Unit eleven Air pollution control

Exercise 1. Train the reading of the following words, phrases and abbreviations.

items, devices, either, exhaust, SO2 emission, cyclonic, gravity, mixtures, variety, furnace, liquid, desulfurization, advantage, semidry, easier, expensive, initially, slurry, atomize, evaporates, neutralizes, alkali, precipitator, efficiency, ESP, induced, charge, impede, periodically, concentration, ppm, Refrigerated Vapour Condensation, Solvent Vapour Adsorption, flaring, chosen, allowable, option, reserved, expensive, bubbled, partial vacuum, incineration, regenerative, adsorption, exchanger, preheat, incinerator, activated, pressure, achieve, effectiveness, hundred, per million, conventional, target, catalytic, reduction, SCR, injected, ratio, tendency, carriers, Exxon, DeNOx, optimum.

Exercise 2. Guess the meaning of the words without a dictionary.

transportation, cyclone, separator, rotational, spray, desulfurization, medium, soda, atomize, evaporate, neutralize, electrostatic, precipitator, fabric, minimally, periodically, offline, condensation, adsorption, vacuum, regenerate, pressure, selective, catalytic, reaction, optimum.

Exercise 3. Read and translate the text. Choose an abstract of ten lines and get ready to read it aloud.

Air pollution control

The following items are commonly used as pollution control devices by industry or transportation. They can either destroy contaminants or remove them from an exhaust stream before it is emitted into the atmosphere.

Particulate and SO2 Emissions

A. Cyclone Separators

Cyclonic separation is a method of removing particulates from an air, gas or liquid stream, without the use of filters, through vortex separation. Rotational effects and gravity are used to separate mixtures of solids and fluids. The method can also be used to separate fine droplets of liquid from a gaseous stream.

B. Scrubbers

The term describes a variety of devices that use pollutants from a furnace flue gas or from other gas streams. In a wet scrubber, the polluted gas stream is brought into contact with the scrubbing liquid, by spraying it with the liquid, by forcing it through a pool of liquid, or by some other contact method, so as to remove the pollutants. The most common application is flue gas desulfurization using ammonia as the solvent or spray liquid.

C. Semidry Scrubbers

The advantage of semidry scrubbers is in that they remove contaminates by way of a solid waste that is easier to dispose of and less expensive. Initially, the scrubbing medium is wet (such as a lime or soda ash slurry), and a spray dryer is used to atomize the slurry into the gas which evaporates the water in the droplets. As this takes place, the acid in the gas neutralizes the alkali material and forms a fine white solid. Most of the white solids are removed at the bottom of the scrubber while some are carried into the gas stream and have to be removed by a filter or electrostatic precipitator. Although semidry systems cost 5-15% more than wet systems, when combined with a fabric filter, they can achieve 90-95% efficiencies.

D. Electrostatic Precipitators

An electrostatic precipitator (ESP) or electrostatic air cleaner is a particulate collection device that removes particles from a flowing gas (such as air) using the force of an induced electrostatic charge. Electrostatic precipitators are highly efficient filtration devices that minimally impede the flow of gases through the device, and can easily remove fine particulate matter such as dust and smoke from the air stream. Periodically, the precipitators have to be taken offline and cleaned.