OIL SPILL SKIMMERS

References

1.0 INTRODUCTION

This section describes skimmer types, how they are used, and the general level of performance that can be expected of each type. This follows the format of earlier editions, but there are some important changes in how the information is organized. Specifically, there is more detail to skimmer definitions, and they now more closely follow those contained in the American Society for Testing and Materials (ASTM) Standard F1778 [1], which were adapted from the definitions used in previous editions of the World Catalog.

As in previous editions, skimmers are shown in sections according to their expected use in Calm Water, Protected Water, and Open Water. As before, categorizing skimmers in this way can be a difficult process. For containment booms there are clear rules for classification based on the physical characteristics of the boom. These rules have been recorded and published in an ASTM Standard. With few exceptions, classifying booms is relatively easy; classifying skimmers can be more difficult.

Very large, dedicated skimming vessels are obviously intended for use in Open Water. Small, hand-deployed units are just as obviously intended for Calm Water. However, there are a great many devices between these two extremes that can be used in more than one environment. For recent editions of the Catalog we have completed an extensive review of how skimmers have been classified and how they should be classified. Although we have not developed precise rules that can exactly classify every device, we have developed tables that describe every skimmer type listed in the Catalog. While the system is not perfect, it does provide good guidance for the classification process. In spite of the many skimmer characteristics that can be considered for classification purposes, size and weight are dominant considerations. The other defining feature can be the type of skimming element that is used and how it responds to wave conditions.

In recent editions there have been some important changes to the skimmers data sheets. These are described at the end of this section with the information about data sheets, but since these changes are important and of continuing interest, they are mentioned again here.

There is a data entry row showing skimmer application, which is designated as Self-Propelled, Stationary, Advancing, and Stationary / Advancing. This will help the user of the Catalog understand the intended use of the skimmer. Use of standard phrasing also allows easier use and better functionality in our Database.

In earlier editions skimmer pumping rate and recovery rate were reported in gallons per minute (gpm). This is now the more universally used barrels per hour (bbl/h), and cubic metres per hour (m³/h). On the skimmer data sheets, storage capacity is reported in barrels and spill encounter rate in barrels per hour. It is therefore more convenient to have these other capacities also in bbl/h so that requirements can be compared and computed more easily. The conversion to gallons per minute is easy (bbl/h = gpm x 0.7), and this is noted on each data sheet.

Finally, we have deleted the data sheet entry that indicated the sea state in which the equipment could operate. We found that sea state is not well understood by many Catalog users and that sea state use claims were often overstated by manufacturers. Since skimmer use is already separated according to the standard environments, we believe that sea state identification does not provide any additional useful information.

The format for this section follows a familiar pattern. Specifically, the following will be considered:

• Skimmer types
• Factors that affect skimmer performance
• Skimmer definitions and selection criteria
• Test results

Notice that the section with skimmer definitions includes selection considerations. In the past these were termed advantages and disadvantages, which can be highly subjective in that an advantage for one user may be a disadvantage for another. In spite of this fact, each device has characteristics and capabilities that should be noted. Therefore, Selection Considerations have been substituted for Advantages and Disadvantages, and the user can decide what is an advantage and disadvantage for their application. This follows the practice in ASTM Standard F1778 for the selection of skimmers.

We also identify skimmers intended for industrial use. Most of these are dual-purpose skimmers suitable for industrial applications as well as for Calm Water and Protected Water spills. As a result, industrial skimmers are identified on the data sheets in the Calm Water and Protected Water sections of the Catalog. To help the user find the equipment needed, there is an Industrial Skimmers index.

Vessel-of-opportunity skimming systems (VOSS) are also identified on data sheets. These are designed for use on a variety of vessels that may be pressed into service during a major spill.

Skimmer Test Data. In previous editions we have summarized recent test data. That has been removed from this edition, and will be archived on the Catalog website in the future. We have replaced this section with a summary of new developments in the field, including an improved design of drum-type skimmers, development of skimmers for oil recovery in ice environments, and the development of a standard test method for determining the nameplate recovery rate of a skimmer.

A book completely devoted to skimmer test data was recently published in cooperation with ASTM. Oil spill response professionals have long recognized the requirement to estimate the likely performance level of various kinds of skimmers using controlled test data. To date this has generally not been possible because test data have not been assembled, analyzed, and summarized for general use. Recognizing this requirement, the ASTM F20 Committee on Hazardous Substances and Oil Spill Response authorized the preparation of the Oil Spill Response Performance Review of Skimmers. This Review is a volume of about 150 pages containing fifteen chapters, one for each skimmer type. Each chapter reviews all available test reports for a skimmer type, analyzing data and using results to suggest the likely performance of that skimmer in the environmental conditions tested. An appendix provides a summary of results by skimmer type providing the user with quick access to information on any skimmer type desired. Data in this Review can be used to determine areas where additional research and development is required, and in some cases, to estimate the performance of skimmer types in certain environments.

Robert Schulze, founder and former editor of the World Catalog, authored the Performance Review of Skimmers. It can be ordered through the ASTM publications section (contact info at end of this chapter).

(Thirty pages of text and references followed by sixty-six pages of skimmer data listings)