Tank bottoms get less crude

Reducing the amount of carbon in petrochemical sludges dramatically reduces their disposal costs and environmental impact. Ondeo has refined its analysis techniques to help a range of producers achieve this.

Ondeo Industrial Solutions (OIS), part of French company Suez, has trialled a sludge separations technique that combines centrifugation and a chemical treatment developed by its partner company, Surface Active Solutions (SAS).

The technique is being employed to exploit the potential for reducing sludge disposal costs and providing environmental benefits. In this age, it is essential for companies to explore new methods and techniques to address environmental challenges and reduce their impact on the environment.

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.

To give an idea of the problem, Europe produces about 650,000m3 of tank bottoms every year. It generally contains water, crude oil and solid particles in various proportions depending on its origin.

The oil component is made up of a variety of compounds that can include free oil, waxes and asphaltenes. And it is these substances that contribute most significantly to the residual percentage of 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, among other parameters, is below the 6% necessary under the waste acceptance criteria (Wac) required for hazardous landfill disposal. The Wac are analytical parameters used to define a quality of a sludge or solid waste.

Normally, hazardous waste must only be disposed of to a hazardous waste landfill. But, 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, among other parameters, is less than 5%. Doing this potentially halves sludge disposal costs.

Therefore, the key to 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, OIS has focused on removing the residual free oil.

Growing concerns about 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.

OIS manages and optimises water systems on various refinery and petrochemical sites in the UK and Europe, and has been investigating different methods of Toc reduction in tank bottoms.

The most promising technology was combining the SAS super concentrate MicroEmulsion products, with high-speed decanting centrifuge separation.

Initial trial results have been promising, says OIS, with considerable free oil removal. But they have not quite achieved the 5% Toc levels on the particular sludge involved because of the residual wax and asphaltene content.

All tank bottoms have different compositions depending on their origins. Therefore, with results being so close to achieving SNRHW status, OIS realised that improved analysis techniques would be needed to differentiate between free oil, waxes, asphaltene and solids.

As a result, the company has developed a tool box of analysis techniques. Oil removal techniques, such as solvent washing, may dissolve some of the solid components of the sludge sample, so a bench scale centrifuge method was developed to accurately account for all the solids in the tank bottoms.

Results suggested that the bench centrifuge provided a quick, convenient and reliable method to determine sludge solids content. In addition, the development of a safer separation system is seen as a major improvement in managing tank bottoms waste in the oil and petrochemical industry.

Overall, OIS and SAS have made progress in developing a safer separation system, reducing tank bottoms’ Toc levels to meet SHRHW status. With the continued investment in one of the UK’s first gas purged and heated centrifuges, analysis techniques and further micro-emulsions testing, they hope to be able to treat a wide variety of tank bottoms from different refineries across Europe in the near future.

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