Bed Materials Filling process in AFBC Boiler
In this article (Bed Materials Filling process in AFBC Boiler) we discussed about the boiler bed materials specifications and their spical characteristics and also know about the process of how to fill bed materials into the boiler Major portion of the bed volume contains inert bed materials bed materials is obtained from crushed refectory bricks or sieved ash
The bed consists of two layers:
1. the active, fluidized layer above the air jets
2. the static layer of 100 mm thickness all around air nozzles (bubbling nozzles), which acts as an Insulation protecting the bottom plate from the heat of the bed Bed material is usually sand, ash, or crushed refractory in a size range of 0.5–1.2 mm. Sand Should be rounded river or lake sand with no abrasive alpha quartz to avert any chances of erosion. Sea sand should not be used because it contains alkalies and chlorides.
Fuels with ash >15% do not require bed ash replenishment. For firing fuels with lower ash, a bed material silo and a feeding system are required. Crushed refractory for bed material is less aggressive but more expensive than sand. Stoker ash, properly sized, suits very well. High under bed pressure in FBC boilers drives away most of the ash, and only the heavier particles, which are fuel impurities such as stones and shale separate out as bed ash.
BED MATERIALS SPECIFICATION – CRUSHED REFRACTORY
|Chemical composition||Percentage limits|
|SIO2||55 - 60|
|AL2O3||37-40 , Min 30% required|
|BULK DENSITY||1000 -1050 kg/m3 for sand|
Special Characteristics Boiler Bed Materials
• Accurate Particle Size Distribution
• Exceptional Chemical Purity
• Fully Screened Material through Classifiers
• High I.D.T. (Initial Deformation Temperature)
• No Formation Clinker
• Low Alkalies
• No Dust Particles
• No Free Iron Particles
• Perfect Density
BOILER BED MATERIAL FELLING PROCESS.
1. Bed material size and chemicals properties must be maintained strictly as per the
Specification for smooth start up and efficient operation.
2. Shift the bed material to the feeding /operating platform
3. Start the ID fan as per start up procedure
4.Adjust the furnace pressure to – 2 mmWC
5.start FD fan as per fan start up procedure
6. Open all the compartments wind box dampers
7. Isolation dampers to over fire and PA lines shall be kept closed.
8. Open FD fan suction damper or increase the fan speed and maintain the wind box pressure 100 – 125 mmWC
9. Maintained furnace pressure -2 mmWC during bed material filling.
10. Note down the wind box pressure of individual compartments
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11.Bed material may be filled manually through furnace manholes
12.Bed material filling should be done in batches; it should not be in one stretch as it will causes
13.accumulation of material at the drop point and restrict the fluidization of bed material at the location
14.Bed material shall be filled up to 275 – 300 mm heights above the bubbling cap top , which is to be verified physically.
15. After confirm the bed height it is recommended to fluidize the compartments thoroughly to spread the material uniformly. It may required fluidization the compartments one by one with higher wind box pressure so as to distribute the bed materials evenly across the combustor
16.On confirming the uniform distribution of bed material , it is a must to study the minimum fluidization wind box pressure record the minimum fluidization wind box pressure and airflow for the startup compartment as the same is a guiding parameter during coal firing
After the trial keep note of damper position of FD fan and dampers to be closed ( fans also be stopped depending upon the time gap ).
Conclusion :– after reading above article bed materials filling process in AFBC boiler “we finally said that during filling the bed materials lots of things kept into the mind like bed materials are used for the boiler is according to which is suggested by the boiler manufacturer , and also bed materials characteristics should be match according to the recommended bed materials like their size , bulk density , fusion temperature etc. after that we bed materials introduced into boiler proper draft should be maintained and proper coordination should be between man and control for achieving better performance during bed materials filling .
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