328 Questions
What is the primary requirement for a perfectly sealed boiler system?
At least one kilogram of water must enter for each kilogram of steam or hot water produced
What is a common source of water loss in steam heating systems?
Steam leaks and processes that consume steam
What is the term for the total water fed to a boiler?
Feedwater
What is a characteristic of well water that can be problematic in boilers?
It is very hard and forms waterside scale
What is the term for untreated source water?
Raw water
Why is water treatment necessary for make-up water in steam systems?
To remove hardness and other impurities
What is the primary reason for recovering and reusing condensate?
All of the above
What is the purpose of the clarifier in Figure 2?
To remove suspended matter and organics from the water
What is the term for water treatment performed by adding chemicals to the boiler drum or shell?
Internal water treatment
What is the purpose of the deaerator in the make-up water treatment system?
To remove dissolved oxygen from the water
What happens to the deaerator level if too little condensate returns?
The level drops
What is the primary difference between the make-up water treatment systems shown in Figure 1 and Figure 2?
The complexity of the system
What is the purpose of the feedwater reserve receiver?
To provide up to 24 hours of make-up water if the water treatment plant is out of service
What is the term for the water that is formed when steam transfers latent heat of evaporation to process equipment?
Condensate
What is the primary purpose of a condensate receiver in a feedwater system?
To return the clean condensate to the boiler
Why is it important to reuse condensate?
Both b and c
What type of compounds may be present in the condensate returns from leaking heat exchangers?
Scale-forming compounds
What is the purpose of a deaerator in a feedwater system?
To remove impurities from the feedwater
What is the purpose of the vented condensate receiver in the condensate return system?
To receive and store condensate
What is the name of the code that specifies the requirements for the construction of high-pressure boiler piping systems?
ASME B31.1 Power Piping Code
What is the purpose of a level control valve in a feedwater system?
To adjust the flow of feedwater to maintain a constant drum level
What is the classification of the weakest valve class in a feedwater system?
Class 150
What is the purpose of a check valve in a feedwater system?
To prevent the boiler from draining when the feedwater pump is not operating
Why is it necessary to service a feedwater check valve only after appropriate lockout and safe work permits are obtained?
To ensure the safety of the maintenance personnel
What is the name of the type of steam-assisted gravity drainage plants that create highly contaminated condensate?
SAGD
What is the purpose of a gate valve in a feedwater system?
To isolate equipment for maintenance
What is the primary purpose of loop controllers in boiler water level regulation?
To maintain precise water level control
What is the function of a globe bypass valve in a feedwater PID control loop?
To regulate feedwater flow manually
What is the characteristic of self-powered level control valves?
They develop the force needed to operate their valve mechanisms on their own
What is the purpose of the generator in a thermo-hydraulic feedwater regulator?
To transfer heat from the inner tube to the surrounding water
What happens when the water level in the boiler drops in a thermo-hydraulic feedwater regulator?
The valve opens further
What is the function of the tube in a single-element thermal expansion regulator?
To expand and contract in response to boiler water level changes
What type of valve is used for throttling service in feedwater flow regulation?
Globe valve
What is the purpose of the flanged connections in a fully modulating control valve?
To permit the removal of the valve for repair or replacement
What happens when the water level in the boiler rises in a thermo-hydraulic feedwater regulator?
The valve closes further
What is the advantage of self-powered level control valves in the event of a power failure?
They can still perform their function
What is the primary purpose of a check valve in a boiler feedwater system?
To prevent boiler water from flowing back to the feed pumps
In a feedwater system, what type of valves are used to control the boiler water level?
Control valves
What is the minimum design temperature required for a check valve in a boiler feedwater system?
Saturation temperature of the boiler water
In a boiler feedwater system, which type of pumps are capable of developing enough pressure to damage piping components?
All of the above
What is the purpose of a pressure control valve in a feedwater system?
To relieve excess pressure from deaerators or other components
In a single-boiler plant, how is the boiler water level typically controlled?
Using a float- or probe-actuated switch
What is the requirement for the design pressure of a check valve in a boiler feedwater system?
It must be at least the maximum allowable working pressure of the boiler plus 1550 kPa
In a boiler feedwater system, what is the primary purpose of a gate valve?
To isolate the boiler feedwater pump
What is the requirement for the installation of check valves in a boiler feedwater system?
A check valve is required at the boiler feedwater inlet
In a multi-boiler plant, what is the purpose of a level control valve in the feedwater line to each boiler?
To match the feedwater flow to the steam production rate of each boiler
What is the consequence of faulty heat exchangers in hot water heating systems?
Need for replacement water
Why is water treatment necessary for make-up water in steam systems?
To remove impurities from the water
What is the primary characteristic of well water that can be problematic in boilers?
It is hard and forms waterside scale
What is the term for the total water fed to a boiler, including both condensate returns and make-up water?
Feedwater
In a steam heating system, what is the primary source of water loss?
Steam leaks and processes that consume steam
What is the consequence of a steam system losing water from blowoff, blowdown, and soot blowing?
Make-up water is required to compensate for water losses
What is the primary reason for designing a feedwater system to accommodate changes in feedwater demand?
To provide system capacity and prevent water shortages
What is the main purpose of the demineralizers in the make-up water treatment system shown in Figure 2?
To purify the water
What is the primary benefit of reusing condensate in a steam system?
All of the above
What is the purpose of the clarifier in the make-up water treatment system shown in Figure 2?
To remove organics and suspended matter from the water
What is the primary difference between the make-up water treatment systems shown in Figure 1 and Figure 2?
The complexity of the treatment system
What is the purpose of the feedwater reserve receiver in the make-up water treatment system?
To provide system capacity to accommodate changes in feedwater demand
What is the primary reason for directing make-up water to the condensate receiver in the system shown in Figure 1?
To maintain the deaerator level
What is the purpose of the deaerator level controls in the make-up water treatment system?
To maintain the deaerator level
What is the primary reason for using hot condensate in a steam system?
To reduce fuel consumption and emissions
What is the term for the water treatment process performed by adding chemicals to the boiler drum or shell?
Internal water treatment
What is the primary function of a condensate pump in a feedwater system?
To transfer condensate from the hot well to the deaerator
What is the main purpose of a boiler feedwater pump in a feedwater system?
To maintain a constant drum level in the boiler
What is the purpose of a level control valve in a feedwater system?
To ensure the boiler is fed enough water to maintain a constant drum level
What is the primary reason for treating make-up water in a feedwater system?
To reduce the risk of scaling in the boiler
What is the classification of the strongest valve class in a feedwater system?
Class 4500
What is the purpose of a deaerator in a feedwater system?
To preheat and deaerate the feedwater
What is the primary purpose of a check valve in a boiler feedwater system?
To prevent backflow into the boiler
What is the term for the water that is lost from the system and must be replenished with make-up water?
Steam lost
What is the purpose of a globe valve in a feedwater system?
To throttle feedwater flow
What is the primary requirement for the design pressure of a check valve in a boiler feedwater system?
It must be greater than the boiler operating pressure
What is the primary function of a fully modulating control valve in a feedwater PID control loop?
To control the feedwater flow
In a thermo-hydraulic feedwater regulator, what causes the bellows to expand?
The heat transferred from the inner tube to the surrounding water
What is the purpose of the flanged connections in a fully modulating control valve?
To allow for the removal of the valve for repair or replacement
What is the primary characteristic of self-powered level control valves?
They develop the force needed to operate their valve mechanisms on their own
What is the function of the tube in a single-element thermal expansion regulator?
To respond to changes in boiler water level
What is the purpose of a globe bypass valve in a feedwater PID control loop?
To manually regulate the feedwater flow when the main control valve is out of service
What is the advantage of using self-powered level control valves in a feedwater system?
They are not affected by power failure
What is the primary purpose of a thermo-hydraulic feedwater regulator?
To control the feedwater flow in proportion to the boiler water level
What is the primary function of loop controllers in boiler water level regulation?
To tune the boiler water level control system
What is the purpose of the generator in a thermo-hydraulic feedwater regulator?
To create a pressure difference between the inner and outer tubes
What is the primary purpose of a check valve installed at the boiler feedwater inlet?
To prevent boiler water from flowing back to the feed pumps
What is the requirement for the design pressure of a check valve in a boiler feedwater system?
It must exceed the maximum allowable working pressure of the boiler by either 25% or 1550 kPa, whichever is less
In a multi-boiler plant, where must the level control valve be located in the feedwater line to each boiler?
Between the check valve and the boiler feed pump
What is the purpose of a pressure control valve in a feedwater system?
To regulate the pressure of the boiler water
In a single-boiler plant, how is the boiler water level typically controlled?
Using a float- or probe-actuated switch to start the boiler feedwater pump
What is the primary purpose of a gate valve in a boiler feedwater system?
To seal tight in isolation
What type of pumps are capable of developing enough pressure to damage piping components in a feedwater system?
Positive displacement, turbine-style, or multi-stage centrifugal pumps
What is the minimum design temperature required for a check valve in a boiler feedwater system?
At least the saturation temperature of the boiler water
What is the purpose of a control valve in a feedwater system?
To control the level, flow, or pressure of the boiler water
What is the requirement for the installation of check valves in a boiler feedwater system according to ASME B31.1?
Check valves must be installed at the boiler feedwater inlet
What is the primary sensing element used in single-element feedwater control systems?
All of the above
What type of feedwater control systems are typically used in power boilers with small diameter drums or rapidly fluctuating steam loads?
Two-element
In a fully modulating single-element feedwater control system, what is the purpose of the reference head?
To provide a constant column of water
What is the main advantage of using single-element feedwater control systems in steam heating boilers?
They are more cost-effective
What is the primary characteristic of single-element feedwater control systems?
They respond only to drum level
In a single-element feedwater control system, what is the purpose of the modulating control valve?
To regulate the flow of feedwater
What is the purpose of the drum level controller in a boiler feedwater system?
To maintain the desired water level in the boiler drum
What is the effect of a sudden increase in steam flow on the drum level?
The drum level will increase momentarily
What is the primary function of the drum level transmitter in a two-element feedwater control system?
To sense the drum level and adjust the feedwater valve accordingly
Why are two- and three-element feedwater control systems not used in heating boilers?
They are too expensive to install and maintain
What is the purpose of the orifice plate and DP cell in a two-element feedwater control system?
To measure the drum level and steam flow
What is the effect of swell on the drum level in a two-element feedwater control system?
It increases the drum level
What is the phenomenon called when the drum level increases momentarily due to a sudden increase in steam flow?
Swell
How does the steam flow transmitter output affect the feedwater valve in a two-element feedwater control system?
It opens the valve to increase feedwater flow
What is the purpose of the computing relay in a two-element feedwater control system?
To override the drum level signal during periods of swell or shrinkage
Why does a single-element feedwater control system reduce feedwater flow when the drum level increases due to swell?
Because the controller is designed to respond to drum level changes
What is the advantage of using a two-element feedwater control system over a single-element system?
It reduces the effect of swell and shrinkage
What is the primary advantage of a three-element feedwater control system over a two-element system?
It reduces the effect of swell and shrinkage
What is the purpose of the ratio controller in a three-element feedwater control system?
To maintain the ratio of feedwater to steam flow
Why is it necessary to consider steam flow, feedwater flow, and drum level when designing a feedwater control system for a boiler?
To accommodate fluctuating steam loads and smaller diameter drums
What happens to the feedwater valve when the steam flow increases in a three-element feedwater control system?
It opens to increase feedwater flow
What is the primary reason why heating boilers do not experience the negative consequences of swell and shrinkage?
They have a larger shell size to water content ratio
How does the drum level transmitter signal affect the feedwater valve in a three-element feedwater control system during periods of no swell or shrinkage?
It adjusts the valve to maintain the desired drum level
What happens to the drum level when the steam flow suddenly decreases?
It decreases momentarily
What is the purpose of the hand/auto selector on the controller faceplate in a three-element feedwater control system?
To permit manual adjustment of the feedwater valve
What is the purpose of the drum level recorder in a three-element feedwater control system?
To track the drum level continuously
What is the primary function of the low water fuel cut-off in a boiler?
To shut off the boiler burner system if boiler water level drops to an unsafe level
According to CSA B51 Code 6.3.2, how many low-water fuel cut-off devices are required for steam boilers not continuously attended by a certified operator?
Two
What is the purpose of the combined feeder/cut-off control in a boiler?
To add water to the boiler and cut off the boiler when a low water condition occurs
Where is the lowest permissible water level (LPWL) identified?
By the boiler manufacturer
What is the purpose of the manual-automatic transfer station in a boiler control room?
To allow the operator to manually control the drum level during startup
What is the primary function of the condensate receiver in a feedwater system?
To receive and store condensate returns
What is the purpose of the recorders in a boiler control system?
To monitor the steam flow, feedwater flow, and drum level
What happens when a low water condition occurs in a boiler equipped with a combined feeder/cut-off control?
The burner is shut off and the control resets when the water level recovers
What is the requirement for the installation of low water fuel cut-off devices in boilers under continuous supervision, according to CSA B51?
No devices are required
What is the purpose of the float cage in a combined feeder/cut-off control?
To attach the float to the boiler and provide piping connections
What is the purpose of a strainer in a boiler feedwater system?
To remove particles from the make-up water that may interfere with the valve operation
What is the function of a float-controlled switch in a boiler feedwater system?
To provide a low water alarm and cut-off
What is the purpose of a condensate receiver in a steam system?
To collect and store condensate from the heat exchangers and equipment
Why is it important to vent a condensate receiver?
To allow air to enter the receiver and prevent explosion
What is the purpose of a gauge glass in a condensate receiver?
To regularly observe the condensate level and determine if the pump switch and pump are working correctly
What happens when the condensate level in the receiver drops to a set level?
The pump stops running
What is the purpose of a float switch in a condensate receiver?
To start the condensate pump when the condensate level in the receiver is high
What is a common problem that can occur with float switches in a condensate receiver?
The float switch becomes waterlogged or dislodged from its actuating rod
What is the importance of regularly observing the gauge glass in a condensate receiver?
To identify problems with the pump switch or pump
What is the safety concern related to condensate receivers?
They can over-pressurize and explode
What is the purpose of taking condensate samples and testing them for pH?
To ensure the proper amount of water treatment chemical is added to the steam to protect the condensate return lines from corrosion.
What is the function of a return loop or Hartford Loop in a steam heating system?
To prevent low-pressure steam boilers from sustaining low water conditions.
Why is it necessary to have a low water cut-off or a return loop in a gravity-fed steam heating system?
To prevent low water conditions and damage to the boiler.
What is the requirement for steam heating boilers with gravity condensate returns according to ASME IV HG-703.2 and ASME VI 3.05?
To have a return loop.
What is the purpose of the equalizing pipe in a return loop?
To connect the boiler steam outlet to the boiler's water inlet piping.
What is the advantage of using a return loop in a pumped return system?
It prevents the backup of condensate into the return receiver when the condensate pump is not in operation.
What is the difference between a gravity return system and a pumped return system?
Gravity return systems rely on gravity to return condensate, while pumped return systems use pumps.
What is the purpose of a check valve in a pumped return system?
To prevent the backup of condensate into the return receiver when the condensate pump is not in operation.
What is the requirement for the installation of stop valves and check valves in the condensate return lines according to ASME IV?
One stop valve and one check valve are required for each boiler in the system.
What is the purpose of a condensate receiver and pump in a heating system?
To return condensate to the boiler.
What happens when the boiler water level drops below normal in a gravity return system?
The float opens the make-up water valve
What is the purpose of the additional dedicated low water cut-off in a gravity return system?
To stop the burner if the combined feeder/cut-off control fails
What is the advantage of a millivolt system in a gravity return system?
It can continue to operate during an electrical power outage
What is the difference between the systems shown in Figures 17 and 18?
One requires an external electric power supply, while the other does not
Why is it preferable to introduce corrosive make-up water to a condensate receiver rather than a boiler?
Because the condensate receiver is less expensive to replace than the boiler
What happens when the supply of make-up water fails or is insufficient in a gravity return system?
The water level continues to drop
What is the purpose of the float controlled switches in a gravity return system?
To control the make-up water solenoid valve
What type of system is limited to smaller heating plants?
Gravity return system
What happens when the boiler feed pump fails in a pumped return system?
The float shuts down the burner
What is the purpose of the check valve in a pumped return system?
To prevent water from flowing back to the condensate receiver
What is the purpose of the low water cut-off in a steam boiler?
To shut off the burner before the water level reaches the lowest visible part of the gauge glass
What happens when the water level in the boiler drops to level C?
The burner circuit opens
What is the purpose of the float cage in the condensate receiver?
To control the make-up water valve
What is the function of the pump control/low water cut-off in a boiler?
To turn off the boiler feed pump if the receiver level falls too low
What is the purpose of the motorized feedwater control valves in a battery of steam heating boilers?
To open or close the feedwater valve as feedwater is required
What happens when the water level in an individual boiler continues to drop despite the motorized feedwater valve being open?
The float control turns off the burner
What is the purpose of the feedwater line check valve in a steam heating system?
To prevent backflow of condensate
What is the primary advantage of using independent feedwater controls for multiple steam heating boilers in a battery?
Better control of individual boilers
What is the purpose of the level control switch in a battery of steam heating boilers?
To energize the motorized feedwater valve
What is the consequence of a faulty low water cut-off in a steam heating boiler?
The boiler may run dry and sustain damage
What is the main advantage of using single-element feedwater control systems in power boilers with large steam drums or shells?
They provide satisfactory boiler water level control
What is the function of the reference head in the DP cell shown in Figure 9?
To form a constant column of water
Why are two-element and three-element feedwater control systems more suitable for power boilers with small diameter drums or rapidly fluctuating steam loads?
They can respond to drum level, steam flow, and water flow
What is the primary sensing element that can be used in single-element feedwater control systems?
Float, probe, or differential pressure cell
What is the main characteristic of single-element feedwater control systems?
They respond only to drum level
What type of control valves can be used in single-element feedwater control systems?
Self-powered or control loop operated modulating valves
When the steam flow suddenly increases in a boiler, what happens to the drum level?
It momentarily rises due to the flash of saturated boiler water to steam
Why are two- and three-element feedwater control systems not used in low-pressure heating boilers?
Because they are too expensive to install and maintain
What is the purpose of the second element in a two-element feedwater control system?
To detect steam flow and consult with the drum level element
What is the result of shrinkage on the feedwater control system?
The controller detects a decrease in drum level and increases feedwater flow
What is the advantage of using a two-element feedwater control system over a single-element system?
It is more effective in controlling drum level and reducing the effects of swell and shrinkage
What is the purpose of the drum level controller in a feedwater control system?
To detect changes in drum level and adjust feedwater flow accordingly
What happens when the boiler steam flow suddenly decreases?
The drum level momentarily decreases due to the collapse of steam bubbles
Why is it necessary to consider steam flow, feedwater flow, and drum level when designing a feedwater control system for boilers with fluctuating steam loads?
Because it is necessary to reduce the effects of swell and shrinkage on the control system
What is the purpose of the hand/auto selector on the controller faceplate in a feedwater control system?
To permit manual feedwater valve operation
What is the characteristic of the drum level in a boiler with a single-element feedwater control system during periods of swell or shrinkage?
It responds in the opposite direction to the change in steam flow
What is the primary function of the computing relay in a two-element feedwater control system?
To override the drum level signal when steam flow increases
In a three-element feedwater control system, what is the purpose of the ratio relay?
To adjust the feedwater flow ratio to the steam flow
What is the primary advantage of using a three-element feedwater control system over a two-element system?
Reduced effect of swell and shrinkage
What is the primary function of the low water fuel cut-off in a steam boiler?
To shut off the boiler burner system if the boiler water level drops to an unsafe level
When steam flow increases in a two-element feedwater control system, what happens to the drum level?
It swells and then decreases
What is the primary function of the drum level transmitter in a three-element feedwater control system?
To sense the drum level and send a signal to the controller
What is the requirement for the installation of low water fuel cut-off devices in steam boilers according to CSA B51 Code 6.3.2?
At least two devices are required for steam boilers not continuously attended by a certified operator
What is the purpose of the combined feeder/cut-off control in a steam boiler?
To add water to the boiler and cut off the boiler when a low water condition occurs
What happens when the boiler adjusts to the change in steam demand in a two-element feedwater control system?
Swell and shrinkage cease, and the water level stabilizes
What is the effect of a manual-automatic transfer station in the control room of a steam boiler?
It allows the operator to control the drum level manually
In a three-element feedwater control system, what is the purpose of the orifice plate and DP cell?
To measure the feedwater flow and steam flow
What is the primary difference between a two-element and a three-element feedwater control system?
The number of control elements
What is the purpose of the float cage in a combined feeder/cut-off control?
To attach the float to the boiler
What is the purpose of the hand/auto selector on the controller faceplate in a three-element feedwater control system?
To permit manual feedwater valve operation
What is the requirement for the lowest cut-off device in a steam boiler according to CSD-1?
It must be situated above the LPWL
What happens when a low water condition occurs in a steam boiler with a combined feeder/cut-off control?
The boiler shuts off and requires manual operator intervention to restart
What is the primary advantage of using a PI or PID control output signal in a feedwater control system?
Improved stability and responsiveness to system disturbances
What is the purpose of the recorders in a steam boiler control system?
To monitor and record steam flow, feedwater flow, and drum level
What is the primary advantage of a manual-automatic transfer station in the control room of a steam boiler?
It allows the operator to control the drum level manually during startup or in case of an emergency
What is the purpose of the condensate receiver in a steam boiler system?
To receive and store condensate returned from the steam system
What is the primary purpose of a float-controlled switch in a boiler feedwater system?
To control the feedwater pump start/stop
What is the effect of a low water level in a boiler on a float-controlled switch?
The switch opens, starting the feedwater pump
What is the purpose of a vent in a condensate receiver?
All of the above
What is a common problem that can occur with float switches in a condensate receiver?
They can become waterlogged
What is the purpose of a gauge glass in a condensate receiver?
To monitor the condensate level
What is the primary function of a strainer in a boiler feedwater system?
To remove particles from the make-up water
What is the purpose of a low water cut-off switch in a boiler?
To stop the burner when the water level drops
What is the effect of a high water level in a boiler on a float-controlled switch?
The switch opens, stopping the feedwater pump
What is the purpose of a manual reset button in a float-controlled switch?
To reset the switch after a low water cut-off
What is the purpose of a condensate receiver in a heating system?
To collect and store condensate
What is the primary purpose of testing the pH of condensate samples?
To determine the amount of water treatment chemical needed to protect the condensate return lines from corrosion
In a gravity-fed steam heating system, what is the primary function of the return loop?
To prevent low-pressure steam boilers from sustaining low water conditions
What is the requirement for steam heating boilers with gravity condensate returns according to ASME IV?
Installation of a stop valve and check valve in the condensate return lines
In a pumped return system, what is the purpose of the check valve?
To prevent the backup of condensate into the return receiver when the condensate pump is not in operation
What is the primary advantage of using a return loop in a pumped return system?
It prevents the boiler from sustaining low water conditions
In which type of heating system is the condensate returned to the boiler by gravity?
Gravity return system
What is the primary reason why heating boilers do not experience the negative consequences of swell and shrinkage?
Because they operate at low pressure
What is the purpose of the equalizing pipe in a return loop?
To connect the boiler steam outlet to the boiler's water inlet piping
In a pumped return system, where should the return line connection to the boiler be made according to ASME VI?
At the base of the return loop
What is the primary purpose of the stop valve and check valve in the condensate return lines according to ASME IV?
To prevent the backup of condensate into the return receiver when the condensate pump is not in operation
If the supply of make-up water fails or is insufficient, what will happen to the boiler water level?
It will continue to drop
What is the purpose of the additional dedicated low water cut-off required by CSA B51 and ASME CSD-1?
To stop the burner if the water level drops too low
What is the primary advantage of using a gravity return system?
It can operate without electrical power
What is the purpose of the contact switches in the feeder?
To shut off the burner if a low water condition arises
Why is it preferable to introduce corrosive water to a condensate receiver rather than a boiler?
Because the condensate receiver is less expensive to replace
What happens when the boiler water level drops below normal in a gravity return system?
The float opens the make-up water valve
What is the primary purpose of the float controlled switches in a gravity return system?
To shut off the burner if a low water condition arises
What is the primary advantage of using a pumped return system over a gravity return system?
It is more suitable for large heating plants
What happens when the pump fails in a pumped return system?
The float shuts down the burner
What is the primary purpose of the check valve in a pumped return system?
To prevent water from flowing back to the condensate receiver
What is the primary function of the float cage in the condensate receiver?
To maintain the level of water in the condensate receiver
What happens when the water level in the boiler drops to level B?
The feedwater supply switch is closed
Why is a low water cut-off necessary in a steam heating boiler?
To prevent the pump from running dry and sustaining damage
What is the purpose of the alarm switch in a steam heating boiler?
To alert the operator of a low water condition
What is the difference between level A and level B in a steam heating boiler?
Level A is the highest normal operating level, while level B is the lowest normal operating level
Why are individual controls needed for multiple steam heating boilers installed in a common system?
Because each boiler can be operated independently of the others
What is the purpose of the motorized feedwater control valves in a battery of steam heating boilers?
To admit or shut off feedwater to individual boilers
What happens when a boiler needs water in a battery of steam heating boilers?
The float operated switch closes to energize and open the motorized feedwater control valve
Why is it necessary to have a dedicated low water cut-off for each boiler in a battery of steam heating boilers?
To shut off the burner in case of a low water condition in an individual boiler
What is the purpose of the check valve in a pumped return system?
To prevent backflow of condensate into the boiler
What is the primary purpose of a condensate receiver in a well-designed boiler feedwater system?
To hold a volume equivalent to the water evaporated by the boiler in a twenty to thirty minute period
What happens when a condensate receiver is undersized?
The receiver overflows, resulting in a waste of heat and purified water
Why is it important for a condensate receiver to have sufficient capacity during startup?
To handle the initial condensate return surge that occurs shortly after the system is charged and hot
What is the issue with an unreliable make-up feeder in a boiler feedwater system?
It can waste water by feeding too much make-up water, causing the receiver to overflow
What is the consequence of a condensate receiver running dry during the initial startup?
The boiler shuts down due to low water conditions
Why is it important to size a condensate receiver properly?
To prevent the receiver from overflowing and wasting heat and purified water
When is a smaller size receiver used in a steam heating system?
When the condensate returns easily
What is the purpose of the make-up float in a condensate receiver?
To maintain the water level at a minimum of 1/3 full
Why is an externally mounted float controlled feeder valve preferred in most installations?
Because it dampens the receiver level fluctuations
What is the purpose of the diaphragm valve in a make-up water line?
To control the flow of make-up water
What happens when the receiver level drops slightly below normal in a make-up water line?
The float control valve opens slightly
What is the purpose of a low water cut-off switch in a condensate receiver?
To prevent damage to the pump
What is the difference between high-pressure and low-pressure heating plants?
High-pressure plants do not have combined feeder/cut-off controls, while low-pressure plants do
What is the purpose of a float-controlled switch in a condensate receiver?
To control the flow of make-up water
What happens when the level in the receiver is normal and no make-up is required?
The float control valve closes
What is the advantage of using an electric float control actuating a motorized valve in the make-up water line?
It opens in proportion to the drop in water level in the receiver
What is the primary function of the thermometer and pressure gauge in a deaerator?
To monitor the temperature and pressure of the water in the vessel
Why is it important to vent carbon dioxide and oxygen from the deaerator?
To prevent waterside corrosion in the deaerator, feedwater piping, and boilers
What is the purpose of the level controller and control valve in a deaerator?
To control the condensate return and make-up water flow
What happens if the condensate transfer pumps fail when the deaerator is calling for water?
The deaerator water level will drop to the 'make-up start' level
What is the purpose of the safety valve in a deaerator?
To provide pressure relief in the event of an overpressure condition
Why is it important to maintain a minimum vent flow in a deaerator?
To prevent carbon dioxide and oxygen from building up in the deaerator
What is the purpose of the gauge glass in a deaerator?
To provide a visual indication of the water level in the deaerator
What happens if the feedwater pumps shut off in a deaerator?
The boilers will trip on low water
Why is it important to control the water level in a deaerator?
All of the above
What is the purpose of the overflow controller and control valve in a deaerator?
To drain the deaerator if the water level becomes too high
What is the minimum number of independent low water fuel cut-off devices required in a steam boiler not continuously attended by a certified operator?
Two
What is the purpose of a deaerator in a high-pressure steam plant?
To remove dissolved gases from the feedwater
What is the requirement for the installation of low water cut-off devices in boilers fired by gaseous, liquid, or solid fuels in suspension, according to ASME BPVC Section I, PG-61.2?
They must be installed as an alternative to a secondary means of feeding water to boilers
What is the purpose of a feedwater regulating valve in a multiple-boiler system fed from a common source?
To permit the addition of water to the boiler if the regulating valve fails
What is the primary function of condensate receivers and condensate pumps in a high-pressure steam plant?
To serve as a reservoir from which to pump condensate
What is the requirement for the installation of low water cut-off devices in automatically fired high-pressure steam boilers, according to ASME CSD-1, CW-140?
They must be installed in individual chambers attached to the boiler
What is the purpose of a feedwater control valve in a high-pressure steam plant?
To control the boiler water level
What is the purpose of the minimum flow recirculation systems in boiler feedwater pumps?
To prevent cavitation and overheating
What is the purpose of a check valve in a multiple-boiler system fed from a common source?
To prevent backflow from one boiler to another
What is the primary function of a deaerator heater section in a high-pressure steam plant?
To preheat the feedwater to lessen thermal shock at the boiler
Why is it necessary to design feedwater piping for pressure higher than the boiler's maximum allowable working pressure?
To ensure the piping can handle the high pressure when the boiler drum level control valve is partially shut
What is the requirement for the installation of low water cut-off devices in boilers under continuous supervision, according to ASME CSD-1, CW-140?
They are not required
What is the purpose of the discharge outlet check valves in redundant boiler feedwater pumps?
To prevent recirculation of feedwater through a standby pump
What is the requirement for the design pressure of feedwater piping according to ASME B31.1?
It must exceed the boiler's maximum allowable working pressure by either 25% or 1550 kPa, whichever is less
Why do boiler feedwater pumps need to be large enough to provide all the feedwater required at maximum firing rate?
To provide all the feedwater required even when the boiler rarely operates at maximum firing rate
What is the purpose of equipping boiler feedwater pumps with minimum flow recirculation systems in systems where the pumps operate continuously?
To prevent damage to the pumps by cavitation and overheating
What is the primary reason for ensuring a condensate receiver has sufficient capacity?
To handle the initial condensate return surge during system startup
What is the consequence of an undersized condensate receiver?
The receiver will overflow, resulting in a waste of heat and purified water
During seasonal heating system startup, what is the key indicator of a properly sized condensate receiver?
The receiver's ability to handle the initial condensate return surge
What is the primary purpose of a reliable make-up water feeder in a boiler system?
To prevent low water conditions during normal operation
Why does it take longer for condensate to return to the receiver during system startup?
Because the condensate needs time to exchange heat, condense, and travel the length of the return piping
What is the consequence of an unreliable make-up water feeder in a boiler system?
The boiler may shut down due to low water conditions or waste water by feeding too much make-up water
When condensate returns easily, which size of receiver can be used?
Smaller size receiver
What is the purpose of the float mechanism in the receiver?
To maintain the water level in the receiver
What type of valve is preferred for make-up water feeders and controls?
Externally mounted float controlled valve
What happens when the level in the receiver drops slightly below normal?
The float control valve opens slightly
What is the purpose of a low water cut-off switch in a condensate receiver?
To prevent damage to the pump
What is the advantage of using an externally mounted float controlled valve?
It dampens the receiver level fluctuations
What is the purpose of a float-controlled feeder valve in a make-up water line?
To actuate a high capacity diaphragm valve
What is the purpose of a motorized valve in a make-up water line?
To modulate the water flow in proportion to the drop in receiver level
What is the difference between high-pressure and low-pressure steam plants in terms of feedwater system components?
High-pressure plants do not use combined feeder/cut-off controls
What is the code requirement that applies to high-pressure and low-pressure boilers?
CSA B51, 6.3.2
What is the primary purpose of a minimum flow recirculation system in a boiler feedwater pump?
To prevent cavitation and overheating
What is the requirement for the design pressure of a feedwater pump according to ASME BPVC Section I?
3% higher than the highest setting of any pressure relief valve on the boiler
What is the purpose of the discharge outlet check valves in a redundant boiler feedwater pump system?
To prevent water from flowing back into the standby pump
What is the requirement for the design pressure of feedwater piping according to ASME B31.1 Power Piping Code?
The lesser of 25% higher than the maximum allowable working pressure of the boiler or 1550 kPa
What is the primary purpose of a redundant boiler feedwater pump system?
To ensure continuous feedwater flow to the boiler in case of pump failure
Why is it important to design the feedwater piping for a pressure considerably higher than the boiler MAWP?
To prevent damage to the boiler due to high water pressure
What is the primary purpose of the heater section in a deaerator?
To preheat the feedwater to lessen thermal shock at the boiler
What is the requirement for the installation of low water cut-off devices according to ASME CSD-1, CW-140?
Only for automatically fired boilers
What is the purpose of the feedwater regulating valve in a multiple boiler system?
To regulate the feedwater flow to each individual boiler
What is the consequence of not having a sufficient water head in the deaerator?
Cavitation and vapor binding of the boiler feedwater pumps
What is the purpose of the check valve in the condensate return line?
To ensure the correct direction of condensate flow
What is the primary function of the float operated switches in a high-pressure steam boiler?
To cut off the boiler fuel or energy supply when the water level falls below the lowest permissible level
What is the requirement for the installation of low water cut-off devices according to ASME VII Recommended Guidelines?
Each automatically fired boiler should have at least two independent low water cut-offs
What is the purpose of the isolation valve in the feedwater regulating valve?
To isolate the feedwater regulating valve for maintenance
What is the primary advantage of using a deaerator in a high-pressure steam boiler system?
It removes dissolved gases from the feedwater
What is the requirement for the installation of stop valves and check valves in the condensate return lines according to ASME BPVC Section I?
Each boiler’s feedwater connection must have a stop valve as close as practicable to the boiler
What happens when the deaerator water level drops to the "make-up start" level?
A control valve opens to admit treated make-up water to the deaerator.
What is the primary concern of the level controller and control valve in the deaerator?
To keep boiler feedwater pumps from running dry and maintain an uninterrupted boiler feedwater supply.
What is the purpose of the gauge glass in the deaerator?
To show the water level in the storage compartment of the deaerator.
What happens if the deaerator vent is inadvertently shut or blocked?
Non-condensable gases will be trapped in the vessel, causing corrosion.
What is the purpose of the safety valve in the deaerator?
To relieve excess pressure in the deaerator.
What type of valve is used to regulate the amount of gases being expelled from the deaerator?
Gate-type valve.
What is the primary concern of the overflow controller and control valve in the deaerator?
To prevent the deaerator water level from rising too high.
What happens if the condensate transfer pumps fail when the deaerator is calling for water?
The make-up water control valve will open to admit treated make-up water to the deaerator.
What is the purpose of the thermometer and pressure gauge in the deaerator?
To monitor the temperature and pressure of the water in the deaerator.
What happens when the feedwater pumps shut off?
The boiler will trip on low water.
Study Notes
Feedwater Systems
- Feedwater systems supply water to boilers, which produce steam for various applications.
- The system consists of make-up water, condensate return, and feedwater treatment systems.
Make-up Water System
- Make-up water compensates for water losses in the system, such as blowoff, blowdown, and leaks.
- Sources of make-up water include municipal water, rivers, lakes, and wells.
- Each source has unique qualities, such as hardness, biological material, and suspended solids.
- Water treatment is necessary to prepare make-up water for use in the boiler.
Condensate Return System
- Condensate is the liquid formed when steam transfers its latent heat to process equipment.
- Condensate is often pure and hot, making it suitable for reuse in the boiler.
- Reusing condensate reduces the amount of raw water required, decreasing treatment chemicals and energy consumption.
- Condensate return systems can be simple (single receiver and pump) or complex (multiple receivers and pumps).
Feedwater Systems Components
- Condensate receiver or condenser hot well
- Condensate pumps
- Low and high-pressure feedwater heaters
- Deaerator
- Boiler feedwater pumps
- Boiler feedwater control valves
- Isolation valves, bypass valves, and check valves
Feedwater System Operation
- Make-up water and condensate are combined in the deaerator.
- The combined water is fed to the boiler using boiler feedwater pumps.
- Level control valves ensure the boiler is fed enough water to maintain a constant drum level.
- Valves are used to control flow, isolate equipment, and prevent backflow.
Valves in Feedwater Systems
- Gate valves are used for isolation and are not suitable for throttling.
- Globe valves are used for throttling and are suitable for feedwater bypass service.
- Check valves are required to prevent backflow and ensure boiler water level is maintained.
- Control valves regulate level, flow, and pressure in the feedwater system.
- Self-powered valves respond to changes in boiler water level and do not require an external energy supply.
Safety and Code Requirements
- The ASME B31.1 Power Piping Code has specific requirements for feedwater system components.
- Isolation valves are required by code to allow for maintenance and operation of the system.
- Valves must be suitable for the temperature and pressure conditions they will encounter.
- Safety precautions, such as lockout and safe work permits, must be followed when servicing valves and equipment.### Isolation Valves in Feedwater Systems
- Isolation valves are required by code to operate, maintain, and isolate feedwater system components
- ASME B31.1 Power Piping Code 122.1.7 states that feedwater piping for all power boilers shall be provided with a check valve and a stop valve or cock between the check valve and the boiler
Gate Valves and Check Valves
- Gate valves are commonly used in feedwater systems because they seal tight
- Check valves are used to prevent boiler water from flowing back to the feed pumps if the feedwater pumps stop
Control Valves in Feedwater Systems
- Level control valves regulate deaerator level, condensate receiver level, and boiler water level
- Flow control valves regulate steam flow to the deaerator and recirculation flow from the boiler feed pumps
- Pressure control valves relieve excess pressure from deaerators or other feedwater system components
Boiler Feedwater Pumps and Control
- Boiler feedwater pumps operate continuously in larger plants with multiple boilers
- In smaller single-boiler plants, boiler feedwater pumps operate intermittently
- Control valves may be self-powered or part of a PID control loop
Make-Up Water System
- Make-up water sources can be municipal water, rivers, lakes, or wells
- Water treatment is necessary to make boiler-quality water from raw water
- Simplified make-up water treatment systems are used for high-quality sources, while more complex systems are used for poorer quality sources
Condensate Return System
- Condensate is hot and has considerable sensible heat, making it important to recover and reuse
- Recovering condensate reduces water treatment needs and increases plant thermal efficiency
- Impure condensate must be treated before reuse
Feedwater Systems
- The feedwater system includes the condensate receiver or deaerator, feedwater pumps, and boiler feedwater control valves
- Make-up water and condensate are combined and treated before being fed to the boiler
Valves in Feedwater Systems
- Valves are used to control flow, isolate equipment, and prevent backflow
- Valve classes range from Class 150 (weakest) to Class 4500 (strongest)
- Replacement valves must be suitable for the pressures and temperatures they will encounter### Drum Level Control Systems
- Drum level control systems are used to regulate the water level in a boiler drum
- The pressure at the base of the column does not vary, but the pressure at the base of the piping connection varies with boiler drum level
- Variations in drum level are transmitted to the drum level controller, which compares the process variable (drum level) to its set point and sends a signal to the feedwater control valve
Single-Element Feedwater Control
- Single-element feedwater control systems respond to drum level only
- Water level below set point causes the controller to open the valve, and water level above set point causes the controller to close the valve
- The control output signal may be proportional, PI, or PID
- The controller has a hand/auto selector to permit manual feedwater valve operation and accepts changes in drum level set point
Swell and Shrinkage
- Swell occurs when steam flow increases, causing a momentary drop in drum pressure and an increase in drum level
- Shrinkage occurs when steam flow decreases, causing a momentary increase in drum pressure and a decrease in drum level
- Single-element feedwater control systems can be affected by swell and shrinkage, leading to incorrect feedwater flow
Two-Element Feedwater Control
- Two-element feedwater control systems respond to drum level and steam flow
- The system uses two elements to "consult" each other and verify the circumstances of the water level change
- The system is effective when the feedwater pressure is fairly constant and the drum capacity is small
Three-Element Feedwater Control
- Three-element feedwater control systems respond to drum level, steam flow, and feedwater flow
- The system maintains the steam flow and feedwater flow in the same ratio
- The drum level transmitter signal is used to correct the level when swell and shrinkage are not occurring
- The system is more effective in reducing the effects of swell and shrinkage than two-element systems
Heating Boiler Feedwater Systems
- Heating boiler feedwater systems can be classified into gravity return systems and pumped return systems
- Gravity return systems use gravity to provide enough feedwater pressure to overcome boiler pressure
- Pumped return systems are used in larger heating plants where condensate must flow long distances to return to the boiler
Low Water Fuel Cut-Off
- Low water fuel cut-off (LWCO) is a float or probe-operated switch that directly detects the level of water in a boiler
- The LWCO shuts off the boiler burner system if the boiler water level drops to an unsafe level
- CSA B51 and ASME CSD-1 require the installation of LWCOs in steam boilers
Return Loop (Hartford Loop)
- A return loop or Hartford Loop is a special condensate return piping connection that prevents low-pressure steam boilers from sustaining low water conditions
- The return loop has an additional equalizing pipe that connects the boiler steam outlet to the boiler's water inlet piping
- The return loop ensures that the boiler will have sufficient water to cover the heating surfaces to prevent overheating
Test your understanding of boiler systems, including steam and hot water production, and the factors that affect water balance. Learn about the importance of water input and losses due to various processes and faults. Improve your knowledge of steam heating and hot water heating systems.
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