Velox Boiler

Velox boiler transfers heat from the gas at a much higher rate than the rate achieved with the sub-sonic flow when the gas velocity exceeds the sound velocity. The advantages of this theory are taken to effect the large heat transfer from a smaller surface area in this boiler.

In Velox boiler, air is compressed to 2.5 bar with the help of a compressor run by a gas turbine before supplying to the combustion chamber to get the supersonic velocity of the gases passing through the combustion chamber and gas tubes and high heat release rates (40 MW/m³). The burned gases in the combustion chamber are passed through the annulus of the tubes. The heat is transferred from gases to water while passing through the annulus to generate the steam. The mixture of water and steam is thus formed and then passes into a separator designed to enter the mixture with a spiral flow. The centrifugal force thus produced causes the heavier water particles to be thrown outward on the walls. This effect separates the steam from the water. The separated steam is further passed to the superheater and then supplied to the prime-mover. The water removed from the steam in the separator is again passed into the water tubes with the help of a pump.

The gases coming out from the annulus at the top are further passed over the superheater, where its heat is used to superheat the steam. The gases from a superheater are used to run a gas turbine as they carry sufficient kinetic energy. The gas turbine's power output is used to run the air compressor. The exhaust gases coming out from the gas turbine are passed through the economizer to utilize the remaining heat of the gases. The extra power required to run the compressor is supplied with the help of an electric motor. Feedwater of 10 to 20 times the weight of steam generated is circulated through the tubes with the help of the water-circulating pump. This prevents the overheating of metal walls.

The size of the Velox boiler is limited to 100 tons per hour because 400 KW is required to run the air compressor at this output. The power developed by the gas turbine is not sufficient to run the compressor and therefore some power from an external source must be supplied as mentioned above.

Key Features and Working Principles of Velox Boiler:

1. Forced Air Circulation: The forced air circulation into the combustion chamber enables the Velox boiler to maintain high combustion rates and steam output, even at high pressures.
2. Rapid Steam Generation: Due to the high air and gas flow velocity, the Velox boiler can achieve fast steam production, making it suitable for industrial and power applications.
3. High Pressure and Efficiency: These boilers operate efficiently at pressures up to 100 bar, which can lead to better overall efficiency and fuel usage.
4. Water-Tube Design: The Velox boiler uses water-tube technology, where water flows through tubes and is heated by hot gases from the combustion chamber.

Applications of Velox Boiler:

Due to its fast response time and high efficiency, the Velox boiler is typically used in:

1. Power generation plants requiring high-pressure steam
2. Industries where quick and efficient steam production is crucial
3. Specific naval and aerospace applications due to its compact design

Advantages of Velox Boiler:

1. Very high combustion rates, such as 40 MJ/m3 of combustion chamber volume, are possible.
2. Excess air is required as the pressurized air is used and the drought problem is simplified.
3. It is a very compact generating unit and has greater flexibility.
4. It can be quickly started even though the separator has a storage capacity of about 10% of the maximum hourly output.