Magazine September 2012
Páginas: 11 (2567 palabras)
Publicado: 14 de octubre de 2012
Selected questions
Chapter 4.1: Boiler Short type questions 1. In the absence of steam flow meter, suggest a method by which steam quantity can be assessed in a boiler. Ans. The feed water flow into the boiler can be used as an effective tool to quantify the steam flow rate from a boiler. The feed water flow rate also can be quantified either by measuring water flow with the help of water flowmeter or by noting the change in level of feed water tank for a specified period of time. Care must be taken to ensure that blowdown is avoided during the trial period. 2. List out the merits and demerits of direct method of boiler efficiency. Ans. Merits • Plant people can evaluate quickly the efficiency of boilers • Requires few parameters for computation • Needs few instruments for monitoringDemerits • Does not give clues to the operator as to why efficiency of system is lower • Does not calculate various losses accountable for various efficiency levels • Evaporation ratio and efficiency may mislead, if the steam is highly wet due to water carryover 3. In the indirect method of boiler efficiency evaluation, list any two additional losses computed for solid fuel fired boilers ascompared to liquid and gas fired boilers? Ans. • • 4. Unburnt losses in fly ash (Carbon) Unburnt losses in bottom ash (Carbon)
What are the main losses which are not accounted in an indirect method of boiler efficiency testing? Ans. • • • • Standby losses Blow down loss Soot blower steam Auxiliary equipment energy consumption
5.
In the absence of data for evaluation of surface heat loss ofboiler, what percentage value can be assumed for the following three categories of boilers? a b c Ans a b c Industrial fire tube / packaged boiler Industrial water tube boiler Power station boiler For industrial fire tube / packaged boiler = 1.5 to 2.5% For industrial water tube boiler = 2 to 3% For power station boiler = 0.4 to 1%
SQ - 4.1 - Boiler (table format)
1
Selected questions
6.Define evaporation ratio. Ans. Evaporation ratio is the ratio of quantity of steam generation to the quantity of fuel consumption. Evaporation ratio =
Quantity of steam generation Quantity of fuel consumption
7.
State two causes for rise in exit flue gas temperature in a boiler Ans. The rise in exist flue gas temperature in a boiler can be due to a. b. Scale deposit inside the boilertubes Soot deposit on the outer surface of the boiler tube
8.
Write the formula for evaluation of boiler efficiency by direct method. Ans.
Boiler efficiency ,%
Where,
=
Q × (H − h)x100 q × GCV
h = Enthalpy of fed water kcal/kg q = fuel firing rate kg/hr
Q = Steam flow rate in kg/hr H = Steam enthalpy in kcal/kg
GCV = Gross calorific value of fuel, kcal/kg 9. List out any fourloss components in a heat balance of a boiler. Ans. a. b. c. d. 10. Dry flue gas loss Surface heat loss Loss due to incomplete combustion Loss due to hydrogen in fuel
Find out the excess air percentage supplied for a boiler if the theoretical CO2 is 20.67% and the actual CO2 measured in the flue gas is 14%. Ans. Excess air supplied =
7900 x (20.67 − 14) 14 x (100 − 20.67 )
=
47.44%Long type questions 1. For the evaluation of boiler efficiency by direct method, describe how the heat input can be quantified for the following three cases: • • • Ans. For gaseous fuel: A gas meter of the approved type can be used and the measured volume should Gaseous fuels Liquid fuels Solid fuels
SQ - 4.1 - Boiler (table format)
2
Selected questions
be corrected for temperatureand pressure. A sample of gas can be collected for calorific value determination, but it is usually acceptable to use the calorific value declared by the gas suppliers. For liquid fuel: Heavy fuel oil is very viscous, and this property varies sharply with temperature. The meter, which is usually installed on the combustion appliance, should be regarded as a rough indicator only and, for test...
Chapter 4.1: Boiler Short type questions 1. In the absence of steam flow meter, suggest a method by which steam quantity can be assessed in a boiler. Ans. The feed water flow into the boiler can be used as an effective tool to quantify the steam flow rate from a boiler. The feed water flow rate also can be quantified either by measuring water flow with the help of water flowmeter or by noting the change in level of feed water tank for a specified period of time. Care must be taken to ensure that blowdown is avoided during the trial period. 2. List out the merits and demerits of direct method of boiler efficiency. Ans. Merits • Plant people can evaluate quickly the efficiency of boilers • Requires few parameters for computation • Needs few instruments for monitoringDemerits • Does not give clues to the operator as to why efficiency of system is lower • Does not calculate various losses accountable for various efficiency levels • Evaporation ratio and efficiency may mislead, if the steam is highly wet due to water carryover 3. In the indirect method of boiler efficiency evaluation, list any two additional losses computed for solid fuel fired boilers ascompared to liquid and gas fired boilers? Ans. • • 4. Unburnt losses in fly ash (Carbon) Unburnt losses in bottom ash (Carbon)
What are the main losses which are not accounted in an indirect method of boiler efficiency testing? Ans. • • • • Standby losses Blow down loss Soot blower steam Auxiliary equipment energy consumption
5.
In the absence of data for evaluation of surface heat loss ofboiler, what percentage value can be assumed for the following three categories of boilers? a b c Ans a b c Industrial fire tube / packaged boiler Industrial water tube boiler Power station boiler For industrial fire tube / packaged boiler = 1.5 to 2.5% For industrial water tube boiler = 2 to 3% For power station boiler = 0.4 to 1%
SQ - 4.1 - Boiler (table format)
1
Selected questions
6.Define evaporation ratio. Ans. Evaporation ratio is the ratio of quantity of steam generation to the quantity of fuel consumption. Evaporation ratio =
Quantity of steam generation Quantity of fuel consumption
7.
State two causes for rise in exit flue gas temperature in a boiler Ans. The rise in exist flue gas temperature in a boiler can be due to a. b. Scale deposit inside the boilertubes Soot deposit on the outer surface of the boiler tube
8.
Write the formula for evaluation of boiler efficiency by direct method. Ans.
Boiler efficiency ,%
Where,
=
Q × (H − h)x100 q × GCV
h = Enthalpy of fed water kcal/kg q = fuel firing rate kg/hr
Q = Steam flow rate in kg/hr H = Steam enthalpy in kcal/kg
GCV = Gross calorific value of fuel, kcal/kg 9. List out any fourloss components in a heat balance of a boiler. Ans. a. b. c. d. 10. Dry flue gas loss Surface heat loss Loss due to incomplete combustion Loss due to hydrogen in fuel
Find out the excess air percentage supplied for a boiler if the theoretical CO2 is 20.67% and the actual CO2 measured in the flue gas is 14%. Ans. Excess air supplied =
7900 x (20.67 − 14) 14 x (100 − 20.67 )
=
47.44%Long type questions 1. For the evaluation of boiler efficiency by direct method, describe how the heat input can be quantified for the following three cases: • • • Ans. For gaseous fuel: A gas meter of the approved type can be used and the measured volume should Gaseous fuels Liquid fuels Solid fuels
SQ - 4.1 - Boiler (table format)
2
Selected questions
be corrected for temperatureand pressure. A sample of gas can be collected for calorific value determination, but it is usually acceptable to use the calorific value declared by the gas suppliers. For liquid fuel: Heavy fuel oil is very viscous, and this property varies sharply with temperature. The meter, which is usually installed on the combustion appliance, should be regarded as a rough indicator only and, for test...
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