2019 Question of the Month

 

 

QUESTION of the Month for May 2019 

QUESTION:

What is a flame safeguard system?

ANSWER:

 

 

QUESTION of the Month for April 2019 

QUESTION:

What does foaming mean?

ANSWER:

Foaming and priming in boilers

Boiler water carry-over is the contamination of the steam with boiler-water solids. Bubbles or froth actually build up on the surface of the boiler water and pass out with the steam. This is called foaming and it is caused by high concentration of any solids in the boiler water. It is generally believed, however, that specific substances such as alkalis, oils, fats, greases, certain types of organic matter and suspended solids are particularly conducive to foaming. In theory suspended solids collect in the surface film surrounding a steam bubble and make it tougher. The steam bubble therefore resists breaking and builds up foam. It is believed that the finer the suspended particles the greater their collection in the bubble.

Priming is the carryover of varying amounts of droplets of water in the steam (foam and mist), which lowers the energy efficiency of the steam and leads to the deposit of salt crystals on the super heaters and in the turbines. Priming may be caused by improper construction of boiler, excessive ratings, or sudden fluctuations in steam demand. Priming is sometimes aggravated by impurities in the boiler-water.

Some mechanical entrainment of minute drops of boiler water in the steam always occurs. When this boiler water carryover is excessive, steam-carried solids produce turbine blade deposits. The accumulations have a composition similar to that of the dissolved solids in the boiler water. Priming is common cause of high levels of boiler water carryover. These conditions often lead to super heater tube failures as well. Priming is related to the viscosity of the water and its tendency to foam. These properties are governed by alkalinity, the presence of certain organic substances and by total salinity or TDS. The degree of priming also depends on the design of the boiler and its steaming rate.

The most common measure to prevent foaming and priming is to maintain the concentration of solids in the boiler water at reasonably low levels. Avoiding high water levels, excessive boiler loads, and sudden load changes also helps. Very often contaminated condensate returned to the boiler system causes carry-over problems. In these cases the condensate should be temporarily wasted until the source of contamination is found and eliminated. The use of chemical anti-foaming and anti-priming agents, mixtures of surface-active agents that modify the surface tension of a liquid, remove foam and prevent the carry-over of fine water particles in the stream, can be very effective in preventing carry-over due to high concentrations of impurities in the boiler-water.

 

 

QUESTION of the Month for March 2019 

QUESTION:

In a rotary cup burner, atomization is achieved by?

A:  Fuel oil pressure

B: Air pressure

C: The rotary cup

D: The rotary cup and primary air

 

ANSWER:

D: The rotary cup and primary air

Structure of Rotary Cup Burner

 

The rotary cup burner forms a film of fuel oil by the centrifugal power of the cup rotation. By giving high air pressure to this film spread fuel, the rotary cup burner creates very fine oil mist which is necessary for good combustion.

The most dominant characteristic of the rotary cup burner is the way of its atomization.
Unlike the pressure jet burner which needs a small nozzle for atomizing, the rotary cup burner uses a cup with wider holes, meaning the structure of the rotary cup burner secures the burner from choking. By this characteristic, the rotary cup burner is capable of firing high viscosity oil.  Moreover, the rotary cup burner utilizes the centrifugal power for atomizing, which means that high pressure is needless for atomization. The low oil pressure of the rotary cup burner is safer to use when there is any leakage from the piping.

QUESTION of the Month for February 2019

QUESTION:

A boiler steam pressure gauge should have a range of?

A:  1 to 1 1/2 times safety valve setting

B:  1 1/2 to 2 times the safety valve setting

C:  2 to 2 1/2 times the safety valve setting

D:  10% of MAWP

ANSWER:

B:  1 1/2 to 2 times the safety valve setting

The range of the instrument should be approximately
one and half  (1 1/2) to twice  (2) the maximum operating pressure. Too low a range may result in:

(a) low fatigue life of the elastic element due to high operating stress and (b) susceptibility to overpressure set due to pressure transients that exceed the normal operating pressure.

Too high a range may yield insufficient resolution for the application.

QUESTION of the Month for January 2019