Explore topic-wise InterviewSolutions in .

Right answer is (d) Once through boiler

The best I can EXPLAIN: The once through boiler has higher load RESPONSE characteristics due to the fact that it does not have drum and has MUCH lower water inventory. Many times load CHANGE response is dictated by the firing system and its controls RATHER than the boiler, per-say.

The correct choice is (a) Steam can be generated at a faster even if the boiler is cold

The BEST I can explain: Rate of evaporation is more as area of heating surface is more due to presence of large SMALL diameter TUBES. Due to that smaller WATER ratio is ALLOWED to steam space where in the steam can be generated as a faster rate even if the boiler is cold. As the rate of evaporation is more, it is preferred in steam power plants for power generation.

Right answer is (a) When STEAM demand is fluctuating

To explain I would say: Whenever the steam demand is fluctuating, it BECOMES very difficult to maintain uniform PRESSURE. In such of these cases pressure reducing valve is made utilized by connecting to steam supply line. FUNCTION of the pressure reducing valve is to maintain constant pressure on the delivery side of the valve with the fluctuating boiler pressure.

The CORRECT answer is (d) Hand PUMP

Easy explanation: Hand pump is the example of a reciprocating pump. Reciprocating pumps when made use inside a boiler. They are continuously run by STEAM from the same boiler to which the water is fed. Water is pumped by reciprocating ACTION.

The CORRECT ANSWER is (b) 2

The EXPLANATION is: Two types of safety valves are used in practice

i) Spring LOADED safety VALVE

ii) Dead weight safety valve

Correct choice is (c) There is no control over the TEMPERATURE of COOLED water

To explain I would say: The cooling effect is reduced with the decrease in WIND VELOCITY and if the load on the plant increases, the pond does not respond to the requirement. When the maximum cooling is required during increased load, it PROVIDES minimum cooling in absence of wind flow.

Right answer is (C) 3

Explanation: Sulfur in the atmosphere exists in three (3) forms:

i. Sulfur dioxide, SO2 which COMES from artificial causes.

ii. Hydrogen SULFIDE, H2S which comes from natural causes.

iii. Various sulfates, coming from sea SPRAY and oxidation of SO2.

The correct choice is (B) Oxides of carbon

The explanation is: Oxides of carbon such as CO, CH4 and CO2 are major contaminants in the atmosphere. Carbon monoxide is caused by natural causes partially, such as marsh gas, coal, vegetation and forest fires. This CONTRIBUTION is small compared to human generated causes. 90% of CO is produced by motor VEHICLES, where as power plants contribute less than 1%. The TOTAL amount of CO produced per year is 230 million tones.

Right answer is (a) HEAT the air entering FURNACE

To elaborate: It is EVIDENT that the draught is created at the cost of thermal efficiency of boiler plant installation since a portion of flue gases carried away by the flue gases to produce the required draught could have been USED EITHER in heating the air entering the furnace or in heating the feed water, which would increase the thermal efficiency.

Right choice is (a) Forced steam draught

Best explanation: Forced steam draught system is ALSO is KNOWN as turbine draught. In this case, steam from the BOILER is throttled to a PRESSURE of 1.5 to 2 bar and passed through a SERIES of nozzles fitted to a diffuser pipe.

The CORRECT ANSWER is (c) Economizer

For explanation: The combustion GAS coming out of the super heater is used to run gas turbine which runs at air compressor. The EXHAUST gases coming out of the gas turbine are passed through the economizer to heat the feed water. Feed water is recirculated with the HELP of a pump.

Right choice is (a) Natural circulation

Best explanation: Natural circulation is used in the primary circuit of a Schmidt-Hartmann boiler and this is sufficient enough to affect the desired rate of HEAT TRANSFER and to overcome the thermo-siphon head of HEIGHT about 2 to 10 METERS. This boiler has GOT 2 pressure cycles.

The CORRECT choice is (a) Saturated steam

Easiest explanation: The steam GENERATED by the EVAPORATOR tube of the LAMONT boiler is saturated steam. If it is directly used in steam turbine, it can cause the corrosion. So the saturated steam SENDS to the super heater where it increases the temperature of steam.

The correct ANSWER is (b) Economizer

The best I can explain: Feed water from the hot WELL is passed through the economizer tubes before entering the steam and water DRUM. During its flow through the economizer tubes, water gains maximum sensible heat from the flue gases ESCAPING to the exhaust.

Correct choice is (d) WATER tube boiler

The explanation: Water tube boilers are those in which the products of combustion (Hot FLUE gas) surround the water tubes from outside. COLD water enters the tubes and leaves hot. These boilers operate at very high PRESSURES and are used for power generation.

Ex: Babcock-Wilcox boiler, Stirling boiler.

The correct choice is (c) Positive forced circulation boiler

The explanation is: In positive forced boilers, water enters the bottom of the tubes and completely transforms into steam as it passes through the tubes and reaches at the top. THUS, these boilers do not NEED a steam drum and hence often referred as drum-less boilers. These boilers WORK at very high pressures.

Correct ANSWER is (b) Recover the HEAT from flue gas

To explain: Function of air PREHEATER is to recover the heat of a portion of exhaust flue gases before the flue gases enter the chimney. It is places along the PASSAGE of the exhaust flue gases in between the economizer and the chimney.

Correct answer is (a) True

For explanation I would say: The FLUE gases of natural draught are at higher temperature when compared to flue gases of artificial GAS because to maintain CERTAIN minimum temperature required to produce a given draught for the given HEIGHT of the chimney. Due to higher flue gas temperature, the heat lost with flue gases is more in natural draught.

The correct CHOICE is (d) High working pressure

Easy explanation: Due to high working pressure and positive circulation of water, chances of sediments DEPOSITING inside water tubes in the SHELL is less. This high working pressure of boiler in the shell can WITHSTAND high temperature or thermal stresses.

The correct option is (d) Depending tubular heating surface

Explanation: Based on the CONTENTS of the tubular heating surface, boilers are primarily CLASSIFIED as FIRE tube boiler and water tube boiler. Fire tube boilers those in which production of COMBUSTION PASS through the tubes and water tube boilers are those in which the products of combustion surround the water tubes from outside.

The correct answer is (d) BOILER

Best explanation: The boiler may have a water circulation either by NATURAL means due to difference in density or by external means (forced circulation). All modern high pressure boiler PLANTS USE a pump to force the water to circulate through the boiler PLANT. The use of natural circulation is limited to the subcritical boilers.

The correct answer is (a) Condensing

Explanation: Condensing economizers are used in natural gas fired thermal power PLANT. They reduced the flue gas TEMPERATURE below condensation temperature as low as 25^oC. They increase the BOILER efficiency by 10-15%. While USING the CONDENSER the fuel should not contain sulfur.

Right option is (a) Pump water at HIGH pressure

The explanation: FUNCTION of feed water pump is to pump water at high pressure to the water space of the BOILER drum. There are many types of feed pumps, in which they are mainly classified into ROTARY and reciprocating pumps.

The correct CHOICE is (c) Baffle walls

Explanation: In direct flow system the hot water coming out of the condenser ENTERS the middle CHANNEL. On reaching the far end it is divided into TWO currents being DIRECTED by the baffle walls so as to transverse the pond several times before uniting at intake point.

Right ANSWER is (d) 4

Easiest explanation: Modules in spray pond COOLING system contain 4 spray nozzles. The surface area of contact of water is increased when it is sprayed in AIR. Cooling OCCURS DUE to the evaporation of water vapours as the spray propels upwards and falls down to the surface.

Right choice is (a) Cellular light weight concrete

The best I can explain: Cellular light weight cement can be manufactured by a PROCESS involving the mixing of fly ash, cement, coarse sand fine and a foaming agent. The slurry FORMED is poured in moulds and allowed to SET. The BLOCKS are then removed and cured by spraying water on the stack. The blocks are especially useful in high rise CONSTRUCTION reducing the dead weight of the structure.

Correct choice is (d) Induced Steam draught SYSTEM

To EXPLAIN: Induced steam draught system is used in a boiler for a locomotive. When the locomotive is stationary steam generated in the boiler is fed to the SMOKE box through the nozzle to create the draught. When locomotive is moving air ENTERS through the DAMPERS and makes its way through grate and smoke box.

Right answer is (C) When draught produced by chimney is not sufficient

The best explanation: This type of draught is preferred when draught produced by the chimney is not sufficient or when a certain draught is to be MAINTAINED irrespective of ATMOSPHERIC temperature. ARTIFICIAL draught as no flexibility, as poor efficiency and REQUIRES tall chimney.

The correct choice is (b) 150 tonnes/hr & above

Explanation: Feed water from the hot-well is forced through the economizer tubes. The hot water enters the radiant SECTION of the EVAPORATOR TUBS and then PASSES through convective section of the evaporator tubes. Since the boiler has no drum, thee steam generated in the evaporator enters the super heater tube where it is heated above the critical pressure. So the Steam rising capacity of the boiler is 150 tonnes/hr & above.

Right answer is (c) Water CIRCULATION is limited inside boiler shell

To explain: Water circulation is limited inside the boiler shell. Water NEED not be that much pure and needs minimum treatment like passing through a pressure filter. Cleaning and repairing is not easy due to inaccessible parts, furnace cannot be ALTERED and is used for ONE fuel only.

The correct option is (c) 30^o

For EXPLANATION: In this following method of a superheater temperature control BURNERS in the furnace are tilted up or down through a range of 30^o. When burners are tilted downwards much of heat is GIVEN to the water WALLS by the gas and the gas entering the SUPER heater region is relatively cool.

Right answer is (b) 2

The explanation: TWO types of steam traps are GENERALLY used in the BOILER. The function of steam trap is to drain off water resulting from the partial condensation of steam in the steam pipe lines and JACKETS without allowing the steam to ESCAPE through it.

The correct answer is (b) once through system

The BEST explanation: Open system is ALSO called as once through system, in this system the water is drawn directly from the upstream side of the river PUMPED through the condenser and DISCHARGED to the downstream side of the river at temperature 5 to 10°C in excess of inlet temperature.

Correct option is (a) Cast-in-situ fly ash walls

To explain: Using high fly ash comprising of CEMENT, lime fly ash and sand in appropriate proportions depending UPON the quality of fly ash with pre-measured water cement ratio, cast-in-situ can be built. These can be cast to any thickness using steel shuttering. By using this system we can ACHIEVE 20% of economy, quicker construction, good FINISH on both SIDES of wall and more carpet area.

The correct choice is (a) 84000MW

The best explanation: India’s current total INSTALLED capacity of power plants is 84000MW, out of which coal-fired thermal plants contribute 54000MW (65% of total). The World Bank estimated coal BASED power GENERATION to increase by another 81000MW by 2010 which WOULD have further increased fly ash load of 56 million tons per year.

The correct answer is (a) P = H (Wa-WG)

Explanation: The pressure acting on the grate from chimney SIDE,

P1 = Pa + Wg H

Pressure acting on the grate from atmospheric side

P2 = Pa + Wa H

Where, Pa = Atm pressure

Wa = weight density of air

Wg = Weight density of hot gases

 The net pressure acting on the combustion chamber due to the pressure exerted by gas column and air column is given by

P = P2– P1(as Wa> Wg )

P = (pa + Wa H) – (Pa+ Wa H)

P = H (Wa– Wg )

This pressure difference is known as static draught and is responsible for CAUSING the flow of air through the chimney.

The correct option is (a) AVOID excessive heating of tube

The BEST I can EXPLAIN: The boiler is started from cold by circulating the feed water from the hot WELL by operating the starting VALVE. While taking the boiler on range, starting valve is closed and valve 2 is opened. This method avoids excessive heating of tubes.

Correct option is (d) 1925

For explanation I would SAY: The Lamont boiler was invented by Walter Douglas Lamont in year 1925; He bought the idea from papers to EXISTENCE. He also introduced the concept of forced circulation boiler. The INITIAL design of Lamont for this boiler CONFIRMED lighter, safer and higher rates of heat transfer.

Right option is (d) Babcock-Wilcox BOILER

The explanation is: If the boilers are used at one place only they are TERMED as stationary boilers. These boilers are used for either PROCESS heating in industries or for power generation in steam power plants. These are used at central station utility power plants, for plant process etc. EX: Babcock-Wilcox boiler, Fluidized Bed Combustion (FBC) boiler.

Right choice is (d) Non-Condensing

To explain: The most common type of economizer used in thermal power plant is the Non-condensing thermal power plant. They are HEAT exchanger TUBES with FINS around the in the FORM of spiral and they are located inside the duct at the exit region of the BOILER.

Right answer is (b) 120-160bar

Easiest explanation: The Lamont boiler OPERATES between the PRESSURE range of 120-160bar, due to this natural circulation is limited because of DENSITY DIFFERENCE between the liquid and vapor. HENCE the external centrifugal pump is used to assist the circulation.