12. Filtration. Filters

Filtration, In many industrial processes it is necessary to separate finely divided solid materials

from liquids. 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 44

purifying the liquid. Many types of filter 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.

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. 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 fiber, porous carbon and other solids, rayons and other synthetics, porous rubber, etc.

Filters. Filters used in chemical processing are classified into two distinct groups: continuous and intermittent.

Continuous filters. 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.

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 (1-1 mm) 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.

It is estimated that over 25 000 rotary drum filters are in operation worldwide at present.

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 ' -

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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.

Intermittent filters. 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.

Words and word combinations :

1. medium - среда, вещеса?во filter medium - фильтрующая среда

2. recovery - восстановление

3. for the sake of - ради, для

4. to purify - очищать

5. in respect to - в отношении

6. mixture - смесь

7. slurry - суспензия

8. septum- септа, перегородка

9. to accumulate - накапливаться accumulation -накопление, скопление

10. filter cake - осадок после фильтрования

11. continuous filter - аналоговый фильтр intermittent filter - импульсный фильтр

12. interruption - остановка, перерыв

13. rotary drum filter - ротационный барабанный фильтр

14. means (pi.) - средство, способ

15. soluble - зд.: растворимый компонент

16. clarified effluent - очищенный поток

17. sticky -липкий, клейкий

18. sludge - отстой

19. unit - агрегат

20. to designate - определять

21. to discharge - разгружать

Answer the following questions :

1. What does the process of filtration consist in?

2. What is the purpose of the filtration process?

3. What is called the slurry (filtrate, filter medium, filter cake)?

4. What are filter media manufactured from?

5. What two groups of filters do you know?

6. How do continuous filters operate?

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

8. What do you know about the varying filtration characteristics of slurries?

9. How many rotary drum filters are in operation worldwide' at present?

10. What do you know about the design of a rotary disk filter? ■

11. How do intermittent filters operate?

Exercises I. Translate into Russian paying attention to the word

1. It was known long ago that oil could be used as a raw materi-al.

2. As the evaporation continues, the temperature of the water gradually drops.

3. He works a£ a turner.

4. This experiment is as interesting as the previous one,

5. As this question is of outmost importance, we shall discuss it at once.

^' As to me I prefer to spend my vacation in the South. 7. Filters that operate without interruption are known as continuous filters.

II. Translate the sentences into Russian. Mind the . Gerund and Gerund Groups:

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1. Solid bodies have the property of keeping their shape.

2. Upon being heated, the molecules begin moving very quickly.

3. Without being treated this substance cannot be used.

4. At last our research-workers succeeded in getting good results.

5. The teacher insists on carrying out this experiment in our laboratory.

6. Upon carrying out a number of experiments oar students solved many interesting problems.

7. Heating the wire from 0° to 100° increases the resistance

approximately by 4 0%,

8. They finished looking through the papers as soon as they had found the article concerned.

9. The engineer told us about his having invited to that research institute.

10. She engineer having constructed a new type of a filter was

not known to us,

11. We know of the new laboratory having been built in our institute. 12. We were surprised at Peter's having got an excellent mark in physics.

III. Use the following sentences in all the forms and tenses adding suitable adverbial modifiers where necessary:

1. Many new enterprises are built in Siberia.

2. Our engineers develop new devices.