Question of the Month: 2013

Question of the Month for December 2013

The throttling calorimeter determines?

a. heat in the condensate

             b. saturated steam temperature

                c. superheated steam temperature

                        d. the amount of moisture in the steam

Answer:     d. the amount of moisture in the steam

The presence of moisture in steam causes a loss, not only in the practical waste of the heat utilized to raise this moisture from the temperature of the feed water to the temperature of the steam, but also through the increased initial condensation in an engine cylinder and through friction and other actions in a steam turbine. The presence of such moisture also interferes with proper cylinder lubrication, causes a knocking in the engine and a water hammer in the steam pipes. In steam turbines it will cause erosion of the blades.

The percentage by weight of steam in a mixture of steam and water is called the quality of the steam.

The apparatus used to determine the moisture content of steam is called a calorimeter though since it may not measure the heat in the steam, the name is not descriptive of the function of the apparatus. The first form used was the “barrel calorimeter”, but the liability of error was so great that its use was abandoned. Modern calorimeters are in general of either the throttling or separator type.

Throttling Calorimeter

Throttling Calorimeter and Sampling Nozzle

The instrument and all pipes and fittings leading to it should be thoroughly insulated to diminish radiation losses. Care must be taken to prevent the orifice from becoming choked with dirt and to see that no leaks occur. The exhaust pipe should be short to prevent back pressure below the disk.

When steam passes through an orifice from a higher to a lower pressure, as is the case with the throttling calorimeter, no external work has to be done in overcoming a resistance. Hence, if there is no loss from radiation, the quantity of heat in the steam will be exactly the same after passing the orifice as before passing. If the higher steam pressure is 160 pounds gauge and the lower pressure that of the atmosphere, the total heat in a pound of dry steam at the former pressure is 1195.9 B. t. u. and at the latter pressure 1150.4 B. t. u., a difference of 45.4 B. t. u. As this heat will still exist in the steam at the lower pressure, since there is no external work done, its effect must be to superheat the steam. Assuming the specific heat of superheated steam to be 0.47, each pound passing through will be superheated 45.40.47 = 96.6 degrees. If, however, the steam had contained one per cent of moisture, it would have contained less heat units per pound than if it were dry. Since the latent heat of steam at 160 [Pg 130] pounds gauge pressure is 852.8 B. t. u., it follows that the one per cent of moisture would have required 8.5 B. t. u. to evaporate it, leaving only 45.4 – 8.5 = 36.9 B. t. u. available for superheating; hence, the superheat would be 36.90.47 = 78.5 degrees, as against 96.6 degrees for dry steam. In a similar manner, the degree of superheat for other percentages of moisture may be determined.

Let

H

= total heat of one pound of steam   at boiler pressure,

L

= latent heat of steam at boiler   pressure,

h

= total heat of steam at reduced   pressure after passing orifice,

t1

= temperature of saturated steam at   the reduced pressure,

t2

= temperature of steam after   expanding through the orifice in the disc,

0.47

= the specific heat of saturated   steam at atmospheric pressure,

x

= proportion by weight of moisture   in steam.

The difference in B. t. u. in a pound of steam at the boiler pressure and after passing the orifice is the heat available for evaporating the moisture content and superheating the steam. Therefore,

For practical work it is more convenient to dispense with the upper thermometer in the calorimeter and to measure the pressure in the steam main by an accurate steam pressure gauge.

Question of the Month for November 2013

Smoke is the result of_____?

     a.  complete combustion

        b.  incomplete combustion

c.  too much excess air

   d.  too much primary air

Answer:  b.  incomplete combustion 

Incomplete combustion occurs when there isn’t enough oxygen to allow the fuel (usually a hydrocarbon) to react completely with the oxygen to produce carbon dioxide and water, also when the combustion is quenched by a heat sink such as a solid surface or flame trap. When a hydrocarbon burns in air, the reaction will yield carbon dioxide, water, carbon monoxide, pure carbon (soot or ash) and various other compounds such as nitrogen oxides. Incomplete combustion is much more common and will produce large amounts of byproducts, and in the case of burning fuel in automobiles, these byproducts can be quite unhealthy and damaging to the environment.

Quality of combustion can be improved by design of combustion devices, such as burners and internal combustion engines. Further improvements are achievable by catalytic after-burning devices (such as catalytic converters). Such devices are required by environmental legislation for cars in most countries, and may be necessary in large combustion devices, such as thermal power plants, to reach legal emission standards.

 Question of the Month for October 2013

An ignition arch is used in a ____ stoker?

a.  sidefeed

b.  spreader

 c.  underfeed

  d.  chain grate

Answer:

d. Chain grate

 

A flat or curved refractory roof over a furnace at the point of fuel entrance
that promotes ignition by reflection of heat

chain grate storker

a wide endless traveling chain that feeds and supports the fuel in a boiler furnace

|

|

Question of the Month for September 2013

What type of draft fan must be used to overcome resistance caused by gases of combustion leaving the boiler when an economizer is used?

Answer:

Induced Fan.

Question of the Month for August 2013

The sequence of three numbers found on the data plate attached to a recriporcating feedwater pump indicates?

Answer:

Diameter of steam stroke, diameter of steam piston, and length of pump stroke.

Question of the Month for July 2013

 Boiler water having a high alkalinity could develop?

Answer:

 Caustic embrittlement

 As water evaporates in the boiler, the concentration of sodium carbonate increases in the boiler. Sodium carbonate is used in softening of water by lime soda process, due to this some sodium carbonate maybe left behind in the water. As the concentration of sodium carbonate increases, it undergoes hydrolysis to form sodium hydroxide.

Na2CO3 + H2O2NaOH + CO2

The presence of sodium hydroxide makes the water alkaline. This alkaline water enters minute cracks present in the inner walls of the boiler by capillary action. Inside the cracks, the water evaporates and amount of hydroxide keeps on increasing progressively. This sodium hydroxide attacks the surrounding material and the dissolves the iron of the boiler as sodium ferrate. This causes embrittlement of boiler parts like rivets, bends and joints, which are under stress.

 Question of the Month for June 2013

To aid in the delivery of moisture-free steam, the steam leaves the steam and water drum through the ?

 Answer:

 A Dry Pipe

Question of the Month for May 2013

 Can a globe valve be used as a Main Steam Stop on a Boiler?

 Answer:

a “globe valve” is never  to be used as a main steam stop valve
a “globe valve” restricts a flow of steam passing through it, resulting in a drop in pressure

Question of the Month for February 2013

What are the general welding requirements in Wisconsin?


Answer:

Rather than think in terms of general requirements, fabricators must ensure that welding procedures comply with all of the details of the adopted standard that applies to that specific type of work being completed.

Consult the applicable codes for the specific type of work:
Structural steel welding for buildings use SPS 362.2208, welding with the adoption of AWS D1.1 and D1.3. Credential requirements are in the SPS 305,

Licensing, Certifications, and Registrations Code, specifically 305.34 and 305.35. Structural steel welders on job sites must have a valid wallet card issued by the

Department of Safety and Professional Services, Safety and Buildings Division.


New boiler and pressure vessel construction welding requirements are contained in the SPS 341, Boilers and Pressure Vessels Code, which adopts ASME Boiler

and Pressure Vessel Code, Sections 1 through 12; the National Board Inspection Code, NB-23; ASME B31.1 Power Piping; and ASME B31.3 Process Piping

Refrigeration Systems: ASME B31.5 Refrigeration Piping Code; SPS 345, Mechanical Refrigeration Code

Gas Systems: SPS 340 Gas Systems Code; NFPA-54; NFPA-58


Anhydrous Ammonia: SPS 343, Anhydrous Ammonia Code; ANSI K61.1; ASHREA Codes

Amusement Rides: SPS 334, Amusement Rides Code

Elevators: Comm 18, Elevators Code

Question of the Month for January 2013

Who is the Bureau Section Chief for the Department of Safety & Professional Services?

Answer:

Rick Merkle, State of Wisconsin Section Chief
Department of Safety and Professional Services

141 NW Barstow St 4th FL

Waukesha, WI 53188-3789

Primary Ph: 262-521-5065

Secondary Ph: 608-266-3037

Fax: 608-283-7415

e-mail: rick.merkle@wisconsin.gov