Experimental Procedure for Laboratory Studies of In Situ Burning : Flammability and Burning Efficiency of Crude Oil

Summary

Here, we present a protocol to simultaneously study the flammability and burning efficiency of fresh and weathered crude oil under conditions that simulate in situ burning operations on the sea.

Abstract

A new method for the simultaneous study of the flammability and burning efficiency of fresh and weathered crude oil through two experimental laboratory setups is presented. The experiments are easily repeatable compared to operational scale experiments (pool diameter ≥2 m), while still featuring quite realistic in situ burning conditions of crude oil on water. Experimental conditions include a flowing water sub-layer that cools the oil slick and an external heat flux (up to 50 kW/m²) that simulates the higher heat feedback to the fuel surface in operational scale crude oil pool fires. These conditions enable a controlled laboratory study of the burning efficiency of crude oil pool fires that are equivalent to operational scale experiments. The method also provides quantitative data on the requirements for igniting crude oils in terms of the critical heat flux, ignition delay time as a function of the incident heat flux, the surface temperature upon ignition, and the thermal inertia. This type of data can be used to determine the required strength and duration of an ignition source to ignite a certain type of fresh or weathered crude oil. The main limitation of the method is that the cooling effect of the flowing water sub-layer on the burning crude oil as a function of the external heat flux has not been fully quantified. Experimental results clearly showed that the flowing water sub-layer does improve how representative this setup is of in situ burning conditions, but to what extent this representation is accurate is currently uncertain. The method nevertheless features the most realistic in situ burning laboratory conditions currently available for simultaneously studying the flammability and burning efficiency of crude oil on water.

Introduction

In situ burning of spilled crude oil on water is a marine oil spill response method that removes the spilled oil from the water surface by burning it and converting it to soot and gaseous combustion products. This response method was successfully applied during the Exxon Valdez¹ and Deepwater Horizon² oil spills and is regularly mentioned as a potential oil spill response method for the Arctic^3,4,5,6. Two of the key parameters that determine whether in situ burning of oil will....

Protocol

This protocol makes use of two different experimental setups that are used in steps 4-8, as shown in the accompanying schematics. The first setup is the Crude Oil Flammability Apparatus (COFA) (Figure 1 and Figure 4), which is a 1.0 × 1.0 × 0.50 m³ metal water basin designed to conduct small scale in situ burning of crude oil experiments, as shown for example in Van Gelderen, Brogaard, et al.²² The second setup is a cone heater²³ with a spark igniter that features a custom-made sample holder and a gas analyzer that measures t....

Results

Figure 5 shows the evaporation curve of a light crude oil that was evaporated over multiple days to a loss of 30 wt% using the method described in step 2. The figure clearly shows that after the first day (19 h) of evaporative weathering, the evaporation rate is reduced significantly, which allows for pauses as mentioned in the protocol.

Figure 6 shows the ignition dela.......

Discussion

The two weathering methods discussed in this paper are a relatively simple approximation of the weathering processes that a spilled oil on water is subjected to¹⁷. Other, more sophisticated weathering methods can also be used to provide weathered crude oil samples, such as the circulating flume described by Brandvik and Faksness³⁵. The advantage of the presented methods is that they require simple equipment and can be easily conducted in a laboratory environment. The result.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
DUC Crude Oil	Maersk	N/A	Light crude oil with r = 0.853 g/ml and h = 6.750 mPa*s.
Grane Crude Oil	Statoil	N/A	Heavy crude oil with r = 0.925 g/ml and h = 133.6 mPa*s.
SVM 3000 Stabinger Viscometer	Anton Paar	C18IP007EN-P	Viscosity and density meter for the fresh and weathered crude oils.
Laboshake RO500	Gerhardt	11-0002	Rotary shaking table for emulsifying water and oil mixtures.
Jebao Wave Maker RW-4	Jebao	N/A	Propeller (flow of 500-4000 L/h) used in the COFA setup to generate a current.
Aquabee UP 3000	Aquabee	UP 3000	Aquarium pump for cooling of heat flux gauge.
Adventurer Precision Electronic Balance	OHAUS	AX5205	Load scale used to weigh the oil for the COFA experiments and in the custom-made cone sample holder for the cone setup.
3M Oil Sorbent Pads	VWR	MMMAHP156	Hydrophobic absorption pads used to collect oil residues to determine the burning efficiency of the fire.
Mass Loss Calorimeter	Fire Testing Technology (FTT)	B11325-650-1-1608	A custom-made, circular holder was used for the testing of crude oil rather than the standard square sample holder. Includes a heat flux gauge with a range up to 100 kW/m2.
34972A Data Acquisition / Data Logger Switch Unit	RS Components Ltd.	702-7958	Produced by Keysight Technologies. Operated by Keysight benchLink data logger 3 software and equipped with a 20-channel multiplexer.
Keysight Technologies 34901A 20-channel multiplexer	RS Components Ltd.	702-7939	Produced by Keysight Technologies.
Bellows-Sealed Valve	Swagelok	SS-1GS6MM	Toggle valve to open/close the water in- and outlet of the custom-made cone sample holder for the cone setup.
Kronos 50 Peristaltic Pump	SEKO	KRFM0210M6000	Peristaltic pump used to cool the custom-made cone sample holder for the cone setup.
ARCTIC A28 Refrigerated Circulater	ThermoFisher Scientific	152-5281	Water cooling reservoir used to cool the cooling water that flows through the custom-made cone sample holder for the cone setup. Includes a SC 100 Immersion Circulator controller.
Gas Analysis Instrumentation Console with Duct Insert	Fire Testing Technology (FTT)	B11328-650-1-1609	Gas analyzer for O2, CO2 and CO. Uses a 34972A Data Acquisition / Data Logger Switch Unit.
Ceramic & Stainless Steel 2.5mm Electrode	Fire Testing Technology (FTT)	M015-4	Spark igniter from the Mass Loss Calorimeter. Used in the COFA setup to measure the surface temperature upon ignition.
Infrared Emitter-Module M110/348	Heraeus	80046199	Original Infrared heaters on which the new design with a water-cooled holder for the heating elements was based. Includes two short wave twin tube emitters (09751751). Operated by a type CB1x25 P power controller.
Power Controller Heratron	Heraeus	80055836	Type CB1x25 P power controller for the infrared heaters.