4. Supply prepositions:

1. Feed water is the water supplied … a boiler … the feed pump.

2. The impurities … the boiler remain … the form of the salt deposits.

3. Alkalis or phosphate are put … marine boilers to prevent scale.

4. Oil is very injurious … a boiler as it adheres … the tube surfaces.

5. Priming may be due … improper construction of boiler.

6. To prevent priming it is necessary to maintain the water … the lowest level.

7. Corrosion results … the dissolved gases found … feed water.

8. Acids may be neutralized … the addition of sodium carbonate.

5. Answer the questions:

1. What is feed water?

2. By what device is the feed water supplied to the boiler?

3. What substances remain in the boiler as the water is evaporated?

4. What problems may water containing impurities lead to?

5. How can a soft sludge be removed?

6. What salt produces a hard scale?

7. What may foaming be the result of?

8. What priming may be due to?

9. What gases cause corrosion?

10. How often must a chemical analysis of the feed water be run?

6. Translate into English:

1. Питательная вода подается в котел насосом.

2. Примеси воды остаются в котле в виде отложений.

3. Мягкий шлак может быть удален из котла продуванием.

4. Некоторые соли образуют твердую накипь.

5. Для предотвращения накипи в котле используются щелочи и фосфаты.

6. Содержание в воде органических веществ может привести к вспениванию.

7. В случае вскипания применяется продувание и добавляется свежая вода.

8. Растворенные в питательной воде кислород и углекислота вызывают коррозию стенок котлов.

9. Химический анализ питательной воды должен производиться на судне не реже одного раза в день.

TEXT B

Purity of boiler feed water

Modern boilers require very pure feed water. The water required for boiler feed purposes, i.e. for steam generation should be of very high quality and thus requires a lot of treatment. Untreated water, containing impurities may lead to the following problems in boilers.

Most pure water will contain some dissolved salts. These salts then adhere to the heating surfaces as a scale and reduce heat transfer, which can result in local overheating and failure of the tubes. Other salts remain in solution and may produce acids which will attack the metal of the boiler. An excess of alkaline salts in a boiler will cause cracking of the metal which may lead to serious failure.

The presence of dissolved oxygen and carbon dioxide in boiler feed water can cause considerable corrosion of the boiler and feed systems. When boiler water is contaminated by suspended matter, an excess of salts or oil, foaming may occur. This is foam which collects on the water surface in the boiler drum. Foaming leads to priming which is the carry-over of water with the steam leaving the boiler drum. Any water present in the steam entering a turbine will do considerable damage.

Various amounts of different metal salts can be found in water. These include the chlorides, sulphates and carbonates of calcium, magnesium. These dissolved salts in water make up the 'hardness' of the water. Calcium and magnesium salts are the main causes of hardness.

TEXT C

CONTAMINATION OF FEED water

The quality of boiler water plays an important role in boiler operation. Contamination of boiler water leads to several types of problems, including the main ones – corrosion and scale formation. 

Inside the boiler system, the boiler feed water passes through a series of tubes and equipment. The feed water is always chemically treated to reduce the effects of harmful minerals and gases.

The main problem starts when a lot of this boiler feed water is lost through leakages and processes such as boiler blow down, soot blowing etc., and make-up water is added to compensate this loss. This make-up water brings in a lot of the impurities into the boiler system.

How is the make-up feed water contaminated?

Boiler feed water is mainly taken from the fresh water generator. The sea water contains a large amount of salts and other dissolved minerals and gases. Many of them are harmful and eventually lead to boiler problems.

Salt deposits act as insulators and lower the heat transfer rate.

The insulating effect of deposits also causes the boiler metal temperature to rise and lead to tube-failure by overheating.

Large amounts of such deposits throughout the boiler can reduce the heat transfer and decrease the overall boiler efficiency.

 

UNIT 6

TEXT A

BOILER PARTS. THE FURNACE

A furnace provides steady burning of fuel.

The furnaces of marine water-tube boilers are lined with refractory firebrick backed up by the insulating bricks. This brickwork acts as furnace insulation and also, by maintaining a high furnace wall temperature, assists combustion.

Water walls are used in water-tube boilers to contain the heat of the furnace and reduce the amount of refractory material required. Water walls consist of a number of tubes and extend along the sides of the furnace setting.

To provide the efficient combustion process of burning oil fuel, a certain set of conditions is necessary: maintenance of high furnace temperature, provision of continuous oil fuel and air supply and removing products of combustion.

The oil is first heated in steam or electric fuel oil heaters. This reduces its viscosity and makes it easier to pump, filter, and finally to atomize. The heated oil passes through the burners where it is atomized; this process breaks it up into a fine spray of droplets presenting a very large surface area of oil to the combustion processes.

Different types of burners have been designed for burning liquid fuel. Mechanical oil burners and steam-assisted ones are employed to obtain efficient atomization. Mechanical atomizing oil burners may be classified according to their method of atomization as centrifugal atomizers and rotary cup atomizers.

Steam-assisted oil burners are widely spread in marine practice. Their advantages are high quality atomization and a wide range of fuel oil feed control.