Eco-friendly paddy boiler circulating fluidized bed boiler cfb power plant

Fluidization regimes and classification

1. Fixed Bed: When the fluid is passed through the bottom of the bed at a low flow rate, the fluid merely percolates through the void spaces between stationary particles.

2. Minimum fluidization: When the gas velocity reaches minimum fluidization velocity, and all the particle are just suspended by the upward flowing fluid.

3. Bubbling Fluid Bed: When the flow rate increases beyond the minimum fluidization velocity, bed starts bubbling. The gas-solid system shows large instabilities with bubbling and gas channelling with rise in flow rate beyond minimum fluidization. Such a bed is called aggregative, heterogeneous, or bubbling fluidized.

4. Turbulent Fluidized Bed: When the gas flow rate sufficiently increases, the terminal velocity of solids is exceeded, the upper surface of the bed disappears, entrainment becomes appreciable instead of bubbling,

5. Fast Fluidized Bed: With further increasing in gas velocity, solids are carried out of the bed with the gas making a lean phase fluidized, this regime is used for operating CFB. In the present work, fast fluidized bed is used to operate the CFB where the pressure drop decreases dramatically in this regime.

6. Pneumatic Transport: Beyond the circulating fluidized bed operating regime, there is the pneumatic transport region, pressure drop increases in this regime.

Fluidized Bed Introduction

1. Circulating fluidized bed is a relatively new technology with the ability to achieve lower emission of pollutants. Extensive research has been conducted on this technology within the past 15 years due to increasing concerns over pollution caused by traditional methods of combusting coal and its sustainability. The importance of this technology has grown recently because of tightened environmental regulations for pollutant emission.

2. The Mercury and Air Toxic Standards enacted in December 2011 by the EPA have forced all the countries in Europe and America to strictly adhere to this policy. This means that emissions such as metals, acid gases, organic compound, flue gas acids and other pollutants from power plants or industrial facilities have to meet the requirements set by EPA and upgrades have to be done for facilities that do not meet the standards. As a result, the demand for circulating fluidized bed technology is predicted to sky rocket.

Circulation

1. Fine particles of partly burned coal, ash and bed material are carried along with the flue gases to the upper areas of the furnace and then into a cyclone. In the cyclone the heavier particles separate from the gas and falls to the hopper of the cyclone. 2. This returns to the furnace for recirculation. Hence the name Circulating Fluidized Bed combustion. The hot gases from the cyclone pass to the heat transfer surfaces and go out of the boiler.

Bed Material

1. To start with the bed material is sand. Some portion is lost in the ash during the operation and this has to be made-up. In coal fired boilers the ash from the coal itself will be the makeup material.

2. When firing bio fuels with very low ash content sand will be the makeup bed material. For high Sulphur coals Limestone addition to the bed material reduces SO2 emissions.

Main Specifications of Circulation Fluidized Bed Boiler