Hi all my APP ( Ask Power Plant) readers I hope everything gonna be all right. I got many requests from my readers about who appeared in the BOE [ Boiler OPeration Engineering ] exam this year for the past couple of months. so as per looking into their request I started working on their request and start writing articles on BOE PAST EXAM PAPERS SOLUTIONS PART-4 so today I write about A.P (ANDHRA PRADESH BOE -2010 EXAM PAPERS SOLUTIONS PART-4 this article helps those readers who want to give BOE exam in this year as well as who preparing for BOE examination for upcoming BOE exam which conducting by different-2 states. this article also helps for those who wants to give viva-voce for BOE examination and also for who face the job interview for power plant hire. so let us discuss A.P (ANDHRA PRADESH BOE -2010 EXAM PAPERS SOLUTIONS PART-4
Q.8 a) What do you understand by internal treatment for a boiler? What are the chemicals used for this purpose? Why are they used?
In internal treatment, chemicals are added to the boiler water. These chemicals react with dissolved salts to convert them into less harmful sludge, which can stay in the boiler water without harming the boiler tube. Later on, this sludge can be removed from the boiler water by blowdown. The main aim of internal treatment is to precipitate the impurities present in the boiler water to get harmless salts or sludge. Following interior treatments are normally carried out in a boiler.
Soda Ash (Sodium Carbonate or Na2CO3) Treatment :
Soda ash (Na2CO3) treatment is done in a smaller size boiler. In this process, soda ash is added to the boiler water, which reacts with chlorides and sulfates of magnesium and calcium to form insoluble sludge.
CaCl2 + Na2CO3 –> CaCO3 + 2NaCl
MgSO4 + Na2CO3 –> MgCO3 + Na2SO4
CaSO4 + Na2CO3 –> CaCO3 + Na2SO4
Phosphate Treatment or High Pressure (HP) Dosing :
In a high-pressure boiler, soda ash treatment cannot be used, as it forms caustic soda and increases with the increase in temperature. Hence, it is difficult to maintain the pH of the boiler water. Also, at higher pH, the solubility of calcium carbonate increases. So, phosphate treatment is preferred as internal treatment in a high-pressure boiler.
Q 8. b) Describe the solid wall Boiler setting ?
Answer: This is the commonest form of setting wall construction in older small and medium size boiler plants . The interior of the combustion chamber and furnace is lined with first grade firebrick or a plastic refractory material made especially for this purpose. The outer wall is constructed of second grade firebricks or a good quality of common red bricks . The firebricks forming the
Furnace lining are not laid in mortar but are merely dipped into a thin mixture of fire clay and water and rubbed into place so as to leave as thin a joint as possible . Common practice is to make the firebrick lining one brick thick , with a row of headers ( bricks laid endwise ) every fifth or sixth row to bond the lining to the outer wall.
Bricks in the outer part of the wall are usually laid in a mortar of lime and sand , or of cement ,lime and sand in the approximate proportion 1:1:5 by volume. Thickness of the setting walls depends on size of boiler and weight ( if any ) to be carried by the walls .
Q 9. a) Discuss about FSS ( Flame safety System )
Answer : In order to prevent such accidents of explosions, control systems known as ‘Furnace Safety Systems’ have been devised in modern boilers. Such control systems have also been given such names as ‘Flame Safety Supervisor System’ or ‘Furnace Safeguard Supervisory System’ and are commonly abbreviated as ‘FSSS’ as also ‘Master Fuel Trip’ Logic, abbreviated as ‘MFT’. FSS takes care of interlocks required for starting, supervising the operating and safe shut down of the equipment connected with fuel firing system.
Other devices burner management system and programmable logic control system are used now a day. The earlier control systems for interlock and protection used electromagnetic relays for implementation of logic. Later solid-state hardwired systems were used. Presently, sophisticated distributed control systems are used for boiler auxiliaries interlock and protection system and furnace safe guard supervisory system.
Q 9. b) How can it be concluded that steam is contaminated?
Answer While main steam chemical parameter is being monitored at the regular interval. Steam is showing the marginal value of conductivity or hardness or silica form its sample collected from sample coller. It is the indication of little bit contamination are there in boiler water as well as which is pass on to steam conversion. It may be because of higher level of TDS(Total dissolved solids) in Boiler water.
Q 9. c) How the combustion control can be upgraded economically?
Answer The basic requirements necessary to be fulfilled for efficient and perfect combustion installations are:
a) Thorough mixing of fuel and air.
b) Optimum fuel-air ratio leading to most complete combustion possible and maintained over full load range.
c) Ready and accurate response of rate of fuel feed to load demand.
d) Continuous and reliable ignition of fuel.
e) Practical distillation of volatile components of coal followed by adequate action covered as above.
f) Adequate control over point of formation and accumulation of ash, when coal is the fuel.
g) Excess air should be as minimum as possible without. CO in flue gas. CO2 in flue gas should be maximum and O2 in flue gases should be minimum. For Furnace oil/LSHS fuel oil etc. liquid fuel, the flame should be bright golden yellow of appropriate length, without sparkles/fire at the end. For natural gas (NG) firing, the flame should be bright blue colored of appropriate length.
Q 9.d) What are ECR and MCR of a boiler? What is the relation between ECR and MCR?
Answer : ECR means Economic Continuous Rating of any boiler. MCR means Maximum Continuous Rating of any boiler. The Economic continuous rating is most offend 70 to 80 % of maximum continuous rating in any boiler.
Q 9.e) : Briefly discuss about Atomization of Furnace oil?
Answer : Just by preheating and lowering viscosity of oil to flow ability level alone cannot help in firing fuel oil. For efficient firing the oil is to be broken to minute particles and sprayed into the furnace, where already sufficient ignition atmosphere is available. Only when it is broken to minute particles, the fuel oil can get thoroughly mixed with combustion air and can form a good air fuel combination. By systematically breaking the fuel into minute particles and spraying, the fuel oil surface contact to combustion air is enormously increased and every particle can get required oxygen and burn efficiently. One common method of atomizing is carried out by means of a pressure jet burner. The fuel oil is supplied to burners at a very high temperature (just less than its flash point level) and pressure up to a needle valves which controls its flow and a swirling motion is imparted to the oil by means of a helix on the burner stem. As a result the oil is broken up by centrifugal force and enters the combustion chamber in the form of fine cone of spray. Other methods of atomization of fuel oil is carried out by making the oil to get thoroughly mixed up with a stream of air or steam which carries the oil from Gun Tip to the space in the furnace in thoroughly broken form.
Q 9. f) : How oil enters a feed water system?
IMPURITY : Oil & Grease
RESULTING IN : Foaming, deposits in boiler
GOT RID OF BY : Coagulation & filtration
SOURCE OF ENETRING IN FEED WATER SYSTEM : Enters boiler with condensate
Q 9. g) What does pH value mean in water chemistry?
Answer : pH value in water chemistry has very vital role. pH is a numeric scale used to specify the acidity or alkalinity of an aqueous solution. It is the negative of the logarithm to base 10 of the activity of the hydrogen ion. Solutions with a pH less than 7 are acidic and solutions with a pH greater than 7 are alkaline or basic. Pure water has a pH of 7 and is neutral being neither acid or alkaline. Contrary to popular belief, the pH value can be less than 0 or greater than 14 for very strong acids and alkaline respectively.
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