4AE3 U12 C3 Review

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What is the main cause of a fuel-rich mixture in a furnace?

Insufficient combustion air (correct)

Poor flue gas removal

Incorrect burner design

Insufficient fuel supply

What is the term used to describe the pressure difference that causes a flow of gas in a boiler furnace?

Draft (correct)

Pressure gradient

Combustion velocity

Flow rate

Where is boiler draft commonly measured?

Only at the superheater bank

Only at the base of the chimney

Only at the furnace

At several points in the boiler gas passes (correct)

What is the primary function of draft equipment in a boiler?

To supply combustion air Signup and view all the answers

What is the result of a continuous fuel supply without adequate combustion air?

A fuel-rich mixture Signup and view all the answers

What is the purpose of a burner in a boiler?

To mix air with fuel Signup and view all the answers

What is the purpose of burners in combustion systems?

To reduce emissions and maximize efficiency Signup and view all the answers

What is the typical method of air supply for combustion in fuel-burning systems?

Three streams of air: primary, secondary, and tertiary Signup and view all the answers

What is the purpose of primary air in a solid fuel stoker?

To admit air below the grates Signup and view all the answers

What is the purpose of tertiary air in combustion systems?

To burn the resulting carbon monoxide and release the remaining heat of combustion Signup and view all the answers

What is the principle behind the movement of fluids from one location to another?

The Second Law of Thermodynamics Signup and view all the answers

What is the term for the pressure difference that drives the movement of combustion air?

Draft Signup and view all the answers

How do natural draft systems provide combustion air to a furnace?

By relying on the difference in density between hot and cold gases Signup and view all the answers

What happens to the mass of a gas when it is heated?

It decreases Signup and view all the answers

What is the purpose of swirling primary air in a fluid-fired burner?

To promote thorough mixing of fuel and air Signup and view all the answers

What is the effect of increasing the pressure difference between two points in a fluid flow system?

The flow rate increases Signup and view all the answers

What is the main factor that affects the pressure differential in a natural draft chimney?

The temperature of the cool air column Signup and view all the answers

Why do power engineers have no control over the ambient air temperature?

Because it is a variable that cannot be controlled Signup and view all the answers

What is the primary function of the chimney in a natural draft system?

To provide draft for the combustion process Signup and view all the answers

What is the effect of increasing the chimney temperature on the draft?

It increases the draft Signup and view all the answers

What is the limitation of increasing the chimney height to increase the draft?

It is costly to build Signup and view all the answers

What is the purpose of the dust collectors, precipitators, and scrubbers in the ductwork between the furnace and the chimney?

To reduce the emissions of particulate and combustion products Signup and view all the answers

What type of lining is required in a brick chimney?

Firebrick or clay lining Signup and view all the answers

What is the advantage of using steel chimneys?

They are less costly to construct and lighter than masonry or concrete chimneys Signup and view all the answers

What is the purpose of the factory-built chimneys?

To provide a low-cost and lightweight chimney system for packaged boiler installations Signup and view all the answers

What is the material used for the inner wall of the factory-built chimneys?

Corrosion-resistant stainless steel Signup and view all the answers

What is the primary purpose of mechanical draft equipment?

To provide the exact amount of combustion air required regardless of atmospheric conditions Signup and view all the answers

What is the limitation of natural draft in providing combustion air?

It is limited by atmospheric conditions, flue gas temperature, and chimney height Signup and view all the answers

What is the function of the induced draft fan in a boiler system?

To increase the flow of combustion air into the furnace and flue gas into the chimney Signup and view all the answers

What is the effect of an induced draft fan on the furnace pressure?

It produces a lower pressure in the furnace Signup and view all the answers

What is the purpose of the variable inlet vane dampers in an induced draft fan?

To adjust the flow of gas into the impeller eye Signup and view all the answers

What is the shape of the fan casing in an induced draft fan?

Volute-shaped Signup and view all the answers

What is the advantage of mechanical draft systems over natural draft?

They can provide the exact amount of combustion air required regardless of atmospheric conditions Signup and view all the answers

What is the purpose of the chimney sections in a factory-built chimney?

To adapt round chimney sections to square or rectangular boiler outlets Signup and view all the answers

What is the consequence of using only an induced draft fan in a boiler system?

The boiler may draw in uncontrolled excess air, resulting in lower efficiency Signup and view all the answers

What is the name given to factory-built chimneys that are positively sealed?

PS chimneys Signup and view all the answers

What is the primary function of a forced draft fan in a boiler system?

To provide combustion air to the furnace Signup and view all the answers

What is the purpose of the windbox in a forced draft boiler system?

To distribute combustion air to the burners Signup and view all the answers

How is the fan capacity regulated in a forced draft system?

By both varying the fan speed and damper position Signup and view all the answers

Why is it important to balance the airflow through each burner in a multiple-burner installation?

To ensure proper combustion air/fuel ratio Signup and view all the answers

What is the purpose of the louvres in a forced draft boiler system?

To balance the airflow through each burner Signup and view all the answers

Why is it important to cool the boiler slowly when taking it off-line?

To prevent thermal shock Signup and view all the answers

What is the characteristic of a pressurized furnace?

It is under positive pressure Signup and view all the answers

In a balanced draft system, what is the function of the induced draft fan?

To remove combustion gases from the furnace Signup and view all the answers

What is the advantage of a balanced draft system over a forced draft system?

It prevents combustion products from leaking out of the boiler Signup and view all the answers

Why is balanced draft commonly used for large boilers and steam generating units?

Because it is necessary for large, complex boiler systems Signup and view all the answers

What is the primary function of the control system in a boiler?

To maintain the proper ratio of air to fuel Signup and view all the answers

What is the main reason for using an induced draft fan in solid fuel fired boilers?

To maintain a negative furnace pressure Signup and view all the answers

What is the purpose of a register or damper in a natural draft boiler?

To regulate the flow of combustion air Signup and view all the answers

What is an advantage of mechanical draft systems over natural draft systems?

They can operate in a wider range of atmospheric conditions Signup and view all the answers

What is the advantage of using a variable speed fan in a boiler?

It provides more accurate control of airflow Signup and view all the answers

How does a variable frequency drive control the speed of a fan?

By changing the frequency of the alternating current Signup and view all the answers

Why are induced draft fans larger than forced draft fans?

Because they handle a larger volume of gas Signup and view all the answers

What is a benefit of using mechanical draft systems in terms of environmental targets?

They permit the installation of flue gas cleaning equipment Signup and view all the answers

What is the purpose of an outlet damper in a boiler?

To throttle the fan output Signup and view all the answers

Why are induced draft fans more expensive to maintain than forced draft fans?

Because they handle hot, potentially dirty gases Signup and view all the answers

How does an inlet damper control the flow of combustion air?

By restricting the flow of air at the fan inlet Signup and view all the answers

What is the purpose of regulating combustion air and fuel in a boiler furnace?

To regulate the steam demand Signup and view all the answers

What is the purpose of the combustion control system in a boiler?

To control the flow of combustion air Signup and view all the answers

What is an advantage of balanced draft systems over induced draft systems?

They do not cause very low furnace pressure Signup and view all the answers

Why is it important to prevent the formation of an explosive gas mixture in the furnace?

To ensure safe and efficient combustion Signup and view all the answers

What is the advantage of using a variable speed coupling in a boiler?

It provides more accurate control of fan speed Signup and view all the answers

Why are chimneys used in mechanical draft systems shorter than those used in natural draft systems?

Because they do not need to be as tall to adequately disperse the flue gases Signup and view all the answers

How does the combustion control system respond to a decrease in steam demand?

By decreasing the fuel supply before decreasing the airflow Signup and view all the answers

What is a difference between induced draft fans and forced draft fans?

Induced draft fans handle hot, potentially dirty gases Signup and view all the answers

What is a benefit of using induced draft in solid fuel fired boilers?

It prevents combustion products from entering the boiler room Signup and view all the answers

What is the result of an increase in air and fuel flow in a furnace?

Furnace pressure increases Signup and view all the answers

What is the purpose of the furnace pressure controller?

To maintain a furnace pressure set point Signup and view all the answers

Why is it important to provide indoor fuel-burning equipment with fresh outside air?

For combustion Signup and view all the answers

What is the effect of inadequate combustion air provision?

Incomplete combustion and hazardous conditions Signup and view all the answers

What is the unit of measurement used to express low-pressure readings in a manometer?

Millimetres of water Signup and view all the answers

What is the purpose of a diaphragm gauge in low-pressure measurements?

To measure small pressure changes Signup and view all the answers

What is the conversion factor for millimetres of water to Pascals?

1 mm of water = 9.81 Pa Signup and view all the answers

What is the purpose of measuring pressures in combustion air systems?

To control draft and maintain efficiency Signup and view all the answers

Which code is used to determine the minimum combustion air and ventilation air requirements for natural gas and propane-fired appliances?

CSA B149.1 Signup and view all the answers

What is the purpose of a 'U' tube manometer in low-pressure measurements?

To measure small pressure changes Signup and view all the answers

What is the main reason why a fuel-rich mixture can rapidly develop in a furnace?

Insufficient combustion air supply Signup and view all the answers

What is the primary function of draft equipment in a boiler?

To supply combustion air to burners Signup and view all the answers

What is the term used to describe the pressure difference that causes a flow of gas in a boiler furnace?

Draft Signup and view all the answers

What is the consequence of inadequate combustion air provision in a furnace?

Fuel-rich mixture Signup and view all the answers

What is the purpose of measuring pressure differences in a boiler system?

To ensure adequate combustion air supply Signup and view all the answers

What is the primary function of burners in a combustion system?

To mix air with fuel Signup and view all the answers

What is the primary purpose of tertiary air in a combustion system?

To burn the resulting carbon monoxide and release the remaining heat of combustion Signup and view all the answers

What is the effect of withholding some combustion air in a burner system?

Less NOX production and lower combustion temperatures Signup and view all the answers

What is the purpose of swirling primary air in a fluid-fired burner?

To promote thorough mixing of fuel and air Signup and view all the answers

What is the driving force behind the movement of combustion air in a natural draft system?

The difference in density between the hot gases and the colder atmospheric air Signup and view all the answers

What is the result of increasing the pressure difference between the fluid source and the destination?

Increased fluid flow Signup and view all the answers

What is the purpose of introducing jets of overfire air in a solid fuel fired system?

To create turbulence in the fuel bed Signup and view all the answers

What is the characteristic of the air admitted to a solid fuel stoker below the grates?

Primary air Signup and view all the answers

What is the effect of a decrease in pressure difference between the fluid source and the destination?

Decreased fluid flow Signup and view all the answers

What is the purpose of using fans or compressors in a combustion system?

To increase the source pressure of a gas Signup and view all the answers

What is the result of heating a gas?

It expands in volume Signup and view all the answers

What is the primary reason why mechanical draft systems are used in boilers instead of natural draft systems?

To provide a consistent airflow regardless of atmospheric conditions Signup and view all the answers

What is the effect of an induced draft fan on the furnace pressure?

It decreases the pressure below atmospheric Signup and view all the answers

What is the purpose of the variable inlet vane dampers in an induced draft fan?

To regulate the flow of combustion air Signup and view all the answers

What is the advantage of using a balanced draft system over an induced draft system?

It reduces the risk of drawing in uncontrolled excess air Signup and view all the answers

What is the function of the impeller in an induced draft fan?

To convey energy to the incoming gases Signup and view all the answers

What is the reason for the increase in draft during cold winter weather?

The decrease in ambient air temperature Signup and view all the answers

What is the primary function of the dust collectors, precipitators, and scrubbers in the ductwork between the furnace and the chimney?

To reduce emissions from solid fuel fired boilers Signup and view all the answers

What is the limitation of natural draft in providing combustion air?

It is limited by the atmospheric conditions and chimney height Signup and view all the answers

Why do tall chimneys not solve pollution issues?

Because they are subject to the same emissions restrictions as shorter chimneys Signup and view all the answers

What is the purpose of the chimney sections in a factory-built chimney?

To adapt round chimney sections to square or rectangular boiler outlets Signup and view all the answers

What is the effect of atmospheric pressure on the draft in a natural draft system?

It decreases the draft when additional draft is required Signup and view all the answers

What is the reason for the decrease in the overall effect of draft as chimneys become taller?

The cooling of the flue gas inside the chimney, making it increasingly dense Signup and view all the answers

What is the advantage of using steel chimneys?

They are less costly to construct and lighter than masonry or concrete chimneys Signup and view all the answers

What is the purpose of the induced draft fan in a boiler system?

To increase the flow of combustion air into the furnace Signup and view all the answers

What is the advantage of using mechanical draft systems over natural draft systems?

They provide a consistent airflow regardless of atmospheric conditions Signup and view all the answers

What is the purpose of the refractory lining in steel chimneys?

To reduce heat loss through the chimney Signup and view all the answers

What is the result of increasing the temperature of the flue gas?

An increase in draft Signup and view all the answers

What is the purpose of the chimney in a natural draft system?

To provide combustion air to the furnace Signup and view all the answers

What is the reason for the limitation of increasing the chimney height to increase the draft?

The economic considerations that limit the height of the chimney Signup and view all the answers

What is the effect of the mortar in brick chimneys?

It reduces the available draft Signup and view all the answers

What is the primary function of the windbox in a forced draft boiler system?

To distribute combustion air to the upper and lower burner rows Signup and view all the answers

What is the purpose of the adjustable louvres in a forced draft boiler system?

To balance the airflow through each burner and prevent air starvation Signup and view all the answers

What is the primary reason for using a balanced draft system in solid fuel fired boilers?

To prevent combustion products from being expelled through openings Signup and view all the answers

In a balanced draft system, what is the function of the induced draft fan?

To maintain a negative furnace pressure set point Signup and view all the answers

What is the limitation of natural draft systems in boilers with air heaters and economizers?

They cannot develop enough draft to move adequate quantities of combustion air and flue gas Signup and view all the answers

What is the result of inadequate combustion air provision in a furnace?

A fuel-rich mixture forms in the furnace Signup and view all the answers

What is the purpose of the damper assembly in a forced draft fan?

To vary the position of the damper assembly to meet the combustion airflow demand Signup and view all the answers

Why do induced draft fans require more maintenance than forced draft fans?

Because they handle hot, potentially dirty gases Signup and view all the answers

What is the advantage of mechanical draft systems in regulating combustion air?

They can accurately regulate combustion air over a wide range of firing rates Signup and view all the answers

What is the advantage of using a balanced draft system in large boilers and steam generating units?

It reduces the risk of combustion product leakage Signup and view all the answers

What is the purpose of the air heater in a forced draft boiler system?

To preheat the combustion air before it enters the furnace Signup and view all the answers

What is the purpose of the combustion control system in a boiler?

To control the fuel and airflow into the furnace Signup and view all the answers

What is the function of the adjustable louvres in a multiple-burner installation?

To balance the airflow through each burner and prevent air starvation Signup and view all the answers

What is the primary function of the induced draft fan in a boiler system?

To handle the flue gas and maintain the furnace pressure below atmospheric Signup and view all the answers

What is the consequence of shutting off all the louvres when the boiler is taken off-line?

The boiler cools slowly and at a controlled rate Signup and view all the answers

What is the advantage of using a balanced draft system over a forced draft system?

It prevents combustion products from being expelled through openings Signup and view all the answers

What is the result of using only an induced draft fan in solid fuel fired boilers?

It causes very low furnace pressure, which negatively affects boiler efficiency Signup and view all the answers

What is the primary function of the forced draft fan in a boiler system?

To provide combustion air to the furnace Signup and view all the answers

What is the advantage of mechanical draft systems in installing heat recovery equipment?

It permits the installation of heat recovery equipment in the flue gas stream Signup and view all the answers

What is the characteristic of induced draft fans in comparison to forced draft fans?

They are larger in size and cost more to manufacture Signup and view all the answers

What is the primary reason for controlling furnace pressure?

To ensure efficient combustion Signup and view all the answers

What is the purpose of measuring pressure differences in combustion air systems?

To ensure efficient combustion Signup and view all the answers

What is the characteristic of the pressure measured in combustion air systems?

Low pressure Signup and view all the answers

What is the purpose of the inclined U-tube manometer?

To measure low pressure Signup and view all the answers

What is the effect of inadequate combustion air provision on natural draft appliances?

It causes combustion products to spill from the boiler vent hood Signup and view all the answers

What is the conversion factor for millimetres of water to Pascals?

1 mmH2O = 9.81 Pa Signup and view all the answers

What is the purpose of the combustion air openings in boiler rooms?

To provide fresh outside air for combustion Signup and view all the answers

What is the purpose of the draft measuring instruments in combustion systems?

To measure combustion air and flue gas pressures Signup and view all the answers

What is the effect of an increase in air and fuel flow on furnace pressure?

It increases furnace pressure Signup and view all the answers

What is the purpose of the furnace pressure controller?

To maintain a furnace pressure set point Signup and view all the answers

What is the primary function of the combustion control system in a boiler?

To vary the amount of steam produced in accordance with boiler or main steam header pressure Signup and view all the answers

What is the purpose of the air registers in a natural draft boiler?

To control the flow of combustion air to the furnace Signup and view all the answers

What is the benefit of using variable speed fans in combustion systems?

To reduce the fan power consumption at reduced loads Signup and view all the answers

How is the fan capacity regulated in a balanced draft system?

By controlling the furnace pressure Signup and view all the answers

What is the purpose of the chimney uptake damper in a natural draft boiler?

To prevent the formation of an explosive gas mixture in the furnace Signup and view all the answers

What is the advantage of using inlet vane dampers in an induced draft fan?

They reduce fan power consumption at reduced loads Signup and view all the answers

What is the purpose of the outlet damper control in a combustion system?

To throttle the fan output and control the airflow Signup and view all the answers

What is the benefit of using a variable speed coupling in a combustion system?

It gives excellent fan speed control and is used for electric motors too large for a variable frequency drive Signup and view all the answers

What is the purpose of the combustion airflow control in a boiler system?

To ensure the furnace is never fuel rich Signup and view all the answers

What is the benefit of using a steam turbine driven fan in a combustion system?

It allows for automatic control of the fan speed with a throttle valve Signup and view all the answers