Study of key properties of expansion foam for process safety incident mitigation using an improved foam generator
Introduction
High expansion foam is aqueous foam with an expansion ratio between 200 and 1000, or higher, usually consisting of foaming agent, co-solvent, stabilizer, antifreeze and water. High expansion foam can be used to mitigate or extinguish Class A or Class B fires (National Fire Protection Association, 2016). High expansion foam has a large product rate, so it can fill the space or cover the surface quickly to provide a good isolation effect on the heat input;It has a low water content, making it cause less damage to the equipment with a fire, or more suitable for cryogenic fuels, such as Liquefied Natural Gas (LNG). The foam generation apparatus is easy to operate and at a low-cost.
With all these advantages, high expansion foam has a broad application on mitigating the hazards of process safety incident, such as controlling fires in confined spaces, such as underground oil depots, ship cabins, mines, thermal power plants, and other locations where space is restricted, and mitigating the vapor and fire hazards of LNG release. High expansion foam can be used for chemical decontamination if a proper decontamination agent was added in the foam solution (Harding et al., 2016b).
High expansion foam is effective in mitigating the hazards of cryogenic releases. Cryogenic liquids will vaporize violently once released in the atmospheric conditions; its volume expands dramatically to form a huge vapor cloud (Ahammad et al., 2016; Gopalaswami et al., 2015; Véchot et al., 2013). High expansion foam can mitigate the vapor cloud and fire hazard if the cryogenic liquid is flammable. Most of the studies in this area focus on the LNG hazard mitigation. In terms of vapor cloud, high expansion foam helps to reduce the vaporization rate (Takeno et al., 1996; Zhang et al., 2014, 2016), and warm the vapor to enhance dispersion upwards in the atmosphere (Krishnan et al., 2018, 2019; Zhang et al., 2014). Therefore, the size of flammable LNG vapor cloud decreases. In terms of fire hazard, high expansion foam helps to reduce the mass burning rate, flame size and thermal radiation (Zhang et al., 2018).
The foam expansion ratio, production rate and foam stability of foam studied in this paper are very important for foam disaster mitigation in process safety. First of all, different types of leaks and fire accidents require high-expansion foams with different expansion ratio. For example, Oil flow fires need to be extinguished by high-expansion foams with an expansion ratio of about 200. LNG pool fires require high-expansion foams with an expansion ratio of about 500. Leaking vapor cloud hazards of cryogenic liquids, such as liquid hydrogen, LNG, etc., require high-expansion foam with an expansion rate of 700–1000 or even higher for disaster mitigation (Harding, 2016) (Zhang, 2015). In addition, the foam production rate affects the efficiency of high-expansion foam disaster reduction, and the high-expansion foam stability affects the disaster reduction result. These properties of foam are closely related to the disaster reduction part of process safety. Research on the mechanism that affects foam properties is also an important part of process safety research.
The creation and improvement of safety protection facilities promotes the development of process safety. Industrial foam generator was used primarily to study the mitigation effect of high expansion foam on LNG releases (Harding et al., 2016a) (Suardin, 2008) (Yun et al., 2011). The hydraulic foam generator has a large capacity to produce foam; however, its operation parameters cannot be delicately controlled, making it impossible to study the mechanism of foam generation. Harding and Zhang et al. (Harding et al., 2016a)pioneered to build a research foam generator, and investigated the effect of foam solution flow rate (Fsol) on expansion ratio, and the effect of air exposure time of foam solution on foam stability. Furthermore, nanoplates additives were added in the foam solution to improve foam stability (Krishnan et al., 2019). Yang also built a similar foam generator to study the effects of operation and containment conditions on foam stability (Yang et al., 2018). However, the foam generators used in the previous work could not study the effects of air flow rate (Fair) and mesh hole diameter (Dmesh) on foam properties. In addition, there is no mathematical model to predict the key properties of expansion foam.
This paper aims to improve the current design of foam generator, enabling to study the effects of Fair and Dmesh on foam properties, quantitatively. This work will focus on the experimental study of key properties of expansion foam, i.e., foam expansion ratio, foam production rate and foam stability. The experimental data will be used to develop predictive models of expansion ratio and production rate. The findings of this study will provide a scientific basis for the design of foam generation system and the guideline of hazard mitigation operation.
Section snippets
Foam generator
A research foam generator was built in this study to meet the research requirements. Industrial foam generators are driven by a hydraulic method using pressurized water, making it impossible to delicately control the operation conditions. A research foam generator was built in the previous work, allowing to control foam solution flow rate and air flow rate separately (Harding et al., 2016a); however, the air flow rate was not measured. A new version of foam generator and a foam collection
Results and discussion
The properties of high expansion foam can significantly impact its performance for LNG hazard mitigation. The expansion ratio determines the water content in the foam, and water can vaporize LNG. Therefore, the expansion ratio is a key property for LNG hazard mitigation. The foam production rate determines how quickly the LNG pool can be effectively covered by the foam. The foam breaking rate affects both LNG vaporization rate and LNG vapor temperature, because the breaking foam will release
Conclusion
Properties such as foam expansion ratio、production rate and foam stability are critical to process safety. This research provides a reference to the production of high-quality foam.
In this work, an improved foam generator was constructed to study the key properties of expansion foam for mitigating process safety incident. The improved foam generator enables to study the effects of air flow rate and mesh hole size quantitatively. The main conclusions are as follows.
The effects of Fsol, Fair, and
Author contribution statement
Yingchun Liu contributed to building the experimental apparatus, data Formal analysis, developing the mathematical model of foam expansion ratio, and drafting the manuscript; Mingju Jing contributed to foam experiment and sorting out experimental data; Rongcen Xu contributed to developing the mathematical model of foam production rate; Xiaoyang Luan contributed to foam experiment and data analysis; Juncheng Jiang contributed to the constructive discussion on the results; Bin Zhang contributed
Declaration of competing interest
The authors declare that they have no conflicts of interest to this work.
Acknowledgements
This work is supported by the Talent Research Start-up Fund of Nanjing Tech University, the program of Jiangsu Specially-Appointed Professor, the Key Project of the Natural Science Foundation of the Jiangsu Higher Education Institutions of China [grant numbers 19KJA460007], and Postgraduate Research and Innovation Project in Jiangsu Province [grant numbers KYCX20_1116].
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