Stacking methods
Stacking in a Portal Scraper store is normally done by a ST stacker or an overhead Tripper.
Cone Shell
The Cone Shell method is the most common used stacking method in Portal Scraper stores.
The pile is formed by depositing material in a single cone from a fixed position. When this conical pile is full, the depositing of material moves to a new position and a new cone is formed against the shell of the first one.
This process continues in the longitudinal direction of the store until the stockpile is complete.
Windrow – open pile
With the Windrow method material is deposited from a number of positions across the full width of the pile.
The method prevents segregation and ensures more even distribution of fine and coarse particles across the pile.
The Windrow method is preferred in cases where segregation would make an open pile base unacceptable – typically in coal stores due to spontaneous ignition.
In order to be able to stack the material according to the windrow method the stacker must be a slewing type stacker.
Chevron
With the Chevron method material is deposited by the stacker moving to and fro over the centre line of the pile.
The method causes segregation of the material with fine particles in the central part of the pile and coarse particles on the surface and at the bottom of the pile.
Due to the reclaiming method used in a Portal Scraper store it is not possible to achieve any considerable blending effect with the chevron stacking method.
Reclaiming methods
The Portal Scraper runs on rails along each side of the pile and is usually operated in On/Off mode.
The Portal Scraper consists of a portal frame which is carried by bogies and a primary and a secondary scraper arm which are linked together.
The materials are reclaimed when the scraper chain is in physical contact with the stockpile while the portal moves forward. The flow of material is carried to an outgoing belt conveyor and proceeds to a silo.
The maximum speed of the scraper chain is 0.63m/s. The reclaiming capacity is a function of the pile size, the cut depth and the width of the scraper blades.