Presented at National Boiler Workshop 2015 - Presented by R.Nagarajaprasath, Shanti GD Ispat & Power

1. By
R.NAGARAJAPRASATH, B.E(Mech), BOE
SHANTI GD ISPAT & POWER PVT LTD, CHATTISGARH

2. CFBC Vs AFBC

3. HEAT TRANSFER IN CFBC WATER
WALL

4. o Case Study On Husk Firing In CFBC
o Importance of loop seal air nozzle arrangement.
o Panel super heater failure in CFBC.
CASE STUDIES

5. The CFBC boiler was supplied by a Chinese company has been
operated for a year. Boiler was designed for 80% Rice husk + 20
% Indian coal / 100% Indian coal. Boiler parameters are 75 TPH,
90 Kg/cm2, 515 Deg C with the feed water temperature of 190
Deg C.
CASE STUDY ON HUSK FIRING IN CFBC
Cracks developed in cyclone outlet cone

6. CASE STUDY ON HUSK FIRING IN CFBC

7. CASE STUDY ON HUSK FIRING IN CFBC

8. CASE STUDY ON HUSK FIRING IN CFBC

9. IMPORTANCE OF LOOP SEAL AIR NOZZLE
ARRANGEMENT

10. Loop is mechanical device which transfers the un-combusted
(coarser) particles to the furnace, which was collected by cyclone.
It transfers the ash particles from low pressure cyclone to the high
pressure combustor. It protects the direct flow of flue gas from
furnace to cyclone.
There are two types of air nozzles were provided in loop seal. The
purpose of nozzle types is to shift the collected ash back to
furnace and also to control the gas bye-passing from furnace to
cyclone. Down leg side nozzles were provided for aeration
purpose only and in the riser leg side nozzles were provided for
fluidization purpose.
If loopseal air nozzles were erected in wrong manner then this
cause in boiler loading because ash will not transferred from
cyclone to furnace.
IMPORTANCE OF LOOP SEAL AIR NOZZLE
ARRANGEMENT

11. IMPORTANCE OF LOOP SEAL AIR NOZZLE
ARRANGEMENT
The is the philosophy of loop seal design by Foster wheeler.

12. IMPORTANCE OF LOOP SEAL AIR NOZZLE
ARRANGEMENT

13. The CFBC boiler was supplied by a Chinese company has been
operated for 3 years. Boiler was designed for 100%
Imported/Indian coal. Boiler parameters are 130 TPH, 100
Kg/cm2, 540 Deg C & feed water temperature is 180 Deg C. The
arrangement is shown in below
One and half year after commissioning they were faced frequent
failure in panel super heater tubes. Due to the frequent failure in
panel super heater tubes they can’t able to run the boiler more
than a month continuously. Especially failure was occurred in
bottom of super heater. Arrangement of panel super heater was
shown in photo-02. At the time of visit boiler was in operating
condition. However failed tubes were available for inspection. In
my presence boiler was stopped due to panel super heater failure,
boiler was inspected from inside.
PANEL SUPERHEATER FAILURE IN CFBC

14. PANEL SUPERHEATER FAILURE IN CFBC
Reason for Failure,
1. From the available failed tube, it
was understood that the anchoring
arrangement was not proper to hold
the refractory. They do not have the
anchors at bottom and at front.
2. Tubes are provided with 6mm dia x
30mm long studs.
3. Due to that insufficient anchoring,
refractory may fail from the first
firing itself. After refractory
falling, tubes were start eroding
from bottom.

15. PANEL SUPERHEATER FAILURE IN CFBC
Failed tubes, shows no anchors in
bend
New studs added with modified
arrangement.

16. PANEL SUPERHEATER FAILURE IN CFBC
Thickness measured in the outer coil during the shutdown time. Tube
thickness was observed 2.83mm against the original thickness of 5mm.

17. Recommendation,
1. For the proper holding of refractory, more studs were added
additionally with the existing stud arrangement.
2. New studs also with the same dimension.
3. Phosphate bonded high alumina castable was applied over a
coil up to the tip only. Phoscast will give better life in the high
velocity & high erosive zone also. This was practically
experienced in AFBC boilers.
PANEL SUPERHEATER FAILURE IN CFBC

18. SEE YOU WITH NEW
CASE STUDIES
THANK YOU !!!