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DESIGN PRINCIPLES OF THE MITSUBISHI PROCESS

1. Simplicity of Design, Construction and Operation

One of the most important principles of the Mitsubishi Process is the simplicity of its design, construction, operation and maintenance;

  1. All of the furnaces are stationary, and driving mechanisms which are normally required for conventional converters, such as furnace tilting, tuyere punching, and hood driving, are not necessary.
  2. Molten products are transferred by gravity to the next furnace through a launder and therefore large-scale ladles or crane systems are not required.
  3. Molten products overflow continuously through the outlet holes of the furnaces. Therefore, such operations as matte tapping and slag skimming, which are inevitable in conventional practices, are not necessary, making the furnace operations far more straightforward and easy to operate.
  4. Additional facilities such as slag floatation plant, matte granulation, drying ,grinding, and sieving system, shaft furnace for anode scrap treatment and so on, are not necessary.
Such simplicity on the design and construction significantly reduces the capital cost and man-power requirements for the operation.


2. Multi-Furnace System

Sulfide copper ores are normally treated in two stages; the matte making stage,(where matte and slag are produced by smelting), and the converting stage,(where iron and sulfur in matte are progressively oxidized for the production of blister copper). Although the chemical reactions in both process steps are oxidations, there is a significant difference in the required oxygen potential. The first stage is less oxidizing so that low copper slag can be produced, while the second stage is strongly oxidizing so that iron and sulfur can be sufficiently removed from the blister.

These two quite distinct reaction conditions can only be maintained efficiently if each stage is performed in the respective individual vessels (furnaces). The Mitsubishi Process is a multi-furnace system, each furnace performing its respective function, thus optimizing the reaction conditions in each step of the process.

In addition to the above, the process is distinct from conventional smelting methods in that the matte grade can be raised up to 65-69% while maintaining a low level of copper loss in the discard slag. This feature has made the reduction in the amount of slag formed in the converting furnace to less than 10% of the initial charge of concentrates possible. Because of the reduced amount of the converting furnace slag, returning this slag to the smelting furnace has been greatly simplified.

Ferrous calcium silicate (FCS) slag has been tried to use at Ausmelt converter, but in this case the amount of slag to be recycled to the smelting stage would be much larger and it is not always economical.


3. Top Blowing through Lances

Experiments into the use of tuyeres for the injection of concentrates were carried out in the initial stage of the development work, but were abandoned because of a limitation in the campaign life. The application of lances, which can be supplied without involving a furnace shutdown, was then examined.

The lances used in steel-making LD converter could not be applied directly due to the fundamental differences between steel-making and copper-making. The development of lances suitable for the Mitsubishi Process was then carried out in accordance with the following principles: (a) to be operable with low pressure blast, (b) to have a simple structure and (c) to be made from inexpensive material easily available in the market. After a series of modifications and improvements, the lances which satisfied these requirements were successfully developed. The original lances used in the pilot plant were relatively small in diameter, but were gradually increased to enlarge the feeding capacity of each lance. The lance diameter affects the amount of splash generated beneath lances, which may attack the side wall. The estimation method of the splash amount was developed, and by using that lance position can be arranged properly.


4. Environmental Awareness

The nature of the Mitsubishi Process allows for a more efficient capture of the offgas stream. This produces a rich stable SO2 offgas stream, resulting in increased operating efficiency of the acid plant which reduces SO2 and SO3 emissions.

Additionally, transportation of molten materials such as matte, CL-slag, C-slag, and blister consists of launders with covers made from refractory thus minimizing gas emissions.

Also, critical areas such as furnace outlets and launders have ventilation hoods where the air is led through high-efficiency baghouses to reduce fugitive emissions.


5. Straightforward and Stable Operation

One of the advantages of a continuous process is that it enables a straightforward and stable operation. Compared to other smelting processes, the S furnace within the Mitsubishi Process is able to continuously produce a consistent amount and grade of matte, which is continuously converted in the C furnace. In conventional batch-wise converters, the condition of the melt keeps changing constantly with time and a lot of accumulated experience is required to operate such furnaces. However, by making the process continuous and keeping the melt condition stable, such experience is no longer vital in maintaining successful operations, instead of which relatively inexperienced operators are able to control the furnace.

Gresik is the first copper smelter and refinery in Indonesia, and almost all Indonesian employee had no experience with its operation. After the initial training and start-up assistance by Mitsubishi, the smelter has been successfully operated by themselves. It proves the simplicity of the process control and operation..

In addition, a Computer Assisted Learning and Instruction System(CALIS), has been developed, which will greatly assist operators new to the Mitsubishi process and will be an important strategic tool in the export of the process

The development of the computer system (CALIS) including video manuals began to achieve the following goals:



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