Velox Boiler: Principle, Construction, Working & More

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Velox Boiler-

A Velox boiler is a type of high pressure, forced circulation, water tube boiler.

It was developed in the 1930s by Brown Boveri company of Switzerland. The first public demonstration of Velox was at VDI scientific conference in Berlin in October 1932.

Working Principle of Velox Boiler-

Volex boiler is based on the principle of, when the velocity of gas becomes more than the velocity of sound, the transmission of heat by gas becomes much higher as compared to heat transmission of heat at sub-sonic speed, ie, lower than the speed of sound. In a Velox boiler velocity of the gas is higher than the velocity of sound.

In this boiler heat transfer rate or steam generation rate can be increased without increasing the size of the boiler.

It can be increased by simply increasing the speed of gas.

Related Article- LaMont Boiler: Definition, Parts, Working, Application, Advantages, Disadvantages

Construction & Parts of Velox Boiler-

Velox Boiler consists of several parts

  • Feed pump
  • Economizer
  • Water circulation Pump
  • Combustion chamber
  • Gas turbine
  • Axial Compressor
  • Steam Separator
  • Super Heater

The feed pump supplies water inside the boiler. Then, this water goes to the economiser where this device preheats the water with the help of combustion chamber heat.

The water circulation pump helps to circulate the water into the entire boiler, Where the combustion chamber helps to provide needed heat by burning fuel.

The axial compressor is used to compress and pressurize steam and the steam separator sends the dry steam to the superheater and non-steam liquid back.

A superheater is used to superheat the steam and send it to a gas turbine where the energy of high-pressure steam will be converted into mechanical energy or generate electricity.

These were the Mounting and Accessories of this boiler.

Velox boiler diagram-

velox boiler diagram

Related Article- Schmidt-Hartmann Boiler

Working of Velox Boiler-

  • At first, water is fed to the economiser from the feed pump.
  • The economiser heats the water but does not heat up to the boiling point.
  • Then the warm water from the economiser is passed to the water circulating pump.
  • Then the water enters the tube evaporating section which is inside the combustion chamber.
  • On the other hand, a gas turbine drives an axial air compressor.
  • A gas turbine converts gas into mechanical energy and with that mechanical energy axial air compressor is driven.
  • In an axial air compressor, the air flows through the axis of rotation of the compressor.
  • The compressed air by the air compressor enters the combustion chamber and passes from it.
  • When this compressed air passes from the combustion chamber more heat is released by the fuel which increases the velocity of flue gases up to the sound velocity.
  • Flue gases pass from the fire tubes near the bottom of the combustion chamber.
  • These fire tubes are surrounded by evaporator water tubes. when the water enters the evaporating tube at high speed, the formation of gas happens at a very high rate due to the high speed of water and gas.
  • After that mixture of water and steam is formed which is passed through a water and steam separator.
  • This separator separates the steam from the water. The steam from the steam separator is passed to the superheater.
  • The remaining water again passes from the evaporator tube and this process continues until the water is converted into steam.
  • The flue gases from fire tubes are sent to the superheater for heating the steam.
  • After that the flue gas from the superheater is sent to the gas turbine where it rotates the gas turbine and after that gas passes the economiser used to heat the water initially which is coming from the feed pump.
  • This is how the Velox boiler works.

Related Article- Locomotive Boiler: Parts, Working, Advantages, disadvantages, Applications

Here are Velox boiler advantages and disadvantages-

Advantages of Velox Boiler-

Here are some advantages of the Velox boiler-

  1. Velox Boiler is very compact and requires very little space as compared to other boilers.
  2. It can be started quickly and easily
  3. It has good flexibility
  4. It has a high thermal efficiency of about 90-95%
  5. It has a high heat transfer rate.
  6. High Combustion rate
  7. Easy to use

Related Article- Top 35 Boiler Questions and Answers [With PDF]

Disadvantages of Velox boiler-

Here are some of the drawbacks of this boiler-

  • High Initial Cost
  • Complex Design
  • Limited Capacity
  • High Noise Level
  • Efficiency challenges
  • High operation temperature
  • Limited fuel flexibility


Still, having a lack of clarity?

This video guide will help you to gain a sense of clarity, Have a look-

Related Article- Loeffler Boiler: Definition, Parts, Working, Advantages, Disadvantages, and Applications


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If you want to read more, then here is some suggested article, you should consider going through-

Benson Boiler: Working Principle, Pros and Cons and Applications

Cornish Boiler: Parts and Construction, Working, Applications and More

Lancashire Boiler: Working. Parts, Advantages, Applications

Why do nuclear power plants have such wide chimneys?

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Velox boiler pdf Velox boiler pdf 
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Here are some Frequently asked questions And MCQs, you should consider staying there for some time.



Which type of water circulation found in the Velox boiler?

Forced type of water circulation found in Velox boiler.

What is the Velox boiler pressure in a bar?

The pressure of Velox boiler is 2.5 to 3 bar.

The fusible plug in small boilers is located-
A. In the drum
B. In the fire tube
C. Above steam dome
D. Over the combustion chamber

Answer- D. Over the combustion chamber

An economizer is fitted with a boiler to-
A. Increase the steam pressure
B. Heat the fuel of low CV
C. Heat the air entering fire grate
D. Heat the feed water by waste gases

Answer- D. Heat the feed water by waste gases

The term heating surface in a boiler means-
A. Area of grate
B. Volume of furnace
C. Outer surface area of boiler
D. Surface area which is in contact with flue gases

Answer- D. Surface area which is in contact with flue gases

The boiler ratings is usually defined in terms of
A. maximum temperature of steam
B. Heat transfer rate in kJ/hr
C. Steam output in kg/hr
D. Heating surface area

Answer- C. Steam output in kg/hr

The amount of water evaporated from and 100C into dry saturated steam at atmospheric pressure is called-
A. Equivalent evaporation
B. Evaporative capacity
C. Boiler horsepower
D. Generation rate

Answer- A. Equivalent evaporation

The ratio of actual heat used in steam generating to the heat librated in the boiler furnace by the combustion of fuel is called-
A. Boiling rate
B. Boiler efficiency
C. Generating factor
D. Equivalent evaporation

Answer- B. Boiler efficiency

The steam jet draught is used in-
A. Cochran boiler
B. Locomotive boiler
C. Lancashire boiler
D. Babcock-Wilcox boiler

Answer- B. Locomotive boiler

The amount of water evaporated into steam in a period of one hour is known as-
A. Boiler efficiency
B. Equivalent efficiency
C. Capacity of boiler
D. None of these

Answer- C. Capacity of boiler


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