Formatted Title
Balancing Act in Southeast Asia's Largest ISTR Project: Achieving 350°C in Saturated Zones versus Mitigating Unexpected Sulfide-Induced Odor and Acid Dilemmas
Background/Objectives
Set against the intricate backdrop of Southeast Asia, this monumental project stands as the pinnacle of in situ thermal remediation (ISTR) endeavors in the region. Spanning an expansive treatment area of about 31,400 m2, the site presents a unique challenge, primarily due to its saturated zone enriched with marine clay. Achieving a temperature of 350°C in such conditions was not merely ambitious; it was groundbreaking. This temperature target necessitated the complete desiccation of the soil, meaning the removal of all groundwater. While these aggressive heating methods were pivotal for the efficient extraction of hazardous polycyclic aromatic hydrocarbons (PAHs), an unforeseen adversary emerged: unexpected sulfide compounds. Absent from initial site investigation reports, these compounds threw a spanner in the works, introducing significant odor and acid-related predicaments, thereby complicating the vapor treatment trajectory.
Approach/Activities
The sheer scale and nature of the project dictated a multifaceted approach. To fortify the site against water from external sources and support this desiccation process, the strategic installation of sheet piling became crucial. Achieving the desired 350°C meant that the soil had to be heated aggressively. This aggressive heating was imperative to ensure the remediation of PAHs and total petroleum hydrocarbon (TPH).
However, this strategy's success led to another challenge. The rigorous heating unearthed an 'acid ocean' below, releasing a torrent of sulfide compound vapor. Addressing these challenges involved nuanced modifications. Firstly, the vapor treatment strategy had to accommodate the high H2S concentrations from sulfide compounds. This meant integrating a secondary scrubber after the existing system. The corrosive nature of the sulfides also necessitated enhanced maintenance measures, with a particular emphasis on manifold piping and vessels, given their vulnerability to the corrosive sulfides.
Moreover, it became evident that the vapor treatment system could be overwhelmed if heating remained too aggressive. A delicate balancing act was required. Thus, the project saw modifications in fuel injection rates and heating strategies. By carefully staging the heating processes, the project managed to oscillate between the dual objectives of achieving the temperature goals and curtailing the excessive production of H2S from the sulfides.
Results/Lessons Learned
With the completion of five batches successfully, the project underscores the significance of adaptability and forward planning. While we met our temperature and remediation objectives, effectively addressing all PAHs and TPHs, the initiative also provided insights into handling unforeseen challenges. The emergence of the 'acid ocean' and its associated complications highlighted the importance of agility in large-scale remediation projects. This ISTR project not only stands as an exemplar of remediation efforts but also offers a blueprint for future international endeavors, showcasing the need to harmoniously align ambition with adaptability in the face of evolving challenges.