High Expansion Foam
Two major hazards of LNG spills are vapor hazard and fire hazard. The vapor hazard is the flammable LNG vapor cloud at the ground due to the dense gas behavior. The fire hazard is the thermal radiation of an LNG pool fire. High expansion foam has been proven to be effective to mitigate vapor hazard and fire hazard. The work conducted by MKOPSC involves experiments in the lab, wind tunnel and open field.
Flame Retardant
The polymeric materials provide numerous advantages to society in everyday life, like being versatile, lightweight, corrosion-resistant, electrically insulating, and easily processable. However, the high flammability of many synthetic polymers is one obvious drawback, due to their energy-dense hydrocarbon-based chemical structure. Therefore, improving the flame retardancy of polymeric materials is an increasingly important strategy to limit the exposure of life safety to more fire hazards, especially in this era when those polymeric materials are widely used almost everywhere in buildings, housing, vehicles, aircraft, commercial products, etc. However, with improper flame retardants, the use of flame retardants may have such adverse effects on life safety and property as toxic gas emission or negative environmental impact. To comprehensively address the fire hazard and risk, there is an increased demand from consumers, government, and industry for improved durability, fire safety, and reduced environmental impact of flame retardant polymeric materials. The research of flame retardant in the Mary Kay O’Connor Process Safety Center includes the following areas:
- Development of environmentally friendly flame retardant polymer nanocomposites: This research is focused on the usage of nanomaterials as fillers to improve the flame retardant performance, while still maintaining or even enhancing the mechanical properties of polymers, especially for engineering plastics, including polypropylene (PP), acrylonitrile butadiene styrene (ABS), and polyamide (PA).
- Development of sustainable plastics: This research is focused on the development of flame retardant polymers that not only have excellent properties during their useful life, but also offer options for end-of-life management. This research is beneficial to improve the efficiency of polymer production, reduce energy inputs, and even use waste plastics, biologically-derived feedstocks or even CO2 as raw materials to make new flame retardant plastics.
- Fundamental study of flame retardant mechanisms: The polymer combustion process is comprised of multiple interacted steps involving both the condensed phase and the gaseous phase. The theory behind flame retardant additives is that these additives may act to prevent, minimize, or even stop any step in the self-sustaining polymer combustion process and consequently control the burning rate or even extinguish the flame. This research is focused on developing a fundamental understanding of the physical and chemical characteristics of polymer composite combustion and the effects of different flame retardant mechanisms, which will provide guidance on how to design more effective flame retardant systems for polymers.
Lab Tests
The lab tests required building a foam generator and a foam test apparatus. The foam generator is an improved version based on the schematic design in NFPA 11. The new features of the foam generator allow and facilitate the study of foam application on an LNG pool. Liquid nitrogen (LN2) was used in the lab tests as a safe analogue of LNG. This work aims to study the physical interaction between LNG vapor and foam, including the heat transfer between LNG vapor and foam, the formation of channels for vapor to escape, and foam breaking rate.
Foam Research Lab Test
Wind Tunnel Tests
A small scale experiment has been performed to study the blanketing effect on LNG spill, in which LN2 was used due to its similar thermal properties and the associated benefits in terms of safety and financial flexibility. The foam blanket exerts two effects that lead to opposite results: Foam blanket blocks convection and radiation to reduce heat input for LN2 vaporization, while water drainage induced by convection, radiation and direct contact with LN2 adds extra heat to vaporize LN2.
Foam Research Wind Tunnel
The performance of foam on eliminating heat input from convection and radiation, and the additional heat input due to water drainage were evaluated based on the vaporization rate measurement using a balance. The analysis of the experimental data concluded that high expansion foam is effective for reducing LN2 vaporization by blocking convection and radiation; the water drainage due to direct contact of foam with LN2 at the initial stage does add extra heat, but it is less significant compared with the reduction of convection and radiation. A correlation between heat inputs with and without foam effects was proposed, and reduction factor was determined for this specific experiment.
LNG vapor dispersion mitigation
The experimental work conducted in Brayton Fire Training Field (BFTF) by MKOPSC aims to examine the performance of high expansion foam to mitigate the vapor hazard of an LNG spill, and provide a guidance for industrial practice based on a study of various parameters. The experiments were conducted in pits up to a scale of 6.5m x 10m. The performance of high expansion foam to reduce the vapor hazard was evaluated by the vapor concentration in the downwind direction at the ground level.
Foam Research Field Test
More than 100 thermocouples were placed at various elevations in the LNG pool, in the foam blanket and above foam blanket to study the thermal effects of high expansion foam on LNG system. The experimental results indicate a significant reduction of vapor concentration in the downwind direction, and the “vapor exclusion zone” (lower flammable limit distance) was determined with the foam application. The elevated vapor temperature above the foam blanket indicates a warming effect of foam. A minimum effective foam depth of 0.64m was determined based on the ability of foam to increase the vapor buoyancy to a positive level, which can be used to guide industrial application of high expansion foam for LNG vapor hazard mitigation.
LNG Pool Fire Mitigation
An LNG pool fire may cause a thermal hazard to personnel, properties and the environment. The experiments performed at BFTF by MKOPSC aims to examine the effectiveness of high expansion foam on reducing the thermal hazard of an LNG pool fire, and provide a guidance of the design and operation parameters for the industrial application. The experiments were conducted in pits up to a scale of 6.5m x 10m. The radiant heat of the LNG pool fire was monitored at the surrounding area and above the pits.
Foam Research Field Test
With the same manner as the vapor dispersion study with high expansion foam, temperature was measured to provide extra information to understand the effects of high expansion foam to suppress the pool fire. The “thermal exclusion zone” (5 kW/m2 radiation distance) was determined experimentally to guide facility siting in the LNG plant. The control time is defined as the time required for 90% radiant heat reduction after high expansion foam application at a certain distance, and it was used as a criterion to determine the effective foam application rate. This work concluded that high expansion foam application reduces the “thermal exclusion zone” by 50%. A foam application rate of 10 L min-1 m-2 was recommended to mitigation thermal hazard of pool fire
