yashchuk_tsepkalo (1)

8.Pick up the key words from the text “Industrial dryers”. Make up your own sentences with them.

9.Write an abstract to the text “Industrial dryers”.

10.Get ready for presenting the topic “Industrial dryers” at the conference ”Innovations in Science and Engineering” based on the following questions of Task 4.

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LESSON 4

1.Read and memorize the following word and word combinations:

3.Read and translate the text into Ukrainian.

Filtration and filters

In many industrial processes it is necessary to separate finely divided solid materials from liquids. Filtration is a mechanical or physical operation which is

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used for the separation of solids from fluids (liquids or gases) by interposing a medium through which only the fluid can pass. Filtration is also important and widely used as one of the unit operations of chemical engineering. It may be simultaneously combined with other unit operations to process the feed stream. The process of filtration consists in passing the liquid through a porous medium, which retains the solid particles. In some cases the recovery of the solid material is the main object; in others the filtration is done for the sake of purifying the liquid.

The mixture to be separated is called the slurry: the fluid that passes through the septum is called the filtrates and the septum is called the filter medium, and the equipment assembly that holds the medium and provides space for the accumulated solids is called a filter. The fluid may be a gas or a liquid. The solid particles may be very fine, and their concentration in the suspension may be extremely low (a few parts per million) or quite high (>50%).

When the separated solids accumulate in amounts that visibly cover the medium, they are called the filter cake or simply the cake.

Filter media are manufactured from cotton, wool, linen, silk, glass fibre, porous carbon and other solids, rayons and other synthetics, porous rubber, etc. Many types of filters are in use today. They differ in respect to the various materials which are available for filtration, and the construction of the apparatus in which these are applied.

Filters used in chemical processing are classified into two distinct groups: continuous and intermittent. Filters that operate without interruption for weeks to months are classified as continuous filters. The main types are the rotary drum and disk filters and various horizontal designs.

Rotary drum filters are the most widely used continuous filters in the chemical process industries. The design provides means for concentrating slurry solids to dry (moist) cakes, washing solubles from such cakes when required, and producing a clarified effluent.

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Many design configurations have been developed to utilize most effectively the basic principle for the varying filtration characteristics of slurries, ranging from extremely fine particles to very coarse particles (50 - 150 mm) and from thin, sticky cakes to thick, fairly dry sludges. These filters are used in some form in practically every process operation involving slurries where solids must be recovered from the liquor for further processing.

Rotary disk filter is a version of the rotary drum filter. A series of parallel disks provides vertical filtering surfaces in place of the cylindrical surface on the rotary drum. Thus, the rotary-disk unit provides more filter area (up to 3.5 times) than a drum type. When the filtering surface operates in a horizontal plane, the filter is designated as a horizontal type.

Filters whose continued vibration is limited by their solid-collecting capacity are known as intermittent filters. Their cycle must be interrupted periodically when the solids accumulation has to be discharged.

3.Answer the questions to the text:

1.What is filtration? What does the process of filtration consist in?

2.Why may filtration be combined with other unit operations?

3.What is the main object of filtration?

4.What is a filter?

5.What is a filter cake?

6.What are filter media manufactured from?

7.What are continuous filters? How do continuous filters operate?

8.What are the main types of continuous filters?

9.What does the design of a rotary drum filter provide?

10.What are intermittent filters? How do intermittent filters operate?

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4.Match the words from the text with their synonyms on the right:

5. Fill in the gaps with the words from the text and translate them into

Ukrainian:

Ukrainian translation

1.to process the feed __________

2.to provide __________ for the accumulated solids

3.visibly cover __________

4.two __________ groups

5.operate without __________

6.various __________ designs

7.producing __________ effluent

8.must be recovered from __________

liquor

9.solid-collecting __________

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6.Change the following sentences according to the model.

Model A: People can use heat, electricity and light for many purposes.

B: People are able to use heat, electricity and light for many purposes.

1.We can produce heat by means of chemical action.

2.Chemists could obtain coke by heating coal in special forms of apparatus.

3.The workers can use this motor to drive compressors tomorrow.

4.Geologists could find oxides of many elements in the earth’s crust.

5.We can consume great quantities of oxygen in the burning of coal and wood.

7. Work in pairs. One of the student is a journalist from a scientific journal whose task is to write an article about innovative solutions to the filtration in industrial processes. The second student to be interviewed is an engineer working on filtration equipment design. Think over possible questions and answers. Act the interview out.

7.Pick up the key words from the text “Filtration and filters”. Make up your own sentences with them.

8.Write an abstract to the text “Filtration and filters”.

9.Get ready for presenting the topic “Filtration and filters” at the conference ”Innovations in Science and Engineering” based on the following questions of Task 3.

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LESSON 5

1.Read and memorize the following words:

2.Read and memorize the following word combinations

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3.Read and translate the text into Ukrainian.

Centrifuges

A centrifuge is a piece of equipment, generally driven by a motor that puts an object in rotation around a fixed axis, applying force perpendicular to the axis. The centrifuge works using the sedimentation principle, where the centripetal acceleration is used to separate substances of greater and lesser density.

The first successful centrifuge was built in 1883 by Carl G. P. de Laval, a Swedish engineer, whose design was used chiefly for cream separators. The ultracentrifuge, devised in the 1920s by the Swedish chemist Theodor Svedberg, found wide application in scientific research.

A mechanical method of separating immiscible liquids or solids from liquids by the application of centrifugal force. This force can be very great, and separations which proceed slowly by gravity can be speeded up enormously in centrifugal equipment.

Centrifugal force is generated inside stationary equipment by introducing a high-velocity fluid stream tangentially into a cylindrical-conical chamber, forming a vortex of considerable intensity.

Much higher centrifugal forces than in stationary equipment are generated in rotating equipment (mechanically driven bowls or baskets, usually of metal, turning inside a stationary casing). Rotating a cylinder at high speed induces a

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considerable tensile stress in the cylinder wall. This limits the centrifugal force which can be generated in a unit of a given size and material of construction. Very high forces, therefore, can be developed only in very small centrifuges.

There are two major types of centrifuges: sedimenters and filters. A sedimenting centrifuge contains a solid-wall cylinder or cone rotating about a horizontal or vertical axis. An annular layer of liquid, of fixed thickness, is held against the wall by centrifugal force; because this force is so large compared with that of gravity, the liquid surface is essentially parallel with the axis of rotation regardless of the orientation of the unit. Heavy phases “sink” outwardly from the centre, and less dense phases “rise” inwardly. Heavy solid particles collect on the wall and must be periodically or continuously removed.

A filtering centrifuge operates on the same principle as the spinner in a household washing machine. The basket wall is perforated and lined with a filter medium such as a cloth or a fine screen; liquid passes through the wall, impelled by centrifugal force, leaving behind a cake of solids on the filter medium. The filtration rate increases with the centrifugal force and with the permeability of the solid cake. Some compressible solids do not filter well in a centrifuge because the particles deform under centrifugal force and the permeability of the cake is greatly reduced. The amount of liquid adhering to the solids after they have been spun also depends on the centrifugal force applied; in general, it is substantially less than in the cake from other types of filtration devices.

There are many different kinds of centrifuges, including those for very specialised purposes. The decision to use either a batch or a continuous machine depends on several factors. Unlike batch centrifuges, continuous machines are limited to a wash/solids ratio of approximately 10%, with only a short period allocated to the wash zone prior to the finish of the cycle.

If, for example, the material to be processed has low residual impurities and a high washing requirement, the greater flexibility of the batch process

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allows the necessary adjustments such as extended washes and longer residence times.

Particle size, distribution and shape are also important factors when determining separation capabilities, and whether a batch or continuous centrifuge is the best option. Generally speaking, materials of 45 microns and above that are relatively incompressible are highly suitable for separation by filtration. On the other hand, finer or more compressible materials lend themselves to separation by sedimentation techniques.

Compared with other methods of liquid-solid separation, centrifugal processing provides a number of unique advantages. For example, centrifuges can be installed in a relatively small footprint, have a high washing capability, produce low cake moisture, achieve a high capacity throughput and provide the end user with a totally enclosed, vapour tight processing system.

4.Answer the questions to the text:

1)What is a centrifuge?

2)What was the first successful centrifuge used for?

3)How can separations be speeded up enormously in centrifugal equipment?

4)In what way is centrifugal force is generated?

5)What does rotating a cylinder at high speed induce?

6)What is the design of a sedimenting centrifuge?

7)What is the principle of action of a filtering centrifuge?

8)What are the advantages of batch machines?

9)What factors are important when determining separation capabilities, and whether a batch or continuous centrifuge is the best option?

10)What are the advantages of centrifugal processing compared with other methods of liquid-solid separation?

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