Crone Fluidized Bed Boiler (CFB)
In the early 1980’s in co-operation with “the British Coal Board” , F&H Crone developed a fluidized bed boiler that produces heat fired on coal. Later it turned out, that this system also worked fine with other (bio)fuels such as various sorts of wood (pellets, chips, etc.). Only condition is that the dimensions of the fuel part may not exceed ± 4 cm.
Wood is CO2 neutral and therefore it contributes to CO2 emission reduction and it reduces the dependency on fossil fuels. A very hot item nowadays. The wood may have a moisture content of 45% as a maximum. Beyond that point it is hardly any use as the efficiency drops dramatically and you are only ‘burning’ water.
The most crucial part of a system like that is the feeding system. This needs to be adapted and custom made to the fuel that is chosen. Also one should think of storage, internal and external logistics as well as processing the fuel parts.
After the combustion process, flue gases need to be cleaned thoroughly in order to meet local rules and regulations. There are various solutions obtainable, depending on your location (rural, suburban). F&H Crone markets a complete solution together with our partners in biomass systems.
The F&H Crone CFB boiler is available in capacities ranging from 1 to 8 MW.
- High Efficiency FBC boilers can burn fuel with a combustion efficiency of over 95% irrespective of ash content. FBC boilers can operate with overall efficiency of 84% (plus or minus 2%).
- Reduction in Boiler Size High heat transfer rate over a small heat transfer area immersed in the bed result in overall size reduction of the boiler.
- Fuel Flexibility FBC boilers can be operated efficiently with a variety of fuels. Even fuels like flotation slimes, washer rejects, agro waste can be burnt efficiently. These can be fed either independently or in combination with coal into the same furnace;
- Ability to Burn Low Grade Fuel FBC boilers would give the rated output even with inferior quality fuel. The boilers can fire coals with ash content as high as 62% and having calorific value as low as 2,500 kcal/kg. Even carbon content of only 1% by weight can sustain the fluidized bed combustion.
- Ability to Burn Fines Coal containing fines below 6 mm can be burnt efficiently in FBC boiler, which is very difficult to achieve in conventional firing system;
- Pollution Control SO2 formation can be greatly minimized by addition of limestone or dolomite for high sulphur coals. 3% limestone is required for every 1% sulphur in the coal feed. Low combustion temperature eliminates NO x formation.
- Low Corrosion and Erosion The corrosion and erosion effects are less due to lower combustion temperature, softness of ash and low particle velocity (of the order of m/sec);
- Easier Ash Removal – No Clinker Formation Since the temperature of the furnace is in the range of 750 – 900 o C in FBC boilers, even coal of low ash fusion temperature can be burnt without clinker formation. Ash removal is easier as the ash flows like liquid from the combustion chamber. Hence less manpower is required for ash handling;
- Less Excess Air – Higher CO2 in Flue Gas The CO2 in the flue gases will be of the order of 14 – 15% at full load. Hence, the FBC boiler can operate at low excess air - only 20 – 25%.
- Simple Operation, Quick Start-Up High turbulence of the bed facilitates quick start up and shut down. Full automation of start up and operation using reliable equipment is possible.
- Fast Response to Load Fluctuations Inherent high thermal storage characteristics can easily absorb fluctuation in fuel feed rates. Response to changing load is comparable to that of oil fired boilers.
- No Slagging in the Furnace-No Soot Blowing In FBC boilers, volatilization of alkali components in ash does not take place and the ash is non sticky. This means that there is no slagging or soot blowing.
- Provisions of Automatic Coal and Ash Handling System Automatic systems for coal and ash handling can be incorporated, making the plant easy to operate comparable to oil or gas fired installation.
- Provision of Automatic Ignition System Control systems using micro-processors and automatic ignition equipment give excellent control with minimum manual supervision.
- High Reliability The absence of moving parts in the combustion zone results in a high degree of reliability and low maintenance costs.
- Reduced Maintenance Routine overhauls are infrequent and high efficiency is maintained for long periods.
- Quick Responses to Changing Demand A fluidized bed combustor can respond to changing heat demands more easily than stoker fired systems. This makes it very suitable for applications such as thermal fluid heaters, which require rapid responses.
- High Efficiency of Power Generation By operating the fluidized bed at elevated pressure, it can be used to generate hot pressurized gases to power a gas turbine. This can be combined with a conventional steam turbine to improve the efficiency of electricity generation and give a potential fuel savings of at least 4%.