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
boiler capacity
items | 35t/h | 75t/h | 130t/h |
| rated steam capacity t/h | 35 | 75 | 130 |
| rated working pressure Mpa | 3.82 | 3.82 | 5.3 |
| rated steam temperature℃ | 450 | 450 | 450 |
| feed water temperature ℃ | 105 | 130 | 150 |
| combustion method | Circulation fludized bed combustion | Circulation fludized bed combustion | Circulation fludized bed combustion |
| applicable coal | Coal | Coal | Coal |
| design the fuel low level caloric | 12670 | 8117 | 6520 |
| the coal consumption at full load operation(Kg/h) | 9045 | 20417 | 38792 |
| designed efficiency % | 88.6 | 88 | 88 |
| exit gas temperature ℃ | 150 | 145 | 150 |
| De-sulfur efficiency % | 88 | 88 | 88 |
| fuel particle requirement mm | ≤10 | ≤8 | ≤10 |
| lime stone particle requirement mm | ≤2 | ≤2 | ≤2 |
| drum central line elevation mm | 25000 | 28300 | 33000 |
| the highest point elevation l mm | 26750 | 33950 | 54270 |
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