Cascading And Exhaust Systems

Question 1

What occurs when high pressure hot condensate is released to a lower pressure?

Answer 1

Its temperature must quickly drop to the boiling temperature of the lower pressure commonly known as flashing.

Question 2

What is a flash vessel used to separate?

Answer 2

Condensate and flash steam

Question 3

Flash steam may be used to heat domestic hot water. True or false?

Answer 3

True

Question 4

The pipe size for low pressure steam must be small diameter. True or false?

Answer 4

False. Low pressure systems require larger diameter pipe.

Question 5

________ ________ from large diameter pipe reduces the benefits of flash steam recovery.

Answer 5

Heat loss

Question 6

Ideally, the demand for ______ ____________ steam should be greater than the demand for flash steam.

Answer 6

Low pressure

Question 7

The amount of flash steam is dependent upon the pressure and temperature of what?

Answer 7

The pressure and temperature of the steam, upstream and downstream of the trap.

Question 8

Which tank orientation is preferred for flash steam recovery? Horizontal or vertical?

Answer 8

Vertical

Question 9

Through which valve is surplus flash steam sent?
A. Pressure relief valve.
B. Safety valve.
C. Back pressure control valve.

Answer 9

Pressure control valve

Question 10

The use of two or more flash vessels in series is called what?

Answer 10

Cascading

Question 11

Which kind of turbine dumps exhaust steam to the atmosphere?

Answer 11

A non-condensing turbine

Question 12

The exhaust team from the high-pressure turbine must first pass through the condenser before being reused, true or false?

Answer 12

False

Question 13

What must be done to the exhausting before it can be used in the deaerator?

Answer 13

The steam must be cleaned by passing through an oil separator to prevent contamination of the feed water or process.

Question 14

What is the purpose of an oil separator?

Answer 14

An oil separator prevents exhaust steam from contaminating the product.

Question 15

What does an exhaust head do?

Answer 15

Removes moisture and oil from the exhaust steam.

Question 16

Does a surplussing valve since the downstream pressure or upstream pressure for its operation?

Answer 16

Upstream

Question 17

Why is the discharge pipe from a safety valve slashed at a 45° angle?

Answer 17

To reduce thrust

Question 18

When hot condensate rev evaporates, it is referred to as what?

Answer 18

Flash steam

Question 19

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.

Answer 19

B. 10 ft./s.

Question 20

Which ASME code is referenced when a flash vessel, 6 inches in diameter is used?

Answer 20

B31.1

Question 21

What is the most important dimension on a flash tank?

Answer 21

The diameter

Question 22

In general which piece of equipment provides useable exhaust steam?
A. Turbine.
B. Economizer.
C. Heat exchanger.

Answer 22

A. Turbine.

Question 23

What type of force is used to remove moisture from vapour in an exhaust head?

Answer 23

Centrifugal

Question 24

Why is proper sizing of the flash vessel important?

Answer 24

To prevent carryover

Question 25

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.

Answer 25

A. Steam space pressure is less than flash vessel pressure.

Question 26

What are some common pieces of trim found on a flash tank?

Answer 26

Safety valve, a pressure gauge, a steam trap, a strainer, a thermostatic, air vent, and a drain

Question 27

Is a flash vessel sized to allow for an increased velocity OR reduced velocity for the separation of the flash steam and condensate?

Answer 27

Reduced.

Question 28

What does ASHRAE recommend the target velocity is to ensure the proper separation of flash steam, and condensate in a flash vessel?

Answer 28

The target velocity is 3 m/s or 10 ft./s

Question 29

What ASME section do flash tanks generally fall under?

Answer 29

ASME section 8 rules for construction of pressure vessels.

Question 30

Our flash tanks classified as fired, or un-fired pressure vessels?

Answer 30

Unfired.

Question 31

Why is it preferable to select an application for the flash steam that is reasonably close to the high-pressure condensate source?

Answer 31

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.

Question 32

What is the purpose of the Tangential nozzle on a flash tank?

Answer 32

To force the steam into a vortex upon entry of the vessel to absorb condensate off the walls.

Question 33

What is a dash pot?

Answer 33

A device for cushioning or damping in the movement of the mechanical parts of a weight and lever pressure control valve to avoid shock.

Question 34

If the back pressure control valve is open and the flash steam vessel pressure still exceeds its maximum, what occurs?

Answer 34

The safety valve will release this over pressure to atmosphere through the thermostatic vent or exhaust head.

Question 35

Why is the vertical style of flash vessel configuration preferred?

Answer 35

Because of its ability to provide better separation of water and steam.

Question 36

Would the back pressure control valve be set to a higher or lower pressure than the safety valve?

Answer 36

Lower

Question 37

What is exhaust steam?

Answer 37

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.

Question 38

What are the four general components of an exhaust steam system?

Answer 38

Back pressure valve, exhaust head, drain and oil separator

Question 39

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?

Answer 39

1 inch minimum

Question 40

What are the four broad classes of oil separators?

Answer 40

Reverse current, centrifugal force, baffle plate, and mesh