Gravity settling tanks, water

Probably more relevant to the chemical industry is the scale-up of thickeners. Thickeners are basically gravity settling tanks that, apart from producing a clear overflow, are designed to have a thick underflow with as Htfle water content as possible. The feed into a thickener is generally more concentrated than the feed into a clarifier, and quite often exhibits zone-settling behavior because of the appHcation of flocculants. 

Separation of two liquid phases, immiscible or partially miscible liquids, is a common requirement in the process industries. For example, in the unit operation of liquid-liquid extraction the liquid contacting step must be followed by a separation stage (Chapter 11, Section 11.16). It is also frequently necessary to separate small quantities of entrained water from process streams. The simplest form of equipment used to separate liquid phases is the gravity settling tank, the decanter. Various proprietary equipment is also used to promote coalescence and improve separation in difficult systems, or where emulsions are likely to form. Centrifugal separators are also used. 

Chemical additives are demulsifiers generally injected in the oil upstream of the dehydration system. The use of demulsifiers with a gravity separation device such as a three phase separator or settling tank can successfully remove as much as 95 percent of the produced water present in the oil. Removal of the remainder of the water droplets through... 

The principle of a simple continuous lime-soda softener is shown in Fig. 8.4 to 8.6. There are four essential features a chemical measuring device, a reaction chamber, a settling tank, and a filter. The hard water enters through a feed pipe into one of the compartments of the tipping bucket (Fig. 8.4). When the compartment is full the centre of gravity is... 

As all skimmers recover some water with the oil, a device to separate oil and water is usually required. The oil must be separated from the recovery mixture for disposal, recycling, or direct reuse by a refinery. Sometimes settling tanks or gravity separators are incorporated into skimmers, but separators are more often installed on recovery ships or barges. Portable storage tanks are often used as separators, with outlets installed on the bottom of the tanks so that water that has settled to the bottom of the tank can be drained off, leaving the oil in the tank. Vacuum trucks are also used in this way to separate oil and water. Screens or other devices for removing debris are also incorporated into separators. 

The raw water, enriched with flocculant chemicals, flows into the bottom part of the reaction tank, causing an upward spiral current. The settled matter in the form of a sludge is periodically removed from the reaction tank by means of a ring conduit placed near the bottom of the settling tank. The pre-clarifled water then flows down into the automatic gravity filter from the top of the water surface level of the reaction tank. By its own head the water moves down through the Alter layer and out to service. 

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