Formatted Title
Smoldering Combustion (STAR and STARx): Adaptive Remedy Implementation in Complex Environments
Background/Objectives
Background/Objectives
Smoldering is a self-sustaining remediation process following a short duration, ‘ignition event’ for low volatility, high energy compounds such as petroleum hydrocarbons, and has been used to remediate impacted soils and destroy liquid organic wastes at midstream / upstream oil and gas facilities and brownfields redevelopment sites worldwide. The process is robust and well-suited to a range of contaminant and soil types; however, like many remediation technologies, contaminant and geological heterogeneities can have a significant impact on the execution and efficacy of the technology requiring in-field and engineering design adaptations.
Approach/Activities
Approach/Activities
For self-sustaining smoldering to be successful, certain key criteria must be present: sufficient permeability (e.g., silty sands or coarser), sufficient contaminant or ‘fuel’ concentrations (e.g., greater than ~3,000 – 5,000 mg/kg total petroleum hydrocarbons [TPH]), and presence of low volatility contaminants. In cases where one or more of these criteria are not met at a given site (or in certain areas of a site), adaptive implementation strategies have been evaluated across lab, pilot, and full-scale smoldering applications.
This presentation will provide an overview of smoldering combustion applied in situ (STAR) and ex situ (STARx), then present a series of case studies highlighting implementation challenges associated with highly heterogenous environments and complex feedstock, as well as the techniques and strategies developed to mitigate these challenges. Challenges such as “clean” gaps and interbedded clay layers, fugitive emissions, contaminant mobility, and the use of surrogate fuels for treatment of recalcitrant compounds during smoldering combustion implementation will be discussed.
Results/Lessons Learned
Results/Lessons Learned
Heterogeneous and discontinuous contaminant distributions, particularly in complex geologic settings, can impact STAR smoldering front propagation due to the fuel requirements for maintaining a self-sustaining reaction as well as impact combustion gas collection efficiency at surface. A laboratory study was conducted to demonstrate smoldering can tolerate “gaps” in contaminant distribution several feet thick. Field pilot demonstrations have further demonstrated smoldering can successfully treat above and below discontinuous low permeability layers. Novel collection systems were employed at a full-scale STAR project to intercept horizontally migrating combustion gases to protect both onsite and offsite receptors during targeted “seek and destroy” operations.
Mobility of higher volatility waste and consolidated oily sludge components can complicate STARx treatment of enriched feedstocks using Savron’s Hottpad systems. Engineering modifications such as flow diversion elements, and procedural strategies including a real-time injection flow protocol were employed at two full-scale STARx plants to increase operational uptime.
Surrogate fuels can be used to facilitate self-sustaining smoldering of high volatility or low energy contaminants, either in situ or ex situ. Emulsified vegetable oil (EVO) was injected prior to STAR to treat gasoline-range organics at a former refinery site. This demonstrated enhanced treatment over areas where no amendments were applied. Similarly, low concentrations of surrogate fuels can also be used to facilitate ex situ treatment of contaminants such as per- and polyfluoroalkyl substances (PFAS) or chloronitrobenzenes. Several viable surrogate fuels have been demonstrated including clean or spent granular activated carbon (GAC) and other sustainable waste products such as coconut husks or eucalyptus bark.
This presentation will illustrate adaptive implementation strategies utilized to achieve efficient and cost-effective deployment of smoldering combustion when targeting treatment of subsurface contaminants in complex environments using STAR, and challenging contaminants in feedstock using STARx.