1、American 1220 L Street, Northwest Petroleum Washington, D.C. 20005-4070 Institute 202-682-8000 Identification of Oils that Produce non-Buoyant In Situ Burning Residues and Methods for their Recovery Regulatory and Scientific Affairs PUBLICATION NUMBER DR145 FEBRUARY 20 02 American Petroleum -1 Insti
2、tute American Petroleum Institute Environmental, Health, and Safety Mission and Guiding Principles MISSION The members of the American Petroleum Institute are dedicated to continuous efforts to improve the compatibility of our operations with the environment while economically developing energy reso
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10、oducts, and wastes. Identification of Oils that Produce non-Buoyant ln Situ Burning Residues and Methods for their Recovery Regulatory and Scientific Affairs API PUBLICATION NUMBER DR145 FEBRUARY 2002 PREPARED UNDER CONTRACT BY: S.L. Ross ENVIRONMENTAL RESEARCH LTD. OTTAWA, ONTARIO CANADA American P
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15、oleum Institute GRI DISCLAIMER LEGAL NOTICE: This report was prepared as an account of work sponsored, in part, by the Gas Research Institute (GRI). Neither GRI, members of GRI, nor any person acting on behalf of either: a. Makes any warranty or representation, express or implied, with respect to th
16、e accuracy, completeness, or usefulness of the information contained in this report, or that the use of any apparatus, method, or process disclosed in this report may not infringe privately owned rights; or b. Assumes any liability with respect to the use of, or for damages resulting from the use of
17、, any information, apparatus, method, or process disclosed in this report. iv ACKNOWLEDGMENTS THE FOLLOWING PEOPLE ARE RECOGNIZED FOR THEIR CONTRIBUTIONS OF TIME AND EXPERTISE DURING THIS STUDY AND IN THE PREPARATION OF THIS REPORT API AND GRI STAFF CONTACT Thomas Purcell, Regulatory, Analysis and S
18、cientific Affairs ASA) Alexis Steen*, Regulatory and Scientific Affairs (no longer with API) MEMBERS OF THE OIL SPILL SCIENCE however, surface countermeasures would only be applicable for a short period-a maximum of 30 minutes-before the residue cooled to ambient temperatures and began to sink. A mo
19、re realistic countermeasure would be to suspend a fine-mesh net from the bottom of the fire- containment boom, such that it extends across the apex of the burn area. This might allow the capture of bum residues as they cool, become more viscous, and start to sink. ES- 1 There are two recommendations
20、 from the study: 1) large-scale in situ burn tests should be conducted to confirm the validity of the correlations developed in this study and 2) a prototype of the netting concept should be constructed and subjected to tank testing to confirm its viability for residue containment and to document it
21、s effect on boom performance. ES-2 Section 1 INTRODUCTION Research has established that the smoke plume from an oil spill in situ burning (ISB) operation will not pose a threat to persons if they are located more than about a mile or two downwind from the bum. This fidmg, among others, has led to ad
22、vances in obtaining regulatory approval for burning. Now, another environmental concern has surfaced. This is the possible sinking of residues from in situ burns, leading to environmental damage at the sea bottom. Existing operational protocols do not consider this problem, and cleanup systems have
23、not been developed and put in place to collect non- buoyant residues from ISB operations. This “sinking” problem was not considered in the past because it had been observed in many in situ bum experiments that ISB residues, although dense and viscous, did not sink. Concerns started to develop in the
24、 early 1990s when two separate tanker spills involving heavy crude (the Haven and the Honam Jade) accidentally caught fire, bumed, and produced large quantities of residue that did indeed sink. These observations suggested that the residues from the earlier experimental work did not sink because the
25、 starting oil involved relatively thin slicks andor relatively light oils. Hindsight suggests that the more important factor was the relative thinness of the starting slick, which was usually on the order of one or two centimeters. S.L. Ross examined the problem in a preliminary study completed for
26、MSRC in 1995 entitled Laboratory Studies of the Properties of In situ Burn Residues (S.L. Ross, 1995). The study indicated that there is a large range of oils that may produce non-buoyant residues after an ISB operation involving thick slicks. Subsequently, in another S.L. Ross study completed for t
27、he U.S. Minerals Management Service (S.L. Ross, 1997), this was confirmed with a number of oils produced on the U.S. Outer Continental Shelf (OCS). Despite the small scale of the experiments, the results, which are discussed in detail later, suggest that non-buoyant residues may be produced more oft
28、en than not in burn operations. There is thus a demand to develop a real-time capability to predict whether a particular oil and ISB operation will produce residues that sink. At the same time there is a need to develop appropriate countermeasures to deal with such residues. 1-1 Section 2 OBJECTIVE
29、AND LIMITATIONS OF STUDY The objective of this study was to start the process of establishing operational tools and procedures for dealing with the problem of non-buoyant residues that may result from the in situ burning of marine oil spills. The following are the two tasks of the study: Task 1. Dev
30、elop simple protocols, based on available information, for identifying oils that are likely to sink if set afire and burned efficiently. Task 2. Evaluate options for dealing with non-buoyant residues in the field. The only studies that provide quantitative burn residue information of value to Task 1
31、 are the laboratory work completed for MSRC and the follow up work for MMS mentioned in the Introduction. These studies involved very small, efficient burns under controlled conditions. Preliminary theoretical considerations suggest that large-diameter bums in the field might produce residues that a
32、re less dense than those from small-diameter burns of the same oil and slick thickness. The results from small-scale experiments must thus be considered preliminary in terms of predicting residue densities for large burns in the field. Further research needs to be undertaken to explore the effects o
33、f scale (i.e., fire size and other bum-controlling factors) on bum residue properties. Despite the above uncertainties, and for want of better data, attempts are made in this study to use the results of the small-scale experiments to predict results in the field. It is clear, however, that the resul
34、ts should be used with extreme caution. It is hoped that more reliable predictions will be developed once larger-scale experiments are conducted to confirm or reject the predictions presented here. 2- 1 Section 3 IDENTIFICATION OF OILS THAT YIELD NON-BUOYANT ISB RESIDUES The three most important fac
35、tors that determine whether an ISB residue will sink or not are the properties of the starting oil, its thickness and the efficiency of the bum process. Some oils that are already relatively heavy will certainly produce residues that will sink in seawater, but only if the bum process is efficient an
36、d uninterrupted. The purpose of this section of the report is to predict which oils will produce non-buoyant residues if the burn process is assumed to be “efficient.” Here “efficient” means as efficient as that experienced in controlled, small-scale burns. It is theoretically possible to control bu
37、rn efficiencies operationally in the field and thereby control the density of the bum residue. These operational possibilities are dealt with in the next section. CONFLICTING THEORIES OF INSITU BURNING (The following is a summary of the discussion in S.L. Ross, 1995.) In situ buming of an oil slick
38、on water proceeds because the hydrocarbon vapor above the liquid bums. The key process is radiative heat transfer from the flame back to the surface of the slick. Some of this heat transfers through the slick to the underlying water, but most vaporizes the liquid hydrocarbons, which rise to mix with
39、 air above the slick. Oxidation then occurs, releasing heat to continue the buming process. Once ignited, a buming thick oil slick reaches a quasi-steady-state in which the vaporization rate sustains the necessary heat transfer back to the slick surface. There is uncertainty about the process by whi
40、ch oil vaporizes during in situ buming. Three possibilities exist: (1) Batch Distillation, (2) Equilibrium Flash Vaporization (EFV), or (3) a combination of the two. In Batch Distillation the lightest, most volatile components are boiled off from the entire slick first, followed by progressively hea
41、vier, less volatile components. If this happened exclusively during in situ buming, the temperature of the oil slick would increase over the bum period, and the residue remaining after the burn would contain no lighter hydrocarbons and would be much heavier than the original oil. 3-1 In contrast, th
42、e theory of Equilibrium Flash Vaporization (EFV) indicates that, over the entire course of the burn period, vapor of essentially constant composition is produced by a feed of oil of essentially constant composition. Researchers believe that EFV is a key vapor-producing mechanism in ISB because of th
43、e following experimental observations: (1) the surface temperatures of burning oil slicks tend to remain relatively constant during steady-state buming; (2) a steep temperature profile exists in the buming slick, indicating a poorly-mixed oil layer, as required for EFV; and, (3) the presence of ligh
44、ter ends in the oil residue remaining after a bum. It is believed that EFV occurs during in situ burning because the hot flames and the insulating characteristics of the oil combine to create high temperatures in a thin surface layer of the slick known as the “hot zone.” This promotes near-complete
45、vaporization of the surface of the oil slick with minimal mixing and heat transfer to the underlying oil and/or water layers. Despite the above indications it is clear that the vaporization process that occurs during the in situ buming of crude oils is some combination of Batch Distillation and EFV.
46、 It is well known that the burn residue, while still containing some lighter ends, differs markedly from the original oil. The residues high density and viscosity strongly indicate that there is a progressive concentration of the very high molecular weight compounds in the remaining slick as in situ
47、 burning proceeds. It is likely this concentration of heavy compounds in the residue over time that determines whether a residue will sink or not. Residues from burns of thick crude oil slicks are more likely to sink than residues from bums of thin slicks of the same crude because of the extra conce
48、ntrating potential in the thick-slick case. This possibility that the vaporization process is a combination of two very different processes greatly complicates ones ability to predict the properties of bum residues and whether they will sink or not. If the vaporization process were pure EFV, the den
49、sity and other properties of the residue would simply be the same as the original oil. If the process were pure Batch Distillation, one could simply refer to standard crude oil distillation data for the oils under consideration, and use these for prediction purposes. Neither situation applies, unfortunately, and it becomes necessary to consider more complicated methods for predicting the properties of bum residues. 3 -2 RESULTS OF EARLIER LABORATORY STUDY The laboratory study for MSRC (S.L. Ross, 1995) was conducted to better understand the ISB residue problem, especially the possible tende
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