Velox boiler

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A Velox boiler is a high pressure, forced circulation, water-tube boiler. It was developed in 1930's by Brown Boveri Company of Switzerland.[1][2] The first public demonstration of Velox was at VDI Scientific Conference in Berlin on 15th October 1932.[3]


Velox principle[edit]

From Brown Boveri Review[4]

The Velox principle combines the use of combustion under pressure, with very high flue gas velocities and with a gas turbine, whereby the pressure in the combustion chamber, the high gas velocities and the pressure drop of the gases for production of work are created by means of a compressor driven by the gas turbine, the latter being actuated by the products of combustion.

The great significance of the Velox idea lies in the fact that by means of the increase in pressure and velocities the components are greatly reduced in size, and the processes are accelerated without impairing the efficiency.


Velox boiler is based on the principle that heat transfer rate increases when velocity of flue gas is more than speed of sound. This increases steam generation rate.[5] Flue gases are used to turn turbine which is connected to the compressor. It increases the flow of hot air to speed of sound. This increases the rate of heat transfer to the water coming from economizer into evaporating section causing it to generate more steam that goes in superheater via steam separator. Steam from superheater is at high temperature and pressure. This is used to operate turbines.


  • Water feed pump
  • Economizer for water preheating
  • Hot water circulating pump
  • Tube evaporating section
  • Turbine
  • Compressor
  • Steam separator
  • Superheater


Velox boiler was primarily marketed for electricity generation. They were anticipated to be used in steam locomotives on land as well as on sea but eventually lost to efficiency and cost effectiveness of supercharged diesel engine and constant pressure combustion gas turbine. Advantages of somewhat reduced weight and purely rotary motion were greatly offset by the fact that Velox boilers were little over half efficient compared to diesel engines.[6]


  • Compact design.
  • Flexibility of design.
  • High combustion rate.
  • It can be quickly started.


Requires additional parts[8]

  • Electric starter.
  • Gas turbine to drive air compressor.
  • Steam turbine for water circulation.