BENSON BOILER (SUPERCRITICAL BOILER)
The main difficulty experienced in the La Mont boiler is the formation and attachment of bubbles on the inner surfaces of the heating tubes. The attached bubbles reduce the heat flow and steam generation as it offers higher thermal resistance compared to water film. Benson of siemens- West Germany in 1922 argued that if the boiler pressure was raised to critical pressure (225 atm.), the steam and water would have the same density and therefore the danger of bubble formation can be completely removed.
1. Economiser – The feed water from the well passes through the economiser where it is pre-heated by the pre-heat of exhaust hot flue gases.
2. Radiant evaporator – The feed water after circulation through the economiser flows through the radiant evaporator tubes. Water is heated up by the radiation heat from the combustion chamber. Here, part of the water is converted to steam directly.
3. Convective evaporator – The mixture of water and steam coming out from the radiant evaporator enters the convective evaporator tubes. The hot flue gases passing over the evaporator tubes transfer a large portion of heat to the water by convection. Thus, water becomes steam in the convective evaporator.
4. Superheater – The steam from the convective evaporator enters the superheater tubes where it is superheated by the hot flue gases passing over them. The superheated steam then enters the steam turbine to develop power.
5. Air pre-heater – The hot flue gases then passes through the air pre-heater where the
air required for combustion is pre-heated.
1. As there is no drum, the total weight of Benson boiler is 20% less than other boilers. This reduces the cost of the boiler.
2. Floor space requirements of Benson boiler are very less.
3. Transportation of Benson boiler parts and its erection is very easy as there are no drums.
4. Natural circulation boilers require expansion joints in pipes but the pipes in Benson boilers are welded.
1. As the Benson boiler operates at high pressure and temperature, special alloy materials are required.
2. Maintenance costs are very high.
3. This is more efficient, resulting in slightly less fuel use.