Petroleum review

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Courtesy of SAS Environmental Services Ltd

In an era highly focused on climate change and the importance of reducing environmental footprints, the refinery and petrochemical industry is faced with growing political, economic, demographic and environmental challenges. It is essential for refining and petrochemical companies to explore new methods and techniques to address these challenges and reduce their impact on the environment.

As part of this drive, UK-based Ondeo Industrial Solutions (SUEZ) has trialled a new sludge separations technique combining cen-trifugation and a chemical treatment, developed with Surface Active Solutions (SAS). The technique has already been used both on- and offshore on drilling mud related waste streams and is now being brought downstream to reduce sludge disposal costs and provide environmental benefits to the refining and petrochemical sector.
Since crude oil was first processed in the mid 1800s, the refining of oil has produced waste by-products and residual materials. These are mixed together and are usually referred to as 'tank bottoms', which need to be disposed of. There is approximately 650,000 cm of tank bottoms produced every year in Europe, according to Ondeo.

Waste regulations
Tank bottoms generally contain crude oil. water and solid particles in various proportions depending on its origin. The oil component is made up of a wide variety of compounds that are classified into free oil, waxes and asphaltenes. It is the waxes and asphaltenes that under normal circumstances act as solid components and are not removed in conventional oil/solids techniques such as non-chemically enhanced centrifugation. It is these substances that contribute most significantly to the residual percentage total organic carbon (TOC) in dewatered sludges.

The European Hazardous Waste Directive classifies tank bottoms as hazardous waste and can only be landfilled if its TOC is below the 6% necessary under the waste acceptance criteria that is required for landfill disposal. Normally, hazardous waste must only be disposed of to a hazardous waste landfill; however, if the quality of the waste can be improved, it can be classified as stable non-reactive hazardous waste (SNRHW) as long as the TOC is less than 5%. By doing this, it halves sludge disposal costs.

The key to substantially lowering disposal costs is to reduce the amount of free oil, waxes, asphaltenes and water so that the solids fraction can be disposed of at a SNRHW landfill. As a large percentage of the TOC comes from the free oil and high molecular weight waxes and asphaltenes that are difficult to break down and remove, Ondeo has focused on removing the residual free oil.

Growing concerns over hazardous landfill sites and their decreasing capacity has led to increased landfill taxes and regulations, and industrial waste producers need to find alternative waste disposal methods or implement waste reduction processes.

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