Smoldering Combustion (STAR): Meeting Remedial Goals in

Complex EnvironmentsGavin Grant, Ph.D., P.Eng.(ON)

Operations ManagerSavron

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Overview

• Background and Applicability of STAR (in situ)• Advantages• Limitations and Mitigation Strategies• Costs

Background and Applicability of STAR

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Smoldering Combustion

STAR is based on the process of smoldering combustion:Exothermic reaction converting carbon compounds to CO2 + H2O Fuel

Heat Oxidant

Smoldering possible due to large surface area of organic liquids (e.g., NAPL) within the presence of a porous matrix (e.g., aquifer)

Combustion

Contaminated Soil

Injected AirHeater Element

(for ignition only)

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Application of Smoldering In Situ (STAR)

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• Silty sands and coarser• Low volatility compounds

• coal tar, creosote, heavy hydrocarbons, fuel oils, etc.

• Threshold concentration for self-sustained smoldering ~ 3,000 mg/kg TPH• Note: Any concentration can be combusted, but 3,000 mg/kg or greater has enough energy for SS propagation

General Applicability

Advantages of STAR

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Rapid

Advantages

• Propagation rates typically 1-2 ft/d through NAPL source areas

Scalable

• Multiple IPs operated simultaneously

• Multiple treatment systems

Node (max distance to power source)

Ignition Point

Cell(group of Ignition Points treated at the same time)

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In Situ Destruction

Advantages (con’t)

• 98-99% of mass is destroyed via combustion (conversion to CO / CO2)

• 1-2% recovered and treated (typically light hydrocarbons)

• No handling/disposal of NAPL

Targeted / Surgical Implementation

• Treat only what is necessary

• Can reduce treatment footprint through real-time assessment

• “Seek and destroy” implementation

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Sustainability

Advantages (con’t)

• Low energy (self-sustaining process)

• No heavy equipment

• Example: “Greatest benefits for both environmental and social considerations at the site” (IFEM, Taiwan)

Health and Safety

• No heavy equipment

• Reaction can be instantly terminated

Remedial Alternatives Evaluated for NJ Site

Photo: Operating System, MI

Limitations and Mitigation Strategies

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Potential Limitations

Fuel

Heat Oxidant

Combustion

Contaminant must be smolderable(i.e., low volatility)

Soils must be sufficiently permeable(i.e., silts and coarser)

Minimum required fuel content (concentration) to overcome heat sinks (e.g., groundwater, soil, losses, etc.)

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Limitations

• High volatility• Gasoline/diesel range organics /

chlorinated solvents

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Limitations

• “Clean” (or low-concentration) zones• Below minimum required fuel content for

SS smoldering

Coal Tar-Impacted Soil

“Clean” Zone

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Limitations

• Heterogeneity• Clay layers

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Limitations

• Shallow wide-spread contamination• Issue in O&G

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High Volatility

Mitigation Strategy:• Target low-volatility

compounds • Coal tar, creosote, heavy hydrocarbons

• Use of surrogate fuels (Emulsified Vegetable Oil [EVO]) • Enhance thermal desorption via EVO

smoldering

Case Study – Former Refinery, MI• GRO/DRO impacted fine sands• Compare “Standard” v. “EVO-

enhanced” STAR

ROI = 4.5ft

ROI = 10ft

“Standard” STAR “EVO-enhanced” STAR

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“Clean Gaps”

Mitigation Strategy:• Heat transfer across gaps can “re-ignite”

contaminants

Case Study – USEPA / EPRI• ~1-2 foot gaps can be crossed

Gap Jumping Study

Clean Gap Contaminated LayerHot Remediated Layer

Air F

lux

Tem

pera

ture

(°

C)

Distance (cm)Gap Begins

Gap Ends

TCombustion

TIgnition

TAmbient

TAmbient TCombustion Tignition

CpKtherm

ΦSw

kperm

Time 1Time 2

EStorage EStorage

ELoss

ELoss

HEAT TRANSFER

Critical Point

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Heterogeneity

Mitigation Strategy:• STAR not suitable for clay

• Silts and coarser materials viable

• However, can tolerate some clay layers / lens

Case Study – NSFO, VA• NSFO contamination ~ 16–21 ft bgs• Clay layer ~ 18–19 ft bgs• IP screened below clay 20–21 ft bgs

11,809 mg/kg

16 ft 17 ft 18 ft 20 ft19 ft

1,271 mg/kg 15,701 mg/kg 9,471 mg/kg

57 mg/kg ND ND ND

CLAY

Clay

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Shallow Contamination

Mitigation Strategy:• STARx (ex situ

smoldering)• HottpadTM systems

• Low-profile, engineering base

• Scalable

• Shippable

• Cost effective

Case Study – Active O&G Terminal, SE Asia• Co-treatment of oily sludge and oil-impacted soils

150 m3 Hottpad System

Before After

Costs

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Costs

Cost Drivers:• Radius of

Influence (ROI)• Governs IP (well)

spacing

• Propagation rates• Governs operation time

Case Study – Former Industrial Facility, NJ• Full-scale treatment in progress

Lagoon F

• Basis• Lagoon & Tank Farm

• ~12 ft bgs

• ~2 acre area released for use

• 35,700 CY Total

• 230 Ignition Points

• 6 month operating period

• 4,200 lbs

• Treatment Costs: $2.5M, ~$70/CY

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Summary

• STAR is robust and works both above and below the water table • Applicable under fully saturated conditions

• Well suited for coal tar, creosote, and petroleum hydrocarbons• But enhancement techniques can expand range of applicability

• Can be applied in situ or ex situ (Hottpad systems)• STAR is rapid, sustainable, and cost-effective• Limitations exist (as for all in situ technologies)

• But mitigation strategies have been developed to overcome many of them

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Questions?savronsolutions.com

ggrant@savronsolutions.com