Miller - FGD Gypsum Production, Processing, And Disposal

8/12/2019 Miller - FGD Gypsum Production, Processing, And Disposal

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FLUE GAS DESULFURIZATION (FGD)GYPSUM PRODUCTION, PROCESSING

AND DISPOSAL

Presented ByE. Cheri Miller

Specialist, Fuel By-Products and MarketingTennessee Valley Authority


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WHAT ARE FGD SCRUBBERS?


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FGD PRODUCTS

Many different products from the variousFGD processes, primarily: Lime/limestone force oxidized (LSFO) =

Calcium sulfate dihydrate (gypsum) Lime/limestone unoxidized = Calcium sulfite

Fluidized bed ash and dry scrubbers =mixtures of char/fly ash and spent bed

material or sorbent containing CaO, CaSO4,CaSO3 and ash

Wet ammonia = ammonium sulfate


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FGD PRODUCTS (cont.)

Products of Lime/Limestone Forced Oxidation processesare most often sought for agricultural use Readily dewater to 7-12% moisture even without mechanical

dewatering equipment Are easily reclaimed from ponds, stored, transported and spread

using conventional equipmentUnoxidized Lime/Limestone FGD products arethixotropic sludges (consistency of toothpastemayliquify when shaken) Difficult to dewater

Require some sort of processing or admixture such as fly ash orlime to achieve moisture levels that can be handled Cannot be easily stored, transported or spread with conventional

agricultural equipment


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FGD Gypsum ManagementIn once-through systems, bleed stream from

the scrubber absorber tank is usually at 12-30% solids and low chloride levels. Filtratefrom gypsum dewatering is not recycled

In closed loop systems, absorber tank willconcentrate chloride levels to very high levels(20,000 ppm or more) as filtrate from gypsumdewatering is recycled back into the scrubber

cycle


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Limestone Forced Oxidation

Process


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FGD Gypsum Management(cont.)

Gypsum can be mechanically dewatered

using vacuum filters, rotary drum filters orcentrifugesMechanical dewatering results in a gypsum

cake product which can have moisture levels

as low as 5%Mechanical dewatering also allows for

control of particle size, chloride content andremoval of impurities


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Vacuum Filter Belt


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FGD Gypsum Management(cont.)

Gypsum can also be dewatered in ponds

managed as rim ditch stacksThe large size of FGD gypsum particles (average

45 microns) allows the material to readily dewaterin ponds

Gypsum ponds/stacks can dewater product to

7-12% moisture by natural gravity drainage anddrying depending on temperature and rainfall


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Overview of LSFO Operation

Gypsum Pond with Fly Ash Silosin Foreground


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Rim Ditch Stacking


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Rim Ditch Stacking (cont.)

FGD Gypsum which has been

deposited in a pond or stack is easilyreclaimed for marketing using eitherconventional earth moving equipment,

orCan be reclaimed using a hydraulic

dredge and re-slurried back through the

mechanical dewatering system


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Hydraulic Dredging from GypsumStack


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Mining Gypsum from RimDitch Stack Using Earthmoving

Equipment


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FGD Gypsum Handling Issues

Dewatered gypsum is usually stored in a

roofed storage shed to avoid accumulatingadditional moisture from precipitation and toprovide wind screens to prevent dusting

Reclaimed gypsum on ponds will form acrust which helps shed water and preventsdusting so long as it is undisturbed. If thecrust is broken it can cause a dusting

problem


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Loading Trucks with GypsumInside Covered Storage Shed


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FGD Gypsum Handling Issues

Even at moisture contents as low as

5% loading does not usually cause adust problem

Covered conveyors help prevent dustproblems at transfer points


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Gypsum Truck Dump-CoveredConveyor


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Loading Barge


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Aerial View of Barge

Loadout


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Cost/BenefitMarketing/Disposal

The O&M cost of FGD gypsum disposal in rimditch ponds is very low1 million tons/year because in reality you aremoving less than 10-20% of the material in theperimeter dikesthe rest stacks itself in the center ofthe rim ditch stack

Non-routine O&M is also lowPlacement of cover material and revegetation on side slopesRaising spillwaysDust controlGW/Surface water monitoring


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Cost/BenefitMarketing/Disposal(cont.)

Once a utility has paid to place material in a disposalfacility, the cost of disposal is a sunk cost which cannotbe recovered

In order to avoid disposal costs, material must be

diverted beforedisposalreclaiming material afterdisposal has no cost savings benefits

In addition, even if you divert material before disposal,you will not realize any cost savings unless you moveenough material to be able to reduce manpower or

equipment at the disposal facilityWhy? Because the relationship between disposal costand tons is not a straight-line relationship


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Avoided Cost of Disposal

Tons to Landfill

To

talCost

FixedCost

Average

Cost

ActualCost

Averagewith

FixedCost

Break Points


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Example:

Total annual O&M cost of facility = $500K

Total tons disposed = 500K/year

Nominal disposal cost = $1/ton/year

Sell 50,000 tons/year

No cost savings because your manpower and

equipment costs have not been reduced In fact, your cost/ton actually increases (e.g.

$500K/450K tons = $1.11/ton)


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In order to divert FGD gypsum prior to disposal, the material mustbe mechanically dewatered Cost of dewatering facility = $3-6 M capital Costs about $3/ton to operate dewatering facility

It is doubtful that mechanical dewatering can be justified basedsolely on an agricultural market

At sites where FGD gypsum must be mechanically dewatered sothat it can be hauled to a stacking area for disposal, the utility mayavoid a significant disposal cost by developing agricultural marketsCost of hauling to a stacking area for disposal will be very sitespecific dependent upon the distance hauled, site developmentcosts and regulatory requirements.Rule-of-Thumb for estimating trucking costs: $1/ton to load truck,$1/ton for first mile, $0.10/ton for each additional mile hauled.


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Potential Markets for FGDGypsum

North American Production2004 =

12 M tons

Use - 2004Wallboard = 8.1 M tons

Cement = 0.74 M tons

Agriculture = 0.13 M tons

Other = 0.025 M tons


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Future North American Production

2015 = over 20 million tonsWallboard

Five new wallboard plants have been announced

which will run on FGD GypsumTotal usage in these plants will approach 3-5 M

tons/yr accounting for 12 M tons/yr


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New Wallboard PlantsDesigned for Synthetic Gypsum

1

8

7

9

5

6

2

4

3

10 11

12**

United States Gypsum Company - February 17, 2005


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Cement

Although several newcement kilns are planned forNorth America, use in cement(as a set retardant and

grinding aid) will notsignificantly increase FGDGypsum use


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AgricultureUse of FGD Gypsum in agriculture is

the market with the greatest potentialfor expanding gypsum use

Application rates will average 1-5tons/acre

Concerns about heavy metals in

FGD Gypsum may dampenacceptance in this market


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Conclusions

Total amount of FGD gypsum available for agricultural use will be ~ 7-8 million tons/year by 2015Not all FGD gypsum will be acceptable for agricultural use because ofhigh chloride content and potential perception issues associated withheavy metalsMany FGD gypsum sources will not be located in areas where the

cost/benefit of using FGD gypsum for soil amendment will justify thecost of transporting and handling the materialAgricultural use of FGD gypsum will probably be opportunistic,developing primarily in agricultural areas very close to sources ofmaterial, or at sites where the utility has disposal costs that are veryhighAt power plants where the FGD gypsum cannot be diverted prior to

disposal and/or where significant quantities cannot be marketed, theutility will not be able to justify paying subsidies to market FGDgypsumIf FGD gypsum is to be accepted as a bona fidecommodity, the cost ofutilizing the material should be borne by the end userpayment ofsubsidies for use of byproduct materials is usually viewed withsuspicion by regulators

Miller - FGD Gypsum Production, Processing, And Disposal

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