I. Iron mineral magnetization roasting diagram
The weak magnetic iron oxide mineral is transformed into a ferromagnetic iron oxide mineral, and the magnetization roasting process can be studied by using an iron-oxygen diagram. It is generally referred to as iron mineral magnetization roasting as shown below:
The graph shows the relationship between the temperature and the various oxides of iron. In the figure, point A is hematite (about 30% oxygen and 70% iron), point L is limonite, and point C is siderite.
The siderite begins to decompose at 400 ° C and ends at 500 ° C (CBD line segment) to complete the magnetization process.
The limonite starts dehydration at 300-400 ° C, and after dehydration, it becomes hematite.
Hematite starts to deoxidize in a reducing atmosphere at 400 ° C, and becomes magnetite (point D) at 570 ° C.
When the hematite reduction reaction ends at point D or point G, it becomes magnetite and the magnetization process is completed.
When the magnetite is rapidly cooled in an oxygen-free atmosphere, its composition remains the same, still magnetite (DM line segment).
Magnetite below 400 ° C, cooled in air, is oxidized to strong magnetic (γ-Fe 2 O 3 (DEN line); if it is cooled above 400 ° C, it is oxidized to weak magnetic a-Fe 2 O 3 (DB line segment).
It can be seen from the figure that the optimum magnetization process is performed along the ABDM or ABDEN line segment. The calcination temperature should be appropriate. When the temperature is too high, a weak magnetic rich body (Fe 3 O 4 -FeO solid solution) and iron silicate are formed; when the temperature is too low, the reduction reaction rate is slow, which affects the productivity. In industrial production, the lower limit of the effective reduction temperature of hematite ore is 450 ° C, and the upper limit is 700 to 800 ° C. If a solid reducing agent is used, the reduction temperature is 800 to 900 ° C. [next]
Second, the calcination temperature and reduction time The main factors affecting the magnetization roasting are the calcination temperature and the reduction time. The length of the reduction time is related to the calcination temperature, the ore particle size, the ore properties and the reducing agent composition. In the process of reduction roasting, iron ore is generally determined by calcination conditions to determine the appropriate calcination temperature and reduction time. It can also be calculated by the following empirical formula:
t———ore reduction time, min;
--- A coal flow rate coefficient, flow rate slower shaft furnace, a = b-10 converter flow rate fast fluidized bed furnace a = 0;
b, c - - the coefficient related to the nature of the ore, for Anshan type iron ore b = 1 ~ 1.5, c = 2 ~ 3;
T———baking temperature, using absolute temperature T=t+273;
A, B———constant, when H 2 is used as reducing agent, A=2762, B=5.3; when CO is used as reducing agent, A=2306, B=3.36;
P——the partial pressure of the reducing agent, which is equal to the gas pressure multiplied by the volume percentage of the reducing agent component;
R———Roasting ore radius, mm.
It can be seen from the formula that the longer the particle size of the calcined ore is, the longer the reduction time is. When the radius of the calcined ore is the same, the higher the temperature, the shorter the reduction time required. The higher the flow rate of the layer, the shorter the reduction time
Third, roasting fuel and reducing agent
The ore magnetization roasting heating fuel and the reducing agent for the reduction process can be classified into gas, liquid and solid. The most commonly used in the industry are gas, heavy oil and coal.
(1) Gas and natural gas The commonly used gas is coke oven, blast furnace and producer gas.
Coke oven gas has a high methane content and is required to be decomposed at 1026 ° C. It is often unable to participate in the reaction during the reduction process. Therefore, the effect of using coke oven gas as a reducing agent is poor. At the same time, when the ore is heated, the ore is heated. It is also often the case that roasting m coke oven gas is not suitable for ore with low calcination point.
The flammable component and calorific value of blast furnace gas are low. When used in combination with coke oven gas, it becomes a good fuel and reducing agent for iron ore magnetization roasting. The mixing ratio of blast furnace and coke oven gas in China is 78:
Producer gas can be used to separate iron ore magnetic roasting of manganese, may also be mixed with coke oven gas.
The combustible component of natural gas is mainly methane, which has a high calorific value and can be used for directly heating ore. When used as a reducing agent, it needs to be cracked before it can be used.
(2) Heavy oil Heavy oil can be used to heat ore, and cracking gas can be produced by thermal storage cracking.
(III) Coal The solid fuel and reducing agent used for magnetization roasting are mainly coal. It can be used according to local conditions, but lignite and bituminous coal are often used in magnetization roasting.
(4) Certain characteristics of various fuels Gas is toxic and explosive. When roasting is produced, it must be carried out in strict accordance with the safety technical operating procedures.
When the gas in the air reaches a certain concentration, it will cause an explosion if it encounters fire.
ZHONGSHAN LAVI HARDWARE PRODUCTS CO., LIMITED , https://www.lavimedal.com