Effect of operational parameters on the recovery rate of an oleophilic drum skimmer

doi:10.1016/j.jhazmat.2007.02.017

Journal of Hazardous Materials

Volume 148, Issues 1–2, 5 September 2007, Pages 136-143

https://doi.org/10.1016/j.jhazmat.2007.02.017 Get rights and content

Abstract

The primary objective of this research was to determine the relationship between operational variables and oil spill recovery rates, by performing a full-scale oil spill recovery test using an oleophilic drum skimmer. Prototype interchangeable oleophilic skimmer drums with aluminum, polyethylene and Neoprene surfaces were fabricated and tested at the field scale at the Ohmsett-National Oil Spill Response Test Facility. This study determined the effect of the recovery surface material, oil properties, oil slick thickness, temperature and drum rotational speed on the oleophilic drum skimmer recovery rates. It was found that the selection of the recovery surface material can increase the recovery rates up to 20%. The increase in oil slick thickness from 10 to 25 mm led to up to two times higher recovery rates for a viscous oil, but did not have any noticeable effect on the recovery rates of light oil.

Introduction

Mechanical recovery is the most commonly used oil spill response technique [1]. This technique physically removes oil from the water surface, even in the presence of ice [2]. Unlike other cleanup techniques, mechanical recovery can be efficiently applied to treat emulsified oils as well as oils of variable viscosities (6–20,000 mPa s). A weakness of mechanical cleanup is the recovery rate. It may be very time consuming and expensive when employed on a large scale, and require a large amount of personnel and equipment, and every additional hour of cleanup time can significantly increase the cost of recovery. A more efficient recovery device can thus reduce the cost significantly and reduce the risk of oil reaching the shoreline.

The adhesion (oleophilic) skimmer is one of the most common types of mechanical recovery equipment. It is based on the adhesion of oil to a rotating skimmer surface. The rotating surface lifts the oil out of the water to an oil removal device (e.g., scraper, roller, etc.). A number of studies have been undertaken to test the recovery rate of various skimmers [3], [4], [5], [6], [7], [8], [9], [10], [11]. The goal of these studies was to compare the recovery rates of various skimmers, but they did not perform a systematic analysis of the effect of operational parameters such as spill thickness, temperature, drum rotational speed, etc., on oil recovery rates. The skimmers tested in these studies had different configurations, dimensions, capacities and recovery modes. In most cases several operational parameters were changed simultaneously during each test making it difficult to distinguish the effect of each variable separately. The current study specifically evaluated both design and operational parameters independently, providing key information about the influence of these parameters on the overall oil recovery rate.

Prior to this study, the interfacial tension between different materials that could be used in the recovery surface of the skimmer and various oils was evaluated [12]. Although interfacial tension is a very important factor in the initial adhesion of oil to the recovery surface, the wetting sequence is important. Under typical conditions, the skimmer's drum rotates first into the oil, and then lifts the oil towards the scraper. Interfacial tension plays an important role in wetting the recovery surface in the first rotation. However, oil viscosity and cohesion become more important as the oil is transported up to the scraper, since they control the thickness of the oil on the recovery surface and significantly influence overall recovery rates. Since the scraper does not remove 100% of the oil from the drum, a thin oil film is present in subsequent rotations. The ability of oil to form and maintain a thicker film on the surface and the ability of the material to retain oil becomes more important.

Section snippets

General

Ohmsett (Oil and Hazardous Materials Simulated Test Tank) is the world's largest tow/wave tank designed to evaluate the performance of equipment that detects, monitors, and cleans up oil spills under environmentally safe conditions. Ohmsett is located on the waterfront of the Naval Weapons Station Earle, in New Jersey. The facility is maintained and operated by the U.S. Department of the Interior, Minerals Management Service (MMS) and is open year-round for use by industry, academia, and

Results

Oil recovery rate was defined in terms of the net amount of oil recovered per unit time (in liters per minute). The amount of recovered oil was estimated by subtracting the volumes of free and emulsified water from the volume of the total recovered product. The estimated experimental error in determining the recovery rate is ±0.5 l/min or less for all experimental runs. Fig. 2 shows the recovery rate and composition of fluid (oil and water) using various drams at 40 rpm.

In most cases, net oil

Conclusions

The full-scale oil spill recovery tests with oleophilic drum skimmer showed that:

•
The material on the recovery surface can affect the recovery rates. For a thicker oil slick and low viscosity oil, the Neoprene drum was slightly more efficient than aluminum or polyethylene drums. For 25 and 50 mm oil slicks, the difference between materials was about 20%. The difference between materials was much more pronounced in the case of 10 mm oil slick (up to 100%). For thin slicks, polyethylene was found to

Acknowledgements

This project was funded by the U.S. Minerals Management Service (US MMS) through Contract 1435-01-04-RP-36248, the University of California Toxic Substances Research and Teaching Program and a seed grant from the UCSB Academic Senate. The authors would like to thank Mr. Joseph Mullin for his support and advice in this project. The authors also would like to thank personnel of the Ohmsett National Oil Spill Response Test Facility for their support during the field tests and Elastec/American

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Effect of operational parameters on the recovery rate of an oleophilic drum skimmer

Abstract

Introduction

Section snippets

General

Results

Conclusions

Acknowledgements

Mar. Pollut. Bull.

J. Colloid Interface Sci.

Improvement in at sea combating techniques over the last 20 years: dispersion and mechanical oil recovery

Experimental study and improvement of the rotating disc skimmer

Offshore testing of booms and skimmers