Vapor Mitigation Using Fixed Water Spray System

Vapor Mitigation Using Fixed Water

Spray System

Murtaza Gandhi, P.E.Alexander Fergusson

Dr. Jin Zhao, P.E.Joseph Kao

(BakerRisk ®)

Outline

Introduction

Findings from previously published tests

Summary of results from dispersion study

Test setup

Results

Observations

Introduction

• Deluge systems are deployed in facilities to suppress incipient fires.

• The intent of these systems is to mitigate escalation in order to provide more time for response

• The NFPA 15 committee is interested in evaluating whether these systems could also be used to mitigate loss of containment events prior to ignition.

Importance of Deluge to Mitigate Vapor

Deluge is designed to mitigate vapors by entraining air into the spray cone and mixing air and water droplets, thus diluting the flammable vapor

NFPA 15 provides guidance on fixed water spray, but does not provide the design criteria regarding the quantity of water or the pressure that is required to mitigate vapor

In the event of an ignition, the amount of water and pressure required to control the fire is not defined

A test project was proposed by Fire Protection Research Foundation (FPRF) to compile results for vapor mitigation in support of developing such a criteria

Project Background

• Task 1: Literature review• Task 2: Dispersion Modeling• Task 3: CFD Modeling• Task 4: Experimental Tests• Task 5: Results and report

Five Main Tasks

• FPRF• Sponsors--Chevron, Dooley Tackaberry,

Honeywell, The Viking Corp.• Testing team--BakerRisk (tests performed at

Wilfred E. Baker Test Facility, La Vernia, TX)

Participants

Findings from previously

published tests

Literature Review – move to appendix• Literature review completed

• Water Spray Curtains: A Promising Technique to Fight Against Major Industrial Hazards, LNG Conference 2001

• Protecting Against Vapor Explosions With Water Mist, 2010, Mawhinny et al, Halun Options Technical Working Conference

• Chevron Fire Mitigation Testing, Chevron and BakerRisk 2013-2016• Forced Dispersion of LNG Vapor Clouds with water spray curtain application,

2009, Morshed Rana, TAMU• Experimental Study of Effective Water Spray Curtain Application in Dispersing

LNG Vapor Clouds, Rana et al• Review of Water Spray Mitigation of Vapor Cloud Explosions, 2005,

BakerRisk, Ketchum et al • Heavy Gas Dispersion by Water Spray Curtains, A Research Methodology,

Hald et al

Literature Review• Published material was reviewed to prepare for the tests. The

research most relevant to this project was conducted by Rana et al.

• Rana – conducted tests on LNG vapor cloud control using water curtain systems

• Work evaluated different water curtain flow patterns and focused on curtains oriented upwards to disperse the cloud

• Conclusion 1– Use of water curtain mitigation systems on LNG vapor clouds effectively reduces the concentration of flammable vapors at grade, at other grades stayed similar to release without any water spray

• Conclusion 2 – Water spray affects the vapor cloud by entraining air into the spray, reducing the concentration by mixing, changing the temperature of cloud, and changing the path of cloud

Summary of previous tests conducted by Chevron and

BakerRisk

• A series of tests were conducted between 2013 and 2016 on the subject of interest

• Dispersion models for the test scenarios were developed in BakerRisk’s SafeSite3G

©

• Various point and open path detectors were placed at different locations to detect concentrations of flammable vapors at various distances/orientations from the discharge point

• Conclusion – Water spray may have been pushing the cloud further away from the release point, however, it was difficult to validate that effect further without using additional detectors

Dispersion Modeling• Vapor cloud dispersion modeling was performed

(without deluge) in BakerRisk’s SafeSite3G© software

• These models were used in placement of detectors for the experimental validation phase

Dispersion Modeling Results• Saturated Propane (0.1 kg/s and 0.3 kg/s)

• Propane Vapor (0.1 kg/s and 0.3 kg/s)

• Observations• Saturated propane

vapors travel further than propane vapor for the same flow rate

• Saturated propane stays closer to the ground than propane vapor

Dispersion Modeling Results

• Methane Vapor (0.1 kg/s and 0.3 kg/s) • Observations• Cloud side views for

methane vapors look very similar to propane vapors for same flow rates

CFD Modeling

• CFD Modeling was performed for saturated propane at 0.1 kg/s and 0.3 kg/s without and with deluge in Fire Dynamics Simulator (FDS) software

CFD Modeling

CFD Modeling

Results Summary

• Saturated propane release with both 0.1kg/s and 0.3kg/s release cases with/without deluge system were modeled with FDS; results show:

• At center line 0.5m above ground, x<6m, propane concentration for case with water spray is lower than that without water spray.

• At center line 0.5m above ground, x from 6-8m, propane concentration for case with water spray is higher than that without water spray.

• At center line 1m above ground, propane concentration for case with water spray is higher than that without water spray

• At 0.5m away from center line and 0.5m above ground, 0.1kg/s release with and without water spray cases propane concentration are very close but for 0.3kg/s release, at x=0~1 m propane concentration with water spray is higher than that without water spray while at x=1-3m propane concentration with water spray is lower than that without water spray

Propane –0.1 kg/s

0.0%

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Propane vapor mol% (5s-10s) along y=0,z=0.5

with spray without spray

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Propane vapor mol% (5s-10 s) along y=0,z=1


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Prop

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Propane –0.3 kg/s

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Experimental Test Setup

Test Pad

Test Rig

Control Room

Water Supply

Tests performed at Wilfred E Baker Test Facility, La Vernia, TX


Saturated Propane Propane and Methane Vapor

Detector Layout

Experimental Setup – Deluge Nozzles• Two types of nozzles were used for the

test• Spiral spray nozzles (K-factor of 6.4)• Medium velocity spray nozzles

(K-factor of 7.2)

Experimental Setup

Test Summary

• Series of fire tests were run before dispersion testing• Used to determine the water pressure necessary

for deluge system to effectively control a fire at the desired hydrocarbon flow rates of 0.1 kg/s. It was determined to be 65 psig

• Maintained water pressure at 65 psig for the tests• Total of 63 dispersion and 12 fire tests were run• Deluge nozzles were located at 4ft, 5ft and 6ft

alternately through the tests• For each test, dispersion was run to establish a steady

state flow rate close to the rate identified in test matrix, followed by deluge

• Effects of water to the gas detector response was ignored in evaluation

Experimental Setup – Test summary

Table shows a sample of tests performed, NFPA report has the complete table.

Results

Results – keys to

understanding the plots

• Based on the analysis of the data, distance of 12ft and 17ft from the release nozzle were considered to be of prime interest. Results from the 22ft detectors were non-deterministic

• Detectors were placed at grade and 2ft elevation at the distances specified above

• Plots show the relative change in concentrations pre-and post-deluge

• Green bubble indicates a rise in concentration at the location

• Red bubble indicates a decline in concentration at the location

• Size of the bubble indicates relative rise/decline in concentration

Results – Saturated Propane 0.1 kg/s (Medium Velocity Nozzle)

• Time averaged concentration increased for most detectors post-deluge• Concentration decreased on east while increased on west due to wind effects

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Test 21 - Medium Velocity NozzleChange in Average Concentration (%LFL) at X= 12 ft.

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Results – Saturated Propane 0.1 kg/s (Spiral Nozzle)

• An increase in concentration at almost all detectors• A decrease in the centerline at an elevation of 2 ft

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Test 29 - Spiral NozzleChange in Average Concentration (%LFL) at X= 12 ft.

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• An increase in flammable concentration at 12ft and 17ft detector locations. • Note that the bubble chart does not show an increase in flammable gas concentration at the

detectors along the centerline of the cloud (Y = 0 ft.), as the gas detectors at these locations were reading at 100% LFL both before and after the activation of the deluge system.

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Results – Saturated Propane 0.3 kg/s (Spiral Nozzle)

• An increase in flammable concentration at 12ft and 17ft detector locations. • Note that the bubble chart does not show an increase in flammable gas concentration at the

detectors along the centerline of the cloud (Y = 0 ft.), as the gas detectors at these locations were reading at 100% LFL both before and after the activation of the deluge system.

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Test 43 - Spiral NozzleChange in Average Concentration (%LFL) at X = 12 ft.

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Results –Saturated

Propane Test

• The spiral deluge nozzle typically resulted in a greater increase in flammable gas concentration at 12ft and 17ft from the release point.

• Activation of the deluge system often results in an increase in flammable gas concentration for detectors away from the centerline (Y ≠ 0)

• The activation of the deluge system, regardless of nozzle type, typically results in:

• Increase of flammable concentration at grade and at 2ft-elevation• Increase at grade was more significant• Propane concentration remained above 100% LFL at the centerline

for a 0.3kg/s release

• No meaningful trends were observed for: • Detectors in the far field (where X is ≥ 22 ft.) • Detectors placed in front of deluge nozzles (X < 12) • Distance from discharge point to the deluge had no noticeable effect.• For the 0.3 kg/s release, as the concentration at the centerline was

>100% LFL, it is indeterminable the effect the activation of the deluge system had on these detectors.

Results – Propane Vapor 0.1 kg/s (Medium Velocity Nozzle)

• Activation of the deluge system resulted in a lower concentration of propane along the centerline, but resulted in an increase in flammable gas concentration for the remaining detectors within the row.

• Activation of the deluge system also resulted in higher concentrations of hydrocarbons at grade.

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Test 17 - Medium Velocity NozzleChange in Average Concentration (%LFL) at X = 12 ft.

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Results –Propane Vapor 0.1 kg/s (Spiral Nozzle)

• The spiral nozzle shows similar performance to the medium velocity nozzle• Activation of the deluge resulted in lower concentrations along the centerline of the cloud (Y = 0), and

an increase at other locations. • Concentrations at grade increased more than those at an elevation of 2 ft

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Results –Propane Vapor 0.3 kg/s (Medium Velocity Nozzle)

• Medium velocity nozzle shows similar trends as the 0.1 kg/s vapor propane release. • The flammable concentration at grade generally increase more than the flammable concentration at

an elevation of 2 ft. The only detector to show a decrease in concentration was the one along the center line (Y = 0), and at an elevation of 2 ft

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• An increase in concentration at grade, and a decrease at centerline. • The plots also show potential wind effects resulting in a decrease in concentration at negative Y

values and an increase in concentration at positive Y values.

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Results –Propane Vapor

Test

• The two deluge nozzles considered showed similar increases in flammable gas concentration upon activation of the deluge system

• Activation of the deluge system typically results in a greater increase of flammable concentration at grade than at an elevation of 2 ft. regardless of the nozzle type.

• No meaningful trends were observed for: • Detectors in the far field (where X is ≥ 22 ft.) • Detectors placed in front of the deluge nozzles (X < 12)• The distance from the discharge point to the deluge had no

noticeable effect.

Results – Methane Vapor 0.1 kg/s (Medium Velocity Nozzle)

• Methane test has similar trends to the propane tests• The flammable gas concentration increases at grade, and increases much less, or decreases slightly at an elevation of 2 ft• Gas concentration at the centerline also increases much less, or even decreases when compared to the locations around it

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Test 57 - Medium Velocity NozzleChange in Average Concentration (%LFL) at X = 17

ft.


• The spiral nozzle shows similar performance to the medium velocity nozzle• Concentration at grade increased, while the concentration at the centerline

decreased at an elevation of 2 ft

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Results –Methane Vapor 0.3 kg/s (Medium Velocity Nozzle)

• An increase in flammable gas concentration at grade due to the activation of the water spray system. The increase in flammable gas concentration only occurs on the west side (Y > 0), perhaps indicating a slight shift in wind.

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Test 54 - Medium Velocity NozzleChange in Average Concentration (%LFL) at X = 17

ft.

Results –Methane Vapor 0.3 kg/s (Spiral Nozzle)

• Plots show some influence of wind shifting the centerline of the flammable gas cloud to the west (Y > 0). • The activation of the water spray system has resulted in an increase in flammable concentration at

grade and at an elevation of 2 ft

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Results –Methane Vapor

Test

• The spiral deluge nozzles resulted in a higher increase in flammable gas concentration upon activation of the deluge system for the set of tests

• Activation of the deluge system typically results in a greater increase of flammable concentration at grade than at an elevation of 2 ft. regardless of the nozzle type.

• No meaningful trends were observed for: • Detectors in the far field (where X is ≥ 22 ft.) • Detectors placed in front of the deluge nozzles (X < 12)• The distance from the discharge point to the deluge had no

noticeable effect.

Overall Observations from the tests

Observations

Activation of water spray typically results in higher concentration of flammable gas at grade and elevation of 2 ft for detectors at horizontal distance of X = 12 ft. & X = 17 ft.

There is a greater rise in flammable gas concentration at grade than at 2 ft.

Activation of water spray also results in reduction of flammable gas concentration along centerline (Y = 0) for the farther detectors (at 12ft and 17ft from release point).

Effect of water spray at detectors in the far field (X ≥ 22 ft.) is unclear, and may be primarily driven by weather effects.

No significant changes in flammable concentrations were observed for detectors located between the hydrocarbon discharge point and water spray.The distance from the hydrocarbon discharge point and water spray did not result in any noticeable difference in the behavior of the flammable cloud. Deluge nozzle type and material (propane vapor vs methane vapor) did not result in any appreciable change in response of flammable cloud to the water spray mitigation.

Observations

The phase of the material (propane) did result in a difference in the effectiveness of the water spray mitigation system.

Activation of the deluge system typically resulted in a lower concentration of flammable gas for detectors at an elevation of 2 ft for propane/methane vapors.

• Trend did not occur for the saturated propane• Flammable concentration stayed the same or increased with the activation of the deluge system.

• This may be due to the higher density and inertia of saturated propane release to be more resistant to the effects of the water spray.

Generally, it appears that the deluge spray imparts momentum into the hydrocarbon discharge. The result is:

• Rapidly diluting the concentrated core of the dispersion• Flattening and potentially extending the overall cloud volume

The dispersion jet is not encapsulated by the water spray, even at flows of 0.1 kg/s at the discharge conditions tested.

For the tests performed, the water spray performed better for low flow rate, low momentum releases

• They were more affected by the momentum from the deluge spray.

Vapor Mitigation Using Fixed Water Spray System

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