Two main types of rotor furnaces are currently used at the plants:
- a stationary rotor drum furnace with a fixed axis;
- a rotary-type rotor drum furnace.
Stationary rotor drum furnaces are more outdated models; as modernization progresses, they are gradually replaced by rotary-type rotor furnaces which are more efficient.
The main purpose of rotor furnaces is melting of small-lump aluminum scrap. Use of rotor furnaces provides the maximum flexibility in case of melting of lump aluminum scrap of various brands; chippings and scums with the metal content of less than 20%. During the operation of a rotor furnace, the loaded raw materials is moving to create a cascade due to the drum rotation. The furnace charge driven by centrifugal force and friction resulting from it goes up to a certain height and then goes down. A new layer of loaded materials that are in contact with furnace gases and the furnace lining falls onto the surface. This results in a more rapid and more even charge preheating than preheating in reverberating furnaces.
Melting in rotor drum furnaces is performed using salts. Salts have a variety of applications. Their most crucial task is to cover aluminum lumps to protect them against any effects of the furnace atmosphere and minimize oxidation of this metal. Sufficient amounts of salts are required to achieve this goal. When using a rotary-type rotor furnace, the salt discharge reduces by 30% as compared with a fixed-axis furnace, since the contact surface of raw materials in the furnace is decreased in the inclined position.
Each metal particle, due to the high oxidation capacity of aluminum is covered with a thin layer of oxide layer. Salt destructs the oxide layer once the melting process is completed. The liquid drops resulting from melting are to coagulate and turn into molten metal. Use of salts ensures the occurrence of this effect, the salt absorbs and removes metal pollution.
There are several variants of the lining currently used for drum rotor furnaces:
1st working lining is made of single-piece refractories (brickwork lining);
2nd combined working lining;
3rd monolithic working lining.
Single-piece working lining of rotor furnaces
The brickwork working lining of rotary-type rotor furnaces for melting aluminum scrap is more outdated but the cheapest variant. According to the data available, fire-clay grog and mullite-corundum products for the working lining of rotary-type rotor furnaces are used in the Russian Federation. Depending on the type of single-piece products used for the lining, the working layer resistance varies from 4 to 12 months.
Combined working lining of rotor furnaces
In case of combined lining, the working layer of the cylindrical end of a rotor furnace is normally made from single-piece products, while the conic end is filled with concrete.
Monolithic working lining
The monolithic working lining of rotor furnaces is the most potentially productive. Today, use of monolithic linings is 100% recommended in the projects of newly-designed rotor drum furnaces.
As a heat insulation layer of the lining, it is strongly recommended to use cutting-edge insulation materials: calcium silicate based slabs, or fiber boards, or soft rolled materials. The recommended thicknesses of the heat insulation layer are less than 25 mm. Considering the best practices of operation of a 16-tonne rotor furnace at PAO Secondary Metals and Alloys Plant, the lining may be designed without a heat insulation layer.
CERALIT CAST AL58007 concrete is recommended for the working lining of the cylindrical end and the bottom.
CERALIT CAST AL58007 MF concrete is recommended for the lining of the conic (feed) end of a rotor furnace.
We can offer several options for the lining of the lid, as determined by the customer's requirements (heat transfer capacity, the weight of a lid with a lining, etc.):
Option 1: CERALIT CAST AL58007, CERALIT CAST CR50069, CERALIT CAST CL45134 dense concretes;
Option 2: CERALIT LWCAST CR40059 or CERALIT LWCAST CR27060 insulation concretes;
Option 3: two-layer lining consisting of insulation concrete (CERALIT LWCAST CR27060, CERALIT LWCAST VR32028, CERALIT LWCAST VR32105) and dense concrete (CERALIT CAST AL58007, CERALIT CAST CR50069, CERALIT CAST CL45134).