Cascading And Exhaust Systems Flashcards
What occurs when high pressure hot condensate is released to a lower pressure?
Its temperature must quickly drop to the boiling temperature of the lower pressure commonly known as flashing.
What is a flash vessel used to separate?
Condensate and flash steam
Flash steam may be used to heat domestic hot water. True or false?
True
The pipe size for low pressure steam must be small diameter. True or false?
False. Low pressure systems require larger diameter pipe.
________ ________ from large diameter pipe reduces the benefits of flash steam recovery.
Heat loss
Ideally, the demand for ______ ____________ steam should be greater than the demand for flash steam.
Low pressure
The amount of flash steam is dependent upon the pressure and temperature of what?
The pressure and temperature of the steam, upstream and downstream of the trap.
Which tank orientation is preferred for flash steam recovery? Horizontal or vertical?
Vertical
Through which valve is surplus flash steam sent?
A. Pressure relief valve.
B. Safety valve.
C. Back pressure control valve.
Pressure control valve
The use of two or more flash vessels in series is called what?
Cascading
Which kind of turbine dumps exhaust steam to the atmosphere?
A non-condensing turbine
The exhaust team from the high-pressure turbine must first pass through the condenser before being reused, true or false?
False
What must be done to the exhausting before it can be used in the deaerator?
The steam must be cleaned by passing through an oil separator to prevent contamination of the feed water or process.
What is the purpose of an oil separator?
An oil separator prevents exhaust steam from contaminating the product.
What does an exhaust head do?
Removes moisture and oil from the exhaust steam.
Does a surplussing valve since the downstream pressure or upstream pressure for its operation?
Upstream
Why is the discharge pipe from a safety valve slashed at a 45° angle?
To reduce thrust
When hot condensate rev evaporates, it is referred to as what?
Flash steam
What velocity does ASHRAE recommend for proper separation of flash steam in a flash vessel?
A. 12 ft./s.
B. 10 ft./s.
C. 8 ft./s.
B. 10 ft./s.
Which ASME code is referenced when a flash vessel, 6 inches in diameter is used?
B31.1
What is the most important dimension on a flash tank?
The diameter
In general which piece of equipment provides useable exhaust steam?
A. Turbine.
B. Economizer.
C. Heat exchanger.
A. Turbine.
What type of force is used to remove moisture from vapour in an exhaust head?
Centrifugal
Why is proper sizing of the flash vessel important?
To prevent carryover
In a flash steam system, waterlogging of equipment is caused by which?
A. Steam space pressure is less than flash vessel pressure.
B. Flash vessel pressure is less than steam space pressure.
A. Steam space pressure is less than flash vessel pressure.
What are some common pieces of trim found on a flash tank?
Safety valve, a pressure gauge, a steam trap, a strainer, a thermostatic, air vent, and a drain
Is a flash vessel sized to allow for an increased velocity OR reduced velocity for the separation of the flash steam and condensate?
Reduced.
What does ASHRAE recommend the target velocity is to ensure the proper separation of flash steam, and condensate in a flash vessel?
The target velocity is 3 m/s or 10 ft./s
What ASME section do flash tanks generally fall under?
ASME section 8 rules for construction of pressure vessels.
Our flash tanks classified as fired, or un-fired pressure vessels?
Unfired.
Why is it preferable to select an application for the flash steam that is reasonably close to the high-pressure condensate source?
Due to the low pressure steam system requiring larger diameter piping, as it is more costly to install, and the heat loss from the large diameter pipes reduces the benefits of flash steam recovery.
What is the purpose of the Tangential nozzle on a flash tank?
To force the steam into a vortex upon entry of the vessel to absorb condensate off the walls.
What is a dash pot?
A device for cushioning or damping in the movement of the mechanical parts of a weight and lever pressure control valve to avoid shock.
If the back pressure control valve is open and the flash steam vessel pressure still exceeds its maximum, what occurs?
The safety valve will release this over pressure to atmosphere through the thermostatic vent or exhaust head.
Why is the vertical style of flash vessel configuration preferred?
Because of its ability to provide better separation of water and steam.
Would the back pressure control valve be set to a higher or lower pressure than the safety valve?
Lower
What is exhaust steam?
Exhaust steam is classified as the steam that is dumped to atmosphere from non-condensing turbines, or the exhaust steam, or still useable steam that exits a turbine, piston pump or similar piece of equipment.
What are the four general components of an exhaust steam system?
Back pressure valve, exhaust head, drain and oil separator
What is the minimum pipe size for a drain when installed on the bottom of a vessel? In order to remove sludge or unwanted condensate when the vessel is not in service?
1 inch minimum
What are the four broad classes of oil separators?
Reverse current, centrifugal force, baffle plate, and mesh
