(OH) 2 injection into the boiler may reduce pr oblems associated with ash slagging. This may allow better fuel flexibility for the utility.

• For plants where FGD wastewater treatm ent is required, reco very of magnesium hydroxide would substantially reduce load on the treatment plant. Although the magnesium hydroxide slurry produced is typically 20-wt. % solids density, it may be cost competitive with commercial magne sium hydroxide slurry and especially caustic for commercial sale within a reasonable radius from the plant. Caustic availability has become an issue lately sin ce caustic production has been cu rtailed, especially in the northwest US, due to escalating power costs. 5

Magnesium hydroxide recovery in the process begins by taking the (magnesium) chloride purge stream that also contains high levels of soluble magnesi um sulfate and feeding it to a regeneration tank. In the regeneration tank, calcium hydroxide from the lime slurry reacts with the oxidized liquor to form and precip itate gypsum and magnesium hydroxide solids.

MgSO 4 + Ca(OH) 2 + 2H 2 O ➜ CaSO 4 •2H 2 O + Mg(OH) 2 MgCl 2 + Ca(OH) 2 ➜ Mg(OH) 2 + CaCl 2Gypsum crystals that form in the regeneration tank are an order of magnitude larger than the co-precipitating magnesium hydroxide crystals. Hydroclones are used to exploit this size difference in separating gypsum from magnesium hydroxide.

The overflow streams from the operating primary hydroclones in a single bank flow to a common catch basin from which the combined stream flows into the feed well of the magnesium hydroxide thickener. Only one thickener may need to be in service at a time depending on whether the Mg(OH) 2 slurry is exported or not. If slurry is used exclusively on site, lower product slurry density of 10 to 15- wt.% may be tolerated and a single thickener will suffice. However, if maximum product slurry density is important, a second thickener is needed to insure product slurry density exceed s 20-wt.% and provides additional storage of magnesium hydroxide. Several flocculating ag ents available commercially have proven effective in promoting solids settling.

The underflow stream consists of most of th e gypsum produced by the regeneration process and some residual magnesium hydroxide. This u nderflow stream is colle cted in an agitated tank and pumped to the oxidizer. Any residual alkali contained in this stream is consumed in the oxidizer.

Figure 3 is a flow diagram of the BSO process and Figure 4 shows the flow diagram of the BSO process with a magnesium hydroxide recovery circuit.Figure 3. BSO Process without Magnesi um Hydroxide Recovery

AIR Flue gas in Flue gas

out FRESH
WATER

LIME
SLURRY SULFURIC ACID FROM
TRUCK

CAKE WASH

WATER

GYPSUM TO
CONVEYOR

MAKE UP
WATER

TO WASTE

POND OXIDIZER FILTER SULFURIC

ACID TANK

FINES CLARIFIER ABSORBERS ~ ~

A B C D D

C

B

A

1 2 3 4 5 6 7 8 876 54321

Figure 4. BSO Process with Magnesium Hydroxide Recovery

~

A B C D D

C

B

A

1 2 3 4 5 6 7 8 876 54321

STORAGE

TANK A IR Flue gas in Flue gas

out

Mg(OH) 2 THICKENER CAKE WASH WATER

GYPSUM TO CONVEYOR

MAKE UP WATER

TO WASTE

POND

LIME SLURRY Mg(OH) 2 PRODUCT BLEED LIME SLURRY

FRESH WATER

FILTER

OXIDIZER
ABSORBERS

REGENERATION TANK FINES CLARIFIER

~ ~

### Retrofit and New Applications
Retrofit Applications The recent applications of improved MEL FGD processes on commercial scale projects at the four different sites are primarily retrofits to pre-existing Thiosorbic ® MEL FGD operations. The actual processes em ployed at each of these plants vary in process details and are adapted to the available equipment and othe r constraints specific to the plants. Although the four applications differ to some degree, all three facilities ar e supplying gypsum to wallboard plants.

Working with one of our utility customers, te sts were conducted at p ilot scale for extended periods of time and a process was developed to oxidize the sulfite solids from a thickener underflow at the Mansfield station. 1 This plant needed to use feed from a scrubber operation where all of the fly ash is removed in the wet scrubber and the feed to the oxidizer therefore contained a large proportion of this fly ash. One of the process challenges was to minimize the coarse fly ash content upstream and fine fl y ash content downstream of the oxidizer. Following the oxidizer circuit the fine as h was separated by using a Hydroseparator ® . This plant has been routinely pr oducing acceptable quality gypsum for the modern wallboard plant.

Another application was to take the oxidizer feed from the scrubber bleeds, which would otherwise be routed to a gravit y thickener for settling. In this plant the scrubbe rs are supplied a mixed reagent of lime slurry and recovered Mg(OH) 2 from the back end of the process. The scrubber has a rich magnesium based chemistry to maintain high SO 2 removals. The oxidizer receives a stream of recycled gypsum seed crystals and these grow as the oxidation process progresses. This plan t produces a high purity gypsum.

The third application of the oxi dized MEL process is at the Z immer station of CINergy. This 1,397 MW plus system uses the low pH bleed fr om the scrubber modules using a specially designed scoop placed strategically inside each of the scrubber modules. This plant also used a converted existing thickener underflow tank 3 as the external oxidizer. This method of oxidizing the low pH bleed from the scrubber gives the most cost effective and simple oxidation system for process control purposes. Zimmer curren tly uses sulfuric acid to maintain oxidizer pH during scrubber operation upsets. These are the major unique design features of this plant.

In the case of retrofits from existing unoxi dized MEL to oxidized MEL processes it is important to address the specifics of the ex isting plant equipment and operating needs to determine the optimum retrofit process modifi cation. The most likely process for those applications where there is a need for minimizi ng the process control ci rcuits and the retrofit costs is the bleed stream oxidati on (BSO) with or without Mg(OH) 2 recovery.

If the plant can use the recovered Mg(OH) 2 at the station for 1) SO 3 control 4 or for 2) other possible benefits (to be established) and 3) a greater fuel flexibility towards optimizing ash fusion properties in the boiler, a utility will have to seriously consider producing Mg(OH) 2
. The high cost of commercial Mg(OH) 2 has prevented to date a number of high sulfur burningutilities from considering this option. It is known that the minimization of SO 3 will let the air preheater exit temperature be lowered and not be limited by the high acid dewpoint; low SO 3 levels will also reduce the frequency with which the preheater needs to be cleaned.

New Applications

All of the retrofit oxidation M EL projects to date use an exte rnal oxidizer. The external oxidizer allows the advantage of running the scrubbers at conditions optimal for SO 2 removal while permitting optimization of the oxidizer operation indepe ndently from the scrubber circuit. Optimization of the oxidizer gives better quality control of the gypsum product.

Application of the oxidized MEL process today will most likely be the bleed stream oxidation process with or without Mg(OH) 2 recovery. As mentioned earlier the BSO process has the minimum equipment needs and is easy to c ontrol. An external oxidizer would be the preferred design for flexibility.

A byproduct Mg(OH) 2 recovery system would become f easible if there is a need for Mg(OH) 2 in the plant for:

• Boiler injection for SO 3 reduction (new SCR may di ctate this need also)

• Treatment of water prior to disposal to reduce TDS and maintain desired pH control

• Boiler injection for better slag fusion prope rties (may allow greater fuel flexibility)

Production of Mg(OH) 2 can be accomplished with minimal additional equipment. If quantities of Mg(OH) 2 in excess of that av ailable by using the conventional 3-7% MgO lime reagent is needed, this can be accomplishe d by increasing the reagent MgO content by blending the lime with dolomitic fines.

Figure 5 summarizes some of the charac teristics of typi cal byproduct Mg(OH) 2 recovered from the process. Note in the SEM photogr aph the fine size of the magnesium hydroxide compared to the gypsum crystal present.

Figure 5

. SEM Image and Analysis for Typi cal Magnesium Hydroxide Product

Typical Magnesium Hy droxide Chemical Analysis MgO as Mg(OH) 2 , wt. % 55-80 Gypsum as CaSO 4 • 2H 2 0, wt. % 16-26
Inerts, wt. % 4-19 Total Suspended Solids, % 12-20 BET Specific Surface Area,

m 2 /g 50-55

Particle Size D50 2-4 micronThe oxidized MEL scrubber can achieve SO 2 removals of 99% with high sulfur coals at L/G substantially lower than the LSFO. The oxidize d MEL scrubber will ha ve a lower parasitic load of at least 0.5% less than the LSFO process.



### Design Considerations
In addition to meeting ever more strict e nvironmental regulations, recovery of salable byproducts that must meet customer minimum specifications necessarily complicates the FGD process and forces attenti on to operating and maintenance de tails in areas where neither was previously required. The magnesium-enhanced lime forced oxidation process has several circuits in its operation th at require additional attention.

Scrubber Operation – Slurry density in absorber modul es should be maintained at 15 wt.%. Mist eliminator wash water is a blend of fr esh water and recycled FGD process water to maintain less than 50% gypsum sa turation in the wash water.

Lime Slaking – Production of gypsum to meet customer specifications requires attention to lime quality and lime slaking. The main issue is minimizing grit production both to insure maximum lime utilization and minimal impact on gypsum quality, mainly pH. In a ball-mill or vertical mill slaker, grinding of grit to le ss than 200 mesh allows lime utilization to reach 99.9% and allows only a minimal amount of unreacted lime into the gypsum product.

Gypsum pH – The range of gypsum pH specified by wa llboard producers is between 5 and 9. While gypsum from the MEL process ach ieves residual alkalinity (as CaCO 3 ) of 0.2 to 0.5 mg/g, corresponding to lime utilization of 99.9%, a portion of the alkalinity is present as CaO. This CaO can elevate gypsum pH. As a result, treatment of th e filter cake with a minor amount of acid is sometime s required to neutralize the porti on of the residual alkalinity that is CaO to bring gypsum into specification with respect to pH.

Water Management – Forced oxidation FGD plants requir es special attention to balancing water use and loss within the plant because little water l eaves in the gypsum product. Lime slaking, scrubber mist eliminators, and gypsum va cuum filters require fresh water that must be absorbed without placing an undue burden on waste water treatmen t plants while also limiting soluble chloride concentration within th e process. Creative ways of balancing these competing demands begins in the engineeri ng phase and continues through day-to-day operation. Examples of creative water use incl ude reuse of process liquors by treatment and handling that reduces potentia l for both gypsum and calcium carbonate scaling, and minimizing water use by filters by having fresh water perform multiple tasks such as belt and cloth washing prior to fi lter cake washing.



### Economics of MEL Process
Capital and Operating Costs Estimating generic capital and operating costs is difficult since any particular station has unique requirements and situations to consider . EPA recently evaluate d capital and operatingcost of major FGD processes 8 including the new MEL proces s. The capital and operating costs of the MEL process were competitive with LSFO.Effect on Fuel Cost Economic advantage can be taken of the MEL pro cess by burning cheaper, higher sulfur fuel. The MEL process has a proven ability to handle flue gases from burning of high sulfur (>4%) coal. Historically, higher sulfur bituminous coal is usually lowe r in cost than lower sulfur bituminous coal. 6 Recent coal pricing trends indicat e an even more dramatic difference between moderate and high sulfur bituminous coal. 7 Savings by burning of lower cost, high sulfur fuel could more than offsets added FGD costs.

A number of MEL customers menti on their desire to be as flexible with the type of fuel burned as environmental regula tions and boiler operation allo w. From the environmental aspect, it is necessary to maintain emission limits imposed by state and federal governmental agencies. Depending on the boiler type, highe r sulfur containing fuels have ash slagging characteristics that may at leas t require a derate to remove de posits or be incompatible with the boiler altogether. The proven ability of BSO to scrub high sulfur fuels and the option of producing highly reactive magnesium hydroxide bypr oduct, with the pote ntial for effective use as a boiler injection additive for slag control, gives the utility fuel flexibility that may not have been possible before.

### CONCLUSION
Several years of R&D efforts by Dravo has cu lminated in the development of new MEL FGD options for the industry. The newly convert ed commercial operatio ns had their share of process difficulties and a number of issues rela ted to the process controls and product quality that were solved systematically. Most of these issues are detailed in a number of earlier presentations 1, 2, 3 and continued in this paper. Th ese plants are now routinely producing gypsum and are supplying the new wallboard pl ants. Dravo Lime Inc. is continuing its efforts to assist the plants in optimizin g the operations and addressing any remaining operating and product quality related issues.

The new MEL FGD process retains all of the benefits of the well known Thiosorbic ® lime based FGD including high SO 2 removals with low L/G ratio due to the high liquor alkalinity, low parasitic load, and high system availabil ity. In addition, it prov ides a high purity and consistent quality gypsum for use by the modern wallboard plants.

With fuel price increases in recent months and wi th utilities thus seeki ng lower cost coals, the BSO process with Mg(OH) 2 recovery may afford the utility a greater fuel flexibility. If the utility customer desires to make a byproduct Mg(OH) 2 for in-plant use as an acid water treatment reagent prior to dis posal and/or for the recently demonstrated boiler injection process in a coal fired boiler for pl ume opacity contro l by capturing the SO 3 4 , the Mg(OH) 2 slurry production process is available and can be implemented with minimal additional equipment.

### ACKNOWLDEGMENTS
The authors wish to acknowledge the assistan ce of Daniel Berisko, Mario Panella, Sandra DeWitt, Sean Tremba and Dr. Shiaw Tseng of the Dravo Lime Technology Center in the preparation of this paper.



### REFERENCES
1. M. Golightley et.al., " Lime-Based Forced Oxidation to Gypsum at First Energy's Bruce Mansfield Station" , Proceedings: EPRI-DOE-EPA, Combined Utility Air Pollutant Control Symposium, Atlanta, GA, August 1999.

2. K. Smith et.al., "Review of 18 Months of Thioclea r® FGD Operation at AES Beaver Valley Cogeneration" , Proceedings EPRI-DOE-EPA, Co mbined Utility Air Pollutant Control Symposium, Atlanta, GA, August 1999.

3. W. Brockman et.al., "Concept Development, Pilot Testing, and Design Leading to Conversion of the Wm. H. Zimmer FGD System to Bleed Stream Oxidation"

, Combined Utility Air Pollutant Contro l Symposium, Atlanta, GA, August 1999.

4. G. Blythe et.al ., "Furnace Injection of Alkaline So rbents for Sulfuric Acid Control"

, The Mega Symposium in conjunction w ith A&WMA's Mercury Fate, Effects and Control Specialty Conference, Chicago, IL, August 2001.

5. Pioneer Companies, Inc., Press Release, March 7, 2001; "Pioneer Announces Tacoma Plant Curtailment".

6. Federal Energy Regulatory Commission, Form 423: Monthly Report of Cost and Quality of Fuels for Electric Plants: http://www.fere.gov/electric/f423/f423.htm

7. Coal Outlook, Volumes 24 and 25 (2000, 2001).

8. Controlling SO 2 Emissions: A Review of T echnologies, EPA/600/R-00/0093, November 2000.



### KEYWORDS
Magnesium-Enhanced Lime (MEL) Flue Gas Desulfurization (FGD) Magnesium Hydroxide Scrubbers Acid Rain Forced Oxidation Gypsum