Reaping the benefits of sludge processing

Apart from the obvious environmental benefits of recovering hydrocarbons from their crude oil sludge, many oil tank owners are also discovering significant commercial benefits. Mr. Steve Scott, explains how sludge processing can generate additional revenues.

Where there’s muck there’s brass
In the UK there is a saying: ‘Where there’s muck there’s brass’. Generally, this is understood to mean whenever there is a horrible mess, there is money to be made. Never is this more true than with crude oil sludge.

Crude oil constitutes a wide range of hydrocarbons from methane gas to high molecular weight aliphatic and aromatic waxes. In the formation of oil, subject to geothermal temperatures and pressure, the majority of these waxes are in solution.

You may discover a fortune in your sludge. Recovering the hydrocarbons often represents more than the costs of cleaning the tank.

In storage, however, our oil is subjected to ambient conditions, for example 20 degrees Celsius and atmospheric pressure. Under these conditions, a proportion of the waxes will tend to crystallise out of solution and, combining with water, sand, scale, rust and the like, will form what we commonly call ‘sludge’ on the floor of the storage tank.

“Where there”s muck there”s brass”. Sludge inside a tank.

Tank volume: ca. 600,000 bbl (approx. 100,000 m³)
Tank diameter: ca. 80 metre
Sludge volume: ca. 2000 m³

This is fairly light deposition; some tanks contain up to 15,000 m³ of sludge. These tanks reveal additional problems as sludge levels of this magnitude exceed the roof landing height. In this example, you may be surprised to learn that 2000 m³ of sludge in an 80m-diameter tank equates to a level profile depth of only 0.4 metres (ignoring the floor cone).

Our sludge in the tank will analyse at approximately 5% BS & W; not suitable for processing, and even worse, is likely to be semi-solid in nature making transfer difficult, if not impossible. Proprietary separation systems can recover the majority of the valuable hydrocarbon in a useable form.

Let us assume that our separation system can recover a fairly conservative 90% of the available hydrocarbons:

2000 m³ sludge containing 95% hydrocarbons = 1900 m³ hydrocarbon

Assuming 90 percent of these hydrocarbons are recovered, this gives a recovered volume of:
1900 x 90%=1710 m³, or approximately 10,500 bbl.

Today’s crude oil price is USD 28.9 per bbl.

Our recovered oil is therefore worth approximately USD 300,000.

Processing Cost
It is almost impossible to arrive at an average figure for sludge processing. Parameters such as the choice of two-phase or three-phase processing, location, local conditions and the physico-chemical characteristics of the sludge will all affect the cost. In my experience, costs can vary between USD 10 and USD 20 per bbl. Even at the high end, the hydrocarbon recovery element of your tank refurbishment programme can be seen to be self-financing.

Alternative solutions
It has become increasingly difficult to define an alternative to sludge processing that is both environmentally acceptable and not restrictively expensive. Reduce, recycle an recover are the three R’s of our industry. Sludge processing for hydrocarbon recovery and waste minimisation meet all of the criteria for sound environmental management as well as providing a considerable commercial bonus.

Published: 2004-03-17

Oreco A/S . Oldvej 1A . DK-3540 Lynge . Denmark . TEL. +45 4332 0200 .

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