2.8.1 Bottom Ash Hopper Discharge Gate
The furnace Bottom Ash Water Impounded Hopper shall be provided with 4 Nos. discharge gates (minimum 900mmX900mm size), one on each opposing slope of each hopper section. Each gate shall be capable of discharging 100% of the contents of one hopper section, within the specified time.
The scope includes necessary drives to open and close the ash gates. Electric drives are not acceptable. In case the drives are air assisted, oil shall be used as medium for movement of gate. The Bidder shall elaborate the features that ensure smooth and guided opening/closing of the gates to limit friction and wear.
Adjustment of the ash gate seal shall be provided preferably from outside the gate housing. As the movement or distortion of the hopper could affect the operation or leak tightness of the ash gates, all ash gates shall be inclined at the same slope as the hopper, and each ash gate and housing should be of integral construction. Gate housing mating flanges shall not be fabricated from more than one piece of material, and manufacturing tolerances on flange surface finish and flatness shall suit the service. Further, the gate housing shall be adequately stiffened to provide the required structural rigidity for preventing the possibility of leakages due to distortion. Thickness of the gate housing shall not be less than 10 mm.
Wear protection liners with a high degree of surface finish shall be provided on the gates and all other sliding surfaces coming in contact with the gate. Wear liner/impingement plates shall be provided on the inside of the gate housing, in the areas of slurry impingement.
The ash gate housing shall include an access door of at least 450 mm diameter, a pressurised air lancing and a poke door, a suitable venting system, ash observation window with electric light and flushing nozzles on either side of the feed gate. The observation window shall be protected from inside by a shield which shall be operable from outside the housing. The ash gate housing sumps shall also be provided with drain and flushing connections with necessary valves.
All joints, door accessories etc. shall be assembled to be completely water tight.
Material of construction shall be as follows:
| Material of Construction |
|
| Gates | Cast Iron IS:210, Gr.FG-260. |
| Gate wear liners | 6 mm thick SS:316 |
| Housing wear plates/ Impingement Plates | 25 mm thick Cast Iron IS: FG-260219,Gr. |
| Housing | 10 mm thick (min) Mild St eel IS:226. |
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