Research and Development on Fluidized Bed Combustion Technology

Fluidized bed combustion has the ability to burn an exremely wide variety of fuels with varying moisture and ash content, such as lignite, sludge, peat, chip wood, rice husk, baggasses, petroleum coke, and palm fiber, etc. And the ability to overcome the environmental emission problems have been selected by the National Research Council (DRN) as one of the R&D activities on Clean Coal Technologies (CCT).

In order to burn those fuels with several operating conditions, a 1.5 ton/h of fluidized bed boiler has been constructed at Energy Technology Laboratory (UPT-LSDE), BPP Teknologi, PUSPIPTEK, Serpong since the end of 1994. The figure below shows an Atmospheric Bubbling Fluidized Bed Boiler in LSDE's laboratory.

The unit is 6 m high and supported by I-Beam steel structure at the base. The diameter of combustion chamber is 0.8 m (i.d) consisting of oil atomizer for start-up, water tube, bubble cap distributor, plenum chamber and ash discharge pipe. In the combustion process, fule is fed to the fluidized bed consisting of inert material of sand (bed depth~25 cm). For solid fuels such as coal, the fuel content of the bed is between 5-10 %. The hot bed particles acts as a heat reservoir and stabilize teh combustion process, making the fluidized bed a very desirable device for burning low-grade coals and waste materials.

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The superficial velocity of the air through the bed is around 1 m/s (adjustable through a damper) at a bed temperature 750-950 ⁰C. A secondary air as a staged combustion is also introduced in the perimeter of the middle freeboard.

The products of combustion leaving the bed contain a large portion of unburned carbon particles that are collected in a multi-cyclone separator, which seperates these particles from the gas by imparting a centrifugal acceleration by means of an induced darft fan (I.D.F) on the mixture.

Heat is extracted through the furnace wall by boiler water tubes. The production of steam is approximately 1,500 kg/hr at 9.5 bar,~180⁰C and will be fed to a steam turbine for power generation (~40 kWe)in the near future. Emission of CO₂, CO, SO₂ and NO_x is monitor by portable gas analizer.

Thermocouples are located at point of concern for combustion studies such as the freeboard, boiler entry, boiler exit, in-bed, and cycloneentry and outlet temperature.

Three control strategies were employed by the system, namely bed temperature, steam flowrate, and freeboard control strategies, so to ensure the maximum combustion efficiency and the safety operation can be maintain.