Question of the Month: 2016

Question of the Month for November 2016

QUESTION:

What is the purpose of a blowdown connection?

ANSWER:

  1.  To remove precipitated sludge or loose scale.
  2.  To permit rapid lowering of the boiler water level if it has become to high.
  3.  As a means of removing water from the boiler system so fresh water may be added to keep concentration of solids in the boiler below the point where difficulties may be experienced.

 The blowdown valves are a very popular category of pipe valves, used in a wide variety of applications. They are used for operation in open position. The main function of blowdown valve is mainly to control a continuous flow of steam /fluid under high differential pressure.

Dissolved solids and particles in the make-up water will remain in the boiler when steam is generated. During operation the total dissolved solids (TDS) builds up finally reaching a concentration level where the operation of the boiler becomes impossible.

  • Total Dissolved Solids – TDS – is normally measured in ppm

If solids are not purged from the boiler they can lead to

  • scale formation
  • carryover
  • corrosion
  • embrittlement

Chemical treatments and continuous surface blowdowns are commonly used to eliminate solids at the same rate as they are added from the feed water.

Recommended maximum TDS levels depends on the type of boiler – normally ranging 2000 – 10000 ppm. TDS can be monitored by measuring the electrical conductivity of the boiler water. A rise in conductivity indicates contaminated water.

In general

  • short frequent blowdowns are more effective in removing boiler water sludge than
  • a one long infrequent blowdown

Note that blowdown tanks are required by the Uniform Plumbing Code (UPC) and Uniform Mechanical Code (UMC) Codes on any hi-pressure installations exceeding 15 psig.

The International Association of Plumbing and Mechanical Officials (IAPMO) develops the Uniform Plumbing Code (UPC) which is widely adopted in western United States.

Due to high pressure and temperature in the boilers – large amounts of flash steam are generated during blowdown. BE AWARE that the hot water and flash steam are DANGEROUS. Care must be taken during design, construction and operation.

Manual Blowdown

Manual blowdown can be accomplished through taping at the bottom of the boiler where settled solids are removed. With manual blowdown water level control devices and cutoff devices are kept clean of any solids interfering with their operation.

All steam boilers requires an arrangement for manual blowdown even if they are supplied with automatic continuous blowdown systems or not.

Automatic Continuous Blowdown

A continuous blowdown system use a calibrated valve and a blowdown tap near the boiler water surface. Water is continuously taken from the top of the boiler at a predetermined rate.

ASME Guidelines for Water Quality in Watertube Boilers

Maximum allowable water impurities:

Boiler Pressure
(psig)
Iron Concentration
(ppm)
Copper Concentration
(ppm)
Hardness CaCO3
(ppm)
Silica Concentration
(ppm)
Alkalinity CaCO3
(ppm)
Total Dissolved Solids
– TDS – 
(ppm)
Specific Conductivity
(μS/cm)*
0 – 300 0.1 0.05 0.3 150 700 3500 7000
300 – 450 0.05 0.025 0.3 90 600 3000 6000
450 – 600 0.03 0.02 0.2 40 500 2500 5000
600 – 750 0.025 0.02 0.2 30 400 1000 4000
750 – 900 0.02 0.015 0.1 20 300 750 3000
900 – 1000 0.02 0.015 0.05 8 200 625 2000

 electrical conductivity is measured in 1/ohms m, 1/Ω m, siemens/m, S/m or mho/m.

  • 1 S/m = 104 μS/cm
  • 0.042 µS/cm – Ultrapure water (20°C)
  • 0.5  – 5 µS/cm – Deionized water
  • 100 – 300 µS/cm – Soft ground water
  • 45000 – 55000 µS/cm – Sea water
  • > 100000 µS/cm – Concentrated acids or lyes (highly concentrated aqueous solution of potassium hydroxide or sodium hydroxide (caustic soda))

Image result for boiler blowdown valves

Question of the Month for October 2016

QUESTION:

Safety Valves on a High Pressure Boiler can be Tested?

a.  only by hand

b.  only by pressure

c.  by hand by pressure, bench tested

d.  bench tested

e.  safety valves should never be tested

ANSWER:

c.

First off only qualified person should test boiler safety valves as testing can present many hazards.  Each State or Jurisdiction has requirements for testing of safety  devices, or they will reference the American Society of Mechanical Engineers (ASME) or/and the National Board (NB).  Remember to document all testing!

Safety Valves can be tested one of three (3) ways.  These are

                                                                                                                                                                                Operated in place

Tested in place

Bench tested

Question of the Month for September 2016

QUESTION:

A therm of Natural Gas has 10,000 BTU’s?

ANSWER:

False!

A therm is a measurement of the amount of heat energy in natural gas, equal to 100,000 BTUs. A BTU, or British Thermal Unit, is the quantity of heat required to raise the temperature of one pound of water by one degree Fahrenheit.

Question of the Month for August 2016

QUESTION:

In a rotary cup burner, atomization is achieved by?

Fuel Pressure

Air Pressure

      The Rotary Cup

                                    The Rotary Cup and Primary Air

ANSWER:

                             The Rotary Cup and Primary Air

What is rotary cup burner?

Fuel oil is guided to inside of the cup spinning in high speed, formed thin film by centrifugal power, hit by high air pressure for

atomization. It is the mechanism of rotary cup burner.

The pressure jet burner atomizes fuel oil by high oil pressure through very small hole of nozzle tip. Comparing to it, the rotary cup

burner does not need to have this small hole due to above mechanism, and can accept wide viscosity range of fuel. There is no

concern of fuel oil stuck during heavy fuel oil burning and the rotary cup burner can obtain stable combustion for long period.

Additionally one of big advantage is easy handling at start of burner in cold condition and while continuous running, in a range

from small boiler to large boiler. Because it does not require any special procedures nor maintenance due to no assisting steam for

combustion. Another advantage is to dispose waste oil which generates onboard.

Wider range of viscosity can be accepted for the fuel oil applying to the rotary cup burner. Recently we have to switch two fuel oils

which have totally different characteristics: one is low-sulphur low-viscosity good-quality fuel oil used in emission control harbor

areas and the other is high-viscosity heavy fuel oil used in other area. Because wider range of viscosity can be accepted in the fuel

oil applying to the rotary cup burner and as it does not require oil pressure for atomization, the complicated adjustment or

maintenance jobs are not required when you switchover the fuels. It would require only minimum adjustment and can be handled

easily.

Question of the Month for July 2016

QUESTION:

What is the purpose of the water column on a high pressure boiler?

ANSWER:

A water column is used on a steam boiler to reduce the turbulence and fluctuation of the water level so the gage glass can provide a steady, accurate water level reading. The use of a water column is not mandatory.

Question of the Month for June 2016

QUESTION:

What is gross calorific value and net calorific value of coal?

ANSWER:

1.calorific value:- It is the amount of heat liberated with a unit mass of coal for  1g Kcal.

2.Gross calorific value:-It is the amount of heat liberated by the complete  combustion of unit weight of fuel with subsequent cooling of   product(moisture/water vapor) . G.C.V is more than N.C.V.

3. Net calorific value :- It is the heat produced in complete combustion when the product of combustion are allowed to escaped.

N.C.V = G.C.V – Latent heat of water vapor.            N.C.V = (G.C.V-0.09×587)cal/gm.

Question of the Month for May 2016

QUESTION:

What is the inherent problem in Composite Boiler?

ANSWER:

There are different types of composite boilers. Normally one part of the boiler is heated by means of a fuel oil burner and the other part is heated by the exhaust gases from a diesel engine.

  • Heating of one part of a boiler at the time often causes thermal stress that may lead to leakage.
  • One single composite boiler does not fulfill normal requirement of redundancy when the steam is used for essential service purpose.

Question of the Month for April 2016

QUESTION:

What are the service restrictions for a potable water heater built to Section IV?

ANSWER:

Pressure not exceeding 160psi and water temperature not in excess of 210ºF, per HLW-101.1

Question of the Month for March 2016

QUESTION:

Is a Bi Color Water Gage glass acceptable on a 2000 psi boiler?

ANSWER:

Yes

Good to 3000 psi.

Question of the Month for January 2016

QUESTION:

Which valve is between the boiler and the return pump?

ANSWER:

Check Valve