Tanker cleaning water

Cleaning tankers before periodical maintenance involves the use of powerful hydraulic jets to scour off thick crusts of viscous bitumen- or asphaltic-base slops. Sometimes massive amounts of detergents (0.1 to 3 g-T ) must be used and sometimes the water must be heated or alkalinized. 

This effluent involves very small volumes (0.2 to 4 m h ), but it is very rich in Na salts, in phenols and in S. This precludes dilution and necessitates independent treatments which are discussed in Chapter 4. 

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In oil-containing aqueous effluents the oil is present as finely dispersed droplets in a relatively clean water phase, for example oilfield produced water, refinery process water, ballast water from cargo tankers [32]. Factors preventing coalescence include the droplet s negative electrostatic charge, stabilisation by surface active components and steric stability caused by fine solids. 

The transport of phthalates by road tankers and ships within Europe is carried out by international companies with sophisticated tank cleaning facihties. Wash waters from these modem faciUties are passed through a series of separators to remove any residual plasticizer which is then incinerated. It is estimated that, as a result of cleaning and spillages, the maximum emission to the environment is 80 t/yr. 

Temperature control Adequately sized pressure relief Elimination of contaminants, including metallic residues, from process streams and equipment Selection of materials of construction compatible with the chemicaKs) in use, properly cleaned and passivated Elimination of ingress of reactive chemicals, e.g. water, air Date labelling and inventory control in storage Cleaning and inspection of reusable containers, tankers etc. before refilling ... 

These are relatively clean processes because care is taken to avoid loss of product through spillage. The primary source of waste material is from the washing of railroad tank cars or tankers prior to loading finished products. These wash waters are high in emulsified oil. 

In recent years there have been many oil tanker disasters, just like the one shown in Figure 2.20. These have resulted in millions of litres of oil being washed into the sea. Oil and water do not mix easily. They are said to be immiscible. When cleaning up disasters of this type, a range of chemicals can be added to the oil to make it more soluble. This results in the oil and water mixing with each other. They are now said to be miscible. The following techniques can be used to separate mixtures of liquids. 

Bilge washings—Hydrocarbon-contaminated water that results from cleaning of the petroleum-holding compartments of a tanker, and that may be discharged to the environment. 

Several industrial systems involve emulsions, of which the following are worthy of mention. Food emulsions include mayonnaise, salad creams, deserts, and beverages, while personal care and cosmetics emulsions include hand creams, lotions, hair sprays, and sunscreens. Agrochemical emulsions include self-emulsifiable oils that produce emulsions on dilution with water, emulsion concentrates with water as the continuous phase, and crop oil sprays. Pharmaceutical emulsions include anaesthetics (O/W emulsions), hpid emulsions, and double and multiple emulsions, while paints may involve emulsions of alkyd resins and latex. Some dry-cleaning formulations may contain water droplets emulsified in the dry cleaning oil that is necessary to remove soils and clays, while bitumen emulsions are prepared stable in their containers but coalesce to form a uniform fihn of bitumen when apphed with road chippings. In the oil industry, many crude oils (e.g.. North sea oil) contain water droplets that must be removed by coalescence followed by separation. In oil slick dispersion, the oil spilled from tankers must be emulsified and then separated, while the emulsification of waste oils is an important process for pollution control. 

In February of 1976, there was a fire onboard the tanker "San-Peter" carrying 33 thousand tons of petroleum as it was navigating its way from Peru to Colombia. The vessel sank and the petroleum content poured into the sea. The seamen from Colombia tried unsuccessfully for ten days to clean the waters in the area of the disaster. 

Supply of Sea Water. Sea water was collected from Port Phillip Bay at Frankston, Victoria, some 30 miles from Melbourne, the nearest point to the laboratories at which clean sea water of salinity approximating that of standard sea water (1) could be regularly obtained. The water was transported in 3000-gallon batches by road tanker and delivered into two large rubber-lined tanks at the laboratories. Analyses of the batches over a period of two years gave the results reported in Table I. 

The source of the pollution of the hydrosphere by constituents of the oil are of different origin. They begin at the site of petroleum exploitation itself (on land as well as in the sea), then during transport, when the water of oceans is polluted by fairly frequent breakdowns and occasional ship-wrecks. For example, in the wreck of the oil-tanker Torrey Canyon in 1967, 118,000 t of oil was spread on the surface of the English Channel. Within this ecological disaster 25,000 sea birds died. The use of cleaning preparations turned out to be even more harmful for the sea life than the... 

Though there do not seem to be any generally available technical reports, there are genuine stories of explosions and burn accidents caused by the inadvertent formation and subsequent decomposition of hydrates of hydrocarbons in railway tank cars in the cold climate of Canada. Incidents occurred due to the practice of washing empty tank carr following their use for transporting liquid hydrocarbons. In a cold winter climate, it is possible to form hydrates with small amounts of hydrocarbon residues, which later decompose when the tank car warms up, e.g., when exposed to sunshine. For example, the clathrate hydrate of isobutene (2-methyl-propene, b.p. -6.9" C) needs only 1.12 bar at 273 K to be stable. Precautions were not taken around such nominally clean and empty tankers, and exposure to sparks or naked flames led to flash fires and explosions. While the main content of the tankers was butane, other hydrocarbons were present. In another kind of industrial accident, a worker was killed by H2S gas liberated from H2S hydrate residue in a heavy water production plant, during a shutdown for maintenance. 

Before loading a clean product it is standard practice to check the internal dryness and cleanliness of a tanker, but it is also important if loading a hot water-immiscible material (e.g. a distillation residue) to ensure that a tanker is dry, since a foam-over can occur if water beneath such a material boils. 

A flexible supply of clean running water must be available where tankers are off-loaded and where hypochlorite is handled or used. Provision of an emergency shower is essential. 

QUESTIOM Oil tankers that transport oil to refineries have sometimes run aground, resulting in the spilling of oil into our oceans. Does the oil mix with the water Would the addition of soap be an effective way to clean up an oil spill Why or why not ... 

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