Formatted Title
Introducing Pit-Pile Ex Situ Thermal Desorption (PP-ESTD) for Petroleum Sludge: An Innovative Technique Integrating Multi-Phase Extraction (MPE), Low-Temperature Processing, and LNAPL Recovery
Background/Objectives
Traditional ex situ thermal treatments for petroleum sludge, such as pyrolysis methods and thermal desorption techniques like rotary kilns, have encountered significant operational challenges. Constraints on the sludge's oil and water content, complex pre-treatments, potential secondary pollution risks due to inadequate exhaust gas treatment, and interruptions in large-scale machinery have been persistent issues. While in-pile ex situ thermal desorption (pile-ESTD) provided some respite, the unveiling of Pit-Pile ESTD (PP-ESTD) aims to revolutionize the treatment process, embodying a tri-fold purpose: sludge pretreatment, detoxification, and resource recovery in a single treatment process.
Approach/Activities
Initiating with a sludge-filled pit, the PP-ESTD process then incorporates a standard pile atop it, optimizing treatment volume without necessitating extra space. Designed with ditches, the pit effectively directs and gathers liquid contaminants. Integrated seamlessly is the in situ multi-phase extraction (MPE) method. At temperatures ranging from 40 to 70°C, MPE tubes facilitate the extraction of liquid contaminants, bypassing the need for exhaustive dehydration stages.
As temperatures are cautiously elevated to near 100°C, a transformative process begins. The soil experiences a comprehensive 'steam sweeping,' effectively purging residual contaminants. This critical phase ensures a significant decline in oil content even before traditional thermal desorption processes are activated. Subsequently, the temperature is adjusted to a range of approximately 300 to 350°C, a level determined to sufficiently reduce TPH or other PAHs to strict remediation standards. The moderate temperature range, in contrast to other high-temperature ex situ thermals, benefits from prolonged heating periods and enhanced vapor flow rate, attributes that have been validated by multiple pile-ESTD projects.
The PP-ESTD method, when juxtaposed with pile-ESTD, offers unique advantages. While both methods effectively preserve soil structure, facilitating its reuse in applications such as pavement or industrial use post-treatment, the PP-ESTD stands out due to its space-efficiency. By using the same footprint, it processes a greater volume of contaminants. Additionally, the trench design at the base of PP-ESTD acts as an efficient NAPL collection system. Instead of relying on combustion or oxidation, the extracted petroleum is routed for recycling as LNAPLs, emphasizing resource recovery without aggressive techniques.
Results/Lessons Learned
The innovative PP-ESTD method represents a significant leap in petroleum sludge treatment, transitioning from traditional ex situ methods to the pile technique and now the avant-garde PP-ESTD. The first PP-ESTD pile, currently under construction, is poised to demonstrate its efficiency by the close of 2023. Further capitalizing on this pioneering approach, a 50,000-ton-per-year sludge treatment facility is on track for inauguration in China in 2024. Significantly, this facility emerges as a successor to a larger traditional rotary kiln that couldn't deliver, highlighting the robust faith in PP-ESTD's potential to redefine benchmarks in sludge treatment.