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Q8. (a) Sketch diagrammatically an auxiliary boiler automatic combustion control system and explain how it operates.

(b) Specify how ‘fail-safe’ conditions are ensured.

(c) How, the master controller follows steam pressure variations and air fuel ratio is adjusted?

Q9. a) List the design problems associated with safety valves for high-pressure boilers.

b) State the factors that determine

(i) The relationship between the working pressure of the boiler and the setting pressure of the safety valve

(ii) The blow down setting of a safety valve

c) State what determines the settings of

(i) The super heater safety valve

(ii) The drum safety valve.

Q7. (a) Specify with reasons those parts requiring particularly close scrutiny during internal and external examinations of independently fired auxiliary boilers.

(b) With reference to these examinations distinguish between metal fatigue due to caustic embrittlement, corrosion fatigue, overheating (plastic flow) and direct overpressure.

Q8. With reference to main boiler super heater arrangements:

A. Compare the advantages and disadvantages of contra flow with parallel flow design.

B. Describe how the element tube banks are supported yet allow for expansion.

C. Describe how boiler carryover affects super heater effectiveness and condition.

Q5. Sketch and explain the construction of a feed Check Valve. Why is it known as double shut off arrangement. (16)

Q6. With reference to feed regulation: A. Describe, with the aid of sketches, the operation of a boiler feed water regulator controlled by at least two other parameters besides water level in the drum; B. Give reasons for the inclusion of the other elements besides water level in controlling feed flow; C. Deduce the possible effects on the system when the drain valve in the constant leg in the level transmitter starts to leak.

Q4: An auxiliary boiler water level control system has a differential pressure transmitter as the detecting element for water level.

A. Sketch and describe such an arrangement; B. If the transmitter was damaged describe how a replacement unit would be calibrated.

Q7. An Auxiliary boiler is periodically unattended and equipped with alarms to cover low water level, high steam pressure, and air and flame failure.

A. State why and how fuel the burners are automatically cut off under alarm conditions of water level, steam pressure, air and flame failure.

B. Describe how and when each of the above alarms is tested without endangering the boiler.

Q6. An auxiliary boiler water level control system has a differential pressure transmitter as the detecting element for water level.

A. Sketch and describe such an arrangement; B. If the transmitter was damaged describe how a replacement unit would be calibrated

Q3. With reference to a cylindrical boiler which has undergone major repairs, explain: - A. How is the boiler prepared for carrying out hydraulic test? B. What is the test pressure to which boiler is subjected to? C. What inspection should be made before, during and after the test?

Q6. Draw a line diagram of a Boiler combustion control system labelling the principal items, explain how the system functions and in particular how feed water supply, fuel supply and air/fuel ratio are regulated to match steam pressure and flow variation.

Explain how these controls can be tested for alarm conditions without upsetting the balance of the system.

Q7. With reference to a waste heat boiler/economiser:

a. Write a procedure for the cleaning the gas side of an exhaust gas boiler/economiser when the  associated main engine is:

(i) running;    (ii) stopped.

b. Write a procedure for operation of the main engine when the associated waste heat boiler/economiser cannot be operated due to tube failure.