Bottom Ash System.pdf

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1 (6)

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MULTI FUEL CFB BOILER SIMULATOR Author: JJA Document title:

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SYSTEM DESCRIPTION BOTTOM ASH SYSTEM Submitted for:

Bottom ash system

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ATON: 16828

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BOTTOM ASH SYSTEM

ESB – West Offaly Power PROCESS DESCRIPTION OF ASH REMOVAL FROM THE BOILER

1. General Removal of furnace bed ash takes place in cycles determined by the boiler operation, as well as removal of ash from intrex.

Picture; Ash handling

2. Slide gates; manually operated & pneumatic Bed ash from the furnace, as well as ash from the intrex, is removed through the boiler slide gates. The manually operated slide gates above the pneumatic slide gates are always open in normal operation. They are closed only for maintenance purposes. The manually operated gates are not equipped with any limit switches.

Bottom ash system

ATON: 16828

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BOTTOM ASH SYSTEM

Each one of pneumatically operated slide gate is equipped with two limit switches to stop the travel of the pneumatic cylinder as well as to monitor the position of the slide gate. The pneumatically operated slide gates are normally in closed position. The gate - one or more at the same time – is opened from that point under the furnace bottom (or intrex), from which there is need to remove ash. After the desired amount of ash has been removed from furnace or intrex, will the pneumatically operated slide gate be closed. 3. Water cooled screw conveyors (5ea.) Ash, removed from the furnace and intrex, flows through the slide gates and lands in the screw, at the inlet point. At the inlet point the filling factor of the screw is 100% as long as the pneumatically operated slide gate is in open position. When conveying ash forwards, will the filling factor decrease slowly, because of the geometrical changes of the screw flights. Ash is conveyed slowly to the chain conveyor S1ETG01AF101 and cooled down at the same time by the screws. Two of the screws have inlets (2 ea. /screw) only for bed ash; S1HDA20AF301 and S1HDA40AF301 Three of the screws have one inlet for bed ash and these are equipped also with intrex inlet; S1HDA10AF301, S1HDA30AF302 and S1HDA50AF301 Cooling water is led both in the mantle of the screw and inside the screw pipe shaft. Both at the furnace inlets and outlets of the screws are equipped with expansion bellows to compensate the thermal expansions of the boiler. Screw conveyors are suspended from the bottom of the boiler. The capacity is adjusted by a frequency converter. The capacity of each screw can be adjusted from 0.5 to 4 m3/h For the three screws with the intrex inlets, the capacity ratio between bed ash and intrex ash is 70% / 30%, when taking these both out from boiler simultaneously.

Bottom ash system

ATON: 16828

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BOTTOM ASH SYSTEM

4. Drag chain conveyor (S1ETG01AF101) The ash from the five cooling screws falls down onto the drag chain conveyor. The ash flows through the upper chain to the bottom of the conveyor for further conveying to the following chain conveyor. The chain conveyor is equipped with a frequency converter to adjust the amount of ash removed from the boiler. The speed of the conveyor is determined according to the need for emptying the boiler. During normal operation the capacity is ~ 3 m3/h. When emptying the furnace, the capacity is 20 m3/h.

5. Drag chain conveyor (S1ETG02AF102) The ash from the preceding chain conveyor flows down onto the drag chain conveyor (S1ETG02AF102). The ash flows through the upper chain to the bottom of the conveyor for further conveying to the inlet chute of the rotary screen (S1ETG03AT401). The chain conveyor is equipped with a frequency converter to adjust the amount of ash removed from the boiler. The speed of the conveyor is determined according to the need for emptying the boiler. During normal operation the capacity is ~ 3 m3/h. When emptying the furnace, the capacity is 20 m3/h.

Bottom ash system

ATON: 16828

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BOTTOM ASH SYSTEM

6. Rotary screen for bottom ash (S1ETG03AT401) The ash from the chain conveyor flows down in the inlet point of the rotary screen. The screen separates from the bed ash and sand the oversized particles (=reject) from the fine, reusable ones (=accept). There are two concentric cylindrical screening meshes, from which the inner one is coarse and the outer one is fine. The ash is fed inside the inner screening mesh, which separates at first the coarsest particles, and these will go straight as reject to the crusher from the outlet end of the mesh cylinder. Those particles, which pass through the coarse mesh, will drop inside the fine mesh. The fine screening mesh will pass through only the accept grain size, and the coarse reject material will go to the crusher from the outlet end of the mesh cylinder During normal operation the accept material from the rotary screen goes to the pneumatic ash transmitter (S1ETG03AF501), and from there it is blown to the bed material silo. Reject material from the screen is discharged to an ash crusher (S1ETG04AJ101). The crushing result from there is led to another pneumatic ash transmitter (S1ETG04AF501), and from there it is blown to a bottom ash silo. Underneath the inlet point of the rotary screen there is a manually operated slide gate S1ETG03AA001. This slide gate is equipped with two limit switches to monitor the position of the gate (open / closed). During normal operation is the slide gate in closed position. When bypassing the rotary screen, the slide gate will be opened, and the ash will be discharged from the chain conveyor straight to the screw conveyor S1ETG02AF301. Maximum capacity of the rotary screen is 5 m3/h.

Bottom ash system

ATON: 16828

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BOTTOM ASH SYSTEM

7. Screw conveyor (S1ETG02AF301) When, if only, one of next equipment is out of service; - The rotary screen (S1ETG03AT401) - The ash crusher (S1ETG04AJ101) - Either of ash transmitters (S1ETG03AF501 / S1ETG04AF501) Then the ash coming from the chain conveyor S1ETG02AF102 is discharged to the screw conveyor S1ETG02AF301, by opening the manually operated slide gate S1ETG03AA001 underneath the rotary screen inlet point. Same way the furnace bed sand will be emptied, when this is necessary (emergency emptying). Screw conveyor discharges the ash directly; Into a lorry, on a pile on the ground, or into an ash container. The capacity is adjusted by a frequency converter. The capacity of the screw can be adjusted from 3 to 20 m3/h

Bottom ash system

ATON: 16828