RAPID SOLIDIFICATION OF COAL COMBUSTION RESIDUALS (CCR) DREDGE SLURRIES & WET ASH WASTES

M.Khire1, C.Hardin2, Q.Barefoot3, J.Meagher4, and R.Traver5

ABSTRACT

This paper presents the Phase I evaluation of the use of a 100% Super Absorbent Polymer product along with blended amendment combinations for the rapid (<30 minute) solidification of five different saturated coal combustion residual (CCR) waste materials along with the configuration of full-scale (88 Cys/hr [67 m3/hr] & 600 Cys/hr [460 m3/hr]) high solids CCR dredging, SAP solidification operations and positive displacement pumping of SAP solidified CCR paste materials.

Keywords: Coal combustion residuals; high-solids dredging, slurry solidification & transport.

INTRODUCTION

The following are the two major environmental releases of Coal combustion residuals (CCRs) have brought huge public scrutiny on the management and closure of waste storage impoundments:

• On December 22, 2008, the retention wall of a coal ash-holding pond failed at the TVA Fossil Plant in Roane County, Tenn., about 30 miles west of Knoxville. More than 5.4 million cubic yards (4.1 million m3) of coal ash, mixed with 327 million gallons (1.24 billion liters) of water, spilled into the Emory River. The release covered approximately 300 acres (1.2 x 106 m2) outside the TVA coal ash dewatering and storage areas, uprooting trees and destroying two dozen homes in its path. The estimated cost of remediation is over $1 billion with an additional estimated cost of $40 million for long-term monitoring that will continue for 30 years at five-year intervals. The Natural Resources Damages assessment were $11 million.

• On February 2, 2014, due to a pipeline failure, Duke Energy released nearly 39,000 tons (35,380 metric tonnes) of coal ash and 24 million gallons (90.4 billion liters) of wastewater into the Dan River near Eden, North Carolina. That’s a total of 140,000 tons (127,000 metric tonnes) of toxic waste and wastewater combined into the sensitive eco-system of the Dan River. Duke Energy Carolinas incurred approximately $15 million of repairs and remediation expense related to this incident. Duke has paid $102 million in fines and restitution for illegally discharging pollution from coal-

1Associate Director, Energy Production & Infrastructure Center (EPIC) – University of North Carolina – Charlotte; T:704.687.0069; Email: mkhire@uncc.edu

2Managing Director, Energy & Environment Innovation Foundation, LLC (EEIF); T:704.962.8040; Email: chardin@energyenviro.org 3Managing Partner, Zappa-Stewart, LLC; T:336.378.6004; Email: qbarefoot@chasecorp.com 4Principal, Mineral Processing Services, LLC; T:207.741.2955; Email: jmmps@maine.rr.com 5Principal, Pace Engineering, LLC; T:609.410.1630; Email: rtraver@gmail.com

Figure 1. – TVA Kingston CDF Release

Figure 2. – Duke Energy Dan River CDF Release

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ash dumps at five North Carolina power plants.

Coal combustion residuals (CCRs) include fly ash, bottom ash, boiler slag and flue gas desulfurization, or scrubber, materials such as synthetic gypsum, which are produced when coal is burned for electricity generation. CCRs are one of the largest industrial waste streams generated in the United States. In 2012, more than 470 coal-fired electric utilities burned over 800 million tons of coal, generating approximately 110 million tons (99.7 million metric tonnes) of CCRs in 47 states and Puerto Rico(1).

In the Southeast alone, there are ≈400 known coal ash storage facilities with a total capacity to hold over 584,234,000 Cys (446,678,900 m3) of ash. The Southeast is home to over 50 documented contamination sites where there is known pollution to the ground or surface water along with at least 20 “high hazard” coal ash dams determined by the EPA assessment(2).

CCRs may be generated wet or dry, and some CCRs are dewatered while others are mixed with water to facilitate transport (e.g., sluiced). CCRs can be disposed in off-site landfills, placed/capped in on-site landfills or surface impoundments. In 2012, approximately 40 percent of the CCRs generated were beneficially used, with the remaining 60 percent disposed in surface impoundments and landfills. Of that 60 percent, approximately 80 percent was disposed in on-site disposal units. CCR disposal currently occurs at more than 310 active on-site landfills, averaging more than 120 acres (485,600 m2)

in size with an average depth of over 40 feet (12.3 meters), and at more than 735 active on-site surface impoundments, averaging more than 50 acres in

size with an average depth of 20 feet (6.1 meters) (https://www.epa.gov/coalash/frequent-questions-about-coal-ash-disposal-rule#33).

Coal Ash Liquid Management (CALM) Initiative (https://calminitiative.com), part of the Energy & Environment Innovation Foundation (https://energyenviro.org/), utilizes, compliments and leverages the expertise at University of North Carolina Charlotte Research Institute (https://cri.uncc.edu/) by utilizing a wide variety of coal ash and coal combustion energy, and wastewater treatment experts from a membership roster represented by power utilities, consultants, technology vendors and remedial contractors.

Rapid Solidification of CCR Slurries

Since its development in the early 1960s, the application of Super Absorbent Polymers (SAP – Sodium Polyacrylate) has been used to solidify liquid industrial /radioactive waste streams, dredge sediments, biosolids and

Figure 3. – Coal Ash Storage Facilities Map

Figure 4. – Typical CCR Impoundment

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Figure 7. Pocket Vane Shear (Torvane) Figure 8. Penetrometer

Figure 9. Mini-Unconfined Compression

sludges associated with remediation projects, landfill closures, petrochemical spills, and other environmental cleanup projects (http://zappa-tec.com/superabsorbent-polymer-applications/superabsorbent-polymers-mining-drilling/). SAPs reduce waste transportation and disposal costs from these operations by solidifying liquid waste while minimizing an increase in weight and volume. With the capability of solidifying up to 300x its weight in water, 1# of SAP can solidify ≈36 gallons (136 liters) of water. SAP application has been typically “broadcasting” the SAP on top of the waste matrix at application rates of 2 – 5%, dependent upon how careful the

operator was and how cost-conscious the superintendent was. The CALM CCR/SAP solidification treatability results have shown that the application of significantly less SAP (0.5%) will just as effectively solidify a waste slurry – or in other words, “Less is Move”. Super absorbent polymers have numerous advantages over commodity solidification media like kiln dust, Portland cement or sawdust. Super absorbent polymers: • Chemically bond with water, and don’t biodegrade and release liquid Minimize waste volume; • typical expansion is less than 1% Mix quickly to improve production efficiency Pass the EPA Test Method

9095 paint filter test. After solidification, many waste streams pass EPA Test Method 1311 for RCRA metals; • As SAP does not biodegrade, solidified waste materials are

regulatorily approved for landfill use.

Due to the extraordinary pending quantities of wet CCR (>50% moisture) requiring either wet excavation or dredging prior to either dewatering or solidification, CALM has undertaken a detailed bench-scale evaluation of multiple grades of ZappaTec Super Absorbent Polymer blends to provide the ideal balance of cost and performance using five wet CCR waste samples secured from four different power utilities. The following ZappaTec blends have been evaluated by CALM for pre- and post-moisture content, specific gravity, bulk density, Vane Shear, Undrained Cyclic Triaxial Testing and Unconfined Compressive Strength.

Figure 6. 55-60% Moisture for CCR Paint Fillter Press Failaure

Figure 5. – SAP Open Pit Excavator Rock Rake Blending

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0

2

4

6

8

10

P100-1% P4-1% P4-2% P7-2% P7-4%

1 Hr24 Hr48 Hr72 Hr

Aver

age

Und

rain

ed C

ohes

ion

(psi

)

Figure 10. Mini-Unconfined Compression Test Samples

SAP Test Blends & Ratios: • ZapZorb - 100% SAP • ZapZorb P2 Formulation - 50% ZapZorb SAP + 50% Bentonite • ZapZorb P4 Formulation - 50% ZapZorb SAP + 25% Bentonite + 25% Portland Cement • ZapZorb P6 Formulation – 75% ZapZorb SAP + Portland + Bentonite + wood flour • ZapZorb P7 Formulation – 25% ZapZorb SAP + 75% wood fibers • Power Pellets - 5% ZapZorb SAP + 95% wood pellets

Phase I Summary of Conclusions

1. As little as 0.5% of SAP by dry weight was sufficient to stabilize the moisture in fly ash containing as high as 70% water

2. All polymers stabilized free water and the strength improved from a material that is at liquid limit to a material that can stand at undrained shear strength ranging from 2 to 10 psi.

3. P2, P-4 and P-7 provided the most strength for the amount of SAP they contained.

Figure 10. Comparison of Phase I SAP & Blends Evaluated

Figure 11. CCR Ash M1, M2, and U Effect of P100, P4 & P7 Pocket Penetrometer Results

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Configuration of Full-scale Applications for CCR Dredging & SAP Solidification Applications

Concurrently with the Phase I bench-scale evaluations being performed by CALM, Mineral Processing Services (www.mpsmaine.com) independent testing supporting full-scale operations showed that the addition of as low as 0.3% ZapZorb SAP in a 3-stage sequential blending operation of a 65% moisture CCR slurry for a 3 minute contact time would produce a solidified CCR matrix passing EPA Paint Filter criteria.

It is to be noted that MPS also evaluated a ZapZorb R3 SAP product that provides an 80% SAP “suspension” in either vegetable or mineral oil. The resultant solidified CCR sample exhibited the most cohesiveness of all sample evaluated as shown in Figure 12, however, the cost of the ZapZorb R3 product is not as economical as the dry, granular ZapZorb SAP.

MPS has designed two full-scale CCR dredge slurry processing systems:

• 2,500 gpm (9500 lpm) Toyo TO-150 Pump high-solids (up to 70% solids) dredge feed

o Vibratory Debris Scalping Screen for separation/dewatering +3/8” (9.5mm) fractions

o Screw Auger Classifier for separation/dewatering -3/8” (9.5 mm) x 200 mesh fractions

o MPS SmartFeed® measuring slurry density, flow providing real-time polymer addition to 2,500 gpm (9500 lpm) feed to MPS High-rate Clarifier/Paste Thickener

2,200 gpm (8,300 lpm) clarifier overflow returned to CCR impoundment

300 gpm (1,135 lpm) 50 – 60% solids paste underflow

o MPS SmartFeed® measuring clarifier paste underflow slurry density, flow providing real-time SAP polymer addition via VFD tube chain conveyor

Figure 12. Free Moisture Comparison of SAP & SAP w/wood fines

Figure 13. 1,600 gpm Cutterhead Toyo TO-75 CCR

Dredging ≈50-150 Cys/hr

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o 300 gpm (1,135 lpm) paste slurry feed to SmartFeed® Sequential Blending Module processing ≈88 Cys/hr (≈83 tons/hr [75 metric tonnes]) into stackable material in 3 minutes

o Solidified CCR waste to a Beitzel 29 CY capacity Mudster Live Bottom Feeder Module provided flooded suction feed to Putzmeister High Density Solids Positive Displacement Pump

• 10,000 gpm (37900 lpm) – 2 Toyo TO-400 Pumps high-solids (up to 70% solids) dredge feed

o 4 - Vibratory Debris Scalping Screen for separation/dewatering +3/8” (9.5 mm)fractions

o 5 -Screw Auger Classifiers for separation/dewatering -3/8” (9.5 mm) x 200 mesh fractions

o 2 - MPS SmartFeed® measuring slurry density, flow providing real-time polymer addition to 2,000 gpm (7,600 lpm) feed to each of 5 - MPS High-rate Clarifier/Paste Thickeners

8,000 gpm (30,300 lpm) clarifier overflow returned to CCR impoundment

2,000 gpm (7,600 lpm) 50 – 60% solids paste underflow

o MPS SmartFeed® measuring clarifier paste underflow slurry density, flow providing real-time SAP polymer addition via VFD tube chain conveyor

o 2,000 gpm (7,600 lpm) paste slurry feed to SmartFeed® Sequential Blending Module processing ≈600 Cys/hr (460 m3) (≈570 tons/hr [517 metric tonnes]) into stackable material in 3 minutes

o Solidified CCR waste to a Beitzel 100 CY (76 m3)capacity MegaMudster Live Bottom Feeder Module provided flooded suction feed to 3 - Putzmeister High Density Solids Positive Displacement Pumps

Advantages blending as low as 0.3% ZapZorb SAP admixture will ensure the CCR waste or dredged sediment material will pass EPA Paint Filter Test within 3 minutes of blending (expediting direct load-out without the need for interim stockpiles and rehandling expenses), ensure no free liquids are generated during OTR/rail transport prior to arrival at the final destination and will significantly improve strength of the ZapZorb SAP amended material for either support of a final closure cap or to be bladed-out and compacted within a mono-fill.

Figure 14. 3,000 gpm Toyo TO-150 CCR Dredging ≈175 – 200 Cys/hr

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Dual CCR Slurry Processing Operations:

1. SmartFeed™ Sequential Mixer for Blending of ZapZorb Amendments with TOYO Pump high-solids CCR dredged waste materials for >45% CCR solids feed

2. High-rate Clarifier/ Paste Thickener conditioning operations for <45% CCR solids feed operations followed by ZapZorb Amendment Blending

Figure 16. CCR Paste Hydraulic Conveyance Elements

The sequential addition of 2% EnviroBlend (www.enviroblend.com - a magnesium based pH buffered pozzolan) followed with 0.3% - 0.5% ZapZorb SAP addition has shown to be very effective in stabilizing liquid waste streams, slurries, sludges and saturated sediment containing heavy metals in meeting TCLP leaching standards.

Handling & Hydraulic Pumping Conveyance of CCR Paste

Effect handling of the solidified CCR paste waste is accommodate with a direct discharge from the SmartFeed® Sequential Blending Module into a Beitzel Live Bottom Feeder Module that provides a “flooded” suction to a Putzmeister High Pressure Positive Displacement Piston Pump.

❶

❷

SAP Solidified CCR from SmartFeed Sequential Blending

Beitzel Live Bottom Feeder Unit Flood Suction from Feeder Module to PD Pump

Putzmeister KOS 25150 HP High Density Solids Pump: 250 yd³ / hr – 3,500’

CCR Paste Discharge at Disposal Cell

Figure 15. 5,000 gpm Dual CCR Slurry Processing Operations

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CONCLUSIONS

The dredging of CCR waste impoundments at in-situ moisture content using high-solids Toyo dredge pumps can be hydraulically conveyed to a computer-controlled slurry processing operation that continuously monitors flow-rate and sludge density for the controlled metering of as little as 0.3% SAP into a sequential blending module. With the ability to solid a 70% CCR moisture slurry within 5 minutes of SAP addition, the integrated use of a live bottom feeder module providing a flooded suction for high-pressure positive displacement piston pumps can convey to solidified CCR paste to either waste disposal cells or into 110-ton (100 metric tonnes) gondola railcars for off-site disposal – all without any intermediate rehandling steps.

The cost and time savings for the application of <0.5% SAP versus the traditional addition of 8-10% portland cement for the solidification of the millions of cubic yards of wet CCR wastes will have a dramatic impact on reducing costs, shortening project schedules and minimizing the volume of CCR waste to be transported and placed with new impoundment cells.

REFERENCES

DANGEROUS WATERS: AMERICA’S COAL ASH CRISIS – “Map of CCR Impoundments with the USA” (http://www.eenews.net/assets/2014/05/15/document_gw_02.pdf)

Southeast Coal Ash Waste – “Map of CCR Impoundments in the Southeast”, http://www.southeastcoalash.org/

James M Parker, P.E.; Gordon D Criswell, P.E - PPL Montana Coalstrip, Montana. “COLSTRIP STEAM ELECTRIC STATION COAL COMBUSTION BY-PRODUCT DISPOSAL”

Putzmeister Industrial Technology – “Handling of fuel coal paste and waste coal sludges”

Sue Longo, Golder - “Locking Away Coal Combustion Wastewater Problem with Paste Technology”; Coal Age – 4/26/16

CITATIONS

Khire, M; Hardin, C; Traver, R; Barefoot, Q; Meagher, J; “Rapid Solidification of Coal Combustion Residuals (CCR) Leachate & Wet Ash Wastes” SAME - 10th Symposium on Design and Construction Issues at Hazardous Waste Sites - Society of American Military Engineers, Philadelphia, PA, USA, April 3 - 5, 2017.

Khire, M; Annamraju, S; Hardin, C; Traver, R; Barefoot, Q; “Coal Ash Pond Water Management using Super Absorbent Polymers” Proceedings of the 2017 World of Coal Ash Conference (WOCA), Lexington, KY, USA, May 8-11, 2017.

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