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Research Papers

How Does Concrete Affect Evaporation of Cryogenic Liquids: Evaluating Liquefied Natural Gas Plant Safety

[+] Author and Article Information
Alfonso Ibarreta

Exponent, Inc.,
9 Strathmore Road, Natick 01760, MA
e-mail: aibarreta@exponent.com

Ryan J. Hart

Exponent, Inc.,
4580 Weaver Parkway, Suite 100, Warrenville 60555, IL
e-mail: rhart@exponent.com

Nicolas Ponchaut

Exponent, Inc.,
9 Strathmore Road, Natick 01760, MA
e-mail: nponchaut@exponent.com

Delmar “Trey” Morrison

Exponent, Inc.,
4580 Weaver Parkway, Suite 100, Warrenville 60555, IL
e-mail: tmorrison@exponent.com

Harri Kytömaa

Exponent, Inc.,
9 Strathmore Road, Natick 01760, MA
e-mail: hkytomaa@exponent.com

Manuscript received February 18, 2015; final manuscript received June 5, 2015; published online November 20, 2015. Assoc. Editor: Chimba Mkandawire.

ASME J. Risk Uncertainty Part B 2(1), 011005 (Nov 20, 2015) (5 pages) Paper No: RISK-15-1023; doi: 10.1115/1.4030947 History: Received February 18, 2015; Accepted June 29, 2015

With the impending natural gas boom in the United States, many companies are pursuing Department of Energy (DOE) approval for exporting liquefied natural gas (LNG), which is a cryogenic liquid. The next decade also promises to demonstrate growth in LNG-fueled fleets of vehicles and marine vessels, as well as growth in other natural gas uses. The future expansion in the LNG infrastructure will lead to an increased focus on managing the risks associated with spills of LNG. Risk analysis involving LNG spill scenarios and their consequences requires determining the size of resulting ignitable flammable vapor clouds. This in turn depends strongly on the rate of evaporation of the spilled LNG. The evaporation of a cryogenic LNG spill (and thus the flammable vapor cloud hazard) can be quite a complex process, and it is primarily controlled by the rate of spreading of the pool and by the transient conductive heat transfer from the ground to the spilled liquid. Radiative and convective heat transfer are also present, but the conductive heat transfer rate dominates in the evaporation of a cryogenic liquid spilled into a trench or sump initially at ambient temperature. The time-dependent evaporation rate can be calculated using a variety of models, such as the built-in model in PHAST Det Norske Veritas (DNV) or other proprietary models that account for pool spreading, heat conduction within the substrate, and phase change. Trenches and sumps used to contain LNG spills are normally lined with various types of concrete, including insulated or aerated concrete. The authors have found that for a cryogenic liquid, the choice of thermal properties for concrete can greatly affect the source term. This paper presents a sensitivity study of the effects of substrate properties on the evaporation rate of LNG. The study will look at the dependence for a range of sump diameters. The PHAST model results will be compared to results obtained using an in-house shallow water equation (SWE) liquid propagation and heat transfer model. The results of the paper will provide guidance for the selection of substrate properties during modeling as well as a comparison of the relative evaporation rates expected for different surfaces, such as regular concrete and insulated concrete.

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References

Ponchaut, N. F., Kytömaa, H. K., Morrison, D. R., and Chernovsky, M. K., 2011, “Modeling the Vapor Source Term Associated With the Spill of LNG Into a Sump or Impoundment Area,” JLPP, 24(6), pp. 870–878 10.1016/j.jlp.2011.06.020.
Ponchaut, N. F., Ibarreta, A. F., and Kytömaa, H. K., 2012, “Modeling of LNG Spills Into Trenches and Troughs,” AIChE Spring Meeting, 12th Topical Conference on Gas Utilization, Houston, TX, Apr. 1–5.
Webber, D. M., Gant, S. E., Ivings, M. J., and Jagger, S. F., 2009, “LNG Source Term Models for Hazard Analysis: A Review of the State-of-the-Art and An Approach to Model Assessment,” Prepared by Health & Safety Laboratory for the Fire Protection Research Foundation, Final Report.
Witlox, H. W. M., and Holt, A., 1999, “A Unified Model for Jet, Heavy and Passive Dispersion Including Droplet Rainout and Re-Evaporation,” International Conference and Workshop on Modeling the Consequences of Accidental Releases of Hazardous Materials, CCPS, San Francisco, CA, Sept. 28–Oct. 1, pp. 315–344.
PHMSA Docket No. 2011-0075, October 11, 2011, www.regulations.gov.
PHAST Pool Vapourisation (PVAP) Theory Document, January 2006.
Lentz, A. E., and Monfore, G. E., 1966, “Thermal Conductivities of Portland Cement Paste, Aggregate, and Concrete Down to Very Low Temperatures,” Bulletin/Research and Development Laboratories of the Portland Cement Association Research Department.
ACI 207.2R, 2007, “Report on Thermal and Volume Change Effects on Cracking of Mass Concrete,” American Concrete Institute, Farmington Hills, MI.
ACI 122R-02, 2002, “Guide to Thermal Properties of Concrete and Masonry Systems,” American Concrete Institute, Farmington Hills, MI.
49 CFR Part 193 - Liquefied Natural Gas Facilities: Federal Safety Standards, October 1, 2011, U.S. Government Publishing Office, www.gpo.gov
NFPA 59A Standard for the Production, 2001, “Storage, and Handling of Liquefied Natural Gas (LNG),” National Fire Protection Association.
40 CFR Part 68 - Chemical Accident Prevention Systems, July 1, 2011, U.S. Government Publishing Office, www.gpo.gov.

Figures

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Fig. 1

Block diagram for PHAST

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Fig. 2

PHAST vaporization model results for the four substrate types and two circular sump impoundment diameters (10 and 20 ft). The spill rate was 20  lb/s and originated in the center of the impoundment

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Fig. 3

Comparison of vaporization rates calculated using the PHAST and SWE models for the 10-ft diameter sump

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Fig. 4

Peak evaporation rates for all cases considered as a function of the lumped thermal parameter κ/α1/2

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Fig. 5

Normalized evaporated amount after 2 mins as a function of the lumped thermal parameter κ/α1/2

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