If we want to reduce alumina consumption in the production process, we must pay attention to the following skills and methods:
1. The particle size of alumina should be controlled well and should not be too fine, preferably sandy alumina. During blanking, the upper sealing material of anode should reduce flying, and the window should be closed during processing.
2. When changing the anode, the material on the old electrode shall be raked off and the alumina on the residual electrode shall be cleaned.
3. Control the precipitation to prevent excessive precipitation and precipitation hardening.
Alumina production can be divided into narrow sense and broad sense. In a narrow sense, alumina output refers to alumina obtained by roasting aluminum hydroxide, also known as metallurgical grade alumina or roasted alumina, which is the raw material for electrolytic aluminum production; Alumina output in a broad sense refers to the total amount of metallurgical grade alumina, commercial ordinary aluminum hydroxide and other products converted into alumina. It is traditionally called the total amount of finished alumina. It is mostly used to calculate the production capacity, issue the output plan and check the completion of the plan.
According to different statistical methods, the indicators reflecting the output of alumina products can include: the amount of metallurgical grade alumina, the converted amount of commercial aluminum hydroxide, the converted amount of alumina of other products, and the actual output of calculating the production level.
1. Metallurgical grade alumina content
Metallurgical grade alumina refers to the alumina obtained by roasting aluminum hydroxide, which is the raw material for electrolytic aluminum production.
2. Converted amount of commercial ordinary aluminum hydroxide
Commercial ordinary aluminum hydroxide refers to aluminum hydroxide sold as a commodity (excluding aluminum hydroxide used for roasting into alumina). When calculating the total amount of finished alumina, it is necessary to convert commercial ordinary aluminum hydroxide into metallurgical grade alumina. The actual weighing number is used and calculated on a dry basis, and the conversion coefficient is 0.647. The moisture content shall be subject to the sampling and analysis number at the packaging place. The calculation formula for converting commercial ordinary aluminum hydroxide into alumina is:
Commercial ordinary aluminum hydroxide converted into alumina (T) = amount of commercial aluminum hydroxide (dry basis) × zero point six four seven
3. Alumina conversion of other products
The amount of alumina converted from other products refers to the amount of metallurgical grade alumina converted from decomposition slurry and commercial semen other than commercial ordinary aluminum hydroxide.
(1) Decomposition slurry refers to the amount of decomposition slurry taken out from the decomposition tank of alumina production process and sold as commodities. The calculation formula converted into metallurgical grade alumina is as follows:
Alumina converted from decomposed slurry (T) = volume of decomposed slurry (M3) × Solid content of decomposed slurry (kg / m3) × 0.647/1000 + alumina content in slurry phase of decomposition material (T)
(2) Commercial semen refers to the amount of semen taken from the semen in the alumina production process and sold as commodities.
The calculation formula converted into metallurgical grade alumina is as follows:
Semen volume (T) = commercial semen volume (M3) × Alumina concentration in semen (kg / m3) × 0.9/1000, where: 0.9 is the alumina recovery rate.
4. Calculate the actual output of alumina production level
Due to the long production cycle of alumina and the large fluctuation of products in process and semi-finished products at the end and beginning of the period, in order to accurately reflect the actual production level, the concept of actual output is usually adopted in production to calculate the actual production consumption and other indicators.
Actual production of alumina (T) = metallurgical grade alumina (T) + converted amount of commercial ordinary aluminum hydroxide (T) + converted amount of alumina of other products (T) ± converted amount of metallurgical grade alumina by increase or decrease of solid and liquid phase content of aluminum hydroxide in decomposition tank ± converted amount of metallurgical grade alumina by increase or decrease of aluminum hydroxide bin (T)
Where “+” means increase and “-” means decrease.
5. Output of aluminum hydroxide
The output of aluminum hydroxide is an important output index reflecting the actual level of alumina production in the reporting period.
① Aluminum hydroxide output (T) = semen flow (M3) × Semen alumina concentration (kg / m3) × Decomposition rate / 0.647/1000 ② monthly output of aluminum hydroxide (T) = output of metallurgical grade alumina / 0.647 + dry packaging volume of commercial aluminum hydroxide + alumina equivalent to other products / 0.647 ± aluminum hydroxide warehouse stock difference calculation Description:
(1) 0.647 is the constant converted from aluminum hydroxide to alumina.
(2) All products are calculated on a dry basis.
(3) The increase or decrease of solid content in the decomposition tank is generally not calculated as the output of aluminum hydroxide.
The total recovery rate of alumina refers to the percentage of alumina content in the produced alumina in the alumina content in the consumed materials (aluminum ore, limestone, etc.), and its calculation formula is:
Total alumina recovery rate = output alumina / input alumina × 100% calculation Description:
(1) Alumina output in the reporting period = roasted alumina output × (1 – impurity content) + export aluminum hydroxide (T) × 0.647 ± increase or decrease of aluminum hydroxide solid and liquid alumina content in decomposition tank × 0.647 ± increase and decrease of aluminum hydroxide warehouse (T) × [1 – moisture (%)] × 0.647.
(2) Alumina input in the report period = aluminum ore consumption (T) × Percentage of alumina in ore × [1 – moisture (%) + lime consumption (T) × Percentage of alumina in lime ± increase and decrease of alumina in the process (T).
Where: input and output materials are calculated on a dry basis.
Alumina alkali consumption refers to the NaOH (100%) consumed in the production of 1t alumina. Its calculation formula is: alumina alkali consumption = NaOH consumption in the reporting period (kg) / actual alumina production in the reporting period (T).
(1) NaOH consumption in the reporting period (kg) = the amount of liquid alkali converted into 100% NaOH in the reporting period (kg) ± the increase and decrease of sodium oxide in the process (kg) × 1.29.
(2) The liquid alkali is converted into 100% NaOH.
(3) The NaOH conversion coefficient of sodium oxide is 1.29.
(4) In the process, if the sodium oxide at the end of the period is higher than that at the beginning of the period, it will be “-” in calculation; if the sodium oxide at the end of the period is lower than that at the beginning of the period, it will be “+” in calculation.
Alkali consumption consists of chemical loss, attached loss, ah loss and other losses (running, emitting, dripping and leakage).
Chemical loss = amount of red mud discharged during the reporting period × The discharged red mud contains Na2O × 1.29 / actual alumina production in the reporting period attached loss = (amount of red mud discharged in the reporting period) × Liquid solid ratio of discharged red mud × Liquid attached total alkali NT × 1.29 – total alkali content in return water) / actual alumina production in the reporting period
Ah = output of aluminum hydroxide in the reporting period × Aluminum hydroxide containing Na2O × 1.29 / actual alumina production in the reporting period other loss = total alkali consumption – chemical loss – Additional Loss – ah loss, where: ah is the abbreviation of aluminum hydroxide [al (OH) 3].
The energy consumption of alumina process refers to the energy directly consumed in the production of 1t alumina, including electricity, coal, steam, coke, gas, fresh water and other consumption.
The calculation process is time-consuming. Only the primary energy consumed by the enterprise is calculated, and the secondary energy consumed by the enterprise is converted to primary energy. Its energy consumption can be expressed by kilogram of standard coal or ton of standard coal, which is calculated by multiplying each energy consumption by the coefficient of converted standard coal.
The calculation formula is:
Alumina process energy consumption = (∑ process energy consumption of coal, coke, steam, electricity, gas, fresh water, etc.) × Unit calorific value converted into standard coal) / actual alumina production, where: process energy consumption of a certain energy = (basic production consumption + pipe distribution and line loss) / actual alumina production. The calorific value of standard coal is 29307.6kj/kg, and the coefficient of converted standard coal = Unit calorific value of certain energy / 29307.6. Electrothermal conversion: 3600kj / kWh. The calorific value of other energy consumption shall be subject to the actual measured data in the laboratory (reference value steam: 2900 kJ / kg, coking gas: 17000 ~ 18000kj / m3, coal: 26000 ~ 28000 kJ / kg).
The comprehensive energy consumption of alumina is the comprehensive energy consumption for the production of 1t alumina, including electricity, coal, steam, coke, gas, fresh water and so on.