Scaling-up experiments of smouldering combustion as a remediation technology for contaminated soil

Self-sustaining Treatment for Active Remediation (STAR) is a novel, patent-pending process that uses smouldering combustion as a remediation technology for land contaminated with hazardous organic liquids. Compounds such as chlorinated solvents, coal tar and petroleum products, called Non-Aqueous Phase Liquids (NAPLs) for their low miscibility with water, have a long history of use in the industrialised world and are among the most ubiquitous of contaminants worldwide. These contaminants are toxic and many are suspected or known carcinogens. Existing remediation technologies are expensive and ineffective at reducing NAPL source zones sufficiently to restore affected water resources to appropriate quality levels. STAR introduces a self-sustaining smouldering reaction within the NAPL pool in the subsurface and allows that reaction to provide all of the post-ignition energy required by the reaction to completely remediate the NAPL source zone in the soil. Results from laboratory and field experiments have been very promising. Laboratory experiments have demonstrated STAR across a wide range of NAPL fuels and focused on coal tar to identify key parameters for successful remediation. Modelling has suggested that STAR efficiency will improve with scale as effects such as heat losses from boundaries become less significant. Observations from field experiments support the modelling theory - significantly lower relative air flow in a smouldering field experiment (330L) led to faster smouldering front propagation than observed in laboratory experiments (1L and 3L). Preliminary emissions monitoring by Fourier Transform Infrared (FTIR) spectroscopy has suggested that STAR emissions might be low enough to meet regulatory requirements, but further study is necessary. As emissions are expected to vary with each contaminant, activated carbon filters are being developed and tested in case emissions filtration is necessary. Experiments at all scales have demonstrated that STAR is controllable and self-terminating. Pilot-scale (2500L) field trials are underway to demonstrate STAR on excavated contaminated soil. The materials that will be studied in these trials are manufactured coal tar in coarse sand (which is the same material as used in the laboratory and field experiments) as well as two soils obtained from coal tar contaminated sites. This poster focuses on the scale-up to these field trials, including small scale characterisation, large scale performance, emissions monitoring and post-treatment soil analysis

Experimental studies of self-sustaining thermal aquifer remediation (STAR) for non-aqueous phase liquid (NAPL) sources

Self-sustaining Thermal Aquifer Remediation (STAR) is a novel technology that employs smouldering combustion for the remediation of subsurface contamination by non-aqueous phase liquids (NAPLs). Smouldering is a form of combustion that is slower and less energetic than flaming combustion. Familiar examples of smouldering involve solid fuels that are destroyed by the reaction (e.g., a smouldering cigarette or peat smouldering after a wildfire). In STAR, the NAPL serves as the fuel within an inert, porous soil medium. Results from experiments across a range of scales are very promising. Detailed characterisation has focused on coal tar, a common denser-than-water NAPL (DNAPL) contaminant. Complete remediation is demonstrated across this range of scales. Visual observations are supported bychemical extraction results. Further experiments suggest that STAR can be self-sustaining, meaning that once ignited the process can supply its own energy to propagate. Costly energy input is reduced significantly. Comparison of large scale to small scale laboratory experiments, a volume increase by a factor of 100, suggests that STAR process efficiency increases with scale. This increase in efficiency results from reduced heat losses at larger scales while maximum the temperature achieved by STAR is unaffected. The research also demonstrates the controllability of STAR, where the termination of airflow to the reaction terminates the STAR process. The scale-up process provides important guidance to the development of full scale STAR for ex situ remediation of NAPL-contaminated soil

IMPROVED TRAVELLING FIRES METHODOLOGY - iTFM

Current design codes and most of the understanding of behaviour of structures in fire are based on small enclosure fires. The World Trade Centre Tower fires in 2001 have highlighted the need of a more realistic design tools to represent fires in large compartments. Following the events Travelling Fires Methodology (TFM) has been developed by Stern-Gottfried and Rein to account for the travelling nature of fires. In this study the TFM is refined to account for more realistic fire dynamics. Equations are introduced to reduce the range of possible fire sizes. The analytical equations describing reducing far-field temperatures are presented. The concept of flame flapping is introduced to account for variation of temperatures in the near-field region due to natural fire oscillations. The need for more fundamental research and experimental evidence in large compartments for further development of and improvements on TFMis highlighted

FireGrid: Forecasting Fire Dynamics to Lead the Emergency Response

The predictions of future events has fascinated humanity since the beginning of history. This attraction has permeated into science and engineering, where several disciplines has emerged providing the capability to forecast dynamics within some lead time. Weather forecast is the most important and the most developed one. The concept of FireGrid is a paradigm shift in the response to emergencies, providing the fire service with essential sensor information. This information will also include forecast of the fire dynamics. But many questions remain to be answered. This talk explores the potential methodology to forecast fire dynamics in enclosures, drawing lessons also from weather forecast. www.firegrid.or

From Pyrolysis Kinetics to Models of Condensed-Phase Burning

invited paperThe state-of-the-art of fire modelling is currently hindered due to a poor capability to model the burning of solid fuels. Current fire modelling tools provide good predictions of the thermal effects of a fire (e.g. the resulting thermal environment) but fail to predict properly the fire development (e.g. flame spread and fire growth). The consequence is that current fire modelling cannot predict the transient evolution of the heat release rate of a fire. The development of fire spread models that can accurately predict the ignition and burning of solid-fuels will be a major advancement. In this work, the effects of the kinetic parameters of a one-step and a two-step pyrolysis are studied by combining it with a simple heat transfer model. The issue of the required level of complexity in the models for parameter-estimation is a concern. Simplifications are required where the necessary precision does not warrant the inclusion of higher levels of complexity. This paper advocates for the use of blind predictions in combination with sensitivity studies and the identification of the simplest model that can predict the experimental data. Results are presented here in that direction

Gains and Threats from Smouldering Combustion to Biochar Production and Storage

Poster presented at the 2008 Conference of the International Biochar Initiative, Newcastle, 9th Sept 2008Biochar is an environmentally beneficial way of locking carbon emissions into a solid phase and storage for very long periods of time. On the one hand, smouldering combustion can be used in a pyrolysis reactor to provide energy-efficient conversion of biomass into biochar. This reactor design could run with minimal or zero energy costs and high yield since the smouldering process would provide the energy supply released from the slow oxidation of a fraction of the biomass itself. On the other hand, smouldering fires of organic soils occurs at a global scale and are a mayor menace to biochar storage fields and can reduce them to ashes. This is about the only hazard that can led to an accidental release to the atmosphere of the stored carbon in the biochar. The technology to enhanced production and safer storage of biochar is currently being developed at Edinburgh from fundamental knowledge on smouldering combustion

Smouldering Combustion Phenomena in Science and Technology

Invited review paper for the first issue of the journal IRECHE - International Review of Chemical Engineering - Rapid Communications.Smouldering is the slow, low-temperature, flameless form of combustion of a condensed fuel. It poses safety and environmental hazards and allows novel technological application but its fundamentals remain mostly unknown to the scientific community. The terms filtering combustion, smoking problem, deep seated fires, hidden fires, peat or peatlands fires, lagging fires, low oxygen combustion, in-situ combustion, fireflood and underground gasification, all refer to smouldering combustion phenomena. This paper attempts to synthesize a comprehensive view of smouldering combustion bringing together contributions from diverse scientific disciplines. Smouldering is the leading cause of deaths in residential fires and a source of safety concerns in space and commercial flights. Smouldering wildfires destroy large amounts of biomass and cause great damage to the soil, contributing significantly to atmospheric pollutant and green house gas emissions. Subsurface fires in coal mines and seams burn for very long periods of time, making them the oldest continuously burning fires on Earth. Worthy of consideration are the novel environmental and energy technologies being developed based on the direct application of smouldering combustion. These include the remediation of contaminated soils, production of biochar for long term storage of carbon, enchanted oil extraction from reservoirs and gasification of coal seams. The prospect of new opportunities for science and engineering in smouldering combustion are noticeable, but a much larger international research effort is required to increase the number of multidisciplinary experimental, theoretical and field studies

Forward and Opposed Smoldering Combustion

A computational study has been carried out to investigate smoldering ignition and propagation in polyurethane foam. The onedimensional, transient, governing equations for smoldering combustion in a porous fuel are solved accounting for improved solid-phase chemical kinetics. A systematic methodology for the determination of solid-phase kinetics suitable for numerical models has been developed and applied to the simulation of smoldering combustion. This methodology consists in the correlation of a mathematical representation of a reaction mechanism with data from previous thermogravimetric experiments. Geneticalgorithm and trail-and-error techniques are used as the optimization procedures. The corresponding kinetic parameters for two different mechanisms of polyurethane foam smoldering kinetics are quantified: a previously proposed 3-step mechanism and a new 5-step mechanism. These kinetic mechanisms are used to model one-dimensionalsmoldering combustion, numerically solving for the solid-phase and gasphase conservation equations in microgravity with a forced flow of oxidizer gas. The results from previously conducted microgravity experiments with flexible polyurethane foam are used for calibration and testing of the model predictive capabilities. Both forward and opposed smoldering configurations are examined. The model describes well both opposed and forward propagation. Specifically, the model predicts the reaction-front thermal and species structure, the onset of smoldering ignition, and the propagation rate. The model results reproduce the most important features of the smolder process and represent a significant step forward in smoldering combustion modeling

Incendio latente bajo las Tablas de Daimiel

Invited short article about the peat fire in Las Tablas de Daimiel National Park, Spain, in 2009.El incendio de las turberas secas del Parque Nacional de Las Tablas de Daimiel que se detectó en el verano de 2009 llevó a la sociedad española a conocer de primera mano y de golpe la amenaza que representan los incendios latentes. La combustión latente (smouldering, en inglés) es la forma lenta y sin llama que muestran algunos sólidos al quemarse. Se desarrolla por el calor desprendido cuando el oxígeno en la fase gaseosa reacciona con el carbono en la fase sólida. La reacción tiene lugar sobre la superficie del sólido y no en el gas como en una llama. El rango de temperaturas, la velocidad de propagación y el calor liberado son bajos comparados con una flama. En Daimiel, la escalada incontrolada del incendio se evitó con las grandes labores de extinción y prevención llevadas acabo a finales del otoño, que redujeron y contuvieron el incendio. Y al final, las turberas del parque se inundaron completamente por la intervención de la madre naturaleza, que envió un invierno muy húmedo para La Mancha, y, en menor medida, por la ayuda del transvase desde el Tajo

Small-scale forward smouldering experiments for remediation of coal tar in inert media

This paper presents a series of experiments conducted to assess the potential of smouldering combustion as a novel technology for remediation of contaminated land by water-immiscible organic compounds. The results from a detailed study of the conditions under which a smouldering reaction propagates in sand embedded with coal tar are presented. The objective of the study is to provide further understanding of the governing mechanisms of smouldering combustion of liquids in porous media. A small-scale apparatus consisting of a 100 mm in diameter quartz cylinder arranged in an upward configuration was used for the experiments. Thermocouple measurements and visible digital imaging served to track and characterize the ignition and propagation of the smouldering reaction. These two diagnostics are combined here to provide valuable information on the development of the reaction front. Post-treatment analyses of the sand were used to assess the amount of coal tar remaining in the soil. Experiments explored a range of inlet airflows and fuel concentrations. The smouldering ignition of coal tar was achieved for all the conditions presented here and self-sustained propagation was established after the igniter was turned off. It was found that the combustion is oxygen limited and peak temperatures in the range 800-1080 °C were observed. The peak temperature increased with the airflow at the lower range of flows but decreased with airflow at the higher range of flows. Higher airflows were found to produce faster propagation. Higher fuel concentrations were found to produce higher peak temperatures and slower propagation. The measured mass removal of coal tar was above 99% for sand obtained from the core and 98% for sand in the periphery of the apparatus