CFBC, preferred Technology for lignite fuel - Experiences - Infraline
CFBC, preferred Technology for lignite fuel - Experiences - Infraline
CFBC, preferred Technology for lignite fuel - Experiences - Infraline
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
<strong>CFBC</strong> boiler is operational friendly. This boiler is called dark boiler because of<br />
absence of any flame in the combustor. Hence, there is no boiler tripping due to flame<br />
failure/ furnace disturbance. As this boiler has huge refractory and very large amount<br />
of bed ash in circulation, there is no need to trip the turbine in case of all <strong>fuel</strong> cut off<br />
to boiler <strong>for</strong> about 20 minutes. Boiler continues generating steam within specified<br />
parameters <strong>for</strong> sustaining turbine at reduced loads. <strong>CFBC</strong> combustor is a reservoir of<br />
heat energy. This energy is used in case of all <strong>fuel</strong> failure <strong>for</strong> short duration be<strong>for</strong>e<br />
restoration of one of the <strong>fuel</strong> available (<strong>lignite</strong> or oil). <strong>CFBC</strong> boilers do not<br />
experience large sharp fluctuations in boiler pressure due to very stable firing system.<br />
Oil support is not required even at part loads of about 25 % and combustor<br />
temperatures, steam parameters are maintained. <strong>CFBC</strong> boilers have almost zero<br />
combustibles in bottom ash with share of bottom ash of about 30-40%. The intense<br />
heat storage capacity of this boiler makes it useful <strong>for</strong> quick hot re-starts.<br />
One of the disadvantages of <strong>CFBC</strong> boiler is longer cold start-up and shut down time.<br />
Cold start-up time is about 10-12 hours as boiler is to be heated up slowly at specified<br />
heating rates as per refractory heat up curves. Similarly during shutdown also, gradual<br />
cooling is required. A typical boiler start-up is given Fig: 1. As lime is added in<br />
<strong>CFBC</strong> boiler <strong>for</strong> capturing Sulfur, the units with <strong>CFBC</strong> boilers have more number of<br />
auxiliary equipments such as air blowers, limestone handling, milling and<br />
transporting system. Hence, auxiliary power consumption is on higher side <strong>for</strong> lower<br />
capacity units.<br />
Figure-1: Typical Boiler start-up curve from light-up to Synchronization of Unit<br />
700<br />
600<br />
Temperature in deg C<br />
500<br />
400<br />
300<br />
200<br />
100<br />
0<br />
30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480 510 540 570 600<br />
Time in Minutes<br />
Lower bed Temp Middle bed Temp FG temp after Cyclone FG temp after Economiser FG temp after APH<br />
Using Lignite as <strong>fuel</strong> with <strong>CFBC</strong> boilers, following environmental parameters can be achieved.<br />
SOx (ppm) NOx (ppm) CO (mg/N.Cu.M) SPM(mg/N.Cu.M)<br />
< 50 < 20