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The Phurnacite plant, carbonisation process

Pyrolisys – Defined as the heating of a substance in the absence of air. When the substance being heated is coal the process is more commonly called a Carbonisation process.

The production of Phurnacite from raw Oviods is achieved on a rapid carbonisation process using Disticoke batteries. These batteries are constructed on a concrete raft on piles. Pile caps and raft are built to compensate for expansion.

The brick work is of semi silica, these are special bricks around the charge-holes and squares and first quality fire clay.

Each battery has 40 ovens built in groups of 8. The capacity of each oven is 2.3tons of raw Ovoids, that’s 18.4 tons per block of 8. The sole of the oven is inclined at an angle of 43 degrees. The width of each oven is 200mm. The oven doors are 3 feet 8 inches in height.

To build – Bricking time took aproximatly 30 weeks, then pre heating another 8 weeks . Steel work was needed for the roof over the battery and to support bunkers.

The raw Ovoids are charged into ovens from the storage/shuttle bunkers. A simplified cross section of an oven is shown below.

Each oven chamber when charged will contain 2 and half tons of raw fuel. (Each Chamber being operated in groups of 8 known as a “block”. A block of ovens cannot be operated as individual units, they are designated to operate as an integrated unit.) Once a block has been charged / filled it contains 20 tons of raw fuel; and is left to carbonise for four hours. After this time the charged fuel will have reached a temperature of 900 degrees centigrade and net volatile content of the raw charge will have been reduced from 11% down to 2%.

Preheated air is the distributed to heating flues where it is mixed with gas and the resultant flue gas is subsequently passed back through the recuperator where it preheats the incoming air before it is sent into the atmosphere via a waste flue stack.

Gas flow

Gas evolved during the carbonisation process is extracted from the batteries using an Exhauster (gas pump). The diagram below illustrates the process undergone.

Layout of a gas Exhauster or gas pump
Layout of a gas Exhauster or gas pump

Each oven chamber when charged will contain 2 and half tons of raw fuel. (Each Chamber being operated in groups of 8 known as a “block”. A block of ovens cannot be operated as individual units, they are designated to operate as an integrated unit.) Once a block has been charged / filled it contains 20 tons of raw fuel; and is left to carbonise for four hours. After this time the charged fuel will have reached a temperature of 900 degrees centigrade and net volatile content of the raw charge will have been reduced from 11% down to 2%.

This process of gas purification is carried on in the “By Products Plant”. The By products plant performs the following functions:

A. Removes the various chemicals from the un-purified gas so that the resultant purified gases are of the correct quality for combustion.

B. Refines the extracted chemicals to usable form – this being achieved in other by products, those being: Tar / Liquor separation plant; Ammonia concentration plant; Naphthalene removal / extraction plant.