ΕΛΛΗΝΙΚΗ ΔΗΜΟΚΡΑΤΙΑ

Ανώτατο Εκπαιδευτικό Ίδρυμα Πειραιά

Τεχνολογικού Τομέα

Ξενόγλωσση Τεχνική Ορολογία

Ενότητα: Boiler operation

Παναγιώτης Τσατσαρός

Τμήμα Μηχανολόγων Μηχανικών ΤΕ

Άδειες Χρήσης

· Το παρόν εκπαιδευτικό υλικό υπόκειται σε άδειες χρήσης Creative Commons.

· Για εκπαιδευτικό υλικό, όπως εικόνες, που υπόκειται σε άλλου τύπου άδειας χρήσης, η άδεια χρήσης αναφέρεται ρητώς.

Χρηματοδότηση

· Το παρόν εκπαιδευτικό υλικό έχει αναπτυχθεί στα πλαίσια του εκπαιδευτικού έργου του διδάσκοντα.

· Το έργο «Ανοικτά Ακαδημαϊκά Μαθήματα στο Ανώτατο Εκπαιδευτικό Ίδρυμα Πειραιά Τεχνολογικού Τομέα» έχει χρηματοδοτήσει μόνο την αναδιαμόρφωση του εκπαιδευτικού υλικού.

· Το έργο υλοποιείται στο πλαίσιο του Επιχειρησιακού Προγράμματος «Εκπαίδευση και Δια Βίου Μάθηση» και συγχρηματοδοτείται από την Ευρωπαϊκή Ένωση (Ευρωπαϊκό Κοινωνικό Ταμείο) και από εθνικούς πόρους.

1.Σκοποί ενότητας4

2.Περιεχόμενα ενότητας4

3.Boiler Operation5

3.1Burner matching, control and maintenance5

3.2Feed and boiling water5

4.Comprehension exercises7

4.1Exercise A:Open Questions7

4.2Exercise B:Sentence Completion7

4.3Exersice C:Checking facts and Ideas8

4.4Exercise D: Matching Terms and Definitions9

Σκοποί ενότητας

The aims of this unit are to:

· Provide authentic text and vocabulary specific to the needs of students of Mechanical Engineering

· Encourage students to combine their knowledge of English with their technical knowledge

· Enable students to find out facts about a topic

· Encourage students to make deductions

· Enable students to check facts and ideas

· Help students match terms and definitions

Περιεχόμενα ενότητας

Contents of the unit :

· Burner matching, control and maintenance

· Feed and boiling water

· Objectives of water treatment

· Filling the boiler

· Contact with the atmosphere

· Deposit and Scale

· Foaming

· Corrosion

Boiler OperationBurner matching, control and maintenance

The formulation of the requirements and recommendations of this standard was carried out bearing in mind the need for satisfactory matching of a burner or burners to the boiler. The limitations on furnace heat input related to furnace diameter and on maximum calculated tube plate ligament metal temperature given in section three are intended to ensure reliable service of the boiler unit in an environment of good engineering control and maintenance. It is, therefore, important that the heat input for which the boiler is designed should not be exceeded in service.

It is also important that combustion quality is maintained throughout the life of the boiler in order to obtain efficient operation and to avoid damage to heat transfer surfaces. Particular attention is drawn to the effects of poor fuel/air mixing, which can result in carbon monoxide, generated within the furnace tube, burning at the first tube pass entrance, causing increased metal temperature. A systematic maintenance programme to discover and correct the effects of wear, and loosening and fouling of the combustion equipment is recommended.

Feed and boiling water

· General

The two main functions of a «steam boiler are to transfer heat to the water to produce steam and to separate the steam from the water in the boiler. The boiler can only carry out these functions effectively if the qualities of the feed water and of the boiler water are properly controlled.

· Objectives of water treatment

The objectives of water treatment are to keep those parts of the plant that are in contact with water and steam clean and intact and to facilitate the production of clean steam. The selection, application and control of water treatment should be consistent with these aims.

Steel in contact with water or steam quickly forms upon its surface a film of iron oxide, which may or may not be protective. Water treatment to prevent corrosion should so adjust the quality of the water, that a film of protective oxide is maintained.

· Filling the boiler

On initial start up and on subsequent refilling after the boiler and/or system have been drained down, the boiler and system should be filled only with fully treated water. If the system is a large one, it may be advisable to fill with demineralized water. Before filling the system and boiler, the water should be analyzed and the pH and oxygen scavenger content should be adjusted to conform with table 2 of BS 2486 : 19/8. Neglect of this has been known to cause serious failures with hot water boilers.

· Contact with the atmosphere

It is not correct to assume that a hot water system is fully closed. There will be some leakage from the system, thus requiring make up and, at some stage, system water may be in contact with the atmosphere, e.g. in a header tank or over-flow vessel. The requirements for feed water and boiler water in BS 2486 should be followed.

· Deposit

Impurities introduced into the boiler with feed water can produce scale or other deposits, which impede the transfer of heat and may restrict the flow water. In addition to reducing boiler efficiency, either effect leads to insufficient cooling of the metal heat transfer surface, which may then become so hot, that it is no longer strong enough to withstand the operating pressure. Deposits may also lead to corrosion by shielding the underlying metal from protective conditions in the water-system.

· Scale

Calcium, magnesium and silicon compounds are the main constituents and can form scales of wide differing characteristics with thermal conductivities varying from 216 to 3450 Wmm/(m3 Kp):. In practice this means that some silicon based scales of only 0,1 mm thickness impede the transfer of heat as effectively as a calcium sulphate scale 1,6 mm thick. It is therefore important that any scale build-up is detected and removed as soon as possible. It is essential that the cause also be investigated and corrected as in many instances it is not possible to determine the composition of the scale without chemical analysis. Some silicon- based scales are almost invisible to the naked eye and are detected more easily by the use of a special instrument.

· Foam

There is always a small unavoidable degree of carry over of water with the steam generated from a boiler. However, under certain conditions when contaminants are present the boiler water may foam badly and this can cause the following difficulties:

1. Gross carry-out of boiler water into the steam main can occur. Traps may be overloaded and pipes flooded leading to a dangerous water hammer. Slugs of water traveling at speeds approaching one hundred and fifty kilometers an hour can cause serious damage.

2. Float switches are designed to float in water not in foam. Lockout of the boiler may result from malfunctioning of float switches.

3. Foam in contact with heated surfaces does not conduct heat away from them as

4. Effectively as water. The boiler metal may overheat, perhaps dangerously.

Causes of foam include the following:

1. Detergents, oils, and fats.

2. Excessive alkalinity (this can cause other problems, e.g. chemical attack on gauge glasses).

3. Suspended solids.

4. High total dissolved solids content

· Corrosion

Corrosion is most commonly due to presence of oxygen in the boiler water and it is therefore necessary to ensure that the oxygen content of the feed water is at the lowest possible level. The use of hot feed water and, where economically feasible, the installation of deaeration equipment is recommended, but in all cases a suitable oxygen scavenging agents should be present in reserve in the boiler water at all times, even when the boiler is idle.

· Some modes of failure

Overheating in a boiler can be caused by shortage of water, following the failure of water level controls to operate correctly, the accumulation of scale and internal deposits, which can affect the satisfactory operating of water level controls or the use of contaminated feed.

Comprehension exercisesExercise A:Open Questions

· Answer the questions

1. What is referred to as "burner matching"?................................................................

2. What are the main functions of a steam boiler?.......................................................

3. What is feedwater?..................................................................................................

4. What should water treatment aim at?......................................................................

5. What are the effects of the production of scale or deposits on boiler surface? ................................................................................................................................

6. What happens if the metal heat transfer surface is insufficiently cooled?....................................................................................................................

7. What may scale be formed of?................................................................................

8. Under what circumstances may foam be formed?..................................................

9. What problems may the presence of foam cause?.................................................

10. How may a low level of oxygen content in the feedwater be established? ................................................................................................................................

Exercise B:Sentence Completion

· Finish up the incomplete sentences with information from the text:

1. In order to formulate the requirements and the recommendations of the boiler operation we must: …….…………………………………………………………….

2. We should consider all limitations on furnace heat input in order to guarantee ……………………………………………………………………………………………..

3. Efficient operation and avoidance of damage to heat transfer surfaces can be achieved by ……………………………………………………………………………….

4. Particular attention should be drawn to the effects of poor fuel or air mixing since these ……………………………………………………………………………………….

5. A systematic maintenance program aims at ..…………………………………………

6. The boiler cannot carry out its functions effectively unless .…………………………

7. If we wish to be consistent with the objectives of water treatment, we should ………………………………………………………………………………………………

8. Water treatment to prevent corrosion should so adjust the quality of the water as to……………………………………………………………………………………………

9. Deposits can be produced by …..……………………………………………………….

10. Deposits not only ……………………………………………but also ………………….

11. Shielding the underlying metal of the boiler from protective conditions in the water systems results in …..…………………………………………………………………….

12. Scale must be detected and removed so as not to ..…………………………………

Exersice C:Checking facts and Ideas

· Cheek if the following statements are True or False. Refer to the text to justify your answers.

1. The factor of heat input in the boiler operation is not of great importance to the boiler itself…………………………………………………………………………….

2. Since combustion quality is crucial, particular attention should be paid to it at least at the beginning of the cycle of life of the boiler.

…………………………………………………………………………………………

3. Poor fuel and air mixing are causing dioxides released in atmosphere, thus polluting the atmosphere.

…………………………………………………………………………………………

4. Water treatment is closely related to steam in several different ways.

…………………………………………………………………………………………

5. A film of iron oxide created upon the surface of steel ensures the necessary protection for the boiler.

…………………………………………………………………………………………

6. The simple refill of the boiler with fully treated or demineralized water is the prerequisite for its satisfying operation.

…………………………………………………………………………………………

7. According to the text, the process of filling the system should be carried out following strict specifications and figures.

…………………………………………………………………………………………

8. The operation of a closed hot water system such as the boiler is discourages any leakage……………………………………………………………………………...

Exercise D: Matching Terms and Definitions

· Match the technical terms from the text with their corresponding definitions:

α/α

Question

Answer

1

Combustion

a. a device wherein heat is released, then directly or indirectly transferred to a solid or liquid mass in order to influence a chemical or physical procedure taking place

2

Foaming

b. the damage that happens to an object in normal and ordinary use during a time period

3

Corrosion

c. to cause extended stains or block operation due to wear

4

Furnace tube

d. deposits on internal surfaces caused by salts

5

Conductivity

e. the burning process of a fuel releasing energy, carbon, monoxides and dioxides

6

Compound

f. fixing in position for use

7

Impurities

g. the deterioration of metal by chemical action

8

Scale

h. entering or escaping accidentally

9

Installation

i. consisting of two or more different elements

10

Foul

j. bubbling caused by excessive alkalinity or the presence of oil on the water surface

11

Wear

k. the property of transmitting heat, electricity, etc.

12

Leakage

l. elements mixed with foreign matter

8