Lesson 9. BOILERS. OPERATION AND MAINTENANCE

Notes:

Feed Water Treatment

Modern high - pressure, high temperature boiler requires very pure feed water. Most рurе water contains some dissolved salts which come out of solution on boiling. These salts then adhere to the heating surfaces as a scale and reduce heat transfer which сал result in local overheating or failure of the tubes. Other salts remain in solution and may produce acids which will attack the metal of the boiler. Therefore feedwater treatment is employed. The actual treatment involves adding chemicals into the samples of boiler water with a lest kit. This test kit is usually supplied by the treatment chemical manufacturer with simple instructions for its use. Regular and correct use of marine chemicals will cut corrosion to a minimum. Otherwise due to corrosion a number of tubes of a ship's boiler may start leaking and have to be plugged which results in a low working pressure of the boiler.

Preparations

The uptakes should be checked; any dampers should be operated and then correctly positioned. All vents, alarm, water and pressure gauge connections should be opened. The superheater circulating valve or drains should be opened. All the other boiler drains and blow-down valves should be checked. The boiler should then be filled to slightly below the working level with hot de-aerated water. The various header vents should be closed. The economiser, should be checked. The operation of the forced draught fan should be checked and exhaust gas air heaters if any should be bypassed. The fuel oil system should be checked for correct positioning of valves. The fuel oil should then be circulated and heated.

Raising Steam

The forced draught fan should be started and air passed through the furnace for several minutes. The air slides(checks) at every register except " the lighting up " burner should then be closed . The operating burner should then be lit and adjusted. The fuel oil pressure and forced draught pressure should be matched. The superheater header vents may be closed once steam issues from them. When the drum pressure is about 210 КPa (2:1 bar) the drum air vent may be closed. The boiler must be brought slowly up to the working pressure. The main and auxiliary steam lines should now be warmed through and then the drains closed. The water level gauges should be blown through and checked for correct reading. When the steam pressure is about 300 k Pa (3 bar) below the normal operating value the safety valves should be lifted and released using the easing gear,

Once at operating pressure the boiler may be put on load and the superheater circulating valves closed. All other vents, drains and bypasses should then be closed. The water level in the boiler should be carefully checked and the automatic water regulating arrangements observed for correct operation.

Exercise 1. Answer the following questions.

1) What does the modern boiler require?

2) What can be the cause of local over heating?

3) Why are the acids dangerous?

4) What does the treatment involve?

5) What can cut corrosion to a minimum?

6) What should the boiler be filled with?

7) How long should air be passed through the furnace?

8) Why should the fuel oil pressure be matched with that of the draught?

9) When may the drum air went be closed?

10) Why is it necessary to blow through the water level gauges?

11) When may the boiler be put on load?

Exercise 2. Give the Russian equivalents of the following.

1) Pressure gauge connection

2) Superheater circulating valve

3) Blow-down valves

4) Feedwater treatment

5) The lighting up burner

Exercise 3. Translate into English.

1) Водотрубные котлы широко используются в морской практике:

2) Котел - это сердце паросиловой установки.

3) Главный котел производит пар для главной турбины, приводящей в движение винт.

4) Вспомогательный котел производит пар только для вспомогательных механизмов.

5) Паровой барабан частично заполнен водой.

6) Эти барабаны соединены пучками труб, которые также содержат воду.

7) Нисходящие трубки расположены вне газовой системы и действуют в качестве питателей к водяным барабанам.

8) В котел дополнительно введены (добавлены) перегреватели, чтобы увеличить его КПД (эффективность).

9) Предохранительные клапаны нужны (для того), чтобы выпускать из котла избыток пара,

10) Главный стопорный (запорный) клапан необходим, чтобы управлять прохождением пара машинам.

11) Питательные клапаны установлены, чтобы добавлять воду в котел.

12) Указатель уровня воды используется, чтобы показать уровень воды в котле.

13) Термометры и манометры установлены, чтобы показывать температуру и давление внутри котла.

14) Для того, чтобы выпускать воду из системы, установлены спускные клапаны.

15) Для того, чтобы брать пробы воды, устанавливается солемер.

16) Клапаны дозировки химикатов нужны, чтобы можно было добавлять химикаты прямо в котел.

17) Котлы подразделяются на котлы низкого, среднего и высокого давления.

18) Котлы могут быть одно-, двух- и трех барабанные.

19) Наклон котельных трубок может быть от 30 до 90.

20) Паронагреватель располагается вертикально или горизонтально в котле.

21) Водотрубные котлы бывают однопроточными и двухпроточными.

Exercise 4. Make up a dialogue of your own based on the dialogues given below.

STEAM BOILER

Notes:

Mr. Wilson - What repairs, namely, does the steam boiler require?

Ch.Eng. - Cleaning on the water and fire sides and repairing all the accessories and automic devices - that's what our boiler needs. Besides we are also planning to have 3 failed water tubes replaced.

Mr. Wilson - What's' the trouble?

Ch. Eng. - You see they are distorted near the upper tube plate.

Mr. Wilson - Oh, that! As a rule, the most usual cause of tube failure is shortage of water. That's why I'd like to know if there was any water leakage from the boiler.

Ch.Eng. - No, there wasn't. But the tubes exposed in their upper part. The diameter is 36 mm.

Mr. Wilson - I am sorry to say but we have no heat-resistant tubes of such a diameter.

Ch.Eng. - Really? It's a pity. At any case you might let us know about this beforehand.

Mr. Wilson - Don't worry, we'll settle this mater somehow or other.

Exercise 5. Speak on the marine boilers. And here are the points for discussion.

1) Function of the boiler. Its main types.

2) Boiler's design.

3) Principle of operation. . .

4) Types of valves an what they are used for.

5) Classification of boilers.

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